Developmental regulation of HBV biosynthesis by FoxA and DNA methylation

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Hepatitis B virus (HBV) infection is a worldwide health problem. It is estimated that there are 200 to 500 million HBV chronic carriers in the world for whom, to date, there is no reliable treatment. HBV causes both acute and chronic liver disease and is responsible for an estimated one million deaths annually. Currently available therapies reduce viral loads but fail to resolve chronic HBV infections. Therefore, effective treatments for chronic HBV infection are urgently required. The major obstacle to the resolution of chronic HBV infections is the eradication or inactivation of nuclear HBV covalently closed circular (CCC) DNA which is the template for viral transcription. To this end, we have developed HNF1α-null HBV transgenic mice and liver-specific FoxA/HNF3-deficient HBV transgenic mice. HNF1α-null HBV transgenic mice synthesize nuclear HBV CCC DNA. Liver-specific FoxA/HNF3-deficient HBV transgenic mice are viable but lack detectable HBV transcription and replication (i.e. they are effectively “cured”) suggesting FoxA/HNF3 not only plays an important developmental role in the hepatocyte-specific transcription factor network governing the hepatic phenotype but is also essential for viral biosynthesis. The observation that FoxA/HNF3-deficient HBV transgenic mice display hyper-methylation of HBV genomic DNA suggests that FoxA/HNF3 is epigenetically governing HBV transcription by modulating viral chromatin structure in vivo and hence determines the level of viral biosynthesis. Defining the precise temporal requirements for FoxA/HNF3 expression associated with HBV transcription and replication will indicate the liver developmental stages when viral biosynthesis is susceptible to inhibition by FoxA/HNF3 deficiency. This will be achieved by modulating FoxA/HNF3 expression in the FoxA/HNF3-deficient HBV transgenic mouse model using the TET/OFF system. Using this system, the developmental control of HBV transcription, viral biosynthesis and HBV DNA methylation by FoxA/HNF3 expression will be established and correlated with the epigenetic histone marks and chromatin structure associated with the HBV genome. Finally, similar studies will be performed using the HNF1α-null FoxA/HNF3-deficient HBV transgenic mouse model of chronic viral infection so the developmental control of HBV transcription, viral biosynthesis, HBV DNA methylation, epigenetic histone marks and chromatin structure by FoxA/HNF3 expression associated with the HBV genome can be compared between the HBV transgene DNA and the nuclear HBV CCC DNA. Defining the nature of the changes and the molecular signals responsible for the loss of HBV biosynthesis due to FoxA/HNF3 deficiency may lead to the identification of cellular therapeutic targets that are amenable to the development of novel modalities to resolve rather than simply treat chronic HBV infection.