HepG2 cells stably transfected with a full-length, infectious hepatitis C virus (HCV) cDNA demonstrated consistent replication of HCV for more than 3 years. Intracellular minus strand HCV RNA was present. Minus strand synthesis was NS5B dependent, and was sensitive to interferon alpha (IFNa) treatment. NS5B and HCV core protein were detectable. HCV stimulated HepG2 cell growth and survival in culture, in soft agar, and accelerated tumor growth in SCID mice. These mice becameHCVRNApositive in blood, where the virus was also sensitive to IFNa. The RNA banded at the density of HCV, and was resistant to RNase prior to extraction. Hence,HCVstably replicates inHepG2cells, stimulates epatocellular growth and tumorigenesis, and is susceptible to IFNa both in vitro and in vivo. J. Cell. Physiol. 201: 447-458, 2004.

The development of hepatocellular carcinoma (HCC) is a multistep process associated with changes in host gene expression, some of which correlate with the appearance and progression of tumor. reneoplastic changes in gene expression result from altered DNA methylation, the actions of hepatitis B and C viruses, and point mutations or loss of heterozygosity (LOH) in selected cellular genes. Tumor progression is characterized by LOH involving tumor suppressor genes on many chromosomes and by gene ampli

The role of hepatitis B virus X antigen in the development of hepatocellular carcinoma was explored by stably transfecting HepG2 cells with an X antigen expression vector, and identifying the ierences in gene expression that distinguish X positive from X negative cells by subtractive PCR. One ierentially expressed gene, the human homolog of sui1 (hu-sui1), encodes a translation initiation factor whose expression was suppressed by X antigen in HepG2 cells. Hu-Sui1 was also expressed in nontumor liver but not in tumor cells from patients with hepatocellular carcinoma. ntroduc-tion of hu-sui1 into HepG2 cells inhibited cell growth in culture, in soft agar, and partially inhibited tumor formation in nude mice. Hence, the suppression of hu-sui1 by X antigen may result in the abrogation of negative growth regulation and contribute to the development of epatocellular carcinoma.

Hepatitis B and related viruses that infect mammalian hosts encode the "X" protein that has been shown to contribute importantly to the pathogenesis of chronic liver disease (CLD) and to the evelopment of hepatocellular carcinoma (HCC). In a variety of tissue culture systems, hepatitis B virus (HBV) X antigen, or HBxAg, has been shown to trigger apoptosis, while other evidence suggests that HBxAg inhibits apoptosis and stimulates the cell cycle by constitutively activating a number of signaling pathways that are important for hepatocellular growth and survival. These apparently contrasting properties of HBxAg may be associated with differences in the X protein itself, since carboxy-terminaltruncated forms of HBxAg appear to be associated with HCC lesions. Alternatively, or in addition, these differences may be due to the cell type, state of cell differentiation, and whether expression occurs in resting or dividing cells. Further, the association between HBxAg expression and chromosomal instability, may also contribute to the apparently contrasting fates of HBxAg positive cells. It is proposed that in many of these systems, the different outcomes of HBxAg expression may be due to the nature of the cellular response to HBxAg, and not due to differences in the fundamental properties of HBxAg, the latter of which promote cell survival, cell cycle rogression, and the development of HCC.

The hepatitis B virus (HBV)-encoded X antigen (HBxAg) may contribute to the development of epatocellular carcinoma (HCC) through the upregulated expression of selected cellular genes. To identify these genes, RNAs isolated from HBxAg-positive and -negative HepG2 cells were compared by PCR select cDNA subtraction. One gene overexpressed in HBxAg-positive cells by Northern and Western blotting is the ribosomal protein S15a. The S15a mRNA is 535 base pairs, encoding a protein 130 amino acids long with a molecular weight of 14.3kDa. S15a expression was upregulated in HBV-infected livers, where it costained with HBxAg. Overexpression of S15a stimulated cell growth, colony formation in soft agar, and tumor formation in SCID mice. Hence, HBxAg upregulated the expression of S15a, the latter of which participates in the development of HCC, perhaps by altering the integrity of translation.