Role of MyD88 in phosphatidylinositol 3-kinase activation by flagellin/toll-like receptor 5 engagement in colonic epithelial cells
Role of MyD88 in phosphatidylinositol 3-kinase activation by flagellin/toll-like receptor 5 engagement in colonic epithelial cells
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DOI：
10.1074/jbc.m513861200
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发表时间：
2006-07-07
影响因子：
4.8
通讯作者：
Pothoulakis, Charalabos
中科院分区：
文献类型：
--
作者：
Rhee, Sang Hoon;Kim, Ho;Pothoulakis, Charalabos
被toll样受体（TLR） 5识别的细菌鞭毛蛋白被认为与结肠炎症有关。然而，鞭毛蛋白/TLR5参与介导的详细信号机制尚不清楚。在这里，我们剖析了TLR5参与介导结肠上皮细胞中磷脂酰肌醇3-激酶（PI3K）激活的生化机制。我们证明，在未转化的人结肠上皮细胞中沉默TLR5表达可阻断鞭毛蛋白诱导的PI3K激活，这表明鞭毛蛋白/TLR5结合可特异性激活PI3K。此外，我们确定TLR5将PI3K的p85调节亚基募集到其细胞质TIR结构域以响应鞭毛蛋白。然而，TLR5细胞质TIR结构域Src同源结合的“YXXM”基序并未参与p85的募集，这意味着TLR5间接募集了p85。事实上，我们证明了接头分子MyD88与TLR5相关，沉默MyD88的表达通过破坏TLR5和p85之间的关联来阻断PI3K的激活。此外，我们发现MyD88在鞭毛蛋白的作用下与p85结合。此外，我们确定阻断PI3K激活可减少人结肠上皮细胞中鞭毛蛋白诱导的白细胞介素-8的产生。总之，MyD88在TLR5参与和PI3K激活对鞭毛蛋白的响应之间架起了桥梁。
Bacterial flagellin, recognized by Toll-like receptor (TLR) 5, is suggested to be involved in colonic inflammation. However, the detailed signaling mechanisms mediated by flagellin/TLR5 engagement are not clear. Here we dissected the biochemical mechanism by which TLR5 engagement mediates phosphatidylinositol 3-kinase (PI3K) activation in colonic epithelial cells. We demonstrate that silencing TLR5 expression in nontransformed human colonic epithelial cells blocks flagellin-induced PI3K activation, indicating specific activation of PI3K by flagellin/TLR5 engagement. Moreover, we determine that TLR5 recruits the p85 regulatory subunit of PI3K to its cytoplasmic TIR domain in response to flagellin. However, the Src homology binding "YXXM" motif in the cytoplasmic TIR domain of TLR5 is not involved in p85 recruitment, implying that TLR5 indirectly recruits p85. Indeed, we demonstrate that the adaptor molecule MyD88 associates with TLR5 and silencing MyD88 expression blocks PI3K activation by disrupting the association between TLR5 and p85. Furthermore, we show that MyD88 associates with p85 in response to flagellin. Additionally, we determine that blocking PI3K activation reduces interleukin-8 production induced by flagellin in human colonic epithelial cells. Together, MyD88 bridges TLR5 engagement to PI3K activation in response to flagellin.