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DNA Viruses : : Pathogens, Therapies and Compasses for Navigating Cancer

  • Author(s): Espantman, Kristen Carolyn
  • et al.
Abstract

The study of DNA virus-host protein interactions has revealed cellular proteins critical for cell growth and survival. In addition, the adenovirus has potential as a potent cancer therapy against the majority of tumors which lack a functional p53 pathway. For this oncolytic adenovirus to be realized, the ability of adenovirus to inactivate the p53 pathway must be eliminated. In Chapter 1, we reveal that a small early adenovirus protein E4-ORF3 prevents p53 from accessing DNA by instigating de novo heterochromatin formation specifically at p53 target genes. Unfortunately, full deletion of E4-ORF3 and another adenovirus protein that inactivates p53, E1B-55K, renders the virus defective for replication, even in cells lacking p53 function. Therefore, it is imperative to reveal the critical functions and residues of E4-ORF3 necessary to block p53 activation and support viral replication. In Chapter 2, we show that among the 7 diverse adenovirus subgroups, only Subgroup C E4-ORF3 proteins are capable of supporting viral replication and inactivating p53 target genes in an E1B-55K deleted adenovirus. Furthermore, we reveal that MRN mislocalization is also specific to Subgroup C E4-ORF3 while targeting of PML, TRIM24 and TRIM33 is conserved across subgroups. Thus, comparison of E4-ORF3 protein sequences from disparate subgroups reveals residues likely to be required for p53 target gene inactivation leading to creation of an oncolytic adenovirus in which this function is removed. Conserved E4 -ORF3 targets PML, TRIM24 and TRIM33 are members of the superfamily of Tripartite Motif proteins (TRIMs) that have similar oligomeric N-terminal domain structures and varied C-termini. E4-ORF3 may be targeting a critical subset of TRIM proteins for the benefit of adenovirus replication. In Chapter 3, we show that the TRIM interactome including first order interacting proteins contains over 900 nodes and 12,500 edges with members regulating a plethora of cellular pathways disrupted during virus replication. Using high-throughput imaging, we reveal 21 additional TRIMs that interact with E4-ORF3 and show that disparate PML targeting viral proteins Herpes Simplex Virus-1 ICP0 and Cytomegalovirus IE2 also disrupt 18 or 7 TRIMs, respectively. Moreover, we demonstrate that these viral proteins do not target a common TRIM domain, and that oligomerization among TRIMs can contribute to TRIM-viral protein interactions. Taken together, this work reveals novel functions of DNA virus proteins that will contribute to anti-viral and anti-cancer therapies to facilitate the human pursuit of life and happiness

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