Cyclic nucleotide phosphodiesterase 3B is a downstream target of protein kinase B and may be involved in regulation of effects of protein kinase B on thymidine incorporation in FDCP2 cells

Wild-type (F/B), constitutively active (F/B*), and three kinase-inactive (F/Ba-, F/Bb(-), F/Bc(-)) forms of Akt/protein kinase B (PKB) were permanently overexpressed in FDCP2 cells. In the absence of insulin-like growth factor-1 (IGF-1), activities of PRE, cyclic nucleotide phosphodiesterase 3B (PDE3B), and PDE4 were similar in nontransfected FDCP2 cells, mock-transfected (FN) cells, and F/B and F/B- cells. In FN cells, IGF-1 increased PKB, PDE3B, and PDE4 activities similar to 2-fold. In F/B cells, IGF-1, in a wortmannin-sensitive manner, increased PKB activity similar to 10-fold and PDE3B phosphorylation and activity (similar to 4-fold), but increased PDE4 to the same extent as in FN cells. In F/B* cells, in the absence of IGF-1, PKB activity was markedly increased (similar to 10-fold) and PDE3B was phosphorylated and activated (3- to 4-fold); wortmannin inhibited these effects, In F/B* cells, IGF-1 had little further effect on PKB and activation/phosphorylation of PDE3B, In F/B- cells, IGF-1 activated PDE4, not PDE3B, suggesting that kinase-inactive PKB behaved as a dominant negative with respect to PDESB activation. Thymidine incorporation was greater in F/B* cells than in FN cells and was inhibited to a greater extent by PDE3 inhibitors than by rolipram, a PDE4 inhibitor. In F/B cells, IGF-1-induced phosphorylation of the apoptotic protein BAD was inhibited by the PDE3 inhibitor cilostamide, Activated PKB phosphorylated and activated rPDE3B in vitro. These results suggest that PDE3B, not PDE4, is a target of PKB and that activated PDE3B may regulate cAMP pools that modulate effects of PKB on thymidine incorporation and BAD phosphorylation in FDCP2 cells.