Insulin activates phospholipase C-gamma1 via a PI-3 kinase dependent mechanism in 3T3-L1 adipocytes

Previously we have shown that the insulin receptor and phospholipase C-gamma1 physically interact in the 3T3-L1 adipocyte cell line. In this study, we investigated the ability of insulin and PDGF to stimulate PLC-gamma1 enzyme activity as measured by PI-(4,5)P(2) hydrolysis. Both insulin and PDGF caused a rapid (<1 min) increase in PLC activity associated with the respective receptor. PDGF treatment resulted in a higher and more sustained stimulation of PLC-gamma1 activity compared to insulin (0.95 pmol/min/mg vs 0.68 pmol/min/mg). Furthermore, insulin and PDGF promoted increases in total cellular DAG, one of the products of PI-(4,5)P(2) hydrolysis. Insulin-stimulated PLC activity appears to be downstream of PI-3Kinase as the DAG increase was partially blocked by Wortmannin and addition of PI-(3,4,5)P(3) activated PLC-gamma1 in vitro. Inhibition of PLC using U73122 or an inhibitory peptide caused a decrease in insulin-stimulated 2-deoxyglucose transport and GLUT4 translocation that was rescued by the addition of OAG, a cell-permeable synthetic DAG.