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, V 1.1, respectively); however, the functions of NaV1.1 V 1.1 are unclear. In this study, we investigated the role of SCN1A and NaV1.1 V 1.1 in human mesenchymal stem cells (MSCs). We found that SCN1A was expressed in MSCs, and abundant expression of NaV1.1 V 1.1 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 4 Cl revealed that both the ubiquitin-proteasome system and the autophagy and endolysosome 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 V 1.1 contributes to the cell cycle of MSCs by regulating the post-translational control of AKT and CDK2.