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Kondo T, Okawa H, Hokugo A, Shokeen B, Sundberg O, Zheng Y, McKenna CE, Lux R, Nishimura I. Oral microbial extracellular DNA initiates periodontitis through gingival degradation by fibroblast-derived cathepsin K in mice. Commun Biol 2022; 5:962. [PMID: 36104423 PMCID: PMC9474870 DOI: 10.1038/s42003-022-03896-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2022] [Accepted: 08/25/2022] [Indexed: 11/11/2022] Open
Abstract
Periodontitis is a highly prevalent disease leading to uncontrolled osteoclastic jawbone resorption and ultimately edentulism; however, the disease onset mechanism has not been fully elucidated. Here we propose a mechanism for initial pathology based on results obtained using a recently developed Osteoadsorptive Fluogenic Sentinel (OFS) probe that emits a fluorescent signal triggered by cathepsin K (Ctsk) activity. In a ligature-induced mouse model of periodontitis, a strong OFS signal is observed before the establishment of chronic inflammation and bone resorption. Single cell RNA sequencing shows gingival fibroblasts to be the primary cellular source of early Ctsk. The in vivo OFS signal is activated when Toll-Like Receptor 9 (TLR9) ligand or oral biofilm extracellular DNA (eDNA) is topically applied to the mouse palatal gingiva. This previously unrecognized interaction between oral microbial eDNA and Ctsk of gingival fibroblasts provides a pathological mechanism for disease initiation and a strategic basis for early diagnosis and treatment of periodontitis.
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Affiliation(s)
- Takeru Kondo
- Weintraub Center for Reconstructive Biotechnology, Division of Regenerative & Reconstructive Sciences, UCLA School of Dentistry, Los Angeles, CA, 90095, USA
- Division of Molecular and Regenerative Prosthodontics, Tohoku University Graduate School of Dentistry, Sendai, Miyagi, 980-8575, Japan
| | - Hiroko Okawa
- Weintraub Center for Reconstructive Biotechnology, Division of Regenerative & Reconstructive Sciences, UCLA School of Dentistry, Los Angeles, CA, 90095, USA
- Division of Molecular and Regenerative Prosthodontics, Tohoku University Graduate School of Dentistry, Sendai, Miyagi, 980-8575, Japan
| | - Akishige Hokugo
- Weintraub Center for Reconstructive Biotechnology, Division of Regenerative & Reconstructive Sciences, UCLA School of Dentistry, Los Angeles, CA, 90095, USA
- Regenerative Bioengineering and Repair Laboratory, Division of Plastic and Reconstructive Surgery, Department of Surgery, David Geffen School of Medicine at UCLA, Los Angeles, CA, 90095, USA
| | - Bhumika Shokeen
- Section of Biosystems and Function, UCLA School of Dentistry, Los Angeles, CA, 90095, USA
| | - Oskar Sundberg
- Department of Chemistry, Dana and David Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Yiying Zheng
- Department of Chemistry, Dana and David Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Charles E McKenna
- Department of Chemistry, Dana and David Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Renate Lux
- Section of Biosystems and Function, UCLA School of Dentistry, Los Angeles, CA, 90095, USA
| | - Ichiro Nishimura
- Weintraub Center for Reconstructive Biotechnology, Division of Regenerative & Reconstructive Sciences, UCLA School of Dentistry, Los Angeles, CA, 90095, USA.
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2
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Mielcarska MB, Gregorczyk-Zboroch KP, Szulc-Da̧browska L, Bossowska-Nowicka M, Wyżewski Z, Cymerys J, Chodkowski M, Kiełbik P, Godlewski MM, Gieryńska M, Toka FN. Participation of Endosomes in Toll-Like Receptor 3 Transportation Pathway in Murine Astrocytes. Front Cell Neurosci 2020; 14:544612. [PMID: 33281554 PMCID: PMC7705377 DOI: 10.3389/fncel.2020.544612] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 10/26/2020] [Indexed: 12/25/2022] Open
Abstract
TLR3 provides immediate type I IFN response following entry of stimulatory PAMPs into the CNS, as it is in HSV infection. The receptor plays a vital role in astrocytes, contributing to rapid infection sensing and suppression of viral replication, precluding the spread of virus beyond neurons. The route of TLR3 mobilization culminating in the receptor activation remains unexplained. In this research, we investigated the involvement of various types of endosomes in the regulation of the TLR3 mobility in C8-D1A murine astrocyte cell line. TLR3 was transported rapidly to early EEA1-positive endosomes as well as LAMP1-lysosomes following stimulation with the poly(I:C). Later, TLR3 largely associated with late Rab7-positive endosomes. Twenty-four hours after stimulation, TLR3 co-localized with LAMP1 abundantly in lysosomes of astrocytes. TLR3 interacted with poly(I:C) intracellularly from 1 min to 8 h following cell stimulation. We detected TLR3 on the surface of astrocytes indicating constitutive expression, which increased after poly(I:C) stimulation. Our findings contribute to the understanding of cellular modulation of TLR3 trafficking. Detailed analysis of the TLR3 transportation pathway is an important component in disclosing the fate of the receptor in HSV-infected CNS and may help in the search for rationale therapeutics to control the replication of neuropathic viruses.
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Affiliation(s)
- Matylda B Mielcarska
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Karolina P Gregorczyk-Zboroch
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Lidia Szulc-Da̧browska
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Magdalena Bossowska-Nowicka
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Zbigniew Wyżewski
- Institute of Biological Sciences, Cardinal Stefan Wyszynski University in Warsaw, Warsaw, Poland
| | - Joanna Cymerys
- Division of Microbiology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Marcin Chodkowski
- Division of Microbiology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Paula Kiełbik
- Division of Physiology, Department of Physiological Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Michał M Godlewski
- Division of Physiology, Department of Physiological Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Małgorzata Gieryńska
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland
| | - Felix N Toka
- Division of Immunology, Department of Preclinical Sciences, Institute of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland.,Center for Integrative Mammalian Research, Department of Biomedical Sciences, Ross University School of Veterinary Medicine, Basseterre, Saint Kitts and Nevis
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3
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Karapetyan L, Luke JJ, Davar D. Toll-Like Receptor 9 Agonists in Cancer. Onco Targets Ther 2020; 13:10039-10060. [PMID: 33116588 PMCID: PMC7553670 DOI: 10.2147/ott.s247050] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 08/16/2020] [Indexed: 12/19/2022] Open
Abstract
Toll-like receptor 9 (TLR9) is a pattern recognition receptor that is predominantly located intracellularly in immune cells, including dendritic cells, macrophages, natural killer cells, and other antigen-presenting cells (APC). The primary ligands for TLR9 receptors are unmethylated cytidine phosphate guanosine (CpG) oligodinucleotides (ODN). TLR9 agonists induce inflammatory processes that result in the enhanced uptake and killing of microorganisms and cancer cells as well as the generation of adaptive immune responses. Preclinical studies of TLR9 agonists suggested efficacy both as monotherapy and in combination with several agents, which led to clinical trials in patients with advanced cancer. In these studies, intravenous, intratumoral, and subcutaneous routes of administration have been tested; with anti-tumor responses in both treated and untreated metastatic sites. TLR9 agonist monotherapy is safe, although efficacy is minimal in advanced cancer patients; conversely, combinations appear to be more promising. Several ongoing phase I and II clinical trials are evaluating TLR9 agonists in combination with a variety of agents including chemotherapy, radiotherapy, targeted therapy, and immunotherapy agents. In this review article, we describe the distribution, structure and signaling of TLR9; discuss the results of preclinical studies of TLR9 agonists; and review ongoing clinical trials of TLR9 agonists singly and in combination in patients with advanced solid tumors.
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Affiliation(s)
- Lilit Karapetyan
- University of Pittsburgh Medical Center (UPMC) Hillman Cancer Center (HCC), Pittsburgh, PA, USA
| | - Jason J Luke
- University of Pittsburgh Medical Center (UPMC) Hillman Cancer Center (HCC), Pittsburgh, PA, USA.,Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Diwakar Davar
- University of Pittsburgh Medical Center (UPMC) Hillman Cancer Center (HCC), Pittsburgh, PA, USA.,Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
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4
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Gruber E, Heyward C, Cameron J, Leifer C. Toll-like receptor signaling in macrophages is regulated by extracellular substrate stiffness and Rho-associated coiled-coil kinase (ROCK1/2). Int Immunol 2019; 30:267-278. [PMID: 29800294 DOI: 10.1093/intimm/dxy027] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 04/04/2018] [Indexed: 02/07/2023] Open
Abstract
Macrophages participate in immunity, tissue repair and tissue homeostasis. Activation of Toll-like receptors (TLRs) by conserved exogenous or endogenous structures initiates signaling cascades that result in the release of cytokines such as tumor necrosis factor α (TNFα). Extracellular substrate stiffness is known to regulate functions of non-immune cells through a process called mechanotransduction, yet less is known about how physical cues affect macrophage function or TLR signaling. To investigate this question, we cultured murine primary bone marrow-derived macrophages (BMMs) and RAW264.7 cells on fibronectin-coated polyacrylamide (PA) gels of defined stiffnesses (1, 20 and 150 kPa) that approximate the physical properties of physiologic tissues. BMMs on all gels were smaller and more circular than those on rigid glass. Macrophages on intermediate stiffness 20 kPa PA gels were slightly larger and less circular than those on either 1 or 150 kPa. Secretion of the pro-inflammatory cytokine, TNFα, in response to stimulation of TLR4 and TLR9 was increased in macrophages grown on soft gels versus more rigid gels, particularly for BMMs. Inhibition of the rho-associated coiled-coil kinase 1/2 (ROCK1/2), key mediators in cell contractility and mechanotransduction, enhanced release of TNFα in response to stimulation of TLR4. ROCK1/2 inhibition enhanced phosphorylation of the TLR downstream signaling molecules, p38, ERK1/2 and NFκB. Our data indicate that physical cues from the extracellular environment regulate macrophage morphology and TLR signaling. These findings have important implications in the regulation of macrophage function in diseased tissues and offer a novel pharmacological target for the manipulation of macrophage function in vivo.
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Affiliation(s)
- Erika Gruber
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Christa Heyward
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Jody Cameron
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Cynthia Leifer
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
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5
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Biswas C, Rao S, Slade K, Hyman D, Dersh D, Mantegazza AR, Zoltick PW, Marks MS, Argon Y, Behrens EM. Tyrosine 870 of TLR9 is critical for receptor maturation rather than phosphorylation-dependent ligand-induced signaling. PLoS One 2018; 13:e0200913. [PMID: 30024926 PMCID: PMC6053202 DOI: 10.1371/journal.pone.0200913] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 07/04/2018] [Indexed: 11/21/2022] Open
Abstract
Toll like receptors (TLRs) share a conserved structure comprising the N-terminal ectodomain, a transmembrane segment and a C-terminal cytoplasmic Toll/IL-1 receptor (TIR) domain. Proper assembly of the TIR domain is crucial for signal transduction; however, the contribution of individual motifs within the TIR domain to TLR trafficking and signaling remains unclear. We targeted a highly conserved tyrosine (Y870) located in the box 1 region of the TIR domain of most TLRs, including TLR9, previously described to be a critical site of phosphorylation in TLR4. We reconstituted bone marrow-derived dendritic cells (BMDC) from Tlr9-/- mice WT TLR9 or Y870F or Y870A mutants. Despite normal interactions with the luminal chaperones GRP94 and UNC93B1, Y870F conferred only partial responsiveness to CpG, and Y870A had no activity and functioned as a dominant negative inhibitor when coexpressed with endogenous TLR9. This loss of function correlated with reduction or absence, respectively, of the 80 kDa mature form of TLR9. In Y870F-expressing cells, CpG-dependent signaling correlated directly with levels of the mature form, suggesting that signaling did not require tyrosine phosphorylation but rather that the Y870F mutation conferred reduced receptor levels due to defective processing or trafficking. Microscopy revealed targeting of the mutant protein to an autophagolysosome-like structure for likely degradation. Collectively we postulate that the conserved Y870 in the TIR domain does not participate in phosphorylation-induced signaling downstream of ligand recognition, but rather is crucial for proper TIR assembly and ER egress, resulting in maturation-specific stabilization of TLR9 within endolysosomes and subsequent pro-inflammatory signaling.
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Affiliation(s)
- Chhanda Biswas
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - Sheila Rao
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - Katharine Slade
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - David Hyman
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - Devin Dersh
- Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States of America
| | - Adriana R. Mantegazza
- Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States of America
| | - Philip W. Zoltick
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - Michael S. Marks
- Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States of America
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Yair Argon
- Department of Pathology and Laboratory Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States of America
| | - Edward M. Behrens
- Division of Pediatric Rheumatology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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6
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Veleeparambil M, Poddar D, Abdulkhalek S, Kessler PM, Yamashita M, Chattopadhyay S, Sen GC. Constitutively Bound EGFR-Mediated Tyrosine Phosphorylation of TLR9 Is Required for Its Ability To Signal. THE JOURNAL OF IMMUNOLOGY 2018. [PMID: 29531172 DOI: 10.4049/jimmunol.1700691] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Mammalian TLRs recognize microbial infection or cell death-associated danger signals and trigger the appropriate cellular response. These responses determine the strength and the outcome of the host-microbe interaction. TLRs are transmembrane proteins located on the plasma or the endosomal membrane. Their ectodomains recognize specific microbial or endogenous ligands, and the cytoplasmic domains interact with specific proteins to activate intracellular signaling pathways. TLR9, an endosomal TLR, is activated by endocytosed DNA. Activated TLR9 recruits the cytoplasmic adapter MyD88 and other signaling proteins to induce the synthesis of inflammatory cytokines and IFN. Uncontrolled activation of TLR9 leads to the undesired overproduction of inflammatory cytokines and consequent pathogenesis. Therefore, appropriate activation and the regulation of TLR9 signaling are critical. Tyrosine (Tyr) phosphorylation of TLR9 is essential for its activation; however, the role of specific Tyr kinases is not clear. In this article, we report that epidermal growth factor receptor (EGFR), a membrane-bound protein Tyr kinase, is essential for TLR9 signaling. Genetic ablation of EGFR or pharmacological inhibition of its kinase activity attenuates TLR9-mediated induction of genes in myeloid and nonmyeloid cell types. EGFR is constitutively bound to TLR9; upon ligand stimulation, it mediates TLR9 Tyr phosphorylation, which leads to the recruitment of MyD88, activation of the signaling kinases and transcription factors, and gene induction. In mice, TLR9-mediated liver injury and death are blocked by an EGFR inhibitor or deletion of the EGFR gene from myeloid cells, which are the major producers of inflammatory cytokines.
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Affiliation(s)
- Manoj Veleeparambil
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Darshana Poddar
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Samar Abdulkhalek
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Patricia M Kessler
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Michifumi Yamashita
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Saurabh Chattopadhyay
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Ganes C Sen
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
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7
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Leifer CA. Dendritic cells in host response to biologic scaffolds. Semin Immunol 2017; 29:41-48. [PMID: 28214177 DOI: 10.1016/j.smim.2017.01.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 01/23/2017] [Accepted: 01/31/2017] [Indexed: 02/03/2023]
Abstract
Tissue regeneration and repair require a highly complex and orchestrated series of events that require inflammation, but can be compromised when inflammation is excessive or becomes chronic. Macrophages are one of the first cells to contact and respond to implanted materials, and mediate the inflammatory response. The series of events following macrophage association with biomaterials has been well-studied. Dendritic cells (DCs) also directly interact with biomaterials, are critical for specific immune responses, and can be activated in response to interactions with biomaterials. Yet, much less is known about the responses by DCs. This review discusses what we know about DC response to biomaterials, the underlying mechanisms involved, and how DCs can be influenced by the macrophage response to biomaterials. Lastly, I will discuss how biomaterials can be manipulated to enhance or suppress DC function to promote a specific desirable immune response - a major goal for implantable biologically active therapeutics.
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Affiliation(s)
- Cynthia A Leifer
- Department of Microbiology and Immunology College of Veterinary Medicine, C5-153 Cornell University, Ithaca, NY, USA.
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8
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Majer O, Liu B, Barton GM. Nucleic acid-sensing TLRs: trafficking and regulation. Curr Opin Immunol 2016; 44:26-33. [PMID: 27907816 DOI: 10.1016/j.coi.2016.10.003] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 10/28/2016] [Indexed: 12/11/2022]
Abstract
Toll-like receptors (TLRs) play an important role in innate immune responses against pathogenic microorganisms or tissue damage. Nucleic acid (NA)-sensing TLRs localize in intracellular vesicular compartments and recognize foreign-derived and host-derived nucleic acid ligands. Inappropriate activation of NA-sensing TLRs can cause pathogenic inflammation and autoimmunity. Multiple regulatory mechanisms exist to limit recognition of self-NAs. This review summarizes recent progress that has been made in understanding how NA-sensing TLRs are regulated via trafficking, proteolytic cleavage, as well as ligand processing and recognition.
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Affiliation(s)
- Olivia Majer
- Division of Immunology & Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, United States
| | - Bo Liu
- Division of Immunology & Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, United States
| | - Gregory M Barton
- Division of Immunology & Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, United States
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9
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Sinha SS, Cameron J, Brooks JC, Leifer CA. Complex Negative Regulation of TLR9 by Multiple Proteolytic Cleavage Events. THE JOURNAL OF IMMUNOLOGY 2016; 197:1343-52. [PMID: 27421483 DOI: 10.4049/jimmunol.1502357] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 06/14/2016] [Indexed: 11/19/2022]
Abstract
TLR9 is an innate immune receptor important for recognizing DNA of host and foreign origin. A mechanism proposed to prevent excessive response to host DNA is the requirement for proteolytic cleavage of TLR9 in endosomes to generate a mature form of the receptor (TLR9(471-1032)). We previously described another cleavage event in the juxtamembrane region of the ectodomain that generated a dominant-negative form of TLR9. Thus, there are at least two independent cleavage events that regulate TLR9. In this study, we investigated whether an N-terminal fragment of TLR9 could be responsible for regulation of the mature or negative-regulatory form. We show that TLR9(471-1032), corresponding to the proteolytically cleaved form, does not function on its own. Furthermore, activity is not rescued by coexpression of the N-terminal fragment (TLR9(1-440)), inclusion of the hinge region (TLR9(441-1032)), or overexpression of UNC93B1, the last of which is critical for trafficking and cleavage of TLR9. TLR9(1-440) coimmunoprecipitates with full-length TLR9 and TLR9(471-1032) but does not rescue the native glycosylation pattern; thus, inappropriate trafficking likely explains why TLR9(471-1032) is nonfunctional. Lastly, we show that TLR9(471-1032) is also a dominant-negative regulator of TLR9 signaling. Together, these data provide a new perspective on the complexity of TLR9 regulation by proteolytic cleavage and offer potential ways to inhibit activity through this receptor, which may dampen autoimmune inflammation.
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Affiliation(s)
- Siddhartha S Sinha
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853; and
| | - Jody Cameron
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853; and
| | - James C Brooks
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853; and Glycobia Inc., Ithaca, NY 14853
| | - Cynthia A Leifer
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853; and
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10
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Leifer CA, Medvedev AE. Molecular mechanisms of regulation of Toll-like receptor signaling. J Leukoc Biol 2016; 100:927-941. [PMID: 27343013 DOI: 10.1189/jlb.2mr0316-117rr] [Citation(s) in RCA: 184] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 06/01/2016] [Indexed: 01/22/2023] Open
Abstract
TLRs play a critical role in the detection of microbes and endogenous "alarmins" to initiate host defense, yet they can also contribute to the development and progression of inflammatory and autoimmune diseases. To avoid pathogenic inflammation, TLR signaling is subject to multilayer regulatory control mechanisms, including cooperation with coreceptors, post-translational modifications, cleavage, cellular trafficking, and interactions with negative regulators. Nucleic acid-sensing TLRs are particularly interesting in this regard, as they can both recognize host-derived structures and require internalization of their ligand as a result of intracellular sequestration of the nucleic acid-sensing TLRs. This review summarizes the regulatory mechanisms of TLRs, including regulation of their access to ligands, receptor folding, intracellular trafficking, and post-translational modifications, as well as how altered control mechanism could contribute to inflammatory and autoimmune disorders.
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Affiliation(s)
- Cynthia A Leifer
- Department of Microbiology and Immunology, Cornell University, Ithaca, New York, USA; and
| | - Andrei E Medvedev
- Department of Immunology, University of Connecticut Heath Center, Farmington, Connecticut, USA
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