Morphological modifications induced by HCV infection in the TOFE human lymphoblastoid cell line

Topology of the membrane-associated hepatitis C virus protein NS4B

Hepatitis C virus (HCV) belongs to the Hepacivirus genus in the Flaviviridae family. Among the least known viral proteins in this family is the nonstructural protein NS4B, which has been suggested to be a part of the replication complex. Hydrophobicity plots indicate a common profile among the NS4B proteins from different members of the Flaviviridae family, suggesting a common function. In order to gain a deeper understanding of the nature of HCV NS4B, we have determined localization and topology of this protein by using recombinant HCV NS4B constructs. The protein localized to the endoplasmic reticulum (ER), but also induced a pattern of cytoplasmic foci positive for markers of the ER. Computer predictions of the membrane topology of NS4B suggested that it has four transmembrane segments. The N and C termini were anticipated to be localized in the cytoplasm, because they are processed by the cytoplasmic NS3 protein. By introducing glycosylation sites at various positions in HCV NS4B, we show that the C terminus is cytoplasmic and the loop around residue 161 is lumenal as predicted. Surprisingly, the N-terminal tail was translocated into the lumen in a considerable fraction of the NS4B molecules, most likely by a posttranslational process. Interestingly, NS4B proteins of the yellow fever and dengue viruses also have their N termini located in the ER lumen due to an N-terminal signal peptide not found in NS4B of HCV. A shared topology achieved in two different ways supports the notion of a common function for NS4B in FLAVIVIRIDAE:

Ultrastructure characteristics of HCV infected human trophoblast cells in culture

AIM: To investigate whether the cultured trophoblastic cells can be infected with hepatitis C virus (HCV) and observe the ultrastructural features of infected cells.

METHODS: Human placentae were digested with trypsin and then centrifuged with percoll density gradient to obtain trophoblastic cells, and then incubated in HCV positive serum. The HCV RNA in HCV infected syncytiotroblasts was quantitated with RT-PCR. Ultrastructural characteristics of infected syncytiotroblasts were observed with transmission electron microscope.

RESULTS: HCV RNA was detected in supernatant of the cultured medium during 40 day periods of incubation. The antibody of HCV NS5 was observed around the nucleus with confocal microscope. The Ultrastructure of infected throphotoblast cells differed obviously from that of normal cells, and manifested with hyperplasia of lysosomes and rough endoplasmic, appearance of vacuoles and virus-like particles, and decreased lipid droplets.

CONCLUSION: Trophoblastic cells could be infected by HCV, and the cellular ultrastructure changed dramatically following infection of HCV.

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Inducible system in human hepatoma cell lines for hepatitis C virus production

We cloned the complete complementary DNA of an isolate of the hepatitis C virus, HCV-S1, into a tetracycline-inducible expression vector and stably transfected it into two human hepatoma cell lines, Huh7 and HepG2. Twenty-six Huh7 and two HepG2-positive clones were obtained after preliminary screening. Two Huh7 (SH-7 and -9) and one HepG2 (G-19) clones were chosen for further characterisation. Expression of HCV proteins in these cells accumulated from 6 h to 4 days posttreatment. Full-length viral plus-strand RNA was detected by Northern analyses. Using RT-PCR and ribonuclease protection assay, we also detected the synthesis of minus-strand HCV RNA. Plus- and minus-strand viral RNA was still detected after treatment with actinomycin D. Indirect immunofluorescence staining with anti-E2, NS4B, and NS5A revealed that these proteins were mostly localised to the endoplasmic reticulum (ER). Culture media from tet-induced SH-9 cells was separated on sucrose density gradients and analysed for the presence of HCV RNA. Viral RNA levels peaked at two separate ranges, one with a buoyant density of 1.08 g/ml and another from 1.17 to 1.39 g/ml. Electron microscopy demonstrated the presence of subviral-like particles (approximately 20-25 nm in diameter) in the cytoplasm of SH-9 and G-19 cells, which were positively labelled by anti-HCV core antibodies. Anti-E2 antibodies strongly labelled cytoplasmic vesicular structures and some viral-like particles. Complete viral particles of about 50 nm which reacted with anti-E2 antibodies were observed in the culture media of tet-induced SH-9 cells following negative staining. Supernatant from tet-treated SH-9 cells was found to infect nai;ve Huh7 and stable Huh7-human CD81 cells.

A novel strand-specific RT-PCR for detection of hepatitis C virus negative-strand RNA (replicative intermediate): evidence of absence or very low level of HCV replication in peripheral blood mononuclear cells

Hepatitis C virus (HCV) is reported to be lymphotropic under certain circumstances. In order to evaluate viral replication in peripheral blood mononuclear cells (PBMCs), a novel strand-specific RT-PCR was developed for the determination of HCV negative-strand RNA. The detection limit of this strand-specific RT-PCR was 100 copies of HCV negative-strand RNA in the presence of 1 microg liver RNA and 10(7)-10(8) copies of positive-strand RNA. False positive PCR signals occurred only when HCV positive-strand RNA exceeded 10(9) copies. With this RT-PCR, the replicative-intermediates could be detected specifically in eight of ten liver tissues, but not in any samples of serum or plasma (0/65) of patients with chronic hepatitis C. When examining the PBMCs of 46 hepatitis C patients, including 12 patients who had undergone orthotopic liver transplantation, HCV negative-strand RNA was detected in only one patient (1/46). In addition, HCV replicative intermediates were not detected in PBMCs of patients using immunosuppressive agents. It is concluded that the replication of HCV in PBMCs is very unusual.

Expression of the hepatitis C virus structural proteins in mammalian cells induces morphology similar to that in natural infection

Like many positive-strand RNA viruses, replication of the hepatitis C virus (HCV) is associated with cytoplasmic membrane rearrangements. However, it is unclear which HCV proteins induce these ultrastructural features. This work examined the morphological changes induced by expression of the HCV structural proteins, core, E1 and E2, expressed from a Semliki Forest Virus (SFV) recombinant RNA replicon. Electron microscopy of cells expressing these proteins showed cytoplasmic vacuoles containing membranous and electron-dense material that were distinct from the type I cytoplasmic vacuoles induced during SFV replicon replication. Immunogold labelling showed that the core and E2 proteins localized to the external and internal membranes of these vacuoles, but at times were also associated with some of the internal amorphous material. Dual immunogold labelling with antibodies raised against the core protein and against an endoplasmic reticulum (ER)-resident protein (protein disulphide isomerase) showed that the HCV-induced vacuoles were associated with ER-labelled membranes. This report has identified an association between the HCV core and E2 proteins with induced cytoplasmic vacuoles which are morphologically similar to those observed in HCV-infected liver tissue, suggesting that the HCV structural proteins may be responsible for the induction of these vacuoles during HCV replication in vivo.

[Hepatitis C virus culture systems]

Hepatitis C virus pathogenesis and cycle are difficult to study because of the lack of culture system able to replicate efficiently the virus. Furthermore such a system will permit screen new antiviral drugs. Studies were realized to select cell culture system able to allow hepatitis C virus replication. Primary cell cultures and cell lines were used to performed HCV culture. Most of these works used lymphocyte and hepatocyte primary cultures or cell lines because of HCV tropism in these cells in vivo. Animals and arthropods cell lines were used as well for their capacity to bind and replicate HCV. The aim of this review is to present the different cell systems used to replicate HCV in culture and the results obtained.