Two independent binding sites on monolayers of human endothelial cells are responsible for interaction with coagulation factor VII and factor VIIa

U. Reuning, K. T. Preissner, G. Muller-Berghaus

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18 Scopus citations

Abstract

The interaction of radiolabeled factor VII (FVII) and factor VIIa (FVlIa) with endotoxin-stimulated endothelial cells (EC), known to express tissue factor (TF), and unstimulated EC was studied. FVII FVIIa binding to EC-monolayers was saturable within 4.5-6 h, reversible, temperature and calcium dependent on both, endotoxin-stimulated and on unstimulated EC. Upon 2 h of incubation on EC, FVII was partially converted to FVIIa in the absence of protease inhibitors. The affinity of this binding was K(d) = 45.4 ± 18.7 nM with a calculated number of binding sites B(max) = 3.75 ± 0.31 x106 molecules/cell. In addition to unlabeled FVII and FVlIa, other vitamin K-dependent proteins reduced binding of [125I]-FVII/FVIIa to about 60-70%, and this type of common binding site for vitamin K-dependent proteins revealed a K(d) = 32.2 ± 5.6 nM and a B(max) = 3.03 ± 0.14 x106 molecules/ cell. Moreover, in the presence of 1 μM prothrombin to suppress common binding sites, only on endotoxin-stimulated EC additional inhibition of FVII FVlIa binding was achieved by anti-TF antibodies. The characteristics of the FVII/FVIIa-TF interaction with a K(d) = 17.2 ± 5.2 nM and a B(max) = 342,000 ± 1,100 binding sites/cell revealed a similar saturation kinetics in radioligand binding and in functional factor X activation within 90-120 min. These data indicate the presence of at least two independent binding sites for FVII/FVIIa on stimulated EC of which about 10% are TF specific. The existence of binding sites common for vitamin K-dependent proteins on both types of EC may improve the availability of FVII/FVIIa once EC become stimulated and express TF on their surface.

Original languageEnglish
Pages (from-to)197-204
Number of pages8
JournalThrombosis and Haemostasis
Volume69
Issue number2
DOIs
StatePublished - 1993
Externally publishedYes

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