Diacylglycerol acyltransferase-1 localizes hepatitis C virus NS5A protein to lipid droplets and enhances NS5A interaction with the viral capsid core.

The triglyceride-synthesizing enzyme acyl CoA:diacylglycerol acyltransferase 1 (DGAT1) plays a critical role in hepatitis C virus (HCV) infection by recruiting the HCV capsid protein core onto the surface of cellular lipid droplets (LDs). Here we find a new interaction between the non-structural protein NS5A and DGAT1 and show that the trafficking of NS5A to LDs depends on DGAT1 activity. DGAT1 forms a complex with NS5A and core and facilitates the interaction between both viral proteins. A catalytically inactive mutant of DGAT1 (H426A) blocks the localization of NS5A, but not core, to LDs in a dominant-negative manner and impairs the release of infectious viral particles, underscoring the importance of DGAT1-mediated translocation of NS5A to LDs in viral particle production. We propose a model whereby DGAT1 serves as a cellular hub for HCV core and NS5A proteins, guiding both onto the surface of the same subset of LDs, those generated by DGAT1. These results highlight the critical role of DGAT1 as a host factor for HCV infection and as a potential drug target for antiviral therapy.

HCV infection induces a unique hepatic innate immune response associated with robust production of type III interferons.

BACKGROUND & AIMS: Polymorphisms in the IL28B gene have been associated with clearance of hepatitis C virus (HCV), indicating a role for type III interferons (IFNs) in HCV infection. Little is known about the function of type III IFNs in intrinsic antiviral innate immunity. METHODS: We used in vivo and in vitro models to characterize the role of the type III IFNs in HCV infection and analyzed gene expression in liver biopsy samples from HCV-infected chimpanzees and patients. Messenger RNA and protein expression were studied in HCV-infected hepatoma cell lines and primary human hepatocytes. RESULTS: HCV infection of primary human hepatocytes induced production of chemokines and type III IFNs, including interleukin (IL)-28, and led to expression of IFN-stimulated genes (ISGs). Chimpanzees infected with HCV showed rapid induction of hepatic type III IFN, associated with up-regulation of ISGs and minimal induction of type I IFNs. In liver biopsy specimens from HCV-infected patients, hepatic expression of IL-28 correlated with levels of ISGs but not of type I IFNs. HCV infection produced extensive changes with gene expression in addition to ISGs in primary human hepatocytes. The induction of type III IFNs is regulated by IFN regulatory factor 3 and nuclear factor κB. Type III IFNs up-regulate ISGs with a different kinetic profile than type 1 IFNs and induce a distinct set of genes, which might account for their functional differences. CONCLUSIONS: HCV infection results predominantly in induction of type III IFNs in livers of humans and chimpanzees; the level of induction correlates with hepatic levels of ISGs. These findings might account for the association among IL-28, level of ISGs, and recovery from HCV infection and provide a therapeutic strategy for patients who do not respond to IFN therapy.