Abstract 5719: Epigallocatechin-3-gallate, a green tea polyphenol, reactivates silenced tumor suppressor gene by modifying DNA methylation and histones in human skin cancer cells

Epigenetics, the heritable processes that modulate gene activity without changes in the DNA sequence, have gained considerable interest in cancer development and molecular targets of cancer treatment. Cancer epigenetics deal with important processes like DNA methylation and histone modification patterns that can either activate oncogenes or inactivate tumor suppressor genes, the crucial steps in tumor development. Accumulating data suggest that dietary factors may alter cancer risk by modifications of epigenetic processes in the cancer cell. Therefore, the present study was designed to investigate whether (−)-epigallocatechin-3-gallate (EGCG), a most potent polyphenol from green tea which has anti-carcinogenic activity, would alter epigenetic events to regulate methylation-silenced tumor suppressor genes in human skin cancer cells. DNA methylation, histone modification and gene expression profile were studied using human epidermoid carcinoma A431 cells and melanoma cells as an in vitro model after EGCG treatment using RT-PCR, western blot analysis, cytostaining, southwestern dot-blot analysis, chromatin immunoprecipitation, enzymatic activity assays and fluorescence activated cell sorting (FACS) analysis of apoptotic cell death. Our study shows that treatment of A431 cells for 3 or 6 days with EGCG at lower concentrations (5, 10 and 20 μg/ml) resulted in DNA demethylation and reduction in the mRNA and protein levels of DNA methyltransferases (DNMTs) 1 and 3a and 3b and the activity of DNMTs in A431 cells in a dose- and time-dependent manner. EGCG also increased the levels of acetylated lysine 9 and lysine 14 on histone H3 (H3-Lys 9, H3-Lys 14), but decreased levels of methylated H3-Lys 9. Under identical conditions, EGCG re-expressed mRNA and protein levels of tumor suppressor genes, p16^INK4a and p21WAF1/CIP1, in A431 cells in a dose-dependent manner. Re-expression of p16^INK4a and p21 by EGCG treatment of the A431 cells leads to the inhibition of cell proliferation and induction of apoptosis of A431 cells. Together, our study demonstrates that EGCG can epigenetically modulate DNA and histones to activate methylation-silenced tumor suppressor genes. These epigenetic modifications by EGCG may contribute to skin cancer prevention/treatment strategies in humans.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5719.