ERK2 mediates oxytocin-stimulated PGE₂ synthesis

Oxytocin (OT) induces PG synthesis by both uterine endometrial and amnion cells. We showed previously that CHO cells stably transfected with the rat oxytocin receptor (CHO-OTR cells) also synthesize PGE₂ 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 solubilized OTR complexes and ADP ribosylation. OT treatment caused the rapid 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 of ERK2 phosphorylation was linked to G(q), as inhibitors of both phospholipase C (U-73122) and protein kinase C (GF-109203X) blocked OT-induced ERK2 phosphorylation. OT-stimulated c-fos expression was also mediated by ERK2 phosphorylation. The ERK-c-fos pathway has been shown to be associated with cell proliferation, but OT had no effect on [³H]thymidine uptake by CHO-OTR cells. However, inhibition of OT-induced ERK2 phosphorylation with an ERK kinase inhibitor (PD-98059) markedly reduced OT-stimulated PGE₂ synthesis, pointing to the importance of ERK2 activation in OT action.