title: Cultured bovine aortic endothelial cells promote activated protein C-protein S-mediated inactivation of factor Va.
abstract: Previous studies have demonstrated that protein S is required for optimal activated protein C-mediated inactivation of Factor Va on the surface of either the platelet or phospholipid vesicles. In this report we demonstrate assembly of the activated protein C-protein S complex on the surface of cultured bovine aortic endothelial cells. Endothelial cell surface acceleration of Factor Va inactivation by activated protein C required the presence of protein S. Kinetic studies indicated that the rate of Factor Va inactivation was half-maximal at a protein S concentration of 0.2 nM and an activated protein C concentration of 0.05 nM. Binding of 125I-activated protein C to endothelial cell monolayers was absolutely dependent on the presence of protein S. At saturating levels of protein S, activated protein C binding was saturable with Kd = 0.04 nM. In contrast, specific, time-dependent, and saturable binding of 125I-protein S to endothelium occurred in the absence of activated protein C. Addition of activated protein C increased the affinity of protein S from Kd = 11 nM to 0.2 nM, but did not change the number of molecules bound per cell at saturation (85,000 molecules/cell). These studies suggest that activated protein C increases the affinity of protein S for pre-existing sites on the endothelial cell surface. The close correlation between the parameters of protein S-activated protein C binding to endothelium and Factor Va inactivation supports the concept that it is bound protein S and activated protein C that are the active species. Formation of functional activated protein C-protein S complexes thus occurs effectively on the endothelial cell surface and represents a new addition to the list of vessel wall anticoagulant properties.
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology*; D001667:Binding, Competitive; D002417:Cattle; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004727:Endothelium / Q000166:cytology; D005165:Factor V / Q000037:antagonists & inhibitors*; D015943:Factor Va; D006023:Glycoproteins / Q000378:metabolism*; D008433:Mathematics; D011486:Protein C; D017293:Protein S
chemical_list: D006023:Glycoproteins; D011486:Protein C; D017293:Protein S; D015943:Factor Va; D005165:Factor V