Hong Sungki, Freeberg Mallory A, Han Ting, Kamath Avani, Yao Yao, Fukuda Tomoko, Suzuki Tsukasa, Kim John K, Inoki Ken
Life Sciences Institute, University of Michigan, Ann Arbor, United States.
Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, United States.
Elife. 2017 Jun 26;6:e25237. doi: 10.7554/eLife.25237.
The RNA binding protein, LARP1, has been proposed to function downstream of mTORC1 to regulate the translation of 5'TOP mRNAs such as those encoding ribosome proteins (RP). However, the roles of LARP1 in the translation of 5'TOP mRNAs are controversial and its regulatory roles in mTORC1-mediated translation remain unclear. Here we show that LARP1 is a direct substrate of mTORC1 and Akt/S6K1. Deep sequencing of LARP1-bound mRNAs reveal that non-phosphorylated LARP1 interacts with both 5' and 3'UTRs of RP mRNAs and inhibits their translation. Importantly, phosphorylation of LARP1 by mTORC1 and Akt/S6K1 dissociates it from 5'UTRs and relieves its inhibitory activity on RP mRNA translation. Concomitantly, phosphorylated LARP1 scaffolds mTORC1 on the 3'UTRs of translationally-competent RP mRNAs to facilitate mTORC1-dependent induction of translation initiation. Thus, in response to cellular mTOR activity, LARP1 serves as a phosphorylation-sensitive molecular switch for turning off or on RP mRNA translation and subsequent ribosome biogenesis.
RNA结合蛋白LARP1被认为在mTORC1下游发挥作用，以调节5'TOP mRNA（如编码核糖体蛋白（RP）的mRNA）的翻译。然而，LARP1在5'TOP mRNA翻译中的作用存在争议，其在mTORC1介导的翻译中的调节作用仍不清楚。在这里，我们表明LARP1是mTORC1和Akt/S6K1的直接底物。对LARP1结合的mRNA进行深度测序发现，未磷酸化的LARP1与RP mRNA的5'和3'非翻译区（UTR）相互作用并抑制其翻译。重要的是，mTORC1和Akt/S6K1对LARP1的磷酸化使其从5'UTR解离，并解除其对RP mRNA翻译的抑制活性。同时，磷酸化的LARP1在具有翻译活性的RP mRNA的3'UTR上搭建mTORC1，以促进mTORC1依赖的翻译起始诱导。因此，响应细胞的mTOR活性，LARP1作为一种磷酸化敏感的分子开关，用于开启或关闭RP mRNA翻译及随后的核糖体生物合成。
