Regulation of alternative splicing of protein kinase Cβby insulin

Abstract

Insulin regulates a diverse array of cellular signaling processes involved in the control of growth, differentiation, and cellular metabolism. Insulin increases glucose transport via a protein kinase C (PKC)-dependent pathway in BC3H-1 myocytes, but the function of specific PKC isozymes in insulin action has not been elucidated. Two isoforms of PKCβ result via alternative splicing of precursor mRNA. As now shown, both isoforms are present in BC3H-1 myocytes, and insulin induces alternative splicing of the PKCβ mRNA thereby switching expression from PKCβI to PKCβII mRNA. This effect occurs rapidly (15 min after insulin treatment) and is dose-dependent. The switch in mRNA is reflected by increases in the protein levels of PKCβII. High levels of 12-0-tetradecanoylphorbol-13-acetate, which are commonly used to deplete or down-regulate PKC in cells, also induce the switch to PKCβII mRNA following overnight treatment, and protein levels of PKCβII reflected mRNA increases. To investigate the functional importance of the shift in PKCβ isoform expression, stable transfectants of NIH-3T3 fibroblasts overexpressing PKCβI and PKCβ11 were established. The overexpression of PKCβII but not PKCβI in NIH-3T3 cells significantly enhanced insulin effects on glucose transport. This suggests that PKCβII may be more selective than PKCβI for enhancing the glucose transport effects of insulin in at least certain cells and, furthermore, that insulin can regulate the expression of PKCβII by alternative mRNA splicing.