Impact of mRNA modification on innate immune recognition

To sense viral infections, the mammalian innate immune system is equipped with several receptors for specific recognition of foreign RNAs. Upon activation, these receptors either induce the expression of cytokines or directly activate antiviral pathways. Thus, an attractive strategy for viruses to successfully establish host cell infection is to avoid recognition of viral RNA by the innate immune system. Cellular mRNAs are characterized by a 5`-cap structure, a polyA tail, and post-transcriptional modifications such as methylation of nucleotides. Many cytoplasmically replicating viruses encode their own RNA-modifying enzymes. This includes N7- and 2`O- methyltransferases, which are engaged in 5`-cap formation and methylation of viral RNA. We hypothesize that viral RNA methylation impacts on two fundamental cellular processes, namely protein synthesis and the detection of molecular signatures for non-self RNA recognition. In the proposed project I want to test this hypothesis using the murine model for Mouse Hepatitis Virus (MHV). I will use reverse genetics to generate mutant viruses with inactivated RNA-methyltransferases, and determine the methylation status of mutant virus RNAs. This will be followed by a detailed phenotypic analysis of the biological consequences of RNA methylation on innate immune recognition and mRNA translation in vitro and in vivo. The proposed project will increase our understanding on foreign RNA recognition by the innate arm of the immune system and on control of mRNA translation under cellular stress conditions, such as virus infection.