NUTRITIONAL REGULATION OF RAS PROTO-ONCOGENE ACTIVITY

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The primary goal of this project is to investigate the links between nutritional factors and the activity of ras proteins in a cell culture system. The important role of mutated ras gene products in a variety of human cancers is well established. In addition, many (but not all) studies suggest that elevated levels of unmutated ras proteins are found in many colon and breast cancers. Although the function of ras in the cell remains to be determined, escape by ras from normal regulation can result in morphological transformation and appears to be a frequent event in the multi-step genesis of cancer. Several observations suggest that nutritional status may affect ras activity. First, the equivalent of a key regulatory protein of ras activity appears to act as a sensor for nutritional status in yeast; similar functions may have been conserved in higher eucaryotes. Second, specific lipids have been shown to have direct and indirect effects on ras activity in vitro. Third, nutritional parameters may modulate ras activity by influencing the post-translational lipid modifications of the proteins that are required for activity. Conceivably, such lipid effects could be involved in the epidemiologic correlations between dietary fat and colon and breast cancers. Our first goal has been to set up a cell culture system. In most cells ras expression is low and difficult to detect. We have confirmed that Y-1 cells and MCF-7 cells, respectively, express 20-50 and 5-10 fold the level of normal ras protein seen in other cell lines. These cells will enable us to investigate the effects of a variety of lipids, growth factors and other modulators on ras activity, as assessed by ras membrane localization, post- translational modifications, bound guanine nucleotide ratios, and messenger RNA levels.