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 #
2R01NS059690-06
Application #
8503691
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
2013-09-25
Budget End
2014-07-31
Support Year
6
Fiscal Year
2013
Total Cost
$458,062
Indirect Cost
$166,303
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
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
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
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
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
Zuiderweg, Erik R P; Gestwicki, Jason E (2016) Backbone and methyl resonance assignments of the 42 kDa human Hsc70 nucleotide binding domain in the ADP state. Biomol NMR Assign :
Morozova, Kateryna; Clement, Cristina C; Kaushik, Susmita et al. (2016) Structural and Biological Interaction of hsc-70 Protein with Phosphatidylserine in Endosomal Microautophagy. J Biol Chem 291:18096-106
Ouimet, Claire M; Shao, Hao; Rauch, Jennifer N et al. (2016) Protein Cross-Linking Capillary Electrophoresis for Protein-Protein Interaction Analysis. Anal Chem 88:8272-8
Fontaine, Sarah N; Martin, Mackenzie D; Akoury, Elias et al. (2015) The active Hsc70/tau complex can be exploited to enhance tau turnover without damaging microtubule dynamics. Hum Mol Genet 24:3971-81
Li, Xiaokai; Colvin, Teresa; Rauch, Jennifer N et al. (2015) Validation of the Hsp70-Bag3 protein-protein interaction as a potential therapeutic target in cancer. Mol Cancer Ther 14:642-8
Fontaine, Sarah N; Rauch, Jennifer N; Nordhues, Bryce A et al. (2015) Isoform-selective Genetic Inhibition of Constitutive Cytosolic Hsp70 Activity Promotes Client Tau Degradation Using an Altered Co-chaperone Complement. J Biol Chem 290:13115-27

Showing the most recent 10 out of 70 publications