To assess the effects of constitutive hepatitis C virus (HCV) gene expression on liver, transgenic mice carrying the entire HCV open reading frame inserted in the a1 antitrypsin (A1AT) gene were generated. Expression of A1AT/HCV mRNA was found to be mainly limited to perivascular areas of the liver as indicated by in situ hybridization analysis. HCV core protein was detected in Western blots of liver extracts, whereas the expression of E2, NS3 and NS5 proteins was revealed by immunostaining of liver samples using HCV-specific antisera. Histological analysis of HCV transgenic mice showed that these animals develop extensive steatosis, but very little necrosis of liver tissue. Moreover, a consistent T cell infiltrate and a slight hepatocyte proliferation were observed. Phenotypic analysis of cells infiltrating the liver indicated that recruitment and/or expansion of residing CD8 + , NK, NKT and cd T cells occurred in transgenic animals. Among these cells, a large fraction of CD8 + T lymphocytes released mainly IL-10 and, to a lesser extent, IFN-c upon mitogenic stimulation in vitro. Furthermore, both intrahepatic lymphocytes and splenocytes did not produce cytokines in response to HCV antigens. Thus, these data indicate that constitutive expression of HCV proteins may be responsible for intrahepatic lymphocyte recruitment in absence of viral antigen recognition. This response is likely to be driven by virus-induced cellular factors and may play a significant role in the immunopathology of chronic HCV infection and liver disease. INTRODUCTIONHepatitis C virus (HCV) is a member of the Flaviviridae and is the major cause of non-A, non-B hepatitis (Choo et al., 1989;Houghton et al., 1991;Kuo et al., 1989). HCV has a single-stranded RNA genome of positive polarity of about 9?5 kb that contains a long open reading frame (ORF) encoding a polyprotein of approximately 3000 amino acids Kato et al., 1990;Takamizawa et al., 1991). The polyprotein precursor has the following gene order: NH 2 C-E1-E2-p7-NS2-NS3-NS4a-NS4b-NS5a-NS5b COOH (Eckart et al., 1993;Grakoui et al., 1993; Hijikata et al., 1993a, b;Lin et al., 1994;Tomei et al., 1993) C is an RNA-binding protein (Santolini et al., 1994) and is considered to be the viral nucleocapsid; E1 and E2 are thought to be the virion glycoproteins; p7 is a protein involved in the formation of ion channels (Griffin et al., 2004) and is inefficiently cleaved from the E2 polypeptide (Mizushima et al., 1994). Processing of the structural polypeptides is mediated by cellular signal peptidase (Hijikata et al., 1993b;Santolini et al., 1994). The HCVencoded metalloproteinase and serine protease located in the NS2 to NS3 region and N-terminal one-third of NS3 protein, respectively, mediate cleavages in the nonstructural region (Clarke, 1997).More than 170 million people worldwide are infected with HCV, and the complications of liver cirrhosis and hepatocellular carcinoma cause significant morbidity and mortality. The virus is cleared in a minority of patients and 70-80 % develop chronic infec...

The c-Met tyrosine kinase receptor and its ligand, Hepatocyte Growth Factor/ Scatter Factor, have been implicated in human cancer. We have previously described that the transgenic expression of a truncated form of human c-Met (cyto-Met) in the liver confers resistance to several apoptotic stimuli. Here we show the impact of cyto-Met expression on liver proliferation and transformation. Despite a sixfold increase of hepatocyte proliferation, adult transgenic livers displayed normal size and architecture. We present evidence showing that activation of TGF-b1 signalling controls the liver mass in cyto-Met mice. The oncogenic potential of cyto-Met was further assessed in the context of c-Myc-induced hepatocarcinogenesis, using WHV/c-Myc transgenic mice. Co-expression of cyto-Met and c-Myc further enhanced hepatocyte proliferation and caused a dramatic acceleration of the Myc-induced tumorigenesis, leading to the emergence of hepatocarcinomas in 3 ± 4-month-old animals. Importantly, the TGF-b receptor type II expression was strongly downregulated in most tumours, indicating that impairment of TGF-b1-mediated growth inhibition plays a major role in accelerated neoplastic development. The strong potential of cyto-Met for oncogenic cooperation without direct transforming activity designates cyto-Met mice as an ideal tool for studying the early steps of multistage hepatocarcinogenesis and for identi®cation of prognostic markers of transformation.