In vitro monitoring activation by the ligands and specific DNA-binding of the glucocorticoid receptors.

The glucocorticoid receptor is a member of the steroid and thyroid hormone receptor superfamily and acts as a ligand-activated transcription factor. To reconstitute the molecular mechanisms underlying the cellular response to soluble receptor ligands, we have exploited a cell-free system that exhibits glucocorticoid-induced activation of the latent cytosolic glucocorticoid receptor to an active DNA-binding species. We demonstrate here that cytosol from a rat hepatoma cell, M1.19, contains glucocorticoid receptor-specific immunoreactivities and target DNA-binding activities. Moreover, specific DNA-binding activities of M1.19 cytosol were dose-dependently induced by dexamethasone treatment, and linearly correlated with the hormonal induction of chloramphenicol acetyltransferase activity at the corresponding concentrations. These results indicate that the cytosolic glucocorticoid receptor could be converted in a DNA-binding form under cell-free conditions and the ligand appears to play a crucial role in the direct control of the level of functional activity of a given ligand-receptor complex.