Evolution and Antiviral Specificity of IFIT Genes

The cell intrinsic immune response serves as the first line of defense against pathogens. In particular, pattern recognition of foreign nucleotides allows the cell to upregulate expression of the signaling cytokine, type I interferon. This results in the production of interferon-stimulated genes (ISGs) while mounting an antiviral response within the cell. In order for ISGs to continually antagonize viral replication within the cell they must be able to co-evolve with the rapid evolution and mutation rate of viruses. Phylogenetic analyses show rapid evolution among mammalian interferon-induced tetratricopeptide repeats (IFITs). The antiviral mechanisms of Human IFIT1 and Mouse IFIT1B are well discerned; each of these proteins is able to specifically recognize viral mRNAs and prevent their translation. However, the antiviral mechanisms of IFIT2 and IFIT3 are not well understood. Prior work from the Daugherty lab revealed that expression of IFIT2 and IFIT3 show antiviral activity against some viruses. This activity is not seen when IFIT2 and IFIT3 alone are singularly expressed. Knowing this, two questions remained. First, how are IFIT2 and IFIT3 interacting with each other to confer antiviral activity? And second, how do IFIT2 and IFIT3 recognize viral RNA? In order to research the latter, I took advantage of the observation that IFIT2/3 preferentially binds to viral mRNAs at a location immediately surrounding the start codon. I therefore designed and tested an eGFP reporter system with altered 5’UTR lengths and sequences proximal to the start codon. Our findings indicate that protein translation was inhibited by altering the mRNA near the start codon sequence and the untranslated region to make them resemble viral mRNAs. Further studies of IFIT2/3 antiviral activity will elucidate which viral pathogens are susceptible to this cell intrinsic immune response and provide more insight to the mechanisms behind the inhibition of viruses at the translational level