Direct binding of progesterone receptor to nonconsensus DNA sequences represses rat GnRH

The mechanisms by which steroid receptors repress gene expression are not well understood. In this report, we show that progesterone receptor (PR), in the presence of progesterone (P) directly represses rat gonadotropin releasing hormone (rGnRH) gene transcription. Deletion analysis studies using transient transfection assays in GT1-7 neuronal cells mapped the effects of P to sequences in the proximal rGnRH promoter between -171 and -73. This DNA sequence lacks any consensus steroid response element binding sites. Cotransfection of a mutant progesterone receptor that lacks a functional DNA binding region (hPRcys) abolished repression of the rGnRH promoter by P. Gel mobility shift assays confirmed that PR directly binds to the DNA fragments -171/-126, -126/-73, and -111/-73, which encompass the negative progesterone response element (nPRE) of the rGnRH promoter. Mutagenesis of the rGnRH nPRE -171/-126 DNA fragment resulted in a loss of PR binding. Thus, direct DNA binding of PR to nonconsensus elements in the proximal rGnRH promoter inhibits rGnRH gene expression.