Modulation of DNA methylation status by dietary zinc: role in cancer prevention

描述（由申请人提供）： 表观遗传过程是致癌的关键驱动力，并受到饮食中必需营养素的调节。特别是，缺锌（ZD）减少了大鼠肝脏中S-腺苷甲硫氨酸（SAM）的甲基利用，导致整体DNA低甲基化。然而，ZD对癌发生中DNA甲基化的影响在很大程度上尚未探索。流行病学研究表明，饮食ZD与上呼吸消化道（UADT）癌症有关，包括食管癌和口腔癌。我们已经开发了体内癌症模型，重现了人类UADT癌症的特征。在啮齿类动物中，ZD单独通过引起细胞增殖和基因表达的广泛变化在UADT中产生癌前状态，从而增强致癌作用。锌补充（ZR）迅速逆转细胞增殖，纠正异常基因表达，并抑制肿瘤发生。重要的是，ZD饮食的p53+/-小鼠显示出低剂量致癌物导致UADT癌症的快速发展和进展。我们的新数据显示，DNA甲基转移酶DNMT 3A和DNMT 1在ZD与ZS大鼠食管中的过表达及其对ZR的抑制。基于这些观察结果，我们假设：A）低锌摄入增加了ZR通过调节表观遗传过程降低的UADT癌症风险;和B）ZD：p53+/-小鼠中锌和p53的联合缺乏诱导了有利于UADT肿瘤进展的特异性甲基化模式，其与ZS：p53+/-、ZD：p53+/+或ZS：p53+/+小鼠中显示的那些不同。目标1.使用体内ZD和ZR大鼠食管系统来确定：A）DNA甲基化是否是受膳食锌影响的表型和遗传变化的基础机制，通过在癌前ZD食管、正常锌充足（ZS）食管和恢复的ZR食管中确定：1）SAM、S-腺苷高半胱氨酸（SAH）的细胞内水平、Dnmt酶的活性和总体DNA甲基化状态，2）特定基因调控区CpG岛的甲基化状态，包括肿瘤抑制基因CDKN 2A和FHIT、修复基因MGMT和应激诱导基因MT-1;和B）DNA甲基转移酶抑制剂5-氮杂-2 ′-脱氧胞苷是否可以纠正ZD调节的表观遗传过程并抑制ZD大鼠中化学诱导的食管癌发生。目标二。采用限制性标记基因组扫描（RLGS）方法和小鼠NotI-EcoRV阵列文库，研究ZD：p53 +/-、ZS：p53+/-、ZD：p53+/+和ZS：p53+/+小鼠UADT癌变过程中食管和舌癌基因组启动子甲基化。本AIM将确定是否可以在ZD/ZS饮食的p53+/-和p53+/-小鼠中建立DNA甲基化模式与不同致瘤结果之间的联系。这些研究的结果将为膳食锌如何影响UADT癌症发展和预防中的表观遗传过程提供新的理解。此外，研究结果将确定这种致命癌症的化学预防，诊断和治疗的目标。

DESCRIPTION (provided by applicant): Epigenetic processes are key driving forces in carcinogenesis and are modulated by essential nutrients in the diet. In particular, zinc deficiency (ZD) reduces the utilization of methyl groups from S-adenosylmethionine (SAM) in rat liver, resulting in global DNA hypomethylation. The impact of ZD on DNA methylation in carcinogenesis, however, is largely unexplored. Epidemiological studies have shown that dietary ZD is associated with cancer of the upper aerodigestive tract (UADT), including esophageal and oral cancers. We have developed in vivo cancer models that reproduce features of human UADT cancer. In rodents, ZD alone creates a precancerous condition in the UADT by causing cell proliferation and extensive changes in gene expression, thereby enhancing carcinogenesis. Zinc replenishment (ZR) rapidly reverses cell proliferation, corrects abnormal gene expression, and inhibits tumorigenesis. Importantly, p53+/- mice on a ZD diet show speedy development and progression of UADT cancer by low doses of carcinogens. Our new data showed overexpression of DNA methyltransferase enzymes DNMT3A and DNMT1 in ZD versus ZS rat esophagus and their repression upon ZR. Based on these observations, we hypothesized: A) low zinc intake increases the risk of UADT cancer that ZR reduces through modulation of epigenetic processes; and B) combined deficiency of zinc and p53 in ZD:p53+/- mice induces specific methylation patterns that favor UADT tumor progression, which are different from those displayed in ZS:p53+/-, ZD:p53+/+ or ZS:p53+/+ mice. Aim 1. Use the in vivo ZD and ZR rat esophagus system to determine: A) whether DNA methylation is a mechanism that underlies the phenotypic and genetic changes effected by dietary zinc, by determining in precancerous ZD esophagus, normal zinc-sufficient (ZS) esophagus, and restored ZR esophagus: 1) intracellular levels of SAM, S- adenosylhomocysteine (SAH), activity of Dnmt enzymes, and global DNA methylation status, and 2) methylation status of CpG islands in regulatory regions of specific genes, including the tumor suppressor genes CDKN2A and FHIT, the repair gene MGMT, and the stress-inducible gene MT-1; and B) if the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine can correct ZD-modulated epigenetic processes and inhibit chemically induced esophageal carcinogenesis in ZD rats. Aim 2. To study genome-wide promoter methylation in esophagus and tongue in DNA from ZD:p53+/-, ZS:p53+/-, ZD:p53+/+, and ZS:p53+/+ mice during UADT carcinogenesis, by using restriction landmark genomic scanning (RLGS) method and the mouse NotI-EcoRV arrayed library. This AIM will determine whether linkages can be established between DNA methylation patterns and the diverse tumorigenic outcomes in p53+/- and p53+/- mice on ZD/ZS diets. The results of these studies will provide a new understanding of how dietary zinc impacts epigenetic processes in UADT cancer development and prevention. In addition, the results will identify targets for chemoprevention, diagnosis, and treatment of this deadly cancer.