CACUL1 (CDK2-associated and cullin domain-containing protein 1; also known as CAC1 / C10orf46) is a poorly characterized 369-amino-acid human protein containing a single cullin-repeat-like domain with disordered N- and C-terminal regions. Despite its name and cullin-fold homology, it is much shorter than canonical cullins (~750-900 aa) and there is no experimental evidence that it nucleates a functional cullin-RING ubiquitin ligase or carries a neddylation/RBX module. The best-supported activity, from a single study, is physical association with the cyclin-dependent kinase CDK2 and promotion of CDK2 kinase activity, consistent with a role in G1/S cell-cycle progression and proliferation; the protein is highly expressed in cancer tissues and cell lines, and its abundance varies across the cell cycle. CACUL1 also acts as a nuclear-receptor transcriptional corepressor: it is a SIRT1-interacting protein that binds PPARgamma (and estrogen receptor alpha) and represses their transcription by coordinating SIRT1 and the histone demethylase LSD1/KDM1A at target promoters (lowering H3K9 acetylation and raising H3K9 methylation), thereby suppressing adipocyte differentiation. Separately, although CACUL1 does not itself nucleate a cullin-RING ligase, it binds the Cul3-Keap1-Rbx1 (CRL3-Keap1) ubiquitin-ligase complex and attenuates its ubiquitination of the transcription factor Nrf2 (NFE2L2), stabilizing Nrf2 and promoting the antioxidant response. CACUL1 has also been recovered as a yeast two-hybrid interactor of ARMC5. Overall, CACUL1 is a multifunctional protein linking CDK2-associated cell-cycle progression, nuclear-receptor corepression, and negative regulation of Nrf2 ubiquitination.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000082
G1/S transition of mitotic cell cycle
|
IBA
GO_REF:0000033 |
KEEP AS NON CORE |
Summary: Phylogenetic (IBA) transfer of a G1/S cell-cycle role. This is consistent with the direct experimental evidence in the same gene (PMID:19829063), where CACUL1/CAC1 knockdown induces G1/S arrest. Retained but as a non-core/secondary process annotation since the defining molecular activity is the CDK2 interaction rather than the broader cell-cycle process itself.
Reason: Supported indirectly by direct knockdown evidence (PMID:19829063) that CACUL1 loss causes G1/S arrest, but this is a downstream process rather than a precise molecular function; treat as a non-core involvement.
Supporting Evidence:
PMID:19829063
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S arrest.
|
|
GO:0019901
protein kinase binding
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Phylogenetic (IBA) transfer of protein kinase binding. This is the same molecular function directly demonstrated for CACUL1 via its physical interaction with CDK2 (PMID:19829063). Accept as it reflects the best-supported molecular activity of the protein.
Reason: Directly corroborated by experimental CDK2 binding (PMID:19829063); the IBA call coincides with the strongest molecular evidence for this protein.
Supporting Evidence:
PMID:19829063
this protein is physically associated with CDK2
|
|
GO:0006511
ubiquitin-dependent protein catabolic process
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: The IEA InterPro2GO transfer (cullin-repeat domain IPR001373) implies direct participation in ubiquitin-dependent catabolism, which remains unsupported: CACUL1 is too short to be a CRL scaffold and carries no RBX/neddylation module. However, Kigoshi et al. 2015 (PMID:26238671) show CACUL1 binds the Cul3-Keap1-Rbx1 ubiquitin-ligase complex and ATTENUATES Nrf2 ubiquitination, stabilizing Nrf2. The experimentally supported role is therefore NEGATIVE regulation of (Nrf2) ubiquitination, not direct participation in catabolism; modify accordingly.
Reason: Direct participation in ubiquitin-dependent catabolism is a domain-only over-annotation, but CACUL1 has experimentally demonstrated activity as a negative regulator of Nrf2 ubiquitination via the Cul3-Keap1-Rbx1 complex (PMID:26238671); replace with negative regulation of protein ubiquitination.
Proposed replacements:
negative regulation of protein ubiquitination
Supporting Evidence:
PMID:26238671
CACUL1 attenuates Nrf2 ubiquitination
PMID:26238671
CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
|
|
GO:0031625
ubiquitin protein ligase binding
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: Although the IEA call was originally a pure cullin-domain (IPR001373) transfer, it is now experimentally supported: Kigoshi et al. 2015 (PMID:26238671) demonstrate that CACUL1 binds Keap1, Cul3 and Rbx1 - the components of the ubiquitin ligase (CRL3) responsible for Nrf2 ubiquitination - and thereby modulates that ligase's activity toward Nrf2. The ubiquitin-protein-ligase-binding molecular function is therefore retained with direct experimental support.
Reason: Experimentally demonstrated binding to the Cul3-Keap1-Rbx1 ubiquitin ligase complex (PMID:26238671) directly supports this molecular function; it is no longer a domain-only over-annotation.
Supporting Evidence:
PMID:26238671
we further assessed CACUL1 binding with Keap1, Cul3 and Rbx1, the components of the Ubiquitin ligase responsible for Nrf2 ubiquitination.
|
|
GO:0005515
protein binding
|
IPI
PMID:23178685 Negative regulation of ERα by a novel protein CAC1 through a... |
MODIFY |
Summary: This IPI annotation (WITH ESR1/P03372) records the physical interaction between CACUL1/CAC1 and estrogen receptor alpha (ERalpha), corroborated by IntAct (NbExp=5). The bare "protein binding" term is uninformative; a more specific molecular function is warranted given the established, directional ERalpha interaction.
Reason: The interaction partner is a specific nuclear receptor (ERalpha); replace the uninformative protein binding term with nuclear estrogen receptor binding to capture the actual molecular function.
Proposed replacements:
nuclear estrogen receptor binding
Supporting Evidence:
PMID:23178685
The CoRNR box of CAC1 was required for the binding to and inactivation of ERα.
|
|
GO:0005515
protein binding
|
IPI
PMID:28169274 Armc5 deletion causes developmental defects and compromises ... |
MARK AS OVER ANNOTATED |
Summary: This IPI annotation (WITH ARMC5/Q96C12) derives from a yeast two-hybrid screen in which CACUL1 was one of 16 ARMC5-binding partners. The paper characterizes ARMC5, not CACUL1, and provides no functional context for CACUL1. The bare "protein binding" term is uninformative and rests on a single high-throughput Y2H datum.
Reason: Uninformative bare protein binding from a single Y2H hit in an ARMC5-focused study; no specific function or biology for CACUL1 is established.
Supporting Evidence:
PMID:28169274
Yeast 2-hybrid assays identify 16 ARMC5-binding partners.
|
|
GO:0000082
G1/S transition of mitotic cell cycle
|
IMP
PMID:19829063 Identification and characterization of CAC1 as a novel CDK2-... |
KEEP AS NON CORE |
Summary: Direct experimental evidence: RNAi knockdown of CACUL1/CAC1 induces G1/S arrest, indicating involvement in the G1/S transition. This is a genuine process annotation but downstream of the protein's molecular role in activating CDK2; retained as a non-core involvement.
Reason: Well-supported by knockdown phenotype, but the broad cell-cycle process is secondary to the precise CDK2-activating molecular function.
Supporting Evidence:
PMID:19829063
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S arrest.
|
|
GO:0008284
positive regulation of cell population proliferation
|
IMP
PMID:19829063 Identification and characterization of CAC1 as a novel CDK2-... |
KEEP AS NON CORE |
Summary: Direct experimental evidence: CACUL1/CAC1 knockdown inhibits cell proliferation, supporting a positive role in proliferation. This is a real but downstream phenotypic process annotation; kept as non-core relative to the underlying CDK2-activating molecular function.
Reason: Supported by knockdown phenotype but is a broad downstream process rather than the precise molecular activity.
Supporting Evidence:
PMID:19829063
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S arrest.
|
|
GO:0019901
protein kinase binding
|
IPI
PMID:19829063 Identification and characterization of CAC1 as a novel CDK2-... |
ACCEPT |
Summary: Direct experimental evidence (IPI, WITH CDK2/P24941) for physical association of CACUL1/CAC1 with the cyclin-dependent kinase CDK2. This is the best-supported molecular function of the protein and represents a core activity.
Reason: Directly demonstrated CDK2 binding; an informative molecular-function term reflecting the protein's defining characterized interaction.
Supporting Evidence:
PMID:19829063
this protein is physically associated with CDK2
|
|
GO:0045860
positive regulation of protein kinase activity
|
IMP
PMID:19829063 Identification and characterization of CAC1 as a novel CDK2-... |
ACCEPT |
Summary: Direct experimental evidence that CACUL1/CAC1 promotes CDK2 kinase activity. This captures the functional consequence of the CDK2 interaction and is a core aspect of the protein's characterized activity, though the molecular mechanism of activation remains undefined.
Reason: Supported by experiments showing CAC1 promotes CDK2 kinase activity; a well-evidenced functional annotation.
Supporting Evidence:
PMID:19829063
CAC1 interacts with CDK2 and promotes the kinase activity of CDK2 protein
|
|
GO:0003714
transcription corepressor activity
|
IDA
PMID:29233982 CACUL1 reciprocally regulates SIRT1 and LSD1 to repress PPAR... |
NEW |
Summary: Proposed NEW molecular-function annotation (not in current GOA). CACUL1 represses PPARgamma- (PMID:29233982) and ERalpha- (PMID:23178685) dependent transcription by coordinating SIRT1 and LSD1 at target promoters, i.e. it acts as a nuclear-receptor transcription corepressor. This is the informative MF underlying the existing bare protein-binding / nuclear estrogen receptor binding annotations.
Reason: Two independent studies show CACUL1 physically binds nuclear receptors (PPARgamma, ERalpha) and represses their transcriptional activity via SIRT1/LSD1; transcription corepressor activity captures this MF.
Supporting Evidence:
PMID:29233982
CACUL1, identified as a novel SIRT1 interacting protein, physically interacts with PPARγ and represses its transcriptional activity, suppressing adipocyte differentiation
PMID:23178685
CAC1, associated with LSD1, functions as an ERα corepressor
|
|
GO:0042975
peroxisome proliferator activated receptor binding
|
IPI
PMID:29233982 CACUL1 reciprocally regulates SIRT1 and LSD1 to repress PPAR... |
NEW |
Summary: Proposed NEW molecular-function annotation (not in current GOA). CACUL1 physically interacts with PPARgamma, providing the receptor-binding basis for its corepressor activity at PPARgamma-responsive promoters.
Reason: Direct physical interaction of CACUL1 with PPARgamma demonstrated (PMID:29233982); a specific, informative nuclear-receptor-binding MF.
Supporting Evidence:
PMID:29233982
CACUL1, identified as a novel SIRT1 interacting protein, physically interacts with PPARγ and represses its transcriptional activity, suppressing adipocyte differentiation
|
|
GO:0031397
negative regulation of protein ubiquitination
|
IMP
PMID:26238671 CACUL1/CAC1 Regulates the Antioxidant Response by Stabilizin... |
NEW |
Summary: Proposed NEW process annotation (not in current GOA), also offered as the MODIFY replacement for the domain-only GO:0006511 IEA. CACUL1 binds the Cul3-Keap1-Rbx1 complex and attenuates Nrf2 ubiquitination, stabilizing Nrf2 - a negative regulatory role in protein ubiquitination.
Reason: Experimentally demonstrated attenuation of Nrf2 ubiquitination by CACUL1 (PMID:26238671) supports negative regulation of protein ubiquitination.
Supporting Evidence:
PMID:26238671
CACUL1 attenuates Nrf2 ubiquitination
PMID:26238671
CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
file:human/CACUL1/CACUL1-deep-research-falcon.md
CACUL1 associates with the Cul3-Keap1-Rbx1 ubiquitin ligase complex
|
|
GO:0050821
protein stabilization
|
IMP
PMID:26238671 CACUL1/CAC1 Regulates the Antioxidant Response by Stabilizin... |
NEW |
Summary: Proposed NEW process annotation (not in current GOA). By attenuating its ubiquitination, CACUL1 stabilizes the transcription factor Nrf2 (half-life ~10 -> ~30 min), the downstream consequence of its CRL3-Keap1 modulation.
Reason: CACUL1 lengthens Nrf2 half-life by limiting its ubiquitination (PMID:26238671), consistent with a protein-stabilization role.
Supporting Evidence:
PMID:26238671
CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
|
Q: Does CACUL1 act as a bona fide CDK2 regulator through a direct structural/allosteric mechanism, or indirectly via cyclin or CDK-inhibitor levels?
Q: Is the nuclear-receptor co-regulatory activity of CACUL1 (ERalpha repression via LSD1, and the separately reported androgen-receptor co-regulation) physiologically significant, and how is its directionality (corepressor vs coactivator) determined?
Q: CACUL1 binds the Cul3-Keap1-Rbx1 (CRL3) complex and negatively regulates Nrf2 ubiquitination (PMID:26238671) without nucleating its own ligase - does its cullin-repeat-like domain mediate this CRL3 association, and is the regulation Nrf2-specific or a more general modulation of CRL3-Keap1 substrate ubiquitination?
Experiment: In vitro reconstituted CDK2 kinase assays with purified recombinant CACUL1 to test whether it directly stimulates CDK2 activity, and structural/biophysical mapping (e.g., cryo-EM or co-crystallization, HDX-MS) of the CACUL1-CDK2 interface.
Hypothesis: CACUL1 directly binds and allosterically activates CDK2 independent of cyclin levels.
Type: biochemical/structural
Experiment: Affinity purification-mass spectrometry of endogenous CACUL1 across cell-cycle stages to define its stable interactome and test for any RBX/neddylation or cullin-RING ligase components.
Hypothesis: CACUL1 does not assemble a canonical cullin-RING ligase and instead functions through CDK2 and nuclear-receptor/chromatin partners.
Type: proteomics
Experiment: ChIP-seq and reporter assays for CACUL1 at ERalpha- and androgen-receptor- responsive promoters with and without LSD1, to define its co-regulatory direction and chromatin effects.
Hypothesis: CACUL1 modulates nuclear-receptor target genes through LSD1-dependent changes in histone methylation.
Type: genomics/transcription
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The direct biochemical mechanism by which CACUL1 promotes CDK2 kinase activity remains unresolved: it is unclear whether CACUL1 allosterically activates CDK2, alters cyclin/CDK-inhibitor availability, changes substrate engagement, or acts through another cell-cycle regulatory complex.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: CACUL1 physically associates with CDK2, promotes CDK2 kinase activity, is expressed in a cell-cycle-dependent manner, and RNAi knockdown causes reduced proliferation with G1/S arrest. The unresolved part is the immediate molecular mechanism connecting CACUL1 binding to increased CDK2 activity.
Significance: CDK2 regulation is the best-supported CACUL1 activity, but without a mechanism it is hard to distinguish a direct CDK2 co-regulator from an indirect cell-cycle phenotype.
What would resolve it: Reconstitute purified CACUL1-CDK2-cyclin complexes for kinase kinetics, map the binding interface, and test whether CACUL1 changes cyclin binding, CDK-inhibitor binding, or substrate phosphorylation in cells.
Provenance (the field's own admissions):
Gap: The role of CACUL1's cullin-repeat-like domain in CRL3-Keap1/Nrf2 regulation is unresolved, and CACUL1 should not be curated as a bona fide cullin-RING scaffold unless future experiments show that it assembles or positions an E3 ubiquitin ligase complex.
OPEN BIOLOGYCURATION RESIDUAL_SUBGAP
What is known: CACUL1 binds Keap1, Cul3, and Rbx1 and attenuates Nrf2 ubiquitination, supporting ubiquitin-ligase binding and negative regulation of Nrf2 ubiquitination. The gap is whether the short cullin-like region is the binding/regulatory interface and whether CACUL1 modulates only CRL3-Keap1/Nrf2 or broader CRL3 substrate ubiquitination.
Significance: This boundary prevents domain-only over-propagation of cullin scaffold activity while preserving the experimentally supported CRL3-Keap1/Nrf2 regulatory role.
What would resolve it: Map CACUL1 deletion mutants against Keap1, Cul3, Rbx1, and Nrf2; assay CRL3 ubiquitination activity with purified components; and test whether CACUL1 affects other CRL3-Keap1 or Cul3 substrates.
Provenance (the field's own admissions):
Gap: The physiological context and directionality of CACUL1 nuclear-receptor coregulation remain only partly defined, especially whether ERalpha, androgen receptor, and PPARgamma effects represent one general chromatin mechanism or distinct receptor- and cell-type-specific activities.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: CACUL1 can bind nuclear receptors and repress ERalpha- and PPARgamma-dependent transcription with LSD1/SIRT1-linked chromatin changes. The unresolved part is which tissues and metabolic or hormonal states require this activity in vivo, and when CACUL1 acts as a corepressor versus a co-regulator with different directionality.
Significance: Nuclear-receptor corepression is experimentally supported but may be highly context-dependent; resolving context will determine whether CACUL1 should be treated as a broadly relevant transcriptional regulator or a narrower adipocyte and hormone-response modulator.
What would resolve it: Combine receptor-specific ChIP-seq/CUT&RUN, transcriptomics, and CACUL1 loss- and gain-of-function in relevant adipocyte and hormone-responsive models, followed by in vivo perturbation where feasible.
Provenance (the field's own admissions):
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.
CACUL1 (also designated CAC1) encodes CDK2-associated cullin domain-containing protein 1 in Homo sapiens (UniProt: Q86Y37). The protein is classified as a member of the cullin family and is characterized by the presence of a cullin domain and two conserved co-repressor nuclear receptor (CoRNR) boxes that mediate protein-protein interactions (kigoshi2015cacul1cac1regulatesthe pages 1-2, jang2017cacul1reciprocallyregulates pages 1-2, chen2019cac1knockdownreverses pages 1-2). The gene symbol CACUL1 is unambiguous in the literature, with consistent nomenclature across multiple studies.
CACUL1 is a presumptive cullin domain-containing protein whose structure includes two critical CoRNR boxes, with CoRNR box 2 playing an essential role in mediating interactions with multiple binding partners (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4). Domain mapping studies have demonstrated that CoRNR box 2 is necessary for binding to SIRT1, with deletion mutants lacking this region (CoR2Δ) or substitution mutants (AxxTT, where amino acids LQSIV are changed to AQSTT) abolishing interactions with nuclear receptor partners (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4). The cullin domain structure itself has been proposed to facilitate association with ubiquitin ligase complexes, though the precise structural basis remains incompletely characterized (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4).
CACUL1 functions as a modulator of ubiquitin-mediated protein degradation through its association with cullin-RING E3 ubiquitin ligase complexes. The most thoroughly characterized function involves regulation of the Nrf2 (nuclear factor erythroid 2-related factor 2) antioxidant response pathway (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5). CACUL1 associates with the Cul3-Keap1-Rbx1 ubiquitin ligase complex, as demonstrated by co-immunoprecipitation experiments showing direct binding to Keap1, Cul3, and Rbx1 (kigoshi2015cacul1cac1regulatesthe pages 2-4). This association results in attenuation of Nrf2 ubiquitination, prolonging Nrf2 protein half-life from approximately 15 minutes in control cells to approximately 30 minutes upon CACUL1 overexpression, as measured by cycloheximide chase experiments (kigoshi2015cacul1cac1regulatesthe pages 4-5). Importantly, CACUL1 stabilizes Nrf2 without disrupting the formation of the Cul3-Keap1-Nrf2 complex itself, suggesting it acts as a negative regulator of the ligase activity rather than a disruptor of complex assembly (kigoshi2015cacul1cac1regulatesthe pages 2-4).
The functional consequence of this regulation is context-dependent. Under basal conditions, CACUL1 overexpression does not significantly increase Nrf2 target gene transcription or alter Nrf2 subcellular localization (kigoshi2015cacul1cac1regulatesthe pages 4-5). However, under oxidative stress conditions (induced by tert-butylhydroquinone or butylated hydroxyanisole), CACUL1 sensitizes cells for enhanced Nrf2 activation, leading to increased expression of antioxidant response element (ARE)-driven genes including NQO1 and HO-1 (kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5). CACUL1 expression itself is induced by oxidative stress in both cultured cells and in mouse kidneys following BHA feeding, suggesting a feedback mechanism whereby stress-induced CACUL1 amplifies the Nrf2 response (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4). Functionally, CACUL1 knockdown reduces cell viability under oxidative stress and increases apoptosis, demonstrating its importance for cellular survival in stress conditions (kigoshi2015cacul1cac1regulatesthe pages 4-5, kigoshi2015cacul1cac1regulatesthe pages 5-7).
CACUL1 functions as a transcriptional co-repressor for nuclear receptors, with its most extensively studied role being in the regulation of peroxisome proliferator-activated receptor γ (PPARγ)-mediated adipogenesis (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7). CACUL1 was initially identified as a SIRT1-binding protein through yeast two-hybrid screening and subsequently shown to physically interact with PPARγ through its CoRNR box 2, which binds to the E/F domain of PPARγ (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4). These interactions were confirmed through multiple biochemical approaches including co-immunoprecipitation, GST pull-down assays, and detection of endogenous CACUL1-PPARγ-SIRT1 complexes in 3T3-L1 preadipocytes (jang2017cacul1reciprocallyregulates pages 2-4).
The mechanism of PPARγ repression involves coordinated epigenetic regulation through reciprocal modulation of two histone-modifying enzymes: SIRT1 (a histone deacetylase) and LSD1 (lysine-specific demethylase 1) (jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11). Chromatin immunoprecipitation (ChIP) experiments at PPARγ-responsive gene promoters (including the aP2/FABP4 promoter) demonstrate that CACUL1 depletion leads to decreased SIRT1 recruitment, increased LSD1 recruitment, elevated histone H3K9 acetylation (an activating mark), and reduced H3K9 methylation (a repressive mark) (jang2017cacul1reciprocallyregulates pages 4-7). Conversely, under conditions that activate SIRT1 (fasting or resveratrol treatment), CACUL1 and SIRT1 recruitment to PPARγ target promoters increases, H3K9 acetylation decreases, LSD1 binding is reduced, and H3K9 methylation increases (jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11). Luciferase reporter assays confirm that CACUL1 cooperates with SIRT1 to repress PPARγ transcriptional activity while antagonizing LSD1-mediated activation (jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7).
Functionally, CACUL1 overexpression strongly inhibits adipocyte differentiation in both mouse 3T3-L1 cells and human adipose-derived stem cells, as measured by Oil Red O staining and quantification of lipid accumulation (jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 7-11). CACUL1 knockdown produces the opposite effect, enhancing adipogenesis (jang2017cacul1reciprocallyregulates pages 2-4). RNA sequencing analysis of CACUL1-overexpressing and CACUL1-depleted 3T3-L1 cells during differentiation identified 644 commonly regulated genes, with gene ontology enrichment showing strong associations with adipogenesis, PPARγ signaling, and lipid metabolism (jang2017cacul1reciprocallyregulates pages 7-11). Gene set enrichment analysis (GSEA) confirmed downregulation of adipogenesis-associated genes in CACUL1-overexpressing cells and upregulation upon CACUL1 depletion (jang2017cacul1reciprocallyregulates pages 7-11).
Beyond PPARγ, CACUL1 has been reported to function as a co-repressor for other nuclear receptors including estrogen receptor α (ERα), androgen receptor (AR), and retinoic acid receptor α (RARα), although these interactions have been less extensively characterized in the available literature (kigoshi2015cacul1cac1regulatesthe pages 1-2, jang2017cacul1reciprocallyregulates pages 1-2, chen2019cac1knockdownreverses pages 2-4).
CACUL1 has been implicated in cell cycle regulation and proliferation across multiple cancer types, though the precise molecular mechanisms remain less well-defined than its roles in ubiquitination and transcriptional regulation. CACUL1 is widely expressed in colorectal cancer (CRC) tissues, with significantly higher expression in tumor tissues compared to normal tissues (P<0.05) in immunohistochemical analysis of 83 CRC cases (chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4). Expression levels correlate with lymph node metastasis and advanced TNM staging (chen2019cac1knockdownreverses pages 2-4).
In 5-fluorouracil (5-FU)-resistant colorectal cancer cell lines (SW480/5-FU and LoVo/5-FU), CACUL1 expression is elevated compared to parental sensitive cells (chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4). CACUL1 knockdown in these resistant cells induces G1/S phase cell cycle arrest and increases sensitivity to 5-FU by promoting apoptosis (chen2019cac1knockdownreverses pages 1-2). Functionally, CACUL1 depletion reduces colony formation, invasion, migration in vitro, and tumorigenicity and metastatic capacity in nude mouse xenograft models (chen2019cac1knockdownreverses pages 2-4). Mechanistically, CACUL1 knockdown decreases expression of the ABC transporters P-glycoprotein (P-gp) and multidrug resistance protein 1 (MRP-1), which are key mediators of chemoresistance (chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4).
In advanced prostate cancer, CACUL1 was identified among a network of pro-proliferation mRNAs characterized by guanine-rich cis-regulatory elements that are particularly sensitive to eIF4F translation initiation complex hyperactivity in androgen receptor-deficient disease states (liu2019theandrogenreceptor pages 1-3). Gene silencing experiments demonstrated that CACUL1, along with KLF5 and DENR, contributes to proliferation programs in this context (liu2019theandrogenreceptor pages 1-3).
The most recent characterization of CACUL1 function comes from a 2023 study identifying the NSF-CDC5L-CACUL1 axis in hepatocellular carcinoma (HCC) (zhu2023nsfmediatescdc5l pages 1-5, zhu2023nsfmediatescdc5l pages 5-7). This work demonstrated that N-ethylmaleimide-sensitive factor (NSF) promotes nuclear import of cell division cycle 5-like protein (CDC5L), which then functions as a transcription factor to activate CACUL1 expression (zhu2023nsfmediatescdc5l pages 1-5). CUT&Tag analysis revealed that 39.88% of CDC5L binding sites are located in gene promoters, with strong CDC5L and H3K27ac (active chromatin) signals detected at the CACUL1 promoter region (zhu2023nsfmediatescdc5l pages 5-7). ChIP-qPCR and dual-luciferase reporter assays confirmed that CDC5L directly occupies and activates the CACUL1 promoter (zhu2023nsfmediatescdc5l pages 5-7). Functionally, NSF expression is upregulated in HCC and correlates with poor patient survival; NSF knockdown reduces tumor growth and intrahepatic metastasis, effects that can be rescued by CACUL1 re-expression (zhu2023nsfmediatescdc5l pages 1-5, zhu2023nsfmediatescdc5l pages 5-7). This work establishes CACUL1 as a critical downstream effector in an oncogenic signaling axis relevant to HCC progression.
CACUL1 exhibits compartment-specific functions in both the cytoplasm and nucleus. In the context of Nrf2 regulation, CACUL1 associates with the cytoplasmic Cul3-Keap1 ubiquitin ligase complex (kigoshi2015cacul1cac1regulatesthe pages 2-4). However, CACUL1 also clearly functions in the nucleus where it interacts with transcription factors and chromatin-modifying enzymes at gene promoters (jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11). ChIP experiments detecting CACUL1 occupancy at PPARγ-responsive promoters and the observation that CDC5L transcriptionally activates CACUL1 in the nucleus both support nuclear localization and function (jang2017cacul1reciprocallyregulates pages 4-7, zhu2023nsfmediatescdc5l pages 5-7). The protein likely shuttles between compartments depending on cellular context and signaling state, though detailed localization studies using immunofluorescence or subcellular fractionation have not been extensively reported in the available literature.
| Pathway/Process | CACUL1 Role/Mechanism | Key Molecular Partners | Cellular Outcome | Experimental Evidence | Citation |
|---|---|---|---|---|---|
| Nrf2-Keap1-Cul3 antioxidant response pathway | CACUL1 is a stress-induced positive regulator of Nrf2 signaling. It associates with the Cul3-Keap1-Rbx1 ligase complex, decreases Nrf2 ubiquitination, prolongs Nrf2 half-life, and enhances induction of ARE target genes under oxidative stress without strongly altering basal Nrf2 localization. | Nrf2, Keap1, Cul3, Rbx1, HO-1, NQO1 | Greater oxidative-stress tolerance and cell survival; higher Nrf2 target-gene activation during stress; reduced viability and more apoptosis when CACUL1 is depleted | Co-immunoprecipitation with Keap1/Rbx1/Cul3/Nrf2, His-ubiquitin pull-down assays, cycloheximide chase for Nrf2 half-life, qRT-PCR of NQO1/HO-1, BHA/tBHQ stress assays, cell-viability and apoptosis assays | (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5, kigoshi2015cacul1cac1regulatesthe pages 5-7) |
| PPARγ-mediated adipogenesis and epigenetic regulation | CACUL1 directly binds PPARγ and functions as a corepressor. Through CoRNR box 2, it recruits/coordinates SIRT1 and reciprocally opposes LSD1 at PPARγ-responsive promoters, reducing H3K9 acetylation and increasing repressive H3K9 methylation to suppress adipogenic transcription. | PPARγ, SIRT1, LSD1, RXR, aP2/FABP4, LPL | Repression of PPARγ transcriptional activity, reduced adipocyte differentiation, reduced lipid accumulation, downregulation of adipogenic gene expression in 3T3-L1 cells and human adipose-derived stem cells | Yeast two-hybrid, co-IP, GST pull-down, domain mapping, luciferase reporter assays, ChIP-qPCR at aP2 promoter, Oil Red O staining, RT-qPCR, RNA-seq/GSEA, gain- and loss-of-function experiments in mouse and human adipogenic models | (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11) |
| Cell cycle regulation and proliferation in cancer | CACUL1 is described as a cullin-family, CDK2-associated regulator that promotes cell-cycle progression and is recurrently linked to proliferative programs in cancer. Recent translational profiling in prostate cancer also places CACUL1 among pro-proliferation mRNAs associated with aggressive growth states. | CDK2, cell-cycle machinery, proliferation-associated translational regulon components | Increased proliferation and cell-cycle progression in cancer-associated contexts | Literature synthesis in CRC study introduction; cancer-expression/proliferation associations noted in Nrf2 study discussion; translational regulon analysis in advanced prostate cancer | (kigoshi2015cacul1cac1regulatesthe pages 1-2, chen2019cac1knockdownreverses pages 1-2, liu2019theandrogenreceptor pages 1-3) |
| Drug resistance mechanisms in colorectal cancer | CACUL1 is overexpressed in CRC and especially in 5-FU-resistant CRC cells. Knockdown causes G1/S arrest, increases apoptosis after 5-FU exposure, and lowers expression of the ABC transporters P-gp and MRP-1, implicating CACUL1 in chemoresistance maintenance. | CDK2, P-gp, MRP-1, 5-FU resistance pathways | Higher chemoresistance, invasion, migration, tumorigenicity, and metastasis when CACUL1 is elevated; resensitization to 5-FU after CACUL1 knockdown | Immunohistochemistry in 83 CRC cases, shRNA knockdown in SW480/5-FU and LoVo/5-FU cells, flow cytometry, colony formation, invasion/migration assays, xenograft experiments, transporter protein analysis | (chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4) |
| NSF-CDC5L-CACUL1 axis in hepatocellular carcinoma | CACUL1 acts as a downstream effector in an oncogenic transport/transcription axis. NSF promotes nuclear import of CDC5L; CDC5L then occupies and activates the CACUL1 promoter, increasing CACUL1 expression and contributing to malignant phenotypes. | NSF, CDC5L, CACUL1 promoter, H3K27ac/H3K4me3-associated active chromatin | Enhanced HCC proliferation and metastasis; restoration of growth and migration when CACUL1 is re-expressed downstream of NSF loss | RNA-seq, STRING/interactome analysis, Co-IP for NSF-CDC5L, CUT&Tag, ChIP-qPCR, dual-luciferase CACUL1 promoter assays, rescue experiments with CACUL1 overexpression after NSF knockdown | (zhu2023nsfmediatescdc5l pages 1-5, zhu2023nsfmediatescdc5l pages 5-7) |
| Nuclear receptor transcriptional regulation | CACUL1 functions as a nuclear receptor corepressor. Prior studies cited in the primary papers report repression of ERα, AR, and RARα transcriptional activity, and the adipogenesis work shows that its CoRNR box 2 is central to nuclear-receptor-related repression mechanisms. | ERα, AR, RARα, SIRT1, LSD1, CoRNR box-containing repression complex | Suppressed nuclear receptor-driven transcriptional programs, linking CACUL1 to hormone-response and differentiation control | Prior interaction/repression studies summarized in primary articles; mechanistic support from CoRNR box mapping and nuclear-receptor repression framework in adipogenesis study | (kigoshi2015cacul1cac1regulatesthe pages 1-2, jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, chen2019cac1knockdownreverses pages 2-4) |
Table: This table summarizes the main biological pathways and cellular processes currently supported for CACUL1, emphasizing mechanism, partner proteins, and experimental basis. It is useful for functional annotation because it separates well-supported molecular roles from broader cancer-associated observations.
| Interaction Partner | Binding Domain (on CACUL1) | Binding Domain (on Partner) | Experimental Evidence Method | Functional Consequence | Citation |
|---|---|---|---|---|---|
| SIRT1 | CoRNR box 2 required; CoR2Δ and AxxTT mutants impair binding | N-terminal region of SIRT1 | Yeast two-hybrid, co-immunoprecipitation, reverse co-IP, GST pull-down, deletion mapping | CACUL1 binds SIRT1 and cooperates with it to repress PPARγ transcriptional activity, reduce H3K9 acetylation at PPARγ target genes, and inhibit adipogenesis | (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11) |
| LSD1 | Exact CACUL1 binding surface not mapped in retrieved text; functionally opposed by CACUL1, likely through CACUL1 corepressor module | Not specified in retrieved text | Luciferase assays, ChIP-qPCR at aP2 promoter, adipogenesis assays; prior association referenced in study text | CACUL1 antagonizes LSD1-enhanced PPARγ activation, promotes reduced LSD1 occupancy at PPARγ-responsive promoters, increases repressive H3K9 methylation state, and suppresses adipogenesis | (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11) |
| PPARγ | CoRNR box 2 required; CoR2Δ and AxxTT mutants impair binding | PPARγ E/F domain | Co-immunoprecipitation, GST pull-down, deletion mapping, endogenous IP in 3T3-L1 cells, luciferase reporter assays | Direct binding enables repression of PPARγ transcriptional activity, reduced expression of adipogenic genes such as aP2/FABP4 and LPL, and inhibition of adipocyte differentiation | (jang2017cacul1reciprocallyregulates pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11) |
| Cul3 | Not mapped; association attributed in part to CACUL1 cullin-domain-containing architecture | Not mapped | Endogenous co-immunoprecipitation with HA-CACUL1 pull-down | CACUL1 associates with the Cul3-Keap1 ligase complex and decreases Cul3-complex ubiquitin ligase activity toward Nrf2, thereby stabilizing Nrf2 | (kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5) |
| Keap1 | Not mapped | Not mapped | Co-immunoprecipitation with FLAG-Keap1 and HA-CACUL1; Nrf2 co-IP strengthened by Keap1 coexpression | CACUL1 binds Keap1 and is recruited into the Cul3-Keap1-Nrf2 complex, where it attenuates Nrf2 ubiquitination without disrupting Keap1-Cul3 or Keap1-Nrf2 complex formation | (kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5) |
| Rbx1 | Not mapped | Not mapped | Co-immunoprecipitation of Myc-Rbx1 with HA-CACUL1 | Supports CACUL1 incorporation into the Cul3-Keap1-Rbx1 ubiquitin ligase complex regulating Nrf2 stability | (kigoshi2015cacul1cac1regulatesthe pages 2-4) |
| Nrf2 | No strong direct CACUL1-binding surface mapped; interaction appears weak/indirect and enhanced by Keap1 | Not mapped | GFP-Nrf2 co-immunoprecipitation with CACUL1 ± Keap1; His-ubiquitin pull-down; cycloheximide chase; qPCR of Nrf2 target genes | CACUL1 decreases Nrf2 ubiquitination, prolongs Nrf2 half-life (~15 to ~30 min on overexpression), sensitizes stressed cells for stronger Nrf2 target-gene induction, and improves survival under oxidative stress | (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5, kigoshi2015cacul1cac1regulatesthe pages 5-7) |
| CDC5L | No direct protein-binding evidence for CACUL1-CDC5L in retrieved text; CDC5L acts upstream at CACUL1 promoter | CDC5L promoter-binding activity; exact DNA-binding determinant not resolved here | CUT&Tag, ChIP-qPCR, dual-luciferase promoter assays, RNA-seq after CDC5L silencing | CDC5L transcriptionally activates CACUL1 expression in HCC, placing CACUL1 downstream of the NSF-CDC5L oncogenic axis | (zhu2023nsfmediatescdc5l pages 1-5, zhu2023nsfmediatescdc5l pages 5-7) |
| ERα | CoRNR box-containing corepressor region implicated by prior work cited in paper | Not specified in retrieved text | Prior interaction/repression studies referenced by primary paper; not experimentally detailed in retrieved passages | CACUL1 represses ERα transcriptional activity and is described as associating with LSD1 in nuclear-receptor repression contexts | (kigoshi2015cacul1cac1regulatesthe pages 1-2, jang2017cacul1reciprocallyregulates pages 1-2, chen2019cac1knockdownreverses pages 2-4) |
| AR | CoRNR box-containing corepressor region implicated by prior work cited in paper | Not specified in retrieved text | Prior interaction/repression studies referenced by primary paper; not experimentally detailed in retrieved passages | CACUL1 represses androgen receptor transcriptional activity; prior literature cited by adipogenesis paper places CACUL1 in AR/LSD1 corepressor regulation | (jang2017cacul1reciprocallyregulates pages 1-2, chen2019cac1knockdownreverses pages 2-4) |
| RARα | CoRNR box-containing corepressor region implicated by prior work cited in paper | Not specified in retrieved text | Prior interaction/repression studies referenced by primary papers; not experimentally detailed in retrieved passages | CACUL1 represses RARα transcriptional activity and is described as a nuclear receptor corepressor in earlier studies | (kigoshi2015cacul1cac1regulatesthe pages 1-2, chen2019cac1knockdownreverses pages 2-4) |
Table: This table compiles the main CACUL1 protein interactions supported by the gathered primary literature and indicates where domain mapping is available versus still unresolved. It is useful for functional annotation because it links each interaction to mechanism, assay type, and biological consequence.
The functional characterization of CACUL1 is supported by diverse experimental approaches across multiple studies. Key experimental methods include:
Protein interaction studies: Yeast two-hybrid screening, co-immunoprecipitation with epitope-tagged and endogenous proteins, reverse co-IP, GST pull-down assays, domain deletion mapping, and substitution mutagenesis (jang2017cacul1reciprocallyregulates pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 2-4, jang2017cacul1reciprocallyregulates pages 2-4).
Ubiquitination assays: His-ubiquitin pull-down under denaturing conditions, cycloheximide chase experiments to measure protein half-life, and proteasome inhibition studies (kigoshi2015cacul1cac1regulatesthe pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5).
Transcriptional regulation studies: Luciferase reporter assays with PPRE and ARE elements, ChIP-qPCR at target gene promoters, RT-qPCR for target gene expression, CUT&Tag for genome-wide transcription factor binding, dual-luciferase promoter assays (jang2017cacul1reciprocallyregulates pages 2-4, jang2017cacul1reciprocallyregulates pages 4-7, zhu2023nsfmediatescdc5l pages 5-7).
Functional cellular assays: Oil Red O staining and quantification for adipogenesis, flow cytometry for cell cycle analysis, colony formation assays, transwell migration and invasion assays, cell viability assays under stress conditions, apoptosis detection (chen2019cac1knockdownreverses pages 1-2, jang2017cacul1reciprocallyregulates pages 2-4, chen2019cac1knockdownreverses pages 2-4, kigoshi2015cacul1cac1regulatesthe pages 4-5).
Genome-wide analyses: RNA sequencing in gain- and loss-of-function models, gene ontology enrichment, gene set enrichment analysis (GSEA), hierarchical clustering (zhu2023nsfmediatescdc5l pages 5-7, jang2017cacul1reciprocallyregulates pages 7-11).
In vivo studies: Mouse xenograft subcutaneous and orthotopic tumor models, BHA feeding experiments in mice to induce oxidative stress, immunohistochemistry in clinical specimens (kigoshi2015cacul1cac1regulatesthe pages 1-2, chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4).
CACUL1 expression patterns and functional roles suggest potential clinical relevance across multiple disease contexts. In colorectal cancer, elevated CACUL1 expression correlates with lymph node metastasis, advanced TNM stage, and chemoresistance to 5-FU, one of the standard chemotherapeutic agents (chen2019cac1knockdownreverses pages 1-2, chen2019cac1knockdownreverses pages 2-4). The ability of CACUL1 knockdown to resensitize resistant cells to 5-FU through downregulation of drug efflux transporters suggests CACUL1 could be a therapeutic target to overcome chemoresistance (chen2019cac1knockdownreverses pages 1-2).
In hepatocellular carcinoma, high NSF expression (which drives CACUL1 transcription) associates with malignant features and poor patient outcomes, and the NSF-CDC5L-CACUL1 axis represents a potential therapeutic vulnerability (zhu2023nsfmediatescdc5l pages 1-5, zhu2023nsfmediatescdc5l pages 5-7).
Conversely, CACUL1's role in enhancing Nrf2-mediated antioxidant responses suggests protective functions in oxidative stress-related pathologies. CACUL1 has been reported to be downregulated in hippocampus of Alzheimer's disease patients, and CACUL1 knockdown in neuroblastoma cells leads to increased oxidative stress, suggesting potential neuroprotective roles (kigoshi2015cacul1cac1regulatesthe pages 1-2, kigoshi2015cacul1cac1regulatesthe pages 5-7).
In metabolic disease, CACUL1's ability to epigenetically repress PPARγ and inhibit adipogenesis suggests potential relevance for obesity and metabolic syndrome, with SIRT1 activators (resveratrol, SRT1720) or LSD1 inhibitors partially requiring CACUL1 for their anti-adipogenic effects (jang2017cacul1reciprocallyregulates pages 4-7, jang2017cacul1reciprocallyregulates pages 7-11).
CACUL1 emerges as a multifunctional adapter protein that integrates ubiquitin-mediated proteostasis, transcriptional regulation, and epigenetic control across diverse cellular contexts. The protein's cullin domain and CoRNR boxes enable assembly of distinct regulatory complexes: association with Cul3-Keap1-Rbx1 to modulate Nrf2 stability and stress responses, and recruitment of SIRT1/LSD1 to nuclear receptors to control differentiation programs. CACUL1's designation as "CDK2-associated" reflects its broader involvement in cell cycle regulation and proliferation, particularly in cancer contexts where it promotes chemoresistance and malignant phenotypes. The context-dependent nature of CACUL1 function—protective in oxidative stress, pro-oncogenic in cancer, anti-adipogenic in metabolism—highlights the complexity of targeting this protein therapeutically and underscores the need for tissue- and disease-specific approaches.
Key primary research articles span 2015-2023:
- Kigoshi et al., Scientific Reports, August 2015 (Nrf2 regulation) (kigoshi2015cacul1cac1regulatesthe pages 1-2)
- Jang et al., Cell Death & Disease, December 2017 (PPARγ and adipogenesis) (jang2017cacul1reciprocallyregulates pages 1-2)
- Chen et al., PLoS ONE, September 2019 (colorectal cancer drug resistance) (chen2019cac1knockdownreverses pages 1-2)
- Liu et al., Science Translational Medicine, July 2019 (prostate cancer translational regulon) (liu2019theandrogenreceptor pages 1-3)
- Zhu et al., Research Square preprint, March 2023 (NSF-CDC5L-CACUL1 axis in HCC) (zhu2023nsfmediatescdc5l pages 1-5)
Most primary mechanistic studies were published between 2015-2022, with limited highly recent (2023-2024) literature specifically focused on CACUL1, suggesting this remains a relatively under-studied protein with opportunities for further characterization.
References
(kigoshi2015cacul1cac1regulatesthe pages 1-2): Yu Kigoshi, Tomomi Fukuda, Tomoyuki Endo, Nami Hayasaka, Shun-ichiro Iemura, Toru Natsume, Fuminori Tsuruta, and Tomoki Chiba. Cacul1/cac1 regulates the antioxidant response by stabilizing nrf2. Scientific Reports, Aug 2015. URL: https://doi.org/10.1038/srep12857, doi:10.1038/srep12857. This article has 14 citations and is from a peer-reviewed journal.
(jang2017cacul1reciprocallyregulates pages 1-2): Min Jun Jang, Ui-Hyun Park, Jeong Woo Kim, Hanbyeul Choi, Soo-Jong Um, and Eun-Joo Kim. Cacul1 reciprocally regulates sirt1 and lsd1 to repress pparγ and inhibit adipogenesis. Cell Death & Disease, Dec 2017. URL: https://doi.org/10.1038/s41419-017-0070-z, doi:10.1038/s41419-017-0070-z. This article has 42 citations and is from a peer-reviewed journal.
(chen2019cac1knockdownreverses pages 1-2): Nanzheng Chen, Ying Kong, Yunhua Wu, Qi Gao, Junke Fu, Xuejun Sun, and Qianqian Geng. Cac1 knockdown reverses drug resistance through the downregulation of p-gp and mrp-1 expression in colorectal cancer. PLoS ONE, 14:e0222035, Sep 2019. URL: https://doi.org/10.1371/journal.pone.0222035, doi:10.1371/journal.pone.0222035. This article has 20 citations and is from a peer-reviewed journal.
(jang2017cacul1reciprocallyregulates pages 2-4): Min Jun Jang, Ui-Hyun Park, Jeong Woo Kim, Hanbyeul Choi, Soo-Jong Um, and Eun-Joo Kim. Cacul1 reciprocally regulates sirt1 and lsd1 to repress pparγ and inhibit adipogenesis. Cell Death & Disease, Dec 2017. URL: https://doi.org/10.1038/s41419-017-0070-z, doi:10.1038/s41419-017-0070-z. This article has 42 citations and is from a peer-reviewed journal.
(kigoshi2015cacul1cac1regulatesthe pages 2-4): Yu Kigoshi, Tomomi Fukuda, Tomoyuki Endo, Nami Hayasaka, Shun-ichiro Iemura, Toru Natsume, Fuminori Tsuruta, and Tomoki Chiba. Cacul1/cac1 regulates the antioxidant response by stabilizing nrf2. Scientific Reports, Aug 2015. URL: https://doi.org/10.1038/srep12857, doi:10.1038/srep12857. This article has 14 citations and is from a peer-reviewed journal.
(kigoshi2015cacul1cac1regulatesthe pages 4-5): Yu Kigoshi, Tomomi Fukuda, Tomoyuki Endo, Nami Hayasaka, Shun-ichiro Iemura, Toru Natsume, Fuminori Tsuruta, and Tomoki Chiba. Cacul1/cac1 regulates the antioxidant response by stabilizing nrf2. Scientific Reports, Aug 2015. URL: https://doi.org/10.1038/srep12857, doi:10.1038/srep12857. This article has 14 citations and is from a peer-reviewed journal.
(kigoshi2015cacul1cac1regulatesthe pages 5-7): Yu Kigoshi, Tomomi Fukuda, Tomoyuki Endo, Nami Hayasaka, Shun-ichiro Iemura, Toru Natsume, Fuminori Tsuruta, and Tomoki Chiba. Cacul1/cac1 regulates the antioxidant response by stabilizing nrf2. Scientific Reports, Aug 2015. URL: https://doi.org/10.1038/srep12857, doi:10.1038/srep12857. This article has 14 citations and is from a peer-reviewed journal.
(jang2017cacul1reciprocallyregulates pages 4-7): Min Jun Jang, Ui-Hyun Park, Jeong Woo Kim, Hanbyeul Choi, Soo-Jong Um, and Eun-Joo Kim. Cacul1 reciprocally regulates sirt1 and lsd1 to repress pparγ and inhibit adipogenesis. Cell Death & Disease, Dec 2017. URL: https://doi.org/10.1038/s41419-017-0070-z, doi:10.1038/s41419-017-0070-z. This article has 42 citations and is from a peer-reviewed journal.
(jang2017cacul1reciprocallyregulates pages 7-11): Min Jun Jang, Ui-Hyun Park, Jeong Woo Kim, Hanbyeul Choi, Soo-Jong Um, and Eun-Joo Kim. Cacul1 reciprocally regulates sirt1 and lsd1 to repress pparγ and inhibit adipogenesis. Cell Death & Disease, Dec 2017. URL: https://doi.org/10.1038/s41419-017-0070-z, doi:10.1038/s41419-017-0070-z. This article has 42 citations and is from a peer-reviewed journal.
(chen2019cac1knockdownreverses pages 2-4): Nanzheng Chen, Ying Kong, Yunhua Wu, Qi Gao, Junke Fu, Xuejun Sun, and Qianqian Geng. Cac1 knockdown reverses drug resistance through the downregulation of p-gp and mrp-1 expression in colorectal cancer. PLoS ONE, 14:e0222035, Sep 2019. URL: https://doi.org/10.1371/journal.pone.0222035, doi:10.1371/journal.pone.0222035. This article has 20 citations and is from a peer-reviewed journal.
(liu2019theandrogenreceptor pages 1-3): Yuzhen Liu, Jessie L. Horn, Kalyan Banda, Asha Z. Goodman, Yiting Lim, Sujata Jana, Sonali Arora, Alexandre A. Germanos, Lexiaochuan Wen, William R. Hardin, Yu C. Yang, Ilsa M. Coleman, Robin G. Tharakan, Elise Y. Cai, Takuma Uo, Smitha P. S. Pillai, Eva Corey, Colm Morrissey, Yu Chen, Brett S. Carver, Stephen R. Plymate, Slobodan Beronja, Peter S. Nelson, and Andrew C. Hsieh. The androgen receptor regulates a druggable translational regulon in advanced prostate cancer. Science Translational Medicine, Jul 2019. URL: https://doi.org/10.1126/scitranslmed.aaw4993, doi:10.1126/scitranslmed.aaw4993. This article has 74 citations and is from a highest quality peer-reviewed journal.
(zhu2023nsfmediatescdc5l pages 1-5): Hongxu Zhu, Yixiu Wang, Li Zhang, Weiqi Xu, Longrong Wang, weiping zhu, Yiming Zhao, Ti Zhang, and Lu Wang. Nsf mediates cdc5l nuclear import to promote cell growth and metastasis in hepatocellular carcinoma. Unknown journal, Mar 2023. URL: https://doi.org/10.21203/rs.3.rs-2608617/v1, doi:10.21203/rs.3.rs-2608617/v1.
(zhu2023nsfmediatescdc5l pages 5-7): Hongxu Zhu, Yixiu Wang, Li Zhang, Weiqi Xu, Longrong Wang, weiping zhu, Yiming Zhao, Ti Zhang, and Lu Wang. Nsf mediates cdc5l nuclear import to promote cell growth and metastasis in hepatocellular carcinoma. Unknown journal, Mar 2023. URL: https://doi.org/10.21203/rs.3.rs-2608617/v1, doi:10.21203/rs.3.rs-2608617/v1.
Falcon deep research has now completed (file:human/CACUL1/CACUL1-deep-research-falcon.md,
6 citations). Unlike the prior review, it surfaces several functional papers not
previously considered here, and they materially affect two assessments above.
NOTE: these PMIDs/DOIs come from the Falcon report and should be verified against
PubMed and the cached publications before any YAML change.
1. Direct evidence CACUL1 engages a Cul3-RING ligase — revisit the
"ubiquitin-ligase IEA = over-annotation" call. Kigoshi et al. 2015
(CACUL1/CAC1 regulates the Nrf2 antioxidant response) report co-IP of CACUL1
with Keap1, Cul3 and Rbx1, and show CACUL1 attenuates Nrf2 ubiquitination
(Nrf2 t½ ~15→30 min by CHX chase) without disrupting the Cul3-Keap1-Nrf2
complex — i.e. it acts as a negative regulator of the ligase's activity toward
Nrf2, and CACUL1 is itself oxidative-stress-induced (ARE genes NQO1/HO-1). This is
experimental support for GO:0031625 ubiquitin protein ligase binding (it
binds Cul3/Rbx1/Keap1), which the prior review had flagged as a domain-only
over-annotation. It does NOT make CACUL1 a CRL scaffold, and for the
catabolic-process term the accurate framing is negative regulation of
ubiquitin-dependent (Nrf2) catabolism, not participation. → Recommend MODIFYing
the assessment: keep/again-support ubiquitin-protein-ligase binding with this
experimental basis; represent the process role as negative regulation of Nrf2
ubiquitination rather than over-annotation.
2. Nuclear-receptor corepressor role is broader/better-supported than the ERα
datum alone. Jang et al. 2017 show CACUL1 is a SIRT1-binding protein and
PPARγ corepressor: via its CoRNR box it recruits SIRT1 and antagonizes LSD1 at
PPARγ targets (aP2/FABP4), lowering H3K9ac and raising H3K9me3, and inhibiting
adipogenesis (3T3-L1, human ADSCs; RNA-seq of 644 genes enriched for
PPARγ/lipid metabolism). With the ERα corepressor data (PMID:23178685) and
reported AR/RARα interactions, this supports a genuine nuclear-receptor
corepressor molecular function (SIRT1/LSD1-coupled) — stronger than "bare protein
binding". → Candidate informative MF beyond GO:0005515.
3. Cancer context (non-core). Colorectal-cancer 5-FU chemoresistance via
P-gp/MRP-1 (Chen 2019); androgen-receptor-deficient prostate-cancer proliferation
program (Liu 2019); NSF-CDC5L-CACUL1 oncogenic axis in HCC (Zhu 2023). Consistent
with the CDK2/proliferation core but disease-specific; keep non-core.
Net: the CDK2-associated cell-cycle/proliferation core (PMID:19829063) stands,
but the deep research upgrades two previously-skeptical calls: the
ubiquitin-protein-ligase-binding term now has experimental backing (Cul3-Keap1-Rbx1;
Kigoshi 2015), and a SIRT1/LSD1-coupled nuclear-receptor-corepressor MF is now
well-supported (Jang 2017). These should be re-adjudicated in the YAML after PMID
verification.
*-deep-research*.md file found in this gene directory.UPS|E3 ubiquitin and UBL ligases|Cullin|degenerate, possible CUL3 inhibitor ; PN-node mapping: type node degenerate, possible CUL3 inhibitor no_mapping; group node Cullin mapped → GO:0160072 ubiquitin ligase complex scaffold activity (ok_for_propagation, new_to_goa); class context_only (GO:0061630, too_broad).degenerate, possible CUL3 inhibitor) is correctly no_mapping, but the group→GO:0160072 projection should be suppressed/excepted for CACUL1 because it is a degenerate non-scaffold member. The group mapping may be fine for bona fide cullins, but CACUL1 should be flagged as a member that does not inherit it.This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
id: Q86Y37
gene_symbol: CACUL1
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
CACUL1 (CDK2-associated and cullin domain-containing protein 1; also known as
CAC1 / C10orf46) is a poorly characterized 369-amino-acid human protein
containing a single cullin-repeat-like domain with disordered N- and C-terminal
regions. Despite its name and cullin-fold homology, it is much shorter than
canonical cullins (~750-900 aa) and there is no experimental evidence that it
nucleates a functional cullin-RING ubiquitin ligase or carries a neddylation/RBX
module. The best-supported activity, from a single study, is physical association
with the cyclin-dependent kinase CDK2 and promotion of CDK2 kinase activity,
consistent with a role in G1/S cell-cycle progression and proliferation; the
protein is highly expressed in cancer tissues and cell lines, and its abundance
varies across the cell cycle. CACUL1 also acts as a nuclear-receptor
transcriptional corepressor: it is a SIRT1-interacting protein that binds
PPARgamma (and estrogen receptor alpha) and represses their transcription by
coordinating SIRT1 and the histone demethylase LSD1/KDM1A at target promoters
(lowering H3K9 acetylation and raising H3K9 methylation), thereby suppressing
adipocyte differentiation. Separately, although CACUL1 does not itself nucleate a
cullin-RING ligase, it binds the Cul3-Keap1-Rbx1 (CRL3-Keap1) ubiquitin-ligase
complex and attenuates its ubiquitination of the transcription factor Nrf2
(NFE2L2), stabilizing Nrf2 and promoting the antioxidant response. CACUL1 has
also been recovered as a yeast two-hybrid interactor of ARMC5. Overall, CACUL1 is
a multifunctional protein linking CDK2-associated cell-cycle progression,
nuclear-receptor corepression, and negative regulation of Nrf2 ubiquitination.
alternative_products:
- name: '1'
id: Q86Y37-1
- name: '2'
id: Q86Y37-2
sequence_note: VSP_013936, VSP_013937
- name: '4'
id: Q86Y37-4
sequence_note: VSP_013933
existing_annotations:
- term:
id: GO:0000082
label: G1/S transition of mitotic cell cycle
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: involved_in
review:
summary: >-
Phylogenetic (IBA) transfer of a G1/S cell-cycle role. This is consistent
with the direct experimental evidence in the same gene (PMID:19829063),
where CACUL1/CAC1 knockdown induces G1/S arrest. Retained but as a
non-core/secondary process annotation since the defining molecular activity
is the CDK2 interaction rather than the broader cell-cycle process itself.
action: KEEP_AS_NON_CORE
reason: >-
Supported indirectly by direct knockdown evidence (PMID:19829063) that
CACUL1 loss causes G1/S arrest, but this is a downstream process rather than
a precise molecular function; treat as a non-core involvement.
supported_by:
- reference_id: PMID:19829063
supporting_text: >-
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S
arrest.
- term:
id: GO:0019901
label: protein kinase binding
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
Phylogenetic (IBA) transfer of protein kinase binding. This is the same
molecular function directly demonstrated for CACUL1 via its physical
interaction with CDK2 (PMID:19829063). Accept as it reflects the
best-supported molecular activity of the protein.
action: ACCEPT
reason: >-
Directly corroborated by experimental CDK2 binding (PMID:19829063); the
IBA call coincides with the strongest molecular evidence for this protein.
supported_by:
- reference_id: PMID:19829063
supporting_text: this protein is physically associated with CDK2
- term:
id: GO:0006511
label: ubiquitin-dependent protein catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: involved_in
review:
summary: >-
The IEA InterPro2GO transfer (cullin-repeat domain IPR001373) implies direct
participation in ubiquitin-dependent catabolism, which remains unsupported:
CACUL1 is too short to be a CRL scaffold and carries no RBX/neddylation
module. However, Kigoshi et al. 2015 (PMID:26238671) show CACUL1 binds the
Cul3-Keap1-Rbx1 ubiquitin-ligase complex and ATTENUATES Nrf2 ubiquitination,
stabilizing Nrf2. The experimentally supported role is therefore NEGATIVE
regulation of (Nrf2) ubiquitination, not direct participation in catabolism;
modify accordingly.
action: MODIFY
reason: >-
Direct participation in ubiquitin-dependent catabolism is a domain-only
over-annotation, but CACUL1 has experimentally demonstrated activity as a
negative regulator of Nrf2 ubiquitination via the Cul3-Keap1-Rbx1 complex
(PMID:26238671); replace with negative regulation of protein ubiquitination.
proposed_replacement_terms:
- id: GO:0031397
label: negative regulation of protein ubiquitination
supported_by:
- reference_id: PMID:26238671
supporting_text: CACUL1 attenuates Nrf2 ubiquitination
- reference_id: PMID:26238671
supporting_text: CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
- term:
id: GO:0031625
label: ubiquitin protein ligase binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
Although the IEA call was originally a pure cullin-domain (IPR001373)
transfer, it is now experimentally supported: Kigoshi et al. 2015
(PMID:26238671) demonstrate that CACUL1 binds Keap1, Cul3 and Rbx1 - the
components of the ubiquitin ligase (CRL3) responsible for Nrf2 ubiquitination
- and thereby modulates that ligase's activity toward Nrf2. The
ubiquitin-protein-ligase-binding molecular function is therefore retained
with direct experimental support.
action: ACCEPT
reason: >-
Experimentally demonstrated binding to the Cul3-Keap1-Rbx1 ubiquitin ligase
complex (PMID:26238671) directly supports this molecular function; it is no
longer a domain-only over-annotation.
supported_by:
- reference_id: PMID:26238671
supporting_text: >-
we further assessed CACUL1 binding with Keap1, Cul3 and Rbx1, the
components of the Ubiquitin ligase responsible for Nrf2 ubiquitination.
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:23178685
qualifier: enables
review:
summary: >-
This IPI annotation (WITH ESR1/P03372) records the physical interaction
between CACUL1/CAC1 and estrogen receptor alpha (ERalpha), corroborated by
IntAct (NbExp=5). The bare "protein binding" term is uninformative; a more
specific molecular function is warranted given the established, directional
ERalpha interaction.
action: MODIFY
reason: >-
The interaction partner is a specific nuclear receptor (ERalpha); replace
the uninformative protein binding term with nuclear estrogen receptor
binding to capture the actual molecular function.
proposed_replacement_terms:
- id: GO:0030331
label: nuclear estrogen receptor binding
supported_by:
- reference_id: PMID:23178685
supporting_text: >-
The CoRNR box of CAC1 was required for the binding to and inactivation
of ERα.
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:28169274
qualifier: enables
review:
summary: >-
This IPI annotation (WITH ARMC5/Q96C12) derives from a yeast two-hybrid
screen in which CACUL1 was one of 16 ARMC5-binding partners. The paper
characterizes ARMC5, not CACUL1, and provides no functional context for
CACUL1. The bare "protein binding" term is uninformative and rests on a
single high-throughput Y2H datum.
action: MARK_AS_OVER_ANNOTATED
reason: >-
Uninformative bare protein binding from a single Y2H hit in an ARMC5-focused
study; no specific function or biology for CACUL1 is established.
supported_by:
- reference_id: PMID:28169274
supporting_text: Yeast 2-hybrid assays identify 16 ARMC5-binding partners.
- term:
id: GO:0000082
label: G1/S transition of mitotic cell cycle
evidence_type: IMP
original_reference_id: PMID:19829063
qualifier: involved_in
review:
summary: >-
Direct experimental evidence: RNAi knockdown of CACUL1/CAC1 induces G1/S
arrest, indicating involvement in the G1/S transition. This is a genuine
process annotation but downstream of the protein's molecular role in
activating CDK2; retained as a non-core involvement.
action: KEEP_AS_NON_CORE
reason: >-
Well-supported by knockdown phenotype, but the broad cell-cycle process is
secondary to the precise CDK2-activating molecular function.
supported_by:
- reference_id: PMID:19829063
supporting_text: >-
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S
arrest.
- term:
id: GO:0008284
label: positive regulation of cell population proliferation
evidence_type: IMP
original_reference_id: PMID:19829063
qualifier: involved_in
review:
summary: >-
Direct experimental evidence: CACUL1/CAC1 knockdown inhibits cell
proliferation, supporting a positive role in proliferation. This is a real
but downstream phenotypic process annotation; kept as non-core relative to
the underlying CDK2-activating molecular function.
action: KEEP_AS_NON_CORE
reason: >-
Supported by knockdown phenotype but is a broad downstream process rather
than the precise molecular activity.
supported_by:
- reference_id: PMID:19829063
supporting_text: >-
Knockdown of CAC1 by RNAi inhibits cell proliferation and induces G(1)/S
arrest.
- term:
id: GO:0019901
label: protein kinase binding
evidence_type: IPI
original_reference_id: PMID:19829063
qualifier: enables
review:
summary: >-
Direct experimental evidence (IPI, WITH CDK2/P24941) for physical
association of CACUL1/CAC1 with the cyclin-dependent kinase CDK2. This is
the best-supported molecular function of the protein and represents a core
activity.
action: ACCEPT
reason: >-
Directly demonstrated CDK2 binding; an informative molecular-function term
reflecting the protein's defining characterized interaction.
supported_by:
- reference_id: PMID:19829063
supporting_text: this protein is physically associated with CDK2
- term:
id: GO:0045860
label: positive regulation of protein kinase activity
evidence_type: IMP
original_reference_id: PMID:19829063
qualifier: involved_in
review:
summary: >-
Direct experimental evidence that CACUL1/CAC1 promotes CDK2 kinase
activity. This captures the functional consequence of the CDK2 interaction
and is a core aspect of the protein's characterized activity, though the
molecular mechanism of activation remains undefined.
action: ACCEPT
reason: >-
Supported by experiments showing CAC1 promotes CDK2 kinase activity; a
well-evidenced functional annotation.
supported_by:
- reference_id: PMID:19829063
supporting_text: >-
CAC1 interacts with CDK2 and promotes the kinase activity of CDK2 protein
- term:
id: GO:0003714
label: transcription corepressor activity
evidence_type: IDA
original_reference_id: PMID:29233982
qualifier: enables
review:
summary: >-
Proposed NEW molecular-function annotation (not in current GOA). CACUL1
represses PPARgamma- (PMID:29233982) and ERalpha- (PMID:23178685) dependent
transcription by coordinating SIRT1 and LSD1 at target promoters, i.e. it
acts as a nuclear-receptor transcription corepressor. This is the
informative MF underlying the existing bare protein-binding / nuclear
estrogen receptor binding annotations.
action: NEW
reason: >-
Two independent studies show CACUL1 physically binds nuclear receptors
(PPARgamma, ERalpha) and represses their transcriptional activity via
SIRT1/LSD1; transcription corepressor activity captures this MF.
supported_by:
- reference_id: PMID:29233982
supporting_text: >-
CACUL1, identified as a novel SIRT1 interacting protein, physically
interacts with PPARγ and represses its transcriptional activity,
suppressing adipocyte differentiation
- reference_id: PMID:23178685
supporting_text: CAC1, associated with LSD1, functions as an ERα corepressor
- term:
id: GO:0042975
label: peroxisome proliferator activated receptor binding
evidence_type: IPI
original_reference_id: PMID:29233982
qualifier: enables
review:
summary: >-
Proposed NEW molecular-function annotation (not in current GOA). CACUL1
physically interacts with PPARgamma, providing the receptor-binding basis
for its corepressor activity at PPARgamma-responsive promoters.
action: NEW
reason: >-
Direct physical interaction of CACUL1 with PPARgamma demonstrated
(PMID:29233982); a specific, informative nuclear-receptor-binding MF.
supported_by:
- reference_id: PMID:29233982
supporting_text: >-
CACUL1, identified as a novel SIRT1 interacting protein, physically
interacts with PPARγ and represses its transcriptional activity,
suppressing adipocyte differentiation
- term:
id: GO:0031397
label: negative regulation of protein ubiquitination
evidence_type: IMP
original_reference_id: PMID:26238671
qualifier: involved_in
review:
summary: >-
Proposed NEW process annotation (not in current GOA), also offered as the
MODIFY replacement for the domain-only GO:0006511 IEA. CACUL1 binds the
Cul3-Keap1-Rbx1 complex and attenuates Nrf2 ubiquitination, stabilizing
Nrf2 - a negative regulatory role in protein ubiquitination.
action: NEW
reason: >-
Experimentally demonstrated attenuation of Nrf2 ubiquitination by CACUL1
(PMID:26238671) supports negative regulation of protein ubiquitination.
supported_by:
- reference_id: PMID:26238671
supporting_text: CACUL1 attenuates Nrf2 ubiquitination
- reference_id: PMID:26238671
supporting_text: CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
- reference_id: file:human/CACUL1/CACUL1-deep-research-falcon.md
supporting_text: >-
CACUL1 associates with the Cul3-Keap1-Rbx1 ubiquitin ligase complex
- term:
id: GO:0050821
label: protein stabilization
evidence_type: IMP
original_reference_id: PMID:26238671
qualifier: involved_in
review:
summary: >-
Proposed NEW process annotation (not in current GOA). By attenuating its
ubiquitination, CACUL1 stabilizes the transcription factor Nrf2 (half-life
~10 -> ~30 min), the downstream consequence of its CRL3-Keap1 modulation.
action: NEW
reason: >-
CACUL1 lengthens Nrf2 half-life by limiting its ubiquitination
(PMID:26238671), consistent with a protein-stabilization role.
supported_by:
- reference_id: PMID:26238671
supporting_text: CACUL1 stabilizes Nrf2 by regulating Nrf2 ubiquitination
core_functions:
- description: >-
Binds the cyclin-dependent kinase CDK2 and promotes its kinase activity,
contributing to G1/S cell-cycle progression and cell proliferation. This is
the best-characterized activity but rests on a single study and the molecular
mechanism of CDK2 activation is undefined.
molecular_function:
id: GO:0019901
label: protein kinase binding
directly_involved_in:
- id: GO:0045860
label: positive regulation of protein kinase activity
- id: GO:0000082
label: G1/S transition of mitotic cell cycle
supported_by:
- reference_id: PMID:19829063
supporting_text: >-
CAC1 interacts with CDK2 and promotes the kinase activity of CDK2 protein
- reference_id: PMID:19829063
supporting_text: this protein is physically associated with CDK2
- description: >-
Acts as a context-dependent nuclear-receptor co-regulator: binds estrogen
receptor alpha (ERalpha) via its CoRNR box and, in association with the
histone demethylase LSD1/KDM1A, can repress ERalpha-dependent transcription.
This is a secondary, less-established function reported by a single study.
molecular_function:
id: GO:0030331
label: nuclear estrogen receptor binding
supported_by:
- reference_id: PMID:23178685
supporting_text: >-
The CoRNR box of CAC1 was required for the binding to and inactivation of
ERα.
- reference_id: PMID:23178685
supporting_text: CAC1, associated with LSD1, functions as an ERα corepressor
- description: >-
Functions as a nuclear-receptor transcriptional corepressor. CACUL1 is a
SIRT1-interacting protein that also physically binds PPARgamma (and estrogen
receptor alpha) and represses their transcriptional activity by reciprocally
coordinating the histone deacetylase SIRT1 and the demethylase LSD1/KDM1A at
target promoters, lowering H3K9 acetylation and raising H3K9 methylation; for
PPARgamma this suppresses adipocyte differentiation.
molecular_function:
id: GO:0003714
label: transcription corepressor activity
supported_by:
- reference_id: PMID:29233982
supporting_text: >-
CACUL1, identified as a novel SIRT1 interacting protein, physically
interacts with PPARγ and represses its transcriptional activity,
suppressing adipocyte differentiation
- reference_id: PMID:29233982
supporting_text: >-
CACUL1 functionally associates with SIRT1 and LSD1 at the PPARγ-responsive
gene promoter, and regulates the level of histone H3K9 acetylation and
methylation to repress PPARγ during adipocyte differentiation
- reference_id: PMID:23178685
supporting_text: CAC1, associated with LSD1, functions as an ERα corepressor
- description: >-
Negatively regulates protein ubiquitination by binding the Cul3-Keap1-Rbx1
(CRL3-Keap1) ubiquitin-ligase complex and attenuating its ubiquitination of
the transcription factor Nrf2 (NFE2L2), thereby stabilizing Nrf2 and
sensitizing cells for the antioxidant/ARE response. This couples a
cullin-RING-ligase-binding activity to a regulatory, rather than catalytic,
role in the ubiquitin system.
molecular_function:
id: GO:0031625
label: ubiquitin protein ligase binding
directly_involved_in:
- id: GO:0031397
label: negative regulation of protein ubiquitination
- id: GO:0050821
label: protein stabilization
supported_by:
- reference_id: PMID:26238671
supporting_text: >-
we further assessed CACUL1 binding with Keap1, Cul3 and Rbx1, the
components of the Ubiquitin ligase responsible for Nrf2 ubiquitination.
- reference_id: PMID:26238671
supporting_text: CACUL1 attenuates Nrf2 ubiquitination
knowledge_gaps:
- gap_statement: >-
The direct biochemical mechanism by which CACUL1 promotes CDK2 kinase activity
remains unresolved: it is unclear whether CACUL1 allosterically activates CDK2,
alters cyclin/CDK-inhibitor availability, changes substrate engagement, or acts
through another cell-cycle regulatory complex.
boundary: >-
CACUL1 physically associates with CDK2, promotes CDK2 kinase activity, is
expressed in a cell-cycle-dependent manner, and RNAi knockdown causes reduced
proliferation with G1/S arrest. The unresolved part is the immediate molecular
mechanism connecting CACUL1 binding to increased CDK2 activity.
gap_kind:
- BIOLOGY
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
CDK2 regulation is the best-supported CACUL1 activity, but without a mechanism
it is hard to distinguish a direct CDK2 co-regulator from an indirect cell-cycle
phenotype.
resolution: >-
Reconstitute purified CACUL1-CDK2-cyclin complexes for kinase kinetics, map the
binding interface, and test whether CACUL1 changes cyclin binding, CDK-inhibitor
binding, or substrate phosphorylation in cells.
provenance:
- reference_id: PMID:19829063
supporting_text: >-
but how CDK2 is regulated is still incompletely understood
reference_section_type: ABSTRACT
- reference_id: PMID:19829063
supporting_text: >-
provide insight into the mechanism by which CDK2 is regulated
reference_section_type: ABSTRACT
- gap_statement: >-
The role of CACUL1's cullin-repeat-like domain in CRL3-Keap1/Nrf2 regulation
is unresolved, and CACUL1 should not be curated as a bona fide cullin-RING
scaffold unless future experiments show that it assembles or positions an E3
ubiquitin ligase complex.
boundary: >-
CACUL1 binds Keap1, Cul3, and Rbx1 and attenuates Nrf2 ubiquitination, supporting
ubiquitin-ligase binding and negative regulation of Nrf2 ubiquitination. The gap
is whether the short cullin-like region is the binding/regulatory interface and
whether CACUL1 modulates only CRL3-Keap1/Nrf2 or broader CRL3 substrate
ubiquitination.
gap_kind:
- BIOLOGY
- CURATION
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
This boundary prevents domain-only over-propagation of cullin scaffold activity
while preserving the experimentally supported CRL3-Keap1/Nrf2 regulatory role.
resolution: >-
Map CACUL1 deletion mutants against Keap1, Cul3, Rbx1, and Nrf2; assay CRL3
ubiquitination activity with purified components; and test whether CACUL1 affects
other CRL3-Keap1 or Cul3 substrates.
provenance:
- reference_id: PMID:26238671
supporting_text: >-
CACUL1 is a regulator of Nrf2 ubiquitination, adding another regulatory layer
to the Nrf2 antioxidant stress response.
reference_section_type: ABSTRACT
- reference_id: file:human/CACUL1/CACUL1-pn-notes.md
supporting_text: >-
there is no experimental evidence that it nucleates a functional cullin-RING
ubiquitin ligase or carries a neddylation/RBX module
- gap_statement: >-
The physiological context and directionality of CACUL1 nuclear-receptor
coregulation remain only partly defined, especially whether ERalpha, androgen
receptor, and PPARgamma effects represent one general chromatin mechanism or
distinct receptor- and cell-type-specific activities.
boundary: >-
CACUL1 can bind nuclear receptors and repress ERalpha- and PPARgamma-dependent
transcription with LSD1/SIRT1-linked chromatin changes. The unresolved part is
which tissues and metabolic or hormonal states require this activity in vivo,
and when CACUL1 acts as a corepressor versus a co-regulator with different
directionality.
gap_kind:
- BIOLOGY
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
Nuclear-receptor corepression is experimentally supported but may be highly
context-dependent; resolving context will determine whether CACUL1 should be
treated as a broadly relevant transcriptional regulator or a narrower adipocyte
and hormone-response modulator.
resolution: >-
Combine receptor-specific ChIP-seq/CUT&RUN, transcriptomics, and CACUL1 loss-
and gain-of-function in relevant adipocyte and hormone-responsive models,
followed by in vivo perturbation where feasible.
provenance:
- reference_id: PMID:29233982
supporting_text: >-
The physiological significance of CACUL1-mediated PPARγ repression under
different dietary conditions is of potential interest.
reference_section_type: DISCUSSION
- reference_id: PMID:29233982
supporting_text: >-
Therefore, adipogenesis may be fine-tuned by dynamic regulation of PPARγ in
response to different dietary conditions.
reference_section_type: DISCUSSION
proposed_new_terms: []
suggested_questions:
- question: >-
Does CACUL1 act as a bona fide CDK2 regulator through a direct
structural/allosteric mechanism, or indirectly via cyclin or CDK-inhibitor
levels?
- question: >-
Is the nuclear-receptor co-regulatory activity of CACUL1 (ERalpha repression
via LSD1, and the separately reported androgen-receptor co-regulation)
physiologically significant, and how is its directionality (corepressor vs
coactivator) determined?
- question: >-
CACUL1 binds the Cul3-Keap1-Rbx1 (CRL3) complex and negatively regulates Nrf2
ubiquitination (PMID:26238671) without nucleating its own ligase - does its
cullin-repeat-like domain mediate this CRL3 association, and is the regulation
Nrf2-specific or a more general modulation of CRL3-Keap1 substrate
ubiquitination?
suggested_experiments:
- description: >-
In vitro reconstituted CDK2 kinase assays with purified recombinant CACUL1 to
test whether it directly stimulates CDK2 activity, and structural/biophysical
mapping (e.g., cryo-EM or co-crystallization, HDX-MS) of the CACUL1-CDK2
interface.
experiment_type: biochemical/structural
hypothesis: >-
CACUL1 directly binds and allosterically activates CDK2 independent of cyclin
levels.
- description: >-
Affinity purification-mass spectrometry of endogenous CACUL1 across cell-cycle
stages to define its stable interactome and test for any RBX/neddylation or
cullin-RING ligase components.
experiment_type: proteomics
hypothesis: >-
CACUL1 does not assemble a canonical cullin-RING ligase and instead functions
through CDK2 and nuclear-receptor/chromatin partners.
- description: >-
ChIP-seq and reporter assays for CACUL1 at ERalpha- and androgen-receptor-
responsive promoters with and without LSD1, to define its co-regulatory
direction and chromatin effects.
experiment_type: genomics/transcription
hypothesis: >-
CACUL1 modulates nuclear-receptor target genes through LSD1-dependent changes
in histone methylation.
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: PMID:19829063
title: Identification and characterization of CAC1 as a novel CDK2-associated cullin.
findings:
- statement: >-
CACUL1/CAC1 is a 369-aa cullin-domain protein that physically associates
with CDK2, promotes CDK2 kinase activity, and is required for G1/S
progression and proliferation; highly expressed in cancers.
supporting_text: >-
CAC1 interacts with CDK2 and promotes the kinase activity of CDK2 protein,
we propose that CAC1 is a novel cell cycle associated protein capable of
promoting cell proliferation.
- id: PMID:23178685
title: Negative regulation of ERα by a novel protein CAC1 through association with
histone demethylase LSD1.
findings:
- statement: >-
CAC1 binds ERalpha via its CoRNR box and, in association with LSD1,
functions as an ERalpha corepressor, increasing H3K9me3 at ERalpha target
promoters.
supporting_text: >-
CAC1, associated with LSD1, functions as an ERα corepressor, implicating a
potential antitumor target in ERα-positive breast cancer.
- id: PMID:28169274
title: Armc5 deletion causes developmental defects and compromises T-cell immune
responses.
findings:
- statement: >-
CACUL1 was recovered as one of 16 ARMC5-binding partners in a yeast
two-hybrid screen; the study characterizes ARMC5, not CACUL1.
supporting_text: Yeast 2-hybrid assays identify 16 ARMC5-binding partners.
- id: PMID:26238671
title: CACUL1/CAC1 Regulates the Antioxidant Response by Stabilizing Nrf2.
findings:
- statement: >-
CACUL1 binds the Cul3-Keap1-Rbx1 ubiquitin-ligase complex and attenuates
Nrf2 ubiquitination, stabilizing Nrf2 (half-life ~10 -> ~30 min) and
sensitizing cells for the antioxidant (ARE) response; CACUL1 is itself
oxidative-stress-induced.
supporting_text: >-
we further assessed CACUL1 binding with Keap1, Cul3 and Rbx1, the
components of the Ubiquitin ligase responsible for Nrf2 ubiquitination.
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID resolved from DOI 10.1038/srep12857 via NCBI and the cached title
matches; supporting_text quotes are verbatim from the cached full text.
Provides experimental support that upgrades the previously domain-only
ubiquitin-ligase-binding (GO:0031625) and reframes the ubiquitin-catabolism
IEA as negative regulation of ubiquitination (GO:0031397).
- id: PMID:29233982
title: CACUL1 reciprocally regulates SIRT1 and LSD1 to repress PPARγ and inhibit
adipogenesis.
findings:
- statement: >-
CACUL1 is a SIRT1-interacting protein that physically binds PPARgamma and
represses its transcriptional activity by coordinating SIRT1 and LSD1 at
target promoters (altering H3K9 acetylation/methylation), suppressing
adipocyte differentiation.
supporting_text: >-
CACUL1, identified as a novel SIRT1 interacting protein, physically
interacts with PPARγ and represses its transcriptional activity,
suppressing adipocyte differentiation
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID resolved from DOI 10.1038/s41419-017-0070-z via NCBI and the cached
title matches; supporting_text quotes are verbatim from the cached full
text. Establishes a SIRT1/LSD1-coupled nuclear-receptor (PPARgamma)
transcription-corepressor activity, broadening the ERalpha co-regulator
report.