NaV1.1 contributes to the cell cycle of human mesenchymal stem cells by regulating AKT and CDK2

Non-excitable cells express sodium voltage-gated channel alpha subunit 1 gene and protein (known as SCN1A and NaV1.1, respectively); however, the functions of NaV1.1 are unclear. In this study, we investigated the role of SCN1A and NaV1.1 in human mesenchymal stem cells (MSCs). We found that SCN1A was expressed in MSCs, and abundant expression of NaV1.1 was observed in the endoplasmic reticulum; however, this expression was not found to be related to Na+ currents. SCN1A-silencing reduced MSC proliferation and delayed the cell cycle in the S phase. SCN1A silencing also suppressed the protein levels of CDK2 and AKT (herein referring to total AKT), despite similar mRNA expression, and inhibited AKT phosphorylation in MSCs. A cycloheximide-chase assay showed that SCN1A-silencing induced CDK2 but not AKT protein degradation in MSCs. A proteolysis inhibition assay using epoxomicin, bafilomycin A1 and NH4Cl revealed that both the ubiquitin-proteasome system and the autophagy and endo-lysosome system were irrelevant to CDK2 and AKT protein reduction in SCN1A-silenced MSCs. The AKT inhibitor LY294002 did not affect the degradation and nuclear localization of CDK2 in MSCs. Likewise, the AKT activator SC79 did not attenuate the SCN1A-silencing effects on CDK2 in MSCs. These results suggest that NaV1.1 contributes to the cell cycle of MSCs by regulating the post-translational control of AKT and CDK2.