Mechanism of mda-5 Inhibition by Paramyxovirus V Proteins

Abstract

The RNA helicases encoded by melanoma differentiation-associated gene 5 (mda-5) and retinoic acidinducible gene I (RIG-I) detect foreign cytoplasmic RNA molecules generated during the course of a virus infection, and their activation leads to induction of type I interferon synthesis. Paramyxoviruses limit the amount of interferon produced by infected cells through the action of their V protein, which binds to and inhibits mda-5. Here we show that activation of both mda-5 and RIG-I by double-stranded RNA (dsRNA) leads to the formation of homo-oligomers through self-association of the helicase domains. We identify a region within the helicase domain of mda-5 that is targeted by all paramyxovirus V proteins and demonstrate that they inhibit activation of mda-5 by blocking dsRNA binding and consequent self-association. In addition to this commonly targeted domain, some paramyxovirus V proteins target additional regions of mda-5. In contrast, V proteins cannot bind to RIG-I and consequently have no effect on the ability of RIG-I to bind dsRNA or to form oligomers.Mammalian cells contain a variety of pattern recognition receptors that recognize foreign macromolecules termed pathogenassociated molecular patterns (PAMPs). Viral PAMPs generated in the cytosol during replication are recognized by the DExD/H-box RNA helicases coded for by melanoma differentiation-associated gene 5 (mda-5) and retinoic acid-inducible gene I (RIG-I) (reviewed in reference 30) and stimulate the production of type I interferon (IFN), which constitutes a major component of the innate immune response to virus infection (reviewed in reference 21). It is becoming clear that viruses generate a variety of different PAMPs and that, rather than being redundant, mda-5 and RIG-I show ligand specificity and are therefore differentially sensitive to activation by different viruses. For example, RIG-I seems to be more important for IFN induction in response to hepatitis C virus (HCV) (6, 24) and influenza A virus (12, 19), while mda-5 is necessary for responses to picornaviruses (7,12). Both mda-5 and RIG-I can be activated by the synthetic double-stranded RNA (dsRNA) poly(I-C), but a recent study suggests that the length of the dsRNA influences whether IFN induction is dependent on mda-5 or RIG-I, with mda-5 being more important for induction by long dsRNA and RIG-I more important for induction by short dsRNA (11). In addition to length, other structural features of viral RNAs can also determine receptor activation. For example, single-stranded RNA (ssRNA) and dsRNA molecules bearing a 5Ј triphosphate induce IFN via RIG-I and not mda-5 (10, 19). This motif is recognized as nonself, since most cellular RNAs are either capped or have a 5Ј monophosphate. IFN induction by RNA purified from influenza A virus, vesicular stomatitis virus, and rabies virus requires RIG-I and is dependent on the presence of a 5Ј triphosphate, underlining the importance of this motif as a genuine viral PAMP (8,10,19).mda-5 and RIG-I share a common domain structure with two tandem C...

Strain-to-strain difference of V protein of measles virus affects MDA5-mediated IFN-β-inducing potential

“…Accordingly, we found that the MV V protein interacted with MDA5 via the cysteine-rich region. Childs et al (2009) reported that the V protein of paramyxovirus specifically inhibited activation of the MDA5 pathway, but not the RIG-I pathway, by specifically binding to the helicase domain of MDA5 and hindering MDA5 from recruiting dsRNA. Consistent with their report, the V protein thus blocks sensing dsRNA via MDA5 to disassemble oligomerization of MDA5.…”

“…Hence, the 272C residue is crucial for the V protein to block MDA5 function and MDA5 is the molecule which V protein targets for inhibition of the initial induction of IFN-E. For this reason, the ED strain used in this study allowed infected cells to induce IFN-E mRNA even in the absence of DI RNA. A previous report showed that the V protein of Sendai virus binds MDA5 via the cysteine-rich region which is conserved among paramyxoviruses (Childs et al, 2009). Accordingly, we found that the MV V protein interacted with MDA5 via the cysteine-rich region.…”

“…The V and C proteins of MV are not essential products (Radecke and Billeter, 1996) but play important roles in MV virulence (Patterson et al, 2000). The V protein has been shown to inhibit IFN induction via binding to MDA5 (Childs et al, 2007(Childs et al, , 2009). On the other hand, the C protein does not block the IFN-inducing pathway, but affects infectivity by acting as a regulator of viral RNA synthesis (Nakatsu et al, 2008).…”

Hepatitis B virus X protein suppresses virus-triggered IRF3 activation and IFN-β induction by disrupting the VISA-associated complex

“…18,19 The V proteins of paramyxoviruses interact with MDA-5 to block its activity, which leads to a reduction in IFN-b promoter activation. 20 The cysteine protease NS3/4A of hepatitis C virus cleaves VISA and the TLR3 adapter protein TRIF, thereby blocking RIG-I-and TLR3-mediated induction of the type I IFNs. 21,22 The A52 and A46 proteins of vaccinia virus target multiple TIR proteins, including TRIF, to block TLR3-and TLR4-mediated induction of type I IFNs.…”

Paramyxovirus evasion of innate immunity: Diverse strategies for common targets

“…The V proteins of at least 13 paramyxoviruses tested bind to MDA5 to inhibit IFN induction [32,[69][70][71] . 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] .…”