PP2A^Rts1 antagonizes Rck2-mediated hyperosmotic stress signaling in yeast

In Saccharomyces cerevisiae, impairment of protein phosphatase PP2A^Rts1 leads to temperature and hyperosmotic stress sensitivity, yet the underlying mechanism and the scope of action of the phosphatase in the stress response remain elusive. Using a quantitative mass spectrometry-based approach we have identified a set of putative substrate proteins that show both hyperosmotic stress- and PP2A^Rts1-dependent changes in their phosphorylation pattern. A comparative analysis with published MS-shotgun data revealed that the phosphorylation status of many of these sites is regulated by the MAPKAP kinase Rck2, suggesting that the phosphatase antagonizes Rck2 signaling. Detailed gel mobility shift assays and protein-protein interaction analysis strongly indicate that Rck2 activity is directly regulated by PP2A^Rts1 via a SLiM B56-family interaction motif, revealing how PP2A^Rts1 influences the response to hyperosmotic stress in Yeast.