All organisms require maintenance of DNA integrity to grow and proliferate. Replication and repair of DNA damage requires the increased synthesis of DNA nucleotides, a process that is dependent on the activity of the kinases such as ATM and ATR. Misregulation of DNA replication can result in either cell death or cancer. Studies by our lab and others have shown that many DNA damage response (DDR) proteins (such as ATM, ATR, XRCC1 and RNR) are stabilized by the molecular chaperones Hsp70 and Hsp90. These proteins perform a variety of functions in the cell including protein folding of both newly synthesized and denatured proteins, protein transport across membranes and disaggregation of oligomerized proteins. Research has primarily focused on how chaperone function specificity arises through regulation of expression, isoform differences and the variety of co- chaperone proteins that bind to the Hsp70 and Hsp90 molecules. Despite the identification of several phosphorylation sites on both yeast and mammalian Hsp70 through global proteomic screens (known as the chaperone code), the biological function of these remains unclear. Our studies published in Cell determined that CDK-mediated phosphorylation of a single site on Hsp70 can regulate chaperone function by altering both co- chaperone and client protein interactions. In this proposal, we aim to understand how the activation of DDR can promote changes in the pattern of Hsp70 chaperone code. We predict that in line with several Hsp90-kinase interactions, Hsp70 phosphorylation during DNA damage creates a feedback system whereby chaperone phosphorylation increases stability of DDR proteins, amplifying the signal of the DNA damage response. We propose to use both molecular biology and state-of-the-art mass spectrometric techniques on both Saccharomyces cerevisiae and mammalian cell culture cells to achieve the aims of the objectives in our proposal. Identification and study of functional phosphorylation sites on Hsp70 in both yeast and mammalian cells will provide us with a completely novel way to target chaperone activity. Hsp70 activity may be suppressed using specific phosphatase/kinase inhibitors. It may be possible to target specific ?client? proteins though 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 both the DNA damage response and molecular chaperone function, including many types of cancer and neurodegenerative illnesses caused by protein aggregation (Huntington?s disease, Alzheimer?s disease and Creutzfeld-Jakob disease).
This study will allow us to understand how modifications on an essential housekeeping protein (Hsp70) are regulated and how these modifications affect the stability of important proteins that bind to Hsp70, particularly those associated with direct regulation of DNA synthesis and repair. The scope of this work has broad implications for a variety of diseases associated with both the DNA damage response and molecular chaperone function, including many types of cancer.
