Abstract 818: Chronic oxidative stress induces conversion of estrogen-dependent non-aggressive breast cancer cells into estrogen-independent aggressive phenotype

Abstract

Abstract We have recently reported increased growth and tumorigenic potential of estrogen receptor (ER) positive breast cancer cells with chronic exposure to oxidative stress. In this study, we evaluated mechanistic basis for chronic oxidative stress-induced aggressiveness in ER positive MCF-7 breast cancer cells. Loss of estrogen dependency is known to be associated with acquisition of aggressive form in breast cancer cells. Therefore, the objective of this study was to evaluate changes in estrogen response in ER-positive breast cancer cells exposed to chronic oxidative stress. MCF-7 cells were exposed to hydrogen peroxide (H2O2)-induced oxidative stress for chronic period (6 months). Using these cells, growth response to 17-β estradiol was evaluated by MTT assay and cell cycle analysis. Surprisingly, in response to 17-β estradiol treatment, there was no significant growth stimulation in cells exposed to chronic oxidative stress. Cell cycle analysis by flow cytometry further confirmed the cell growth data. Quantitative RT-PCR analysis also revealed significant down regulation of ER-α in chronically exposed breast cancer cells. To understand the role of epigenetic mechanism, the expression of epigenetic regulatory genes were determined at both transcript and protein level. In addition, the levels of histone modifications were also evaluated by Western blot analysis. Changes in both the expression of epigenetic regulatory genes (DNMT1, DNMT3b, HDAC1, MBD4, and HAT1) and the levels of histone modifications (H3K27 tri-methylation and H3K18 acetylation) were observed in MCF-7 cells chronically exposed to H2O2. Treatment with DNA de-methylating agent (5-aza-2′-deoxycytidine) restored the ER-α expression level, estrogen-induced growth and oxidative stress induced histone modifications. To summarize, the findings of this study suggest that chronic exposure to oxidative stress can convert estrogen-dependent non-aggressive breast cancer cells into estrogen-independent aggressive form potentially by epigenetic mechanism. Citation Format: Prathap Kumar S. Mahalingaiah, Logeswari Ponnusamy, Kamaleshwar P. Singh. Chronic oxidative stress induces conversion of estrogen-dependent non-aggressive breast cancer cells into estrogen-independent aggressive phenotype. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 818. doi:10.1158/1538-7445.AM2015-818