Activation of Heat Shock Protein 70 as a Potential Therapeutic Strategy for the Treatment of Protein Folding Disease
Authors: Davis Amanda , Zhang Haoming , Lau Miranda , Chakraborty Sumita , Morishima Yoshihiro , Lieberman Andrew , Osawa Yoichi 
Published: June 2021

The heat shock protein 90 and 70 (Hsp90/70) chaperone system provides an essential protein quality control mechanism for the cell. Heme containing enzymes, such as cytochrome P450s and neuronal nitric oxide synthase (nNOS), are susceptible to damage by xenobiotics and inactivation by specific environmental toxins or drugs leading to the selective degradation of these proteins. In the course of studies on the inactivation of nNOS, we discovered that covalent alteration of the heme binding cleft leads to misfolding of the cleft, which is selectively recognized by Hsp90/70. Hsp70 recruits the c‐terminus of Hsp70 interacting protein (CHIP), an E3 ubiquitin ligase, leading to ubiquitination and proteasomal degradation of nNOS. In an analogous manner the Hsp90/70 chaperone system also regulates other client proteins that are prone to misfolding and aggregation, such as the polyglutamine‐androgen receptor (polyQ‐AR) a genetic mutant whose misfolding and aggregation leads to muscular‐ and neuro‐degeneration in Kennedy's disease. We have demonstrated that genetic and pharmacological activation of Hsp70 increases the ubiquitination and degradation of misfolded nNOS and polyQ‐AR in cells and alleviates neurotoxicity in a Drosophila model of Kennedy's disease. To advance the development of Hsp70 activation as a therapeutic strategy for the treatment of neurodegenerative diseases, we have established a workflow to identify novel Hsp70 modulators that enhance degradation of misfolded Hsp90/70 client proteins, utilizing nNOS as a model. We have developed a thermal shift high‐throughput screen to identify novel compounds that bind and thermostabilize Hsp70. Preliminary results suggest that this method can be utilized to identify compounds that increase nNOS ubiquitination in vitro and promote degradation of nNOS in HEK293 cells. We are currently working to develop high‐throughput ELISA‐based secondary assays for the quantification of nNOS ubiquitination in vitro and nNOS levels and ubiquitination in cells. This workflow has the potential to advance the development of therapeutics for the treatment of Kennedy's disease and other neurodegenerative diseases such as Alzheimer's, Huntington's, and Parkinson's disease which are caused by misfolding and aggregation of the Hsp90/70 client proteins tau, huntingtin, and α‐synuclein.Support or Funding InformationThis work was supported, in whole or in part, by National Institutes of Health Grant R01‐GMO77430 and R21‐NS101030, the University of Michigan Medical School's Protein Folding Diseases Initiative, and University of Michigan's Center for the Discovery of New Medicines. AD is an awardee of a PhRMA Foundation Pre‐Doctoral Fellowship in Pharmacology/Toxicology and a trainee of the University of Michigan, Pharmacological Sciences Training Program T32‐GM007767.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.