Hyperosmotic stress induced inclusion formation of a prionogenic transcriptional corepressor is regulated by glycerol accumulation.

Abstract

Environmental stressors cause severe perturbations in homeostasis that, if left unchecked, can severely damage cells. In order to cope with a constantly changing environment, organisms have evolved complex signaling programs that allow for adaptation in the face of stress. These programs require a host of post-translational modifications, including attachment of the small ubiquitin-like modifier SUMO/SMT3. SUMOylation has been shown to be critical for the response to environmental stress, and many targets of SUMOylation have been characterized. What remains unclear, however, are the factors regulating stress-induced SUMOylation and the consequences of these SUMOylation events. It has been shown previously that the major targets of hyperosmotic stress-triggered SUMOylation in the budding yeast Saccharomyces cerevisiae are the transcriptional corepressor complex Cyc8-Tup1. Here, I show that the osmostress responsive MAP kinase Hog1 is a critical regulator of Cyc8-Tup1 SUMOylation via its role in upregulating the biosynthesis of the compatible osmolyte and chemical chaperone glycerol. Mutations that ablate SUMOylation of Cyc8 are sufficient to rescue the osmosensitivity of hog1∆ cells, and this is facilitated by inappropriate derepression of glycerol biosynthesis genes in the absence of HOG1. We previously showed that Cyc8 forms transient nuclear foci during hyperosmotic stress, and I show here that cells unable to synthesize glycerol display Cyc8 inclusions that are persistent, soluble, and dynamic. These observations unveil a novel intersection between phosphorylation and SUMOylation networks, which are critical for shifting gene expression and metabolic programs during stress adaptation. Moreover, this work provides new insights into metabolic factors regulating the biomolecular condensation of proteins that have important implications for prion biology.