Theophylline inhibits NF-κB activation and IκBα degradation in human pulmonary epithelial cells

Previous studies demonstrated that theophylline modulates NF-κB activation in mast cells and pulmonary epithelial cells. We examined whether or not this modulation of NF-κB activation by theophylline is due to inhibition of the degradation of the IκBα protein, which suppresses NF-κB activation. TNF-α-induced NF-κB activation in a human pulmonary epithelial cell line (A549) was evaluated by Western blotting and a chloramphenicol acetyltransferase (CAT) assay. Expression of the IκBα protein was evaluated by Western blotting. Western blotting of nuclear extracts of A549 cells demonstrated that theophylline suppresses NF-κB-p65 nuclear translocation. The CAT assay indicated that NF-κB-dependent reporter gene expression is inhibited in A549 cells pretreated with theophylline. Western blotting of cytoplasmic extracts of A549 cells revealed that this inhibition was linked to theophylline-induced protection of expression of the IκBα protein. Moreover, theophylline inhibited interleukin-6 production induced by TNF-α in A549 cells. These findings are consistent with the idea that theophylline suppresses the production of proinflammatory cytokines via inhibition of NF-κB activation through protection of the IκBα protein.