Bannon Ciara, Davies Pam J, Collett Andrew, Warhurst Geoffrey
Salford Royal NHS Foundation Trust, UK.
Biochem J. 2009 Sep 14;423(1):119-28. doi: 10.1042/BJ20090392.
Flagellin acting via TLR5 (Toll-like receptor 5) is a key regulator of the host response to the gut microbial flora in both health and disease. The present study has investigated regulation of flagellin-TLR5 signalling in human colonocytes (HT29-19A) by IFNgamma (interferon-gamma), a cytokine released early in the inflammatory process which has multiple effects on gut epithelial function that may facilitate abnormal responses to enteric bacteria. Flagellin induced a dose-dependent secretion of chemokines CXCL8 and CCL2 in the human colonocyte line, HT29-19A. Exposure to IFNgamma did not induce chemokine secretion, but markedly potentiated responses to flagellin, increasing CXL8 gene expression and protein secretion by approx. 4-fold. Potentiation by IFNgamma was independent of changes in TLR5 and was associated with a rapid, sustained increase in expression of the downstream adaptor molecule MyD88 (myeloid differentiation factor 88). Knockdown of MyD88 expression using siRNA (small interfering RNA) abolished flagellin-dependent CXCL8 secretion and the potentiating effect of IFNgamma. Exposure of non-transformed mouse and human colonocytes to IFNgamma also increased MyD88 expression. STAT (signal transducer and activator of transcription) 1 knockdown and use of the broad-spectrum JAK (Janus kinase)-STAT inhibitor AG490 had no effect on IFNgamma-mediated up-regulation of MyD88. The findings of the present study suggest that IFNgamma sensitizes colonic epithelial cells to bacterial flagellin via a largely STAT-independent up-regulation of MyD88 expression leading to increased secretion of immunomodulatory factors. These results indicate that epithelial responses to flagellin are potentiated by IFNgamma, most likely mediated by increased MyD88 expression. The present study adds to our understanding of the spectrum of effects of this cytokine on gut epithelium that may contribute to bacterial-driven inflammation in the gut.
通过Toll样受体5（TLR5）起作用的鞭毛蛋白是宿主在健康和疾病状态下对肠道微生物群反应的关键调节因子。本研究调查了γ干扰素（IFNγ）对人结肠上皮细胞（HT29-19A）中鞭毛蛋白-TLR5信号传导的调节作用，γ干扰素是一种在炎症过程早期释放的细胞因子，对肠道上皮功能有多种影响，可能会促进对肠道细菌的异常反应。鞭毛蛋白在人结肠上皮细胞系HT29-19A中诱导趋化因子CXCL8和CCL2呈剂量依赖性分泌。暴露于γ干扰素不会诱导趋化因子分泌，但会显著增强对鞭毛蛋白的反应，使CXL8基因表达和蛋白分泌增加约4倍。γ干扰素的增强作用与TLR5的变化无关，并且与下游衔接分子髓样分化因子88（MyD88）表达的快速、持续增加有关。使用小干扰RNA（siRNA）敲低MyD88表达可消除鞭毛蛋白依赖性CXCL8分泌以及γ干扰素的增强作用。未转化的小鼠和人结肠上皮细胞暴露于γ干扰素也会增加MyD88表达。信号转导和转录激活因子（STAT）1敲低以及使用广谱Janus激酶（JAK）-STAT抑制剂AG490对γ干扰素介导的MyD88上调没有影响。本研究结果表明，γ干扰素通过MyD88表达在很大程度上不依赖于STAT的上调，使结肠上皮细胞对细菌鞭毛蛋白敏感，从而导致免疫调节因子分泌增加。这些结果表明，γ干扰素增强了上皮细胞对鞭毛蛋白的反应，最有可能是由MyD88表达增加介导的。本研究增进了我们对这种细胞因子对肠道上皮细胞作用谱的理解，这些作用可能导致肠道细菌驱动的炎症。
