ROLES OF PI-3-KINASE AND RAS ON INSULIN-STIMULATED GLUCOSE-TRANSPORT IN 3T3-L1 ADIPOCYTES

The dominant negative p85 alpha regulatory subunit (Delta p85 alpha) o f phosphatidylinositol (PI) 3-kinase or dominant negative Ras (N17Ras) was overexpressed in 3T3-L1 adipocytes using an adenovirus-mediated g ene transduction system. Functional expression of Delta p85 alpha and N17Ras was confirmed by marked inhibition of insulin-stimulated PI 3-k inase activity and mitogen-activated protein kinase activity, respecti vely. N17Ras expression did not affect glucose transport activity, whe reas Delta p85 alpha expression inhibited insulin-stimulated glucose t ransport with impairment of GLUT-4 translocation, although inhibition of glucose transport activity was less remarkable than that of PI 3-ki nase activity in Delta p85 alpha-expressing cells. Thus the Ras signal ing pathway does not play a major part in either translocation or intr insic activity of glucose transporters, but PI 3-kinase activation, vi a phosphotyrosyl proteins and heterodimeric PI 3-kinase, plays a pivot al role in insulin-stimulated glucose transport. However, a discrepanc y was observed between PI 3-kinase activity and glucose transport acti vity, suggesting a possibility that a different pathway(s) is involved in insulin-stimulated intrinsic activity of glucose transporters.