title: IGFBP-3/transferrin/transferrin receptor 1 complexes as principal mediators of IGFBP-3 delivery to colon cells in non-cancer and cancer tissues.
abstract: OBJECTIVE
  The aim of this work was to study the involvement of IGFBP-3/Tf complexes in the pathology of colorectal carcinoma (CRC), quantify them, investigate their relation to iron concentration and binding to transferrin receptor (TfR) in colon tissue (non-cancer and cancer), and to assess the priority of this pathway for internalization of IGFBP-3.
  
  
  METHODS
  The presence of IGFBP-3/Tf complexes was analyzed in sera from healthy persons and patients with CRC, and in colon tissue by immunoblotting. Complexes were immunoprecipitated, quantified by immunoassay and structurally characterized by immunoblotting, lectin blotting and mass spectrometry. Complexes which interacted with colon cells were immunoprecipitated with anti-TfR1 antibody and studied. Colon tissue slides were subjected to immunohistochemical analysis.
  
  
  RESULTS
  The concentration of IGFBP-3/Tf complexes was three times lower in patients with CRC. They were increasingly carbonylated, sialylated, contained more Galβ4GlcNAc units, expressed altered charge density and increased affinity for metal ions. Immunoprecipitation experiments revealed more TfR1 on membranes than in cytosol of colon cells, also more in cancer than non-cancer tissue. TfR1 on membranes were less occupied with IGFBP-3/Tf complexes than in cytosol. Immunofluorescent staining indicated a remarkable degree of co-localization of IGFBP-3 and TfR1, evenly distributed in non-cancer tissue and both evenly and cell surface concentrated in cancer tissue.
  
  
  CONCLUSIONS
  Increased expression of TfR1 on colon cell membranes in patients with CRC compensates for the reduced extracellular availability of IGFBP-3/Tf and TfR1 is the principal binding partner of extracellular IGFBP-3. IGFBP-3/Tf complexes in patients with CRC exhibit increased affinity for iron ions.
authors.affiliation: Institute for the Application of Nuclear Energy, University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia. Electronic address: goranm@inep.co.rs.
authors.forename: Goran
authors.initials: G
authors.lastname: Miljuš
authors.affiliation: Clinical Medical Centre "Bežanijska Kosa", Bežanijska kosa b.b., 11080 Belgrade, Serbia.
authors.forename: Vesna
authors.initials: V
authors.lastname: Malenković
authors.affiliation: Clinical Medical Centre "Bežanijska Kosa", Bežanijska kosa b.b., 11080 Belgrade, Serbia.
authors.forename: Blagoje
authors.initials: B
authors.lastname: Đukanović
authors.affiliation: Institute for the Application of Nuclear Energy, University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia.
authors.forename: Nikola
authors.initials: N
authors.lastname: Kolundžić
authors.affiliation: Institute for the Application of Nuclear Energy, University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia.
authors.forename: Olgica
authors.initials: O
authors.lastname: Nedić
mesh_terms: D000328:Adult; D000368:Aged; D015703:Antigens, CD / Q000378:metabolism*; D002277:Carcinoma / Q000175:diagnosis / Q000378:metabolism*; D016022:Case-Control Studies; D002462:Cell Membrane / Q000378:metabolism; D003110:Colonic Neoplasms / Q000175:diagnosis / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D011485:Protein Binding; D021381:Protein Transport; D011990:Receptors, Transferrin / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; C068126:CD71 antigen; C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D011990:Receptors, Transferrin; D014168:Transferrin; D007501:Iron
keywords: Co-localization; Colorectal cancer; Insulin-like growth factor -binding protein 3; Transferrin; Transferrin receptor