Glora P. Larson

Research Title.  Gene Correlation Analysis Identifies Functional Pro- and Anti-Viral Factors for Influenza Virus Infection.

Research Description. Influenza A virus (IAV), like all viruses, must co-opt host cellular machinery to support successful infection. Gloria’s research uses an unbiased genetic screen to identify host factors that regulate IAV infection. Top candidates included the potential antiviral suppressor poly-ADP-ribose polymerase 8 (PARP8) and pro-viral enhancer epidermal growth factor receptor (EGFR) pathway substrate 8 (EPS8). PARP8 is a member of the PARP family of enzymes, also termed ADP-ribosyltransferase Diphtheria toxin-like enzymes (ARDTs), which post-translationally modify target proteins with ADP-ribose. Gloria’s project seeks to understand how ADP-ribosylation affects IAV polymerase function and how the virus counteracts the putative antiviral activity of PARPs. Data generated has showen that PARP family members specifically inhibit viral polymerase function and replication, and select PARPs interacted with the viral polymerase. In addition, a subset of PARPs including PARP8 appeared to directly impact viral protein ADP-ribosylation. The Mehle lab has also acquired evidence for viral evasion of ADP-ribosylation; preliminary data suggests that the IAV non-structural protein 1 (NS1) prevents ADP-ribosylation of one viral polymerase subunit. Indeed, further experiments showed that NS1 counteracted the antiviral activity of multiple PARPs. Gloria is now investigating how NS1 blocks ADP-ribosylation to determine whether this alters modification of other viral proteins. Thus, the viral accessory protein NS1 may be a mechanism by which IAV counteracts ADP- ribosylation. The putative viral enhancer EPS8 is a multifunctional protein involved in signaling and endocytosis processes. A pro-viral role for EPS8 has been confirmed by showing that overexpression increased viral gene expression and viral titer, whereas knockout of EPS8 decreased infection and replication. Initial data also suggested that EPS8 levels increase upon infection. Gloria probed the role of EPS8 at various steps throughout the viral life cycle. These experiments revealed that EPS8 functions following virion attachment during the process of viral entry. Gloria has showed that this enhancing activity of EPS8 also increased MERS-CoV infection. Gloria’s current work is focused on determining the mechanism(s) by which EPS8 enhances IAV replication. Preliminary mutant analyses suggest that the actin remodeling functions of EPS8 may be important for viral entry enhancement. By exploring an alternative screen approach, this work identified previously unknown viral host factors with opposing effects on viral infection outcome. Gloria and her colleagues are defining the molecular actions of these newly identified pro- and anti-viral factors. Their results will expand the knowledge of how IAV co-opts host cellular machinery to support successful infection and potential anti-viral drug targets.