The translation initiation factor DAP5 promotes IRES-driven translation of p53 mRNA
The translation initiation factor DAP5 promotes IRES-driven translation of p53 mRNA
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DOI：
10.1038/onc.2012.626
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发表时间：
2014-01-30
期刊：
影响因子：
8
通讯作者：
Kimchi, A.
中科院分区：
文献类型：
--
作者：
Weingarten-Gabbay, S.;Khan, D.;Kimchi, A.
P53 mRNA的翻译调控可以决定P53与其N端截短异构体之间的比例，因此在决定P53调控的信号通路中具有重要作用。尽管它在细胞命运决定中的重要性已被反复证明，但人们对决定这一比例的调控机制知之甚少。位于5‘非编码区的两个内部核糖体进入位点(IRESS)和p53基因的编码序列分别驱动全长P53和Delta 40P53亚型的翻译。在这里，我们报告了DAP5，一种翻译启动因子，被证明可以积极地调节各种含有mRNAs的IRES的翻译，促进IRES驱动的P53 mRNA的翻译。当DAP5耗尽时，P53和Delta 40P53蛋白水平降低，对N端截短异构体的影响更大。利用驱动这两个IRES报告基因表达的双顺反子载体进行的功能分析表明，DAP5优先促进位于编码序列中的第二IRES的翻译。此外，携带第二个IRES的质粒表达的P53 mRNA在DAP5被敲除后选择性地转移到较轻的多聚体上。因此，Delta 40p53的蛋白水平和随后的14-3-3 sigma基因的转录激活显著减少，14-3-3 sigma基因是Delta 40p53的已知靶标。此外，我们在体外和体内结合研究中表明DAP5与P53 IRES元件相互作用，首次证明DAP5直接结合目标mRNA。因此，通过调节依赖于IRES的p53 mRNA的翻译，DAP5可能控制由单个mRNA编码的不同p53亚型之间的比率。
Translational regulation of the p53 mRNA can determine the ratio between p53 and its N-terminal truncated isoforms and therefore has a significant role in determining p53-regulated signaling pathways. Although its importance in cell fate decisions has been demonstrated repeatedly, little is known about the regulatory mechanisms that determine this ratio. Two internal ribosome entry sites (IRESs) residing within the 5'UTR and the coding sequence of p53 mRNA drive the translation of full-length p53 and Delta 40p53 isoform, respectively. Here, we report that DAP5, a translation initiation factor shown to positively regulate the translation of various IRES containing mRNAs, promotes IRES-driven translation of p53 mRNA. Upon DAP5 depletion, p53 and Delta 40p53 protein levels were decreased, with a greater effect on the N-terminal truncated isoform. Functional analysis using bicistronic vectors driving the expression of a reporter gene from each of these two IRESs indicated that DAP5 preferentially promotes translation from the second IRES residing in the coding sequence. Furthermore, p53 mRNA expressed from a plasmid carrying this second IRES was selectively shifted to lighter polysomes upon DAP5 knockdown. Consequently, Delta 40p53 protein levels and the subsequent transcriptional activation of the 14-3-3 sigma gene, a known target of Delta 40p53, were strongly reduced. In addition, we show here that DAP5 interacts with p53 IRES elements in in vitro and in vivo binding studies, proving for the first time that DAP5 directly binds a target mRNA. Thus, through its ability to regulate IRES-dependent translation of the p53 mRNA, DAP5 may control the ratio between different p53 isoforms encoded by a single mRNA.