Han P, Werber J, Surana M, Fleischer N, Michaeli T
Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 1999 Aug 6;274(32):22337-44. doi: 10.1074/jbc.274.32.22337.
To understand the role cAMP phosphodiesterases (PDEs) play in the regulation of insulin secretion, we analyzed cyclic nucleotide PDEs of a pancreatic beta-cell line and used family and isozyme-specific PDE inhibitors to identify the PDEs that counteract glucose-stimulated insulin secretion. We demonstrate the presence of soluble PDE1C, PDE4A and 4D, a cGMP-specific PDE, and of particulate PDE3, activities in betaTC3 insulinoma cells. Selective inhibition of PDE1C, but not of PDE4, augmented glucose-stimulated insulin secretion in a dose-dependent fashion thus demonstrating that PDE1C is the major PDE counteracting glucose-dependent insulin secretion from betaTC3 cells. In pancreatic islets, inhibition of both PDE1C and PDE3 augmented glucose-dependent insulin secretion. The PDE1C of betaTC3 cells is a novel isozyme possessing a K(m) of 0.47 microM for cAMP and 0.25 microM for cGMP. The PDE1C isozyme of betaTC3 cells is sensitive to 8-methoxymethyl isobutylmethylxanthine and zaprinast (IC(50) = 7.5 and 4.5 microM, respectively) and resistant to vinpocetine (IC(50) > 100 microM). Increased responsiveness of PDE1C activity to calcium/calmodulin is evident upon exposure of cells to glucose. Enhanced cAMP degradation by PDE1C, due to increases in its responsiveness to calcium/calmodulin and in intracellular calcium, constitutes a glucose-dependent feedback mechanism for the control of insulin secretion.
为了解环磷酸腺苷磷酸二酯酶（PDEs）在胰岛素分泌调节中所起的作用，我们分析了一种胰腺β细胞系中的环核苷酸PDEs，并使用家族特异性和同工酶特异性PDE抑制剂来确定那些能对抗葡萄糖刺激的胰岛素分泌的PDEs。我们证实在βTC3胰岛素瘤细胞中存在可溶性PDE1C、PDE4A和4D、一种cGMP特异性PDE以及颗粒性PDE3的活性。选择性抑制PDE1C而非PDE4，能以剂量依赖的方式增强葡萄糖刺激的胰岛素分泌，从而表明PDE1C是对抗βTC3细胞葡萄糖依赖性胰岛素分泌的主要PDE。在胰岛中，抑制PDE1C和PDE3均可增强葡萄糖依赖性胰岛素分泌。βTC3细胞的PDE1C是一种新型同工酶，对cAMP的K(m)为0.47微摩尔，对cGMP的K(m)为0.25微摩尔。βTC3细胞的PDE1C同工酶对8-甲氧基甲基异丁基甲基黄嘌呤和扎普司特敏感（IC(50)分别为7.5和4.5微摩尔），对长春西汀耐药（IC(50)>100微摩尔）。当细胞暴露于葡萄糖时，PDE1C活性对钙/钙调蛋白的反应性增加明显。由于PDE1C对钙/钙调蛋白的反应性及细胞内钙增加，导致其对cAMP的降解增强，这构成了一种葡萄糖依赖性反馈机制，用于控制胰岛素分泌。
