Post-translational modification of delta antigen of hepatitis D virus.

Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, and Hepatitis Research Center, National Taiwan University Hospital, Taipei.
Current topics in microbiology and immunology (Impact Factor: 3.47). 02/2006; 307:91-112. DOI: 10.1007/3-540-29802-9_5
Source: PubMed

ABSTRACT The hepatitis delta virus (HDV) genome has only one open reading frame, which encodes the viral small delta antigen. After RNA editing, the same open reading frame is extended 19 amino acids at the carboxyl terminus and encodes the large delta antigen. These two viral proteins escort the HDV genome through different cellular compartments for the complicated phases of replication, transcription and, eventually, the formation of progeny virions. To orchestrate these events, the delta antigens have to take distinct cues to traffic to the right compartments and make correct molecular contacts. In eukaryotes, post-translational modification (PTM) is a major mechanism of dictating the multiple functions of a single protein. Multiple PTMs, including phosphorylation, isoprenylation, acetylation, and methylation, have been identified on hepatitis delta antigens. In this chapter we review these PTMs and discuss their functions in regulating and coordinating the life cycle of HDV.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Clinical studies have shown that hepatitis Delta virus (HDV) infection can persist for years and intrahepatic latency of large Delta antigen (HDAg) has been detected following liver transplantation. However, large HDAg arising via RNA-editing is associated with increasing amounts of non-infectious HDV quasi-species. This study investigated whether HDV could persist intrahepatically in the absence of HBV in vivo and whether infectious HDV could subsequently be released following HBV super-infection. Humanized mice were infected with HDV particles lacking HBV. To test for rescue of latent HDV infection 3 and 6 weeks HDV mono-infected mice were super-infected with HBV. Viral loads and cell toxicity were determined by qRT-PCR and immunohistochemistry. The presence of HDAg-positive human hepatocytes determined after 2, 3 and 6 weeks of HDV inoculation demonstrated establishment and maintenance of intrahepatic HDV mono-infection. Although intrahepatic amounts of large HDAg and edited HDV-RNA forms increased over time in HDV mono-infected livers, HBV super-infection led to prompt viremia development (up to 10(8) HDV-RNA and 10(7) HBV-DNA copies/ml) even after 6 weeks of latent mono-infection. Concurrently, the number of HDAg-positive human hepatocytes increased, demonstrating intrahepatic HDV spreading. The infectivity of the rescued HDV virions was verified by serial passage in naive chimeric mice. HDV mono-infection can persist intrahepatically for at least 6 weeks before being rescued by HBV. Conversion of a latent HDV infection to a productive HBV/HDV co-infection may contribute to HDV persistence even in patients with low HBV replication and in the setting of liver transplantation.
    Journal of Hepatology 11/2013; · 9.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Immigration is fuelling a new reservoir of hepatitis D virus (HDV) in Europe, and hepatitis D still represents an important medical problem in the USA. The disease continues to be a major medical scourge in the developing world, in particular in countries such as Pakistan, Mongolia and Mauritania. New therapeutic strategies are being developed to disrupt interactions between HDV and its viral partner HBV, or with the host. Blocking or modifying the hepatitis B surface antigen (HBsAg) might interfere with the uptake or release of the hepatitis D virion; interference with host-mediated post-translational changes of proteins that are crucial to the HDV life cycle, such as prenylation, is another potential therapeutic option. At present, however, the only realistic option is to optimize IFN-α therapy. As eradication of HBsAg is the ultimate end point of therapy, long-term interferon administration might be required, raising an issue of tolerance in patients. Treatment with IFN-λ is a potential alternative approach to IFN-α; treatment of hepatitis C with this cytokine seems to cause fewer adverse effects than IFN-α and, therefore, might be more suitable for long-term treatment of HDV.
    Nature Reviews Gastroenterology &#38 Hepatology 09/2013; · 10.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Hepatitis delta virus (HDV) is an RNA virus and eight clades of HDV have been identified. HDV clade 3 (HDV-3) is isolated only in the northern area of South America. The outcome of HDV-3 infection is associated with severe fulminant hepatitis. Variations in the large delta antigen (LDAg) between HDV clade 1 (HDV-1) and HDV-3 have been proposed to contribute to differences in viral secretion efficiency, but which changes might be relevant remains unclear. The control of subcellular localization of LDAg has been reported to be associated with post-translational modifications, such as phosphorylation and isoprenylation. We have observed evidence for acetylation on the LDAg of HDV-3 (LDAg-3) and LDAg of HDV-1 (LDAg-1). Green fluorescent protein-fused LDAg-3 (GFP-LD3) was used to investigate the cellular distribution and secretion of the protein. Sequence alignment of LDAg amino acids suggested that lysine-71 of LDAg-3 could be an acetylation site. Expression of a mutant form of LDAg-3 with an arginine-substitution at lysine-71 (GFP-LD3K71R) showed a distribution of the protein predominantly in the cytoplasm instead of the nucleus. Western blot analyses of secreted empty viral particles (EVPs) revealed a higher amount of secreted GFP-LD3K71R compared to GFP-LD3. Furthermore, the ectopic expression of p300, a histone acetyltransferase, led to a reduction of GFP-LD3 in EVPs. By contrast, expression of three histone deacetylases (HDAC-4, -5, and -6) facilitated the secretion of GFP-LD3. Combined, our observations support the hypothesis that the acetylation status of LDAg-3 plays a role in regulating LDAg-3's localization inside the nucleus or cytoplasm, and its secretion.
    Virus Research 09/2012; · 2.83 Impact Factor