Mapping Contacts between Unpurified Human Progesterone Receptor and the Hormone Response Element of Mouse Mammary Tumor Virus

Binding of steroid hormone receptors to specific recognition sites of hormone-inducible genes is one of the events required for hormonal regulation of gene transcription. We have employed an immunoprecipitation assay to map the interaction between unpurified human progesterone receptors from crude nuclear extracts of T47D cells and the hormone response element of the mouse mammary tumor virus (MMTV). DNase I footprints and methylation interference patterns are similar to those reported with highly purified rabbit progesterone receptors, suggesting that both human and rabbit receptors recognize similar features in the hormone response element. More importantly, these patterns suggest that if other factors are associated with unpurified nuclear receptor, they do not alter the contacts made by receptor nor do they make contacts themselves with MMTV DNA in a manner detected by DNase I or methylation interference assays. The sites of interaction of receptors bound with the clinically important progestin antagonist, RU 486, are comparable to those observed with an agonist–receptor complex. These results suggest that the antagonist prevents receptor action at a step after its recognition and binding to specific sites on a hormone-responsive enhancer element.