Short-term modulation of interleukin-1β signaling by hyperoxia: Uncoupling of IκB kinase activation and NF-κB-dependent gene expression

We have been interested in elucidating how simultaneous stimuli modulate inflammation-related signal transduction pathways in lung parenchymal cells. We previously demonstrated that exposing respiratory epithelial cells to 95% oxygen (hyperoxia) synergistically increased tumor necrosis factor-α (TNF-α)-mediated activation of NF-κB and NF-κB-dependent gene expression by a mechanism involving increased activation of IκB kinase (IKK). Because the signal transduction mechanisms induced by IL-1β are distinct to that of TNF-α, herein we sought to determine whether hyperoxia modulates IL-1β-dependent signal transduction. In A549 cells, simultaneous treatment with hyperoxia and IL-1β caused increased activation of IKK, prolonged the degradation of IκBα, and prolonged the nuclear translocation and DNA binding of NF-κB compared with cells treated with IL-1β alone in room air. Hyperoxia did not affect IL-1β-dependent degradation of the interleukin receptor-associated kinase differently from treatment with IL-β alone. In contrast to the effects on the IKK/IκBα/NF-κB pathway, simultaneous treatment with hyperoxia and IL-1β did not augment NF-κB-dependent gene expression compared with treatment with IL-1β alone. Similar observations were made in a different human respiratory epithelial cell line, BEAS-2B cells. In addition, simultaneous treatment with hyperoxia and IL-1β caused hyperphosphorlyation of the NF-κB p65 subunit compared with treatment with IL-1β alone. In summary, concomitant treatment of A549 cells with hyperoxia and IL-1β augments activation of IKK, prolongs degradation of IκBα, and prolongs nuclear translocation and DNA binding of NF-κB. This activation, however, is not coupled to increased expression of NF-κB-dependent genes, and the mechanism of this decoupling is not related to decreased phosphorylation of p65.