Interactions of the Cellular SUMOylation System with Influenza A Virus and its Non-Structural Protein NS1A (NS1A)

The most important current anti-influenza weapons, vaccination and antiviral drugs, can be rapidly rendered fully ineffective thanks to the virus\u27s high mutational rate, which produces viruses exhibiting new antigenic properties and structural proteins insensitive to the drug\u27s mechanism of action. One attractive alternative is to develop drugs that modulate the activity of cellular systems either required for viral growth or able to neutralize viral growth. Here we demonstrate that the cellular SUMOylation system, a post-translational modification involving the conjugation of the Small Ubiquitin-like MOdifier (SUMO) to specific protein targets using a Ubiquitin-like enzymatic cascade, interacts closely with influenza virus during infection and therefore provides new targets for the development of anti-influenza therapeutics targeting cellular components. Briefly, in vitro SUMOylation assays performed using in vitro synthesized viral proteins demonstrated that most influenza viral proteins are readily SUMOylated in vitro and therefore constitute potential SUMO targets. Transfection experiments leading to the over-expression of specific viral proteins in the presence or absence of various recombinant DNA constructs designed to modulate the activity of the cellular SUMOylation system demonstrated that various viral proteins are also SUMOylated when over-expressed in mammalian cells. Furthermore, experiments performed using recombinant adenoviruses able to modulate the activity of the cellular SUMOylation system demonstrated the SUMOylation of specific viral proteins during influenza infection. Finally, this study characterizes the SUMOylation of the non-stuctural viral protein NS1A, the best SUMO target of all the viral proteins produced during infection, explores some of the potential effects exerted by SUMOylation on the functions of this viral protein, and introduces the use of artificial SUMO ligases as an innovative method to increase the SUMOylation of specific targets in the cell and facilitate the characterization of the effects mediated by SUMOylation on protein function. Collectively, our studies provide new insights into the virus-host interactions established during influenza virus infections