RNase L releases a small RNA from HCV RNA that refolds into a potent PAMP

Abstract

Triggering and propagating an intracellular innate immune response is essential for control of viral infections. RNase L is a host endoribonuclease and a pivotal component of innate immunity that cleaves viral and cellular RNA within single-stranded loops releasing small structured RNAs with 59-hydroxyl (59-OH) and 39-monophosphoryl (39-p) groups. In 2007, we reported that RNase L cleaves self RNA to produce small RNAs that function as pathogen-associated molecular patterns (PAMPs). However, the precise sequence and structure of PAMP RNAs produced by RNase L is unknown. Here we used hepatitis C virus RNA as substrate to characterize RNase L mediated cleavage products [named suppressor of virus RNA (svRNA)] for their ability to activate RIG-I like receptors (RLR). The NS5B region of HCV RNA was cleaved by RNase L to release an svRNA that bound to RIG-I, displacing its repressor domain and stimulating its ATPase activity while signaling to the IFN-b gene in intact cells. All three of these RIG-I functions were dependent on the presence in svRNA of the 39-p. Furthermore, svRNA suppressed HCV replication in vitro through a mechanism involving IFN production and triggered a RIG-I-dependent hepatic innate immune response in mice. RNase L and OAS (required for its activation) were both expressed in hepatocytes from HCV-infected patients, raising the possibility that the OAS/RNase L pathway might suppress HCV replication in vivo. It is proposed that RNase L mediated cleavage of HCV RNA generates svRNA that activates RIG-I, thus propagating innate immune signaling to the IFN-b gene.

VPg-Primed RNA Synthesis of Norovirus RNA-Dependent RNA Polymerases by Using a Novel Cell-Based Assay

“…The fact that RIG-I can respond to the RNAs made in the presence of VPg raises questions about ligand recognition by RIG-I. RIG-I also recognizes viral RNAs processed at their 3Ј terminus by the endoribonuclease RNase L, which leaves a 3Ј-phosphate in the RNA (40,41). Therefore, we examined whether RNase L can process VPg-linked RNAs in the context of the NoV-5BR assay.…”

The Interferon-Inducible Gene viperin Restricts West Nile Virus Pathogenesis

“…The redundancy of the antiviral IFN system likely results in relatively modest phenotypes when individual ISGs are deleted compared to the targeted knockout of the type I IFN receptor, pathogen recognition receptors, or key IRF signaling intermediates (11,44), which initiate the induction of hundreds of ISGs. Previous experiments in mice showed that the deletion of PKR, RNase L, or OAS1b correlated with increased susceptibility to WNV in mice (33,37,46), although more recent works suggested that at least some of the phenotypes (for PKR and RNase L) could be due to amplification rather than an execution of IFN signals (31,32,49). Given the increasing number of putative antiviral ISGs that regulate infection by WNV and other viruses (48), the expectation that the targeted deletion of any single gene will have dramatic effects may be unrealistic, and the more modest phenotype observed with viperin Ϫ/Ϫ mice should be expected.…”

Sensing of latent EBV infection through exosomal transfer of 5′pppRNA

“…Retinoic acid-inducible gene I (RIG-I) (14), IFN-induced proteins with tetratricopeptide repeats (IFITs) (15), and the double-stranded RNA-dependent protein kinase (PKR) can recognize 5′triphosphates (5′ppp)-bearing viral RNA in the cytoplasm (16). Antiviral signaling is also induced by modified self-RNAs under physiological stress conditions (17)(18)(19). Removal of proinflammatory self-RNAs, while maintaining the ability to selectively recognize virus-produced RNAs in the cell's cytoplasm, is essential for proper regulation of antiviral response.…”