In this study, we investigated the effect of prostaglandin E(2) (PGE(2)) on MAPK ERK1/2 protein phosphorylation and on proliferation of epithelial cells of the human endometrium. Treatment of proliferative phase endometrium with PGE(2) induced rapid phosphorylation of ERK1/2 proteins in glandular epithelial and endothelial cells. Treatment of human endometrial tissue with PGE(2) for 24 h resulted in increased incorporation of 5-bromo-2'-deoxyuridine (a marker of cellular proliferation) in glandular epithelial cells. To investigate further the effect of PGE(2) on proliferation of epithelial cells, we used an endometrial epithelial cell line (HES). HES cells express functional EP4 (with absence of expression of EP1, EP2, and EP3) receptors and stimulate cAMP release and rapid phosphorylation of ERK1/2 proteins in response to PGE(2) or forskolin. Treatment of HES cells with PGE(2) or forskolin alone resulted in a significant increase in HES cell proliferation compared with control untreated cells (P < 0.05). Cotreatment of the cells with PGE(2) or forskolin and PD98059 abolished the increase in cellular proliferation. These data demonstrate ERK1/2 phosphorylation in response to PGE(2) in the human endometrium and suggest that PGE(2) via EP4 receptor may induce glandular epithelial cell proliferation in ERK1/2- dependent manner during the proliferative phase of the menstrual cycle.