title: Stimulation of hepatitis B virus genome replication by HBx is linked to both nuclear and cytoplasmic HBx expression.
abstract: HBx, a small regulatory protein of hepatitis B virus, plays an important role in stimulating viral genome replication. HBx was shown to be associated with diverse subcellular locations, such as the nucleus, cytoplasm and mitochondria. Some studies have linked the stimulation of genome replication by HBx to its cytoplasmic function, while other reports have attributed this function to its nuclear component. To clarify this discrepancy, we measured viral genome replication by complementing an HBx-null replicon in two different ways: by (i) co-transfecting with an increasing amount of HBx expression plasmid and (ii) co-transfecting with re-targeted variants of HBx that are confined to either the nucleus or the cytoplasm due to either the nuclear localization signal (NLS) or the nuclear export signal (NES) tags, respectively. Intriguingly, immunostaining analysis indicated that the subcellular localization of HBx is primarily influenced by its abundance; HBx is confined to the nucleus at low levels but is usually detected in the cytoplasm at high levels. Importantly, HBx, whether re-targeted by either the NLS or NES tag, stimulates viral genome replication to a level comparable to that of the wild-type. Furthermore, similar to the wild-type, the stimulation of viral genome replication by the re-targeted HBx occurred at the transcription level. Thus, we concluded that the stimulation of viral genome replication by HBx is linked to both nuclear and cytoplasmic HBx, although the underlying mechanism of stimulation most likely differs.
authors.affiliation: Department of Biochemistry, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Man-Young
authors.initials: MY
authors.lastname: Cha
authors.affiliation: Department of Biochemistry, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Dong-Kyun
authors.initials: DK
authors.lastname: Ryu
authors.affiliation: Department of Biochemistry, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Hyeon-Sik
authors.initials: HS
authors.lastname: Jung
authors.affiliation: Department of Biochemistry, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Ho-Eun
authors.initials: HE
authors.lastname: Chang
authors.affiliation: Department of Biochemistry, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Wang-Shick
authors.initials: WS
authors.lastname: Ryu
mesh_terms: D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004261:DNA Replication; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D012367:RNA, Viral / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D012367:RNA, Viral; D015534:Trans-Activators; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein