Exploitation of cytoplasmic and nuclear actin by baculoviruses

Abstract

Diverse bacterial and viral pathogens hijack the actin cytoskeleton of host cells to facilitate processes such as attachment, internalization, or spread. Among known pathogens, baculoviruses are unique in their ability to manipulate actin both in the cell cytoplasm and nucleus. We seek to determine how baculoviruses exploit actin to reveal new roles for actin in pathogenesis, and to illuminate the poorly understood function and regulation of nuclear actin. Using time‐lapse microscopy, we find that Autographa californica Multiple Nucleopolyhedrovirus (AcMNPV) undergoes actin‐based motility within the cell cytoplasm. Motility requires p78/83, a viral capsid protein that mimics host WASP proteins and activates actin assembly with the host Arp2/3 complex. As with other pathogens, moving AcMNPV are propelled into surface projections that may function in cell‐to‐cell spread. However, unlike other pathogens, motility also enhances viral collision with the nucleus, enabling translocation into the nucleus, where replication takes place. Once in the nucleus, AcMNPV induces nuclear actin accumulation, and then assembles nuclear actin using p78/83 to activate the host Arp2/3 complex. Nuclear actin assembly by p78/83 and Arp2/3 complex is essential for progeny production. Further study of this novel mode of pathogenesis will likely reveal elusive details about the regulation and function of nuclear actin.