Protein kinase C delta 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 p ossibility that activation of PKC delta by insulin participates in the medi ation of insulin effects on glucose transport in skeletal muscle. Studies w ere performed on primary cultures of rat skeletal myotubes. The role of PKC delta in insulin-induced glucose uptake was evaluated both by selective ph armacological blockade and by overexpression of wild-type and point-mutated inactive PKC delta isoforms in skeletal myotubes. We found that insulin in duces tyrosine phosphorylation and translocation of PKC delta to the plasma membrane and increases the activity of this isoform. Insulin-induced effec ts on translocation and phosphorylation of PKC delta were blocked by a low concentration of rottlerin, whereas the effects of insulin on other PKC iso forms were not. This selective blockade of PKC delta by rottlerin also inhi bited insulin-induced translocation of glucose transporter 4 (GLUT4), but n ot glucose transporter 3 (GLUT3), and significantly reduced the stimulation of glucose uptake by insulin. When overexpressed in skeletal muscle, PKC d elta and PKC alpha were both active. Overexpression of PKC delta induced th e translocation of GLUT4 to the plasma membrane and increased basal glucose uptake to levels attained by insulin. Moreover, insulin did not increase g lucose uptake further in cells overexpressing PKC delta. Overexpression of PKC alpha did not affect basal glucose uptake or GLUT4 location. Stimulatio n of glucose uptake by insulin in cells overexpressing PKC alpha was simila r to that in untransfected cells. Transfection of skeletal myotubes with do minant negative mutant PKC delta did not alter basal glucose uptake but blo cked insulin-induced GLUT4 translocation and glucose transport. These resul ts demonstrate that insulin activates PKC delta and that activated PKC delt a is a major signaling molecule in insulin-induced glucose transport.