TLR4 signaling inhibitory pathway induced by green tea polyphenol epigallocatechin-3-gallate through 67-kDa laminin receptor.
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.
Hong Byun
Eui
E
Laboratory of Food Chemistry, Division of Applied Biological Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Fukuoka, Japan.
Fujimura
Yoshinori
Y
Yamada
Koji
K
Tachibana
Hirofumi
H
D000818:Animals; D002392:Catechin / Q000031:analogs & derivatives* / Q000502:physiology / Q000633:toxicity; D002460:Cell Line; D015536:Down-Regulation / Q000276:immunology*; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D018836:Inflammation Mediators / Q000037:antagonists & inhibitors / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D021381:Protein Transport / Q000235:genetics / Q000276:immunology; D017474:Receptors, Laminin / Q000037:antagonists & inhibitors / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000502:physiology*
D018836:Inflammation Mediators; D047908:Intracellular Signaling Peptides and Proteins; D017474:Receptors, Laminin; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C485837:Tollip protein, mouse; D002392:Catechin; C045651:epigallocatechin gallate