Subcellular relocalization of a trans-acting factor regulates XIAP IRES-dependent translation
Subcellular relocalization of a trans-acting factor regulates XIAP IRES-dependent translation
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DOI：
10.1091/mbc.e06-06-0515
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发表时间：
2007-04-01
影响因子：
3.3
通讯作者：
Holcik, Martin
中科院分区：
文献类型：
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作者：
Lewis, Stephen M.;Veyrier, Anne;Holcik, Martin
X连锁的凋亡抑制剂（XIAP）的翻译通过内部核糖体进入位点（IRES）介导的起始进行，这是一个生理学上重要的过程，因为XIAP表达对于在受损的帽依赖性翻译（例如细胞应激）条件下的细胞存活是必不可少的。内部启动的调节需要IRES反式作用因子（ITAFs）与IRES元件的相互作用。我们使用RNA亲和层析来鉴定XIAP ITAF并分离异质核核糖核蛋白A1（hnRNP A1）。我们发现hnRNP A1在体外和体内都与XIAP TRES RNA相互作用，并且hnRNP A1负调节XIAP TRES活性。此外，XIAP IRES依赖的翻译显着减少时，hnRNP A1积累在细胞质中。渗透压休克，一种引起hnRNP A1细胞质积累的细胞应激，也导致XIAP水平降低，其通过敲低hnRNP A1表达而被消除。这些结果表明，hnRNP A1的亚细胞定位是其负调控XIAP IRES活性的能力的重要决定因素，表明ITAF的亚细胞分布在调节IRES依赖性翻译中起着关键作用。我们的研究结果表明，细胞质hnRNP A1是XIAP IRES依赖性翻译的负调节因子，表明这种蛋白质的细胞质形式具有新的功能。
Translation of the X-linked inhibitor of apoptosis (XIAP) proceeds by internal ribosome entry site (IRES)-mediated initiation, a process that is physiologically important because XIAP expression is essential for cell survival under conditions of compromised cap-dependent translation, such as cellular stress. The regulation of internal initiation requires the interaction of IRES trans-acting factors (ITAFs) with the IRES element. We used RNA-affinity chromatography to identify XIAP ITAFs and isolated the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). We find that hnRNP A1 interacts with XIAP TRES RNA both in vitro and in vivo and that hnRNP A1 negatively regulates XIAP TRES activity. Moreover, XIAP IRES-dependent translation is significantly reduced when hnRNP A1 accumulates in the cytoplasm. Osmotic shock, a cellular stress that causes cytoplasmic accumulation of hnRNP A1, also leads to a decrease in XIAP levels that is abrogated by knockdown of hnRNF A1 expression. These results suggest that the subcellular localization of hnRNP A1 is an important determinant of its ability to negatively regulate XIAP IRES activity, suggesting that the subcellular distribution of ITAFs plays a critical role in regulating IRES-dependent translation. Our findings demonstrate that cytoplasmic hnRNP A1 is a negative regulator of XIAP IRES-dependent translation, indicating a novel function for the cytoplasmic form of this protein.