The Molecular Chaperones Hsp90 and Hsc70 Are Both Necessary and Sufficient to Activate Hormone Binding by Glucocorticoid Receptor

Abstract

Glucocorticoid receptors must be complexed with Hsp90 in order to bind steroids, and it has been reported that at least three other proteins, Hop, Hsc70, and a J-domain protein (either Hsp40 or Ydj1), are required for formation of active Hsp90-steroid receptor complex. In the present study, we reinvestigated activation of stripped steroid receptors isolated from either L cells or WCL2 cells. Surprisingly, we found, using highly purified proteins, that only Hsp90 and Hsc70 are required for the activation of glucocorticoid receptors in the presence of steroids; in the absence of steroids, either p23 or molybdate are also required as reported previously. Addition of Hop or Ydj1 had no affect on the rate or magnitude of the activation of the stripped receptors, and quantitative Western blots confirmed that neither Hop or Hsp40 were present in our protein preparations or in the stripped receptors. Furthermore, a truncated recombinant Hsp70 that does not bind Hop or Hsp40 was as effective as wild-type Hsp70 in activating stripped receptor. Since Hsc70 does not bind directly to Hsp90 but both proteins bind to Hop, it has been suggested that Hop acts as a bridge between Hsp90 and Hsp70. However, we found that after Hsc70 or Hsp90 bind directly to the stripped receptors, they are fully reactivated by Hsp90 or Hsc70, respectively. We, therefore, conclude that Hsp90 and Hsc70 bind independently to stripped glucocorticoid receptors and alone are sufficient to activate them to bind steroids.

Functional Domain and Motif Analyses of Androgen Receptor Coregulator ARA70 and Its Differential Expression in Prostate Cancer

“…Before ligand binding, some SRs are located in the cytosol (61) and are associated with HSPs. HSPs behave as protein chaperones in maintaining the proper conformation of SRs, thereby assisting in their consequent activation (5)(6)(7). It is anticipated that other cytosolic proteins may also contribute to the proper functioning of the receptors, including cytosolic mediators of signal transduction phosphorylation cascades, transportation, anchoring, ubiquination, or degradation of SRs.…”

Monoclonal antibody to novel cell surface epitope on Hsc70 promotes morphogenesis of bile ducts in newborn rat liver

“…Supporting this assumption is an emerging regulatory role for Hsc70 in cell signaling, a role suggested by signaling complexes composed of Hsc70 and CXCR4 (Triantafilou et al 2001), CXCR2 (Fan et al 2002), and the G protein-coupled A1 adenosine receptor (Sarrio et al 2000). Hsc70 binding has also been shown to be required for the activation of glucocorticoid receptors in the presence of steroids (Rajapandi et al 2000).…”

Sti1 and Cdc37 Can Stabilize Hsp90 in Chaperone Complexes with a Protein Kinase

“…It is unclear whether folding occurs while the receptor is in association with Hsp90 or after its release. Whether the cochaperones are required for this reaction is not clear, because purified Hsp70 and Hsp90 can together facilitate folding of GR in vitro, whereas cochaperones such as Hop stimulate the reaction (Morishima et al, 2000;Rajapandi et al, 2000). Furthermore, deletion of yeast Hop (STI1), or p23 (SBA1) does not result in a slow growth phenotype except under stress conditions (Nicolet and Craig, 1989;Chang et al, 1997;Bohen, 1998;Fang et al, 1998).…”