title: Structural requirements for the BARD1 tumor suppressor in chromosomal stability and homology-directed DNA repair.
abstract: The BRCA1 tumor suppressor exists as a heterodimeric complex with BARD1, and this complex is thought to mediate many of the functions ascribed to BRCA1, including its role in tumor suppression. The two proteins share a common structural organization that features an N-terminal RING domain and two C-terminal BRCT motifs, whereas BARD1 alone also contains three tandem ankyrin repeats. In normal cells, the BRCA1/BARD1 heterodimer is believed to enhance chromosome stability by promoting homology-directed repair (HDR) of double strand DNA breaks. Here we have investigated the structural requirements for BARD1 in this process by complementation of Bard1-null mouse mammary carcinoma cells. Our results demonstrate that the ankyrin and BRCT motifs of BARD1 are each essential for both chromosome stability and HDR. Tandem BRCT motifs, including those found at the C terminus of BARD1, are known to form a phosphoprotein recognition module. Nonetheless, the HDR function of BARD1 was not perturbed by synthetic mutations predicted to ablate the phospho-recognition activity of its BRCT sequences, suggesting that some functions of the BRCT domains are not dependent on their ability to bind phosphorylated ligands. Also, cancer-associated missense mutations in the BRCT domains of BARD1 (e.g. C557S, Q564H, V695L, and S761N) have been observed in patients with breast, ovarian, and endometrial tumors. However, none of these was found to affect the HDR activity of BARD1, suggesting that any increased cancer risk conferred by these mutations is not because of defects in this repair mechanism.
authors.affiliation: Institute for Cancer Genetics, Department of Pathology and Cell Biology, Columbia University College of Physicians & Surgeons, 1130 St. Nicholas Avenue, New York, NY 10032, USA.
authors.forename: Marsha
authors.initials: M
authors.lastname: Laufer
authors.forename: Subhadra V
authors.initials: SV
authors.lastname: Nandula
authors.forename: Ami P
authors.initials: AP
authors.lastname: Modi
authors.forename: Shuang
authors.initials: S
authors.lastname: Wang
authors.forename: Maria
authors.initials: M
authors.lastname: Jasin
authors.forename: Vundavalli V V S
authors.initials: VV
authors.lastname: Murty
authors.forename: Thomas
authors.initials: T
authors.lastname: Ludwig
authors.forename: Richard
authors.initials: R
authors.lastname: Baer
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D017487:Ankyrins / Q000235:genetics; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D043171:Chromosomal Instability / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000235:genetics; D005260:Female; D005816:Genetic Complementation Test; D006801:Humans; D008297:Male; D015674:Mammary Neoplasms, Animal / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D054829:RING Finger Domains / Q000235:genetics; D012307:Risk Factors; D013329:Structure-Activity Relationship; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D017487:Ankyrins; D019313:BRCA1 Protein; D046912:Multiprotein Complexes; D025521:Tumor Suppressor Proteins; C491163:Bard1 protein, mouse; D044767:Ubiquitin-Protein Ligases