To clarify the effects of hepatitis C virus (HCV) infection on hepatocytes, we analyzed and compared the induction of intracellular signals by HCV and hepatitis B virus (HBV) proteins. We examined the influence of 7 HCV (core, NS2, NS3, NS4A, NS4B, NS5A, and NS5B) and 4 HBV (precore, core, polymerase, and X) proteins on 5 well-defined intracellular signaling pathways associated with cell proliferation, differentiation, and apoptosis by use of a reporter assay. Viral protein-expression vectors were cotransfected into mammalian cells with reporter vectors having a luciferase gene driven by the following inducible cis-enhancer elements: the cyclic adenosine monophosphate response element, the serum response element (SRE), and the binding sites for nuclear factor kappaB (NF-kappaB), activator protein 1 (AP-1), and serum response factor (SRF). In addition, the activation of signals by HCV proteins was examined in a reporter plasmid having a natural interleukin-8 (IL-8) promoter upstream of a luciferase gene. Of 11 HCV and HBV proteins, HCV core had the strongest influence on intracellular signals, especially NF-kappaB-, AP-1-, and SRE-associated pathways. HCV core's activation level exceeded that of HBV X protein, a well-characterized transactivator of these signals. Moreover, HCV core activated the IL-8 promoter through NF-kappaB and AP-1. For the other proteins, HCV NS4B showed signal activation, but signals were activated at a lesser extent. The luciferase reporter assay, a recently introduced technique, helped in the elucidation of molecular events underlying the inflammatory and proliferation process in the liver induced by HCV.

Hepatitis B virus (HBV) infection is a major health problem, with 1.2 million deaths per year worldwide according to the 1997 World Health Organization report. 1 It causes acute and chronic liver diseases, including life-threatening fulminant hepatitis, cirrhosis, and hepatocellular carcinoma. 2 Despite the existence of an effective vaccine, no effective antiviral treatment has been developed for the patients chronically infected with HBV. Although interferon therapy benefits some patients with chronic hepatitis B, the overall response rate is less than 40% and interferon has doselimiting side-effects. 3,4 Because the replication of HBV DNA proceeds through reverse transcription of a pregenomic RNA intermediate, 5 the use of reverse-transcriptase inhibitors as an antiviral drug for hepatitis B has become an attractive option. Lamivudine, or (-)-␤-L-2Ј,3Ј-dideoxy-3Ј-thiacytidine (3TC), is one many of reverse-transcriptase inhibitors and has antiviral activity against human immunodeficiency virus (HIV) 6 and HBV. [7][8][9][10][11][12][13] Recently, lamivudine was used to treat patients with chronic hepatitis B and reduced HBV DNA to an undetectable level, with few adverse effects. 8 Lamivudine also proved useful in preventing HBV reinfection of the graft after liver transplantation. [11][12][13] However, recent studies reported the emergence of lamivudine-resistant HBV during treatment. 14-17 Lamivudine-resistant HBV was revealed to have methionine (M) to isoleusine (I) or valine (V) substitutions in the tyrosine (Y), methionine (M), aspartate (D), aspartate (D) motif (YMDD motif) of the RNA-dependent DNA polymerase, as was seen in lamivudine-resistant HIV. The YMDD motif is one of the highly conserved domains in RNAdependent DNA polymerase present in retroviruses, hepadnaviruses, retrotransposons, group II intron, bacterial retrons, and the catalytic subunit of telomerase, and is involved in nucleotide binding in the catalytic site of the polymerase. [18][19][20][21][22][23] Amino acid substitutions in this motif were also associated with the resistance of HIV to other nucleoside analogues, such as ddC and FTC (5-fluoro-derivative of lamivudine). 21 Emergence of resistant viruses to nucleoside analogues has stimulated a heightened interest in the study of the YMDD motif, and more appropriate knowledge of HBV drugresistance patterns to lamivudine is considered imperative in improving patient management. The present study was designed to evaluate replication competence and the susceptibility to lamivudine of the YMDD motif variants of HBV in human hepatoma cells transiently transfected by full-length HBV DNA.

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Many viruses can inhibit protein synthesis in their host cells by targeting translation ("translational shutoff"). There are few reports on the effects of hepatitis C virus (HCV) infection on protein synthesis, because of the lack of a reproducible tissue culture system for HCV. In this study, the influence of seven HCV proteins (core, NS2, NS3, NS4A, NS4B, NS5A, NS5B) on protein synthesis was examined using a reporter assay. In addition, it was determined whether the HCV proteins inhibit protein synthesis via transcription or translation using an RNase protection assay and the effect of HCV proteins on translation from the HCV internal ribosome entry site (IRES) was also examined using a bicistronic reporter. Of the seven HCV proteins, NS4A and NS4B proteins inhibited cellular protein synthesis by targeting the process of translation. They also inhibited translation from the HCV IRES. Moreover, NS4A protein, induced under the control of doxycycline, inhibited the proliferation of HeLa cells. In conclusion, HCV NS4A and NS4B proteins have an effect of translational inhibition. This novel function may be involved in HCV infection and help its survival in host cells.