The role of the cyclic GMP-inhibited cyclic AMP-specific phosphodiesterase(PDE3) in regulating clonal BRIN-BD11 insulin secreting cell survival

We report here that the cyclic GMP-inhibited cyclic AMP specific phosphodie sterase (PDE3B) is expressed as a membrane-bound protein in clonal insulin- secreting BRIN-BD11 cells. This was shown using SKF94836 (PDE3 inhibitor) w hich maximally inhibited membrane-bound cyclic AMP PDE activity by similar to 25-30% and by RT-PCR. We also demonstrated that insulin growth factor-1 (IGF-1) activates PDE3B in BRIN-BD11 cells. We therefore evaluated the role of phosphoinositide 3-kinase (PI3K) and p42/p44 mitogen-activated protein kinase (p42/p44 MAPK) pathways in regulating this enzyme. We report here th at the PI3K inhibitor, wortmannin, prevented the IGF-1-dependent stimulatio n of PDE3B activity. In contrast, the inhibitor of MEK-1 activation, PD0980 59 (which reduced IGF-1-stimulated p42/p44 MAPK phosphorylation), had no ef fect on PDE3B activation. Furthermore, IGF-1-dependent stimulation of p42/p 44 MAPK and PDE3B was abolished in serum-deprived cells and this was associ ated with apoptosis. We propose that the deregulation of the PI3K/PDE3B pat hway might result in increased intracellular cyclic AMP accumulation, which promotes apoptosis. This was supported by the finding that the adenylyl cy clase activator, forskolin, also induced apoptosis. Finally, we found that orthovanadate (a phosphotyrosine phosphatase inhibitor) fully restored the activation of p42/p44 MAPK in serum-deprived cells, but had only a small ef fect on PDE activity. This confirmed that p42/p44 MAPK is on a separate pat hway to PDE3B. Therefore, IGF-1-dependent regulation of PDE3B may be linked to cell survival through PI3K and not p42/p44 MAPK. (C) 2000 Elsevier Scie nce Inc. All rights reserved.