Encephalomyocarditis virus protein 2B* antagonises innate immune signalling by interacting with 14-3-3 protein family members

Abstract

ABSTRACTEncephalomyocarditis virus (EMCV) has for decades served as an important model RNA virus. Although most of the EMCV proteins are obtained via proteolytic cleavage of a long polyprotein, 2B* is expressed from a short overlapping open reading frame via an unusual protein-stimulated temporally dependent ribosomal frameshifting mechanism. The function of 2B* has not yet been characterised, though mutant viruses that are unable to express 2B* have a small plaque phenotype. Here we show that 2B* binds all seven members of the 14-3-3 protein family during virus infection. Binding is dependent on the 2B* C-terminal sequence RRNSS. IFN-β and IL-6 signalling are impeded following overexpression of 2B* but not a truncated version lacking the RRNSS residues, thus suggesting a 14-3-3-dependent role for 2B* in inhibiting MAVS signalling. We also find that this function is distinct from the effect of 2B* on plaque size, as a virus in which 2B* was similarly truncated exhibited near-wildtype plaque size, thus indicating that 2B* also harbours additional functions. This work provides the first identification of a role of 2B* in innate immune antagonism and expands our knowledge of the protein complement of this important model virus.IMPORTANCEEncephalomyocarditis virus (EMCV) infects a range of species, causing economically important reproductive disorders in pigs and encephalitis and myocarditis in rodents. Due to its wide host range, it is an important model pathogen for investigating virus-host interactions. EMCV expresses an accessory protein, 2B*, from an overlapping open reading frame via an unusual ribosomal frameshifting mechanism. Although the frameshifting mechanism has been established, the function of the 2B* protein had not previously been explored. Here, we determined the host proteins to which 2B* binds and found that it specifically binds to the entire 14-3-3 protein family which, among other roles, contribute to the innate immune response to viral infection in mammalian cells. This interaction requires a specific stretch of amino acids at the end of 2B*. By interacting with the 14-3-3 proteins, 2B* blocks immune response activation. Thus, 2B* is a novel antagonist of innate immunity.