Inhibition of Interferon Regulatory Factor 3 Activation by Paramyxovirus V Protein

Abstract

The V protein of Sendai virus (SeV) suppresses innate immunity, resulting in enhancement of viral growth in mouse lungs and viral pathogenicity. The innate immunity restricted by the V protein is induced through activation of interferon regulatory factor 3 (IRF3). The V protein has been shown to interact with melanoma differentiation-associated gene 5 (MDA5) and to inhibit beta interferon production. In the present study, we infected MDA5-knockout mice with V-deficient SeV and found that MDA5 was largely unrelated to the innate immunity that the V protein suppresses in vivo. We therefore investigated the target of the SeV V protein. We previously reported interaction of the V protein with IRF3. Here we extended the observation and showed that the V protein appeared to inhibit translocation of IRF3 into the nucleus. We also found that the V protein inhibited IRF3 activation when induced by a constitutive active form of IRF3. The V proteins of measles virus and Newcastle disease virus inhibited IRF3 transcriptional activation, as did the V protein of SeV, while the V proteins of mumps virus and Nipah virus did not, and inhibition by these proteins correlated with interaction of each V protein with IRF3. These results indicate that IRF3 is important as an alternative target of paramyxovirus V proteins. The family Paramyxoviridae includes numerous human and animal pathogens such as measles virus (MeV), mumps virus (MuV), respiratory syncytial virus, canine distemper virus, Newcastle disease virus (NDV), Nipah virus (NiV), and Hendra virus. Paramyxoviruses possess accessory proteins that are not essential for minimal virus growth but are essential for efficient and pathogenic infection. Sendai virus (SeV), which belongs to the family Paramyxoviridae, is a respiratory tract pathogen of rodents and has accessory proteins C and V. The SeV genome, which is approximately 15.4 kb, comprises six genes, N, P, M, F, HN, and L, and the genes individually encode one polypeptide. The P gene exceptionally encodes the C and V proteins as well as the P protein (27, 32).The C proteins, C=, C, Y1, and Y2, are synthesized from the colinear transcript of the P gene in an open reading frame (ORF) shifted from that of the P protein by alternative translational starts and a common stop codon. The C proteins have multiple functions, including interruption of the Jak/Stat pathway to inhibit interferon (IFN)-responsive gene activation (8, 10), inhibition of apoptosis (13, 26), viral RNA synthesis regulation (2,5,6,14,45), and assistance with virus particle formation (15,38,41). Inhibition of apoptosis may be linked to proper regulation of viral RNA synthesis by viral polymerase with the assistance of the C protein (13, 43).The V protein is synthesized from an additional mRNA, which is generated from the P gene by inserting a pseudotemplated G residue at the specific editing site in the middle of the gene (46, 47). Consequently, the P and V proteins share the same 317 residues at the amino terminus (P/V common region), and the V protein has a...

Paramyxovirus evasion of innate immunity: Diverse strategies for common targets

“…MeV C protein also inhibits IFN induction, correlating with its nuclear localisation [83] , although MeV C does not affect IRF-3 directly, and appears to have an undetermined nuclear target [83] . By contrast, cytoplasmic NDV and SeV V protein bind directly to IRF-3, thereby preventing its nuclear translocation [76] . Thus, paramyxovirus targeting of IRF-3-mediated signalling involves mechanisms that appear to differ significantly between species.…”

“…This unfolding disturbs the ATPase hydrolysis site, and it was shown using MeV V that increasing concentrations of V correlate with decreasing ATPase activity [74] . The MDA5 binding site has been mapped to the C-terminal region of the V proteins of PIV5, MeV, MuV, Newcastle disease virus (NDV), NiV, HeV and SeV [32,[69][70][71]75,76] , with conserved residues of the zinc-finger critical to the interaction. However, the precise molecular details differ between specific paramyxoviruses, with conserved cysteine residues in the large zinc finger loop, but not the smaller loop, of PIV5 V and NiV V dispensable for antagonism of IFN induction [32] , whereas MuV V and MeV V required all conserved cysteine residues [32] .…”

“…Rubulaviruses including MuV, hPIV2, and PIV5 use V protein as a decoy substrate for the IRF-3 kinases TANK-binding kinase 1 (TBK-1) and inhibitor of NF-κB kinase (IKK)e (Figure 3), both inhibiting phosphorylation of IRF-3 and facilitating IKKe/TBK-1 polyubiquitination and degradation to prevent further signalling [81] . Henipavirus V proteins do not cause IKKe/TBK-1 degradation [81] or block TLR-3/IRF-3 dependent signalling [76,81] . For henipaviruses, this appears to be a function of the W protein, as NiV W, although having no effect on MDA5 signalling, inhibited TLR-3-dependent phosphorylation of IRF-3 [82] .…”

“…Indeed, several transfection studies in different laboratories have generated conflicting mechanistic data for the same viral protein, including SeV C and MeV V protein [103][104][105][106][107]116,117,120,121] , suggesting that some reported differences between IFN antagonists of different paramyxovirus species/genera might arise from experimental rather than biological differences. Importantly, however, recent studies comparing in parallel the functions of V proteins from panels of paramyxoviruses have confirmed clear divergence in specific mechanisms/interactions [70,71,76] , indicating genuine divergence at the molecular level.…”

Human Parainfluenza Virus Type 2 V Protein Inhibits TRAF6-Mediated Ubiquitination of IRF7 To Prevent TLR7- and TLR9-Dependent Interferon Induction

“…The V protein of the human parainfluenza virus type 2 (HPIV2), mumps virus, and parainfluenza virus 5 in the genus Rubulavirus interacts with inducible I-kappa B (IB) kinase (IKKi)/TANK-binding kinase 1 (TBK1) and inhibits activation of interferon regulatory factor 3 (IRF3) by acting as alternative substrates for IKKi/TBK1 (15). On the other hand, the V proteins of Sendai virus (SeV), measles virus (MeV), and Newcastle disease virus interact with IRF3 and suppress the transcriptional activity of IRF3 (16). In contrast to these extensive studies on the blockade of RLR-dependent signaling, the molecular basis for the blockade of TLR7/9-dependent signaling has not been well characterized.…”