Differential Regulatory Effects of Nitric Oxide on Estrogen Stimulated MCF7 Breast Cancer Cell Growth

Abstract

17-β estradiol (E2) stimulates the growth of estrogen receptor (ER)positive cells such as MCF7 line of human breast cancer cells. There have been reports showing E2 affects the level of endothelial nitric oxide synthase (eNOS) expression and its activity in vitro. Using ER positive MCF7 breast cancer cells as a model, we have studied the relationship between E2 and NO in controlling cell growth. MCF7 cells were cultured in medium containing 5% charcoal-stripped fetal bovine serum (SFBS) or serum-free medium (SFM) respectively. Using [methyl-3H]thymidine incorporation as the growth assay, E2 stimulated cell growth in a dose-response manner under both conditions. In the presence of 5 mM N-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOS, an enhancement of E2 stimulation on MCF7 cell growth of up to 2 folds was observed when cultured with 5% SFBS, however, it completely blocked the stimulatory effect of E2 on cell growth under serum-free condition. Fluorescent agent DAF-2A was used to measure NO production by MCF7 cells under different treatments. We found 1 nM E2 decreased NO production by 50% compared with untreated cells in 5% SFBS but did not significantly change NO production under serum-free condition. 5 mM L-NAME suppressed NO production in all conditions below their respective untreated control level. Our data show that in spite of the stimulatory effect of E2 on MCF7 cell growth, there is a differential regulation of NO production by E2 under different culture conditions and NO in turn differentially regulates the growth activity of breast cancer cells.