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HGNC Approved Gene Symbol: CNKSR3
Cytogenetic location: 6q25.2 Genomic coordinates (GRCh38): 6:154,387,515-154,510,685 (from NCBI)
CNKSR3 is an aldosterone-induced scaffold protein required for assembly of an epithelial sodium channel (ENaC; see 600228) regulatory complex (Soundararajan et al., 2012).
A read-through transcript of CNKSR3 and IPCEF1 (619948) produces a protein that binds to cytohesin-2 (CYTH2; 602488) and is involved in regulation of cell shape and movement (Attar et al., 2012).
CNK3-IPCEF1 Spliced Read-Through Transcript
Using RT-PCR, Attar et al. (2012) showed that CNK3 and IPCEF1 are encoded by 2 halves of the same gene in both Caco2 human colorectal carcinoma cells and Madin-Darby canine kidney (MDCK) cells. The CNK3 and IPCEF1 sequences produce a single spliced mRNA encoding a protein with the overall domain structure of other CNK family proteins, including an N-terminal SAM domain, followed by a CRIC domain, a PDZ domain, a PH domain, and a C-terminal CRAC domain. Immunoprecipitation-Western blot analysis detected only a 95-kD protein representing the fused CNK3/IPCEF1 sequence in Caco2 and MDCK cells. Small interfering RNA (siRNA) experiments confirmed that the protein observed in Caco2 cells represents the fused CNK3/IPCEF1 sequence. The authors suggested that alternative splicing may produce CNK3, IPCEF1, or fused CNK3/IPCEF1 in different tissues.
Using 2-dimensional SDS-PAGE of ENaC-containing multiprotein complexes from mouse cortical collecting duct (CCD) cells, Soundararajan et al. (2012) observed increased ENaC expression after exposure to aldosterone and detected Nedd4-2 (NEDD4L; 606384), Sgk1 (602958), and Cnk3 in an ENaC regulatory complex (ERC). Transfection of human embryonic kidney cells with ENaC and ERC proteins resulted in increased ENaC expression compared with transfection of ENaC alone. The putative ENaC regulator, Gilz1 (TSC22D3; 300506), was not detected in the ERC. Depletion of Cnk3 in mouse CCD cells reduced aldosterone-stimulated Na+ transport. Mutation analysis showed that interaction of the ERC at the plasma membrane with ENaC alpha and beta tails depended on the Cnk3 PDZ domain. Soundararajan et al. (2012) concluded that CNK3 is an aldosterone-induced scaffolding protein that orchestrates assembly of the ERC.
CNK3-IPCEF1 Protein
By immunoprecipitation analysis in transfected Caco2 and HEK293 cells, Attar et al. (2012) showed that the C-terminal CRAC domain of CNK3/IPCEF1 mediated its interaction with ARNO (CYTH2). Knockdown of CNK3/IPCEF1 via siRNA showed that HGF (142409)-stimulated migration of epithelial cells required CNK3/IPCEF1 for ARF6 (600464) activation.
Attar et al. (2012) determined that the CNK3 gene contains at least 13 exons.
Gross (2017) mapped the CNK3 gene to chromosome 6q25.2 based on an alignment of the CNK3 sequence (GenBank BC060761) with the genomic sequence (GRCh38).
Attar, M. A., Salem, J. C., Pursel, H. S., Santy, L. C. CNK3 and IPCEF1 produce a single protein that is required for HGF dependent Arf6 activation and migration. Exp. Cell Res. 318: 228-237, 2012. [PubMed: 22085542] [Full Text: https://doi.org/10.1016/j.yexcr.2011.10.018]
Gross, M. B. Personal Communication. Baltimore, Md. 5/10/2017.
Soundararajan, R., Ziera, T., Koo, E., Ling, K., Wang, J., Borden, S. A., Pearce, D. Scaffold protein connector enhancer of kinase suppressor of Ras isoform 3 (CNK3) coordinates assembly of a multiprotein epithelial sodium channel (ENaC)-regulatory complex. J. Biol. Chem. 287: 33014-33025, 2012. [PubMed: 22851176] [Full Text: https://doi.org/10.1074/jbc.M112.389148]