The Mitogen-Activated Protein Kinase Slt2 Regulates Nuclear Retention of Non-Heat Shock mRNAs during Heat Shock-Induced Stress

Abstract

Cellular adaptation to environmental stress conditions requires rapid and specific changes in gene expression. During heat shock, most polyadenylated mRNAs are retained in the nucleus, whereas the export of heat shock-induced mRNAs is allowed. Although essential mRNA export factors are known, the precise mechanism for regulating transport is not fully understood. Here we find that during heat shock in Saccharomyces cerevisiae, the mRNA-binding protein Nab2 is phosphorylated on threonine 178 and serine 180 by the mitogen-activated protein (MAP) kinase Slt2/Mpk1. Slt2 is required for nuclear poly(A⁺) mRNA accumulation upon heat shock, and thermotolerance is decreased in a nup42 nab2-T178A/S180A mutant. Coincident with phosphorylation, Nab2 and Yra1 colocalize in nuclear foci with Mlp1, a protein involved in mRNA retention. Nab2 nuclear focus formation and Nab2 phosphorylation are independent, suggesting that heat shock induces multiple cellular alterations that impinge upon transport efficiency. Under normal conditions, we find that the mRNA export receptor Mex67 and Nab2 directly interact. However, upon heat shock stress, Mex67 does not localize to the Mlp1 nuclear foci, and its association with Nab2 complexes is reduced. These results reveal a novel mechanism by which the MAP kinase Slt2 and Mlp1 control mRNA export factors during heat shock stress.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank Michael Rout and Marlene Oeffinger for sharing cell lysis and immunopurification protocols, John Aitchison for yeast plasmids, W. Hayes McDonald for phospho-proteomic and mass spectrometry analysis, Yingna Zhou, Laura Terry, and Ryan Baldridge for assistance with experiments, and members of the Wente laboratory for discussions.

This work was supported by grants from the National Institutes of Health: R01-GM51219 (S.R.W.), R01-GM058728-11 (A.H.C.), National Research Service Awards (NRSA) 5T32-GM008554 (S.R.C.), 5T32-CA009383 (E.J.T.), and 1F32-GM075459 (E.J.T.). Mass spectrometry data were acquired by the Vanderbilt Mass Spectrometry Research Center (supported by NIH/NCI 3P30 CA068485-13 Cancer Center support grant to Vanderbilt University).