Tumor necrosis factor‐α regulates interleukin‐33 expression through extracellular signal‐regulated kinase, p38, and nuclear factor–κB pathways in airway epithelial cells

Background Interleukin (IL)‐33 plays an important role in controlling immune responses in barrier tissues, and is a potent mediator of inflammatory diseases such as asthma, rheumatoid disease, and chronic rhinosinusitis. The aims of the present study were 2‐fold: (1) to determine the stimulatory effect of tumor necrosis factor‐α (TNF‐α) on IL‐33 production in nasal epithelial and A549 cells; and (2) to identify downstream pathways that activate IL‐33 production. Methods Primary nasal epithelial cells (PNECs) from 5 normal patients were isolated and cultured. To identify which cytokines stimulate IL‐33 production, we performed reverse‐transcription polymerase chain reaction (RT‐PCR), enzyme‐linked immunosorbent assay (ELISA), and immunofluorescence staining. Three mitogen‐activated protein kinases (MAPKs) (p38, extracellular signal‐regulated kinase [ERK], and c‐Jun N‐terminal kinase [JNK]) and nuclear factor κB (NF‐κB) were evaluated as downstream signaling molecules by RT‐PCR, ELISA, Western blot analysis, and luciferase reporter assay. Results The IL‐33 messenger RNA (mRNA) and protein levels were increased significantly by TNF‐α in PNECs and A549 cells. TNF‐α stimulated the expression of IL‐33 in a dose‐ and time‐dependent manner in A549 cells. PNECs and A549 cells were treated with TNF‐α in the presence of specific inhibitors of p38, ERK, JNK, and NF‐κB. In both cell types, inhibitors of ERK, p38, and NF‐κB reversed TNF‐α–induced IL‐33 production. In the luciferase reporter assay, NF‐κB activity was inhibited not only by an NF‐κB inhibitor, but also by ERK and p38 inhibitors. Conclusion TNF‐α stimulated IL‐33 expression through ERK, p38, and NFκB pathways in PNECs and A549 cells.