NUTRITIONAL REGULATION OF RAS PROTO-ONCOGENE ACTIVITY

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The goal of this project is to investigate links between nutritional factors and the activity of ras proteins in a cell culture system. Although the cellular function of this proto-oncogene product 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. Nutritional status may affect ras activity by influencing the post-translational lipid modifications of the protein that are required for plasma membrane localization and hence activity. Conceivably, such lipid effects could be involved in the epidemiologic correlations between dietary fat and colon and breast cancers. To investigate the effects of nutrients and anutrients on ras activity, as assessed by relative protein levels and cellular localization, we have developed a sensitive and semi-quantitative immunoassay. Such sensitivity obviates the need for cell lines expressing mutationally activated or genetically amplified levels of ras protein, cells in which ras may be inappropriately regulated or may exhibit abnormal activities. Being able to use cells that express the normally low and difficult-to-detect levels of protein may be crucial to elucidating how nutritional factors affect ras. We are using this system to investigate the effects of compounds that seem to have anti-cancer activity. We have found that the steroid dehydroepiandrosterone (DHEA) decreases levels of ras protein in a variety of cell lines. DHEA is a potent uncompetitive inhibitor of glucose-6-phosphate dehydrogenase, a key enzyme of intermediate metabolism, but may also modulate cellular activity through effects on endogenous mevalonate pools. This system will enable us to investigate the effects of this and other potential modulators of ras activity.