VIIa/Tissue Factor Interaction Results in a Tissue Factor Cytoplasmic Domain-independent Activation of Protein Synthesis, p70, and p90 S6 Kinase Phosphorylation

FVIIa binding to tissue factor (TF) and subsequent signal transduction have now been implicated in a variety of pathophysiological processes, including cytokine production during sepsis, tumor angiogenesis and neoangiogenesis, and leukocyte diapedesis. The molecular details, however, by which FVIIa/TF affects gene expression and cellular physiology, remain obscure. Here we show that FVIIa induces a transient phosphorylation of p70/p85S6K and p90RSK in BHK cells stably transfected with either full-length TF or with a cytoplasmic domain-truncated TF but not in wild type BHK cells. Phosphorylation of these kinases was also observed in HaCaT cells, expressing endogenous TF. Phosphorylation of p70/p85S6K coincided with protein kinase B and GSK-3β phosphorylation. Activation of p70/p85S6K was sensitive to inhibitors of phosphatidylinositol 3-kinase and to rapamycin, whereas phosphorylation of p90RSK was sensitive to PD98059. FVIIa stimulation of p70/p85S6K and p90RSK correlated with phosphorylation of the eukaryotic initiation factor eIF-4E, up-regulation of protein levels of eEF1α and eEF2, and enhanced [35S]methionine incorporation. These effects were not influenced by inhibitors of thrombin or FXa generation and were strictly dependent on the presence of the extracellular domain of TF, but they did not require the intracellular portion of TF. We propose that a TF cytoplasmic domain-independent stimulation of protein synthesis via activation of S6 kinase contributes to FVIIa effects in pathophysiology.