Nonredundant roles of topoisomerase 2α and 2β in the cytosolic replication of vaccinia virus.

Vaccinia virus is a large enveloped DNA virus, which, like all poxviruses, replicates in the cytoplasm of infected cells. Vaccinia was historically thought to encode all the proteins required for its replication. However, more recent findings have shown that nuclear host proteins are redirected to the cytoplasm to facilitate viral replication. Among these, topoisomerase 2α (TOP2A) and 2β (TOP2B), which mediate nuclear transcription, DNA replication, and chromosome segregation are the most abundant host proteins associated with nascent viral genomes. Here, we investigate the mechanisms driving TOP2A and TOP2B cytoplasmic translocation and their role in viral replication. We found that early viral protein synthesis induces the cytosolic relocalization of both isoforms, which are subsequently recruited to viral factories by an interaction of their C-terminal domains with the viral ligase, A50. TOP2A promotes replication by interacting with the vaccinia DNA replication machinery. In contrast, TOP2B suppresses replication by enhancing the formation of double-stranded RNA and antiviral granules, containing components of the tRNA splicing ligase complex. Our analysis provides new insights into host-pathogen interactions during poxvirus infection and the role of topoisomerase 2 outside of the nucleus.