Reactive oxygen species mediate virus-induced STAT activation: role of tyrosine phosphatases

Respiratory syncytial virus (RSV) is the leading cause of epidemic respiratory tract illness in children in the United States and worldwide. RSV infection of airway epithelial cells induces formation of reactive oxygen species (ROS), whose production mediates the expression of cytokines and chemokines involved the immune/inflammatory responses of the lung. In this study, we have investigated the role of ROS in RSV-induced signal transducers and activators of transcription (STAT) activation and interferon regulatory factor (IRF) gene expression in human airway epithelial cells. Our results indicate that RSV replication induces IRF-1 and -7 gene transcription, a response abrogated by antioxidants. RSV infection induces binding of STAT to the IRF-1 gamma-interferon-activated sequence (GAS) and IRF-7 interferon-stimulated responsive element (ISRE). STAT1 and STAT3 bind IRF-1 GAS, whereas STAT1, STAT2, IRF-1, and IRF-9 bind IRF-7 ISRE. Antioxidant treatment blocks RSV-induced STAT binding to both the IRF-1 GAS and IRF-7 ISRE by inhibition of inducible STAT1 and STAT3 tyrosine phosphorylation, suggesting that RSV-induced ROS formation is required for STAT activation and IRF gene expression. Although protein tyrosine phosphorylation is necessary for RSV-induced STAT activation, Janus kinase and Src kinase activation do not mediate this effect. Instead, RSV infection inhibits intracellular tyrosine phosphatase activity, which is restored by antioxidant treatment. Pharmacological inhibition of tyrosine phosphatases induces STAT activation. Together, these results suggest that modulation of phosphatases could be an important mechanism of virus-induced STAT activation. Treatment of alveolar epithelial cells with the NAD(P)H oxidase inhibitor diphenylene iodonium abolishes RSV-induced STAT activation, indicating that NAD(P)H oxidase-produced ROS are required for downstream activation of the transcription factors IRF and STAT in virus-infected airway epithelial cells.