Differential effects of estrogen and estrogen receptor antagonist, ICI 182 780, on the expression of calbindin-D9k in rat pituitary prolactinoma GH3 cells

Objective: To detect the effects of 17β-estradiol (E2) on the expression of calbindin-D9k (CaBP-9k) in pituitary GH3 cells, and to determine the antagonistic effect of a selective estrogen receptor (ER) antagonist (ICI 182 780) on CaBP-9k expression. Methods: A rat pituitary prolactinoma cell line (GH3 cells) was used in an in vitro model. The localization of CaBP-9k in GH3 cells was observed by immunofluorescence. GH3 cells were cultured with the addition of E2 medium for 24 hours. The levels of CaBP-9k mRNA and protein expression in different groups were analyzed by RT-PCR and Western blot analysis. The ER antagonist, ICI 182 780, was added to GH3 cells before E2 (10-8 M) at a concentration of 10-6 M to investigate the regulation of an ER-mediated pathway on CaBP-9k expression. Results: E2 had a stimulatory effect on CaBP-9k expression of GH3 cells in a dose-dependent manner; the level of CaBP-9k expression was higher when treated with a higher concentration of E2. ICI 182 780 suppressed the stimulatory effect of E2 on CaBP-9k expression in GH3 cells. The level of CaBP-9k expression was significantly reduced by co-administration of E2 with ICI 182 780 in GH3 cells. The immunoprecipitation results confirmed that CaBP-9k interacts directly with ERα, and E2 increases the interaction between CaBP-9k and ERα. Conclusion: Estrogen induces CaBP-9k expression via an ERα-mediated pathway and CaBP-9k directly combines with ERα, suggesting that CaBP-9k is involved in the biological effects mediated by an ER pathway in GH3 cells.