Regulation of IRP–IRE interactions. Under iron rich conditions, IRP1 contains a[4Fe–4S] cluster and is unable to bind to the IRE, though loss of iron from the cluster(destabilization) under iron deficient conditions allows IRP1 to bind to the IRE. IRP2does not contain a [4Fe–4S] cluster and is degraded by F-box/LRR-repeat protein 5(FBXL5)-dependent ubiquitination. Iron chelators, nitric oxide (NO), hypoxia, and hydrogen peroxide (H2O2) increase IRP/IRE interaction. H2O2 destabilizes the [4Fe–4S]cluster of IRP1 and also stabilizes IRP2 protein by preventing FBXL5-dependent ubiquitination. Increasing IRP–IRE interaction in 5′UTR results in translational block of ferritin(Ft), ferroportin (Fpn), aminolevulinic acid synthase-2 (ALAS2), hypoxia induciblefactor-2 α (HIF-2 α), amyloid precursor protein (APP), and NADH dehydrogenase (ubiquinone) Fe–S protein 1 (NDUFS1) genes, but in the 3′UTR it results in mRNA stabilization of transferrin receptor (TfR), divalent metal transporter 1 (DMT1), hydroxyacidoxidase 1 (HAO-1), myotonic dystrophy kinase-related Cdc42-binding kinase alpha(MRCK α), and CDC14 cell division cycle 14 homolog A (CDC14A).
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