A progesterone responsive element maps to the far upstream steroid dependent DNase hypersensitive site of chicken lysozyme chromatin.

We have investigated the influence of the 5'-flanking region of the chicken lysozyme gene on steroid dependent gene expression. By transient transfection of lysozyme-CAT fusion genes into the human breast cancer cell line T-47D, a DNA element was identified which stimulates CAT expression when transfected cells are treated with progesterone. This element is distinct from a second hormone responsive element (HRE) located in the lysozyme promoter region; it activates the lysozyme and the TK promoter, irrespective of orientation and distance, and is therefore referred to as hormone responsive element on its own. The location of this newly discovered HRE between -2250 and -1815 relative to the transcriptional start site, corresponds to the position of a steroid inducible DNase I-hypersensitive site in chromatin of oviduct cells. This observation suggests a physiological role for the upstream element. In vitro DNase I protection experiments revealed six binding sites for both progesterone and glucocorticoid receptors within the sequences of the upstream HRE. The three distal binding sites are not required for hormonal stimulation of the TK promoter, while the three proximal binding sites, which are contiguously arranged, work in a cooperative manner.