The RIG‐I‐like receptor LGP2 inhibits Dicer‐dependent processing of long double‐stranded RNA and blocks RNA interference in mammalian cells

Abstract

In vertebrates, the presence of viral RNA in the cytosol is sensed by members of the RIG‐I‐like receptor (RLR) family, which signal to induce production of type I interferons (IFN). These key antiviral cytokines act in a paracrine and autocrine manner to induce hundreds of interferon‐stimulated genes (ISGs), whose protein products restrict viral entry, replication and budding. ISGs include the RLRs themselves: RIG‐I, MDA5 and, the least‐studied family member, LGP2. In contrast, the IFN system is absent in plants and invertebrates, which defend themselves from viral intruders using RNA interference (RNAi). In RNAi, the endoribonuclease Dicer cleaves virus‐derived double‐stranded RNA (dsRNA) into small interfering RNAs (siRNAs) that target complementary viral RNA for cleavage. Interestingly, the RNAi machinery is conserved in mammals, and we have recently demonstrated that it is able to participate in mammalian antiviral defence in conditions in which the IFN system is suppressed. In contrast, when the IFN system is active, one or more ISGs act to mask or suppress antiviral RNAi. Here, we demonstrate that LGP2 constitutes one of the ISGs that can inhibit antiviral RNAi in mammals. We show that LGP2 associates with Dicer and inhibits cleavage of dsRNA into siRNAs both in vitro and in cells. Further, we show that in differentiated cells lacking components of the IFN response, ectopic expression of LGP2 interferes with RNAi‐dependent suppression of gene expression. Conversely, genetic loss of LGP2 uncovers dsRNA‐mediated RNAi albeit less strongly than complete loss of the IFN system. Thus, the inefficiency of RNAi as a mechanism of antiviral defence in mammalian somatic cells can be in part attributed to Dicer inhibition by LGP2 induced by type I IFNs. LGP2‐mediated antagonism of dsRNA‐mediated RNAi may help ensure that viral dsRNA substrates are preserved in order to serve as targets of antiviral ISG proteins.

LGP2 virus sensor regulates gene expression network mediated by TRBP-bound microRNAs

“…van der Veen et al. reported that LGP2 had no impact on miRNA processing by in vitro assay ( 54 ). They showed that the processing of let-7a and miR-16, which are revealed to be TRBP-bound miRNAs in our study, are not inhibited by LGP2 even in the presence of Dicer.…”

“…The interaction between LGP2 and Dicer is weakened but not abolished by RNase treatment. Then, they deduced that long dsRNA-bound CTD domain of LGP2 undergoes structural rearrangements that allow it to associate with Dicer to inhibit its activity, then further strengthened in a cooperative manner by the presence of the helicase domain ( 54 ). Thus, the processing of miRNAs and long dsRNAs might be differently regulated by LGP2.…”

Harnessing host–virus evolution in antiviral therapy and immunotherapy

“…MDA5 is activated by large RNA molecules, while LGP2 recognises RNA as short as 12 nt irrespective of phosphorylation or hydroxylation at the 5′ end. LGP2 activation supports MDA5‐dependent signalling while inhibiting both RIG‐I and Dicer . TLR and RLR activation stimulates IFN‐I expression, which activates JAK‐STAT signalling to modulate expression of hundreds of IFN‐stimulated genes, thereby placing infected cells and local tissues in an antiviral state .…”

Viruses Seen by Our Cells: The Role of Viral RNA Sensors

“…According to this model, LGP2 can leverage upon its ATP-dependent/RNA helicase activity to assist and increase interactions of a larger subset of nucleic acid-derived PAMP with RIG-I or MDA5 and finally potentiate antiviral signaling. Additionally, it was recently shown that LGP2 inhibits a DICER-mediated processing of vRNA [ 58 ]. In contrast to the elaborated protein-based system found in mammals, plants and invertebrates rely on their RNA interference (RNAi) machinery to degrade vRNA and subvert viral replication [ 59 ].…”