Acosta, Francisco M.

Abstract Description Innate immune sensing of viral double-stranded (ds) RNA induces the transcription of hundreds of interferon stimulated genes (ISGs) that shift the cell into an antiviral state. We have shown that measles virus (MeV) utilizes the 150 kDa isoform of adenosine deaminase acting on RNA 1 (ADAR1-p150) to prevent activation of protein kinase R (PKR), thereby subverting a type-I interferon response. Hypothesizing that cytoplasmic localization of ADAR1-p150 is required for this pro-viral activity, we generated cell lines expressing single isoforms and localization mutants of ADAR1. Based on MeV replication studies in these cells, we concluded that both nuclear and cytoplasmic ADAR1-p150 prevents PKR activation. However, only cytoplasmic but not nuclear ADAR1-p110 can efficiently prevent PKR activation. These observations suggest a bimodal activation of IFN responses. Initial sensing of viral dsRNA leads to upregulation of a subset of ISGs forming p150-specific self-RNA substrates driving PKR activation. Through ADAR editome analyses, we have identified candidate p150- and p110-specific self-RNA substrates that may be the drivers of this positive feedback loop. RNA immunoprecipitation studies to identify the specific substrates of ADAR1-p150 and PKR during MeV infection are underway to strengthen this novel model of a positive feedback loop driven by self-RNAs. Altogether, our findings shift the paradigm on the regulatory properties of self-RNA on amplifying antiviral innate immunity. Topic Categories Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)

Abstract Measles virus (MeV) is a highly contagious pathogen capable of infecting immune cells and thereby causing immunosuppression and immune amnesia. A live-attenuated MeV vaccine is highly efficacious and has been safely administered for over 60 years. However, a detailed mechanistic understanding of the mode of its attenuation remains elusive. Here, we determined the molecular mechanisms underlying MeV vaccine attenuation in primary human immune cells. Enhanced infection of innate immune cells resulting in uncontrolled viral RNA synthesis and reduced ability to evade host antiviral responses induced a strong type-I interferon signature that arrested replication of the vaccine strain. In contrast, the wild type virus replicated slowly but steadily, avoiding detection by innate immunity.