The liver is frequently challenged by surgery-induced metabolic overload, viruses or toxins, which induce the formation of reactive oxygen species. To determine the effect of oxidative stress on liver regeneration and to identify the underlying signaling pathways, we studied liver repair in mice lacking the Nrf2 transcription factor. In these animals, expression of several cytoprotective enzymes was reduced in hepatocytes, resulting in oxidative stress. After partial hepatectomy, liver regeneration was significantly delayed. Using in vitro and in vivo studies, we identified oxidative stress-mediated insulin/insulin-like growth factor resistance as an underlying mechanism. This deficiency impaired the activation of p38 mitogenactivated kinase, Akt kinase and downstream targets after hepatectomy, resulting in enhanced death and delayed proliferation of hepatocytes. Our results reveal novel roles of Nrf2 in the regulation of growth factor signaling and in tissue repair. In addition, they provide new insight into the mechanisms underlying oxidative stress-induced defects in liver regeneration. These findings may provide the basis for the development of new strategies to improve regeneration in patients with acute or chronic liver damage.

Chronic hepatitis C virus (HCV) infection is a major cause of liver disease worldwide.Restriction of HCV infection to human hepatocytes suggests that liver-specific host factors play a role in the viral life cycle. Using a yeast-two-hybrid system, we identified apolipoprotein E (apoE) as a liver-derived host factor specifically interacting with HCV nonstructural protein 5A (NS5A) but not with other viral proteins. The relevance of apoE-NS5A interaction for viral infection was confirmed by co-immunoprecipitation and co-localization studies of apoE and NS5A in an infectious HCV cell culture model system. Silencing apoE expression resulted in marked inhibition of infectious particle production without affecting viral entry and replication. Analysis of particle production in liver-derived cells with silenced apoE expression showed impairment of infectious particle assembly and release. The functional relevance of the apoE-NS5A interaction for production of viral particles was supported by loss or decrease of apoE-NS5A binding in assembly-defective viral mutants. H epatitis C virus (HCV) is a major cause of liver disease, including liver cirrhosis and hepatocellular carcinoma. 1 Current treatment by interferon-alpha and ribavirin is limited by resistance, toxicity, and high costs. 1,2 Novel treatment approaches are therefore urgently needed. HCV is an enveloped single-stranded RNA virus of positive polarity that is a member of the genus Hepacivirus within the family Flaviviridae. 3,4 The HCV RNA genome encodes a unique polyprotein of approximately 3000 amino acids and is flanked at its 5Ј and 3Ј ends by two highly conserved untranslated regions involved in the transla- Conclusion: These results suggest that recruitment of apoE by NS5A is important for viral assembly and release of infectious viral particles. These findings have important implications

The large hepatitis B virus (HBV) surface protein (LHBs) and C-terminally truncated middle size surface proteins (MHBs t ) form the family of the PreS2 activator proteins of HBV. Their transcriptional activator function is based on the cytoplasmic orientation of the PreS2 domain. MHBs t activators are paradigmatic for this class of activators. Here we report that MHBs t is protein kinase C (PKC)-dependently phosphorylated at Ser28. The integrity of the phosphorylation site is essential for the activator function. MHBs t triggers PKC-dependent activation of c-Raf-1/Erk2 signaling that is a prerequisite for MHBs t -dependent activation of AP-1 and NF-kB. To analyze the pathophysiological relevance of these data in vivo, transgenic mice were established that produce the PreS2 activator MHBs t speci®cally in the liver. In these mice, a permanent PreS2-dependent speci®c activation of c-Raf-1/Erk2 signaling was observed, resulting in an increased hepatocyte proliferation rate. In transgenics older than 15 months, an increased incidence of liver tumors occurs. These data suggest that PreS2 activators LHBs and MHBs t exert a tumor promoter-like function by activation of key enzymes of proliferation control.

In addition to infectious viral particles, hepatitis B virus-replicating cells secrete large amounts of subviral particles assembled by the surface proteins, but lacking any capsid and genome. Subviral particles form spheres (22-nm particles) and filaments. Filaments contain a much larger amount of the large surface protein (LHBs) compared to spheres. Spheres are released via the constitutive secretory pathway, while viral particles are ESCRT-dependently released via multivesicular bodies (MVBs). The interaction of virions with the ESCRT machinery is mediated by ␣-taxilin that connects the viral surface protein LHBs with the ESCRT component tsg101. Since filaments in contrast to spheres contain a significant amount of LHBs, it is unclear whether filaments are released like spheres or like virions. To study the release of subviral particles in the absence of virion formation, a core-deficient HBV mutant was generated. Confocal microscopy, immune electron microscopy of ultrathin sections and isolation of MVBs revealed that filaments enter MVBs. Inhibition of MVB biogenesis by the small-molecule inhibitor U18666A or inhibition of ESCRT functionality by coexpression of transdominant negative mutants (Vps4A, Vps4B, and CHMP3) abolishes the release of filaments while the secretion of spheres is not affected. These data indicate that in contrast to spheres which are secreted via the secretory pathway, filaments are released via ESCRT/MVB pathway like infectious viral particles. IMPORTANCEThis study revises the current model describing the release of subviral particles by showing that in contrast to spheres, which are secreted via the secretory pathway, filaments are released via the ESCRT/MVB pathway like infectious viral particles. These data significantly contribute to a better understanding of the viral morphogenesis and might be helpful for the design of novel antiviral strategies.T he human hepatitis B virus (HBV) is a spherical particle, 42 nm in diameter, consisting of an outer envelope and an inner icosahedral nucleocapsid. The nucleocapsid is formed by the core protein and harbors the viral genomic DNA. The HBV genome encodes at least four different open reading frames, coding for the viral polymerase, the core and the e antigen (HBcAg and HBeAg), the regulatory X protein (HBx), and the three different surface proteins (HBsAg): the large HBV surface protein (LHBs), the middle surface protein (MHBs) and the small surface protein (SHBs) (1). LHBs encompasses the PreS1 domain, the PreS2 domain, and the S domain, MHBs consists of the PreS2 and the S domain, and SHBs contains the S domain. These surface proteins are not only constitutive components of the envelope of viral particles but also assemble to capsid-free subviral particles lacking any viral genome having the shape of spheres and filaments (2) that are secreted in 1,000-to 100,000-fold excess relative to infectious viral particles. SHBs, the predominant part of these subviral particles, can assemble to 22-nm spherical particles. The incorporation ...