POSTTRANSCRIPTIONAL REGULATION OF MACROPHAGE TISSUE FACTOR EXPRESSIONBY ANTIOXIDANTS

Tissue factor (TF) expression by cells of monocyte/macrophage lineage represents an important mechanism underlying the initiation of fibrin deposition at sites of extravascular inflammation. Recent evidence sug gests a role for oxidant stress in the signalling pathway of various c ell types by virtue of its ability to induce DNA binding of various tr anscription factors, including nuclear factor kappa B and AP-1. The ef fect of antioxidant treatment on lipopolysaccharide (LPS)-induced TF e xpression was examined in murine peritoneal macrophages and human mono cytes, Both pyrrolidine dithiocarbamate, an oxidant scavenger, and N-a cetyl-cysteine, a precursor of the endogenous antioxidant glutathione, inhibited stimulation of macrophage procoagulant activity by LPS. Nor thern blot analysis showed that neither of these agents reduced LPS-st imulated TF mRNA accumulation, thereby suggesting a posttranscriptiona l mechanism for the effect, Immunofluorescence studies of human monocy tes using polyclonal anti-TF antibody showed that N-acetyl-cysteine tr eatment prevented the characteristic plasmalemmal localization of TF a ntigen that occurs in response to LPS. Western blot analysis showed th at N-acetyl-cysteine reduced the accumulation of the 47-kD mature glyc oprotein in LPS-treated cells, a finding consistent with the results o f the immunofluorescence studies, Furthermore, these conditions did no t result in an accumulation of the less mature forms of TF. When consi dered together, these data suggest that antioxidants exert their effec ts by impairing translation and/or by causing degradation of newly tra nslated protein. The effect of antioxidants on tumor necrosis factor a ppeared to be species specific, with no effect on LPS-induced tumor ne crosis factor in murine cells, but with inhibition in human monocytes, The posttranscriptional effect of antioxidants on TF expression data suggests a novel mechanism whereby these agents might modulate monocyt e/macrophage activation. (C) 1995 by The American Society of Hematolog y.