Dietary polyphenols are common in the human diet and have chemopreventive and anticancer activities. Green tea is one of the most consumed beverages worldwide and a major constituent of green tea is the polyphenol (-)-epigallocatechin gallate (EGCG). Many studies have shown that EGCG has potent anticancer properties but the mechanisms whereby EGCG imparts these effects are unknown. Recent studies have indicated that this dietary polyphenol alters the activity of DNA methyltransferase I leading to changes in the expression of methylation-controlled cancer genes. Telomerase is an important gene involved in oncoqenesis that is controlled through DNA methvlation and we have found that EGCG down-regulates transcription of hTERT (the catalytic subunit of telomerase) in cancer cells leading to apoptosis. In addition to the DNA methyltransferases, histone deacetylases are also important epigenetic regulators of the telomerase gene in cancer. The main hypothesis of this proposal is that EGCG alters the epigenetic expression of telomerase in cancer cells leading to telomerase inhibition and induction of apoptosis. A secondary hypothesis is that this occurs through the effects of EGCG on the DNA methyltransferases and/or histone deacetylases which alter telomerase gene expression. To test these hypotheses, Aim 1 is to measure changes in DNA methylation and histone acetylation of the hTERT promoter in EGCG-treated and -untreated cancer and control cells.
Aim 2 is to detect the binding of the E2F-1 methylation-sensitive repressor to the hTERT promoter in ECGC-treated and -untreated cancer and control cells.
Aim 3 is to evaluate the in vivo mechanisms of EGCG-mediated telomerase inhibition using xenografts implanted into nude mice. The goal of this project is to elucidate the in vitro and in vivo epigenetic mechanisms whereby EGCG, a common dietary component, causes growth inhibition of cancer cells. Ultimately, completion of this proposal may lead to elucidation of the mechanisms through which dietary polyphenols mediate their chemopreventive and anticarcinogenic effects thereby facilitating more effective uses of green tea and/or polyphenols in cancer prevention and therapy. ? ?
|Berletch, Joel B; Liu, Canhui; Love, William K et al. (2008) Epigenetic and genetic mechanisms contribute to telomerase inhibition by EGCG. J Cell Biochem 103:509-19|
|DeAngelis, J Tyson; Farrington, Woodrow J; Tollefsbol, Trygve O (2008) An overview of epigenetic assays. Mol Biotechnol 38:179-83|
|Cunningham, Amanda P; Andrews, Lucy G; Tollefsbol, Trygve O (2007) Retrovirus-mediated RNA interference. Targeting hTERT through stable expression of short-hairpin RNA. Methods Mol Biol 405:39-46|
|Hansen, Nathan J; Wylie, Rebecca C; Phipps, Sharla M O et al. (2007) The low-toxicity 9-cis UAB30 novel retinoid down-regulates the DNA methyltransferases and has anti-telomerase activity in human breast cancer cells. Int J Oncol 30:641-50|
|Lai, Serene R; Cunningham, Amanda P; Huynh, Vu Q et al. (2007) Evidence of extra-telomeric effects of hTERT and its regulation involving a feedback loop. Exp Cell Res 313:322-30|
|Liu, L; Andrews, L G; Tollefsbol, T O (2006) Loss of the human polycomb group protein BMI1 promotes cancer-specific cell death. Oncogene 25:4370-5|
|Cunningham, A P; Love, W K; Zhang, R W et al. (2006) Telomerase inhibition in cancer therapeutics: molecular-based approaches. Curr Med Chem 13:2875-88|