Virus research
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The nonstructural protein 9 (Nsp9) of porcine reproductive and respiratory syndrome virus (PRRSV) has been recognized to play important roles in viral replication. The present study first screened that the DEAD-box RNA helicase 5 (DDX5) was a cellular protein interacting with the Nsp9 of PRRSV by a yeast two-hybrid method in a pulmonary alveolar macrophages (PAMs) cDNA library. Next, DDX5 was shown to interact with viral Nsp9 in the co-transfected HEK293 cells with the DDX5- and Nsp9-expressing plasmids, and the interaction between endogenous DDX5 and Nsp9 was also confirmed in MARC-145 cells infected with the Nsp9-expressing lentiviruses. ⋯ Moreover, in the HEK293 cells, MARC-145 cells and PAM cell lines co-transfected with the DDX5- and Nsp9-expressing plasmids, Nsp9 was shown to co-localize with DDX5 in the cytoplasm with a perinuclear pattern, and meanwhile in PRRSV-infected MARC-145 cells and PAMs, endogenous DDX5 was also found to co-localize with Nsp9. Finally, silencing the DDX5 gene in MARC-145 cells significantly impacted the replication of PRRSV, and while the over-expression of DDX5 could slightly enhance viral replication. These findings indicate that DDX5 positively regulates the replication of PRRSV via its interaction with viral Nsp9 in vitro.