Cleaved/Associated TLR3 Represents the Primary Form of the Signaling Receptor

Toscano, Florent; Estornes, Yann; Virard, François; Garcia-Cattaneo, Alejandra; Pierrot, Audrey; Vanbervliet, Béatrice; Bonnin, Marc; Ciancanelli, Michael J.; Zhang, Shen-Ying; Funami, Kenji; Seya, Tsukasa; Matsumoto, Misako; Pin, Jean-Jacques; Casanova, Jean‐Laurent; Renno, Toufic; Lebecque, Serge

doi:10.4049/jimmunol.1202173

Cited by 57 publications

(61 citation statements)

References 39 publications

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“…It is interesting if shorter RNAs with mismatched duplex, such as PV5-D2 and -D4, are recognized by proteaseprocessed TLR3 in mouse DCs or bone marrow-derived macrophages with different binding modes from intact TLR3 38 . Indeed, the cleaved form of TLR3 is predominant in mouse macrophages 39 , but less present in HEK293 cells 40 , which may explain the different TLR3 responses to these RNAs between mouse DCs/macrophages and human HEK293 cells (Fig. 7).…”

Section: Discussionmentioning

confidence: 99%

Toll-like receptor 3 recognizes incomplete stem structures in single-stranded viral RNA

et al. 2013

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Endosomal Toll-like receptor 3 (TLR3) serves as a sensor of viral infection and sterile tissue necrosis. Although TLR3 recognizes double-stranded RNA, little is known about structural features of virus-or host-derived RNAs that activate TLR3 in infection/inflammatory states. Here we demonstrate that poliovirus-derived single-stranded RNA segments harbouring stem structures with bulge/internal loops are potent TLR3 agonists. Functional poliovirus-RNAs are resistant to degradation and efficiently induce interferon-a/b and proinflammatory cytokines in human and mouse cells in a TLR3-dependent manner. The N-and C-terminal doublestranded RNA-binding sites of TLR3 are required for poliovirus-RNA-mediated TLR3 activation. Like polyriboinosinic:polyribocytidylic acid, a synthetic double-stranded RNA, these RNAs are internalized into cells via raftlin-mediated endocytosis and colocalized with TLR3. Raftlin-associated RNA uptake machinery and the TLR3 RNA-sensing system appear to recognize an appropriate topology of multiple RNA duplexes in poliovirus-RNAs. Hence, TLR3 is a sensor of extracellular viral/host RNA with stable stem structures derived from infection or inflammation-damaged cells.

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Section: Discussionmentioning

confidence: 99%

Toll-like receptor 3 recognizes incomplete stem structures in single-stranded viral RNA

et al. 2013

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“…Independently expressed TLR3N and TLR3C were associated with each other According to the previous reports (14,15), dsRNA sensing by TLR3C alone is still controversial. One report shows that TLR3C responds to dsRNA (15), whereas another report shows that TLR3C fails to respond to dsRNA (14).…”

Section: Pat3 Specifically Binds To Tlr3nmentioning

confidence: 99%

“…TLR3, a dsRNA sensor, is cleaved, but the precise cleavage site has been only suggested (13,14). TLR3N is suggested to be associated with TLR3C and required for dsRNA sensing (14,15). However, the direct evidence for TLR3N requirement in dsRNA sensing has not been shown.…”

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confidence: 98%

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Roles of the Cleaved N-Terminal TLR3 Fragment and Cell Surface TLR3 in Double-Stranded RNA Sensing

Murakami

Fukui

Motoi

et al. 2014

The Journal of Immunology

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TLR3 senses viral dsRNA in endolysosomes. The TLR3 ectodomain is cleaved by proteases such as cathepsins in endolysosomes. It remains controversial whether the N-terminal fragment of TLR3 ectodomain (TLR3N) is cleaved off or remains associated with the C-terminal TLR3 fragment (TLR3C). In addition to endosomes, TLR3 is reported to be expressed on the surface of human fibroblasts, but not of human monocyte-derived dendritic cells. Less is known about roles of TLR3N and cell surface TLR3 in dsRNA sensing. In this study, we show the cleavage site of the TLR3 ectodomain and cell surface expression of TLR3 on mouse primary immune cells. TLR3C, which started at 343S, was associated with TLR3N. Both TLR3N and TLR3C were required for activation of IFN-β and NF-κB promoters by dsRNA, demonstrating that dsRNA is sensed by the TLR3N+C complex. Newly established mAbs to mouse TLR3 revealed that cell surface TLR3 was highly expressed on splenic CD8+ dendritic cells and marginal zone B cells. Cell surface expression of TLR3 on these cells was dependent on the TLR-specific transporter Unc93B1. Although cell surface TLR3 was only weakly expressed on macrophages, TLR3 mAb specifically enhanced TLR3 responses to dsRNA. These results demonstrate that dsRNA is sensed by the TLR3N+C complex and that cell surface TLR3 is a promising target for modulating TLR3 responses.

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“…Functions attributed to cysteine cathepsins include cell death and inflammasome signaling (36), antigen presentation (37), collagen turnover in bone and cartilage (38), vascular remodeling (39) and neuropeptide and hormone processing (40). Interestingly, endosomal TLRs, including TLR3, 7 and 9 require cleavage that can involve cathepsins B, K and H for ligand recognition and activation (41)(42)(43)(44)(45)(46)(47)(48). In the setting of rheumatoid arthritis involving TLR4 (49), psoriasis-like lesions involving TLR7 (50) and collagen-induced arthritis involving TLR9 (51), cathepsins have been shown to influence disease.…”

Section: Discussionmentioning

confidence: 99%

The HIV Protease Inhibitor Saquinavir Inhibits HMGBl-Driven Inflammation by Targeting the Interaction of Cathepsin V with TLR4/MyD88

Pribis

Al‐Abed

Yang

et al. 2015

Mol Med

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Extracellular high-mobility group box 1 (HMGB1) (disulfide form), via activation of toll-like receptor 4 (TLR4)-dependent signaling, is a strong driver of pathologic inflammation in both acute and chronic conditions. Identification of selective inhibitors of HMGB1-TLR4 signaling could offer novel therapies that selectively target proximal endogenous activators of inflammation. A cell-based screening strategy led us to identify first generation HIV-protease inhibitors (PI) as potential inhibitors of HMGB1-TLR4 driven cytokine production. Here we report that the first-generation HIV-PI saquinavir (SQV), as well as a newly identified mammalian protease inhibitor STO33438 (334), potently block disulfide HMGB1-induced TLR4 activation, as assayed by the production of TNF-α by human monocyte-derived macrophages (THP-1). We further report on the identification of mammalian cathepsin V, a protease, as a novel target of these inhibitors. Cellular as well as recombinant protein studies show that the mechanism of action involves a direct interaction between cathepsin V with TLR4 and its adaptor protein MyD88. Treatment with SQV, 334 or the known cathepsin inhibitor SID26681509 (SID) significantly improved survival in murine models of sepsis and reduced liver damage following warm liver ischemia/reperfusion (I/R) models, both characterized by strong HMGB1-TLR4 driven pathology. The current study demonstrates a novel role for cathepsin V in TLR4 signaling and implicates cathepsin V as a novel target for first-generation HIV-PI compounds. The identification of cathepsin V as a target to block HMGB1-TLR4-driven inflammation could allow for a rapid transition of the discovery from the bench to the bedside. Disulfide HMGB1 drives pathologic inflammation in many models by activating signaling through TLR4. Cell-based screening identified the mammalian protease cathepsin V as a novel therapeutic target to inhibit TLR4-mediated inflammation induced by extracellular HMGB1 (disulfide form). We identified two protease inhibitors (PIs) that block cathepsin V and thereby inhibit disulfide HMGB1-induced TLR4 activation: saquinavir (SQV), a firstgeneration PI targeting viral HIV protease and STO33438 (334), targeting mammalian proteases. We discovered that cathepsin V binds TLR4 under basal and HMGB1-stimulated conditions, but dissociates in the presence of SQV over time. Thus cathepsin V is a novel target for first-generation HIV PIs and represents a potential therapeutic target of pathologic inflammation. teraction of the complex with the cognate receptor of the ligand-binding partner (3). Second, the redox status of the three cysteines (C23, C45 and C106) within HMGB1 determines both the efficiency of binding to other ligands as well as the specificity of HMGB1 for certain receptors (5). For example, when in the all-thiol configuration, HMGB1 binds to CXCL12 (SDF1) to amplify the activation of CXCR4 on immune and progenitor cells promoting chemotaxis. In contrast, under mild oxidizing conditions, C23 and C45 can form a disulfide bond an...

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Cleaved/Associated TLR3 Represents the Primary Form of the Signaling Receptor

Cited by 57 publications

References 39 publications

Toll-like receptor 3 recognizes incomplete stem structures in single-stranded viral RNA

Toll-like receptor 3 recognizes incomplete stem structures in single-stranded viral RNA

Roles of the Cleaved N-Terminal TLR3 Fragment and Cell Surface TLR3 in Double-Stranded RNA Sensing

The HIV Protease Inhibitor Saquinavir Inhibits HMGBl-Driven Inflammation by Targeting the Interaction of Cathepsin V with TLR4/MyD88

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