Defective trafficking and localization of mutated transferrin receptor 2: implications for type 3 hereditary hemochromatosis

Transferrin receptor 2 (TfR2), a homologue of transferrin receptor 1 (TfR1), is a key molecule involved in the regulation of iron homeostasis. Mutations in TfR2 result in iron overload with similar features to HFE-associated hereditary hemochromatosis. The precise role of TfR2 in iron metabolism and the functional consequences of disease-causing mutations have not been fully determined. We have expressed wild-type and various mutant forms of TfR2 that are associated with human disease in a mouse liver cell line. Intracellular and surface analysis shows that all the TfR2 mutations analyzed cause the intracellular retention of the protein in the endoplasmic reticulum, whereas the wild-type protein is expressed in endocytic structures and at the cell surface. Our results indicate that the majority of mutations that cause type 3 hereditary hemochromatosis are a consequence of the defective localization of the protein.

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The Functional Versatility of Transferrin Receptor 2 and Its Therapeutic Value

Pharmaceuticals ◽

10.3390/ph11040115 ◽

2018 ◽

Vol 11 (4) ◽

pp. 115 ◽

Cited By ~ 6

Author(s):

Antonella Roetto ◽

Mariarosa Mezzanotte ◽

Rosa Pellegrino

Keyword(s):

Transferrin Receptor ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Iron Regulation ◽

Role Taking ◽

Therapeutic Value ◽

Living Organisms ◽

Type 3 ◽

Functional Versatility ◽

Transferrin Receptor 2

Iron homeostasis is a tightly regulated process in all living organisms because this metal is essential for cellular metabolism, but could be extremely toxic when present in excess. In mammals, there is a complex pathway devoted to iron regulation, whose key protein is hepcidin (Hepc), which is a powerful iron absorption inhibitor mainly produced by the liver. Transferrin receptor 2 (Tfr2) is one of the hepcidin regulators, and mutations in TFR2 gene are responsible for type 3 hereditary hemochromatosis (HFE3), a genetically heterogeneous disease characterized by systemic iron overload. It has been recently pointed out that Hepc production and iron regulation could be exerted also in tissues other than liver, and that Tfr2 has an extrahepatic role in iron metabolism as well. This review summarizes all the most recent data on Tfr2 extrahepatic role, taking into account the putative distinct roles of the two main Tfr2 isoforms, Tfr2α and Tfr2β. Representing Hepc modulation an effective approach to correct iron balance impairment in common human diseases, and with Tfr2 being one of its regulators, it would be worthwhile to envisage Tfr2 as a therapeutic target.

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Blunted hepcidin response to inflammation in the absence of Hfe and transferrin receptor 2

Blood ◽

10.1182/blood-2010-08-303859 ◽

2011 ◽

Vol 117 (10) ◽

pp. 2960-2966 ◽

Cited By ~ 18

Author(s):

Daniel F. Wallace ◽

Cameron J. McDonald ◽

Lesa Ostini ◽

V. Nathan Subramaniam

Keyword(s):

Transferrin Receptor ◽

Serum Iron ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Homeostatic Regulation ◽

Wild Type ◽

Regulatory Peptide ◽

Basal Expression ◽

Low Levels ◽

Transferrin Receptor 2

AbstractThe induction of the iron-regulatory peptide hepcidin by proinflammatory cytokines is thought to result in the withholding of iron from invading pathogens. Hfe and transferrin receptor 2 (Tfr2) are involved in the homeostatic regulation of hepcidin and their disruption causes hereditary hemochromatosis (HH). To determine whether either Hfe or Tfr2 is involved in the inflammatory pathway regulating hepcidin, we analyzed the effect of inflammation in 3 mouse models of HH. The inflammatory response and indicators of iron homeostasis were measured in wild-type, Hfe−/−, Tfr2−/−, and Hfe−/−/Tfr2−/− mice injected with lipopolysaccharide (LPS). The administration of LPS significantly reduced serum iron in wild-type and Hfe−/− mice, with smaller reductions in Tfr2−/− and Hfe−/−/Tfr2−/− mice. Low basal levels of hepcidin in the Hfe−/−/Tfr2−/− mice were increased in response to LPS, but remained significantly lower than in the other strains of mice. These results suggest that despite the absence of Hfe and Tfr2, hepcidin is responsive to inflammation; however, the low basal expression and subsequent low levels of circulating hepcidin are insufficient to reduce serum iron effectively. This suggests that in HH, the iron-withholding response to invading pathogens may be inadequate, and this is especially the case in the absence of both Hfe and Tfr2.

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Functional consequences of transferrin receptor‐2 mutations causing hereditary hemochromatosis type 3

Molecular Genetics & Genomic Medicine ◽

10.1002/mgg3.136 ◽

2015 ◽

Vol 3 (3) ◽

pp. 221-232 ◽

Cited By ~ 8

Author(s):

Ricky Joshi ◽

Maya Shvartsman ◽

Erica Morán ◽

Sergi Lois ◽

Jessica Aranda ◽

...

Keyword(s):

Transferrin Receptor ◽

Hereditary Hemochromatosis ◽

Functional Consequences ◽

Type 3 ◽

Transferrin Receptor 2

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Iron absorption and hepatic iron uptake are increased in a transferrin receptor 2 (Y245X) mutant mouse model of hemochromatosis type 3

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00278.2006 ◽

2007 ◽

Vol 292 (1) ◽

pp. G323-G328 ◽

Cited By ~ 32

Author(s):

S. F. Drake ◽

E. H. Morgan ◽

C. E. Herbison ◽

R. Delima ◽

R. M. Graham ◽

...

Keyword(s):

Gene Expression ◽

Mouse Model ◽

Transferrin Receptor ◽

Mutant Mouse ◽

Hereditary Hemochromatosis ◽

Mutant Mice ◽

Wild Type ◽

Hepcidin Expression ◽

Fe Uptake ◽

Type 3

Hereditary hemochromatosis type 3 is an iron (Fe)-overload disorder caused by mutations in transferrin receptor 2 (TfR2). TfR2 is expressed highly in the liver and regulates Fe metabolism. The aim of this study was to investigate duodenal Fe absorption and hepatic Fe uptake in a TfR2 (Y245X) mutant mouse model of hereditary hemochromatosis type 3. Duodenal Fe absorption and hepatic Fe uptake were measured in vivo by 59Fe-labeled ascorbate in TfR2 mutant mice, wild-type mice, and Fe-loaded wild-type mice (2% dietary carbonyl Fe). Gene expression was measured by real-time RT-PCR. Liver nonheme Fe concentration increased progressively with age in TfR2 mutant mice compared with wild-type mice. Fe absorption (both duodenal Fe uptake and transfer) was increased in TfR2 mutant mice compared with wild-type mice. Likewise, expression of genes participating in duodenal Fe uptake ( Dcytb, DMT1) and transfer (ferroportin) were increased in TfR2 mutant mice. Nearly all of the absorbed Fe was taken up rapidly by the liver. Despite hepatic Fe loading, hepcidin expression was decreased in TfR2 mutant mice compared with wild-type mice. Even when compared with Fe-loaded wild-type mice, TfR2 mutant mice had increased Fe absorption, increased duodenal Fe transport gene expression, increased liver Fe uptake, and decreased liver hepcidin expression. In conclusion, despite systemic Fe loading, Fe absorption and liver Fe uptake were increased in TfR2 mutant mice in association with decreased expression of hepcidin. These findings support a model in which TfR2 is a sensor of Fe status and regulates duodenal Fe absorption and liver Fe uptake.

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Diferric transferrin regulates transferrin receptor 2 protein stability

Blood ◽

10.1182/blood-2004-06-2477 ◽

2004 ◽

Vol 104 (13) ◽

pp. 4287-4293 ◽

Cited By ~ 163

Author(s):

Martha B. Johnson ◽

Caroline A. Enns

Keyword(s):

Transferrin Receptor ◽

Iron Homeostasis ◽

Transmembrane Protein ◽

Hereditary Hemochromatosis ◽

Pcr Analysis ◽

Mrna Levels ◽

Dependent Manner ◽

Diferric Transferrin ◽

In Cells ◽

Transferrin Receptor 2

Abstract Transferrin receptor 2 (TfR2) is a type 2 transmembrane protein expressed in hepatocytes that binds iron-bound transferrin (Tf). Mutations in TfR2 cause one form of hereditary hemochromatosis, a disease in which excessive absorption of dietary iron can lead to liver cirrhosis, diabetes, arthritis, and heart failure. The function of TfR2 in iron homeostasis is unknown. We have studied the regulation of TfR2 in HepG2 cells. Western blot analysis shows that TfR2 increases in a time- and dose-dependent manner after diferric Tf is added to the culture medium. In cells exposed to diferric Tf, the amount of TfR2 returns to control levels within 8 hours after the removal of diferric Tf from the medium. However, TfR2 does not increase when non–Tf-bound iron (FeNTA) or apo Tf is added to the medium. The response to diferric Tf appears to be hepatocyte specific. Real-time quantitative reverse transcription–polymerase chain reaction (qRT-PCR) analysis shows that TfR2 mRNA levels do not change in cells exposed to diferric Tf. Rather, the increase in TfR2 is attributed to an increase in the half-life of TfR2 protein in cells exposed to diferric Tf. Our results support a role for TfR2 in monitoring iron levels by sensing changes in the concentration of diferric Tf.

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The Effect of the Flavonol Rutin on Serum and Liver Iron Content in a Genetic Mouse Model of Iron Overload

Bioscience Reports ◽

10.1042/bsr20210720 ◽

2021 ◽

Author(s):

Zachary Hawula ◽

Eriza Secondes ◽

Daniel Wallace ◽

Gautam Rishi ◽

V. Nathan Subramaniam

Keyword(s):

Mouse Model ◽

Iron Overload ◽

Transferrin Receptor ◽

Iron Homeostasis ◽

Binding Capacity ◽

Hereditary Hemochromatosis ◽

Transferrin Saturation ◽

Iron Loading ◽

Genetic Mouse Model ◽

Transferrin Receptor 2

The flavonol rutin has been shown to possess antioxidant and iron chelating properties in vitro and in vivo. These dual properties are beneficial as therapeutic options to reduce iron accumulation and the generation of reactive oxygen species resultant from excess free iron. The effect of rutin on iron metabolism has been limited to studies performed in wild type mice either injected or fed high iron diets. The effect of rutin on iron overload caused by genetic dysregulation of iron homeostasis has not yet been investigated. In this study we examined the effect of rutin treatment on tissue iron loading in a genetic mouse model of iron overload, which mirrors the iron loading associated with Type 3 hereditary hemochromatosis patients who have a defect in Transferrin Receptor 2. Male Transferrin Receptor 2 knockout mice were administered rutin via oral gavage for 21 continuous days. Following treatment, iron levels in serum, liver, duodenum, and spleen were assessed. In addition, hepatic ferritin protein levels were determined by western blotting, and expression of iron homeostasis genes by quantitative real-time PCR. Rutin treatment resulted in a significant reduction in hepatic ferritin protein expression and serum transferrin saturation. In addition, trends towards decreased iron levels in the liver and serum, and increased serum unsaturated iron binding capacity were observed. This is the first study to explore the utility of rutin as a potential iron chelator and therapeutic in an animal model of genetic iron overload.

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Transferrin receptor 2 is emerging as a major player in the control of iron metabolism

Open Life Sciences ◽

10.2478/s11535-007-0007-0 ◽

2007 ◽

Vol 2 (1) ◽

pp. 34-55 ◽

Cited By ~ 1

Author(s):

Alessia Calzolari ◽

Isabella Oliviero ◽

Ugo Testa

Keyword(s):

Iron Metabolism ◽

Transferrin Receptor ◽

Cellular Localization ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Essential Element ◽

Biological Properties ◽

The Body ◽

Major Player ◽

Type 3

AbstractOur knowledge of mammalian iron metabolism has advanced dramatically over recent years. Iron is an essential element for virtually all living organisms. Its intestinal absorption and accurate cellular regulation is strictly required to ensure the coordinated synthesis of the numerous iron-containing proteins involved in key metabolic processes, while avoiding the uptake of excess iron that can lead to organ damage. A range of different proteins exist to ensure this fine control within the various tissues of the body. Among these proteins, transferrin receptor (TFR2) seems to play a key role in the regulation of iron homeostasis. Disabling mutations in TFR2 are responsible for type 3 hereditary hemochromatosis (Type 3 HH). This review describes the biological properties of this membrane receptor, with a particular emphasis paid to the structure, function and cellular localization. Although much information has been garnered on TFR2, further efforts are needed to elucidate its function in the context of the iron regulatory network.

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Heterotypic interactions between transferrin receptor and transferrin receptor 2

Blood ◽

10.1182/blood-2002-09-2742 ◽

2003 ◽

Vol 101 (5) ◽

pp. 2008-2014 ◽

Cited By ~ 31

Author(s):

Todd M. Vogt ◽

Aaron D. Blackwell ◽

Anthony M. Giannetti ◽

Pamela J. Bjorkman ◽

Caroline A. Enns

Keyword(s):

Transferrin Receptor ◽

Iron Uptake ◽

Iron Homeostasis ◽

Critical Role ◽

Hereditary Hemochromatosis ◽

Metabolic Labeling ◽

Western Blots ◽

Cellular Iron ◽

Transferrin Receptor 2

Cellular iron uptake in most tissues occurs via endocytosis of diferric transferrin (Tf) bound to the transferrin receptor (TfR). Recently, a second transferrin receptor, transferrin receptor 2 (TfR2), has been identified and shown to play a critical role in iron metabolism. TfR2 is capable of Tf-mediated iron uptake and mutations in this gene result in a rare form of hereditary hemochromatosis unrelated to the hereditary hemochromatosis protein, HFE. Unlike TfR, TfR2 expression is not controlled by cellular iron concentrations and little information is currently available regarding the role of TfR2 in cellular iron homeostasis. To investigate the relationship between TfR and TfR2, we performed a series of in vivo and in vitro experiments using antibodies generated to each receptor. Western blots demonstrate that TfR2 protein is expressed strongest in erythroid/myeloid cell lines. Metabolic labeling studies indicate that TfR2 protein levels are approximately 20-fold lower than TfR in these cells. TfR and TfR2 have similar cellular localizations in K562 cells and coimmunoprecipitate to only a very limited extent. Western analysis of the receptors under nonreducing conditions reveals that they can form heterodimers.

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