A Novel Chromosome Region Maintenance 1-independent Nuclear Export Signal of the Large Form of Hepatitis Delta Antigen That Is Required for the Viral Assembly

Lee, Chia-Huei; Chang, Shih‐Chieh; Wu, Chin-Chin; Chang, Shan‐Chwen

doi:10.1074/jbc.m004477200

Cited by 79 publications

(104 citation statements)

References 42 publications

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“…On the other hand, neither BFA nor wortmannin affected the assembly of small HBsAg. According to the findings from the current study and our previous studies (24,47), we propose that small HBsAg may form 22-nm subviral particles at post-ER, pre-Golgi (intermediate) membranes and/or proximal Golgi membranes, but not TGN, and secrete from cells. On the other hand, HDAg-L forms complexes with HDAg-S and viral genomic RNA (vRNPs) in the nucleus.…”

Section: Discussionmentioning

confidence: 93%

“…Nevertheless, in the presence of small HBsAg, HDAg-L localizes to both the nucleus and the cytoplasm. A nuclear export signal (NES) at the unique C terminus of HDAg-L was identified (24). Recently, we also identified a cellular protein, NESI, which specifically interacts with the NES of HDAg-L and is essential for HDAg-L-mediated nuclear export of HDV RNA (47).…”

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confidence: 97%

“…To determine the package activities of HDAg-L and HBsAg, HDV-and HBV-like particles were collected from culture media 4 days posttransfection, and the procedures were followed as described previously (24).…”

Section: Plasmidsmentioning

confidence: 99%

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Large Hepatitis Delta Antigen Is a Novel Clathrin Adaptor-Like Protein

Huang

Chang

et al. 2007

J Virol

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Clathrin-mediated endocytosis is a common pathway for viral entry, but little is known about the direct association of viral protein with clathrin in the cytoplasm. In this study, a putative clathrin box known to be conserved in clathrin adaptors was identified at the C terminus of the large hepatitis delta antigen (HDAg-L). Similar to clathrin adaptors, HDAg-L directly interacted with the N terminus of the clathrin heavy chain through the clathrin box. HDAg-L is a nucleocytoplasmic shuttle protein important for the assembly of hepatitis delta virus (HDV). Here, we demonstrated that brefeldin A and wortmannin, inhibitors of clathrinmediated exocytosis and endosomal trafficking, respectively, specifically blocked HDV assembly but had no effect on the assembly of the small surface antigen of hepatitis B virus. In addition, cytoplasm-localized HDAg-L inhibited the clathrin-mediated endocytosis of transferrin and the degradation of epidermal growth factor receptor. These results indicate that HDAg-L is a new clathrin adaptor-like protein, and it may be involved in the maturation and pathogenesis of HDV coinfection or superinfection with hepatitis B virus through interaction with clathrin.Hepatitis delta virus (HDV) causes fulminant hepatitis and progressive chronic liver cirrhosis in patients superinfected or coinfected with hepatitis B virus (HBV) (1, 38). HDV particles are enveloped by the HBV surface antigen (HBsAg) (22), but replication of the viral genome is independent of the helper HBV (21). The HDV genome is a single-stranded circular RNA molecule of approximately 1.7 kilobases that encodes the only known HDV protein, hepatitis delta antigen (HDAg). Two forms of HDAg, small HDAg (HDAg-S) and large HDAg (HDAg-L), which contain 195 (24 kDa) and 214 (27 kDa) amino acid residues, respectively, were detected in the livers and sera of HDV-infected patients (5, 49). The HDAgs are translated from the same initiation codon of a single open reading frame (25) and share identical functional domains except for an additional 19-amino-acid motif at the C terminus of the HDAg-L resulting from RNA editing (33,34).HDAg-S is essential for the replication of HDV RNA (21), whereas HDAg-L is required for HDV assembly in a later stage of viral multiplication (4,8). The unique C-terminal domain of HDAg-L bears an isoprenylation motif (211-CRPQ-214). Isoprenylation and proline-rich motifs at the unique C terminus are important for the interaction of HDAg-L with HBsAg and the assembly of HDV (8,9,17,20). Both HDAg-S and HDAg-L possess nuclear localization signals (NLSs) spanning amino acid residues 35 to 88 and are mainly localized to the nucleus in the absence of HBsAg (6, 7). Nevertheless, in the presence of small HBsAg, HDAg-L localizes to both the nucleus and the cytoplasm. A nuclear export signal (NES) at the unique C terminus of HDAg-L was identified (24). Recently, we also identified a cellular protein, NESI, which specifically interacts with the NES of HDAg-L and is essential for HDAg-L-mediated nuclear export of HDV RNA (47...

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Section: Discussionmentioning

confidence: 93%

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confidence: 97%

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Large Hepatitis Delta Antigen Is a Novel Clathrin Adaptor-Like Protein

Huang

Chang

et al. 2007

J Virol

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“…The nuclear export of genomic HDV RNA may be related to the virion assembly process and may not be part of HDV RNA replication per se. If this is so, it might be expected that its export would be dependent on the presence of LHDAg, as suggested by a recent study (11). To address this question, we constructed a mutant HDV genome similar to that described in an earlier study (2), in which a uridine nucleotide was inserted immediately after the UAG stop codon for S-HDAg.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, since HBsAg is present only in the cytoplasm and HDV RNA replication occurs in the nucleus, the nuclear export of genomic HDV RNA at certain points of the viral replication cycle must also be required. It has been suggested that this is dependent on L-HDAg, which contains a nuclear export signal near the COOH terminus (11). However, the role of this signal in RNA packaging has yet to be demonstrated.…”

Section: Discussionmentioning

confidence: 99%

Genomic but Not Antigenomic Hepatitis Delta Virus RNA Is Preferentially Exported from the Nucleus Immediately after Synthesis and Processing

Macnaughton¹,

Lai

2002

J Virol

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Hepatitis delta virus (HDV) contains a viroid-like circular RNA that replicates via a double rolling circle replication mechanism. It is generally assumed that HDV RNA is synthesized and remains exclusively in the nucleus until being exported to the cytoplasm for virion assembly. Using a [ 32 P]orthophosphate metabolic labeling procedure to study HDV RNA replication (T. B. Macnaughton, S. T. Shi, L. E. Modahl, and M. M. C. Lai. J. Virol. 76:3920-3927, 2002), we unexpectedly found that a significant amount of newly synthesized HDV RNA was detected in the cytoplasm. Surprisingly, Northern blot analysis revealed that the genomic-sense HDV RNA is present almost equally in both the nucleus and cytoplasm, whereas antigenomic HDV RNA was mostly retained in the nucleus, suggesting the specific and highly selective export of genomic HDV RNA. Kinetic studies showed that genomic HDV RNA was exported soon after synthesis. However, only the monomer and, to a lesser extent, the dimer HDV RNAs were exported to the cytoplasm; very little higher-molecular-weight HDV RNA species were detected in the cytoplasm. These results suggest that the cleavage and processing of HDV RNA may facilitate RNA export. The export of genomic HDV RNA was resistant to leptomycin B, indicating that a cell region maintenance 1 (Crm1)-independent pathway was involved. The large form of hepatitis delta antigen (L-HDAg), which is responsible for virus packaging, was not required for RNA export, as a mutant HDV RNA genome unable to synthesize L-HDAg was still exported. The proportions of genomic HDV RNA in the nucleus and cytoplasm remained relatively constant throughout replication, indicating that export of genomic HDV RNA occurred continuously. In contrast, while antigenomic HDV RNA was predominately in the nucleus, there was a proportionally large fraction of antigenomic HDV RNA in the cytoplasm at early time points of RNA replication. These findings uncover a previously unrecognized presence of HDV RNA in the cytoplasm, which may have implications for viral RNA synthesis and packaging.

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Structure and Molecular Virology

Negro

2013

Viral Hepatitis

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A Novel Chromosome Region Maintenance 1-independent Nuclear Export Signal of the Large Form of Hepatitis Delta Antigen That Is Required for the Viral Assembly

Abstract: Hepatitis delta virus (HDV) is a satellite virus of hepatitis B virus, as it requires hepatitis B virus for virion Hepatitis delta virus (HDV)

Cited by 79 publications

References 42 publications

Large Hepatitis Delta Antigen Is a Novel Clathrin Adaptor-Like Protein

Large Hepatitis Delta Antigen Is a Novel Clathrin Adaptor-Like Protein

Genomic but Not Antigenomic Hepatitis Delta Virus RNA Is Preferentially Exported from the Nucleus Immediately after Synthesis and Processing

Structure and Molecular Virology

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