Influenza A virus interference in the mallard duck (Anas platyrhynchos) RIG-I pathway

• Author / Creator

  Evseev, Danyel

• Influenza A viruses are a major cause of human and animal disease worldwide. Periodically, avian influenza A viruses from wild waterfowl, like ducks, pass through intermediate agricultural hosts and emerge into the human population as zoonotic diseases with high mortality rates and pandemic potential. Dabbling ducks are the primordial hosts of influenza A viruses and remain an important ecological reservoir. Presumably because of their long co-evolutionary history, ducks are uniquely resistant to influenza disease compared to other birds, animals, and humans. However, relatively little is known about host-pathogen interactions in these hosts that may be contributing to their resistance. Appropriate innate immune signaling, especially through the RIG-I pathway, appears to be crucial for controlling viral replication early and for the survival advantage of ducks infected with highly-pathogenic influenza A viruses. To discover potential unique adaptations between ducks and influenza A viruses, I investigated the interactions of three viral proteins with the duck RIG-I pathway and compared to what is known about these interactions in humans and other hosts.
  The non-structural protein 1 (NS1) of influenza A viruses is an important virulence factor that regulates viral replication and controls host cell immune responses. In human cells, NS1 proteins inhibit the induction of innate immune signaling and type-I interferon by preventing the activation of the RIG-I receptor by the ubiquitin ligase TRIM25. It is unclear whether the inhibition of human TRIM25 is a universal function of all influenza A NS1 proteins or is strain-dependent. It is also unclear if NS1 proteins similarly target the TRIM25 and RIG-I pathway of mallard ducks. To answer these questions, I compared the ability of five different NS1 proteins to interact with human and duck TRIM25 and the consequences this had on RIG-I ubiquitination and signaling in both species. I show that allele A and allele B NS1 proteins from low-pathogenic and highly pathogenic avian influenza viruses efficiently inhibit RIG-I ubiquitination and interferon induction in human cells. In contrast, avian NS1 proteins do not affect duck RIG-I ubiquitination and signaling, despite interacting with duck TRIM25 in co-immunoprecipitations. Avian influenza viruses may lack the ability to dampen RIG-I signaling in ducks, as they do in humans. I also show that a variant NS1 from A/Puerto Rico/8/1934 (H1N1) can enhance TRIM25-mediated human RIG-I ubiquitination, but inhibits interferon by a TRIM25-independent mechanism that involves NS1 residue glycine-184.
  PB1-F2 is an accessory protein encoded by most, but not all influenza A virus strains. Several immunomodulatory functions are ascribed to PB1-F2 in mammalian cells, including an interaction with the signal transducer MAVS to inhibit type-I interferon induction. In collaboration with a colleague, I show that PB1-F2 from A/Puerto Rico/8/1934 (H1N1) interacts with duck MAVS and inhibits interferon signaling in avian cells. I also show that PB1-F2 is capable of suppressing TRIM25-mediated RIG-I ubiquitination of both human and duck orthologues. These interactions of PB1-F2 provide an example of the conservation of function across host species.
  Finally, the viral polymerase subunit PB2 is also known to traffic to mitochondria and interact with MAVS to suppress interferon in human cells. Mitochondrial localization, but not MAVS interaction specifically, depends on a host-species-specific amino acid polymorphism at position 9 in the PB2 peptide. With a colleague, I show that several avian and one human PB2 proteins all interact with duck MAVS irrespective of the substitution at position 9 or at two other species-specific polymorphism sites close by. However, interferon inhibition efficiencies differed between the PB2 proteins and suggest the involvement of one or more of the polymorphisms in mitochondrial targeting, as in human cells.
  This thesis addresses the understudied subject of host-pathogen interactions of influenza A viruses in their natural host – mallard ducks. The results contribute to our understanding of the mechanisms of host-pathogen co-adaptation and the selective pressures that drive influenza A virus evolution in the reservoir host.

• Subjects / Keywords

  • NS1
  • virology
  • immune
  • immunology
  • interferon
  • duck
  • innate
  • RIG-I
  • influenza

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-txyz-dm66

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.