Factor XII interacts with the multiprotein assembly of urokinase plasminogen activator receptor, gC1qR, and cytokeratin 1 on endothelial cell membranes.
Investigations were performed to define the factor XII (FXII) binding site(s) on cultured endothelial cells (HUVECs). Biotin- or fluorescein isothiocyanate (FITC)-FXII in the presence of 10 microM Zn(2+) specifically binds to HUVEC monolayers or cells in suspension. Collagen-stimulated platelets release sufficient Zn(2+) to support FXII binding. On laser scanning confocal microscopy or electron microscopy, FITC-FXII or Nanogold-labeled FXII, respectively, specifically bind to HUVECs. Antibodies to gC1qR, urokinase plasminogen activator receptor (uPAR) and, to a lesser extent, cytokeratin 1 (CK1) block FXII binding to HUVECs as determined by flow cytometry and soluble or solid phase binding assays. FITC-FXII on endothelial cells colocalizes with gC1qR, uPAR and, to a lesser extent, CK1 antigen. Combined recombinant soluble uPAR and CK1 inhibit 80% FITC-FXII binding to HUVECs. Peptide Y(39)HKCTHKGR(47) (YHK9) from the N-terminal region of FXII and peptide H(479)KHGHGHGKHKNKGKKNGKH(498) from HK's domain 5 cell-binding site block FITC-FXII binding to HUVECs. Peptide YHK9 also inhibits FXIIa's activation of prekallikrein and FXI on HUVECs. These combined investigations indicate that FXII through a region on its fibronectin type II domain binds to the same multiprotein receptor complex that comprises the HK binding site of HUVECs. However, plasma concentrations of HK and vitronectin inhibit FXII binding to HUVECs 100% and 50%, respectively, and plasma albumin and other proteins prevent a sufficient level of free Zn(2+) to be available to support FXII binding to HUVECs. Thus, physiologic FXII expression on HUVECs is secondary to HK binding and highly restricted in its ability to initiate prekallikrein or FXI activation.
Mahdi
Fakhri
F
Department of Internal Medicine and Pathology, University of Michigan, Ann Arbor, MI 48109-0640, USA.
Madar
Zia Shariat
ZS
Figueroa
Carlos D
CD
Schmaier
Alvin H
AH
D001665:Binding Sites; D001667:Binding, Competitive; D001792:Blood Platelets / Q000502:physiology; D002352:Carrier Proteins; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005172:Factor XI / Q000378:metabolism; D005174:Factor XII / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors; D007633:Keratins / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D046912:Multiprotein Complexes; D011288:Prekallikrein / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011951:Receptors, Complement / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D015032:Zinc / Q000494:pharmacology
C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D046912:Multiprotein Complexes; C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D011951:Receptors, Complement; D055293:Receptors, Urokinase Plasminogen Activator; C032402:complement 1q receptor; D007633:Keratins; D005174:Factor XII; D005172:Factor XI; D011288:Prekallikrein; D015032:Zinc