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Jiang Q, Paramasivam M, Aressy B, Wu J, Bellani M, Tong W, Seidman MM, Greenberg RA. MERIT40 cooperates with BRCA2 to resolve DNA interstrand cross-links. Genes Dev 2015; 29:1955-68. [PMID: 26338419 PMCID: PMC4579352 DOI: 10.1101/gad.264192.115] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 08/13/2015] [Indexed: 01/19/2023]
Abstract
Jiang et al. found that Merit40−/− mice displayed marked hypersensitivity to DNA interstrand cross-links (ICLs) but not whole-body irradiation. This study implicates MERIT40 in the earliest stages of ICL repair and defines specific functional interactions between RAP80 complex-dependent ubiquitin recognition and the FA–BRCA ICL repair network. MERIT40 is an essential component of the RAP80 ubiquitin recognition complex that targets BRCA1 to DNA damage sites. Although this complex is required for BRCA1 foci formation, its physiologic role in DNA repair has remained enigmatic, as has its relationship to canonical DNA repair mechanisms. Surprisingly, we found that Merit40−/− mice displayed marked hypersensitivity to DNA interstrand cross-links (ICLs) but not whole-body irradiation. MERIT40 was rapidly recruited to ICL lesions prior to FANCD2, and Merit40-null cells exhibited delayed ICL unhooking coupled with reduced end resection and homologous recombination at ICL damage. Interestingly, Merit40 mutation exacerbated ICL-induced chromosome instability in the context of concomitant Brca2 deficiency but not in conjunction with Fancd2 mutation. These findings implicate MERIT40 in the earliest stages of ICL repair and define specific functional interactions between RAP80 complex-dependent ubiquitin recognition and the Fanconi anemia (FA)–BRCA ICL repair network.
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Abstract
The BRCA1 tumor suppressor protein is a central constituent of several distinct macromolecular protein complexes that execute homology-directed DNA damage repair and cell cycle checkpoints. Recent years have borne witness to an exciting phase of discovery at the basic molecular level for how this network of DNA repair proteins acts to maintain genome stability and suppress cancer. The clinical dividends of this investment are now being realized with the approval of first-in-class BRCA-targeted therapies for ovarian cancer and identification of molecular events that determine responsiveness to these agents. Further delineation of the basic science underlying BRCA network function holds promise to maximally exploit genome instability for hereditary and sporadic cancer therapy.
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Cho NW, Dilley RL, Lampson MA, Greenberg RA. Interchromosomal homology searches drive directional ALT telomere movement and synapsis. Cell 2015; 159:108-121. [PMID: 25259924 DOI: 10.1016/j.cell.2014.08.030] [Citation(s) in RCA: 249] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2014] [Revised: 06/16/2014] [Accepted: 08/25/2014] [Indexed: 12/17/2022]
Abstract
Telomere length maintenance is a requisite feature of cellular immortalization and a hallmark of human cancer. While most human cancers express telomerase activity, ∼10%-15% employ a recombination-dependent telomere maintenance pathway known as alternative lengthening of telomeres (ALT) that is characterized by multitelomere clusters and associated promyelocytic leukemia protein bodies. Here, we show that a DNA double-strand break (DSB) response at ALT telomeres triggers long-range movement and clustering between chromosome termini, resulting in homology-directed telomere synthesis. Damaged telomeres initiate increased random surveillance of nuclear space before displaying rapid directional movement and association with recipient telomeres over micron-range distances. This phenomenon required Rad51 and the Hop2-Mnd1 heterodimer, which are essential for homologous chromosome synapsis during meiosis. These findings implicate a specialized homology searching mechanism in ALT-dependent telomere maintenance and provide a molecular basis underlying the preference for recombination between nonsister telomeres during ALT.
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Greenberg RA, Weingarten K. When health care professionals say "more" and parents say "enough". Paediatr Child Health 2015; 20:131-4. [PMID: 25914570 DOI: 10.1093/pch/20.3.131] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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55
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Yu Q, Katlinskaya YV, Carbone CJ, Zhao B, Katlinski KV, Zheng H, Guha M, Li N, Chen Q, Yang T, Lengner CJ, Greenberg RA, Johnson FB, Fuchs SY. DNA-damage-induced type I interferon promotes senescence and inhibits stem cell function. Cell Rep 2015; 11:785-797. [PMID: 25921537 DOI: 10.1016/j.celrep.2015.03.069] [Citation(s) in RCA: 173] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 02/18/2015] [Accepted: 03/27/2015] [Indexed: 02/07/2023] Open
Abstract
Expression of type I interferons (IFNs) can be induced by DNA-damaging agents, but the mechanisms and significance of this regulation are not completely understood. We found that the transcription factor IRF3, activated in an ATM-IKKα/β-dependent manner, stimulates cell-autonomous IFN-β expression in response to double-stranded DNA breaks. Cells and tissues with accumulating DNA damage produce endogenous IFN-β and stimulate IFN signaling in vitro and in vivo. In turn, IFN acts to amplify DNA-damage responses, activate the p53 pathway, promote senescence, and inhibit stem cell function in response to telomere shortening. Inactivation of the IFN pathway abrogates the development of diverse progeric phenotypes and extends the lifespan of Terc knockout mice. These data identify DNA-damage-response-induced IFN signaling as a critical mechanism that links accumulating DNA damage with senescence and premature aging.
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Yu Q, Carbone CJ, Katlinskaya YV, Zheng H, Zheng K, Luo M, Wang PJ, Greenberg RA, Fuchs SY. Type I interferon controls propagation of long interspersed element-1. J Biol Chem 2015; 290:10191-9. [PMID: 25716322 DOI: 10.1074/jbc.m114.612374] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Indexed: 01/01/2023] Open
Abstract
Type I interferons (IFN) including IFNα and IFNβ are critical for the cellular defense against viruses. Here we report that increased levels of IFNβ were found in testes from mice deficient in MOV10L1, a germ cell-specific RNA helicase that plays a key role in limiting the propagation of retrotransposons including Long Interspersed Element-1 (LINE-1). Additional experiments revealed that activation of LINE-1 retrotransposons increases the expression of IFNβ and of IFN-stimulated genes. Conversely, pretreatment of cells with IFN suppressed the replication of LINE-1. Furthermore, the efficacy of LINE-1 replication was increased in isogenic cell lines harboring inactivating mutations in diverse elements of the IFN signaling pathway. Knockdown of the IFN receptor chain IFNAR1 also stimulated LINE-1 propagation in vitro. Finally, a greater accumulation of LINE-1 was found in mice that lack IFNAR1 compared with wild type mice. We propose that LINE-1-induced IFN plays an important role in restricting LINE-1 propagation and discuss the putative role of IFN in preserving the genome stability.
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Sawyer SL, Tian L, Kähkönen M, Schwartzentruber J, Kircher M, Majewski J, Dyment DA, Innes AM, Boycott KM, Moreau LA, Moilanen JS, Greenberg RA. Biallelic mutations in BRCA1 cause a new Fanconi anemia subtype. Cancer Discov 2014; 5:135-42. [PMID: 25472942 DOI: 10.1158/2159-8290.cd-14-1156] [Citation(s) in RCA: 226] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
UNLABELLED Deficiency in BRCA-dependent DNA interstrand crosslink (ICL) repair is intimately connected to breast cancer susceptibility and to the rare developmental syndrome Fanconi anemia. Bona fide Fanconi anemia proteins, BRCA2 (FANCD1), PALB2 (FANCN), and BRIP1 (FANCJ), interact with BRCA1 during ICL repair. However, the lack of detailed phenotypic and cellular characterization of a patient with biallelic BRCA1 mutations has precluded assignment of BRCA1 as a definitive Fanconi anemia susceptibility gene. Here, we report the presence of biallelic BRCA1 mutations in a woman with multiple congenital anomalies consistent with a Fanconi anemia-like disorder and breast cancer at age 23. Patient cells exhibited deficiency in BRCA1 and RAD51 localization to DNA-damage sites, combined with radial chromosome formation and hypersensitivity to ICL-inducing agents. Restoration of these functions was achieved by ectopic introduction of a BRCA1 transgene. These observations provide evidence in support of BRCA1 as a new Fanconi anemia gene (FANCS). SIGNIFICANCE We establish that biallelic BRCA1 mutations cause a distinct FA-S, which has implications for risk counselling in families where both parents harbor BRCA1 mutations. The genetic basis of hereditary cancer susceptibility syndromes provides diagnostic information, insights into treatment strategies, and more accurate recurrence risk counseling to families.
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Greenberg RA. Abstract IA23: The BRCA1 tumor suppressor network. Cancer Res 2014. [DOI: 10.1158/1538-7445.cansusc14-ia23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
BRCA1 is an essential component of multiple distinct protein complexes that are dedicated to DNA damage recognition and repair. Germline heterozygous mutations to genes encoding multiple BRCA associated proteins result in cancer susceptibility, while biallelic mutations lead to developmental abnormalities, cancer predisposition, and systemic hypersensitivity to chemotherapy. BRCA1 associates with the RAP80 complex to recognize lysine63-linked ubiquitin chains at DNA damage sites. Three members of the RAP80 complex are mutated in hereditary breast cancer, implicating ubiquitin recognition as a bona fide component of BRCA1 dependent tumor suppression. This presentation will describe in vivo interactions between BRCA1 associated DNA damage site ubiquitin recognition and other protein complexes that are dedicated to homologous recombination mediated DNA repair to S-phase. Relevance to cancer etiology and response to therapy will be discussed.
Citation Format: Roger A. Greenberg. The BRCA1 tumor suppressor network. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Susceptibility and Cancer Susceptibility Syndromes; Jan 29-Feb 1, 2014; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(23 Suppl):Abstract nr IA23. doi:10.1158/1538-7445.CANSUSC14-IA23
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Li ML, Yuan G, Greenberg RA. Chromatin yo-yo: expansion and condensation during DNA repair. Trends Cell Biol 2014; 24:616-618. [PMID: 25305135 DOI: 10.1016/j.tcb.2014.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Accepted: 09/22/2014] [Indexed: 12/12/2022]
Abstract
DNA double-strand breaks are repaired by nonhomologous end-joining (NHEJ) and homologous recombination (HR). Disrupting the balance between these pathways results in toxic chromosomal rearrangements. Several recent studies are revealing that dynamic changes in chromatin conformation can regulate DNA repair pathway choice both spatially and temporally.
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Greenberg RA, Anstey KW, Macri R, Heesters A, Bean S, Zlotnik Shaul R. Bioethics consultation practices and procedures: a survey of a large Canadian community of practice. HEC Forum 2013; 26:135-46. [PMID: 24306818 DOI: 10.1007/s10730-013-9230-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The literature fails to reflect general agreement over the nature of the services and procedures provided by bioethicists, and the training and core competencies this work requires. If bioethicists are to define their activities in a consistent way, it makes sense to look for common ground in shared communities of practice. We report results of a survey of the services and procedures among bioethicists affiliated with the University of Toronto Joint Centre for Bioethics (JCB). This is the largest group of bioethicists working in healthcare organizations in Canada. The results suggest there are many common services and procedures of JCB bioethicists. This survey can serve as a baseline for further exploration of the work of JCB bioethicists. Common practices exist with respect to the domains of practice, individual reporting relationships, service availability within business hours and the education and training of the bioethicist.
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Hendzel MJ, Greenberg RA. Conversations between chromatin modifications and DNA double strand break repair: a commentary. Mutat Res 2013; 750:1-4. [PMID: 23994712 PMCID: PMC3827952 DOI: 10.1016/j.mrfmmm.2013.08.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
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Campbell M, Wright L, Greenberg RA, Grant D. How young is too young to be a living donor? Am J Transplant 2013; 13:1643-9. [PMID: 23750824 DOI: 10.1111/ajt.12307] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 03/28/2013] [Accepted: 04/16/2013] [Indexed: 01/25/2023]
Abstract
Assessing people in adolescence and early adulthood who wish to become living organ donors (LDs) provides unique challenges. In several Canadian provinces, 16-year-old can legally consent to living organ donation. While the World Health Organization states that adolescence corresponds roughly to the ages of 10-19 years, parts of the brain associated with judgment continue to develop into the mid-20s. Therefore, it is legally possible for some young people to donate organs before their capacity to judge the benefits and risks of surgery has fully matured. Potential young living donors (YLDs) may be financially and/or psychologically dependent on their recipients (e.g. parents), which can make it difficult to determine if the YLD's donation is voluntary. This paper suggests ways to manage three ethical challenges in the use of young people as LDs: (1) determining the YLD's ability to appreciate the consequences of living organ donation, (2) determining whether the YLD's donation is voluntary and (3) evaluating the unique risks and benefits to the YLD. We conclude that there are compelling ethical reasons to offer the opportunity of living donation to selected young people. A thorough and fair evaluation process can address social, emotional and developmental issues associated with YLDs.
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Abstract
How does BRCA1's evolutionarily conserved E3 ligase activity contribute to DNA damage responses? Genetically engineered cells containing a BRCA1 RING domain mutation have been used to identify Claspin as a new target of BRCA1 E3 ligase activity in response to specific forms of DNA damage.
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65
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Guzzo CM, Berndsen CE, Zhu J, Gupta V, Datta A, Greenberg RA, Wolberger C, Matunis MJ. RNF4‐Dependent Hybrid SUMO‐Ubiquitin Chains are Signals for RAP80 and thereby Mediate the Recruitment of BRCA1 to Sites of DNA Damage. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.782.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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66
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Abstract
Recent advances have led to several systems to study transcription from defined loci in living cells. It has now become possible to address long-standing questions regarding the interplay between the processes of DNA damage repair and transcription-two disparate processes that can occur on the same stretch of chromatin and which both lead to extensive chromatin change. Here we describe the development of a system to create enzymatically induced DNA double-strand breaks (DSBs) at a site of inducible transcription and methods to study the interplay between these processes.
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67
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Domchek SM, Tang J, Stopfer J, Lilli DR, Hamel N, Tischkowitz M, Monteiro ANA, Messick TE, Powers J, Yonker A, Couch FJ, Goldgar DE, Davidson HR, Nathanson KL, Foulkes WD, Greenberg RA. Biallelic deleterious BRCA1 mutations in a woman with early-onset ovarian cancer. Cancer Discov 2012; 3:399-405. [PMID: 23269703 DOI: 10.1158/2159-8290.cd-12-0421] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
UNLABELLED BRCA1 and BRCA2 are the most important breast and ovarian cancer susceptibility genes. Biallelic mutations in BRCA2 can lead to Fanconi anemia and predisposition to cancers, whereas biallelic BRCA1 mutations have not been confirmed, presumably because one wild-type BRCA1 allele is required during embryogenesis. This study describes an individual who was diagnosed with ovarian carcinoma at age 28 and found to have one allele with a deleterious mutation in BRCA1, c.2457delC (p.Asp821Ilefs*25), and a second allele with a variant of unknown significance in BRCA1, c.5207T>C (p.Val1736Ala). Medical records revealed short stature, microcephaly, developmental delay, and significant toxicity from chemotherapy. BRCA1 p.Val1736Ala cosegregated with cancer in multiple families, associated tumors showed loss of wild-type BRCA1, and BRCA1 p.Val1736Ala showed reduced DNA damage localization. These findings represent the first validated example of biallelic deleterious human BRCA1 mutations and have implications for the interpretation of genetic test results. SIGNIFICANCE Accurate assessment of genetic testing data for BRCA1 mutations is essential for clinical monitoring and treatment strategies. Here, we report the fi rst validated example of an individual with biallelic BRCA1 mutations, early-onset ovarian cancer, and clinically significant hypersensitivity to chemotherapy.
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68
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Guzzo CM, Berndsen CE, Zhu J, Gupta V, Datta A, Greenberg RA, Wolberger C, Matunis MJ. RNF4-dependent hybrid SUMO-ubiquitin chains are signals for RAP80 and thereby mediate the recruitment of BRCA1 to sites of DNA damage. Sci Signal 2012; 5:ra88. [PMID: 23211528 DOI: 10.1126/scisignal.2003485] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The DNA repair function of the breast cancer susceptibility protein BRCA1 depends in part on its interaction with RAP80, which targets BRCA1 to DNA double-strand breaks (DSBs) through recognition of K63-linked polyubiquitin chains. The localization of BRCA1 to DSBs also requires sumoylation. We demonstrated that, in addition to having ubiquitin-interacting motifs, RAP80 also contains a SUMO-interacting motif (SIM) that is critical for recruitment to DSBs. In combination with the ubiquitin-binding activity of RAP80, this SIM enabled RAP80 to bind with nanomolar affinity to hybrid chains consisting of ubiquitin conjugated to SUMO. Furthermore, RNF4, a SUMO-targeted ubiquitin E3 ligase that synthesizes hybrid SUMO-ubiquitin chains, localized to DSBs and was critical for the recruitment of RAP80 and BRCA1 to sites of DNA damage. Our findings, therefore, connect ubiquitin- and SUMO-dependent DSB recognition, revealing that RNF4-synthesized hybrid SUMO-ubiquitin chains are recognized by RAP80 to promote BRCA1 recruitment and DNA repair.
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69
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Solyom S, Aressy B, Pylkäs K, Patterson-Fortin J, Hartikainen JM, Kallioniemi A, Kauppila S, Nikkilä J, Kosma VM, Mannermaa A, Greenberg RA, Winqvist R. Breast cancer-associated Abraxas mutation disrupts nuclear localization and DNA damage response functions. Sci Transl Med 2012; 4:122ra23. [PMID: 22357538 DOI: 10.1126/scitranslmed.3003223] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Breast cancer is the most common cancer in women in developed countries and has a well-established genetic component. Germline mutations in a network of genes encoding BRCA1, BRCA2, and their interacting partners confer hereditary susceptibility to breast cancer. Abraxas directly interacts with the BRCA1 BRCT (BRCA1 carboxyl-terminal) repeats and contributes to BRCA1-dependent DNA damage responses, making Abraxas a candidate for yet unexplained disease susceptibility. Here, we have screened 125 Northern Finnish breast cancer families for coding region and splice-site Abraxas mutations and genotyped three tagging single-nucleotide polymorphisms within the gene from 991 unselected breast cancer cases and 868 female controls for common cancer-associated variants. A novel heterozygous alteration, c.1082G>A (Arg361Gln), that results in abrogated nuclear localization and DNA response activities was identified in three breast cancer families and in one additional familial case from an unselected breast cancer cohort, but not in healthy controls (P = 0.002). On the basis of its exclusive occurrence in familial cancers, disease cosegregation, evolutionary conservation, and disruption of critical BRCA1 functions, the recurrent Abraxas c.1082G>A mutation connects to cancer predisposition. These findings contribute to the concept of a BRCA-centered tumor suppressor network and provide the identity of Abraxas as a new breast cancer susceptibility gene.
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70
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Beishline K, Kelly CM, Olofsson BA, Koduri S, Emrich J, Greenberg RA, Azizkhan-Clifford J. Sp1 facilitates DNA double-strand break repair through a nontranscriptional mechanism. Mol Cell Biol 2012; 32:3790-9. [PMID: 22826432 PMCID: PMC3430196 DOI: 10.1128/mcb.00049-12] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Accepted: 07/08/2012] [Indexed: 12/18/2022] Open
Abstract
Sp1 is a ubiquitously expressed transcription factor that is phosphorylated by ataxia telangiectasia mutated kinase (ATM) in response to ionizing radiation and H(2)O(2). Here, we show by indirect immunofluorescence that Sp1 phosphorylated on serine 101 (pSp1) localizes to ionizing radiation-induced foci with phosphorylated histone variant γH2Ax and members of the MRN (Mre11, Rad50, and Nbs1) complex. More precise analysis of occupancy of DNA double-strand breaks (DSBs) by chromatin immunoprecipitation (ChIP) shows that Sp1, like Nbs1, resides within 200 bp of DSBs. Using laser microirradiation of cells, we demonstrate that pSp1 is present at DNA DSBs by 7.5 min after induction of damage and remains at the break site for at least 8 h. Depletion of Sp1 inhibits repair of site-specific DNA breaks, and the N-terminal 182-amino-acid peptide, which contains targets of ATM kinase but lacks the zinc finger DNA binding domain, is phosphorylated, localizes to DSBs, and rescues the repair defect resulting from Sp1 depletion. Together, these data demonstrate that Sp1 is rapidly recruited to the region immediately adjacent to sites of DNA DSBs and is required for DSB repair, through a mechanism independent of its sequence-directed transcriptional effects.
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71
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Li ML, Greenberg RA. Links between genome integrity and BRCA1 tumor suppression. Trends Biochem Sci 2012; 37:418-24. [PMID: 22836122 DOI: 10.1016/j.tibs.2012.06.007] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2012] [Revised: 06/26/2012] [Accepted: 06/29/2012] [Indexed: 01/07/2023]
Abstract
BRCA1 and BRCA2 are two major breast and ovarian cancer susceptibility genes. BRCA1 was the first discovered and has been a focus of research for these cancers. BRCA1 mediates tumor suppression in part through pleiotropic interactions with a network of DNA repair proteins on chromatin. BRCA1 mutations cause homologous recombination (HR)-mediated DNA repair deficiency, genomic instability, and DNA-damaging agent hypersensitivity. Although BRCA1 and BRCA2 have some shared functions in cancer predisposition and therapy response, there are also key differences indicating divergent roles for each protein. This review summarizes and highlights recent insights into the molecular events responsible for BRCA1 tumor suppression, emphasizing the DNA repair function of BRCA1 as a nexus between its roles in cancer development and therapy.
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72
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Tang JB, Greenberg RA. Connecting the Dots: Interplay between Ubiquitylation and SUMOylation at DNA Double-Strand Breaks. Genes Cancer 2011; 1:787-96. [PMID: 21113239 DOI: 10.1177/1947601910382774] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Protein modifications, including phosphorylation, ubiquitylation, and SUMOylation, have emerged as essential components of the response to DNA double-strand breaks (DSBs). Mutations within the genes encoding effectors of these components lead to genomic instability and in selected cases, human radiosensitivity and cancer susceptibility syndromes. In this review, we highlight recent advances in the study of DSB-associated signaling events by ubiquitylation and SUMOylation and discuss how coordination among protein modification systems integrates components of the DNA damage response into a network that regulates DNA repair and transcriptional processes on contiguous stretches of chromatin.
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73
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74
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Greenberg RA. Histone tails: Directing the chromatin response to DNA damage. FEBS Lett 2011; 585:2883-90. [PMID: 21621538 DOI: 10.1016/j.febslet.2011.05.037] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 05/13/2011] [Accepted: 05/13/2011] [Indexed: 01/09/2023]
Abstract
Considerable energetic investment is devoted to altering large stretches of chromatin adjacent to DNA double strand breaks (DSBs). Immediately ensuing DSB formation, a myriad of histone modifications are elicited to create a platform for inducible and modular assembly of DNA repair protein complexes in the vicinity of the DNA lesion. This complex signaling network is critical to repair DNA damage and communicate with cellular processes that occur in cis and in trans to the genomic lesion. Failure to properly execute DNA damage inducible chromatin changes is associated with developmental abnormalities, immunodeficiency, and malignancy in humans and in genetically engineered mouse models. This review will discuss current knowledge of DNA damage responsive histone changes that occur in mammalian cells, highlighting their involvement in the maintenance of genome integrity.
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Coleman KA, Greenberg RA. The BRCA1-RAP80 complex regulates DNA repair mechanism utilization by restricting end resection. J Biol Chem 2011; 286:13669-80. [PMID: 21335604 DOI: 10.1074/jbc.m110.213728] [Citation(s) in RCA: 173] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The tumor suppressor protein BRCA1 is a constituent of several different protein complexes and is required for homology-directed repair (HDR) of DNA double strand breaks (DSBs). The most recently discovered BRCA1-RAP80 complex is recruited to ubiquitin structures on chromatin surrounding the break. Deficiency of any member of this complex confers hypersensitivity to DNA-damaging agents by undefined mechanisms. In striking contrast to other BRCA1-containing complexes that are known to promote HDR, we demonstrate that the BRCA1-RAP80 complex restricts end resection in S/G(2) phase of the cell cycle, thereby limiting HDR. RAP80 or BRCC36 deficiency resulted in elevated Mre11-CtIP-dependent 5' end resection with a concomitant increase in HDR mechanisms that rely on 3' single-stranded overhangs. We propose a model in which the BRCA1-RAP80 complex limits nuclease accessibility to DSBs, thus preventing excessive end resection and potentially deleterious homology-directed DSB repair mechanisms that can impair genome integrity.
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