ENDOTOXIN-INDUCED TISSUE FACTOR IN HUMAN MONOCYTES IS DEPENDENT UPON PROTEIN-KINASE-C ACTIVATION

Tissue factor (TF) is a transmembrane receptor which, in association w ith factors VII and VII a, activates factor IX and X, thereby activati ng the coagulation protease cascades. In response to bacterial lipopol ysaccharide (LPS) monocytes transcribe, synthesize and express TF on t heir surface. We investigated whether LPS-induced TF in human monocyte s is mediated by protein kinase C (PKC) activation. The PKC agonists p horbol 12-myristate 13-acetate (PMA) and phorbol 12, 13 dibutyrate (Pd Bu) were both potent inducers of TF in human monocytes, whereas 4 alph a-12, 13 didecanoate (4 alpha-Pdd) had no such effect. Both LPS- and P MA-induced TF activity were inhibited, in a concentration dependent ma nner, by three different PKC inhibitors: H7, staurosporine and calphos tin C. TF antigen determination confirmed that LPS-induced cell-surfac e TF protein levels decreased in parallel to TF functional activity un der staurosporine treatment. Moreover, Northern blot analysis of total RNA from LPS- or PMA-stimulated monocytes showed a concentration-depe ndent decrease in TF mRNA levels in response to H7 and staurosporine. The decay rate of LPS-induced TF mRNA evaluated after the arrest of tr anscription by actinomycin D was not affected by the addition of staur osporine, suggesting that its inhibitory effect occurred at a transcri ptional level. We conclude that LPS-induced production of TF and its m RNA by human monocytes are dependent on PKC activation.