Post-translational modifications of Hsp90 and their contributions to chaperone regulation

AbstractMolecular chaperones, as the name suggests, are involved in folding, maintenance, intracellular transport, and degradation of proteins as well as in facilitating cell signaling. Heat shock protein 90 (Hsp90) is an essential eukaryotic molecular chaperone that carries out these processes in normal and cancer cells. Hsp90 function in vivo is coupled to its ability to hydrolyze ATP and this can be regulated by co-chaperones and post-translational modifications. In this review, we explore the varied roles of known post-translational modifications of cytosolic and nuclear Hsp90 (phosphorylation, acetylation, S-nitrosylation, oxidation and ubiquitination) in fine-tuning chaperone function in eukaryotes. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90)

Mutation of the co-chaperone Tsc1 in bladder cancer diminishes Hsp90 acetylation and reduces drug sensitivity and selectivity

The molecular chaperone Heat shock protein 90 (Hsp90) is essential for the folding, stability, and activity of several drivers of oncogenesis. Hsp90 inhibitors are currently under clinical evaluation for cancer treatment, however their efficacy is limited by lack of biomarkers to optimize patient selection. We have recently identified the tumor suppressor tuberous sclerosis complex 1 (Tsc1) as a new co-chaperone of Hsp90 that affects Hsp90 binding to its inhibitors. Highly variable mutations of TSC1 have been previously identified in bladder cancer and correlate with sensitivity to the Hsp90 inhibitors. Here we showed loss of TSC1 leads to hypoacetylation of Hsp90-K407/K419 and subsequent decreased binding to the Hsp90 inhibitor ganetespib. Pharmacologic inhibition of histone deacetylases (HDACs) restores acetylation of Hsp90 and sensitizes Tsc1-mutant bladder cancer cells to ganetespib, resulting in apoptosis. Our findings suggest that TSC1 status may predict response to Hsp90 inhibitors in patients with bladder cancer, and co-targeting HDACs can sensitize tumors with Tsc1 mutations to Hsp90 inhibitors

A Systematic Protocol for the Characterization of Hsp90 Modulators

This is the author's accepted manuscript. Made available by the permission of the publisher.Several Hsp90 modulators have been identified including the N-terminal ligand geldanamycin (GDA), the C-terminal ligand novobiocin (NB), and the co-chaperone disruptor celastrol. Other Hsp90 modulators elicit a mechanism of action that remains unknown. For example, the natural product gedunin and the synthetic anti-spermatogenic agent H2-gamendazole, recently identified Hsp90 modulators, manifest biological activity through undefined mechanisms. Herein, we report a series of biochemical techniques used to classify such modulators into identifiable categories. Such studies provided evidence that gedunin and H2-gamendazole both modulate Hsp90 via a mechanism similar to celastrol, and unlike NB or GDA

Tumor suppressor Tsc1 is a new Hsp90 co-chaperone that facilitates folding of kinase and non-kinase clients

The tumor suppressors Tsc1 and Tsc2 form the tuberous sclerosis complex (TSC), a regulator of mTOR activity. Tsc1 stabilizes Tsc2; however, the precise mechanism involved remains elusive. The molecular chaperone heat-shock protein 90 (Hsp90) is an essen- tial component of the cellular homeostatic machinery in eukary- otes. Here, we show that Tsc1 is a new co-chaperone for Hsp90 that inhibits its ATPase activity. The C-terminal domain of Tsc1 (998–1,164 aa) forms a homodimer and binds to both protomers of the Hsp90 middle domain. This ensures inhibition of both subunits of the Hsp90 dimer and prevents the activating co- chaperone Aha1 from binding the middle domain of Hsp90. Conversely, phosphorylation of Aha1-Y223 increases its affinity for Hsp90 and displaces Tsc1, thereby providing a mechanism for equilibrium between binding of these two co-chaperones to Hsp90. Our findings establish an active role for Tsc1 as a facilita- tor of Hsp90-mediated folding of kinase and non-kinase clients— including Tsc2—thereby preventing their ubiquitination and proteasomal degradation

The FNIP co-chaperones decelerate the Hsp90 chaperone cycle and enhance drug binding

The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone function. The co-chaperone Aha1 stimulates Hsp90 ATPase activity, tailoring the chaperone function to specific "client" proteins. The intracellular signaling mechanisms directly regulating Aha1 association with Heat shock protein-90 (Hsp90) is an essential molecular chaperone in eukaryotes involved in maintaining the stability and activity of numerous signalling proteins, also known as clients. Hsp90 ATPase activity is essential for its chaperone function and it is regulated by co-chaperones. Here we show that the tumour suppressor FLCN is an Hsp90 client protein and its binding partners FNIP1/FNIP2 function as co-chaperones. FNIPs decelerate the chaperone cycle, facilitating FLCN interaction with Hsp90, consequently ensuring FLCN stability. FNIPs compete with the activating co-chaperone Aha1 for binding to Hsp90, thereby providing a reciprocal regulatory mechanism for chaperoning of client proteins. Lastly, downregulation of FNIPs desensitizes cancer cells to Hsp90 inhibitors, whereas FNIPs overexpression in renal tumours compared with adjacent normal tissues correlates with enhanced binding of Hsp90 to its inhibitors. Our findings suggest that FNIPs expression can potentially serve as a predictive indicator of tumour response to Hsp90 inhibitors

The multiple facets of the Hsp90 machine

International audienceThe Ninth International Conference on the Hsp90 Chaperone Machine concluded in October 2018, in Leysin, Switzerland. The program highlighted findings in various areas, including integrated insight into molecular mechanism of Hsp90, cochaperones, and clients’ structure and function.Heat shock protein-90 (Hsp90) is a molecular chaperone critical for the folding, stability, and activity of client proteins 1. Hsp90 and its orthologs, including bacterial HtpG, mitochondrial TRAP1 and endoplasmic reticulum Grp94, exist as dimers, hydrolyze ATP, and cycle between distinct conformational states. Hsp90 preferentially binds proteins in near native states facilitating their remodeling for protein interactions and signaling. At the 9th International Conference on the Hsp90 Chaperone Machine approximately one-third of the attendees shared their data on Hsp90 structure and function through short talks (Figure 1). Here, we distill and summarize their finding

Asymmetric Hsp90 N domain SUMOylation recruits Aha1 and ATP-competitive inhibitors

The stability and activity of numerous signaling proteins in both normal and cancer cells depends on the dimeric molecular chaperone heat shock protein 90 (Hsp90). Hsp90's function is coupled to ATP binding and hydrolysis and requires a series of conformational changes that are regulated by cochaperones and numerous posttranslational modifications (PTMs). SUMOylation is one of the least-understood Hsp90 PTMs. Here, we show that asymmetric SUMOylation of a conserved lysine residue in the N domain of both yeast (K178) and human (K191) Hsp90 facilitates both recruitment of the adenosine triphosphatase (ATPase)-activating cochaperone Aha1 and, unexpectedly, the binding of Hsp90 inhibitors, suggesting that these drugs associate preferentially with Hsp90 proteins that are actively engaged in the chaperone cycle. Importantly, cellular transformation is accompanied by elevated steady-state N domain SUMOylation, and increased Hsp90 SUMOylation sensitizes yeast and mammalian cells to Hsp90 inhibitors, providing a mechanism to explain the sensitivity of cancer cells to these drugs. © 2014 Elsevier Inc

Seventh BHD international symposium: recent scientific and clinical advancement.

The 7th Birt-Hogg-Dubé (BHD) International Symposium convened virtually in October 2021. The meeting attracted more than 200 participants internationally and highlighted recent findings in a variety of areas, including genetic insight and molecular understanding of BHD syndrome, structure and function of the tumor suppressor Folliculin (FLCN), therapeutic and clinical advances as well as patients' experiences living with this malady

First virtual international congress on cellular and organismal stress responses, november 5–6, 2020

Members of the Cell Stress Society International (CSSI), Patricija van Oosten-Hawle (University of Leeds, UK), Mehdi Mollapour (SUNY Upstate Medical University, USA), Andrew Truman (University of North Carolina at Charlotte, USA) organized a new virtual meeting format which took place on November 5–6, 2020. The goal of this congress was to provide an international platform for scientists to exchange data and ideas among the Cell Stress and Chaperones community during the Covid-19 pandemic. Here we will highlight the summary of the meeting and acknowledge those who were honored by the CSSI