Yeast Protein Phosphatase 2A-Cdc55 Regulates the Transcriptional Response to Hyperosmolarity Stress by Regulating Msn2 and Msn4 Chromatin Recruitment

Abstract

We have identified Cdc55, a regulatory B subunit of protein phosphatase 2A (PP2A), as an essential activating factor for stress gene transcription in Saccharomyces cerevisiae. The presence of PP2A-Cdc55 is required for full activation of the environmental stress response mediated by the transcription factors Msn2 and Msn4. We show that PP2A-Cdc55 contributes to sustained nuclear accumulation of Msn2 and Msn4 during hyperosmolarity stress. PP2A-Cdc55 also enhances Msn2-dependent transactivation, required for extended chromatin recruitment of the transcription factor. We analyzed a possible direct regulatory role for PP2A-Cdc55 on the phosphorylation status of Msn2. Detailed mass spectrometric and genetic analysis of Msn2 showed that stress exposure causes immediate transient dephosphorylation of Msn2 which is not dependent on PP2A-Cdc55 activity. Furthermore, the Hog1 mitogen-activated protein kinase pathway activity is not influenced by PP2A-Cdc55. We therefore propose that the PP2A-Cdc55 phosphatase is not involved in cytosolic stress signal perception but is involved in a specific intranuclear mechanism to regulate Msn2 and Msn4 nuclear accumulation and chromatin association under stress conditions.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00834-12.

ACKNOWLEDGMENTS

We thank E. Ogris for comments and N. Romanov and S. Y. Kumar for critical reading of the manuscript. We thank E. Csaszar for measurements on the QSTAR instrument and S. Frosch, R. Gith, and V. Unterwurzacher for technical assistance at the MS facility of MFPL.

This work was supported by the Herzfelder Foundation (to C.S.), Austrian Science Fund FWF projects B23355 and P19966 (to C.S.), and grant I031-B (University of Vienna). C.B. was financed by the Elise-Richter Program of Austrian Science Fund project V39B09. W.R. and I.D. were supported by the Christian Doppler Society and the 7th EU framework project UNICELLSYS. The project was also supported by Austrian Science Fund project F3402-B03 and the European Commission via the FP7 project Prime-XS.