The role of transferrin receptor 1 and 2 in transferrin-bound iron uptake in human hepatoma cells

Herbison, Carly E.; Thorstensen, Ketil; Chua, Anita; Graham, Ross M.; Leedman, Peter J.; Olynyk, John K.; Trinder, Debbie

doi:10.1152/ajpcell.00649.2008

Cited by 76 publications

(55 citation statements)

References 45 publications

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“…In support of this, we recently observed in hepatoma cells that changes in iron uptake were small when Tfr2 protein expression was modified by diferric transferrin, Tfr2 overexpression, and Tfr2 underexpression using small interfering RNA. 39 In addition, in vivo hepatic iron uptake from plasma transferrin in Tfr2 (Y245X) mutant mice with nonfunctional Tfr2 was only approximately 20% lower than in iron-loaded wild-type mice. 40 This provides further support for a limited role of Tfr2 in liver iron transport and suggests that other transferrinbound iron transport pathways exist.…”

Section: Discussionmentioning

confidence: 99%

The role of Hfe in transferrin-bound iron uptake by hepatocytes

et al. 2008

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HFE-related hereditary hemochromatosis results in hepatic iron overload. Hepatocytes acquire transferrin-bound iron via transferrin receptor (Tfr) 1 and Tfr1-independent pathways (possibly Tfr2-mediated). In this study, the role of Hfe in the regulation of hepatic transferrin-bound iron uptake by these pathways was investigated using Hfe knockout mice. Iron and transferrin uptake by hepatocytes from Hfe knockout, non-iron-loaded and iron-loaded wild-type mice were measured after incubation with 50 nM 125 I-Tf-59 Fe (Tfr1 pathway) and 5 M 125 I-Tf-59 Fe (Tfr1-independent or putative Tfr2 pathway). Tfr1 and Tfr2 messenger RNA (mRNA) and protein expression were measured by real-time polymerase chain reaction and western blotting, respectively. Tfr1-mediated iron and transferrin uptake by Hfe knockout hepatocytes were increased by 40% to 70% compared with iron-loaded wild-type hepatocytes with similar iron levels and Tfr1 expression. Iron and transferrin uptake by the Tfr1-independent pathway was approximately 100-fold greater than by the Tfr1 pathway and was not affected by the absence of Hfe. Diferric transferrin increased hepatocyte Tfr2 protein expression, resulting in a small increase in transferrin but not iron uptake by the Tfr1-independent pathway. Conclusion: Tfr1-mediated iron uptake is regulated by Hfe in hepatocytes. The Tfr1-independent pathway exhibited a much greater capacity for iron uptake than the Tfr1 pathway but it was not regulated by Hfe. A homozygous C282Y mutation in the HFE gene results in hereditary hemochromatosis and is characterized by increased iron absorption and transferrin saturation that leads to hepatic iron overload. The hemochromatosis protein, HFE, is closely associated with transferrin receptor 1 (TFR1) and competes with transferrin for the same binding sites on TFR1. 1 Hepatocytes acquire transferrin-bound iron via TFR1 by a high-affinity endocytic process. 2 A second transferrin receptor has been identified and was named transferrin receptor 2 (TFR2). Like TFR1, it transports transferrin-bound iron by a receptor-mediated endocytic process, 3 although the affinity of this pathway is up to 30-fold lower than that of TFR1. 4 In iron overload, transferrin saturation and diferric transferrin levels are increased, resulting in an up-regulation of TFR2 protein expression, 5,6 suggesting that hepatocyte iron loading may involve TFR2. It has been postulated that TFR2 may mediate the TFR1-independent uptake process described previously in hepatic cells. [7][8][9] In addition to its role in iron transport, TFR2 also has a role in the regulation of cellular iron metabolism because mutations in TFR2 cause hepatic iron overload. 10,11 TFR2 is predominantly expressed in hepatocytes 12 and has recently been shown to interact with HFE. 13 Unlike TFR1, TFR2 is not regulated by intracellular iron levels because there are no iron-responsive elements in the untranslated region of its messenger RNA (mRNA). 12 Hepcidin is synthesized by hepatocytes and is a key regulator of iron homeostasis. 14 It ...

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Section: Discussionmentioning

confidence: 99%

The role of Hfe in transferrin-bound iron uptake by hepatocytes

et al. 2008

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“…Recently, Herbison et al (36) showed that knockdown of TFR1 in HuH7 cells resulted in 80% less assimilation of iron from 50 nM TF compared with controls. The lower iron levels were due to diminished uptake of TF because TF uptake was also 80% lower.…”

Section: Discussionmentioning

confidence: 99%

ZRT/IRT-like Protein 14 (ZIP14) Promotes the Cellular Assimilation of Iron from Transferrin

Zhao

Gao

Enns

et al. 2010

Journal of Biological Chemistry

145

127

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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 nontransferrin-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. Most cells acquire iron from transferrin (TF),2 a circulating plasma protein that can carry up to two ferric (Fe 3ϩ ) iron atoms. After Fe-TF binds to cell surface TF receptor 1 (TFR1), the plasma membrane invaginates into clathrin-coated pits, which internalize the Fe-TF⅐TFR1 complex into endosomes. Upon endosomal acidification, Fe 3ϩ is released and subsequently reduced to Fe 2ϩ . The liberated Fe 2ϩ is then transported across the endosomal membrane and into the cytosol (1).The assimilation of iron from TF has been best characterized in developing erythroid cells, the most avid consumers of TFbound iron (TBI). In these cells, reduction of Fe 3ϩ is catalyzed by the oxidoreductase Steap3 (2), and iron transport out of the endosome is facilitated by the transmembrane protein divalent metal transporter 1 (DMT1) (3, 4). Accordingly, mice lacking either Steap3 or DMT1 cannot incorporate sufficient iron into developing erythrocytes and become anemic (2, 3). After the erythroid marrow, the second largest consumer of TBI is the liver, accounting for 10 -20% of iron exchange with the plasma (5). Interestingly, anemic Steap3-mutant mice or DMT1-null mice are able to take up iron into the liver (6, 7), indicating that Steap3 and DMT1 are dispensable for hepatic iron uptake.Under normal conditions, Ͼ95% of plasma iron is TBI. Studies in perfused rat liver document that the liver takes up TBI, almost exclusively into he...

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“…Enhanced iron intake or suppressed iron excretion can be assumed to be responsible for increased iron deposition in the liver. In general, Tfr1 plays an important role in hepatic iron uptake (Herbison et al, 2009), but Tfr2 as well as Tfr1 may have contributed to an increase in hepatic iron levels in experiment 1. In the duodenum, the mRNA levels of DMT1, ferritin H, and hephaestin were more significantly elevated in the CE group than the C group, whereas DMT1 mRNA expression tended to be increased in the HE group compared with the H group.…”

Section: Effects Of Ezetimibe On Iron Metabolismmentioning

confidence: 99%

Ezetimibe Increases Hepatic Iron Levels in Mice Fed a High-Fat Diet

Kishino

Tanaka

Ikeda

et al. 2013

J Pharmacol Exp Ther

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Accumulating evidence suggests that ezetimibe may be a promising agent for treatment of nonalcoholic fatty liver disease and steatohepatitis (NAFLD/NASH). Phlebotomy and dietary iron restriction reduce serum transaminase in NAFLD/NASH patients. Recent studies have shown that a mutual effect exists between lipid metabolism and iron metabolism. Accordingly, we examined the effect of ezetimibe on iron metabolism in mice fed a high-fat diet with or without iron. We fed C57BL/6 mice the following diets for 12 weeks. and duodenum were removed after 12 weeks. In experiment 1, the hepatic iron levels were higher in HE than H, whereas there was no difference between C and CE. Hepatic mRNA expression of transferrin receptor 1 and 2, ferritins, and hepcidin were increased more in CE than C, and more in HE than H. In the duodenum, divalent metal transporter 1, ferritin H, and hephaestin mRNA levels were increased in CE compared with C. In experiment 2, hepatic iron concentrations were higher in HIE than HI. Hepatic mRNA expression of ferritin L and hepcidin were increased in HIE compared with HI. In duodenum, ferritin L mRNA was increased in HIE compared with CIE. Ezetimibe induced hepatic iron uptake transporter expression in mice fed a high-fat diet, causing increased hepatic iron concentrations.

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The role of transferrin receptor 1 and 2 in transferrin-bound iron uptake in human hepatoma cells

Cited by 76 publications

References 45 publications

The role of Hfe in transferrin-bound iron uptake by hepatocytes

The role of Hfe in transferrin-bound iron uptake by hepatocytes

ZRT/IRT-like Protein 14 (ZIP14) Promotes the Cellular Assimilation of Iron from Transferrin

Ezetimibe Increases Hepatic Iron Levels in Mice Fed a High-Fat Diet

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