title: Does Tyrosyl DNA Phosphodiesterase-2 Play a Role in Hepatitis B Virus Genome Repair?
abstract: Hepatitis B virus (HBV) replication and persistence are sustained by a nuclear episome, the covalently closed circular (CCC) DNA, which serves as the transcriptional template for all viral RNAs. CCC DNA is converted from a relaxed circular (RC) DNA in the virion early during infection as well as from RC DNA in intracellular progeny nucleocapsids via an intracellular amplification pathway. Current antiviral therapies suppress viral replication but cannot eliminate CCC DNA. Thus, persistence of CCC DNA remains an obstacle toward curing chronic HBV infection. Unfortunately, very little is known about how CCC DNA is formed. CCC DNA formation requires removal of the virally encoded reverse transcriptase (RT) protein from the 5' end of the minus strand of RC DNA. Tyrosyl DNA phosphodiesterase-2 (Tdp2) was recently identified as the enzyme responsible for cleavage of tyrosyl-5' DNA linkages formed between topoisomerase II and cellular DNA. Because the RT-DNA linkage is also a 5' DNA-phosphotyrosyl bond, it has been hypothesized that Tdp2 might be one of several elusive host factors required for CCC DNA formation. Therefore, we examined the role of Tdp2 in RC DNA deproteination and CCC DNA formation. We demonstrated Tdp2 can cleave the tyrosyl-minus strand DNA linkage using authentic HBV RC DNA isolated from nucleocapsids and using RT covalently linked to short minus strand DNA produced in vitro. On the other hand, our results showed that Tdp2 gene knockout did not block CCC DNA formation during HBV infection of permissive human hepatoma cells and did not prevent intracellular amplification of duck hepatitis B virus CCC DNA. These results indicate that although Tdp2 can remove the RT covalently linked to the 5' end of the HBV minus strand DNA in vitro, this protein might not be required for CCC DNA formation in vivo.
authors.affiliation: Department of Microbiology and Immunology, Hershey, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States of America.
authors.forename: Xiuji
authors.initials: X
authors.lastname: Cui
authors.affiliation: Department of Microbiology and Immunology, Hershey, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States of America.
authors.forename: Rebecca
authors.initials: R
authors.lastname: McAllister
authors.affiliation: Department of Microbiology and Immunology, Hershey, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States of America.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Boregowda
authors.affiliation: Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Ji A
authors.initials: JA
authors.lastname: Sohn
authors.affiliation: Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER)-CSIC, Av. Américo Vespucio s/n, 41092 Sevilla, Spain.
authors.forename: Felipe
authors.initials: F
authors.lastname: Cortes Ledesma
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, Science Park Road, Falmer, Brighton, Sussex BN1 9RQ, United Kingdom.
authors.forename: Keith W
authors.initials: KW
authors.lastname: Caldecott
authors.affiliation: Fox Chase Cancer Center, Philadelphia, Pennsylvania, United States of America.
authors.forename: Christoph
authors.initials: C
authors.lastname: Seeger
authors.affiliation: Department of Microbiology and Immunology, Hershey, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States of America.
authors.forename: Jianming
authors.initials: J
authors.lastname: Hu
mesh_terms: D004270:DNA, Circular / Q000235:genetics / Q000378:metabolism*; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D055785:Gene Knockdown Techniques; D055786:Gene Knockout Techniques; D016679:Genome, Viral; D056945:Hep G2 Cells; D006509:Hepatitis B / Q000235:genetics / Q000378:metabolism*; D015611:Hepatitis B Virus, Duck / Q000235:genetics / Q000502:physiology; D006515:Hepatitis B virus / Q000235:genetics / Q000502:physiology*; D004371:Hepatitis Virus, Duck / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases; D012194:RNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication
chemical_list: D004270:DNA, Circular; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D012194:RNA-Directed DNA Polymerase; D010727:Phosphoric Diester Hydrolases; C474866:TDP2 protein, human