title: High affinity binding of beta 2-glycoprotein I to human endothelial cells is mediated by annexin II.
abstract: Beta(2)-glycoprotein I (beta(2)GPI) is an abundant plasma phospholipid-binding protein and an autoantigen in the antiphospholipid antibody syndrome. Binding of beta(2)GPI to endothelial cells targets them for activation by anti-beta(2)GPI antibodies, which circulate and are associated with thrombosis in patients with the antiphospholipid antibody syndrome. However, the binding of beta(2)GPI to endothelial cells has not been characterized and is assumed to result from association of beta(2)GPI with membrane phospholipid. Here, we characterize the binding of beta(2)GPI to endothelial cells and identify the beta(2)GPI binding site. (125)I-beta(2)GPI bound with high affinity (K(d) approximately 18 nm) to human umbilical vein endothelial cells (HUVECs). Using affinity purification, we isolated beta(2)GPI-binding proteins of approximately 78 and approximately 36 kDa from HUVECs and EAHY.926 cells. Amino acid sequences of tryptic peptides from each of these were identical to sequences within annexin II. A role for annexin II in binding of beta(2)GPI to cells was confirmed by the observations that annexin II-transfected HEK 293 cells bound approximately 10-fold more (125)I-beta(2)GPI than control cells and that anti-annexin II antibodies inhibited the binding of (125)I-beta(2)GPI to HUVECs by approximately 90%. Finally, surface plasmon resonance studies revealed high affinity binding between annexin II and beta(2)GPI. These results demonstrate that annexin II mediates the binding of beta(2)GPI to endothelial cells.
authors.affiliation: Hematology-Oncology Division, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4937, USA.
authors.forename: K
authors.initials: K
authors.lastname: Ma
authors.forename: R
authors.initials: R
authors.lastname: Simantov
authors.forename: J C
authors.initials: JC
authors.lastname: Zhang
authors.forename: R
authors.initials: R
authors.lastname: Silverstein
authors.forename: K A
authors.initials: KA
authors.lastname: Hajjar
authors.forename: K R
authors.initials: KR
authors.lastname: McCrae
mesh_terms: D000595:Amino Acid Sequence; D017306:Annexin A2 / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D005353:Fibronectins / Q000494:pharmacology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010743:Phospholipids / Q000378:metabolism; D014471:Umbilical Veins; D053482:beta 2-Glycoprotein I
chemical_list: D017306:Annexin A2; D005353:Fibronectins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D010446:Peptide Fragments; D010743:Phospholipids; D053482:beta 2-Glycoprotein I