MOLECULAR MECHANISMS OF DIET-INDUCED CARCINOGENESIS

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Epidemiological and clinical studies have demonstrated that folate deficiency in humans could lead to susceptibility to certain types of cancers. Premalignant dysplasia could be reversed by folate supplementation. Elucidation of the molecular mechanisms underlying folate deficiency and predisposition to cancer is, therefore, of critical importance in determining the role of folate and other dietary elements in cancer prevention. An excellent rat model system is available to study the role of diet low in methionine, choline and folate (lipotrope-deficient or LD diet) on the induction of hepatocarcinogenesis in the absence of any exogenous xenobiotic agents. It is known that a key tumor suppressor (p53) gene is methylated in the hepatoma induced by LD diet. Using this model system, we will (a) explore by Bisulfite genomic sequencing and Ms-SNuPe (Methylation- sensitive single nucleotide primer extension) the methylation status of CpG dinucleotides on p53 promoter at different stages of hepatocarcinogenesis (b) investigate the role of methylation of specific CpG dinucleotides in p53 promoter inactivation by transient transfection assay (c) investigate the mechanism of methylation-mediated alteration in chromatin structure and identify the key factors involved in consequent silencing of p53 promoter with progression of tumorigenesis, by restriction endonuclease accessibility assay and chromatin immunoprecipitation (ChIP) with antibodies specific to methyl CpG binding proteins (MeCPs) (d) study the regulation of expression and activity of different DNA methyltransferase isozymes (involved in maintenance and de novo methylation) during hepatocarcinogenesis induced by LD diet (e) identify the proteins that interact with de novo methylases (f) clone the genes, specifically the three genes that are methylated in preneoplastic liver as detected by RLGS technique, identify them, investigate their expression levels at different stages of tumorigenesis and study functional significance of silencing of these genes in tumorigenesis. It is hoped that this study will yield important information concerning the relationship of folate/methyl deficiency to regional hypermethylation of growth/tumor suppressor genes or genes encoding proteins that suppress the growth regulatory genes at different stages of tumorigenesis, and their silencing that lead to tumor formation.