Folate, DNA Methylation and Breast Tumorigenesis

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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.