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

Abstract

An endogenous 17β-estradiol (E₂) metabolite, 2-methoxyestradiol (2-ME₂), has been reported to exhibit estrogen receptor (ER)-independent anti-angiogenic and anti-tumor effects. Several mechanisms have been proposed for 2-ME₂ 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-ME₂, E₂ 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-ME₂ (1 nM – 10 µM), 10 nM E₂ 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-ME₂ 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-ME₂ 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-ME₂ 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-ME₂. In a concentration dependent manner, treatment with 2-ME₂ 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.

Keywords:

• 2-Methoxyestradiol
• breast cancer
• estrogen
• p53
• tumor suppressor protein

Acknowledgments

This research was made possible by support from Oakland University Cancer Research Program and Provost's Graduate Student Research Awards to AES and ALS. SD acknowledges support from Center for Biomedical Research, Oakland University.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.