title: Hepcidin, the hormone of iron metabolism, is bound specifically to alpha-2-macroglobulin in blood.
abstract: Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify alpha2-macroglobulin (alpha2-M) as the specific hepcidin-binding molecule in blood. Interaction of 125I-hepcidin with alpha2-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. Hepcidin binding to nonactivated alpha2-M displays high affinity (Kd 177 +/- 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated alpha2-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (Kd 0.3 microM) hepcidin-binding sites. This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for its effector functions. Because alpha2-M rapidly targets ligands to cells via receptor-mediated endocytosis, the binding of hepcidin to alpha2-M may influence its functions. In fact, the alpha2-M-hepcidin complex decreased ferroportin expression in J774 cells more effectively than hepcidin alone. The demonstration that alpha2-M is the hepcidin transporter could lead to better understanding of hepcidin physiology, methods for its sensitive measurement and the development of novel drugs for the treatment of iron-related diseases.
authors.affiliation: Institute of Hematology and Blood Transfusion, Prague, Czech Republic.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Peslova
authors.forename: Jiri
authors.initials: J
authors.lastname: Petrak
authors.forename: Katerina
authors.initials: K
authors.lastname: Kuzelova
authors.forename: Ivan
authors.initials: I
authors.lastname: Hrdy
authors.forename: Petr
authors.initials: P
authors.lastname: Halada
authors.forename: Philip W
authors.initials: PW
authors.lastname: Kuchel
authors.forename: Shan
authors.initials: S
authors.lastname: Soe-Lin
authors.forename: Prem
authors.initials: P
authors.lastname: Ponka
authors.forename: Robert
authors.initials: R
authors.lastname: Sutak
authors.forename: Erika
authors.initials: E
authors.lastname: Becker
authors.forename: Michael Li-Hsuan
authors.initials: ML
authors.lastname: Huang
authors.forename: Yohan
authors.initials: Y
authors.lastname: Suryo Rahmanto
authors.forename: Des R
authors.initials: DR
authors.lastname: Richardson
authors.forename: Daniel
authors.initials: D
authors.lastname: Vyoral
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism*; D015153:Blotting, Western; D027682:Cation Transport Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002850:Chromatography, Gel; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D064451:Hepcidins; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000511:alpha-Macroglobulins / Q000378:metabolism*; D000098742:Ferroportin
chemical_list: D023181:Antimicrobial Cationic Peptides; D027682:Cation Transport Proteins; C578702:HAMP protein, human; C579599:Hamp protein, mouse; D064451:Hepcidins; D000511:alpha-Macroglobulins; D000098742:Ferroportin; D007501:Iron