Stabilization of iron regulatory protein 2, IRP2, by aluminum

AbstractIron regulatory protein 2 (IRP2) is one of the central regulators of iron homeostasis. IRP2 regulates expression of molecules involved in iron metabolism by binding to iron responsive elements (IREs) in the transcripts of those molecules in iron depletion. IRP2 is regulated by the accelerated degradation initiated by the iron-catalyzed oxidation. Here we report that aluminum antagonizes the iron-induced decrease in IRE binding activity of IRP2. Aluminum also inhibits iron-induced oxidation of IRP2 in vitro. These results suggest that aluminum stabilizes IRP2 by interfering with the iron-catalyzed oxidation, which results in perturbation of iron metabolism

HSCB, a co-chaperone in mitochondrial iron-sulfur cluster biogenesis, is a novel candidate gene for congenital sideroblastic anemia

Congenital sideroblastic anemias (CSA) are inherited diseases resulting from defects in heme biosynthesis, mitochondrial iron-sulfur cluster (ISC) assembly, or mitochondrial translation. CSAs are characterized by pathological iron deposits in the mitochondria of bone marrow erythroblasts. Recently the Fleming Lab at Boston Children’s Hospital has reported mutations in HSPA9, a chaperone involved in ISC assembly, as a cause of nonsyndromic CSA. Here we identified a CSA patient harboring two variants in HSCB, encoding a binding partner of HSPA9: a paternally inherited promoter variant (c-134C>A) and a maternally inherited frameshift variant (T87fs) predicted to result in a truncated protein. To better understand the pathophysiology of these variants, we investigated HSCB protein expression and function in patient-derived skin fibroblasts. Patient fibroblasts show evidence of decreased HSCB protein levels. shRNA targeting HSCB was employed to specifically suppress HSCB expression in the K562 erythroid-like cell line model. shRNA-infected K562 cells presented with perturbed iron homeostasis, a shift to glycolytic energy production, and diminished hemoglobinization. Targeted deletion of murine Hscb is embryonic lethal prior day E7.0. Tissue-specific lox-Cre transgenic lines, including Vav-, EpoR- and Mx-Cre demonstrate that Hscb is essential for hematopoiesis and erythropoiesis. Mutant mice present with hematopoietic defects similar to the index patient. Vav-Cre animals die prior to post-natal day 9 with decreased red cell counts, white cell counts, and decreased hemoglobin compared to wild-type animals. Floxed-null EpoR-Cre animals die before embryonic day 13. To excise Hscb specifically in the hematopoietic compartment of adult animals, conditional Mx-Cre animals were generated through bone marrow transplantation and temporally induced with polyinosinic-polycytidylic acid treatment. The animals died 22 days post-injection with decreased red blood cells, white blood cells, hemoglobin, and an overall decline in hematopoiesis of the bone marrow. These data demonstrate that HSCB is required for erythropoiesis and hematopoiesis and that the patient mutations are a pathogenic cause of CSA

Abnormal Brain Iron Metabolism in Irp2 Deficient Mice Is Associated with Mild Neurological and Behavioral Impairments

Iron Regulatory Protein 2 (Irp2, Ireb2) is a central regulator of cellular iron homeostasis in vertebrates. Two global knockout mouse models have been generated to explore the role of Irp2 in regulating iron metabolism. While both mouse models show that loss of Irp2 results in microcytic anemia and altered body iron distribution, discrepant results have drawn into question the role of Irp2 in regulating brain iron metabolism. One model shows that aged Irp2 deficient mice develop adult-onset progressive neurodegeneration that is associated with axonal degeneration and loss of Purkinje cells in the central nervous system. These mice show iron deposition in white matter tracts and oligodendrocyte soma throughout the brain. A contrasting model of global Irp2 deficiency shows no overt or pathological signs of neurodegeneration or brain iron accumulation, and display only mild motor coordination and balance deficits when challenged by specific tests. Explanations for conflicting findings in the severity of the clinical phenotype, brain iron accumulation and neuronal degeneration remain unclear. Here, we describe an additional mouse model of global Irp2 deficiency. Our aged Irp2−/− mice show marked iron deposition in white matter and in oligodendrocytes while iron content is significantly reduced in neurons. Ferritin and transferrin receptor 1 (TfR1, Tfrc), expression are increased and decreased, respectively, in the brain from Irp2−/− mice. These mice show impairments in locomotion, exploration, motor coordination/balance and nociception when assessed by neurological and behavioral tests, but lack overt signs of neurodegenerative disease. Ultrastructural studies of specific brain regions show no evidence of neurodegeneration. Our data suggest that Irp2 deficiency dysregulates brain iron metabolism causing cellular dysfunction that ultimately leads to mild neurological, behavioral and nociceptive impairments

Iron-dependent degradation of IRP2 requires its C-terminal region and IRP structural integrity

<p>Abstract</p> <p>Background</p> <p>Iron regulatory protein 2 (IRP2), a post-transcriptional regulator of cellular iron metabolism, undergoes iron-dependent degradation via the ubiquitin-proteasome pathway. A stretch of 73 amino acids within the N-terminal domain 1 of the protein was reported to function as an iron sensor. However, mutants lacking this fragment remain sensitive to degradation in iron-replete cells.</p> <p>Results</p> <p>To identify elements within IRP2 involved in the control of its stability, we undertook a systematic mutagenesis approach. Truncated versions of IRP2 were expressed in H1299 cells and analyzed for their response to iron. Deletion mutants lacking the entire C-terminal domain 4 (amino acids 719–963) of IRP2 remained stable following iron treatments. Moreover, the replacement of domain 4 of IRP1 with the corresponding region of IRP2 sensitized the chimerical IRP1_1–3/IRP2₄protein to iron-dependent degradation, while the reverse manipulation gave rise to a stable chimerical IRP2_1–3/IRP1₄protein. The deletion of just 26 or 34 C-terminal amino acids stabilized IRP2 against iron. However, the fusion of C-terminal IRP2 fragments to luciferase failed to sensitize the indicator protein for degradation in iron-loaded cells.</p> <p>Conclusion</p> <p>Our data suggest that the C-terminus of IRP2 contains elements that are necessary but not sufficient for iron-dependent degradation. The functionality of these elements depends upon the overall IRP structure.</p

Tumorigenic Properties of Iron Regulatory Protein 2 (IRP2) Mediated by Its Specific 73-Amino Acids Insert

Iron regulatory proteins, IRP1 and IRP2, bind to mRNAs harboring iron responsive elements and control their expression. IRPs may also perform additional functions. Thus, IRP1 exhibited apparent tumor suppressor properties in a tumor xenograft model. Here we examined the effects of IRP2 in a similar setting. Human H1299 lung cancer cells or clones engineered for tetracycline-inducible expression of wild type IRP2, or the deletion mutant IRP2Δ73 (lacking a specific insert of 73 amino acids), were injected subcutaneously into nude mice. The induction of IRP2 profoundly stimulated the growth of tumor xenografts, and this response was blunted by addition of tetracycline in the drinking water of the animals, to turnoff the IRP2 transgene. Interestingly, IRP2Δ73 failed to promote tumor growth above control levels. As expected, xenografts expressing the IRP2 transgene exhibited high levels of transferrin receptor 1 (TfR1); however, the expression of other known IRP targets was not affected. Moreover, these xenografts manifested increased c-MYC levels and ERK1/2 phosphorylation. A microarray analysis identified distinct gene expression patterns between control and tumors containing IRP2 or IRP1 transgenes. By contrast, gene expression profiles of control and IRP2Δ73-related tumors were more similar, consistently with their growth phenotype. Collectively, these data demonstrate an apparent pro-oncogenic activity of IRP2 that depends on its specific 73 amino acids insert, and provide further evidence for a link between IRPs and cancer biology

Lattice fermions with gauge noninvariant measure

We define Weyl fermions on a finite lattice in such a way that in the path integral the action is gauge invariant but the functional measure is not. Two variants of such a formulation are tested in perturbative calculation of the fermion determinant in chiral Schwinger model. We find that one of these variants ensures restoring the gauge invariance of the nonanomalous part of the determinant in the continuum limit. A `perfect' perturbative regularization of the chiral fermions is briefly discussed.Comment: footnotes 2, 7 are extended, two references are adde

Possible involvement of iron-induced oxidative insults in neurodegeneration.

Involvement of iron in the development of neurodegenerative disorders has long been suggested, and iron that cannot be stored properly is suggested to induce iron toxicity. To enhance iron uptake and suppress iron storage in neurons, we generated transgenic (Tg) mice expressing iron regulatory protein 2 (IRP2), a major regulator of iron metabolism, in a neuron-specific manner. Although very subtle, IRP2 was expressed in all regions of brain examined. In the Tg mice, mitochondrial oxidative insults were observed including generation of 4-hydroxynonenal modified proteins, which appeared to be removed by a mitochondrial quality control protein Parkin. Inter-crossing of the Tg mice to Parkin knockout mice perturbed the integrity of neurons in the substantia nigra and provoked motor symptoms. These results suggest that a subtle, but chronic increase in IRP2 induces mitochondrial oxidative insults and accelerates neurodegeneration in a mouse model of Parkinson's disease. Thus, the IRP2 Tg may be a useful tool to probe the roles of iron-induced mitochondrial damages in neurodegeraration research