Nuclear-resident RIG-I senses viral replication inducing antiviral immunity

Abstract

The nucleus represents a cellular compartment where the discrimination of self from non-self nucleic acids is vital. While emerging evidence establishes a nuclear non-self DNA sensing paradigm, the nuclear sensing of non-self RNA, such as that from nuclear-replicating RNA viruses, remains unexplored. Here, we report the identification of nuclear-resident RIG-I actively involved in nuclear viral RNA sensing. The nuclear RIG-I, along with its cytoplasmic counterpart, senses influenza A virus (IAV) nuclear replication leading to a cooperative induction of type I interferon response. Its activation signals through the canonical signaling axis and establishes an effective antiviral state restricting IAV replication. The exclusive signaling specificity conferred by nuclear RIG-I is reinforced by its inability to sense cytoplasmic-replicating Sendai virus and appreciable sensing of hepatitis B virus pregenomic RNA in the nucleus. These results refine the RNA sensing paradigm for nuclear-replicating viruses and reveal a previously unrecognized subcellular milieu for RIG-I-like receptor sensing.

Innate Immune Evasion by Human Respiratory RNA Viruses

“…RNA sensors like the RIG-I-like sensors or TLRs were thought to be absent there, and therefore replication inside the nucleus may have been an alternative solution to avoid innate immune recognition of viral RNA intermediates during replication. However, recent data indicated that RIG-I can be active in the nucleus against influenza RNA [51]. The viral genome, packaged in nucleocapsid proteins and bearing a panhandle-and 5′-triphosphate structure is recognized by RIG-I, presumably in the cytosol while on its way to the nucleus, or when being incorporated into new virus particles [52][53][54].…”

Acquisition of Avian-Origin PB1 Facilitates Viral RNA Synthesis by the 2009 Pandemic H1N1 Virus Polymerase

“…The relative quantitation of vRNA and cRNA in the cRNA stabilization assay was determined by a strand-specific real-time RT-PCR as previously described [23,27,28]. Briefly, total RNA (350 ng) was reverse-transcribed at 60 • C for 1 h in a 20-µL reaction containing 10 pmol 5 -tagged RT primer, 0.5 mM dNTP mix, 1 × first-strand buffer, 5 mM DTT, 50 U RNaseOUT, 200 U SuperScript III reverse transcriptase (Invitrogen, Carlsbad, CA, USA), and 32.5% saturated trehalose (Sigma).…”

Inhibition of Ongoing Influenza A Virus Replication Reveals Different Mechanisms of RIG-I Activation

“…To avoid the possibility that the RNA extraction procedure was inefficient in extracting viral immunostimulatory RNA generated during NP deprivation or disrupted the native RNA structures of these RNAs, we determined in situ RIG-I activation during RNP reconstitution in the presence or absence of NP. Since IAV RNA synthesis takes place in the nucleus, supplementation of reporter cells with a nuclear-localized RIG-I (NLS-RIG-I) provided a more sensitive measurement of IFN-␤ promoter activation in response to RNP reconstitution (6). Furthermore, this may also shed light on the specialized sensing by nuclear RIG-I of a subset of unknown viral RNAs in the nucleus.…”

“…For over a decade, it has been clear that RIG-I plays an indispensable role in type I IFN induction by IAV (2,3). Recent identification of RIG-I in the nuclear milieu sheds further light on its spatiotemporal detection of IAV replication (6). In contrast, the physiological RIG-I agonists produced from IAV remain underexplored.…”