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Deletion of the Vaccinia B1 Kinase Reveals Essential Functions of this Enzyme Complemented Partly by the Homologous Cellular Kinase VRK2.

Research paper by Annabel T AT Olson, Amber B AB Rico, Zhigang Z Wang, Gustavo G Delhon, Matthew S MS Wiebe

Indexed on: 19 May '17Published on: 19 May '17Published in: Journal of virology



Abstract

The vaccinia B1 kinase is highly conserved among poxviruses and is essential for the viral lifecycle. B1 exhibits a remarkable degree of similarity to VRKs, a family of cellular kinases, suggesting that the viral enzyme has evolved to mimic VRK activity. Indeed, B1 and VRKs have been demonstrated to target a shared substrate, the DNA binding protein BAF, elucidating a signaling pathway important for both mitosis and the antiviral response. In this study, we further characterize the role of B1 during vaccinia infection to gain novel insights into its regulation and integration with cellular signaling pathways. We begin by describing the construction and characterization of the first B1 deletion virus (vvΔB1) produced using a complementing cell line expressing the viral kinase. Examination of vvΔB1 revealed that B1 is critical for production of infectious virions in various cell types and is sufficient for BAF phosphorylation. Interestingly, the severity of the defect in DNA replication following loss of B1 varied between cell types, leading us to posit that cellular VRKs partly complement for B1 in some cell lines. Using cell lines devoid of either VRK1 or VRK2 we tested this hypothesis and discovered that VRK2 expression facilitates DNA replication and allows later stages of the viral lifecycle to proceed in the absence of B1. Finally, we present evidence that the impact of VRK2 on vaccinia is largely independent of BAF phosphorylation. These data support a model in which B1 and VRK2 share additional substrates important for replication of cytoplasmic poxviruses.IMPORTANCE Viral mimicry of cellular signaling modulators provides clear evidence that the pathogen is targeting an important host pathway during infection. Poxviruses employ numerous viral homologs of cellular proteins, the study of which have yielded insights into signaling pathways used by both virus and cells alike. The vaccinia B1 protein is a homolog of cellular VRKs (vaccinia-related kinases) and is needed for viral DNA replication and likely other stages of the viral lifecycle. However, much remains to be learned about how B1 and VRKs overlap functionally. This study utilizes new tools including a B1 deletion virus and VRK knockout cells to further characterize the functional links between the viral and cellular enzymes. As a result, we have discovered that B1 and VRK2 target a common set of substrates vital to productive infection of this large cytoplasmic DNA virus.