Folate, DNA Methylation and Breast Tumorigenesis

描述(申请人提供)：异常的DNA甲基化是包括乳腺肿瘤在内的癌细胞的特征。癌细胞DNA通常是低甲基化的，但表现出高甲基化的区域，特别是在保护细胞免受致癌转化的基因(例如肿瘤抑制基因)的启动子区域。这种由甲基-CpG结合蛋白介导的超甲基化抑制了基因的表达，表明这些基因的去甲基化可能有助于控制或逆转肿瘤的发生过程。叶酸是合成S-腺苷甲硫氨酸所必需的维生素B，腺苷甲硫氨酸是DNA甲基化的甲基供体。在肿瘤发生过程中，叶酸状态的改变可能会影响DNA甲基化。这项建议的总体目标是评估叶酸状态和DNA去甲基化对乳腺癌前病变向恶性肿瘤转化的影响。将要测试的假设是：1)与叶酸充足的对照组相比，叶酸缺乏的小鼠和DNA去甲基化剂5-氮杂脱氧胞苷治疗的小鼠的癌前病变生长、肿瘤发生率和肿瘤大小降低，肿瘤潜伏期延长；2)与叶酸充足的对照组相比，饲喂过量叶酸的小鼠癌前病变生长和肿瘤发生率及大小增加，肿瘤潜伏期缩短；3)与叶酸充足和叶酸过量的小鼠相比，叶酸缺乏和5-氮杂脱氧胞苷治疗的小鼠乳腺癌前病变中一组高甲基化基因发生去甲基化，从而使其过度表达。为了验证这些假设，癌前雌激素受体阳性的乳腺病变，称为乳腺上皮内瘤变(MIN-O‘s)，具有既定的和一致的恶变率，将被移植到饲喂叶酸充足、不足和过量饮食的小鼠的乳房脂肪垫中，以及暴露于5-氮杂脱氧胞苷的叶酸充足的小鼠的乳房脂肪垫中。将比较治疗组之间的Min-O生长、肿瘤潜伏期、发病率和大小、病理特征、基因表达谱、基因特异性启动子甲基化和甲基CpG结合蛋白的基因靶向。预计这些研究将证明叶酸和DNA甲基化在乳腺肿瘤发生中的作用，并将识别特定的高甲基化基因，这些基因有助于乳腺癌前病变向恶性肿瘤的转变。

DESCRIPTION (provided by applicant): Aberrant DNA methylation is a characteristic of cancer cells, including mammary tumors. Cancer cell DNA is typically hypomethylated, but exhibits areas of hypermethylation, particularly in the promoter regions of genes that protect cells from tumorigenic transformation (e.g. tumor suppressor genes). Such hypermethylation, mediated by methyl-CpG-binding proteins, inhibits gene expression, suggesting that demethylation of these genes may prove beneficial in controlling or reversing the tumorigenesis process. The B vitamin, folate, is required for the synthesis of S-adenosylmethionine, the methyl donor for DNA methylation. Alterations in folate status may affect DNA methylation during tumorigenesis. The overall goal of this proposal is to assess the influence of folate status and demethylation of DNA on the transformation of premalignant mammary lesions to malignancy. The hypotheses to be tested are: 1) premalignant mammary lesion growth and tumor incidence and size are decreased, and tumor latency is prolonged in folate-deficient mice and in mice treated with the DNA-demethylating agent, 5-aza-deoxycytidine, compared with folate-replete controls, 2) premalignant lesion growth and tumor incidence and size are increased, and tumor latency is reduced in mice fed excess folate compared with folate-replete controls, and 3) a subset of hypermethylated genes are demethylated and consequently become over-expressed in premalignant mammary lesions from both folate-deficient and 5-aza-deoxycytidine-treated mice compared with folate- replete and folate-excess mice. To test these hypotheses, premalignant, estrogen receptor positive mammary lesions, known as mammary intraepithelial neoplasia outgrowths (MIN-O's), with an established and consistent rate of malignant transformation, will be transplanted into the mammary fat pads of mice fed folate-replete, deficient, and excess diets, as well as in folate-replete mice exposed to 5-aza-deoxycytidine. MIN-O growth, tumor latency, incidence and size, pathological characterizations, gene expression profiles, gene-specific promoter methylation, arid gene targeting by methyl-CpG-binding proteins will be compared among the treatment groups. It is expected that these studies will demonstrate roles of folate and DNA methylation in mammary tumorigenesis, and will identify specific hypermethylated genes that contribute to the transition from premalignant mammary lesions to malignancy.