Heat shock protein 70 (Hsp70) is a molecular chaperone that plays a central role in protein quality control (PQC). Hsp70 is considered a """"""""triage chaperone"""""""" because it is important in protein folding, while it also blocks aggregation and targets misfolded proteins for degradation by the ubiquitin proteasome system (UPS) and the chaperone-mediated autophagy (CMA) pathway. How does Hsp70 """"""""decide"""""""" if a protein can be folded? What molecular and structural mechanisms link Hsp70 to the various fates of its protein substrates? These questions are essential to our understanding of how cells maintain protein homeostasis (i.e. proteostasis). Based on the findings obtained in the first funding cycle (2008-present), we have developed a model in which the dwell time of a substrate in the Hsp70 complex might be one factor that contributes to whether a protein is ultimately folded or degraded. This model emerged from experiments in which we used high throughput screening (HTS) to uncover new chemical probes that """"""""tune"""""""" the ATPase activity of Hsp70. Using these molecules, we showed that inhibiting ATP turnover favored degradation of multiple Hsp70 substrates, such as tau and polyglutamine (polyQ) expanded huntingtin (polyQ-Htt) and androgen receptor (polyQ-AR), while stimulating activity led to substrate accumulation and proteotoxicity. Because ATP turnover in Hsp70 is allosterically linked to substrate affinity, we now hypothesize that prolonged interactions with Hsp70 may be a molecular """"""""trigger"""""""" that favors recruitment of UPS components. In the proposed work, we will explore this idea in the following specific aims: (1) develop a suite of chemical probes and point mutants that trap Hsp70 in either its tight or loose affinity forms, (2) explore the role of substrate affinity in stabilization of te unfolded model proteins, tau and polyQ-Htt, and (3) understand how Hsp70 discriminates between normal AR and misfolded, polyQ-AR. From these studies, we expect to better understand how Hsp70 makes key triage decisions. This study is significant because Hsp70 has been linked to many protein-misfolding diseases, including neurodegenerative disorders. Thus, the proposed studies will clarify the logic of Hsp70-mediated PQC and, perhaps, suggest new methods for treating these diseases. This work is innovative because we will use a comprehensive chemical biology approach, combining new chemical probes with point mutants and cell-based models of disease to explore fundamental mechanisms of PQC.

Public Health Relevance

Neurodegenerative disorders, including Huntington's disease (HD), are devastating, progressive diseases that have no known cure. These diseases are thought to involve an imbalance in protein quality control (PQC) that allows accumulation of misfolded protein. The proposed work explores whether the heat shock protein 70 (Hsp70) could be an under-explored therapeutic target for HD and other protein misfolding diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS059690-07
Application #
8739314
Study Section
Macromolecular Structure and Function B Study Section (MSFB)
Program Officer
Sutherland, Margaret L
Project Start
2008-02-01
Project End
2018-07-31
Budget Start
2014-08-01
Budget End
2015-07-31
Support Year
7
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Neurology
Type
Schools of Medicine
DUNS #
City
San Francisco
State
CA
Country
United States
Zip Code
94143
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Rauch, Jennifer N; Tse, Eric; Freilich, Rebecca et al. (2017) BAG3 Is a Modular, Scaffolding Protein that physically Links Heat Shock Protein 70 (Hsp70) to the Small Heat Shock Proteins. J Mol Biol 429:128-141
Zuiderweg, Erik R P; Hightower, Lawrence E; Gestwicki, Jason E (2017) The remarkable multivalency of the Hsp70 chaperones. Cell Stress Chaperones 22:173-189
Rauch, Jennifer N; Olson, Steven H; Gestwicki, Jason E (2017) Interactions between Microtubule-Associated Protein Tau (MAPT) and Small Molecules. Cold Spring Harb Perspect Med 7:
Khachatoorian, Ronik; Riahi, Rana; Ganapathy, Ekambaram et al. (2016) Allosteric heat shock protein 70 inhibitors block hepatitis C virus assembly. Int J Antimicrob Agents 47:289-96
Young, Zapporah T; Rauch, Jennifer N; Assimon, Victoria A et al. (2016) Stabilizing the Hsp70-Tau Complex Promotes Turnover in Models of Tauopathy. Cell Chem Biol 23:992-1001
Rauch, Jennifer N; Zuiderweg, Erik R P; Gestwicki, Jason E (2016) Non-canonical Interactions between Heat Shock Cognate Protein 70 (Hsc70) and Bcl2-associated Anthanogene (BAG) Co-Chaperones Are Important for Client Release. J Biol Chem 291:19848-57
Martin, Mackenzie D; Baker, Jeremy D; Suntharalingam, Amirthaa et al. (2016) Inhibition of Both Hsp70 Activity and Tau Aggregation in Vitro Best Predicts Tau Lowering Activity of Small Molecules. ACS Chem Biol 11:2041-8
Li, Xiaokai; Shao, Hao; Taylor, Isabelle R et al. (2016) Targeting Allosteric Control Mechanisms in Heat Shock Protein 70 (Hsp70). Curr Top Med Chem 16:2729-40
Gabai, Vladimir L; Yaglom, Julia A; Wang, Yongmei et al. (2016) Anticancer Effects of Targeting Hsp70 in Tumor Stromal Cells. Cancer Res 76:5926-5932

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