Tumour necrosis factor α activates a p22phox-based NADH oxidase in vascular smooth muscle

Increasing experimental evidence suggests that non-phagocytic cells express a potent superoxide (O2-.)-producing NADH oxidase that might be related to the phagocytic NADPH oxidase. Here we show that the cytokine tumour necrosis factor alpha (TNF-alpha) activates, in a time- and dose-dependent manner, a O2-.-producing NADH oxidase in cultured rat aortic smooth-muscle cells. Dose-response experiments for NADH showed an upward shift of the curve for TNF-alpha-treated cells, suggesting that TNF-alpha increased the amount of available enzyme. Using the anti-sense transfection technique, we further demonstrate that the molecular identity of this oxidase includes p22(phox) (the alpha subunit of cytochrome b558 and part of the electron transfer component of the phagocytic NADPH oxidase), which we recently cloned from a rat vascular smooth-muscle cell cDNA library. In addition, prolonged treatment with TNF-alpha increased p22phox mRNA expression without affecting p22phox mRNA stability, and only when transcriptional activity was intact. These findings identify a p22phox-containing NADH oxidase as a source for cytokine-induced free radical production in vascular smooth-muscle cells and clarify some of the mechanisms involved in the regulation of vascular oxidase activity.