Involvement of MAPK activation in bacterial endotoxin-inducible tissue factor upregulation in human monocytic THP-1 cells

Background. Monocytic tissue factor (mTF) hypercoagulation leading to throm botic complications is commonly observed following sepsis. Objective. We herein study the intracellular mechanism of mTF upregulation in human model monocytic THP-1 cells in response to bacterial endotoxin (li popolysaccharide, LPS; Escherichia coli O111:B04), determining if mitogen-a ctivated protein kinase (MAPK) activation is involved in the signaling. Methods. We assessed mTF upregulation by its cell surface expression, prote in synthesis, and functional activity based on flow cytometry, Western blot ting analysis, and a single-stage clotting assay, respectively. Results. A 3-h challenge with LPS (100 ng/ml) drastically induced mTF funct ional activity, accompanied by elevated surface mTF expression and synthesi s. The suppression by genistein (G) of LPS-inducible mTF upregulation impli ed the involvement of protein tyrosine kinase activation in mTF upregulatio n. LPS activated MAPK, which was significantly depressed by G, SB 203580 (S B), and PD 98058 (PD). Interestingly, inclusion of SB and PD also markedly diminished LPS-inducible mTF upregulation. The parallelism between MAPK and mTF activities revealed the involvement of MAPK activation in such mTF upr egulation. Based on the ability of SB and PD to respectively block LPS-indu cible tyrosine phosphorylation of p38 MAPK and Erk1/2, it was evident that tyrosine phosphorylation of MAPKs is required for mediating LPS-inducible m TF synthesis and upregulation. Contrasting with the established prevention of mTF upregulation by these inhibitors, failure to offset the already LPS- induced mTF activity seemed to be consistent with the view that LPS readily activated MAPK responsible for mTF synthesis. Conclusion. Our data suggest that the tyrosine phosphorylation of MAPKs (p3 8 and Erk1/2) leading to their activation could be a prerequisite for LPS i nduction of mTF synthesis contributing to the upregulation of mTF-initiated extrinsic coagulation. (C) 2001 Academic Press.