Baculovirus Infection Induces a DNA Damage Response That Is Required for Efficient Viral Replication

Abstract

Several mammalian viruses have been shown to induce a cellular DNA damage response during replication, and in some cases, this response is required for optimal virus replication. However, nothing is known about whether a DNA damage response is stimulated by DNA viruses in invertebrates. Cell cycle arrest and apoptosis are two of the downstream effects of the DNA damage response, and both are stimulated by baculovirus infection, suggesting a possible relationship between baculoviruses and the DNA damage response. In the study described in this report, we found that replication of the baculovirus Autographa californica M nucleopolyhedrovirus (AcMNPV) in the cell line Sf9, derived from the lepidopteran insect Spodoptera frugiperda, stimulated a DNA damage response, as indicated by an increased abundance of the S. frugiperda P53 protein (SfP53) and phosphorylation of the histone variant protein H2AX. Stimulation of the DNA damage response was dependent on viral DNA replication. Inhibition of the DNA damage response prevented both the increase in SfP53 accumulation and H2AX phosphorylation and also caused a 10-to 100-fold reduction in virus production, along with decreased viral DNA replication and late gene expression. However, silencing of Sfp53 expression by RNA interference did not significantly affect AcMNPV replication or induction of apoptosis by a mutant of AcMNPV lacking the antiapoptotic gene p35, indicating that these processes are not dependent on SfP53 in Sf9 cells.Eukaryotic cells constantly monitor the integrity of their genomes and rapidly respond to the presence of damaged DNA by activating DNA damage response pathways, which are initiated largely through the activation of two members of the phosphatidylinositol 3-kinase superfamily, ataxia telangiectasia mutated (ATM) and ATM and rad-3 related (ATR) (for a recent review, see reference 50). ATM is activated mainly in response to double-strand breaks in DNA, while ATR responds mainly to single-strand breaks and stalled replication forks. However, there is overlap in the downstream substrates of these kinases. ATM and ATR phosphorylate numerous effector proteins which function in cell cycle checkpoints, DNA repair, and stimulation of apoptosis. One of the many important substrates of ATM and ATR is the transcription factor P53, which regulates the expression of numerous genes that function in all three of these processes. Studies in Drosophila melanogaster have demonstrated that DNA damage responses, including the roles of ATM, ATR, and P53, share many similarities in insects and mammals (53).There is increasing evidence that the ability to manipulate the DNA damage response and associated downstream pathways is crucial for the replication of many viruses. Several mammalian viruses stimulate DNA damage response pathways as a consequence of infection, and these viruses have in turn evolved mechanisms to manipulate these pathways for their own benefit by exploiting or actively inhibiting different parts of the pathways (reviewed in reference 7). For exam...

Baculoviruses Modulate a Proapoptotic DNA Damage Response To Promote Virus Multiplication

“…Yields of budded virus were reduced ϳ100,000-fold. Thus, our findings agree with those of Huang et al (22), who found that the AcMNPV-induced DDR contributes to virus replication. Notably, the baculoviruses can usurp host DDR activities to promote vDNA replication by virtue of their ability to efficiently block the proapoptotic outcome at downstream steps with caspase inhibitors (Fig.…”

“…Despite the detrimental effects of virus-induced apoptosis, some viruses hijack components of the host's DNA damage response, including ATM and ATR, to promote virus multiplication (66). Caffeine's inhibitory effect on AcMNPV has suggested that baculoviruses do the same (22). To further explore this possibility, we also quantified the effects of ATM and ATR inhibition on AcMNPV replication.…”

“…AcMNPV also triggers a DDR in cultured cells of the natural lepidopteran host Spodoptera frugiperda (22). To further examine the connection between virus-induced apoptosis and the DDR, we compared the responses in Drosophila and Spodoptera, two evolutionarily distinct insect lineages that diverged ϳ350 million years ago (15).…”

“…Thus, our findings indicate that loss of cellular IAP function is a consequence of DDR activation. Because the Spodoptera DDR stimulates AcMNPV DNA replication (see below and reference 22), it is also possible that the DDR accelerates apoptosis by contributing directly to vDNA synthetic events in a type of feedback loop (Fig. 1).…”

“…The replication of mammalian virus DNA (vDNA) is a well-established initiator of the DDR, which is also a trigger for apoptosis in both vertebrates and invertebrates (reviewed in references 61 and 66). Indeed, AcMNPV DNA replication stimulates the DDR in cells derived from the permissive moth Spodoptera frugiperda (22). However, as is the case for many DNA viruses, the replication events that initiate the DDR are unknown.…”