Coagulation factors VIIa and Xa induce cell signaling leading to up-regulation of the egr-1 gene

Intracellular signaling induced by the coagulation factors (F) VIIa and Xa is poorly understood. We report here studies on these processes in a human keratinocyte line (HaCaT), which is a constitutive producer of tissue facto r (TF) and responds to both FVIIa and FXa with elevation of cytosolic Ca2+, phosphorylation of extracellular signal-regulated kinase (Erk) 1/2, p38(MA PK), and c-Jun N-terminal kinase, and up-regulation of transcription of the early growth response gene-1 (egr-1). Using egr-1 as end point, we observe d with both agonists that phosphatidylinositol-specific phospholipase C and the mitogen-activated protein kinase/Erk kinase/Erk pathway were mediators of the responses. The responses to FVIIa were TF-dependent and up-regulati on of egr-1 mRNA did not require presence of the TF cytoplasmic domain. Ant ibodies to EPR-1 and factor V had no effect on the response to FXa. We have provided evidence that TF is not the sole component of the FVIIa receptor. The requirement for proteolytic activity of both FVIIa and FXa suggests th at protease-activated receptors may be involved. We now report evidence sug gesting that protease-activated receptor 2 or a close homologue may be a ne cessary but not sufficient component of this particular signal transduction pathway. The up-regulation of egr-1 describes one way by which the initiat ion of blood coagulation may influence gene transcription. The ability of t hese coagulation proteases to induce intracellular signals at concentration s at or below the plasma concentrations of their zymogen precursors suggest s that these processes may occur also in vivo.