The role of host DNA ligases in hepadnavirus covalently closed circular DNA formation

• DOI: 10.1371/journal.ppat.1006784
• Publication Date: 2017-12-29T18:37:18Z
• Authors: Quanxin Long; Ran Yan; Jieli Hu; Dawei Cai; Bidisha Mitra; Elena S. Kim; Alexander Marchetti; Hu Zhang; Soujuan Wang; Yuanjie Liu; Ailong Huang; Haitao Guo
• Keywords: Strand ligation; Viral transcription template; 570; Hepatitis B virus; DNA Ligases; DNA Repair; QH301-705.5; DNA repair; 612; DNA replication; Biosynthesis; Hepadnaviridae; Genomic relaxed circular DNA; Cell Line; DNA Ligase ATP; Gene Knockout Techniques; 03 medical and health sciences; Humans; DNA ligases; Biology (General); Poly-ADP-Ribose Binding Proteins; 0303 health sciences; Hep G2 Cells; RC581-607; 3. Good health; Hepadnavirus; HEK293 Cells; Viral infection; Gene Knockdown Techniques; DNA, Viral; Host-Pathogen Interactions; Hepatocytes; Immunologic diseases. Allergy; DNA, Circular; Metabolic Networks and Pathways; Research Article

Hepadnavirus covalently closed circular (ccc) DNA is the bona fide viral transcription template, which plays a pivotal role in viral infection and persistence. Upon infection, the non-replicative cccDNA is converted from the incoming and de novo synthesized viral genomic relaxed circular (rc) DNA, presumably through employment of the host cell's DNA repair mechanisms in the nucleus. The conversion of rcDNA into cccDNA requires preparation of the extremities at the nick/gap regions of rcDNA for strand ligation. After screening 107 cellular DNA repair genes, we herein report that the cellular DNA ligase (LIG) 1 and 3 play a critical role in cccDNA formation. Ligase inhibitors or functional knock down/out of LIG1/3 significantly reduced cccDNA production in an in vitro cccDNA formation assay, and in cccDNA-producing cells without direct effect on viral core DNA replication. In addition, transcomplementation of LIG1/3 in the corresponding knock-out or knock-down cells was able to restore cccDNA formation. Furthermore, LIG4, a component in non-homologous end joining DNA repair apparatus, was found to be responsible for cccDNA formation from the viral double stranded linear (dsl) DNA, but not rcDNA. In conclusion, we demonstrate that hepadnaviruses utilize the whole spectrum of host DNA ligases for cccDNA formation, which sheds light on a coherent molecular pathway of cccDNA biosynthesis, as well as the development of novel antiviral strategies for treatment of hepatitis B.