RIG-I like receptors (RLRs) detect viral infections and triggers appropriate immune responses to limit viral infection and spread. RIG-I, the best studied member of RLRs, binds to viral RNA in the cytosol and triggers a signaling cascade that leads to the production of type-I interferons and other antiviral molecules. We have previously identified a mitochondrial antiviral signaling protein termed MAVS (also known as IPS-1, VISA or CARDIF), which plays a pivotal role in the RIG-I signaling cascade. MAVS resides on the mitochondrial outer membrane and it activates cytosolic protein kinases including IKK and TBK1, which phosphorylate the transcription factors NF-?B and IRF3, respectively. NF-?B, IRF3 and other transcription factors function together in the nucleus to turn on the expression of antiviral genes. In order to understand the mechanism of signal transduction in the RIG-I pathway, we have recently established a cell-free system that faithfully recapitulates the activation of IRF3 by viral RNA. Initial dissection of this system leads to the discovery that RIG-I activation requires not only viral RNA, but also a unique form of polyubiquitination involving lysine-63 (K63) of ubiquitin. Further investigation shows that unanchored K63 polyubiquitin chains, which are not conjugated to any cellular protein, binds to the N-terminal CARD domains of RIG-I, resulting in RIG-I activation. These studies provide a strong foundation for further dissection of the RIG-I signaling pathway. In this application, we propose to elucidate the mechanism of RIG-I regulation by RNA and K63 ubiquitin chains (Aim 1). We will also investigate how RIG-I activates MAVS on the mitochondrial membrane (Aim 2). Finally, we will delineate the pathways through which MAVS activate TBK1 and IKK in the cytosol (Aim 3). Together, these lines of investigation should fill some of the major gaps in our current understanding of the RIG-I signaling cascade, and provide mechanistic insights into antiviral innate immunity.

Public Health Relevance

The RIG-I pathway is largely responsible for the first line of immune defense against viral infection in human and many other organisms. In this application, we propose to elucidate the mechanism of signal transduction in key steps of the RIG-I pathway using an innovative biochemical approach. If successful, our research should significantly advance the fields of immunology and virology, and provide new approaches to harness the host innate immunity to combat viral and autoimmune diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI093967-02
Application #
8225150
Study Section
Cellular and Molecular Immunology - A Study Section (CMIA)
Program Officer
Palker, Thomas J
Project Start
2011-02-15
Project End
2016-01-31
Budget Start
2012-02-01
Budget End
2013-01-31
Support Year
2
Fiscal Year
2012
Total Cost
$396,771
Indirect Cost
$146,771
Name
University of Texas Sw Medical Center Dallas
Department
Biochemistry
Type
Schools of Medicine
DUNS #
800771545
City
Dallas
State
TX
Country
United States
Zip Code
75390
Liu, Siqi; Cai, Xin; Wu, Jiaxi et al. (2015) Phosphorylation of innate immune adaptor proteins MAVS, STING, and TRIF induces IRF3 activation. Science 347:aaa2630
Collins, Angela C; Cai, Haocheng; Li, Tuo et al. (2015) Cyclic GMP-AMP Synthase Is an Innate Immune DNA Sensor for Mycobacterium tuberculosis. Cell Host Microbe 17:820-8
Shi, Heping; Wu, Jiaxi; Chen, Zhijian J et al. (2015) Molecular basis for the specific recognition of the metazoan cyclic GMP-AMP by the innate immune adaptor protein STING. Proc Natl Acad Sci U S A 112:8947-52
Gao, Daxing; Li, Tuo; Li, Xiao-Dong et al. (2015) Activation of cyclic GMP-AMP synthase by self-DNA causes autoimmune diseases. Proc Natl Acad Sci U S A 112:E5699-705
Ren, Junyao; Chen, Xiang; Chen, Zhijian J (2014) IKKβ is an IRF5 kinase that instigates inflammation. Proc Natl Acad Sci U S A 111:17438-43
Cai, Xin; Chiu, Yu-Hsin; Chen, Zhijian J (2014) The cGAS-cGAMP-STING pathway of cytosolic DNA sensing and signaling. Mol Cell 54:289-96
El Maadidi, Souhayla; Faletti, Laura; Berg, Birgit et al. (2014) A novel mitochondrial MAVS/Caspase-8 platform links RNA virus-induced innate antiviral signaling to Bax/Bak-independent apoptosis. J Immunol 192:1171-83
Xu, Hui; He, Xiaojing; Zheng, Hui et al. (2014) Structural basis for the prion-like MAVS filaments in antiviral innate immunity. Elife 3:e01489
Cai, Xin; Chen, Jueqi; Xu, Hui et al. (2014) Prion-like polymerization underlies signal transduction in antiviral immune defense and inflammasome activation. Cell 156:1207-22
Wu, Jiaxi; Chen, Zhijian J (2014) Innate immune sensing and signaling of cytosolic nucleic acids. Annu Rev Immunol 32:461-88

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