PKB inhibition prevents the stimulatory effect of insulin on glucose transport and protein translocation but not the antilipolytic effect in rat adipocytes

We identified 1-(5 chloronaphthalenesulfonyl)-1H-hexahydro-1,4-diazepine, a lso known as ML-9, as a powerful inhibitor of PKB activity in different cel ls as well as of recombinant PKB, It also inhibits other downstream serine/ threonine kinases, such as PKA and p90 Se kinase, but not upstream tyrosine phosphorylation or PI3-kinase activation in response to insulin, We compar ed the effects of ML-9 and wortmannin on several insulin-stimulated effects in isolated rat fat cells. Both ML-9 and wortmannin inhibited glucose tran sport and GLUT4/IGF II receptor translocation to the plasma membrane. In co ntrast, only wortmannin inhibited the antilipolytic effect and PDE3B activa tion by insulin. Thus, ML-9 inhibits PKB but not PI3-kinase activation in r esponse to insulin and is useful to differentiate between these effects, Bo th PI3-kinase and PKB are important for glucose transport and intracellular protein translocation while PKB does not appear to play an important role for the antilipolytic effect or activation of PDE3B in response to insulin. (C) 2000 Academic Press.