Recurrent background mutations in WHI2 impair proteostasis and degradation of misfolded cytosolic proteins in Saccharomyces cerevisiae

Sophie A Comyn,Thibault Mayor,Stéphane Flibotte

doi:10.1038/s41598-017-04525-8

Abstract

Proteostasis promotes viability at both the cellular and organism levels by maintaining a functional proteome. This requires an intricate protein quality control (PQC) network that mediates protein folding by molecular chaperones and removes terminally misfolded proteins via the ubiquitin proteasome system and autophagy. How changes within the PQC network can perturb proteostasis and shift the balance between protein folding and proteolysis remain poorly understood. However, given that proteostasis is altered in a number of conditions such as cancer and ageing, it is critical that we identify the factors that mediate PQC and understand the interplay between members of the proteostatic network. In this study, we investigated the degradation of a thermally unstable cytosolic model substrate and identified a surprisingly high number of strains in the yeast knockout collection that displayed impaired turnover of the misfolded substrate. We found that this phenotype was caused by frequent background mutations in the general stress response gene WHI2. We linked this proteostatic defect to the lack of activity of the stress response transcription factor Msn2, potentially under conditions where the TOR pathway is active. Our results underscore how changes to the elaborate PQC network can perturb proteostasis and impair degradation of misfolded cytosolic proteins.

Highlights

Protein homeostasis is maintained by an extensive protein quality control (PQC) network that promotes and mediates protein folding by molecular chaperones and prevents the accumulation of misfolded proteins by targeting them for degradation via the ubiquitin proteasome system or autophagy[1]
We found that degradation of a model misfolded substrate was impaired in a surprisingly high number of strains from the yeast knockout (YKO) collection, which were associated to secondary mutations in the stress response gene WHI2
Ubiquitin ligase responsible for the degradation of the Guk1-7-GFP model substrate, we screened a collection of 70 non-essential E3 ligase deletion strains that were individually transformed with a plasmid encoding the Guk1-7-GFP fusion under the GPD promoter

Summary

Introduction

Protein homeostasis (proteostasis) is maintained by an extensive PQC network that promotes and mediates protein folding by molecular chaperones and prevents the accumulation of misfolded proteins by targeting them for degradation via the ubiquitin proteasome system or autophagy[1]. We found that degradation of a model misfolded substrate was impaired in a surprisingly high number of strains from the yeast knockout (YKO) collection, which were associated to secondary mutations in the stress response gene WHI2. We linked this proteostasis defect to a deficiency in the Msn2/Msn[4] transcription factor response that altered the cell’s capacity to adeptly degrade misfolded cytosolic proteins in conditions where the target of rapamycin (TOR) pathway was active

Methods

Results

Conclusion