Chronic infection with Hepatitis B virus (HBV) is a major cause of liver disease and cancer, resulting in a million deaths yearly. Removing HBV from the liver would reduce disease and oncogenesis, but current therapies with interferon alpha or lamivudine do not provide long-term benefits to the majority of patients. As there are nearly 400 million chronically infected individuals, there is an urgent need to develop antiviral therapies. HBV is a DNA virus that replicates by reverse transcription catalyzed by a virally encoded polymerase. The polymerase is presumed to be made in trace quantities and to be localized exclusively within viral particles. We recently discovered that a large majority of the polymerase from the duck hepatitis B virus (DHBV) accumulates in the cytoplasm, outside of viral particles. This non-encapsidated polymerase is tightly bound to a cellular structure(s) in at least two complexes. This is a highly unexpected result, and it indicates that the polymerase may have function(s) that are completely unrelated to its role in replicating the viral genome.
Two aims will be performed to validate non- encapsidated HBV polymerase as a target for anti-viral intervention or diagnosis.
Aim 1, Confirm that HBV produces a non-encapsidated form of its polymerase. Antibodies to the HBV polymerase are prevalent in patients, and there are hints that the polymerase may be detectable in human hepatocytes. This provides strong preliminary evidence for the existence of non-encapsidated HBV polymerase. We will detect and characterize non-encapsidated HBV polymerase by immunoprecipitation, immunofluorescence, and immunohistochemistry. Detection of non-encapsidated HBV polymerase will allow us to extend mechanistic studies with DHBV to the medically relevant virus, HBV.
Aim 2. Assess the effects of non-encapsidated HBV polymerase on interferon alpha responses. Chronic HBV infection is associated with hyporesponsiveness to interferon alpha, and this hyporesponsiveness is believed to contribute to persistence of HBV. The HBV polymerase has been implicated in inhibiting induction of at least one interferon-responsive gene. Therefore we will test the hypothesis that the non-encapsidated polymerase down-regulates responses to interferon alpha. We will introduce the HBV polymerase into cells and determine if the polymerase inhibits interferon alpha-mediated signaling and responses.
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| Yao, Ermei; Tavis, John E (2003) Kinetics of synthesis and turnover of the duck hepatitis B virus reverse transcriptase. J Biol Chem 278:1201-5 |
