title: Immune cells and hepatocytes express glycosylphosphatidylinositol-anchored ceruloplasmin at their cell surface.
abstract: BACKGROUND
  Ceruloplasmin is a positive acute-phase protein with both anti- and pro-oxidant activities, thus having still unclear physiological functions in inflammatory processes. Importantly, ceruloplasmin has been implicated in iron metabolism due to its ferroxidase activity, assisting ferroportin on cellular iron efflux. Ceruloplasmin can be expressed as a secreted or as a membrane glycosylphosphatidylinositol-anchored protein (GPI-ceruloplasmin), this latter one being reported as expressed mostly in the brain.
  
  
  METHODS
  We studied the expression of both ceruloplasmin isoforms in human peripheral blood lymphocytes, monocytes, mouse macrophages and human hepatocarcinoma cell line HepG2, using immunofluorescence and immunoblotting techniques. Co-localization of ceruloplasmin and ferroportin was also investigated by immunofluorescence in mouse macrophages.
  
  
  RESULTS
  Ceruloplasmin was detected by immunoblotting and immunofluorescence in membrane and cytosol of all cell types. The cell surface ceruloplasmin was identified as the GPI-isoform and localized in lipid rafts from monocytes, macrophages and HepG2 cells. In macrophages, increased expression levels and co-localization of ferroportin and GPI-ceruloplasmin in cell surface lipid rafts were observed after iron treatment. Such iron upregulation of ceruloplasmin was not observed in HepG2.
  
  
  CONCLUSIONS
  Our results revealed an unexpected ubiquitous expression of the GPI-ceruloplasmin isoform in immune and hepatic cells. Different patterns of regulation of ceruloplasmin in these cells may reflect distinct physiologic functions of this oxidase. In macrophages, GPI-ceruloplasmin and ferroportin likely interact in lipid rafts to export iron from cells. Precise knowledge about ceruloplasmin isoforms expression and function in various cell types will help to clarify the role of ceruloplasmin in many diseases related to iron metabolism, inflammation and oxidative biology.
authors.affiliation: National Institute of Health Dr Ricardo Jorge, Lisbon, Portugal.
authors.forename: Liliana
authors.initials: L
authors.lastname: Marques
authors.forename: Anne
authors.initials: A
authors.lastname: Auriac
authors.forename: Alexandra
authors.initials: A
authors.lastname: Willemetz
authors.forename: João
authors.initials: J
authors.lastname: Banha
authors.forename: Bruno
authors.initials: B
authors.lastname: Silva
authors.forename: François
authors.initials: F
authors.lastname: Canonne-Hergaux
authors.forename: Luciana
authors.initials: L
authors.lastname: Costa
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D002570:Ceruloplasmin / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D009000:Monocytes / Q000378:metabolism*; D000098742:Ferroportin
chemical_list: D027682:Cation Transport Proteins; D017261:Glycosylphosphatidylinositols; D007527:Isoenzymes; D000098742:Ferroportin; D007501:Iron; D002570:Ceruloplasmin