Identification of a WD40 repeat-containing isoform of PHIP as a novel regulator of β-cell growth and survival
Identification of a WD40 repeat-containing isoform of PHIP as a novel regulator of β-cell growth and survival
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DOI：
10.1128/mcb.02409-06
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发表时间：
2007-09-01
影响因子：
5.3
通讯作者：
Rozakis-Adcock, Maria
中科院分区：
文献类型：
--
作者：
Podcheko, Alexey;Northcott, Paul;Rozakis-Adcock, Maria
普列克底物蛋白同源结构域相互作用蛋白（PHIP）最初被鉴定为一个902个氨基酸（aa）的蛋白质，调节胰岛素受体刺激的GLUT 4易位在骨骼肌细胞。胰腺β-细胞的免疫印迹和免疫组织学分析揭示了206-kDa PHIP同种型仅限于细胞核的显著表达。在此，我们报告了这个较大的，1,821-aa的异构体，PHIP（PHIP 1），这是一种新的WD 40重复包含蛋白质的克隆。我们证明，PHIP 1过表达刺激胰岛素样生长因子1依赖和非依赖的β细胞增殖，这与细胞周期蛋白D2启动子的转录上调和细胞周期蛋白D2蛋白的积累相关的事件。INS-I细胞中PHIP 1的RNA干扰敲除消除了胰岛素受体底物2（IRS 2）介导的DNA合成，从而为PHIP 1在增强IRS 2依赖性信号传导反应中发挥特定作用，从而导致β细胞生长。最后，我们提供的证据表明，PHIP 1过表达阻断游离脂肪酸诱导的INS-1细胞凋亡，这是伴随着显着的磷酸蛋白激酶B（PKB）/AKT的激活和caspase-9和caspase-3裂解的抑制。我们的研究发现，PHIP 1对β细胞脂毒性的恢复作用可以通过显性负性PKB的过表达而减弱，这表明PKB在PHIP 1介导的细胞保护中起关键作用。总之，这些发现为PHIP 1作为β细胞功能的新型正调节因子提供了强有力的支持。我们认为，PHIP 1可能参与诱导长期基因表达程序，以促进β细胞有丝分裂和生存。
The pleckstrin homology domain-interacting protein (PHIP) was originally identified as a 902-amino-acid (aa) protein that regulates insulin receptor-stimulated GLUT4 translocation in skeletal-muscle cells. Immunoblotting and inummohistological analyses of pancreatic beta-cells reveal prominent expression of a 206-kDa PHIP isoform restricted to the nucleus. Herein, we report the cloning of this larger, 1,821-aa isoform, of PHIP (PHIP1), which represents a novel WD40 repeat-containing protein. We demonstrate that PHIP1 overexpression stimulates insulin-like growth factor 1-dependent and -independent proliferation of beta-cells, an event which correlates with transcriptional upregulation of the cyclin D2 promoter and the accumulation of cyclin D2 protein. RNA interference knockdown of PHIP1 in INS-I cells abrogates insulin receptor substrate 2 (IRS2)-mediated DNA synthesis, providing for a specific role for PHIP1 in the enhancement of IRS2-dependent signaling responses leading to beta-cell growth. Finally, we provide evidence that PHIP1 overexpression blocks free fatty acid-induced apoptosis in INS-1 cells, which is accompanied by marked activation of phosphoprotein kinase B (PKB)/AKT and the concomitant inhibition of caspase-9 and caspase-3 cleavage. Our finding that the restorative effect of PHIP1 on beta-cell lipotoxicity can be attenuated by the overexpression of dominant-negative PKB suggests a key role for PKB in PHIP1-mediated cytoprotection. Taken together, these findings provide strong support for PHIP1 as a novel positive regulator of beta-cell function. We suggest that PHIP1 may be involved in the induction of long-term gene expression programs to promote beta-cell mitogenesis and survival.