Regulation of the human oxytocin receptor by nuclear factor-κB and CCAAT/enhancer-binding protein-β

Abstract

Context: Increased myometrial sensitivity to oxytocin at term is mediated through increased oxytocin receptor (OTR) expression. OTR promoter contains putative transcription factor-binding sites for activating protein-1 (AP-1), CCAAT/enhancer-binding protein (C/EBP), and nuclear factor-κB (NF-κB), which may be activated by IL-1β, whose concentrations increase with labor. Objective: The objective of this study was to examine the effect of IL-1β on OTR expression and the roles of AP-1, C/EBP, and NF-κB in OTR promoter function. Results: IL-1β induces an increase in OTR mRNA concentrations and OTR ligand binding in myometrial cells, which is maximal at 4 h and decreased after 20 h. IL-1β activates the transcription factors AP-1 C/EBPβ, and NF-κB. Using computer-based analysis and EMSA studies, we have identified three AP-1, nine C/EBP, and three NF-κB DNA-binding sites in the OTR promoter. In transient transfection studies, OTR promoter activity was increased by C/EBPβ and NF-κB, but not by AP-1. C/EBPβ and NF-κB together had a synergistic action in the induction of OTR promoter activity. Site-directed mutagenesis of each individual C/EBP and NF-κB site had no effect on the ability of C/EBPβ, NF-κB, or their combination to activate OTR promoter. However, mutation of both NF-κB sites inhibited promoter activation by NF-κB alone, but not that by the combination of C/EBPβ and NF-κB. Deletion studies showed that a region between -851 and -656 of the OTR confers responsiveness to the combination of C/EBPβ and NF-κB. Conclusion: IL-1β has a biphasic effect on OTR expression in myometrial cells, and C/EBP and NF-κB play synergistic roles in OTR promoter activation. Copyright © 2006 by The Endocrine Society.