title: Endothelial cell-mediated conversion of Glu-plasminogen to Lys-plasminogen. Further evidence for assembly of the fibrinolytic system on the endothelial cell surface.
abstract: Lysine-plasminogen (Lys-PLG), the plasmin-modified form of native glutamic acid-plasminogen (Glu-PLG), displays enhanced binding affinity for fibrin and also enhanced activation by urokinase and tissue plasminogen activator. We previously demonstrated high-affinity, specific, and functional binding of Glu-PLG as well as tissue plasminogen activator to cultured human umbilical vein endothelial cells (HUVEC). In the present study, we demonstrate binding of Lys-PLG to HUVEC, as well as conversion of Glu-PLG to Lys-PLG at the cell surface. Binding of Lys-PLG to HUVEC was saturable, reversible, epsilon-aminocaproic acid-sensitive, and involved two saturable sites with Kd's of 142 pM and 120 nM, respectively. Upon incubation with Glu-PLG, HUVEC, as well as endothelium in situ, partially converted the ligand to a Lys-PLG-like species. Conversion by HUVEC was blocked by diisopropyl-fluorophosphate, but not by other serine protease inhibitors, including alpha 2-plasmin inhibitor. Eluates of intact umbilical cord vessels contained Lys-PLG by immunoblot analysis. Lys-PLG was also identified immunohistochemically on the endothelial surface of vessels from a variety of normal and inflamed tissues. Thus, endothelial cells appear to actively modify circulating Glu-PLG, bind Lys-PLG to their surface, and thus enhance the fibrinolytic potential of the blood vessel wall.
mesh_terms: D001665:Binding Sites; D004730:Endothelium, Vascular / Q000166:cytology* / Q000378:metabolism; D005342:Fibrinolysis; D006801:Humans; D007150:Immunohistochemistry; D007531:Isoflurophate / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism*; D010958:Plasminogen / Q000378:metabolism*; D013499:Surface Properties; D010959:Tissue Plasminogen Activator / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; C018998:lysyl-plasminogen; D007531:Isoflurophate; D010958:Plasminogen; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator