title: Beta-cell PDE3B regulates Ca2+-stimulated exocytosis of insulin.
abstract: cAMP signaling is important for the regulation of insulin secretion in pancreatic beta-cells. The level of intracellular cAMP is controlled through its production by adenylyl cyclases and its breakdown by cyclic nucleotide phosphodiesterases (PDEs). We have previously shown that PDE3B is involved in the regulation of nutrient-stimulated insulin secretion. Here, aiming at getting deeper functional insights, we have examined the role of PDE3B in the two phases of insulin secretion as well as its localization in the beta-cell. Depolarization-induced insulin secretion was assessed and in models where PDE3B was overexpressed [islets from transgenic RIP-PDE3B/7 mice and adenovirally (AdPDE3B) infected INS-1 (832/13) cells], the first phase of insulin secretion, occurring in response to stimulation with high K(+) for 5 min, was significantly reduced ( approximately 25% compared to controls). In contrast, in islets from PDE3B(-/-) mice the response to high K(+) was increased. Further, stimulation of isolated beta-cells from RIP-PDE3B/7 islets, using successive trains of voltage-clamped depolarizations, resulted in reduced Ca(2+)-triggered first phase exocytotic response as well as reduced granule mobilization-dependent second phase, compared to wild-type beta-cells. Using sub-cellular fractionation, confocal microscopy and transmission electron microscopy of isolated mouse islets and INS-1 (832/13) cells, we show that endogenous and overexpressed PDE3B is localized to insulin granules and plasma membrane. We conclude that PDE3B, through hydrolysis of cAMP in pools regulated by Ca(2+), plays a regulatory role in depolarization-induced insulin secretion and that the enzyme is associated with the exocytotic machinery in beta-cells.
authors: Department of Experimental Medical Science, Biomedical Center C11, Lund University, SE-221 84 Lund, Sweden. Helena.Walz@med.lu.se
authors: Helena A
authors: HA
authors: Walz
authors: Nils
authors: N
authors: Wierup
authors: Jenny
authors: J
authors: Vikman
authors: Vincent C
authors: VC
authors: Manganiello
authors: Eva
authors: E
authors: Degerman
authors: Lena
authors: L
authors: Eliasson
authors: Lena Stenson
authors: LS
authors: Holst
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D005089:Exocytosis / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D011188:Potassium / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D022142:Secretory Vesicles / Q000187:drug effects; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology
chemical_list: D007328:Insulin; D001120:Arginine; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; C517291:PDE3B protein, human; C517293:Pde3b protein, mouse; D011188:Potassium; D002118:Calcium