Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
Graduate School for Cellular and Biomedical Sciences, University of Bern, Mittelstrasse 43, CH-3012 Bern, Switzerland.
Nucleic Acids Res. 2020 Oct 9;48(18):10259-10279. doi: 10.1093/nar/gkaa758.
To gain insight into the mechanistic link between translation termination and nonsense-mediated mRNA decay (NMD), we depleted the ribosome recycling factor ABCE1 in human cells, resulting in an upregulation of NMD-sensitive mRNAs. Suppression of NMD on these mRNAs occurs prior to their SMG6-mediated endonucleolytic cleavage. ABCE1 depletion caused ribosome stalling at termination codons (TCs) and increased ribosome occupancy in 3' UTRs, implying enhanced TC readthrough. ABCE1 knockdown indeed increased the rate of readthrough and continuation of translation in different reading frames, providing a possible explanation for the observed NMD inhibition, since enhanced readthrough displaces NMD activating proteins from the 3' UTR. Our results indicate that stalling at TCs triggers ribosome collisions and activates ribosome quality control. Collectively, we show that improper translation termination can lead to readthrough of the TC, presumably due to ribosome collisions pushing the stalled ribosomes into the 3' UTR, where it can resume translation in-frame as well as out-of-frame.
为了深入了解翻译终止与无义介导的 mRNA 降解（NMD）之间的机制联系，我们在人类细胞中耗尽核糖体回收因子 ABCE1，导致 NMD 敏感的 mRNA 上调。这些 mRNA 的 NMD 抑制发生在 SMG6 介导的内切酶切割之前。ABCE1 耗尽导致终止密码子（TC）处的核糖体停滞，并增加 3'UTR 中的核糖体占有率，暗示增强了 TC 通读。ABCE1 敲低确实增加了不同阅读框中转录通读和翻译的速率，为观察到的 NMD 抑制提供了可能的解释，因为增强的通读将 NMD 激活蛋白从 3'UTR 中置换出来。我们的结果表明，TC 处的停滞引发核糖体碰撞并激活核糖体质量控制。总的来说，我们表明不适当的翻译终止会导致 TC 的通读，这可能是由于核糖体碰撞将停滞的核糖体推向 3'UTR，从而可以在框架内以及框架外恢复翻译。
