Cellular Proteins PML and Daxx Mediate an Innate Antiviral Defense Antagonized by the Adenovirus E4 ORF3 Protein

Abstract

ABSTRACT The adenovirus (Ad) E4 ORF3 protein is both necessary and sufficient to reorganize a nuclear subdomain, the PML nuclear body (PML-NB), from punctate structures into elongated nuclear tracks. PML-NB disruption is recapitulated by a variety of DNA viruses that encode proteins responsible for compromising PML-NB integrity through different mechanisms. PML-NB disruption has been correlated with the antagonism of both innate and intrinsic immune responses. The E4 ORF3 protein is required for adenoviral DNA replication in the interferon (IFN)-induced antiviral state. This may reflect the fact that PML itself, in addition to several other PML-NB proteins, is encoded by an interferon-stimulated gene. Here, we demonstrate that reorganization of the PML-NB by E4 ORF3 antagonizes an innate antiviral response mediated by both PML and Daxx. Reduction of either of these proteins is sufficient to restore the replicative capacity of virus with the E4 ORF3 protein deleted in the IFN-induced antiviral state. Further, we provide evidence that both the HSV1 ICP0 and HCMV IE1 proteins, which disrupt PML-NBs by mechanistically distinct strategies, behave in a manner functionally analogous to E4 ORF3 with respect to antagonizing the IFN-induced antiviral state. In addition, we assert that this innate antiviral strategy mediated by PML and Daxx does not involve transcriptional repression. While early gene transcription is modestly diminished in the absence of E4 ORF3 protein expression, this reduction does not affect early protein function. We propose that, in addition to its ability to repress gene expression, the PML-NB participates in additional innate immune activities.