Extracellular superoxide dismutase is upregulated with inducible nitric oxide synthase after NFk B activation

Brady, Todd C., Ling-Yi Chang, Brian J. Day, and James D. Crapo. Extracellular superoxide dismutase is upregulated with inducible nitric oxide synthase after NF-kB activation. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L1002–L1006, 1997.—Inflammatory cytokines have been shown to upregulate secretion of the antioxidant enzyme extracellular superoxide dismutase (EC-SOD) in dermal fibroblasts and, in other cells, to stimulate production of nitric oxide (zNO). Because superoxide rapidly scavenges zNO, forming the injurious peroxynitrite anion (OONO2), we hypothesize that stimulated cells upregulate EC-SOD expression concurrently with zNO release. To test for coregulation of EC-SOD and zNO within the same cell, the timing of inducible nitric oxide synthase (iNOS) and EC-SOD transcription was measured after exposure of a rat type II pneumocyte analog, the L2 cell line, to a combination of interferon-g (IFN-g) and tumor necrosis factor-a (TNF-a). Upregulation of iNOS and EC-SOD transcription occurred after 6 h of exposure, and transcription of both genes was linked by activation of the transcription factor nuclear factor-kB. Both EC-SOD and iNOS were elevated in rat lung homogenates 24 h after intratracheal instillation with IFN-g and TNF-a. The observation that EC-SOD and iNOS are temporally coregulated after cytokine exposure suggests the possibility of a critical mechanism by which cells might protect zNO and avoid the formation of OONO2 during inflammation.