title: Endothelial cell protein C receptor acts as a cellular receptor for factor VIIa on endothelium.
abstract: Although factor VII/factor VIIa (FVII/FVIIa) is known to interact with many non-vascular cells, activated monocytes, and endothelial cells via its binding to tissue factor (TF), the interaction of FVII/FVIIa with unperturbed endothelium and the role of this interaction in clearing FVII/FVIIa from the circulation are unknown. To investigate this, in the present study we examined the binding of radiolabeled FVIIa to endothelial cells and its subsequent internalization. (125)I-FVIIa bound to non-stimulated human umbilical vein endothelial cells (HUVEC) in time- and dose-dependent manner. The binding is specific and independent of TF and negatively charged phospholipids. Protein C and monoclonal antibodies to endothelial cell protein C receptor (EPCR) blocked effectively (125)I-FVIIa binding to HUVEC. FVIIa binding to EPCR is confirmed by demonstrating a marked increase in (125)I-FVIIa binding to CHO cells that had been stably transfected with EPCR compared with the wild-type. Binding analysis revealed that FVII, FVIIa, protein C, and activated protein C (APC) bound to EPCR with similar affinity. FVIIa binding to EPCR failed to accelerate FVIIa activation of factor X or protease-activated receptors. FVIIa binding to EPCR was shown to facilitate FVIIa endocytosis. Pharmacological concentrations of FVIIa were found to impair partly the EPCR-dependent protein C activation and APC-mediated cell signaling. Overall, the present data provide convincing evidence that EPCR serves as a cellular binding site for FVII/FVIIa. Further studies are needed to evaluate the pathophysiological consequences and relevance of FVIIa binding to EPCR.
authors.affiliation: Biomedical Research Division, The University of Texas Health Center at Tyler, Tyler, Texas 75708, USA.
authors.forename: Samit
authors.initials: S
authors.lastname: Ghosh
authors.forename: Usha R
authors.initials: UR
authors.lastname: Pendurthi
authors.forename: Anne
authors.initials: A
authors.lastname: Steinoe
authors.forename: Charles T
authors.initials: CT
authors.lastname: Esmon
authors.forename: L Vijaya Mohan
authors.initials: LV
authors.lastname: Rao
mesh_terms: D000818:Animals; D001665:Binding Sites; D001779:Blood Coagulation Factors / Q000502:physiology*; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005167:Factor VII / Q000378:metabolism*; D015942:Factor VIIa / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism; D006801:Humans; D011486:Protein C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000502:physiology*; D015398:Signal Transduction; D014471:Umbilical Veins / Q000166:cytology
chemical_list: D001779:Blood Coagulation Factors; D011486:Protein C; D011956:Receptors, Cell Surface; C091963:activated protein C receptor; D005167:Factor VII; D015942:Factor VIIa; D015951:Factor Xa