Altered metabolic regulation has long been observed in human cancer and broadly used in the clinic for tumor detection. Two recent findings-direct regulation of metabolism by frequently mutated cancer genes and mutations of metabolic enzymes in cancer-have renewed interest in cancer metabolism. Three frequently mutated cancer genes, p53, Myc, and Ras, have been found to directly regulate the expression of various metabolic enzymes involved in glycolysis. Severn metabolic genes encoding for four different metabolic enzymes are frequently mutated in human cancer, including fumarate hydratase (FH), succinate gehygrogenase (SDHB, SDHC, SDHD and SDH5), and isocitrate dehydrogenase-1 and -2 (IDH1, IDH2). Tumor mutations targeting IDH1 and IDH2 occur frequently in gliomas and leukemia and cause simultaneous loss and gain of activities in the production of a-ketoglutarate (a-KG) and 2-hydroxyglutarate (2-HG), respectively. Our preliminary studies demonstrated that 2-HG functions as an a-KG antagonist by binding to the same space in the catalytic site and competitively inhibiting the activity of a-KG-dependent dioxygenases, including both a-KG-dependent histone demethylases and TET family 5-methycytosine hydroxylases. Thus mutation of IDH1/2 leads to global alterations of both histone and DNA methylations in cultured cells and in primary gliomas. We further demonstrate that succinate and fumarate, two metabolites that are structurally similar to 2-HG and are accumulated in cells expressing tumor-derived mutant SOH and FH, similarly inhibit histone demethylases in vivo and in vitro. These preliminary studies have led us to propose a novel and unified a-KG pathway that underlies the contribution to the tumorigenesis by the mutations in these seven metabolic genes. We hypothesize that multiple cellular metabolites can function as a-KG antagonists, and that abnormal accumulation of anyone of these metabolites competitively inhibits a-KG-dependent histone demethylases and TET hydroxylases, leading to their reduced activity and altered epigenetic control and cell fate. Combining the unique clinical expertise in glioma and computational expertise in cancer bioinformatics brought in by two co-investigators, we propose three Specific Aims to determine the cellular function, mechanism, genes and targets of the a-KG pathway.
Aim 1 : Determine the function of IDH mutations in cell transformation Aim 2: Determine the mechanism of SDH and FH gene mutations in tumorigenesis Aim 3: Elucidate the genes and targets of a-KG pathway
This proposal seeks to understand how mutation of metabolic genes contributes to the development of human cancer. Specifically, we will examine how mutations in isocitrate dehydrogenase, which are found in about 20% of acute myeloid leukemias and more than 75% secondary glioblastomas, promote tumor formation. We will investigate the possibility that additional cancer-associated mutations in metabolic enzymes, including succinate dehydrogenase (mutated in familial paraganglioma) and fumarate hydratase (mutated in renal cell carcinoma and uterine leiomyomata), contribute to cancer development in a similar fashion. Accomplishment of these research objectives will have a direct and broad impact on the field of metabolism and cancer.
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