Dai Feihan F, Zhang Yi, Kang Youhou, Wang Qinghua, Gaisano Herbert Y, Braunewell Karl-Heinz, Chan Catherine B, Wheeler Michael B
Departments of Physiology and Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Signal Transduction Research Group, Neuroscience Research Center of the Charité, Universitätsmedizin Berlin, 10117 Berlin, Germany.
J Biol Chem. 2006 Aug 4;281(31):21942-21953. doi: 10.1074/jbc.M512924200. Epub 2006 May 26.
Visinin-like protein-1 (VILIP-1) is a member of the neuronal Ca2+ sensor protein family that modulates Ca2+-dependent cell signaling events. VILIP-1, which is expressed primarily in the brain, increases cAMP formation in neural cells by modulating adenylyl cyclase, but its functional role in other tissues remains largely unknown. In this study, we demonstrate that VILIP-1 is expressed in murine pancreatic islets and beta-cells. To gain insight into the functions of VILIP-1 in beta-cells, we used both overexpression and small interfering RNA knockdown strategies. Overexpression of VILIP-1 in the MIN6 beta-cell line or isolated mouse islets had no effect on basal insulin secretion but significantly increased glucose-stimulated insulin secretion. cAMP accumulation was elevated in VILIP-1-overexpressing cells, and the protein kinase A inhibitor H-89 attenuated increased glucose-stimulated insulin secretion. Overexpression of VILIP-1 in isolated mouse beta-cells increased cAMP content accompanied by increased cAMP-responsive element-binding protein gene expression and enhanced exocytosis as detected by cell capacitance measurements. Conversely, VILIP-1 knockdown by small interfering RNA caused a reduction in cAMP accumulation and produced a dramatic increase in preproinsulin mRNA, basal insulin secretion, and total cellular insulin content. The increase in preproinsulin mRNA in these cells was attributed to enhanced insulin gene transcription. Taken together, we have shown that VILIP-1 is expressed in pancreatic beta-cells and modulates insulin secretion. Increased VILIP-1 enhanced insulin secretion in a cAMP-associated manner. Down-regulation of VILIP-1 was accompanied by decreased cAMP accumulation but increased insulin gene transcription.
类视锥蛋白样蛋白-1（VILIP-1）是神经元钙传感器蛋白家族的成员，可调节钙依赖性细胞信号转导事件。VILIP-1主要在大脑中表达，通过调节腺苷酸环化酶增加神经细胞中cAMP的形成，但其在其他组织中的功能作用仍 largely unknown。在本研究中，我们证明VILIP-1在小鼠胰岛和β细胞中表达。为了深入了解VILIP-1在β细胞中的功能，我们使用了过表达和小干扰RNA敲低策略。在MIN6β细胞系或分离的小鼠胰岛中过表达VILIP-1对基础胰岛素分泌没有影响，但显著增加了葡萄糖刺激的胰岛素分泌。在过表达VILIP-1的细胞中cAMP积累增加，蛋白激酶A抑制剂H-89减弱了葡萄糖刺激的胰岛素分泌增加。在分离的小鼠β细胞中过表达VILIP-1增加了cAMP含量，同时伴随着cAMP反应元件结合蛋白基因表达的增加以及通过细胞电容测量检测到的胞吐作用增强。相反，小干扰RNA敲低VILIP-1导致cAMP积累减少，并使胰岛素原前体mRNA、基础胰岛素分泌和细胞总胰岛素含量显著增加。这些细胞中胰岛素原前体mRNA的增加归因于胰岛素基因转录的增强。综上所述，我们表明VILIP-1在胰腺β细胞中表达并调节胰岛素分泌。VILIP-1增加以cAMP相关方式增强胰岛素分泌。VILIP-1的下调伴随着cAMP积累减少但胰岛素基因转录增加。
