mBio (Dec 2023)
Early enterovirus translation deficits extend viral RNA replication and elicit sustained MDA5-directed innate signaling
Abstract
ABSTRACTEnteroviruses (EVs)—positive-sense single-strand RNA viruses of Picornaviridae—are among the most common human viral pathogens. Unlike other cytoplasmic viral RNAs (vRNAs), which are detected by RIG-I, sensing of EV RNAs is mediated primarily by MDA5. EVs evolved with rapid, cytotoxic life cycles as a means of host cell interference, ostensibly to suppress MDA5-orchestrated antiviral type-I interferon (IFN) responses. At the core of this strategy are viral 2A protease (2Apro)-directed cleavage of the eukaryotic initiation factor (eIF)4G—the central translation initiation scaffold and ribosome adaptor—and degradation of nuclear pores. EV MDA5 agonism has an intriguing innate footprint, characterized by polar TBK1-IFN regulatory factor 3 (IRF3) signaling, which fuels sustained type-I IFN release to provide context for antitumor CD8+ T-cell priming after in situ cancer vaccination. Here we compared EV-host interactions between wild-type EVs and the highly attenuated recombinant polio:rhinovirus chimera and cancer immunotherapy agent (PVSRIPO) to test how targeted inhibition of discrete steps in the viral life cycle affects the innate antiviral response. Our investigations demonstrate that sustained MDA5-TBK1-IRF3 signaling elicited by PVSRIPO is the result of inefficient immediate 2Apro-directed eIF4G degradation, while wild-type EVs counter host innate type-I IFN defenses via rapid eIF4G cleavage. The MDA5-directed innate signature of profoundly attenuated EVs may provide efficient innate immune-stimulatory assets, for example, in in situ cancer vaccination strategies.IMPORTANCEMultiple pattern recognition receptors sense vRNAs and initiate downstream innate signaling: endosomal Toll-like receptors (TLRs) 3, 7, and 8 and cytoplasmic RIG-I-like receptors (RLRs) RIG-I, and MDA5. They engage distinct signaling scaffolds: mitochondrial antiviral signaling protein (RLR), MyD88, and TLR-adaptor interacting with SLC15A4 on the lysosome (TLR7 and TLR8) and toll/IL-1R domain-containing adaptor inducing IFN (TLR3). By virtue of their unusual vRNA structure and direct host cell entry path, the innate response to EVs uniquely is orchestrated by MDA5. We reported that PVSRIPO’s profound attenuation and loss of cytopathogenicity triggers MDA5-directed polar TBK1-IRF3 signaling that generates priming of polyfunctional antitumor CD8+ T-cell responses and durable antitumor surveillance in vivo. Here we unraveled EV-host relations that control suppression of host type-I IFN responses and show that PVSRIPO’s deficient immediate host eIF4G cleavage generates unopposed MDA5-directed downstream signaling cascades resulting in sustained type-I IFN release.
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