Yeast Hog1 proteins are sequestered in stress granules under high-temperature stress

The yeast high-osmolarity glycerol (HOG) pathway plays a central role in stress responses. It is activated by various stress stimuli including hyperosmotic stress, oxidative stress, high-temperature stress, and arsenite. Hog1, the critical MAP kinase of the pathway, localizes to the nucleus in response to high-osmolarity conditions, but otherwise little is known about its intracellular dynamics and regulation. Using the methylotrophic yeast Candida boidinii, we found that CbHog1-Venus formed intracellular dot structures after high-temperature stress, in a reversible manner. Microscopic observation revealed that CbHog1-mCherry was colocalized with CbPab1-Venus, a marker protein of stress granules (SGs). Hog1 homologs in Pichia pastoris and Schizosaccharomyces pombe also exhibited similar dot formation under high-temperature stress, whereas Saccharomyces cerevisiae Hog1 (ScHog1)-GFP did not. Analysis of CbHog1-Venus in C. boidinii revealed that a β-sheet structure in the N-terminal region was necessary and sufficient for its localization to SGs. Physiological studies revealed that sequestration of activated Hog1 proteins in SGs was responsible for downregulation of Hog1 activity under high-temperature stress.