NUCLEAR ORPHAN RECEPTORS COUP-TFII AND EAR-2 - PRESENCE IN OXYTOCIN-PRODUCING UTERINE CELLS AND FUNCTIONAL INTERACTION WITH THE OXYTOCIN GENE PROMOTER

We have previously demonstrated that the oxytocin (OT) gene is express ed in the rat uterine epithelium and that its expression is upregulate d in vivo and in vitro by estrogen. This hormonal regulation is mediat ed by a hormone response element (HRE) located in the OT gene promoter . Here we show that the same OT-HRE is also capable of interacting wit h two novel members of the orphan nuclear receptor family, rat COUP-TF II and Ear-2, and that this interaction antagonizes the estrogenic ind uction of the OT promoter. By Northern blot analysis and immunocytoche mistry, using specific cDNA probes and antibodies, respectively, we de monstrate furthermore that both orphan receptors are expressed in uter ine epithelial cells. Therefore. the present findings indicate that ut erine OT gene expression is under stimulatory as well as inhibitory in fluences which are both mediated by the same HRE. More detailed analys is of the sequences necessary for estrogen receptor action and for orp han receptor action, using site-directed mutagenesis, revealed that th e specific recognition sequences are overlapping but distinct: whereas the (imperfect) palindromic structure of the HRE constitutes the estr ogen response element (ERE), orphan receptor action relies on an under lying direct TGACC repeat which forms part of the OT-HRE structure and overlaps with the estrogen response element. (C) 1998 Elsevier Scienc e Ireland Ltd. All rights reserved.