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CS5-2 Tipping the balance: ADAR1 deaminase and PKR kinase can display opposing roles during viral infection
Cytokine 52 (2010) 70–71
Contents lists available at ScienceDirect
Cytokine journal homepage: www.elsevier.com/locate/issn/10434666
Interferons and Viral Infections CS5-1 Multiple antiviral pathways are activated by TLR3 and RIG-I signaling Ganes C. Sen, Michifumi Yamashita, Paramananda Saikia, Volker Fensterl, Christine White, Saurabh Chattopadhyay, Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, Cleveland, OH USA Viral homeostasis is maintained by the balance of cellular antiviral responses to infection and viral evasion of them. The cellular response is often initiated by double-stranded (ds) RNA, produced by both RNA and DNA viruses, causing activation of signaling cascades that lead to transcriptional induction of antiviral genes. Among the prominent antiviral genes are members of the IFIT1 (ISG56) family. We and others have shown that proteins encoded by this gene family inhibit replication of papillomaviruses and flaviviruses; there are other antiviral proteins which target other virus families. However, it is becoming increasingly clear that all antiviral responses are not mediated by induced proteins. We have recently uncovered two pathways that get activated by dsRNA or virus infection, but are gene induction-independent. The first pathway is mediated by the oncoprotein Src, which is activated by its binding to dsRNA-stimulated TLR3 in a TRIF- independent manner. DsRNA-mediated Src activation causes profound changes in many cellular processes including cell migration and recruitment of immune cells to the site of inflammation. The second gene induction-independent pathway leads to apoptosis of virus infected cells. This apoptotic pathway, triggered by both RNA and DNA viruses, requires RIG-I signaling to IRF-3. In this branch of RIG-I signaling, activated IRF-3 binds to the pro-apoptotic protein Bax and they initiate apoptosis by translocating together to mitochondria. Appropriate analyses, with cells defective in the apoptotic branch of signaling, show that premature apoptosis of infected cells impairs virus replication considerably. Thus, cytoplasmic receptor-mediated cellular antiviral response constitutes of both gene induction-dependent and independent components.
doi:10.1016/j.cyto.2010.07.294
CS5-2 Tipping the balance: ADAR1 deaminase and PKR kinase can display opposing roles during viral infection Charles E. Samuel, Zhiqun Li, Annie M. Toth, Christopher A. McAllister, Kristina Okonski, Nora Taghavi, Ying Wang, Cyril X. George, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA Adenosine deaminase acting on RNA (ADAR1) catalyzes the deamination of adenosine (A) to generate inosine (I) in double-stranded (ds) RNAs. Because I is recognized as G instead of A, A-to-I editing can lead to destabilization of dsRNA structures and genetic recoding. ADAR1, like the dsRNA-dependent protein kinase PKR, is interferon (IFN) inducible. Two size forms of ADAR1 are expressed in cultured cells and animal tissues: an IFN inducible 150-kDa protein and a constitutively expressed N-terminally truncated 110-kDa protein. The roles of ADAR1 and PKR during the replication of representative RNA and DNA viruses, wild-type and mutant, were assessed using human cell clones made stably deficient in ADAR1 or PKR by an RNA interference silencing strategy. The E3L protein of vaccinia virus, the C protein of measles virus, and the VAI RNA of adenovirus are known to promote virus growth and among the cellular proteins implicated as their targets are PKR, and also ADAR in the cases of E3L and VAI. The effects of ADAR1 or PKR deficiency on virus growth, beta IFN induction, and virus-induced cell death were assessed. Taken together, the results obtained suggest that ADAR1 suppresses activation of PKR in virus-infected and plasmid-transfected cells. As exemplified by measles virus, PKR is anti-viral and pro-apoptotic, whereas ADAR1 is a pro-viral and anti-apoptotic host factor. The anti-apoptotic activities of ADAR1 correlate with the suppression of activation of pro-apoptotic activities exemplified by PKR. Our results furthermore reveal multiple consequences of C pro-
tein expression and document an important function for PKR as an enhancer of beta IFN induction via adaptor IPS-1 dependent signaling during measles virus infection. (Supported by NIAID, NIH). doi:10.1016/j.cyto.2010.07.295
CS5-3 The role of interferon epsilon in viral infection of the reproductive tract Niamh E. Mangan 1, Ka Yee Fung 1, Sebastian Stifter 1, Daniel J. Carr 2, Paul J. Hertzog 1, 1 Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia, 2 Department of Opthalmology, University of Oklahoma Health Sciences Center, OK, USA Sexually transmitted infections (STIs) represent a critical global health and socioeconomic problem with over 1 billion new cases per annum. Genital herpes, caused primarily by herpes simplex virus 2 (HSV-2) is one of the most prevalent STIs in the world and is associated with substantial morbidity, compounded by the lack of a current vaccine. This is partly due to our lack of a comprehensive understanding of how the immune system in the female reproductive tract functions. We have investigated the importance of interferon (IFN) signaling in HSV-2 infection in mice. Using IFN receptor (Ifnar) 1- and Ifnar 2-deficient mice we have addressed the role of differential Ifnar responses in the immune response to HSV-2. Significantly, we have discovered a new protein, designated IFNepsilon, that is exclusively expressed in the female reproductive tract. We have demonstrated that IFNepsilon acts via Ifnar 1 and Ifnar 2. However, IFNepsilon is unique, because unlike other related type I IFNs, it is constitutively expressed and regulated by hormones but not by pathogens. Importantly, using our IFNepsilon-gene targeted mice, we have demonstrated that this novel cytokine regulates innate immunity, protecting mice from STIs. IFNepsilon-deficient mice are more susceptible to intra-vaginal infection with HSV-2 compared to infected wildtype mice, as measured by clinical score of disease pathology and increased viral titres in tissues. The associated immune response in the IFNepsilon-deficient mice correlates with increased infection in these mice as they have increased immune cell infiltrates. We describe a new mechanistic role for IFNs in HSV-2 infection in mice. doi:10.1016/j.cyto.2010.07.296
CS5-4 TRIM79, A novel interferon stimulated gene, restricts flavivirus replication by degrading the viral RNA polymerase R. Travis Taylor, Kirk J. Lubick, Sonja M. Best, Laboratory of Virology, Rocky Mountain Laboratories, DIR, NIAID, NIH, Hamilton MT USA The host interferon-a/b (IFNa/b) response is critical to controlling virus infection. Genes transcriptionally induced by IFNa/b (IFN stimulated genes or ISGs) establish an anti-viral state within both infected and uninfected cells. Flaviviruses including dengue virus, West Nile virus (WNV) and tick-borne encephalitis (TBE) virus are a significant cause of human morbidity and mortality worldwide. IFNa/b responses are essential for recovery from flavivirus infection although the roles of most ISGs in protection are unknown. We have identified a novel murine tripartite motif (TRIM) protein, designated TRIM79, as an ISG induced during Langat virus (LGTV, a member of the TBE viruses) replication. TRIM proteins are emerging as a family of ISGs that mediate species-specific virus restriction and regulate host innate immunity. These properties prompted us to examine the role of TRIM79 in LGTV infection. TRIM79 bound to LGTV NS5 during virus replication. NS5 encodes the viral RNA polymerase
Contents lists available at ScienceDirect
Cytokine journal homepage: www.elsevier.com/locate/issn/10434666
Interferons and Viral Infections CS5-1 Multiple antiviral pathways are activated by TLR3 and RIG-I signaling Ganes C. Sen, Michifumi Yamashita, Paramananda Saikia, Volker Fensterl, Christine White, Saurabh Chattopadhyay, Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, Cleveland, OH USA Viral homeostasis is maintained by the balance of cellular antiviral responses to infection and viral evasion of them. The cellular response is often initiated by double-stranded (ds) RNA, produced by both RNA and DNA viruses, causing activation of signaling cascades that lead to transcriptional induction of antiviral genes. Among the prominent antiviral genes are members of the IFIT1 (ISG56) family. We and others have shown that proteins encoded by this gene family inhibit replication of papillomaviruses and flaviviruses; there are other antiviral proteins which target other virus families. However, it is becoming increasingly clear that all antiviral responses are not mediated by induced proteins. We have recently uncovered two pathways that get activated by dsRNA or virus infection, but are gene induction-independent. The first pathway is mediated by the oncoprotein Src, which is activated by its binding to dsRNA-stimulated TLR3 in a TRIF- independent manner. DsRNA-mediated Src activation causes profound changes in many cellular processes including cell migration and recruitment of immune cells to the site of inflammation. The second gene induction-independent pathway leads to apoptosis of virus infected cells. This apoptotic pathway, triggered by both RNA and DNA viruses, requires RIG-I signaling to IRF-3. In this branch of RIG-I signaling, activated IRF-3 binds to the pro-apoptotic protein Bax and they initiate apoptosis by translocating together to mitochondria. Appropriate analyses, with cells defective in the apoptotic branch of signaling, show that premature apoptosis of infected cells impairs virus replication considerably. Thus, cytoplasmic receptor-mediated cellular antiviral response constitutes of both gene induction-dependent and independent components.
doi:10.1016/j.cyto.2010.07.294
CS5-2 Tipping the balance: ADAR1 deaminase and PKR kinase can display opposing roles during viral infection Charles E. Samuel, Zhiqun Li, Annie M. Toth, Christopher A. McAllister, Kristina Okonski, Nora Taghavi, Ying Wang, Cyril X. George, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA Adenosine deaminase acting on RNA (ADAR1) catalyzes the deamination of adenosine (A) to generate inosine (I) in double-stranded (ds) RNAs. Because I is recognized as G instead of A, A-to-I editing can lead to destabilization of dsRNA structures and genetic recoding. ADAR1, like the dsRNA-dependent protein kinase PKR, is interferon (IFN) inducible. Two size forms of ADAR1 are expressed in cultured cells and animal tissues: an IFN inducible 150-kDa protein and a constitutively expressed N-terminally truncated 110-kDa protein. The roles of ADAR1 and PKR during the replication of representative RNA and DNA viruses, wild-type and mutant, were assessed using human cell clones made stably deficient in ADAR1 or PKR by an RNA interference silencing strategy. The E3L protein of vaccinia virus, the C protein of measles virus, and the VAI RNA of adenovirus are known to promote virus growth and among the cellular proteins implicated as their targets are PKR, and also ADAR in the cases of E3L and VAI. The effects of ADAR1 or PKR deficiency on virus growth, beta IFN induction, and virus-induced cell death were assessed. Taken together, the results obtained suggest that ADAR1 suppresses activation of PKR in virus-infected and plasmid-transfected cells. As exemplified by measles virus, PKR is anti-viral and pro-apoptotic, whereas ADAR1 is a pro-viral and anti-apoptotic host factor. The anti-apoptotic activities of ADAR1 correlate with the suppression of activation of pro-apoptotic activities exemplified by PKR. Our results furthermore reveal multiple consequences of C pro-
tein expression and document an important function for PKR as an enhancer of beta IFN induction via adaptor IPS-1 dependent signaling during measles virus infection. (Supported by NIAID, NIH). doi:10.1016/j.cyto.2010.07.295
CS5-3 The role of interferon epsilon in viral infection of the reproductive tract Niamh E. Mangan 1, Ka Yee Fung 1, Sebastian Stifter 1, Daniel J. Carr 2, Paul J. Hertzog 1, 1 Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia, 2 Department of Opthalmology, University of Oklahoma Health Sciences Center, OK, USA Sexually transmitted infections (STIs) represent a critical global health and socioeconomic problem with over 1 billion new cases per annum. Genital herpes, caused primarily by herpes simplex virus 2 (HSV-2) is one of the most prevalent STIs in the world and is associated with substantial morbidity, compounded by the lack of a current vaccine. This is partly due to our lack of a comprehensive understanding of how the immune system in the female reproductive tract functions. We have investigated the importance of interferon (IFN) signaling in HSV-2 infection in mice. Using IFN receptor (Ifnar) 1- and Ifnar 2-deficient mice we have addressed the role of differential Ifnar responses in the immune response to HSV-2. Significantly, we have discovered a new protein, designated IFNepsilon, that is exclusively expressed in the female reproductive tract. We have demonstrated that IFNepsilon acts via Ifnar 1 and Ifnar 2. However, IFNepsilon is unique, because unlike other related type I IFNs, it is constitutively expressed and regulated by hormones but not by pathogens. Importantly, using our IFNepsilon-gene targeted mice, we have demonstrated that this novel cytokine regulates innate immunity, protecting mice from STIs. IFNepsilon-deficient mice are more susceptible to intra-vaginal infection with HSV-2 compared to infected wildtype mice, as measured by clinical score of disease pathology and increased viral titres in tissues. The associated immune response in the IFNepsilon-deficient mice correlates with increased infection in these mice as they have increased immune cell infiltrates. We describe a new mechanistic role for IFNs in HSV-2 infection in mice. doi:10.1016/j.cyto.2010.07.296
CS5-4 TRIM79, A novel interferon stimulated gene, restricts flavivirus replication by degrading the viral RNA polymerase R. Travis Taylor, Kirk J. Lubick, Sonja M. Best, Laboratory of Virology, Rocky Mountain Laboratories, DIR, NIAID, NIH, Hamilton MT USA The host interferon-a/b (IFNa/b) response is critical to controlling virus infection. Genes transcriptionally induced by IFNa/b (IFN stimulated genes or ISGs) establish an anti-viral state within both infected and uninfected cells. Flaviviruses including dengue virus, West Nile virus (WNV) and tick-borne encephalitis (TBE) virus are a significant cause of human morbidity and mortality worldwide. IFNa/b responses are essential for recovery from flavivirus infection although the roles of most ISGs in protection are unknown. We have identified a novel murine tripartite motif (TRIM) protein, designated TRIM79, as an ISG induced during Langat virus (LGTV, a member of the TBE viruses) replication. TRIM proteins are emerging as a family of ISGs that mediate species-specific virus restriction and regulate host innate immunity. These properties prompted us to examine the role of TRIM79 in LGTV infection. TRIM79 bound to LGTV NS5 during virus replication. NS5 encodes the viral RNA polymerase