• DNA primase 1;
  • FVIIa;
  • PAR-1;
  • PAR-2;
  • thrombin

Summary.  In addition to its hemostatic functions, factor (F)VIIa exhibits cell proliferative properties as seen in angiogenesis and tumor growth. A role for tissue factor (TF) and protease-activated receptors (PAR)-1 and -2 in cell proliferation remain to be clarified. We tested the hypothesis that FVIIa induces cell proliferation by a mechanism involving TF and PAR-2. Human recombinant FVIIa induced cell proliferation of human BOSC23 cells transfected with plasmid containing human TF DNA sequence. Because DNA primase 1 (PRIM1) plays an essential role in cell proliferation, we used the cloned PRIM1 promoter upstream of the reporter gene chloramphenicol acetyl transferase (CAT) to elucidate the mode of action of FVIIa. FVIIa evoked a dose-dependent increase in cell proliferation and PRIM1 induction, which were markedly potentiated (4–5-fold) by the presence of TF and abrogated by TF antisense oligonucleotide. PRIM1 induction by FVIIa was also abolished by PAR-2 but not by PAR-1 antisense. In contrast, thrombin induced a small increase in CAT activity which was unaffected by TF, but was prevented only by PAR-1 antisense as well as the thrombin inhibitor hirudin. Proliferative properties of FVIIa were associated with a TF-dependent increase in intracellular calcium and were mediated by a concordant phosphorylation of p44/42 MAP kinase. In conclusion, data reveal that FVIIa induces PRIM1 and ensuing cellular proliferation via a TF- and of the PARs entirely PAR-2-dependent pathway, in distinction to that of thrombin which is PAR-1-dependent and TF-independent. We speculate that FVIIa-TF-PAR-2 inhibitors may be effective in suppressing cell proliferation.