Laboratory of Food Chemistry, Division of Applied Biological Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Fukuoka, Japan.
J Immunol. 2010 Jul 1;185(1):33-45. doi: 10.4049/jimmunol.0903742. Epub 2010 May 28.
Epigallocatechin-3-gallate (EGCG), a major active polyphenol of green tea, has been shown to downregulate inflammatory responses in macrophages; however, the underlying mechanism has not been understood. Recently, we identified the 67-kDa laminin receptor (67LR) as a cell-surface EGCG receptor that mediates the anticancer action of EGCG at physiologically relevant concentrations (0.1-1 microM). In this study, we show the molecular basis for the downregulation of TLR4 signal transduction by EGCG at 1 microM in macrophages. Anti-67LR Ab treatment or RNA interference-mediated silencing of 67LR resulted in abrogation of the inhibitory action of EGCG on LPS-induced activation of downstream signaling pathways and target gene expressions. Additionally, we found that EGCG reduced the TLR4 expression through 67LR. Interestingly, EGCG induced a rapid upregulation of Toll-interacting protein (Tollip), a negative regulator of TLR signaling, and this EGCG action was prevented by 67LR silencing or anti-67LR Ab treatment. RNA interference-mediated silencing of Tollip impaired the TLR4 signaling inhibitory activity of EGCG. Taken together, these findings demonstrate that 67LR plays a critical role in mediating anti-inflammatory action of a physiologically relevant EGCG, and Tollip expression could be modulated through 67LR. These results provide a new insight into the understanding of negative regulatory mechanisms for the TLR4 signaling pathway and consequent inflammatory responses that are implicated in the development and progression of many chronic diseases.
没食子儿茶素-3-没食子酸酯（EGCG）是绿茶中的一种主要活性多酚，已被证明可下调巨噬细胞中的炎症反应；然而，其潜在机制尚不清楚。最近，我们发现 67kDa 层粘连蛋白受体（67LR）是 EGCG 在生理相关浓度（0.1-1μM）下发挥抗癌作用的细胞表面 EGCG 受体。在这项研究中，我们展示了 EGCG 在 1μM 时下调巨噬细胞中 TLR4 信号转导的分子基础。抗 67LR Ab 处理或 67LR 的 RNA 干扰介导的沉默导致 EGCG 对 LPS 诱导的下游信号通路和靶基因表达的抑制作用丧失。此外，我们发现 EGCG 通过 67LR 降低 TLR4 的表达。有趣的是，EGCG 诱导 Toll 相互作用蛋白（Tollip）的快速上调，Tollip 是 TLR 信号的负调节剂，而 67LR 的沉默或抗 67LR Ab 处理阻止了这种 EGCG 作用。Tollip 的 RNA 干扰介导的沉默损害了 EGCG 对 TLR4 信号抑制活性。总之，这些发现表明 67LR 在介导生理相关 EGCG 的抗炎作用中起着关键作用，并且可以通过 67LR 调节 Tollip 的表达。这些结果为理解 TLR4 信号通路和随后的炎症反应的负调控机制提供了新的见解，这些机制与许多慢性疾病的发展和进展有关。
