101
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Abstract
The formation of RAD51 foci in response to ionizing radiation (IR) represents an important step in the repair of DNA double-strand breaks. RAD51 foci also appear during S phase and are thought to be required for the restart of stalled or broken replication forks. The RAD51 recombinase interacts directly with the breast cancer-associated tumour suppressor BRCA2, an interaction that is required for normal recombination proficiency, radiation resistance and genome stability. In CAPAN-1 cells, which express a truncated form of BRCA2 that is cytoplasmic because of loss of the nuclear localization signal, the formation of IR-induced RAD51 foci is impaired. In this work, we show that S-phase RAD51 foci form normally in CAPAN-1 cells expressing truncated BRCA2. Moreover, we find that RAD51 specifically associates with chromatin at S phase in a reaction that is BRCA2-independent. The observed BRCA2-dependent and independent formation of RAD51 foci shows that intact BRCA2 is not required for RAD51 focus formation per se, leading us to suggest that S phase and IR-induced RAD51 foci assemble by distinct pathways with defined protein requirements.
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Affiliation(s)
- Madalena Tarsounas
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, UK
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102
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Abstract
Homologous recombination has been recognized in recent years to be an important DNA repair pathway in mammalian cells, for such damage as chromosomal double-strand breaks. Cells mutated for the genes involved in the hereditary breast and ovarian cancer susceptibility syndromes, i.e. BRCA1 and BRCA2, show defects in DNA repair by homologous recombination, implicating this repair pathway in protecting individuals against tumorigenesis. This review summarizes recent advances in our understanding of BRCA1 and BRCA2 in DNA repair, as well as insight into these proteins gleaned from structure determination of domains of these proteins and the broader evolutionary conservation than previously appreciated.
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Affiliation(s)
- Maria Jasin
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
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103
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Abstract
BRCA1 and BRCA2 mutations are estimated to be responsible for the great majority of familial breast and ovarian cancers. Much progress has been made toward the understanding of the function of these proteins through genetic, biochemical, and structural studies. The embryonic lethality encountered in the knockout mouse initially hindered the development of mouse models aimed at studying tumor suppression. However, mice that harbor hypomorphic Brca1 and Brca2 alleles and cre-mediated tissue-specific deletions for Brca1 and Brca2 have been generated. Mice deficient for either Brca1 or Brca2 sustain a wide range of carcinoma and mammary epithelium deleted for Brca1 or Brca2 is highly susceptible to mammary tumorigenesis. Mammary (and other) tumors occur at long latency as compared to oncogene-induced mouse tumors. p53 deficiency is highly cooperative with both Brca1 and Brca2 in promoting tumorigenesis. Analysis of Brca1-associated mammary tumors reveals significant similarities to BRCA1-associated breast cancer in regard to high tumor grade, hormone receptor negativity, a high incidence of p53 mutations and genetic instability.
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Affiliation(s)
- Mary Ellen Moynahan
- Department of Medicine, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
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104
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Symington LS. Role of RAD52 epistasis group genes in homologous recombination and double-strand break repair. Microbiol Mol Biol Rev 2002; 66:630-70, table of contents. [PMID: 12456786 PMCID: PMC134659 DOI: 10.1128/mmbr.66.4.630-670.2002] [Citation(s) in RCA: 790] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The process of homologous recombination is a major DNA repair pathway that operates on DNA double-strand breaks, and possibly other kinds of DNA lesions, to promote error-free repair. Central to the process of homologous recombination are the RAD52 group genes (RAD50, RAD51, RAD52, RAD54, RDH54/TID1, RAD55, RAD57, RAD59, MRE11, and XRS2), most of which were identified by their requirement for the repair of ionizing-radiation-induced DNA damage in Saccharomyces cerevisiae. The Rad52 group proteins are highly conserved among eukaryotes, and Rad51, Mre11, and Rad50 are also conserved in prokaryotes and archaea. Recent studies showing defects in homologous recombination and double-strand break repair in several human cancer-prone syndromes have emphasized the importance of this repair pathway in maintaining genome integrity. Although sensitivity to ionizing radiation is a universal feature of rad52 group mutants, the mutants show considerable heterogeneity in different assays for recombinational repair of double-strand breaks and spontaneous mitotic recombination. Herein, I provide an overview of recent biochemical and structural analyses of the Rad52 group proteins and discuss how this information can be incorporated into genetic studies of recombination.
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Affiliation(s)
- Lorraine S Symington
- Department of Microbiology and Institute of Cancer Research, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
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105
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Yang H, Jeffrey PD, Miller J, Kinnucan E, Sun Y, Thoma NH, Zheng N, Chen PL, Lee WH, Pavletich NP. BRCA2 function in DNA binding and recombination from a BRCA2-DSS1-ssDNA structure. Science 2002; 297:1837-48. [PMID: 12228710 DOI: 10.1126/science.297.5588.1837] [Citation(s) in RCA: 509] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Mutations in the BRCA2 (breast cancer susceptibility gene 2) tumor suppressor lead to chromosomal instability due to defects in the repair of double-strand DNA breaks (DSBs) by homologous recombination, but BRCA2's role in this process has been unclear. Here, we present the 3.1 angstrom crystal structure of a approximately 90-kilodalton BRCA2 domain bound to DSS1, which reveals three oligonucleotide-binding (OB) folds and a helix-turn-helix (HTH) motif. We also (i) demonstrate that this BRCA2 domain binds single-stranded DNA, (ii) present its 3.5 angstrom structure bound to oligo(dT)9, (iii) provide data that implicate the HTH motif in dsDNA binding, and (iv) show that BRCA2 stimulates RAD51-mediated recombination in vitro. These findings establish that BRCA2 functions directly in homologous recombination and provide a structural and biochemical basis for understanding the loss of recombination-mediated DSB repair in BRCA2-associated cancers.
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Affiliation(s)
- Haijuan Yang
- Department of Pharmacology, Sloan-Kettering Division, Joan and Sanford I. Weill Graduate School of Medical Sciences, Cornell University, New York, NY 10021, USA
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106
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Mérel P, Prieur A, Pfeiffer P, Delattre O. Absence of major defects in non-homologous DNA end joining in human breast cancer cell lines. Oncogene 2002; 21:5654-9. [PMID: 12165865 DOI: 10.1038/sj.onc.1205742] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2002] [Revised: 05/22/2002] [Accepted: 06/07/2002] [Indexed: 02/01/2023]
Abstract
Structural abnormalities of chromosomes, including translocations and deletions, are extremely frequent in human cancer cells and particularly in breast cancer cells. One hypothesis to account for these alterations is a deficiency in the repair of DNA double-strand breaks (DSB). This repair process relies on two distinct pathways, homologous recombination (HR) and non-homologous DNA end joining (NHEJ). To investigate this latter pathway, we have studied the ability of cell-free extracts from a variety of human cells to rejoin different types of DSBs. The end joining activity of eleven sporadic breast cancer cell lines (BCCLs) was compared with that of control cells including primary human fibroblasts and cells harbouring a limited number of chromosome abnormalities. In vitro rejoining activity was not detected in extracts from MO59J DNA-PKcs-deficient cells and was strongly inhibited by wortmannin in control extracts. In contrast, most sporadic BCCLs and BRCA1 or BRCA2 deficient cells demonstrated similar efficiencies and accuracies of in vitro NHEJ than control cells. Only two BCCLs, SKBR3 and MDA-MB-453 exhibited decreased in vitro NHEJ. This study therefore indicates that a major defect in the NHEJ pathway is unlikely to account for the high number of chromosomes abnormalities observed in sporadic and hereditary BCCLs.
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Affiliation(s)
- Philippe Mérel
- Laboratoire de Pathologie Moléculaire des Cancers, INSERM U509, Institut Curie, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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107
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Larminat F, Germanier M, Papouli E, Defais M. Deficiency in BRCA2 leads to increase in non-conservative homologous recombination. Oncogene 2002; 21:5188-92. [PMID: 12140769 DOI: 10.1038/sj.onc.1205659] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2002] [Revised: 04/17/2002] [Accepted: 05/10/2002] [Indexed: 11/10/2022]
Abstract
The BRCA2 tumor suppressor has been implicated in the maintenance of genomic integrity through a function in cellular responses to DNA damage. The BRCA2 protein directly associates with Rad51, that is essential for repair of double-strand breaks (DSBs) by homologous recombination (HR). In this report, we study the BRCA2-defective Chinese hamster cell mutant V-C8 for its ability to perform homology-directed repair (HDR) between repeated sequences. V-C8 cells were recently shown to be defective in Rad51 foci formation in response to DNA damage. Strikingly, we find that these BRCA2 mutant cells exhibit a strong stimulation of HDR activity compared to the V79 parental cells, which harbor a wild-type BRCA2. Furthermore, molecular characterization of the HDR products shows that loss of BRCA2 in V-C8 cells leads to significant reduction in Rad51-dependent gene conversion but strong enhancement of Rad51-independent single-strand annealing (SSA) events frequency. These data imply that, when HDR by conservative gene conversion is impaired, DSBs usually repaired by this pathway are instead resolved by other non-conservative HDR subpathways. Therefore, high chromosomal instability in BRCA2-deficient cells presumably results from enhancement of error-prone repair mechanisms, such as SSA.
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Affiliation(s)
- Florence Larminat
- Institut de Pharmacologie et de Biologie Structurale, UMR 5089, C.N.R.S., 205, Route de Narbonne, 31077 Toulouse Cedex 4, France.
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108
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Affiliation(s)
- Emily Witt
- The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London SW3 6JB, UK.
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109
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Takata M, Tachiiri S, Fujimori A, Thompson LH, Miki Y, Hiraoka M, Takeda S, Yamazoe M. Conserved domains in the chicken homologue of BRCA2. Oncogene 2002; 21:1130-4. [PMID: 11850831 DOI: 10.1038/sj.onc.1205168] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2001] [Revised: 11/02/2001] [Accepted: 11/07/2001] [Indexed: 01/12/2023]
Abstract
Germline mutation of the BRCA2 gene causes a high risk of developing breast and ovarian cancer. Although the BRCA2 protein has been implicated in homologous recombination (HR) of DNA and in transcription, it is still unclear how mutation leads to tumorigenesis. We have identified a non-mammalian homologue of BRCA2 from chicken, which encodes a protein with 3397 amino acids (aa) and shows only 40% identity to human BRCA2. However, comparison of the mammalian and chicken sequences revealed remarkably high homology in several segments. These include a N-terminal region (approximately 100 aa), which was previously shown to possess intrinsic transcriptional activity, and a C-terminal region (aa residue approximately 2480-approximately 3180 in human BRCA2), which has not been clearly assigned any function. In contrast, although the eight BRC repeats of mammalian BRCA2 are believed to play an important role in HR by interacting with Rad51, the BRC3, BRC5, and BRC6 repeats exhibit virtually no similarity to their mammalian counterparts. Among 311 missense mutations listed as unclassified variants in the NIH Breast Cancer Information Core database, only 83 of these sites are identical in chicken BRCA2. Thus, chicken BRCA2 may provide a means to identify domains and residues associated with cancer predisposition.
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Affiliation(s)
- Minoru Takata
- Department of Immunology and Molecular Genetics, Kawasaki Medical School, 577 Matsushima, Kurashiki 701-0192, Japan.
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110
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Kraakman-van der Zwet M, Overkamp WJI, van Lange REE, Essers J, van Duijn-Goedhart A, Wiggers I, Swaminathan S, van Buul PPW, Errami A, Tan RTL, Jaspers NGJ, Sharan SK, Kanaar R, Zdzienicka MZ. Brca2 (XRCC11) deficiency results in radioresistant DNA synthesis and a higher frequency of spontaneous deletions. Mol Cell Biol 2002; 22:669-79. [PMID: 11756561 PMCID: PMC139737 DOI: 10.1128/mcb.22.2.669-679.2002] [Citation(s) in RCA: 265] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2001] [Revised: 07/21/2001] [Accepted: 10/08/2001] [Indexed: 12/20/2022] Open
Abstract
We show here that the radiosensitive Chinese hamster cell mutant (V-C8) of group XRCC11 is defective in the breast cancer susceptibility gene Brca2. The very complex phenotype of V-C8 cells is complemented by a single human chromosome 13 providing the BRCA2 gene, as well as by the murine Brca2 gene. The Brca2 deficiency in V-C8 cells causes hypersensitivity to various DNA-damaging agents with an extreme sensitivity toward interstrand DNA cross-linking agents. Furthermore, V-C8 cells show radioresistant DNA synthesis after ionizing radiation, suggesting that Brca2 deficiency affects cell cycle checkpoint regulation. In addition, V-C8 cells display tremendous chromosomal instability and a high frequency of abnormal centrosomes. The mutation spectrum at the hprt locus showed that the majority of spontaneous mutations in V-C8 cells are deletions, in contrast to wild-type V79 cells. A mechanistic explanation for the genome instability phenotype of Brca2-deficient cells is provided by the observation that the nuclear localization of the central DNA repair protein in homologous recombination, Rad51, is reduced in V-C8 cells.
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Affiliation(s)
- Maria Kraakman-van der Zwet
- Department of Radiation Genetics and Chemical Mutagenesis-MGC, Leiden University Medical Center, The Netherlands
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111
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Sarkisian CJ, Master SR, Huber LJ, Ha SI, Chodosh LA. Analysis of murine Brca2 reveals conservation of protein-protein interactions but differences in nuclear localization signals. J Biol Chem 2001; 276:37640-8. [PMID: 11477095 DOI: 10.1074/jbc.m106281200] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this report, we have analyzed the protein encoded by the murine Brca2 locus. We find that murine Brca2 shares multiple properties with human BRCA2 including its regulation during the cell cycle, localization to nuclear foci, and interaction with Brca1 and Rad51. Murine Brca2 stably interacts with human BRCA1, and the amino terminus of Brca2 is sufficient for this interaction. Exon 11 of murine Brca2 is required for its stable association with RAD51, whereas the carboxyl terminus of Brca2 is dispensable for this interaction. Finally, in contrast to human BRCA2, we demonstrate that carboxyl-terminal truncations of murine Brca2 localize to the nucleus. This finding may explain the apparent inconsistency between the cytoplasmic localization of carboxyl-terminal truncations of human BRCA2 and the hypomorphic phenotype of mice homozygous for similar carboxyl-terminal truncating mutations.
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Affiliation(s)
- C J Sarkisian
- Department of Molecular and Cellular Engineering, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6160, USA
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112
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Sonoda E, Takata M, Yamashita YM, Morrison C, Takeda S. Homologous DNA recombination in vertebrate cells. Proc Natl Acad Sci U S A 2001; 98:8388-94. [PMID: 11459980 PMCID: PMC37448 DOI: 10.1073/pnas.111006398] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The RAD52 epistasis group genes are involved in homologous DNA recombination, and their primary structures are conserved from yeast to humans. Although biochemical studies have suggested that the fundamental mechanism of homologous DNA recombination is conserved from yeast to mammals, recent studies of vertebrate cells deficient in genes of the RAD52 epistasis group reveal that the role of each protein is not necessarily the same as that of the corresponding yeast gene product. This review addresses the roles and mechanisms of homologous recombination-mediated repair with a special emphasis on differences between yeast and vertebrate cells.
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Affiliation(s)
- E Sonoda
- Department of Radiation Genetics, Faculty of Medicine, Kyoto University, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan
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113
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Xia F, Taghian DG, DeFrank JS, Zeng ZC, Willers H, Iliakis G, Powell SN. Deficiency of human BRCA2 leads to impaired homologous recombination but maintains normal nonhomologous end joining. Proc Natl Acad Sci U S A 2001; 98:8644-9. [PMID: 11447276 PMCID: PMC37489 DOI: 10.1073/pnas.151253498] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Carriers of BRCA2 germline mutations are at high risk to develop early-onset breast cancer. The underlying mechanisms of how BRCA2 inactivation predisposes to malignant transformation have not been established. Here, we provide direct functional evidence that human BRCA2 promotes homologous recombination (HR), which comprises one major pathway of DNA double-strand break repair. We found that up-regulated HR after transfection of wild-type (wt) BRCA2 into a human tumor line with mutant BRCA2 was linked to increased radioresistance. In addition, BRCA2-mediated enhancement of HR depended on the interaction with Rad51. In contrast to the tumor suppressor BRCA1, which is involved in multiple DNA repair pathways, BRCA2 status had no impact on the other principal double-strand break repair pathway, nonhomologous end joining. Thus, there exists a specific regulation of HR by BRCA2, which may function to maintain genomic integrity and suppress tumor development in proliferating cells.
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Affiliation(s)
- F Xia
- Laboratory of Molecular and Cellular Radiation Biology, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, 149 13th Street, Charlestown, MA 02129, USA
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114
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Hohenstein P, Kielman MF, Breukel C, Bennett LM, Wiseman R, Krimpenfort P, Cornelisse C, van Ommen GJ, Devilee P, Fodde R. A targeted mouse Brca1 mutation removing the last BRCT repeat results in apoptosis and embryonic lethality at the headfold stage. Oncogene 2001; 20:2544-50. [PMID: 11420664 DOI: 10.1038/sj.onc.1204363] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2000] [Revised: 02/06/2001] [Accepted: 02/12/2001] [Indexed: 11/09/2022]
Abstract
A mouse model with a targeted mutation in the 3' end of the endogenous Brca1 gene, Brca1(1700T), was generated to compare the phenotypic consequences of truncated Brca1 proteins with other mutant Brca1 models reported in the literature to date. Mice heterozygous for the Brca1(1700T) mutation do not show any predisposition to tumorigenesis. Treatment of these mice with ionizing radiation or breeding with Apc, Msh-2 or Tp53 mutant mouse models did not show any change in the tumor phenotype. Like other Brca1 mouse models, the Brca1(1700T) mutation is embryonic lethal in homozygous state. However, homozygous Brca1(1700T) embryos reach the headfold stage but are delayed in their development and fail to turn. Thus, in contrast to Brca1(null) models, the mutant embryos do not undergo growth arrest leading to a developmental block at 6.5 dpc, but continue to proliferate and differentiate until 9.5 dpc. Homozygous embryos die between 9.5-10.5 dpc due to massive apoptosis throughout the embryo. These results indicate that a C-terminal truncating Brca1 mutation removing the last BRCT repeat has a different effect on normal cell function than does the complete absence of Brca1.
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Affiliation(s)
- P Hohenstein
- Department of Human & Clinical Genetics, Leiden University Medical Center, P.O.Box 9503, 2300 RA, The Netherlands
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115
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Takata M, Sasaki MS, Tachiiri S, Fukushima T, Sonoda E, Schild D, Thompson LH, Takeda S. Chromosome instability and defective recombinational repair in knockout mutants of the five Rad51 paralogs. Mol Cell Biol 2001; 21:2858-66. [PMID: 11283264 PMCID: PMC86915 DOI: 10.1128/mcb.21.8.2858-2866.2001] [Citation(s) in RCA: 428] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The Rad51 protein, a eukaryotic homologue of Escherichia coli RecA, plays a central role in both mitotic and meiotic homologous DNA recombination (HR) in Saccharomyces cerevisiae and is essential for the proliferation of vertebrate cells. Five vertebrate genes, RAD51B, -C, and -D and XRCC2 and -3, are implicated in HR on the basis of their sequence similarity to Rad51 (Rad51 paralogs). We generated mutants deficient in each of these proteins in the chicken B-lymphocyte DT40 cell line and report here the comparison of four new mutants and their complemented derivatives with our previously reported rad51b mutant. The Rad51 paralog mutations all impair HR, as measured by targeted integration and sister chromatid exchange. Remarkably, the mutant cell lines all exhibit very similar phenotypes: spontaneous chromosomal aberrations, high sensitivity to killing by cross-linking agents (mitomycin C and cisplatin), mild sensitivity to gamma rays, and significantly attenuated Rad51 focus formation during recombinational repair after exposure to gamma rays. Moreover, all mutants show partial correction of resistance to DNA damage by overexpression of human Rad51. We conclude that the Rad51 paralogs participate in repair as a functional unit that facilitates the action of Rad51 in HR.
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Affiliation(s)
- M Takata
- CREST Research Project, Radiation Genetics, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
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116
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Abstract
BRCA1 and BRCA2 are breast cancer susceptibility genes. Mutations within BRCA1 and BRCA1 are responsible for most familial breast cancer cases. Targeted deletion of Brca1 or Brca2 in mice has revealed an essential function for their encoded products, BRCA1 and BRCA2, in cell proliferation during embryogenesis. Mouse models established from conditional expression of mutant Brca1 alleles develop mammary gland tumors, providing compelling evidence that BRCA1 functions as a breast cancer suppressor. Human cancer cells and mouse cells deficient in BRCA1 or BRCA2 exhibit radiation hypersensitivity and chromosomal abnormalities, thus revealing a potential role for both BRCA1 and BRCA2 in the maintenance of genetic stability through participation in the cellular response to DNA damage. Functional analyses of the BRCA1 and BRCA2 gene products have established their dual participation in transcription regulation and DNA damage repair. Potential insight into the molecular basis for these functions of BRCA1 and BRCA2 has been provided by studies that implicate these two tumor suppressors in both the maintenance of genetic stability and the regulation of cell growth and differentiation.
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Affiliation(s)
- L Zheng
- Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 78245, USA
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