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. ? ?
