title: Activated protein C binds directly to Tie2: possible beneficial effects on endothelial barrier function.
abstract: Activated protein C (APC) is a natural anticoagulant with strong anti-inflammatory, anti-apoptotic, and barrier stabilizing properties. These cytoprotective properties of APC are thought to be exerted through its pathway involving the binding of APC to endothelial protein C receptor and cleavage of protease-activated receptors. In this study, we found that APC enhanced endothelial barrier integrity via a novel pathway, by binding directly to and activating Tie2, a transmembrane endothelial tyrosine kinase receptor. Binding assays demonstrated that APC competed with the only known ligands of Tie2, the angiopoietins (Angs). APC bound directly to Tie2 (Kd ~3 nM), with markedly stronger binding affinity than Ang2. After binding, APC rapidly activated Tie2 to enhance endothelial barrier function as shown by Evan's blue dye transfer across confluent cell monolayers and in vivo studies. Blocking Tie2 restricted endothelial barrier integrity. This study highlights a novel mechanism by which APC binds directly to Tie2 to enhance endothelial barrier integrity, which helps to explain APC's protective effects in vascular leakage-related pathologies.
authors.affiliation: Sutton Arthritis Research Laboratories, Institute of Bone and Joint Research, Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, Level 10, The Kolling Building, St. Leonards, NSW, 2065, Australia.
authors.forename: Nikita
authors.initials: N
authors.lastname: Minhas
authors.affiliation: Sutton Arthritis Research Laboratories, Institute of Bone and Joint Research, Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, Level 10, The Kolling Building, St. Leonards, NSW, 2065, Australia.
authors.forename: Meilang
authors.initials: M
authors.lastname: Xue
authors.affiliation: Sutton Arthritis Research Laboratories, Institute of Bone and Joint Research, Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, Level 10, The Kolling Building, St. Leonards, NSW, 2065, Australia. chris.jackson@sydney.edu.au.
authors.forename: Christopher J
authors.identifier: 0000-0002-9234-9116
authors.initials: CJ
authors.lastname: Jackson
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects*; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D020011:Protective Agents / Q000494:pharmacology*; D011485:Protein Binding; D011486:Protein C / Q000494:pharmacology*; D042787:Receptor, TIE-2 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D020011:Protective Agents; D011486:Protein C; D011994:Recombinant Proteins; D042787:Receptor, TIE-2; C421124:drotrecogin alfa activated
keywords: Biacore; Endothelial barrier integrity; Immunoprecipitation; Protease-activated receptor; Protein C; RCR252; SDS-PAGE; Sepsis; Solid-phase binding assay