Association of the glucocorticoid receptor binding subunit with the 90K nonsteroid-binding component is stabilized by both steroidal and nonsteroidal antiglucocorticoids in intact cells.

The interaction of various antiglucocorticoids with the glucocorticoid receptor from intact rat thymocytes was investigated. Reversible antiglucocorticoids (RU 486, cortexolone, progesterone) underwent more limited nuclear transfer than potent glucocorticoids (dexamethasone, triamcinolone acetonide, progesterone). This behavior was correlated with an impeded dissociation of cytosolic antiglucocorticoid receptor complexes preformed in intact cells, as assayed by high-performance size exclusion chromatography in physiological conditions (i.e., isotonic molybdate-free buffer). Antagonist-receptor complexes remained in a 7-8-nm form whatever the antiglucocorticoid tested (including dexamethasone mesylate and trifluoroperazine, a nonsteroidal antiglucocorticoid) and the incubation time at 37 degrees C, whereas agonist-receptor complexes were rapidly converted into 5-nm species. This stabilization was not detectable by conventional sucrose gradient centrifugation because of artifactual dissociation of untransformed complexes, a pitfall overcome by resorting to vertical tube centrifugation. Moreover, the low amount of nuclear antiglucocorticoid receptor complexes was also in the undissociated form, in contrast with nuclear agonist-receptor complexes. Immunological probes demonstrated that the 90-kDa non-steroid-binding component was associated with the antiglucocorticoid-stabilized receptor. Thus, whatever their chemical structure and their affinity for the receptor, antiglucocorticoids stabilize the oligomeric form of the glucocorticoid receptor in intact cells. Our data, demonstrating for the first time that all antiglucocorticoids probably act via a common mechanism, suggest a key role for subunit dissociation during in vivo receptor activation.