Low‐level oxidative stress increases chaperone protein activity and alters steroid receptor•hsp90 heterocomplex formation

Abstract

The interruption and subsequent restoration of oxygenated blood flow leads to oxidative stress and localized tissue damage, known as ischemia‐reperfusion injury. Two likely intracellular components involved in protecting the cell against ischemia‐reperfusion‐related damage are the molecular chaperone proteins hsp90 and hsp70. The objective of this study was to determine the impact of oxidative stress on hsp90/hsp70 chaperone protein activity using a glucocorticoid receptor‐based in vitro reconstitution assay. We assessed the hypothesis that increasing concentrations of free radicals (0–300 μM H2O2) would stimulate hsp90/hsp70 function. We observed through western blotting and hsp90‐dependent ligand binding that the hsp90/hsp70 chaperone machinery remained catalytically active and bound to the receptor until oxidative stress levels >100 μM H2O2. Oxidative conditions exceeding 100 μM were correlated with dissociation of steroid receptor•hsp90 heterocomplexes and loss of hsp90/hsp70 functional activity. Most interestingly, there was an observed 25–40% increase in hsp90‐dependent ligand binding activity under mild oxidative stress (~1 μM H2O2). We posit a biochemical explanation for the role of hsp90 in ischemic preconditioning, where mild rounds of ischemia and reperfusion confer a protective effect within the cell against future, prolonged periods of oxidative stress.