Identification of RNase L-dependent, 3'-end-modified, viral small RNAs in Sindbis virus-infected mammalian cells.

unlabelledSmall RNAs play a critical role in host-pathogen interaction. Indeed, small RNA-mediated silencing or RNA interference (RNAi) is one of the earliest forms of antiviral immunity. Although it represents the main defense system against viruses in many organisms, the antiviral role of RNAi has not been clearly proven in higher vertebrates. However, it is well established that their response to viral infection relies on the recognition of viral RNAs by host pattern recognition receptors (PRRs) to trigger activation of the interferon pathway. In the present work, we report the existence of a novel small noncoding RNA population produced in mammalian cells upon RNA virus infection. Using Sindbis virus (SINV) as a prototypic arbovirus model, we profiled the small RNA population of infected cells in both human and African green monkey cell lines. Here, we provide evidence for the presence of discrete small RNAs of viral origin that are not associated with the RNA-induced silencing complex (RISC), that are highly expressed and detected by Northern blot analysis, and that accumulate as 21- to 28-nucleotide (nt) species during infection. We report that the cellular antiviral endoribonuclease RNase L cleaves the viral genome, producing in turn the small RNAs. Surprisingly, we uncovered the presence of a modification on the 3'-end nucleotide of SINV-derived viral small RNAs (SvsRNAs) that might be at the origin of their stability. Altogether, our findings show that stable modified small viral RNAs could represent a novel way to modulate host-virus interaction upon SINV infection. IMPORTANCE: In a continuous arms race, viruses have to deal with host antiviral responses in order to successfully establish an infection. In mammalian cells, the host defense mechanism relies on the recognition of viral RNAs, resulting in the activation of type I interferons (IFNs). In turn, the expression of many interferon-stimulated genes (ISGs) is induced to inhibit viral replication. Here we report that the cytoplasmic, interferon-induced, cellular endoribonuclease RNase L is involved in the accumulation of a novel small RNA population of viral origin. These small RNAs are produced upon SINV infection of mammalian cells and are stabilized by a 3'-end modification. Altogether, our findings indicate that in our system RNA silencing is not active against Sindbis virus (SINV) and might open the way to a better understanding of the antiviral response mediated by a novel class of small RNAs.