Baculovirus 25K hijacks host UAP56 to facilitate nuclear export of viral mRNA in insect cells.

Bombyx mori nucleopolyhedrovirus (BmNPV) is a baculovirus that hijacks host genes to cause viral infections. UAP56 is highly conserved in different species. Previous studies have shown that UAP56 is involved in several viral infections. However, its role in insect-baculovirus interactions remains unknown. In this study, we aimed to identify which BmNPV proteins interact with host UAP56 and to characterize the associated mechanism underlying viral infection using a BmNPV-silkworm model. Our data indicated that CCT018159, an inhibitor of UAP56, could suppress the proliferation of BmNPV and that the addition of CCT018159 within 12 h post-infection had a significant protective effect on BmE cells. To identify the interacting viral proteins, recombinant UAP56-GST was constructed through prokaryotic expression for pull-down screening. Further, immunofluorescence, co-immunoprecipitation, and pull-down analyses demonstrated that the late viral protein, 25K, directly binds to UAP56. CCT018159 did not affect the co-localization of 25K and UAP56 but disrupted the interaction between them, resulting in significant upregulation of viral mRNA content in the nucleus and opposite trend in the cytoplasm. Overexpression of 25K and UAP56 caused a significant reduction in viral mRNA content in the nucleus and a significant increase in the cytoplasm. The addition of CCT018159 counteracted this effect. Overall, our data show that the baculovirus 25K protein hijacks host UAP56 to facilitate the nuclear export of viral mRNA to cause infections.IMPORTANCENuclear export of viral mRNA is essential for viral proliferation. UAP56 is highly conserved among species and is involved in multiple viral infections. In this study, we found that the Bombyx mori nucleopolyhedrovirus 25K protein hijacks host UAP56 to facilitate viral mRNA nuclear export, and disruption of their interactions can inhibit viral proliferation. Our results provide novel insights into the mechanism of insect-baculovirus interaction and emphasize the important role that 25K plays in baculovirus infection. This research not only deepens our understanding of the transcription and translation mechanisms of baculoviruses but also provides potential targets for antiviral research.