Protein kinase Cδ mediates insulin-induced glucose transport in primary cultures of rat skeletal muscle

Insulin activates certain protein kinase C (PKC) isoforms that are involved in insulin-induced glucose transport. In this study, we investigated the possibility that activation of PKC delta by insulin participates in the mediation of insulin effects on glucose transport in skeletal muscle. Studies were performed on primary cultures of rat skeletal myotubes. The role of PKC delta in insulin-induced glucose uptake was evaluated both by selective pharmacological blockade and by overexpression of wild-type and point-mutated inactive PKC delta isoforms in skeletal myotubes. We found that insulin induces tyrosine phosphorylation and translocation of PKC delta to the plasma membrane and increases the activity of this isoform. Insulin-induced effects on translocation and phosphorylation of PKC delta were blocked by a low concentration of rottlerin, whereas the effects of insulin on other PKC isoforms were not. This selective blockade of PKC delta by rottlerin also inhibited insulin-induced translocation of glucose transporter 4 (GLUT4), but not glucose transporter 3 (GLUT3), and significantly reduced the stimulation of glucose uptake by insulin. When overexpressed in skeletal muscle, PKC delta and PKC alpha were both active. Overexpression of PKC delta induced the translocation of GLUT4 to the plasma membrane and increased basal glucose uptake to levels attained by insulin. Moreover, insulin did not increase glucose uptake further in cells overexpressing PKC delta. Overexpression of PKC alpha did not affect basal glucose uptake or GLUT4 location. Stimulation of glucose uptake by insulin in cells overexpressing PKC alpha was similar to that in untransfected cells. Transfection of skeletal myotubes with dominant negative mutant PKC delta did not alter basal glucose uptake but blocked insulin-induced GLUT4 translocation and glucose transport. These results demonstrate that insulin activates PKC delta and that activated PKC delta is a major signaling molecule in insulin-induced glucose transport.