Human Molecular Genetics Advance Access originally published online on June 15, 2006
Human Molecular Genetics 2006 15(14):2239-2249; doi:10.1093/hmg/ddl149
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Nucleolar localization of aprataxin is dependent on interaction with nucleolin and on active ribosomal DNA transcription
1 Queensland Institute of Medical Research, Radiation Biology and Oncology Laboratory, Brisbane, Queensland 4029, Australia, 2 Département Intégrité du Génôme de l'UMR 7175, CNRS, Ecole Supérieure de Biotechnologie de Strasbourg, Boulevard Sébastien Brant, BP 10413, F-67412 Illkirch Cedex, France, 3 Gesellschaft für Schwerionenforschung mBH, Planckstr. 1, 64291 Darmstadt, Germany and 4 Central Clinical Division, University of Queensland, Brisbane, Australia
* To whom correspondence should be addressed. Tel: +61 7 3362 0335; Fax: +61 7 3362 0106; Email: martinL{at}qimr.edu.au
Received March 22, 2006; Accepted June 3, 2006
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.
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