HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Herbison, C. E Articles by Trinder, D. PubMed PubMed Citation Articles by Herbison, C. E Articles by Trinder, D., Prof

Research Article

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

¹The University of Western Australia ²The Norwegian University of Science and Technology ³University of Western Australia

Submitted 19 December 2008 ; revised 3 August 2009 ; accepted in final form 13 October 2009

Transferrin receptor (TFR) 1 and 2 are expressed in the liver; TFR1 levels are regulated by cellular iron levels whilst 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 siRNA knockdown and [3] transfection with a hTFR2 plasmid. TBI uptake was measured using ⁵⁹Fe-¹²⁵I-Tf and mRNA and protein expression by real-time PCR and western blot analysis, respectively. Fe₂Tf, Co₂Tf and Mn₂Tf increased TFR2 protein expression indicating the upregulation was not specifically regulated by iron-transferrin but also other metal-transferrins. Also, Co₂Tf and Mn₂Tf upregulated TFR1, reduced ferritin and increased hypoxia-inducible factor-1 (HIF-1) protein expression suggesting 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 5µM 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 a high capacity TFR independent pathway exists in hepatoma cells.

TFR1; TFR2; cobalt; siRNA; chemical hypoxia