TY - JOUR
T1 - The Nucleolar Phosphoprotein B23 Interacts with Hepatitis Delta Antigens and Modulates the Hepatitis Delta Virus RNA Replication
AU - Huang, Wen Hung
AU - Yung, Benjamin Y M
AU - Syu, Wan Jr
AU - Wu Lee, Yan-Hwa
PY - 2001/7/6
Y1 - 2001/7/6
N2 - Hepatitis delta virus (HDV) encodes two isoforms of delta antigens (HDAgs). The small form of HDAg is required for HDV RNA replication, while the large form of HDAg inhibits the viral replication and is required for virion assembly. In this study, we found that the expression of B23, a nucleolar phosphoprotein involved in disparate functions including nuclear transport, cellular proliferation, and ribosome biogenesis, is up-regulated by these two HDAgs. Using in vivo and in vitro experimental approaches, we have demonstrated that both isoforms of HDAg can interact with B23 and their interaction domains were identified as the NH2-terminal fragment of each molecule encompassing the nuclear localization signal but not the coiled-coil region of HDAg. Sucrose gradient centrifugation analysis indicated that the majority of small HDAg, but a lesser amount of the large HDAg, co-sedimented with B23 and nucleolin in the large nuclear complex. Transient transfection experiments also indicated that introducing exogenous full-length B23, but not a mutated B23 defective in HDAg binding, enhanced HDV RNA replication. All together, our results reveal that HDAg has two distinct effects on nucleolar B23, up-regulation of its gene expression and the complex formation, which in turn regulates HDV RNA replication. Therefore, this work demonstrates the important role of nucleolar protein in regulating the HDV RNA replication through the complex formation with the key positive regulator being small HDAg.
AB - Hepatitis delta virus (HDV) encodes two isoforms of delta antigens (HDAgs). The small form of HDAg is required for HDV RNA replication, while the large form of HDAg inhibits the viral replication and is required for virion assembly. In this study, we found that the expression of B23, a nucleolar phosphoprotein involved in disparate functions including nuclear transport, cellular proliferation, and ribosome biogenesis, is up-regulated by these two HDAgs. Using in vivo and in vitro experimental approaches, we have demonstrated that both isoforms of HDAg can interact with B23 and their interaction domains were identified as the NH2-terminal fragment of each molecule encompassing the nuclear localization signal but not the coiled-coil region of HDAg. Sucrose gradient centrifugation analysis indicated that the majority of small HDAg, but a lesser amount of the large HDAg, co-sedimented with B23 and nucleolin in the large nuclear complex. Transient transfection experiments also indicated that introducing exogenous full-length B23, but not a mutated B23 defective in HDAg binding, enhanced HDV RNA replication. All together, our results reveal that HDAg has two distinct effects on nucleolar B23, up-regulation of its gene expression and the complex formation, which in turn regulates HDV RNA replication. Therefore, this work demonstrates the important role of nucleolar protein in regulating the HDV RNA replication through the complex formation with the key positive regulator being small HDAg.
UR - http://www.scopus.com/inward/record.url?scp=0035816633&partnerID=8YFLogxK
U2 - 10.1074/jbc.M010087200
DO - 10.1074/jbc.M010087200
M3 - Article
C2 - 11309377
AN - SCOPUS:0035816633
SN - 0021-9258
VL - 276
SP - 25166
EP - 25175
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 27
ER -