Distinct effects of gonadotropin-releasing hormone analogs and 4-hydroxytamoxifen on pS2 mRNA expression with respect to cell proliferation in MCF-7 breast cancer cells.

Gonadotropin-releasing hormone (GnRH) analogs and antiestrogens display direct antiestrogenic effects on the proliferation of hormone-sensitive breast cancer cells. This study aimed to determine whether growth inhibition of 17 beta-estradiol-stimulated MCF-7 breast cancer cells by the agonist D-Trp6 GnRH, the GnRH antagonist BIM 21009C and 4-hydroxy-tamoxifen (OHT) respectively occurred through alterations of the estrogen receptor (ER)-mediated intracellular pathway. The pS2 mRNA expression is primarily dependent on activated ER in MCF-7 cells, and pS2 protein could act as a growth factor. Drug effect on pS2 mRNAs were qualitatively compared to those on the cell cycle. Unlike OHT, GnRH analogs did not suppress the 17 beta-estradiol-induced pS2 mRNA expression whilst the cell cycle was blocked. The pS2 mRNA expression was induced by D-Trp6 GnRH alone without effect on the cell cycle. The outcome of our study is double. Firstly, GnRH analogs are distinct from OHT as regards their effects on the ER-mediated intracellular pathway. Secondly, pS2 mRNA expression is not strictly related to MCF-7 cell proliferation, suggesting that pS2 protein has a function other than that of critical growth regulator.