Oxidants Positively or Negatively Regulate Nuclear Factor κB in a Context-dependent Manner

Redox-based mechanisms play critical roles in the regulation of multiple cellular functions. NF-kappa B, a master regulator of inflammation, is an inducible transcription factor generally considered to be redox-sensitive, but the modes of interactions between oxidant stress and NF-kappa B are incompletely defined. Here, we show that oxidants can either amplify or suppress NF-kappa B activation in vitro by interfering both with positive and negative signals in the NF-kappa B pathway. NF-kappa B activation was evaluated in lung A549 epithelial cells stimulated with tumor necrosis factor alpha (TNF alpha), either alone or in combination with various oxidant species, including hydrogen peroxide or peroxynitrite. Exposure to oxidants after TNF alpha stimulation produced a robust and long lasting hyperactivation of NF-kappa B by preventing resynthesis of the NF-kappa B inhibitor I kappa B, thereby abrogating the major negative feedback loop of NF-kappa B. This effect was related to continuous activation of inhibitor of kappa B kinase (IKK), due to persistent IKK phosphorylation consecutive to oxidant-mediated inactivation of protein phosphatase 2A. In contrast, exposure to oxidants before TNF alpha stimulation impaired IKK phosphorylation and activation, leading to complete prevention of NF-kappa B activation. Comparable effects were obtained when interleukin-1 beta was used instead of TNF alpha as the NF-kappa B activator. This study demonstrates that the influence of oxidants on NF-kappa B is entirely context-dependent, and that the final outcome (activation versus inhibition) depends on a balanced inhibition of protein phosphatase 2A and IKK by oxidant species. Our findings provide a new conceptual framework to understand the role of oxidant stress during inflammatory processes.