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Nuclear Signaling Cascades during Poxvirus Infection: Pro-viral Contributions from the Cellular VRK1 Kinase that Are Dictated by the B12 Pseudokinase
Poxvirus proteins remodel signaling throughout the cell by targeting host enzymes for inhibition and redirection. Vaccinia virus (VACV) proteins modulate a hostile cytoplasmic environment containing bountiful cytoplasmic DNA sensors and host defense proteins to successfully undergo their lifecycle. While the molecular mechanisms involved are incompletely understood, the VACV B1 kinase and B12 pseudokinase intersect with signaling processes mediated by their cellular homologs termed the vaccinia-related kinases (VRKs) to modulate VACV replication. In this PhD dissertation, we expand upon previous studies of the B1-B12 signaling axis to gain insights into B12 function. These studies began by demonstrating a pro-viral function for VRK1 to phosphorylate BAF and inhibit BAF anti-viral activity. We find that B12 and VRK1 form a complex that modulates VRK1 activity and inhibits VRK1-mediated BAF phosphorylation. Further investigation into B12 and VRK1 co-regulation demonstrated that VRK1 stabilizes B12 and that both proteins coinfluence their respective solubility and subcellular localization, suggesting that B12 and VRK1 may be tethered cooperatively to chromatin. Interestingly, we characterize a point mutation of B12 that disrupts interaction with VRK1 and renders B12 non-repressive during infection. Lastly, examination of VRK1 interacting partners revealed that a subset of its interacting partners were either increased or decreased upon infection. Strikingly, a correlation between loss of VRK1/BAF interaction and inhibition of VRK1-mediated BAF phosphorylation is demonstrated. Furthermore, we discover that the host chromatin-modifying HUSH complex interacts with VRK1 and its core member TASOR1 decreases in protein abundance upon VACV infection. In addition, another member MPP8 was found to interact with several VACV host-modulation viral proteins found at replication factories. Taken together, these findings suggest VACV manipulates a previously uncharacterized role of the HUSH complex to act as a poxvirus anti-viral factor. Overall, the studies within this PhD dissertation characterize a B12 signaling axis governing VRK1 regulation and provide novel insights into the complex mechanisms that poxviruses use to hijack homologous cellular signaling pathways during infection.
Linville, Alexandria C, "Nuclear Signaling Cascades during Poxvirus Infection: Pro-viral Contributions from the Cellular VRK1 Kinase that Are Dictated by the B12 Pseudokinase" (2022). ETD collection for University of Nebraska - Lincoln. AAI29321002.