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TNF-α 诱导肺泡 II 型上皮细胞中 IL-6 的表达:JNK/c-Jun/AP-1 元件、C/EBPδ/C/EBP 结合位点和 IKK/NF-κB p65/κB 位点的贡献。

TNF-α induction of IL-6 in alveolar type II epithelial cells: Contributions of JNK/c-Jun/AP-1 element, C/EBPδ/C/EBP binding site and IKK/NF-κB p65/κB site.

机构信息

Department of Pathogenic Biology and Immunology, Medical School of Southeast University, Nanjing, 210009, China.

Department of Pathogenic Biology and Immunology, Medical School of Southeast University, Nanjing, 210009, China.

出版信息

Mol Immunol. 2018 Sep;101:585-596. doi: 10.1016/j.molimm.2018.05.004. Epub 2018 Jun 7.

Abstract

Although participation of IL-6 in lung inflammation has been widely elucidated, the transcriptional regulation of its generation in alveolar type II cells stimulated by TNF-α remain unclear. Here, we find that TNF-α significantly induces IL-6 production, and TNF-α induction of IL-6 is mainly regulated at transcriptional level. Upon stimulated by TNF-α, Activator Protein-1 (AP-1)-mediated transcriptional activity is apparently increased in alveolar type II epithelial cells, which might be derived from elevated phosphorylation of JNK and subsequent activation of c-Jun. Either down-regulation of c-Jun or the AP-1 site mutation leads to significant reduction of IL-6 expression. In contrast, ectopic expression of c-Jun notably increases IL-6 generation. So, c-Jun, one of the AP-1 family members, plays a pivotal role in TNF-α-induced IL-6 generation. CCAAT/enhancer binding protein δ (C/EBPδ) expression is significantly amplified by TNF-α, which may contribute to the rise of C/EBP activity in alveolar type II cells. C/EBPδ shRNA treatment results in attenuation of IL-6 expression in the cells, which is consistent with data by introduction of mutations into the C/EBP site in the promoter. However, overexpression of C/EBPδ greatly increases the IL-6 promoter activity. In addition, data regarding another transactivator in the family-C/EBPβ show that it does not affect IL-6 production. We also find that the IKK/NF-κB p65 pathway is activated in TNF-α-treated alveolar type II epithelial cells, and plays an essential role in positive regulation of IL-6 expression in TNF-α-treated alveolar type II epithelial cells via knockdown or forced expression of NF-κB p65, or elimination of κB sites in the IL-6 promoter. Notably, IL-6 promoter-driven luciferase production in primary alveolar type II epithelial cells can also be increased by the ectopic expression of c-Jun, C/EBPδ, and NF-κB p65, respectively. Collectively, our data provide insights into molecular mechanism involved in IL-6 expression in alveolar type II epithelial cells on TNF-α treatment, which provides a theoretical basis for specific inhibition of IL-6 production at the transcriptional level.

摘要

虽然白细胞介素 6(IL-6)在肺部炎症中的作用已经得到广泛阐明,但 TNF-α 刺激肺泡 II 型细胞产生 IL-6 的转录调控仍不清楚。在这里,我们发现 TNF-α 可显著诱导 IL-6 的产生,并且 TNF-α 诱导的 IL-6 主要在转录水平上受到调控。在受到 TNF-α刺激后,II 型肺泡上皮细胞中的激活蛋白 1(AP-1)介导的转录活性明显增加,这可能源于 JNK 的磷酸化水平升高和随后的 c-Jun 激活。c-Jun 的下调或 AP-1 位点突变会导致 IL-6 表达的显著减少。相反,c-Jun 的异位表达显著增加了 IL-6 的产生。因此,AP-1 家族成员之一的 c-Jun 在 TNF-α 诱导的 IL-6 产生中发挥关键作用。CCAAT/增强子结合蛋白 δ(C/EBPδ)的表达被 TNF-α 显著放大,这可能有助于肺泡 II 型细胞中 C/EBP 活性的升高。C/EBPδ shRNA 处理导致细胞中 IL-6 表达减弱,这与启动子中 C/EBP 位点突变的数据一致。然而,C/EBPδ 的过表达大大增加了 IL-6 启动子的活性。此外,关于家族中的另一个转录激活子 C/EBPβ 的数据表明,它不会影响 IL-6 的产生。我们还发现,在 TNF-α 处理的肺泡 II 型上皮细胞中,IKK/NF-κB p65 途径被激活,并通过 NF-κB p65 的敲低或过表达,或消除 IL-6 启动子中的 κB 位点,在 TNF-α 处理的肺泡 II 型上皮细胞中,对 IL-6 表达的正向调节中发挥重要作用。值得注意的是,在原代肺泡 II 型上皮细胞中,c-Jun、C/EBPδ 和 NF-κB p65 的异位表达也分别增加了 IL-6 启动子驱动的荧光素酶的产生。总之,我们的数据为 TNF-α 处理肺泡 II 型上皮细胞中 IL-6 表达的分子机制提供了深入的了解,为在转录水平上特异性抑制 IL-6 产生提供了理论依据。

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