ERK2 MEDIATES OXYTOCIN-STIMULATED PGE(2) SYNTHESIS

Oxytocin (OT) induces PCT synthesis by both uterine endometrial and am nion cells. We showed previously that CHO cells stably transfected wit h the rat oxytocin receptor (CHO-OTR cells) also synthesize PGE(2) in response to OT. In the present work we have demonstrated that OTRs are coupled to both G(i) and G(q/11), using immunoprecipitation of solubi lized OTR complexes and ADP ribosylation. OT treatment caused the rapi d phosphorylation of extracellular signal-regulated protein kinase 2 ( ERK2 or p42(MAPK)), which was partially inhibited by pertussis toxin ( PTX), consistent with OTR-G(i) coupling. The PTX-insensitive portion o f ERK2 phosphorylation was linked to G(q), as inhibitors of both phosp holipase C (U-73122) and protein kinase C (GF-109203X) blocked OT-indu ced ERK2 phosphorylation. OT-stimulated c-fos expression was also medi ated by ERK2 phosphorylation. The ERK-c-fos pathway has been shown to be associated with cell proliferation, but OT had no effect on [H-3]th ymidine uptake by CHO-OTR cells. However, inhibition of OT-induced ERK 2 phosphorylation with an ERK kinase inhibitor (PD-98059) markedly red uced OT-stimulated PGE(2) synthesis, pointing to the importance of ERK 2 activation in OT action.