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 #
3R01NS059690-07S1
Application #
8923487
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
2014-09-01
Budget End
2015-07-31
Support Year
7
Fiscal Year
2014
Total Cost
$88,503
Indirect Cost
$32,503
Name
University of California San Francisco
Department
Neurology
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Meister-Broekema, Melanie; Freilich, Rebecca; Jagadeesan, Chandhuru et al. (2018) Myopathy associated BAG3 mutations lead to protein aggregation by stalling Hsp70 networks. Nat Commun 9:5342
Shao, Hao; Li, Xiaokai; Moses, Michael A et al. (2018) Exploration of Benzothiazole Rhodacyanines as Allosteric Inhibitors of Protein-Protein Interactions with Heat Shock Protein 70 (Hsp70). J Med Chem 61:6163-6177
Ran, Xu; Burchfiel, Eileen T; Dong, Bushu et al. (2018) Rational design and screening of peptide-based inhibitors of heat shock factor 1 (HSF1). Bioorg Med Chem 26:5299-5306
Cesa, Laura C; Shao, Hao; Srinivasan, Sharan R et al. (2018) X-linked inhibitor of apoptosis protein (XIAP) is a client of heat shock protein 70 (Hsp70) and a biomarker of its inhibition. J Biol Chem 293:2370-2380
Freilich, Rebecca; Betegon, Miguel; Tse, Eric et al. (2018) Competing protein-protein interactions regulate binding of Hsp27 to its client protein tau. Nat Commun 9:4563
Freilich, Rebecca; Arhar, Taylor; Abrams, Jennifer L et al. (2018) Protein-Protein Interactions in the Molecular Chaperone Network. Acc Chem Res 51:940-949
Mok, Sue-Ann; Condello, Carlo; Freilich, Rebecca et al. (2018) Mapping interactions with the chaperone network reveals factors that protect against tau aggregation. Nat Struct Mol Biol 25:384-393
Ran, Xu; Gestwicki, Jason E (2018) Inhibitors of protein-protein interactions (PPIs): an analysis of scaffold choices and buried surface area. Curr Opin Chem Biol 44:75-86
Young, Zapporah T; Mok, Sue Ann; Gestwicki, Jason E (2018) Therapeutic Strategies for Restoring Tau Homeostasis. Cold Spring Harb Perspect Med 8:
Yaglom, Julia A; Wang, Yongmei; Li, Amy et al. (2018) Cancer cell responses to Hsp70 inhibitor JG-98: Comparison with Hsp90 inhibitors and finding synergistic drug combinations. Sci Rep 8:3010

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