A Genetic Screen Identifies Interferon-α Effector Genes Required to Suppress Hepatitis C Virus Replication

BACKGROUND & AIMS: Hepatitis C virus (HCV) infection is a leading cause of end-stage liver disease. Interferon-alpha (IFN alpha) is an important component of anti-HCV therapy; it up-regulates transcription of IFN-stimulated genes, many of which have been investigated for their antiviral effects. However, all of the genes required for the antiviral function of IFN alpha (IFN effector genes [IEGs]) are not known. IEGs include not only IFN-stimulated genes, but other nontranscriptionally induced genes that are required for the antiviral effect of IFN alpha. In contrast to candidate approaches based on analyses of messenger RNA (mRNA) expression, identification of IEGs requires a broad functional approach. METHODS: We performed an unbiased genome-wide small interfering RNA screen to identify IEGs that inhibit HCV. Huh7.5.1 hepatoma cells were transfected with small interfering RNAs incubated with IFN alpha and then infected with JFH1 HCV. Cells were stained using HCV core antibody, imaged, and analyzed to determine the percent infection. Candidate IEGs detected in the screen were validated and analyzed further. RESULTS: The screen identified 120 previously unreported IEGs. From these, we more fully evaluated the following: asparagine-linked glycosylation 10 homolog (yeast, alpha-1,2-glucosyltransferase); butyrylcholinesterase; dipeptidylpeptidase 4 (CD26, adenosine deaminase complexing protein 2); glucokinase (hexokinase 4) regulator; guanylate cyclase 1, soluble, beta 3; MYST histone acetyltransferase 1; protein phosphatase 3 (formerly 2B), catalytic subunit, beta isoform; peroxisomal proliferator-activated receptor-gamma-DBD-interacting protein 1; and solute carrier family 27 (fatty acid transporter), member 2; and demonstrated that they enabled IFN alpha-mediated suppression of HCV at multiple steps of its life cycle. Expression of these genes had more potent effects against flaviviridae because a subset was required for IFN alpha to suppress dengue virus but not influenza A virus. In addition, many of the host genes detected in this screen (92%) were not transcriptionally stimulated by IFN alpha; these genes represent a heretofore unknown class of non-IFN-stimulated gene IEGs. CONCLUSIONS: We performed a whole-genome loss-of-function screen to identify genes that mediate the effects of IFN alpha against human pathogenic viruses. We found that IFN alpha restricts HCV via actions of general and specific IEGs.