title: Nuclear export of human hepatitis B virus core protein and pregenomic RNA depends on the cellular NXF1-p15 machinery.
abstract: Hepatitis B virus (HBV) core protein (HBc) can shuttle between nucleus and cytoplasm. Cytoplasm-predominant HBc is clinically associated with severe liver inflammation. Previously, we found that HBc arginine-rich domain (ARD) can associate with a host factor NXF1 (TAP) by coimmunoprecipitation. It is well known that NXF1-p15 heterodimer can serve as a major export receptor of nuclear mRNA as a ribonucleoprotein complex (RNP). In the NXF1-p15 pathway, TREX (transcription/export) complex plays an important role in coupling nuclear pre-mRNA processing with mRNA export in mammalian cells. Here, we tested the hypothesis whether HBc and HBV specific RNA can be exported via the TREX and NXF1-p15 mediated pathway. We demonstrated here that HBc can physically and specifically associate with TREX components, and the NXF1-p15 export receptor by coimmunoprecipitation. Accumulation of HBc protein in the nucleus can be induced by the interference with TREX and NXF1-p15 mediated RNA export machinery. HBV transcripts encodes a non-spliced 3.5 kb pregenomic RNA (pgRNA) which can serve as a template for reverse transcription. Cytoplasmic HBV pgRNA appeared to be reduced by siRNA treatment specific for the NXF1-p15 complex by quantitative RT-qPCR and Northern blot analyses. This result suggests that the pgRNA was also exported via the NXF1-p15 machinery. We entertain the hypothesis that HBc protein can be exported as an RNP cargo via the mRNA export pathway by hijacking the TREX and NXF1-p15 complex. In our current and previous studies, HBc is not required for pgRNA accumulation in the cytoplasm. Furthermore, HBc ARD can mediate nuclear export of a chimeric protein containing HBc ARD in a pgRNA-independent manner. Taken together, it suggests that while both pgRNA and HBc protein exports are dependent on NXF1-p15, they are using the same export machinery in a manner independent of each other.
authors.affiliation: Taiwan International Graduate Program (TIGP) in Molecular Medicine, National Yang-Ming University and Academia Sinica, Taipei, Taiwan; Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Ching-Chun
authors.initials: CC
authors.lastname: Yang
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Er-Yi
authors.initials: EY
authors.lastname: Huang
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Hung-Cheng
authors.initials: HC
authors.lastname: Li
authors.affiliation: Taiwan International Graduate Program (TIGP) in Molecular Medicine, National Yang-Ming University and Academia Sinica, Taipei, Taiwan; Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Pei-Yi
authors.initials: PY
authors.lastname: Su
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Chiaho
authors.initials: C
authors.lastname: Shih
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus; D003593:Cytoplasm / Q000235:genetics; D004261:DNA Replication; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006801:Humans; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D049790:Nuclear Export Signals; D029543:Nucleocytoplasmic Transport Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012313:RNA; D034443:RNA Transport / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering; D012367:RNA, Viral / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D014758:Viral Core Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; C122111:NXF1 protein, human; D049790:Nuclear Export Signals; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D014758:Viral Core Proteins; D012313:RNA