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Mirman Z, Sasi NK, King A, Chapman JR, de Lange T. 53BP1-shieldin-dependent DSB processing in BRCA1-deficient cells requires CST-Polα-primase fill-in synthesis. Nat Cell Biol 2022; 24:51-61. [PMID: 35027730 PMCID: PMC8849574 DOI: 10.1038/s41556-021-00812-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Accepted: 11/09/2021] [Indexed: 12/19/2022]
Abstract
The efficacy of poly(ADP)-ribose polymerase 1 inhibition (PARPi) in BRCA1-deficient cells depends on 53BP1 and shieldin, which have been proposed to limit single-stranded DNA at double-strand breaks (DSBs) by blocking resection and/or through CST-Polα-primase-mediated fill-in. We show that primase (like 53BP1-shieldin and CST-Polα) promotes radial chromosome formation in PARPi-treated BRCA1-deficient cells and demonstrate shieldin-CST-Polα-primase-dependent incorporation of BrdU at DSBs. In the absence of 53BP1 or shieldin, radial formation in BRCA1-deficient cells was restored by the tethering of CST near DSBs, arguing that in this context, shieldin acts primarily by recruiting CST. Furthermore, a SHLD1 mutant defective in CST binding (SHLD1Δ) was non-functional in BRCA1-deficient cells and its function was restored after reconnecting SHLD1Δ to CST. Interestingly, at dysfunctional telomeres and at DNA breaks in class switch recombination where CST has been implicated, SHLD1Δ was fully functional, perhaps because these DNA ends carry CST recognition sites that afford SHLD1-independent binding of CST. These data establish that in BRCA1-deficient cells, CST-Polα-primase is the major effector of shieldin-dependent DSB processing.
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Affiliation(s)
- Zachary Mirman
- Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY, USA
| | - Nanda Kumar Sasi
- Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY, USA
| | - Ashleigh King
- Medical Research Council (MRC) Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - J Ross Chapman
- Medical Research Council (MRC) Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY, USA.
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2
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Krais JJ, Wang Y, Bernhardy AJ, Clausen E, Miller JA, Cai KQ, Scott CL, Johnson N. RNF168-Mediated Ubiquitin Signaling Inhibits the Viability of BRCA1-Null Cancers. Cancer Res 2020; 80:2848-2860. [PMID: 32213544 PMCID: PMC7335334 DOI: 10.1158/0008-5472.can-19-3033] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 02/10/2020] [Accepted: 03/11/2020] [Indexed: 11/16/2022]
Abstract
BRCA1 gene mutations impair homologous recombination (HR) DNA repair, resulting in cellular senescence and embryonic lethality in mice. Therefore, BRCA1-deficient cancers require adaptations that prevent excessive genomic alterations from triggering cell death. RNF168-mediated ubiquitination of γH2AX at K13/15 (ub-H2AX) serves as a recruitment module for the localization of 53BP1 to DNA break sites. Here, we found multiple BRCA1-mutant cancer cell lines and primary tumors with low levels of RNF168 protein expression. Overexpression of ectopic RNF168 or a ub-H2AX fusion protein induced cell death and delayed BRCA1-mutant tumor formation. Cell death resulted from the recruitment of 53BP1 to DNA break sites and inhibition of DNA end resection. Strikingly, reintroduction of BRCA1 or 53BP1 depletion restored HR and rescued the ability of cells to maintain RNF168 and ub-H2AX overexpression. Thus, downregulation of RNF168 protein expression is a mechanism for providing BRCA1-null cancer cell lines with a residual level of HR that is essential for viability. Overall, our work identifies loss of RNF168 ubiquitin signaling as a proteomic alteration that supports BRCA1-mutant carcinogenesis. We propose that restoring RNF168-ub-H2AX signaling, potentially through inhibition of deubiquitinases, could represent a new therapeutic approach. SIGNIFICANCE: This study explores the concept that homologous recombination DNA repair is not an all-or-nothing concept, but a spectrum, and that where a tumor stands on this spectrum may have therapeutic relevance.See related commentary by Wang and Wulf, p. 2720.
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Affiliation(s)
- John J Krais
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Yifan Wang
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Andrea J Bernhardy
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Emma Clausen
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Jessica A Miller
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Kathy Q Cai
- Histopathology Facility, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Clare L Scott
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Neil Johnson
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania.
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3
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Abstract
The spatial and temporal organization of the genome has emerged as an additional level of regulation of nuclear functions. Structural proteins associated with the nuclear envelope play important roles in the organization of the genome. The nuclear lamina, a polymeric meshwork formed by lamins (A- and B-type) and lamin-associated proteins, is viewed as a scaffold for tethering chromatin and protein complexes regulating a variety of nuclear functions. Alterations in lamins function impact DNA transactions such as transcription, replication, and repair, as well as epigenetic modifications that change chromatin structure. These data, and the association of defective lamins with a whole variety of degenerative disorders, premature aging syndromes, and cancer, provide evidence for these proteins operating as caretakers of the genome. In this chapter, we summarize current knowledge about the function of lamins in the maintenance of genome integrity, with special emphasis on the role of A-type lamins in the maintenance of telomere homeostasis and mechanisms of DNA damage repair. These findings have begun to shed some light onto molecular mechanisms by which alterations in A-type lamins induce genomic instability and contribute to the pathophysiology of aging and aging-related diseases, especially cancer.
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Affiliation(s)
- Susana Gonzalo
- Department of Biochemistry and Molecular Biology, St Louis University School of Medicine, 1100 S Grand Ave, St. Louis, MO, 63104, USA,
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4
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Okumura K, Kinashi Y, Kubota Y, Kitajima E, Okayasu R, Ono K, Takahashi S. Relative biological effects of neutron mixed-beam irradiation for boron neutron capture therapy on cell survival and DNA double-strand breaks in cultured mammalian cells. J Radiat Res 2013; 54:70-75. [PMID: 22966174 PMCID: PMC3534280 DOI: 10.1093/jrr/rrs079] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2012] [Revised: 07/27/2012] [Accepted: 08/03/2012] [Indexed: 06/01/2023]
Abstract
Understanding the biological effects of neutron mixed-beam irradiation used for boron neutron capture therapy (BNCT) is important in order to improve the efficacy of the therapy and to reduce side effects. In the present study, cell viability and DNA double-strand breaks (DNA-DSBs) were examined in Chinese hamster ovary cells (CHO-K1) and their radiosensitive mutant cells (xrs5, Ku80-deficient), following neutron mixed-beam irradiation for BNCT. Cell viability was significantly impaired in the neutron irradiation groups compared to the reference gamma-ray irradiation group. The relative biological effectiveness for 10% cell survival was 3.3 and 1.2 for CHO-K1 and xrs5 cells, respectively. There were a similar number of 53BP1 foci, indicators of DNA-DSBs, in the neutron mixed-beam and the gamma-ray groups. In addition, the size of the foci did not differ between groups. However, neutron mixed-beam irradiation resulted in foci with different spatial distributions. The foci were more proximal to each other in the neutron mixed-beam groups than the gamma-ray irradiation groups. These findings suggest that neutron beams may induce another type of DNA damage, such as clustered DNA-DSBs, as has been indicated for other high-LET irradiation.
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Affiliation(s)
- Kakuji Okumura
- Research Reactor Institute, Kyoto University, Kumatori-cho, Sennann-gun, Osaka 590-0494, Japan
| | - Yuko Kinashi
- Research Reactor Institute, Kyoto University, Kumatori-cho, Sennann-gun, Osaka 590-0494, Japan
| | | | | | | | - Koji Ono
- Research Reactor Institute, Kyoto University, Kumatori-cho, Sennann-gun, Osaka 590-0494, Japan
| | - Sentaro Takahashi
- Research Reactor Institute, Kyoto University, Kumatori-cho, Sennann-gun, Osaka 590-0494, Japan
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5
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Oplustilova L, Wolanin K, Mistrik M, Korinkova G, Simkova D, Bouchal J, Lenobel R, Bartkova J, Lau A, O’Connor MJ, Lukas J, Bartek J. Evaluation of candidate biomarkers to predict cancer cell sensitivity or resistance to PARP-1 inhibitor treatment. Cell Cycle 2012; 11:3837-50. [PMID: 22983061 PMCID: PMC3495826 DOI: 10.4161/cc.22026] [Citation(s) in RCA: 123] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Impaired DNA damage response pathways may create vulnerabilities of cancer cells that can be exploited therapeutically. One such selective vulnerability is the sensitivity of BRCA1- or BRCA2-defective tumors (hence defective in DNA repair by homologous recombination, HR) to inhibitors of the poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme critical for repair pathways alternative to HR. While promising, treatment with PARP-1 inhibitors (PARP-1i) faces some hurdles, including (1) acquired resistance, (2) search for other sensitizing, non-BRCA1/2 cancer defects and (3) lack of biomarkers to predict response to PARP-1i. Here we addressed these issues using PARP-1i on 20 human cell lines from carcinomas of the breast, prostate, colon, pancreas and ovary. Aberrations of the Mre11-Rad50-Nbs1 (MRN) complex sensitized cancer cells to PARP-1i, while p53 status was less predictive, even in response to PARP-1i combinations with camptothecin or ionizing radiation. Furthermore, monitoring PARsylation and Rad51 foci formation as surrogate markers for PARP activity and HR, respectively, supported their candidacy for biomarkers of PARP-1i responses. As to resistance mechanisms, we confirmed the role of the multidrug resistance efflux transporters and its reversibility. More importantly, we demonstrated that shRNA lentivirus-mediated depletion of 53BP1 in human BRCA1-mutant breast cancer cells increased their resistance to PARP-1i. Given the preferential loss of 53BP1 in BRCA-defective and triple-negative breast carcinomas, our findings warrant assessment of 53BP1 among candidate predictive biomarkers of response to PARPi. Overall, this study helps characterize genetic and functional determinants of cellular responses to PARP-1i and contributes to the search for biomarkers to exploit PARP inhibitors in cancer therapy.
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Affiliation(s)
- Lenka Oplustilova
- Danish Cancer Society Research Center; Copenhagen, Denmark
- AstraZeneca; iMed Oncology; Macclesfield, Cheshire, UK
| | - Kamila Wolanin
- Danish Cancer Society Research Center; Copenhagen, Denmark
| | - Martin Mistrik
- Institute of Molecular and Translational Medicine; Faculty of Medicine and Dentistry; Palacky University; Olomouc, Czech Republic
| | - Gabriela Korinkova
- Institute of Molecular and Translational Medicine; Faculty of Medicine and Dentistry; Palacky University; Olomouc, Czech Republic
| | - Dana Simkova
- Institute of Molecular and Translational Medicine; Faculty of Medicine and Dentistry; Palacky University; Olomouc, Czech Republic
| | - Jan Bouchal
- Institute of Molecular and Translational Medicine; Faculty of Medicine and Dentistry; Palacky University; Olomouc, Czech Republic
| | - Rene Lenobel
- Laboratory of Growth Regulators; Palacky University Olomouc; Olomouc, Czech Republic
| | | | - Alan Lau
- AstraZeneca; iMed Oncology; Macclesfield, Cheshire, UK
| | | | - Jiri Lukas
- Danish Cancer Society Research Center; Copenhagen, Denmark
- Novo Nordisk Foundation Center for Protein Research; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen, Denmark
| | - Jiri Bartek
- Danish Cancer Society Research Center; Copenhagen, Denmark
- Institute of Molecular and Translational Medicine; Faculty of Medicine and Dentistry; Palacky University; Olomouc, Czech Republic
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Chapman JR, Sossick AJ, Boulton SJ, Jackson SP. BRCA1-associated exclusion of 53BP1 from DNA damage sites underlies temporal control of DNA repair. J Cell Sci 2012; 125:3529-34. [PMID: 22553214 PMCID: PMC3445322 DOI: 10.1242/jcs.105353] [Citation(s) in RCA: 242] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2012] [Indexed: 12/18/2022] Open
Abstract
Following irradiation, numerous DNA-damage-responsive proteins rapidly redistribute into microscopically visible subnuclear aggregates, termed ionising-radiation-induced foci (IRIF). How the enrichment of proteins on damaged chromatin actually relates to DNA repair remains unclear. Here, we use super-resolution microscopy to examine the spatial distribution of BRCA1 and 53BP1 proteins within single IRIF at subdiffraction-limit resolution, yielding an unprecedented increase in detail that was not previously apparent by conventional microscopy. Consistent with a role for 53BP1 in promoting DNA double-strand break repair by non-homologous end joining, 53BP1 enrichment in IRIF is most prominent in the G0/G1 cell cycle phases, where it is enriched in dense globular structures. By contrast, as cells transition through S phase, the recruitment of BRCA1 into the core of IRIF is associated with an exclusion of 53BP1 to the focal periphery, leading to an overall reduction of 53BP1 occupancy at DNA damage sites. Our data suggest that the BRCA1-associated IRIF core corresponds to chromatin regions associated with repair by homologous recombination, and the enrichment of BRCA1 in IRIF represents a temporal switch in the DNA repair program. We propose that BRCA1 antagonises 53BP1-dependent DNA repair in S phase by inhibiting its interaction with chromatin proximal to damage sites. Furthermore, the genomic instability exhibited by BRCA1-deficient cells might result from a failure to efficiently exclude 53BP1 from such regions during S phase.
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Affiliation(s)
- J. Ross Chapman
- Wellcome Trust and Cancer Research UK Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms EN6 3LD, UK
| | - Alex J. Sossick
- Wellcome Trust and Cancer Research UK Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK
| | - Simon J. Boulton
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms EN6 3LD, UK
| | - Stephen P. Jackson
- Wellcome Trust and Cancer Research UK Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK
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7
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Lee JH, Goodarzi AA, Jeggo PA, Paull TT. 53BP1 promotes ATM activity through direct interactions with the MRN complex. EMBO J 2010; 29:574-85. [PMID: 20010693 PMCID: PMC2830698 DOI: 10.1038/emboj.2009.372] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Accepted: 11/11/2009] [Indexed: 12/27/2022] Open
Abstract
The Mre11/Rad50/Nbs1 (MRN) complex has a central function in facilitating activation of the ATM protein kinase at sites of DNA double-strand breaks (DSBs). However, several other factors are also required in human cells for efficient signalling through MRN and ATM, including the tumour suppressor proteins p53-binding protein 1 (53BP1) and BRCA1. In this study, we investigate the functions of these mediator proteins in ATM activation and find that the presence of 53BP1 and BRCA1 can amplify the effects of MRN when interactions between MRN and ATM are compromised. This effect is dependent on a direct interaction between MRN and the tandem breast cancer carboxy-terminal (BRCT) repeats in 53BP1, and is accompanied by hyper-phosphorylation of both Nbs1 and 53BP1. We also find that the BRCT domains of 53BP1 affect the overall structure of 53BP1 multimers and that this structure is important for promoting ATM phosphorylation of substrates as well as for the repair of DNA DSBs in mammalian cells.
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Affiliation(s)
- Ji-Hoon Lee
- Howard Hughes Medical Institute and the Department of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX, USA
| | - Aaron A Goodarzi
- The Genome Damage and Stability Centre, University of Sussex, East Sussex, UK
| | - Penny A Jeggo
- The Genome Damage and Stability Centre, University of Sussex, East Sussex, UK
| | - Tanya T Paull
- Howard Hughes Medical Institute and the Department of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX, USA
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8
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Watrin E, Peters JM. The cohesin complex is required for the DNA damage-induced G2/M checkpoint in mammalian cells. EMBO J 2009; 28:2625-35. [PMID: 19629043 PMCID: PMC2738698 DOI: 10.1038/emboj.2009.202] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Accepted: 06/22/2009] [Indexed: 01/05/2023] Open
Abstract
Cohesin complexes mediate sister chromatid cohesion. Cohesin also becomes enriched at DNA double-strand break sites and facilitates recombinational DNA repair. Here, we report that cohesin is essential for the DNA damage-induced G2/M checkpoint. In contrast to cohesin's role in DNA repair, the checkpoint function of cohesin is independent of its ability to mediate cohesion. After RNAi-mediated depletion of cohesin, cells fail to properly activate the checkpoint kinase Chk2 and have defects in recruiting the mediator protein 53BP1 to DNA damage sites. Earlier work has shown that phosphorylation of the cohesin subunits Smc1 and Smc3 is required for the intra-S checkpoint, but Smc1/Smc3 are also subunits of a distinct recombination complex, RC-1. It was, therefore, unknown whether Smc1/Smc3 function in the intra-S checkpoint as part of cohesin. We show that Smc1/Smc3 are phosphorylated as part of cohesin and that cohesin is required for the intra-S checkpoint. We propose that accumulation of cohesin at DNA break sites is not only needed to mediate DNA repair, but also facilitates the recruitment of checkpoint proteins, which activate the intra-S and G2/M checkpoints.
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Affiliation(s)
- Erwan Watrin
- Research Institute of Molecular Pathology (I.M.P.), Vienna, Austria
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9
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Abstract
The product of the Nijmegen breakage syndrome gene (NBS1) plays crucial roles in DNA damage response through its association with many proteins, including MRE11 and RAD50. However, it remains to be determined exactly how NBS1 accumulates at or near DNA double-strand breaks. Here we report that MDC1 directly binds to NBS1 and targets NBS1 to the sites of DNA damage. The MDC1-NBS1 interaction occurs through a specific region (residues 200-420) of MDC1, which contains multiple consensus casein kinase 2 (CK2) phosphorylation sites. In addition, this interaction requires both the forkhead-associated (FHA) and tandem BRCA1 C-terminal (BRCT) domains of NBS1. Disruption of the MDC1-NBS1 interaction results in failure of NBS1 accumulation at DNA double-strand breaks and impairment of intra-S checkpoint activation. These studies provide important mechanistic insights as to how MDC1 regulates NBS1 and the intra-S-phase checkpoint in response to DNA damage.
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Affiliation(s)
- Liming Wu
- *Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520; and
| | - Kuntian Luo
- Division of Oncology Research, Department of Oncology, Mayo Clinic, Rochester, MN 55905
| | - Zhenkun Lou
- Division of Oncology Research, Department of Oncology, Mayo Clinic, Rochester, MN 55905
| | - Junjie Chen
- *Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520; and
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10
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Silverman J, Takai H, Buonomo SBC, Eisenhaber F, de Lange T. Human Rif1, ortholog of a yeast telomeric protein, is regulated by ATM and 53BP1 and functions in the S-phase checkpoint. Genes Dev 2004; 18:2108-19. [PMID: 15342490 PMCID: PMC515289 DOI: 10.1101/gad.1216004] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2004] [Accepted: 06/21/2004] [Indexed: 01/06/2023]
Abstract
We report on the function of the human ortholog of Saccharomyces cerevisiae Rif1 (Rap1-interacting factor 1). Yeast Rif1 associates with telomeres and regulates their length. In contrast, human Rif1 did not accumulate at functional telomeres, but localized to dysfunctional telomeres and to telomeric DNA clusters in ALT cells, a pattern of telomere association typical of DNA-damage-response factors. After induction of double-strand breaks (DSBs), Rif1 formed foci that colocalized with other DNA-damage-response factors. This response was strictly dependent on ATM (ataxia telangiectasia mutated) and 53BP1, but not affected by diminished function of ATR (ATM- and Rad3-related kinase), BRCA1, Chk2, Nbs1, and Mre11. Rif1 inhibition resulted in radiosensitivity and a defect in the intra-S-phase checkpoint. The S-phase checkpoint phenotype was independent of Nbs1 status, arguing that Rif1 and Nbs1 act in different pathways to inhibit DNA replication after DNA damage. These data reveal that human Rif1 contributes to the ATM-mediated protection against DNA damage and point to a remarkable difference in the primary function of this protein in yeast and mammals.
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Affiliation(s)
- Joshua Silverman
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10021, USA
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11
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Joo WS, Jeffrey PD, Cantor SB, Finnin MS, Livingston DM, Pavletich NP. Structure of the 53BP1 BRCT region bound to p53 and its comparison to the Brca1 BRCT structure. Genes Dev 2002; 16:583-93. [PMID: 11877378 PMCID: PMC155350 DOI: 10.1101/gad.959202] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Brca1 C-terminal (BRCT) domains are a common protein-protein interaction motif in proteins involved in the DNA damage response and DNA repair. The DNA-damage response protein 53BP1 has two BRCT domains that bind to the DNA-binding domain of p53. The 53BP1 tandem-BRCT region is homologous to the tandem-BRCT region of Brca1, which is involved in double-strand break repair and homologous recombination and which binds BACH1, a member of the DEAH helicase family. Here we report the structures of a human 53BP1-p53 complex and of the rat Brca1 BRCT repeats. The 53BP1-p53 structure shows that the two BRCT repeats are arranged tandemly and pack extensively through an interface that also involves the inter-repeat linker. The first BRCT repeat and the linker together bind p53 on a region that overlaps with the DNA-binding surface of p53 and involves p53 residues that are mutated in cancer and are important for DNA binding. Comparison with the structure of the tandem-BRCT region of Brca1 shows a remarkable conservation of the repeat arrangement and of the inter-BRCT repeat interface. Analysis of human BRCA1 tumor-derived mutations and conservation identifies a potential protein-binding site that we show through mutagenesis is involved in BACH1 binding. The BACH1-binding region of Brca1 consists of a unique insertion in the first BRCT repeat and the inter-repeat linker and is analogous to the region of 53BP1 that binds p53.
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Affiliation(s)
- Woo S Joo
- Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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12
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Abstract
The tumor suppressor p53 binding protein 1 (53BP1) binds to the DNA-binding domain of p53 and enhances p53-mediated transcriptional activation. 53BP1 contains two breast cancer susceptibility gene 1 COOH terminus (BRCT) motifs, which are present in several proteins involved in DNA repair and/or DNA damage-signaling pathways. Thus, we investigated the potential role of 53BP1 in DNA damage-signaling pathways. Here, we report that 53BP1 becomes hyperphosphorylated and forms discrete nuclear foci in response to DNA damage. These foci colocalize at all time points with phosphorylated H2AX (gamma-H2AX), which has been previously demonstrated to localize at sites of DNA strand breaks. 53BP1 foci formation is not restricted to gamma-radiation but is also detected in response to UV radiation as well as hydroxyurea, camptothecin, etoposide, and methylmethanesulfonate treatment. Several observations suggest that 53BP1 is regulated by ataxia telangiectasia mutated (ATM) after DNA damage. First, ATM-deficient cells show no 53BP1 hyperphosphorylation and reduced 53BP1 foci formation in response to gamma-radiation compared with cells expressing wild-type ATM. Second, wortmannin treatment strongly inhibits gamma-radiation-induced hyperphosphorylation and foci formation of 53BP1. Third, 53BP1 is readily phosphorylated by ATM in vitro. Taken together, these results suggest that 53BP1 is an ATM substrate that is involved early in the DNA damage-signaling pathways in mammalian cells.
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Affiliation(s)
- Irene Rappold
- Division of Oncology Research, Mayo Clinic, Rochester, Minnesota 55905
| | | | - Takayasu Date
- Department of Biochemistry, Kanazawa Medical University, Ishikawa 920-0293, Japan
| | - Junjie Chen
- Division of Oncology Research, Mayo Clinic, Rochester, Minnesota 55905
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13
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Abstract
p53 binding protein 1 (53BP1), a protein proposed to function as a transcriptional coactivator of the p53 tumor suppressor, has BRCT domains with high homology to the Saccharomyces cerevisiae Rad9p DNA damage checkpoint protein. To examine whether 53BP1 has a role in the cellular response to DNA damage, we probed its intracellular localization by immunofluorescence. In untreated primary cells and U2OS osteosarcoma cells, 53BP1 exhibited diffuse nuclear staining; whereas, within 5-15 min after exposure to ionizing radiation (IR), 53BP1 localized at discreet nuclear foci. We propose that these foci represent sites of processing of DNA double-strand breaks (DSBs), because they were induced by IR and chemicals that cause DSBs, but not by ultraviolet light; their peak number approximated the number of DSBs induced by IR and decreased over time with kinetics that parallel the rate of DNA repair; and they colocalized with IR-induced Mre11/NBS and gamma-H2AX foci, which have been previously shown to localize at sites of DSBs. Formation of 53BP1 foci after irradiation was not dependent on ataxia-telangiectasia mutated (ATM), Nijmegen breakage syndrome (NBS1), or wild-type p53. Thus, the fast kinetics of 53BP1 focus formation after irradiation and the lack of dependency on ATM and NBS1 suggest that 53BP1 functions early in the cellular response to DNA DSBs.
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Affiliation(s)
- Linda B. Schultz
- Department of Molecular Genetics, The Wistar Institute, Philadelphia, Pennsylvania 19104
- Graduate Program in Cell and Molecular Biology, School of Medicine
| | - Nabil H. Chehab
- Department of Molecular Genetics, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - Asra Malikzay
- Department of Molecular Genetics, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - Thanos D. Halazonetis
- Department of Molecular Genetics, The Wistar Institute, Philadelphia, Pennsylvania 19104
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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