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Affiliation(s)
- Karl J. Wallace
- The Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS, USA
| | - Ashley D. G. Johnson
- The Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS, USA
| | - W. Scott Jones
- The Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS, USA
| | - Erendra Manandhar
- The Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS, USA
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2
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Bresgen N, Eckl PM. Oxidative stress and the homeodynamics of iron metabolism. Biomolecules 2015; 5:808-47. [PMID: 25970586 PMCID: PMC4496698 DOI: 10.3390/biom5020808] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Revised: 04/21/2015] [Accepted: 04/22/2015] [Indexed: 12/12/2022] Open
Abstract
Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress.
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Affiliation(s)
- Nikolaus Bresgen
- Department of Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria.
| | - Peter M Eckl
- Department of Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria.
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3
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Yanatori I, Yasui Y, Noguchi Y, Kishi F. Inhibition of iron uptake by ferristatin II is exerted through internalization of DMT1 at the plasma membrane. Cell Biol Int 2015; 39:427-34. [DOI: 10.1002/cbin.10403] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 10/30/2014] [Indexed: 01/11/2023]
Affiliation(s)
- Izumi Yanatori
- Department of Molecular Genetics; Kawasaki Medical School; 577 Matsushima; Kurashiki Okayama 701-0192 Japan
| | - Yumiko Yasui
- Department of Molecular Genetics; Kawasaki Medical School; 577 Matsushima; Kurashiki Okayama 701-0192 Japan
| | - Yumiko Noguchi
- Department of Molecular Genetics; Kawasaki Medical School; 577 Matsushima; Kurashiki Okayama 701-0192 Japan
| | - Fumio Kishi
- Department of Molecular Genetics; Kawasaki Medical School; 577 Matsushima; Kurashiki Okayama 701-0192 Japan
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Lok HC, Sahni S, Richardson V, Kalinowski DS, Kovacevic Z, Lane DJR, Richardson DR. Glutathione S-transferase and MRP1 form an integrated system involved in the storage and transport of dinitrosyl-dithiolato iron complexes in cells. Free Radic Biol Med 2014; 75:14-29. [PMID: 25035074 DOI: 10.1016/j.freeradbiomed.2014.07.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Revised: 06/26/2014] [Accepted: 07/01/2014] [Indexed: 12/11/2022]
Abstract
Nitrogen monoxide (NO) is vital for many essential biological processes as a messenger and effector molecule. The physiological importance of NO is the result of its high affinity for iron in the active sites of proteins such as guanylate cyclase. Indeed, NO possesses a rich coordination chemistry with iron and the formation of dinitrosyl-dithiolato iron complexes (DNICs) is well documented. In mammals, NO generated by cytotoxic activated macrophages has been reported to play a role as a cytotoxic effector against tumor cells by binding and releasing intracellular iron. Studies from our laboratory have shown that two proteins traditionally involved in drug resistance, namely multidrug-resistance protein 1 and glutathione S-transferase, play critical roles in intracellular NO transport and storage through their interaction with DNICs (R.N. Watts et al., Proc. Natl. Acad. Sci. USA 103:7670-7675, 2006; H. Lok et al., J. Biol. Chem. 287:607-618, 2012). Notably, DNICs are present at high concentrations in cells and are biologically available. These complexes have a markedly longer half-life than free NO, making them an ideal "common currency" for this messenger molecule. Considering the many critical roles NO plays in health and disease, a better understanding of its intracellular trafficking mechanisms will be vital for the development of new therapeutics.
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Affiliation(s)
- H C Lok
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - S Sahni
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - V Richardson
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - D S Kalinowski
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - Z Kovacevic
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - D J R Lane
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia
| | - D R Richardson
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia.
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5
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Abstract
DMT1 (divalent metal transporter 1) is the main iron importer found in animals, and ferrous iron is taken up by cells via DMT1. Once ferrous iron reaches the cytosol, it is subjected to subcellular distribution and delivered to various sites where iron is required for a variety of biochemical reactions in the cell. Until now, the mechanism connecting the transporter and cytosolic distribution had not been clarified. In the present study, we have identified PCBP2 [poly(rC)-binding protein 2] as a DMT1-binding protein. The N-terminal cytoplasmic region of DMT1 is the binding domain for PCBP2. An interaction between DMT1 and PCBP1, which is known to be a paralogue of PCBP2, could not be demonstrated in vivo or in vitro. Iron uptake and subsequent ferritin expression were suppressed by either DMT1 or PCBP2 knockdown. Iron-associated DMT1 could interact with PCBP2 in vitro, whereas iron-chelated DMT1 could not. These results indicate that ferrous iron imported by DMT1 is transferred directly to PCBP2. Moreover, we demonstrated that PCBP2 could bind to ferroportin, which exports ferrous iron out of the cell. These findings suggest that PCBP2 can transfer ferrous iron from DMT1 to the appropriate intracellular sites or ferroportin and could function as an iron chaperone.
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6
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Ahmed U, Oates PS. Dietary fat level affects tissue iron levels but not the iron regulatory gene HAMP in rats. Nutr Res 2012; 33:126-35. [PMID: 23399663 DOI: 10.1016/j.nutres.2012.11.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Revised: 10/26/2012] [Accepted: 11/14/2012] [Indexed: 02/06/2023]
Abstract
Because dietary fats affect the regulation and use of body iron, we hypothesized that iron regulatory and transport genes may be affected by dietary fat. A model of early-stage I to II, nonalcoholic fatty liver was used in which rats were fed standard (35% energy from fat) or high-fat (71% energy from fat) liquid diets with normal iron content (STD/HF groups). In addition, intraperitoneal injections of iron dextran were given to iron-loaded (STD+/HF+ groups) and iron-deficient diets to STD-/HF- groups. Plasma osmolality, hemoglobin level, and mean corpuscular hemoglobin concentration were increased in all STD diet groups compared with all HF diet groups. Plasma iron and transferrin saturation were affected by an interaction between dietary fat and iron. They were high in the STD group (normal iron) compared with their respective HF group. Similarly, this group also showed a 4-fold increase in the messenger RNA expression of the hepatic hemochromatosis gene. Spleen iron was high in the iron-loaded STD+ group compared with all other groups. Hepatic iron and messenger RNA expression of peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein α, interleukin-6, and iron transport genes (transferrin receptor 2, divalent metal transporter 1 iron-responsive element, and divalent metal transporter 1 non-iron-responsive element) were increased, whereas tumor necrosis factor α was decreased in the HF diet groups. The expression of iron regulatory gene HAMP was not increased in the HF diet groups. Iron regulatory and transport genes involved in cellular and systemic iron homeostasis may be affected by the macronutrient composition of the diet.
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Affiliation(s)
- Umbreen Ahmed
- Department of Physiology, National University of Sciences and Technology, Rawalpindi, Pakistan
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7
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Xu Y, Feng Y, Li H, Gao Z. Ferric citrate CYP2E1-independently promotes alcohol-induced apoptosis in HepG2 cells via oxidative/nitrative stress which is attenuated by pretreatment with baicalin. Food Chem Toxicol 2012; 50:3264-72. [PMID: 22699086 DOI: 10.1016/j.fct.2012.05.061] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2012] [Revised: 05/19/2012] [Accepted: 05/31/2012] [Indexed: 12/26/2022]
Abstract
In the case of alcoholic liver injury, an iron overload is always present. Both alcohol and iron can individually induce oxidative stress in liver. However, the combined effect of physiological concentrations of alcohol and iron on oxidative stress in hepatocytes remains unknown. Baicalin has been demonstrated to be an antioxidant or iron chelator in animal experiments. In this study, we investigated the injury to hepatocytes CYP2E1-independently induced by the combination of alcohol and iron and the protective effect of baicalin. Compared with cells treated with ethanol alone, ferric citrate enhanced the accumulation of reactive oxygen and nitrogen species, increased the occurrence of protein carbonylation/nitration and the levels of 4-hydroxy-2-nonenal, changed the distribution of iNOS, and eventually resulted in apoptosis. However, pretreatment with baicalin inhibited the oxidative stress induced by the combination of alcohol and iron, mainly by chelating iron. Our findings therefore suggest that iron could CPY2E1-independently enhance the oxidative stress induced by alcohol, which probably contributes to the pathogenesis of alcoholic liver disease. Baicalin is a promising phytomedicine for preventing alcoholic liver disease.
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Affiliation(s)
- Yan Xu
- School of Chemistry and Chemical Engineering, Huazhong University of Science & Technology, Wuhan 430074, PR China
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Zhao N, Gao J, Enns CA, Knutson MD. ZRT/IRT-like protein 14 (ZIP14) promotes the cellular assimilation of iron from transferrin. J Biol Chem 2010; 285:32141-50. [PMID: 20682781 PMCID: PMC2952215 DOI: 10.1074/jbc.m110.143248] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Revised: 08/02/2010] [Indexed: 12/21/2022] Open
Abstract
ZIP14 is a transmembrane metal ion transporter that is abundantly expressed in the liver, heart, and pancreas. Previous studies of HEK 293 cells and the hepatocyte cell lines AML12 and HepG2 established that ZIP14 mediates the uptake of non-transferrin-bound iron, a form of iron that appears in the plasma during pathologic iron overload. In this study we investigated the role of ZIP14 in the cellular assimilation of iron from transferrin, the circulating plasma protein that normally delivers iron to cells by receptor-mediated endocytosis. We also determined the subcellular localization of ZIP14 in HepG2 cells. We found that overexpression of ZIP14 in HEK 293T cells increased the assimilation of iron from transferrin without increasing levels of transferrin receptor 1 or the uptake of transferrin. To allow for highly specific and sensitive detection of endogenous ZIP14 in HepG2 cells, we used a targeted knock-in approach to generate a cell line expressing a FLAG-tagged ZIP14 allele. Confocal microscopic analysis of these cells detected ZIP14 at the plasma membrane and in endosomes containing internalized transferrin. HepG2 cells in which endogenous ZIP14 was suppressed by siRNA assimilated 50% less iron from transferrin compared with controls. The uptake of transferrin, however, was unaffected. We also found that ZIP14 can mediate the transport of iron at pH 6.5, the pH at which iron dissociates from transferrin within the endosome. These results suggest that endosomal ZIP14 participates in the cellular assimilation of iron from transferrin, thus identifying a potentially new role for ZIP14 in iron metabolism.
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Affiliation(s)
- Ningning Zhao
- From the Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida 32611 and
| | - Junwei Gao
- the Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Caroline A. Enns
- the Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Mitchell D. Knutson
- From the Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida 32611 and
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Anderson GJ, Vulpe CD. Mammalian iron transport. Cell Mol Life Sci 2009; 66:3241-61. [PMID: 19484405 PMCID: PMC11115736 DOI: 10.1007/s00018-009-0051-1] [Citation(s) in RCA: 216] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2009] [Revised: 04/21/2009] [Accepted: 05/12/2009] [Indexed: 02/07/2023]
Abstract
Iron is essential for basic cellular processes but is toxic when present in excess. Consequently, iron transport into and out of cells is tightly regulated. Most iron is delivered to cells bound to plasma transferrin via a process that involves transferrin receptor 1, divalent metal-ion transporter 1 and several other proteins. Non-transferrin-bound iron can also be taken up efficiently by cells, although the mechanism is poorly understood. Cells can divest themselves of iron via the iron export protein ferroportin in conjunction with an iron oxidase. The linking of an oxidoreductase to a membrane permease is a common theme in membrane iron transport. At the systemic level, iron transport is regulated by the liver-derived peptide hepcidin which acts on ferroportin to control iron release to the plasma.
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Affiliation(s)
- Gregory Jon Anderson
- Iron Metabolism Laboratory, Queensland Institute of Medical Research, PO Royal Brisbane Hospital, QLD, Australia.
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Zhang AS, Canonne-Hergaux F, Gruenheid S, Gros P, Ponka P. Use of Nramp2-transfected Chinese hamster ovary cells and reticulocytes from mk/mk mice to study iron transport mechanisms. Exp Hematol 2008; 36:1227-35. [PMID: 18722041 PMCID: PMC2655630 DOI: 10.1016/j.exphem.2008.04.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 04/21/2008] [Accepted: 04/24/2008] [Indexed: 01/09/2023]
Abstract
OBJECTIVE We investigated mechanisms involved in iron (Fe) transport by DMT1 (endosomal Fe(II) exporter, encoded by the Nramp2 gene) using wild-type Chinese hamster ovary (CHO) cells and Nramp2-transfected CHO cells, as well as reticulocytes from normal and mk/mk mice that have a defect in DMT1. MATERIALS AND METHODS CHO cells and reticulocytes were incubated with 59Fe bound to various ligands. The radioiron was present in its Fe(II) or Fe(III) forms or bound to transferrin (Tf), and the internalized 59Fe measured under varying experimental conditions. Additionally, 125I-Tf interaction with reticulocytes was investigated and 59Fe incorporation into their heme was determined. RESULTS Hyperexpression of DMT1 in CHO cells greatly increases their capacity to acquire ferrous iron. Although CHO-Nramp2 cells showed an increase in Fe(III) uptake as compared to CHO cells, they transported Fe(III) with much lower efficacy than Fe(II). In addition to their defect in Fe uptake, mk/mk reticulocytes also showed a decrease in Tf receptor levels. CONCLUSIONS Given that CHO cells acquire iron from Fe(II)-ascorbate with much higher rates than from Fe(III)-Tf, Tf-receptor levels represent the rate-limiting step in their iron uptake. As Fe(III) transport by CHO-Nramp2 cells can be inhibited by the impermeable oxidant K3Fe(CN)6, a membrane ferric reductase is probably needed for reduction of Fe(III) to Fe(II), which is then transported by DMT1. DMT1 is not a limiting factor in Fe acquisition by normal reticulocytes and their heme synthesis.
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Affiliation(s)
- An-Sheng Zhang
- Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, OR, USA
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11
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Chua ACG, Graham RM, Trinder D, Olynyk JK. The regulation of cellular iron metabolism. Crit Rev Clin Lab Sci 2008; 44:413-59. [PMID: 17943492 DOI: 10.1080/10408360701428257] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
While iron is an essential trace element required by nearly all living organisms, deficiencies or excesses can lead to pathological conditions such as iron deficiency anemia or hemochromatosis, respectively. A decade has passed since the discovery of the hemochromatosis gene, HFE, and our understanding of hereditary hemochromatosis (HH) and iron metabolism in health and a variety of diseases has progressed considerably. Although HFE-related hemochromatosis is the most widespread, other forms of HH have subsequently been identified. These forms are not attributed to mutations in the HFE gene but rather to mutations in genes involved in the transport, storage, and regulation of iron. This review is an overview of cellular iron metabolism and regulation, describing the function of key proteins involved in these processes, with particular emphasis on the liver's role in iron homeostasis, as it is the main target of iron deposition in pathological iron overload. Current knowledge on their roles in maintaining iron homeostasis and how their dysregulation leads to the pathogenesis of HH are discussed.
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Affiliation(s)
- Anita C G Chua
- School of Medicine and Pharmacology, University of Western Australia, Fremantle, Western Australia, Australia
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Graham RM, Reutens GM, Herbison CE, Delima RD, Chua ACG, Olynyk JK, Trinder D. Transferrin receptor 2 mediates uptake of transferrin-bound and non-transferrin-bound iron. J Hepatol 2008; 48:327-34. [PMID: 18083267 DOI: 10.1016/j.jhep.2007.10.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2007] [Revised: 09/07/2007] [Accepted: 10/12/2007] [Indexed: 12/11/2022]
Abstract
BACKGROUND/AIMS Transferrin receptor 2 appears to have dual roles in iron metabolism; one is signalling, the other is iron transport. It is sensitive to high levels of diferric transferrin, which is associated with disorders of iron overload. Also present in these disorders are increased levels of plasma non-transferrin-bound iron. This study sought to clarify the role of transferrin receptor 2 in the uptake of transferrin-bound and non-transferrin-bound iron. METHODS Variant Chinese Hamster Ovary (CHO) cells, transfected with transferrin receptor 2, were incubated with radio-labelled transferrin-bound or non-transferrin-bound iron. Competition studies were performed in the presence of unlabelled dimetallic transferrin; knockdown was performed using specific siRNA. RESULTS Cells expressing transferrin receptor 2 bound and internalised transferrin and transferrin-bound iron. Transferrin recycling occurred with an average cycling time of 11-15 min. Interestingly, the presence of transferrin receptor 2 was also associated with uptake of non-transferrin-bound iron which was inhibited by unlabelled transferrin-bound metals. Knockdown reduced transferrin-bound and non-transferrin-bound iron uptake by approximately 60%. CONCLUSIONS Transferrin receptor 2 mediates transferrin-bound iron uptake by receptor-mediated endocytosis. It is also involved in the uptake of non-transferrin-bound iron and the inhibition of non-transferrin-bound iron uptake by diferric transferrin in CHO cells.
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Affiliation(s)
- Ross M Graham
- School of Medicine and Pharmacology, The University of Western Australia, Fremantle Hospital, P.O. Box 480, Fremantle, WA 6959, Australia.
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Abstract
The liver plays a central role in iron metabolism. It is the major storage site for iron and also expresses a complex range of molecules which are involved in iron transport and regulation of iron homeostasis. An increasing number of genes associated with hepatic iron transport or regulation have been identified. These include transferrin receptors (TFR1 and 2), a ferrireductase (STEAP3), the transporters divalent metal transporter-1 (DMT1) and ferroportin (FPN) as well as the haemochromatosis protein, HFE and haemojuvelin (HJV), which are signalling molecules. Many of these genes also participate in iron regulatory pathways which focus on the hepatic peptide hepcidin. However, we are still only beginning to understand the complex interactions between liver iron transport and iron homeostasis. This review outlines our current knowledge of molecules of iron metabolism and their roles in iron transport and regulation of iron homeostasis.
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Affiliation(s)
- Ross-M Graham
- School of Medicine and Pharmacology, Fremantle Hospital, University of Western Australia, PO Box 480, Fremantle 6959, Western Australia, Australia
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Sturm B, Lassacher U, Ternes N, Jallitsch A, Goldenberg H, Scheiber-Mojdehkar B. The influence of gallium and other metal ions on the uptake of non-transferrin-bound iron by rat hepatocytes. Biochimie 2006; 88:645-50. [PMID: 16460863 DOI: 10.1016/j.biochi.2005.12.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Revised: 11/29/2005] [Accepted: 12/09/2005] [Indexed: 11/28/2022]
Abstract
BACKGROUND Under conditions of iron overload non-transferrin-bound iron (NTBI) occurs in the circulation and is mainly cleared by the liver. Beside iron, gallium and aluminum enhance accumulation of NTBI. We try to characterize the mechanism and metal-mediated regulation of NTBI uptake using cultivated primary rat hepatocytes. METHODS Hepatocytes from rat liver were incubated with 0.1 mg/ml transferrin (as control), with ferric ammonium citrate or other di- and trivalent metal salts and the uptake of (55)Fe-labeled Fe-diethylene triammine pentaacetate was measured. RESULTS Uptake rates for iron increased from 0.3 to 2.1 pmol/mg protein per min in cells preincubated for 5 hours with 300 microM ferric ammonium citrate, to 1.7 pmol/mg protein per min with gallium and to 1.2 pmol/mg protein per min with aluminum. Maximal stimulation was obtained with 300 microM iron and 600 microM gallium. Preincubation with divalent metals was ineffective. NTBI uptake was specific for iron, partly inhibited by gallium citrate, diferric transferrin and completely inhibited by apotransferrin in control and gallium-treated cells. In iron-loaded cells, inhibition of NTBI uptake by diferric transferrin completely disappeared within 2 hours. CONCLUSIONS These experiments show that hepatocytes do respond to the presence of trivalent metals by an increased transport capacity to sequester these ions. The metals seem to have at least partly different mechanisms of transport stimulation.
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Affiliation(s)
- B Sturm
- Department of Medical Chemistry, Medical University of Vienna, Waehringerstr. 10, 1090 Vienna, Austria
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Priwitzerova M, Nie G, Sheftel AD, Pospisilova D, Divoky V, Ponka P. Functional consequences of the human DMT1 (SLC11A2) mutation on protein expression and iron uptake. Blood 2005; 106:3985-7. [PMID: 16091455 DOI: 10.1182/blood-2005-04-1550] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously described a case of severe hypochromic microcytic anemia caused by a homozygous mutation in the divalent metal transporter 1 (DMT1 1285G > C). This mutation encodes for an amino acid substitution (E399D) and causes preferential skipping of exon 12 during processing of the DMT1 mRNA. To examine the functional consequences of this mutation, full-length DMT1 transcript with the patient's point mutation or a DMT1 transcript with exon 12 deleted was expressed in Chinese hamster ovary (CHO) cells. Our results demonstrate that the E399D substitution has no effect on protein expression and function. In contrast, deletion of exon 12 led to a decreased expression of the protein and disruption of its subcellular localization and iron uptake activity. We hypothesize that the residual protein in hematopoietic cells represents the functional E399D DMT1 variant, but because of its quantitative reduction, the iron uptake activity of DMT1 in the patient's erythroid cells is severely suppressed.
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Affiliation(s)
- Monika Priwitzerova
- Department of Biology, Faculty of Medicine, Palacky University, Olomouc, Czech Republic
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Juang HH. Modulation of iron on mitochondrial aconitase expression in human prostatic carcinoma cells. Mol Cell Biochem 2005; 265:185-94. [PMID: 15543948 DOI: 10.1023/b:mcbi.0000044395.59739.1f] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The mitochondrial aconitase (mACON) containing a [4Fe-4S] cluster is regarded as the key enzyme for citrate oxidation in the epithelial cells of human prostate. In vitro studies using the human prostatic carcinoma cells, PC-3 cells, found that both hemin and ferric ammonium citrate (FAC) significantly increased mACON enzymatic activity and gene expression. The effect of FAC on mACON was enhanced 2-fold by co-treating with ascorbic acid but blocked by co-treating with iron chelator, deferoxamine mesylate. Hemin treatments blocked 30% of citrate secretion from PC-3 cells but upregualted 2-fold of intracellular ATP biosynthesis. Results from reporter assay by using a cytomegalovirus enhance/promoter driven luciferase mRNA ligated to the iron response element (IRE) of mACON as a reporter construct demonstrated that modulation of FAC on gene translation of mACON gene is dependent on the IRE. Transient gene expression assays indicated that upregulation of mACON gene transcription by FAC may through the putative antioxidant response element (ARE) signal pathway. This study provides the first evidence of the biologic mechanism of human mACON gene translation/transcription and suggests a regulatory link between the energy utilization and the iron metabolism in human prostatic carcinoma cells.
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Affiliation(s)
- Horng-Heng Juang
- Department of Anatomy, Chang Gung University, Tao-Yuan 333, Taiwan, ROC.
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Chua ACG, Olynyk JK, Leedman PJ, Trinder D. Nontransferrin-bound iron uptake by hepatocytes is increased in the Hfe knockout mouse model of hereditary hemochromatosis. Blood 2004; 104:1519-25. [PMID: 15155457 DOI: 10.1182/blood-2003-11-3872] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Hereditary hemochromatosis (HH) is an iron-overload disorder caused by a C282Y mutation in the HFE gene. In HH, plasma nontransferrin-bound iron (NTBI) levels are increased and NTBI is bound mainly by citrate. The aim of this study was to examine the importance of NTBI in the pathogenesis of hepatic iron loading in Hfe knockout mice. Plasma NTBI levels were increased 2.5-fold in Hfe knockout mice compared with control mice. Total ferric citrate uptake by hepatocytes isolated from Hfe knockout mice (34.1 +/- 2.8 pmol Fe/mg protein/min) increased by 2-fold compared with control mice (17.8 +/- 2.7 pmol Fe/mg protein/min; P <.001; mean +/- SEM; n = 7). Ferrous ion chelators, bathophenanthroline disulfonate, and 2',2-bipyridine inhibited ferric citrate uptake by hepatocytes from both mouse types. Divalent metal ions inhibited ferric citrate uptake by hepatocytes, as did diferric transferrin. Divalent metal transporter 1 (DMT1) mRNA and protein expression was increased approximately 2-fold by hepatocytes from Hfe knockout mice. We conclude that NTBI uptake by hepatocytes from Hfe knockout mice contributed to hepatic iron loading. Ferric ion was reduced to ferrous ion and taken up by hepatocytes by a pathway shared with diferric transferrin. Inhibition of uptake by divalent metals and up-regulation of DMT1 expression suggested that NTBI uptake was mediated by DMT1.
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Affiliation(s)
- Anita C G Chua
- School of Medicine and Pharmacology, The University of Western Australia, Fremantle Hospital, PO Box 480, Fremantle 6959, WA, Australia
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Thomas C, Oates PS. Differences in the uptake of iron from Fe(II) ascorbate and Fe(III) citrate by IEC-6 cells and the involvement of ferroportin/IREG-1/MTP-1/SLC40A1. Pflugers Arch 2004; 448:431-7. [PMID: 15114483 DOI: 10.1007/s00424-004-1290-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2003] [Accepted: 01/20/2004] [Indexed: 10/26/2022]
Abstract
Dietary iron is present in the intestine as Fe(II) and Fe(III). Since enterocytes take up Fe(II) by the divalent metal transporter (DMT1), Fe(III) must be reduced. Whether other Fe(III) transport processes are present is unknown. Release of iron from the enterocyte into the plasma involves the iron-regulated transporter-1/metal transporter protein-1 (IREG-1/MTP-1, ferroportin) but ferroportin is also found on the apical membrane. We compared the uptake of iron from Fe(II):ascorbate and Fe(III):citrate using the rat intestinal enterocyte cell line-6 (IEC-6), in the presence of ferrous chelators, a blocking antibody to ferroportin, at different pH and during the over-expression of DMT1. Firstly, surface ferrireduction was absent. Secondly, blocking ferroportin partly and totally reduced Fe(II) and Fe(III) uptake, respectively. Thirdly, optimal Fe(II) uptake occurred at pH 5.5 but Fe(III) uptake was unaffected by pH and, fourthly, over-expression of DMT1 increased uptake of Fe(II) and Fe(III). This indicates that an increased extracellular H+ concentration facilitates DMT1-mediated Fe(II) uptake at the cell membrane. However, since Fe(III) uptake required DMT1, but not cell surface ferrireduction, and was independent of variations in extracellular pH, it appears that Fe(III) is internalised before ferrireduction and transport by DMT1. Ferroportin may function as a modulator of DMT1 activity and play a role in Fe(III) uptake, possibly by affecting the number or affinity of citrate binding sites.
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Affiliation(s)
- Carla Thomas
- Physiology, M311, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, WA 6009, Crawley, Australia
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Musílková J, Kovár J. Additive stimulatory effect of extracellular calcium and potassium on non-transferrin ferric iron uptake by HeLa and K562 cells. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1514:117-26. [PMID: 11513809 DOI: 10.1016/s0005-2736(01)00367-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We studied the effects of Ca(2+) and K(+) on non-transferrin iron uptake from ferric citrate complex by HeLa and K562 cells. Uptake experiments in Na-HEPES buffer (137 mM NaCl, 4 mM KCl) showed that extracellular Ca(2+) stimulated the iron uptake. The rate of iron uptake in 4 mM Ca(2+) was about 3-5 times higher than without Ca(2+). The iron uptake in K-HEPES buffer (68 mM NaCl, 75 mM KCl) with a high K(+) level was transiently stimulated during the first 10 min. The rate of iron uptake for 0.4 mM Ca(2+) was approximately 3 times higher in K-HEPES buffer than in Na-HEPES buffer. The calcium channel blockers verapamil (50 microM) and nifedipine (5 microM) had no effect on the uptake either in control Na-HEPES buffer or after K(+) stimulation in K-HEPES buffer. The sodium channel blocker lidocaine (50 microM) also had no effect on the uptake of iron in Na-HEPES buffer as well as after K(+) stimulation. Furthermore, the iron uptake was not significantly affected when Na(+) in the Na-HEPES and K-HEPES buffers was replaced by isotonic saccharose. We conclude that extracellular calcium per se, and not intracellular calcium or Ca(2+) transport, stimulates ferric iron uptake by both HeLa and K562 cells. A high level of extracellular K(+) also stimulates the uptake, probably via cell membrane depolarization. Na(+) is not involved in these stimulations of iron uptake. The transient K(+) effect and continuous Ca(2+) effect seem to be additive.
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Affiliation(s)
- J Musílková
- Cell Growth Control Laboratory, Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Vídenská 1083, 142 20 Prague 4, Czech Republic
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Abstract
Iron homeostasis is maintained by regulating its absorption: Under conditions of deficiency, assimilation is enhanced but iron uptake is otherwise limited to prevent toxicity due to overload. Iron deficiency remains the most important micronutrient deficiency worldwide, but increasing awareness of the genetic basis for iron-loading diseases points to iron overload as a major public health issue as well. Recent identification of mutant alleles causing iron uptake disorders in mice and humans provides new insights into the mechanisms involved in iron transport and its regulation. This article summarizes these discoveries and discusses their impact on our current understanding of iron transport and its regulation.
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Affiliation(s)
- M Wessling-Resnick
- Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
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Watts RN, Richardson DR. Nitrogen monoxide (no) and glucose: unexpected links between energy metabolism and no-mediated iron mobilization from cells. J Biol Chem 2001; 276:4724-32. [PMID: 11078730 DOI: 10.1074/jbc.m006318200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Nitrogen monoxide (NO) affects cellular iron metabolism due to its high affinity for this metal ion. Indeed, NO has been shown to increase the mRNA binding activity of the iron-regulatory protein 1, which is a major regulator of iron homeostasis. Recently, we have shown that NO generators increase (59)Fe efflux from cells prelabeled with (59)Fe-transferrin (Wardrop, S. L., Watts, R. N., and Richardson, D. R. (2000) Biochemistry 39, 2748-2758). The mechanism involved in this process remains unknown, and in this investigation we demonstrate that it is potentiated upon adding d-glucose (d-Glc) to the reincubation medium. In d-Glc-free or d-Glc-containing media, 5.6 and 16.5% of cellular (59)Fe was released, respectively, in the presence of S-nitrosoglutathione. This difference in (59)Fe release was observed with a variety of NO generators and cell types and was not due to a change in cell viability. Kinetic studies showed that d-Glc had no effect on the rate of NO production by NO generators. Moreover, only the metabolizable monosaccharides d-Glc and d-mannose could stimulate NO-mediated (59)Fe mobilization, whereas other sugars not easily metabolized by fibroblasts had no effect. Hence, metabolism of the monosaccharides was essential to increase NO-mediated (59)Fe release. Incubation of cells with the citric acid cycle intermediates, citrate and pyruvate, did not enhance NO-mediated (59)Fe release. Significantly, preincubation with the GSH-depleting agents, l-buthionine-[S,R]-sulfoximine or diethyl maleate, prevented NO-mediated (59)Fe mobilization. This effect was reversed by incubating cells with N-acetyl-l-cysteine that reconstitutes GSH. These results indicate that GSH levels are essential for NO-mediated (59)Fe efflux. Hence, d-Glc metabolism via the hexose monophosphate shunt resulting in the generation of GSH may be essential for NO-mediated (59)Fe release. These results have important implications for intracellular signaling by NO and also NO-mediated cytotoxicity of activated macrophages that is due, in part, to iron release from tumor target cells.
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Affiliation(s)
- R N Watts
- Iron Metabolism and Chelation Group, the Heart Research Institute, 145 Missenden Rd, Camperdown, Sydney, New South Wales 2050, Australia
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Scheiber-Mojdehkar B, Zimmermann I, Dresow B, Goldenberg H. Differential response of non-transferrin bound iron uptake in rat liver cells on long-term and short-term treatment with iron. J Hepatol 1999; 31:61-70. [PMID: 10424284 DOI: 10.1016/s0168-8278(99)80164-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
BACKGROUND Uptake of non-transferrin-bound iron by the liver is important as a clearance mechanism in iron overload. In contrast to physiological uptake via receptor-mediated endocytosis of transferrin, no regulatory mechanisms for this process are known. This study compares the influence of long-term and short-term depletion and loading of hepatocytes with iron on the uptake of non-transferrin bound iron, its affinity, specificity and the interaction with the transferrin-mediated pathways. METHODS Rats were fed iron-deficient, normal and 3,5,5-trimethylhexanoyl-ferrocene-containing diets to obtain livers with the corresponding desired status and the hepatocytes from these livers were used for transport studies. Hepatocytes from normal rats were depleted or loaded with iron by short-term treatment with desferrioxamine or ferric ammonium citrate, respectively. Uptake of non-transferrin bound iron was assayed from ferric citrate and from ferric diethylene triammine pentaacetate. RESULTS Uptake of non-transferrin-bound iron in hepatocytes could be seen as consisting of a high-affinity (Km=600 nM) and a low-affinity component. Whereas in normal and in iron-starved rats the high-affinity component was more prominent, it disappeared altogether in hepatocytes from rats with iron overload resulting from prolonged feeding with TMH-ferrocene-enriched diet. Overloading also led to loss of inhibition by diferric transferrin, which occured in starved as well as normal cells. In contrast, short-term iron-depletion of isolated hepatocytes with desferrioxamine had only a weak stimulatory effect, whereas treatment with ferric ammonium citrate strongly increased the uptake rates. However, the inhibition by diferric transferrin also disappeared. In both cases, uptake of non-transferrin bound iron was inhibited by apotransferrin. CONCLUSIONS Non-transferrin bound iron uptake in liver cells is apparently regulated by the iron status of the liver. The mode of response to iron loading depends on the method of loading in terms of time course and the form of iron used. It cannot be explained by the behavior of the iron regulatory protein, and it is complex, seeming to involve more than one transport system.
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Richardson DR, Chua AC, Baker E. Activation of an iron uptake mechanism from transferrin in hepatocytes by small-molecular-weight iron complexes: implications for the pathogenesis of iron-overload disease. THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE 1999; 133:144-51. [PMID: 9989766 DOI: 10.1016/s0022-2143(99)90007-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The liver is one of the principal sites of iron overload in diseases such as hemochromatosis and beta thalassemia. Hence, much effort has been invested in examining the mechanisms of Fe uptake by hepatocytes. In the present study we have examined the effect of small molecular weight (M(r)) Fe complexes on Fe uptake from iron 59-labeled transferrin (Tf) and 59Fe-labeled citrate by primary cultures of hepatocytes. This was important to assess because Fe-citrate and saturated diferric Tf coexist in the serum of patients with untreated Fe overload. Preincubation of hepatocytes with the low-M(r) Fe complex ferric ammonium citrate (FAC; 25 microg/mL; (Fe) = 4.4 microg/mL) followed by incubation with 59Fe-Tf or 59Fe-citrate ((Fe) = 0.25 to 25 micromol/L) resulted in the marked stimulation of 59Fe uptake. For example, at a physiologically relevant Tf-Fe concentration of 25 micromol/L, there was an 8-fold increase in 59Fe uptake by cells incubated with FAC compared to control cells. In contrast, at Tf-Fe concentrations of 0.25 to 2.5 micromol/L, 59Fe uptake in FAC-treated cells was only 1-fold to 3-fold greater than that in the corresponding controls. These data suggest that the FAC-activated Fe uptake process predominates at physiologically relevant Tf concentrations above the saturation of the Tf receptor (TfR). This is the first study to demonstrate that preincubation of hepatocytes with Iow-M(r)Fe complexes can markedly increase Fe uptake from diferric Tf. In conclusion, these results may help to explain the loading of hepatocytes with Fe that occurs in Fe-overload disease despite marked down-regulation of the TfR.
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Affiliation(s)
- D R Richardson
- Department of Medicine, Royal Brisbane Hospital, Queensland, Australia
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