Differential effects of Ydj1 and Sis1 on Hsp70-mediated clearance of stress granules in Saccharomyces cerevisiae.

Robert W Walters,Denise Muhlrad,Roy Parker,Jennifer Garcia

doi:10.1261/rna.053116.115

Robert W Walters, Denise Muhlrad + Show 2 more

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https://doi.org/10.1261/rna.053116.115

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Abstract

Stress granules and P-bodies are conserved assemblies of nontranslating mRNAs in eukaryotic cells that can be related to RNA–protein aggregates found in some neurodegenerative diseases. Herein, we examine how the Hsp70/Hsp40 protein chaperones affected the assembly and disassembly of stress granules and P-bodies in yeast. We observed that Hsp70 and the Ydj1 and Sis1 Hsp40 proteins accumulated in stress granules and defects in these proteins led to decreases in the disassembly and/or clearance of stress granules. We observed that individual Hsp40 proteins have different effects on stress granules with defects in Ydj1 leading to accumulation of stress granules in the vacuole and limited recovery of translation following stress, which suggests that Ydj1 promotes disassembly of stress granules to promote translation. In contrast, defects in Sis1 did not affect recovery of translation, accumulated cytoplasmic stress granules, and showed reductions in the targeting of stress granules to the vacuole. This demonstrates a new principle whereby alternative disassembly machineries lead to different fates of components within stress granules, thereby providing additional avenues for regulation of their assembly, composition, and function. Moreover, a role for Hsp70 and Hsp40 proteins in stress granule disassembly couples the assembly of these stress responsive structures to the proteostatic state of the cell.

Highlights

An emerging aspect of cytoplasmic mRNA biology is the formation of P-bodies and stress granules, which aggregate nontranslating mRNAs and RNA-binding proteins into large mRNP granules
To determine how Hsp70 function affects stress granules and P-bodies in yeast, we examined the dynamics of stress granules and P-bodies in strains defective in Hsp70 function
S. cerevisiae has four genes for cytoplasmic Hsp70 proteins. Two of these genes are constitutively expressed (SSA1 and SSA2) and two are induced by stress conditions (SSA3 and SSA4) (Werner-Washburne et al 1987). Since these proteins are largely redundant in their function, we examined stress granules and P-bodies in three strains (Werner-Washburne et al 1987; Hasin et al 2014): a wild-type strain, a triple mutant which retains Hsp70 function (SSA1 ssa2Δ ssa3Δ ssa4Δ), and a quadruple mutant where the remaining SSA1 gene is compromised with a temperature-sensitive allele (Becker et al 1996; Taxis et al 2003)

Summary

Introduction

An emerging aspect of cytoplasmic mRNA biology is the formation of P-bodies and stress granules, which aggregate nontranslating mRNAs and RNA-binding proteins into large mRNP granules. The prion-related domains on RNA-binding proteins have been shown to form homotypic and heterotypic higher order assemblies in vitro (Alberti et al 2009; Guo et al 2011; Kato et al 2012).

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