Baculovirus DNA Replication-Specific Expression Factors Trigger Apoptosis and Shutoff of Host Protein Synthesis during Infection

Abstract

ABSTRACT Apoptosis is an important antivirus defense. To define the poorly understood pathways by which invertebrates respond to viruses by inducing apoptosis, we have identified replication events that trigger apoptosis in baculovirus-infected cells. We used RNA silencing to ablate factors required for multiplication of Autographa californica multicapsid nucleopolyhedrovirus (Ac M NPV). Transfection with double-stranded RNA (dsRNA) complementary to the Ac M NPV late expression factors ( lef s) that are designated as replicative lef s ( lef-1 , lef-2 , lef-3 , lef-11 , p143 , dnapol , and ie-1 / ie-0 ) blocked virus DNA synthesis and late gene expression in permissive Spodoptera frugiperda cells. dsRNAs specific to designated nonreplicative lef s ( lef-8 , lef-9 , p47 , and pp31 ) blocked late gene expression without affecting virus DNA replication. Thus, both classes of lef s functioned during infection as defined. Silencing the replicative lef s prevented Ac M NPV-induced apoptosis of Spodoptera cells, whereas silencing the nonreplicative lef s did not. Thus, the activity of replicative lef s or virus DNA replication is sufficient to trigger apoptosis. Confirming this conclusion, Ac M NPV-induced apoptosis was suppressed by silencing the replicative lef s in cells from a divergent species, Drosophila melanogaster . Silencing replicative but not nonreplicative lef s also abrogated Ac M NPV-induced shutdown of host protein synthesis, suggesting that virus DNA replication triggers inhibition of host biosynthetic processes and that apoptosis and translational arrest are linked. Our findings suggest that baculovirus DNA replication triggers a host cell response similar to the DNA damage response in vertebrates, which causes translational arrest and apoptosis. Pathways for detecting virus invasion and triggering apoptosis may therefore be conserved between insects and mammals.