Paramyxovirus V Proteins Interact with the RNA Helicase LGP2 To Inhibit RIG-I-Dependent Interferon Induction

Abstract

b RIG-I and mda-5 are activated by viral RNA and stimulate type I interferon production. Laboratory of genetics and physiology 2 (LGP2) shares homology with RIG-I and mda-5 but lacks the CARD domains required for signaling. The V proteins of paramyxoviruses limit interferon induction by binding mda-5 and preventing its activation; however, they do not bind RIG-I and have not been considered inhibitors of RIG-I signaling. Here we uncover a novel mechanism of RIG-I inhibition in which the V protein of parainfluenzavirus type 5 (PIV5; formerly known as simian virus type 5 [SV5]) interacts with LGP2 and cooperatively inhibits induction by RIG-I ligands. A complex between RIG-I and LGP2 is observed in the presence of PIV5-V, and we propose that this complex is refractory to activation by RIG-I ligands. The V proteins from other paramyxoviruses also bind LGP2 and demonstrate LGP2-dependent inhibition of RIG-I signaling. This is significant, because it demonstrates a general mechanism for the targeting of the RIG-I pathway by paramyxoviruses. Virus infection stimulates innate immune responses in the host, among which the production of type I interferon (IFN) plays a critical role in restricting virus replication, via the upregulation of a large number of IFN-stimulated genes, and through the modulation of subsequent adaptive immune responses (reviewed in reference 37). IFN induction is triggered by the recognition of pathogen-associated molecular patterns (PAMPs), principally those associated with viral nucleic acids, which are seen as foreign by cellular pattern recognition receptors (PRRs; reviewed in reference 21). The RNA helicases RIG-I and mda-5 are the two bestcharacterized cytoplasmic PRRs; RIG-I preferentially recognizes RNA molecules with an uncapped 5=-triphosphate in a short region of blunt double-stranded RNA (dsRNA), while mda-5 recognizes longer molecules of dsRNA which need not be 5=-triphosphorylated (13,16,32,33,42,44; reviewed in reference 43). Viral RNA binds to the C-terminal regulatory domain (RD) of RIG-I or mda-5, and it is this region that confers specificity of PAMP recognition, although the central RNA helicase domain may also be involved in binding longer RNA molecules (22,24,28,49,52). RNA binding causes a conformational change which promotes oligomerization and allows interaction of the N-terminal CARD domains of RIG-I or mda-5 with the mitochondrial adapter protein IPS-1 (also known as VISA, MAVS, and CARDIF). This initiates a signaling cascade leading to activation and nuclear translocation of the transcription factors IRF-3 and NF-B, which are needed to turn on transcription of the IFN-␤ gene.While the interactions between synthetic PAMPs and RIG-I or mda-5 have been well characterized, the types of PAMPs recognized by RIG-I and mda-5 during viral infections are less clear. Mice lacking mda-5 showed no IFN induction in response to the picornavirus encephalomyocarditis virus (EMCV) (10, 17), consistent with the generation of a dsRNA replicative intermediate for this virus; RIG-I 0/0 mice...

Toward a crystal-clear view of the viral RNA sensing and response by RIG-I-like receptors

“…56 This evasion strategy, while apparently specific for MDA5 and LGP2, may also indirectly act against RIG-I through LGP2 via an undefined mechanism. 56,57 Very little is known about how similar or different LGP2 is from RIG-I or MDA5 in recognizing various RNA ligands. However, recently, Bruns et al demonstrated that robust basal ATPase activity allows LGP2 to diversify its RNA recognition capacity.…”

Paramyxovirus evasion of innate immunity: Diverse strategies for common targets

“…Rinderpest virus (RPV) may differ, as it appears to use the C protein rather than V to inhibit MDA5 signalling, although the binding of RPV V to MDA5 has not been examined [72] . and Salem virus (SalV) were shown to bind a specific region within/proximal to residues 701-816 of the MDA5 helicase domain, independently of the MDA5 ligand dsRNA [70,71,73] , thereby blocking dsRNA-MDA5 interaction [70] . Although a recent study of PIV5 V identified a change in the dsRNA-binding properties of MDA5 when V was co-expressed, rather than a complete inhibition, suggesting that V may still allow non-cooperative dsRNA binding [74] .…”

“…However, recent data has indicated that V proteins can inhibit RIG-Ⅰ by interaction with another cellular helicase, the laboratory of genetics and physiology 2 (LGP2) [73] , via a region of LGP2 homologous to the V protein binding region in MDA5 [71,73] . The interaction appears to be dependent on the unique C-terminal domain of V protein, as PIV5 P protein did not bind to LGP2, but the C-terminal domains of MeV and MuV V proteins were necessary and sufficient for the interaction [71,73] .…”

Roles of nuclear trafficking in infection by cytoplasmic negative-strand RNA viruses: paramyxoviruses and beyond

“…LGP2 (Cyt) (Childs et al, 2012); STAT1 and STAT2 (Cyt or Nuc ¶) (Ulane & Horvath, 2002); DDB1 (Cyt or Nuc ¶) (Ulane & Horvath, 2002); Cul4A (Cyt) (Ulane & Horvath, 2002); IKK" and TBK1 (Cyt) (Lu et al, 2008) …”

“…LGP2 (Cyt) (Childs et al, 2012); STAT1, STAT2 and STAT3 (Cyt or Nuc ¶) (Palosaari et al, 2003); JAK1 (PM) (Caignard et al, 2007); IRF-9 Cyt & Nuc (Precious et al, 1995) Cyt & Nuc (Paterson et al, 1995) N (Randall & Bermingham, 1996) MDA5 (Cyt) (Andrejeva et al, 2004);…”