Intracellular Shuttling and Mitochondrial Function of Thioredoxin-interacting Protein
Intracellular Shuttling and Mitochondrial Function of Thioredoxin-interacting Protein
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DOI：
10.1074/jbc.m109.034421
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发表时间：
2010-02-05
影响因子：
4.8
通讯作者：
Shalev, Anath
中科院分区：
文献类型：
--
作者：
Saxena, Geetu;Chen, Junqin;Shalev, Anath
硫氧还蛋白相互作用蛋白TXNIP是一种普遍表达的氧化还原蛋白，可促进细胞凋亡。最近，我们发现TXNIP缺乏通过抑制β细胞凋亡和维持胰腺β细胞质量来预防1型和2型糖尿病，表明TXNIP在β细胞生物学中起关键作用。然而，关于TXNIP的细胞内定位和功能知之甚少，尽管TXNIP被认为是细胞质蛋白，但我们在β细胞中的免疫组织化学研究令人惊讶地揭示了TXNIP的核定位，这表明TXNIP可能在细胞内穿梭。使用免疫组织化学/共聚焦成像和细胞分级/免疫共沉淀，我们发现，在生理条件下，TXNIP主要定位于胰腺β细胞的细胞核中，而氧化应激导致TXNIP穿梭进入线粒体。在线粒体中，TXNIP结合并氧化Trx 2，从而减少Trx 2与ASK 1的结合，并允许ASK 1磷酸化/活化，导致诱导细胞色素c释放和caspase-3裂解的线粒体凋亡途径。TXNIP过表达和Trx 2（但不是胞质Trx 1）沉默模拟这些效果。因此，我们发现TXNIP穿梭于亚细胞区室之间以响应氧化应激，并鉴定了一种新的氧化还原敏感的线粒体TXNIP-Trx 2-ASK 1信号级联。
The thioredoxin-interacting protein TXNIP is a ubiquitously expressed redox protein that promotes apoptosis. Recently, we found that TXNIP deficiency protects against type 1 and 2 diabetes by inhibiting beta cell apoptosis and maintaining pancreatic beta cell mass, indicating that TXNIP plays a key role in beta cell biology. However, very little is known about the intracellular localization and function of TXNIP, and although TXNIP has been thought to be a cytoplasmic protein, our immunohistochemistry studies in beta cells surprisingly revealed a nuclear TXNIP localization, suggesting that TXNIP may shuttle within the cell. Using immunohistochemistry/confocal imaging and cell fractionation/co-immunoprecipitation, we found that, under physiological conditions, TXNIP is localized primarily in the nucleus of pancreatic beta cells, whereas oxidative stress leads to TXNIP shuttling into the mitochondria. In mitochondria, TXNIP binds to and oxidizes Trx2, thereby reducing Trx2 binding to ASK1 and allowing for ASK1 phosphorylation/activation, resulting in induction of the mitochondrial pathway of apoptosis with cytochrome c release and caspase-3 cleavage. TXNIP overexpression and Trx2 (but not cytosolic Trx1) silencing mimic these effects. Thus, we discovered that TXNIP shuttles between subcellular compartments in response to oxidative stress and identified a novel redox-sensitive mitochondrial TXNIP-Trx2-ASK1 signaling cascade.