HIGH-LEVELS OF NONACTIVATED RECEPTORS IN GLUCOCORTICOID-SENSITIVE S49(WT) MOUSE LYMPHOMA-CELLS INCUBATED WITH DEXAMETHASONE

Upon agonist binding the heteromeric glucocorticoid receptor complex u ndergoes a conformational change (receptor activation). This event inv olves the dissociation of a dimer of 90 kDa heat shock proteins. Where as receptor activation in cytosolic assays is both rapid and irreversi ble, less is known about the receptor activation and translocation in intact cells during challenge with an agonist. In this paper we report on the receptor status of glucacorticoid-sensitive murine S49 lymphom a cells during dexamethasone exposure. By three different assays, liga nd (re)binding, nuclear translocation and hsp90 co-immunoprecipitation , it was found that the majority of the glucocorticoid receptor protei n was in a non-activated conformation. Furthermore, prolonged exposure to dexamethasone did not result in increased levels of activated rece ptors. By assessing receptor activation in situ we found that physiolo gical temperature was less effective in dissociating hsp90 compared to room temperature. These findings indicate that the physiological temp erature negatively controls receptor activation, probably due to a the rmolabile interaction between the hormone and its cognate receptor.