Ribosomal protein S7 ubiquitination during ER stress in yeast is associated with selective mRNA translation and stress outcome

Yasuko Matsuki,Toshifumi Inada,Yoshitaka Matsuo,Nicholas T Ingolia,Yu Nakano,Tohru Yoshihisa,Keiji Tanaka,Hideyuki Yoko,Tsuyoshi Udagawa,Yasushi Saeki,Sihan Li,Shintaro Iwasaki

doi:10.1038/s41598-020-76239-3

Abstract

eIF2α phosphorylation-mediated translational regulation is crucial for global translation repression by various stresses, including the unfolded protein response (UPR). However, translational control during UPR has not been demonstrated in yeast. This study investigated ribosome ubiquitination-mediated translational controls during UPR. Tunicamycin-induced ER stress enhanced the levels of ubiquitination of the ribosomal proteins uS10, uS3 and eS7. Not4-mediated monoubiquitination of eS7A was required for resistance to tunicamycin, whereas E3 ligase Hel2-mediated ubiquitination of uS10 was not. Ribosome profiling showed that the monoubiquitination of eS7A was crucial for translational regulation, including the upregulation of the spliced form of HAC1 (HAC1i) mRNA and the downregulation of Histidine triad NucleoTide-binding 1 (HNT1) mRNA. Downregulation of the deubiquitinating enzyme complex Upb3-Bre5 increased the levels of ubiquitinated eS7A during UPR in an Ire1-independent manner. These findings suggest that the monoubiquitination of ribosomal protein eS7A plays a crucial role in translational controls during the ER stress response in yeast.

Highlights

The protein folding capacity of cells is important for maintaining endoplasmic reticulum (ER) homeostasis
In contrast to not4∆ and the eS7-4KR mutant, the hel2∆ mutant did not show sensitivity to Tm (Fig. 1b). These results suggest that Not4-mediated monoubiquitination of the ribosomal protein eS7A is indispensable for cell survival under ER stress conditions, whereas Hel2-mediated polyubiquitination of eS7A is not
The findings of this study indicate that ribosome eS7 monoubiquitination is required for translational controls during ER stress responses in yeast

Summary

Introduction

The protein folding capacity of cells is important for maintaining endoplasmic reticulum (ER) homeostasis. Not4-mediated monoubiquitinated eS7A is required for translational controls in the UPR in yeast. (b) The Not[4] ubiquitination of ribosomal protein eS7A is crucial for UPR in yeast. ZNF598, the mammalian homologue of Hel[2], ubiquitinates the ribosomal proteins eS10 at K138/K139 and uS10 at K4/K8, thereby inducing translational arrest and RQC triggered by poly-lysine sequences in m RNA25–27. Ribosome profiling showed that ubiquitination of eS7A was required for translational controls during the UPR. These findings indicate that Not4-mediated monoubiquitination of eS7A is essential for controlling the translation of specific mRNAs during the ER stress response, including through the upregulation of HAC1i mRNA and the downregulation of HNT1 mRNA

Methods

Results

Conclusion