PROTEIN-TYROSINE KINASE ACTIVATION IS REQUIRED FOR LPS AND PMA INDUCTION OF TISSUE FACTOR MESSENGER-RNA IN HUMAN BLOOD MONOCYTES

Tissue factor (TF) is a transmembrane glycoprotein which assembles wit h factor VIIa on cell surfaces to form a proteolytically active co-fac tor-enzyme complex; the TF/VIIa complex initiates the coagulation prot ease cascade. In response to bacterial lipopolysaccharide (LPS) and ph orbol-12 myristate 13-acetate (PMA), monocytes synthesize and express TF on their surface. However, the mechanisms by which LPS and PMA acti vate TF synthesis by human blood monocytes are not fully understood. A s it has been established that LPS and PMA activate protein tyrosine k inase (PTK) in monocytes, we studied the role of PTK in LPS and PMA in duction of TF by human blood monocytes. Both LPS- and PMA-induced TF a ctivity was inhibited in a concentration-dependent manner by the prote in 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 und er herbimycin A and genistein treatment. Northern blot analysis of tot al RNA from LPS- and PMA-stimulated monocytes showed a concentration-d ependent decrease in TF mRNA levels in response to herbimycin A and ge nistein. The rate of decay of LPS-induced TF mRNA, evaluated after the arrest of transcription by actinomycin D was not affected by genistei n and herbimycin A, suggesting that the inhibitory effects occur at le ast partly at the transcriptional level. We conclude that LPS- and PMA -induced TF production by human monocytes is dependent on tyrosine kin ase activation.