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Part I: Dynamics of Histone Exchange and Epigenetic Modifications during Transcription in vivo Part II: Hijacking of the DDB1 Ubiquitin Ligase by the HBV X Protein: What Role during Infection and Associated Liver Cancer?

English title Part I: Dynamics of Histone Exchange and Epigenetic Modifications during Transcription in vivo Part II: Hijacking of the DDB1 Ubiquitin Ligase by the HBV X Protein: What Role during Infection and Associated Liver Cancer?
Applicant Strubin Michel
Number 127384
Funding scheme Project funding (Div. I-III)
Research institution Dépt Microbiologie et Médecine Moléculaire Faculté de Médecine Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Molecular Biology
Start/End 01.10.2009 - 30.09.2013
Approved amount 415'000.00
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Keywords (1)

HBx protein

Lay Summary (English)

Lead
Lay summary
Research in our laboratory focuses on two main objectives: 1. We are using the yeast Saccharomyces cerevisiae as a model system to address fundamental questions about the mechanisms by which genes are transcribed in a controlled fashion. We are particularly interested in understanding how the basal transcription machinery, a large complex that contains many proteins in addition to the RNA polymerase, assembles at the promoter of genes and how this event is regulated. More recently, we initiated a new study on the dynamics and epigenetic modifications of chromatin associated with transcription. The basic building block of chromatin is the nucleosome, which consists of DNA wrapped around an octamer of the four histone proteins H2A, H2B, H3 and H4. We found that nucleosomes are surprisingly dynamic structures in vivo, with histones H2A and H2B exchanging continuously at both transcriptionally active and inactive genes. By contrast, histones H3 and H4 only exchange in the promoter regions of active genes. We further obtained evidence that an active mechanism prevents histones H3 and H4 from exchanging throughout the body of transcribed genes. These findings raise fundamental questions about the role of these events in regulated gene transcription and associated epigenetic events. 2. We aim at understanding the role of the HBx protein of hepatitis B virus (HBV) during infection and in the pathogenesis of liver cancer. Chronic HBV infection affects over 350 million people worldwide and is a leading cause of hepatocellular carcinoma, one of the most common human cancers. HBV encodes a small regulatory protein, known as HBx, which is essential for viral infection and has been implicated in HBV-mediated liver oncogenesis. The basis for HBx function in either process remains elusive and is the focus of our studies. We obtained structural, biochemical and genetic evidence that HBx stimulates HBV gene expression and causes chromosomal instability by binding to DDB1, an essential subunit of a cellular E3 ubiquitin ligase complex. Our results strongly suggest that HBx functions by hijacking the DDB1 E3 ligase to target cellular proteins for ubiquitination and, perhaps, subsequent degradation. We now aim to identify the substrate(s) of HBx and further explore the molecular mechanism whereby HBx stimulates HBV gene expression through its association with the E3 ligase. Given the likely fundamental importance of the interaction of HBx and the DDB1 E3 ligase for natural HBV infection and associated liver cancer, this virus-host protein interaction may represent a promising new target for therapeutic intervention.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Hepatitis B virus X protein stimulates gene expression selectively from extrachromosomal DNA templates.
van Breugel Pieter C, Robert Eva I, Mueller Henrik, Decorsière Adrien, Zoulim Fabien, Hantz Olivier, Strubin Michel (2012), Hepatitis B virus X protein stimulates gene expression selectively from extrachromosomal DNA templates., in Hepatology (Baltimore, Md.), 56(6), 2116-24.
Hepatitis B virus X protein is essential to initiate and maintain virus replication after infection.
Lucifora Julie, Arzberger Silke, Durantel David, Belloni Laura, Strubin Michel, Levrero Massimo, Zoulim Fabien, Hantz Olivier, Protzer Ulrike (2011), Hepatitis B virus X protein is essential to initiate and maintain virus replication after infection., in Journal of hepatology, 55(5), 996-1003.
A promiscuous alpha-helical motif anchors viral hijackers and substrate receptors to the CUL4-DDB1 ubiquitin ligase machinery
Li Ti, Robert Eva Isabelle, van Breugel Pieter Cornelis, Strubin Michel, Zheng Ning (2010), A promiscuous alpha-helical motif anchors viral hijackers and substrate receptors to the CUL4-DDB1 ubiquitin ligase machinery, in Nat Struct Mol Biol, 17(1), 105-111.

Collaboration

Group / person Country
Types of collaboration
Ning Zheng (Seattle) United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Olivier Hantz et Fabien Zoulim (INSERM 1052 - UMR CNRS 5286, Lyon) France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events



Self-organised

Title Date Place
SKMB Gene Regulation workshop 03.09.2010 Lausanne, Switzerland

Communication with the public

Communication Title Media Place Year
Other activities Accueil de classes de collégiens Western Switzerland 2010
Media relations: print media, online media Deux virus étrangers s’attaquent à la même cible Tribune de Genève Western Switzerland 2009

Associated projects

Number Title Start Funding scheme
112496 The hepatitis B virus encoded HBx protein and its interaction with host cell protein DDB1: Implications for viral infection and the pathogenesis of liver cancer 01.09.2006 Project funding (Div. I-III)
149626 Role of hepatitis B virus X protein during viral infection and associated liver cancer 01.10.2013 Project funding (Div. I-III)
112496 The hepatitis B virus encoded HBx protein and its interaction with host cell protein DDB1: Implications for viral infection and the pathogenesis of liver cancer 01.09.2006 Project funding (Div. I-III)
149626 Role of hepatitis B virus X protein during viral infection and associated liver cancer 01.10.2013 Project funding (Div. I-III)

Abstract

SUMMARYResearch in our laboratory focuses on two main objectives: 1. We combine the genetic and molecular approaches uniquely available in the yeast Saccharomyces cerevisiae to address fundamental questions about the mechanisms by which eukaryotic activator proteins control gene expression. Recently, we initiated a new project concerning the dynamic exchange of histones within chromatin and its role in transcription regulation and associated epigenetic modifications. The basic building block of chromatin is the nucleosome, which consists of DNA wrapped around an octamer of the four histone proteins H2A, H2B, H3 and H4. We found that while histones H2A and H2B are continuously exchanging genome-wide outside of S phase, histones H3 and H4 only exchange in the promoter regions of active loci. Furthermore, we obtained evidence that an active mechanism prevents histones H3 and H4 from exchanging throughout the body of transcribed genes. These findings raise fundamental questions about the role of these events in regulated gene transcription and associated epigenetic events. Firstly, is the exchange of histones at promoters a cause or a consequence of transcription? Secondly, are some of the histone post-translational modifications typically seen at active promoters required for, or are they a result of, histones exchanging within these regions? Thirdly, what role do the histone chaperones that have been implicated in diverse nucleosome transactions play in this process? The experiments outlined in Part I of the present proposal are meant to provide some answers to these questions.2. We aim at understanding the role of the hepatitis B virus-encoded HBx protein and its interaction with host cell proteins during infection and in the pathogenesis of liver cancer. Chronic infection by hepatitis B virus (HBV) affects more than 350 million people worldwide and is leading cause of hepatocellular carcinoma, one of the most common human cancers. HBV encodes a small regulatory protein, known as HBx, which is essential for viral infection and has been implicated in HBV-mediated liver oncogenesis. The basis for HBx function in either process remains elusive and is the focus of our studies. We obtained structural, biochemical and genetic evidence that HBx stimulates HBV gene expression and causes chromosomal instability in cultured cells by binding to host cell protein DDB1, an essential subunit of an E3 ubiquitin ligase complex implicated in the regulation of diverse cellular functions. Our current results are consistent with HBx exerting its activities by subverting the normal function of the DDB1 E3 ligase complex to target cellular proteins for ubiquitination and, perhaps, subsequent degradation. We now aim to identify the cellular substrate(s) of HBx and further explore the molecular mechanism whereby HBx stimulates HBV gene expression through its association with the E3 ligase. We also wish to investigate the relevance of HBx binding to DDB1 under experimental conditions closer to natural HBV infection. Given the likely fundamental importance of the interaction of HBx and the DDB1 E3 ligase for natural HBV infection and associated liver cancer, this virus-host protein interaction may represent a promising new target for therapeutic intervention.
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