Park, B. et al. Proteolytic cleavage in an endolysosomal compartment is required for activation of Toll-like receptor 9. Nat. Immunol. 9, 1407-1414

Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02115, USA.
Nature Immunology (Impact Factor: 20). 11/2008; 9(12):1407-14. DOI: 10.1038/ni.1669
Source: PubMed


Toll-like receptors (TLRs) activate the innate immune system in response to pathogens. Here we show that TLR9 proteolytic cleavage is a prerequisite for TLR9 signaling. Inhibition of lysosomal proteolysis rendered TLR9 inactive. The carboxy-terminal fragment of TLR9 thus generated included a portion of the TLR9 ectodomain, as well as the transmembrane and cytoplasmic domains. This cleavage fragment bound to the TLR9 ligand CpG DNA and, when expressed in Tlr9(-/-) dendritic cells, restored CpG DNA-induced cytokine production. Although cathepsin L generated the requisite TLR9 cleavage products in a cell-free in vitro system, several proteases influenced TLR9 cleavage in intact cells. Lysosomal proteolysis thus contributes to innate immunity by facilitating specific cleavage of TLR9.

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Available from: Melanie Brinkmann, Sep 29, 2015
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    • "Addition of inhibitors of endosomal acidification such chloroquine or the proton pump inhibitor bafilomycin A1 prevents activation of endosomal TLR signaling (De Bouteiller et al., 2005; Gibbard et al., 2006; Lee et al., 2003; Rutz et al., 2004). This pH sensitive process involves activation of proteases within the endosome which cleave TLRs 3, 7, 8 and 9 causing a truncation of the N terminal domain within the LRRs (Ewald et al., 2011; Ishii et al., 2014; Park et al., 2008). Intriguingly, the cleaved C-terminal portion and the main part of the receptor appear to remain associated with both portions participating in ligand binding (Kanno et al., 2013; Murakami et al., 2014; Onji et al., 2013; Tanji et al., 2013). "
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    ABSTRACT: As we learn more about the biology of the Toll-like receptors (TLRs), a wide range of molecules that can activate this fascinating family of pattern recognition receptors emerges. In addition to conserved pathogenic components, endogenous danger signals created upon tissue damage are also sensed by TLRs. Detection of these types of stimuli results in TLR mediated inflammation that is vital to fight pathogenic invasion and drive tissue repair. Aberrant activation of TLRs by pathogenic and endogenous ligands has also been linked with the pathogenesis of an increasing number of infectious and autoimmune diseases, respectively. Most recently, allergen activation of TLRs has also been described, creating a third broad class of TLR stimulus that has helped to shed light on the pathogenesis of allergic disease. To date, microbial activation of TLRs remains best characterized. Each member of the TLR family senses a specific subset of pathogenic ligands, pathogen associated molecular patterns (PAMPS), and a wealth of structural and biochemical data continues to reveal the molecular mechanisms of TLR activation by PAMPs, and to demonstrate how receptor specificity is achieved. In contrast, the mechanisms by which endogenous molecules and allergens activate TLRs remain much more mysterious. Here, we provide an overview of our current knowledge of how very diverse stimuli activate the same TLRs and the structural basis of these modes of immunity.
    Critical Reviews in Biochemistry and Molecular Biology 04/2015; DOI:10.3109/10409238.2015.1033511 · 7.71 Impact Factor
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    • "In addition to being regulated by UNC93B1 trafficking, TLR3, 7, 8, and 9 need to be cleaved by various proteases such as cathepsins, asparagine endopeptidase, and furin-like proprotein convertases (Ewald et al., 2008, 2011; Park et al., 2008; Sepulveda et al., 2009; Garcia-Cattaneo et al., 2012; Maschalidi et al., 2012; Hipp et al., 2013). The proteolysis occurs as the TLRs are transported through acidic endosomal compartments where these enzymes are active. "
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    ABSTRACT: To prevent the spread of infection, an invading pathogen must first be recognized by the innate immune system. Host pattern recognition receptors detect distinct pathogen-associated molecules and induce the transcription and release of interferon and inflammatory molecules to resolve infection. Unlike infections with pathogens that replicate autonomously from the host, viral infections blur the boundaries of self and non-self. Differentiation of host from virus is achieved by restricting localization of host nucleic acids and by placing pattern recognition receptors in specific subcellular compartments. Within this review, we discuss how several families of pattern recognition receptors act to provide a comprehensive surveillance network that has the potential to induce interferon expression in response to any viral infection. Copyright © 2015 Elsevier Inc. All rights reserved.
    Virology 03/2015; 479-480. DOI:10.1016/j.virol.2015.02.051 · 3.32 Impact Factor
    • "Furthermore, for TLRs located in the lysosomal compartments of macrophages, an acidic pH is critical for optimal function. For example, TLR9, the receptor for bacterial DNA, requires an acidic environment to facilitate the release of a Cterminal fragment, via cathepsin L cleavage, which enhances the production of the pro-inflammatory cytokine, tumour necrosis factor (TNF) (Ewald et al., 2008; Park et al., 2008). Similarly, cleavage of TLR3, by lysosomal cathepsins B and H, appears to be essential for its signalling (Garcia-Cattaneo et al., 2012). "
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    ABSTRACT: Parasitic worms (helminths) reside in their mammalian hosts for many years. This is attributable, in part, to their ability to skew the host's immune system away from pro-inflammatory responses and towards anti-inflammatory or regulatory responses. This immune modulatory ability ensures helminth longevity within the host, while simultaneously minimises tissue destruction for the host. The molecules that the parasite releases clearly exert potent immune-modulatory actions, which could be exploited clinically, for example in the prophylactic and therapeutic treatment of pro-inflammatory and autoimmune diseases. We have identified a novel family of immune-modulatory proteins, termed helminth defense molecules (HDMs), which are secreted by several medically important helminth parasites. These HDMs share biochemical and structural characteristics with mammalian cathelicidin-like host defense peptides (HDPs), which are significant components of the innate immune system. Like their mammalian counterparts, parasite HDMs block the activation of macrophages via toll like receptor (TLR) 4 signaling, however HDMs are significantly less cytotoxic than HDPs. HDMs can traverse the cell membrane of macrophages and enter the endolysosomal system where they reduce the acidification of lysosomal compartments by inhibiting vacuolar (v)-ATPase activity. In doing this, HDMs can modulate critical cellular functions, such as cytokine secretion and antigen processing/presentation. Here, we review the role of macrophages, specifically their lysosomal mediated activities, in the initiation and perpetuation of pro-inflammatory immune responses. We also discuss the potential of helminth defense molecules (HDMs) as therapeutics to counteract the pro-inflammatory responses underlying autoimmune disease. Given the current lack of effective, non-cytotoxic treatment options to limit the progression of autoimmune pathologies, HDMs open novel treatment avenues.
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