Activation of functional oxytocin receptors stimulates cell proliferation in human trophoblast and choriocarcinoma cell lines

Despite oxytocin receptors (OTR) being present in human chorio-decidual tis sues, their expression and role in placental trophoblast cells in the conte xt of tumor growth or physiological functions related to cell proliferation have never been examined. In the present study we demonstrate the presence and functionality of OTR in normal human trophoblast cell lines (ED77 and ED27) and a choriocarcinoma cell line (BeWo). RT-PCR and immunofluorescence analysis revealed the presence of OTR messenger RNA and protein in these c ells. Binding studies using [I-125]oxytocin ([I-125]OT) antagonist confirme d the presence of specific binding sites in ED27, ED77, and BeWo cells. OTR functionality was demonstrated by measuring the OT-induced increase in the intracellular calcium concentrations. This effect was dose dependent and w as blocked by the selective OT antagonist d(CH2)(5)[Tyr(Me)(2),Thr(4), Tyr- NH29]OVT (OT antagonist). Furthermore, two proteins with apparent molecular masses of 125 and 60 kDa became tyrosine phosphorylated in all of the cell lines after OT stimulation (and an additional protein of 45 kDa in BeWo ch oriocarcinoma cells), suggesting that this peptide can stimulate tyrosine k inase activity. Finally, we observed a dose-dependent OT stimulation of cel l proliferation associated with OTR activation that was completely abolishe d by the selective OT antagonist. These findings provide the first evidence of the presence of functional OTR in normal trophoblast cell lines as well as in choriocarcinoma cells and show that a specific effect of OT on norma l and neoplastic trophoblast is to promote cellular proliferation.