| dcterms.abstract | Adenovirus (Ad) is a human DNA tumor virus that has been used extensively as a model to understand many fundamental cellular processes and host-pathogen interactions. During infection, the Ad type 5 (Ad5) early protein, E4-ORF3, forms unique track-like structures throughout nuclei of infected cells. E4-ORF3 tracks serve to relocalize and sequester many cellular proteins, including Mre11 and Nbs1, two antiviral components of the DNA damage-responsive MRN complex. Relocalization of Mre11 and Nbs1 to E4-ORF3 tracks facilitates their post-translational modification with the small ubiquitin-like modifier, SUMO. SUMOylation is essential to the regulation of many cellular processes, including transcription, replication, and DNA repair, and can have diverse substrate-specific effects on proteins. Since many cellular proteins are recruited to E4-ORF3 tracks, we hypothesized that E4-ORF3 may induce SUMOylation of additional unidentified cellular factors during Ad infection. The studies detailed herein focus on identifying cellular proteins SUMOylated in an E4-ORF3-dependent manner, describing the functional consequences of E4-ORF3-induced SUMOylation, and characterizing the precise molecular mechanisms regulating these processes. My studies revealed that E4-ORF3 induces SUMOylation of the general transcription factor, TFII-I, which was previously shown to be a transcriptional repressor of the Ad L4 promoter. I found that SUMOylation of TFII-I during Ad infection was dependent on its relocalization into E4-ORF3 tracks. I subsequently found that TFII-I SUMOylation leads to its ubiquitination and proteasome-dependent degradation. Finally, I focused on identifying the specific cellular factors involved in E4-ORF3-mediated modulation of TFII-I. My work showed that Ad usurps the activities of two DNA repair factors to aid in the proteolytic processing of TFII-I during infection: RNF4, a SUMO-targeted ubiquitin ligase responsible for ubiquitination of SUMOylated proteins, and VCP/p97, an ATPase that extracts ubiquitinated proteins from large macromolecular structures and mediates their degradation by the ubiquitin-proteasome system. Together, these studies identify TFII-I as a novel target of the Ad5 E4-ORF3 protein and elucidate the functional consequences of E4-ORF3-induced SUMOylation of TFII-I. My studies show that E4-ORF3-induced SUMOylation leads to proteasome-dependent degradation of restrictive host factors, including TFII-I, and provide in-depth mechanistic insight into how a small viral protein like E4-ORF3 can regulate diverse antiviral processes during infection. | |
