ISG56 and IFITM1 Proteins Inhibit Hepatitis C Virus Replication

Abstract

Hepatitis C virus (HCV) is a hepatotropic Flavivirus in theHepacivirus genus. The virus genome contains a linear, positive-strand RNA molecule of ϳ9,500 nucleotides. The HCV genome encodes a polyprotein precursor of about 3,000 amino acids, which is cleaved by both viral and host proteases into structural (core, E1, E2, and p7) and nonstructural (NS2, NS3, NS4A, NS4B, NS5A, and NS5B) proteins. A number of HCV genomes have been cloned, and sequence divergences indicate several genotypes and a series of subtypes for the virus (19). An estimated 200 million people worldwide and 4 million people in the United States are infected with HCV. The majority of the chronically HCV-infected patients develop end-stage liver disease. Currently, the treatment is limited to a combination therapy of ribavirin and alpha interferon (IFN-␣). This combination therapy is expensive and effective in ϳ50% of HCV genotype 1-infected individuals (45), and the reason for this limited efficacy is not clear. Both viral and host factors may play roles that ultimately affect the level and extent of IFNstimulated gene (ISG) expression and function induced during the course of IFN therapy (11,12,27,28). Thus, there is an urgent need to identify novel antivirals or cellular molecules that can be used for therapy. Viral proteins and nucleic acids are detected by pathogen recognition receptors (PRRs) as pathogen-associated molecular patterns (PAMPs). Subsequently, the signal transduction pathways are activated and trigger type I IFN and the production of other cytokines. Type I IFN then augments the expression of several ISGs and subverts virus replication by a variety of mechanisms (29,32). IFN orchestrates a large number of genes of this antiviral response (14). However, many viruses deploy anti-IFN countermeasures, which for HCV are enacted primarily by the viral protein NS3/4A (5). To identify host factors that modify viral replication, we performed pathwayspecific microarray of IFN-related genes. Our results identified 56 genes that were modulated between HCV-infected immortalized human hepatocytes (IHH) and IFN-pretreated, HCVinfected IHH. After validation, we focused on two IFN effector molecules, ISG56 (also known as IFIT1) and IFITM1, in determining antiviral effect in the current study. The overexpression of ISG56 is known to suppress HCV internal ribosome entry site (IRES)-mediated transcription, suggesting its potential as an anti-HCV molecule (43). On the other hand, IFITM family proteins are emerging as antiviral ISGs (2, 13, 24). Our results revealed that the exogenous expression of ISG56 or IFITM1 inhibits HCV replication and growth in infected hepatocytes. MATERIALS AND METHODSCell lines and IFN-␣. The generation of immortalized human hepatocytes (IHH) by the transfection of the HCV core was described previously (30). Huh7, Huh7.5, and IHH were maintained in Dulbecco's modified Eagle's medium (DMEM) (Cambrex, Walkersville, MD) containing 10% fetal bovine serum (FBS), 100 U/ml of penicillin G, and 100 g/ml of streptomycin at 37°C in...

Human respiratory syncytial virus infection is inhibited by IFN-induced transmembrane proteins

“…Compared with other viruses inhibited by IFITM proteins, the restriction of RSV was more profound than for human immunodeficiency virus, hepatitis C virus and influenza virus A at the same m.o.i. (Huang et al, 2011;Lu et al, 2011;Raychoudhuri et al, 2011). However, Rift Valley fever virus infection also displayed intensive inhibition by IFITM3 (Mudhasani et al, 2013).…”

“…Recently, one family of ISGs, called IFN-inducible transmembrane (IFITM) proteins, and known to play diverse roles in cell signalling, adhesion, tumour genesis and immune regulation, was found to have the ability to restrict the cell entry and replication of a number of viruses. Most of the viruses restricted by the IFITM proteins are enveloped viruses, such as influenza A, dengue virus and West Nile virus (Brass et al, 2009;Weidner et al, 2010;Huang et al, 2011;Lu et al, 2011;Raychoudhuri et al, 2011;Mudhasani et al, 2013), but reovirus, which is a non-enveloped dsRNA virus, was also recently reported to be sensitive to IFITM3 repression (Anafu et al, 2013). IFITM3 has been reported to restrict cell infection of RSV and control disease pathogenesis in the Ifitm3 knockout mouse model (Everitt et al, 2013).…”

Differential proteomic analysis of respiratory samples from patients suffering from influenza

“…The IFIT family, especially IFIT1 and IFIT3, restrict DNA and RNA virus replication, such as hepatitis B virus (HBV), human papillomavirus (HPV), hepatitis C virus (HCV), West Nile virus (WNV) and others [26,30]. Knock down of IFIT1 though RNA interference in human hepatocytes enhanced HCV replication during infection [31]. Eukaryotic translation initiation factor 4H (eIH4) is involved in regulation of translation initiation during protein synthesis.…”

Lambda-Interferons Inhibit Herpes Simplex Virus Type 2 Replication in Human Cervical Epithelial Cells by Activating the JAK/STAT Pathway

“…expression by various members of the IFN-family, as ISGs have been reported to play important roles in IFN-mediated antiviral activity (35,36).…”