Porcine cGAS-STING signalling induced apoptosis negatively regulates STING downstream IFN response and autophagy via different mechanisms

The innate immune cGAS-STING signalling pathway recognizes double-stranded DNA and induces the interferon (IFN) response, autophagy and apoptosis, exerting a broad antiviral effect. However, the mechanisms and interrelationship between STING induced downstream IFN, autophagy, and apoptosis in livestock have not been fully elucidated. Our previous study defined porcine STING (pSTING) induced IFN, autophagy and apoptosis, and showed that IFN does not affect autophagy and apoptosis, whereas autophagy inhibits both IFN and apoptosis, likely by promoting pSTING degradation. In this study, we further explored the underlying mechanism of pSTING induced apoptosis and the regulation of IFN and autophagy by apoptosis. First, pSTING induces endoplasmic reticulum (ER) stress and mitochondrial damage to activate caspases 9, 3, and 7, which drive intrinsic apoptosis. Second, pSTING triggered apoptosis inhibits the IFN response by activating caspase 7, which cleaves pIRF3 at the species specific D197/D198 site. Third, pSTING activated apoptotic caspases 9, 3, and 7 reduce the expression of ATG proteins, and cleave the ATG5-ATG12L1 complex, effectively inhibiting autophagy. Fourth, knockout of pSTING activated apoptosis heightens the IFN response and autophagy, while suppressing the replication of Herpes Simplex Virus type 1 (HSV-1), Vesicular Stomatitis Virus (VSV) and Pseudorabies Virus (PRV). This study sheds light on the molecular mechanisms of innate immunity in pigs.