Mechanism of action of a steroidal antiglucocorticoid in lymphoid cells

We compared the biochemical properties of receptors extracted from mouse lymphoma cells and complexed with the glucocorticoid, triamcinolone acetonide, or with the high affinity antiglucocorticoid RU 38486 17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)-17 alpha-(1-propynyl)-estra- 4,9-diene-3-one]. Upon salt treatment the high molecular weight receptor complexes of both types yielded dissociated forms that had the same affinity for DNA. Increased temperature caused subunit dissociation of the agonist complex but ligand dissociation of the antagonist complex. The latter was prevented if subunit dissociation was blocked by sodium molybdate but not by chemical cross-linking of the heteromeric receptor. Immunochemical studies suggest that the instability of the RU 38486 complex only affects the level of bound ligand but not the integrity of the receptor polypeptide. In intact cells at 37 degrees C the receptor polypeptide associated with nuclei only in the presence of hormone but not in its absence or if the antihormone was present. Cells incubated at 37 degrees C with RU 38486 retained in the cytosol the high molecular weight receptor in its ligand bound form. The data suggest that in intact cells under physiological conditions the antagonist binds to the heteromeric receptor and blocks its dissociation into subunits thus preventing nuclear receptor translocation.