Abstract
Recognition of viral RNA structures by the intracytosolic RNA helicase RIG-I triggers induction of innate immunity. Efficient induction requires RIG-I ubiquitination by the E3 ligase TRIM25, its interaction with the mitochondria-bound MAVS protein, recruitment of TRAF3, IRF3- and NF-κB-kinases and transcription of Interferon (IFN). In addition, IRF3 alone induces some of the Interferon-Stimulated Genes (ISGs), referred to as early ISGs. Infection of hepatocytes with Hepatitis C virus (HCV) results in poor production of IFN despite recognition of the viral RNA by RIG-I but can lead to induction of early ISGs. HCV was shown to inhibit IFN production by cleaving MAVS through its NS3/4A protease and by controlling cellular translation through activation of PKR, an eIF2α-kinase containing dsRNA-binding domains (DRBD). Here, we have identified a third mode of control of IFN induction by HCV. Using HCVcc and the Huh7.25.CD81 cells, we found that HCV controls RIG-I ubiquitination through the di-ubiquitine-like protein ISG15, one of the early ISGs. A transcriptome analysis performed on Huh7.25.CD81 cells silenced or not for PKR and infected with JFH1 revealed that HCV infection leads to induction of 49 PKR-dependent genes, including ISG15 and several early ISGs. Silencing experiments revealed that this novel PKR-dependent pathway involves MAVS, TRAF3 and IRF3 but not RIG-I, and that it does not induce IFN. Use of PKR inhibitors showed that this pathway requires the DRBD but not the kinase activity of PKR. We then demonstrated that PKR interacts with HCV RNA and MAVS prior to RIG-I. In conclusion, HCV recruits PKR early in infection as a sensor to trigger induction of several IRF3-dependent genes. Among those, ISG15 acts to negatively control the RIG-I/MAVS pathway, at the level of RIG-I ubiquitination.These data give novel insights in the machinery involved in the early events of innate immune response.
Highlights
IFN induction in response to several RNA viruses involves the intracytosolic pathogen recognition receptor (PRR) CARDcontaining DexD/H RNA helicase RIG-I
We show that Hepatitis C virus (HCV) inhibits RIG-I activation through the ubiquitin-like protein ISG15 and that HCV triggers rapid induction of 49 genes, including ISG15, through a novel signaling pathway that precedes RIG-I and involves PKR as an adapter to recruit MAVS
HCV infection negatively controls RIG-I ubiquitination We recently reported that the HCV permissive Huh7.25.CD81 cells [19] that we used to identify the pro-HCV action of PKR, did not induce IFN in response to HCV infection, unless after ectopic expression of TRIM25 [8]
Summary
IFN induction in response to several RNA viruses involves the intracytosolic pathogen recognition receptor (PRR) CARDcontaining DexD/H RNA helicase RIG-I. Following its binding to viral RNA, RIG-I undergoes a change in its conformation through Lys63-type ubiquitination by the E3 ligase TRIM25 This allows its N-terminal CARD domain to interact with the CARD domain of the mitochondria-bound adapter MAVS [1,2]. One reason for this comes from the ability of its NS3 protease to cleave MAVS [7]. Another relates to the ability of HCV to trigger activation of the dsRNA-dependent eIF2a kinase PKR [8,9] which leads to inhibition of IFN expression through general control of translation while the viral genome can be translated from its eIF2a-insensitive IRES structure [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
