Hepatitis C Virus NS5A Protein Impairs TNF-Mediated Hepatic Apoptosis, but Not by an Anti-FAS Antibody, in Transgenic Mice

Abstract

Hepatitis C virus (HCV) is a major etiologic agent of chronic hepatitis worldwide and may lead to the development of hepatocellular carcinoma. However, the mechanism of development of chronic hepatitis or hepatocarcinogenesis by HCV remains unclear. In the present study, we have investigated the effect of nonstructural protein 5A (NS5A) on TNF- and Fas-mediated apoptosis in the liver of transgenic mice. For this purpose, transgenic mice were generated by targeting the HCV NS5A genomic region cloned under the control of a liver-specific apoE promoter. The transgenic animals were phenotypically similar to their normal littermates and did not exhibit a detectable histological change in the liver at 8-12 weeks of age. Intraperitoneal injection of recombinant TNF induced hepatic injury and apoptosis in normal mice. In contrast, transgenic mice expressing NS5A protein were protected against hepatic apoptosis after injection of TNF. However, injection of anti-Fas antibody into transgenic mice did not significantly influence hepatic apoptosis compared to the normal littermates. These results suggested distinct effects of TNF and anti-Fas antibody in transgenic mice expressing NS5A. We subsequently investigated the effect of NS5A in signaling pathways involved in these two cytokine-mediated apoptosis. A physical association between NS5A and TRADD was observed by pull-down assay, coimmunoprecipitation, and colocalization experiments. Furthermore, NS5A prevented the association between TRADD and FADD and blocked TRADD-mediated NF-kappaB activation. Together, our results suggest that NS5A impairs TNF-mediated apoptosis by interfering upstream of the signal transduction pathway and may play a role in HCV-mediated pathogenesis.

Toll-like receptor 4 mediates synergism between alcohol and HCV in hepatic oncogenesis involving stem cell marker Nanog

“…However, whether NS5A induces TLR4 in the liver of the whole animal is yet to be determined. To address this question, NS5A was expressed in a hepatocyte-specific manner in mice with the use of an apoE promoter (23,24). RT-PCR and immunoblot analyses confirmed induction of TLR4 mRNA and protein levels in the NS5A Tg mouse liver compared with the wild-type (WT) mouse liver ( Fig.…”

Tumor initiation and progression in hepatocellular carcinoma: risk factors, classification, and therapeutic targets

“…The HCV core protein seems to be involved in overcoming apoptosis since it interferes with for example TNFα signaling [38] . HCV core protein in particular also can induce insulin resistance and this might further trigger development of HCC [39,40] .…”

Signal transduction cascades and hepatitis B and C related hepatocellular carcinoma

“…135 However, other forms (p50, p53) have also been described in the Huh-7 hepatoma cell line. 136 Though expression of this protein in transgenic mice has not demonstrated direct oncongenicity, 137,138 NS5a has been associated with cell transformation in vitro. [139][140][141] Transfecting murine embryo fibroblasts (NIH 3T3) with NS5a results in a transformed phenotype, defined by increased proliferation, colony formation in soft-agar medium, and tumor formation in nude mice.…”