Finlin Brian S, Mosley Amber L, Crump Shawn M, Correll Robert N, Ozcan Sabire, Satin Jonathan, Andres Douglas A
Department of Molecular and Cellular Biochemistry, University of Kentucky, College of Medicine, Lexington, Kentucky 40536, USA.
J Biol Chem. 2005 Dec 23;280(51):41864-71. doi: 10.1074/jbc.M414261200. Epub 2005 Feb 22.
Voltage-dependent calcium (Ca2+) channels are involved in many specialized cellular functions and are controlled by a diversity of intracellular signals. Recently, members of the RGK family of small GTPases (Rem, Rem2, Rad, Gem/Kir) have been identified as novel contributors to the regulation of L-type calcium channel activity. In this study, microarray analysis of the mouse insulinoma MIN6 cell line revealed that the transcription of Rem2 gene is strongly induced by exposure to high glucose, which was confirmed by real-time reverse transcriptase-PCR and RNase protection analysis. Because elevation of intracellular Ca2+ in pancreatic beta-cells is essential for insulin secretion, we tested the hypothesis that Rem2 attenuates Ca2+ currents to regulate insulin secretion. Co-expression of Rem2 with CaV 1.2 or CaV1.3 L-type Ca + channels in a heterologous expression system completely inhibits de novo Ca2+ current expression. In addition, ectopic overexpression of Rem2 both inhibited L-type Ca2+ channel activity and prevented glucose-stimulated insulin secretion in pancreatic beta-cell lines. Co-immunoprecipitation studies demonstrate that Rem2 associates with a variety of CaVbeta subunits. Importantly, surface biotinylation studies demonstrate that the membrane distribution of Ca2+ channels was not reduced at a time when channel activity was potently inhibited by Rem2 expression, indicating that Rem2 modulates channel function without interfering with membrane trafficking. Taken together, these data suggest that inhibition of L-type Ca2+ channels by Rem2 signaling may represent a new and potentially important mechanism for regulating Ca2+-triggered exocytosis in hormone-secreting cells, including insulin secretion in pancreatic beta-cells.
电压依赖性钙（Ca2+）通道参与多种特殊的细胞功能，并受多种细胞内信号的调控。最近，小GTP酶RGK家族成员（Rem、Rem2、Rad、Gem/Kir）已被确定为L型钙通道活性调节的新因子。在本研究中，对小鼠胰岛素瘤MIN6细胞系进行微阵列分析发现，高糖刺激可强烈诱导Rem2基因的转录，实时逆转录聚合酶链反应和核糖核酸酶保护分析证实了这一点。由于胰腺β细胞内Ca2+浓度升高对胰岛素分泌至关重要，我们检验了Rem2通过减弱Ca2+电流来调节胰岛素分泌的假说。在异源表达系统中，Rem2与CaV 1.2或CaV1.3 L型Ca+通道共表达可完全抑制新生成的Ca2+电流表达。此外，Rem2异位过表达既抑制了L型Ca2+通道活性，又阻止了胰腺β细胞系中葡萄糖刺激的胰岛素分泌。免疫共沉淀研究表明，Rem2与多种CaVβ亚基相关联。重要的是，表面生物素化研究表明，在Rem2表达强烈抑制通道活性时，Ca2+通道的膜分布并未减少，这表明Rem2在不干扰膜转运的情况下调节通道功能。综上所述，这些数据表明，Rem2信号通路对L型Ca2+通道的抑制可能代表了一种新的、潜在的重要机制，用于调节激素分泌细胞中Ca2+触发的胞吐作用，包括胰腺β细胞中的胰岛素分泌。
