MicroRNA let-7g cooperates with interferon/ribavirin to repress hepatitis C virus replication

MicroRNAs (miRNA) have been implicated in HCV infection. The present study analyzed the effects of let-7g on HCV infection in vitro, in clinical tissue and serum samples. Here, we show that the expression of let-7g in serum and liver tissue is significantly higher in patients with sustained virologic response (SVR). We show that interferon (IFN)/ribavirin (RBV) induces let-7g expression through p38/AP-1 signaling. Overexpression of let-7g reduced HCV gene or core protein level and inhibited the HCV viral load. The let-7g and IFN/RBV have additively inhibitory effect on HCV replication. These data implicate let-7g as a new therapeutic drug to additively cooperate with IFN/RBV to repress HCV replication. Key messages: let-7g expression is increased in serum and liver tissue of patients with SVR. Interferon/ribavirin induces let-7g expression through p38/AP-1 signaling. Overexpression of let-7g can repress HCV replication. Let-7g additively cooperates with interferon/ribavirin to repress HCV replication. Lin28B silencing can reverse let-7g expression and repress HCV replication.

Hepatitis C virus replication in mouse cells is restricted by IFN-dependent and -independent mechanisms

BACKGROUND & AIMS

Current treatment strategies for hepatitis C virus (HCV) infection include pegylated interferon (IFN)-alfa and ribavirin. Approximately 50% of patients control HCV infection after treatment, but the broad range of patients' outcomes and responses to treatment, among all genotypes, indicates a role for host factors. Although the IFN system is important in limiting HCV replication, the virus has evolved mechanisms to circumvent the IFN response. However, direct, IFN-independent antiviral processes also might help control HCV replication. We examined the role of IFN-independent responses against HCV replication.

METHODS

We analyzed replication of the subgenomic JFH1 replicon in embryonic fibroblasts and primary hepatocytes from mice with disruptions in genes encoding factors in the IFN-dependent and alternative antiviral pathways (signal transducers and activators of transcription 1 [STAT1], protein kinase R, interferon regulatory factors (IRF) IRF-1, IRF-3, IRF-5, IRF-7, mitochondrial antiviral signaling molecule [MAVS], and IFN receptor [IFNAR]). We also assessed the effects of expression of these factors by mouse primary hepatocytes on HCV replication.

RESULTS

In addition to IRF-3- and IFN-mediated antiviral responses, IFN-independent, but IRF-1- and IRF-5-dependent mechanisms, restrict HCV replication in mouse embryonic fibroblasts. In primary hepatocytes these IFN-independent require MAVS and IRF-1.

CONCLUSIONS

HCV replication is limited by interferon-mediated pathways as well pathways that are independent of type I IFNs. IRF1 and IRF5 control IFN-independent signaling events that lead to antiviral responses. We observed antiviral roles of IRF1 and IRF5 that were IFN-independent and cell-type specific. These mechanisms are important in controlling viruses that interfere with the IFN signaling because cells retain the ability to induce functional but local antiviral states through expression of interferon-stimulated genes.

Arylacetamide deacetylase: a novel host factor with important roles in the lipolysis of cellular triacylglycerol stores, VLDL assembly and HCV production

BACKGROUND & AIMS

Very low density lipoproteins (VLDLs) are triacylglycerol (TG)-rich lipoproteins produced by the human liver. VLDLs derive the majority of their TG cargo from the lipolysis of TG stored in hepatocellular lipid droplets (LDs). Important roles for LDs and the VLDL secretory pathway in the cell culture production of infectious hepatitis C virus (HCV) have been established. We hypothesized that TG lipolysis and VLDL production are impaired during HCV infection so that these cellular processes can be diverted towards HCV production.

METHODS

We used an HCV permissive cell culture system (JFH-1/HuH7.5 cells) to examine the relationship between TG lipolysis, VLDL assembly, and the HCV lifecycle using standard biochemical approaches.

RESULTS

Lipolysis of cellular TG and VLDL production were impaired in HCV infected cells during the early peak of viral infection. This was partially explained by an apparent deficiency of a putative TG lipase, arylacetamide deacetylase (AADAC). The re-introduction of AADAC to infected cells restored cellular TG lipolysis, indicating a role for HCV-mediated downregulation of AADAC in this process. Defective lipolysis of cellular TG stores and VLDL production were also observed in HuH7.5 cells stably expressing a short hairpin RNA targeting AADAC expression, proving AADAC deficiency contributes to these defective pathways. Finally, impaired production of HCV was observed with AADAC knockdown cells, demonstrating a role for AADAC in the HCV lifecycle.

CONCLUSIONS

This insight into the biology of HCV infection and possibly pathogenesis identifies AADAC as a novel and translationally relevant therapeutic target.