Isocitrate Dehydrogenase 1/2 Mutational Analyses and 2-Hydroxyglutarate Measurements in Wilms Tumors
ABSTRACT L-2-Hydroxyglutaric aciduria (L-2-HGA) is an uncommon inborn error of metabolism, in which the patients are predisposed to develop brain tumors. Elevated levels of D-2-hydroxyglutarate have been demonstrated with malignant gliomas and myeloid leukemias associated with somatic mutations of the genes encoding NADP(+)-dependent isocitrate dehydrogenases (IDH1 and IDH2, respectively). Recently, we noted a Wilms tumor in a child with L-2-HGA. Given the accumulating evidence that both enantiomers of 2-hydroxyglutarate are associated with cellular transformation, we investigated if sporadic Wilms tumors are associated with IDH1 or IDH2 mutations or with elevated levels of 2-hydroxyglutarate.
We retrieved 21 frozen Wilms tumor tissues. In 20 cases, we sequenced exon 4 and flanking intronic regions of IDH1 and IDH2. In all 21 cases, we measured 2-hydroxyglutarate levels by liquid chromatography-tandem mass spectrometry.
We did not find mutations at the hot spots IDH1 codon 132 or IDH2 codon 172. Two cases (1 with favorable histology and 1 with unfavorable histology) showed heterozygous change c.211G>A (p.Val71Ile) in IDH1, a change previously reported as a mutation but listed as a single nucleotide polymorphism in the NCBI SNP database. We did not find increased levels of 2-hydroxygluatric acid in any sample.
Our results suggest that IDH1 codon 132 or IDH2 codon 172 mutations or elevated 2-hydroxyglutarate levels do not play a role in the biology of sporadic Wilms tumors. The significance of heterozygous change c.211G>A (p.Val71Ile) in IDH1, seen in two tumors, is not clear.
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ABSTRACT: Approximately 20% of unselected cases and 30% cytogenetically diploid cases of acute myeloid leukemia (AML) and 80% of grade II-III gliomas and secondary glioblastomas carry mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes. IDH1/2 mutations prevent oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) and modulate the function of IDH (neomorphic activity) thereby facilitating reduction of α-KG to D-2-hydroxyglutarate (D-2HG), a putative oncometabolite. D-2HG is thought to act as a competitive inhibitor of α-KG-dependent dioxygenases that include prolyl hydroxylases and chromatin-modifying enzymes. The end result is a global increase of cellular DNA hypermethylation and alterations of the cellular epigenetic state, which has been proposed to play a role in the development of a variety of tumors. In this review, we provide an update on potential molecular mechanisms linking IDH1/2 mutations and the resulting oncometabolite, D-2HG, with malignant transformation. In addition, in patients with AML and glioma we focus on the associations between IDH1/2 mutations and clinical, morphologic, cytogenetic, and molecular characteristics.Frontiers in Oncology 07/2013; 3:169. DOI:10.3389/fonc.2013.00169
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ABSTRACT: Mammalian cells generate citrate by decarboxylating pyruvate in the mitochondria to supply the tricarboxylic acid (TCA) cycle. In contrast, hypoxia and other impairments of mitochondrial function induce an alternative pathway that produces citrate by reductively carboxylating α-ketoglutarate (AKG) via NADPH-dependent isocitrate dehydrogenase (IDH). It is unknown how cells generate reducing equivalents necessary to supply reductive carboxylation in the setting of mitochondrial impairment. Here, we identified shared metabolic features in cells using reductive carboxylation. Paradoxically, reductive carboxylation was accompanied by concomitant AKG oxidation in the TCA cycle. Inhibiting AKG oxidation decreased reducing equivalent availability and suppressed reductive carboxylation. Interrupting transfer of reducing equivalents from NADH to NADPH by nicotinamide nucleotide transhydrogenase increased NADH abundance and decreased NADPH abundance while suppressing reductive carboxylation. The data demonstrate that reductive carboxylation requires bidirectional AKG metabolism along oxidative and reductive pathways, with the oxidative pathway producing reducing equivalents used to operate IDH in reverse.Cell Reports 05/2014; 7(5). DOI:10.1016/j.celrep.2014.04.037 · 7.21 Impact Factor