Expression of melatoninergic receptors in human placental choriocarcinoma cell lines

BACKGROUND: Melatonin crosses the placenta and enters the fetalcirculation. Moreover, experimental data suggest a possibleinfluence of melatonin on placental function and fetal developmentin humans. To date, the expression and role of melatonin receptorsin human placenta choriocarcinoma cell lines and in human termplacental tissues remain to be elucidated. METHODS AND RESULTS:Results from RT–PCR, western blotting and confocal microscopydemonstrated that the MT1, MT2 and ROR1 melatonin receptorsare expressed in the human term placental tissues and in choriocarcinomacell lines JEG-3 and BeWo. Furthermore, enzyme-linked immunosorbentassay showed that 6-chloromelatonin (a melatonin agonist) inhibits,in a dose-dependent manner, forskolin-stimulated hCG- secretionin JEG-3 (P < 0.001) and BeWo (P < 0.05) cells but hadno effect on basal human chorionic gonadotrophin (hCG-) levels.This effect of 6-chloromelatonin on forskolin-stimulated HCG-secretion was abolished by pertussis toxin (PTX), suggestingthat melatonin regulates hCG- production by an action involvingan inhibitory Gi/o protein. In PTX-treated BeWo cells, 6-chloromelatoninstimulated basal hCG- secretion (P < 0.001). CONCLUSION:These results demonstrate, for the first time, the expressionof melatonin receptors in human term placental tissues and inchoriocarcinoma cells and suggest a possible paracrine/autocrinefunction for melatonin in human placenta.