Inhibition of c-jun N-terminal kinase pathway improves cell viability in response to oxidant injury

Oxidant insults can lead to apoptotic and nonapoptotic cell death. Lung epithelial cells exposed to high levels of oxygen do not die via apoptosis, but through a much slower, morphologically distinct process involving cell and nuclear swelling. In contrast, H2O2 induces a rapid apoptotic cell death. We first assessed the effect of oxidant exposure on activator protein-1 (c-Jun and Fos) and c-Jun N-terminal kinase (INK) regulation in MLE12 cells. Both oxidants induced c-Jun and Fos expression, albeit with a different pattern of regulation-hyperoxia (95% O-2) induced a biphasic response, whereas H2O2 (500 muM) induced a sustained response. We then examined the role of INK by Western blot, INK activity assay, and a pull-down assay and observed an identical pattern of regulation. To assess whether INK functions in a pro-death or pro-survival capacity, we generated stable cell lines that constitutively express a dominant-negative mutation of INK resulting in significant inhibition of INK activity. Inhibition of the INK pathway in this manner prevented hyperoxic and H2O2-induced cell death. These results demonstrate that hyperoxic cell death is pathway-driven and that both modes of death involve the INK signaling pathway.