title: Okadaic acid activates atypical protein kinase C (zeta/lambda) in rat and 3T3/L1 adipocytes. An apparent requirement for activation of Glut4 translocation and glucose transport.
abstract: Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, is known to provoke insulin-like effects on GLUT4 translocation and glucose transport, but the underlying mechanism is obscure. Presently, we found in both rat adipocytes and 3T3/L1 adipocytes that okadaic acid provoked partial insulin-like increases in glucose transport, which were inhibited by phosphatidylinositol (PI) 3-kinase inhibitors, wortmannin and LY294002, and inhibitors of atypical protein kinase C (PKC) isoforms, zeta and lambda. Moreover, in both cell types, okadaic acid provoked increases in the activity of immunoprecipitable PKC-zeta/lambda by a PI 3-kinase-dependent mechanism. In keeping with apparent PI 3-kinase dependence of stimulatory effects of okadaic acid on glucose transport and PKC-zeta/lambda activity, okadaic acid provoked insulin-like increases in membrane PI 3-kinase activity in rat adipocytes; the mechanism for PI 3-kinase activation was uncertain, however, because it was not apparent in phosphotyrosine immunoprecipitates. Of further note, okadaic acid provoked partial insulin-like increases in the translocation of hemagglutinin antigen-tagged GLUT4 to the plasma membrane in transiently transfected rat adipocytes, and these stimulatory effects on hemagglutinin antigen-tagged GLUT4 translocation were inhibited by co-expression of kinase-inactive forms of PKC-zeta and PKC-lambda but not by a double mutant (T308A, S473A), activation-resistant form of protein kinase B. Our findings suggest that, as with insulin, PI 3-kinase-dependent atypical PKCs, zeta and lambda, are required for okadaic acid-induced increases in GLUT4 translocation and glucose transport in rat adipocytes and 3T3/L1 adipocytes.
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D003847:Deoxyglucose / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051275:Glucose Transporter Type 4; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D019319:Okadaic Acid / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D000077191:Wortmannin; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta