Regulation of transferrin receptor 2 protein levels by transferrin.

Transferrin receptor 2 (TfR2) plays a critical role in iron homeostasis because patients carrying disabling mutations in the TFR2 gene suffer from hemochromatosis. In this study, iron-responsive regulation of TfR2 at the protein level was examined in vitro and in vivo. HepG2 cell TfR2 protein levels were up-regulated after exposure to holotransferrin (holoTf) in a time- and dose-responsive manner. ApoTf or high-iron treatment with non-Tf-bound iron failed to elicit similar effects, suggesting that TfR2 regulation reflects interactions of the iron-bound ligand. Hepatic TfR2 protein levels also reflected an adaptive response to changing iron status in vivo. Liver TfR2 protein levels were down- and up-regulated in rats fed an iron-deficient and a high-iron diet, respectively. TfR2 was also up-regulated in Hfe(-/-) mice, an animal model that displays liver iron loading. In contrast, TfR2 levels were reduced in hypotransferrinemic mice despite liver iron overload, supporting the idea that regulation of the receptor is dependent on Tf. This idea is confirmed by up-regulation of TfR2 in beta-thalassemic mice, which, like hypotransferrinemic mice, are anemic and incur iron loading, but have functional Tf. Based on these combined results, we hypothesize that TfR2 acts as a sensor of iron status such that receptor levels reflect Tf saturation.

[1]  W. Hofmann,et al.  Mutation analysis of transferrin-receptor 2 in patients with atypical hemochromatosis. , 2002, Blood.

[2]  S. Bahram,et al.  Experimental hemochromatosis due to MHC class I HFE deficiency: immune status and iron metabolism. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[3]  G. Anderson,et al.  Changes in the expression of intestinal iron transport and hepatic regulatory molecules explain the enhanced iron absorption associated with pregnancy in the rat , 2004, Gut.

[4]  C. Lok,et al.  The transferrin receptor: role in health and disease. , 1999, The international journal of biochemistry & cell biology.

[5]  C. Enns,et al.  Diferric transferrin regulates transferrin receptor 2 protein stability. , 2004, Blood.

[6]  Hiroshi Kawabata,et al.  Transferrin Receptor 2-α Supports Cell Growth Both in Iron-chelated Cultured Cells and in Vivo * , 2000, The Journal of Biological Chemistry.

[7]  H. Koeffler,et al.  Molecular Cloning of Transferrin Receptor 2 , 1999, The Journal of Biological Chemistry.

[8]  Bernstein Se.  Hereditary hypotransferrinemia with hemosiderosis, a murine disorder resembling human atransferrinemia. , 1987 .

[9]  Bothwell Th,et al.  A simple technique for measuring storage iron concentrations in formalinised liver samples. , 1968 .

[10]  M. M. Bradford.  A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. , 1976, Analytical biochemistry.

[11]  M. Hentze,et al.  An Hfe-dependent pathway mediates hyposideremia in response to lipopolysaccharide-induced inflammation in mice , 2004, Nature Genetics.

[12]  A. Sapino,et al.  Structural, functional, and tissue distribution analysis of human transferrin receptor-2 by murine monoclonal antibodies and a polyclonal antiserum. , 2002, Blood.

[13]  S. Orkin,et al.  Heme‐regulated eIF2α kinase (HRI) is required for translational regulation and survival of erythroid precursors in iron deficiency , 2001, The EMBO journal.

[14]  N. Andrews,et al.  Comparison of the Interactions of Transferrin Receptor and Transferrin Receptor 2 with Transferrin and the Hereditary Hemochromatosis Protein HFE* , 2000, The Journal of Biological Chemistry.

[15]  R. Eisenstein,et al.  Dietary iron intake modulates the activity of iron regulatory proteins and the abundance of ferritin and mitochondrial aconitase in rat liver. , 1997, The Journal of nutrition.

[16]  D. M. Penny,et al.  The hemochromatosis gene product complexes with the transferrin receptor and lowers its affinity for ligand binding. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[17]  M. Hentze,et al.  Balancing Acts Molecular Control of Mammalian Iron Metabolism , 2004, Cell.

[18]  K. Pantopoulos.  Iron Metabolism and the IRE/IRP Regulatory System: An Update , 2004, Annals of the New York Academy of Sciences.

[19]  N. Andrews,et al.  The molecular defect in hypotransferrinemic mice. , 2000, Blood.

[20]  D. Purdie,et al.  Disrupted hepcidin regulation in HFE-associated haemochromatosis and the liver as a regulator of body iron homoeostasis , 2003, The Lancet.

[21]  D. Girelli,et al.  Clinical and pathologic findings in hemochromatosis type 3 due to a novel mutation in transferrin receptor 2 gene. , 2002, Gastroenterology.

[22]  C. Lok,et al.  Identification of a Hypoxia Response Element in the Transferrin Receptor Gene* , 1999, The Journal of Biological Chemistry.

[23]  L. Skow,et al.  A mouse model for beta-thalassemia. , 1983, Cell.

[24]  Nancy Andrews,et al.  Transferrin receptor is necessary for development of erythrocytes and the nervous system , 1999, Nature Genetics.

[25]  L. Skow,et al.  A mouse model for β-thalassemia , 1983, Cell.

[26]  T. Bothwell,et al.  A simple technique for measuring storage iron concentrations in formalinised liver samples. , 1968, The South African journal of medical sciences.

[27]  G. Jörning,et al.  Ferritin in liver, plasma and bile of the iron-loaded rat. , 1985, Biochimica et biophysica acta.

[28]  W. Stremmel,et al.  Expression of hepcidin in hereditary hemochromatosis: evidence for a regulation in response to the serum transferrin saturation and to non-transferrin-bound iron. , 2003, Blood.

[29]  J. Hoke,et al.  Tissue iron deposition in untransfused beta-thalassemic mice. , 1989, Experimental hematology.

[30]  M. Hentze,et al.  Regulatory defects in liver and intestine implicate abnormal hepcidin and Cybrd1 expression in mouse hemochromatosis , 2003, Nature Genetics.

[31]  W. Sly,et al.  HFE gene knockout produces mouse model of hereditary hemochromatosis. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[32]  H. Koeffler,et al.  Regulation of expression of murine transferrin receptor 2. , 2001, Blood.

[33]  Dena E. Cohen,et al.  The C282Y mutation causing hereditary hemochromatosis does not produce a null allele. , 1999, Blood.

[34]  A S Jackson,et al.  Generalized equations for predicting body density of men , 1978, British Journal of Nutrition.

[35]  N. Andrews,et al.  Constitutive hepcidin expression prevents iron overload in a mouse model of hemochromatosis , 2003, Nature Genetics.

[36]  M McCarthy,et al.  Hepatology , 1999, Rapid Medicine.

[37]  Paolo Gasparini,et al.  The gene TFR2 is mutated in a new type of haemochromatosis mapping to 7q22 , 2000, Nature Genetics.

[38]  A. Pietrangelo,et al.  Non-HFE Hemochromatosis , 2005, Seminars in liver disease.

[39]  W. Sly,et al.  Transferrin receptor 2: continued expression in mouse liver in the face of iron overload and in hereditary hemochromatosis. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[40]  E. Artner-Dworzak,et al.  Duodenal HFE expression and hepcidin levels determine body iron homeostasis: modulation by genetic diversity and dietary iron availability , 2004, Journal of Molecular Medicine.

[41]  W. Griffiths,et al.  Co-localization of the Mammalian Hemochromatosis Gene Product (HFE) and a Newly Identified Transferrin Receptor (TfR2) in Intestinal Tissue and Cells , 2003, The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society.

[42]  M. Gobbi,et al.  New mutations inactivating transferrin receptor 2 in hemochromatosis type 3. , 2001, Blood.

[43]  J. E. Hunter,et al.  Variable effects of iron status on the concentration of ferritin in rat plasma, liver, and spleen. , 1978, The Journal of nutrition.

[44]  W. Sly,et al.  Association of the transferrin receptor in human placenta with HFE, the protein defective in hereditary hemochromatosis. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[45]  P. Bjorkman,et al.  Heterotypic interactions between transferrin receptor and transferrin receptor 2. , 2003, Blood.

[46]  L. Bianchi,et al.  Transferrin Receptor Induction by Hypoxia , 1999, The Journal of Biological Chemistry.

[47]  R. Klausner,et al.  Two genetic loci participate in the regulation by iron of the gene for the human transferrin receptor. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[48]  R. Simpson,et al.  Importance of anemia and transferrin levels in the regulation of intestinal iron absorption in hypotransferrinemic mice. , 1999, Blood.

[49]  M. Awai,et al.  Transferrin Receptor Expression in Normal, Iron‐deficient and Iron‐overloaded Rats , 1989, Acta pathologica japonica.

[50]  R. Simpson,et al.  Intestinal iron absorption studies in mouse models of iron‐overload , 1994, British journal of haematology.

[51]  W. Stremmel,et al.  Iron uptake by human upper small intestine microvillous membrane vesicles. Indication for a facilitated transport mechanism mediated by a membrane iron-binding protein. , 1990, The Journal of clinical investigation.

[52]  W. Sly,et al.  Mouse strain differences determine severity of iron accumulation in Hfe knockout model of hereditary hemochromatosis , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[53]  W. Sly,et al.  Targeted mutagenesis of the murine transferrin receptor-2 gene produces hemochromatosis , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[54]  C. Peschle,et al.  Transferrin receptor 2 protein is not expressed in normal erythroid cells. , 2004, The Biochemical journal.

[55]  L. Kühn,et al.  The human transferrin receptor gene: genomic organization, and the complete primary structure of the receptor deduced from a cDNA sequence , 1984, Cell.