Tyrosine phosphorylation of specific protein kinase C isoenzymes participates in insulin stimulation of glucose transport in primary cultures of rat skeletal muscle.

Abstract

Several reports indicate that protein kinase C (PKC) plays a role in insulin-induced glucose transport in certain cells. The precise effects of insulin on specific PKC isoforms are as yet unknown. Utilizing primary cultures of rat skeletal muscle, we investigated the possibility that insulin may influence the activation state of PKC isoenzymes by inducing their translocation and tyrosine phosphorylation. This, in turn, may mediate insulin effects on glucose transport. We identified and determined the glucose transporters and PKC isoforms affected by insulin and 12-O-tetradecanoylphorbol-13-acetate (TPA). Insulin and TPA each caused an increase in glucose uptake. Insulin translocated GLUT3 and GLUT4 without affecting GLUT1. In contrast, TPA translocated GLUT1 and GLUT3 without affecting GLUT4. Insulin translocated and tyrosine phosphorylated and activated PKC-beta2 and -zeta; these effects were blocked by phosphatidylinositol 3-kinase (PI3K) inhibitors. TPA translocated and activated PKC-alpha, -beta2, and -delta; these effects were not noticeably affected by PI3K inhibitors. Furthermore, wortmannin significantly inhibited both insulin and TPA effects on GLUT translocation and glucose uptake. Finally, insulin-induced glucose transport was blocked by the specific PKC-beta2 inhibitor LY379196. These results indicate that specific PKC isoenzymes, when tyrosine-phosphorylated, are implicated in insulin-induced glucose transport in primary cultures of skeletal muscle.