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.
