Christine Schuberth-Wagner 1 , 7 , Janos Ludwig 1 , 7 , Ann Kristin Bruder 1 , 7 , Anna-Maria Herzner 1 , Thomas Zillinger 1 , 2 , Marion Goldeck 1 , Tobias Schmidt 3 , Jonathan L. Schmid-Burgk 3 , Romy Kerber 4 , Steven Wolter 1 , Jan-Philip Stümpel 1 , Andreas Roth 1 , 6 , Eva Bartok 1 , Christian Drosten 5 , Christoph Coch 1 , Veit Hornung 3 , Winfried Barchet 1 , 2 , Beate M. Kümmerer 5 , Gunther Hartmann 1 , 8 , Martin Schlee 1 , 8 , ∗
14 July 2015
The cytosolic helicase retinoic acid-inducible gene-I (RIG-I) initiates immune responses to most RNA viruses by detecting viral 5′-triphosphorylated RNA (pppRNA). Although endogenous mRNA is also 5′-triphosphorylated, backbone modifications and the 5′-ppp-linked methylguanosine ( m7G) cap prevent immunorecognition. Here we show that the methylation status of endogenous capped mRNA at the 5′-terminal nucleotide (N 1) was crucial to prevent RIG-I activation. Moreover, we identified a single conserved amino acid (H830) in the RIG-I RNA binding pocket as the mediator of steric exclusion of N 1-2′O-methylated RNA. H830A alteration (RIG-I(H830A)) restored binding of N 1-2′O-methylated pppRNA. Consequently, endogenous mRNA activated the RIG-I(H830A) mutant but not wild-type RIG-I. Similarly, knockdown of the endogenous N 1-2′O-methyltransferase led to considerable RIG-I stimulation in the absence of exogenous stimuli. Studies involving yellow-fever-virus-encoded 2′O-methyltransferase and RIG-I(H830A) revealed that viruses exploit this mechanism to escape RIG-I. Our data reveal a new role for cap N 1-2′O-methylation in RIG-I tolerance of self-RNA.
N 1-2′O-methylation is crucial to block RIG-I activation by viral and self RNA
Self-RNA exclusion is singularly governed by the conserved H830 in RIG-I
H830A alteration leads to indiscriminate recognition of endogenous RNA by RIG-I
Cellular N 1-2′O-methyltransferase knockdown renders endogenous RNA stimulatory
The cytosolic receptor RIG-I initiates immune responses against most RNA viruses by detecting viral RNA. Schlee and colleagues report that a conserved amino acid in the RNA binding pocket prevents recognition of endogenous RNA bearing a N 1-2′O-methyl group as a marker of “self” and that flaviviruses exploit this tolerance mechanism for immunoescape.