Department of Physiology, Center for Inflammation, Translational and Clinical Lung Research, Temple University School of Medicine, Philadelphia, PA 19140, USA.
J Immunol. 2012 Feb 15;188(4):2014-22. doi: 10.4049/jimmunol.1102405. Epub 2012 Jan 16.
MUC1 is a membrane-tethered mucin glycoprotein expressed on the apical surface of mucosal epithelial cells. Previous in vivo and in vitro studies established that MUC1 counterregulates airway inflammation by suppressing TLR signaling. In this article, we elucidate the mechanism by which MUC1 inhibits TLR5 signaling. Overexpression of MUC1 in HEK293 cells dramatically reduced Pseudomonas aeruginosa-stimulated IL-8 expression and decreased the activation of NF-κB and MAPK compared with cells not expressing MUC1. However, overexpression of MUC1 in HEK293 cells did not affect NF-κB or MAPK activation in response to TNF-α. Overexpression of MyD88 abrogated the ability of MUC1 to inhibit NF-κB activation, and MUC1 overexpression inhibited flagellin-induced association of TLR5/MyD88 compared with controls. The MUC1 cytoplasmic tail associated with TLR5 in all cells tested, including HEK293T cells, human lung adenocarcinoma cell line A549 cells, and human and mouse primary airway epithelial cells. Activation of epidermal growth factor receptor tyrosine kinase with TGF-α induced phosphorylation of the MUC1 cytoplasmic tail at the Y46EKV sequence and increased association of MUC1/TLR5. Finally, in vivo experiments demonstrated increased immunofluorescence colocalization of Muc1/TLR5 and Muc1/phosphotyrosine staining patterns in mouse airway epithelium and increased Muc1 tyrosine phosphorylation in mouse lung homogenates following P. aeruginosa infection. In conclusion, epidermal growth factor receptor tyrosine phosphorylates MUC1, leading to an increase in its association with TLR5, thereby competitively and reversibly inhibiting recruitment of MyD88 to TLR5 and downstream signaling events. This unique ability of MUC1 to control TLR5 signaling suggests its potential role in the pathogenesis of chronic inflammatory lung diseases.
黏蛋白 1（MUC1）是一种膜结合的黏蛋白糖蛋白，表达于黏膜上皮细胞的顶膜表面。先前的体内和体外研究证实，MUC1 通过抑制 TLR 信号来拮抗气道炎症。在本文中，我们阐明了 MUC1 抑制 TLR5 信号的机制。与不表达 MUC1 的细胞相比，HEK293 细胞中 MUC1 的过表达显著降低了铜绿假单胞菌刺激的 IL-8 表达，并降低了 NF-κB 和 MAPK 的激活。然而，HEK293 细胞中 MUC1 的过表达并不影响 TNF-α 诱导的 NF-κB 或 MAPK 激活。MyD88 的过表达消除了 MUC1 抑制 NF-κB 激活的能力，并且 MUC1 的过表达抑制了鞭毛蛋白诱导的 TLR5/MyD88 之间的关联，与对照相比。在所有测试的细胞中，包括 HEK293T 细胞、人肺腺癌细胞系 A549 细胞以及人和小鼠原代气道上皮细胞，MUC1 细胞质尾部与 TLR5 相关。表皮生长因子受体酪氨酸激酶用 TGF-α 激活后，在 Y46EKV 序列处磷酸化 MUC1 细胞质尾部，并增加 MUC1/TLR5 的关联。最后，体内实验表明，在铜绿假单胞菌感染后，小鼠气道上皮细胞中 Muc1/TLR5 和 Muc1/磷酸酪氨酸染色模式的免疫荧光共定位增加，并且小鼠肺匀浆中的 Muc1 酪氨酸磷酸化增加。总之，表皮生长因子受体酪氨酸使 MUC1 磷酸化，导致其与 TLR5 的关联增加，从而竞争性且可逆地抑制 MyD88 向 TLR5 的募集和下游信号事件。MUC1 控制 TLR5 信号的这种独特能力表明其在慢性炎症性肺部疾病发病机制中的潜在作用。
