Baculoviruses Modulate a Proapoptotic DNA Damage Response To Promote Virus Multiplication

Abstract

The baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) initiates apoptosis in diverse insects through events triggered by virus DNA (vDNA) replication. To define the proapoptotic pathway and its role in antivirus defense, we investigated the link between the host's DNA damage response (DDR) and apoptosis. We report here that AcMNPV elicits a DDR in the model insect Drosophila melanogaster. Replication of vDNA activated DDR kinases, as evidenced by ATM-driven phosphorylation of the Drosophila histone H2AX homolog (H2Av), a critical regulator of the DDR. Ablation or inhibition of ATM repressed H2Av phosphorylation and blocked virus-induced apoptosis. The DDR kinase inhibitors caffeine and KU55933 also prevented virus-induced apoptosis in cells derived from the permissive AcMNPV host, Spodoptera frugiperda. This block occurred at a step upstream of virus-mediated depletion of the cellular inhibitor-of-apoptosis protein, an event that initiates apoptosis in Spodoptera and Drosophila. Thus, the DDR is a conserved, proapoptotic response to baculovirus infection. DDR inhibition also repressed vDNA replication and reduced virus yields 100,000-fold, demonstrating that the DDR contributes to virus production, despite its recognized antivirus role. In contrast to virus-induced phosphorylation of Drosophila H2Av, AcMNPV blocked phosphorylation of the Spodoptera H2AX homolog (SfH2AX). Remarkably, AcMNPV also suppressed SfH2AX phosphorylation following pharmacologically induced DNA damage. These findings indicate that AcMNPV alters canonical DDR signaling in permissive cells. We conclude that AcMNPV triggers a proapoptotic DDR that is subsequently modified, presumably to stimulate vDNA replication. Thus, manipulation of the DDR to facilitate multiplication is an evolutionarily conserved strategy among DNA viruses of insects and mammals.

Baculovirus F-Box Protein LEF-7 Modifies the Host DNA Damage Response To Enhance Virus Multiplication

“…As is the case for most DNA viruses, the baculovirus replication events that initiate the DDR are unknown, but it is expected that rolling-circle-and recombination-related intermediates (16) that resemble damaged DNA are involved. Despite required participation of the host DDR, ␥-H2AX is suppressed during AcMNPV DNA replication (3). Furthermore, Ac-MNPV is capable of repressing ␥-H2AX triggered by DNA damage-inducing pharmacological agents.…”

“…pGFP HA -SfH2AX and pHSEpiHis expression plasmids for AcMNPV replication factors (kindly provided by L. Passarelli, Kansas State University) were described previously (3,29). LEF-7 residues 15 to 52 were replaced with Gly-Ser and residues Leu15-Pro16 were replaced with Ala-Ala by site-directed mutagenesis to generate expression plasmids pHSEpiHis/LEF-7(⌬F-box) and pHSEpiHis/LEF-7(LP/AA), respectively.…”

“…The DDR is capable of detecting incoming or replicating viral DNA (vDNA) and activating potent antiviral defenses, including apoptosis (reviewed in reference 1). Nonetheless, certain DNA viruses, such as the mammalian herpesviruses and insect baculoviruses, require the host DDR for efficient multiplication (2)(3)(4)(5)(6)(7). Therefore, these viruses frequently activate the DDR but alter this response to ablate its antiviral effects and exploit its proviral functions (1,8).…”

“…In contrast, the prototype baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) represses ␥-H2AX during infection of permissive insect hosts (3). Replication of the circular DNA genome (134 kb) of AcMNPV activates the DDR, which provides activities essential for efficient virus multiplication (2,3). As is the case for most DNA viruses, the baculovirus replication events that initiate the DDR are unknown, but it is expected that rolling-circle-and recombination-related intermediates (16) that resemble damaged DNA are involved.…”

“…In contrast, the prototype baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) represses ␥-H2AX during infection of permissive insect hosts (3). Replication of the circular DNA genome (134 kb) of AcMNPV activates the DDR, which provides activities essential for efficient virus multiplication (2,3).…”