Reactivation of GSTP1 Gene by Green Tea Polyphenols

描述(由申请人提供) 通过DNA甲基化改变基因表达和通过组蛋白重塑染色质被认为是前列腺癌发生和发展中最重要的表观遗传学变化。其中一种改变是通过5‘调控区CpG岛上脱氧胞苷残基的甲基化来沉默谷胱甘肽S转移酶p1的表达，GSTP1是致癌物质防御的关键酶。GSTP1功能缺失似乎是前列腺上皮内瘤变病变的特征，自始至终代表前列腺癌的先兆。近年来，绿茶作为一种防癌药物引起了人们的极大兴趣，我们最近证明，在人类可达到的剂量下，口服绿茶多酚(GTP)可显著抑制转基因小鼠前列腺癌(TRAMP)模型的前列腺癌发生，重要的是提高这些小鼠(PROC)的无瘤生存和总存活率。娜塔莉。阿卡德。SCI。美国98：10350-5,2001年)。这项研究为绿茶可以作为前列腺癌的补充和替代药物(CAM)提供了理论基础。在细胞培养系统和有限的动物模型中进行的广泛的实验室研究进一步证明，绿茶多酚对不同类型的致癌物具有保护作用，并诱导II相酶活性，从而增强解毒过程。重要的是，如果饮用绿茶可以恢复或补偿前列腺癌中GSTP1的活性，并可以减缓前列腺癌的发生过程，这可能与预防和/或治疗前列腺癌有关。由于DNA甲基化受DNA甲基转移酶(DNMT)和DNA组蛋白脱乙酰酶(HDAC)的相对活性的影响，本研究的创新之处在于绿茶多酚可能通过调节DNMT和HDAC的活性来重新激活人前列腺癌LNCaP和MDA Pca 2b细胞中GSTP1的表达。重要的是，这些酶的基础水平是良性前列腺增生症和正常人类前列腺上皮细胞的两到三倍，并包含完全高甲基化的GSTP1 CpG岛等位基因。具体地说，我们将研究绿茶多酚在以下方面的潜在作用：1)GSTP1基因启动子区域高甲基化的CpG岛等位基因的去甲基化及其重新激活；2)调节DNMT和HDAC的活性和表达；3)改变LNCaP和MDA PCA 2b细胞中总的和乙酰化的组蛋白H3和H4的蛋白表达。这项提案的成功完成将为确定绿茶多酚在调节前列腺癌表观遗传事件中的作用建立一个平台，这可能有助于开发绿茶作为用于前列腺癌患者的CAM。

DESCRIPTION (provided by applicant) Modifications in gene expression through DNA methylation and remodeling of chromatin via histone proteins are believed to be the most important epigenetic changes observed in initiation and development of prostate cancer. One such alteration is silencing of the expression of glutathione S-transferase-pi (GSTP1), a critical enzyme of carcinogen defense, through methylation of deoxycytidine residue in CpG islands in the 5'- regulating region. Loss of GSTP1 function appears to be the characteristic of prostatic intraepithelial neoplasia lesions, throughout to represent prostate cancer precursors. In recent years, green tea has gained considerable interest as a cancer preventive agent and we have recently demonstrated that oral consumption of green tea polyphenols (GTP) at human achievable dose results in significant inhibition of prostate carcinogenesis in transgenic adenocarcinoma of the mouse Prostate (TRAMP) model and importantly lead to increased tumor free and overall survival of these mice (Proc. Natl. Acad. Sci. USA 98: 10350-5, 2001). This study provides rationale that green tea could be developed as complementary and alternative medicine (CAM) for prostate cancer. Extensive laboratory studies in cell culture systems and in limited animal models have further demonstrated that green tea polyphenols afford protective effects from diverse types of carcinogens and induce phase II enzyme activity that could lead to enhanced detoxification process. Importantly, if drinking green tea can restore or compensate the GSTP1 activity in the prostate and can slow down the process of prostate carcinogenesis that may have relevance for prevention and/or treatment of this disease. Since DNA methylation is influenced by the relative activities of DNA methyltransferases (DNMT) and DNA histone deacetylases (HDAC), the innovative idea to be tested in this proposal is that green tea polyphenols has potential to reactivate the expression of GSTP1 by modulating the enzyme activity of DNMT and HDAC in human prostate carcinoma LNCaP and MDA PCa 2b cells. Importantly, the basal levels of these enzymes are two- to three- folds higher than benign prostatic hyperplasia and normal human prostate epithelial cells and contain completely hypermethylated GSTP1 CpG island alleles. Specifically, we will investigate the potential of green tea polyphenols in i) demethylation of the hypermethylated CpG island alleles in the promoter region of GSTP1 gene and its reactivation, ii) modulation of DNMT and HDAC activity and expression, and iii) alteration in the total and acetylated histone H3 and H4 protein expression in LNCaP and MDA PCa 2b cells. Successful completion of this proposal will set a platform to define the role of green tea polyphenols in modulating epigenetic events in prostate cancer that may contribute to the development of green tea as CAM for its use in prostate cancer patients.