ADP-ribosylation is an important post-translational modification that directly influences several biological processes including cancer, allergy, and infectious disease. ADP-ribose can be added to proteins as one or more consecutive units by ADP-ribosyltransferases, also termed PARPs, resulting in mono- or poly- ADP-ribosylation (mAR or pAR). Most mARylating PARPs are upregulated by interferon (IFN) upon virus infection and several are predicted to have antiviral functions. In addition, several viral families, including the Coronaviridae and Togaviridae, encode for macrodomain proteins that have mono-ADP-ribosyl hydrolase (ARH) activity. This activity allows these viruses the ability to specifically counteract the effects of mAR, further implicating mAR in the mammalian antiviral response. Despite these findings, there are only a few known examples where mAR is known to inhibit virus replication. This is largely due to the lack of cell culture models of virus infections where the mAR status of a cell can be specifically controlled, such as models using mutant viruses or PARP knockout cells that have significant phenotypes. Importantly, the PI has established a virus infection system using a model coronavirus, Murine Hepatitis Virus (MHV), where virus lacking ARH activity is i) significantly impaired in virus replication and ii) independently induces a robust IFN response. These phenotypes are reversed by PARP inhibitors, establishing mAR as a key factor driving this anti-viral response. The investigator?s long-term goal is to determine mechanistically how mAR inhibits virus replication and enhances the innate immune response following virus infection. This gap in knowledge will be resolved by answering the following questions: 1) How does mAR inhibit MHV infection? Does it inhibit the entry, RNA replication, protein translation, assembly, or release of MHV? 2) What step(s) of the IFN induction pathway is enhanced by mAR, and does mAR also affect the IFN response in bats, which are known to harbor many highly pathogenic viruses? 3) What proteins are modified by PARPs following virus infection and which substrates are relevant for specific phenotypes? The rationale for this research is that it will enhance our understanding of mAR, including its ability to modulate protein function and will uncover novel cellular proteins or processes that mediate virus replication. The work is innovative because: i) it will bridge a significant knowledge gap between ADP-ribose biology, the innate immune response, and virus replication; ii) it utilizes unique models of infection utilizing both mutant viruses and PARP knockout cells; and iii) will be the first to address the role of mAR in bats. Finally, these projects are significant and relevant to the NIGMS mission because they will provide a thorough understanding of how mAR impacts the anti-viral response that could lay the foundation for advances in the treatment of virus infections or other human diseases impacted by mAR.
The mammalian anti-viral response is partially regulated by post-translational modifications (PTMs) like phosphorylation. ADP-ribosylation is another type of PTM that is implicated in the anti-viral response, however little is known about how it hinders virus infections. The primary objective of this proposal is to determine how ADP-ribosylation inhibits virus replication and enhances the host immune response, with the goal of developing a better understanding of the mammalian anti-viral response that could lead to novel anti-viral therapies.
