Negative Self-Regulation of TLR9 Signaling by Its N-Terminal Proteolytic Cleavage Product

Lee, Sungwook; Kang, Dongju; A., Eun; Lee, Taeyun A.; Ploegh, Hidde L.; Park, Boyoun

doi:10.4049/jimmunol.1400210

Cited by 18 publications

(16 citation statements)

References 29 publications

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“…This proteolytic event generates a soluble form of the receptor that is capable of binding CpG DNA and inhibiting signaling through the full-length receptor. Additionally, when TLR9 1-440 was fused to a transmembrane domain, it acted as a dominant negative inhibitor of signaling (27). Thus, we next investigated whether the N-terminal fragment, without a transmembrane domain, could associate with full-length TLR9 and negatively regulate TLR9 signaling.…”

Section: Resultsmentioning

confidence: 99%

“…Thus it is interesting that two different studies obtained conflicting results regarding the function of the N-terminal fragment. Onji et al suggest it is required for signaling (32), while Lee et al suggested that the N-terminal fragment associates with full-length TLR9 and is a negative regulator (27). We have observed that our soluble TLR9 proteolytic fragment can be additionally cleaved to generate the same N-terminal fragment (data not shown and (26)).…”

Section: Discussionmentioning

confidence: 99%

“…This soluble ectodomain bound to CpG DNA ligand and was a negative regulator of signaling (26). Similarly, Lee and colleagues showed that attaching a transmembrane lysosomal targeting domain on an N-terminal fragment (LRR1-14) inhibited the ability of full-length TLR9 to signal (27). These data suggest that the cleavage events and their regulation are complex.…”

Section: Introductionmentioning

confidence: 99%

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Complex Negative Regulation of TLR9 by Multiple Proteolytic Cleavage Events

Sinha

Cameron

Brooks

et al. 2016

The Journal of Immunology

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Toll like receptor 9 (TLR9) is an innate immune receptor important for recognizing DNA, both 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 (TLR9471-1032). 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. Here we investigated whether an N-terminal fragment of TLR9 could be responsible for regulation of the mature- or negative regulatory-form. We show that TLR9471-1032, corresponding to the proteolytically cleaved form, does not function on its own. Furthermore, activity is not rescued by co-expression of the N-terminal fragment (TLR91-440), inclusion of the hinge region (TLR9441-1032) or overexpression of UNC93B1, the latter of which is critical for trafficking and cleavage of TLR9. TLR91-440 co-immunoprecipitates with full-length TLR9 and TLR9471-1032, but does not rescue the native glycosylation pattern, thus inappropriate trafficking likely explains why TLR9471-1032 is nonfunctional. Lastly, we show that TLR9471-1032 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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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Complex Negative Regulation of TLR9 by Multiple Proteolytic Cleavage Events

Sinha

Cameron

Brooks

et al. 2016

The Journal of Immunology

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“…In addition to its participation in ligand binding, the N‐terminal fragment of TLR9 might have an additional regulatory role . Lee et al .…”

Section: Proteolytic Processing Of the Extracellular Lrrsmentioning

confidence: 99%

“…In addition to its participation in ligand binding, the N-terminal fragment of TLR9 might have an additional regulatory role (80). Lee et al (80) fused the N-terminal fragment of TLR9 to its transmembrane domain and a cytosolic green fluorescent protein (GFP) in order to target the N-terminal part of TLR9 into the physiologically relevant compartment. Using this construct, the authors found that the presence of the N-terminal fragment induced pepstatin A-sensitive degradation of the C-terminal fragment.…”

Section: Cleavage Of Tlr9mentioning

confidence: 99%

Nucleic acid‐sensing TLRs and autoimmunity: novel insights from structural and cell biology

Pelka

Shibata

Miyake

et al. 2015

Immunological Reviews

104

116

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Invasion of pathogenic microorganisms or tissue damage activates innate immune signaling receptors that sample subcellular locations for foreign molecular structures, altered host molecules, or signs of compartment breaches. Upon engagement of innate immune receptors an acute but transient inflammatory response is initiated, aimed at the clearance of pathogens and cellular debris. Among the molecules that are sensed are nucleic acids, which activate several members of the transmembrane Toll-like receptor (TLR) family. Inappropriate recognition of nucleic acids by TLRs can cause inflammatory pathologies and autoimmunity. Here, we review the mechanisms involved in triggering nucleic acid-sensing TLRs and indicate checkpoints that restrict their activation to endolysosomal compartments. These mechanisms are crucial to sample the content of endosomes for nucleic acids in the context of infection or tissue damage, yet prevent accidental activation by host nucleic acids under physiological conditions. Decoding the molecular mechanisms that regulate nucleic acid recognition by TLRs is central to understand pathologies linked to unrestricted nucleic acid sensing and to develop novel therapeutic strategies.

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Below the surface: The inner lives of TLR4 and TLR9

Marongiu

Gornati

Artuso

et al. 2019

Journal of Leukocyte Biology

108

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TLRs are a class of pattern recognition receptors (PRRs) that detect invading microbes by recognizing pathogen-associated molecular patterns (PAMPs). Upon PAMP engagement, TLRs activate a signaling cascade that leads to the production of inflammatory mediators. The localization of TLRs, either on the plasma membrane or in the endolysosomal compartment, has been considered to be a fundamental aspect to determine to which ligands the receptors bind, and which transduction pathways are induced. However, new observations have challenged this view by identifying complex trafficking events that occur upon TLR-ligand binding. These findings have highlighted the central role that endocytosis and receptor trafficking play in the regulation of the innate immune response. Here, we review the TLR4 and TLR9 transduction pathways and the importance of their different subcellular localization during the inflammatory response. Finally, we discuss the implications of TLR9 subcellular localization in autoimmunity.

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Negative Self-Regulation of TLR9 Signaling by Its N-Terminal Proteolytic Cleavage Product

Cited by 18 publications

References 29 publications

Complex Negative Regulation of TLR9 by Multiple Proteolytic Cleavage Events

Complex Negative Regulation of TLR9 by Multiple Proteolytic Cleavage Events

Nucleic acid‐sensing TLRs and autoimmunity: novel insights from structural and cell biology

Below the surface: The inner lives of TLR4 and TLR9

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