Relationship between glucocorticoid receptor steroid-binding capacity and association of the Mr 90,000 heat shock protein with the unliganded receptor

Treatment of rat liver cytosol with hydrogen peroxide (H2O2) or sodium molybdate (MoO4(2-)) inhibits thermal inactivation of glucocorticoid receptor steroid-binding capacity at 25 degrees C. Dithiothreitol (DTT) prevents the stabilization of receptors by H2O2. Heating (25 degrees C) of immune pellets formed by immunoadsorption of L-cell murine glucocorticoid receptor complexes to protein-A-Sepharose with an anti-receptor monoclonal antibody (BuGR2) results in dissociation of the M 90,000 heat shock protein (hsp90) from the steroid binding protein. Such thermal-induced dissociation of hsp90 is inhibited by H2O2. Pretreatment of immunoadsorbed receptor complexes with the thiol derivatizing agent, methyl methanethiosulfonate (MMTS) prevents the ability of H2O2 to stabilize the hsp90-receptor interaction. These data suggest a role for hsp90 in maintaining an active steroid-binding conformation of the glucocorticoid receptor.