Inhibition of PP1 Phosphatase Activity by HBx: A Mechanism for the Activation of Hepatitis B Virus Transcription

Oncogenèse et Virologie Moléculaire, Institut Pasteur, 28 Rue du Dr. Roux, 75724 Paris Cedex 15, France.
Science Signaling (Impact Factor: 6.28). 01/2012; 5(205):ra1. DOI: 10.1126/scisignal.2001906
Source: PubMed


The regulatory protein HBx is essential for hepatitis B virus (HBV) replication in vivo and for transcription of the episomal HBV genome. We previously reported that in infected cells HBx activates genes targeted by the transcription factor CREB [cyclic adenosine monophosphate (cAMP) response element-binding protein]. cAMP induces phosphorylation and activation of CREB, and CREB inactivation is promoted by protein phosphatase 1 (PP1), which binds to CREB through histone deacetylase 1 (HDAC1). We showed that CREB was recruited to HBV DNA. Phosphorylation induced by cAMP had a longer half-life when CREB was bound to the episomal HBV genome compared to when it was bound to the promoter of a host target gene not regulated by HBx, suggesting that the virus has developed a mechanism to favor its own transcription. This mechanism required HBx, which interacted with and inhibited PP1 to extend the half-life of CREB phosphorylation. Silencing of PP1 rescued replication of an HBx-deficient HBV genome, suggesting that HBx enhances viral transcription in part by neutralizing PP1 activity. Our results illustrate a previously unknown mechanism of HBV transcriptional activation by HBx in which HBx interferes with the inactivation of CREB by the PP1 and HDAC1 complex.

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    • "HBV particles were concentrated from the clarified supernatant by overnight precipitation with 5% PEG 8000 and centrifugation at 4°C for 60 min at 5000 rpm. Enveloped DNA-containing viral particles were tittered by immunoprecipitation with an anti-PreS1 antibody (kindly provided by C. Sureau) followed by qPCR quantification of viral RC DNA with the primers RC 5' and RC 3' (Supplementary Table 2) [6]. dHepaRG cells or PHH were infected as previously described with normalized amounts of virus at the indicated MOI [11]. "
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    • "Firstly, we could confirm existing data concerning the recruitment, in vivo, of H3/H4 histones and of HBV core protein on the cccDNA minichromosome [34]. Subsequently, using the same approach, we and others showed that several cellular transcription factors, including CREB, ATF, STAT1, and STAT2, and different chromatin modifying enzymes can bind the cccDNA in cells replicating HBV [36, 37]. Indeed, using antiacetylated-H3 or antiacetylated-H4 cccDNA ChIP assay, we found that HBV replication is regulated, both in cell-based replication systems and in the liver of HBV chronically infected patients, by the acetylation status of H3/H4 histones bound to the viral cccDNA in the nuclei of HBV-infected hepatocytes. "
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