DEAD-box RNA helicase 21 interacts with the nucleocapsid protein and inhibits porcine deltacoronavirus infection through upregulation of interferon responses

DEAD-box RNA helicase 21 (DDX21), a conserved RNA helicase of the DEAD-box family, serves as a key regulator of multiple fundamental cellular processes, including RNA metabolism, ribosome biogenesis, transcriptional regulation, and genomic stability. Our previous work has demonstrated an interaction between DDX21 and the nucleocapsid (N) protein of porcine deltacoronavirus (PDCoV). However, the specific role of DDX21 during PDCoV infection remains largely elusive. In the present study, we show that overexpression of DDX21 significantly restricts PDCoV infection in PK15, IPEC-J2, and HeLa cells, whereas knockout of DDX21 markedly enhances PDCoV replication in HeLa cells. Mechanistically, we identified that the N-terminal domainNTD of PDCoV N binds to the 1-217 amino acid region of DDX21, thereby inducing the cytoplasmic redistribution of DDX21 from the nucleus. Furthermore, DDX21-mediated suppression of PDCoV replication coincides with elevated interferon-β (IFN-β) production and interferon-stimulated geneISG expression. Importantly, PDCoV infection significantly downregulates DDX21 expression to antagonize its antiviral function, and similar antagonistic effects are observed for the coronaviruses from different genera. Collectively, our findings demonstrate that DDX21 interacts with the nucleocapsid protein and correlates with altered interferon signaling during coronavirus infection, which provides novel insights into the development of strategies for the prevention and control of coronavirus infections. IMPORTANCE: . Conversely, PDCoV infection markedly downregulates DDX21 expression. Furthermore, we demonstrated that the N-terminal 1-217 amino acid domain of DDX21 specifically interacts with the N-terminal domain (NTD) of the PDCoV nucleocapsid (N) protein. This interaction facilitates the nuclear-to-cytoplasmic translocation of DDX21, which correlates with an elevated host immune response. The upregulated interferon signature coincides with suppressed PDCoV replication. In addition, DDX21 exhibits antiviral activity against multiple coronaviruses from different genera. Collectively, this study provides novel insights into host-coronavirus interaction mechanisms and identifies a candidate target for anti-CoV therapeutic development.