Oxidative stress disrupts insulin-induced cellular redistribution of insulin receptor substrate-1 and phosphatidylinositol 3-kinase in 3T3-L1 adipocytes - A putative cellular mechanism for impaired protein kinase B activation and GLUT4 translocation

In a recent study we have demonstrated that 3T3-L1 adipocytes exposed to lo w micromolar H2O2 concentrations display impaired insulin stimulated GLUT4 translocation from internal membrane pools to the plasma membrane (Rudich, A., Tirosh, A., Potashnik, R., Hemi, R., Kannety, H., and Bashan, N, (1998) Diabetes 47, 1562-1569), In this study we further characterize the cellula r mechanisms responsible for this observation, Two-hour exposure to similar to 25 mu M H2O2 (generated by adding glucose oxidase to the medium) result ed in disruption of the normal insulin stimulated insulin receptor substrat e (IRS)-1 and phosphatidylinositol (PI) 3-kinase cellular redistribution be tween the cytosol and an internal membrane pool (low density microsomal fra ction (LDM)). This was associated with reduced insulin-stimulated IRS-1 and p85 associated PI 3-kinase activities in the LDM (84 and 96% inhibition, r espectively). The effect of this finding on the downstream insulin signal w as demonstrated by a 90% reduction in insulin stimulated protein kinase B ( PKB) serine 473 phosphorylation and impaired activation of PKB alpha and PK B gamma. Both control and oxidized cells exposed to heat shock displayed a wortmannin insensitive PKB serine phosphorylation and activity. These data suggest that activation of PKB and GLUT4 translocation are insulin signalin g events dependent upon a normal insulin induced cellular compartmentalizat ion of PI 3-kinase and IRS-1, which is oxidative stress-sensitive. These fi ndings represent a novel cellular mechanism for the induction of insulin re sistance in response to changes in the extracellular environment.