The IL-17F signaling pathway is involved in the induction of IFN-γ-inducible protein 10 in bronchial epithelial cells

Background: IL-17F is involved in airway inflammation, but its biologic activity and signaling pathway remain incompletely defined. Interferon-γ-inducible protein 10 (IP-10) is widely expressed and plays a role in airway inflammatory diseases. Objective: We sought to investigate the functional linkage between IL-17F and IP-10 expression in bronchial epithelial cells. Methods: Bronchial epithelial cells were cultured in the presence or absence of IL-17F, and/or a T_H1 cytokine, T_H2 cytokines, proinflammatory cytokines, various kinase inhibitors, or a Raf1 dominant-negative mutant to analyze the expression of IP-10. Moreover, the involvement of p90 ribosomal S6 kinase (p90RSK) and cyclic AMP response element-binding protein (CREB) in IL-17F-induced IP-10 expression were investigated. Results: IL-17F induces the gene and protein expression of IP-10. The addition of IFN-γ, IL-1β, and TNF-α augmented IL-17F-induced IP-10 expression. The mitogen-activated protein kinase kinase (MEK) inhibitors PD98059, U0126, and Raf1 kinase inhibitor I significantly inhibited its production. In contrast, a p38 inhibitor, a JNK inhibitor, protein kinase C inhibitors, and a phosphatidylinositol 3-kinase inhibitor, showed no inhibitory effect. Furthermore, overexpression of a Raf1 dominant-negative mutant inhibited its expression. Of interest, IL-17F phosphorylated p90RSK and CREB, and transfection of the cells with a short interfering RNA for p90RSK or CREB inhibited its expression, suggesting p90RSK and CREB as novel signaling molecules of IL-17F. Conclusion: IL-17F is a potent inducer of IP-10 in bronchial epithelial cells through the activation of the Raf1-MEK1/2-extracellular signal-regulated kinase 1/2-p90RSK-CREB pathway, supporting its regulatory role in airway inflammation. Clinical implications: The IL-17F-IP-10 axis might be a novel and critical therapeutic target for airway inflammatory diseases.