Easom R A, Landt M, Colca J R, Hughes J H, Turk J, McDaniel M
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Biol Chem. 1990 Sep 5;265(25):14938-46.
The influence of the insulin secretagogues, carbachol and glucose, on protein kinase C activation in isolated pancreatic islets has been examined by determination of the phosphorylation state of an endogenous 80-kDa protein substrate of protein kinase C. The islet 80-kDa protein was identified as the myristoylated alanine-rich C kinase substrate previously described (Stumpo D. J., Graff, J. M., Albert, K. A., Greengard, P., and Blackshear, P. J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 4012-4016) by immunoprecipitation studies. The muscarinic agonist, carbachol (500 microM), induced insulin secretion and a time-dependent increase in the phosphorylation state of this protein in islets. This phosphorylation was maximal (220 +/- 24% of control) at 5 min and was suppressed by the protein kinase C inhibitor, staurosporine. Concentrations of glucose (28 mM) which induce maximal insulin secretion did not induce a statistically significant increase in 80-kDa phosphorylation. The combination of carbachol and a submaximally stimulatory concentration of glucose (10 mM), when added simultaneously, exerted a marked synergistic effect on insulin secretion and a synergistic effect on the phosphorylation of the 80-kDa protein kinase C substrate. These data suggest that the activation of protein kinase C may play an important role in carbachol-induced insulin secretion and in the potentiation by carbachol of insulin secretion induced by glucose. However, the activation of protein kinase C does not appear to be a primary determinant of insulin secretion induced by glucose alone.
通过测定蛋白激酶C内源性80 kDa蛋白底物的磷酸化状态，研究了胰岛素促分泌剂、卡巴胆碱和葡萄糖对分离的胰岛中蛋白激酶C激活的影响。通过免疫沉淀研究，将胰岛80 kDa蛋白鉴定为先前描述的肉豆蔻酰化富含丙氨酸的C激酶底物（Stumpo D.J., Graff, J.M., Albert, K.A., Greengard, P., and Blackshear, P.J. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 4012 - 4016）。毒蕈碱激动剂卡巴胆碱（500 μM）诱导胰岛素分泌，并使胰岛中该蛋白的磷酸化状态随时间增加。这种磷酸化在5分钟时达到最大值（对照的220±24%），并被蛋白激酶C抑制剂星形孢菌素抑制。诱导最大胰岛素分泌的葡萄糖浓度（28 mM）并未诱导80 kDa磷酸化有统计学意义的增加。当同时添加卡巴胆碱和亚最大刺激浓度的葡萄糖（10 mM）时，对胰岛素分泌产生显著的协同作用，并对80 kDa蛋白激酶C底物的磷酸化产生协同作用。这些数据表明，蛋白激酶C的激活可能在卡巴胆碱诱导的胰岛素分泌以及卡巴胆碱对葡萄糖诱导的胰岛素分泌的增强作用中起重要作用。然而，蛋白激酶C的激活似乎不是单独由葡萄糖诱导的胰岛素分泌的主要决定因素。
