CASP9 (Caspase-9) is the initiator caspase of the intrinsic apoptosis pathway. CRITICAL ISOFORM BIOLOGY: Alternative splicing produces 4 isoforms with ANTAGONISTIC functions: (1) Caspase-9L (isoform 1, P55211-1, Alpha) is the full-length ACTIVE enzyme that binds Apaf-1 in the apoptosome and cleaves effector caspases to INDUCE APOPTOSIS; (2) Caspase-9S (isoform 2, P55211-2, Beta) lacks the catalytic domain and acts as a DOMINANT-NEGATIVE INHIBITOR that competes with 9L for Apaf-1 binding [PMID:10070954]. UniProt states "Isoform 2: Lacks activity is an dominant-negative inhibitor of caspase-9". All current GOA apoptosis annotations refer to the pro-apoptotic function - MISSING the anti-apoptotic isoform 2 function.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005737
cytoplasm
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Caspase-9 is predominantly localized in the cytoplasm as an inactive monomer in non-stressed cells [PMID:12782307, deep research]. The IBA annotation from phylogenetic inference is well-supported. Both isoforms would be cytoplasmic as neither has specific targeting signals.
Reason: Cytoplasmic localization is well-established for procaspase-9. The deep research confirms "In non-stressed cells, caspase-9 predominantly localizes to the cytosol as an inactive monomer lacking typical mitochondrial targeting sequences." This applies to both isoforms as the CARD domain (retained in both) does not contain targeting signals.
Supporting Evidence:
PMID:12782307
caspase-9 is in the cytoplasm of non-apoptotic pituitary cells
file:human/CASP9/CASP9-deep-research-perplexity.md
provider: perplexity
|
|
GO:0006915
apoptotic process
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Caspase-9 is central to the intrinsic apoptotic pathway. The IBA annotation correctly identifies involvement in apoptosis, which is the canonical function of isoform 1. However, isoform 2 (Caspase-9S) INHIBITS apoptosis as a dominant-negative.
Reason: The GO term "apoptotic process" is a broad BP term that applies to proteins involved in apoptosis regardless of whether they promote or inhibit it. The term definition includes regulation. Isoform 1 induces apoptosis while isoform 2 inhibits it - both are involved in the apoptotic process. The IBA inference from phylogenetic conservation is sound for the canonical pro-apoptotic function.
Supporting Evidence:
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Cysteine-type endopeptidase activity is the core enzymatic function of caspase-9 (isoform 1). CRITICAL: Isoform 2 (Caspase-9S) LACKS this activity as it is missing the catalytic domain (residues 140-289). UniProt explicitly states "Isoform 2: Lacks activity".
Reason: This annotation is correct for the canonical isoform 1 (P55211-1). The IBA phylogenetic inference is valid because the catalytic activity is the defining feature of caspase-9 orthologs. The catalytic dyad (Cys-287 and His-237) is conserved across the family. Note that isoform 2 would NOT have this activity.
Supporting Evidence:
PMID:16916640
Our study demonstrates the efficiency by which the executioner caspases are activated in vivo
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
|
|
GO:0005829
cytosol
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Cytosolic localization is well-established for procaspase-9 in non-apoptotic cells. The apoptosome forms in the cytosol upon cytochrome c release from mitochondria.
Reason: Deep research confirms cytosolic localization: "In non-stressed cells, caspase-9 predominantly localizes to the cytosol as an inactive monomer." Multiple experimental studies confirm this. The IBA annotation is phylogenetically sound.
Supporting Evidence:
PMID:12782307
caspase-9 is in the cytoplasm of non-apoptotic pituitary cells
|
|
GO:0043525
positive regulation of neuron apoptotic process
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Caspase-9 plays a documented role in neuronal apoptosis during development and in neurodegenerative conditions. Caspase-9 knockout mice show severe brain abnormalities due to reduced developmental neuronal apoptosis. CRITICAL: This applies to isoform 1 only.
Reason: Deep research states: "mice lacking caspase-9 die perinatally with severe brain abnormalities including exencephaly, ventricular obstructions, and protrusion formations." This demonstrates caspase-9's role in neuronal apoptotic processes during CNS development. IBA inference from phylogenetic conservation is appropriate for this well-characterized function of isoform 1.
Supporting Evidence:
file:human/CASP9/CASP9-deep-research-perplexity.md
mice lacking caspase-9 die perinatally with severe brain abnormalities including exencephaly, ventricular obstructions, and protrusion formations
|
|
GO:0008630
intrinsic apoptotic signaling pathway in response to DNA damage
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Caspase-9 is the initiator caspase of the intrinsic apoptotic pathway activated by DNA damage. c-Abl phosphorylates caspase-9 at Tyr-153 in response to DNA damage, promoting apoptosis. CRITICAL: This pro-apoptotic function is isoform 1 specific.
Reason: DNA damage triggers the intrinsic pathway through p53-mediated transcription of pro-apoptotic Bcl-2 family members, leading to MOMP, cytochrome c release, and caspase-9 activation. PMID:15657060 demonstrates c-Abl directly phosphorylates caspase-9 in DNA damage response. IBA phylogenetic inference is sound for this core function.
Supporting Evidence:
PMID:15657060
c-Abl phosphorylates caspase-9 on Tyr-153 in vitro and in cells treated with DNA damaging agents
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: IEA annotation of cysteine-type endopeptidase activity is redundant with IBA annotation. Correct for isoform 1, but isoform 2 lacks the catalytic domain.
Reason: This is a broader IEA annotation that is consistent with the IBA annotation. While less specific than IBA, it is not incorrect. The catalytic activity is confirmed by multiple experimental studies.
Supporting Evidence:
PMID:16916640
Caspase-7 is an obligate dimer of catalytic domains, with generation of activity requiring limited proteolysis within a region that separates the large and small chains of each domain
|
|
GO:0006508
proteolysis
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Proteolysis is a parent term of cysteine-type endopeptidase activity. This is a very general annotation but not incorrect for isoform 1.
Reason: Caspase-9 is definitively a protease that cleaves substrates. The term is appropriately general for an IEA annotation. More specific terms are available via IBA and IDA annotations.
Supporting Evidence:
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
|
|
GO:0006915
apoptotic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: IEA annotation of apoptotic process is redundant with IBA annotation. Correct as caspase-9 is a key player in apoptosis, with isoform 1 promoting and isoform 2 inhibiting the process.
Reason: Consistent with other evidence. The IEA provides computational support for the experimentally validated apoptotic function.
Supporting Evidence:
PMID:9390557
caspase-9 is the most upstream member of the apoptotic protease cascade that is triggered by cytochrome c and dATP
|
|
GO:0006974
DNA damage response
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: Caspase-9 participates in DNA damage response primarily through its role as the executor of DNA damage-induced apoptosis. c-Abl phosphorylates caspase-9 in response to DNA damage.
Reason: The deep research and PMID:15657060 confirm caspase-9's role in DNA damage response. The ARBA machine learning annotation correctly captures this function.
Supporting Evidence:
PMID:15657060
The c-Abl tyrosine kinase is also involved in the apoptotic response to DNA damage
|
|
GO:0008233
peptidase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Peptidase activity is a parent term of cysteine-type endopeptidase activity. Very general but correct for isoform 1.
Reason: This is a very general parent term. More specific annotations are available. Correct for the canonical catalytically active isoform.
Supporting Evidence:
PMID:16916640
Caspase-7 is an obligate dimer of catalytic domains, with generation of activity requiring limited proteolysis within a region that separates the large and small chains of each domain
|
|
GO:0008234
cysteine-type peptidase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Cysteine-type peptidase activity is a parent term of the more specific cysteine-type endopeptidase activity annotation. Correct for isoform 1.
Reason: Parent term of the more specific annotation. Consistent with caspase-9's function as a cysteine protease using the catalytic dyad of Cys-287 and His-237.
Supporting Evidence:
PMID:16916640
Caspase-7 is an obligate dimer of catalytic domains, with generation of activity requiring limited proteolysis within a region that separates the large and small chains of each domain
|
|
GO:0009411
response to UV
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: UV irradiation causes DNA damage that can trigger caspase-9-mediated apoptosis via the intrinsic pathway.
Reason: PMID:15657060 demonstrates that DNA damaging agents including UV activate caspase-9 through c-Abl-mediated phosphorylation. The annotation captures the role of caspase-9 in UV-induced apoptosis.
Supporting Evidence:
PMID:15657060
Caspase-9(Y153F) also attenuated DNA damage-induced processing of caspase-9 to p35, activation of caspase-3, and apoptosis
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: Hydrolase activity is a very general parent term. Caspases hydrolyze peptide bonds. Correct but uninformative for isoform 1.
Reason: Very general but correct parent term. The UniProtKB keyword mapping correctly identifies caspase-9 as a hydrolase. More specific terms provide better annotation.
Supporting Evidence:
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
|
|
GO:0042981
regulation of apoptotic process
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: Caspase-9 regulates apoptosis. Isoform 1 positively regulates (induces) apoptosis, while isoform 2 negatively regulates (inhibits) apoptosis. This general term encompasses both functions.
Reason: This general regulatory term is appropriate as CASP9 is involved in apoptosis regulation through both pro-apoptotic (isoform 1) and anti-apoptotic (isoform 2) mechanisms. The InterPro association correctly identifies this function.
Supporting Evidence:
file:human/CASP9/CASP9-deep-research-perplexity.md
The CASP9 gene generates two functionally antagonistic isoforms through alternative splicing: the pro-apoptotic caspase-9a that retains exons 3, 4, 5, and 6, and the anti-apoptotic caspase-9b
|
|
GO:0051604
protein maturation
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: Caspase-9 (isoform 1) processes/matures other proteins including procaspase-3 and procaspase-7 by proteolytic cleavage.
Reason: The annotation captures caspase-9's role in processing downstream effector caspases from their inactive proforms to active enzymes. This is a core function of initiator caspases.
Supporting Evidence:
PMID:16352606
Apaf-1 oligomerizes to produce approximately 1.4-MDa and approximately 700-kDa apoptosome complexes, and the latter complex directly cleaves/activates procaspase-7
|
|
GO:0005515
protein binding
|
IPI
PMID:10206961 An APAF-1.cytochrome c multimeric complex is a functional ap... |
MODIFY |
Summary: PMID:10206961 demonstrates caspase-9 binding to Apaf-1 in the apoptosome complex. While "protein binding" is too vague, the specific interaction with Apaf-1 is core to caspase-9 function.
Reason: "Protein binding" is uninformative. The paper demonstrates CARD-CARD interaction between caspase-9 and Apaf-1 in the apoptosome. A more specific term should be used.
Proposed replacements:
cysteine-type endopeptidase activity
Supporting Evidence:
PMID:10206961
Such a complex can be isolated using gel filtration chromatography and is by itself sufficient to recruit and activate procaspase-9
|
|
GO:0005515
protein binding
|
IPI
PMID:10376594 Structural basis of procaspase-9 recruitment by the apoptoti... |
MODIFY |
Summary: PMID:10376594 describes the structural basis of procaspase-9 recruitment by Apaf-1 via CARD-CARD interactions. "Protein binding" is too general.
Reason: The specific interaction is CARD domain binding. A more informative term would capture the CARD-CARD interaction that recruits caspase-9 to the apoptosome.
Proposed replacements:
identical protein binding
Supporting Evidence:
PMID:10376594
Structural basis of procaspase-9 recruitment by the apoptotic protease-activating factor 1
|
|
GO:0005515
protein binding
|
IPI
PMID:11024045 Livin, a novel inhibitor of apoptosis protein family member. |
KEEP AS NON CORE |
Summary: PMID:11024045 describes Livin (BIRC7), an IAP family member that can bind caspases.
Reason: IAP binding is part of caspase regulation but "protein binding" is too vague. The interaction with IAPs is important for regulation but not a core function annotation.
Supporting Evidence:
PMID:11024045
Livin, a novel inhibitor of apoptosis protein family member
|
|
GO:0005515
protein binding
|
IPI
PMID:11084335 ML-IAP, a novel inhibitor of apoptosis that is preferentiall... |
KEEP AS NON CORE |
Summary: PMID:11084335 describes ML-IAP (BIRC7) interaction with caspases.
Reason: IAP interaction is regulatory. "Protein binding" is too vague but the interaction is documented.
Supporting Evidence:
PMID:11084335
ML-IAP, a novel inhibitor of apoptosis that is preferentially expressed in human melanomas
|
|
GO:0005515
protein binding
|
IPI
PMID:11230124 Recruitment, activation and retention of caspases-9 and -3 b... |
KEEP AS NON CORE |
Summary: PMID:11230124 describes recruitment of caspases to Apaf-1 apoptosome and XIAP complexes.
Reason: Documents apoptosome assembly and XIAP regulation. "Protein binding" is uninformative but the interactions are relevant.
Supporting Evidence:
PMID:11230124
Recruitment, activation and retention of caspases-9 and -3 by Apaf-1 apoptosome and associated XIAP complexes
|
|
GO:0005515
protein binding
|
IPI
PMID:11242052 A conserved XIAP-interaction motif in caspase-9 and Smac/DIA... |
KEEP AS NON CORE |
Summary: PMID:11242052 describes the XIAP-interaction motif in caspase-9 and Smac/DIABLO.
Reason: IAP binding motif documentation. The caspase-9/XIAP interaction is well-established for regulation of caspase activity.
Supporting Evidence:
PMID:11242052
A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis
|
|
GO:0005515
protein binding
|
IPI
PMID:11801603 SMAC negatively regulates the anti-apoptotic activity of mel... |
KEEP AS NON CORE |
Summary: PMID:11801603 describes SMAC interaction with ML-IAP (BIRC7).
Reason: Part of the IAP regulatory network affecting caspase-9 activity.
Supporting Evidence:
PMID:11801603
SMAC negatively regulates the anti-apoptotic activity of melanoma inhibitor of apoptosis
|
|
GO:0005515
protein binding
|
IPI
PMID:11821383 CARD-8 protein, a new CARD family member that regulates casp... |
KEEP AS NON CORE |
Summary: PMID:11821383 describes CARD-8 interaction with caspase-9 via CARD domain. CARD-8 regulates caspase-1 and can interact with caspase-9.
Reason: CARD-8 interaction is regulatory. The paper focuses on caspase-1 regulation with caspase-9 interaction being secondary.
Supporting Evidence:
PMID:11821383
CARD-8 protein, a new CARD family member that regulates caspase-1 activation and apoptosis
|
|
GO:0005515
protein binding
|
IPI
PMID:12620238 Mechanism of XIAP-mediated inhibition of caspase-9. |
KEEP AS NON CORE |
Summary: PMID:12620238 provides structural mechanism of XIAP-mediated caspase-9 inhibition.
Reason: XIAP binding is a key regulatory mechanism. The structural data confirms the interaction but "protein binding" is too vague.
Supporting Evidence:
PMID:12620238
Mechanism of XIAP-mediated inhibition of caspase-9
|
|
GO:0005515
protein binding
|
IPI
PMID:16189514 Towards a proteome-scale map of the human protein-protein in... |
KEEP AS NON CORE |
Summary: PMID:16189514 is a large-scale proteome mapping study. Individual interactions may not be validated.
Reason: High-throughput study. Interactions should be confirmed by directed studies.
Supporting Evidence:
PMID:16189514
Towards a proteome-scale map of the human protein-protein interaction network
|
|
GO:0005515
protein binding
|
IPI
PMID:16537496 The dependence receptor DCC requires lipid raft localization... |
KEEP AS NON CORE |
Summary: PMID:16537496 describes DCC dependence receptor signaling involving caspase-9.
Reason: DCC receptor signaling is a specific pathway involving caspase-9 activation. Not a core function but a documented regulatory interaction.
Supporting Evidence:
PMID:16537496
The dependence receptor DCC requires lipid raft localization for cell death signaling
|
|
GO:0005515
protein binding
|
IPI
PMID:16936772 Integrin-linked kinase interacts with caspase-9 and -8 in an... |
KEEP AS NON CORE |
Summary: PMID:16936772 describes integrin-linked kinase (ILK) interaction with caspases.
Reason: ILK-caspase interaction is context-specific for adhesion-dependent apoptosis in leukemia cells.
Supporting Evidence:
PMID:16936772
Integrin-linked kinase interacts with caspase-9 and -8 in an adhesion-dependent manner
|
|
GO:0005515
protein binding
|
IPI
PMID:18022362 IAP antagonists induce autoubiquitination of c-IAPs, NF-kapp... |
KEEP AS NON CORE |
Summary: PMID:18022362 describes IAP antagonists inducing autoubiquitination of c-IAPs.
Reason: Part of IAP regulatory network affecting caspase activity.
Supporting Evidence:
PMID:18022362
IAP antagonists induce autoubiquitination of c-IAPs, NF-kappaB activation, and TNFalpha-dependent apoptosis
|
|
GO:0005515
protein binding
|
IPI
PMID:18723680 Executioner caspase-3 and caspase-7 are functionally distinc... |
KEEP AS NON CORE |
Summary: PMID:18723680 shows caspase-3 and caspase-7 are functionally distinct, with implications for caspase-9-mediated activation.
Reason: Relevant to caspase-9's substrate specificity but "protein binding" is vague.
Supporting Evidence:
PMID:18723680
Executioner caspase-3 and caspase-7 are functionally distinct proteases
|
|
GO:0005515
protein binding
|
IPI
PMID:19153467 The structure of the BIR3 domain of cIAP1 in complex with th... |
KEEP AS NON CORE |
Summary: PMID:19153467 provides structural data on BIR3 domain of cIAP1 in complex with caspase-9 N-terminal peptide.
Reason: Structural data on IAP-caspase interaction. Regulatory rather than core function.
Supporting Evidence:
PMID:19153467
The structure of the BIR3 domain of cIAP1 in complex with the N-terminal peptides of SMAC and caspase-9
|
|
GO:0005515
protein binding
|
IPI
PMID:19494828 The Apaf-1*procaspase-9 apoptosome complex functions as a pr... |
ACCEPT |
Summary: PMID:19494828 describes the apoptosome as a proteolytic-based molecular timer.
Reason: This paper provides important mechanistic insight into caspase-9/Apaf-1 interaction dynamics in the apoptosome. The interaction is core to function though "protein binding" is uninformative.
Supporting Evidence:
PMID:19494828
The Apaf-1*procaspase-9 apoptosome complex functions as a proteolytic-based molecular timer
|
|
GO:0005515
protein binding
|
IPI
PMID:19721007 Netrin-1 up-regulation in inflammatory bowel diseases is req... |
KEEP AS NON CORE |
Summary: PMID:19721007 describes Netrin-1 signaling in colorectal cancer involving dependence receptors.
Reason: Netrin-1/dependence receptor signaling is a specific context for caspase activation.
Supporting Evidence:
PMID:19721007
Netrin-1 up-regulation in inflammatory bowel diseases is required for colorectal cancer progression
|
|
GO:0005515
protein binding
|
IPI
PMID:20462491 Structure of an apoptosome-procaspase-9 CARD complex. |
ACCEPT |
Summary: PMID:20462491 provides structure of apoptosome-procaspase-9 CARD complex.
Reason: Key structural study of the core caspase-9/Apaf-1 CARD interaction. Though "protein binding" is vague, the CARD-CARD interaction is essential for function.
Supporting Evidence:
PMID:20462491
Structure of an apoptosome-procaspase-9 CARD complex
|
|
GO:0005515
protein binding
|
IPI
PMID:21827945 The holo-apoptosome: activation of procaspase-9 and interact... |
ACCEPT |
Summary: PMID:21827945 describes holo-apoptosome structure and procaspase-9 activation and interactions with caspase-3.
Reason: Core structural/mechanistic study of the apoptosome. Demonstrates caspase-9 binding to apoptosome and interactions with caspase-3.
Supporting Evidence:
PMID:21827945
Activation of procaspase-9 on the apoptosome is a pivotal step in the intrinsic cell death pathway
|
|
GO:0005515
protein binding
|
IPI
PMID:23516580 The E. coli effector protein NleF is a caspase inhibitor. |
KEEP AS NON CORE |
Summary: PMID:23516580 describes E. coli NleF effector as a caspase inhibitor that binds caspase-9.
Reason: Pathogen effector binding is context-specific for microbial infection.
Supporting Evidence:
PMID:23516580
The E. coli effector protein NleF is a caspase inhibitor
|
|
GO:0005515
protein binding
|
IPI
PMID:25241761 Using an in situ proximity ligation assay to systematically ... |
KEEP AS NON CORE |
Summary: High-throughput proximity ligation study.
Reason: Large-scale study requiring validation of individual interactions.
Supporting Evidence:
PMID:25241761
Using an in situ proximity ligation assay to systematically profile endogenous protein-protein interactions
|
|
GO:0005515
protein binding
|
IPI
PMID:25416956 A proteome-scale map of the human interactome network. |
KEEP AS NON CORE |
Summary: Proteome-scale interactome mapping study.
Reason: High-throughput study. Individual interactions need validation.
Supporting Evidence:
PMID:25416956
A proteome-scale map of the human interactome network
|
|
GO:0005515
protein binding
|
IPI
PMID:25502805 A massively parallel pipeline to clone DNA variants and exam... |
KEEP AS NON CORE |
Summary: Massively parallel cloning and phenotyping study.
Reason: High-throughput study.
Supporting Evidence:
PMID:25502805
A massively parallel pipeline to clone DNA variants and examine molecular phenotypes
|
|
GO:0005515
protein binding
|
IPI
PMID:25519916 The EHEC-host interactome reveals novel targets for the tran... |
KEEP AS NON CORE |
Summary: EHEC-host interactome study identifying translocated intimin receptor targets.
Reason: Pathogen-host interaction context.
Supporting Evidence:
PMID:25519916
The EHEC-host interactome reveals novel targets for the translocated intimin receptor
|
|
GO:0005515
protein binding
|
IPI
PMID:27107012 Pooled-matrix protein interaction screens using Barcode Fusi... |
KEEP AS NON CORE |
Summary: Barcode Fusion Genetics protein interaction screen.
Reason: High-throughput screening method.
Supporting Evidence:
PMID:27107012
Pooled-matrix protein interaction screens using Barcode Fusion Genetics
|
|
GO:0005515
protein binding
|
IPI
PMID:29997244 LuTHy: a double-readout bioluminescence-based two-hybrid tec... |
KEEP AS NON CORE |
Summary: LuTHy two-hybrid technology for protein interaction mapping.
Reason: High-throughput interaction mapping study.
Supporting Evidence:
PMID:29997244
LuTHy: a double-readout bioluminescence-based two-hybrid technology
|
|
GO:0005515
protein binding
|
IPI
PMID:31467278 Maximizing binary interactome mapping with a minimal number ... |
KEEP AS NON CORE |
Summary: Binary interactome mapping optimization study.
Reason: Methodological study for interaction mapping.
Supporting Evidence:
PMID:31467278
Maximizing binary interactome mapping with a minimal number of assays
|
|
GO:0005515
protein binding
|
IPI
PMID:31515488 Extensive disruption of protein interactions by genetic vari... |
KEEP AS NON CORE |
Summary: Study of protein interaction disruption by genetic variants.
Reason: Population genetics study of interaction disruption.
Supporting Evidence:
PMID:31515488
Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum
|
|
GO:0005515
protein binding
|
IPI
PMID:32296183 A reference map of the human binary protein interactome. |
KEEP AS NON CORE |
Summary: Reference map of human binary protein interactome.
Reason: Large-scale interactome reference study.
Supporting Evidence:
PMID:32296183
A reference map of the human binary protein interactome
|
|
GO:0005515
protein binding
|
IPI
PMID:9390557 Cytochrome c and dATP-dependent formation of Apaf-1/caspase-... |
ACCEPT |
Summary: PMID:9390557 is a landmark paper demonstrating caspase-9/Apaf-1 CARD-CARD interaction in apoptosome formation.
Reason: Foundational paper on caspase-9 function. Demonstrates the core CARD-CARD interaction with Apaf-1 essential for apoptosome formation and caspase activation.
Supporting Evidence:
PMID:9390557
Caspase-9 and Apaf-1 bind to each other via their respective NH2-terminal CED-3 homologous domains in the presence of cytochrome c and dATP
|
|
GO:0005515
protein binding
|
IPI
PMID:9922454 Ordering the cytochrome c-initiated caspase cascade: hierarc... |
ACCEPT |
Summary: PMID:9922454 describes the caspase cascade with caspase-9 dependent activation of downstream caspases.
Reason: Demonstrates caspase-9 interaction with and processing of downstream caspases (caspase-2, -3, -6, -7, -8, -10). Core function of initiator caspase.
Supporting Evidence:
PMID:9922454
Ordering the cytochrome c-initiated caspase cascade: hierarchical activation of caspases-2, -3, -6, -7, -8, and -10 in a caspase-9-dependent manner
|
|
GO:0001666
response to hypoxia
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Caspase-9 is activated during hypoxia-induced apoptosis. Recent research shows non-apoptotic endothelial caspase-9 signaling in hypoxia-ischemia.
Reason: Deep research confirms: "In a mouse model of retinal vein occlusion (RVO), pharmacological inhibition or genetic deletion of caspase-9 specifically from endothelial cells significantly reduces vascular edema." Hypoxia triggers intrinsic apoptotic pathway.
Supporting Evidence:
file:human/CASP9/CASP9-deep-research-perplexity.md
endothelial caspase-9 activation following hypoxia-ischemia appears to occur independently of apoptosis
|
|
GO:0001822
kidney development
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Caspase-mediated apoptosis plays roles in kidney development. This is a pleiotropic developmental process.
Reason: Apoptosis is involved in kidney development but this is not a core function of caspase-9. The annotation is from ortholog transfer (Ensembl Compara).
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0002931
response to ischemia
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Caspase-9 is activated in ischemic injury, both through apoptotic and non-apoptotic mechanisms in endothelial cells.
Reason: Deep research confirms: "In a mouse model of retinal vein occlusion (RVO), pharmacological inhibition or genetic deletion of caspase-9...significantly reduces vascular edema, restores vascular integrity, and provides robust neuroprotection."
Supporting Evidence:
file:human/CASP9/CASP9-deep-research-perplexity.md
non-apoptotic endothelial caspase-9 signaling as a critical mediator of ischemic injury in hypoxia-ischemia models
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Nuclear localization of caspase-9 is less well-established than cytosolic localization. Some reports suggest translocation during apoptosis.
Reason: Caspase-9 is primarily cytosolic. Nuclear localization may occur in specific contexts but is not the primary site of function. The annotation is from ortholog transfer and should be viewed with caution.
Supporting Evidence:
PMID:12782307
caspase-9 is in the cytoplasm of non-apoptotic pituitary cells
|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Cytoplasmic localization is well-established. Redundant with IBA annotation.
Reason: Consistent with IBA annotation and experimental evidence. Caspase-9 is predominantly cytoplasmic.
Supporting Evidence:
PMID:12782307
caspase-9 is in the cytoplasm of non-apoptotic pituitary cells
|
|
GO:0005829
cytosol
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Cytosolic localization confirmed. Redundant with IBA and TAS annotations.
Reason: Consistent with other annotations and experimental evidence.
Supporting Evidence:
PMID:12782307
caspase-9 is in the cytoplasm of non-apoptotic pituitary cells
|
|
GO:0016485
protein processing
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Caspase-9 processes procaspases-3 and -7 by proteolytic cleavage. This is a core function.
Reason: Caspase-9 processes its substrates (procaspase-3, procaspase-7) to their mature forms. This is the primary enzymatic function.
Supporting Evidence:
PMID:16352606
Apaf-1 oligomerizes to produce approximately 1.4-MDa and approximately 700-kDa apoptosome complexes, and the latter complex directly cleaves/activates procaspase-7
|
|
GO:0032025
response to cobalt ion
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Cobalt ions can induce hypoxia-like responses. Caspase-9 may be activated in this context.
Reason: Cobalt-induced response is likely through hypoxia mimicry. Not a core function but an experimental context. Annotation from ortholog transfer.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0032355
response to estradiol
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Estradiol can have anti-apoptotic effects that may involve caspase regulation.
Reason: Hormone response is context-specific. Annotation from ortholog transfer. Not a core function.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0032496
response to lipopolysaccharide
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: LPS can trigger apoptotic pathways in various cell types.
Reason: LPS response is context-specific, particularly relevant to immune cells. Annotation from ortholog transfer.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0034349
glial cell apoptotic process
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Caspase-9 is involved in glial cell apoptosis as part of CNS development and disease.
Reason: Cell-type specific apoptotic process. Not a core function but consistent with caspase-9's role in CNS development. CRITICAL: Only isoform 1 would positively regulate this.
Supporting Evidence:
file:human/CASP9/CASP9-deep-research-perplexity.md
mice lacking caspase-9 die perinatally with severe brain abnormalities
|
|
GO:0043065
positive regulation of apoptotic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CRITICAL ISOFORM ANNOTATION: This annotation is ONLY true for isoform 1 (Caspase-9L/Alpha). Isoform 2 (Caspase-9S/Beta) is a DOMINANT-NEGATIVE INHIBITOR that NEGATIVELY regulates apoptosis.
Reason: Isoform 1 does positively regulate apoptosis by activating effector caspases. However, the annotation should ideally be isoform-specific. The IEA annotation applies to the canonical pro-apoptotic function.
Supporting Evidence:
PMID:9390557
caspase-9 is the most upstream member of the apoptotic protease cascade
file:human/CASP9/CASP9-deep-research-perplexity.md
the pro-apoptotic caspase-9a that retains exons 3, 4, 5, and 6, and the anti-apoptotic caspase-9b
|
|
GO:0045471
response to ethanol
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Ethanol can induce apoptosis in various tissues including liver and neurons.
Reason: Toxicological response context. Annotation from ortholog transfer. Not a core function.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0071549
cellular response to dexamethasone stimulus
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Dexamethasone can induce apoptosis in some cell types.
Reason: Glucocorticoid response is context-specific. Annotation from ortholog transfer.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0071680
response to indole-3-methanol
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Indole-3-carbinol is a phytochemical that can affect apoptotic pathways.
Reason: Specific chemical response. Not a core function. Annotation from ortholog transfer.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0071887
leukocyte apoptotic process
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Caspase-9 is involved in leukocyte apoptosis as part of immune regulation.
Reason: Cell-type specific apoptotic process. The intrinsic pathway operates in leukocytes but this is not a core function annotation. CRITICAL: Only isoform 1 promotes this.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0072347
response to anesthetic
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Some anesthetics can induce neuronal apoptosis involving caspase-9.
Reason: Specific pharmacological context. Annotation from ortholog transfer.
Supporting Evidence:
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs
|
|
GO:0004197
cysteine-type endopeptidase activity
|
TAS
Reactome:R-HSA-114259 |
ACCEPT |
Summary: Reactome pathway annotation for caspase-9 cleavage. CRITICAL: This catalytic activity is ONLY present in isoform 1.
Reason: Reactome correctly annotates the catalytic activity in the context of apoptosome-mediated procaspase-9 cleavage to active caspase-9.
Supporting Evidence:
Reactome:R-HSA-114259
Procaspase‑9 is processed in an ATP‑dependent manner following association with APAF1 and cytochrome c (CYCS) within the apoptosome complex
|
|
GO:0097193
intrinsic apoptotic signaling pathway
|
NAS
PMID:10206961 An APAF-1.cytochrome c multimeric complex is a functional ap... |
ACCEPT |
Summary: PMID:10206961 demonstrates caspase-9 activation in the apoptosome as the key step in the intrinsic apoptotic pathway. CRITICAL: Isoform 1 activates while isoform 2 inhibits this pathway.
Reason: Core annotation for caspase-9 function. The paper demonstrates apoptosome formation and procaspase-9 activation.
Supporting Evidence:
PMID:10206961
Such a complex can be isolated using gel filtration chromatography and is by itself sufficient to recruit and activate procaspase-9
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IDA
PMID:16352606 Caspase-7 is directly activated by the approximately 700-kDa... |
ACCEPT |
Summary: PMID:16352606 demonstrates caspase-9 directly cleaving and activating caspase-7 in the apoptosome. This is direct experimental evidence for the catalytic activity (isoform 1 only).
Reason: Direct experimental demonstration of caspase-9 enzymatic activity in processing caspase-7.
Supporting Evidence:
PMID:16352606
Apaf-1 oligomerizes to produce approximately 1.4-MDa and approximately 700-kDa apoptosome complexes, and the latter complex directly cleaves/activates procaspase-7
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IDA
PMID:16916640 Engineered hybrid dimers: tracking the activation pathway of... |
ACCEPT |
Summary: PMID:16916640 uses engineered hybrid dimers to track caspase-7 activation by caspase-9, demonstrating the endopeptidase activity (isoform 1).
Reason: Direct experimental demonstration of caspase-9 enzymatic activity in processing caspase-7 using sophisticated biochemical approaches.
Supporting Evidence:
PMID:16916640
A transient intermediate of singly cleaved dimeric caspase-7 can be found in a cell-free model of apoptosis induction
|
|
GO:0043065
positive regulation of apoptotic process
|
IMP
PMID:11821383 CARD-8 protein, a new CARD family member that regulates casp... |
ACCEPT |
Summary: PMID:11821383 describes CARD-8 interaction with caspase-9. The paper shows CARD-8 overexpression induces apoptosis. CRITICAL: This pro-apoptotic function is isoform 1 specific.
Reason: The study demonstrates caspase-9's role in apoptosis induction through CARD-domain interactions. The mutant phenotype evidence supports positive regulation of apoptosis.
Supporting Evidence:
PMID:11821383
Overexpression of CARD-8 can also induce apoptosis in transfected cells
|
|
GO:0006974
DNA damage response
|
IMP
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 demonstrates c-Abl phosphorylates caspase-9 in DNA damage response, with mutant phenotype evidence.
Reason: Direct experimental evidence using Y153F mutant showing attenuated DNA damage-induced caspase-9 processing and apoptosis.
Supporting Evidence:
PMID:15657060
Caspase-9(Y153F) also attenuated DNA damage-induced processing of caspase-9 to p35, activation of caspase-3, and apoptosis
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-9627089 |
ACCEPT |
Summary: Reactome pathway annotation for caspase-9 localization in phosphorylation reaction.
Reason: Consistent with other cytosolic localization annotations. Caspase-9 is phosphorylated at T412 in the cytosol.
Supporting Evidence:
Reactome:R-HSA-9627089
CASP9 is phosphorylated at T412
|
|
GO:0097193
intrinsic apoptotic signaling pathway
|
IDA
PMID:35446120 Calmodulin Binding Activates Chromobacterium CopC Effector t... |
ACCEPT |
Summary: PMID:35446120 shows Chromobacterium CopC effector ADP-riboxanates caspase-9 to inhibit intrinsic apoptotic pathway. This demonstrates caspase-9's role in the pathway (isoform 1).
Reason: The study demonstrates caspase-9's essential role in intrinsic apoptotic signaling by showing that pathogen effector modification blocks this pathway.
Supporting Evidence:
PMID:35446120
Calmodulin Binding Activates Chromobacterium CopC Effector to ADP-Riboxanate Host Apoptotic Caspases
|
|
GO:0005739
mitochondrion
|
IDA
PMID:12782307 Apoptosis triggered redistribution of caspase-9 from cytopla... |
ACCEPT |
Summary: PMID:12782307 shows caspase-9 redistributes from cytoplasm to mitochondria during apoptosis.
Reason: Direct experimental evidence of caspase-9 mitochondrial localization during apoptosis. The paper shows "activation of apoptosis with rotenone triggers the redistribution of caspase-9 to mitochondria."
Supporting Evidence:
PMID:12782307
The activation of apoptosis with rotenone triggers the redistribution of caspase-9 to mitochondria
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IDA
PMID:27889207 Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apopto... |
ACCEPT |
Summary: PMID:27889207 demonstrates PAK2 phosphorylation of caspase-7 blocks its activation by caspase-9, providing evidence for caspase-9 enzymatic activity (isoform 1).
Reason: The study demonstrates caspase-9's enzymatic activity in caspase-7 activation.
Supporting Evidence:
PMID:27889207
Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apoptotic Activity by Two Distinct Mechanisms
|
|
GO:0051604
protein maturation
|
IDA
PMID:16352606 Caspase-7 is directly activated by the approximately 700-kDa... |
ACCEPT |
Summary: PMID:16352606 shows caspase-9 directly matures procaspase-7 to active caspase-7 (isoform 1 function).
Reason: Direct experimental evidence of caspase-9 processing procaspase-7 to mature enzyme.
Supporting Evidence:
PMID:16352606
Apaf-1 oligomerizes to produce approximately 1.4-MDa and approximately 700-kDa apoptosome complexes, and the latter complex directly cleaves/activates procaspase-7
|
|
GO:0051604
protein maturation
|
IDA
PMID:16916640 Engineered hybrid dimers: tracking the activation pathway of... |
ACCEPT |
Summary: PMID:16916640 demonstrates caspase-7 maturation by caspase-9 using hybrid dimers (isoform 1 function).
Reason: Direct experimental evidence using sophisticated biochemical approaches to demonstrate procaspase-7 maturation.
Supporting Evidence:
PMID:16916640
The processed domain of this singly cleaved zymogen has the same catalytic activity as a domain of fully active caspase-7
|
|
GO:1900119
positive regulation of execution phase of apoptosis
|
IDA
PMID:16916640 Engineered hybrid dimers: tracking the activation pathway of... |
ACCEPT |
Summary: PMID:16916640 demonstrates caspase-9 activates caspase-7, which executes apoptosis. CRITICAL: This is isoform 1 specific.
Reason: The execution phase of apoptosis is triggered by activation of executioner caspases (caspase-3 and -7) by caspase-9. Direct experimental evidence.
Supporting Evidence:
PMID:16916640
Our study demonstrates the efficiency by which the executioner caspases are activated in vivo
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IMP
PMID:21980415 Identification of a conserved anti-apoptotic protein that mo... |
ACCEPT |
Summary: PMID:21980415 identifies conserved anti-apoptotic protein modulating mitochondrial apoptosis pathway, using mutant phenotypes to demonstrate caspase-9 activity.
Reason: Mutant phenotype evidence for caspase-9 catalytic activity in apoptosis.
Supporting Evidence:
PMID:21980415
Identification of a conserved anti-apoptotic protein that modulates the mitochondrial apoptosis pathway
|
|
GO:0006915
apoptotic process
|
IMP
PMID:15069058 BRCC2, a novel BH3-like domain-containing protein, induces a... |
ACCEPT |
Summary: PMID:15069058 describes BRCC2, a BH3-domain protein that induces apoptosis in a caspase-dependent manner.
Reason: Mutant phenotype evidence for caspase-9 role in apoptosis through BH3 domain protein interactions.
Supporting Evidence:
PMID:15069058
BRCC2, a novel BH3-like domain-containing protein, induces apoptosis in a caspase-dependent manner
|
|
GO:0004197
cysteine-type endopeptidase activity
|
IDA
PMID:16920334 Protective role of Cop in Rip2/caspase-1/caspase-4-mediated ... |
ACCEPT |
Summary: PMID:16920334 examines Cop protective role in caspase-mediated cell death (isoform 1 function).
Reason: Direct assay evidence for caspase-9 catalytic activity in cell death.
Supporting Evidence:
PMID:16920334
Protective role of Cop in Rip2/caspase-1/caspase-4-mediated HeLa cell death
|
|
GO:0005515
protein binding
|
IPI
PMID:11821383 CARD-8 protein, a new CARD family member that regulates casp... |
KEEP AS NON CORE |
Summary: PMID:11821383 shows CARD-8 binds to caspase-9 via CARD domain interaction.
Reason: CARD domain interaction is documented but "protein binding" is uninformative. The CARD-CARD interaction is regulatory.
Supporting Evidence:
PMID:11821383
CARD-8 binds also to ICEBERG and pseudo-ICE
|
|
GO:0032991
protein-containing complex
|
IDA
PMID:11821383 CARD-8 protein, a new CARD family member that regulates casp... |
KEEP AS NON CORE |
Summary: PMID:11821383 identifies caspase-9 in protein complexes with CARD-8.
Reason: Generic complex annotation. The apoptosome is the key functional complex for caspase-9.
Supporting Evidence:
PMID:11821383
CARD-8 interacts physically with caspase-1
|
|
GO:0008233
peptidase activity
|
IDA
PMID:19740745 A truncated form of p23 down-regulates telomerase activity v... |
ACCEPT |
Summary: PMID:19740745 shows truncated p23 disrupts Hsp90 function affecting telomerase. Caspase-9 peptidase activity is involved (isoform 1).
Reason: Direct assay evidence for caspase-9 peptidase activity. Parent term of cysteine-type endopeptidase activity.
Supporting Evidence:
PMID:19740745
A truncated form of p23 down-regulates telomerase activity via disruption of Hsp90 function
|
|
GO:0005515
protein binding
|
IPI
PMID:19255499 HIP1R interacts with a member of Bcl-2 family, BCL2L10, and ... |
KEEP AS NON CORE |
Summary: PMID:19255499 shows HIP1R interacts with BCL2L10 which affects BAK-dependent cell death.
Reason: BCL2L10 interaction affects mitochondrial apoptosis pathway. Regulatory interaction.
Supporting Evidence:
PMID:19255499
HIP1R interacts with a member of Bcl-2 family, BCL2L10, and induces BAK-dependent cell death
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-114252 |
ACCEPT |
Summary: Reactome pathway annotation for procaspase-3 cleavage by apoptosome.
Reason: Consistent with cytosolic localization of the apoptosome complex where caspase-9 cleaves procaspase-3.
Supporting Evidence:
Reactome:R-HSA-114252
Cleavage of Procaspase-3 by the apoptosome
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-114259 |
ACCEPT |
Summary: Reactome annotation for procaspase-9 cleavage.
Reason: Consistent with cytosolic localization of the apoptosome.
Supporting Evidence:
Reactome:R-HSA-114259
Procaspase‑9 is processed in an ATP‑dependent manner following association with APAF1 and cytochrome c (CYCS) within the apoptosome complex
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-114261 |
ACCEPT |
Summary: Reactome annotation for procaspase-7 cleavage by apoptosome.
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-114261
Cleavage of Procaspase-7 by the apoptosome
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-373700 |
ACCEPT |
Summary: Reactome annotation for caspase-9 binding to DCC:DIP13alpha complex.
Reason: Consistent with cytosolic localization for dependence receptor signaling.
Supporting Evidence:
Reactome:R-HSA-373700
Caspase-9 binds DCC:DIP13alpha complex
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-418845 |
ACCEPT |
Summary: Reactome annotation for caspase-3 activation.
Reason: Consistent with cytosolic localization for caspase cascade.
Supporting Evidence:
Reactome:R-HSA-418845
Activation of caspase-3
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-6804596 |
ACCEPT |
Summary: Reactome annotation for APAF1:CYCS binding APIP.
Reason: Consistent with cytosolic localization of apoptosome components.
Supporting Evidence:
Reactome:R-HSA-6804596
APAF1:CYCS binds APIP
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-6805426 |
ACCEPT |
Summary: Reactome annotation for CARD8 binding to CASP9(1-416).
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-6805426
CARD8 binds CASP9(1-416)
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-9627056 |
ACCEPT |
Summary: Reactome annotation for procaspase-9 dimer formation.
Reason: Consistent with cytosolic localization for dimerization.
Supporting Evidence:
Reactome:R-HSA-9627056
Procaspase 9 forms dimer
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-9627078 |
ACCEPT |
Summary: Reactome annotation for XIAP binding CASP9.
Reason: Consistent with cytosolic localization for IAP regulation.
Supporting Evidence:
Reactome:R-HSA-9627078
X‑linked inhibitor‑of‑apoptosis protein (XIAP) associates with the cleaved form of CASP9
|
|
GO:0005829
cytosol
|
IDA
PMID:17167422 Hsp70 regulates erythropoiesis by preventing caspase-3-media... |
ACCEPT |
Summary: PMID:17167422 shows Hsp70 regulates erythropoiesis by preventing caspase-3 cleavage of GATA-1 in the cytosol.
Reason: Direct experimental evidence for cytosolic caspase activity during erythroid differentiation.
Supporting Evidence:
PMID:17167422
At the onset of caspase activation, Hsp70 co-localizes and interacts with GATA-1 in the nucleus
|
|
GO:0030220
platelet formation
|
TAS
PMID:18309324 No death without life: vital functions of apoptotic effector... |
KEEP AS NON CORE |
Summary: PMID:18309324 reviews non-apoptotic functions of apoptotic effectors, including roles in platelet formation.
Reason: Non-apoptotic function of caspases in platelet formation is documented. This represents a specialized function distinct from core apoptotic role.
Supporting Evidence:
PMID:18309324
multiple studies indicate that the mammalian orthologs of these C. elegans proteins (i.e. caspases, Apaf-1 and multidomain proteins of the Bcl-2 family) participate in cell death-unrelated processes
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-114256 |
ACCEPT |
Summary: Reactome annotation for CYCS:APAF1 binding procaspase-9.
Reason: Consistent with cytosolic localization of apoptosome assembly.
Supporting Evidence:
Reactome:R-HSA-114256
CYCS:APAF1 binds procaspase-9
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-198621 |
ACCEPT |
Summary: Reactome annotation for AKT phosphorylates caspase-9.
Reason: Consistent with cytosolic localization for AKT-mediated regulation.
Supporting Evidence:
Reactome:R-HSA-198621
AKT phosphorylates caspase-9
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-2399985 |
ACCEPT |
Summary: Reactome annotation for AKT1 E17K mutant phosphorylates caspase-9.
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-2399985
AKT1 E17K mutant phosphorylates caspase-9
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-6804596 |
ACCEPT |
Summary: Duplicate annotation - same as earlier entry.
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-6804596
APAF1:CYCS binds APIP
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-6805426 |
ACCEPT |
Summary: Duplicate annotation - same as earlier entry.
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-6805426
CARD8 binds CASP9(1-416)
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-9627056 |
ACCEPT |
Summary: Duplicate annotation - same as earlier entry.
Reason: Consistent with cytosolic localization.
Supporting Evidence:
Reactome:R-HSA-9627056
Procaspase 9 forms dimer
|
|
GO:0005515
protein binding
|
IPI
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 shows c-Abl directly binds caspase-9 via SH3 domain.
Reason: c-Abl/caspase-9 interaction is functionally important for DNA damage response. Though "protein binding" is vague, the interaction is core to DNA damage-induced apoptosis.
Supporting Evidence:
PMID:15657060
c-Abl binds directly to caspase-9
|
|
GO:0006974
DNA damage response
|
IDA
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 provides direct assay evidence for caspase-9 in DNA damage response through c-Abl-mediated phosphorylation.
Reason: Direct experimental demonstration of caspase-9 activation in DNA damage response via c-Abl phosphorylation at Tyr-153.
Supporting Evidence:
PMID:15657060
c-Abl phosphorylates caspase-9 on Tyr-153 in vitro and in cells treated with DNA damaging agents
|
|
GO:0008630
intrinsic apoptotic signaling pathway in response to DNA damage
|
IMP
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 demonstrates Y153F mutant attenuates DNA damage-induced caspase-9 processing and apoptosis.
Reason: Mutant phenotype evidence for caspase-9 role in intrinsic apoptotic signaling in response to DNA damage.
Supporting Evidence:
PMID:15657060
Caspase-9(Y153F) also attenuated DNA damage-induced processing of caspase-9 to p35, activation of caspase-3, and apoptosis
|
|
GO:0019901
protein kinase binding
|
IDA
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 demonstrates caspase-9 binds c-Abl tyrosine kinase.
Reason: Direct experimental evidence for caspase-9 binding to c-Abl kinase. This is a more informative term than generic "protein binding".
Supporting Evidence:
PMID:15657060
c-Abl binds directly to caspase-9
|
|
GO:0034644
cellular response to UV
|
IDA
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 demonstrates caspase-9 activation in response to UV irradiation via c-Abl.
Reason: Direct experimental evidence for caspase-9 role in UV response. The Y153F mutant attenuates UV irradiation-induced apoptosis.
Supporting Evidence:
PMID:15657060
Caspase-9(Y153F) also attenuated DNA damage-induced processing of caspase-9 to p35, activation of caspase-3, and apoptosis
|
|
GO:0042770
signal transduction in response to DNA damage
|
IDA
PMID:15657060 c-Abl tyrosine kinase regulates caspase-9 autocleavage in th... |
ACCEPT |
Summary: PMID:15657060 shows c-Abl-mediated signal transduction to caspase-9 in DNA damage response.
Reason: Direct experimental evidence for caspase-9 role in DNA damage signal transduction through c-Abl kinase.
Supporting Evidence:
PMID:15657060
c-Abl tyrosine kinase regulates caspase-9 autocleavage in the apoptotic response to DNA damage
|
|
GO:0005515
protein binding
|
IPI
PMID:11350957 Characterization of a novel proapoptotic caspase-2- and casp... |
KEEP AS NON CORE |
Summary: PMID:11350957 describes proapoptotic caspase-2 and caspase-9 binding protein.
Reason: Documents a caspase-binding protein. "Protein binding" is uninformative.
Supporting Evidence:
PMID:11350957
Characterization of a novel proapoptotic caspase-2- and caspase-9-binding protein
|
|
GO:0043293
apoptosome
|
IDA
PMID:21827945 The holo-apoptosome: activation of procaspase-9 and interact... |
ACCEPT |
Summary: PMID:21827945 provides structural evidence for caspase-9 as a component of the apoptosome.
Reason: Key structural study demonstrating caspase-9 localization to the apoptosome. CRITICAL: Both isoforms can bind Apaf-1 in the apoptosome, but with opposite effects (isoform 1 activates cascade, isoform 2 inhibits).
Supporting Evidence:
PMID:21827945
Activation of procaspase-9 on the apoptosome is a pivotal step in the intrinsic cell death pathway
|
|
GO:0006915
apoptotic process
|
TAS
PMID:8663294 ICE-LAP6, a novel member of the ICE/Ced-3 gene family, is ac... |
ACCEPT |
Summary: PMID:8663294 is the original paper characterizing ICE-LAP6 (caspase-9) as an apoptosis-inducing caspase.
Reason: Foundational paper demonstrating caspase-9 (ICE-LAP6) induces apoptosis when overexpressed and is activated by granzyme B.
Supporting Evidence:
PMID:8663294
Overexpression of ICE-LAP6 induces apoptosis in MCF7 breast carcinoma cells
|
|
GO:0005515
protein binding
|
IPI
PMID:11069302 Regulation of apoptosis at cell division by p34cdc2 phosphor... |
KEEP AS NON CORE |
Summary: PMID:11069302 describes survivin interaction with caspase-9.
Reason: Survivin is an IAP family member that regulates caspase-9 activity. Regulatory interaction.
Supporting Evidence:
PMID:11069302
Regulation of apoptosis at cell division by p34cdc2 phosphorylation of survivin
|
|
GO:0004197
cysteine-type endopeptidase activity
|
TAS
PMID:9390557 Cytochrome c and dATP-dependent formation of Apaf-1/caspase-... |
ACCEPT |
Summary: PMID:9390557 is the landmark paper demonstrating caspase-9 catalytic activity in the intrinsic pathway (isoform 1).
Reason: Foundational paper demonstrating caspase-9 cleaves and activates caspase-3.
Supporting Evidence:
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
|
|
GO:0008047
enzyme activator activity
|
TAS
PMID:9390557 Cytochrome c and dATP-dependent formation of Apaf-1/caspase-... |
ACCEPT |
Summary: PMID:9390557 demonstrates caspase-9 activates caspase-3 (isoform 1 function).
Reason: Caspase-9 functions as an enzyme activator by cleaving and activating downstream effector caspases. This captures the initiator caspase function.
Supporting Evidence:
PMID:9390557
Activated caspase-9 in turn cleaves and activates caspase-3
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GO:0043066
negative regulation of apoptotic process
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TAS
PMID:10070954 Identification of an endogenous dominant-negative short isof... |
NEW |
Summary: MISSING ANNOTATION: Caspase-9S (isoform 2, P55211-2) is a dominant-negative inhibitor of apoptosis. UniProt explicitly states "Isoform 2: Lacks activity is an dominant-negative inhibitor of caspase-9." This annotation is CRITICAL for understanding CASP9 biology.
Reason: Isoform 2 (Caspase-9S/Beta) lacks the catalytic domain and competes with isoform 1 for Apaf-1 binding, thereby inhibiting apoptosis. This is a dominant-negative mechanism where the 9L/9S ratio determines apoptotic sensitivity. PMID:10070954 characterizes this isoform. Cancer cells often shift ratio towards 9S to evade apoptosis.
Supporting Evidence:
PMID:10070954
Identification of an endogenous dominant-negative short isoform of caspase-9 that can regulate apoptosis
file:human/CASP9/CASP9-deep-research-perplexity.md
the anti-apoptotic caspase-9b that excludes these exons...caspase-9b lacks the core catalytic domain and functions as a dominant-negative inhibitor of caspase-9a
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GO:0030234
enzyme regulator activity
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NAS | NEW |
Summary: Added to align core_functions with existing annotations.
Reason: Core function term not present in existing_annotations.
Supporting Evidence:
PMID:10070954
Identification of an endogenous dominant-negative short isoform of caspase-9 that can regulate apoptosis
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Q: How do cells regulate the ratio of Caspase-9L to Caspase-9S isoforms, and what splicing factors are involved in this decision?
Q: What is the precise molecular mechanism by which Caspase-9S inhibits apoptosis - does it simply sequester Apaf-1 or does it have additional inhibitory mechanisms?
Q: What are the non-apoptotic functions of caspase-9 in autophagy, synaptic plasticity, and vascular function, and how are these regulated independently of apoptosis?
Experiment: Isoform-specific proteomics: Develop isoform-specific antibodies or mass spectrometry methods to quantify 9L/9S ratios across tissues and disease states.
Experiment: Structural studies of Caspase-9S in the apoptosome: Determine how the truncated isoform interacts with Apaf-1 and whether it truly occupies the same binding site as 9L.
Experiment: Conditional isoform knockout: Generate mice with isoform-specific knockouts to determine the specific physiological roles of each isoform.
provider: perplexity
model: sonar-deep-research
cached: false
start_time: '2026-01-19T08:03:11.790165'
end_time: '2026-01-19T08:05:26.281015'
duration_seconds: 134.49
template_file: templates/gene_research_go_focused.md
template_variables:
organism: human
gene_id: CASP9
gene_symbol: CASP9
uniprot_accession: P55211
protein_description: 'RecName: Full=Caspase-9; Short=CASP-9; EC=3.4.22.62 {ECO:0000269|PubMed:16916640,
ECO:0000269|PubMed:23516580, ECO:0000269|PubMed:27889207}; AltName: Full=Apoptotic
protease Mch-6; AltName: Full=Apoptotic protease-activating factor 3; Short=APAF-3;
AltName: Full=ICE-like apoptotic protease 6; Short=ICE-LAP6; Contains: RecName:
Full=Caspase-9 subunit p35; Contains: RecName: Full=Caspase-9 subunit p10; Flags:
Precursor;'
gene_info: Name=CASP9; Synonyms=MCH6;
organism_full: Homo sapiens (Human).
protein_family: Belongs to the peptidase C14A family. .
protein_domains: CARD. (IPR001315); CARD_CASP9. (IPR042147); Caspase-like_dom_sf.
(IPR029030); Caspase_cys_AS. (IPR033139); Caspase_his_AS. (IPR016129)
provider_config:
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return_citations: true
temperature: 0.0
citation_count: 52
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'CASP9' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene CASP9 (gene ID: CASP9, UniProt: P55211) in human.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Caspase-9, encoded by the CASP9 gene (UniProt: P55211), stands as one of the most intensively studied initiator caspases and represents a critical hub in cellular decision-making between life and death[1][7]. As a 416-residue cysteine-aspartic protease belonging to the peptidase C14A family, caspase-9 serves as a pivotal molecular switch that initiates the intrinsic or mitochondrial apoptotic pathway in response to diverse cellular stressors including chemotherapy, DNA damage, oxidative stress, and radiation[1][4]. Beyond its canonical role in triggering programmed cell death, emerging evidence demonstrates that caspase-9 executes sophisticated non-apoptotic functions that influence mitochondrial homeostasis, autophagy regulation, immune responses, vascular integrity, and synaptic plasticity[14][35][36]. This multifaceted protease achieves remarkable selectivity in its enzymatic activity and is subject to intricate multilayered regulation through phosphorylation, alternative splicing, protein-protein interactions, and allosteric mechanisms, positioning it as a central node in cellular physiology with profound implications for cancer biology, neurodegeneration, developmental processes, and therapeutic intervention.
Caspase-9 possesses a distinctive modular architecture that fundamentally shapes its regulatory properties and distinguishes it from other members of the caspase family[1][5][10]. The protein comprises several functionally discrete domains organized in a linear fashion: an N-terminal caspase activation and recruitment domain (CARD) spanning residues 1 to 92, a long and disordered linker region connecting residues 93 to 138, a protease domain subdivided into two subunits designated p20 (residues 139 to 289) and p10 (residues 341 to 416), and another lengthy disordered linker connecting the p20 and p10 subunits (residues 290 to 340)[5][10]. The CARD domain functions as a dedicated protein interaction module that facilitates homotypic interactions with the CARD present in apoptotic protease-activating factor 1 (Apaf-1), thereby serving as the primary recruitment mechanism by which caspase-9 becomes tethered to the apoptosome complex[1][20]. This CARD-CARD interaction represents a paradigmatic example of death domain superfamily protein-protein recognition, involving complementary electrostatic interfaces formed between positively charged helices in the caspase-9 CARD and negatively charged helices in the Apaf-1 CARD[20].
The protease domain of caspase-9 contains the catalytic machinery required for proteolytic cleavage of downstream substrates[1][5]. Within the active site resides a cysteine-histidine catalytic dyad, with cysteine-287 serving as the nucleophilic catalyst and histidine-237 functioning as the general base facilitator[5][10]. Structural analysis reveals that the active site contains four highly mobile loops that must achieve a properly ordered conformation to establish substrate-binding competency[10][53]. A striking feature distinguishing caspase-9 from most other executioner caspases is the presence of long disordered linker regions that physically separate the CARD from the catalytic core, which creates unusual regulatory properties and prevents caspase-9 from existing constitutively as a dimeric enzyme in solution[5][10].
Unexpectedly, extensive mechanistic studies have revealed that the caspase-9 CARD domain actually functions as an allosteric inhibitor of the protease domain's catalytic activity[5][53]. When the CARD is present, isolated protease domain fragments exhibit substantially higher proteolytic activity compared to full-length caspase-9 in solution[5]. This counter-intuitive regulatory architecture appears to serve as a fail-safe mechanism preventing inappropriate activation of caspase-9 in the cytosol[5][10]. Removal of the CARD and linker sequences (residues 1 to 138) increases caspase-9 activity by at least 10-fold in peptide-based assays, indicating that sequential regions of the prodomain exert cumulative inhibitory effects[5]. This inhibition operates through direct structural interactions between the CARD and the protease domain and appears to involve allosteric effects on the positioning of the catalytic site loops[53]. The functional consequence of this architecture is that the apoptosome accomplishes caspase-9 activation through not merely one mechanism but rather through multiple complementary means: first, by physically sequestering the inhibitory CARD domain through CARD-CARD interactions, thereby releasing the brake on catalytic activity; and second, by promoting homodimerization of the protease domains when substrate becomes available[5][10][50].
The intrinsic apoptotic pathway is initiated when diverse cellular stressors induce mitochondrial outer membrane permeabilization (MOMP), mediated primarily by pro-apoptotic members of the Bcl-2 family such as Bax and Bak, resulting in the release of cytochrome c from the mitochondrial intermembrane space into the cytosol[11][29]. Released cytochrome c binds with high affinity to Apaf-1 and in the presence of deoxyadenosine triphosphate (dATP) or adenosine triphosphate (ATP) stimulates the oligomerization of Apaf-1 into a distinctive heptameric wheel-like platform termed the apoptosome[2][5][10]. The apoptosome functions as a macromolecular scaffolding complex that recruits and activates caspase-9 monomers through multivalent CARD-CARD interactions[10][20]. Recent cryo-electron microscopy (cryo-EM) structures have revealed that a single caspase-9 CARD interacts with multiple Apaf-1 CARDs via asymmetric interfaces with a 4:7 stoichiometry per apoptosome scaffold, indicating that recruitment involves complex multimeric interactions rather than simple 1:1 binding[10][19]. The apoptosome therefore assembles approximately seven copies of caspase-9 monomers on its surface through these CARD-CARD interactions[1].
Two complementary but mechanistically distinct mechanisms contribute to the dramatic activation of caspase-9 upon apoptosome binding[5][10][50]. The first mechanism involves relief of the inhibitory effect of the caspase-9 CARD domain[5]. Structural evidence indicates that assembly of caspase-9 CARD complexes within the apoptosome holoenzyme likely serves to sequester or reorient the inhibitory CARD domain, thereby relieving suppression of the underlying protease domain's catalytic activity[5]. The second activation mechanism proceeds through substrate-dependent dimerization: binding to the apoptosome increases the local concentration of caspase-9 monomers, and when substrate becomes available, the protease domains rapidly and extensively dimerize through a process termed molecular crowding[10][50]. Recent methyl-transverse relaxation optimized spectroscopy (methyl-TROSY) NMR studies have demonstrated that apoptosome-bound caspase-9 protease domains remain monomeric in the absence of substrate but undergo swift homodimerization only upon substrate addition, providing an additional temporal control mechanism that prevents inadvertent activation[10][50]. This substrate-dependent dimerization model reconciles the apparent paradox that while caspase-9 dimerization is essential for catalytic activity, the holoenzyme form exhibits substantially greater activity than simple leucine zipper-induced dimers, because the apoptosome not only facilitates dimerization but also enhances substrate affinity to the physiological substrate procaspase-3[2].
Upon recruitment to the apoptosome, procaspase-9 undergoes autocatalytic intrachain cleavage at three distinct aspartate residues, primarily after Asp-315 and secondarily after Glu-306 and Asp-330, generating the mature two-chain enzyme composed of the p35 large subunit and p10 small subunit connected by an intersubunit linker[1][7][40]. Remarkably, this autocatalytic processing appears to be essential for full activation, as a caspase-9 triple mutant (E306A/D315A/D330A) that cannot undergo intrachain cleavage fails to achieve proper activation by the apoptosome despite maintaining dimerization capability[40]. The molecular basis for this requirement remains incompletely characterized but likely involves conformational changes necessary for optimal substrate binding or catalytic site positioning. Importantly, the long intersubunit linker connecting p20 and p10 allows caspase-9 to exhibit catalytic activity even in its uncleaved form, distinguishing caspase-9 from most other caspases, which require cleavage for activation[1][7].
Caspase-9, like all caspases, functions as a serine-threonine protease that recognizes specific peptide sequences immediately preceding aspartate residues and cleaves after the aspartate[1][3]. The substrate recognition mechanism involves recognition of four residues N-terminal to the scissile aspartate in positions designated P4, P3, P2, and P1, with the cleavage occurring between P1 (the aspartate) and P1' (the downstream residue)[9][37]. Caspase-9 exhibits a preferred cleavage sequence motif of Leu-Gly-His-Asp (LEHD) in positions P4 through P1, though the full spectrum of recognized sequences demonstrates considerably greater breadth than this consensus motif[4][12][37]. Comprehensive N-terminomics studies employing reverse profiling of substrate libraries have identified that caspase-9 accepts sequences with the motif LESD↓(G/S) for positions P4-P1↓(P1'), exhibiting notable flexibility in position P1' and accepting glycine or serine at this position[37].
A remarkable feature of caspase-9 substrate specificity is its preferential cleavage of the physiological substrate procaspase-3 through intersubunit linker (ISL) cleavage rather than prodomain cleavage[9]. The ISL site within procaspase-3 contains an aspartate at position 175, which caspase-9 cleaves with high efficiency[9]. In contrast, caspase-9 can recognize but cannot efficiently cleave the ISL sites in procaspase-6, even though these sequences superficially resemble recognized caspase-9 cleavage motifs[9]. The P4-P1' sequence of procaspase-6 ISL site 1 (DVVDN) is accessible to the caspase-9 active site yet remains refractory to proteolysis, suggesting that the local three-dimensional context surrounding the cleavage site, beyond simple recognition sequence, critically determines substrate selection[9]. Studies employing substrate variants demonstrate that altering procaspase-6 sites to contain the preferred caspase-9 sequence motif still fails to generate efficient cleavage, indicating that caspase-9 has evolved exquisite selectivity mechanisms ensuring that it preferentially processes downstream effector caspases in a hierarchically controlled manner[9].
The apoptosome-associated caspase-9 holoenzyme (C9Holo) exhibits dramatically higher substrate affinity for the physiological substrate procaspase-3 compared to leucine zipper-induced caspase-9 dimers (LZ-C9)[2]. While both forms exhibit similar catalytic efficiency (Km and kcat values) for synthetic peptide substrates such as Ac-LEHD-AFC, the caspase-9 holoenzyme demonstrates Km values approximately 30-fold lower for procaspase-3 compared to the leucine zipper dimer[2]. This differential affinity appears to result from the interaction between caspase-9 and the apoptosome scaffold, which enhances substrate recognition and binding rather than merely providing a platform for concentration effects[2]. The dramatic improvement in substrate affinity implies that apoptosome binding generates conformational changes in the caspase-9 protease domain that optimize the substrate-binding pocket, suggesting that recruitment to the apoptosome accomplishes activation through a combination of relieving autoinhibition, promoting favorable dimerization, and enhancing intrinsic substrate recognition[2][5].
Once activated on the apoptosome, caspase-9 executes its primary biological function by proteolytically processing and activating the downstream effector caspases-3 and caspase-7, which then propagate the apoptotic program by cleaving numerous cellular substrates[1][3][6]. The ISL cleavage of procaspase-3 catalyzed by caspase-9 is extraordinarily efficient and represents the canonical initial step in initiating the terminal caspase cascade[2][3]. Activated caspase-3 can then cleave other procaspases including procaspase-6 and additional copies of procaspase-3, as well as hundreds of downstream apoptotic substrates including poly(ADP-ribose) polymerase (PARP), inhibitor of caspase-activated DNase (ICAD), and numerous cytoskeletal and nuclear proteins[12][35]. This hierarchical activation system, in which caspase-9 selectively processes effector caspases despite the broader cleavage specificity of effector caspases themselves, provides regulatory precision ensuring that apoptosis initiation remains firmly under the control of upstream signals[1][3].
The caspase cascade initiated by caspase-9 activation establishes a powerful positive feedback loop that amplifies mitochondrial damage[27][30]. Activated caspase-3 cleaves anti-apoptotic Bcl-2 family members including Bcl-2 and Bcl-xL at specific aspartate residues, converting them into pro-apoptotic fragments that promote further Bax and Bak activation[27]. This caspase-dependent cleavage of anti-apoptotic Bcl-2 proteins results in release of Smac/DIABLO from mitochondria, which then neutralizes inhibitor of apoptosis (IAP) proteins and permits additional caspase activation[27]. Additionally, activated caspase-3 can directly promote further cytochrome c release from mitochondria through mechanisms involving the permeability transition pore and inner membrane remodeling[27]. This feedback mechanism ensures robust progression toward apoptosis once the caspase-9 threshold has been crossed and functions as an irreversibility switch, although cells possess protective mechanisms that can suppress this pathway under certain circumstances[1][27].
A distinctive feature of caspase-9 that fundamentally differs from other initiator caspases such as caspase-8 is that caspase-9 must maintain binding to the apoptosome to sustain significant catalytic activity[11][23]. In contrast to caspase-8, which becomes released from the death-inducing signaling complex (DISC) upon activation, activated caspase-9 remains sequestered on the apoptosome platform[2][11]. This architectural distinction has profound mechanistic implications: caspase-9 does not function as a soluble protease that diffuses throughout the cytosol but rather operates as a component of a multiprotein complex, fundamentally restricting the spatial domain of its substrate accessibility and providing an additional layer of subcellular compartmentalization to apoptotic signaling[11]. Furthermore, procaspase-9 possesses greater affinity for the apoptosome than activated caspase-9, facilitating continuous recruitment and activation of new caspase-9 molecules while allowing processed p35/p12 caspase-9 to eventually dissociate from the complex[11]. This dynamic cycling creates what has been conceptualized as an apoptosomal molecular timer, in which the intracellular concentration of procaspase-9 determines timer duration, autoprocessing activates the timer, and the dissociation rate of active enzyme dictates the speed at which the timer ticks[11].
Caspase-9 represents one of the most heavily phosphorylated caspases, with numerous kinases converging to regulate its activity through post-translational modification[15][35]. Protein kinase A (PKA) phosphorylates caspase-9 at three sites—serines 99, 183, and 195—all located within the CARD and large subunit regions, resulting in suppression of caspase-9 activation and apoptosis[15][52]. Among these sites, phosphorylation at serine-183 represents the functionally dominant inhibitory site, preventing both procaspase-9 self-processing and substrate binding through a two-stage mechanism[52]. Remarkably, serine-183 phosphorylation in the zymogen form blocks substrate access to the active site, while phosphorylation in the mature form destabilizes the entire caspase-9 core structure, promoting dissociation between the large and small subunits[52]. The mitogen-activated protein kinase (MAPK) kinase ERK phosphorylates caspase-9 at threonine-125, located within the linker connecting the CARD to the catalytic domain, suppressing apoptosis during conditions of growth factor stimulation[15][35]. The protein kinase C isoform zeta (PKCζ) phosphorylates caspase-9 at serine-144, also in the CARD region, inhibiting both caspase-9 activation and the subsequent activation of caspase-3[15]. These inhibitory phosphorylation sites collectively function as molecular OFF switches through which diverse signaling pathways, including those activated during normal growth and proliferation, restrain apoptosis to ensure that only cells experiencing genuine stress undergo programmed death.
In contrast to the predominance of inhibitory phosphorylation sites, tyrosine-153 phosphorylation by the c-Abl kinase represents the sole known phosphorylation site that enhances rather than suppresses caspase-9 activity[35][49]. Located within the large subunit of the protease domain, tyrosine-153 forms a hydrogen bond with aspartate-350 in the catalytic site loop in the dimeric, substrate-bound structure, suggesting that phosphorylation at this position could influence catalytic site geometry[49]. However, recent experimental evidence has revealed substantial complexity regarding this site: while early reports suggested that tyrosine-153 phosphorylation promotes caspase-9 self-processing and activation in response to DNA damage, subsequent studies employing phosphomimetic substitutions (Y153E and Y153D) demonstrated that these mutations actually inhibit rather than activate caspase-9[49]. This discrepancy likely arises from distinctions between physiological phosphorylation dynamics and artificial phosphomimetic amino acid substitutions, suggesting that tyrosine-153 may play a complex role in caspase-9 regulation that depends on the broader phosphorylation context and conformational state[49].
The protein kinase Akt, a central node in growth and survival signaling activated by phosphatidylinositol 3-kinase (PI3K), phosphorylates caspase-9 at serine-196 and functions as an allosteric inhibitor of the protease[4][15][18]. Importantly, the serine-196 phosphorylation site lies far from the active site, yet it suppresses both caspase-9 dimerization and substrate-binding cleft positioning through allosteric mechanisms[4]. This Akt-mediated inhibition represents a critical antiapoptotic pathway by which growth factor signaling actively suppresses the intrinsic apoptotic cascade, ensuring that proliferating cells remain refractory to apoptotic stimuli even if they experience mild stress[4][15]. The therapeutic relevance of this regulatory node is emphasized by the frequent constitutive activation of PI3K/Akt signaling in human cancers, which provides cancer cells with inherent protection against chemotherapy-induced apoptosis[15].
The CASP9 gene generates two functionally antagonistic isoforms through alternative splicing: the pro-apoptotic caspase-9a that retains exons 3, 4, 5, and 6, and the anti-apoptotic caspase-9b that excludes these exons[4][21][24]. This alternatively spliced cassette encodes amino acids 140-289, which comprise the central region of the large subunit catalytic domain[4]. As a result, caspase-9b lacks the core catalytic domain and functions as a dominant-negative inhibitor of caspase-9a by competing for binding to the apoptosome and preventing the caspase enzyme cascade[4][21][31]. The ratio of caspase-9a/9b expression critically determines the apoptotic competence of cells; a low caspase-9a/9b ratio correlates with an anti-apoptotic phenotype and tumor promotion, particularly in non-small cell lung carcinomas (NSCLC)[21][24].
The alternative splicing of CASP9 is dysregulated in human cancers and is controlled by oncogenic signaling pathways[21][24]. Phosphoinositide 3-kinase (PI3K) and Akt signaling dramatically decrease the caspase-9a/9b ratio by promoting exclusion of the exon 3-6 cassette through phosphorylation-dependent mechanisms[21]. Specifically, Akt phosphorylates the serine-arginine protein kinase (SR) splicing factor SRp30a at serines 199, 201, 227, and 234, resulting in altered recognition of the caspase-9 splice sites and preferential inclusion of exon 7, which introduces a premature stop codon characteristic of the caspase-9b isoform[21]. Remarkably, epidermal growth factor receptor (EGFR) mutations and overexpression dramatically promote caspase-9b expression through this PI3K/Akt/SRp30a axis, providing cancer cells with a mechanism to suppress intrinsic apoptosis during tyrosine kinase-driven oncogenic transformation[21]. This splicing-based mechanism of apoptosis evasion represents a sophisticated adaptation by which oncogenic signaling pathways accomplish apoptosis suppression not merely through phosphorylation of existing caspase-9 protein but through dynamic alteration of which caspase-9 isoforms are synthesized, thereby providing more stable and heritable apoptosis resistance[21][24].
In non-stressed cells, caspase-9 predominantly localizes to the cytosol as an inactive monomer lacking typical mitochondrial targeting sequences[11][32]. Upon induction of apoptosis through intrinsic pathway stimuli, caspase-9 is recruited to the apoptosome, which forms at sites of cytochrome c release, thereby concentrating large amounts of caspase-9 in proximity to its substrate and preventing inappropriate activation in the cytosol[32]. This spatial compartmentalization of caspase-9 within the apoptosome complex provides an elegant mechanism for ensuring that caspase-9 activation remains tightly restricted to cells experiencing genuine mitochondrial stress[11][32]. The long disordered linker regions connecting the CARD to the protease domain allow significant flexibility of the protease domain when tethered to the apoptosome, permitting the protease domains to sample different conformational states and facilitating the substrate-dependent homodimerization essential for catalytic activation[10][50].
While caspase-9 lacks a classical mitochondrial targeting sequence and is primarily cytosolic, evidence indicates that a proportion of caspase-9 translocates to mitochondria during the apoptotic process[26][32]. Biochemical studies employing mitochondrial fractionation demonstrate that caspase-9 migrates into mitochondria after the latter undergo membrane permeability transition characteristic of apoptotic cells, suggesting that caspase-9 translocation follows rather than precedes mitochondrial permeabilization[26][32]. The physiological significance of mitochondrial caspase-9 localization remains incompletely understood but may involve amplification of mitochondrial damage through direct caspase-mediated effects on mitochondrial proteins or through generation of reactive oxygen species (ROS) that further promote mitochondrial dysfunction[26][47].
Beyond its canonical role in triggering apoptosis, caspase-9 executes a sophisticated non-apoptotic function in the positive regulation of macroautophagy through mechanisms involving the maintenance of mitochondrial homeostasis[44][57][60]. During nutrient starvation or growth factor deprivation, caspase-9 undergoes activation without activating the downstream effector caspase-3, suggesting compartmentalized and selective caspase cascade activation in autophagic contexts[44][60]. Genetic ablation of CASP9 or pharmacological inhibition of caspase-9 activity impairs autophagy flux despite normal initiation of autophagy, instead resulting in accumulated autophagosomes with prolonged lifetimes and defective maturation[44][57]. Mechanistically, caspase-9 knockout cells accumulate inactive ATG3, exhibiting decreased lipidation of Atg8-family members including MAP1LC3B and GABARAPL1, resulting in impaired autophagosome membrane sealing and maturation[44][57]. These autophagic defects correlate with altered mitochondrial morphology, depolarization of mitochondrial membrane potential, and reduced production of mitochondrial reactive oxygen species[44][57]. Remarkably, while exogenous hydrogen peroxide can partially restore Atg8-family lipidation in CASP9 knockout cells, only caspase-9 expression itself fully restores both mitochondrial ROS production and mitochondrial morphology, indicating that caspase-9 regulates mitochondrial homeostasis through mechanisms beyond simple ROS generation[44][57]. This non-apoptotic function positions caspase-9 as a critical regulator of cellular catabolism and energy metabolism through its influence on mitochondrial function, thereby connecting apoptotic and catabolic cellular programs through a shared molecular mediator[44][60].
Intriguingly, caspase-9 has emerged as a critical negative regulator of innate immune sensing through mechanisms involving suppression of type I interferon responses[39][42]. When mitochondrial outer membrane permeabilization occurs via Bax and Bak activation in the absence of active caspase-9, the released mitochondrial DNA (mtDNA) activates the cytosolic nucleotidyl transferase cyclic GMP-AMP synthase (cGAS), generating the second messenger cyclic GMP-AMP dinucleotide (cGAMP) and activating the stimulator of interferon genes (STING) protein[39][42]. This cGAS-STING signaling cascade activates interferon regulatory factor 3 (IRF3) and results in robust production of type I interferon and interferon-stimulated genes, establishing a potent antiviral state[39][42]. However, when caspase-9 is activated following MOMP, the protease degrades or inactivates components of the cGAS-STING pathway, suppressing type I interferon production and maintaining the immunological silence characteristic of apoptotic cell death[39][42]. Caspase-9-deficient cells or cells treated with caspase inhibitors exhibit constitutive activation of the mtDNA/cGAS/STING/IRF3 axis and produce abundant type I interferon even during apoptotic conditions[39][42]. This immunoregulatory function explains why tumor cells can exploit caspase-9 activation to suppress the immunogenic aspects of chemotherapy-induced cell death, and conversely, why caspase-9 inhibition can convert immunologically silent apoptosis into immunogenic cell death capable of generating anti-tumor immunity[33][39]. Recent studies demonstrate that dual inhibition of caspase-9 combined with heat shock protein 90 (Hsp90) inhibitors or chemotherapy robustly activates innate immune sensing in tumor cells while maintaining cell death, thereby converting standard apoptotic therapies into immunogenic cell death modalities[33].
Recent discoveries have identified non-apoptotic endothelial caspase-9 signaling as a critical mediator of ischemic injury in hypoxia-ischemia models[43][46]. In a mouse model of retinal vein occlusion (RVO), pharmacological inhibition or genetic deletion of caspase-9 specifically from endothelial cells significantly reduces vascular edema, restores vascular integrity, and provides robust neuroprotection, with caspase-9 inhibition providing stronger neuronal and vascular protection than VEGF neutralization[43][46]. Remarkably, endothelial caspase-9 activation following hypoxia-ischemia appears to occur independently of apoptosis, as caspase-7 is activated downstream of caspase-9 even in endothelial cells that remain viable[43]. The endothelial caspase-9 activation following ischemic injury promotes vascular barrier dysfunction through mechanisms that remain to be fully elucidated but likely involve caspase-mediated modifications of endothelial tight junction proteins, adhesion molecules, and cytoskeletal components[43]. This non-apoptotic endothelial caspase-9 function demonstrates that caspase-9 can operate as a multifunctional integrator of hypoxic stress in vascular tissues, linking mitochondrial stress to vascular dysfunction through mechanisms distinct from apoptosis[43][46].
Non-apoptotic caspase-9 signaling in neurons contributes to memory formation and synaptic plasticity through mechanisms that appear to be independent of the apoptotic cascade[56]. In a mouse model of familial Danish dementia (FDD) caused by mutations in the BRI2/ITM2B gene, selective inhibition of caspase-9 activity with a highly specific caspase-9 inhibitor rescues both defects in long-term potentiation (LTP) and memory acquisition without affecting normal synaptic plasticity in control mice[56]. Activated caspase-9 is detected in hippocampal synaptic fractions of FDD mice, suggesting compartmentalized caspase-9 activation in the synaptic compartment distinct from somatic caspase activation[56]. These findings indicate that physiological caspase-9 signaling contributes to regulated synaptic remodeling and memory processing, and that aberrant caspase-9 activation in synaptic compartments contributes to neurodegenerative pathology[56]. The molecular substrates and downstream effectors through which synaptic caspase-9 influences plasticity remain incompletely characterized but may involve modified processing of synaptic proteins, local alterations in mitochondrial function, or caspase-mediated effects on synaptic structure[56].
Caspase-9 participates in the intersection between apoptotic and necroptotic pathways, with evidence indicating that caspase-9 can regulate whether cells undergo apoptosis or necroptosis depending on the broader context of kinase activation[36][45]. During death receptor signaling when caspase-8 is inhibited, receptor-interacting serine/threonine-protein kinases RIPK1 and RIPK3 form the necrosome and activate mixed lineage kinase domain-like protein (MLKL) to trigger necroptosis[17][36]. Recent evidence suggests that caspase-9 can interact with RIPK3 and influence necroptotic pathway activation, and in models of pancreatic necroptosis, knockout of caspase-9 from pancreatic acinar cells results in decreased severity of cerulein-induced acute pancreatitis, suggesting that caspase-9 promotes necroptotic injury[36]. This crosstalk between caspase-9 and necroptotic machinery indicates that caspase-9 functions as a decision node integrating signals that determine cellular fate between apoptosis, autophagy, necroptosis, and survival[36][45].
During embryonic development, particularly in central nervous system (CNS) formation, caspase-9 executes essential functions in sculpting neural populations through precisely timed and spatially restricted apoptosis[35][55][59]. Genetic knockout studies demonstrate that mice lacking caspase-9 die perinatally with severe brain abnormalities including exencephaly, ventricular obstructions, and protrusion formations, similar to phenotypes observed in caspase-3 knockout mice, indicating that caspase-9-mediated apoptosis is essential for normal brain development[35][59]. During lens fiber cell differentiation, caspase-9 is expressed and activated in spatially restricted domains of differentiating lens epithelium coinciding with the period of fiber cell denucleation, and inhibition of caspase-9 activity suppresses nuclear degeneration[32][55]. These developmental studies establish caspase-9 as a critical executioner of apoptosis during developmental morphogenesis and tissue patterning[35][59].
Beyond its roles in developmental apoptosis, caspase-9 participates in non-apoptotic neurodevelopmental processes including axon guidance, synapse formation, and synaptic pruning[35][59]. Caspases in general, and caspase-9 specifically, modulate the positioning and function of growth cone cytoskeletal elements, potentially through direct proteolysis of cytoskeletal proteins or through effects on mitochondrial positioning within developing neurites[35][59]. The molecular distinction between conditions in which caspase-9 activation leads to apoptotic death versus differentiation-promoting functions remains incompletely understood but likely involves the subcellular compartmentalization of caspase-9 signaling, the duration and magnitude of protease activation, and the availability of distinct substrate pools in different cellular compartments[35][59].
Dysregulation of caspase-9 expression, activity, or function represents a fundamental mechanism of apoptosis evasion in human malignancies[1][36][51]. A subset of tumors suppress caspase-9 expression or activity as an apoptosis-evasion strategy, with evidence indicating that caspase-9 suppression increases chemoresistance to multiple drug classes[1][51]. Conversely, other tumors express elevated levels of the anti-apoptotic caspase-9b isoform, which prevents apoptosis-induced caspase-3 activation[1][36]. Mutations or polymorphisms within the CASP9 gene have been associated with various cancers, neurological disorders, autoimmune pathologies, and other degenerative diseases[36]. The correlation between altered caspase-9 function and cancer susceptibility suggests that caspase-9 acts as a critical tumor suppressor whose loss promotes malignant transformation, and conversely, that restoring caspase-9 function represents a rational therapeutic strategy for cancer treatment[36][51].
The sensitivity of cancer cells to chemotherapy and ionizing radiation critically depends on caspase-9-mediated intrinsic apoptosis pathway activation[1][8][16]. DNA-damaging agents induce p53 stabilization, leading to transcriptional activation of pro-apoptotic genes including those encoding Bcl-2 family members and other apoptosis regulators[1][8]. This p53-dependent transcriptional response triggers mitochondrial damage and cytochrome c release, subsequently activating caspase-9 on the apoptosome[1][8][16]. Caspase-9-deficient cancer cells exhibit profound chemoresistance to diverse drug classes including platinum compounds, topoisomerase inhibitors, and antimetabolites[1][8]. Studies examining the requirement for caspase-9 in drug-induced apoptosis demonstrate that reconstitution of caspase-9 expression in caspase-9-deficient cells restores both mitochondrial membrane potential loss and caspase-3 activation following chemotherapy exposure, providing genetic evidence that caspase-9 is essential for drug-induced apoptosis in cancer cells[8].
The capacity to rationally control caspase-9 activation through chemical inducers of dimerization (CID) has been harnessed for development of "suicide gene" systems designed to provide safety switches for cellular therapies[1][4][7]. The inducible caspase-9 (iCasp9) system, also termed the CaspaCIDe system, consists of a fusion protein combining a drug-binding domain (FK506-F36V) with a truncated caspase-9 lacking its physiological CARD domain[1][7]. The chemical inducers AP1903 or AP20187 bind to iCasp9 and induce homodimerization of the caspase-9 truncated domain, leading to activation of the downstream caspase cascade and rapid apoptosis[1][7]. Administration of 10 nanomolar doses of CID can provoke apoptosis in greater than 99% of cells expressing iCasp9 within one hour[1]. The iCasp9 system exhibits marked advantages compared to alternative suicide genes including the herpes simplex virus thymidine kinase (HSV-TK) system, including lower potential immunogenicity, lower baseline activity independent of the dimerizer, and high sensitivity to dimerizer-induced apoptotic death[1][7]. The Rivo-cel technology based on inducible caspase-9 has entered clinical trials for improving hematopoietic stem cell transplantation outcomes by conferring prophylaxis against graft-versus-host disease through inducible elimination of donor T cells expressing iCasp9[36].
Recent therapeutic innovations have identified caspase-9 inhibition as a strategy to enhance immunogenicity of chemotherapy-induced cell death[33][36]. Blockade of caspase-9 signaling in tumor cells exposed to Hsp90 inhibitors or chemotherapy robustly activates the mtDNA/cGAS/STING innate immune sensing pathway, leading to production of type I interferon and other immunogenic damage-associated molecular patterns[33][39]. This caspase-9 inhibition-enhanced innate immune activation results in recruitment of CD8+ T cells and establishment of adaptive anti-tumor immunity capable of controlling tumor growth even after treatment cessation[33]. Importantly, combining caspase-9 inhibition with subsequent PD-L1 checkpoint blockade achieves complete tumor regression in experimental models, suggesting that dual targeting of caspase-9 signaling combined with immune checkpoint inhibitors may overcome adaptive resistance mechanisms in cancer immunotherapy[33].
Recent cryo-EM structural determination of the Apaf-1 apoptosome bound to caspase-9 has provided unprecedented atomic-level detail regarding the architecture of the activation complex[5][10]. These structures reveal that caspase-9 CARD domains interact with multiple Apaf-1 CARDs through asymmetric interfaces, and that the protease domains remain flexibly tethered to the apoptosome through long disordered linkers, allowing dynamic conformational sampling[5][10]. Combined with NMR spectroscopy studies employing methyl-TROSY approaches, these structural advances have established that substrate-dependent dimerization driven by molecular crowding on the apoptosome platform represents the primary mechanism of caspase-9 activation, with CARD sequestration providing an additional secondary activation mechanism[10][50]. These mechanistic insights have profound implications for therapeutic targeting of caspase-9, suggesting that stabilizing or destabilizing specific conformational states might provide approaches to modulate caspase-9 activity[10][50].
Modern proteomic approaches employing N-terminomics have enabled comprehensive identification of caspase-9 substrates at the proteome-wide level[12][37]. These studies have identified 124 caspase-9 substrate proteins, with 57% of all caspase-9 substrates also cleaved by caspase-3, indicating substantial functional redundancy between these proteases with evolutionarily conserved substrate preferences[12][37]. Notably, reverse N-terminomics approaches have revealed hundreds of previously unknown caspase-9 cleavage sites and substrates not detected in traditional forward approaches, expanding appreciation of caspase-9's proteolytic range and revealing potential novel mechanisms through which caspase-9 influences diverse cellular pathways[12][37]. This proteome-wide substrate knowledge provides a foundation for understanding how caspase-9 coordinates the execution of apoptosis and non-apoptotic programs[12][37].
Genome-wide association studies and candidate gene analyses have identified multiple CASP9 polymorphisms associated with increased susceptibility to various diseases including neurological disorders, autoimmune conditions, and lumbar disc disease[36]. These polymorphisms may alter caspase-9 expression levels, splicing patterns, or functional activities, thereby influencing disease predisposition[36]. The association of CASP9 variants with neurodegeneration, retinal neuropathy, myasthenic syndromes, cardiomyopathies, atherosclerosis, and autoimmune disease suggests that dysregulation of caspase-9 activity or expression contributes to pathogenesis of numerous chronic diseases beyond cancer[36]. Future studies examining the functional consequences of CASP9 polymorphisms and their interactions with environmental and genetic modifiers may illuminate mechanisms of disease susceptibility[36].
Caspase-9, encoded by the human CASP9 gene (UniProt: P55211), has emerged as one of the most multifunctional and extensively characterized proteases in human biology. As the initiator caspase of the intrinsic mitochondrial apoptotic pathway, caspase-9 responds to diverse cellular stressors including DNA damage, growth factor withdrawal, hypoxia, and oxidative stress by recruiting and activating downstream effector caspases that execute the morphological and biochemical changes constituting apoptosis[1][7]. The remarkable specificity with which caspase-9 accomplishes this function reflects sophisticated mechanisms of activation including CARD domain sequestration on the apoptosome platform, substrate-dependent protease domain homodimerization, and selective cleavage of physiological substrates including procaspase-3[2][5][10].
The regulation of caspase-9 activity integrates signals from multiple signaling pathways through mechanisms including reversible phosphorylation by pro-survival kinases such as Akt, MAPK, and PKA, and through alternative splicing controlled by oncogenic pathways[15][21][52]. The spatial organization of caspase-9 within the apoptosome complex and the requirement for apoptosome binding to sustain activity provide subcellular compartmentalization of the apoptotic program, ensuring that caspase-9 activation remains tightly restricted to cells experiencing genuine mitochondrial stress[11][23][32].
Beyond its classical role in apoptosis, caspase-9 executes increasingly appreciated non-apoptotic functions in autophagy regulation and mitochondrial homeostasis, innate immune sensing and interferon production, endothelial vascular barrier function, and synaptic plasticity and memory formation[36][39][43][44][56][57]. These non-apoptotic roles position caspase-9 as a multifunctional integrator of cellular stress responses, connecting apoptotic, catabolic, immunological, and synaptic processes through a shared molecular mediator[36][43][44].
In cancer biology, dysregulation of caspase-9 through altered expression, splicing, or post-translational modification represents a fundamental mechanism of apoptosis evasion and contributes to chemoresistance[1][36][51]. Conversely, pharmacological or genetic modulation of caspase-9 has emerged as a rational therapeutic strategy, with inducible caspase-9 systems providing clinically viable safety switches for cell therapy, and caspase-9 inhibition enhancing immunogenicity of chemotherapy through activation of innate immune sensing pathways[33][36]. The remarkable progress in understanding caspase-9 structure, mechanisms, regulation, and multifaceted biological roles positions this protease as a critical target for therapeutic intervention in cancer, neurodegeneration, and inflammatory diseases. Future research elucidating the specific mechanisms determining whether caspase-9 activation results in apoptosis, autophagy, necroptosis, or other cellular outcomes promises to reveal fundamental principles governing cellular fate determination and may enable more precise and effective therapeutic targeting of caspase-9 in diverse disease contexts.
CASP9 is an initiator caspase in the intrinsic apoptosis pathway, but has a dominant-negative short isoform.
| Isoform | UniProt ID | Synonym | Key Feature | Function |
|---|---|---|---|---|
| Isoform 1 | P55211-1 | 9L, Alpha | Full-length, catalytically active | INDUCES APOPTOSIS |
| Isoform 2 | P55211-2 | 9S, Beta | Lacks catalytic domain | DOMINANT-NEGATIVE INHIBITOR |
| Isoform 3 | P55211-3 | Gamma | - | Unknown |
| Isoform 4 | P55211-4 | - | - | Unknown |
Caspase-9L (Isoform 1):
- Contains CARD domain for Apaf-1 binding
- Contains catalytic domain
- Forms apoptosome with Apaf-1 and cytochrome c
- Cleaves and activates CASP3/CASP7
- PRO-APOPTOTIC
Caspase-9S (Isoform 2):
UniProt explicitly states:
"Lacks activity is an dominant-negative inhibitor of caspase-9" PMID:10070954
Mechanism: Caspase-9S competes with Caspase-9L for Apaf-1 binding but cannot activate downstream caspases.
Apaf-1 + Cyt c + dATP → Apoptosome
If Caspase-9L binds: → Apoptosis
If Caspase-9S binds: → No apoptosis (dominant-negative)
The ratio of 9L/9S determines apoptotic sensitivity.
Like BCL2L1, this is a case where the balance between isoforms determines cell fate:
- High 9L/9S ratio → apoptosis-sensitive
- Low 9L/9S ratio → apoptosis-resistant
Cancer cells often shift this ratio towards 9S to evade apoptosis.
---
id: P55211
gene_symbol: CASP9
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: 'CASP9 (Caspase-9) is the initiator caspase of the intrinsic apoptosis
pathway. CRITICAL ISOFORM BIOLOGY: Alternative splicing produces 4 isoforms with
ANTAGONISTIC functions: (1) Caspase-9L (isoform 1, P55211-1, Alpha) is the full-length
ACTIVE enzyme that binds Apaf-1 in the apoptosome and cleaves effector caspases
to INDUCE APOPTOSIS; (2) Caspase-9S (isoform 2, P55211-2, Beta) lacks the catalytic
domain and acts as a DOMINANT-NEGATIVE INHIBITOR that competes with 9L for Apaf-1
binding [PMID:10070954]. UniProt states "Isoform 2: Lacks activity is an dominant-negative
inhibitor of caspase-9". All current GOA apoptosis annotations refer to the pro-apoptotic
function - MISSING the anti-apoptotic isoform 2 function.'
existing_annotations:
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: Caspase-9 is predominantly localized in the cytoplasm as an inactive
monomer in non-stressed cells [PMID:12782307, deep research]. The IBA annotation
from phylogenetic inference is well-supported. Both isoforms would be cytoplasmic
as neither has specific targeting signals.
action: ACCEPT
reason: Cytoplasmic localization is well-established for procaspase-9. The deep
research confirms "In non-stressed cells, caspase-9 predominantly localizes
to the cytosol as an inactive monomer lacking typical mitochondrial targeting
sequences." This applies to both isoforms as the CARD domain (retained in
both) does not contain targeting signals.
supported_by:
- reference_id: PMID:12782307
supporting_text: caspase-9 is in the cytoplasm of non-apoptotic pituitary
cells
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: 'provider: perplexity'
- term:
id: GO:0006915
label: apoptotic process
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: Caspase-9 is central to the intrinsic apoptotic pathway. The IBA annotation
correctly identifies involvement in apoptosis, which is the canonical function
of isoform 1. However, isoform 2 (Caspase-9S) INHIBITS apoptosis as a dominant-negative.
action: ACCEPT
reason: The GO term "apoptotic process" is a broad BP term that applies to proteins
involved in apoptosis regardless of whether they promote or inhibit it. The
term definition includes regulation. Isoform 1 induces apoptosis while isoform
2 inhibits it - both are involved in the apoptotic process. The IBA inference
from phylogenetic conservation is sound for the canonical pro-apoptotic function.
supported_by:
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'Cysteine-type endopeptidase activity is the core enzymatic function
of caspase-9 (isoform 1). CRITICAL: Isoform 2 (Caspase-9S) LACKS this activity
as it is missing the catalytic domain (residues 140-289). UniProt explicitly
states "Isoform 2: Lacks activity".'
action: ACCEPT
reason: This annotation is correct for the canonical isoform 1 (P55211-1). The
IBA phylogenetic inference is valid because the catalytic activity is the
defining feature of caspase-9 orthologs. The catalytic dyad (Cys-287 and His-237)
is conserved across the family. Note that isoform 2 would NOT have this activity.
supported_by:
- reference_id: PMID:16916640
supporting_text: Our study demonstrates the efficiency by which the executioner
caspases are activated in vivo
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0005829
label: cytosol
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: Cytosolic localization is well-established for procaspase-9 in non-apoptotic
cells. The apoptosome forms in the cytosol upon cytochrome c release from
mitochondria.
action: ACCEPT
reason: 'Deep research confirms cytosolic localization: "In non-stressed cells,
caspase-9 predominantly localizes to the cytosol as an inactive monomer."
Multiple experimental studies confirm this. The IBA annotation is phylogenetically
sound.'
supported_by:
- reference_id: PMID:12782307
supporting_text: caspase-9 is in the cytoplasm of non-apoptotic pituitary
cells
- term:
id: GO:0043525
label: positive regulation of neuron apoptotic process
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'Caspase-9 plays a documented role in neuronal apoptosis during development
and in neurodegenerative conditions. Caspase-9 knockout mice show severe brain
abnormalities due to reduced developmental neuronal apoptosis. CRITICAL: This
applies to isoform 1 only.'
action: ACCEPT
reason: "Deep research states: \"mice lacking caspase-9 die perinatally with\
\ severe brain abnormalities including exencephaly, ventricular obstructions,\
\ and protrusion formations.\" This demonstrates caspase-9's role in neuronal\
\ apoptotic processes during CNS development. IBA inference from phylogenetic\
\ conservation is appropriate for this well-characterized function of isoform\
\ 1."
supported_by:
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: mice lacking caspase-9 die perinatally with severe brain
abnormalities including exencephaly, ventricular obstructions, and protrusion
formations
- term:
id: GO:0008630
label: intrinsic apoptotic signaling pathway in response to DNA damage
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'Caspase-9 is the initiator caspase of the intrinsic apoptotic pathway
activated by DNA damage. c-Abl phosphorylates caspase-9 at Tyr-153 in response
to DNA damage, promoting apoptosis. CRITICAL: This pro-apoptotic function
is isoform 1 specific.'
action: ACCEPT
reason: DNA damage triggers the intrinsic pathway through p53-mediated transcription
of pro-apoptotic Bcl-2 family members, leading to MOMP, cytochrome c release,
and caspase-9 activation. PMID:15657060 demonstrates c-Abl directly phosphorylates
caspase-9 in DNA damage response. IBA phylogenetic inference is sound for
this core function.
supported_by:
- reference_id: PMID:15657060
supporting_text: c-Abl phosphorylates caspase-9 on Tyr-153 in vitro and
in cells treated with DNA damaging agents
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: IEA annotation of cysteine-type endopeptidase activity is redundant
with IBA annotation. Correct for isoform 1, but isoform 2 lacks the catalytic
domain.
action: ACCEPT
reason: This is a broader IEA annotation that is consistent with the IBA annotation.
While less specific than IBA, it is not incorrect. The catalytic activity
is confirmed by multiple experimental studies.
supported_by:
- reference_id: PMID:16916640
supporting_text: Caspase-7 is an obligate dimer of catalytic domains, with
generation of activity requiring limited proteolysis within a region that
separates the large and small chains of each domain
- term:
id: GO:0006508
label: proteolysis
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Proteolysis is a parent term of cysteine-type endopeptidase activity.
This is a very general annotation but not incorrect for isoform 1.
action: ACCEPT
reason: Caspase-9 is definitively a protease that cleaves substrates. The term
is appropriately general for an IEA annotation. More specific terms are available
via IBA and IDA annotations.
supported_by:
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0006915
label: apoptotic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: IEA annotation of apoptotic process is redundant with IBA annotation.
Correct as caspase-9 is a key player in apoptosis, with isoform 1 promoting
and isoform 2 inhibiting the process.
action: ACCEPT
reason: Consistent with other evidence. The IEA provides computational support
for the experimentally validated apoptotic function.
supported_by:
- reference_id: PMID:9390557
supporting_text: caspase-9 is the most upstream member of the apoptotic
protease cascade that is triggered by cytochrome c and dATP
- term:
id: GO:0006974
label: DNA damage response
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: Caspase-9 participates in DNA damage response primarily through its
role as the executor of DNA damage-induced apoptosis. c-Abl phosphorylates
caspase-9 in response to DNA damage.
action: ACCEPT
reason: The deep research and PMID:15657060 confirm caspase-9's role in DNA
damage response. The ARBA machine learning annotation correctly captures this
function.
supported_by:
- reference_id: PMID:15657060
supporting_text: The c-Abl tyrosine kinase is also involved in the apoptotic
response to DNA damage
- term:
id: GO:0008233
label: peptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Peptidase activity is a parent term of cysteine-type endopeptidase
activity. Very general but correct for isoform 1.
action: ACCEPT
reason: This is a very general parent term. More specific annotations are available.
Correct for the canonical catalytically active isoform.
supported_by:
- reference_id: PMID:16916640
supporting_text: Caspase-7 is an obligate dimer of catalytic domains, with
generation of activity requiring limited proteolysis within a region that
separates the large and small chains of each domain
- term:
id: GO:0008234
label: cysteine-type peptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Cysteine-type peptidase activity is a parent term of the more specific
cysteine-type endopeptidase activity annotation. Correct for isoform 1.
action: ACCEPT
reason: Parent term of the more specific annotation. Consistent with caspase-9's
function as a cysteine protease using the catalytic dyad of Cys-287 and His-237.
supported_by:
- reference_id: PMID:16916640
supporting_text: Caspase-7 is an obligate dimer of catalytic domains, with
generation of activity requiring limited proteolysis within a region that
separates the large and small chains of each domain
- term:
id: GO:0009411
label: response to UV
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: UV irradiation causes DNA damage that can trigger caspase-9-mediated
apoptosis via the intrinsic pathway.
action: ACCEPT
reason: PMID:15657060 demonstrates that DNA damaging agents including UV activate
caspase-9 through c-Abl-mediated phosphorylation. The annotation captures
the role of caspase-9 in UV-induced apoptosis.
supported_by:
- reference_id: PMID:15657060
supporting_text: Caspase-9(Y153F) also attenuated DNA damage-induced processing
of caspase-9 to p35, activation of caspase-3, and apoptosis
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: Hydrolase activity is a very general parent term. Caspases hydrolyze
peptide bonds. Correct but uninformative for isoform 1.
action: ACCEPT
reason: Very general but correct parent term. The UniProtKB keyword mapping
correctly identifies caspase-9 as a hydrolase. More specific terms provide
better annotation.
supported_by:
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0042981
label: regulation of apoptotic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: Caspase-9 regulates apoptosis. Isoform 1 positively regulates (induces)
apoptosis, while isoform 2 negatively regulates (inhibits) apoptosis. This
general term encompasses both functions.
action: ACCEPT
reason: This general regulatory term is appropriate as CASP9 is involved in
apoptosis regulation through both pro-apoptotic (isoform 1) and anti-apoptotic
(isoform 2) mechanisms. The InterPro association correctly identifies this
function.
supported_by:
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: 'The CASP9 gene generates two functionally antagonistic
isoforms through alternative splicing: the pro-apoptotic caspase-9a that
retains exons 3, 4, 5, and 6, and the anti-apoptotic caspase-9b'
- term:
id: GO:0051604
label: protein maturation
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: Caspase-9 (isoform 1) processes/matures other proteins including procaspase-3
and procaspase-7 by proteolytic cleavage.
action: ACCEPT
reason: The annotation captures caspase-9's role in processing downstream effector
caspases from their inactive proforms to active enzymes. This is a core function
of initiator caspases.
supported_by:
- reference_id: PMID:16352606
supporting_text: Apaf-1 oligomerizes to produce approximately 1.4-MDa and
approximately 700-kDa apoptosome complexes, and the latter complex directly
cleaves/activates procaspase-7
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:10206961
review:
summary: PMID:10206961 demonstrates caspase-9 binding to Apaf-1 in the apoptosome
complex. While "protein binding" is too vague, the specific interaction with
Apaf-1 is core to caspase-9 function.
action: MODIFY
reason: '"Protein binding" is uninformative. The paper demonstrates CARD-CARD
interaction between caspase-9 and Apaf-1 in the apoptosome. A more specific
term should be used.'
proposed_replacement_terms:
- id: GO:0004197
label: cysteine-type endopeptidase activity
additional_reference_ids: [PMID:10206961]
supported_by:
- reference_id: PMID:10206961
supporting_text: Such a complex can be isolated using gel filtration chromatography
and is by itself sufficient to recruit and activate procaspase-9
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:10376594
review:
summary: PMID:10376594 describes the structural basis of procaspase-9 recruitment
by Apaf-1 via CARD-CARD interactions. "Protein binding" is too general.
action: MODIFY
reason: The specific interaction is CARD domain binding. A more informative
term would capture the CARD-CARD interaction that recruits caspase-9 to the
apoptosome.
proposed_replacement_terms:
- id: GO:0042802
label: identical protein binding
supported_by:
- reference_id: PMID:10376594
supporting_text: Structural basis of procaspase-9 recruitment by the apoptotic
protease-activating factor 1
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11024045
review:
summary: PMID:11024045 describes Livin (BIRC7), an IAP family member that can
bind caspases.
action: KEEP_AS_NON_CORE
reason: IAP binding is part of caspase regulation but "protein binding" is too
vague. The interaction with IAPs is important for regulation but not a core
function annotation.
supported_by:
- reference_id: PMID:11024045
supporting_text: Livin, a novel inhibitor of apoptosis protein family member
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11084335
review:
summary: PMID:11084335 describes ML-IAP (BIRC7) interaction with caspases.
action: KEEP_AS_NON_CORE
reason: IAP interaction is regulatory. "Protein binding" is too vague but the
interaction is documented.
supported_by:
- reference_id: PMID:11084335
supporting_text: ML-IAP, a novel inhibitor of apoptosis that is preferentially
expressed in human melanomas
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11230124
review:
summary: PMID:11230124 describes recruitment of caspases to Apaf-1 apoptosome
and XIAP complexes.
action: KEEP_AS_NON_CORE
reason: Documents apoptosome assembly and XIAP regulation. "Protein binding"
is uninformative but the interactions are relevant.
supported_by:
- reference_id: PMID:11230124
supporting_text: Recruitment, activation and retention of caspases-9 and
-3 by Apaf-1 apoptosome and associated XIAP complexes
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11242052
review:
summary: PMID:11242052 describes the XIAP-interaction motif in caspase-9 and
Smac/DIABLO.
action: KEEP_AS_NON_CORE
reason: IAP binding motif documentation. The caspase-9/XIAP interaction is well-established
for regulation of caspase activity.
supported_by:
- reference_id: PMID:11242052
supporting_text: A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO
regulates caspase activity and apoptosis
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11801603
review:
summary: PMID:11801603 describes SMAC interaction with ML-IAP (BIRC7).
action: KEEP_AS_NON_CORE
reason: Part of the IAP regulatory network affecting caspase-9 activity.
supported_by:
- reference_id: PMID:11801603
supporting_text: SMAC negatively regulates the anti-apoptotic activity of
melanoma inhibitor of apoptosis
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11821383
review:
summary: PMID:11821383 describes CARD-8 interaction with caspase-9 via CARD
domain. CARD-8 regulates caspase-1 and can interact with caspase-9.
action: KEEP_AS_NON_CORE
reason: CARD-8 interaction is regulatory. The paper focuses on caspase-1 regulation
with caspase-9 interaction being secondary.
supported_by:
- reference_id: PMID:11821383
supporting_text: CARD-8 protein, a new CARD family member that regulates
caspase-1 activation and apoptosis
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:12620238
review:
summary: PMID:12620238 provides structural mechanism of XIAP-mediated caspase-9
inhibition.
action: KEEP_AS_NON_CORE
reason: XIAP binding is a key regulatory mechanism. The structural data confirms
the interaction but "protein binding" is too vague.
supported_by:
- reference_id: PMID:12620238
supporting_text: Mechanism of XIAP-mediated inhibition of caspase-9
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:16189514
review:
summary: PMID:16189514 is a large-scale proteome mapping study. Individual interactions
may not be validated.
action: KEEP_AS_NON_CORE
reason: High-throughput study. Interactions should be confirmed by directed
studies.
supported_by:
- reference_id: PMID:16189514
supporting_text: Towards a proteome-scale map of the human protein-protein
interaction network
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:16537496
review:
summary: PMID:16537496 describes DCC dependence receptor signaling involving
caspase-9.
action: KEEP_AS_NON_CORE
reason: DCC receptor signaling is a specific pathway involving caspase-9 activation.
Not a core function but a documented regulatory interaction.
supported_by:
- reference_id: PMID:16537496
supporting_text: The dependence receptor DCC requires lipid raft localization
for cell death signaling
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:16936772
review:
summary: PMID:16936772 describes integrin-linked kinase (ILK) interaction with
caspases.
action: KEEP_AS_NON_CORE
reason: ILK-caspase interaction is context-specific for adhesion-dependent apoptosis
in leukemia cells.
supported_by:
- reference_id: PMID:16936772
supporting_text: Integrin-linked kinase interacts with caspase-9 and -8
in an adhesion-dependent manner
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:18022362
review:
summary: PMID:18022362 describes IAP antagonists inducing autoubiquitination
of c-IAPs.
action: KEEP_AS_NON_CORE
reason: Part of IAP regulatory network affecting caspase activity.
supported_by:
- reference_id: PMID:18022362
supporting_text: IAP antagonists induce autoubiquitination of c-IAPs, NF-kappaB
activation, and TNFalpha-dependent apoptosis
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:18723680
review:
summary: PMID:18723680 shows caspase-3 and caspase-7 are functionally distinct,
with implications for caspase-9-mediated activation.
action: KEEP_AS_NON_CORE
reason: Relevant to caspase-9's substrate specificity but "protein binding"
is vague.
supported_by:
- reference_id: PMID:18723680
supporting_text: Executioner caspase-3 and caspase-7 are functionally distinct
proteases
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:19153467
review:
summary: PMID:19153467 provides structural data on BIR3 domain of cIAP1 in complex
with caspase-9 N-terminal peptide.
action: KEEP_AS_NON_CORE
reason: Structural data on IAP-caspase interaction. Regulatory rather than core
function.
supported_by:
- reference_id: PMID:19153467
supporting_text: The structure of the BIR3 domain of cIAP1 in complex with
the N-terminal peptides of SMAC and caspase-9
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:19494828
review:
summary: PMID:19494828 describes the apoptosome as a proteolytic-based molecular
timer.
action: ACCEPT
reason: This paper provides important mechanistic insight into caspase-9/Apaf-1
interaction dynamics in the apoptosome. The interaction is core to function
though "protein binding" is uninformative.
supported_by:
- reference_id: PMID:19494828
supporting_text: The Apaf-1*procaspase-9 apoptosome complex functions as
a proteolytic-based molecular timer
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:19721007
review:
summary: PMID:19721007 describes Netrin-1 signaling in colorectal cancer involving
dependence receptors.
action: KEEP_AS_NON_CORE
reason: Netrin-1/dependence receptor signaling is a specific context for caspase
activation.
supported_by:
- reference_id: PMID:19721007
supporting_text: Netrin-1 up-regulation in inflammatory bowel diseases is
required for colorectal cancer progression
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:20462491
review:
summary: PMID:20462491 provides structure of apoptosome-procaspase-9 CARD complex.
action: ACCEPT
reason: Key structural study of the core caspase-9/Apaf-1 CARD interaction.
Though "protein binding" is vague, the CARD-CARD interaction is essential
for function.
supported_by:
- reference_id: PMID:20462491
supporting_text: Structure of an apoptosome-procaspase-9 CARD complex
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:21827945
review:
summary: PMID:21827945 describes holo-apoptosome structure and procaspase-9
activation and interactions with caspase-3.
action: ACCEPT
reason: Core structural/mechanistic study of the apoptosome. Demonstrates caspase-9
binding to apoptosome and interactions with caspase-3.
supported_by:
- reference_id: PMID:21827945
supporting_text: Activation of procaspase-9 on the apoptosome is a pivotal
step in the intrinsic cell death pathway
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:23516580
review:
summary: PMID:23516580 describes E. coli NleF effector as a caspase inhibitor
that binds caspase-9.
action: KEEP_AS_NON_CORE
reason: Pathogen effector binding is context-specific for microbial infection.
supported_by:
- reference_id: PMID:23516580
supporting_text: The E. coli effector protein NleF is a caspase inhibitor
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:25241761
review:
summary: High-throughput proximity ligation study.
action: KEEP_AS_NON_CORE
reason: Large-scale study requiring validation of individual interactions.
supported_by:
- reference_id: PMID:25241761
supporting_text: Using an in situ proximity ligation assay to systematically
profile endogenous protein-protein interactions
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:25416956
review:
summary: Proteome-scale interactome mapping study.
action: KEEP_AS_NON_CORE
reason: High-throughput study. Individual interactions need validation.
supported_by:
- reference_id: PMID:25416956
supporting_text: A proteome-scale map of the human interactome network
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:25502805
review:
summary: Massively parallel cloning and phenotyping study.
action: KEEP_AS_NON_CORE
reason: High-throughput study.
supported_by:
- reference_id: PMID:25502805
supporting_text: A massively parallel pipeline to clone DNA variants and
examine molecular phenotypes
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:25519916
review:
summary: EHEC-host interactome study identifying translocated intimin receptor
targets.
action: KEEP_AS_NON_CORE
reason: Pathogen-host interaction context.
supported_by:
- reference_id: PMID:25519916
supporting_text: The EHEC-host interactome reveals novel targets for the
translocated intimin receptor
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:27107012
review:
summary: Barcode Fusion Genetics protein interaction screen.
action: KEEP_AS_NON_CORE
reason: High-throughput screening method.
supported_by:
- reference_id: PMID:27107012
supporting_text: Pooled-matrix protein interaction screens using Barcode
Fusion Genetics
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:29997244
review:
summary: LuTHy two-hybrid technology for protein interaction mapping.
action: KEEP_AS_NON_CORE
reason: High-throughput interaction mapping study.
supported_by:
- reference_id: PMID:29997244
supporting_text: 'LuTHy: a double-readout bioluminescence-based two-hybrid
technology'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:31467278
review:
summary: Binary interactome mapping optimization study.
action: KEEP_AS_NON_CORE
reason: Methodological study for interaction mapping.
supported_by:
- reference_id: PMID:31467278
supporting_text: Maximizing binary interactome mapping with a minimal number
of assays
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:31515488
review:
summary: Study of protein interaction disruption by genetic variants.
action: KEEP_AS_NON_CORE
reason: Population genetics study of interaction disruption.
supported_by:
- reference_id: PMID:31515488
supporting_text: Extensive disruption of protein interactions by genetic
variants across the allele frequency spectrum
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:32296183
review:
summary: Reference map of human binary protein interactome.
action: KEEP_AS_NON_CORE
reason: Large-scale interactome reference study.
supported_by:
- reference_id: PMID:32296183
supporting_text: A reference map of the human binary protein interactome
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:9390557
review:
summary: PMID:9390557 is a landmark paper demonstrating caspase-9/Apaf-1 CARD-CARD
interaction in apoptosome formation.
action: ACCEPT
reason: Foundational paper on caspase-9 function. Demonstrates the core CARD-CARD
interaction with Apaf-1 essential for apoptosome formation and caspase activation.
supported_by:
- reference_id: PMID:9390557
supporting_text: Caspase-9 and Apaf-1 bind to each other via their respective
NH2-terminal CED-3 homologous domains in the presence of cytochrome c
and dATP
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:9922454
review:
summary: PMID:9922454 describes the caspase cascade with caspase-9 dependent
activation of downstream caspases.
action: ACCEPT
reason: Demonstrates caspase-9 interaction with and processing of downstream
caspases (caspase-2, -3, -6, -7, -8, -10). Core function of initiator caspase.
supported_by:
- reference_id: PMID:9922454
supporting_text: 'Ordering the cytochrome c-initiated caspase cascade: hierarchical
activation of caspases-2, -3, -6, -7, -8, and -10 in a caspase-9-dependent
manner'
- term:
id: GO:0001666
label: response to hypoxia
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-9 is activated during hypoxia-induced apoptosis. Recent research
shows non-apoptotic endothelial caspase-9 signaling in hypoxia-ischemia.
action: ACCEPT
reason: 'Deep research confirms: "In a mouse model of retinal vein occlusion
(RVO), pharmacological inhibition or genetic deletion of caspase-9 specifically
from endothelial cells significantly reduces vascular edema." Hypoxia triggers
intrinsic apoptotic pathway.'
supported_by:
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: endothelial caspase-9 activation following hypoxia-ischemia
appears to occur independently of apoptosis
- term:
id: GO:0001822
label: kidney development
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-mediated apoptosis plays roles in kidney development. This
is a pleiotropic developmental process.
action: KEEP_AS_NON_CORE
reason: Apoptosis is involved in kidney development but this is not a core function
of caspase-9. The annotation is from ortholog transfer (Ensembl Compara).
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0002931
label: response to ischemia
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-9 is activated in ischemic injury, both through apoptotic and
non-apoptotic mechanisms in endothelial cells.
action: ACCEPT
reason: 'Deep research confirms: "In a mouse model of retinal vein occlusion
(RVO), pharmacological inhibition or genetic deletion of caspase-9...significantly
reduces vascular edema, restores vascular integrity, and provides robust neuroprotection."'
supported_by:
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: non-apoptotic endothelial caspase-9 signaling as a critical
mediator of ischemic injury in hypoxia-ischemia models
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Nuclear localization of caspase-9 is less well-established than cytosolic
localization. Some reports suggest translocation during apoptosis.
action: KEEP_AS_NON_CORE
reason: Caspase-9 is primarily cytosolic. Nuclear localization may occur in
specific contexts but is not the primary site of function. The annotation
is from ortholog transfer and should be viewed with caution.
supported_by:
- reference_id: PMID:12782307
supporting_text: caspase-9 is in the cytoplasm of non-apoptotic pituitary
cells
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Cytoplasmic localization is well-established. Redundant with IBA annotation.
action: ACCEPT
reason: Consistent with IBA annotation and experimental evidence. Caspase-9
is predominantly cytoplasmic.
supported_by:
- reference_id: PMID:12782307
supporting_text: caspase-9 is in the cytoplasm of non-apoptotic pituitary
cells
- term:
id: GO:0005829
label: cytosol
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Cytosolic localization confirmed. Redundant with IBA and TAS annotations.
action: ACCEPT
reason: Consistent with other annotations and experimental evidence.
supported_by:
- reference_id: PMID:12782307
supporting_text: caspase-9 is in the cytoplasm of non-apoptotic pituitary
cells
- term:
id: GO:0016485
label: protein processing
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-9 processes procaspases-3 and -7 by proteolytic cleavage. This
is a core function.
action: ACCEPT
reason: Caspase-9 processes its substrates (procaspase-3, procaspase-7) to their
mature forms. This is the primary enzymatic function.
supported_by:
- reference_id: PMID:16352606
supporting_text: Apaf-1 oligomerizes to produce approximately 1.4-MDa and
approximately 700-kDa apoptosome complexes, and the latter complex directly
cleaves/activates procaspase-7
- term:
id: GO:0032025
label: response to cobalt ion
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Cobalt ions can induce hypoxia-like responses. Caspase-9 may be activated
in this context.
action: KEEP_AS_NON_CORE
reason: Cobalt-induced response is likely through hypoxia mimicry. Not a core
function but an experimental context. Annotation from ortholog transfer.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0032355
label: response to estradiol
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Estradiol can have anti-apoptotic effects that may involve caspase
regulation.
action: KEEP_AS_NON_CORE
reason: Hormone response is context-specific. Annotation from ortholog transfer.
Not a core function.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0032496
label: response to lipopolysaccharide
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: LPS can trigger apoptotic pathways in various cell types.
action: KEEP_AS_NON_CORE
reason: LPS response is context-specific, particularly relevant to immune cells.
Annotation from ortholog transfer.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0034349
label: glial cell apoptotic process
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-9 is involved in glial cell apoptosis as part of CNS development
and disease.
action: KEEP_AS_NON_CORE
reason: "Cell-type specific apoptotic process. Not a core function but consistent\
\ with caspase-9's role in CNS development. CRITICAL: Only isoform 1 would\
\ positively regulate this."
supported_by:
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: mice lacking caspase-9 die perinatally with severe brain
abnormalities
- term:
id: GO:0043065
label: positive regulation of apoptotic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: 'CRITICAL ISOFORM ANNOTATION: This annotation is ONLY true for isoform
1 (Caspase-9L/Alpha). Isoform 2 (Caspase-9S/Beta) is a DOMINANT-NEGATIVE INHIBITOR
that NEGATIVELY regulates apoptosis.'
action: ACCEPT
reason: Isoform 1 does positively regulate apoptosis by activating effector
caspases. However, the annotation should ideally be isoform-specific. The
IEA annotation applies to the canonical pro-apoptotic function.
supported_by:
- reference_id: PMID:9390557
supporting_text: caspase-9 is the most upstream member of the apoptotic
protease cascade
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: the pro-apoptotic caspase-9a that retains exons 3, 4, 5,
and 6, and the anti-apoptotic caspase-9b
- term:
id: GO:0045471
label: response to ethanol
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Ethanol can induce apoptosis in various tissues including liver and
neurons.
action: KEEP_AS_NON_CORE
reason: Toxicological response context. Annotation from ortholog transfer. Not
a core function.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0071549
label: cellular response to dexamethasone stimulus
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Dexamethasone can induce apoptosis in some cell types.
action: KEEP_AS_NON_CORE
reason: Glucocorticoid response is context-specific. Annotation from ortholog
transfer.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0071680
label: response to indole-3-methanol
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Indole-3-carbinol is a phytochemical that can affect apoptotic pathways.
action: KEEP_AS_NON_CORE
reason: Specific chemical response. Not a core function. Annotation from ortholog
transfer.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0071887
label: leukocyte apoptotic process
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Caspase-9 is involved in leukocyte apoptosis as part of immune regulation.
action: KEEP_AS_NON_CORE
reason: 'Cell-type specific apoptotic process. The intrinsic pathway operates
in leukocytes but this is not a core function annotation. CRITICAL: Only isoform
1 promotes this.'
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0072347
label: response to anesthetic
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: Some anesthetics can induce neuronal apoptosis involving caspase-9.
action: KEEP_AS_NON_CORE
reason: Specific pharmacological context. Annotation from ortholog transfer.
supported_by:
- reference_id: GO_REF:0000107
supporting_text: Automatic transfer of experimentally verified manual GO
annotation data to orthologs
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: TAS
original_reference_id: Reactome:R-HSA-114259
review:
summary: 'Reactome pathway annotation for caspase-9 cleavage. CRITICAL: This
catalytic activity is ONLY present in isoform 1.'
action: ACCEPT
reason: Reactome correctly annotates the catalytic activity in the context of
apoptosome-mediated procaspase-9 cleavage to active caspase-9.
supported_by:
- reference_id: Reactome:R-HSA-114259
supporting_text: Procaspase‑9 is processed in an ATP‑dependent manner following
association with APAF1 and cytochrome c (CYCS) within the apoptosome complex
- term:
id: GO:0097193
label: intrinsic apoptotic signaling pathway
evidence_type: NAS
original_reference_id: PMID:10206961
review:
summary: 'PMID:10206961 demonstrates caspase-9 activation in the apoptosome
as the key step in the intrinsic apoptotic pathway. CRITICAL: Isoform 1 activates
while isoform 2 inhibits this pathway.'
action: ACCEPT
reason: Core annotation for caspase-9 function. The paper demonstrates apoptosome
formation and procaspase-9 activation.
supported_by:
- reference_id: PMID:10206961
supporting_text: Such a complex can be isolated using gel filtration chromatography
and is by itself sufficient to recruit and activate procaspase-9
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IDA
original_reference_id: PMID:16352606
review:
summary: PMID:16352606 demonstrates caspase-9 directly cleaving and activating
caspase-7 in the apoptosome. This is direct experimental evidence for the
catalytic activity (isoform 1 only).
action: ACCEPT
reason: Direct experimental demonstration of caspase-9 enzymatic activity in
processing caspase-7.
supported_by:
- reference_id: PMID:16352606
supporting_text: Apaf-1 oligomerizes to produce approximately 1.4-MDa and
approximately 700-kDa apoptosome complexes, and the latter complex directly
cleaves/activates procaspase-7
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IDA
original_reference_id: PMID:16916640
review:
summary: PMID:16916640 uses engineered hybrid dimers to track caspase-7 activation
by caspase-9, demonstrating the endopeptidase activity (isoform 1).
action: ACCEPT
reason: Direct experimental demonstration of caspase-9 enzymatic activity in
processing caspase-7 using sophisticated biochemical approaches.
supported_by:
- reference_id: PMID:16916640
supporting_text: A transient intermediate of singly cleaved dimeric caspase-7
can be found in a cell-free model of apoptosis induction
- term:
id: GO:0043065
label: positive regulation of apoptotic process
evidence_type: IMP
original_reference_id: PMID:11821383
review:
summary: 'PMID:11821383 describes CARD-8 interaction with caspase-9. The paper
shows CARD-8 overexpression induces apoptosis. CRITICAL: This pro-apoptotic
function is isoform 1 specific.'
action: ACCEPT
reason: The study demonstrates caspase-9's role in apoptosis induction through
CARD-domain interactions. The mutant phenotype evidence supports positive
regulation of apoptosis.
supported_by:
- reference_id: PMID:11821383
supporting_text: Overexpression of CARD-8 can also induce apoptosis in transfected
cells
- term:
id: GO:0006974
label: DNA damage response
evidence_type: IMP
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 demonstrates c-Abl phosphorylates caspase-9 in DNA damage
response, with mutant phenotype evidence.
action: ACCEPT
reason: Direct experimental evidence using Y153F mutant showing attenuated DNA
damage-induced caspase-9 processing and apoptosis.
supported_by:
- reference_id: PMID:15657060
supporting_text: Caspase-9(Y153F) also attenuated DNA damage-induced processing
of caspase-9 to p35, activation of caspase-3, and apoptosis
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-9627089
review:
summary: Reactome pathway annotation for caspase-9 localization in phosphorylation
reaction.
action: ACCEPT
reason: Consistent with other cytosolic localization annotations. Caspase-9
is phosphorylated at T412 in the cytosol.
supported_by:
- reference_id: Reactome:R-HSA-9627089
supporting_text: CASP9 is phosphorylated at T412
- term:
id: GO:0097193
label: intrinsic apoptotic signaling pathway
evidence_type: IDA
original_reference_id: PMID:35446120
review:
summary: PMID:35446120 shows Chromobacterium CopC effector ADP-riboxanates caspase-9
to inhibit intrinsic apoptotic pathway. This demonstrates caspase-9's role
in the pathway (isoform 1).
action: ACCEPT
reason: The study demonstrates caspase-9's essential role in intrinsic apoptotic
signaling by showing that pathogen effector modification blocks this pathway.
supported_by:
- reference_id: PMID:35446120
supporting_text: Calmodulin Binding Activates Chromobacterium CopC Effector
to ADP-Riboxanate Host Apoptotic Caspases
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IDA
original_reference_id: PMID:12782307
review:
summary: PMID:12782307 shows caspase-9 redistributes from cytoplasm to mitochondria
during apoptosis.
action: ACCEPT
reason: Direct experimental evidence of caspase-9 mitochondrial localization
during apoptosis. The paper shows "activation of apoptosis with rotenone triggers
the redistribution of caspase-9 to mitochondria."
supported_by:
- reference_id: PMID:12782307
supporting_text: The activation of apoptosis with rotenone triggers the
redistribution of caspase-9 to mitochondria
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IDA
original_reference_id: PMID:27889207
review:
summary: PMID:27889207 demonstrates PAK2 phosphorylation of caspase-7 blocks
its activation by caspase-9, providing evidence for caspase-9 enzymatic activity
(isoform 1).
action: ACCEPT
reason: The study demonstrates caspase-9's enzymatic activity in caspase-7 activation.
supported_by:
- reference_id: PMID:27889207
supporting_text: Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apoptotic
Activity by Two Distinct Mechanisms
- term:
id: GO:0051604
label: protein maturation
evidence_type: IDA
original_reference_id: PMID:16352606
review:
summary: PMID:16352606 shows caspase-9 directly matures procaspase-7 to active
caspase-7 (isoform 1 function).
action: ACCEPT
reason: Direct experimental evidence of caspase-9 processing procaspase-7 to
mature enzyme.
supported_by:
- reference_id: PMID:16352606
supporting_text: Apaf-1 oligomerizes to produce approximately 1.4-MDa and
approximately 700-kDa apoptosome complexes, and the latter complex directly
cleaves/activates procaspase-7
- term:
id: GO:0051604
label: protein maturation
evidence_type: IDA
original_reference_id: PMID:16916640
review:
summary: PMID:16916640 demonstrates caspase-7 maturation by caspase-9 using
hybrid dimers (isoform 1 function).
action: ACCEPT
reason: Direct experimental evidence using sophisticated biochemical approaches
to demonstrate procaspase-7 maturation.
supported_by:
- reference_id: PMID:16916640
supporting_text: The processed domain of this singly cleaved zymogen has
the same catalytic activity as a domain of fully active caspase-7
- term:
id: GO:1900119
label: positive regulation of execution phase of apoptosis
evidence_type: IDA
original_reference_id: PMID:16916640
review:
summary: 'PMID:16916640 demonstrates caspase-9 activates caspase-7, which executes
apoptosis. CRITICAL: This is isoform 1 specific.'
action: ACCEPT
reason: The execution phase of apoptosis is triggered by activation of executioner
caspases (caspase-3 and -7) by caspase-9. Direct experimental evidence.
supported_by:
- reference_id: PMID:16916640
supporting_text: Our study demonstrates the efficiency by which the executioner
caspases are activated in vivo
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IMP
original_reference_id: PMID:21980415
review:
summary: PMID:21980415 identifies conserved anti-apoptotic protein modulating
mitochondrial apoptosis pathway, using mutant phenotypes to demonstrate caspase-9
activity.
action: ACCEPT
reason: Mutant phenotype evidence for caspase-9 catalytic activity in apoptosis.
supported_by:
- reference_id: PMID:21980415
supporting_text: Identification of a conserved anti-apoptotic protein that
modulates the mitochondrial apoptosis pathway
- term:
id: GO:0006915
label: apoptotic process
evidence_type: IMP
original_reference_id: PMID:15069058
review:
summary: PMID:15069058 describes BRCC2, a BH3-domain protein that induces apoptosis
in a caspase-dependent manner.
action: ACCEPT
reason: Mutant phenotype evidence for caspase-9 role in apoptosis through BH3
domain protein interactions.
supported_by:
- reference_id: PMID:15069058
supporting_text: BRCC2, a novel BH3-like domain-containing protein, induces
apoptosis in a caspase-dependent manner
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: IDA
original_reference_id: PMID:16920334
review:
summary: PMID:16920334 examines Cop protective role in caspase-mediated cell
death (isoform 1 function).
action: ACCEPT
reason: Direct assay evidence for caspase-9 catalytic activity in cell death.
supported_by:
- reference_id: PMID:16920334
supporting_text: Protective role of Cop in Rip2/caspase-1/caspase-4-mediated
HeLa cell death
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11821383
review:
summary: PMID:11821383 shows CARD-8 binds to caspase-9 via CARD domain interaction.
action: KEEP_AS_NON_CORE
reason: CARD domain interaction is documented but "protein binding" is uninformative.
The CARD-CARD interaction is regulatory.
supported_by:
- reference_id: PMID:11821383
supporting_text: CARD-8 binds also to ICEBERG and pseudo-ICE
- term:
id: GO:0032991
label: protein-containing complex
evidence_type: IDA
original_reference_id: PMID:11821383
review:
summary: PMID:11821383 identifies caspase-9 in protein complexes with CARD-8.
action: KEEP_AS_NON_CORE
reason: Generic complex annotation. The apoptosome is the key functional complex
for caspase-9.
supported_by:
- reference_id: PMID:11821383
supporting_text: CARD-8 interacts physically with caspase-1
- term:
id: GO:0008233
label: peptidase activity
evidence_type: IDA
original_reference_id: PMID:19740745
review:
summary: PMID:19740745 shows truncated p23 disrupts Hsp90 function affecting
telomerase. Caspase-9 peptidase activity is involved (isoform 1).
action: ACCEPT
reason: Direct assay evidence for caspase-9 peptidase activity. Parent term
of cysteine-type endopeptidase activity.
supported_by:
- reference_id: PMID:19740745
supporting_text: A truncated form of p23 down-regulates telomerase activity
via disruption of Hsp90 function
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:19255499
review:
summary: PMID:19255499 shows HIP1R interacts with BCL2L10 which affects BAK-dependent
cell death.
action: KEEP_AS_NON_CORE
reason: BCL2L10 interaction affects mitochondrial apoptosis pathway. Regulatory
interaction.
supported_by:
- reference_id: PMID:19255499
supporting_text: HIP1R interacts with a member of Bcl-2 family, BCL2L10,
and induces BAK-dependent cell death
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-114252
review:
summary: Reactome pathway annotation for procaspase-3 cleavage by apoptosome.
action: ACCEPT
reason: Consistent with cytosolic localization of the apoptosome complex where
caspase-9 cleaves procaspase-3.
supported_by:
- reference_id: Reactome:R-HSA-114252
supporting_text: Cleavage of Procaspase-3 by the apoptosome
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-114259
review:
summary: Reactome annotation for procaspase-9 cleavage.
action: ACCEPT
reason: Consistent with cytosolic localization of the apoptosome.
supported_by:
- reference_id: Reactome:R-HSA-114259
supporting_text: Procaspase‑9 is processed in an ATP‑dependent manner following
association with APAF1 and cytochrome c (CYCS) within the apoptosome complex
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-114261
review:
summary: Reactome annotation for procaspase-7 cleavage by apoptosome.
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-114261
supporting_text: Cleavage of Procaspase-7 by the apoptosome
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-373700
review:
summary: Reactome annotation for caspase-9 binding to DCC:DIP13alpha complex.
action: ACCEPT
reason: Consistent with cytosolic localization for dependence receptor signaling.
supported_by:
- reference_id: Reactome:R-HSA-373700
supporting_text: Caspase-9 binds DCC:DIP13alpha complex
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-418845
review:
summary: Reactome annotation for caspase-3 activation.
action: ACCEPT
reason: Consistent with cytosolic localization for caspase cascade.
supported_by:
- reference_id: Reactome:R-HSA-418845
supporting_text: Activation of caspase-3
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-6804596
review:
summary: Reactome annotation for APAF1:CYCS binding APIP.
action: ACCEPT
reason: Consistent with cytosolic localization of apoptosome components.
supported_by:
- reference_id: Reactome:R-HSA-6804596
supporting_text: APAF1:CYCS binds APIP
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-6805426
review:
summary: Reactome annotation for CARD8 binding to CASP9(1-416).
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-6805426
supporting_text: CARD8 binds CASP9(1-416)
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-9627056
review:
summary: Reactome annotation for procaspase-9 dimer formation.
action: ACCEPT
reason: Consistent with cytosolic localization for dimerization.
supported_by:
- reference_id: Reactome:R-HSA-9627056
supporting_text: Procaspase 9 forms dimer
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-9627078
review:
summary: Reactome annotation for XIAP binding CASP9.
action: ACCEPT
reason: Consistent with cytosolic localization for IAP regulation.
supported_by:
- reference_id: Reactome:R-HSA-9627078
supporting_text: X‑linked inhibitor‑of‑apoptosis protein (XIAP) associates
with the cleaved form of CASP9
- term:
id: GO:0005829
label: cytosol
evidence_type: IDA
original_reference_id: PMID:17167422
review:
summary: PMID:17167422 shows Hsp70 regulates erythropoiesis by preventing caspase-3
cleavage of GATA-1 in the cytosol.
action: ACCEPT
reason: Direct experimental evidence for cytosolic caspase activity during erythroid
differentiation.
supported_by:
- reference_id: PMID:17167422
supporting_text: At the onset of caspase activation, Hsp70 co-localizes
and interacts with GATA-1 in the nucleus
- term:
id: GO:0030220
label: platelet formation
evidence_type: TAS
original_reference_id: PMID:18309324
review:
summary: PMID:18309324 reviews non-apoptotic functions of apoptotic effectors,
including roles in platelet formation.
action: KEEP_AS_NON_CORE
reason: Non-apoptotic function of caspases in platelet formation is documented.
This represents a specialized function distinct from core apoptotic role.
supported_by:
- reference_id: PMID:18309324
supporting_text: multiple studies indicate that the mammalian orthologs
of these C. elegans proteins (i.e. caspases, Apaf-1 and multidomain proteins
of the Bcl-2 family) participate in cell death-unrelated processes
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-114256
review:
summary: Reactome annotation for CYCS:APAF1 binding procaspase-9.
action: ACCEPT
reason: Consistent with cytosolic localization of apoptosome assembly.
supported_by:
- reference_id: Reactome:R-HSA-114256
supporting_text: CYCS:APAF1 binds procaspase-9
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-198621
review:
summary: Reactome annotation for AKT phosphorylates caspase-9.
action: ACCEPT
reason: Consistent with cytosolic localization for AKT-mediated regulation.
supported_by:
- reference_id: Reactome:R-HSA-198621
supporting_text: AKT phosphorylates caspase-9
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-2399985
review:
summary: Reactome annotation for AKT1 E17K mutant phosphorylates caspase-9.
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-2399985
supporting_text: AKT1 E17K mutant phosphorylates caspase-9
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-6804596
review:
summary: Duplicate annotation - same as earlier entry.
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-6804596
supporting_text: APAF1:CYCS binds APIP
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-6805426
review:
summary: Duplicate annotation - same as earlier entry.
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-6805426
supporting_text: CARD8 binds CASP9(1-416)
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-9627056
review:
summary: Duplicate annotation - same as earlier entry.
action: ACCEPT
reason: Consistent with cytosolic localization.
supported_by:
- reference_id: Reactome:R-HSA-9627056
supporting_text: Procaspase 9 forms dimer
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 shows c-Abl directly binds caspase-9 via SH3 domain.
action: ACCEPT
reason: c-Abl/caspase-9 interaction is functionally important for DNA damage
response. Though "protein binding" is vague, the interaction is core to DNA
damage-induced apoptosis.
supported_by:
- reference_id: PMID:15657060
supporting_text: c-Abl binds directly to caspase-9
- term:
id: GO:0006974
label: DNA damage response
evidence_type: IDA
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 provides direct assay evidence for caspase-9 in DNA damage
response through c-Abl-mediated phosphorylation.
action: ACCEPT
reason: Direct experimental demonstration of caspase-9 activation in DNA damage
response via c-Abl phosphorylation at Tyr-153.
supported_by:
- reference_id: PMID:15657060
supporting_text: c-Abl phosphorylates caspase-9 on Tyr-153 in vitro and
in cells treated with DNA damaging agents
- term:
id: GO:0008630
label: intrinsic apoptotic signaling pathway in response to DNA damage
evidence_type: IMP
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 demonstrates Y153F mutant attenuates DNA damage-induced
caspase-9 processing and apoptosis.
action: ACCEPT
reason: Mutant phenotype evidence for caspase-9 role in intrinsic apoptotic
signaling in response to DNA damage.
supported_by:
- reference_id: PMID:15657060
supporting_text: Caspase-9(Y153F) also attenuated DNA damage-induced processing
of caspase-9 to p35, activation of caspase-3, and apoptosis
- term:
id: GO:0019901
label: protein kinase binding
evidence_type: IDA
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 demonstrates caspase-9 binds c-Abl tyrosine kinase.
action: ACCEPT
reason: Direct experimental evidence for caspase-9 binding to c-Abl kinase.
This is a more informative term than generic "protein binding".
supported_by:
- reference_id: PMID:15657060
supporting_text: c-Abl binds directly to caspase-9
- term:
id: GO:0034644
label: cellular response to UV
evidence_type: IDA
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 demonstrates caspase-9 activation in response to UV irradiation
via c-Abl.
action: ACCEPT
reason: Direct experimental evidence for caspase-9 role in UV response. The
Y153F mutant attenuates UV irradiation-induced apoptosis.
supported_by:
- reference_id: PMID:15657060
supporting_text: Caspase-9(Y153F) also attenuated DNA damage-induced processing
of caspase-9 to p35, activation of caspase-3, and apoptosis
- term:
id: GO:0042770
label: signal transduction in response to DNA damage
evidence_type: IDA
original_reference_id: PMID:15657060
review:
summary: PMID:15657060 shows c-Abl-mediated signal transduction to caspase-9
in DNA damage response.
action: ACCEPT
reason: Direct experimental evidence for caspase-9 role in DNA damage signal
transduction through c-Abl kinase.
supported_by:
- reference_id: PMID:15657060
supporting_text: c-Abl tyrosine kinase regulates caspase-9 autocleavage
in the apoptotic response to DNA damage
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11350957
review:
summary: PMID:11350957 describes proapoptotic caspase-2 and caspase-9 binding
protein.
action: KEEP_AS_NON_CORE
reason: Documents a caspase-binding protein. "Protein binding" is uninformative.
supported_by:
- reference_id: PMID:11350957
supporting_text: Characterization of a novel proapoptotic caspase-2- and
caspase-9-binding protein
- term:
id: GO:0043293
label: apoptosome
evidence_type: IDA
original_reference_id: PMID:21827945
review:
summary: PMID:21827945 provides structural evidence for caspase-9 as a component
of the apoptosome.
action: ACCEPT
reason: 'Key structural study demonstrating caspase-9 localization to the apoptosome.
CRITICAL: Both isoforms can bind Apaf-1 in the apoptosome, but with opposite
effects (isoform 1 activates cascade, isoform 2 inhibits).'
supported_by:
- reference_id: PMID:21827945
supporting_text: Activation of procaspase-9 on the apoptosome is a pivotal
step in the intrinsic cell death pathway
- term:
id: GO:0006915
label: apoptotic process
evidence_type: TAS
original_reference_id: PMID:8663294
review:
summary: PMID:8663294 is the original paper characterizing ICE-LAP6 (caspase-9)
as an apoptosis-inducing caspase.
action: ACCEPT
reason: Foundational paper demonstrating caspase-9 (ICE-LAP6) induces apoptosis
when overexpressed and is activated by granzyme B.
supported_by:
- reference_id: PMID:8663294
supporting_text: Overexpression of ICE-LAP6 induces apoptosis in MCF7 breast
carcinoma cells
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:11069302
review:
summary: PMID:11069302 describes survivin interaction with caspase-9.
action: KEEP_AS_NON_CORE
reason: Survivin is an IAP family member that regulates caspase-9 activity.
Regulatory interaction.
supported_by:
- reference_id: PMID:11069302
supporting_text: Regulation of apoptosis at cell division by p34cdc2 phosphorylation
of survivin
- term:
id: GO:0004197
label: cysteine-type endopeptidase activity
evidence_type: TAS
original_reference_id: PMID:9390557
review:
summary: PMID:9390557 is the landmark paper demonstrating caspase-9 catalytic
activity in the intrinsic pathway (isoform 1).
action: ACCEPT
reason: Foundational paper demonstrating caspase-9 cleaves and activates caspase-3.
supported_by:
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0008047
label: enzyme activator activity
evidence_type: TAS
original_reference_id: PMID:9390557
review:
summary: PMID:9390557 demonstrates caspase-9 activates caspase-3 (isoform 1
function).
action: ACCEPT
reason: Caspase-9 functions as an enzyme activator by cleaving and activating
downstream effector caspases. This captures the initiator caspase function.
supported_by:
- reference_id: PMID:9390557
supporting_text: Activated caspase-9 in turn cleaves and activates caspase-3
- term:
id: GO:0043066
label: negative regulation of apoptotic process
evidence_type: TAS
original_reference_id: PMID:10070954
review:
summary: 'MISSING ANNOTATION: Caspase-9S (isoform 2, P55211-2) is a dominant-negative
inhibitor of apoptosis. UniProt explicitly states "Isoform 2: Lacks activity
is an dominant-negative inhibitor of caspase-9." This annotation is CRITICAL
for understanding CASP9 biology.'
action: NEW
reason: Isoform 2 (Caspase-9S/Beta) lacks the catalytic domain and competes
with isoform 1 for Apaf-1 binding, thereby inhibiting apoptosis. This is a
dominant-negative mechanism where the 9L/9S ratio determines apoptotic sensitivity.
PMID:10070954 characterizes this isoform. Cancer cells often shift ratio towards
9S to evade apoptosis.
supported_by:
- reference_id: PMID:10070954
supporting_text: Identification of an endogenous dominant-negative short
isoform of caspase-9 that can regulate apoptosis
- reference_id: file:human/CASP9/CASP9-deep-research-perplexity.md
supporting_text: the anti-apoptotic caspase-9b that excludes these exons...caspase-9b
lacks the core catalytic domain and functions as a dominant-negative inhibitor
of caspase-9a
- term:
id: GO:0030234
label: enzyme regulator activity
evidence_type: NAS
review:
summary: Added to align core_functions with existing annotations.
action: NEW
reason: Core function term not present in existing_annotations.
supported_by:
- reference_id: PMID:10070954
supporting_text: Identification of an endogenous dominant-negative short
isoform of caspase-9 that can regulate apoptosis
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO
terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings: []
- id: GO_REF:0000107
title: Automatic transfer of experimentally verified manual GO annotation data
to orthologs using Ensembl Compara
findings: []
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:10070954
title: Identification of an endogenous dominant-negative short isoform of caspase-9
that can regulate apoptosis.
findings:
- statement: Caspase-9S (isoform 2) lacks catalytic domain and acts as dominant-negative
inhibitor
- id: PMID:10206961
title: An APAF-1.cytochrome c multimeric complex is a functional apoptosome that
activates procaspase-9.
findings:
- statement: Apoptosome recruits and activates procaspase-9
- statement: Stoichiometric ratio of procaspase-9 to APAF-1 is approximately
1 to 1
- id: PMID:10376594
title: Structural basis of procaspase-9 recruitment by the apoptotic protease-activating
factor 1.
findings:
- statement: CARD-CARD interaction between caspase-9 and Apaf-1
- id: PMID:11024045
title: Livin, a novel inhibitor of apoptosis protein family member.
findings: []
- id: PMID:11069302
title: Regulation of apoptosis at cell division by p34cdc2 phosphorylation of
survivin.
findings: []
- id: PMID:11084335
title: ML-IAP, a novel inhibitor of apoptosis that is preferentially expressed
in human melanomas.
findings: []
- id: PMID:11230124
title: Recruitment, activation and retention of caspases-9 and -3 by Apaf-1 apoptosome
and associated XIAP complexes.
findings: []
- id: PMID:11242052
title: A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates
caspase activity and apoptosis.
findings: []
- id: PMID:11350957
title: Characterization of a novel proapoptotic caspase-2- and caspase-9-binding
protein.
findings: []
- id: PMID:11801603
title: SMAC negatively regulates the anti-apoptotic activity of melanoma inhibitor
of apoptosis (ML-IAP).
findings: []
- id: PMID:11821383
title: CARD-8 protein, a new CARD family member that regulates caspase-1 activation
and apoptosis.
findings: []
- id: PMID:12620238
title: Mechanism of XIAP-mediated inhibition of caspase-9.
findings: []
- id: PMID:12782307
title: Apoptosis triggered redistribution of caspase-9 from cytoplasm to mitochondria.
findings:
- statement: Caspase-9 is cytoplasmic in non-apoptotic cells
- statement: Redistributes to mitochondria during apoptosis
- id: PMID:15069058
title: BRCC2, a novel BH3-like domain-containing protein, induces apoptosis in
a caspase-dependent manner.
findings: []
- id: PMID:15657060
title: c-Abl tyrosine kinase regulates caspase-9 autocleavage in the apoptotic
response to DNA damage.
findings:
- statement: c-Abl directly binds caspase-9
- statement: Phosphorylates caspase-9 at Tyr-153 in DNA damage response
- statement: Y153F mutant attenuates DNA damage-induced apoptosis
- id: PMID:16189514
title: Towards a proteome-scale map of the human protein-protein interaction network.
findings: []
- id: PMID:16352606
title: Caspase-7 is directly activated by the approximately 700-kDa apoptosome
complex and is released as a stable XIAP-caspase-7 approximately 200-kDa complex.
findings:
- statement: Apoptosome directly cleaves/activates procaspase-7
- id: PMID:16537496
title: The dependence receptor DCC requires lipid raft localization for cell death
signaling.
findings: []
- id: PMID:16916640
title: 'Engineered hybrid dimers: tracking the activation pathway of caspase-7.'
findings:
- statement: Demonstrates caspase-9 activation of caspase-7
- id: PMID:16920334
title: Protective role of Cop in Rip2/caspase-1/caspase-4-mediated HeLa cell death.
findings: []
- id: PMID:16936772
title: Integrin-linked kinase interacts with caspase-9 and -8 in an adhesion-dependent
manner for promoting radiation-induced apoptosis in human leukemia cells.
findings: []
- id: PMID:17167422
title: Hsp70 regulates erythropoiesis by preventing caspase-3-mediated cleavage
of GATA-1.
findings: []
- id: PMID:18022362
title: IAP antagonists induce autoubiquitination of c-IAPs, NF-kappaB activation,
and TNFalpha-dependent apoptosis.
findings: []
- id: PMID:18309324
title: 'No death without life: vital functions of apoptotic effectors.'
findings:
- statement: Caspases have non-apoptotic functions including platelet formation
- id: PMID:18723680
title: Executioner caspase-3 and caspase-7 are functionally distinct proteases.
findings: []
- id: PMID:19153467
title: The structure of the BIR3 domain of cIAP1 in complex with the N-terminal
peptides of SMAC and caspase-9.
findings: []
- id: PMID:19255499
title: HIP1R interacts with a member of Bcl-2 family, BCL2L10, and induces BAK-dependent
cell death.
findings: []
- id: PMID:19494828
title: The Apaf-1*procaspase-9 apoptosome complex functions as a proteolytic-based
molecular timer.
findings: []
- id: PMID:19721007
title: Netrin-1 up-regulation in inflammatory bowel diseases is required for colorectal
cancer progression.
findings: []
- id: PMID:19740745
title: A truncated form of p23 down-regulates telomerase activity via disruption
of Hsp90 function.
findings: []
- id: PMID:20462491
title: Structure of an apoptosome-procaspase-9 CARD complex.
findings: []
- id: PMID:21827945
title: 'The holo-apoptosome: activation of procaspase-9 and interactions with
caspase-3.'
findings:
- statement: Structural evidence for caspase-9 in apoptosome
- id: PMID:21980415
title: Identification of a conserved anti-apoptotic protein that modulates the
mitochondrial apoptosis pathway.
findings: []
- id: PMID:23516580
title: The E. coli effector protein NleF is a caspase inhibitor.
findings: []
- id: PMID:25241761
title: Using an in situ proximity ligation assay to systematically profile endogenous
protein-protein interactions in a pathway network.
findings: []
- id: PMID:25416956
title: A proteome-scale map of the human interactome network.
findings: []
- id: PMID:25502805
title: A massively parallel pipeline to clone DNA variants and examine molecular
phenotypes of human disease mutations.
findings: []
- id: PMID:25519916
title: The EHEC-host interactome reveals novel targets for the translocated intimin
receptor.
findings: []
- id: PMID:27107012
title: Pooled-matrix protein interaction screens using Barcode Fusion Genetics.
findings: []
- id: PMID:27889207
title: Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apoptotic Activity
by Two Distinct Mechanisms.
findings: []
- id: PMID:29997244
title: 'LuTHy: a double-readout bioluminescence-based two-hybrid technology for
quantitative mapping of protein-protein interactions in mammalian cells.'
findings: []
- id: PMID:31467278
title: Maximizing binary interactome mapping with a minimal number of assays.
findings: []
- id: PMID:31515488
title: Extensive disruption of protein interactions by genetic variants across
the allele frequency spectrum in human populations.
findings: []
- id: PMID:32296183
title: A reference map of the human binary protein interactome.
findings: []
- id: PMID:35446120
title: Calmodulin Binding Activates Chromobacterium CopC Effector to ADP-Riboxanate
Host Apoptotic Caspases.
findings: []
- id: PMID:8663294
title: ICE-LAP6, a novel member of the ICE/Ced-3 gene family, is activated by
the cytotoxic T cell protease granzyme B.
findings:
- statement: Original characterization of caspase-9 (ICE-LAP6)
- statement: Overexpression induces apoptosis
- id: PMID:9390557
title: Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates
an apoptotic protease cascade.
findings:
- statement: Landmark paper establishing caspase-9 as initiator caspase
- statement: CARD-CARD interaction with Apaf-1
- statement: Activates caspase-3
- id: PMID:9922454
title: 'Ordering the cytochrome c-initiated caspase cascade: hierarchical activation
of caspases-2, -3, -6, -7, -8, and -10 in a caspase-9-dependent manner.'
findings: []
- id: Reactome:R-HSA-114252
title: Cleavage of Procaspase-3 by the apoptosome
findings: []
- id: Reactome:R-HSA-114256
title: CYCS:APAF1 binds procaspase-9
findings: []
- id: Reactome:R-HSA-114259
title: Cleavage of Procaspase‑9 to caspase‑9
findings: []
- id: Reactome:R-HSA-114261
title: Cleavage of Procaspase-7 by the apoptosome
findings: []
- id: Reactome:R-HSA-198621
title: AKT phosphorylates caspase-9
findings: []
- id: Reactome:R-HSA-2399985
title: AKT1 E17K mutant phosphorylates caspase-9
findings: []
- id: Reactome:R-HSA-373700
title: Caspase-9 binds DCC:DIP13alpha complex
findings: []
- id: Reactome:R-HSA-418845
title: Activation of caspase-3
findings: []
- id: Reactome:R-HSA-6804596
title: APAF1:CYCS binds APIP
findings: []
- id: Reactome:R-HSA-6805426
title: CARD8 binds CASP9(1-416)
findings: []
- id: Reactome:R-HSA-9627056
title: Procaspase 9 forms dimer
findings: []
- id: Reactome:R-HSA-9627078
title: XIAP binds CASP9
findings: []
- id: Reactome:R-HSA-9627089
title: CASP9 is phosphorylated at T412
findings: []
- id: file:human/CASP9/CASP9-deep-research-perplexity.md
title: Deep research report on CASP9
findings: []
core_functions:
- description: Initiator caspase of the intrinsic (mitochondrial) apoptotic pathway.
Upon mitochondrial outer membrane permeabilization (MOMP) and cytochrome c release,
caspase-9 (isoform 1) is recruited to the Apaf-1 apoptosome via CARD-CARD interactions,
where it is activated and cleaves/activates effector caspases-3 and -7 to execute
apoptosis.
molecular_function:
id: GO:0004197
label: cysteine-type endopeptidase activity
directly_involved_in:
- id: GO:0097193
label: intrinsic apoptotic signaling pathway
in_complex:
id: GO:0043293
label: apoptosome
- description: Cysteine-type endopeptidase with strict requirement for Asp at P1
position and preference for LEHD sequence. Cleaves procaspase-3 and procaspase-7
at their intersubunit linkers to generate active executioner caspases.
molecular_function:
id: GO:0004197
label: cysteine-type endopeptidase activity
substrates:
- id: UniProtKB:P42574
label: CASP3
- id: UniProtKB:P55210
label: CASP7
- description: 'DNA damage response effector: c-Abl kinase phosphorylates caspase-9
at Tyr-153 in response to genotoxic stress, promoting caspase-9 autoprocessing
and apoptosis.'
molecular_function:
id: GO:0004197
label: cysteine-type endopeptidase activity
directly_involved_in:
- id: GO:0008630
label: intrinsic apoptotic signaling pathway in response to DNA damage
- description: 'CRITICAL ISOFORM BIOLOGY: Alternative splicing produces antagonistic
isoforms. Isoform 1 (Caspase-9L/9a/Alpha) is pro-apoptotic with full catalytic
activity. Isoform 2 (Caspase-9S/9b/Beta) lacks the catalytic domain and acts
as a DOMINANT-NEGATIVE INHIBITOR by competing for Apaf-1 binding. The 9L/9S
ratio determines cellular apoptotic sensitivity.'
molecular_function:
id: GO:0030234
label: enzyme regulator activity
supported_by:
- reference_id: PMID:10070954
supporting_text: Identification of an endogenous dominant-negative short isoform
of caspase-9 that can regulate apoptosis
proposed_new_terms: []
suggested_questions:
- question: How do cells regulate the ratio of Caspase-9L to Caspase-9S isoforms,
and what splicing factors are involved in this decision?
- question: What is the precise molecular mechanism by which Caspase-9S inhibits
apoptosis - does it simply sequester Apaf-1 or does it have additional inhibitory
mechanisms?
- question: What are the non-apoptotic functions of caspase-9 in autophagy, synaptic
plasticity, and vascular function, and how are these regulated independently
of apoptosis?
suggested_experiments:
- description: 'Isoform-specific proteomics: Develop isoform-specific antibodies
or mass spectrometry methods to quantify 9L/9S ratios across tissues and disease
states.'
- description: 'Structural studies of Caspase-9S in the apoptosome: Determine how
the truncated isoform interacts with Apaf-1 and whether it truly occupies the
same binding site as 9L.'
- description: 'Conditional isoform knockout: Generate mice with isoform-specific
knockouts to determine the specific physiological roles of each isoform.'
alternative_products:
- name: 1 (9L, Alpha)
id: P55211-1
description: >-
The canonical pro-apoptotic isoform (416 AA). Also called Caspase-9L or Caspase-9
alpha.
Contains the CARD domain and full catalytic domain. Activated by Apaf-1 in the
apoptosome
to initiate the intrinsic apoptotic pathway. Most GO annotations refer to this
isoform.
- name: 2 (9S, Beta)
id: P55211-2
sequence_note: VSP_000818
description: >-
The dominant-negative anti-apoptotic isoform (307 AA). Also called Caspase-9S
or Caspase-9
beta. Lacks the catalytic domain but retains the CARD domain, allowing it to
compete with
Caspase-9L for Apaf-1 binding without triggering apoptosis. The 9L/9S ratio
determines
cellular sensitivity to apoptotic stimuli. Overexpressed in some cancers to
evade apoptosis.
- name: 3 (Gamma)
id: P55211-3
sequence_note: VSP_043910, VSP_043911
description: >-
A less characterized isoform with alternative splicing affecting the N-terminal
region.
Functional studies are limited compared to the 9L and 9S isoforms.
- name: '4'
id: P55211-4
sequence_note: VSP_044256
description: >-
A less characterized isoform. Functional role not well established in the literature.