Widenmaier Scott B, Ao Ziliang, Kim Su-Jin, Warnock Garth, McIntosh Christopher H S
Department of Cellular and Physiological Sciences and the Diabetes Research Group, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
J Biol Chem. 2009 Oct 30;284(44):30372-82. doi: 10.1074/jbc.M109.060178. Epub 2009 Sep 10.
Glucose-dependent insulinotropic polypeptide (GIP) potentiates glucose-stimulated insulin secretion, insulin biosynthesis, and beta-cell proliferation and survival. In previous studies GIP was shown to promote beta-cell survival by modulating the activity of multiple signaling modules and regulating gene transcription of pro- and anti-apoptotic bcl-2 family proteins. We have now evaluated the mechanisms by which GIP regulates the dynamic interactions between cytoplasmic bcl-2 family members and the mitochondria in INS-1 cells during apoptosis induced by treatment with staurosporine (STS), an activator of the mitochondria-mediated apoptotic pathway. STS induced translocation of bad and bimEL, activation of mitochondrial bax, release of mitochondrial cytochrome c, cleavage of caspase-3, and apoptosis. Each response was significantly diminished by GIP. Using selective enzyme inhibitors, overexpression of dominant-negative Akt, and Akt siRNA, it was demonstrated that GIP promoted beta-cell survival via Akt-dependent suppression of p38 MAPK and JNK and that combined inhibition was sufficient to explain the entire pro-survival responses to GIP during STS treatment. This signaling pathway also explained the pro-survival effects of GIP on INS-1 cells exposed to two other promoters of stress: thapsigargin (endoplasmic reticulum stress) and etoposide (genotoxic stress). Importantly, we discovered that GIP suppressed p38 MAPK and JNK via Akt-mediated changes in the phosphorylation state of the apoptosis signal-regulating kinase 1 in INS-1 cells and human islets, resulting in inhibition of its activity. Inhibition of apoptosis by GIP is therefore mediated via a key pathway involving Akt-dependent inhibition of apoptosis signal-regulating kinase 1, which subsequently prevents the pro-apoptotic actions of p38 MAPK and JNK.
葡萄糖依赖性促胰岛素多肽（GIP）可增强葡萄糖刺激的胰岛素分泌、胰岛素生物合成以及β细胞增殖与存活。在先前的研究中，GIP被证明可通过调节多个信号模块的活性以及调控促凋亡和抗凋亡bcl-2家族蛋白的基因转录来促进β细胞存活。我们现在评估了在使用星形孢菌素（STS，一种线粒体介导的凋亡途径激活剂）处理诱导INS-1细胞凋亡过程中，GIP调节细胞质bcl-2家族成员与线粒体之间动态相互作用的机制。STS诱导了bad和bimEL的易位、线粒体bax的激活、线粒体细胞色素c的释放、caspase-3的切割以及凋亡。GIP可显著减轻每种反应。通过使用选择性酶抑制剂、显性负性Akt的过表达以及Akt小干扰RNA，证明了GIP通过Akt依赖的p38丝裂原活化蛋白激酶（MAPK）和应激活化蛋白激酶（JNK）的抑制来促进β细胞存活，并且联合抑制足以解释在STS处理期间对GIP的整个促存活反应。该信号通路也解释了GIP对暴露于另外两种应激诱导剂的INS-1细胞的促存活作用：毒胡萝卜素（内质网应激）和依托泊苷（遗传毒性应激）。重要的是，我们发现GIP通过Akt介导的INS-1细胞和人胰岛中凋亡信号调节激酶1磷酸化状态的变化来抑制p38 MAPK和JNK，从而导致其活性受到抑制。因此，GIP对凋亡的抑制是通过一条关键途径介导的，该途径涉及Akt依赖的凋亡信号调节激酶1的抑制，随后可防止p38 MAPK和JNK的促凋亡作用。
