Construction and characterization of coronavirus nonstructural protein 3-host protein interaction networks unravel an important role of cleavage and polyadenylation specificity factor 6 in regulation of viral RNA replication

Coronavirus nonstructural protein 3 (nsp3) plays a crucial role in viral replication and immune evasion. However, functional and proteomic characterization of this protein, especially the interaction networks between nsp3 from different coronaviruses and host cell factors, is hindered by its huge size, complex structural feature and the presence of multiple transmembrane domains. In this study, we report the application of a high-performance cytoplasmic expression system to efficiently and accurately express the full-length nsp3 from betacoronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and gammacoronavirus infectious bronchitis virus (IBV), to investigate their interactions with host proteins using proteomics approaches. Our study identified 1,150 host proteins that interact with IBV nsp3 and 920 with SARS-CoV-2 nsp3. Among them, 658 are shared by the two nsp3 proteins. Further validation and preliminary characterization of seven selected candidates, DDX5, DDX39, DHX9, elF4A3, SRRT and CPSF6, demonstrated the reproducibility and reliability of the proteomics data. More interestingly, an important regulatory role of the nsp3-CPSF6 interaction in the replication and transcription of IBV gRNA and sgRNA was unraveled. The construction of nsp3-host protein interaction networks from two distantly related coronaviruses would have provided a foundation for future studies of host cell factors in the regulation of coronavirus replication and pathogenesis.