DNA viruses and the cellular DNA repair machinery

When viruses infect cells they have to overcome many obstacles set up by the cell to thwart infection. Viruses accomplish these tasks by either harnessing or destroying cellular processes. Studying virus-host interactions sheds light on how viruses hijack cells and often reveals novel insights into the inner workings of our cells. The work presented in this dissertation was focused on investigating the interactions of the DNA viruses, adenovirus and adeno-associated virus with the cellular DNA damage response and repair machinery. Infection with these viruses presents cells with numerous copies of exogenous viral genomes and replication intermediates containing DNA secondary structures and single stranded DNA, which would be predicted to elicit the cellular DNA repair machinery. Indeed, we found that infection with an adenovirus mutant, which lacks the E4 genetic region induces a cellular DNA damage response that results in concatemer formation of viral genomes. This response is detrimental to adenovirus infection because concatemers are too large to be packaged and viral DNA replication is impaired. We found that wild-type adenovirus prevents the DNA damage response to infection by modulating a complex of cellular proteins called the Mre11 complex, which are involved in DNA repair and cell cycle checkpoint signaling. Using adenovirus as a tool to study the cellular response to DNA damage in the absence of the Mre11 complex, we provided molecular evidence that the Mre11 complex is a sensor of adenovirus infection and DNA damage caused by gamma irradiation and radiomimetic drugs. These results demonstrated that the Mre11 complex is required for the full induction of DNA damage response signaling pathways. We also found that replication of adeno-associated virus induces DNA damage response signaling. In contrast to adenovirus, this signaling does not require the Mre11 complex and does not appear to be detrimental to infection. These results suggest that many viruses have to interact with the cellular DNA damage response machinery and that some viruses have evolved to harness this machinery while others, such as adenovirus, have evolved to disarm it.