Fig. 7. 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. IRP2 does 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 hy- drogen peroxide (H2O2) increase IRP/IRE interaction. H2O2 destabilizes the [4Fe-4S] cluster of IRP1 and also stabilizes IRP2 protein by preventing FBXL5-dependent ubiqui- tination. Increasing IRP-IRE interaction in 5′UTR results in translational block of ferritin (Ft), ferroportin (Fpn), aminolevulinic acid synthase-2 (ALAS2), hypoxia inducible factor-2 (HIF-2), amyloid precursor protein (APP), and NADH dehydrogenase (ubi- quinone) Fe-S protein 1 (NDUFS1) genes, but in the 3′UTR it results in mRNA stabiliza- tion of transferrin receptor (TfR), divalent metal transporter 1 (DMT1), hydroxyacid oxidase 1 (HAO-1), myotonic dystrophy kinase-related Cdc42-binding kinase alpha (MRCK), and CDC14 cell division cycle 14 homolog A (CDC14A). storage/detoxification and less transferrin receptor-1 to halt iron transport into the cells, ultimately reducing excess intracellular iron. In contrast, iron-deficient conditions facilitate the disassembly of
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