Infection with the dengue RNA virus activates TLR9 signaling in human dendritic cells

• Published in: EMBO reports Vol. 19; no. 8
• Main Authors: Lai, Jenn‐Haung, Wang, Mei‐Yi, Huang, Chuan‐Yueh, Wu, Chien‐Hsiang, Hung, Li‐Feng, Yang, Chia‐Ying, Ke, Po‐Yuan, Luo, Shue‐Fen, Liu, Shih‐Jen, Ho, Ling‐Jun
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2018; Springer Nature B.V; John Wiley and Sons Inc
• Subjects: Activation; AMP; Animals; Bone marrow; Cyclic GMP; Cytosol; Cytosol - metabolism; dendritic cell; Dendritic cells; Dendritic Cells - metabolism; Dendritic Cells - pathology; Dendritic Cells - virology; Dendritic structure; Dengue - metabolism; Dengue - pathology; Dengue - virology; Dengue fever; dengue virus; Dengue Virus - physiology; Deoxyribonucleic acid; DNA; DNA, Mitochondrial - genetics; DNA-Binding Proteins - metabolism; EMBO23; EMBO37; Endodeoxyribonucleases - metabolism; Extracellular Space - metabolism; Gene Knockdown Techniques; Humans; Immune response; Immune system; Infections; Inflammasomes; Inflammasomes - metabolism; Interferon; Interferons - genetics; Interferons - metabolism; Membrane permeability; Mice; Mice, Knockout; Mitochondria; Mitochondria - metabolism; Mitochondrial DNA; Mitochondrial permeability transition pore; Mitochondrial Proteins - metabolism; Oxidation-Reduction; Permeability; Phosphorylation; Pores; Proteins; Reactive oxygen species; Reactive Oxygen Species - metabolism; Receptors; Ribonucleic acid; RNA; RNA viruses; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Small Interfering - metabolism; RNA, Viral - metabolism; Rodents; Signal Transduction; Signaling; TLR9; TLR9 protein; Toll-Like Receptor 9 - metabolism; Toll-like receptors; Transcription Factors - metabolism; Vector-borne diseases; Viral diseases; Viruses; TLR9; immune response; mitochondrial DNA; dendritic cell; dengue virus
• ISSN: 1469-221X; 1469-3178; 1469-3178
• DOI: 10.15252/embr.201846182

Toll‐like receptors (TLRs) are important sensors that recognize pathogen‐associated molecular patterns. Generally, TLR9 is known to recognize bacterial or viral DNA but not viral RNA and initiate an immune response. Herein, we demonstrate that infection with dengue virus (DENV), an RNA virus, activates TLR9 in human dendritic cells (DCs). DENV infection induces release of mitochondrial DNA (mtDNA) into the cytosol and activates TLR9 signaling pathways, leading to production of interferons (IFNs). The DENV‐induced mtDNA release involves reactive oxygen species generation and inflammasome activation. DENV infection disrupts the association between transcription factor A mitochondria (TFAM) and mtDNA and activates the mitochondrial permeability transition pores. The side‐by‐side comparison of TLR9 and cyclic GMP‐AMP synthase (cGAS) knockdown reveals that both cGAS and TLR9 comparably contribute to DENV‐induced immune activation. The significance of TLR9 in DENV‐induced immune response is also confirmed in examination with the bone marrow‐derived DCs prepared from Tlr9 ‐knockout mice. Our study unravels a previously unrecognized phenomenon in which infection with an RNA virus, DENV, activates TLR9 signaling by inducing mtDNA release in human DCs. Synopsis Infection of human dendritic cells with a dengue RNA virus activates TLR9—known to recognize bacterial or viral DNA but not viral RNA—through inducing mitochondrial DNA release into the cytosol. Infection of human DCs with DENV induces ROS generation, inflammasome activation, oxidization of mtDNA and opening of the mitochondrial permeability transition pores resulting in the release of both non‐oxidized and oxidized mtDNA into the cytosol. Cytosolic mtDNA increases TLR9 expression, binds to TLR9 and induces immune activation such as anti‐viral interferon production. The significance of TLR9 in DENV infection is confirmed by examining bone marrow‐derived dendritic cells prepared from Tlr9 ‐knockout mice. Graphical Abstract Infection of human dendritic cells with a dengue RNA virus activates TLR9—known to recognize bacterial or viral DNA but not viral RNA—through inducing mitochondrial DNA release into the cytosol.