The glucocorticoid—receptor complex from freshly prepared rat liver cytosol is in a non-activated form, with very little affinity to bind to isolated nuclei. When such preparations were incubated with 5—10 mM-ATP at 4 degrees C, the receptor complex acquired the properties of an ‘activated’ transformed form, which readily bound to nuclei, ATP—Sepharose, phosphocellulose and DNA—cellulose. This transformation was comparable with the activation achieved by warming the steroid—receptor complex at 23 degrees C. The effect of ATP was specific, as it was more effective than ADP, whereas AMP had no such effect on activation. The process of receptor activation was sensitive to the presence of 10 mM-sodium molybdate; the latter blocked activation by both ATP and heat. Bivalent cations had no observable effect on the receptor activation at low temperature, but they decreased the extent of activation by ATP. The steroid-binding properties of glucocorticoid receptor remained intact under the above conditions. However, a significant increase in steroid binding occurred when ATP was preincubated with cytosol receptor before the addition of [3H]triamcinolone acetonide. ATP also stabilized the glucocorticoid—receptor complexes at 23 degrees C. These results suggest a role for ATP in receptor function and offer a convenient method of studying the activation process of glucocorticoid receptor under mild assay conditions.
Transformation of the glucocorticoid receptor in rat liver cytosol by lysosomal enzymes.
