IntroductionTissue factor (TF) is a cell surface receptor initiating blood coagulation, 1 thereby promoting thrombotic events in atherosclerosis, sepsis, and cancer. 2,3 Enhanced endothelial TF expression has been demonstrated in atherosclerotic plaques, 4,5 a process that may account for thrombotic events associated with early and advanced atherosclerosis. TF expression in endothelial cells (ECs) can be induced by a variety of agonists, including inflammatory cytokines, angiogenic growth factors, infectious agents, and minimally modified low-density lipoprotein (MM-LDL). 1,6 MM-LDL regulates TF expression at the level of transcription 5 ; however, the signaling pathways and transcription factors involved in this process are not known. Some of the effects of MM-LDL can be mimicked by oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (PAPC). 7 Three biologically active components of oxidized PAPC (Ox-PAPC) have been structurally identified as 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC), 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphorylcholine (PGPC), 8 and 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine (PEIPC). 9 Which of these components of MM-LDL is responsible for induction of TF is not known.In contrast to interleukin-1 (IL-1) or tumor necrosis factor ␣ (TNF-␣), MM-LDL neither up-regulates E-selectin, intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1), nor stimulates neutrophil binding to human ECs. 7 This suggests that classical inflammatory agonists and MM-LDL activate different signaling mechanisms. The major pathway induced by inflammatory cytokines activates transcription factors of the nuclear factor-B (NF-B) family. 10 Whether NF-B is activated by MM-LDL is a subject of controversy. 6,11 In fact, it was shown that MM-LDL and some of its components were capable of down-regulating NF-B-mediated transcription induced by inflammatory cytokines. 12 Thus, the role of the NF-B pathway in inflammatory activation of ECs by oxidized lipids requires further investigation.Apart from NF-B, 13 transcription of the TF gene can be promoted by early growth response factor 1 (EGR-1) and nuclear factor of activated T cells (NFAT). 14,15 Whereas inflammatory cytokines induce NF-B as well as EGR-1, vascular endothelial In the present study, we investigated signaling pathways and transcription factors mediating induction of TF expression in human ECs by biologically active oxidized phospholipids. We show that expression of TF is elevated by OxPAPC, and that this induction was mainly mediated by EGR-1-and NFAT-dependent transcription, but was independent of NF-B activation. Upstream mechanisms activated by OxPAPC were elevation of cytosolic Ca ϩϩ , activation of protein kinase C (PKC), and the mitogenactivated protein (MAP) kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK MAP kinase cascade. Materials and methods MaterialsCyclosporin A was purchased from Novartis (Vienna, Austria); TNF-␣ from Genzyme (Cambridge...