1
|
Bossaert M, Moreno A, Peixoto A, Pillaire MJ, Chanut P, Frit P, Calsou P, Loparo JJ, Britton S. Identification of the main barriers to Ku accumulation in chromatin. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.03.574002. [PMID: 38260538 PMCID: PMC10802386 DOI: 10.1101/2024.01.03.574002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Repair of DNA double strand breaks by the non-homologous end-joining pathway is initiated by the binding of Ku to DNA ends. Given its high affinity for ends, multiple Ku proteins load onto linear DNAs in vitro. However, in cells, Ku loading is limited to ~1-2 molecules per DNA end. The mechanisms enforcing this limit are currently unknown. Here we show that the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), but not its protein kinase activity, is required to prevent excessive Ku entry into chromatin. Ku accumulation is further restricted by two mechanisms: a neddylation/FBXL12-dependent process which actively removes loaded Ku molecules throughout the cell cycle and a CtIP/ATM-dependent mechanism which operates in S-phase. Finally, we demonstrate that the misregulation of Ku loading leads to impaired transcription in the vicinity of DNA ends. Together our data shed light on the multiple layers of coordinated mechanisms operating to prevent Ku from invading chromatin and interfering with other DNA transactions.
Collapse
Affiliation(s)
- Madeleine Bossaert
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Andrew Moreno
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts 02115
| | - Antonio Peixoto
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Marie-Jeanne Pillaire
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Pauline Chanut
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Philippe Frit
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Patrick Calsou
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| | - Joseph John Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts 02115
| | - Sébastien Britton
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), Toulouse, France
- Equipe labélisée la Ligue contre le Cancer 2018
| |
Collapse
|
2
|
Deshpande RA, Marin-Gonzalez A, Barnes HK, Woolley PR, Ha T, Paull TT. Genome-wide analysis of DNA-PK-bound MRN cleavage products supports a sequential model of DSB repair pathway choice. Nat Commun 2023; 14:5759. [PMID: 37717054 PMCID: PMC10505227 DOI: 10.1038/s41467-023-41544-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 09/07/2023] [Indexed: 09/18/2023] Open
Abstract
The Mre11-Rad50-Nbs1 (MRN) complex recognizes and processes DNA double-strand breaks for homologous recombination by performing short-range removal of 5' strands. Endonucleolytic processing by MRN requires a stably bound protein at the break site-a role we postulate is played by DNA-dependent protein kinase (DNA-PK) in mammals. Here we interrogate sites of MRN-dependent processing by identifying sites of CtIP association and by sequencing DNA-PK-bound DNA fragments that are products of MRN cleavage. These intermediates are generated most efficiently when DNA-PK is catalytically blocked, yielding products within 200 bp of the break site, whereas DNA-PK products in the absence of kinase inhibition show greater dispersal. Use of light-activated Cas9 to induce breaks facilitates temporal resolution of DNA-PK and Mre11 binding, showing that both complexes bind to DNA ends before release of DNA-PK-bound products. These results support a sequential model of double-strand break repair involving collaborative interactions between homologous and non-homologous repair complexes.
Collapse
Affiliation(s)
| | - Alberto Marin-Gonzalez
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- Howard Hughes Medical Institute, Baltimore, MD, 21205, USA
| | - Hannah K Barnes
- The Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Phillip R Woolley
- The Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Taekjip Ha
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- Howard Hughes Medical Institute, Baltimore, MD, 21205, USA
| | - Tanya T Paull
- The Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, 78712, USA.
| |
Collapse
|
3
|
WASH interacts with Ku to regulate DNA double-stranded break repair. iScience 2022; 25:103676. [PMID: 35036867 PMCID: PMC8749218 DOI: 10.1016/j.isci.2021.103676] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 06/12/2021] [Accepted: 12/20/2021] [Indexed: 12/28/2022] Open
Abstract
The Wiskott-Aldrich syndrome protein and SCAR homolog (WASH), an actin nucleation-promoting factor, is present in the nucleus where it regulates gene transcription and maintains nuclear organization. Here, we show that WASH interacts with core non-homologous end-joining (NHEJ) factors including Ku70/Ku80 and DNA-PKcs, and Ku70/Ku80 is involved in the recruitment of WASH to the sites of DNA double-stranded break (DSB). WASH depletion leads to increased cell sensitivity and impaired DNA repair capacity in response to etoposide-induced DSBs and reduces NHEJ efficiency. Mechanistically, we show that loss of WASH inhibits the phosphorylation of DNA-PKcs, H2AX, and KAP1 after DSB induction and reduces chromatin relaxation and the recruitment of several downstream NHEJ factors to DSBs. Moreover, WASH role in DSB repair depends on its conserved C-terminal VCA domain and Arp2/3 activation. Our findings reveal a function and mechanistic insight for WASH in DNA DSB repair by the NHEJ pathway.
Collapse
|
4
|
Wang M, Chen S, Wei Y, Wei X. DNA-PK inhibition by M3814 enhances chemosensitivity in non-small cell lung cancer. Acta Pharm Sin B 2021; 11:3935-3949. [PMID: 35024317 PMCID: PMC8727896 DOI: 10.1016/j.apsb.2021.07.029] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 06/21/2021] [Accepted: 07/09/2021] [Indexed: 11/18/2022] Open
Abstract
A significant proportion of non-small cell lung cancer (NSCLC) patients experience accumulating chemotherapy-related adverse events, motivating the design of chemosensitizating strategies. The main cytotoxic damage induced by chemotherapeutic agents is DNA double-strand breaks (DSB). It is thus conceivable that DNA-dependent protein kinase (DNA-PK) inhibitors which attenuate DNA repair would enhance the anti-tumor effect of chemotherapy. The present study aims to systematically evaluate the efficacy and safety of a novel DNA-PK inhibitor M3814 in synergy with chemotherapies on NSCLC. We identified increased expression of DNA-PK in human NSCLC tissues which was associated with poor prognosis. M3814 potentiated the anti-tumor effect of paclitaxel and etoposide in A549, H460 and H1703 NSCLC cell lines. In the four combinations based on two NSCLC xenograft models and two chemotherapy, we also observed tumor regression at tolerated doses in vivo. Moreover, we identified a P53-dependent accelerated senescence response by M3814 following treatment with paclitaxel/etoposide. The present study provides a theoretical basis for the use of M3814 in combination with paclitaxel and etoposide in clinical practice, with hope to aid the optimization of NSCLC treatment.
Collapse
Key Words
- Cell senescence
- Chemosensitization
- DDR, DNA damage response
- DNA repair
- DNA-PK, DNA-dependent protein kinase
- DNA-PKcs, DNA-dependent protein kinase catalytic subunit
- DNA-dependent protein kinase
- DSB, DNA double-strand breaks
- Etoposide
- HR, homologous recombination
- IHC, immunohistochemistry
- LADC, lung adenocarcinoma
- LCLC, large-cell carcinoma
- LSCC, lung squamous cell carcinoma
- M3814
- NHEJ, non homologous end joining
- NSCLC, non-small cell lung cancer
- Non-small cell lung cancer
- Paclitaxel
- dsDNA, double strand DNA
Collapse
|
5
|
Zahid S, Seif El Dahan M, Iehl F, Fernandez-Varela P, Le Du MH, Ropars V, Charbonnier JB. The Multifaceted Roles of Ku70/80. Int J Mol Sci 2021; 22:ijms22084134. [PMID: 33923616 PMCID: PMC8073936 DOI: 10.3390/ijms22084134] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 03/31/2021] [Accepted: 04/01/2021] [Indexed: 12/11/2022] Open
Abstract
DNA double-strand breaks (DSBs) are accidental lesions generated by various endogenous or exogenous stresses. DSBs are also genetically programmed events during the V(D)J recombination process, meiosis, or other genome rearrangements, and they are intentionally generated to kill cancer during chemo- and radiotherapy. Most DSBs are processed in mammalian cells by the classical nonhomologous end-joining (c-NHEJ) pathway. Understanding the molecular basis of c-NHEJ has major outcomes in several fields, including radiobiology, cancer therapy, immune disease, and genome editing. The heterodimer Ku70/80 (Ku) is a central actor of the c-NHEJ as it rapidly recognizes broken DNA ends in the cell and protects them from nuclease activity. It subsequently recruits many c-NHEJ effectors, including nucleases, polymerases, and the DNA ligase 4 complex. Beyond its DNA repair function, Ku is also involved in several other DNA metabolism processes. Here, we review the structural and functional data on the DNA and RNA recognition properties of Ku implicated in DNA repair and in telomeres maintenance.
Collapse
|
6
|
Yu L, Lang Y, Guo J, Cai J, Shang ZF, Chen BPC. DNA-PKcs inhibition impairs HDAC6-mediated HSP90 chaperone function on Aurora A and enhances HDACs inhibitor-induced cell killing by increasing mitotic aberrant spindle assembly. Cell Cycle 2021; 20:211-224. [PMID: 33404279 DOI: 10.1080/15384101.2020.1867790] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Combining targeted therapeutic agents is an attractive cancer treatment strategy associated with high efficacy and low toxicity. DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is an essential factor in DNA damage repair. Studies from us and others have revealed that DNA-PKcs also plays an important role in normal mitosis progression. Histone deacetylase (HDACs) inhibitors commonly lead to mitotic aberration and have been approved for treating various cancers in the clinic. We showed that DNA-PKcs depletion or kinase activity inhibition increases cancer cells' sensitivity to HDACs inhibitors in vitro and in vivo. DNA-PKcs deficiency significantly enhances HDACs inhibitors (HDACi)-induced mitotic arrest and is followed by apoptotic cell death. Mechanistically, we found that DNA-PKcs binds to HDAC6 and facilitates its acetylase activity. HDACi is more likely to impair HDAC6-induced deacetylation of HSP90 and abrogate HSP90's chaperone function on Aurora A, a critical mitotic kinase that regulates centrosome separation and mitotic spindle assembly in DNA-PKcs-deficient cells. Our current work indicates crosstalk between DNA-PKcs and HDACs signaling pathways, and highlights that the combined targeting of DNA-PKcs and HDACs can be used in cancer therapy. Abbreviations: DNA-PKcs, DNA-dependent protein kinase catalytic subunit, HDACs, Histone deacetylases, DSBs, DNA double-strand breaks, ATM, ataxia telangiectasia mutated, ATR, ATM-Rad3-related.
Collapse
Affiliation(s)
- Lan Yu
- Department of Radiation Oncology, Simmons Comprehensive Cancer Center at UT Southwestern Medical Center , Dallas, TX, USA
| | - Yue Lang
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Medical College of Soochow University, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University , Suzhou, China
| | - Jiaming Guo
- Department of Radiation Oncology, Simmons Comprehensive Cancer Center at UT Southwestern Medical Center , Dallas, TX, USA.,Department of Radiation Medicine, College of Naval Medicine, Naval Medical University , Shanghai, China
| | - Jianming Cai
- Department of Radiation Medicine, College of Naval Medicine, Naval Medical University , Shanghai, China
| | - Zeng-Fu Shang
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Medical College of Soochow University, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University , Suzhou, China
| | - Benjamin P C Chen
- Department of Radiation Oncology, Simmons Comprehensive Cancer Center at UT Southwestern Medical Center , Dallas, TX, USA
| |
Collapse
|
7
|
CC-115, a dual inhibitor of mTOR kinase and DNA-PK, blocks DNA damage repair pathways and selectively inhibits ATM-deficient cell growth in vitro. Oncotarget 2017; 8:74688-74702. [PMID: 29088817 PMCID: PMC5650372 DOI: 10.18632/oncotarget.20342] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 07/25/2017] [Indexed: 12/15/2022] Open
Abstract
CC-115, a selective dual inhibitor of the mammalian target of rapamycin (mTOR) kinase and DNA-dependent protein kinase (DNA-PK), is undergoing Phase 1 clinical studies. Here we report the characterization of DNA-PK inhibitory activity of CC-115 in cancer cell lines. CC-115 inhibits auto-phosphorylation of the catalytic subunit of DNA-PK (DNA-PKcs) at the S2056 site (pDNA-PK S2056), leading to blockade of DNA-PK-mediated non-homologous end joining (NHEJ). CC-115 also indirectly reduces the phosphorylation of ataxia-telangiectasia mutated kinase (ATM) at S1981 and its substrates as well as homologous recombination (HR). The mTOR kinase and DNA-PK inhibitory activity of CC-115 leads to not only potent anti-tumor activity against a large panel of hematopoietic and solid cancer cell lines but also strong induction of apoptosis in a subset of cancer lines. Mechanistically, CC-115 prevents NHEJ by inhibiting the dissociation of DNA-PKcs, X-ray repair cross-complementing protein 4 (XRCC4), and DNA ligase IV from DNA ends. CC-115 inhibits colony formation of ATM-deficient cells more potently than ATM-proficient cells, indicating that inhibition of DNA-PK is synthetically lethal with the loss of functional ATM. In conclusion, CC-115 inhibits both mTOR signaling and NHEJ and HR by direct inhibition of DNA-PK. The mechanistic data not only provide selection of potential pharmacodynamic (PD) markers but also support CC-115 clinical development in patients with ATM-deficient tumors.
Collapse
|
8
|
Graham TGW, Walter JC, Loparo JJ. Two-Stage Synapsis of DNA Ends during Non-homologous End Joining. Mol Cell 2016; 61:850-8. [PMID: 26990988 DOI: 10.1016/j.molcel.2016.02.010] [Citation(s) in RCA: 133] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 12/21/2015] [Accepted: 02/07/2016] [Indexed: 11/28/2022]
Abstract
Repair of DNA double-strand breaks (DSBs) is essential for genomic stability. The most common DSB repair mechanism in human cells, non-homologous end joining (NHEJ), rejoins broken DNA ends by direct ligation. It remains unclear how components of the NHEJ machinery assemble a synaptic complex that bridges DNA ends. Here, we use single-molecule imaging in a vertebrate cell-free extract to show that synapsis of DNA ends occurs in at least two stages that are controlled by different NHEJ factors. DNA ends are initially tethered in a long-range complex whose formation requires the Ku70/80 heterodimer and the DNA-dependent protein kinase catalytic subunit. The ends are then closely aligned, which requires XLF, a non-catalytic function of XRCC4-LIG4, and DNA-PK activity. These results reveal a structural transition in the synaptic complex that governs alignment of DNA ends. Our approach provides a means of studying physiological DNA DSB repair at single-molecule resolution.
Collapse
Affiliation(s)
- Thomas G W Graham
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA.
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
| |
Collapse
|
9
|
Yang K, Guo R, Xu D. Non-homologous end joining: advances and frontiers. Acta Biochim Biophys Sin (Shanghai) 2016; 48:632-40. [PMID: 27217473 DOI: 10.1093/abbs/gmw046] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Accepted: 04/18/2016] [Indexed: 12/21/2022] Open
Abstract
DNA double-strand breaks (DSBs) are the most serious form of DNA damage. In human cells, non-homologous end joining (NHEJ) is the major pathway for the repair of DSBs. Different types of DSBs result in different subsets of NHEJ repair strategies. These variations in NHEJ repair strategies depend on numerous elements, such as the flexible recruitment of NHEJ-related proteins, the complexity of the DSB ends, and the spatial- and temporal-ordered formation of the multi-protein complex. On the one hand, current studies of DNA DSBs repair focus on the repair pathway choices between homologous recombination and classic or alternative NHEJ. On the other hand, increasing researches have also deepened the significance and dug into the cross-links between the NHEJ pathway and the area of genome organization and aging. Although remarkable progress has been made in elucidating the underlying principles during the past decades, the detailed mechanism of action in response to different types of DSBs remains largely unknown and needs further evaluation in the future study.
Collapse
Affiliation(s)
- Kai Yang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Rong Guo
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Dongyi Xu
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| |
Collapse
|
10
|
McGovern S, Baconnais S, Roblin P, Nicolas P, Drevet P, Simonson H, Piétrement O, Charbonnier JB, Le Cam E, Noirot P, Lecointe F. C-terminal region of bacterial Ku controls DNA bridging, DNA threading and recruitment of DNA ligase D for double strand breaks repair. Nucleic Acids Res 2016; 44:4785-4806. [PMID: 26961308 PMCID: PMC4889933 DOI: 10.1093/nar/gkw149] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2015] [Revised: 02/26/2016] [Accepted: 02/29/2016] [Indexed: 01/15/2023] Open
Abstract
Non-homologous end joining is a ligation process repairing DNA double strand breaks in eukaryotes and many prokaryotes. The ring structured eukaryotic Ku binds DNA ends and recruits other factors which can access DNA ends through the threading of Ku inward the DNA, making this protein a key ingredient for the scaffolding of the NHEJ machinery. However, this threading ability seems unevenly conserved among bacterial Ku. As bacterial Ku differ mainly by their C-terminus, we evaluate the role of this region in the loading and the threading abilities of Bacillus subtilis Ku and the stimulation of the DNA ligase LigD. We identify two distinct sub-regions: a ubiquitous minimal C-terminal region and a frequent basic C-terminal extension. We show that truncation of one or both of these sub-regions in Bacillus subtilis Ku impairs the stimulation of the LigD end joining activity in vitro. We further demonstrate that the minimal C-terminus is required for the Ku-LigD interaction, whereas the basic extension controls the threading and DNA bridging abilities of Ku. We propose that the Ku basic C-terminal extension increases the concentration of Ku near DNA ends, favoring the recruitment of LigD at the break, thanks to the minimal C-terminal sub-region.
Collapse
Affiliation(s)
- Stephen McGovern
- Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Sonia Baconnais
- UMR 8126, CNRS, Gustave Roussy Université Paris Sud, Université Paris-Saclay, F-94805 Villejuif, France
| | - Pierre Roblin
- SOLEIL Synchrotron, F- 91192 Gif-sur-Yvette, INRA-URBIA, F-44316 Nantes, France
| | - Pierre Nicolas
- MaIAGE, INRA, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Pascal Drevet
- I2BC, iBiTec-S, CEA Saclay, UMR 9198, F-91191 Gif-sur-Yvette, France
| | - Héloïse Simonson
- Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Olivier Piétrement
- UMR 8126, CNRS, Gustave Roussy Université Paris Sud, Université Paris-Saclay, F-94805 Villejuif, France
| | | | - Eric Le Cam
- UMR 8126, CNRS, Gustave Roussy Université Paris Sud, Université Paris-Saclay, F-94805 Villejuif, France
| | - Philippe Noirot
- Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - François Lecointe
- Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| |
Collapse
|
11
|
Iuchi K, Yagura T. DNA binding activity of Ku during chemotherapeutic agent-induced early apoptosis. Exp Cell Res 2016; 342:135-44. [PMID: 26976509 DOI: 10.1016/j.yexcr.2016.03.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Revised: 03/08/2016] [Accepted: 03/09/2016] [Indexed: 01/09/2023]
Abstract
Ku protein is a heterodimer composed of two subunits, and is capable of both sequence-independent and sequence-specific DNA binding. The former mode of DNA binding plays a crucial role in DNA repair. The biological role of Ku protein during apoptosis remains unclear. Here, we show characterization of Ku protein during apoptosis. In order to study the DNA binding properties of Ku, we used two methods for the electrophoresis mobility shift assay (EMSA). One method, RI-EMSA, which is commonly used, employed radiolabeled DNA probes. The other method, WB-EMSA, employed unlabeled DNA followed by western blot and detection with anti-Ku antiserum. In this study, Ku-DNA probe binding activity was found to dramatically decrease upon etoposide treatment, when examined by the RI-EMSA method. In addition, pre-treatment with apoptotic cell extracts inhibited Ku-DNA probe binding activity in the non-treated cell extract. The inhibitory effect of the apoptotic cell extract was reduced by DNase I treatment. WB-EMSA showed that the Ku in the apoptotic cell extract bound to fragmented endogenous DNA. Interestingly, Ku in the apoptotic cell extract purified by the Resource Q column bound 15-bp DNA in both RI-EMSA and WB-EMSA, whereas Ku in unpurified apoptotic cell extracts did not bind additional DNA. These results suggest that Ku binds cleaved chromosomal DNA and/or nucleosomes in apoptotic cells. In conclusion, Ku is intact and retains DNA binding activity in early apoptotic cells.
Collapse
Affiliation(s)
- Katsuya Iuchi
- Department of Bioscience, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuin, Sanda-shi, Hyogo-ken 669-1337, Japan.
| | - Tatsuo Yagura
- Department of Bioscience, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuin, Sanda-shi, Hyogo-ken 669-1337, Japan
| |
Collapse
|
12
|
Jackson RA, Wu JS, Chen ES. C1D family proteins in coordinating RNA processing, chromosome condensation and DNA damage response. Cell Div 2016; 11:2. [PMID: 27030795 PMCID: PMC4812661 DOI: 10.1186/s13008-016-0014-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 02/22/2016] [Indexed: 12/02/2022] Open
Abstract
Research on the involvement of C1D and its yeast homologues Rrp47 (S. cerevisiae) and Cti1 (S. pombe) in DNA damage repair and RNA processing has remained mutually exclusive, with most studies predominantly concentrating on Rrp47. This review will look to reconcile the functions of these proteins in their involvement with the RNA exosome, in the regulation of chromatin architecture, and in the repair of DNA double-strand breaks, focusing on non-homologous end joining and homologous recombination. We propose that C1D is situated in a central position to maintain genomic stability at highly transcribed gene loci by coordinating these processes through the timely recruitment of relevant regulatory factors. In the event that the damage is beyond repair, C1D induces apoptosis in a p53-dependent manner.
Collapse
Affiliation(s)
- Rebecca A Jackson
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597 Singapore
| | - Jocelyn Shumei Wu
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597 Singapore
| | - Ee Sin Chen
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597 Singapore ; National University Health System (NUHS), Singapore, 119228 Singapore ; NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, 119228 Singapore
| |
Collapse
|
13
|
Role for Artemis nuclease in the repair of radiation-induced DNA double strand breaks by alternative end joining. DNA Repair (Amst) 2015; 31:29-40. [DOI: 10.1016/j.dnarep.2015.04.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 04/14/2015] [Accepted: 04/15/2015] [Indexed: 11/24/2022]
|
14
|
Bose P, Dai Y, Grant S. Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights. Pharmacol Ther 2014; 143:323-36. [PMID: 24769080 PMCID: PMC4117710 DOI: 10.1016/j.pharmthera.2014.04.004] [Citation(s) in RCA: 204] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 04/10/2014] [Indexed: 02/05/2023]
Abstract
Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.
Collapse
Affiliation(s)
- Prithviraj Bose
- Massey Cancer Center, Virginia Commonwealth University, Richmond, VA, USA; Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Yun Dai
- Massey Cancer Center, Virginia Commonwealth University, Richmond, VA, USA; Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Steven Grant
- Massey Cancer Center, Virginia Commonwealth University, Richmond, VA, USA; Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA, USA; Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA, USA; Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA; Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA, USA; Institute of Molecular Medicine, Virginia Commonwealth University, Richmond, VA, USA.
| |
Collapse
|
15
|
DNA-PK: a dynamic enzyme in a versatile DSB repair pathway. DNA Repair (Amst) 2014; 17:21-9. [PMID: 24680878 DOI: 10.1016/j.dnarep.2014.02.020] [Citation(s) in RCA: 260] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Revised: 02/17/2014] [Accepted: 02/24/2014] [Indexed: 11/23/2022]
Abstract
DNA double stranded breaks (DSBs) are the most cytoxic DNA lesion as the inability to properly repair them can lead to genomic instability and tumorigenesis. The prominent DSB repair pathway in humans is non-homologous end-joining (NHEJ). In the simplest sense, NHEJ mediates the direct re-ligation of the broken DNA molecule. However, NHEJ is a complex and versatile process that can repair DSBs with a variety of damages and ends via the utilization of a significant number of proteins. In this review we will describe the important factors and mechanisms modulating NHEJ with emphasis given to the versatility of this repair process and the DNA-PK complex.
Collapse
|
16
|
He Y, Liu Q, Shao Y, Chen F. Ku70 and ku80 null mutants improve the gene targeting frequency in Monascus ruber M7. Appl Microbiol Biotechnol 2013; 97:4965-76. [PMID: 23546425 DOI: 10.1007/s00253-013-4851-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 03/10/2013] [Accepted: 03/11/2013] [Indexed: 01/25/2023]
Abstract
Normally, gene targeting by homologous recombination occurs rarely during a transformation process since non-homologous recombination is predominant in filamentous fungi. In our previous researches, the average gene replacement frequency (GRF) in Monascus ruber M7 was as low as 15 %. To develop a highly efficient gene targeting system for M. ruber M7, two M. ruber M7 null mutants of ku70 (MrΔku70) and ku80 (MrΔku80) were constructed which had no apparent defects in the development including vegetative growth, colony phenotype, microscopic morphology and spore yield compared with M. ruber M7. In addition, the production of some significant secondary metabolites such as pigments and citrinin had no differences between the two disruptants and the wild-type strain. Further results revealed that the GRFs of triA (encoding a putative acetyltransferase) were 42.2 % and 61.5 % in the MrΔku70 and MrΔku80 strains, respectively, while it was only about 20 % in M. ruber M7. Furthermore, GRFs of these two disruptants at other loci (the pigE, fmdS genes in MrΔku70 and the ku70 gene in MrΔku80) were investigated, and the results indicated that GRFs in the MrΔku70 strain and the MrΔku80 strain were doubled and tripled compared with that in M. ruber M7, respectively. Therefore, the ku70 and ku80 null mutants of M. ruber M7, especially the ku80-deleted strain, will be excellent hosts for efficient gene targeting.
Collapse
Affiliation(s)
- Yi He
- College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, Hubei Province, People's Republic of China
| | | | | | | |
Collapse
|
17
|
Abstract
Histone deacetylase inhibitors (HDACis) increase gene expression through induction of histone acetylation. However, it remains unclear whether specific gene expression changes determine the apoptotic response following HDACis administration. Herein, we discuss evidence that HDACis trigger in cancer and leukemia cells not only widespread histone acetylation but also actual increases in reactive oxygen species (ROS) and DNA damage that are further increased following treatment with DNA-damaging chemotherapies. While the origins of ROS production are not completely understood, mechanisms, including inflammation and altered antioxidant signaling, have been reported. While the generation of ROS is an explanation, at least in part, for the source of DNA damage observed with HDACi treatment, DNA damage can also be independently induced by changes in the DNA repair activity and chromatin remodeling factors. Recent development of sirtuin inhibitors (SIRTis) has shown that, similar to HDACis, these drugs induce increases in ROS and DNA damage used singly, or in combination with HDACis and other drugs. Thus, induction of apoptosis by HDACis/SIRTis may result through oxidative stress and DNA damage mechanisms in addition to direct activation of apoptosis-inducing genes. Nevertheless, while DNA damage and stress responses could be of interest as markers for clinical responses, they have yet to be validated as markers for responses to HDACi treatment in clinical trials, alone, and in combination.
Collapse
Affiliation(s)
- Carine Robert
- Department of Radiation Oncology and Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | | |
Collapse
|
18
|
Runkle EA, Zhang H, Cai Z, Zhu Z, Karger BL, Wu SL, O'Rourke DM, Zhou Z, Wang Q, Greene MI. Reversion of the ErbB malignant phenotype and the DNA damage response. Exp Mol Pathol 2012; 93:324-33. [PMID: 23022358 DOI: 10.1016/j.yexmp.2012.09.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 09/14/2012] [Indexed: 12/18/2022]
Abstract
The ErbB or HER family is a group of membrane bound tyrosine kinase receptors that initiate signal transduction cascades, which are critical to a wide range of biological processes. When over-expressed or mutated, members of this kinase family form homomeric or heteromeric kinase assemblies that are involved in certain human malignancies. Targeted therapy evolved from studies showing that monoclonal antibodies to the ectodomain of ErbB2/neu would reverse the malignant phenotype. Unfortunately, tumors develop resistance to targeted therapies even when coupled with genotoxic insults such as radiation. Radiation treatment predominantly induces double strand DNA breaks, which, if not repaired, are potentially lethal to the cell. Some tumors are resistant to radiation treatment because they effectively repair double strand breaks. We and others have shown that even in the presence of ionizing radiation, active ErbB kinase signaling apparently enhances the repair process, such that transformed cells resist genotoxic signal induced cell death. We review here the current understanding of ErbB signaling and DNA double strand break repair. Some studies have identified a mechanism by which DNA damage is coordinated to assemblies of proteins that associate with SUN domain containing proteins. These assemblies represent a new target for therapy of resistant tumor cells.
Collapse
Affiliation(s)
- E Aaron Runkle
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Nagaria P, Robert C, Rassool FV. DNA double-strand break response in stem cells: mechanisms to maintain genomic integrity. Biochim Biophys Acta Gen Subj 2012; 1830:2345-53. [PMID: 22995214 DOI: 10.1016/j.bbagen.2012.09.001] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Revised: 08/09/2012] [Accepted: 09/05/2012] [Indexed: 12/19/2022]
Abstract
BACKGROUND Embryonic stem cells (ESCs) represent the point of origin of all cells in a given organism and must protect their genomes from both endogenous and exogenous genotoxic stress. DNA double-strand breaks (DSBs) are one of the most lethal forms of damage, and failure to adequately repair DSBs would not only compromise the ability of SCs to self-renew and differentiate, but will also lead to genomic instability and disease. SCOPE OF REVIEW Herein, we describe the mechanisms by which ESCs respond to DSB-inducing agents such as reactive oxygen species (ROS) and ionizing radiation, compared to somatic cells. We will also discuss whether the DSB response is fully reprogrammed in induced pluripotent stem cells (iPSCs) and the role of the DNA damage response (DDR) in the reprogramming of these cells. MAJOR CONCLUSIONS ESCs have distinct mechanisms to protect themselves against DSBs and oxidative stress compared to somatic cells. The response to damage and stress is crucial for the maintenance of self-renewal and differentiation capacity in SCs. iPSCs appear to reprogram some of the responses to genotoxic stress. However, it remains to be determined if iPSCs also retain some DDR characteristics of the somatic cells of origin. GENERAL SIGNIFICANCE The mechanisms regulating the genomic integrity in ESCs and iPSCs are critical for its safe use in regenerative medicine and may shed light on the pathways and factors that maintain genomic stability, preventing diseases such as cancer. This article is part of a Special Issue entitled Biochemistry of Stem Cells.
Collapse
Affiliation(s)
- Pratik Nagaria
- Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | | | | |
Collapse
|
20
|
Blundred RM, Stewart GS. DNA double-strand break repair, immunodeficiency and the RIDDLE syndrome. Expert Rev Clin Immunol 2011; 7:169-85. [PMID: 21426255 DOI: 10.1586/eci.10.93] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
DNA double-strand break (DSB) repair is an essential cellular process required to maintain genomic integrity in the face of potentially lethal genetic damage. Failure to repair a DSB can trigger cell death, whereas misrepair of the break can lead to the generation of chromosomal translocations, which is a known causative event in the development or progression of cancer. DSBs can be induced following exposure to certain exogenous agents, such as ionising radiation or radiomimetic chemicals, as well as occurring naturally as intermediates of normal physiological processes, in particular during B and T cell antigen receptor assembly. Human syndromes with deficiencies in DSB repair commonly exhibit immunodeficiency, highlighting the critical nature of this pathway for development and maturation of the immune system. In this article we review the different pathways utilized by the cell to repair DSBs and how an inherited defect in some of the genes that are critical regulators of this process can be the underlying cause of human disorders associated with genome instability and immune system dysfunction. We focus on a newly described human immunodeficiency disorder called radiosensitivity, immunodeficiency dysmorphic features and learning difficulties (RIDDLE) syndrome, with particular reference to the function of the defective gene, RNF168. We also consider the implications of this finding on the mechanisms controlling development of the immune system.
Collapse
Affiliation(s)
- Rachel M Blundred
- School of Cancer Sciences, University of Birmingham, Vincent Drive, Edgbaston, Birmingham, B15 2TT, UK
| | | |
Collapse
|
21
|
Mladenov E, Iliakis G. Induction and repair of DNA double strand breaks: the increasing spectrum of non-homologous end joining pathways. Mutat Res 2011; 711:61-72. [PMID: 21329706 DOI: 10.1016/j.mrfmmm.2011.02.005] [Citation(s) in RCA: 287] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 01/31/2011] [Accepted: 02/06/2011] [Indexed: 04/13/2023]
Abstract
A defining characteristic of damage induced in the DNA by ionizing radiation (IR) is its clustered character that leads to the formation of complex lesions challenging the cellular repair mechanisms. The most widely investigated such complex lesion is the DNA double strand break (DSB). DSBs undermine chromatin stability and challenge the repair machinery because an intact template strand is lacking to assist restoration of integrity and sequence in the DNA molecule. Therefore, cells have evolved a sophisticated machinery to detect DSBs and coordinate a response on the basis of inputs from various sources. A central function of cellular responses to DSBs is the coordination of DSB repair. Two conceptually different mechanisms can in principle remove DSBs from the genome of cells of higher eukaryotes. Homologous recombination repair (HRR) uses as template a homologous DNA molecule and is therefore error-free; it functions preferentially in the S and G2 phases. Non-homologous end joining (NHEJ), on the other hand, simply restores DNA integrity by joining the two ends, is error prone as sequence is only fortuitously preserved and active throughout the cell cycle. The basis of DSB repair pathway choice remains unknown, but cells of higher eukaryotes appear programmed to utilize preferentially NHEJ. Recent work suggests that when the canonical DNA-PK dependent pathway of NHEJ (D-NHEJ), becomes compromised an alternative NHEJ pathway and not HRR substitutes in a quasi-backup function (B-NHEJ). Here, we outline aspects of DSB induction by IR and review the mechanisms of their processing in cells of higher eukaryotes. We place particular emphasis on backup pathways of NHEJ and summarize their increasing significance in various cellular processes, as well as their potential contribution to carcinogenesis.
Collapse
Affiliation(s)
- Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Hufelandstr. 55, 45122 Essen, Germany
| | | |
Collapse
|
22
|
Singh SK, Wu W, Zhang L, Klammer H, Wang M, Iliakis G. Widespread Dependence of Backup NHEJ on Growth State: Ramifications for the Use of DNA-PK Inhibitors. Int J Radiat Oncol Biol Phys 2011; 79:540-8. [DOI: 10.1016/j.ijrobp.2010.08.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Revised: 08/18/2010] [Accepted: 08/18/2010] [Indexed: 11/16/2022]
|
23
|
Dobbs TA, Tainer JA, Lees-Miller SP. A structural model for regulation of NHEJ by DNA-PKcs autophosphorylation. DNA Repair (Amst) 2010; 9:1307-14. [PMID: 21030321 PMCID: PMC3045832 DOI: 10.1016/j.dnarep.2010.09.019] [Citation(s) in RCA: 162] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/30/2010] [Indexed: 11/22/2022]
Abstract
The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and Ku heterodimer together form the biologically critical DNA-PK complex that plays key roles in the repair of ionizing radiation-induced DNA double-strand breaks through the non-homologous end-joining (NHEJ) pathway. Despite elegant and informative electron microscopy studies, the mechanism by which DNA-PK co-ordinates the initiation of NHEJ has been enigmatic due to limited structural information. Here, we discuss how the recently described small angle X-ray scattering structures of full-length Ku heterodimer and DNA-PKcs in solution, combined with a breakthrough DNA-PKcs crystal structure, provide significant insights into the early stages of NHEJ. Dynamic structural changes associated with a functionally important cluster of autophosphorylation sites play a significant role in regulating the dissociation of DNA-PKcs from Ku and DNA. These new structural insights have implications for understanding the formation and control of the DNA-PK synaptic complex, DNA-PKcs activation and initiation of NHEJ. More generally, they provide prototypic information for the phosphatidylinositol-3 kinase-like (PIKK) family of serine/threonine protein kinases that includes Ataxia Telangiectasia-Mutated (ATM) and ATM-, Rad3-related (ATR) as well as DNA-PKcs.
Collapse
Affiliation(s)
- Tracey A. Dobbs
- Departments of Biochemistry & Molecular Biology and Oncology, Southern Alberta Cancer Research Institute, University of Calgary, 3280 Hospital Drive NW, Calgary, Alberta, Canada, T2N 4Z6
| | - John A. Tainer
- Department of Molecular Biology, Skaggs Institute of Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA and Life Sciences Division, Department of Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Susan P. Lees-Miller
- Departments of Biochemistry & Molecular Biology and Oncology, Southern Alberta Cancer Research Institute, University of Calgary, 3280 Hospital Drive NW, Calgary, Alberta, Canada, T2N 4Z6
| |
Collapse
|
24
|
Rassool FV, Tomkinson AE. Targeting abnormal DNA double strand break repair in cancer. Cell Mol Life Sci 2010; 67:3699-710. [PMID: 20697770 PMCID: PMC3014093 DOI: 10.1007/s00018-010-0493-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 07/28/2010] [Indexed: 12/19/2022]
Abstract
A major challenge in cancer treatment is the development of therapies that target cancer cells with little or no toxicity to normal tissues and cells. Alterations in DNA double strand break (DSB) repair in cancer cells include both elevated and reduced levels of key repair proteins and changes in the relative contributions of the various DSB repair pathways. These differences can result in increased sensitivity to DSB-inducing agents and increased genomic instability. The development of agents that selectively inhibit the DSB repair pathways that cancer cells are more dependent upon will facilitate the design of therapeutic strategies that exploit the differences in DSB repair between normal and cancer cells. Here, we discuss the pathways of DSB repair, alterations in DSB repair in cancer, inhibitors of DSB repair and future directions for cancer therapies that target DSB repair.
Collapse
Affiliation(s)
- Feyruz V. Rassool
- Department of Radiation Oncology, Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 655 West Baltimore Street, BRB, Rm 7-025, Baltimore, MD 21201 USA
| | - Alan E. Tomkinson
- Department of Radiation Oncology, Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 655 West Baltimore Street, BRB, Rm 7-025, Baltimore, MD 21201 USA
| |
Collapse
|
25
|
Bombarde O, Boby C, Gomez D, Frit P, Giraud-Panis MJ, Gilson E, Salles B, Calsou P. TRF2/RAP1 and DNA-PK mediate a double protection against joining at telomeric ends. EMBO J 2010; 29:1573-84. [PMID: 20407424 DOI: 10.1038/emboj.2010.49] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Accepted: 03/04/2010] [Indexed: 11/09/2022] Open
Abstract
DNA-dependent protein kinase (DNA-PK) is a double-strand breaks repair complex, the subunits of which (KU and DNA-PKcs) are paradoxically present at mammalian telomeres. Telomere fusion has been reported in cells lacking these proteins, raising two questions: how is DNA-PK prevented from initiating classical ligase IV (LIG4)-dependent non-homologous end-joining (C-NHEJ) at telomeres and how is the backup end-joining (EJ) activity (B-NHEJ) that operates at telomeres under conditions of C-NHEJ deficiency controlled? To address these questions, we have investigated EJ using plasmid substrates bearing double-stranded telomeric tracks and human cell extracts with variable C-NHEJ or B-NHEJ activity. We found that (1) TRF2/RAP1 prevents C-NHEJ-mediated end fusion at the initial DNA-PK end binding and activation step and (2) DNA-PK counteracts a potent LIG4-independent EJ mechanism. Thus, telomeres are protected against EJ by a lock with two bolts. These results account for observations with mammalian models and underline the importance of alternative non-classical EJ pathways for telomere fusions in cells.
Collapse
Affiliation(s)
- Oriane Bombarde
- Institut de Pharmacologie et de Biologie Structurale, Toulouse, France
| | | | | | | | | | | | | | | |
Collapse
|
26
|
Velkova A, Carvalho MA, Johnson JO, Tavtigian SV, Monteiro AN. Identification of Filamin A as a BRCA1-interacting protein required for efficient DNA repair. Cell Cycle 2010; 9:1421-33. [PMID: 20305393 PMCID: PMC3040726 DOI: 10.4161/cc.9.7.11256] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The product of the breast and ovarian cancer susceptibility gene BRCA1 has been implicated in several aspects of the DNA damage response but its biochemical function in these processes has remained elusive. In order to probe BRCA1 function we conducted a yeast two-hybrid screening to identify interacting partners to a conserved motif (Motif 6) in the central region of BRCA1. Here we report the identification of the actin-binding protein Filamin A (FLNA) as BRCA1 partner and demonstrate that FLNA is required for efficient regulation of early stages of DNA repair processes. Cells lacking FLNA display a diminished BRCA1 IR-induced focus formation and a delayed kinetics of Rad51 focus formation. In addition, our data also demonstrate that FLNA is required to stabilize the interaction between components of the DNA-PK holoenzyme, DNA-PKcs and Ku86 in a BRCA1-independent fashion. Our data is consistent with a model in which absence of FLNA compromises homologous recombination and non-homologous end joining. Our findings have implications for the response to irradiation induced DNA damage.
Collapse
Affiliation(s)
- Aneliya Velkova
- Risk Assessment, Detection and Intervention Program, H. Lee Moffitt Cancer Center & Research Institute; Tampa, FL USA
- University of South Florida Cancer Biology PhD Program; Tampa, FL USA
| | - Marcelo A. Carvalho
- Risk Assessment, Detection and Intervention Program, H. Lee Moffitt Cancer Center & Research Institute; Tampa, FL USA
| | - Joseph O. Johnson
- Analytic Microscopy Core, H. Lee Moffitt Cancer Center & Research Institute; Tampa, FL USA
| | - Sean V. Tavtigian
- Department of Oncological Sciences; Huntsman Cancer Institute; University of Utah, Salt Lake City, UT USA
| | - Alvaro N.A. Monteiro
- Risk Assessment, Detection and Intervention Program, H. Lee Moffitt Cancer Center & Research Institute; Tampa, FL USA
| |
Collapse
|
27
|
Taylor EM, Cecillon SM, Bonis A, Chapman JR, Povirk LF, Lindsay HD. The Mre11/Rad50/Nbs1 complex functions in resection-based DNA end joining in Xenopus laevis. Nucleic Acids Res 2009; 38:441-54. [PMID: 19892829 PMCID: PMC2811014 DOI: 10.1093/nar/gkp905] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The repair of DNA double-strand breaks (DSBs) is essential to maintain genomic integrity. In higher eukaryotes, DNA DSBs are predominantly repaired by non-homologous end joining (NHEJ), but DNA ends can also be joined by an alternative error-prone mechanism termed microhomology-mediated end joining (MMEJ). In MMEJ, the repair of DNA breaks is mediated by annealing at regions of microhomology and is always associated with deletions at the break site. In budding yeast, the Mre11/Rad5/Xrs2 complex has been demonstrated to play a role in both classical NHEJ and MMEJ, but the involvement of the analogous MRE11/RAD50/NBS1 (MRN) complex in end joining in higher eukaryotes is less certain. Here we demonstrate that in Xenopus laevis egg extracts, the MRN complex is not required for classical DNA-PK-dependent NHEJ. However, the XMRN complex is necessary for resection-based end joining of mismatched DNA ends. This XMRN-dependent end joining process is independent of the core NHEJ components Ku70 and DNA-PK, occurs with delayed kinetics relative to classical NHEJ and brings about repair at sites of microhomology. These data indicate a role for the X. laevis MRN complex in MMEJ.
Collapse
Affiliation(s)
- Elaine M Taylor
- Divisions of Medicine and Biomedical and Life Sciences, School of Health and Medicine, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK
| | | | | | | | | | | |
Collapse
|
28
|
Kantidze OL, Razin SV. Chromatin loops, illegitimate recombination, and genome evolution. Bioessays 2009; 31:278-86. [PMID: 19260023 DOI: 10.1002/bies.200800165] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Chromosomal rearrangements frequently occur at specific places ("hot spots") in the genome. These recombination hot spots are usually separated by 50-100 kb regions of DNA that are rarely involved in rearrangements. It is quite likely that there is a correlation between the above-mentioned distances and the average size of DNA loops fixed at the nuclear matrix. Recent studies have demonstrated that DNA loop anchorage regions can be fairly long and can harbor DNA recombination hot spots. We previously proposed that chromosomal DNA loops may constitute the basic units of genome organization in higher eukaryotes. In this review, we consider recombination between DNA loop anchorage regions as a possible source of genome evolution.
Collapse
Affiliation(s)
- Omar L Kantidze
- Laboratory of Structural and Functional Organization of Chromosomes, Institute of Gene Biology of the Russian Academy of Sciences, Moscow, Russia
| | | |
Collapse
|
29
|
Shrivastav M, Miller CA, De Haro LP, Durant ST, Chen BPC, Chen DJ, Nickoloff JA. DNA-PKcs and ATM co-regulate DNA double-strand break repair. DNA Repair (Amst) 2009; 8:920-9. [PMID: 19535303 DOI: 10.1016/j.dnarep.2009.05.006] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Revised: 05/09/2009] [Accepted: 05/14/2009] [Indexed: 12/19/2022]
Abstract
DNA double-strand breaks (DSBs) are repaired by nonhomologous end-joining (NHEJ) and homologous recombination (HR). The NHEJ/HR decision is under complex regulation and involves DNA-dependent protein kinase (DNA-PKcs). HR is elevated in DNA-PKcs null cells, but suppressed by DNA-PKcs kinase inhibitors, suggesting that kinase-inactive DNA-PKcs (DNA-PKcs-KR) would suppress HR. Here we use a direct repeat assay to monitor HR repair of DSBs induced by I-SceI nuclease. Surprisingly, DSB-induced HR in DNA-PKcs-KR cells was 2- to 3-fold above the elevated HR level of DNA-PKcs null cells, and approximately 4- to 7-fold above cells expressing wild-type DNA-PKcs. The hyperrecombination in DNA-PKcs-KR cells compared to DNA-PKcs null cells was also apparent as increased resistance to DNA crosslinks induced by mitomycin C. ATM phosphorylates many HR proteins, and ATM is expressed at a low level in cells lacking DNA-PKcs, but restored to wild-type level in cells expressing DNA-PKcs-KR. Several clusters of phosphorylation sites in DNA-PKcs, including the T2609 cluster, which is phosphorylated by DNA-PKcs and ATM, regulate access of repair factors to broken ends. Our results indicate that ATM-dependent phosphorylation of DNA-PKcs-KR contributes to the hyperrecombination phenotype. Interestingly, DNA-PKcs null cells showed more persistent ionizing radiation-induced RAD51 foci (but lower HR levels) compared to DNA-PKcs-KR cells, consistent with HR completion requiring RAD51 turnover. ATM may promote RAD51 turnover, suggesting a second (not mutually exclusive) mechanism by which restored ATM contributes to hyperrecombination in DNA-PKcs-KR cells. We propose a model in which DNA-PKcs and ATM coordinately regulate DSB repair by NHEJ and HR.
Collapse
Affiliation(s)
- Meena Shrivastav
- Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
| | | | | | | | | | | | | |
Collapse
|
30
|
Tyrosyl-DNA phosphodiesterase and the repair of 3'-phosphoglycolate-terminated DNA double-strand breaks. DNA Repair (Amst) 2009; 8:901-11. [PMID: 19505854 DOI: 10.1016/j.dnarep.2009.05.003] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 04/24/2009] [Accepted: 05/11/2009] [Indexed: 11/21/2022]
Abstract
Although tyrosyl-DNA phosphodiesterase (TDP1) is capable of removing blocked 3' termini from DNA double-strand break ends, it is uncertain whether this activity plays a role in double-strand break repair. To address this question, affinity-tagged TDP1 was overexpressed in human cells and purified, and its interactions with end joining proteins were assessed. Ku and DNA-PKcs inhibited TDP1-mediated processing of 3'-phosphoglycolate double-strand break termini, and in the absence of ATP, ends sequestered by Ku plus DNA-PKcs were completely refractory to TDP1. Addition of ATP restored TDP1-mediated end processing, presumably due to DNA-PK-catalyzed phosphorylation. Mutations in the 2609-2647 Ser/Thr phosphorylation cluster of DNA-PKcs only modestly affected such processing, suggesting that phosphorylation at other sites was important for rendering DNA ends accessible to TDP1. In human nuclear extracts, about 30% of PG termini were removed within a few hours despite very high concentrations of Ku and DNA-PKcs. Most such removal was blocked by the DNA-PK inhibitor KU-57788, but approximately 5% of PG termini were removed in the first few minutes of incubation even in extracts preincubated with inhibitor. The results suggest that despite an apparent lack of specific recruitment of TDP1 by DNA-PK, TDP1 can gain access to and can process blocked 3' termini of double-strand breaks before ends are fully sequestered by DNA-PK, as well as at a later stage after DNA-PK autophosphorylation. Following cell treatment with calicheamicin, which specifically induces double-strand breaks with protruding 3'-PG termini, TDP1-mutant SCAN1 (spinocerebellar ataxia with axonal neuropathy) cells exhibited a much higher incidence of dicentric chromosomes, as well as higher incidence of chromosome breaks and micronuclei, than normal cells. This chromosomal hypersensitivity, as well as a small but reproducible enhancement of calicheamicin cytotoxicity following siRNA-mediated TDP1 knockdown, suggests a role for TDP1 in repair of 3'-PG double-strand breaks in vivo.
Collapse
|
31
|
Hromas R, Wray J, Lee SH, Martinez L, Farrington J, Corwin LK, Ramsey H, Nickoloff JA, Williamson EA. The human set and transposase domain protein Metnase interacts with DNA Ligase IV and enhances the efficiency and accuracy of non-homologous end-joining. DNA Repair (Amst) 2008; 7:1927-37. [PMID: 18773976 DOI: 10.1016/j.dnarep.2008.08.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Revised: 07/24/2008] [Accepted: 08/08/2008] [Indexed: 12/22/2022]
Abstract
Transposase domain proteins mediate DNA movement from one location in the genome to another in lower organisms. However, in human cells such DNA mobility would be deleterious, and therefore the vast majority of transposase-related sequences in humans are pseudogenes. We recently isolated and characterized a SET and transposase domain protein termed Metnase that promotes DNA double-strand break (DSB) repair by non-homologous end-joining (NHEJ). Both the SET and transposase domain were required for its NHEJ activity. In this study we found that Metnase interacts with DNA Ligase IV, an important component of the classical NHEJ pathway. We investigated whether Metnase had structural requirements of the free DNA ends for NHEJ repair, and found that Metnase assists in joining all types of free DNA ends equally well. Metnase also prevents long deletions from processing of the free DNA ends, and improves the accuracy of NHEJ. Metnase levels correlate with the speed of disappearance of gamma-H2Ax sites after ionizing radiation. However, Metnase has little effect on homologous recombination repair of a single DSB. Altogether, these results fit a model where Metnase plays a role in the fate of free DNA ends during NHEJ repair of DSBs.
Collapse
Affiliation(s)
- Robert Hromas
- Division of Hematology-Oncology, Cancer Research and Treatment Center, Department of Medicine, University of New Mexico Health Science Center, 900 Camino de Salud, Albuquerque, NM 87131, United States
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Kinner A, Wu W, Staudt C, Iliakis G. Gamma-H2AX in recognition and signaling of DNA double-strand breaks in the context of chromatin. Nucleic Acids Res 2008; 36:5678-94. [PMID: 18772227 PMCID: PMC2553572 DOI: 10.1093/nar/gkn550] [Citation(s) in RCA: 861] [Impact Index Per Article: 53.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
DNA double-strand breaks (DSBs) are extremely dangerous lesions with severe consequences for cell survival and the maintenance of genomic stability. In higher eukaryotic cells, DSBs in chromatin promptly initiate the phosphorylation of the histone H2A variant, H2AX, at Serine 139 to generate γ-H2AX. This phosphorylation event requires the activation of the phosphatidylinositol-3-OH-kinase-like family of protein kinases, DNA-PKcs, ATM, and ATR, and serves as a landing pad for the accumulation and retention of the central components of the signaling cascade initiated by DNA damage. Regions in chromatin with γ-H2AX are conveniently detected by immunofluorescence microscopy and serve as beacons of DSBs. This has allowed the development of an assay that has proved particularly useful in the molecular analysis of the processing of DSBs. Here, we first review the role of γ-H2AX in DNA damage response in the context of chromatin and discuss subsequently the use of this modification as a surrogate marker for mechanistic studies of DSB induction and processing. We conclude with a critical analysis of the strengths and weaknesses of the approach and present some interesting applications of the resulting methodology.
Collapse
Affiliation(s)
- Andrea Kinner
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Hufelandstrasse 55, 45122 Essen, Germany
| | | | | | | |
Collapse
|
33
|
Yannone SM, Khan IS, Zhou RZ, Zhou T, Valerie K, Povirk LF. Coordinate 5' and 3' endonucleolytic trimming of terminally blocked blunt DNA double-strand break ends by Artemis nuclease and DNA-dependent protein kinase. Nucleic Acids Res 2008; 36:3354-65. [PMID: 18440975 PMCID: PMC2425473 DOI: 10.1093/nar/gkn205] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Previous work showed that, in the presence of DNA-dependent protein kinase (DNA-PK), Artemis slowly trims 3′-phosphoglycolate-terminated blunt ends. To examine the trimming reaction in more detail, long internally labeled DNA substrates were treated with Artemis. In the absence of DNA-PK, Artemis catalyzed extensive 5′→3′ exonucleolytic resection of double-stranded DNA. This resection required a 5′-phosphate, but did not require ATP, and was accompanied by endonucleolytic cleavage of the resulting 3′ overhang. In the presence of DNA-PK, Artemis-mediated trimming was more limited, was ATP-dependent and did not require a 5′-phosphate. For a blunt end with either a 3′-phosphoglycolate or 3′-hydroxyl terminus, endonucleolytic trimming of 2–4 nucleotides from the 3′-terminal strand was accompanied by trimming of 6 nt from the 5′-terminal strand. The results suggest that autophosphorylated DNA-PK suppresses the exonuclease activity of Artemis toward blunt-ended DNA, and promotes slow and limited endonucleolytic trimming of the 5′-terminal strand, resulting in short 3′ overhangs that are trimmed endonucleolytically. Thus, Artemis and DNA-PK can convert terminally blocked DNA ends of diverse geometry and chemical structure to a form suitable for polymerase-mediated patching and ligation, with minimal loss of terminal sequence. Such processing could account for the very small deletions often found at DNA double-strand break repair sites.
Collapse
Affiliation(s)
- Steven M Yannone
- Life Sciences Division, Department of Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | | | | | | | | | | |
Collapse
|
34
|
Shrivastav M, De Haro LP, Nickoloff JA. Regulation of DNA double-strand break repair pathway choice. Cell Res 2008; 18:134-47. [PMID: 18157161 DOI: 10.1038/cr.2007.111] [Citation(s) in RCA: 923] [Impact Index Per Article: 57.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
DNA double-strand breaks (DSBs) are critical lesions that can result in cell death or a wide variety of genetic alterations including large- or small-scale deletions, loss of heterozygosity, translocations, and chromosome loss. DSBs are repaired by non-homologous end-joining (NHEJ) and homologous recombination (HR), and defects in these pathways cause genome instability and promote tumorigenesis. DSBs arise from endogenous sources including reactive oxygen species generated during cellular metabolism, collapsed replication forks, and nucleases, and from exogenous sources including ionizing radiation and chemicals that directly or indirectly damage DNA and are commonly used in cancer therapy. The DSB repair pathways appear to compete for DSBs, but the balance between them differs widely among species, between different cell types of a single species, and during different cell cycle phases of a single cell type. Here we review the regulatory factors that regulate DSB repair by NHEJ and HR in yeast and higher eukaryotes. These factors include regulated expression and phosphorylation of repair proteins, chromatin modulation of repair factor accessibility, and the availability of homologous repair templates. While most DSB repair proteins appear to function exclusively in NHEJ or HR, a number of proteins influence both pathways, including the MRE11/RAD50/NBS1(XRS2) complex, BRCA1, histone H2AX, PARP-1, RAD18, DNA-dependent protein kinase catalytic subunit (DNA-PKcs), and ATM. DNA-PKcs plays a role in mammalian NHEJ, but it also influences HR through a complex regulatory network that may involve crosstalk with ATM, and the regulation of at least 12 proteins involved in HR that are phosphorylated by DNA-PKcs and/or ATM.
Collapse
Affiliation(s)
- Meena Shrivastav
- Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine and Cancer Center, Albuquerque, NM 87131, USA
| | | | | |
Collapse
|
35
|
Abstract
DNA double-strand breaks (DSBs) are introduced in cells by ionizing radiation and reactive oxygen species. In addition, they are commonly generated during V(D)J recombination, an essential aspect of the developing immune system. Failure to effectively repair these DSBs can result in chromosome breakage, cell death, onset of cancer, and defects in the immune system of higher vertebrates. Fortunately, all mammalian cells possess two enzymatic pathways that mediate the repair of DSBs: homologous recombination and non-homologous end-joining (NHEJ). The NHEJ process utilizes enzymes that capture both ends of the broken DNA molecule, bring them together in a synaptic DNA-protein complex, and finally repair the DNA break. In this review, all the known enzymes that play a role in the NHEJ process are discussed and a working model for the co-operation of these enzymes during DSB repair is presented.
Collapse
|
36
|
Windhofer F, Wu W, Iliakis G. Low levels of DNA ligases III and IV sufficient for effective NHEJ. J Cell Physiol 2008; 213:475-83. [PMID: 17492771 DOI: 10.1002/jcp.21120] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cells of higher eukaryotes rejoin double strand breaks (DSBs) in their DNA predominantly by a non-homologous DNA end joining (NHEJ) pathway that utilizes the products of DNA-PKcs, Ku, LIG4, XRCC4, XLF/Cernunnos, Artemis as well as DNA polymerase lambda (termed D-NHEJ). Mutants with defects in these proteins remove a large proportion of DSBs from their genome utilizing an alternative pathway of NHEJ that operates as a backup (B-NHEJ). While D-NHEJ relies exclusively on DNA ligase IV, recent work points to DNA ligase III as a component of B-NHEJ. Here, we use RNA interference (RNAi) to further investigate the activity requirements for DNA ligase III and IV in the pathways of NHEJ. We report that 70-80% knock down of LIG3 expression has no detectable effect on DSB rejoining, either in D-NHEJ proficient cells, or in cells where D-NHEJ has been chemically or genetically compromised. Surprisingly, also LIG4 knock down has no effect on repair proficient cells, but inhibits DSB rejoining in a radiosensitive cell line with a hypomorphic LIG4 mutation that severely compromises its activity. The results suggest that complete coverage for D-NHEJ or B-NHEJ is afforded by very low ligase levels and demonstrate residual end joining by DNA ligase IV in cells of patients with mutations in LIG4.
Collapse
Affiliation(s)
- Frank Windhofer
- Institute of Medical Radiation Biology, University Duisburg-Essen Medical School, Essen, Germany
| | | | | |
Collapse
|
37
|
Abstract
The DNA-dependent protein kinase (DNA-PK) is central to the process of nonhomologous end joining because it recognizes and then binds double strand breaks initiating repair. It has long been appreciated that DNA-PK protects DNA ends to promote end joining. Here we review recent work from our laboratories and others demonstrating that DNA-PK can regulate end access both positively and negatively. This is accomplished via distinct autophosphorylation events that result in opposing effects on DNA end access. Additional autophosphorylations that are both physically and functionally distinct serve to regulate kinase activity and complex dissociation. Finally, DNA-PK both positively and negatively regulates DNA end access to repair via the homologous recombination pathway. This has particularly important implications in human cells because of DNA-PK's cellular abundance.
Collapse
Affiliation(s)
- Katheryn Meek
- College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
| | | | | |
Collapse
|
38
|
Ochem AE, Rechreche H, Skopac D, Falaschi A. Stimulation of the DNA unwinding activity of human DNA helicase II/Ku by phosphorylation. Arch Biochem Biophys 2007; 470:1-7. [PMID: 18053790 DOI: 10.1016/j.abb.2007.11.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Revised: 11/07/2007] [Accepted: 11/08/2007] [Indexed: 11/18/2022]
Abstract
The Ku autoantigen is a heterodimeric protein of 70- and 83-kDa subunits, endowed with duplex DNA end-binding capacity and DNA helicase activity (Human DNA Helicase II, HDH II). HDH II/Ku is well established as the DNA binding component, the regulatory subunit as well as a substrate for the DNA-dependent protein kinase DNA-PK, a complex involved in the repair of DNA double-strand breaks and in V(D)J recombination in eukaryotes. The effects of phosphorylation by this kinase on the helicase activity of Escherichia coli-produced HDH II/Ku were studied. The rate of DNA unwinding by recombinant HDH II/Ku heterodimer is stimulated at least fivefold upon phosphorylation by DNA-PK(cs). This stimulation is due to the effective transfer of phosphate residues to the helicase rather than the mere presence of the complex. In vitro dephosphorylation of HeLa cellular HDH II/Ku caused a significant decrease in the DNA helicase activity of this enzyme.
Collapse
Affiliation(s)
- Alexander E Ochem
- International Centre for Genetic Engineering and Biotechnology, Institutional Services and Biosafety, Padriciano 99, 34012 Trieste, Italy.
| | | | | | | |
Collapse
|
39
|
Uematsu N, Weterings E, Yano KI, Morotomi-Yano K, Jakob B, Taucher-Scholz G, Mari PO, van Gent DC, Chen BPC, Chen DJ. Autophosphorylation of DNA-PKCS regulates its dynamics at DNA double-strand breaks. ACTA ACUST UNITED AC 2007; 177:219-29. [PMID: 17438073 PMCID: PMC2064131 DOI: 10.1083/jcb.200608077] [Citation(s) in RCA: 307] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The DNA-dependent protein kinase catalytic subunit (DNA-PK(CS)) plays an important role during the repair of DNA double-strand breaks (DSBs). It is recruited to DNA ends in the early stages of the nonhomologous end-joining (NHEJ) process, which mediates DSB repair. To study DNA-PK(CS) recruitment in vivo, we used a laser system to introduce DSBs in a specified region of the cell nucleus. We show that DNA-PK(CS) accumulates at DSB sites in a Ku80-dependent manner, and that neither the kinase activity nor the phosphorylation status of DNA-PK(CS) influences its initial accumulation. However, impairment of both of these functions results in deficient DSB repair and the maintained presence of DNA-PK(CS) at unrepaired DSBs. The use of photobleaching techniques allowed us to determine that the kinase activity and phosphorylation status of DNA-PK(CS) influence the stability of its binding to DNA ends. We suggest a model in which DNA-PK(CS) phosphorylation/autophosphorylation facilitates NHEJ by destabilizing the interaction of DNA-PK(CS) with the DNA ends.
Collapse
Affiliation(s)
- Naoya Uematsu
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
40
|
Budman J, Kim SA, Chu G. Processing of DNA for Nonhomologous End-joining Is Controlled by Kinase Activity and XRCC4/Ligase IV. J Biol Chem 2007; 282:11950-9. [PMID: 17272270 DOI: 10.1074/jbc.m610058200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Nonhomologous end-joining (NHEJ) repairs DNA double-strand breaks created by ionizing radiation and V(D)J recombination. To repair the broken ends, NHEJ processes noncompatible ends into a ligatable form but suppresses processing of compatible ends. It is not known how NHEJ controls polymerase and nuclease activities to act exclusively on noncompatible ends. Here, we analyzed processing independently of ligation by using a two-stage assay with extracts that recapitulated the properties of NHEJ in vivo. Processing of noncompatible ends required wortmannin-sensitive kinase activity. Since DNA-dependent protein kinase catalytic subunit (DNA-PKcs) brings the ends together before undergoing activation of its kinase, this suggests that processing occurred after synapsis of the ends. Surprisingly, all polymerase and most nuclease activity required XRCC4/Ligase IV. This suggests a mechanism for how NHEJ suppresses processing to optimize the preservation of DNA sequence.
Collapse
Affiliation(s)
- Joe Budman
- Department of Medicine, Stanford University, Stanford, California 94305-5151, USA
| | | | | |
Collapse
|
41
|
Kuhfittig-Kulle S, Feldmann E, Odersky A, Kuliczkowska A, Goedecke W, Eggert A, Pfeiffer P. The mutagenic potential of non-homologous end joining in the absence of the NHEJ core factors Ku70/80, DNA-PKcs and XRCC4-LigIV. Mutagenesis 2007; 22:217-33. [PMID: 17347130 DOI: 10.1093/mutage/gem007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Non-homologous end joining (NHEJ), the major pathway of double-strand break (DSB) repair in mammalian cells, comprises two subpathways: one that requires the three core factors Ku70/80, DNA-PKcs and XRCC4/LigIV (DNA-PK-dependent NHEJ) and the other that is independent of these factors. Using a cell-free NHEJ assay, we have investigated the ability of three Chinese hamster ovary (CHO) mutants deficient in Ku80 (xrs6), DNA-PKcs (XR-C1) and XRCC4 (XR-1) in comparison with CHO-K1 wild-type cells to rejoin non-compatible DSB ends. Both NHEJ efficiency and fidelity are strongly reduced in the mutants with xrs6 and XR-1 exhibiting the strongest reduction and XR-C1 displaying a phenotype intermediate between the wild-type and the other two mutants indicating a non-essential but facilitating role of DNA-PKcs in NHEJ. The decrease in fidelity in the mutants is expressed by an increase of deletion junctions formed at microhomologies (microhom) near the DSB (microhomology-mediated non-homologous end joining: microhomNHEJ). Using a novel microhomNHEJ assay, we show that microhom regions of 6-10 bp that are located directly at the DSB termini strongly enhance the mutagenic microhomNHEJ reaction even in the wild type. Due to its error proneness, DNA-PK-independent microhomNHEJ may actively promote genome instability. It will, therefore, be of increasing importance to examine NHEJ fidelity in the context with tumorigenesis and cellular senescence for which we here provide two efficient and reliable tools.
Collapse
Affiliation(s)
- Steffi Kuhfittig-Kulle
- Department of Biology and Geography, Institute of Genetics, University of Duisburg-Essen, Universitätsstrasse 5, D-45117 Essen, Germany
| | | | | | | | | | | | | |
Collapse
|
42
|
Kantidze OL, Razin SV. Chemotherapy-related secondary leukemias: A role for DNA repair by error-prone non-homologous end joining in topoisomerase II - Induced chromosomal rearrangements. Gene 2006; 391:76-9. [PMID: 17234368 DOI: 10.1016/j.gene.2006.12.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Revised: 12/08/2006] [Accepted: 12/08/2006] [Indexed: 11/22/2022]
Abstract
Chromosome rearrangements are believed to cause the secondary leukemias which constitute frequent complications of antitumor chemotherapy with topoisomerase II-specific drugs. Here we show that inhibition of DNA topoisomerase II in cultured cells stimulates association of components of the non-homologous end joining system with a known breakpoint cluster region of the human AML1 gene, suggesting that errors of DNA repair during NHEJ may be the cause of illegitimate recombination in cells treated with topoisomerase II poisons.
Collapse
Affiliation(s)
- Omar L Kantidze
- Laboratory of Structural and Functional Organization of Chromosomes, Institute of Gene Biology RAS, 34/5 Vavilov Street, 119334 Moscow, Russia
| | | |
Collapse
|
43
|
Willers H, Husson J, Lee LW, Hubbe P, Gazemeier F, Powell SN, Dahm-Daphi J. Distinct mechanisms of nonhomologous end joining in the repair of site-directed chromosomal breaks with noncomplementary and complementary ends. Radiat Res 2006; 166:567-74. [PMID: 17007549 DOI: 10.1667/rr0524.1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2005] [Accepted: 05/09/2006] [Indexed: 11/03/2022]
Abstract
DNA double-strand breaks (DSBs) are considered the most important type of DNA damage inflicted by ionizing radiation. The molecular mechanisms of DSB repair by nonhomologous end joining (NHEJ) have not been well studied in live mammalian cells, due in part to the lack of suitable chromosomal repair assays. We previously introduced a novel plasmid-based assay to monitor NHEJ of site-directed chromosomal I-SceI breaks. In the current study, we expanded the analysis of chromosomal NHEJ products in murine fibroblasts to focus on the error-prone rejoining of DSBs with noncomplementary ends, which may serve as a model for radiation damage repair. We found that noncomplementary ends were efficiently repaired using microhomologies of 1-2 nucleotides (nt) present in the single-stranded overhangs, thereby keeping repair-associated end degradation to a minimum (2-3 nt). Microhomology-mediated end joining was disrupted by Wortmannin, a known inhibitor of DNA-PKcs. However, Wortmannin did not significantly impair the proficiency of end joining. In contrast to noncomplementary ends, the rejoining of cohesive ends showed only a minor dependence on microhomologies but produced fivefold larger deletions than the repair of noncomplementary ends. Together, these data suggest the presence of several distinct NHEJ mechanisms in live cells, which are characterized by the degree of sequence deletion and microhomology use. Our NHEJ assay should prove a useful system to further elucidate the genetic determinants and molecular mechanisms of site-directed DSBs in living cells.
Collapse
Affiliation(s)
- H Willers
- Laboratory of Molecular & Cellular Radiation Biology, Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
| | | | | | | | | | | | | |
Collapse
|
44
|
Hentges P, Ahnesorg P, Pitcher RS, Bruce CK, Kysela B, Green AJ, Bianchi J, Wilson TE, Jackson SP, Doherty AJ. Evolutionary and functional conservation of the DNA non-homologous end-joining protein, XLF/Cernunnos. J Biol Chem 2006; 281:37517-26. [PMID: 17038309 DOI: 10.1074/jbc.m608727200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Non-homologous end-joining is a major pathway of DNA double-strand break repair in mammalian cells, deficiency in which confers radiosensitivity and immune deficiency at the whole organism level. A core protein complex comprising the Ku70/80 heterodimer together with a complex between DNA ligase IV and XRCC4 is conserved throughout eukaryotes and assembles at double-strand breaks to mediate ligation of broken DNA ends. In Saccharomyces cerevisiae an additional NHEJ protein, Nej1p, physically interacts with the ligase IV complex and is required in vivo for ligation of DNA double-strand breaks. Recent studies with cells derived from radiosensitive and immune-deficient patients have identified the human protein, XLF (also named Cernunnos), as a crucial NHEJ protein. Here we show that XLF and Nej1p are members of the same protein superfamily and that this family has members in diverse eukaryotes. Indeed, we show that a member of this family encoded by a previously uncharacterized open-reading frame in the Schizosaccharomyces pombe genome is required for NHEJ in this organism. Furthermore, our data reveal that XLF family proteins can bind to DNA and directly interact with the ligase IV-XRCC4 complex to promote DSB ligation. We therefore conclude that XLF family proteins interact with the ligase IV-XRCC4 complex to constitute the evolutionarily conserved enzymatic core of the NHEJ machinery.
Collapse
Affiliation(s)
- Pierre Hentges
- Genome Damage and Stability Centre, University of Sussex, Brighton BN1 9RQ, United Kingdom
| | | | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Kantidze OL, Iarovaia OV, Klochkov DB, Razin SV. Illegitimate recombination as a possible mechanism of topoisomerase-II-induced chromosomal rearrangements. Mol Biol 2006. [DOI: 10.1134/s0026893306050141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
46
|
Drouet J, Frit P, Delteil C, de Villartay JP, Salles B, Calsou P. Interplay between Ku, Artemis, and the DNA-dependent protein kinase catalytic subunit at DNA ends. J Biol Chem 2006; 281:27784-93. [PMID: 16857680 DOI: 10.1074/jbc.m603047200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Repair of DNA double strand breaks (DSB) by the nonhomologous end-joining pathway in mammals requires at least seven proteins involved in a simplified two-step process: (i) recognition and synapsis of the DNA ends dependent on the DNA-dependent protein kinase (DNA-PK) formed by the Ku70/Ku80 heterodimer and the catalytic subunit DNA-PKcs in association with Artemis; (ii) ligation dependent on the DNA ligase IV.XRCC4.Cernunnos-XLF complex. The Artemis protein exhibits exonuclease and endonuclease activities that are believed to be involved in the processing of a subclass of DSB. Here, we have analyzed the interactions of Artemis and nonhomologous end-joining pathway proteins both in a context of human nuclear cell extracts and in cells. DSB-inducing agents specifically elicit the mobilization of Artemis to damaged chromatin together with DNA-PK and XRCC4/ligase IV proteins. DNA-PKcs is necessary for the loading of Artemis on damaged DNA and is the main kinase that phosphorylates Artemis in cells damaged with highly efficient DSB producers. Under kinase-preventive conditions, both in vitro and in cells, Ku-mediated assembly of DNA-PK on DNA ends is responsible for a dissociation of the DNA-PKcs. Artemis complex. Conversely, DNA-PKcs kinase activity prevents Artemis dissociation from the DNA-PK.DNA complex. Altogether, our data allow us to propose a model in which a DNA-PKcs-mediated phosphorylation is necessary both to activate Artemis endonuclease activity and to maintain its association with the DNA end site. This tight functional coupling between the activation of both DNA-PKcs and Artemis may avoid improper processing of DNA.
Collapse
Affiliation(s)
- Jérôme Drouet
- Institut de Pharmacologie et de Biologie Structurale, CNRS UMR 5089, 205 Route de Narbonne, 31077 Toulouse, Cedex 4, France
| | | | | | | | | | | |
Collapse
|
47
|
Povirk LF. Biochemical mechanisms of chromosomal translocations resulting from DNA double-strand breaks. DNA Repair (Amst) 2006; 5:1199-212. [PMID: 16822725 DOI: 10.1016/j.dnarep.2006.05.016] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Exposure of mammalian cells to agents that induce DNA double-strand breaks typically results in both reciprocal and nonreciprocal chromosome translocations. Over the past decade, breakpoint junctions of a significant number of translocations and other genomic rearrangements, both in clinical tumors and in experimental models, have been analyzed at the DNA sequence level. Based on these data, reasonable inferences regarding the biochemical mechanisms involved in translocations can be drawn. In a few cases, breakpoints have been shown to correlate with sites of double-strand cleavage by agents to which the cells or patients have been exposed, including exogenous rare-cutting endonucleases, radiomimetic compounds, and topoisomerase inhibitors. These results confirm that translocations primarily reflect misjoining of the exchanged ends of two or more double-strand breaks. Many junctions show significant loss of DNA sequence at the breakpoints, suggesting exonucleolytic degradation of DNA ends prior to joining. The size and frequency of these deletions varies widely, both between experimental systems, and among individual events in a single system. Homologous recombination between repetitive DNA sequences does not appear to be a major pathway for translocations associated with double-strand breaks. Rather, the general features of the junction sequences, particularly the high frequency small terminal deletions, the apparent splicing of DNA ends at microhomologies, and gap-filling on aligned double-strand break ends, are consistent with the known biochemical properties of the classical nonhomologous end joining pathway involving DNA-dependent protein kinase, XRCC4 and DNA ligase IV. Nevertheless, cells with deficiencies in this pathway still exhibit translocations, with grossly similar junction sequences, suggesting an alternative but less conservative end joining pathway. Although evidence for participation of specific DNA end processing enzymes in formation of translocations is largely circumstantial, likely candidates include DNA polymerases lambda and mu, Artemis nuclease, polynucleotide kinase/phosphatase, tyrosyl-DNA phosphodiesterase, DNase III, Werner syndrome protein, and the Mre11/Rad50/NBS1 complex.
Collapse
Affiliation(s)
- Lawrence F Povirk
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA 23298, USA.
| |
Collapse
|
48
|
Kantidze OL, Iarovaia OV, Razin SV. Assembly of nuclear matrix-bound protein complexes involved in non-homologous end joining is induced by inhibition of DNA topoisomerase II. J Cell Physiol 2006; 207:660-7. [PMID: 16447266 DOI: 10.1002/jcp.20597] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Topoisomerases maintain the DNA structure by relieving the torsional stress and alleviating other topological problems occurring in DNA during transcription and replication. Topoisomerase II appears to have a close association with the family of proteins involved in the organization of chromatin in a series of loops on the proteinaceous chromosomal matrix. Beyond its physiological functions, topoisomerase II is the target for some of the most active anticancer drugs. Inhibition of the topoisomerase II function can result in DNA double-strand breaks (DSBs) and, thus, lead to chromosomal translocations. The earliest event during DSB repair is phosphorylation of histone H2AX at S139 (so-called gammaH2AX) which is believed to serve as a focal point for the assembly of repair proteins at the DSB. In this work, we have demonstrated the formation of gammaH2AX foci in two human cell lines--K562 and HeLa--after suppression of topoisomerase II activity with etoposide. Furthermore, these foci remained visible at nuclear matrices and colocalized with the major components of non-homologous end joining (NHEJ) system of DSBs repair. Thus, inhibition of topoisomerase II activity triggers assembly of NHEJ complexes at the nuclear matrix.
Collapse
Affiliation(s)
- Omar L Kantidze
- Laboratory of Structural and Functional Organization of Chromosomes, Institute of Gene Biology RAS, Moscow, Russia
| | | | | |
Collapse
|
49
|
Takahagi M, Tatsumi K. Aggregative organization enhances the DNA end-joining process that is mediated by DNA-dependent protein kinase. FEBS J 2006; 273:3063-75. [PMID: 16759233 DOI: 10.1111/j.1742-4658.2006.05317.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The occurrence of DNA double-strand breaks in the nucleus provokes in its structural organization a large-scale alteration whose molecular basis is still mostly unclear. Here, we show that double-strand breaks trigger preferential assembly of nucleoproteins in human cellular fractions and that they mediate the separation of large protein-DNA aggregates from aqueous solution. The interaction among the aggregative nucleoproteins presents a dynamic condition that allows the effective interaction of nucleoproteins with external molecules like free ATP and facilitates intrinsic DNA end-joining activity. This aggregative organization is functionally coacervate-like. The key component is DNA-dependent protein kinase (DNA-PK), which can be characterized as a DNA-specific aggregation factor as well as a nuclear scaffold/matrix-interactive factor. In the context of aggregation, the kinase activity of DNA-PK is essential for efficient DNA end-joining. The massive and functional concentration of nucleoproteins on DNA in vitro may represent a possible status of nuclear dynamics in vivo, which probably includes the DNA-PK-dependent response to multiple double-strand breaks.
Collapse
Affiliation(s)
- Masahiko Takahagi
- Research Center for Radiation Safety, National Institute of Radiological Sciences, Chiba, Japan
| | | |
Collapse
|
50
|
Salles B, Calsou P, Frit P, Muller C. The DNA repair complex DNA-PK, a pharmacological target in cancer chemotherapy and radiotherapy. ACTA ACUST UNITED AC 2006; 54:185-93. [PMID: 16563661 DOI: 10.1016/j.patbio.2006.01.012] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Accepted: 01/30/2006] [Indexed: 10/24/2022]
Abstract
A line of investigation in the search for sensitizing tumor cells to chemotherapy or radiotherapy relies on the selection of DNA repair inhibitors. In the area of DNA repair mechanisms, DNA-dependent protein kinase (DNA-PK) represents a key complex. Indeed DNA-PK is involved in the non-homologous end joining (NHEJ) process that corresponds to the major activity responsible for cell survival after ionizing radiation or chemotherapeutic treatment producing DNA double strand breaks. DNA-PK belongs to the PI3-K related kinase family and specific inhibitors have been recently selected and evaluated as radio- and chemo-sensitizers. These drugs, along with other ways to inhibit the DSBs repair process, are presented and discussed.
Collapse
Affiliation(s)
- B Salles
- Institut de Pharmacologie et Biologie Structurale (IPBS) UMR CNRS 5089, Toulouse, France.
| | | | | | | |
Collapse
|