[en] As a key player involved in various cellular pathways, including innate immune response activation, the human ubiquitin-proteasome system (UPS) is particularly targeted by viral proteins upon infection. Indeed, most viruses have evolved to counteract and hijack this system, as it is the case for the influenza A virus (IAV). The non-structural protein 1 (NS1) is described as the main IAV virulence factor, which is known to interact with several cellular proteins, including some UPS factors that are important for the viral escape of the immune cell response.
We profiled the overall interplay between the NS1 proteins of multiple IAV strains and the human UPS through a high-throughput GPCA screening. We identified 98 UPS factors directly interacting with NS1 of all or a subset of the studied strains, and we functionally studied 18 of them. We highlighted the involvement of these UPS factors in the IAV life cycle by performing viral titrations, minigenome replicon assays and an ISRE-luc (IFN pathway) assays. We then confirmed by Co-IP the interactions between NS1 and 4 UPS factors, namely FZR1, MKRN3, RC3H2 and SHKBP1. Furthermore, we analyzed their expression and subcellular localization of upon IAV infection. IAV infection affected MKRN3, RC3H2 and SHKBP1 abundance, with a slight decrease during the late stages of infection. We also observed relocalization of UPS factors during IAV infection, with accumulation of FZR1 in cytoplasmic foci at 6h and 9h post infection.
This interactomics approach allows for an improved understanding of the interplay between NS1 and UPS pathway in the context of an IAV-mediated inhibition of cellular anti-viral responses.
