Short double-stranded RNAs with an overhanging 5′ ppp-nucleotide, as found in arenavirus genomes, act as RIG-I decoys

Abstract

Arenavirus RNA genomes are initiated by a "prime and realign" mechanism, such that the initiating GTP is found as a single unpaired (overhanging) nucleotide when the complementary genome ends anneal to form double-stranded (ds) RNA panhandle structures. dsRNAs modeled on these structures do not induce interferon (IFN), as opposed to bluntended 5′ pppdsRNA. This study examines whether these viral structures can also act as decoys, by trapping RIG-I in inactive dsRNA complexes. We examined the ability of various dsRNAs to activate the RIG-I ATPase (presumably a measure of helicase translocation on dsRNA) relative to their ability to induce IFN. We found that there is no simple relationship between these two properties, as if RIG-I can translocate on short dsRNAs without inducing IFN. Moreover, we found that 5′ pppdsRNAs with a single unpaired 5′ ppp-nucleotide can in fact competitively inhibit the ability of blunt-ended 5′ pppdsRNAs to induce IFN when co-transfected into cells and that this inhibition is strongly dependent on the presence of the 5′ ppp. In contrast, 5′ pppdsRNAs with a single unpaired 5′ ppp-nucleotide does not inhibit poly(I-C)-induced IFN activation, which is independent of the presence of a 5′ ppp group. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.