Epidermal Growth Factor Receptor Is an Obligatory Intermediate for Oxytocin-Induced Cyclooxygenase 2 Expression and Prostaglandin F2α Production in Bovine Endometrial Epithelial Cells

Abstract

Oxytocin (OT) triggers the luteolytic pulses of prostaglandin F2α (PGF2α) from the endometrial epithelial cells in ruminants. We have proposed that the embryonic signal interferon-τ exerts its antiluteolytic effect by disrupting the OT signaling axis. Accordingly, we have attempted to define the signaling pathway of OT-induced PGF2α production in the bovine endometrium using our newly characterized epithelial cell line (bEEL). OT receptor was coupled to the classical Gαq pathway as evidenced by calcium release and activation of phospholipase C. Similarly, OT-induced PGF2α production was mediated through the canonical ERK1/2 pathway. Because of the importance of receptor and nonreceptor tyrosine kinases in G protein-coupled receptor signaling, we studied the role of epidermal growth factor receptor (EGFR), c-Src, and phosphoinositide 3-kinase (PI3K) on OT-induced PGF2α production in association with cyclooxygenase 2 (COX2) expression and ERK1/2 and Akt phosphorylation. The EGFR inhibitor AG1478 (10 μm) nearly abolished basal and OT-induced PGF2α production and down-regulated COX2 expression and ERK1/2 phosphorylation. Because the transactivated EGFR can serve as a ligand for the signaling proteins with Src homology 2 (SH2) domain, we hypothesized a role for c-Src and PI3K in OT-induced PGF2α production. Inhibitors of c-Src (PP2, 10 μm) and PI3K (LY294002, 25 μm) produced a significant decrease in OT-induced PGF2α production and reduced COX2 expression. Also, PP2, but not LY294002, decreased OT-induced ERK1/2 phosphorylation. Because LY294002 did not affect ERK1/2 phosphorylation, but inhibited PGF2α production and down-regulated COX2 expression, it is likely that the Akt pathway is also involved in PGF2α production. Thus, EGFR may simultaneously activate c-Src and PI3K to amplify the OT signaling to increase the output of PGF2α in bEEL cells.