Guanosine and its modified derivatives are endogenous ligands for TLR7.
Toll-like receptor (TLR) 7and 8 were considered to recognize single-strand RNA (ssRNA) from viruses. Although these receptors also respond to synthetic small chemical ligands, such as CL075 and R848, it remains to be determined whether these receptors sense natural small molecules or not. In the structure of human TLR8 (huTLR8) with ssRNA, there are two ligand-binding sites: one binds a uridine and the other binds an oligoribonucleotide (ORN). This finding demonstrates that huTLR8 recognizes degradation products of ssRNA, suggesting the presence of natural small ligands. We here show that TLR7 works as the sensor for guanosine (G)/2'-deoxyguanosine (dG) in the presence of ORN where ORN strengthens TLR7 interaction with G/dG. In addition, modified nucleosides such as 7-methylguanosine, 8-hydroxyguanosine (8-OHG) and 8-hydroxydeoxyguanosine (8-OHdG) activated TLR7 with ORNs. Importantly, 8-OHdG-a well-known oxidative DNA damage marker with unknown function-induced strong cytokine production comparable to G and dG both in mouse and human immune cells. Although 8-OHdG bound TLR7/ORN with lower affinity than dG did in isothermal titration calorimetry, administered 8-OHdG was metabolically more stable than dG in the serum, indicating that 8-OHdG acts on TLR7 as an endogenous ligand in vivo To address a role of G analogs in the disease state, we also examined macrophages from Unc93b1 (D34A/D34A) mice, which suffer from TLR7-dependent systemic inflammation, and found that Unc93b1 (D34A/D34A) macrophages showed significantly enhanced response to G alone or 8-OHdG with ORN. In conclusion, our results provide evidence that G, dG, 8-OHG and 8-OHdG are novel endogenous ligands for TLR7.
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan CREST, Japan Science and Technology agency, 4-1-8, Honcho, Kawaguchi-shi, Saitama 332-0012, Japan.
Takuma
T
Shibata
Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Umeharu
U
Ohto
First Department of Internal Medicine, Kansai Medical University, Osaka 573-1010, Japan.
Shosaku
S
Nomura
First Department of Internal Medicine, Kansai Medical University, Osaka 573-1010, Japan.
Kayoko
K
Kibata
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan.
Yuji
Y
Motoi
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan.
Yan
Y
Zhang
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan.
Yusuke
Y
Murakami
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan.
Ryutaro
R
Fukui
Department of Dermatology, Kochi Medical School, Kochi University, Kohasu, Okocho, Nankoku 783-8505, Japan.
Tatsushi
T
Ishimoto
Department of Dermatology, Kochi Medical School, Kochi University, Kohasu, Okocho, Nankoku 783-8505, Japan.
Shigetoshi
S
Sano
First Department of Internal Medicine, Kansai Medical University, Osaka 573-1010, Japan.
Tomoki
T
Ito
CREST, Japan Science and Technology agency, 4-1-8, Honcho, Kawaguchi-shi, Saitama 332-0012, Japan Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Toshiyuki
T
Shimizu
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639, Japan kmiyake@ims.u-tokyo.ac.jp.
Kensuke
K
Miyake
D019943:Amino Acid Substitution; D000818:Animals; D006151:Guanosine / Q000031:analogs & derivatives / Q000276:immunology; D006801:Humans; D008024:Ligands; D008264:Macrophages / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000819:agonists* / Q000235:genetics / Q000276:immunology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D051199:Toll-Like Receptor 7 / Q000819:agonists* / Q000235:genetics / Q000276:immunology*
D008024:Ligands; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; C477038:Tlr7 protein, mouse; D051199:Toll-Like Receptor 7; C512254:UNC93B1 protein, mouse; D006151:Guanosine
8-OHG; 8-OHdG; G; TLR7; dG