TLR9 Is Localized in the Endoplasmic Reticulum Prior to Stimulation

Leifer, Cynthia A.; Kennedy, Margaret; Mazzoni, Alessandra; Lee, ChangWoo; Kruhlak, Michael J.; Segal, David M.

doi:10.4049/jimmunol.173.2.1179

Cited by 306 publications

(265 citation statements)

References 25 publications

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“…Members of the TLR9 subfamily (TLR7-TLR9) are expressed at the endosome (reviewed in Ref. 12), presumably upon translocation from ER during biogenesis of the phagoendosome (14,15). It follows that translocation to the phagoendosome allows CpG-OVA complex to enter a crossroad organelle at which competence for cross-presentation meets competence for cross-priming.…”

Section: Discussionmentioning

confidence: 99%

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Protective CD8 T Cell Immunity Triggered by CpG-Protein Conjugates Competes with the Efficacy of Live Vaccines

Heit

Schmitz

O’Keeffe

et al. 2005

The Journal of Immunology

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In contrast to infectious (live) vaccines are those based on subunit Ag that are notoriously poor in eliciting protective CD8 T cell responses, presumably because subunit Ags become insufficiently cross-presented by dendritic cells (DCs) and because the latter need to be activated to acquire competence for cross-priming. In this study, we show that CpG-Ag complexes overcome these limitations. OVA covalently linked to CpG-DNA (CpG-OVA complex), once it is efficiently internalized by DCs via DNA receptor-mediated endocytosis, is translocated to lysosomal-associated membrane protein 1 (LAMP-1)-positive endosomal-lysosomal compartments recently shown to display competence for cross-presentation. In parallel, CpG-OVA complex loaded DCs become activated and acquire characteristics of professional APCs. In vivo, a single s.c. dose of CpG-OVA complex (10 μg of protein) induces primary and secondary clonal expansion/contraction of Ag-specific CD8 T cells similar in kinetics to live vaccines; examples including Listeria monocytogenes genetically engineered to produce OVA (LM-OVA) and two viral vector-based OVA vaccines analyzed. Interestingly, CpG-OVA complex induced almost equal percentages of Ag-specific memory CD8 T cells as did infection with LM-OVA. A single dose vaccination with CpG-OVA complex protected mice against lethal doses of LM-OVA. These data underscore that the synergy imparted by CpG-OVA complex-mediated combined triggering of innate and specific immunity might be key to initiate CD8 T cell-based immunoprotection by synthetic vaccines based on subunit Ag.

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Section: Discussionmentioning

confidence: 99%

“…TLRs are expressed either at the cell membrane (TLR1, 2, 4, 5, and 6) or at the phagoendosome (TLR3, 7, 8, 9) (reviewed in Ref. 12), presumably upon translocation from the ER (14,15). Specifically, TLR9 recognizes at the phagoendosome immunostimulatory CpG-DNA, a process known to lead to maturation of immature DCs into professional APCs (16).…”

mentioning

confidence: 99%

Protective CD8 T Cell Immunity Triggered by CpG-Protein Conjugates Competes with the Efficacy of Live Vaccines

Heit

Schmitz

O’Keeffe

et al. 2005

The Journal of Immunology

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“…Both CpG-A and CpG-B have been shown to activate PDC via TLR9 [23]. Upon phagocytosis PDC lyse microorganisms in phagolysosomes, where microbial DNA interacts with and activates TLR9 derived from the endoplasmic reticulum [24]. TLR9 activation leads to recruitment of the MyD88 adaptor protein and phosphorylation of the IL-1R-associated kinase (IRAK).…”

Section: Introductionmentioning

confidence: 99%

Requirement of HMGB1 and RAGE for the maturation of human plasmacytoid dendritic cells

et al. 2005

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Dendritic cells (DC) are key components of innate and adaptive immune responses. Plasmacytoid DC (PDC) are a specialized DC subset that produce high amounts of type I interferons in response to microbes. High mobility group box 1 protein (HMGB1) is an abundant nuclear protein, which acts as a potent pro-inflammatory factor when released extracellularly. We show that HMGB1 leaves the nucleus of maturing PDC following TLR9 activation, and that PDC express on the plasma membrane the bestcharacterized receptor for HMGB1, RAGE. Maturation and type I IFN secretion of PDC is hindered when the HMGB1/RAGE pathway is disrupted. These results reveal HMGB1 and RAGE as the first known autocrine loop modulating the maturation of PDC, and suggest that antagonists of HMGB1/RAGE might have therapeutic potential for the treatment of systemic human diseases. IntroductionDendritic cells (DC) are potent antigen-presenting cells bridging the innate and adaptive immune responses. To date, two subsets of DC have been identified in humans: myeloid DC and plasmacytoid DC (PDC), the latter also referred to as type I interferon (IFN-a)-producing cells [1][2][3][4][5][6]. PDC recognize viral or bacterial DNA patterns, consisting of unmethylated CpG motifs in the context of species-dependent surrounding sequences (CpG) [7]. As a consequence they produce, within a few hours, large amounts of . Based on their ability to induce IFN-a secretion by PDC, two types of CpG have been described: CpG 2216 (CpG-A), which induces high amounts of IFN-a, and CpG 2006 (CpG-B), which promotes survival, maturation and migration of PDC to the lymph nodes, but induces lower amounts of . PDC sustain the priming of naive T cells and their differentiation into Th1/Th2 effectors [15][16][17] or into regulatory T cells [16,[18][19][20][21][22].Recent studies shed light on the events involved in the recognition of microbial DNA by human PDC, the only subset of human DC that expresses the Toll-like receptor 9 (TLR9) [12]. Both CpG-A and CpG-B have been shown to activate PDC via TLR9 [23]. Upon phagocytosis PDC lyse microorganisms in phagolysosomes, where microbial DNA interacts with and activates TLR9 derived from the endoplasmic reticulum [24]. TLR9 activation leads to recruitment of the MyD88 adaptor protein and phosphorylation of the IL-1R-associated kinase (IRAK). Phosphorylated IRAK associates with the adaptor molecule TNF-associated factor 6 (TRAF6) [25]. Two separate signaling pathways, JNK and NF-jB, are then activated, promoting PDC maturation and survival. IFN-a induction, an event exclusively occurring in PDC, depends on the formation of a complex consisting of MyD88, TRAF6 and the IRF7 transcription factor, as well as on TRAF6-dependent ubiquitination [26].The events that determine the outcome of the interaction of PDC with T cells, and in particular the induction of effector or regulatory immune responses, are poorly characterized. Environmental signals that Here we report that HMGB1 is exported from the nucleus of PDC upon selective engagement of TLR9 an...

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“…Thus, in basal conditions the receptors are located in the endoplasmic reticulum (ER) and translocate to endocytic vesicles only after cell stimulation by TLR ligands. Although all intracellular TLRs reside in the ER 2,3 , the trafficking pathways that move the receptors into the endocytic pathway show considerable variation among intracellular TLRs [4][5][6] . For example, TLR7 traffics from Golgi stacks directly to endosomes using the clathrin adaptor AP4, whereas the TLR9 is directed to the cell surface and reaches the endosomes via AP2-mediated clathrin-dependent endocytosis 6 .…”

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confidence: 99%

IRAP+ endosomes restrict TLR9 activation and signaling

et al. 2017

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Retention of intracellular Toll-Like Receptors (TLRs) in the endoplasmic reticulum prevents their activation under basal conditions. TLR9 is activated by sensing ligands in specific endosomal/lysosomal compartments. Here, we describe the identification of insulin responsive aminopeptidase (IRAP) endosomes as major cellular compartments for the early steps of TLR9 activation in dendritic cells (DCs). Both TLR9 and its ligand CpG were found as cargo in IRAP endosomes. In the absence of IRAP, CpG and TLR9 trafficking to lysosomes and TLR9 signaling were enhanced in DCs and in mice following bacterial infection. IRAP stabilized CpG-containing endosomes by interacting with the actin nucleation factor FHOD4, slowing down TLR9 trafficking towards lysosomes. Thus, endosome retention of TLR9 via IRAP interaction with the actin cytoskeleton is a mechanism that prevents TLR9hyper-activation in DCs. discriminate between different classes of microbial products and initiate specific signaling cascades. While microbial products with no equivalent in mammalian cells, such as the components of the bacterial wall, are recognized by surface TLRs (1, 2, 4, 5 and 6), pathogen derived nucleic acids are sensed by intracellular TLRs (3,7, 8 and 9). Recognition of nucleic acids by intracellular TLRs has the potential to trigger autoimmune diseases through interaction with self nucleic acids 1 . To avoid inappropriate activation of endosomal TLRs, their trafficking is tightly controlled. Thus, in basal conditions the receptors are located in the endoplasmic reticulum (ER) and translocate to endocytic vesicles only after cell stimulation by TLR ligands. Although all intracellular TLRs reside in the ER 2,3 , the trafficking pathways that move the receptors into the endocytic pathway show considerable variation among intracellular TLRs 4-6 . For example, TLR7 traffics from Golgi stacks directly to endosomes using the clathrin adaptor AP4, whereas the TLR9 is directed to the cell surface and reaches the endosomes via AP2-mediated clathrin-dependent endocytosis 6 .In addition to the transfer into the endocytic pathway, a second step that controls the activation of endosomal TLRs is their partial proteolysis by an array of different proteases, specific for each TLR 5,7-12 .Although less often mentioned, the intracellular trafficking of its ligand also controls the activation of TLR9. TLR9 ligands (CpG) are internalized via clathrin-mediated endocytosis in early endosomes and translocate to late LAMP + compartments 2 . TLR9 activation depends on CpG localization, since the abrogation of CpG translocation to LAMP + compartments by specific inhibitors decreased TLR9 signaling 13,14 . Thus, the intracellular trafficking of both, the ligand and the receptor are essential for the control of TLR9 activation. RESULTS IRAP deletion increases TLR9 responseTo address the role of IRAP in TLRs signaling, wild-type and IRAP-deficient bone marrow derived dendritic cells (BMDCs) were stimulated with specific TLR ligands: polyIC for TLR3, Imiquimod fo...

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TLR9 Is Localized in the Endoplasmic Reticulum Prior to Stimulation

Cited by 306 publications

References 25 publications

Protective CD8 T Cell Immunity Triggered by CpG-Protein Conjugates Competes with the Efficacy of Live Vaccines

Protective CD8 T Cell Immunity Triggered by CpG-Protein Conjugates Competes with the Efficacy of Live Vaccines

Requirement of HMGB1 and RAGE for the maturation of human plasmacytoid dendritic cells

IRAP+ endosomes restrict TLR9 activation and signaling

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