Activation of protein kinase C zeta induces serine phosphorylation of VAMP2 in the GLUT4 compartment and increases glucose transport in skeletal muscle

Insulin stimulates glucose uptake into skeletal muscle tissue mainly throug h the translocation of glucose transporter 4 (GLUT4) to the plasma membrane . The precise mechanism involved in this process is presently unknown. In t he cascade of events leading to insulin-induced glucose transport, insulin activates specific protein kinase C (PKC) isoforms. In this study we invest igated the roles of PKC zeta in insulin-stimulated glucose uptake and GLUT4 translocation in primary cultures of rat skeletal muscle. We found that in sulin initially caused PKC zeta to associate specifically with the GLUT4 co mpartments and that PKC zeta together with the GLUT4 compartments were then translocated to the plasma membrane as a complex. PKC zeta and GLUT4 recyc led independently of one another. To further establish the importance of PK C zeta in glucose transport, we used adenovirus constructs containing wild- type or kinase-inactive, dominant-negative PKC zeta (DNPKC zeta) cDNA to ov erexpress this isoform. in skeletal muscle myotube cultures. We found that overexpression of PKC zeta was associated with a marked increase in the act ivity of this isoform. The overexpressed, active PKC zeta coprecipitated wi th the GLUT4 compartments. Moreover, overexpression of PKC zeta caused GLUT 4 translocation to the plasma membrane and increased glucose uptake in the absence of insulin. Finally, either insulin or overexpression of PKC zeta i nduced serine phosphorylation of the GLUT4-compartment-associated vesicle-a ssociated membrane protein 2. Furthermore, DNPKC zeta disrupted the GLUT4 c ompartment integrity and abrogated insulin-induced GLUT4 translocation and glucose uptake. These results demonstrate that PKC zeta regulates insulin-s timulated GLUT4 translocation and glucose transport through the unique colo calization of this isoform with the GLUT4 compartments.