FUNCTIONAL INTERACTIONS OF PHOSPHATIDYLINOSITOL 3-KINASE WITH GTPASE-ACTIVATING PROTEIN IN 3T3-L1 ADIPOCYTES

The role of phosphatidylinositol (PI) 3-kinase in specific aspects of insulin signaling was explored in 3T3-L1 adipocytes, Inhibition of PI 3-kinase activity by LY294002 or wortmannin significantly enhanced bas al and insulin-stimulated GTPase-activating protein (GAP) activity in 3T3-L1 adipocytes. Furthermore, removal of the inhibitory influence of PI 3-kinase on GAP resulted in dose-dependent decreases in the abilit y of insulin to stimulate p21(ras). This effect was specific to adipoc ytes, as inhibition of PI 3-kinase did not influence GAP in either 3T3 -L1 fibroblasts, Rat-1 fibroblasts, or CHO cells, Immunodepletion of e ither of the two subunits of the PI 3 kinase (p85 or p110) yielded sim ilar activation of GAP, suggesting that catalytic activity of p110 pla ys an important role in controlling GAP activity in 3T3-L1 adipocytes, Inhibition of PI 3-kinase activity in 3T3-L1 adipocytes resulted in a brogation of insulin-stimulated glucose uptake and thymidine incorpora tion, In contrast, effects of insulin on glycogen synthase and mitogen -activated protein kinase activity were inhibited only at higher conce ntrations of LY294002. It appears that in adipocytes, PI 3 kinase prev ents activation of GAP, Inhibition of PI 3-kinase activity or immunode pletion of either one of its subunits results in activation of GAP and decrease in GTP loading of p21(ras).