Progression through the cell cycle requires orchestrated synthesis of structural macromolecules, including DNA, proteins and membranes prior to cell division. The regulatory linkage between cell cycle control and control of cellular biosynthetic processes is not yet understood, but there is much new understanding of the regulation of expression of genes for lipid metabolism, including discovery of new transcriptional regulators. Some clinical human cancers, particularly those harboring p53 mutations, overexpress fatty acid synthase (FAS), the key enzyme required for endogenous fatty acid (FA) biosynthesis, and tumor cells incorporate the majority of endogenously synthesized FA into membrane. While tumor cells preferentially utilize endogenous FA synthesis to supply FA, most non-transformed cells preferentially utilize dietary lipids. This metabolic difference provides a therapeutic opportunity. Furthermore, most normal tissues that synthesize FA are fully differentiated and non-proliferating, e.g. liver, adipose tissue. However, there is clearly a subset of both normal tissues and tumors where FAS expression is coordinately linked to proliferation. These observations lead to the following hypothesis: ] elevated FA synthesis is necessary to support proliferation in tumor cells; 2] its activity is regulated by the tumor suppressor/cell cycle regulatory gene, p53, and by SREBP transcription factors; 3] and proliferation-associated FA svnthesis confers sensitivity to anti-metabolites that target FA synthesis.
Specific Aim 1 : To determine whether FA synthase expression level, FA synthetic activity and sensitivity to anti-metabolites that target FA synthesis vary during progression through the cell cycle in parallel with membrane synthesis in cancer cells with elevated FAS expression.
Specific Aim 2 : To directly test for a regulatory effect of p53 on FA synthesis by introduction of either constitutive or temperature sensitive dominant negative mutant p53 genes into cancer cells with wild type p53.
Specific Aim 3 : To determine whether the expression levels and active states of the SREBPs (sterol regulatory element binding proteins) chat occur during changes in FAS expression in carcinoma cells are coffipatible with regulation of FAS by SREBP, and to determine the importance of this regulatory pathway by genetic modulation of SREBP function. Collaborations with Drs. Pasternack and Kastan will substantially enhance this research effort; the recognition and initial characterization of tumor associated FA synthesis has been conducted by Dr. Pasternack's group, and ongoing laboratory efforts in experimental therapeutics are complimentary to this proposal. Dr Kastan provides leading expertise in the study of the cell cycle. The proposed project develops a foundation for an independent research program in the biology of human cancer.
