title: Nucleophosmin/B23 is a candidate substrate for the BRCA1-BARD1 ubiquitin ligase.
abstract: The breast and ovarian tumor suppressor BRCA1 forms a heterodimeric RING-type ubiquitin ligase with BARD1 to catalyze untraditional Lys-6-linked polyubiquitin chains. It is not clear how the BRCA1-BARD1 ligase regulates various cellular processes such as DNA repair, cell-cycle progression, transcriptional regulation, and centrosome duplication. Here we report that BRCA1-BARD1 catalyzes the polyubiquitination of nucleolar phosphoprotein nucleophosmin/B23 (NPM). Two different mass spectrometry screens for protein ubiquitinated by BRCA1-BARD1 both identified NPM. NPM interacts with N-terminal fragments of BRCA1 and BARD1 in a manner dependent upon BRCA1-BARD1 heterodimer formation. NPM colocalizes with BRCA1 and BARD1 in mitotic cells suggesting the possibility of NPM regulation by BRCA1-BARD1 during mitosis. BRCA1-BARD1 catalyzes the ubiquitination of NPM in vitro and in vivo, and BRCA1-BARD1 co-expression in cells causes NPM stabilization rather than degradation. This is consistent with the notion that this ligase catalyzes untraditional polyubiquitin chains. Given the many overlapped functions between NPM and BRCA1, we propose that NPM is a strong candidate as a substrate of the BRCA1-BARD1 ubiquitin ligase.
authors.affiliation: Division of Breast and Endocrine Surgery, St. Marianna University School of Medicine, Kawasaki 216-8511, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Sato
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Hayami
authors.forename: Wenwen
authors.initials: W
authors.lastname: Wu
authors.forename: Toru
authors.initials: T
authors.lastname: Nishikawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nishikawa
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Okuda
authors.forename: Haruki
authors.initials: H
authors.lastname: Ogata
authors.forename: Mamoru
authors.initials: M
authors.lastname: Fukuda
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ohta
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex / Q000378:metabolism; D019556:COS Cells; D002460:Cell Line; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008938:Mitosis; D009687:Nuclear Proteins / Q000276:immunology / Q000378:metabolism*; D000090243:Nucleophosmin; D025821:Polyubiquitin / Q000378:metabolism; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism; D013379:Substrate Specificity; D041701:Swiss 3T3 Cells; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000276:immunology / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000276:immunology / Q000378:metabolism*
chemical_list: D000936:Antigen-Antibody Complex; C000716967:NPM1 protein, human; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D000090243:Nucleophosmin; D025821:Polyubiquitin; C102449:BARD1 protein, human; C491163:Bard1 protein, mouse; D044767:Ubiquitin-Protein Ligases