Labeling of lipids in cultures of glioma progenitors expressing IDH1R132H was minimally influenced by introduction of human GLUD1. demonstrate that exerts a growth-inhibitory effect that is paralleled by deficiency in metabolic flux from glucose and glutamine to lipids. Examining human gliomas, we find that glutamate dehydrogenase 1 (GLUD1) and GLUD2 are overexpressed in mutation on metabolic flux and tumor growth. Further, we report that glutamate, a substrate of GLUD2 and a neurotransmitter abundant in mammalian neocortex, can support growth of glioma progenitor cells irrespective of mutation status. These findings suggest that specialization of human neocortex for high glutamate neurotransmitter flux creates a metabolic niche conducive to growth of mutant tumors. Malignant transformation is widely recognized to require metabolic reprogramming to enable rapid expansion of biomass (1). Reports that mutation or overexpression of metabolic enzymes can drive oncogenesis have spurred intense investigation into metabolic vulnerabilities that distinguish malignant and normal tissue (2); however, the extent to which Isoconazole nitrate specialized metabolism of normal differentiated tissues cooperates with particular oncogenes to facilitate tumor growth has largely escaped notice (3, 4). Glioblastoma (GBM) is a highly aggressive brain malignancy and, until recently, all oncogenes identified in this tumor type constitute components of growth factor signaling pathways that activate anabolic processes. The discovery that mutation of isocitrate dehydrogenase Trp53 1 (mutation promotes an undifferentiated phenotype (10, 11), the role of mutant enzyme in tumor growth is not clear (12, 13). Because mutation on glioma lines must be interpreted with caution. Herein, to gain greater understanding of the mechanisms by which mutation. Because the majority of and display proneural gene expression signature (16), we chose for study a model system of or Nestin-tva mice formed gliomas with 100% penetrance following infection with replication-competent avian sarcoma leukosis virus long terminal repeat with splice acceptor (RCAS) vector encoding PDGF-B (PDGF/RCAS) and subsequent implantation into forebrain of immunocompromised mice (Fig. 1or neural stem cultures expressing PDGF-B or human IDH1R132H (hIDH1R132H). ND, not determined. (and 0.005, ** 0.0005 vs. control, test. (and and human gliomas maintain normal concentrations of -KG but have not identified a mechanism that compensates for diverted flux of -KG into 2-HG (8, 9, 18, 19). In human tumors, mutations in and Isoconazole nitrate are mutually exclusive and invariably heterozygous (7). To examine whether human gliomas up-regulate expression of WT IDH enzymes to negate growth-inhibitory effect of mutant enzyme, we compared expression profiling data from three series of histologically matched and high-grade gliomas. Our analysis revealed no increase in mRNA signals for IDH1, IDH2, or IDH3 subunits in tumors (Fig. 2gliomas, the only probesets corresponding to enzymes were ones annotated as glutamate dehydrogenase 1 (GLUD1) and glutamate dehydrogenase 2 (GLUD2) (Fig. 2GBM relative to GBM (Fig. 2glioma, we examined effects of shRNA to GLUD1/2 on orthotopic grafts of an human glioma line. Two shRNA targeting constructs to GLUD1/2 were used: sh647, which elicited partial reduction of GLUD1/2 protein, and sh662, which resulted in nearly complete elimination of detectable GLUD1/2 protein (Fig. 2and Fig. S2). In addition, sh662-expressing grafts displayed reduction of apparent tumor cell density in H&E-stained sections (Fig. 2and Table S1). These results reveal a dependence of tumor growth on GLUD1 and/or GLUD2 but do not reveal the relative contributions of each of these highly homologous proteins to tumor growth. Open in a separate window Fig. 2. GLUD1 and GLUD2 are overexpressed in human GBM, and knockdown of GLUD1/2 inhibits orthotopic growth of an glioma line. (value less than 1 10?4 (test) in each of three separate Isoconazole nitrate comparisons of vs. high-grade glioma. Values reported represent mean fold change and value for three comparisons. (vs. GBM. (human glioma line BT142. ( 0.05, ** 0.0001, with comparison with shCtr. ( 0.05, ** 0.005, *** 0.0005, for comparison with shCtr, test. AUC, area under the curve. (See Table S1 for all metabolites profiled.) GLUD1 and GLUD2 are mitochondrial enzymes that catalyze the conversion of glutamate to -KG and lie immediately upstream from IDH1 and/or IDH2 in a reductive glutaminolysis pathway critical for lipogenesis and growth under conditions of hypoxia or mitochondrial dysfunction (20C22). To determine whether either GLUD1 or GLUD2 rescues.