INSULIN-INDUCED PHOSPHORYLATION AND ACTIVATION OF PHOSPHODIESTERASE 3B IN RAT ADIPOCYTES - POSSIBLE ROLE FOR PROTEIN-KINASE-B BUT NOT MITOGEN-ACTIVATED PROTEIN-KINASE OR P70 S6 KINASE

Insulin stimulation of adipocytes results in serine phosphorylation/ a ctivation of phosphodiesterase 3E (PDE 3B) and activation of a kinase that phosphorylates PDE 3B in vitro, key events in the anti lipolytic action of this hormone. We have investigated the role for p70 S6 kinas e, mitogen-activated protein kinases (MAP kinases), and protein kinase B (PKB) in the insulin signaling pathway leading to phosphorylation/a ctivation of PDE 3B in adipocytes. Insulin stimulation of adipocytes r esulted in increased activity of p70 S6 kinase, which was completely b locked by pretreatment with rapamycin. However, rapamycin had no effec t on the insulin-induced phosphorylation/ activation of PDE 3B or the activation of the kinase that phosphorylates PDE 3B. Stimulation of ad ipocytes with insulin or phorbol myristate acetate induced activation of MAP kinases. Pretreatment of adipocytes with the MAP kinase kinase inhibitor PD 98059 was without effect on the insulin-induced activatio n of PDE 3B. Furthermore, phorbol myristate acetate stimulation did no t result in phosphorylation/activation of PDE, 3B or activation of the kinase that phosphorylates PDE 3B. Using Mono Q and Superdex chromato graphy, the kinase that phosphorylates PDE 3B was found to co-elute wi th PKB, but not with p70 S6 kinase or MAP kinases. Furthermore, both P KB and the kinase that phosphorylates PDE 3B were found to translocate to membranes in response to peroxovanadate stimulation of adipocytes in a wortmannin-sensitive way. Whereas these results suggest that p70 S6 kinase and MAP kinases are not involved in the insulin-induced phos phorylation/activation of PDE 3B in rat adipocytes, they are consisten t with PKB being the kinase that phosphorylates PDE 3B.