title: In vitro binding of HFE to the cation-independent mannose-6 phosphate receptor.
abstract: Hereditary hemochromatosis is most frequently associated with mutations in HFE, which encodes a class Ib histocompatibility protein. HFE binds to the transferrin receptor-1 (TfR1) in competition with iron-loaded transferrin (Fe-Tf). HFE is released from TfR1 by increasing concentrations of Fe-Tf, and free HFE may then regulate iron homeostasis by binding other ligands. To search for new HFE ligands we expressed recombinant forms of HFE in the human cell line 293T. HFE protein was purified, biotinylated and made into fluorescently labelled tetramers. HFE tetramers bound to TfR1 in competition with Tf, but in addition we detected a binding activity on some cell types that was not blocked by Fe-Tf or by mutations in HFE that prevent binding to TfR1. We identified this second HFE ligand as the cation independent mannose-6-phosphate receptor (CI-MPR, also known as the insulin-like growth factor-2 receptor, IGF2R). HFE:CI-MPR binding was mediated through phosphorylated mannose residues on HFE. Recombinant murine Hfe also bound to CI-MPR. HFE bound to TfR1 was prevented from binding CI-MPR until released by increasing concentrations of Fe-Tf, a feature consistent with an iron sensing mechanism. However, it remains to be determined whether endogenous HFE in vivo also acquires the mannose-6 phosphate modification and binds to CI-MPR.
authors.affiliation: Weatherall Institute, Oxford University, UK.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Schimanski
authors.forename: Hal
authors.initials: H
authors.lastname: Drakesmith
authors.forename: Emma
authors.initials: E
authors.lastname: Sweetland
authors.forename: Judy
authors.initials: J
authors.lastname: Bastin
authors.forename: Dellel
authors.initials: D
authors.lastname: Rezgui
authors.forename: Mariola
authors.initials: M
authors.lastname: Edelmann
authors.forename: Benedikt
authors.initials: B
authors.lastname: Kessler
authors.forename: Alison T
authors.initials: AT
authors.lastname: Merryweather-Clarke
authors.forename: Kathryn J H
authors.initials: KJ
authors.lastname: Robson
authors.forename: Alain R M
authors.initials: AR
authors.lastname: Townsend
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008360:Mannosephosphates / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; C068126:CD71 antigen; C103673:HFE protein, human; D000071020:Hemochromatosis Protein; C499535:Hfe protein, mouse; D015395:Histocompatibility Antigens Class I; D008024:Ligands; D008360:Mannosephosphates; D008565:Membrane Proteins; D017527:Receptor, IGF Type 2; D011990:Receptors, Transferrin; D011994:Recombinant Proteins; D014168:Transferrin; C027693:mannose-6-phosphate