Cigarette Smoke Extract Enhances IL-17A-Induced IL-8 Production via Up-Regulation of IL-17R in Human Bronchial Epithelial Cells

Interleukin-17A (IL-17A) is a pro-inflammatory cytokine mainly derived from T helper 17 cells and is known to be involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS) has been considered as a primary risk factor of COPD. However, the interaction between CS and IL-17A and the underlying molecular mechanisms have not been clarified. In the current study, we investigated the effects of cigarette smoke extract (CSE) on IL-17A-induced IL-8 production in human bronchial epithelial cells, and sought to identify the underlying molecular mechanisms. IL-8 production was significantly enhanced following treatment with both IL-17A and CSE, while treatment with either IL-17A or CSE alone caused only a slight increase in IL-8 production. CSE increased the transcription of IL-17RA/RC and surface membrane expression of IL-17R, which was suppressed by an inhibitor of the phosphoinositide 3-kinase (PI3K)/Akt pathway (LY294002). CSE caused inactivation of glycogen synthase kinase-3β (GSK-3β) via the PI3K/Akt pathway. Blockade of GSK-3β inactivation by overexpression of constitutively active GSK-3β (S9A) completely suppressed the CSE-induced up-regulation of IL-17R expression and the CSE-induced enhancement of IL-8 secretion. In conclusion, inactivation of GSK-3β via the PI3K/Akt pathway mediates CSE-induced up-regulation of IL-17R, which contributes to the enhancement of IL-17A-induced IL-8 production.