Effects of liver growth factors on hepadnavirus replication in chronically infected duck hepatocytes Olivier Schorr, Christelle Borel, Christian Trepo, Fabien Zoulim, Olivier Hantz * INSERM Unit 271, 151 cours Albert Thomas, 69003 Lyon, France Background/Aims: Duck hepatitis B virus (DHBV) replication is up-regulated by cell cycle during the early infection of primary duck but the effect of cell cycle on DHBV replication in chronically infected hepatocyte is not known. Methods: Hepatocytes obtained from DHBV congenitally infected embryos were used. Cell proliferation was controlled by addition of liver growth factors and the impact on viral replication analyzed. Results: EGF induced cell proliferation is associated with a slight increase in CCC DNA synthesis and a decrease in viral transcription. Conversely, TGFb blocked cell cycle progression, diminished CCC DNA synthesis but increased viral transcription. Conclusions: Cell proliferation decreases DHBV transcription but this effect seems to be compensated by an opposite effect on the synthesis of CCC DNA resulting in a global moderate effect on viral replication. Our results also indicate that after division of chronically infected hepatocytes both daughter cells are infected, confirming that liver regeneration is not sufficient to induce CCC DNA eradication as suggested by the lack of effect of some long term anti-HBV therapies. q 2006 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. Keywords: DHBV; Hepatitis; Hepatocyte; Cell cycle 1. Introduction Duck hepatitis B virus (DHBV), an animal model for human hepatitis B virus [1], causes acute or chronic infection of hepatocytes in its host. The hepadnaviral genome is a small, partially double-stranded relaxed circular (RC) DNA molecule that is replicated by reverse transcription of a 3.5 kb terminally redundant mRNA transcript, termed the pre-genome [2]. A cova- lently closed circular (CCC) supercoiled viral DNA molecule is generated initially by the direct conversion of infecting RC virion DNA [3]. This CCC DNA is the template for transcription of viral RNA species, including the pre-genomic RNA, which is packaged into core particles and reverse transcribed. Virus persistence in infected cells during chronic infections depends on the regulation of the pool of transcriptionally active CCC DNA molecules. This control occurs by the recycling of encapsidated viral DNA (core particles) into the nucleus [3]. Cell and/or viral signals that determine whether core particles are either matured as virions that exit the cell or are recycled to the nucleus to maintain the pool of CCC DNA are not fully identified. It has been demonstrated that the DHBV pre-S envelope protein regulates CCC DNA amplification by a negative feedback mechanism [4–6]. The core protein likely plays also a role in regulating CCC DNA levels: nuclear transport of the hepadnavirus core protein [7–10] and/or nucleocapsid disassembly [11–13] may be crucial for entry of the hepadnavirus encapsidated genomic DNA into the nucleus and its conversion to supercoiled DNA. We previously demonstrated that cells proliferation positively regulate CCC DNA amplification that occurs during the early step of DHBV replication after in vitro infection of duck hepatocytes [14,15]. However, it has been demonstrated in transfected hepatoma cell lines and transgenic mice that hepadnaviruses replication occurred Journal of Hepatology 44 (2006) 842–847 www.elsevier.com/locate/jhep 0168-8278/$32.00 q 2006 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jhep.2005.09.014 Received 10 May 2005; received in revised form 28 July 2005; accepted 21 September 2005; available online 2 November 2005 * Corresponding author. Tel.: C33 4 72 68 19 70; fax: C33 4 72 68 19 71. E-mail address: hantz@lyon.inserm.fr (O. Schorr).