Background & Aims: Hepatitis C virus (HCV) is a major cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma. Current therapy with pegylated interferon α (IFN-α) in combination with ribavirin is associated with adverse effects and often fails to induce a sustained response. IFN-λs, recently discovered IFN gene family members, exhibit antiviral and cell stimulatory activities similar to IFN-α. We aimed to determine whether IFN-λ exhibits antiviral activity toward HCV and to compare the signal transduction and effector gene pathways with those of IFN-α. Methods: Using the HCV replicon system and cell culture infectious reporter virus, we compared IFN-α and IFN-λ effects on HCV RNA replication and protein expression, as measured by quantitative reverse-transcriptase polymerase chain reaction, luciferase expression, and Western blot. Receptor expression and signaling pathways were explored using flow cytometry and Western blot. IFN-α- and IFN-λ-mediated gene expression changes were compared using microarray analyses. Results: IFN-λ exhibited dose- and time-dependent HCV inhibition, independent of types I and II IFN receptors. The kinetics of IFN-λ-mediated signal transducers and activators of transcription (STAT) activation and induction of potential effector genes were distinct from those of IFN-α. IFN-λ induced steady increases in levels of known interferon stimulated genes (ISGs), whereas IFN-α ISGs peaked early and declined rapidly. IFN-λ inhibited replication of HCV genotypes 1 and 2 and enhanced the antiviral efficacy of subsaturating levels of IFN-α. Conclusions: These results demonstrate distinct differences in IFN-λ- and IFN-α-induced antiviral states. Understanding these differences may prove useful for developing new HCV treatment strategies. Background & Aims: Hepatitis C virus (HCV) is a major cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma. Current therapy with pegylated interferon α (IFN-α) in combination with ribavirin is associated with adverse effects and often fails to induce a sustained response. IFN-λs, recently discovered IFN gene family members, exhibit antiviral and cell stimulatory activities similar to IFN-α. We aimed to determine whether IFN-λ exhibits antiviral activity toward HCV and to compare the signal transduction and effector gene pathways with those of IFN-α. Methods: Using the HCV replicon system and cell culture infectious reporter virus, we compared IFN-α and IFN-λ effects on HCV RNA replication and protein expression, as measured by quantitative reverse-transcriptase polymerase chain reaction, luciferase expression, and Western blot. Receptor expression and signaling pathways were explored using flow cytometry and Western blot. IFN-α- and IFN-λ-mediated gene expression changes were compared using microarray analyses. Results: IFN-λ exhibited dose- and time-dependent HCV inhibition, independent of types I and II IFN receptors. The kinetics of IFN-λ-mediated signal transducers and activators of transcription (STAT) activation and induction of potential effector genes were distinct from those of IFN-α. IFN-λ induced steady increases in levels of known interferon stimulated genes (ISGs), whereas IFN-α ISGs peaked early and declined rapidly. IFN-λ inhibited replication of HCV genotypes 1 and 2 and enhanced the antiviral efficacy of subsaturating levels of IFN-α. Conclusions: These results demonstrate distinct differences in IFN-λ- and IFN-α-induced antiviral states. Understanding these differences may prove useful for developing new HCV treatment strategies. Hepatitis C virus (HCV) infection is a growing public health problem affecting 170 million people worldwide (approximately 3 million in the United States). 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Recent studies show some specificity to their antiviral effects and differences in efficacy in vitro vs in vivo. Although IFN-λ was not noted to have antiviral activity against HSV-2 in vitro, it demonstrated substantial antiviral effects in vivo, highlighting the possibility that the majority of IFN-λ's antiviral effects may involve immune modulation.30Ank N. West H. Bartholdy C. Eriksson K. Thomsen A.R. Paludan S.R. Lambda interferon (IFN-λ), a type III IFN, is induced by viruses and IFNs and displays potent antiviral activity against select virus infections in vivo.J Virol. 2006; 80: 4501-4509Crossref PubMed Scopus (504) Google Scholar Similar to type I IFN signaling, IFN-λ receptor engagement leads to the formation of the IFN-stimulated gene factor (ISGF) 3 and subsequent transcription of IFN-stimulated response element (ISRE) controlled genes encoding 2′5′OAS or MxA protein.29Kotenko S.V. Gallagher G. Baurin V.V. Lewis-Antes A. Shen M. Shah N.K. Langer J.A. Sheikh F. 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Binding of the IFNs to their cognate receptor subunits leads to dimerization of the receptor chains and activation of the receptor associated Janus kinases (Figure 1B). Phosphorylation of Janus kinases leads to further downstream phosphorylation of the latent cytoplasmic proteins signal transducers and activators of transcription (STATs). Their rapid activation can be detected minutes after receptor engagement. For the IFN-α and IFN-λ signaling cascades, activated STAT1 and STAT2 heterodimerize and together with IRF9 form the trimeric ISGF3 complex competent for nuclear translocation. In the nucleus, ISGF3 binds to the cis-acting DNA element, designated ISRE, upstream of IFN-inducible genes, and modulates their transcription.28Sheppard P. Kindsvogel W. Xu W. Henderson K. Schlutsmeyer S. Whitmore T.E. Kuestner R. Garrigues U. Birks C. Roraback J. Ostrander C. Dong D. Shin J. Presnell S. Fox B. Haldeman B. Cooper E. Taft D. Gilbert T. Grant F.J. Tackett M. Krivan W. McKnight G. Clegg C. 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IFN-γ signaling relies mainly on the formation of STAT1 homodimers, which bind to the cis-acting GAS element in the upstream promoter region of IFN-γ inducible genes.34Ramana C.V. Gil M.P. Schreiber R.D. Stark G.R. Stat1-dependent and -independent pathways in IFN-γ-dependent signaling.Trends Immunol. 2002; 23: 96-101Abstract Full Text Full Text PDF PubMed Scopus (474) Google Scholar Microarray expression studies indicate that the human genome encodes several hundred functionally diverse IFN-stimulated genes (ISGs).35de Veer M.J. Holko M. Frevel M. Walker E. Der S. Paranjape J.M. Silverman R.H. Williams B.R. Functional classification of interferon-stimulated genes identified using microarrays.J Leukoc Biol. 2001; 69: 912-920PubMed Google Scholar, 36Der S.D. Zhou A. Williams B.R. Silverman R.H. 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Characterization of β-R1, a gene that is selectively induced by interferon β (IFN-β) compared with IFN-α.J Biol Chem. 1996; 271: 22878-22884Crossref PubMed Scopus (156) Google Scholar In this report, we examine the antiviral effects of IFN-λ1 (IFN-λ) on HCV replicon and cell culture virus replication in Huh-7.5 hepatoma cells. This system serves as an excellent model to study components of the signaling pathway, the induced genes, and the antiviral effect in response to IFN treatment. By comparing and contrasting IFN-α2 (IFN-α) and IFN-λ, we demonstrate that, although they both share similar intracellular-signaling pathways, clear differences exist in the activation and induction of potential effector genes that ultimately result in different antiviral potencies. Huh-7.5 monolayers were maintained in Dulbecco's modified Eagle's medium (DMEM) (Gibco, Carlsbad, CA) supplemented with 10% heat-inactivated fetal bovine serum (FBS) (Gibco) and 0.1 mmol/L MEM nonessential amino acid solution (Gibco) at 37°C in a humidified atmosphere of 5% CO2. For cells supporting full-length HCV replicons, G418 (Gibco) at 750 μg/mL was added to the culture medium. The full-length HCV Con1 (genotype 1b) bicistronic replicon shown in Figure 1A was used for all replicon studies. In this replicon, the HCV internal ribosome entry site (IRES) drives expression of neomycin phosphotransferase (neo); the EMCV IRES mediates translation of the HCV structural and nonstructural proteins, core through NS5B. This replicon contains the highly adaptive serine to isoleucine substitution in NS5A at polyprotein amino acid 2204.39Blight K.J. McKeating J.A. Marcotrigiano J. Rice C.M. Efficient replication of hepatitis C virus genotype 1a RNAs in cell culture.J Virol. 2003; 77: 3181-3190Crossref PubMed Scopus (294) Google Scholar Stable cell populations were derived by transfection of the highly permissive Huh-7.5 subline39Blight K.J. McKeating J.A. Marcotrigiano J. Rice C.M. Efficient replication of hepatitis C virus genotype 1a RNAs in cell culture.J Virol. 2003; 77: 3181-3190Crossref PubMed Scopus (294) Google Scholar with transcribed RNA followed by G418 selection. This selected cell population is referred to as FL-neo cells throughout this study. Cells were cultured in regular media without the addition of G418 for at least 24 hours before each experiment. FL-J6/JFH-5′C19Rluc2AUbi HCV cell culture virus (HCVcc), a monocistronic HCV genotype 2a virus expressing Renilla luciferase as a ubiquitin- and self-cleavable amino terminal extension of the J6/JFH1 HCV17Lindenbach B.D. Evans M.J. Syder A.J. Wölk B. Tellinghuisen T.L. Liu C.C. Maruyama T. Hynes R.O. Burton D.R. McKeating J.A. Rice C.M. Complete replication of hepatitis C virus in cell culture.Science. 2005; 309: 623-626Crossref PubMed Scopus (1973) Google Scholar polyprotein has been previously described and characterized.40Tscherne D.M. Jones C.T. Evans M.J. Lindenbach B.D. McKeating J.A. Rice C.M. Time- and temperature-dependent activation of hepatitis C virus for low-pH-triggered entry.J Virol. 2006; 80: 1734-1741Crossref PubMed Scopus (327) Google Scholar This virus, designated J6/JFH1 HCVcc, is shown schematically in Figure 1A. HCVcc stocks were generated by collection of the culture medium from Huh-7.5 cells electroporated with in vitro transcribed RNA as described.40Tscherne D.M. Jones C.T. Evans M.J. Lindenbach B.D. McKeating J.A. Rice C.M. Time- and temperature-dependent activation of hepatitis C virus for low-pH-triggered entry.J Virol. 2006; 80: 1734-1741Crossref PubMed Scopus (327) Google Scholar Stock titers (tissue culture infectious dose [TCID]50) were determined as described.17Lindenbach B.D. Evans M.J. Syder A.J. Wölk B. Tellinghuisen T.L. Liu C.C. Maruyama T. Hynes R.O. Burton D.R. McKeating J.A. Rice C.M. Complete replication of hepatitis C virus in cell culture.Science. 2005; 309: 623-626Crossref PubMed Scopus (1973) Google Scholar Infection of Huh-7.5 cells, seeded in 24-well plates the day before, was performed with 200 μL undiluted HCVcc stock (2.15 × 102 TCID50/mL) and allowed to proceed for 2 hours at 37°C, after which unbound virus was washed away with phosphate-buffered saline (PBS), and the medium was replaced. After an additional 48 hours, cells were washed with PBS and assayed for luciferase activity using the Renilla luciferase assay system (Promega, Madison, WI) according to the manufacturer's instructions and as previously described.40Tscherne D.M. Jones C.T. Evans M.J. Lindenbach B.D. McKeating J.A. Rice C.M. Time- and temperature-dependent activation of hepatitis C virus for low-pH-triggered entry.J Virol. 2006; 80: 1734-1741Crossref PubMed Scopus (327) Google Scholar For IFN treatment, cytokine was added to the cells 12 hours prior to infection. After the 2-hour infection, performed in the absence of cytokine, medium containing freshly diluted cytokine was added for the duration of the 48-hour infection period. Human leukocyte IFN-α2 (IFN-α) and human recombinant IFN-γ were obtained from Sigma Chemical Co. (St. Louis, MO). Escherichia coli-produced human IFN-λ1 (IFN-λ) was obtained from Peprotech (Rocky Hill, NJ). Primary antibodies used for immunoblotting were mouse anti-HCV NS5A (Virostat, Portland, ME) (1:100), mouse anti-human β-actin (Sigma Chemical Co.) (1:5000), rabbit anti-human phospho-STAT1 (Tyr701) (Cell Signaling Technology, Beverly, MA) (1:500), rabbit anti-human phospho-STAT2 (Tyr689) (Upstate, Lake Placid, NY) (1:1000), mouse anti-STAT1 (Santa Cruz Biotechnology, Santa Cruz, CA) (1:100), and mouse anti-human STAT2 (Santa Cruz Biotechnology) (1:100). Secondary antibodies used for immunoblotting were rabbit anti-mouse IgG HRP (Pierce, Rockford, IL) and goat anti-rabbit IgG HRP (Pierce) (1:10,000). Primary antibodies used for flow cytometric analysis (FACS) were mouse anti-human IFN-αR2 (USBiological, Swampscott, MA), mouse anti-human IFN-γR1 (R&D Systems, Minneapolis, MN), and goat anti-human IL-10R2 (R&D Systems) at 0.5, 0.5, and 1 μg per 2 × 105 cells, respectively. Secondary antibodies used for FACS analysis were Alexa 488-labeled goat anti-mouse IgG (Molecular Probes, Eugene, OR) and PE-labeled donkey anti-goat IgG (Jackson ImmunoResearch Laboratories, Baltimore, PA) at 0.3 μg for 2 × 105 cells. Normal mouse serum (Jackson ImmunoResearch Laboratories) and normal goat serum (Sigma Chemical Co.) were used as negative controls. Receptor blocking antibodies used for inhibiting cytokine-mediated effector functions were mouse anti-human IFN-αR2 (USBiological), mouse anti-human IFN-γR1 (R&D Systems), and goat anti-human IL-10 R2 (R&D Systems) at 20, 2, and 40 μg/mL, respectively. Total cellular RNA was extracted and isolated using the RNeasy Mini Kit (Qiagen, Valencia, CA) according to the manufacturer's instructions. An 80-ng aliquot of total RNA was used to quantify HCV-specific RNA levels using an ABI Prism 7700 sequence detector (Applied Biosystems, Foster City, CA). Real-time reverse-transcription polymerase chain reaction (RT-PCR) amplifications were performed using the Platinum Quantitative RT-PCR ThermoScript One-Step system (Invitrogen Life Technologies, Carlsbad, CA) and primers specific for the HCV 5′ NTR: 5′-CCTCTAGAGCCATAGTGGTCT-3′ (sense, 10 μmol/L); 5′-CCAAATCTCCAGGCATTGAGC-3′(antisense, 10 μmol/L); and 6-carboxyfluorescein-CACCGGAATTGCCAGGACGACCGG (probe, 10 μmol/L; Applied Biosystems). RT reactions were