Tissue factor is critically important for initiating the activation of coagulation zymogens leading to the generation of thrombin. Quiescent endothelial cells do not express tissue factor on their surface, but many stimuli including cytokines and coagulation proteases can elicit tissue factor synthesis. We challenged human endothelial cells simultaneously with tumor necrosis factor ␣ (TNF␣) and thrombin because many pathophysiological conditions, such as sepsis, diabetes, and coronary artery disease, result in the concurrent presence of circulating inflammatory mediators and activated thrombin. We observed a remarkable synergy in the expression of tissue factor by thrombin plus TNF␣. This was due to altered regulation of the transcription factors c-Jun and c-Fos. The activation of c-Jun was greater and more sustained than that obtained with either thrombin or TNF␣ alone. Thrombin-stimulated expression of c-Fos was both enhanced and prolonged by the concurrent presence of TNF␣. These changes support the increased availability of c-Jun/c-Fos AP-1 complexes for mediating transcription at the tissue factor promoter. Transcription factors downstream of the extracellular signal-regulated kinases as well as changes in NFB regulation were not involved in the synergistic increase in tissue factor expression by thrombin and TNF␣. Thus, concurrent exposure of vascular endothelial cells to cytokines and procoagulant proteases such as thrombin can result in greatly enhanced tissue factor expression on the endothelium, thereby perpetuating the prothrombotic phenotype of the endothelium.Many diseases with a pronounced inflammatory component, such as sepsis, type II diabetes, coronary artery disease, heparin-induced thrombocytopenia, and anti-phospholipid syndrome, also exhibit enhanced activation of coagulation enzymes (1-5). These serine proteases, most notably thrombin, stimulate protease-activated receptors (PARs) 1 on the surface of endothelial cells. Signaling through the PARs shifts the endothelium toward a prothrombotic phenotype, exacerbating the initiating pathophysiological condition. Our interest in thrombin signaling by endothelial cells (6, 7) led us to question how inflammatory mediators such as TNF␣ might alter thrombininitiated signaling events and thereby bolster the prothrombotic phenotype of the endothelium. Normally, the apical surface of endothelial cells is designed to minimize interactions with circulating coagulation zymogens and blood cells. Inflammatory stimuli (cytokines, lipopolysaccharide, vascular endothelial cell growth factor, sphingosine 1-phosphate, thrombin (8 -12)) can alter the anticoagulatory phenotype of the endothelium by promoting the expression of adhesive molecules, receptors, and chemoattractants. Expression of tissue factor (TF), the coagulation Factor VII receptor, on the surface of endothelial cells serves as an excellent marker for an activated endothelium with an inflamed and procoagulant phenotype (13,14). Binding of Factor VII to tissue factor can then initiate the consecutive...

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