Melatonin-induced estrogen receptor α-mediated calbindin-D9k expression plays a role in H2O2-mediated cell death in rat pituitary GH3 cells

Calbindin-D9k (CaBP-9k) is a 9-kDa polypeptide possessing two calcium-binding sites that is expressed in the mammalian intestine, uterus, and pituitary gland. The factors regulating the expression of the estrogen receptor (ER) and CaBP-9k in the pituitary gland are currently unknown. In this study, we investigated whether the ER and CaBP-9k expression are regulated by melatonin during H2O2-induced cell death in rat pituitary GH3 cells. Cell survival increased by approximately 27-36% in H2O2 plus melatonin compared to H2O2 alone, and CaBP-9k expression was augmented by treatment with H2O2 plus melatonin. These results suggest that the increase in cell survival and the melatonin-induced CaBP-9k expression may play a role in protecting cells against H2O2-mediated cell death. This result is also consistent with the increase in CaBP-9k expression leading to rises in p-ERK and p-Bad (S112). Over-expression of CaBP-9k caused an increase in p-ERK. ER alpha expression was higher in H2O2 plus melatonin-treated cells compared to those treated with H2O2 alone, while ER beta expression was not. Also, ER alpha in the nuclear fraction increased in the presence of melatonin and decreased in the presence of ICI 182 780 or ICI 182 780 plus melatonin. The relative binding affinity of ER alpha for melatonin was higher than that of ER beta, suggesting that melatonin has the potential to preferentially bind ER alpha. In conclusion, these results indicate that melatonin may increase CaBP-9k expression through ER alpha.