Protease inhibitors block lipopolysaccharide induction of tissue factor gene expression in human monocytic cells by preventing activation of c-Rel/p65 heterodimers.

Tissue factor (TF) is expressed rapidly by human monocytes exposed to bacterial endotoxin (lipopolysaccharide, or LPS). Transcriptional regulation is mediated by binding of c-Rel/p65 heterodimers to a kappa B-like site in the TF promoter. Nuclear translocation of cytosolic c-Rel/p65 heterodimers and other members of the NF-kappa B/Rel family requires dissociation and proteolytic degradation of the inhibitor protein, I kappa B alpha. The protease inhibitors N alpha-tosylphenylalanyl chloromethyl ketone (TPCK) and N alpha-tosyl-L-lysine chloromethyl ketone (TLCK) block activation of NF-kappa B/Rel proteins by preventing degradation of I kappa B alpha. To determine if TPCK and TLCK inhibited LPS induction of TF expression, freshly isolated human monocytes and monocytic THP-1 cells were pretreated with these inhibitors for 30 min before LPS stimulation. Both TPCK and TLCK inhibited LPS induction of TF protein, TF mRNA and TF promoter activity in a dose-dependent manner. These inhibitors specifically prevented degradation of I kappa B alpha and nuclear translocation of c-Rel/p65 heterodimers. In contrast, TPCK and TLCK did not block induction of an immediate-early gene encoding the transcription factor, Egr-1. Taken together, these data indicated that inhibiting nuclear translocation of c-Rel/p65 heterodimers prevented LPS induction of TF gene transcription in monocytic cells.