The signaling pathway initiated by factor Xa on vascular endothelial cells was investigated. Factor Xa stimulated a 5- to 10-fold increased release of nitric oxide (NO) in a dose-dependent reaction (0.1-2.5 μg/ml) unaffected by the thrombin inhibitor hirudin but abolished by active site inhibitors, tick anticoagulant peptide, or Glu-Gly-Arg-chloromethyl ketone. In contrast, the homologous clotting protease factor IXa or another endothelial cell ligand, fibrinogen, was ineffective. A factor Xa inter- epidermal growth factor synthetic peptide L 83 FTRKL 88 (G) blocking ligand binding to effector cell protease receptor-1 inhibited NO release by factor Xa in a dose-dependent manner, whereas a control scrambled peptide KFTGRLL was ineffective. Catalytically active factor Xa induced hypotension in rats and vasorelaxation in the isolated rat mesentery, which was blocked by the NO synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) but not by D- NAME. Factor Xa/NO signaling also produced a dose-dependent endothelial cell release of interleukin 6 (range 0.55-3.1 ng/ml) in a reaction inhibited by L- NAME and by the inter-epidermal growth factor peptide Leu 83 -Leu 88 but unaffected by hirudin. Maximal induction of interleukin 6 mRNA required a brief, 30-min stimulation with factor Xa, unaffected by subsequent addition of tissue factor-pathway inhibitor. These data suggest that factor Xa- induced NO release modulates endothelial cell-dependent vasorelaxation and cytokine gene expression. This pathway requiring factor Xa binding to effector cell protease receptor-1 and a secondary step of ligand-dependent proteolysis may preserve an anti-thrombotic phenotype of endothelium but also trigger acute phase responses during activation of coagulation in vivo.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Apr 14 1998|
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