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Access Type
WSU Access
Date of Award
January 2023
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Biological Sciences
First Advisor
Haidong H. Gu
Abstract
ND10s are dynamic membrane-less nuclear organelles with numerous functions including antiviral responses. They are formed by the multimerization and subsequent SUMOylation of the PML protein. Various proteins are then recruited to ND10s through interaction with SUMO.Immediately after HSV-1 infection, ND10s converge to the incoming viral DNA to suppress the viral genes. Subsequently, ICP0, the viral immediate-early E3 ubiquitin ligase, localizes at ND10 to degrade PML, disassemble ND10, and de-repress the viral genes. This activation of viral gene expression is followed by the translocation of ICP0 to the cytoplasm. Previously, Gu lab reported that ICP0 can recognize and target PML isoforms differentially. The degradation of PML isoforms II, IV, and VI requires a SUMO interacting motif (SIM) located in ICP0 residues 362-364, whereas this SIM is dispensable for PML I degradation. Instead, residues 1-83 and 245-474 constitute a bipartite domain that can independently facilitate the degradation of PML-I. Here, I investigated the molecular basis and significance of both SIM-dependent and SIM-independent ICP0 substrate recognition. I found that SIM362-364 can target all SUMOylated PML isoforms including PML I. The surrounding 50 amino acids of this SIM are required for its proper function. Furthermore, I showed that in the C-terminus of ICP0, the SUMO-SIM interaction along with other protein binding sites enhances the degradation of PML II demonstrating the influence of ICP0 functional domains on its E3 ligase activity. My results showed that ICP0 has an additional distinctive targeting strategy for PML I. The first 83 residues of ICP0, target PML-I regardless of its SUMOylation status, outside of ND10 and even in the cytoplasm. For the first time, I showed that upon deletion of ICP0’s N-terminus, ND10-like structures reform in the nucleus late in infection and simultaneous with ICP0 cytoplasmic translocation. The reappearance of these ND10-like structures correlated with delayed viral late protein expression and lower viral yield suggesting a suppressive impact of the reformed ND10 on viral propagation. Taken together, I conclude that ICP0 primarily uses a SUMO-targeted strategy to degrade all SUMOylated PML isoforms in early infection to destroy ND10 and activate viral gene expression. The SUMO-independent targeting strategy is important for a continuous clearance of the cell from PML-I to avoid the reformation of ND10 at later hours. The newly found cytoplasmic PML-I degradation might reflect an inhibitory role of these reformed ND10 on the latest virus life cycle events such as assembly and egress.
Recommended Citation
Jan Fada, Behdokht, "Decoding The Dual Substrate Recognition Mechanisms Of Icp0 And Uncovering A Novel Targeting Strategy For Pml Isoform I Degradation" (2023). Wayne State University Dissertations. 3907.
https://digitalcommons.wayne.edu/oa_dissertations/3907