Drosophila RNAi screen identifies host genes important for influenza virus replication

Abstract

Although several alternative antivirals are available for the treatment of influenza virus infection, the risk that viruses resistant to these drugs will emerge means it is important to continue the search for new antiviral targets. Hao et al. have recruited a new ally to this cause: by modifying influenza virus so that it can infect the cells of the fruit fly Drosophila, they have been able to use a powerful genome-wide RNA interference (RNAi) screen to identify scores of host genes that the pathogen requires for successful infection. Several host proteins were found that have key functions in the replication of H5N1 and H1N1 influenza A viruses — but not other viruses — in human cells. The same strategy should be applicable to other viruses, as long as at least part of their replication cycle can be supported in Drosophila cells. In this paper, a screening system based on the specific targeting of Drosophila genes with an RNAi library identifies host factors involved in influenza virus replication. All viruses rely on host cell proteins and their associated mechanisms to complete the viral life cycle. Identifying the host molecules that participate in each step of virus replication could provide valuable new targets for antiviral therapy, but this goal may take several decades to achieve with conventional forward genetic screening methods and mammalian cell cultures. Here we describe a novel genome-wide RNA interference (RNAi) screen in Drosophila1 that can be used to identify host genes important for influenza virus replication. After modifying influenza virus to allow infection of Drosophila cells and detection of influenza virus gene expression, we tested an RNAi library against 13,071 genes (90% of the Drosophila genome), identifying over 100 for which suppression in Drosophila cells significantly inhibited or stimulated reporter gene (Renilla luciferase) expression from an influenza-virus-derived vector. The relevance of these findings to influenza virus infection of mammalian cells is illustrated for a subset of the Drosophila genes identified; that is, for three implicated Drosophila genes, the corresponding human homologues ATP6V0D1, COX6A1 and NXF1 are shown to have key functions in the replication of H5N1 and H1N1 influenza A viruses, but not vesicular stomatitis virus or vaccinia virus, in human HEK 293 cells. Thus, we have demonstrated the feasibility of using genome-wide RNAi screens in Drosophila to identify previously unrecognized host proteins that are required for influenza virus replication. This could accelerate the development of new classes of antiviral drugs for chemoprophylaxis and treatment, which are urgently needed given the obstacles to rapid development of an effective vaccine against pandemic influenza and the probable emergence of strains resistant to available drugs.