Mechanism of dexamethasone 21-mesylate antiglucocorticoid action: II. Receptor-antiglucocorticoid complexes do not interact productively with mouse mammary tumor virus long terminal repeat chromatin.

We have studied the interaction of covalent dexamethasone 21-mesylate (DM) labeled, activated glucocorticoid receptor with mouse mammary tumor virus (MMTV) chromatin. Studies were performed on a murine cell line (904.13) which contains 200 copies per cell of a MMTV long terminal repeat (LTR) v-rasH casette mobilized on bovine papilloma virus based episomes. DM binds covalently to glucocorticoid receptors and displays almost full antagonist activity in this cell line. In situ transcription extension assays indicate that activated receptor-DM complex cannot stimulate LTR-initiated transcription. The receptor-DM complex also fails to induce DNase I hypersensitivity (HSR) and transcription factor loading at the MMTV promoter. Transcription activation, HSR formation, and factor binding induced with the agonist dexamethasone are blocked by covalent occupation of the receptor by DM. Although DM-activated receptor binds specifically to receptor sites on purified LTR DNA, the antagonist receptor complex does not interact productively with MMTV LTR chromatin in vivo.