Editors' ChoiceCancer

Compromising Cellular Antioxidant Activity

Sci. Signal.  30 Jul 2013:
Vol. 6, Issue 286, pp. ec175
DOI: 10.1126/scisignal.2004554

In the tricarboxylic acid cycle, the enzyme fumarate hydratase converts fumarate to malate. Individuals with hereditary leiomyomatosis and renal cell carcinoma (HLRCC) have a loss-of-function mutation in the gene encoding fumarate hydratase. Cancer cells deficient in fumarate hydratase show aberrant stabilization of hypoxia-inducible factors (HIFs) in the presence of normal oxygen tensions, increased reactive oxygen species (ROS) concentrations, and increased histone methylation. Sullivan et al. investigated the mechanism underlying these phenomena in UOK262 cells, which were established from an HLRCC metastasis. Stabilization of HIF-1α required generation of ROS in mitochondria and metabolism of 2-oxoglutarate to fumarate. Furthermore, knockdown of the enzymes that metabolize 2-oxoglutarate to fumarate decreased the generation of ROS in mitochondria and the proliferation of UOK262 cells. In vitro reactions and mass spectrometry analysis of UOK262 cells indicated that fumarate covalently bound to the antioxidant glutathione (GSH) to generate GSF (GSH + fumarate). Concentrations of NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) were decreased in UOK262 cells. Oxidation of NADPH is used by glutathione reductase to generate GSH from oxidized glutathione (GSSG), and thus NADPH is indirectly required for antioxidant activity in cells. Glutathione reductase could also generate GSH from GSF in vitro, and application of GSF to UOK262 cells reconstituted with fumarate hydratase decreased NADPH concentrations, increased ROS concentrations, and stabilized HIF-1α, the latter of which was attenuated by applying an antioxidant that targeted ROS in mitochondria. Reconstitution of UOK262 cells with fumarate hydratase decreased global histone methylation, and fumarate and H2O2 synergized to inhibit the histone demethylase JMJD2A in vitro. Thus, increased fumarate concentrations compromise cellular antioxidant activity, increasing ROS concentrations, HIF-1α abundance, and histone methylation seen in fumarate hydratase–deficient cells.

L. B. Sullivan, E. Martinez-Garcia, H. Nguyen, A. R. Mullen, E. Dufour, S. Sudarshan, J. D. Licht, R. J. Deberardinis, N. S. Chandel, The proto-oncometabolite fumarate binds glutathione to amplify ROS-dependent signaling. Mol. Cell 51, 236–248 (2013). [PubMed]

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