title: Nucleolar localization of aprataxin is dependent on interaction with nucleolin and on active ribosomal DNA transcription.
abstract: The APTX gene, mutated in patients with the neurological disorder ataxia with oculomotor apraxia type 1 (AOA1), encodes a novel protein aprataxin. We describe here, the interaction and interdependence between aprataxin and several nucleolar proteins, including nucleolin, nucleophosmin and upstream binding factor-1 (UBF-1), involved in ribosomal RNA (rRNA) synthesis and cellular stress signalling. Interaction between aprataxin and nucleolin occurred through their respective N-terminal regions. In AOA1 cells lacking aprataxin, the stability of nucleolin was significantly reduced. On the other hand, down-regulation of nucleolin by RNA interference did not affect aprataxin protein levels but abolished its nucleolar localization suggesting that the interaction with nucleolin is involved in its nucleolar targeting. GFP-aprataxin fusion protein co-localized with nucleolin, nucleophosmin and UBF-1 in nucleoli and inhibition of ribosomal DNA transcription altered the distribution of aprataxin in the nucleolus, suggesting that the nature of the nucleolar localization of aprataxin is also dependent on ongoing rRNA synthesis. In vivo rRNA synthesis analysis showed only a minor decrease in AOA1 cells when compared with controls cells. These results demonstrate a cross-dependence between aprataxin and nucleolin in the nucleolus and while aprataxin does not appear to be directly involved in rRNA synthesis its nucleolar localization is dependent on this synthesis.
authors.affiliation: Radiation Biology and Oncology Laboratory, Queensland Institute of Medical Research, Brisbane, Queensland 4029, Australia.
authors.forename: Olivier J
authors.initials: OJ
authors.lastname: Becherel
authors.forename: Nuri
authors.initials: N
authors.lastname: Gueven
authors.forename: Geoff W
authors.initials: GW
authors.lastname: Birrell
authors.forename: Valérie
authors.initials: V
authors.lastname: Schreiber
authors.forename: Amila
authors.initials: A
authors.lastname: Suraweera
authors.forename: Burkhard
authors.initials: B
authors.lastname: Jakob
authors.forename: Gisela
authors.initials: G
authors.lastname: Taucher-Scholz
authors.forename: Martin F
authors.initials: MF
authors.lastname: Lavin
mesh_terms: D000595:Amino Acid Sequence; D001072:Apraxias / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism*; D002524:Cerebellar Ataxia / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000090243:Nucleophosmin; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D035463:Pol1 Transcription Initiation Complex Proteins / Q000378:metabolism; D011485:Protein Binding; D034622:RNA Interference; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D000097796:Nucleolin
chemical_list: D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D010750:Phosphoproteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D000097796:Nucleolin; C438188:APTX protein, human; C000716967:NPM1 protein, human; C063844:transcription factor UBF