Tea Modulation of Colon Carcinogenesis

描述（由申请人提供）：在致癌途径中沉默的重要基因的表观遗传重新表达代表了癌症化学预防的一个令人兴奋的新领域。该项目的长期目标是确定自然发生的植物化学物质，逆转主细胞信号通路的抑制。其中一个主开关是类视黄醇X受体（RXR）。RXR也被认为参与了不依赖apc的β -连环蛋白的降解，这关键地将其置于细胞信号分子串扰的中心，这些信号分子在结肠肿瘤发生中经常被破坏。绿茶中的多酚具有广泛的癌症化学预防作用。据报道，至少一种绿茶儿茶素，表没食子儿茶素没食子酸酯（EGCG）可以恢复鳞状细胞癌中沉默的生长调节基因的活性。我们的初步数据表明，绿茶可以调节RXR α基因启动子的高甲基化，并抑制偶氮氧甲烷处理的ApcMIN/+小鼠肠道肿瘤的发生。我们假设RXRa在结肠癌早期因基因缺失，绿茶多酚通过抑制dmnt和hdac恢复其活性，为结肠癌的化学预防提供了一种新的机制。我们的目标是：在Specific Aim 1中，在结肠癌细胞系和人类结直肠肿瘤中确定RXRa的缺失是结肠癌的早期事件。在Specific Aim 2中，在结肠癌细胞系中，确定EGCG是否负责与RXRa， RAR¿，hMLH1， p14arf和p16INK4a启动子区域相关的hdac的变化，并将其活性与其他已知的hdac抑制剂进行比较。在Specific Aim 3中，我们将确定DNA甲基转移酶（dnmt）的抑制是否是结肠癌细胞系中RXRa活性和其他甲基化靶基因表观遗传调控的重要组成部分。在Specific Aim 4中，我们将研究绿茶/EGCG干预对RXRa+/-结肠癌AOM小鼠RXRa基因剂量的化学预防作用。我们还将研究绿茶/EGCG干预对ApcMIN/+ RXR+/-和ApcMIN/+ RXR+/+双基因小鼠肠道肿瘤发生的影响。这一目标的工作假设是，RXRa缺失会增加RXRa缺陷小鼠的结肠癌发生。我们还探讨了GT和EGCG干预对AOM处理的ApcMIN/+ RXR+/-基因型小鼠中沉默RXRa再激活的影响。

DESCRIPTION (provided by applicant): Epigenetic re-expression of important genes silenced in the pathway of carcinogenesis represents an exciting new area for cancer chemoprevention. The long-range goal of this project is to identify naturally occurring phytochemicals that reverse the inhibition of master cell signaling pathways. One such master switch is the retinoid X receptor (RXR). That RXR is proposed to also be involved in Apc-independent degradation of beta- catenin pivotally places it at the center of crosstalk of cell signaling molecules, often corrupted in colon tumorigenesis. Polyphenols from green tea have widespread cancer chemopreventive activity. At least one of the green tea catechins, epigallocatechin gallate (EGCG) has been reported to restore activity of silenced growth regulatory genes in squamous cell cancers. Our preliminary data suggest that green tea modulates the hypermethylation of RXR alpha gene promoter, and inhibits intestinal tumorigenesis in the azoxymethane- treated ApcMIN/+ mouse. We hypothesize that RXRa is lost early in colon cancer due to gene and that green tea polyphenols restore this activity by inhibition of DMNTs and HDACs, providing a novel mechanism of chemoprevention for colon cancer. Our aims are: In Specific Aim 1, in colon cancer cell lines and in human colorectal tumors establish that loss of RXRa is an early event in colon cancer. In Specific Aim 2, in colon cancer cell lines, determine if EGCG is responsible for changes in HDACs that associate with the promoter region of RXRa, RAR¿, hMLH1, p14arf, and p16INK4a and compare this activity with other known inhibitors of HDACs. In Specific Aim 3, we will determine if inhibition of DNA methyltransferases (DNMTs) is an important component of epigenetic regulation of RXRa activity and other methylated target genes in colon cancer cell lines. In Specific Aim 4 we will examine the chemopreventive effects of green tea/EGCG intervention on RXRa gene dosage in RXRa+/- mice with the colon carcinogen, AOM. We will also examine the effects of green tea/EGCG intervention in intestinal tumorigenesis in ApcMIN/+ RXR+/- and ApcMIN/+ RXR+/+ bigenic mice. The working hypothesis for this aim is that loss of RXRa will augment colon carcinogenesis in RXRa deficient mice. We also explore the effects of GT and EGCG intervention on the reactivation of silenced RXRa in the AOM- treated ApcMIN/+ RXR+/- bigenic mice. PUBLIC HEALTH RELEVANCE: Silencing of critical regulatory genes by epigenetic mechanisms may play a critical role in colon cancer. We hypothesize that green tea polyphenols suppress DNA methyltransferases and histone acetylase activity. This, in turn, may allow re-expression of growth regulatory genes and provide a means of cancer control for this disease. Because RXRa loss involves impairment of regulatory gene networks, the impact of green tea reversal of this transcription factor's loss is significant.