Oxytocin Receptor Down-Regulation Is Not Necessary for Reducing Oxytocin-Induced Prostaglandin F2α Accumulation by Interferon-τ in a Bovine Endometrial Epithelial Cell Line

Interferon-tau (IFN tau) is the embryonic signal responsible for pregnancy recognition in ruminants. The primary action of IFN tau is believed to be mediated through inhibition of prostaglandin F-2 alpha (PGF(2 alpha)) released from the endometrial epithelial cells in response to oxytocin (OT). Our working hypothesis was that the antiluteolytic effect of IFN tau also involved modulation of PG production downstream of OT receptor (OTR) and/or cyclooxygenase 2 (COX2). There is currently no OT-sensitive endometrial cell line to study the molecular mechanisms underlying our hypotheses. Therefore, we established an immortalized bovine endometrial epithelial cell line (bEEL) exhibiting OT response. These cells were cytokeratin positive, expressed steroid receptors, and exhibited preferential accumulation of PGF(2 alpha) over PGE(2). The bEEL cells were highly sensitive to OT, showing time- and concentration-dependent increase in COX2 transcript and protein and PGF(2 alpha) accumulation. Interestingly, IFN tau (20 ng/ml) significantly reduced OT-induced PGF(2 alpha) accumulation, but surprisingly, the effect was not mediated through down-regulation of either OTR or COX2. Rather, IFN tau up-regulated COX2 in a time- and concentration-dependent manner while decreasing OT-induced PG accumulation. This suggests that COX2 is not a primary target for the antiluteolytic effect of IFN tau. Because IFN tau reduced OT-stimulated PGF(2 alpha) accumulation within 3 h, the mechanism likely involves a direct interference at the level of the OT signaling or transcription in addition to the down-regulation of OTR observed in vivo. In summary, bEEL cells offer a unique in vitro model for investigating the cellular and molecular mechanisms underlying OT and IFN tau response in relation with luteolysis and recognition of pregnancy in the bovine. (Endocrinology 150: 897-905, 2009)