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PubMed2001

Pumping iron: the strange partnership of the hemochromatosis protein, a class I MHC homolog, with the transferrin receptor.

People suffering from hereditary hemochromatosis (HH) can not regulate the uptake of iron properly and gradually accumulate iron in their body over their lifetime. The protein involved in HH, HFE, has been recently identified as a class I major histocompatibility complex (MHC) homolog. The wild-type HFE associates and co-traffics with the transferrin receptor (TfR). The mutation responsible for 83% of HH (C260Y) results in the failure of HFE to form a critical disulfide bond, bind beta2 microglobulin, bind TfR, and traffic to the cell surface. In non-polarized cells, the partnership of HFE and TfR results in decreased iron uptake into cells. The mechanism whereby a class I MHC homolog modifies the function of a membrane receptor and how this dynamic complex of molecules regulates iron transport across intestinal epithelial cells is the subject of this review.

Animals↗
PubMed2003

Frequency and spectrum of hemochromatosis mutations in Tunisia.

The occurrence of the C282Y and H63D mutations of the HFE gene, responsible for toxic iron overload in the liver (hereditary hemochromatosis), was still unknown in Tunisia. We report the screening of 194 chromosomes from 97 randomly collected cord blood samples. The mutations were analyzed by PCR followed by DNA sequencing. The mild H63D and the severe C282Y mutations were found in 17.5+/-5.34% and 0.5+/-0.97% of the alleles, respectively. The allele frequency of the IVS 2+4 T --> C polymorphism is high (46.4+/-7.01%) in this population. Risk for homozygosity for the severe C282Y mutation is present in the Tunisian population at a low theoretical incidence. However, due to the relatively high rate of consanguinity in the country, liver pathology due to HH is not to be disregarded.

Amino Acid Substitution↗
PubMed2000

Differential HFE allele expression in hemochromatosis heterozygotes.

BACKGROUND & AIMS: Hereditary hemochromatosis is associated with C282Y homozygosity. Some heterozygotes may also present with abnormal iron parameters. However, the precise role of H63D and C282Y mutations in iron overload is poorly understood. We investigated the level of expression of the mutated and unmutated HFE alleles in these heterozygous patients. METHODS: We studied the expression of HFE messenger RNAs in peripheral blood mononuclear cells from 34 heterozygotes using reverse-transcription polymerase chain reaction (PCR) followed by enzymatic digestion or sequence analysis of the PCR products, which allows relative quantification of mutated and unmutated transcripts. HFE proteins were quantified by Western blotting in Epstein-Barr virus-immortalized lymphocyte extracts from 2 C282Y and H63D homozygotes and a compound heterozygote. RESULTS: (187C > G; H63D) mutated transcripts predominated in H63D and compound heterozygotes and the normal transcripts in C282Y heterozygotes. The amount of HFE protein was increased in the H63D homozygotes and the compound heterozygote compared with the C282Y homozygotes. In addition, we found a new mutation at codon 282 (C282S) associated with severe iron overload. CONCLUSIONS: We demonstrate the existence of differential allelic expression of the HFE alleles, suggesting that the (187C > G; H63D) mutation plays a role in the disease expression in H63D heterozygotes, in particular when associated with environmental or host factors.

Adult↗
PubMed2001

Intestinal iron uptake determined by divalent metal transporter is enhanced in HFE-deficient mice with hemochromatosis.

BACKGROUND & AIMS: Overexpression of duodenal divalent metal transporter (DMT1) messenger RNA occurs in hemochromatosis and HFE-knockout mice, suggesting that DMT1 mediates enhanced absorption of iron; however, increased expression of functional DMT1 protein has yet to be substantiated. We examined the role of DMT1 and the mucosal iron uptake defect in HFE-knockout mice. METHODS: Unidirectional iron uptake of 59Fe by small intestinal mucosa in vitro was compared between matched pairs of HFE-knockout and wild-type mice. DMT1-specific antibodies were used to block iron transport and to quantify duodenal protein expression. RESULTS: Ferrous iron uptake at 3.5-450 micromol/L was greatly enhanced in HFE-knockouts compared with wild-type, the apparent V(max) for Fe2+ transport being doubled (P < 0.01). Supplied as Fe3+, uptake was only enhanced in HFE-knockouts at < or =18 micromol/L, when the iron was almost completely converted to Fe2+ by mucosal ferrireductases. DMT1 antibody reduced the apparent Vmax for mucosal Fe2+ transport in HFE-knockouts to below wild-type control values (P < 0.02); immunoreactive mucosal DMT1 protein was increased nearly 2-fold in HFE-knockouts (P < 0.01). CONCLUSIONS: Disruption of the HFE gene up-regulates functional DMT1 transporters and enhances uptake of ferrous iron by this mechanism; DMT1 also mediates increased uptake after reduction of ferric iron presented at physiological concentrations.

Animals↗
PubMed2003

Cancer risk in patients with hereditary hemochromatosis and in their first-degree relatives.

BACKGROUND & AIMS: Iron overload may be carcinogenic. Patients with hereditary hemochromatosis (HH) are reportedly at a 20-200-fold risk of intrahepatic cancer, but the reported risks for nonhepatobiliary cancers are conflicting. The risk of cancer in heterozygous individuals (estimated allele frequency, 1/10 to 1/20) is unknown. This study aimed to better assess these risks. METHODS: We performed a population-based cohort study of 1847 Swedish patients with HH and 5973 of their first-degree relatives using nationwide, population-based health and census registers. We used standardized incidence ratios (SIRs) as relative risk. RESULTS: With 62 liver cancers and 128 nonhepatobiliary cancers, patients with HH were at a 20-fold risk of liver cancer (SIR, 21; 95% confidence interval [CI], 16-22) but an almost unaltered risk of all other cancers (SIR, 1.2; 95% CI, 1.0-1.4), including nonelevated risks for several gastrointestinal tract cancers. At 10 years of follow-up, the absolute risk of liver cancer was 6% among men and 1.5% among women. With 21 liver cancers and 508 nonhepatobiliary cancers, first-degree relatives were at an unaltered risk of extrahepatic cancer (SIR, 1.0; 95% CI, 0.9-1.1, including unelevated risks for gastrointestinal cancers) but at a modest and historic increased risk of hepatobiliary cancer (SIR, 1.5; 95% CI, 1.0-2.4), the histopathologic spectrum of which differed from the patients. CONCLUSIONS: Patients (particularly men) with HH are at increased risk for hepatocellular cancer, although the magnitude of the risk is lower than previous estimates. Overall cancer risk in first-degree relatives does not seem to be increased.

Adolescent↗
PubMed2001

Liver transplantation for hereditary hemochromatosis.

Although hereditary hemochromatosis (HHC) is relatively common, it is an uncommon indication for orthotopic liver transplantation (OLT). The diagnosis of HHC in patients with end-stage liver disease is difficult because many of these patients have elevated serum and tissue iron levels. Of patients undergoing OLT with iron stores in the range typical for HHC, approximately 10% are homozygous for the C282Y mutation. Most studies published to date noted decreased survival in patients who underwent OLT for HHC compared with those who underwent OLT for other indications. Death in patients with HHC was caused by increased infectious and cardiac complications. Decreased post-OLT survival in patients with iron overload appears to be independent of HFE gene status. This suggests that regardless of the cause, iron overload may be detrimental in patients undergoing OLT. Follow-up of patients undergoing OLT for HHC and case reports of the inadvertent transplantation of a liver from a donor with HHC has furthered our understanding of the pathophysiological state of iron overload in HHC.

HLA Antigens↗
PubMed2003

Natural history of the C282Y homozygote for the hemochromatosis gene (HFE) with a normal serum ferritin level.

BACKGROUND & AIMS: The discovery of a genetic test for hereditary hemochromatosis has identified many individuals who are homozygous for the C282Y mutation of the HFE gene with a normal transferrin saturation and serum ferritin level. The long-term prognosis, rate of iron accumulation, and surveillance guidelines for these individuals are unknown. METHODS: To determine the degree of iron accumulation over time, an updated serum ferritin level was obtained in patients initially identified as homozygous for the C282Y mutation with a normal serum ferritin level. RESULTS: Twenty-two asymptomatic untreated C282Y homozygotes with a normal serum ferritin level were identified, 10 through population screening, 9 through pedigree analysis, and 3 through a general medical work-up. There were 18 women (4 postmenopausal) and 4 men with a median age of 46 years, range 28-76 years. The median follow-up interval was 4 years, range 2-23 years. The serum ferritin levels of 20 of 22 patients remained below the upper limit of normal during the follow-up period. A decline in serum ferritin level was observed in 13 of 22 patients. Three patients had an increase in serum ferritin level of greater than 50%, with only 1 male patient exceeding the upper limit of normal by having a serum ferritin level increase from 295 to 344 microg/L during a 3-year period. CONCLUSIONS: In C282Y homozygotes with a normal ferritin level at the time of diagnosis, 20 of 22 patients failed to show any significant increase in serum ferritin level during a median follow-up of 4 years. This has clinical and economic implications for follow-up and surveillance of this selected population.

Adult↗
PubMed2000

[Genetic hemochromatosis and the HFE gene: from molecular genetics to clinical diagnosis].

More than 90% of patients with genetic hemochromatosis carry a characteristic mutation in the HFE-gene (C282Y). HFE modulates the iron uptake by the transferrin receptor. Duodenal crypt cells of HFE-knockout mice show low intracellular iron concentrations which lead to an upregulation of the divalent metal transporter and enhanced iron uptake by duodenal enterocytes. Heterozygosity for the C282Y mutation appears to alter the course of other liver diseases like porphyria cutanea tarda and nonalcoholic steatohepatitis.

Amino Acid Substitution↗
PubMed2005

Pathophysiology of hereditary hemochromatosis.

Hereditary hemochromatosis (HH) encompasses several inherited disorders of iron homeostasis characterized by increased gastrointestinal iron absorption and tissue iron deposition. The most common form of this disorder is HFE-related HH, nearly always caused by homozygosity for the C282Y mutation. A substantial proportion of C282Y homozygotes do not develop clinically significant iron overload, suggesting roles for environmental factors and modifier genes in determining the phenotype. Recent studies have demonstrated that the pathogenesis of nearly all forms of HH involves inappropriately decreased expression of the iron-regulatory hormone hepcidin. Hepcidin serves to decrease the export of iron from reticuloendothelial cells and absorptive enterocytes. Thus, HH patients demonstrate increased iron release from these cell types, elevated circulating iron, and iron deposition in vulnerable tissues. The mechanism by which HFE influences hepcidin expression is an area of current investigation and may offer insights into the phenotypic variability observed in persons with mutations in HFE.

Absorption↗
PubMed2000

Prevalence of HFE (hemochromatosis gene) mutations in unselected male patients with type 2 diabetes.

To assess the prevalence of mutations in the HFE (hemochromatosis) gene in unselected male patients with type 2 diabetes, we examined 220 white men without known diabetes and 220 age-matched white men with type 2 diabetes for mutations in the HFE gene. Nucleotide 845 (C282Y) and 187(H63D) alleles were amplified by polymerase chain reaction (PCR) with lymphocyte DNA. The PCR products were analyzed by restriction enzyme digestion. One of the 220 patients (0.45%) with diabetes was homozygous for the HFE 845A (C282Y) mutation and 25 (11.3%) were heterozygous for the same mutation, of whom 3 (1.3%) were compound heterozygotes also carrying the HFE 187G (H63D) mutation. These frequencies did not differ significantly from the control population without diabetes. There is no evidence that HFE mutations are found in excess in unselected male patients with type 2 diabetes, and there is no indication for a population-based search for an excess of these alleles in type 2 diabetes.

Adult↗
PubMed2002

The hemochromatosis protein HFE inhibits iron export from macrophages.

Hereditary hemochromatosis (HH) is a disorder of iron metabolism caused by common mutations in the gene HFE. The HFE protein binds to transferrin receptor-1 (TfR1) in competition with transferrin, and in vitro, reduces cellular iron by reducing iron uptake. However, in vivo, HFE is strongly expressed by liver macrophages and intestinal crypt cells, which behave as though they are relatively iron-deficient in HH. These latter observations suggest, paradoxically, that expression of wild-type HFE may lead to iron accumulation in these specialized cell types. Here we show that wild-type HFE protein raises cellular iron by inhibiting iron efflux from the monocytemacrophage cell line THP-1, and extend these results to macrophages derived from healthy individuals and HH patients. In addition, we find that the HH-associated mutant H41D has lost the ability to inhibit iron release despite binding to TfR1 as well as wild-type HFE. Finally, we show that the ability of HFE to block iron release is not competitively inhibited by transferrin. We conclude that HFE has two mutually exclusive functions, binding to TfR1 in competition with Tf, or inhibition of iron release.

Amino Acid Substitution↗
PubMed1997

Hereditary hemochromatosis: effects of C282Y and H63D mutations on association with beta2-microglobulin, intracellular processing, and cell surface expression of the HFE protein in COS-7 cells.

Hereditary hemochromatosis (HH) is the most common autosomal recessive disorder known in humans. A candidate gene for HH called HFE has recently been cloned that encodes a novel member of the major histocompatibility complex class I family. Most HH patients are homozygous for a Cys-282-->Tyr (C282Y) mutation in HFE gene, which has been shown to disrupt interaction with beta2-microglobulin; a second mutation, His-63-->Asp (H63D), is enriched in HH patients who are heterozygous for C282Y mutation. The aims of this study were to determine the effects of the C282Y and H63D mutations on the cellular trafficking and degradation of the HFE protein in transfected COS-7 cells. The results indicate that, while the wild-type and H63D HFE proteins associate with beta2-microglobulin and are expressed on the cell surface of COS-7 cells, these capabilities are lost by the C282Y HFE protein. We present biochemical and immunofluorescence data that indicate that the C282Y mutant protein: (i) is retained in the endoplasmic reticulum and middle Golgi compartment, (ii) fails to undergo late Golgi processing, and (iii) is subject to accelerated degradation. The block in intracellular transport, accelerated turnover, and failure of the C282Y protein to be presented normally on the cell surface provide a possible basis for impaired function of this mutant protein in HH.

Animals↗
PubMed1997

Association of the transferrin receptor in human placenta with HFE, the protein defective in hereditary hemochromatosis.

Hereditary hemochromatosis (HH) is a common autosomal recessive disease associated with loss of regulation of dietary iron absorption and excessive iron deposition in major organs of the body. Recently, a candidate gene for HH (also called HFE) was identified that encodes a novel MHC class I-like protein. Most patients with HH are homozygous for the same mutation in the HFE gene, resulting in a C282Y change in the HFE protein. Studies in cultured cells show that the C282Y mutation abrogates the binding of the recombinant HFE protein to beta2-microglobulin (beta2M) and disrupts its transport to the cell surface. The HFE protein was shown by immunohistochemistry to be expressed in certain epithelial cells throughout the human alimentary tract and to have a unique localization in the cryptal cells of small intestine, where signals to regulate iron absorption are received from the body. In the studies presented here, we demonstrate by immunohistochemistry that the HFE protein is expressed in human placenta in the apical plasma membrane of the syncytiotrophoblasts, where the transferrin-bound iron is normally transported to the fetus via receptor-mediated endocytosis. Western blot analyses show that the HFE protein is associated with beta2M in placental membranes. Unexpectedly, the transferrin receptor was also found to be associated with the HFE protein/beta2M complex. These studies place the normal HFE protein at the site of contact with the maternal circulation where its association with transferrin receptor raises the possibility that the HFE protein plays some role in determining maternal/fetal iron homeostasis. These findings also raise the question of whether mutations in the HFE gene can disrupt this association and thereby contribute to some forms of neonatal iron overload.

Chromatography, Affinity↗
PubMed1997

Immunohistochemistry of HLA-H, the protein defective in patients with hereditary hemochromatosis, reveals unique pattern of expression in gastrointestinal tract.

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder of iron metabolism that leads to excessive iron storage in the liver and other organs. Recently, between 83 and 100% of HH patients have been found to be homozygous for the same mutation in a novel major histocompatibility complex class I-like gene, called the HLA-H gene. The Cys-282 --> Tyr mutation in HH patients would be expected to disrupt the function of the HLA-H gene product by altering a critical disulfide bridge. As a first step in understanding the function of the HLA-H gene product, we generated an antibody to a C-terminal peptide and used it for immunolocalization of the HLA-H protein in the gastrointestinal tract of Finnish and American subjects presumed not to have HH. Although staining for the HLA-H protein was seen in some epithelial cells in every segment of the alimentary canal, its cellular and subcellular expression in the small intestine were quite distinct from those seen in other segments. In contrast to the stomach and colon, where staining was polarized and restricted to the basolateral surfaces, and in contrast to the epithelial cells of the esophagus and submucosal leukocytes, which showed nonpolarized staining around the entire plasma membrane, the staining in small intestine was mainly intracellular and perinuclear, limited to cells in deep crypts. Prior genetic evidence suggested that a defective HLA-H protein is the molecular basis of HH. Here we show that the HLA-H protein not only varies in its pattern of expression along the cranial/caudal axis of the gastrointestinal tract but that it has a unique subcellular localization in the crypts of the small intestine in proximity to the presumed sites of iron absorption.

Cerebral Cortex↗
PubMed1998

HFE gene knockout produces mouse model of hereditary hemochromatosis.

Hereditary hemochromatosis (HH) is a common autosomal recessive disease characterized by increased iron absorption and progressive iron storage that results in damage to major organs in the body. Recently, a candidate gene for HH called HFE encoding a major histocompatibility complex class I-like protein was identified by positional cloning. Nearly 90% of Caucasian HH patients have been found to be homozygous for the same mutation (C282Y) in the HFE gene. To test the hypothesis that the HFE gene is involved in regulation of iron homeostasis, we studied the effects of a targeted disruption of the murine homologue of the HFE gene. The HFE-deficient mice showed profound differences in parameters of iron homeostasis. Even on a standard diet, by 10 weeks of age, fasting transferrin saturation was significantly elevated compared with normal littermates (96 +/- 5% vs. 77 +/- 3%, P < 0.007), and hepatic iron concentration was 8-fold higher than that of wild-type littermates (2,071 +/- 450 vs. 255 +/- 23 microg/g dry wt, P < 0.002). Stainable hepatic iron in the HFE mutant mice was predominantly in hepatocytes in a periportal distribution. Iron concentrations in spleen, heart, and kidney were not significantly different. Erythroid parameters were normal, indicating that the anemia did not contribute to the increased iron storage. This study shows that the HFE protein is involved in the regulation of iron homeostasis and that mutations in this gene are responsible for HH. The knockout mouse model of HH will facilitate investigation into the pathogenesis of increased iron accumulation in HH and provide opportunities to evaluate therapeutic strategies for prevention or correction of iron overload.

Animals↗
PubMed1997

The hemochromatosis founder mutation in HLA-H disrupts beta2-microglobulin interaction and cell surface expression.

We recently reported the positional cloning of a candidate gene for hereditary hemochromatosis (HH), called HLA-H, which is a novel member of the major histocompatibility complex class I family. A mutation in this gene, cysteine 282 --> tyrosine (C282Y), was found to be present in 83% of HH patient DNAs, while a second variant, histidine 63 --> aspartate (H63D), was enriched in patients heterozygous for C282Y. The functional relevance of either mutation has not been described. Co-immunoprecipitation studies of cell lysates from human embryonic kidney cells transfected with wild-type or mutant HLA-H cDNA demonstrate that wild-type HLA-H binds beta2-microglobulin and that the C282Y mutation, but not the H63D mutation, completely abrogates this interaction. Immunofluorescence labeling and subcellular fractionations demonstrate that while the wild-type and H63D HLA-H proteins are expressed on the cell surface, the C282Y mutant protein is localized exclusively intracellularly. This report describes the first functional significance of the C282Y mutation by suggesting that an abnormality in protein trafficking and/or cell-surface expression of HLA-H leads to HH disease.

Base Sequence↗
PubMed1999

The hereditary hemochromatosis protein, HFE, specifically regulates transferrin-mediated iron uptake in HeLa cells.

HFE is the protein product of the gene mutated in the autosomal recessive disease hereditary hemochromatosis (Feder, J. N., Gnirke, A., Thomas, W., Tsuchihashi, Z., Ruddy, D. A., Basava, A., Dormishian, F., Domingo, R. J., Ellis, M. C., Fullan, A., Hinton, L. M., Jones, N. L., Kimmel, B. E., Kronmal, G. S., Lauer, P., Lee, V. K., Loeb, D. B., Mapa, F. A., McClelland, E., Meyer, N. C., Mintier, G. A., Moeller, N., Moore, T., Morikang, E., Prasss, C. E., Quintana, L., Starnes, S. M., Schatzman, R. C., Brunke, K. J., Drayna, D. T., Risch, N. J., Bacon, B. R., and Wolff, R. R. (1996) Nat. Genet. 13, 399-408). At the cell surface, HFE complexes with transferrin receptor (TfR), increasing the dissociation constant of transferrin (Tf) for its receptor 10-fold (Gross, C. N., Irrinki, A., Feder, J. N., and Enns, C. A. (1998) J. Biol. Chem. 273, 22068-22074; Feder, J. N., Penny, D. M., Irrinki, A., Lee, V. K., Lebron, J. A., Watson, N. , Tsuchihashi, Z., Sigal, E., Bjorkman, P. J., and Schatzman, R. C. (1998) Proc. Natl. Acad. Sci. U S A 95, 1472-1477). HFE does not remain at the cell surface, but traffics with TfR to Tf-positive internal compartments (Gross et al., 1998). Using a HeLa cell line in which the expression of HFE is controlled by tetracycline, we show that the expression of HFE reduces 55Fe uptake from Tf by 33% but does not affect the endocytic or exocytic rates of TfR cycling. Therefore, HFE appears to reduce cellular acquisition of iron from Tf within endocytic compartments. HFE specifically reduces iron uptake from Tf, as non-Tf-mediated iron uptake from Fe-nitrilotriacetic acid is not altered. These results explain the decreased ferritin levels seen in our HeLa cell system and demonstrate the specific control of HFE over the Tf-mediated pathway of iron uptake. These results also have implications for the understanding of cellular iron homeostasis in organs such as the liver, pancreas, heart, and spleen that are iron loaded in hereditary hemochromatotic individuals lacking functional HFE.

Biological Transport↗
PubMed2006

Hereditary hemochromatosis protein, HFE, interaction with transferrin receptor 2 suggests a molecular mechanism for mammalian iron sensing.

HFE and transferrin receptor 2 (TFR2) are membrane proteins integral to mammalian iron homeostasis and associated with human hereditary hemochromatosis. Here we demonstrate that HFE and TFR2 interact in cells, that this interaction is not abrogated by disease-associated mutations of HFE and TFR2, and that TFR2 competes with TFR1 for binding to HFE. We propose a new model for the mechanism of iron status sensing that results in the regulation of iron homeostasis.

Animals↗