5′-triphosphate guanosine RNAs recruit GTP-binding proteins to suppress RIG-I/IFN type I signaling

The interferon (IFN) response is crucial for antiviral activity, but its overstimulation can lead to a wide range of autoimmune disorders. The cytoplasmic pattern recognition receptor RIG-I detects viral double-stranded RNAs (dsRNAs) and endogenous polymerase III transcripts carrying a 5′-triphosphate (5′-ppp) or 5′-diphosphate (5′-pp) moiety, triggering phosphorylation of IRF3 and IFN immune response. While many viral RNAs initiate with 5′-ppp-adenosine (5′-pppA) and most endogenous Pol III transcripts in higher eukaryotes start with 5′-ppp-guanosine (5′-pppG), no apparent reason for this bias has been identified so far. Here we demonstrate that dsRNAs initiating with 5′-pppA trigger stronger RIG-I/IFN response than those starting with 5′-pppG. We show that several GTP-binding proteins interact preferentially with 5′-pppG RNAs. Finally, supplementation with guanosine, but not adenosine, which rapidly increases intracellular concentrations of GTP and ATP, respectively, eliminates the difference in immunogenicity between 5′-pppG and 5′-pppA RNAs. Our findings suggest that 5′-pppG RNAs may enable certain RNA viruses and Pol III transcripts to limit detection by innate immune receptors. These results offer new insights into the sequence-dependent activation of the RIG-I/IFN pathway and have important implications for both antiviral immunity and the role of Pol III-derived RNAs in autoimmune diseases.