title: Mac-1 directly binds to the endothelial protein C-receptor: a link between the protein C anticoagulant pathway and inflammation?
abstract: OBJECTIVE
  The endothelial protein C-receptor (EPCR) is an endothelial transmembrane protein that binds protein C and activated protein C (APC) with equal affinity, thereby facilitating APC formation. APC has anticoagulant, antiapoptotic and antiinflammatory properties. Soluble EPCR, released by the endothelium, may bind activated neutrophils, thereby modulating cell adhesion. EPCR is therefore considered as a possible link between the anticoagulant properties of protein C and the inflammatory response of neutrophils. In the present study, we aimed to provide proof of concept for a direct binding of EPCR to the β2-integrin Mac-1 on monocytic cells under static and physiological flow conditions.
  
  
  RESULTS
  Under static conditions, human monocytes bind soluble EPCR in a concentration dependent manner, as demonstrated by flow cytometry. Binding can be inhibited by specific antibodies (anti-EPCR and anti-Mac-1). Specific binding was confirmed by a static adhesion assay, where a transfected Mac-1 expressing CHO cell line (Mac-1+ cells) bound significantly more recombinant EPCR compared to Mac-1+ cells blocked by anti-Mac-1-antibody and native CHO cells. Under physiological flow conditions, monocyte binding to the endothelium could be significantly blocked by both, anti-EPCR and anti-Mac-1 antibodies in a dynamic adhesion assay at physiological flow conditions. Pre-treatment of endothelial cells with APC (drotrecogin alfa) diminished monocyte adhesion significantly in a comparable extent to anti-EPCR.
  
  
  CONCLUSIONS
  In the present study, we demonstrate a direct binding of Mac-1 on monocytes to the endothelial protein C receptor under static and flow conditions. This binding suggests a link between the protein C anticoagulant pathway and inflammation at the endothelium side, such as in acute vascular inflammation or septicaemia.
authors: Department of Cardiology and Angiology I, University Heart Center Freiburg, Freiburg, Germany. katrin.fink@universitaets-herzzentrum.de
authors: Katrin
authors: K
authors: Fink
authors: Hans-Jörg
authors: HJ
authors: Busch
authors: Natascha
authors: N
authors: Bourgeois
authors: Meike
authors: M
authors: Schwarz
authors: Dennis
authors: D
authors: Wolf
authors: Andreas
authors: A
authors: Zirlik
authors: Karlheinz
authors: K
authors: Peter
authors: Christoph
authors: C
authors: Bode
authors: Constantin
authors: C
authors: von Zur Muhlen
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D002478:Cells, Cultured; D000074283:Endothelial Protein C Receptor; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D016177:Macrophage-1 Antigen / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D011485:Protein Binding; D011486:Protein C / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000074283:Endothelial Protein C Receptor; D016177:Macrophage-1 Antigen; C478370:PROCR protein, human; D011486:Protein C; D011956:Receptors, Cell Surface