Species-specific cleavage of cGAS by picornavirus protease 3C disrupts mitochondria DNA-mediated immune sensing.

RNA viruses cause numerous infectious diseases in humans and animals. The crosstalk between RNA viruses and the innate DNA sensing pathways attracts increasing attention. Recent studies showed that the cGAS-STING pathway plays an important role in restricting RNA viruses via mitochondria DNA (mtDNA) mediated activation. However, the mechanisms of cGAS mediated innate immune evasion by RNA viruses remain unknown. Here, we report that seneca valley virus (SVV) protease 3C disrupts mtDNA mediated innate immune sensing by cleaving porcine cGAS (pcGAS) in a species-specific manner. Mechanistically, a W/Q motif within the N-terminal domain of pcGAS is a unique cleavage site recognized by SVV 3C. Three conserved catalytic residues of SVV 3C cooperatively contribute to the cleavage of pcGAS, but not human cGAS (hcGAS) or mouse cGAS (mcGAS). Additionally, upon SVV infection and poly(dA:dT) transfection, pcGAS and SVV 3C colocalizes in the cells. Furthermore, SVV 3C disrupts pcGAS-mediated DNA binding, cGAMP synthesis and interferon induction by specifically cleaving pcGAS. This work uncovers a novel mechanism by which the viral protease cleaves the DNA sensor cGAS to evade innate immune response, suggesting a new antiviral approach against picornaviruses.

Simultaneous detection of porcine reproductive and respiratory syndrome virus and porcine circovirus 3 by SYBR Green І-based duplex real-time PCR.

The SYBR Green І-based duplex real-time PCR assay was developed for simultaneous detection of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus 3 (PCV-3) genomes. PRRSV and PCV-3 were distinguished in the same sample by their distinctive melting temperature (Tm) which was 84 °C for PRRSV and 81.5 °C for PCV-3, and other non-targeted swine viruses showed no specific melting peaks. The detection limits of this assay were 46.1copies/µL for PRRSV and 49.3copies/µL for PCV-3, respectively. Thirty-three lung samples of porcine with respiratory and reproductive failure symptoms were collected and confirmed by the SYBR Green І-based real-time PCR assay and conventional PCR assay. The real-time PCR detection results showed that the PRRSV positive rate was 45.45%, the PCV-3 positive rate was 63.63%, the PRRSV and PCV-3 co-infection positive rate was 36.36%, which were more sensitive than conventional PCR detection. This duplex real-time PCR assay could be a rapid, sensitive and reliable method for the detection of PRRSV and PCV-3 co-infection.