P354	TF-induced endothelial cell apoptosis is mediated via the p53 pathway.
A.Pradier, C.Ettelaie
University of Hull, Hull, GB.

Tissue factor (TF), the principal initiator of blood coagulation, is also known to influence vascular morphology. Previously, we showed that TF is a deciding factor in determining the fate of endothelial cells by inducing either cellular proliferation or apoptosis (1). Here, we report further elucidation of the signalling mechanisms involved in TF-mediated apoptosis in endothelial cells. HUVEC were cultured in serum free medium and treated with combination of exogenous rec-TF, factor VIIa, factor Xa and TFPI. The activation of the p53 pathway was assessed using a luciferase reporter. Moreover, the expression of the pro-apoptotic bax was assessed by semi-quantitative RT-PCR and western blot analysis. At higher concentrations of TF (10-20 U/ml), an increase in transcriptional activity of p53 was observed concurrent with upregulation of bax mRNA and protein. This influence was neither apparent at lower concentration of TF (1 U/ml) nor on addition of FVIIa (5 nM). However, supplementation with FXa (10 nM) or TFPI (5 pM) lead to a similar increases in p53 activity and bax expression. Therefore, we suggest that TF-induced endothelial cells apoptosis is likely to be mediated via the p53 pathway and up-regulation in bax, leading to initiation of the mitochondrial-induced apoptosis. In conclusion, exposure to pathological concentrations of TF within the atherosclerotic plaque, is crucial in the denudation of the endothelial layer. (1) Pradier A., James N.J., Bruckdorfer K.R., Ettelaie C. (2003) The influence of tissue factor (CD 142) on endothelial cell apoptosis and proliferation. Presented at the Internationnal Society on Thrombosis and Haemostasis XIX Congress. Birmingham, UK.

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