Apolipoprotein E Codetermines Tissue Tropism of Hepatitis C Virus and Is Crucial for Viral Cell-to-Cell Transmission by Contributing to a Postenvelopment Step of Assembly

Abstract

cHepatitis C virus (HCV) predominantly infects human hepatocytes, although extrahepatic virus reservoirs are being discussed. Infection of cells is initiated via cell-free and direct cell-to-cell transmission routes. Cell type-specific determinants of HCV entry and RNA replication have been reported. Moreover, several host factors required for synthesis and secretion of lipoproteins from liver cells, in part expressed in tissue-specific fashion, have been implicated in HCV assembly. However, the minimal cell type-specific requirements for HCV assembly have remained elusive. Here we report that production of HCV trans-complemented particles (HCV TCP ) from nonliver cells depends on ectopic expression of apolipoprotein E (ApoE). For efficient virus production by full-length HCV genomes, microRNA 122 (miR-122)-mediated enhancement of RNA replication is additionally required. Typical properties of cell culture-grown HCV (HCVcc) particles from ApoE-expressing nonliver cells are comparable to those of virions derived from human hepatoma cells, although specific infectivity of virions is modestly reduced. Thus, apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTTP), and apolipoprotein C1 (ApoC1), previously implicated in HCV assembly, are dispensable for production of infectious HCV. In the absence of ApoE, release of core protein from infected cells is reduced, and production of extracellular as well as intracellular infectivity is ablated. Since envelopment of capsids was not impaired, we conclude that ApoE acts after capsid envelopment but prior to secretion of infectious HCV. Remarkably, the lack of ApoE also abrogated direct HCV cell-to-cell transmission. These findings highlight ApoE as a host factor codetermining HCV tissue tropism due to its involvement in a late assembly step and viral cell-to-cell transmission. C urrently, around 160 million people are chronically infected with hepatitis C virus (HCV) worldwide (1). A prophylactic vaccine is not available, but direct-acting antivirals (DAA) have recently been approved for treatment (2). However, the novel triple therapy including pegylated alpha interferon (PEG-IFN-␣), ribavirin, and one of two available protease inhibitors is associated with side effects and is not licensed for all viral genotypes. A detailed understanding of the viral life cycle and the roles of specific viral and host factors may reveal novel targets for antiviral therapy and thus help to improve existing therapeutic options.Chronic HCV infection is a leading cause of liver disease, including hepatitis, liver cirrhosis, and hepatocellular carcinoma (3). It is also associated with numerous extrahepatic manifestations, such as cryoglobulenimia and neuronal disorders (reviewed in reference 4). While hepatocytes are thought to be the primary site of HCV replication, a number of studies have highlighted possible extrahepatic sites of replication, including peripheral blood mononuclear cells and cells of neuronal origin (reviewed in references 5 and 6). These observations sugge...

Functional and Biochemical Characterization of Hepatitis C Virus (HCV) Particles Produced in a Humanized Liver Mouse Model

“…The horizontal bars represent the median values. HCVfrg, n ϭ 9; HCVcc, n ϭ 3. apoE function, our findings suggested that apoE is an essential factor for entry of infectious in vivo produced virus (23,(42)(43)(44)(45)(46).…”

Apolipoprotein E Mediates Evasion From Hepatitis C Virus Neutralizing Antibodies

“…This is consistent with the report from Barretto et al 33 Engineering nonhepatic cells to produce HCV through ectopic apoE expression can confer cell-to-cell transmission capacity, albeit to a limited degree relative to the levels observed in the current study. 34 We thus cannot exclude that epitopes not recognized by the utilized anti-apoE antibody play a role in cell-to-cell transmission or that this antibody may have limited access to the virus during this process.…”

Cell death-inducing DFFA-like effector B contributes to assembly of hepatitis C virus (HCV) particles and interacts with HCV NS5A

“…CD81 29 , RACK1 30 , PI4KIIIα [31][32][33] , and ApoE 8,12,17,34 are important cellular factors in HCV entry, IRES-mediated translation, RNA replication, and assembly, respectively. To determine the specific stage of the HCV life cycle that requires CIDEB, a panel of siRNAs targeting these genes was used.…”