Synergistic regulation of human oxytocin receptor promoter by CCAAT/ enhancer-binding protein and RELA

Uterine activation is associated with increased oxytocin receptor (OXTR) expression and myometrial sensitivity to oxytocin. The OXTR promoter contains binding sites for CCAAT/enhancer-binding protein (CEBP) and nuclear factor-kappa B p65 (RELA). RELA and CEBP beta (CEBPB) play a synergistic role in OXTR promoter activation. We created deletions in a DNA construct consisting of 850 bp upstream of the transcription start site linked to luc reporter to identify the CIS element of the OXTR promoter responsible for the synergistic activation by RELA and CEBPB. Deletion from -712 to -692 bp eliminated synergy, demonstrating that the critical region lies within these 20 bp. Binding studies showed that this sequence binds both RELA and CEBPB. The 20-bp critical region for synergistic activation of OXTR requires full-length RELA but only the basic leucine zipper domain of CEBPB.