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

描述(由申请人提供)： 表观遗传过程是癌症发生的关键驱动力，并受饮食中必要营养物质的调节。尤其是缺锌(ZD)使大鼠肝脏中S-腺苷甲硫氨酸(SAM)甲基的利用减少，导致DNA甲基化水平降低。然而，ZD在致癌过程中对DNA甲基化的影响在很大程度上还没有被探索。流行病学研究表明，膳食中的ZD与上呼吸道癌症(UADT)有关，包括食道癌和口腔癌。我们已经开发了体内癌症模型，复制了人类UADT癌症的特征。在啮齿动物中，ZD单独通过引起细胞增殖和基因表达的广泛变化，在UADT中造成癌前状态，从而促进癌症的发生。补锌(ZR)能迅速逆转细胞增殖，纠正基因异常表达，抑制肿瘤发生。重要的是，服用ZD饮食的P53+/-小鼠通过低剂量的致癌物表现出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DNMT3A和DNMT1在ZD和ZS大鼠的食道中过表达，并对ZR有抑制作用。基于这些观察，我们假设：A)低锌摄入增加了ZR通过调节表观遗传过程而降低的UADT癌症的风险；以及B)ZD：P53+/-小鼠中锌和P53的联合缺乏诱导了有利于UADT肿瘤进展的特定甲基化模式，这与ZS：P53+/-、ZD：P53+/+或ZS：P53+/+小鼠中显示的不同。目的1.利用体内ZD和ZR大鼠食道系统，通过检测癌前病变ZD食道、正常缺锌(ZS)食道和修复ZR食道：1)细胞内SAM、S同型半胱氨酸(SAH)、DNMT酶活性和整体DNA甲基化状态，以及2)特定基因(包括抑癌基因CDKN2A和FHIT、修复基因MGMT和应激诱导基因MT-1)调控区域中CpG岛的甲基化状态，来确定DNA甲基化是否是饮食锌影响食道表型和遗传变化的机制；DNA甲基转移酶抑制剂5-氮杂-2‘-脱氧胞苷是否能纠正ZD调控的表观遗传过程并抑制化学诱导的ZD大鼠食道癌的发生。目的2.应用限制性地标基因组扫描(RLGS)方法和小鼠Noti-EcoRV阵列文库，研究UADT致癌过程中ZD：P53+/-、ZS：P53+/-、ZD：P53+/+和ZS：P53+/+小鼠全基因组DNA启动子甲基化情况。这项研究将确定是否可以在ZD/ZS饮食的P53+/-和P53+/-小鼠的DNA甲基化模式和不同的致瘤结果之间建立联系。这些研究的结果将对饮食锌如何影响UADT癌症发展和预防的表观遗传过程提供新的理解。此外，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.