Phosphoinositide-Mediated Adaptor Recruitment Controls Toll-Like Receptor Signaling

Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Cell (Impact Factor: 32.24). 07/2006; 125(5):943-55. DOI: 10.1016/j.cell.2006.03.047
Source: PubMed


Toll-like receptors (TLRs) play a critical role in the immune system as sensors of microbial infection. Signaling downstream from TLRs is initiated by the recruitment of adaptor proteins, including MyD88 and TIRAP. These adaptors play essential roles in TLR signaling, but the mechanism of their function is currently unknown. Here we demonstrate that TIRAP and MyD88 have distinct functions and describe a mechanism of recruitment of TIRAP and MyD88 to TLR4. We find that TIRAP contains a phosphatidylinositol 4,5-bisphosphate (PIP2) binding domain, which mediates TIRAP recruitment to the plasma membrane. TIRAP then functions to facilitate MyD88 delivery to activated TLR4 to initiate signal transduction. These results establish that phosphoinositide-mediated adaptor recruitment initiates a specific signal-transduction pathway.

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    • "The TIR dimer contains a composite surface for the recruitment of downstream TIR domain-containing adapter molecules to propagate the signaling pathway [21]. The TIR domain-containing adapter protein (TIRAP) serves as a bridge to recruit MyD88 to the TLR4 receptor and then activate NF-κB [22] [23]. In this study, we synthesized a TR6 (sequence: " N " -RQIKIWFQNRRMKWK and, -KPGFLRDPWCKYQML- " C " ), derived from region 6 of TIRAP, which represents the N-terminal portion of the third helical region of the TIRAP TIR domain. "
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    ABSTRACT: [TRIAP]-derived decoy peptides have anti-inflammatory properties. In this study, we synthesized a TRIAP-derived decoy peptide (TR6) containing, the N-terminal portion of the third helical region of the [TIRAP] TIR domain (sequence "N"-RQIKIWFQNRRMKWK and -KPGFLRDPWCKYQML-"C"). We evaluated the effects of TR6 on lipopolysaccharide-induced mastitis in mice. In vivo, the mastitis model was induced by LPS administration for 24 h, and TR6 treatment was initiated 1 h before or after induction of LPS. In vitro, primary mouse mammary epithelial cells and neutrophils were used to investigate the effects of TR6 on LPS-induced inflammatory responses. The results showed that TR6 significantly inhibited mammary gland hisopathologic changes, MPO activity, and LPS-induced production of TNF-α, IL-1β and IL-6. In vitro, TR6 significantly inhibited LPS-induced TNF-α and IL-6 production and phosphorylation of NF-κB and MAPKs. In conclusion, this study demonstrated that the anti-inflammatory effect of TR6 against LPS-induced mastitis may be due to its ability to inhibit TLR4-mediated NF-κB and MAPK signaling pathways. TR6 may be a promising therapeutic reagent for mastitis treatment.
    Full-text · Article · Jan 2016 · International immunopharmacology
    • "This finding derived from our studies of the subcellular sites of TLR4 signal transduction (Kagan et al., 2008). The initiation of TLR4 signal transduction occurs in phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2)-rich regions of the plasma membrane, where a sorting adaptor called TIRAP resides (Kagan and Medzhitov, 2006). TIRAP senses active (i.e., dimerized) TLR4 through interactions between the Toll/ IL-1 receptor (TIR) domains present in each of these proteins (Kagan and Barton, 2015). "
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    ABSTRACT: Microbe-induced receptor trafficking has emerged as an essential means to promote innate immune signal transduction. Upon detection of bacterial lipopolysaccharides (LPS), CD14 induces an inflammatory endocytosis pathway that delivers Toll-like receptor 4 (TLR4) to endosomes. Although several regulators of CD14-dependent TLR4 endocytosis have been identified, the cargo-selection mechanism during this process remains unknown. We reveal that, in contrast to classic cytosolic interactions that promoted the endocytosis of transmembrane receptors, TLR4 was selected as cargo for inflammatory endocytosis entirely through extracellular interactions. Mechanistically, the extracellular protein MD-2 bound to and dimerized TLR4 in order to promote this endocytic event. Our analysis of LPS variants from human pathogens and gut commensals revealed a common mechanism by which bacteria prevent inflammatory endocytosis. We suggest that evasion of CD14-dependent endocytosis is an attribute that transcends the concept of pathogenesis and might be a fundamental feature of bacteria that inhabit eukaryotic hosts.
    No preview · Article · Nov 2015 · Immunity
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    • "LPS binds to TLR-4 on the cell membrane and induces NF-κB transcription, mainly through the MyD88 signaling pathway. NF-κB is a transcriptional factor that controls the expression of numerous genes involved in inflammation, which leads to a release of the critical inflammatory molecules, conducting the appropriate immune response (Kagan and Medzhitov, 2006; Peng et al., 2012). Taken together, data presented here from in vivo and in vitro studies show the mechanisms of the antiinflammatory actions of R. officinalis aqueous extract in early phases of inflammation. "
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    ABSTRACT: Rosmarinus officinalis L. phenolic compounds have attracted considerable attention because of their antioxidant and antimicrobial properties, including its ability to treat inflammatory disorders. In this work, we investigated the in vivo and in vitro effects of R. officinalis aqueous extract on neutrophil trafficking from the blood into an inflamed tissue, on cell-derived secretion of chemical mediators, and on oxidative stress. Anti-inflammatory activity was investigated using carrageenan-induced inflammation in the subcutaneous tissue of male Wistar rats orally treated with the R. officinalis extract (100, 200, or 400 mg/kg). The leukocyte influx (optical microscopy), secretion of chemical mediators (prostaglandin E2 (PGE2), TNF-α, interleukin 6 (IL-6), leukotriene B4 (LTB4), and cytokine-induced neutrophil chemoattractant 1 by enzyme-linked immunosorbent assay), and the anti-oxidative profile (super oxide dismutase (SOD), glutathione peroxidase, and thiobarbituric acid reactive substance (TBARS) spectrophotometry) were quantified in the inflamed exudate. N-Formyl-methionine-leucine-phenylalanine-induced chemotaxis, lipopolysaccharide-induced NO2 (-) production (Greiss reaction), and adhesion molecule expression (flow cytometry) were in vitro quantified using oyster glycogen recruited peritoneal neutrophils previous treated with the extract (1, 10, or 100 µg/mL). Animals orally treated with phosphate-buffered saline and neutrophils incubated with Hank's balanced salt solution were used as control. R. officinalis extract oral treatment caused a dose-dependent reduction in the neutrophil migration as well as decreased SOD, TBARS, LTB4, PGE2, IL-6, and TNF-α levels in the inflamed exudate. In vitro treatment with R. officinalis decreased neutrophil chemotaxis, NO2 (-) production, and shedding of L-selectin and β2 integrin expressions. Results here presented show that R. officinalis aqueous extract displays important in vivo and in vitro anti-inflammatory actions by blocking pathways of neutrophil migration and secretion, suggesting its therapeutic application to acute inflammatory reactions. Copyright © 2014 John Wiley & Sons, Ltd.
    Full-text · Article · Oct 2014 · Phytotherapy Research
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