Understanding the role of Hsp70 phosphorylation in proteostasis

Project Summary Hsp70 is vital molecular chaperone that folds a large proportion of the proteome. Research has primarily focused on how Hsp70 function specificity arises through regulation of a) expression of Hsp70, b) isoform differences in the Hsp70 protein family and c) the variety of co-chaperone proteins that bind to the Hsp70 molecule. Despite the identification of several phosphorylation sites on both yeast and mammalian Hsp70 through global proteomic screens, the biological function of most of these sites remains unknown. All organisms must respond to fluctuations in external temperature to maintain viability. Cells cope with heat shock by inducing both the cell integrity and heat shock response pathways. Our preliminary studies have determined that the cell integrity and heat shock response pathways are more intertwined than previously thought. Upon heat shock, yeast Hsp70 is rapidly phosphorylated at a single site and correspondingly mediates the response of yeast to heat stress. In this proposal, we will investigate the impact of this site on chaperone function in yeast. Particularly we will study the role of Hsp70 phosphorylation on aspects of the heat shock response including the formation of both reversible aggregates and stress granules. In addition, we will investigate the hypothesis that phosphorylation of Ssa1 feedbacks into cell integrity signaling by supporting the activity of cell integrity kinases. Understanding the regulation and interplay of Hsp70 phosphorylation in yeast will provide us with a completely novel way to target chaperone activity. It may be possible to target specific oncoproteins through alteration of Hsp70 phosphorylation status and specific Hsp70 phospho-species may have a higher susceptibility to inhibitors. The scope of this work has broad implications for a variety of diseases associated with MAP kinase signaling and molecular chaperone function, including many types of cancer and neurodegenerative illnesses.