Receptor Activator of Nuclear Factor  B Ligand Is a Novel Inducer of Tissue Factor in Macrophages

Rationale: Although recent studies have suggested a role for the receptor activator of nuclear factor kappa B ligand (RANKL) in the late stages of atherosclerosis (eg, plaque destabilization and rupture), the underlying mechanisms and subsequent events are unclear. Objective: Because blood clotting is common after plaque rupture, we hypothesized that RANKL influenced tissue factor (TF) expression and activity to initiate the coagulation cascade. Methods and Results: RANKL increased the TF mRNA level and procoagulant activity in macrophages, as determined by semiquantitative reverse transcription polymerase chain reaction (semiquantitative RT-PCR) and a chromogenic assay. TF promoter analysis revealed that AP-1 and Egr-1 are responsible for RANKL-induced TF transcription. In addition, RANKL increased phosphorylation of c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) 1/2. RANKL-induced TF expression was attenuated by JNK- and MEK1-specific inhibitors and by small interfering RNA knockdown of c-Jun and Egr-1. Conclusion: Our results indicate that RANKL induces TF in macrophages mainly through the cooperative action of AP-1 and Egr-1 via JNK and ERK1/2 pathways. These findings provide strong mechanistic support for the role of RANKL in the thrombogenicity of atherosclerotic plaques. (Circ Res. 2010;107:871-876.)