Direct binding of Nur77/NAK-1 to the plasminogen activator inhibitor 1 (PAI-1) promoter regulates TNFα-induced PAI-1 expression

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Abstract
Plasminogen activator inhibitor 1 (PAI-1) is the main fibrinolysis inhibitor, and high plasma levels are associated with an increased risk for vascular diseases. Inflammatory cytokines regulate PAI-1 through a hitherto unclear mechanism. Using reporter gene analysis, we could identify a region in the PAI-1 promoter that contributes to basal expression as well as to tumor necrosis factor α (TNFα) induction of PAI-1 in endothelial cells. Using this region as bait in a genetic screen, we could identify Nur77 (NAK-1, TR3, NR4A1) as an inducible DNA-binding protein that binds specifically to the PAI-1 promoter. Nur77 drives transcription of PAI-1 through direct binding to an NGFI-B responsive element (NBRE), indicating monomeric binding and a ligand-independent mechanism. Nur77, itself, is transcriptionally up-regulated by TNFα. High expression levels of Nur77 and its colocalization with PAI-1 in atherosclerotic tissues indicate that the described mechanism for PAI-1 regulation may also be operative in vivo.

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