Effects of Estrogen Metabolite 2-Methoxyestradiol on Tumor Suppressor Protein p53 and Proliferation of Breast Cancer Cells

Abstract

An endogenous 17β-estradiol (E(2)) metabolite, 2-methoxyestradiol (2-ME(2)), has been reported to exhibit estrogen receptor (ER)-independent anti-angiogenic and anti-tumor effects. Several mechanisms have been proposed for 2-ME(2) actions, but there is a lack of evidence for a common pathway for all of the cell-types sensitive to this metabolite. We have examined potential alterations in p53 in response to 2-ME(2), E(2) and the microtubule disruptor taxol in T47D breast cancer cells. Cells were cultured for six days in medium depleted of endogenous steroids or effectors. Semi-confluent cells were treated with 2-ME(2) (1 nM - 10 µM), 10 nM E(2) and/or 1 µM taxol and subjected to SDS-PAGE and Western blot analysis, quantitative analysis, or laser-scanning confocal microscopy. Western blot analysis revealed a concentration-dependent biphasic trend in p53 levels. Addition of 10 nM - 1 µM 2-ME(2) induced significant up-regulation in p53, and this response gradually diminished to levels comparable to the control upon treatment with higher concentrations (2.5 - 10 µM). The observed upregulation of p53 induced by 2-ME(2) is inhibited by concurrent treatment with 1 µM taxol. Cell quantitation revealed a significant decrease (50 - 90%) in cell number upon treatment with 1 - 10 µM 2-ME(2) with minimal effect at lower concentrations. No additional effect on cell proliferation was observed when taxol was combined with 10 nM or 1 µM 2-ME(2). In a concentration dependent manner, treatment with 2-ME(2) for 24 h differentially influenced cellular localization of p53. These results may aid in further understanding the relationship between steroid receptors, tumor suppressor proteins, and effects of hormone metabolites on breast cancer cells.