SADS-CoV NS3 induces apoptosis by blocking the formation of Bcl-xL-BAK complex

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an emerging porcine coronavirus with characteristics of bat origin, posing a potential threat to animal welfare and public health. Recent studies have shown that apoptosis induced by SADS-CoV contributes to virus replication. However, the virus proteins involved in SADS-CoV-induced apoptosis and their potential molecular mechanisms remain largely unknown. This study found that the SADS-CoV accessory protein NS3 interacted with the BH3 domain of Bcl-xL in the mitochondria. This interaction disrupted the Bcl-xL-BAK complex, leading to increased activation of BAK and subsequent induction of mitochondrion-mediated apoptosis. Furthermore, knockout of Bcl-xL reduced the NS3-induced apoptosis and increased the replication of SADS-CoV. Additionally, deletion of the NS3 gene decreased SADS-CoV-induced apoptosis and diminished the viral pathogenicity in murine models, indicating that NS3 is a critical determinant of SADS-CoV pathogenicity. In conclusion, our findings firstly reveal the mechanism by which SADS-CoV NS3 regulates apoptosis to enhance the viral replication and pathogenicity.<b>IMPORTANCE</b>Swine acute diarrhea syndrome coronavirus (SADS-CoV) has caused significant disruptions in porcine breeding and raised concerns regarding potential human infection. Thus far, the roles of virus proteins in virus replication and pathogenesis remain largely unknown. Here, we first investigated the functions of SADS-CoV NS3 in apoptosis and viral pathogenicity. Our findings indicated that NS3 blocked the combination of anti-apoptosis protein Bcl-xL with pro-apoptosis protein BAK, then promoting the BAK pore-forming and inducing mitochondrion-mediated apoptosis, thereby enhancing the pathogenicity of virus. Moreover, we also discovered for the first time that Bcl-xL could act as an important antiviral factor to inhibit SADS-CoV replication. These results contribute valuable insights into the novel roles of bat-borne coronavirus accessory proteins in viral replication and pathogenicity in potentially infected hosts.