title: Impact of D181V and A69T on the function of ferroportin as an iron export pump and hepcidin receptor.
abstract: Mutations in the only known mammalian iron exporter ferroportin cause a rare iron overload disorder termed ferroportin disease. Two distinct clinical phenotypes are caused by different disease mechanisms: mutations in ferroportin either cause loss of iron export function or gain of function due to resistance to hepcidin, the peptide hormone that normally downregulates ferroportin. The aim of the present study was to examine the disease mechanisms of the thus far unclassified A69T and D181V ferroportin mutations. We overexpressed wild-type and mutant ferroportin fused to green fluorescent protein in human embryonic kidney cells and used a (59)Fe-assay, intracellular ferritin concentrations, confocal microscopy and flow cytometry to study iron export function, subcellular localization and the responsiveness to hepcidin. While the A69T ferroportin mutation seems not to affect the iron export function it causes dose-dependent hepcidin resistance. We further found that D181V mutated ferroportin is iron export defective and hepcidin resistant, similar to the loss of function mutations A77D and C367X. This indicates that intact iron export might be necessary for hepcidin-induced downregulation of ferroportin. This hypothesis was investigated by studying the hepcidin response under modulation of iron availability. Incubation of wild-type ferroportin overexpressing cells with holo-transferrin increases the hepcidin effect whereas chelating extracellular ferrous iron causes hepcidin resistance. In this study we present data that postulates to classify the D181V ferroportin mutation as loss of function and the A69T mutation as dose-dependent hepcidin resistant and outline a possible causal link between iron export function and the hepcidin effect.
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Anichstrasse 35, A-6020 Innsbruck, Austria.
authors.forename: Roman
authors.initials: R
authors.lastname: Praschberger
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Anichstrasse 35, A-6020 Innsbruck, Austria.
authors.forename: Melanie
authors.initials: M
authors.lastname: Schranz
authors.affiliation: Department of Hepatology, University of Cambridge, UK; Cambridge University Hospitals NHS Foundation Trust, Hills Rd, Cambridge CB2 0QQ, UK.
authors.forename: William J H
authors.initials: WJ
authors.lastname: Griffiths
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Anichstrasse 35, A-6020 Innsbruck, Austria.
authors.forename: Nadja
authors.initials: N
authors.lastname: Baumgartner
authors.affiliation: Department of Anaesthesiology, Medical University of Innsbruck, Innrain 66, A-6020 Innsbruck, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Hermann
authors.affiliation: Department of Radiology, University of Cambridge, UK; Cambridge University Hospitals NHS Foundation Trust, Hills Rd, Cambridge CB2 0QQ, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Lomas
authors.affiliation: Department of Medicine, University Hospital of Modena, Policlinico di Modena, Via del Pozzo 71, 41100 Modena, Italy.
authors.forename: Antonello
authors.initials: A
authors.lastname: Pietrangelo
authors.affiliation: Department of Medicine, University of Cambridge, UK; Cambridge University Hospitals NHS Foundation Trust, Hills Rd, Cambridge CB2 0QQ, UK.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Cox
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Anichstrasse 35, A-6020 Innsbruck, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Vogel
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Anichstrasse 35, A-6020 Innsbruck, Austria. Electronic address: heinz.zoller@i-med.ac.at.
authors.forename: Heinz
authors.initials: H
authors.lastname: Zoller
mesh_terms: D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005293:Ferritins / Q000378:metabolism; D005838:Genotype; D006432:Hemochromatosis / Q000235:genetics* / Q000378:metabolism; D064451:Hepcidins / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D010641:Phenotype; D011956:Receptors, Cell Surface / Q000378:metabolism*; D000098742:Ferroportin
chemical_list: D027682:Cation Transport Proteins; D064451:Hepcidins; D011956:Receptors, Cell Surface; D000098742:Ferroportin; D005293:Ferritins; D007501:Iron
keywords: Ferroxidase; Genetic; Hemochromatosis; Non-HFE hemochromatosis; SLC40A1