The BRCA1/BARD1 heterodimer modulates Ran-dependent mitotic spindle assembly

Dana-Farber Cancer Institute and Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA.
Cell (Impact Factor: 32.24). 12/2006; 127(3):539-52. DOI: 10.1016/j.cell.2006.08.053
Source: PubMed


The heterodimeric tumor-suppressor complex BRCA1/BARD1 exhibits E3 ubiquitin ligase activity and participates in cell proliferation and chromosome stability control by incompletely defined mechanisms. Here we show that, in both mammalian cells and Xenopus egg extracts, BRCA1/BARD1 is required for mitotic spindle-pole assembly and for accumulation of TPX2, a major spindle organizer and Ran target, on spindle poles. This function is centrosome independent, operates downstream of Ran GTPase, and depends upon BRCA1/BARD1 E3 ubiquitin ligase activity. Xenopus BRCA1/BARD1 forms endogenous complexes with three spindle-pole proteins, TPX2, NuMA, and XRHAMM--a known TPX2 partner--and specifically attenuates XRHAMM function. These observations reveal a previously unrecognized function of BRCA1/BARD1 in mitotic spindle assembly that likely contributes to its role in chromosome stability control and tumor suppression.

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Available from: Vladimir Joukov, Dec 18, 2013
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    • "Addition of linear DNA fragments to Xenopus egg extracts mimics the effects of double strand breaks in genomic DNA, enabling study of DNA damage checkpoints in a cell-free model (Willis et al., 2012; You et al., 2007). Detailed methods are also described for studying mitotic spindle assembly and checkpoints (Desai et al., 1999), and many mitotic spindle factors that are altered in cancer are conserved in Xenopus (Cross and Powers, 2009; Joukov et al., 2006). However, Xenopus is not limited to in vitro investigation of cell cycle function; the developing Xenopus embryo also presents an interesting in vivo system to study regulation of proliferation (Woodland, 1974) particularly in view of the changes in the cell cycle regulation during early development (Saka and Smith, 2001). "
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    ABSTRACT: One of the most striking features of the Xenopus system is the versatility in providing a unique range of both in vitro and in vivo models that are rapid, accessible and easily manipulated. Here we present an overview of the diverse contribution that Xenopus has made to advance our understanding of tumour biology and behaviour; a contribution that goes beyond the traditional view of Xenopus as a developmental model organism. From the utility of the egg and oocyte extract system to the use of whole embryos as developmental or induced tumour models, the Xenopus system has been fundamental to investigation of cell cycle mechanisms, cell metabolism, cell signalling and cell behaviour, and has allowed an increasing appreciation of the parallels between early development and the pathogenesis of tumour progression and metastasis. Although not the prototypical oncological model system, we propose that Xenopus is an adaptable and multifunctional tool in the oncologist's arsenal. Copyright © 2015. Published by Elsevier Inc.
    Developmental Biology 02/2015; 119. DOI:10.1016/j.ydbio.2015.02.003 · 3.55 Impact Factor
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    • "The X.l.BRCA1-BARD1 heterodimeric complex was purified from insect cells as in Joukov et al. (2006). Full-length FLAG-BRCA1 and HA-BARD1 were each cloned into pFastBac and used to generate the corresponding recombinant baculoviruses (Bac-to-Bac Baculovirus Expression System, Life Technologies, Carlsbad). "
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    ABSTRACT: The tumor suppressor protein BRCA1 promotes homologous recombination (HR), a high-fidelity mechanism to repair DNA double-strand breaks (DSBs) that arise during normal replication and in response to DNA-damaging agents. Recent genetic experiments indicate that BRCA1 also performs an HR-independent function during the repair of DNA interstrand crosslinks (ICLs). Here we show that BRCA1 is required to unload the CMG helicase complex from chromatin after replication forks collide with an ICL. Eviction of the stalled helicase allows leading strands to be extended toward the ICL, followed by endonucleolytic processing of the crosslink, lesion bypass, and DSB repair. Our results identify BRCA1-dependent helicase unloading as a critical, early event in ICL repair.
    Molecular Cell 09/2014; 56(1). DOI:10.1016/j.molcel.2014.08.012 · 14.02 Impact Factor
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    • "In this study we show that the BRCA1-associated RING domain protein 1 (BARD1) gene expression may be regulated by a large number of microRNAs and by a presumed lncRNA competing for microRNA binding. BARD1 has tumor suppressor functions and is involved in a number of cellular processes including DNA repair, transcriptional regulation, chromatin remodeling, cell cycle checkpoint control, and mitosis (Jin et al., 1997; Hashizume et al., 2001; Westermark et al., 2003; Starita and Parvin, 2003; Irminger-Finger and Jefford, 2006; Joukov et al., 2006; Laufer et al., 2007; Murray et al., 2007; Ryser et al., 2009; Larsen et al., 2010; Li and Yu, 2013). BARD1 has also been shown to be essential for the maintenance of genomic stability (Irminger-Finger et al., 1998; McCarthy et al., 2003; Li and Yu, 2013). "
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    ABSTRACT: Long non-coding RNAs (lncRNAs) are ubiquitously expressed RNA molecules of more than 200 nucleotides without substantial ORFs. LncRNAs could act as epigenetic regulators of gene expression affecting transcription, mRNA stability and transport, and translation, although, precise functions have been attributed to only few of them. Competing endogenous RNAs (ceRNAs) represent one recently emerged type of functional lncRNAs that share microRNA recognition sequences with mRNAs and may compete for microRNA binding and thus affect regulation and function of target mRNAs. We studied the epigenetic regulation of the BARD1 gene. The BARD1 protein acts as tumor suppressor with BRCA1. In cancer, mRNAs encoding the tumor suppressor full length BARD1 are often down-regulated while the expression of oncogenic truncated isoforms is boosted. We found that the BARD1 3'UTR is almost 3000 nt long and harbors a large number of microRNA binding elements. In addition we discovered a novel lncRNA, BARD1 9'L, which is transcribed from an alternative promoter in intron 9 of the BARD1 gene and shares part of the 3'UTR with the protein coding BARD1 mRNAs. We demonstrate with the example of two microRNAs, miR-203 and miR-101, that they down-regulate the expression of FL BARD1 and cancer-associated BARD1 mRNAs, and that BARD1 9'L counteracts the effect of miR-203 and miR-101, As BARD1 9'L is abnormally over-expressed in human cancers, we suggest it might be a tumor promoting factor and treatment target.
    The International Journal of Biochemistry & Cell Biology 07/2014; 54. DOI:10.1016/j.biocel.2014.06.018 · 4.05 Impact Factor
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