Innate sensing of picornavirus infection involves cGAS-STING-mediated antiviral responses triggered by mitochondrial DNA release

Author summaryIt is widely known that picornaviruses inhibit host innate immune responses by regulating retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) pathways. However, the impact of picornavirus infection on cytosolic DNA sensors remains unknown. Here, we found that picornavirus infection causes mitochondrial dysfunction that triggers mitochondrial DNA release via mitochondrial permeability transition pore (mPTP). The released mitochondrial DNA subsequently activates cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING)-mediated signaling transduction, contributing to type I interferon expression. In addition, we identified novel antagonistic mechanisms by which picornavirus 2C proteins antagonize cGAS-STING signaling pathway activation and determined new antagonistic sites in 2C proteins. We conclude that the cGAS-STING signaling pathway is critical for suppressing picornavirus infections, and picornaviral 2C proteins block its activation through multiple strategies to favor virus replication. For the first time, our study determines the antiviral role of cGAS-STING signaling pathway in picornavirus infection and describes a picornavirus-mediated inhibitory effect on DNA-triggered innate immune signaling. Cyclic GMP-AMP synthase (cGAS) plays a key role in the innate immune responses to both DNA and RNA virus infection. Here, we found that enterovirus 71 (EV-A71), Seneca Valley virus (SVV), and foot-and-mouth disease virus (FMDV) infection triggered mitochondria damage and mitochondrial DNA (mtDNA) release in vitro and vivo. These responses were mediated by picornavirus 2B proteins which induced mtDNA release during viral replication. SVV infection caused the opening of mitochondrial permeability transition pore (mPTP) and led to voltage-dependent anion channel 1 (VDAC1)- and BCL2 antagonist/killer 1 (Bak) and Bak/BCL2-associated X (Bax)-dependent mtDNA leakage into the cytoplasm, while EV-A71 and FMDV infection induced mPTP opening and resulted in VDAC1-dependent mtDNA release. The released mtDNA bound to cGAS and activated cGAS-mediated antiviral immune response. cGAS was essential for inhibiting EV-A71, SVV, and FMDV replication by regulation of IFN-beta production. cGAS deficiency contributed to higher mortality of EV-A71- or FMDV-infected mice. In addition, we found that SVV 2C protein was responsible for decreasing cGAS expression through the autophagy pathway. The 9th and 153rd amino acid sites in 2C were critical for induction of cGAS degradation. Furthermore, we also show that EV-A71, CA16, and EMCV 2C antagonize the cGAS-stimulator of interferon genes (STING) pathway through interaction with STING, and highly conserved amino acids Y155 and S156 were critical for this inhibitory effect. In conclusion, these data reveal novel mechanisms of picornaviruses to block the antiviral effect mediated by the cGAS-STING signaling pathway, which will provide insights for developing antiviral strategies against picornaviruses.

Automated summary

This study reveals that picornavirus infection causes mitochondrial dysfunction and leads to the release of mitochondrial DNA through the mitochondrial permeability transition pore. The released mitochondrial DNA activates the cGAS-STING signaling pathway, resulting in the expression of type I interferon and suppression of viral infection. Additionally, picornavirus 2C proteins antagonize the activation of the cGAS-STING signaling pathway through multiple strategies, facilitating virus replication.