title: Modulation of retinoid signaling by a cytoplasmic viral protein via sequestration of Sp110b, a potent transcriptional corepressor of retinoic acid receptor, from the nucleus.
abstract: Hepatitis C virus (HCV) core protein (core) plays a significant role in the development of chronic liver diseases caused by HCV infection. We have discovered that the core sensitized all-trans-retinoic acid (ATRA)-induced cell death in MCF-7 cells. Activation of retinoic acid receptor alpha (RARalpha)-mediated transcription by the core was also seen in all the cell lines tested. By use of a yeast two-hybrid system, we identified Sp110b as a candidate for a core-interacting cellular factor. Although the function of Sp110b has remained unknown, we observed that Sp110b interacts with RARalpha and suppresses RARalpha-mediated transcription. These data suggest that Sp110b is a transcriptional cofactor negatively regulating RARalpha-mediated transcription. RNA interference-mediated reduction of endogenous Sp110b levels depressed the ability of the core to activate RARalpha-mediated transcription, suggesting an essential role for Sp110b in this pathway. The normal nuclear subcellular localization of Sp110b was altered by molecular interaction with the core to the cytoplasmic surface of the endoplasmic reticulum. This evidence suggests a model in which the core sequesters Sp110b from the nucleus and inactivates its corepressor function to activate RARalpha-mediated transcription. These findings likely describe a novel system in which a cytoplasmic viral protein regulates host cell transcription.
authors.affiliation: Laboratory of Human Tumor Viruses, Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Watashi
authors.forename: Makoto
authors.initials: M
authors.lastname: Hijikata
authors.forename: Ayako
authors.initials: A
authors.lastname: Tagawa
authors.forename: Takahiro
authors.initials: T
authors.lastname: Doi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Marusawa
authors.forename: Kunitada
authors.initials: K
authors.lastname: Shimotohno
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005786:Gene Expression Regulation; D016174:Hepacivirus / Q000378:metabolism; D006801:Humans; D015778:Minor Histocompatibility Antigens; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D015398:Signal Transduction / Q000502:physiology*; D014018:Tissue Distribution; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D014758:Viral Core Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D015778:Minor Histocompatibility Antigens; D009687:Nuclear Proteins; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; C412425:Sp110 protein, human; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; D014212:Tretinoin