Effect of dexamethasone on interleukin-1β(IL-1β)-induced nuclear factor-κB (NF-κB) and κB-dependent transcription in epithelial cells

The production of inflammatory mediators by epithelial cells in inflammatory lung diseases may represent an important target for the anti-inflammatory effects of glucocorticoids. Nuclear factor-kappa B (NF-kappa B) is a major activator of inflammatory genes and has been proposed as a target for inhibition by glucocorticoids. We have used human pulmonary type-II A549 and airway epithelial BEAS-2B cells to investigate the effect of glucocorticoids on NF-kappa B regulation and kappa B-dependent transcription. In A549 cells following interleukin-1 beta (IL-1 beta) treatment, there was no effect of dexamethasone on the disappearance of I kappa B alpha protein, its subsequent reappearance 90-min later or the rapid induction of I kappa B alpha mRNA and transcription rate. Expression of p65 and p50/p105 proteins were also unaffected by dexamethasone. In addition, the rapid IL-1 beta-induction of NF-kappa B DNA binding and p65 nuclear localisation was unaffected by short (1-6 hours) dexamethasone pre-treatments. Similarly BEAS-2B cells showed no effect of dexamethasone on IL-1 beta-induced NF-kappa B (p50/p65). Stable transfection of a kappa B-dependent reporter in A549 cells resulted in an 8-9-fold activation by IL-1 beta or phorbol ester, that was repressed 30-40% by dexamethasone. However, in these cells, IL-1 beta induction of inducible nitric oxide synthase, granulocyte macrophage colony stimulating factor and cyclooxygenase-2 mRNA showed 70-90% repression by dexamethsone. We, therefore, conclude that in these epithelial cells, the repressive effects of glucocorticoids are not mediated by up-regulation of I kappa B alpha, decreased p50/p65 gene expression or inhibition of NF-kappa B DNA binding. Furthermore, since the maximal repression of IL-1 beta or phorbol-ester-induced kappa B-dependent transcription by dexamethasone was less than 40%, simple inhibition of kappa B-dependent transcription cannot by itself account for the full repressive effects of glucocorticoids observed in these cells.