Host gene targets for novel influenza therapies elucidated by high-throughput RNA interference screens

Abstract

Influenza virus encodes only 11 viral proteins but replicates in a broad range of avian and mammalian species by exploiting host cell functions. Genome-wide RNA interference (RNAi) has proven to be a powerful tool for identifying the host molecules that participate in each step of virus replication. Meta-analysis of findings from genome-wide RNAi screens has shown influenza virus to be dependent on functional nodes in host cell pathways, requiring a wide variety of molecules and cellular proteins for replication. Because rapid evolution of the influenza A viruses persistently complicates the effectiveness of vaccines and therapeutics, a further understanding of the complex host cell pathways coopted by influenza virus for replication may provide new targets and strategies for antiviral therapy. RNAi genome screening technologies together with bioinformatics can provide the ability to rapidly identify specific host factors involved in resistance and susceptibility to influenza virus, allowing for novel disease intervention strategies.

Figure 1.

RNAi pathway. Endogenous miRNAs are transcribed as Pri-miRNAs that are subsequently processed by Drosha and Dicer to generate mature miRNAs. The guide strand is then incorporated into the RNA-induced silencing complex (RISC) to facilitate gene silencing. Reagents that have been developed for screening include expressed constructs (shRNA and shRNA-miR), as well as synthetic constructs: siRNA, miRNA mimics, and miRNA inhibitors.

Figure 2.

Host signaling factors. On binding to host cell sialic acids, influenza virus activates RTKs to form lipid raft-based signaling platforms that enhance influenza uptake and cell proliferation. HA-mediated activation of protein kinase C (PKC) also aids viral entry and cellular proliferation. RTKs activate phosphatidylinositol 3-kinase (PI3K) signaling, inhibiting cellular apoptosis. The Raf/MEK/ERK cascade downstream of RTKs is required for efficient nuclear export of viral ribonucleoproteins. Viral manipulation of NF-κB inhibits antiviral type I interferon production and resultant interferon-stimulated gene (ISG) production.