Abstract
Mutations in the cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDH1) occur in several types of cancer, and altered cellular metabolism associated with IDH1 mutations presents unique therapeutic opportunities. By altering IDH1, these mutations target a critical step in reductive glutamine metabolism, the metabolic pathway that converts glutamine ultimately to acetyl-CoA for biosynthetic processes. While IDH1-mutated cells are sensitive to therapies that target glutamine metabolism, the effect of IDH1 mutations on reductive glutamine metabolism remains poorly understood. To explore this issue, we investigated the effect of a knock-in, single-codon IDH1-R132H mutation on the metabolism of the HCT116 colorectal adenocarcinoma cell line. Here we report the R132H-isobolome by using targeted (13)C isotopomer tracer fate analysis to trace the metabolic fate of glucose and glutamine in this system. We show that introduction of the R132H mutation into IDH1 up-regulates the contribution of glutamine to lipogenesis in hypoxia, but not in normoxia. Treatment of cells with a d-2-hydroxyglutarate (d-2HG) ester recapitulated these changes, indicating that the alterations observed in the knocked-in cells were mediated by d-2HG produced by the IDH1 mutant. These studies provide a dynamic mechanistic basis for metabolic alterations observed in IDH1-mutated tumors and uncover potential therapeutic targets in IDH1-mutated cancers.
Highlights
Somatic IDH1 mutations are common in several types of cancer
The R132H-Isobolome: IDH1 Mutation Increases the Contribution of Glucose to Palmitate Synthesis—We used targeted 13C isotopomer tracer fate analysis to determine the effect of IDH1 mutation on dynamic metabolic processes that generate acetylCoA
To investigate the carbon source of cytosolic acetyl-CoA in IDH1-mutated cells, we examined the contributions of glucose and of glutamine to new synthesis of a representative metabolite that is synthesized from acetyl-CoA: the lipid palmitate
Summary
Somatic IDH1 mutations are common in several types of cancer. Results: IDH1 mutation increases the proportion of palmitate derived from [13C]glutamine under hypoxic conditions. By altering IDH1, these mutations target a critical step in reductive glutamine metabolism, the metabolic pathway that converts glutamine to acetyl-CoA for biosynthetic processes. Whether the dynamic reductive glutamine pathway to produce acetyl-CoA or other biomolecules such as lipids is altered by IDH1 mutation under normoxia or hypoxia is unknown. To examine the contribution of D-2HG to the metabolic phenotypes observed in IDH1-mutated cells, cells were treated with a cell-permeable ester of D-2HG We compared these systems under normoxic and hypoxic conditions, and characterized oxidative mitochondrial processes in these cell lines. This analysis revealed that the IDH1 mutation causes cancer cells to switch toward reductive glutamine metabolism under hypoxia. We reasoned that the HCT116 colorectal cancer cell line provides a relevant context to investigate the effects of IDH1 mutation on cancer cell metabolism
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