Tissue factor (TF) is a cellular receptor and cofactor for factor VII/VIIa which initiates the blood coagulation cascade. We have investigated the role of 5'-flanking DNA sequences in regulating the expression of the human TF gene in human umbilical vein endothelial cells (HUVEC). Using a chloramphenicol acetyltransferase (CAT) reporter gene, we attempted to transfect primary cultured HUVEC (passage 3-4) with calcium phosphate coprecipitation, DEAE Dextran, lipopolyamine-coated DNA or electroporation. Electroporation in HEPES-buffered saline of 1 x 10(7) cells at 200V and 250 microF was found to be optimal. Using these conditions, varying lengths of TF 5'-flanking sequences coupled to the CAT reporter gene were tested in transient expression studies. CAT expression corrected for variation in transfection efficiency and cell viability revealed that the sequences between -111 and +14 base pairs are essential for minimal transcriptional activity. This region contains consensus sequences for a TATA box and three Sp1 binding sites. A domain from -382 to -111bp, which contains two AP-1 consensus elements, promoted high levels of gene expression. This transcriptional activity was repressed by 50% with constructs containing sequences between -550 and -382 bp. A further 2-fold drop in transcription activity was attributed to the region between -948 and -550 bp. These results suggest that the basal transcription of the human TF gene in HUVEC is mediated through at least two negative regulatory elements upstream of the proximal promoter domain. The proximal promoter region which contains two AP-1 sites is essential for efficient transcription.