Respiratory syncytial virus and TNFalpha induction of chemokine gene expression involves differential activation of Rel A and NF-kappaB1

Background: Respiratory syncytial virus (RSV) infection of airway epithelial cells stimulates the expression and secretion of a variety of cytokines including the chemotactic cytokines interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), and RANTES (regulated upon activation, normal T cell expressed and secreted). Chemokines are important chemoattractants for the recruitment of distinct sets of leukocytes to airway sites of inflammation. Results: We have shown previously that chemokine expression is regulated in airway epithelial cells (A549) in a stimulus-specific manner in part through the redox-responsive transcription factors AP-1 and NF- Kappa B. In this study, we examined the NF- Kappa B-mediated effects of RSV and the proinflammatory cytokine TNF alpha on the induction of IL-8, MCP-1 and RANTES chemokine gene expression in A549 epithelial cells. The results demonstrate that RSV induces chemokine expression with distinct kinetics that is associated with a specific pattern of NF- Kappa B binding activity. This distinction was further demonstrated by the differential effects of the NF- Kappa B inhibitors dexamethasone (DEX) and N-acetyl- L-cysteine (NAC). NAC preferentially inhibited RSV induced chemokine expression, whereas DEX preferentially inhibited TNF alpha induced chemokine expression. DNA binding studies using NF- Kappa B subunit specific binding ELISA demonstrated that RSV and TNF alpha induced different NF- Kappa B binding complexes containing Rel A (p65) and NF- Kappa B1 (p50). Both TNF alpha and RSV strongly induced Rel A the activation subunit of NF- Kappa B, whereas only TNF alpha was able to substantially induce the p50 subunit. Consistent with the expression studies, RSV but not TNF alpha induction of Rel A and p50 were markedly inhibited by NAC, providing a mechanism by which TNF alpha and RSV can differentially activate chemokine gene expression via NF- Kappa B. Conclusions: These data suggest that RSV induction of chemokine gene expression, in contrast to TNF alpha , involves redox-sensitive NF- Kappa B complexes containing predominantly Rel A.