title: Roles of the cleaved N-terminal TLR3 fragment and cell surface TLR3 in double-stranded RNA sensing.
abstract: 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.
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Murakami
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Fukui
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Motoi
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Kanno
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Takuma
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Tanimura
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and.
authors.forename: Shin-ichiroh
authors.initials: S
authors.lastname: Saitoh
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; and Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan kmiyake@ims.u-tokyo.ac.jp.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Miyake
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D011992:Endosomes / Q000276:immunology / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D005786:Gene Expression Regulation; D016899:Interferon-beta / Q000235:genetics / Q000276:immunology*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000276:immunology*; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012330:RNA, Double-Stranded / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology / Q000276:immunology; D051196:Toll-Like Receptor 3 / Q000235:genetics / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D026901:Membrane Transport Proteins; D016328:NF-kappa B; D012330:RNA, Double-Stranded; C519703:TLR3 protein, mouse; D051196:Toll-Like Receptor 3; C512254:UNC93B1 protein, mouse; D016899:Interferon-beta