Interaction of the Hereditary Hemochromatosis Protein HFE with Transferrin Receptor 2 Is Required for Transferrin-Induced Hepcidin Expression

Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, OR 97239, USA.
Cell metabolism (Impact Factor: 16.75). 04/2009; 9(3):217-27. DOI: 10.1016/j.cmet.2009.01.010
Source: PubMed

ABSTRACT The mechanisms that allow the body to sense iron levels in order to maintain iron homeostasis are unknown. Patients with the most common form of hereditary iron overload have mutations in the hereditary hemochromatosis protein HFE. They have lower levels of hepcidin than unaffected individuals. Hepcidin, a hepatic peptide hormone, negatively regulates iron efflux from the intestines into the blood. We report two hepatic cell lines, WIF-B cells and HepG2 cells transfected with HFE, where hepcidin expression responded to iron-loaded transferrin. The response was abolished when endogenous transferrin receptor 2 (TfR2) was suppressed or in primary hepatocytes lacking either functional TfR2 or HFE. Furthermore, transferrin-treated HepG2 cells transfected with HFE chimeras containing only the alpha3 and cytoplasmic domains could upregulate hepcidin expression. Since the HFE alpha3 domain interacts with TfR2, these results supported our finding that TfR2/HFE complex is required for transcriptional regulation of hepcidin by holo-Tf.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Functional inactivation of HFE or hemojuvelin (HJV) is causatively linked to adult or juvenile hereditary hemochromatosis, respectively. Systemic iron overload results from inadequate expression of hepcidin, the iron regulatory hormone. While HJV regulates hepcidin by amplifying bone morphogenetic protein (BMP) signaling, the role of HFE in the hepcidin pathway remains incompletely understood. We investigated the pathophysiological implications of combined Hfe and Hjv ablation in mice. Isogenic Hfe (-)/(-) and Hjv (-)/(-) mice were crossed to generate double Hfe (-)/(-) Hjv (-)/(-) progeny. Wild-type control and mutant mice of all genotypes were analyzed for serum, hepatic, and splenic iron content, expression of iron metabolism proteins, and expression of hepcidin and Smad signaling in the liver, in response to a standard or an iron-enriched diet. As expected, Hfe (-)/(-) and Hjv (-)/(-) mice developed relatively mild or severe iron overload, respectively, which corresponded to the degree of hepcidin inhibition. The double Hfe (-)/(-) Hjv (-)/(-) mice exhibited an indistinguishable phenotype to single Hjv (-)/(-) counterparts with regard to suppression of hepcidin, serum and hepatic iron overload, splenic iron deficiency, tissue iron metabolism, and Smad signaling, under both dietary regimens. We conclude that the hemochromatotic phenotype caused by disruption of Hjv is not further aggravated by combined Hfe/Hjv deficiency. Our results provide genetic evidence that Hfe and Hjv operate in the same pathway for the regulation of hepcidin expression and iron metabolism. Combined disruption of Hfe and Hjv phenocopies single Hjv deficiency. Single Hjv(-)/(-) and double Hfe(-)/(-)Hjv(-)/(-) mice exhibit comparable iron overload. Hfe and Hjv regulate hepcidin via the same pathway.
    Journal of Molecular Medicine 01/2015; DOI:10.1007/s00109-015-1253-7 · 4.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Hepcidin is the central regulator of systemic iron homeostasis; dysregulation of hepcidin expression causes various iron metabolism disorders, including hereditary hemochromatosis and anemia of inflammation. To identify molecules that modulate hepcidin expression, we developed a bioassay system for hepcidin gene (HAMP) promoter activity by stable transfection of Hep3B hepatoma cells with an expression plasmid in which EGFP was linked to a 2.5-kb human HAMP promoter. Interleukin 6, bone morphogenetic protein 6 (BMP-6) and oncostatin M, well-characterized stimulators of the HAMP promoter, strongly enhanced the green fluorescence intensity (GFI) of these cells. Dorsomorphin, heparin and cobalt chloride, known inhibitors of hepcidin expression, significantly suppressed GFI, and these inhibitory effects were more prominent when the cells were stimulated with BMP-6. Employing this system, we screened 1,280 biologically active small molecules, and found several candidate inhibitors of hepcidin expression. Apomorphine, benzamil, etoposide, CGS-15943, kenpaullone, and rutaecarpine (all at 10 μM) significantly inhibited hepcidin mRNA expression by Hep3B cells without affecting cell viability. CGS-15943 was the strongest suppressor of BMP-6-induced hepcidin-25 secretion in these cells. We conclude that our newly developed hepcidin promoter bioassay system is useful for identifying and evaluating compounds that modulate hepcidin expression. Copyright © 2015 ISEH - International Society for Experimental Hematology. Published by Elsevier Inc. All rights reserved.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The maintenance of stable extracellular and intracellular iron concentrations requires the coordinated regulation of iron transport into plasma. Iron is a fundamental cofactor for several enzymes involved in oxidation–reduction reactions. The redox ability of iron can lead to the production of oxygen free radicals, which can damage various cellular components. Therefore, the appropriate regulation of systemic iron homeostasis is decisive in vital processes. Hepcidin has emerged as the central regulatory molecule of systemic iron homeostasis. It is synthesized in hepatocytes and in other cells and released into the circulation. It inhibits the release of iron from enterocytes of the duodenum and from macrophages by binding to the iron exporter protein, ferroportin (FPN). FPN is a transmembrane protein responsible for iron export from cells into the plasma. Hepcidin is internalized with FPN and both are degraded in lysosomes. The hepcidin-FPN axis is the principal regulator of extracellular iron homeostasis in health and disease. Its manipulation via agonists and antagonists is an attractive and novel therapeutic strategy. Hepcidin agonists include compounds that mimic the activity of hepcidin and agents that increase the production of hepcidin by targeting hepcidin-regulatory molecules. The inhibition of hepcidin could be a potentially attractive therapeutic strategy in patients suffering from anaemia or chronic inflammation. In this review, we will summarize the role of hepcidin in iron homeostasis and its contribution to the pathophysiology of inflammation and iron disorders. We will examine emerging new strategies that modulate hepcidin metabolism.
    Pharmacology [?] Therapeutics 09/2014; 146. DOI:10.1016/j.pharmthera.2014.09.004 · 7.75 Impact Factor

Full-text (2 Sources)

Available from
May 30, 2014