DENR promotes translation reinitiation via ribosome recycling to drive expression of oncogenes including ATF4

Jonathan Bohlen,Bernd Bukau,Kai Fenzl,Liza Harbrecht,Aurelio A Teleman,Katharina Clemm Von Hohenberg,Saioa Blanco,Günter Kramer

doi:10.1038/s41467-020-18452-2

Abstract

Translation efficiency varies considerably between different mRNAs, thereby impacting protein expression. Translation of the stress response master-regulator ATF4 increases upon stress, but the molecular mechanisms are not well understood. We discover here that translation factors DENR, MCTS1 and eIF2D are required to induce ATF4 translation upon stress by promoting translation reinitiation in the ATF4 5′UTR. We find DENR and MCTS1 are only needed for reinitiation after upstream Open Reading Frames (uORFs) containing certain penultimate codons, perhaps because DENR•MCTS1 are needed to evict only certain tRNAs from post-termination 40S ribosomes. This provides a model for how DENR and MCTS1 promote translation reinitiation. Cancer cells, which are exposed to many stresses, require ATF4 for survival and proliferation. We find a strong correlation between DENR•MCTS1 expression and ATF4 activity across cancers. Furthermore, additional oncogenes including a-Raf, c-Raf and Cdk4 have long uORFs and are translated in a DENR•MCTS1 dependent manner.

Highlights

Translation efficiency varies considerably between different mRNAs, thereby impacting protein expression
This was observed in Tma[22] (DENR) and Tma[64] double-mutant yeast, and it was ascribed to 80S ribosomes queuing in front of stalled posttermination 40S ribosomes[36], consistent with the known 40S recycling activity of DENRMCTS1 in vitro[35]
We find here that DENR and MCTS1 are required in human cells to induce translation of Activating Transcription Factor 4 (ATF4) via translation reinitiation in response to stress

Summary

Introduction

Translation efficiency varies considerably between different mRNAs, thereby impacting protein expression. To reinitiate translation after a uORF, 40S ribosomes need to release the deacylated tRNA but remain associated with the mRNA, recruit a new initiator tRNA, and resume scanning. These reinitiation processes are currently not well understood[7,8]. The best studied mRNA regulated by translation reinitiation in animals is Activating Transcription Factor 4 (ATF4), the main downstream effector of the integrated stress response (ISR)[14]. When exposed to stresses including proteotoxic stress, dsRNA, low amino acids, or heme deficiency, the kinases PERK, PKR, GCN2, or HRI, respectively, phosphorylate and inactivate eIF2α14,15 This shuts down global translation, while concomitantly activating translation of ATF4 via reinitiation. ATF4 is a developmental transcription factor required for proper formation of the hematopoietic system, brain, bone, and eye[17,18,19,20,21]

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