J Virol 75(22): 11017-11024

Identification of a Hepatic Factor Capable of Supporting Hepatitis C Virus Replication in a Nonpermissive Cell Line

Liver Research Unit^{and Department of Pathology,}^{Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Taipei, Taiwan}

^{Corresponding author. Mailing address: Liver Research Unit, Chang Gung Memorial Hospital, 199 Tung Hwa North Rd., Taipei 105, Taiwan. Phone: 886-3-3281200, ext. 8120. Fax: 886-3-3282824. E-mail:}ten.tenih.41sm@heytac.

Received 2001 Jun 11; Accepted 2001 Aug 16.

Abstract

Although hepatitis C virus E2 protein can bind to human cells by interacting with a putative viral receptor, CD81, the interaction alone is not sufficient to establish permissiveness for hepatitis C virus infection. Using an Epstein-Barr virus-based extrachromosomal replication system, we have screened through a human liver cDNA library and successfully identified a cDNA capable of supporting hepatitis C virus replication in an otherwise nonpermissive cell line. This cDNA encodes a protein exhibiting homology to a group of proteins derived from various evolutionarily distant species, including Oryza sativa submergence-induced protein 2A. The mRNAs encoding this factor are heterogeneous at the 5′ ends and are ubiquitously expressed in multiple tissues, albeit in a very small amount. The longest mRNA contains an in-frame and upstream initiation codon and codes for a larger protein. This 5′-extended form of mRNA was detected in hepatocellular carcinoma, but not in normal liver tissue. Immunofluorescence analysis demonstrated that the hepatic factor was distributed evenly in cells, but occasionally formed aggregations in the peri- or intranuclear areas. In summary, we have identified a hepatic factor capable of supporting hepatitis C virus replication in an otherwise nonpermissive cell line. This factor belongs to a previously uncharacterized protein family. The physiological function of this protein awaits further study.

Abstract

Hepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide (4). Chronic hepatitis C may lead to severe sequelae, such as liver cirrhosis and hepatocellular carcinoma (18, 19). Although scientists have made important progress in understanding molecular mechanisms for HCV replication, few data are available regarding essential cellular factors required for HCV replication (3, 9, 10). It is believed that as an initial step for viral infection, HCV must bind either directly or indirectly to a viral receptor in order to anchor on the cell membrane. Previously, it was proposed that HCV could associate with low-density lipoprotein (LDL) in the blood and that the complexes interacted with LDL receptor before entering the hepatocytes (1, 13). Recently, it was discovered that HCV E2 protein interacted specifically with CD81 on the cell membrane, which was suggested to be the HCV receptor (15, 20). Although several other groups confirmed the specificity of binding between E2 and CD81, subsequent studies indicated that the interaction alone did not predict susceptibility of cells to HCV infection (2, 5, 7, 12, 14). For example, HCV E2 protein was able to bind CD81 that originated from other species not permissive for HCV infection (2, 12). Structure-function analysis revealed that HCV binding to hepatocytes might not entirely depend on CD81 and that CD81 was an attachment receptor with poor capacity to mediate virus entry (14). These results lead to the argument that other species-specific cellular factors or coreceptors are needed for cell entry and thus replication of HCV. In this study, we have developed a strategy to search for such a molecule.

ACKNOWLEDGMENTS

We thank C. Y. Peng for helpful discussions.

This work was supported partly by a 3-year grant (CMRP 752) and partly by a continuous grant for pilot projects (CMRP 800) from the Chang Gung Medical Research Council.

ACKNOWLEDGMENTS

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