Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan.
Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan.
Cell Rep. 2021 Jan 5;34(1):108599. doi: 10.1016/j.celrep.2020.108599.
Ribosome-associated quality control (RQC) relieves stalled ribosomes and eliminates potentially toxic nascent polypeptide chains (NCs) that can cause neurodegeneration. During RQC, RQC2 modifies NCs with a C-terminal alanine and threonine (CAT) tail. CAT tailing promotes ubiquitination of NCs for proteasomal degradation, while RQC failure in budding yeast disrupts proteostasis via CAT-tailed NC aggregation. However, the CAT tail and its cytotoxicity in mammals have remained largely uncharacterized. We demonstrate that NEMF, a mammalian RQC2 homolog, modifies translation products of nonstop mRNAs, major erroneous mRNAs in mammals, with a C-terminal tail mainly composed of alanine with several other amino acids. Overproduction of nonstop mRNAs induces NC aggregation and caspase-3-dependent apoptosis and impairs neuronal morphogenesis, which are ameliorated by NEMF depletion. Moreover, we found that homopolymeric alanine tailing at least partially accounts for CAT-tail cytotoxicity. These findings explain the cytotoxicity of CAT-tailed NCs and demonstrate physiological significance of RQC on proper neuronal morphogenesis and cell survival.
核糖体相关质量控制（RQC）可缓解核糖体停滞，并消除可能导致神经退行性变的有毒新生多肽链（NCs）。在 RQC 过程中，RQC2 用 C 端丙氨酸和苏氨酸（CAT）尾巴修饰 NCs。CAT 尾巴促进 NCs 的泛素化，从而进行蛋白酶体降解，而芽殖酵母中 RQC 的失败会通过 CAT 尾巴修饰的 NC 聚集破坏蛋白质稳态。然而，CAT 尾巴及其在哺乳动物中的细胞毒性在很大程度上仍未被阐明。我们证明，哺乳动物 RQC2 同源物 NEMF 用 C 端尾巴修饰无终止 mRNA 的翻译产物，无终止 mRNA 是哺乳动物中主要的错误 mRNA，C 端尾巴主要由丙氨酸和其他几种氨基酸组成。无终止 mRNA 的过量产生会诱导 NC 聚集和半胱天冬酶-3 依赖性细胞凋亡，并损害神经元形态发生，而 NEMF 缺失可改善这些现象。此外，我们发现同聚丙氨酸尾巴修饰至少部分解释了 CAT 尾巴的细胞毒性。这些发现解释了 CAT 尾巴修饰的 NCs 的细胞毒性，并证明了 RQC 在适当的神经元形态发生和细胞存活方面的生理意义。
