Protein Kinase B/AKT 1 Plays a Pivotal Role in Insulin-like Growth Factor-1 Receptor Signaling Induced 3T3-L1

During 3T3-L1 preadipocyte differentiation induction, the insulin-stimulated insulin-like growth factor-1 (IGF-1) receptor signal is responsible for the induction of adipo-cyte differentiation. Treatment with inhibitors of phos-phatidylinositol 3-kinase, LY294002 or wortmannin, leads to the complete blockade of adipocyte differentiation in 3T3-L1 preadipocytes. Of the three factors (1-methyl-3-isobutylxanthine, dexamethasone, and insulin) inducing 3T3-L1 preadipocyte differentiation, only insulin was able to activate the phosphatidylinositol 3-kinase-protein ki-nase B/Akt signal cascade. In 3T3-L1 preadipocytes, pro-tein kinase B/Akt 1 RNA interference not only suppressed the expression of protein kinase B/Akt 1 but also blocked hormone-induced adipocyte differentiation. In these pro-tein kinase B/Akt 1 RNA interference cells, the signal mol