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Iron Regulatory Protein (iron + regulatory_protein)
Selected AbstractsFolding and turnover of human iron regulatory protein 1 depend on its subcellular localizationFEBS JOURNAL, Issue 4 2007Alain Martelli Aconitases are iron,sulfur hydrolyases catalysing the interconversion of citrate and isocitrate in a wide variety of organisms. Eukaryotic aconitases have been assigned additional roles, as in the case of the metazoan dual activity cytosolic aconitase,iron regulatory protein 1 (IRP1). This human protein was produced in yeast mitochondria to probe IRP1 folding in this organelle where iron,sulfur synthesis originates. The behaviour of human IRP1 was compared with that of genuine mitochondrial (yeast or human) aconitases. All enzymes were functional in yeast mitochondria, but IRP1 was found to form dense particles as detected by electron microscopy. MS analysis of purified inclusion bodies evidenced the presence of human IRP1 and ,-ketoglutarate dehydrogenase complex component 1 (KGD1), one of the subunits of ,-ketoglutarate dehydrogenase. KGD1 triggered formation of the mitochondrial aggregates, because the latter were absent in a KGD1, mutant, but it did not efficiently do so in the cytosol. Despite the iron-binding capacity of IRP1 and the readily synthesis of iron,sulfur clusters in mitochondria, the dense particles were not iron-rich, as indicated by elemental analysis of purified mitochondria. The data show that proper folding of dual activity IRP1-cytosolic aconitase is deficient in mitochondria, in contrast to genuine mitochondrial aconitases. Furthermore, efficient clearance of the aggregated IRP1,KGD1 complex does not occur in the organelle, which emphasizes the role of molecular interactions in determining the fate of IRP1. Thus, proper folding of human IRP1 strongly depends on its cellular environment, in contrast to other members of the aconitase family. [source] Interferon-, and lipopolysaccharide regulate the expression of Nramp2 and increase the uptake of iron from low relative molecular mass complexes by macrophagesFEBS JOURNAL, Issue 22 2000S. L. Wardrop The natural resistance associated macrophage protein 2 (Nramp2) is a transporter that is involved in iron (Fe) uptake from transferrin (Tf) and low molecular mass Fe complexes. Here we describe the effect of the inflammatory mediators interferon-, (IFN-,) and lipopolysaccharide (LPS) on the expression of Nramp2 mRNA and Fe uptake by cells of the macrophage lineage. After incubation of the RAW264.7 macrophage cell line with LPS there was a sevenfold increase in the expression of the 2.3 kb Nramp2 mRNA transcript when compared with the control, but little effect on the Nramp2 3.1 kb transcript. These results indicate differential regulation of the two transcripts. Treatment with LPS resulted in an increase in 59Fe uptake from 59Fe,nitrilotriacetic acid, while transferrin receptor (TfR) mRNA levels and 59Fe uptake from 59Fe,Tf were decreased. Paradoxically, at the same time, an increase in iron regulatory protein (IRP)1 RNA-binding activity was observed. Incubation with IFN-, (50 U·mL,1) resulted in a marked decrease in TfR mRNA levels but had no effect on Nramp2 mRNA expression. Exposure of RAW264.7 cells to both IFN-, and LPS resulted in a fourfold increase in the Nramp2 2.3-kb transcript and a four to fivefold decrease in the 3.1-kb transcript when compared with the control. Furthermore, there was a decrease in TfR mRNA levels despite an increase in IRP1 RNA-binding activity and a marked increase in inducible nitric oxide synthase mRNA expression. Hence, TfR and Nramp2 mRNA expression did not appear to be regulated in a concerted manner. Similar responses to those found above for RAW264.7 cells were also observed in the J774 macrophage cell line and also for primary cultures of mouse peritoneal macrophages. These results are of interest as the TfR and Nramp2 are thought to act together during Fe uptake from Tf. This is the first report to demonstrate regulation of the Nramp2 mRNA transcripts by inflammatory mediators. [source] Iron elevations in the aging Parkinsonian brain: a consequence of impaired iron homeostasis?JOURNAL OF NEUROCHEMISTRY, Issue 2 2010Donna W. Lee Abstract The contribution of iron dysregulation to the etiology of a variety of neuronal diseases comes as no surprise given its necessity in numerous general cellular and neuron-specific functions, its abundance, and its highly reactive nature. Homeostatic mechanisms such as the iron regulatory protein and hypoxia-inducible factor pathways are firmly evolutionarily set in place to prevent ,free' iron from participating in chemical Fenton and Haber-Weiss reactions which can result in subsequent generation of toxic hydroxyl radicals. However, given the multiple layers of complexity in cellular iron regulation, disruption of any number of genetic and environmental components can disturb the delicate balance between the various molecular players involved in maintaining an appropriate metabolic iron homeostasis. In this review, we will primarily focus on: (i) the impact of aging and gender on iron dysfunction as these are important criteria in the determination of iron-related disorders such as Parkinson's disease (PD), (ii) how iron mismanagement via disruption of cellular entry and exit pathways may contribute to these disorders, and (iii) how the availability of non-invasive measurement of brain iron may aid in PD diagnosis. [source] Induction of Transferrin Receptor by Ethanol in Rat Primary Hepatocyte CultureALCOHOLISM, Issue 2004Masako Suzuki Background: It is not uncommon for alcoholics to have iron accumulation in the liver, a condition that may contribute to the development of alcoholic liver disease. Recently, we reported that the expression of transferrin receptor, which mediates cellular iron uptake, was increased in hepatocytes in patients with alcoholic liver disease. To elucidate the mechanism of the iron accumulation in hepatocytes in such disease, we examined whether ethanol exposure induced the transferrin receptor expression and increased the cellular iron uptake. Methods: Rat primary hepatocytes were isolated and cultured in the presence of 20 ,mol/liter of iron and 25 mmol/liter of ethanol. Results: Ethanol exposure to the hepatocytes demonstrated an ,2-fold increase in transferrin receptor expression for 24 hr, shown by Western blot analysis and 35S-methionine metabolic labeling, 19% increase in 59Fe-transferrin uptake by hepatocytes, and 20% increase in activity of iron regulatory protein examined by band shift assay. Conclusion: Ethanol exposure induced the transferrin receptor expression, partially through the activation of iron regulatory protein, and increased the transferrin-bound iron uptake in rat hepatocyte cultures. The induction of transferrin receptor by ethanol might be one of the mechanisms of iron accumulation in the hepatocytes in alcoholic liver disease. [source] Lipooligosaccharide-independent alteration of cellular homeostasis in Neisseria meningitidis -infected epithelial cellsCELLULAR MICROBIOLOGY, Issue 6 2005Robert A. Bonnah Summary Neisseria meningitidis (MC) is an important cause of meningitis and septic shock. Primary loose attachment of MC to host epithelial cells is mediated by type IV pili. Lipooligosaccharide (LOS), opacity (Opa) proteins and glycolipid adhesins facilitate subsequent tight attachment. MC infection causes numerous changes in host epithelial cell homeostasis. These include cortical plaque formation, increased expression of proinflammatory cytokines and alterations in host iron homeostasis. Using both biochemical and genetic approaches, we examined the role of LOS in mediating these events. We first examined specific cellular iron homeostasis changes that occur following addition of purified MC LOS to epithelial cells. Using an MC mutant that completely lacks LOS (MC lps tbp), we examined pili-mediated attachment and cortical plaque formation in human endocervical epithelial cells (A431). We also tested whether the lack of LOS alters cellular homeostasis, including changes in the levels of host stress response factors and proinflammatory cytokines. MC lps tbp elicited the formation of cortical plaques in A431 cells. However, the plaques were less pronounced than those formed by the MC parent. Surprisingly, the proinflammatory cytokine TNF, was upregulated during infection in MC lps tbp -infected cells. Furthermore, alterations in iron homeostasis, including lower transferrin receptor 1 (TfR-1) levels, altered TfR-1 trafficking, an ,iron-starvation' gene expression profile and low iron regulatory protein (IRP) binding activity are independent of LOS. Our results demonstrate that LOS is partially involved in both the attachment to host cells and formation of cortical plaques. However, TNF, induction and changes in iron homeostasis observed in MC-infected epithelial cells are independent of LOS. [source] Iron regulatory protein-independent regulation of ferritin synthesis by nitrogen monoxideFEBS JOURNAL, Issue 16 2006Marc Mikhael The discovery of iron-responsive elements (IREs), along with the identification of iron regulatory proteins (IRP1, IRP2), has provided a molecular basis for our current understanding of the remarkable post-transcriptional regulation of intracellular iron homeostasis. In iron-depleted conditions, IRPs bind to IREs present in the 5,-UTR of ferritin mRNA and the 3,-UTR of transferrin receptor (TfR) mRNA. Such binding blocks the translation of ferritin, the iron storage protein, and stabilizes TfR mRNA, whereas the opposite scenario develops when iron in the intracellular transit pool is plentiful. Nitrogen monoxide (commonly designated nitric oxide; NO), a gaseous molecule involved in numerous functions, is known to affect cellular iron metabolism via the IRP/IRE system. We previously demonstrated that the oxidized form of NO, NO+, causes IRP2 degradation that is associated with an increase in ferritin synthesis [Kim, S & Ponka, P (2002) Proc Natl Acad Sci USA99, 12214,12219]. Here we report that sodium nitroprusside (SNP), an NO+ donor, causes a dramatic and rapid increase in ferritin synthesis that initially occurs without changes in the RNA-binding activities of IRPs. Moreover, we demonstrate that the translational efficiency of ferritin mRNA is significantly higher in cells treated with SNP compared with those incubated with ferric ammonium citrate, an iron donor. Importantly, we also provide definitive evidence that the iron moiety of SNP is not responsible for such changes. These results indicate that SNP-mediated increase in ferritin synthesis is, in part, due to an IRP-independent and NO+ -dependent post-transcriptional, regulatory mechanism. [source] Microelectronic DNA chip for hereditary hyperferritinemia cataract syndrome, a model for large-scale analysis of disorders of iron metabolism,HUMAN MUTATION, Issue 2 2006Francesca Ferrari Abstract Hereditary hyperferritinemia cataract syndrome (HHCS) is caused by mutations in the regulatory iron responsive element (IRE) in the 5,UTR of the L-ferritin transcript that reduce binding affinity to the iron regulatory proteins (IRPs) and lead to a constitutive upregulation of the protein in tissue and serum. Twenty-nine mutations have been reported within the L-ferritin (FTL) IRE sequence, 21 of which were available to us. In addition, we included in this study three new mutations. Thus, we analyzed 24 mutations spanning over a DNA stretch of 48 nucleotides, including four deletions 2,29 nucleotides long and 20 substitutions, seven of which were conservative transversions. With this unique experimental model we developed a microchip diagnostic platform for identifying known molecular defects in the L-ferritin IRE structure with a microelectronic array approach, which we optimized after studying the effects of various parameters. The system enables electronic deposition of biotinylated amplicons to selected pads. Under optimized conditions, no cross-hybridization was found, even for mutations that affected the same or adjacent nucleotide positions. The same cartridge could be serially hybridized with all the 24 reporter probe sets, which allowed correct genotyping right up until the end of the analysis. Extensive validation on 200 samples in a blinded fashion gave total concordance of results. This pilot study represents a first step toward developing a diagnostic microchip for large-scale analyses for epidemiological studies and screening of mutations associated with iron disorders. Hum Mutat 27(2), 201,208, 2006. © 2006 Wiley-Liss, Inc. [source] Divergent modulation of iron regulatory proteins and ferritin biosynthesis by hypoxia/reoxygenation in neurones and glial cellsJOURNAL OF NEUROCHEMISTRY, Issue 5 2005Carlo Irace Abstract Ferritin, the main iron storage protein, exerts a cytoprotective effect against the iron-catalyzed production of reactive oxygen species, but its role in brain injury caused by hypoxia/reoxygenation is unclear. Ferritin expression is regulated mainly at post-transcriptional level by iron regulatory proteins (IRP1 and IRP2) that bind specific RNA sequences (IREs) in the 5,untranslated region of ferritin mRNA. Here, we show that hypoxia decreases IRP1 binding activity in glial cells and enhances it in cortical neurons. These effects were reversed by reoxygenation in both cell types. In glial cells there was an early increase of ferritin synthesis during hypoxia and reoxygenation. Conversely, in cortical neurons, ferritin synthesis increased during the late phase of reoxygenation. Steady-state analysis of ferritin mRNA levels suggested that ferritin synthesis is regulated mainly post-transcriptionally by IRPs in glioma cells, both transcriptionally and post-transcriptionally in type-1 astrocytes, and mainly at transcriptional level in an IRP-independent way in neurons. The different regulation of ferritin expression may account for the different vulnerability of neurons and glial cells to the injury elicited by oxygen and glucose deprivation (OGD)/reoxygenation. The greater vulnerability of cortical neurons to hypoxia-reoxygenation was strongly attenuated by the exogenous administration of ferritin during OGD/reoxygenation, suggesting the possible cytoprotective role exerted by this iron-segregating protein. [source] | ||||||||||