Evidence that reactive oxygen species do not mediate NF-kappaB activation

It has been postulated that reactive oxygen species (ROS) may act as second messengers leading to nuclear factor (NF)-kappaB activation. This hypothesis is mainly based on the findings that N-acetyl-L-cysteine (NAC) and pyrrolidine dithiocarbamate (PDTC), compounds recognized as potential antioxidants, can inhibit NF-kappaB activation in a wide variety of cell types. Here we reveal that both NAC and PDTC inhibit NF-kappaB activation independently of antioxidative function. NAC selectively blocks tumor necrosis factor (TNF)-induced signaling by lowering the affinity of receptor to TNF. PDTC inhibits the IkappaB-ubiquitin ligase activity in the cell-free system where extracellular stimuli-regulated ROS production does not occur. Furthermore, we present evidence that endogenous ROS produced through Rac/NADPH oxidase do not mediate NF-kappaB signaling, but instead lower the magnitude of its activation.