I09 Adenosine deaminae (ADAR1) acting on double-stranded RNA and protein kinase PKR dependent on dsRNA as opposing modulators of antiviral innate immunity

Abstract

Double-stranded RNA (dsRNA) plays a central role in antiviral innate immunity, both as a trigger for the production of interferon (IFN) and also in the actions of IFN. Adenosine deaminases acting on RNA (ADAR) catalyze the C-6 deamination of adenosine (A) to generate inosine (I) in dsRNAs. Because I hydrogen bonds as G with C, not as A with U, A-to-I editing can lead to genetic recoding of RNAs and destabilization of dsRNA structures. The Adar1 gene is IFN inducible and encodes two size forms of ADAR1 protein through alternative promoter utilization; an IFN inducible promoter specifies a p150 protein that is cytoplasmic and nuclear, whereas the constitutive promoters specify a smaller constitutively expressed p110 nuclear protein. Protein kinase PKR also is IFN inducible, is activated by dsRNA, and inhibits translation through eIF-2alpha factor phosphorylation. The roles of ADAR1 p150 and p110, and PKR, during virus replication were examined using human cell clones made stably deficient in ADAR1 or PKR by an RNA interference strategy, and mouse MEF cells genetically deficient in either ADAR1 or 2. Results obtained with wild-type measles virus (MV) and mutants deleted for either C or V expression revealed important roles for both ADAR1 and PKR as modulators of IFN induction and the host response to infection. The effects of ADAR1 deficiency on MV growth, IFN beta gene induction, and virus-induced cytopathic effect generally were opposite to the effects observed for PKR deficiency. The findings indicate that ADAR1 behaves as an anti-apoptotic host factor that, in some instances, is pro-viral. The anti-apoptotic and cell protective effects of ADAR1 correlated with suppression of activation of pro-apoptotic activities exemplified by PKR. Results obtained with mouse cells genetically deficient in adar1 likewise showed a protective role of ADAR1 protein isoforms against virus-induced cytopathic effects. (Supported by NIAID, NIH).