BST-2 Promotes N Protein Degradation and Inhibits Viral Replication Through the MARCHF8/NDP52 Autophagy Pathway

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a recently discovered enteric coronavirus that has caused considerable economic losses in the pig industry. SADS-CoV was first reported in 2017 in Guangdong Province, China, and subsequently in Fujian, Guangxi, Henan and Jiangxi Provinces. Bone marrow stromal cell antigen 2 (BST-2), also known as tetherin, acts as an antiviral protein to limit the release of a wide range of enveloped viruses. However, the relationship between BST-2 and SADS-CoV has rarely been studied. Here, we showed that endogenous BST-2 expression is downregulated by SADS-CoV infection in Vero-E6 and ST cells by 2- to 3-fold. The overexpression of BST-2 inhibited SADS-CoV replication, whereas the knockdown of the BST-2 gene in Vero cells restored SADS-CoV replication. Further study revealed that BST-2 targets the SADS-CoV nucleocapsid protein (N) and decreases N protein expression, and that the BST-2 transmembrane (TM) domain is essential for this activity. Moreover, the degradation of the SADS-CoV N protein promoted by BST-2 is mediated by the membrane-associated ring-CH-type finger 8 (MARCHF8)/calcium binding and coiled-coil domain 2 (NDP52) autophagosome pathway. Overall, we found that BST-2 suppresses viral proliferation by inducing the breakdown of the SADS-CoV N protein via the MARCHF8/NDP52 pathway.