INSULIN STIMULATES PHOSPHATIDYLINOSITOL 3-KINASE ACTIVITY IN RAT NEURONAL PRIMARY CULTURES

We investigated the effect of insulin on phosphatidylinositol (PtdIns) 3-kinase (PtdIns 3-kinase) activity in neuronal cultures to determine if this enzyme is involved with the neurotrophic actions of insulin. Insulin caused a concentration-dependent increase in PtdIns 3-kinase a ctivity in anti-phosphotyrosine immunoprecipitates. The kinase activit y was able to phosphorylate PtdIns, PtdIns 4-phosphate, and PtdIns 4,5 -bisphosphate. In intact neurons, a 1 0-min 1 mM insulin treatment in the presence of [P-32]orthophosphate increased the levels of both 3-[P -32]PtdIns phosphate and 3,4-[P-32]PtdIns bisphosphate by 55 and 193%, respectively. This increase was associated with an increase in neurit e outgrowth mediated by insulin. Our results indicate that insulin tre atment of neuronal cells in primary culture increases PtdIns 3-kinase activity and the formation of the unique D-3-phosphorylated phosphoino sitides, suggesting that growth factor-mediated neuronal growth may in clude the formation of novel phosphoinositide 3-phosphate phospholipid s.