Oxalomalate, a competitive inhibitor of aconitase, modulates the RNA-binding activity of iron-regulatory proteins.
We investigated the effect of oxalomalate (OMA, alpha-hydroxy-beta-oxalosuccinic acid), a competitive inhibitor of aconitase, on the RNA-binding activity of the iron-regulatory proteins (IRP1 and IRP2) that control the post-transcriptional expression of various proteins involved in iron metabolism. The RNA-binding activity of IRP was evaluated by electrophoretic mobility-shift assay of cell lysates from 3T3-L1 mouse fibroblasts, SH-SY5Y human cells and mouse livers incubated in vitro with OMA, with and without 2-mercaptoethanol (2-ME). Analogous experiments were performed in vivo by prolonged incubation (72 h) of 3T3-L1 cells with OMA, and by injecting young mice with equimolar concentrations of oxaloacetate and glyoxylate, which are the precursors of OMA synthesis. OMA remarkably decreased the binding activity of IRP1 and, when present, of IRP2, in all samples analysed. In addition, the recovery of IRP1 by 2-ME in the presence of OMA was constantly lower versus control values. These findings suggest that the severe decrease in IRP1 RNA-binding activity depends on: (i) linking of OMA to the active site of aconitase, which prevents the switch to IRP1 and explains resistance to the reducing agents, and (ii) possible interaction of OMA with some functional amino acid residues in IRP that are responsible for binding to the specific mRNA sequences involved in the regulation of iron metabolism.
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Dipartimento di Farmacologia Sperimentale, Università di Napoli 'Federico II', Via Domenico Montesano 49, I-80131 Napoli, Italy.
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D016475:3T3 Cells; D000154:Aconitate Hydratase / Q000037:antagonists & inhibitors*; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006038:Glyoxylates / Q000494:pharmacology; D006801:Humans; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008623:Mercaptoethanol / Q000494:pharmacology; D051379:Mice; D010070:Oxalates / Q000494:pharmacology*; D062907:Oxaloacetic Acid / Q000494:pharmacology; D020033:Protein Isoforms / Q000187:drug effects / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D006038:Glyoxylates; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D010070:Oxalates; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D062907:Oxaloacetic Acid; C015407:oxalomalic acid; D008623:Mercaptoethanol; D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2; C031150:glyoxylic acid