Upf1 phosphorylation triggers translational repression during nonsense-mediated mRNA decay
Upf1 phosphorylation triggers translational repression during nonsense-mediated mRNA decay
复制标题
DOI：
10.1016/j.cell.2008.02.030
复制
发表时间：
2008-04-18
期刊：
影响因子：
64.5
通讯作者：
Maquat, Lynne E.
中科院分区：
文献类型：
--
作者：
Isken, Olaf;Kim, Yoon Ki;Maquat, Lynne E.
在哺乳动物细胞中，无义介导的 mRNA 衰减 (NMD) 通常要求翻译在首轮翻译期间在剪接后外显子连接复合物 (EJC) 的上游足够终止。随后 Upf1 与 EJC 的结合会触发 Upf1 磷酸化。我们提供的证据表明，在涉及翻译起始因子 eIF3 和 mRNA 衰减因子的步骤中，磷酸化 Upf1 在无义密码子识别后发挥作用。 Phospho-Upf1 直接与 eIF3 相互作用，并抑制 40S/Met-tRNAi(Met)/mRNA 依赖 eIF3 的转化为具有翻译能力的 80S/Met-tRNAi(Met)/mRNA 起始复合物，从而抑制持续的翻译起始。与磷酸化 Upf1 损害 eIF3 功能一致，NMD 无法检测到包含无义转录物的目标，这些转录物独立于来自 CrPV IRES 的 eIF3 启动翻译。越来越多的证据表明，翻译抑制是 mRNA 传递到降解机制之前的一个关键转变。我们的结果揭示了 NMD 过程中的一个关键步骤，将先锋翻译起始复合体转化为翻译受损的 mRNP。
In mammalian cells, nonsense-mediated mRNA decay (NMD) generally requires that translation terminates sufficiently upstream of a post-splicing exon junction complex (EJC) during a pioneer round of translation. The subsequent binding of Upf1 to the EJC triggers Upf1 phosphorylation. We provide evidence that phospho-Upf1 functions after nonsense codon recognition during steps that involve the translation initiation factor eIF3 and mRNA decay factors. Phospho-Upf1 interacts directly with eIF3 and inhibits the eIF3-dependent conversion of 40S/Met-tRNAi(Met)/mRNA to translationally competent 80S/Met-tRNAi(Met)/mRNA initiation complexes to repress continued translation initiation. Consistent with phospho-Upf1 impairing eIF3 function, NMD fails to detectably target nonsense-containing transcripts that initiate translation independently of eIF3 from the CrPV IRES. There is growing evidence that translational repression is a key transition that precedes mRNA delivery to the degradation machinery. Our results uncover a critical step during NMD that converts a pioneer translation initiation complex to a translationally compromised mRNP.