Up-regulation of ICAM-1 by cytokines in human tracheal smooth muscle cells involves an NF-kappa B-dependent signaling pathway that is only partially sensitive to dexamethasone.

Although the precise mechanisms by which steroids mediate their therapeutic effects remain unknown, steroids have been reported to abrogate cytokine-induced activation of the transcription factor NF-kappa B. In some cell types, NF-kappa B activation is necessary to regulate cytokine-mediated cellular functions. However, compelling evidence suggests that the steroid inhibition of NF-kappa B is complex and cell specific. Using EMSA, we show that stimulation with TNF-alpha or IL-1 beta induces NF-kappa B DNA-binding activity in human airway smooth muscle cells. TNF-alpha and IL-1 beta also increased luciferase activity in airway smooth muscle cells transfected with a reporter plasmid containing kappa B enhancer elements. Cytokines activated NF-kappa B by rapidly degrading its cytosolic inhibitor I kappa B alpha, which was then regenerated after 60 min. Cytokine-mediated I kappa B alpha reappearance was completely blocked by the protein synthesis inhibitor cycloheximide. Inhibition of cytokine-mediated I kappa B alpha proteolysis using the protease inhibitors N-tosyl-L -phenylalanine chloromethyl ketone and N-acetyl-L -leucinyl-L -leucinyl-norleucinal also inhibited cytokine-mediated early expression of ICAM-1. Although dexamethasone partially inhibited IL-1 beta- and TNF-alpha-induced up-regulation of ICAM-1 at 4 h, dexamethasone had no effect on cytokine-induced ICAM-1 expression at 18-24 h. In addition, neither cytokine-induced degradation or resynthesis of I kappa B alpha nor NF-kappa B DNA-binding activity were affected by dexamethasone. In cells transfected with the luciferase reporter, dexamethasone did not affect TNF-alpha-induced NF-kappa B-dependent transcription. Interestingly, cytokine-mediated expression of cyclooxygenase-2 was completely abrogated by dexamethasone at 6 h. Together, these data demonstrate that cytokine-mediated NF-kappa B activation and ICAM-1 expression involve activation of a steroid-insensitive pathway.