TY - JOUR
T1 - The role of transferrin receptor 1 and 2 in transferrin-bound iron uptake in human hepatoma cells
AU - Herbison, C.E.
AU - Thorstensen, K.
AU - Chua, Anita
AU - Graham, Ross
AU - Leedman, Peter
AU - Olynyk, John
AU - Trinder, Debbie
PY - 2009
Y1 - 2009
N2 - Transferrin receptor (TFR) 1 and 2 are expressed in the liver; TFR1 levels are regulated by cellular iron levels while TFR2 levels are regulated by transferrin saturation. The aims of this study were to 1) determine the relative importance of TFR1 and TFR2 in transferrin-bound iron (TBI) uptake by HuH7 human hepatoma cells and 2) characterize the role of metal-transferrin complexes in the regulation of these receptors. TFR expression was altered by 1) incubation with metal-transferrin (Tf) complexes, 2) TFR1 and TFR2 small interfering RNA knockdown, and 3) transfection with a human TFR2 plasmid. TBI uptake was measured using 59Fe-125I-labeled Tf and mRNA and protein expression by real-time PCR and Western blot analysis, respectively. Fe2Tf, Co2Tf, and Mn2Tf increased TFR2 protein expression, indicating that the upregulation was not specifically regulated by iron-transferrin but also other metal-transferrins. In addition, Co2Tf and Mn2Tf upregulated TFR1, reduced ferritin, and increased hypoxia-inducible factor-1α protein expression, suggesting that TFR1 upregulation was due to a combination of iron deficiency and chemical hypoxia. TBI uptake correlated with changes in TFR1 but not TFR2 expression. TFR1 knockdown reduced iron uptake by 80% while TFR2 knockdown did not affect uptake. At 5 μM transferrin, iron uptake was not affected by combined TFR1 and TFR2 knockdown. Transfection with a hTFR2 plasmid increased TFR2 protein expression, causing a 15–20% increase in iron uptake and ferritin levels. This shows for the first time that TFR-mediated TBI uptake is mediated primarily via TFR1 but not TFR2 and that a high-capacity TFR-independent pathway exists in hepatoma cells.
AB - Transferrin receptor (TFR) 1 and 2 are expressed in the liver; TFR1 levels are regulated by cellular iron levels while TFR2 levels are regulated by transferrin saturation. The aims of this study were to 1) determine the relative importance of TFR1 and TFR2 in transferrin-bound iron (TBI) uptake by HuH7 human hepatoma cells and 2) characterize the role of metal-transferrin complexes in the regulation of these receptors. TFR expression was altered by 1) incubation with metal-transferrin (Tf) complexes, 2) TFR1 and TFR2 small interfering RNA knockdown, and 3) transfection with a human TFR2 plasmid. TBI uptake was measured using 59Fe-125I-labeled Tf and mRNA and protein expression by real-time PCR and Western blot analysis, respectively. Fe2Tf, Co2Tf, and Mn2Tf increased TFR2 protein expression, indicating that the upregulation was not specifically regulated by iron-transferrin but also other metal-transferrins. In addition, Co2Tf and Mn2Tf upregulated TFR1, reduced ferritin, and increased hypoxia-inducible factor-1α protein expression, suggesting that TFR1 upregulation was due to a combination of iron deficiency and chemical hypoxia. TBI uptake correlated with changes in TFR1 but not TFR2 expression. TFR1 knockdown reduced iron uptake by 80% while TFR2 knockdown did not affect uptake. At 5 μM transferrin, iron uptake was not affected by combined TFR1 and TFR2 knockdown. Transfection with a hTFR2 plasmid increased TFR2 protein expression, causing a 15–20% increase in iron uptake and ferritin levels. This shows for the first time that TFR-mediated TBI uptake is mediated primarily via TFR1 but not TFR2 and that a high-capacity TFR-independent pathway exists in hepatoma cells.
U2 - 10.1152/ajpcell.00649.2008
DO - 10.1152/ajpcell.00649.2008
M3 - Article
C2 - 19828835
SN - 0363-6143
VL - 297
SP - C1567-C1575
JO - American journal of physiology : cell physiology
JF - American journal of physiology : cell physiology
IS - 6
ER -