Dynamic tyrosine phosphorylation modulates cycling of the HSP90-P50(CDC37)-AHA1 chaperone machine

Urologic Oncology Branch, National Cancer Institute, Bethesda, MD 20892, USA.
Molecular cell (Impact Factor: 14.02). 06/2012; 47(3):434-43. DOI: 10.1016/j.molcel.2012.05.015
Source: PubMed


Many critical protein kinases rely on the Hsp90 chaperone machinery for stability and function. After initially forming a ternary complex with kinase client and the cochaperone p50(Cdc37), Hsp90 proceeds through a cycle of conformational changes facilitated by ATP binding and hydrolysis. Progression through the chaperone cycle requires release of p50(Cdc37) and recruitment of the ATPase activating cochaperone AHA1, but the molecular regulation of this complex process at the cellular level is poorly understood. We demonstrate that a series of tyrosine phosphorylation events, involving both p50(Cdc37) and Hsp90, are minimally sufficient to provide directionality to the chaperone cycle. p50(Cdc37) phosphorylation on Y4 and Y298 disrupts client-p50(Cdc37) association, while Hsp90 phosphorylation on Y197 dissociates p50(Cdc37) from Hsp90. Hsp90 phosphorylation on Y313 promotes recruitment of AHA1, which stimulates Hsp90 ATPase activity, furthering the chaperoning process. Finally, at completion of the chaperone cycle, Hsp90 Y627 phosphorylation induces dissociation of the client and remaining cochaperones.

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    • "It is noteworthy that isolated hAha1 and the mutant proteins had no contaminating ATPase activity (Figure S4D). We previously demonstrated that hAha1 co-exists in an hHsp90-kinase client complex (Xu et al., 2012). Therefore, we assessed the impact of Y223F and Y223E mutations on hAha1 interaction with kinase clients. "
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    ABSTRACT: 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 Hsp90 remain unknown. Here, we show that c-Abl kinase phosphorylates Y223 in human Aha1 (hAha1), promoting its interaction with Hsp90. This, consequently, results in an increased Hsp90 ATPase activity, enhances Hsp90 interaction with kinase clients, and compromises the chaperoning of non-kinase clients such as glucocorticoid receptor and CFTR. Suggesting a regulatory paradigm, we also find that Y223 phosphorylation leads to ubiquitination and degradation of hAha1 in the proteasome. Finally, pharmacologic inhibition of c-Abl prevents hAha1 interaction with Hsp90, thereby hypersensitizing cancer cells to Hsp90 inhibitors both in vitro and ex vivo. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
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    • "ylation of Cdc37. Then, phosphorylation of Cdc37 at Tyr298 (for certain kinase clients also at Tyr4) and of Hsp90 at Tyr197 by the Yes kinase induces conformational changes in Hsp90 and accelerates dissociation of Cdc37 (Xu et al., 2012 "
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    No preview · Article · Apr 2015 · Molecular cell
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    • "By contrast, indirect analysis based on the inability of PP5 phosphatase to bind the Hsp90-heme-regulated inhibitor of protein synthesis (HRI) has shown that chaperone phosphorylation enhances HRI activity (Shao et al. 2002). Phosphorylation of tyrosine 197 in human Hsp90α (Y186 in TgHsp90, Table 1) dissociates cdc37 from Hsp90 (Xu et al. 2012). This study also showed that mutation of Y627 (Y604 in T. gondii, Table 1) favours the release of client Cdk4 and co-chaperones (AHA1 and PP5). "
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