Connector enhancer of kinase suppressor of Ras 3 (CNKSR3) is a multi-domain scaffold protein that coordinates signaling complexes at the apical plasma membrane of epithelial cells. Its primary characterized function is regulation of the epithelial sodium channel (ENaC), where it acts as a central organizing platform for aldosterone-induced sodium transport. CNKSR3 also regulates cell migration through Arf6 activation and modulates MAPK signaling.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0007167 enzyme-linked receptor protein signaling pathway | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation based on phylogenetic inference. CNKSR3 is a scaffold protein involved in multiple signaling pathways including HGF-induced Arf6 activation and aldosterone-ENaC signaling. While the protein participates in signaling downstream of receptors, the specific connection to enzyme-linked receptors is indirect and the term is too general for this scaffold protein's core functions. Reason: CNKSR3 participates in signaling downstream of receptor tyrosine kinases, including HGF-induced Arf6 activation, so the propagated pathway context is biologically defensible. The broad term is secondary to CNKSR3's directly characterized ENaC and HGF/Arf6 scaffold roles and is therefore retained as non-core. Supporting Evidence: PMID:22085542 Knockdown of this protein impairs HGF-induced Arf6 activation and migration in response to HGF treatment file:human/CNKSR3/CNKSR3-uniprot.txt Acts as a scaffold protein coordinating the assembly of an ENaC-regulatory complex |
| GO:0030674 protein-macromolecule adaptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for adaptor/scaffold function. This is well-supported and represents a core molecular function of CNKSR3. The protein coordinates assembly of the ENaC-regulatory complex by binding multiple partners including SCNN1A, SCNN1B, NEDD4L, RAF1, and SGK1. It also scaffolds HGF-Arf6 signaling components. Reason: This accurately captures CNKSR3's primary molecular function as a scaffold/adaptor protein that brings together multiple signaling components. Well-supported by experimental evidence. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt Acts as a scaffold protein coordinating the assembly of an ENaC-regulatory complex (ERC). Interacts directly with SCNN1A (ENaC subunit alpha) and SCNN1B (ENaC subunit beta) C-terminal tails. Interacts with ENaC regulatory proteins NEDD4L, RAF1 and SGK1. file:human/CNKSR3/CNKSR3-deep-research-perplexity-lite.md See deep research file for comprehensive analysis file:human/CNKSR3/CNKSR3-deep-research-falcon.md CNKSR3 is positioned as an aldosterone/mineralocorticoid receptor (MR)-regulated scaffold that is required for ENaC-mediated sodium transport in aldosterone-responsive distal nephron epithelia (connecting tubule and cortical collecting duct) |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation based on InterPro domains and UniProtKB subcellular location. CNKSR3 is indeed found in cytoplasm, though its most functionally important localization is at the apical plasma membrane where it regulates ENaC. Cytoplasmic localization is confirmed but represents a secondary or transit location. Reason: Accurate but not the most informative localization. CNKSR3 is present in cytoplasm as stated in UniProt, though apical plasma membrane is the more functionally relevant location. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm. Apical cell membrane; Peripheral membrane protein. |
| GO:0009966 regulation of signal transduction | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro domain IPR010599 (CNK2/3 domain). This is appropriate - CNKSR3 regulates multiple signal transduction pathways including MAPK/ERK signaling (negative regulation) and aldosterone-ENaC signaling (positive regulation of sodium transport). Reason: Accurate representation of CNKSR3's biological role as a regulator of signaling pathways. The protein negatively regulates ERK1/2 cascade and peptidyl-serine phosphorylation while positively regulating ENaC-mediated sodium transport. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt negative regulation of ERK1 and ERK2 cascade; ISS:UniProtKB. negative regulation of peptidyl-serine phosphorylation; ISS:UniProtKB. positive regulation of sodium ion transport; ISS:UniProtKB. PMID:22101317 The first study addressing the mechanistic aspects of CNK3 function revealed that CNK3 expression significantly interferes with the activation of the Raf-1/MEK1/2/ERK1/2 signaling cascade |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: IEA annotation from InterPro. While CNKSR3 is a peripheral membrane protein at the apical plasma membrane, this extremely general term provides minimal information. More specific membrane localization terms are more appropriate. Reason: The term 'membrane' is too general. CNKSR3 specifically localizes to the apical plasma membrane where it functions in ENaC regulation. A more specific term is warranted. Proposed replacements: apical plasma membrane Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt SUBCELLULAR LOCATION: Apical cell membrane; Peripheral membrane protein |
| GO:0016324 apical plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: IEA annotation from UniProtKB subcellular location vocabulary. This is accurate and functionally important - CNKSR3 localizes to the apical plasma membrane of epithelial cells where it coordinates the ENaC-regulatory complex. Reason: This is the most functionally relevant subcellular location for CNKSR3. The protein is specifically targeted to the apical membrane where it regulates ENaC. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm. Apical cell membrane; Peripheral membrane protein. Acts as a scaffold protein coordinating the assembly of an ENaC-regulatory complex (ERC). |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | REMOVE | Summary: IPI evidence from proteome-scale interactome study identifying interaction with NMI (Q13287). While protein binding is technically correct, it is uninformative as a molecular function annotation. CNKSR3's specific function is as a protein-macromolecule adaptor, which is already captured by GO:0030674. Reason: The term 'protein binding' is uninformative per curation guidelines. The specific adaptor function is better captured by GO:0030674 (protein-macromolecule adaptor activity). Large-scale interactome studies often identify interactions that may not be functionally relevant to core gene function. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: IPI evidence from binary protein interactome reference map identifying multiple interactions. While protein binding is correct, it is redundant and uninformative given the more specific GO:0030674 annotation. Reason: Uninformative and redundant with the more specific adaptor activity term. This is from a large-scale binary interactome study. Supporting Evidence: PMID:32296183 Apr 8. A reference map of the human binary protein interactome. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | REMOVE | Summary: IPI evidence from multimodal cell atlas study. Another protein binding annotation that is uninformative compared to the specific adaptor function already annotated. Reason: Uninformative and redundant. Large-scale proteomics study. The specific molecular function is better captured by GO:0030674. Supporting Evidence: PMID:40205054 Apr 9. Multimodal cell maps as a foundation for structural and functional genomics. |
| GO:0005829 cytosol | IDA GO_REF:0000052 | ACCEPT | Summary: IDA evidence from immunofluorescence data (HPA project). Cytosol is a more specific cytoplasmic compartment and represents where CNKSR3 is found when not at the membrane. This is consistent with the protein's peripheral membrane association - it can be in cytosol and recruited to apical membrane. Reason: Supported by direct experimental evidence from immunofluorescence. Cytosol localization is consistent with CNKSR3 being a peripheral (not integral) membrane protein that can shuttle between cytosol and membrane. Supporting Evidence: GO_REF:0000052 Gene Ontology annotation based on curation of immunofluorescence data from Human Protein Atlas project |
| GO:0005515 protein binding | IPI PMID:22085542 CNK3 and IPCEF1 produce a single protein that is required fo... | REMOVE | Summary: IPI evidence from the CNK3/IPCEF1 study showing interactions relevant to HGF-Arf6 signaling. While this paper provides important functional context, the protein binding annotation itself is uninformative. Reason: Although PMID:22085542 is a key functional paper showing CNKSR3 interacts with cytohesin 2 and is required for Arf6 activation, the generic "protein binding" annotation is uninformative. The specific adaptor function (GO:0030674) is more appropriate. Supporting Evidence: PMID:22085542 2011 Nov 7. CNK3 and IPCEF1 produce a single protein that is required for HGF dependent Arf6 activation and migration. |
| GO:0010765 positive regulation of sodium ion transport | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation based on mouse ortholog Q8BMA3. This represents a core function of CNKSR3 - it positively regulates ENaC-mediated sodium transport in response to aldosterone. This is the protein's best-characterized biological role in kidney epithelial cells. Reason: This is a core biological function of CNKSR3. The protein regulates aldosterone-induced ENaC-mediated sodium transport through coordinating the assembly of the ENaC-regulatory complex. Well-supported by multiple studies. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt FUNCTION: Involved in transepithelial sodium transport. Regulates aldosterone-induced and epithelial sodium channel (ENaC)-mediated sodium transport through regulation of ENaC cell surface expression. Acts as a scaffold protein coordinating the assembly of an ENaC-regulatory complex (ERC). PMID:22101317 CNK3 expression correlates with, and is required for, ENaC-mediated Na+ transport in renal epithelial cells PMID:22506713 CNK3 expression correlates with, and is critically required for, ENaC-mediated Na+ transport in renal epithelial cells |
| GO:0033137 negative regulation of peptidyl-serine phosphorylation | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS annotation based on mouse ortholog. CNKSR3 scaffold proteins regulate kinase signaling cascades and this annotation likely reflects regulation of SGK1 or other serine kinases in the ENaC regulatory complex, or broader effects on MAPK pathway serine phosphorylation. Downgraded from ACCEPT to KEEP_AS_NON_CORE per PR #759 review feedback: the rationale cites indirect kinase-interaction evidence without direct biochemical demonstration of CNKSR3 negatively regulating peptidyl- serine phosphorylation. Reason: Indirect evidence — CNKSR3 interacts with SGK1 and RAF1, but no direct biochemical assay shows CNKSR3 reduces serine phosphorylation. The annotation is plausible but uncorroborated by direct evidence. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt Interacts with ENaC regulatory proteins NEDD4L, RAF1 and SGK1. The PDZ domain is required for interaction with ENaC and SGK1, but not for interaction with NEDDL4 and RAF1. |
| GO:0070373 negative regulation of ERK1 and ERK2 cascade | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation based on mouse ortholog. CNKSR3 negatively regulates MAPK/ERK signaling. CNK family proteins are known scaffold proteins in Ras/MAPK pathways, and CNKSR3 specifically acts as a negative regulator of the ERK1/2 cascade. Review literature explicitly links CNK3 to interference with the Raf-1/MEK1/2/ERK1/2 cascade. Reason: Represents an important regulatory function of CNKSR3 beyond its ENaC role. CNK proteins are scaffolds in Ras/MAPK signaling pathways, and CNKSR3 negatively regulates ERK1/2. This is consistent with the protein's domain structure and family membership. Supporting Evidence: file:human/CNKSR3/CNKSR3-uniprot.txt negative regulation of ERK1 and ERK2 cascade; ISS:UniProtKB. SIMILARITY - Belongs to the CNKSR family. PMID:22506713 The first study addressing the mechanistic aspects of CNK3 function revealed that CNK3 expression significantly interferes with the activation of the Raf-1/MEK1/2/ERK1/2 signaling cascade |
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Download this section (compressed HTML)Q: What is the molecular mechanism by which CNKSR3 PDZ domain selectively binds ENaC subunits versus other PDZ domain ligands?
Suggested experts: Structural biologists specializing in PDZ domain interactions, Renal physiologists studying ENaC regulation
Q: How does aldosterone signaling lead to CNKSR3 upregulation and recruitment to the apical membrane?
Suggested experts: Researchers studying mineralocorticoid receptor signaling, Epithelial cell biologists
Q: What is the relative importance of CNKSR3's ENaC regulatory function versus its HGF-Arf6 scaffolding function in different tissue contexts?
Suggested experts: Renal physiologists, Cancer cell migration researchers
Q: Does CNKSR3 have tissue-specific isoforms or splice variants with distinct functions beyond the CNK3/IPCEF1 fusion proteins?
Suggested experts: RNA biology researchers, Epithelial tissue specialists
Experiment: Determine crystal or cryo-EM structure of CNKSR3 PDZ domain in complex with ENaC subunit C-terminal peptides to understand binding specificity
Hypothesis: The PDZ domain has specific structural features that enable high-affinity binding to ENaC tails
Type: Structure determination
Experiment: Live-cell imaging of CNKSR3 dynamics at the apical membrane in response to aldosterone treatment to understand recruitment kinetics
Hypothesis: Aldosterone induces rapid recruitment of CNKSR3 to apical membrane where it stabilizes ENaC
Type: Cell biology/Imaging
Experiment: Reconstitute the complete ENaC-regulatory complex in vitro with purified CNKSR3, ENaC subunits, SGK1, RAF1, and NEDD4L to map binding interfaces and stoichiometry
Hypothesis: CNKSR3 can simultaneously bind multiple complex components through distinct domains
Type: Biochemistry
Experiment: CNKSR3 knockout in kidney epithelial cells with rescue by domain deletion mutants to determine which domains are essential for ENaC regulation versus Arf6/migration functions
Hypothesis: PDZ domain is critical for ENaC function but dispensable for Arf6 scaffolding
Type: Functional genomics
Experiment: Generate CNKSR3 conditional knockout mice and assess blood pressure, sodium handling, and response to aldosterone challenge
Hypothesis: Loss of CNKSR3 will impair aldosterone-mediated sodium retention and blood pressure regulation
Type: Physiological
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