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Her J, Zheng H, Bunting SF. RNF4 sustains Myc-driven tumorigenesis by facilitating DNA replication. J Clin Invest 2024:e167419. [PMID: 38530355 DOI: 10.1172/jci167419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/27/2024] Open
Abstract
The mammalian SUMO-targeted E3 Ubiquitin Ligase, Rnf4, has been reported to act as a regulator of DNA repair, but the importance of RNF4 as a tumor suppressor has not been tested. Using a conditional-knockout mouse model, we deleted Rnf4 in the B cell lineage to test the importance of RNF4 for growth of somatic cells. Although Rnf4 conditional-knockout B cells exhibited substantial genomic instability, Rnf4 deletion caused no increase in tumor susceptibility. In contrast, Rnf4 deletion extended the healthy lifespan of mice expressing an oncogenic c-myc transgene. Rnf4 activity is essential for normal DNA replication, and in its absence, there was a failure in ATR-CHK1 signaling of replication stress. Factors that normally mediate replication fork stability, including members of the Fanconi Anemia gene family and the helicases, PIF1 and RECQL5, showed reduced accumulation at replication forks in the absence of RNF4. RNF4 deficiency also resulted in an accumulation of hyper-SUMOylated proteins in chromatin, including members of the SMC5/6 complex, which contributes to replication failure by a mechanism dependent on RAD51. These findings indicate that RNF4, which shows increased expression in multiple human tumor types, is a potential target for anti-cancer therapy, especially in tumors expressing c-myc.
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Affiliation(s)
- Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, United States of America
| | - Haiyan Zheng
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, United States of America
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, United States of America
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2
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Foo TK, Vincelli G, Huselid E, Her J, Zheng H, Simhadri S, Wang M, Huo Y, Li T, Yu X, Li H, Zhao W, Bunting SF, Xia B. ATR/ATM-mediated phosphorylation of BRCA1 T1394 promotes homologous recombinational repair and G2/M checkpoint maintenance. Cancer Res 2021; 81:4676-4684. [PMID: 34301763 PMCID: PMC8448966 DOI: 10.1158/0008-5472.can-20-2723] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Revised: 06/22/2021] [Accepted: 07/22/2021] [Indexed: 11/16/2022]
Abstract
BRCA1 maintains genome integrity and suppresses tumorigenesis by promoting homologous recombination (HR)-mediated repair of DNA double strand breaks (DSB) and DNA damage-induced cell cycle checkpoints. Phosphorylation of BRCA1 by ATM, ATR, CHK2, CDK, and PLK1 kinases has been reported to regulate its functions. Here we show that ATR and ATM-mediated phosphorylation of BRCA1 on T1394, a highly conserved but functionally uncharacterized site, is a key modification for its function in the DNA damage response. Following DNA damage, T1394 phosphorylation ensured faithful repair of DSBs by promoting HR and preventing single strand annealing, a deletion-generating repair process. BRCA1 T1394 phosphorylation further safeguarded chromosomal integrity by maintaining the G2/M checkpoint. Moreover, multiple patient-derived BRCA1 variants of unknown significance were shown to affect T1394 phosphorylation. These results establish an important regulatory mechanism of BRCA1 function in the DNA damage response and may have implications in the development or prognosis of BRCA1-associated cancers.
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Affiliation(s)
- Tzeh K Foo
- Radiation Oncology, Rutgers Cancer Institute of New Jersey
| | | | - Eric Huselid
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey
| | - Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey
| | | | | | - Meiling Wang
- The University of Texas Health Science Center at San Antonio
| | - Yanying Huo
- Radiation Oncology, Rutgers Cancer Institute of New Jersey
| | - Tao Li
- Department of Medicine/Population Sciences, Rutgers Cancer Institute of New Jersey
| | | | - Hong Li
- Center for advanced proteomics, Rutgers, The State University of New Jersey
| | - Weixing Zhao
- Department of Biochemistry and Structural Biology, The University of Texas Health Science Center at San Antonio
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey
| | - Bing Xia
- Radiation Oncology, Rutgers Cancer Institute of New Jersey
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3
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Her J, Bunting SF. BRCA1 and PALB2 in a Messy Breakup. Cancer Res 2020; 80:4044-4045. [PMID: 33008804 DOI: 10.1158/0008-5472.can-20-2731] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 08/11/2020] [Indexed: 11/16/2022]
Abstract
Mutations in the BRCA1 gene cause an extremely high lifetime risk of breast and ovarian cancer, but the exact mechanism by which the BRCA1 protein acts to prevent cancer onset remains unclear. In this edition of Cancer Research, Park and colleagues describe a new mouse model featuring a single amino acid substitution in the coiled-coil motif of BRCA1. This change prevents BRCA1 from interacting with PALB2 (partner and localizer of BRCA2), causing rapid cancer onset and a loss of blood cells similar to Fanconi anemia.See related article by Park et al., p. 4172.
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Affiliation(s)
- Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey.
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4
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Abstract
Homologous recombination is essential for DNA repair, replication and the exchange of genetic material between parental chromosomes during meiosis. The stages of recombination involve complex reorganization of DNA structures, and the successful completion of these steps is dependent on the activities of multiple helicase enzymes. Helicases of many different families coordinate the processing of broken DNA ends, and the subsequent formation and disassembly of the recombination intermediates that are necessary for template-based DNA repair. Loss of recombination-associated helicase activities can therefore lead to genomic instability, cell death and increased risk of tumor formation. The efficiency of recombination is also influenced by the ‘anti-recombinase’ effect of certain helicases, which can direct DNA breaks toward repair by other pathways. Other helicases regulate the crossover versus non-crossover outcomes of repair. The use of recombination is increased when replication forks and the transcription machinery collide, or encounter lesions in the DNA template. Successful completion of recombination in these situations is also regulated by helicases, allowing normal cell growth, and the maintenance of genomic integrity.
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5
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Sciascia N, Wu W, Zong D, Sun Y, Wong N, John S, Wangsa D, Ried T, Bunting SF, Pommier Y, Nussenzweig A. Suppressing proteasome mediated processing of topoisomerase II DNA-protein complexes preserves genome integrity. eLife 2020; 9:e53447. [PMID: 32057297 PMCID: PMC7089766 DOI: 10.7554/elife.53447] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [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: 11/08/2019] [Accepted: 02/12/2020] [Indexed: 12/19/2022] Open
Abstract
Topoisomerase II (TOP2) relieves topological stress in DNA by introducing double-strand breaks (DSBs) via a transient, covalently linked TOP2 DNA-protein intermediate, termed TOP2 cleavage complex (TOP2cc). TOP2ccs are normally rapidly reversible, but can be stabilized by TOP2 poisons, such as the chemotherapeutic agent etoposide (ETO). TOP2 poisons have shown significant variability in their therapeutic effectiveness across different cancers for reasons that remain to be determined. One potential explanation for the differential cellular response to these drugs is in the manner by which cells process TOP2ccs. Cells are thought to remove TOP2ccs primarily by proteolytic degradation followed by DNA DSB repair. Here, we show that proteasome-mediated repair of TOP2cc is highly error-prone. Pre-treating primary splenic mouse B-cells with proteasome inhibitors prevented the proteolytic processing of trapped TOP2ccs, suppressed the DNA damage response (DDR) and completely protected cells from ETO-induced genome instability, thereby preserving cellular viability. When degradation of TOP2cc was suppressed, the TOP2 enzyme uncoupled itself from the DNA following ETO washout, in an error-free manner. This suggests a potential mechanism of developing resistance to topoisomerase poisons by ensuring rapid TOP2cc reversal.
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Affiliation(s)
- Nicholas Sciascia
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
- Institute for Biomedical Sciences, George Washington UniversityWashingtonUnited States
| | - Wei Wu
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
| | - Dali Zong
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
| | - Yilun Sun
- Developmental Therapeutics Branch, National Institutes of HealthBethesdaUnited States
| | - Nancy Wong
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
| | - Sam John
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
| | - Darawalee Wangsa
- Genetics Branch National Cancer Institute, National Institutes of HealthBethesdaUnited States
| | - Thomas Ried
- Genetics Branch National Cancer Institute, National Institutes of HealthBethesdaUnited States
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers UniversityPiscatawayUnited States
| | - Yves Pommier
- Developmental Therapeutics Branch, National Institutes of HealthBethesdaUnited States
| | - André Nussenzweig
- Laboratory of Genome Integrity, National Institutes of HealthBethesdaUnited States
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6
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Gonzalez-Rodriguez Y, Bunting SF. XLF extends its range from DNA repair to replication. J Cell Biol 2019; 218:2075-2076. [PMID: 31189608 PMCID: PMC6605802 DOI: 10.1083/jcb.201905221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Gonzalez-Rodriguez and Bunting preview work from the Sleckman laboratory describing a new function for the repair protein XLF in the protection of DNA replication fork stability. The close interplay between DNA replication and repair is underscored by a report from Chen et al. (2019. J. Cell Biol.https://doi.org/10.1083/jcb.201808134) in this issue. The authors demonstrate that the non-homologous end-joining factor XLF promotes the stability of replication forks.
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Affiliation(s)
- Yanira Gonzalez-Rodriguez
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
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7
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Song F, Li M, Liu G, Swapna GVT, Daigham NS, Xia B, Montelione GT, Bunting SF. Antiparallel Coiled-Coil Interactions Mediate the Homodimerization of the DNA Damage-Repair Protein PALB2. Biochemistry 2018; 57:6581-6591. [PMID: 30289697 DOI: 10.1021/acs.biochem.8b00789] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Deficits in DNA damage-repair pathways are the root cause of several human cancers. In mammalian cells, DNA double-strand break repair is carried out by multiple mechanisms, including homologous recombination (HR). The partner and localizer of BRCA2 (PALB2), which is an essential factor for HR, binds to the breast cancer susceptibility 1 (BRCA1) protein at DNA double-strand breaks. At the break site, PALB2 also associates with the breast cancer susceptibility 2 (BRCA2) protein to form a multiprotein complex that facilitates HR. The BRCA1-PALB2 interaction is mediated by association of predicted helical coiled-coil regions in both proteins. PALB2 can also homodimerize through the formation of a coiled coil by the self-association of helical elements at the N-terminus of the PALB2 protein, and this homodimerization has been proposed to regulate the efficiency of HR. We have produced a segment of PALB2, designated PALB2cc (PALB2 coiled coil segment) that forms α-helical structures, which assemble into stable homodimers. PALB2cc also forms heterodimers with a helical segment of BRCA1, called BRCA1cc (BRCA1 coiled coil segment). The three-dimensional structure of the homodimer formed by PALB2cc was determined by solution NMR spectroscopy. This PALB2cc homodimer is a classical antiparallel coiled-coil leucine zipper. NMR chemical-shift perturbation studies were used to study dimer formation for both the PALB2cc homodimer and the PALB2cc/BRCA1cc heterodimer. The mutation of residue Leu24 of PALB2cc significantly reduces its homodimer stability, but has a more modest effect on the stability of the heterodimer formed between PALB2cc and BRCA1cc. We show that mutation of Leu24 leads to genomic instability and reduced cell viability after treatment with agents that induce DNA double-strand breaks. These studies may allow the identification of distinct mutations of PALB2cc that selectively disrupt homodimeric versus heterodimeric interactions, and reveal the specific role of PALB2cc homodimerization in HR.
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Affiliation(s)
| | | | | | | | | | - Bing Xia
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers , The State University of New Jersey , New Brunswick , New Jersey 08901 , United States
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Simhadri S, Vincelli G, Huo Y, Misenko S, Foo TK, Ahlskog J, Sørensen CS, Oakley GG, Ganesan S, Bunting SF, Xia B. PALB2 connects BRCA1 and BRCA2 in the G2/M checkpoint response. Oncogene 2018; 38:1585-1596. [PMID: 30337689 PMCID: PMC6408219 DOI: 10.1038/s41388-018-0535-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Revised: 08/13/2018] [Accepted: 09/21/2018] [Indexed: 01/07/2023]
Abstract
The G2/M checkpoint inhibits mitotic entry upon DNA damage thereby preventing segregation of broken chromosomes and preserving genome stability. The tumor suppressor proteins BRCA1, PALB2 and BRCA2 constitute a BRCA1-PALB2-BRCA2 axis that is essential for homologous recombination (HR)-based DNA double strand break repair. Besides HR, BRCA1 has been implicated in both the initial activation and the maintenance of the G2/M checkpoint, while BRCA2 and PALB2 have been shown to be critical for its maintenance. Here we show that all 3 proteins can play a significant role in both checkpoint activation and checkpoint maintenance, depending on cell type and context, and that PALB2 links BRCA1 and BRCA2 in checkpoint response. The BRCA1-PALB2 interaction can be important for checkpoint activation, whereas the PALB2-BRCA2 complex formation appears to be more critical for checkpoint maintenance. Interestingly, the function of PALB2 in checkpoint response appears to be independent of CHK1 and CHK2 phosphorylation. Following ionizing radiation, cells with disengaged BRCA1-PALB2 interaction show greatly increased chromosomal abnormalities due apparently to combined defects in HR and checkpoint control. These findings provide new insights into DNA damage checkpoint control and further underscore the critical importance of the proper cooperation of the BRCA and PALB2 proteins in genome maintenance.
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Affiliation(s)
- Srilatha Simhadri
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA.,Department of Radiation Oncology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA.,Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA
| | - Gabriele Vincelli
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA.,Department of Radiation Oncology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA
| | - Yanying Huo
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA.,Department of Radiation Oncology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA
| | - Sarah Misenko
- Department of Molecular Biology and Biochemistry, School of Arts and Sciences, Rutgers, The State University of New Jersey, Piscataway, NJ, 08854, USA
| | - Tzeh Keong Foo
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA.,Department of Radiation Oncology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA
| | - Johanna Ahlskog
- Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Copenhagen, Denmark
| | - Claus S Sørensen
- Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Copenhagen, Denmark
| | - Gregory G Oakley
- Department of Oral Biology, College of Dentistry, University of Nebraska Medical Center, Lincoln, NE, 68583, USA
| | - Shridar Ganesan
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA.,Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, School of Arts and Sciences, Rutgers, The State University of New Jersey, Piscataway, NJ, 08854, USA
| | - Bing Xia
- Rutgers Cancer Institute of New Jersey, New Brunswick, USA. .,Department of Radiation Oncology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, 08903, USA.
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9
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Khan AJ, Misenko SM, Thandoni A, Schiff D, Jhawar SR, Bunting SF, Haffty BG. VX-984 is a selective inhibitor of non-homologous end joining, with possible preferential activity in transformed cells. Oncotarget 2018; 9:25833-25841. [PMID: 29899825 PMCID: PMC5995231 DOI: 10.18632/oncotarget.25383] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Accepted: 04/25/2018] [Indexed: 12/17/2022] Open
Abstract
PURPOSE DNA double-strand breaks (DSBs) can be repaired by non-homologous end joining (NHEJ) or homologous recombination (HR). We demonstrate the selectivity of VX-984, a DNA-PK inhibitor, using assays not previously reported. EXPERIMENTAL DESIGN The class switch recombination assay (CSR) in primary B cells was used to measure efficiency of NHEJ. A cellular reporter assay (U2OS EJ-DR) was used to assess the efficiency of HR and NHEJ in cells treated with VX-984. Immunofluorescence assays (IF) evaluated γ-H2AX foci for DSB repair kinetics in human astrocytes and T98G glioma cells. Western blotting was used to evaluate phosphorylation of DNA-PKcs substrates. RESULTS We found a dose-dependent reduction in CSR efficiency with VX-984, and through the EJ-DR assay, dramatic dose-dependent increases in HR and mNHEJ. Immunofluorescence assays showed an inability of malignant cells to resolve γ-H2AX foci in the presence of VX-984. Radiation-induced phosphorylation of DNA-PK substrates was further reduced by treatment with VX-984. CONCLUSIONS VX-984 efficiently inhibits NHEJ, resulting in compensatory increases in alternative repair pathways, increases DSBs, and appears to affect transformed cells preferentially.
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Affiliation(s)
- Atif J. Khan
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY 10011, USA
- Department of Radiation Oncology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Sarah M. Misenko
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
| | - Aditya Thandoni
- Department of Radiation Oncology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Devora Schiff
- Department of Radiation Oncology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Sachin R. Jhawar
- Department of Radiation Oncology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Samuel F. Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
| | - Bruce G. Haffty
- Department of Radiation Oncology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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10
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Misenko SM, Patel DS, Her J, Bunting SF. DNA repair and cell cycle checkpoint defects in a mouse model of 'BRCAness' are partially rescued by 53BP1 deletion. Cell Cycle 2018; 17:881-891. [PMID: 29620483 PMCID: PMC6056228 DOI: 10.1080/15384101.2018.1456295] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [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] [Received: 11/29/2017] [Revised: 04/13/2018] [Accepted: 03/17/2018] [Indexed: 10/17/2022] Open
Abstract
'BRCAness' is a term used to describe cancer cells that behave similarly to tumors with BRCA1 or BRCA2 mutations. The BRCAness phenotype is associated with hypersensitivity to chemotherapy agents including PARP inhibitors, which are a promising class of recently-licensed anti-cancer treatments. This hypersensitivity arises because of a deficiency in the homologous recombination (HR) pathway for DNA double-strand break repair. To gain further insight into how genetic modifiers of HR contribute to the BRCAness phenotype, we created a new mouse model of BRCAness by generating mice that are deficient in BLM helicase and the Exo1 exonuclease, which are involved in the early stages of HR. We find that cells lacking BLM and Exo1 exhibit a BRCAness phenotype, with diminished HR, and hypersensitivity to PARP inhibitors. We further tested how 53BP1, an important regulator of HR, affects repair efficiency in our BRCAness model. We find that deletion of 53BP1 can relieve several of the repair deficiencies observed in cells lacking BLM and Exo1, just as it does in cells lacking BRCA1. These results substantiate the importance of BRCAness as a concept for classification of cancer cases, and further clarify the role of 53BP1 in regulation of DNA repair pathway choice in mammalian cells.
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Affiliation(s)
- Sarah M. Misenko
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Dharm S. Patel
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Samuel F. Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
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11
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Abstract
DNA double-strand breaks (DSBs) arise regularly in cells and when left unrepaired cause senescence or cell death. Homologous recombination (HR) and nonhomologous end-joining (NHEJ) are the two major DNA-repair pathways. Whereas HR allows faithful DSB repair and healthy cell growth, NHEJ has higher potential to contribute to mutations and malignancy. Many regulatory mechanisms influence which of these two pathways is used in DSB repair. These mechanisms depend on the cell cycle, post-translational modifications, and chromatin effects. Here, we summarize current research into these mechanisms, with a focus on mammalian cells, and also discuss repair by "alternative end-joining" and single-strand annealing.
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Affiliation(s)
- Joonyoung Her
- From the Department of Molecular Biology and Biochemistry, Rutgers, State University of New Jersey, Piscataway, New Jersey 08540
| | - Samuel F Bunting
- From the Department of Molecular Biology and Biochemistry, Rutgers, State University of New Jersey, Piscataway, New Jersey 08540
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12
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Affiliation(s)
- Joonyoung Her
- a Department of Molecular Biology and Biochemistry , Rutgers, The State University of New Jersey , Piscataway , NJ 08854 , USA
| | - Chandni Ray
- a Department of Molecular Biology and Biochemistry , Rutgers, The State University of New Jersey , Piscataway , NJ 08854 , USA
| | - Samuel F Bunting
- a Department of Molecular Biology and Biochemistry , Rutgers, The State University of New Jersey , Piscataway , NJ 08854 , USA
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13
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Patel DS, Misenko SM, Her J, Bunting SF. BLM helicase regulates DNA repair by counteracting RAD51 loading at DNA double-strand break sites. J Cell Biol 2017; 216:3521-3534. [PMID: 28912125 PMCID: PMC5674892 DOI: 10.1083/jcb.201703144] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 06/28/2017] [Accepted: 08/04/2017] [Indexed: 11/22/2022] Open
Abstract
The BLM gene product, BLM, is a RECQ helicase that is involved in DNA replication and repair of DNA double-strand breaks by the homologous recombination (HR) pathway. During HR, BLM has both pro- and anti-recombinogenic activities, either of which may contribute to maintenance of genomic integrity. We find that in cells expressing a mutant version of BRCA1, an essential HR factor, ablation of BLM rescues genomic integrity and cell survival in the presence of DNA double-strand breaks. Improved genomic integrity in these cells is linked to a substantial increase in the stability of RAD51 at DNA double-strand break sites and in the overall efficiency of HR. Ablation of BLM also rescues RAD51 foci and HR in cells lacking BRCA2 or XRCC2. These results indicate that the anti-recombinase activity of BLM is of general importance for normal retention of RAD51 at DNA break sites and regulation of HR.
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Affiliation(s)
- Dharm S Patel
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
| | - Sarah M Misenko
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
| | - Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
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14
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Patel DS, Misenko SM, Bunting SF. Abstract 2477: Genomic instability in BRCA1-deficient cells is a result of the anti-recombinogenic activity of BLM helicase. Cancer Res 2017. [DOI: 10.1158/1538-7445.am2017-2477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Mutations in BRCA1 are responsible for approximately 5% of cases of breast cancer, and there are few treatment options that substantially alter the probability of disease onset in individuals with BRCA1 mutations. BRCA1-deficient cells exhibit increased genomic instability following DNA damaging treatments due to a defect in the homologous recombination (HR) DNA repair pathway. Presently, Olaparib, a PARP inhibitor, is approved as a targeted monotherapy for germline BRCA1 mutated advanced ovarian cancers. As use of this treatment has expanded, data suggests that patients exhibit a further relapse and resistance to PARP inhibitors via mechanisms that include the development of secondary BRCA1 reversion mutations, enhanced drug efflux relating to P-glycoprotein, and mutations in other DNA repair proteins that restore HR. Here, we show that the RECQ helicase, BLM, mediates the genomic instability observed in BRCA1-deficient cells by a mechanism that depends in part on its anti-recombinogenic activity. We have generated conditional knockout mice with single and combined deficiencies in BRCA1, BLM, and 53BP1 in the B lymphocyte cell population. Ablation of BLM in BRCA1-deficient cells allows the HR repair pathway to be restored, leading to a partial rescue of the genomic instability that is present in BRCA1-deficient cells. The stable accumulation of RAD51, a marker for HR, at DNA double-strand break sites is inhibited by BLM in BRCA1-deficient B cells. However, DNA end resection is not impacted by single or co-deletion of BRCA1 and BLM. Furthermore, cells co-deficient in BRCA1 and BLM display limited sensitivity to PARP inhibition. The rescue in HR and PARPi sensitivity phenotypes following deletion of BLM is only present in hypomorphic BRCA1Δ11/Δ11 cells and not the RING domain deficient BRCA1Δ2/Δ2. These results demonstrate that the anti-recombinogenic activity of BLM is of potentially great significance for regulating the balance of HR versus other error-prone repair pathways. Mutation of BLM in BRCA1-deficient tumors is therefore a potential pathway leading to resistance to PARPi and other DNA damaging agents.
Citation Format: Dharm S. Patel, Sarah M. Misenko, Samuel F. Bunting. Genomic instability in BRCA1-deficient cells is a result of the anti-recombinogenic activity of BLM helicase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2477. doi:10.1158/1538-7445.AM2017-2477
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Li M, Cole F, Patel DS, Misenko SM, Her J, Malhowski A, Alhamza A, Zheng H, Baer R, Ludwig T, Jasin M, Nussenzweig A, Serrano L, Bunting SF. 53BP1 ablation rescues genomic instability in mice expressing 'RING-less' BRCA1. EMBO Rep 2016; 17:1532-1541. [PMID: 27670884 DOI: 10.15252/embr.201642497] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 09/09/2016] [Indexed: 11/09/2022] Open
Abstract
BRCA1 mutations strongly predispose affected individuals to breast and ovarian cancer, but the mechanism by which BRCA1 acts as a tumor suppressor is not fully understood. Homozygous deletion of exon 2 of the mouse Brca1 gene normally causes embryonic lethality, but we show that exon 2-deleted alleles of Brca1 are expressed as a mutant isoform that lacks the N-terminal RING domain. This "RING-less" BRCA1 protein is stable and efficiently recruited to the sites of DNA damage. Surprisingly, robust RAD51 foci form in cells expressing RING-less BRCA1 in response to DNA damage, but the cells nonetheless display the substantial genomic instability. Genomic instability can be rescued by the deletion of Trp53bp1, which encodes the DNA damage response factor 53BP1, and mice expressing RING-less BRCA1 do not show an increased susceptibility to tumors in the absence of 53BP1. Genomic instability in cells expressing RING-less BRCA1 correlates with the loss of BARD1 and a defect in restart of replication forks after hydroxyurea treatment, suggesting a role of BRCA1-BARD1 in genomic integrity that is independent of RAD51 loading.
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Affiliation(s)
- Minxing Li
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Francesca Cole
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.,Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, TX, USA
| | - Dharm S Patel
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Sarah M Misenko
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Joonyoung Her
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Amy Malhowski
- Laboratory of Genome Integrity, Center for Cancer Research, National Cancer Institute National Institutes of Health, Bethesda, MD, USA
| | - Ali Alhamza
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Haiyan Zheng
- Biological Mass Spectrometry Facility, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Richard Baer
- Institute of Cancer Genetics, Department of Pathology & Cell Biology, Columbia University Medical Center, New York, NY, USA
| | - Thomas Ludwig
- Department of Cancer Biology & Genetics, Ohio State University, Columbus, OH, USA
| | - Maria Jasin
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
| | - André Nussenzweig
- Laboratory of Genome Integrity, Center for Cancer Research, National Cancer Institute National Institutes of Health, Bethesda, MD, USA
| | - Lourdes Serrano
- Department of Genetics, Human Genetics Institute of New Jersey, Rutgers The State University of New Jersey, Piscataway, NJ, USA
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ, USA
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16
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Hong X, Liu W, Song R, Shah JJ, Feng X, Tsang CK, Morgan KM, Bunting SF, Inuzuka H, Zheng XFS, Shen Z, Sabaawy HE, Liu L, Pine SR. SOX9 is targeted for proteasomal degradation by the E3 ligase FBW7 in response to DNA damage. Nucleic Acids Res 2016; 44:8855-8869. [PMID: 27566146 PMCID: PMC5062998 DOI: 10.1093/nar/gkw748] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2016] [Accepted: 08/16/2016] [Indexed: 12/20/2022] Open
Abstract
SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis and progression of human tumors by increasing cell proliferation and epithelial-mesenchymal transition. We found that in response to UV irradiation or genotoxic chemotherapeutics, SOX9 is actively degraded in various cancer types and in normal epithelial cells, through a pathway independent of p53, ATM, ATR and DNA-PK. SOX9 is phosphorylated by GSK3β, facilitating the binding of SOX9 to the F-box protein FBW7α, an E3 ligase that functions in the DNA damage response pathway. The binding of FBW7α to the SOX9 K2 domain at T236-T240 targets SOX9 for subsequent ubiquitination and proteasomal destruction. Exogenous overexpression of SOX9 after genotoxic stress increases cell survival. Our findings reveal a novel regulatory mechanism for SOX9 stability and uncover a unique function of SOX9 in the cellular response to DNA damage. This new mechanism underlying a FBW7-SOX9 axis in cancer could have implications in therapy resistance.
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Affiliation(s)
- Xuehui Hong
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Surgery, The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Wenyu Liu
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA
| | - Ruipeng Song
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Surgery, The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Jamie J Shah
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA
| | - Xing Feng
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Radiation Oncology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
| | - Chi Kwan Tsang
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
| | - Katherine M Morgan
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA
| | - Samuel F Bunting
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Biochemistry and Molecular Biology, Rutgers Graduate School of Biomedical Sciences, Piscataway, NJ 08854, USA
| | - Hiroyuki Inuzuka
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
| | - X F Steven Zheng
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
| | - Zhiyuan Shen
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Radiation Oncology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
| | - Hatem E Sabaawy
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Medicine, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903-0019, USA
| | - LianXin Liu
- Department of Surgery, The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Sharon R Pine
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA Department of Medicine, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903-0019, USA
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17
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Hong X, Liu W, Song R, Inuzuka H, Sabaawy HE, Morgan KM, Shah JJ, Bunting SF, Feng X, Tsang CK, Shen Z, Zheng XFS, Liu L, Pine SR. Abstract 4544: FBW7 induces S-phase arrest caused by DNA double strand breaks through targeting SOX9 for proteasomal degradation. Cancer Res 2016. [DOI: 10.1158/1538-7445.am2016-4544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis or progression of many human tumors through increasing cell proliferation and epithelial-mesenchymal transition. We observed that, in response to UV irradiation or certain chemotherapeutic agents, SOX9 is actively and rapidly degraded by a ubiquitin pathway dependent mechanism across several different tumor types including lung cancer, colon cancer, osteosarcoma and melanoma, as well as normal human bronchial epithelial cells. We found that SOX9 is phosphorylated by GSK3β at Ser-236, facilitating the direct binding and degradation of SOX9 via the F box protein, FBW7α. We also determined that the de-ubiquitinase, USP28, stabilizes SOX9 under normal conditions by sequestering FBW7, but is released from FBW7 after UV irradiation, allowing FBW7 to bind SOX9 and target it for destruction. DNA damage-induced SOX9 degradation was independent of p53, ATM, ATR and MAPK pathways. Failure to deplete SOX9 attenuated the DNA damage-induced intra-S-phase checkpoint and increased long-term cell survival. Moreover, mutations within the FBW7 phosphodegron binding site of SOX9 prevented SOX9 degradation after DNA damage, and incurred resistance of non-small cell lung cancer (NSCLC) cells to cisplatin in vivo. We found that cancer patients with tumors expressing high Sox9 and low Fbw7 levels exhibit inferior survival. Our discovery reveals a novel function of SOX9 in the cellular response to DNA damage. Induced degradation of SOX9 may be part of the protection mechanisms to maintain genomic stability. This new regulatory mechanism of the FBW7-SOX9 axis in cancer could have diagnostic and therapeutic implications.
Citation Format: Xuehui Hong, Wenyu Liu, Ruipeng Song, Hiroyuki Inuzuka, Hatem E. Sabaawy, Katherine M. Morgan, Jamie J. Shah, Samuel F. Bunting, Xing Feng, Chi-Kwan Tsang, Zhiyuan Shen, X. F. Steven Zheng, LianXin Liu, Sharon R. Pine. FBW7 induces S-phase arrest caused by DNA double strand breaks through targeting SOX9 for proteasomal degradation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4544.
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Affiliation(s)
- Xuehui Hong
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | - Wenyu Liu
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | - Ruipeng Song
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | | | | | | | - Jamie J. Shah
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | | | - Xing Feng
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | - Chi-Kwan Tsang
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | - Zhiyuan Shen
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
| | | | - LianXin Liu
- 3The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Sharon R. Pine
- 1Rutgers-The Cancer Institute of New Jersey, New Brunswick, NJ
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18
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Abstract
Defective DNA repair leads to increased genomic instability, which is the root cause of mutations that lead to tumorigenesis. Analysis of the frequency and type of chromosome aberrations in different cell types allows defects in DNA repair pathways to be elucidated. Understanding mammalian DNA repair biology has been greatly helped by the production of mice with knockouts in specific genes. The goal of this protocol is to quantify genomic instability in mouse B lymphocytes. Labeling of the telomeres using PNA-FISH probes (peptide nucleic acid - fluorescent in situ hybridization) facilitates the rapid analysis of genomic instability in metaphase chromosome spreads. B cells have specific advantages relative to fibroblasts, because they have normal ploidy and a higher mitotic index. Short-term culture of B cells therefore enables precise measurement of genomic instability in a primary cell population which is likely to have fewer secondary genetic mutations than what is typically found in transformed fibroblasts or patient cell lines.
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Affiliation(s)
- Sarah M Misenko
- Department of Molecular Biology and Biochemistry, Rutgers, the State University of New Jersey
| | - Samuel F Bunting
- Department of Molecular Biology and Biochemistry, Rutgers, the State University of New Jersey;
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19
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Simhadri S, Peterson S, Patel DS, Huo Y, Cai H, Bowman-Colin C, Miller S, Ludwig T, Ganesan S, Bhaumik M, Bunting SF, Jasin M, Xia B. Male fertility defect associated with disrupted BRCA1-PALB2 interaction in mice. J Biol Chem 2014; 289:24617-29. [PMID: 25016020 DOI: 10.1074/jbc.m114.566141] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
PALB2 links BRCA1 and BRCA2 in homologous recombinational repair of DNA double strand breaks (DSBs). Mono-allelic mutations in PALB2 increase the risk of breast, pancreatic, and other cancers, and biallelic mutations cause Fanconi anemia (FA). Like Brca1 and Brca2, systemic knock-out of Palb2 in mice results in embryonic lethality. In this study, we generated a hypomorphic Palb2 allele expressing a mutant PALB2 protein unable to bind BRCA1. Consistent with an FA-like phenotype, cells from the mutant mice showed hypersensitivity and chromosomal breakage when treated with mitomycin C, a DNA interstrand crosslinker. Moreover, mutant males showed reduced fertility due to impaired meiosis and increased apoptosis in germ cells. Interestingly, mutant meiocytes showed a significant defect in sex chromosome synapsis, which likely contributed to the germ cell loss and fertility defect. Our results underscore the in vivo importance of the PALB2-BRCA1 complex formation in DSB repair and male meiosis.
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Affiliation(s)
- Srilatha Simhadri
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, the Departments of Radiation Oncology
| | - Shaun Peterson
- the Developmental Biology Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, New York 10065
| | - Dharm S Patel
- the Department of Molecular Biology and Biochemistry, School of Arts and Sciences, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
| | - Yanying Huo
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, the Departments of Radiation Oncology
| | - Hong Cai
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, the Departments of Radiation Oncology
| | - Christian Bowman-Colin
- the Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, and
| | | | - Thomas Ludwig
- the Department of Molecular and Cellular Biochemistry, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Shridar Ganesan
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, Medicine, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901
| | - Mantu Bhaumik
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, Pediatrics, and
| | - Samuel F Bunting
- the Department of Molecular Biology and Biochemistry, School of Arts and Sciences, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
| | - Maria Jasin
- the Developmental Biology Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, New York 10065
| | - Bing Xia
- From the Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, the Departments of Radiation Oncology,
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20
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Abstract
Fusion genes that are caused by chromosome translocations have been recognized for several decades as drivers of deregulated cell growth in certain types of cancer. In recent years, oncogenic fusion genes have been found in many haematological and solid tumours, demonstrating that translocations are a common cause of malignancy. Sequencing approaches have now confirmed that numerous, non-clonal translocations are a typical feature of cancer cells. These chromosome rearrangements are often highly complex and contain DNA sequence from multiple genomic sites. The factors and pathways that promote translocations are becoming clearer, with non-homologous end-joining implicated as a key source of genomic rearrangements.
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Affiliation(s)
- Samuel F Bunting
- Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey 08854, USA.
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21
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Abstract
The proper choice of repair pathway is critical to tolerating various types of DNA damage. In a recent issue of Molecular Cell, Adamo et al. (2010), along with a second report (Pace et al., 2010), describe how the Fanconi anemia (FA) pathway is involved in preventing aberrant DNA repair. These studies suggest a potentially significant new opportunity for the treatment of FA.
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Affiliation(s)
- Samuel F Bunting
- Experimental Immunology Branch, National Cancer Institute, NIH, Bethesda, MD 20892, USA
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22
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Bunting SF, Callén E, Wong N, Chen HT, Polato F, Gunn A, Bothmer A, Feldhahn N, Fernandez-Capetillo O, Cao L, Xu X, Deng CX, Finkel T, Nussenzweig M, Stark JM, Nussenzweig A. 53BP1 inhibits homologous recombination in Brca1-deficient cells by blocking resection of DNA breaks. Cell 2010; 141:243-54. [PMID: 20362325 DOI: 10.1016/j.cell.2010.03.012] [Citation(s) in RCA: 1223] [Impact Index Per Article: 87.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Revised: 02/12/2010] [Accepted: 03/10/2010] [Indexed: 12/18/2022]
Abstract
Defective DNA repair by homologous recombination (HR) is thought to be a major contributor to tumorigenesis in individuals carrying Brca1 mutations. Here, we show that DNA breaks in Brca1-deficient cells are aberrantly joined into complex chromosome rearrangements by a process dependent on the nonhomologous end-joining (NHEJ) factors 53BP1 and DNA ligase 4. Loss of 53BP1 alleviates hypersensitivity of Brca1 mutant cells to PARP inhibition and restores error-free repair by HR. Mechanistically, 53BP1 deletion promotes ATM-dependent processing of broken DNA ends to produce recombinogenic single-stranded DNA competent for HR. In contrast, Lig4 deficiency does not rescue the HR defect in Brca1 mutant cells but prevents the joining of chromatid breaks into chromosome rearrangements. Our results illustrate that HR and NHEJ compete to process DNA breaks that arise during DNA replication and that shifting the balance between these pathways can be exploited to selectively protect or kill cells harboring Brca1 mutations.
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Affiliation(s)
- Samuel F Bunting
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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23
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Cao L, Xu X, Bunting SF, Liu J, Wang RH, Cao LL, Wu JJ, Peng TN, Chen J, Nussenzweig A, Deng CX, Finkel T. A selective requirement for 53BP1 in the biological response to genomic instability induced by Brca1 deficiency. Mol Cell 2009; 35:534-41. [PMID: 19716796 DOI: 10.1016/j.molcel.2009.06.037] [Citation(s) in RCA: 242] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 05/01/2009] [Accepted: 06/17/2009] [Indexed: 02/06/2023]
Abstract
The molecular pathways leading from genomic instability to cellular senescence and/or cell death remain incompletely characterized. Using mouse embryonic fibroblasts with constitutively increased DNA damage due to the absence of the full-length form of the tumor suppressor Brca1 (Brca1(Delta 11/Delta 11)), we show that deletion of p53 binding protein 1 (53BP1) selectivity abrogates senescence and cell death stimulated by reduced Brca1 activity. Furthermore, the embryonic lethality induced by Brca1 mutation can be alleviated by 53BP1 deletion. Adult Brca1(Delta 11/Delta 11)53BP1(-/-) manifest constitutively high levels of genomic instability, yet age relatively normally, with a surprisingly low incidence of overall tumor formation. Together, these in vitro and in vivo data suggest that 53BP1 is specifically required for the development of premature senescence and apoptosis induced by Brca1 deficiency. These observations may have important implications for Brca1-mediated tumor formation as well as for the molecular pathway leading from genomic instability to organismal aging.
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Affiliation(s)
- Liu Cao
- Translational Medicine Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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