ESTROGEN-RECEPTOR MEDIATED REPRESSION OF RAT GONADOTROPIN-RELEASING-HORMONE (GNRH) PROMOTER ACTIVITY IN HYPOTHALAMIC CELLS

Transient transfection studies were used to examine whether estrogen ( E) regulates the rat gonadotropin releasing hormone (rGnRH) promoter i n GT1-7 hypothalamic neuronal cells. Our data demonstrate that E negat ively regulates rGnRH promoter activity in a ligand and receptor depen dent fashion. Deletion analysis identified a region of the proximal pr omoter from -171 to -126 responsible for E regulation. Interestingly, no classical estrogen response element (ERE) or steroid receptor half- site is present in this region. The rGnRH negative estrogen response e lement (nERE) also conferred repression by E to a neutral heterologous promoter. Additional studies cotransfecting mutant estrogen receptors (ER) demonstrated that an intact ER with a functional DNA binding reg ion is required for the E dependent repression of promoter activity. T he nERE of the rGnRH promoter, however, was unable to directly bind ye ast-expressed human ER even in the presence of two different ER antibo dies, suggesting the need for protein-protein interaction for ER inhib ition of GnRH gene expression. In summary, the rGnRH promoter is negat ively regulated by E in an ER dependent fashion via sequences -171 to -126 which lack an ER consensus DNA binding site. Our studies suggest the use of alternative mechanisms involving protein-protein interactio ns independent of DNA binding of ER in the transcriptional repression of the rat GnRH gene by estrogen.