DIET CANCER AND ONCOGENE EXPRESSION IN INBRED MICE

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The goals of this research are: 1. to determine whether dietary levels of lipotropes (methionine, choline, folic acid, and Vitamin B12) can influence the time of onset and/or severity of tumors in inbred mice of strains that have a high spontaneous incidence of leukemia or hepatomas; 2. to determine what effect the dietary level of lipotropes has on methylation of DNA (overall and of several specific genes); and 3. to determine whether the level of dietary lipotropes affects time and quantity of oncogene expression. Mice of the strains AKR/J, C3H/HeJ, B6C3F1/J and C57BL/6J will be fed semipurified diets that are either deficient, adequate, or enriched with lipotropes. After receiving one of the diets listed above for periods ranging from one week to three months, the animals will be sacrificed and RNA and DNA will be isolated from their excised tissues. Extent of hypomethylation of DNA will be assayed by measuring the ability of DNA to accept methyl groups in vitro in assays with homologous enzymes, by determining the ratio of 5-methylcytosine to cytosine of the DNA, and by determining the susceptibility of genomic DNA to cleavage by restriction endonucleases, whose action is sensitive to the presence of 5-methylcytosine or cytsine residues in their recognition/cleavage sites. We will study the restriction endonuclease digestion patterns of c-myc, c-Ha -ras, c-Ki-ras and several other oncogenes. We will utilize DNA:RNA hybridization techniques to determine the levels of mRNA for these oncogenes. Long term feeding of the diets of differing lipotrope content will be carried out to see whether this results in alterations in the time of spontaneous onset or number and severity of hepatic tumors in C3H and B6C3F1 mice, and the time of on set and severity of leukemia in ARK mice. C57BL/6 mice, which have low spontaneous cancer incidence will be used as controls. It is known that lipotrope-deficient diets promote chemical carcinogenesis in rodents, and that diets supplemented with methionine and choline can cause a decreased response to some carcinogens, but it is not known whether supplements of methionine and choline can suppress or whether lipotrope deficiency can accelerate the development of cancer in animals with an inherited high frequency of neoplasia.