第四型類鐸受體之新型調控機制

The novel regulation of Toll-Like Receptor 4

賴亭諭(Ting-Yu Lai)

指導教授 ： 徐立中

國立臺灣大學/醫學院/分子醫學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.01759

摘要

哺乳類動物中，先天性免疫系統(Innate immunity)是防禦病原菌侵入生物體內的首道防線。先天性免疫反應的防禦機制在於藉由pattern-recognition receptors，如Toll-like receptors (TLRs) ， 以非特異性方式辨識病菌特有的分子特徵(pathogen-associated molecular patterns)而保護生物體不受感染威脅。巨噬細胞是一種有吞噬能力的大型白血球，它可以移動到組織之間去獵取入侵的病源菌，並產生細胞激素以及將抗原表現給其他細胞以活化適應性免疫反應(adaptive immunity)，進行毒殺病原體的動作。
TLR訊息傳導途徑在生物體內通常受到了嚴密精細的調控。失控的全身性發炎反應可能造成全身性發炎反應症候群 (Systemic inflammatory response syndrome,SIRS)、動脈硬化，或是自體免疫性疾病，這些疾病多由體內持續性的發炎反應所造成，進而使內臟器官嚴重受損甚至死亡。在受到病原體刺激之後，TLR透過許多不同的分子經由訊息傳導引發巨噬細胞免疫反應，而這些分子在免疫系統上將可有效的防止免疫反應過量及不足的情況。因此透過這些免疫反應調控因子深入的研究以及了解，臨床上將有助於治療各種發炎引起的疾病。
我們從微陣列資料庫分析中發現了兩種新型調控TLR4訊息傳導的機制。TLR4受到LPS刺激活化後會藉由NF-κB及p38調控之轉錄因子C/EBPβ轉錄出一個重要基因，稱為Tnfaip3，Tnfaip3轉譯出的蛋白質稱為A20。免疫系統中A20可作為廣泛負向調控TLR下游的訊息傳遞，達到關閉發炎反應的作用。另一種機制是藉由一個新型E3連接酶蛋白，ZNRF1所調控。我們發現一旦TLR4受活化後，ZNRF1會藉由和小凹蛋白(Caveolin-1)的結合進而泛素化並降解小凹蛋白的量。ZNRF1和小凹蛋白之間的互動，影響了Akt-GSK3β-CREB路徑，最終使得發炎性細胞激素大量產生同時抑制了抗發炎細胞激素，如IL10，的分泌，進而有效控制發炎過程的平衡。我們揭開了兩種新型態的TLR4調控機制也為發炎性疾病的治療帶來曙光。

關鍵字

巨噬細胞 ； 小凹蛋白 ； 第四型類鐸受體

並列摘要

In mammals, innate immunity is the first line of defense against pathogenic infection, and is mainly mediated by pattern-recognition receptors, including Toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns derived from microbes or endogenous molecules termed damage-associated molecular patterns. Macrophages, a type of phagocytic leukocytes, play a crucial role in innate immunity by producing various cytokines and chemokines and presenting antigens to lymphocytes, both of which are also involved in the activation of adaptive immunity. However, dysregulation of TLRs-mediated inflammatory response can impair host immune homeostasis, and is associated with many autoimmune and inflammatory diseases, such as systemic inflammatory response syndrome (SIRS) and atherosclerosis. Thus, the molecular mechanisms of how TLRs signaling is regulated have been intensively investigated, but the detailed mechanism still remains fragmentary. In this study, we discovered two novel regulatory mechanisms in TLR4-mediated immune response by exploring microarray analysis. We found that TLR4 engagement induced a transcription factor C/EBPβ through p38 MAPK, which subsequently increased A20 expression in conjunction with NF-κB. A20, in turn, negatively regulated TLR4 signaling to terminate inflammatory response. In addition, we identified a novel E3 ubiquitin ligase, ZNRF1, which mediated caveolin-1 (CAV1) ubiquitination and degradation in response to lipopolysaccharide (LPS). Mechanistically, the ZNRF1-CAV1 axis influences Akt-GSK3β activity upon TLR4 activation, eventually resulting in enhanced production of pro-inflammatory cytokines and inhibiting anti-inflammatory cytokine IL-10 expression. Our findings unravel two new regulatory mechanisms of TLR4 signaling pathway and may shed light on treatments for inflammation-related diseases.

並列關鍵字

Macrophage ； Caveolin1 ； TLR4

參考文獻

1. Janeway CA, Jr., Medzhitov R. Innate immune recognition. Annu Rev Immunol 2002; 20:197-216.

2. Hansen JD, Vojtech LN, Laing KJ. Sensing disease and danger: a survey of vertebrate PRRs and their origins. Dev Comp Immunol 2011; 35(9):886-97.

3. Reuven EM, Fink A, Shai Y. Regulation of innate immune responses by transmembrane interactions: lessons from the TLR family. Biochim Biophys Acta 2014; 1838(6):1586-93.

5. Akira S, Uematsu S, Takeuchi O. Pathogen recognition and innate immunity. Cell 2006; 124(4):783-801.

6. Hasan U, Chaffois C, Gaillard C, et al. Human TLR10 is a functional receptor, expressed by B cells and plasmacytoid dendritic cells, which activates gene transcription through MyD88. J Immunol 2005; 174(5):2942-50.