IL-13 regulates IL-17C expression by suppressing NF-κB-mediated transcriptional activation in airway epithelial cells.

The cytokine interleukin (IL)-17C is highly expressed in epithelial tissues and involved in innate immune responses; however, the regulation of IL-17C expression in the airways remains poorly understood. Here, we show that IL-1ß strongly induces both IL-17C mRNA and protein expression in primary normal human bronchial epithelial cells. Conversely, IL-13 significantly reduced the IL-1ß-induced IL-17C expression. Attenuation of the nuclear factor (NF)-κB-signaling pathway using an NF-κB-subunit p65-specific small-interfering RNA (siRNA), reduced IL-1ß-induced IL-17C expression, demonstrating the importance of NF-κB signaling in IL-17C regulation. The inhibitory effects of IL-13 on IL-17C expression were abolished when the Janus kinase (JAK)/signal transducer and activator of transcription 6 (STAT6)-signaling pathway was impaired, using either the JAK inhibitor ruxolitinib or a STAT6-specific siRNA. Western blot analysis demonstrated that IL-1ß promoted both IκB-α phosphorylation and degradation, and p65 nuclear translocation. Although IL-13 induced STAT6 phosphorylation and nuclear translocation, it did not affect the activation of the IL-1ß-mediated NF-κB-pathway. Using chromatin immunoprecipitation, we confirmed that IL-1ß enhanced p65 binding to regions within the IL-17C promoter that flank putative NF-κB-binding sites (-130/-120 and -157/-147). Interestingly, IL-13 treatment reduced the IL-1ß-mediated p65 binding to these regions. These findings demonstrate that NF-κB-mediated transcriptional mechanisms are critically involved in the IL-1ß-mediated IL-17C induction, and that IL-13 negatively regulates this induction by suppressing NF-κB-based transcriptional activation.