Analysis of the importance of nuclear export of the influenzaA virus NS1 protein for viral replication

Abstract number: P582

Tynell J., Melen K., Julkunen I.

Objectives: The NS1 protein of influenza A virus is a multifunctional protein responsible for the inhibition of host cell immune responses. Through its action in the nucleus and the cytoplasm NS1 functions to shut down host cell interferon production and to limit the effects of interferon-inducible antiviral proteins. To study the importance of the intracellular localisation of NS1 we created a recombinant influenza A virus of the strain A/Udorn/72 bearing a mutation to inactivate the nuclear export signal (NES) of NS1.

Methods: The recombinant virus was created using a 12 plasmid transfection system. The intracellular localisation of NS1 was visualised by immunofluorescence microscopy. The growth properties of the virus were analyzed by measuring its growth kinetics on MDCK cells at different multiplicity of infection (MOI) values. The cytokine production of infected A549 cells was measured by ELISA.

Results: The mutated NS1 localised and remained in the nucleus even at late stages of infection. The recombinant virus replicated to titers 10-fold lower compared to the wild type virus and was not able to inhibit the production of interferon-alpha or interferon-beta by the host cell.

Conclusion: The nuclear export of NS1 appears to be important for the replication of influenza A virus and for its ability to inhibit host cell interferon production, although the exact cytoplasmic role of NS1 responsible for the observation cannot be elucidated from these results. The possibility of other properties of NS1 besides the NES being affected by the induced mutation also cannot be ruled out.