Identification of CASC3 as a novel SADS-CoV restriction factor through liquid-liquid phase separation inhibiting viral replication.

Abstract

Swine acute diarrhoea syndrome coronavirus (SADS-CoV) is a newly emerging highly pathogenic virus that likely originated from the closely related HKU2 bat coronaviruses. The cross-species transmission potential of the virus not only caused colossal economic losses but also threatened public health. In this study, we identified 139 differentially expressed proteins (76 upregulated and 63 downregulated) after the infection of highly pathogenic SADS-CoV by unbiased proteomic sequencing. Among these, CASC3 was identified as a novel host restriction factor against SADS-CoV infection by RNA interference and overexpression experiments. Further, CASC3 underwent liquid-liquid phase separation, forming molecular condensates and colocalising with SADS-CoV in ST cells. Liquid-liquid phase separation was identified as a crucial step in CASC3 inhibition of SADS-CoV replication. These findings show that the process of CASC3 LLPS is a novel SADS-CoV potential target for therapeutic drug discovery, especially in the case that the specific receptors of SADS-CoV remain unclear.