title: Stoichiometries of transferrin receptors 1 and 2 in human liver.
abstract: Mutations in either the hereditary hemochromatosis protein, HFE, or transferrin receptor 2, TfR2, result in a similarly severe form of the most common type of iron overload disease called hereditary hemochromatosis. Models of the interactions between HFE, TfR1, and TfR2 imply that these proteins are present in different molar concentrations in the liver, where they control expression of the iron regulatory hormone, hepcidin, in response to body iron loading. The aim of this study was to determine in vivo levels of mRNA by quantitative RT-PCR and concentrations of these proteins by quantitative immunoblotting in human liver tissues. The level of TfR2 mRNA was 21- and 63-fold higher than that of TfR1 and HFE, respectively. Molar concentration of TfR2 protein was the highest and determined to be 1.95 nmol/g protein in whole cell lysates and 10.89 nmol/g protein in microsomal membranes. Molar concentration of TfR1 protein was 4.5- and 6.1-fold lower than that of TfR2 in whole cell lysates and membranes, respectively. The level of HFE protein was below 0.53 nmol/g of total protein. HFE is thus present in substoichiometric concentrations with respect to both TfR1 and TfR2 in human liver tissue. This finding supports a model, in which availability of HFE is limiting for formation of complexes with TfR1 or TfR2.
authors.affiliation: Department of Cell and Developmental Biology, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Mail Code L215, Portland, OR 97239, USA.
authors.forename: Maja
authors.initials: M
authors.lastname: Chloupková
authors.forename: An-Sheng
authors.initials: AS
authors.lastname: Zhang
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Enns
mesh_terms: D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071020:Hemochromatosis Protein; D056945:Hep G2 Cells; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008099:Liver / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008862:Microsomes, Liver; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D011990:Receptors, Transferrin / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014015:Tissue Banks; D014162:Transfection; D014168:Transferrin
chemical_list: D015703:Antigens, CD; C068126:CD71 antigen; C103673:HFE protein, human; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D012333:RNA, Messenger; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; C503640:TFR2 protein, human; D014168:Transferrin