A transcriptional repressor of the tissue factor gene in endothelial cells

Tissue factor, the high-affinity receptor and cofactor for the plasma serin e protease VII/VIIa, is the primary cellular initiator of the blood coagula tion cascade. Inside the vasculature, expression of the tissue factor gene must be tightly controlled. Whereas the endothelium normally does not expre ss tissue factor, on stimulation with inflammatory cytokines or endotoxin t he gene is transcriptionally upregulated leading to a procoagulant state. W e have now detected a repressive cis-acting element in the tissue factor pr omoter that downmodulates tissue factor transcription in endothelial cells. In reporter gene assays, deletion of this element leads to an increase of tissue factor transcription and insertion of a trimerized site reduces tran scription. Specific protein/DNA complexes are formed on the element with nu clear extracts in electrophoretic mobility shift assays and cross-linking o f the proteins followed by SDS-PAGE detects the presence of at least 2 subu nits of approximate to 40 and 60 kDa, respectively. After transfection of d ifferent cell types with the reporter genes, the suppressive effect of the element can only be revealed in endothelial cells. These data suggest that this element represents a novel transcription factor target sequence that f unctions to suppress expression of the tissue factor gene, preferentially i n endothelial cells thereby supporting a noncoagulant state.