REGULATION OF ALTERNATIVE SPLICING OF PROTEIN-KINASE C-BETA BY INSULIN

Insulin regulates a diverse array of cellular signaling processes invo lved in the control of growth, differentiation, and cellular metabolis m. Insulin increases glucose transport via a protein kinase C (PKC) de pendent pathway in BC3H-1 myocytes, but the function of specific PKC i sozymes in insulin action has not been elucidated. Two isoforms of PKC beta result via alternative splicing of precursor mRNA. As now shown, both isoforms are present in BC3H-1 myocytes, and insulin induces alt ernative splicing of the PKC beta mRNA thereby switching expression fr om PKC beta I to PRC beta II 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 PKC beta II. High leve ls of 1a-0-tetradecanoylphorbol-13-acetate, which are commonly used to deplete or down-regulate PKC in cells, also induce the switch to PKC beta II mRNA following overnight treatment, and protein levels of PKC beta II reflected mRNA increases. To investigate the functional import ance of the shift in PKC beta isoform expression, stable transfectants of NIH-3T3 fibroblasts overexpressing PKC beta I and PKC beta II were established. The overexpression of PKC beta II but not PKC beta I in NIH-3T3 cells significantly enhanced insulin effects on glucose transp ort. This suggests that PKC beta II may be more selective than PKC bet a I for enhancing the glucose transport effects of insulin in at least certain cells and, furthermore, that insulin can regulate the express ion of PKC beta II by alternative mRNA splicing.