Nitric oxide suppresses IL-8 transcription by inhibiting C-Jun N-terminal kinase-induced AP-1 activation

The role of activator protein-1 (AP-1) in tumor necrosis factor-alpha (TNF- alpha)-induced interleukin-8 (IL-8) gene expression was evaluated. We showe d that TNF-alpha activates AP-1 in the transformed endothelial cell line EC V304 by transient transfections of IL-8 promoter construct pGL-3BF(2). Muta tion of either the AP-1 site or the NF-IL-6 site on the IL-8 promoter suppr essed the TNF-alpha -induced activation, suggesting cooperation between the se transcription factors and transcription factor NF-kappaB. Overexpression of dominant negative mutants of c-Jun suppressed AP-1-driven transcription of the IL-8 promoter following stimulation by TNF-alpha, suggesting that c ooperative interaction between AP-1 and NF-kappaB is essential for IL-8 tra nscription in the presence of TNF-alpha. We also showed that nitric oxide ( NO), in the form of an exogenous NO donor, suppressed the level of activati on of the AP-1 subunit, c-Jun, by down-regulation of c-Jun NH2 terminal kin ase. This down-regulation could be the putative mechanism of action for NO- mediated inhibition of IL-8 secretion in activated endothelium. These obser vations suggest for the first time that NO has broad suppressive activities on various proinflammatory effecters in activated endothelium. (C) 2001 Ac ademic Press.