A 20-amino-acid Cardiovirus protein exhibits cytokine-mimicry activity to regulate viral replication

Viral protein genome-linked (VPg) is a small protein encoded by several non-enveloped positive-sense RNA viruses, including Cardiovirus . Although VPg is widely recognized as essential for viral RNA synthesis, its additional roles remain largely unexplored. Here, we report an alternative function of Cardiovirus VPg as an interferon-γ receptor agonist. During encephalomyocarditis virus (EMCV) infection, a member of the Cardiovirus genus, we uncovered that VPg from EMCV (VPg EMCV ) is released extracellularly from host cells. VPg EMCV is then sensed by uninfected host cells, activating the interferon-γ signaling cascade and ultimately producing nitric oxide (NO) through inducible NO synthase induction. NO accumulation is crucial for triggering potent cell death in cooperation with tumor necrosis factor α (TNF-α) signaling, with TNF-α also being induced as an antiviral host response during EMCV infection. We demonstrate that VPg EMCV , comprising merely 20 amino acids, can exhibit cytokine-mimicry activity, with the synergistic interplay between VPg EMCV and TNF-α signaling regulating viral replication and disease pathogenesis.