Adenoviruses have evolved multiple mechanisms for modifying the intracellular environment both to promote efficient viral replication and circumvent host defenses. Products of the early region 4 (E4) transcription unit encompass a diverse collection of functions required for efficient viral replication. These functions are mediated through a variety of interactions with key viral and cellular regulatory proteins involved in transcription, cell cycle control, cell signaling, posttranslational modification, apoptosis, and DNA repair. E4-deleted viruses are profoundly deficient for virus replication, highlighting the importance of E4 gene products in the adenovirus life cycle.

Among the mechanisms viruses employ to modify the intracellular environment is the proteasome-mediated degradation of specific host cell proteins via the ubiquitinproteasome pathway. One of the E4 gene products, E4 34k, participates with another viral early protein, E1b 55k, to form the substrate-binding subunit of an F-box type E3 ubiquitin ligase that also contains the cellular Cullin5, Elongins B and C, and Rbx1 proteins. Few substrates of this complex have been indentified. While degradation of the known substrates appear to play roles in enhancing viral replication, they do not seem to account for all of the activities in which E1b 55k and F4 34k are involved. In our studies we have evaluated numerous cellular pathways and identified an additional novel substrate of this viral E3 ubiquitin ligase, DNA ligase IV.

Adenovirus E4 mutants transcribe late genes normally, but accumulate very little nuclear or cytoplasmic late RNA, suggesting that newly synthesized late messages are degraded soon after transcription. To investigate possible molecular mechanisms for this phenotype, we chose to evaluate pathways involved in RNA metabolism and decay, including cytoplasmic structures known as mRNA processing bodies or p-bodies. We demonstrate that adenovirus dramatically reduces the number of p-bodies per cell at times late in infection, and that expression of viral early proteins E4 11k and E1b 55k induce aggresome structures to which specific p-body components are relocalized. At least one of these proteins, Ddx6, is incorporated specifically into E4 11k-induced aggresomes, and interacts physically with E4 11k.