
<ArticleTitle><prot>Interleukin-8</prot> up-regulation by <prot>neutrophil elastase</prot> is mediated by <prot>MyD88</prot>/<prot>IRAK</prot>/<prot>TRAF-6</prot> in human bronchial epithelium.</ArticleTitle>
<AbstractText>Cystic fibrosis is characterized in the lungs by neutrophil-dominated inflammation mediated significantly by <prot>neutrophil elastase</prot> (<prot>NE</prot>). Previous work has shown that <prot>NE</prot> induces <prot>interleukin-8</prot> (<prot>IL-8</prot>) gene expression and protein secretion in bronchial epithelial cells. We sought to determine the intracellular mechanisms by which <prot>NE</prot> up-regulates <prot>IL-8</prot> in bronchial epithelial cells. The data show that stimulation of 16HBE14o(-) cells with <prot>NE</prot> induced <prot>IL-8</prot> protein production and gene expression. Both responses were abrogated by actinomycin D, indicating that regulation is at the transcriptional level. Electrophoretic mobility shift assays demonstrated that <prot>nuclear factor kappaB</prot> (<prot>NFkappaB</prot>) was activated in 16HBE14o(-) cells stimulated with <prot>NE</prot>. Western blot analysis demonstrated that activation of <prot>NFkappaB</prot> by <prot>NE</prot> was preceded by phosphorylation and degradation of <prot>IkappaB</prot> proteins, principally <prot>IkappaBbeta</prot>. In addition, we observed that <prot>interleukin-1 receptor-associated kinase</prot> (<prot>IRAK</prot>) was degraded in 16HBE14o(-) cells stimulated with <prot>NE</prot>. Quantification of <prot>IL-8 reporter</prot> gene activity by luminometry demonstrated that dominant negative <prot>MyD88</prot> (<prot>MyD88Delta</prot>) or <prot>TRAF-6</prot> (<prot>TRAF-6Delta</prot>) inhibited <prot>IL-8 reporter</prot> gene expression in response to <prot>NE</prot>. Furthermore, <prot>MyD88Delta</prot> inhibited <prot>NE</prot>-induced <prot>IRAK</prot> degradation. These results show that <prot>NE</prot> induces <prot>IL-8</prot> gene up-regulation in bronchial epithelial cells through an <prot>IRAK</prot> signaling pathway involving both <prot>MyD88</prot> and <prot>TRAF-6</prot>, resulting in degradation of <prot>IkappaBbeta</prot> and nuclear translocation of <prot>NFkappaB</prot>. These findings may have implications for therapeutic treatments in the cystic fibrosis condition.</AbstractText>
