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Grr1-mediated Ubp3 degradation is crucial for HAC1 mRNA translation and unfolded stress response in yeast [Riboseq]

ABSTRACT: Ribosome ubiquitination induced by ribosome stalling is crucial for quality control pathways targeting mRNA, nascent polypeptides, and non-functional ribosomes. Besides quality control, Not4-mediated monoubiquitination of eS7A is crucial for the efficient translation of HAC1i mRNA in the unfolded protein response (UPR). In this study, we identified a novel E3 ligase, Grr1, an F-box protein component of the SCF ubiquitin ligase complex that is involved in Ubp3 degradation thereby HAC1i mRNA translation. Grr1 degrades Ubp3, a deubiquitinating enzyme of eS7A, under ER stress, thereby increasing eS7A ubiquitination, which facilitates HAC1i translation. Translation of HAC1i mRNA requires Grr1 and eS7 ubiquitination regardless of ER stress. ER stress-specific expression of Hac1 protein is ensured by the multi-step regulation of HAC1u mRNA, including localization on the ER membrane and stress-mediated splicing. Translation of HAC1i mRNA in UPR requires Grr1-mediated eS7 ubiquitination. More importantly, exon 1 of the HAC1i mRNA is crucial for translation activation by eS7 ubiquitination. Collectively, we propose that Grr1 upregulates eS7A monoubiquitination, thereby HAC1i translation and plays a crucial role in UPR.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE260736 | GEO | 2025/02/13

REPOSITORIES: GEO

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Project description:Disruptions of protein homeostasis in the endoplasmic reticulum (ER) elicit activation of the unfolded protein response (UPR), a translation- and transcription-coupled proteostatic stress response pathway. The primary translational control arm of the UPR is initiated by the PERK-dependent phosphorylation of eIF2Î±, leading to a large-scale reprogramming of translation and subsequent activation of an ATF4-mediated transcriptional program. It has remained challenging, however, to accurately evaluate the contribution of each component of the eIF2Î±/ATF4 pathway to the remodelling of transcription and translation. Here, we have used mouse embryonic fibroblasts containing either a knock-in of the non-phosphorylatable eIF2Î± S51A mutant or knock-out for ATF4 by ribosome profiling and mRNA-seq to define the specific contributions of eIF2Î± phosphoryation and ATF4 in controlling the translational and transcriptional components of the UPR. These studies show that the transcriptional and translational targets of each P-eIF2Î±, ATF4, and the other UPR gene expression programs overlapped extensively, leading to a core set of UPR genes whose robust expression in response to ER stress is driven by multiple mechanisms. The identification of other, more factor-specific targets illustrated the potential for functional specialization of the UPR. As the UPR progressed temporally, cells employed distinct combinations of transcriptional and translational mechanisms, initiated by different factors, to adapt to ongoing stress. These effects were accompanied by a buffering effect where changes in mRNA levels were coupled to opposing changes in ribosome loading, a property which makes cooperation between transcription and translation essential to confer robust protein expression. Translational analysis by ribosome profiling and mRNA-seq of PERK pathways mutants during the UPR. Mouse embryonic fibroblasts (MEFs) lacking components of the PERK pathway (eIF2a phosphorylation and ATF4) were subjected to ER stress and analyzed by ribosome profiling.

Project description:Disruption of protein folding in the endoplasmic reticulum triggers the Unfolded Protein Response (UPR), a transcriptional and translational control network designed to restore protein homeostasis. Central to the UPR is PERK phosphorylation of the alpha subunit of eIF2 (eIF2~P), which represses global translation coincident with preferential translation of mRNAs, such as ATF4 and CHOP, that serve to implement the UPR transcriptional regulation. In this study, we used sucrose gradient ultracentrifugation and a genome-wide microarray approach to measure changes in mRNA translation during ER stress. Our analysis suggests that translational efficiencies vary across a broad range during ER stress, with the majority of transcripts being either repressed or resistant to eIF2~P, while a notable cohort of key regulators are subject to preferential translation. From this latter group, we identify IBTKa as being subject to both translation and transcriptional induction during eIF2~P in both cell lines and a mouse model of ER stress. Translational regulation of IBTKalpha mRNA involves the stress-induced relief of two inhibitory uORFs in the 5'-leader of the transcript. Depletion of IBTKalpha by shRNA reduced viability of cultured cells coincident with increased caspase 3/7 cleavage, suggesting that IBTKalpha is a key regulator in determining cell fate during the UPR. We used a genome-wide microarray approach to determine how individual mRNAs were differentially translated during endoplasmic reticulum stress. A microarray analysis from our laboratory identified gene transcripts suggested to be under translation control in mouse embryonic fibroblast (MEF) cells following a 6 hour treatment with thapsigargin, a potent inducer of ER stress, or no stress. The mRNAs were separated by sucrose gradient analyses to yield three fractions, those transcripts associated with large polysomes (?4 ribosomes per mRNA), those associated with monosome, disomes, or trisomes, and those fractionated at the top of the gradient with free ribosomes. RNA was extracted from sucrose gradients corresponding to these fractions and hybridized on Affymetrix microarrays. In parallel, we also measured total levels for each gene transcript in the presence or absence of thapsigargin treatment to address transcription regulation coincident with translational control. Please note that the treatment plus fractionation based on association with different numbers of ribosomes did yield different populations of mRNAs, which resulted in considerable variation in normalized data across the samples.

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Grr1-mediated Ubp3 degradation is crucial for HAC1 mRNA translation and unfolded stress response in yeast [Riboseq]

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