Summary
Tissue factor (TF) is a transmembrane glycoprotein which assembles with factor VIIa on cell surfaces to form a proteolytically active cofactor-enzyme complex; the TF/VIIa complex initiates the coagulation protease cascade. In response to bacterial lipopolysaccharide (LPS) and phorbol-12 myristate 13-acetate (PMA), monocytes synthesize and express TF on their surface. However, the mechanisms by which LPS and PMA activate TF synthesis by human blood monocytes are not fully understood. As it has been established that LPS and PMA activate protein tyrosine kinase (PTK) in monocytes, we studied the role of PTK in LPS and PMA induction of TF by human blood monocytes. Both LPS-and PMA-induced TF activity was inhibited in a concentration-dependent manner by the protein tyrosine kinase-specific inhibitors herbimycin A and genistein. TF antigen determination confirmed that LPS- and PMA-induced cell surface TF protein levels decreased in parallel to TF functional activity under herbimycin A and genistein treatment. Northern blot analysis of total RNA from LPS- and PMA-stimulated monocytes showed a concentration-dependent decrease in TF mRNA levels in response to herbimycin A and genistein. The rate of decay of LPS-induced TF mRNA, evaluated after the arrest of transcription by actinomycin D was not affected by genistein and herbimycin A, suggesting that the inhibitory effects occur at least partly at the transcriptional level. We conclude that LPS- and PMA-induced TF production by human monocytes is dependent on tyrosine kinase activation.
