Analysis of ISG Expression in Chronic Hepatitis C Identifies Viperin as a Potential Antiviral Effector *

Abstract

Interferon (IFN) ␣ inhibits hepatitis C virus (HCV) replication both clinically and in vitro;however, the complete spectrum of interferon-stimulated genes (ISGs) expressed in the HCV-infected liver or the genes responsible for control of HCV replication have not been defined. To better define ISG expression in the chronically infected HCV liver, DNA microarray analysis was performed on 9 individuals with chronic hepatitis C (CHC). A total of 232 messenger RNAs were differentially regulated in CHC compared with nondiseased liver controls. A significant proportion of these were potential ISGs that were transcriptionally elevated, suggesting an ongoing response to endogenous IFN and/or double-stranded RNA. H epatitis C virus (HCV) is the leading cause of chronic hepatitis and liver disease-related morbidity worldwide. A significant proportion of infected individuals escape the host antiviral response and develop a chronic infection, which can result in progressive liver disease such as cirrhosis and hepatocellular carcinoma. 1 The current and only therapy for chronic hepatitis C (CHC) infection is interferon (IFN) ␣/ribavirin combination therapy that results in response rates to sustained viral clearance in at best 50% of patients. Clearly a significant number of individuals cannot be cured of HCV infection, many of whom will progress to serious liver disease.Viral infection activates the host innate antiviral response, which results in the induction of cellular protective genes, including type I IFNs (IFN-␣ and IFN-␤), proinflammatory cytokines, and a subset of interferonstimulated genes (ISGs) that directly limit viral replication. 2,3 Microarray studies in vitro have revealed that hundreds if not thousands of ISGs may be expressed in response to stimulation with IFN, some of which are known to have direct antiviral and immunomodulatory action. 4 Of the best-characterized antiviral ISGs, MxA, double-stranded RNA (dsRNA)-activated protein kinase R, and 2Ј-5Ј-oligoadenylate synthesase (OAS) are most renowned; however, the complete spectrum of ISGs has not been identified, thus ISGs with potential antiviral action remain unknown. The ISGs that limit HCV replication at the molecular level are ill-defined, although recent work has shown that ISG6-16 can enhance the anti-HCV activity of IFN-␣, 5 and ISG-56 has direct anti-HCV activity through its ability to suppress HCV IRES

TLR3 Ligation Activates an Antiviral Response in Human Fetal Astrocytes: A Role for Viperin/cig5

“…Stable expression of the protein inhibited human CMV production in fibroblasts (14). Viperin/cig5 is also highly expressed in liver tissue from patients chronically infected with hepatitis C virus, and again stable transfection of the protein was able to significantly decrease hepatitis C virus replication in a replicon model (23). Using neutralizing Abs to IFN-␤, our data strongly support the conclusion that in astrocytes viperin is predominantly a type 1 ISG.…”

“…In cells of the monocyte/macrophage series viperin is induced by IFNs, with IFN-␤ providing the most potent stimulus (14,23). Because pIC induced IFN-␤ mRNA in human fetal astrocytes, we then tested whether viperin was a direct target of pIC activation of astrocytes, or resulted from autocrine/paracrine signaling by IFN-␤.…”

Genomic response to interferon-α in chimpanzees: Implications of rapid downregulation for hepatitis C kinetics

“…Similar findings have been observed in human liver and peripheral blood mononuclear cells (PBMC) during chronic infection. [13][14][15][16] One potential interpretation of these findings consistent with observations in several systems is that an ongoing IFN-␣/␤ response limits virus replication and spread in the liver. 10,11 The importance of IFN-␣ in HCV clearance has been demonstrated in several studies: (1) the high rate of sustained viral clearance of chronic infections after combined therapy with peg-IFN-␣ and ribavirin, 4,5 (2) the near 100% viral clearance rate using IFN-␣ monotherapy in acutely infected individuals, 17 and (3) the sensitivity of HCV-replicons to IFN-␣.…”

“…[10][11][12][13][14][15] We have proposed a model 11 that reconciles the in vitro observations that HCV proteins block the dsRNA-type I IFN response with the in vivo observations that HCV-infected livers have high levels of ISG transcripts. Based on the level of viral RNA in the liver, we concluded that only a small percentage of hepatocytes are infected, and that turnover of infected hepatocytes results in a constant supply of newly infected cells that secrete IFN until sufficient viral protein is available to inhibit this pathway.…”

“…The classical IFN antiviral genes were expressed by both liver and PBMC; such as MX1, MX2, and OAS1-3. Other genes with known antiviral activity included viperin (RSAD2), 14 phospholipid scramblase, and ADAR. Many genes involved in the IFN response pathway were commonly upregulated in both tissues as well, including STAT1, STAT3, interferon regulatory factor 2 (IRF2), IRF5, IRF7, and IRF9 (ISGF3G) ( Table 1).…”