1
|
Fulneček J, Klimentová E, Cairo A, Bukovcakova SV, Alexiou P, Prokop Z, Riha K. The SAP domain of Ku facilitates its efficient loading onto DNA ends. Nucleic Acids Res 2023; 51:11706-11716. [PMID: 37850645 PMCID: PMC10681742 DOI: 10.1093/nar/gkad850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 09/11/2023] [Accepted: 09/29/2023] [Indexed: 10/19/2023] Open
Abstract
The evolutionarily conserved DNA repair complex Ku serves as the primary sensor of free DNA ends in eukaryotic cells. Its rapid association with DNA ends is crucial for several cellular processes, including non-homologous end joining (NHEJ) DNA repair and telomere protection. In this study, we conducted a transient kinetic analysis to investigate the impact of the SAP domain on individual phases of the Ku-DNA interaction. Specifically, we examined the initial binding, the subsequent docking of Ku onto DNA, and sliding of Ku along DNA. Our findings revealed that the C-terminal SAP domain of Ku70 facilitates the initial phases of the Ku-DNA interaction but does not affect the sliding process. This suggests that the SAP domain may either establish the first interactions with DNA, or stabilize these initial interactions during loading. To assess the biological role of the SAP domain, we generated Arabidopsis plants expressing Ku lacking the SAP domain. Intriguingly, despite the decreased efficiency of the ΔSAP Ku complex in loading onto DNA, the mutant plants exhibited full proficiency in classical NHEJ and telomere maintenance. This indicates that the speed with which Ku loads onto telomeres or DNA double-strand breaks is not the decisive factor in stabilizing these DNA structures.
Collapse
Affiliation(s)
| | | | | | | | | | - Zbynek Prokop
- Loschmidt Laboratories, Department of Experimental Biology and RECETOX, Masaryk University, Brno, Czech Republic
- International Clinical Research Center, St Anne's University Hospital, Brno, Czech Republic
| | - Karel Riha
- CEITEC Masaryk University, Brno, Czech Republic
| |
Collapse
|
2
|
Korn SM, Von Ehr J, Dhamotharan K, Tants JN, Abele R, Schlundt A. Insight into the Structural Basis for Dual Nucleic Acid-Recognition by the Scaffold Attachment Factor B2 Protein. Int J Mol Sci 2023; 24:ijms24043286. [PMID: 36834708 PMCID: PMC9958909 DOI: 10.3390/ijms24043286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 01/30/2023] [Accepted: 02/03/2023] [Indexed: 02/10/2023] Open
Abstract
The family of scaffold attachment factor B (SAFB) proteins comprises three members and was first identified as binders of the nuclear matrix/scaffold. Over the past two decades, SAFBs were shown to act in DNA repair, mRNA/(l)ncRNA processing and as part of protein complexes with chromatin-modifying enzymes. SAFB proteins are approximately 100 kDa-sized dual nucleic acid-binding proteins with dedicated domains in an otherwise largely unstructured context, but whether and how they discriminate DNA and RNA binding has remained enigmatic. We here provide the SAFB2 DNA- and RNA-binding SAP and RRM domains in their functional boundaries and use solution NMR spectroscopy to ascribe DNA- and RNA-binding functions. We give insight into their target nucleic acid preferences and map the interfaces with respective nucleic acids on sparse data-derived SAP and RRM domain structures. Further, we provide evidence that the SAP domain exhibits intra-domain dynamics and a potential tendency to dimerize, which may expand its specifically targeted DNA sequence range. Our data provide a first molecular basis of and a starting point towards deciphering DNA- and RNA-binding functions of SAFB2 on the molecular level and serve a basis for understanding its localization to specific regions of chromatin and its involvement in the processing of specific RNA species.
Collapse
Affiliation(s)
- Sophie M. Korn
- Institute for Molecular Biosciences, Biomolecular Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Julian Von Ehr
- Institute for Molecular Biosciences, Biomolecular Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
- IMPRS on Cellular Biophysics, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Karthikeyan Dhamotharan
- Institute for Molecular Biosciences, Biomolecular Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Jan-Niklas Tants
- Institute for Molecular Biosciences, Biomolecular Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Rupert Abele
- Institute for Biochemistry, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany
| | - Andreas Schlundt
- Institute for Molecular Biosciences, Biomolecular Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
- Correspondence:
| |
Collapse
|
3
|
De Bragança S, Aicart-Ramos C, Arribas-Bosacoma R, Rivera-Calzada A, Unfried JP, Prats-Mari L, Marin-Baquero M, Fortes P, Llorca O, Moreno-Herrero F. APLF and long non-coding RNA NIHCOLE promote stable DNA synapsis in non-homologous end joining. Cell Rep 2023; 42:111917. [PMID: 36640344 DOI: 10.1016/j.celrep.2022.111917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 10/26/2022] [Accepted: 12/13/2022] [Indexed: 01/01/2023] Open
Abstract
The synapsis of DNA ends is a critical step for the repair of double-strand breaks by non-homologous end joining (NHEJ). This is performed by a multicomponent protein complex assembled around Ku70-Ku80 heterodimers and regulated by accessory factors, including long non-coding RNAs, through poorly understood mechanisms. Here, we use magnetic tweezers to investigate the contributions of core NHEJ proteins and APLF and lncRNA NIHCOLE to DNA synapsis. APLF stabilizes DNA end bridging and, together with Ku70-Ku80, establishes a minimal complex that supports DNA synapsis for several minutes under piconewton forces. We find the C-terminal acidic region of APLF to be critical for bridging. NIHCOLE increases the dwell time of the synapses by Ku70-Ku80 and APLF. This effect is further enhanced by a small and structured RNA domain within NIHCOLE. We propose a model where Ku70-Ku80 can simultaneously bind DNA, APLF, and structured RNAs to promote the stable joining of DNA ends.
Collapse
Affiliation(s)
- Sara De Bragança
- Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB), CSIC, Madrid, Spain
| | - Clara Aicart-Ramos
- Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB), CSIC, Madrid, Spain
| | - Raquel Arribas-Bosacoma
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
| | - Angel Rivera-Calzada
- Structural Biology Programme, Spanish National Cancer Research Center (CNIO), Madrid, Spain
| | - Juan Pablo Unfried
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel; Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra (UNAV), Pamplona, Spain
| | - Laura Prats-Mari
- Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra (UNAV), Pamplona, Spain
| | - Mikel Marin-Baquero
- Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB), CSIC, Madrid, Spain
| | - Puri Fortes
- Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra (UNAV), Pamplona, Spain; Navarra Institute for Health Research (IdiSNA), Pamplona, Spain; Liver and Digestive Diseases Networking Biomedical Research Centre (CIBERehd), Spanish Network for Advanced Therapies (TERAV ISCIII), Madrid, Spain
| | - Oscar Llorca
- Structural Biology Programme, Spanish National Cancer Research Center (CNIO), Madrid, Spain.
| | - Fernando Moreno-Herrero
- Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB), CSIC, Madrid, Spain.
| |
Collapse
|
4
|
Acetylation of the nuclear localization signal in Ku70 diminishes the interaction with importin-α. Biochem Biophys Rep 2022; 33:101418. [PMID: 36620088 PMCID: PMC9811216 DOI: 10.1016/j.bbrep.2022.101418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 12/19/2022] [Accepted: 12/22/2022] [Indexed: 12/31/2022] Open
Abstract
Proteins are functionally regulated by various types of posttranslational modifications (PTMs). Ku, a heterodimer complex of Ku70 and Ku80 subunits, participates in DNA repair processes. Ku is distributed not only in the nucleus but also in the cytoplasm, suggesting that the function of Ku is regulated by its subcellular localization. Although Ku70 undergoes PTMs including phosphorylation or acetylation, it remains unknown whether the PTMs of Ku70 affect the subcellular localization of Ku. Using a cell-free pull-down assay technique, we show that Nε-acetylation of lysine residues in the synthetic peptide matched to Ku70's nuclear localization signal (NLS) reduces the peptide's interaction with the nuclear transport factor importin-α. The reduced interaction by acetylation was supported by molecular simulation analysis. In addition, when expressed in the endogenous Ku80-defective Chinese hamster ovary xrs-6 cells, some full-size human Ku70 mutants with substitutions of glutamine, a possible structural mimetic of Nε-acetyl-lysine, for lysine at the specific NLS positions exhibited no nuclear distribution. These findings imply that acetylation of particular lysine residues in the Ku70 NLS regulates nuclear localization of Ku.
Collapse
|
5
|
Payliss BJ, Tse YWE, Reichheld SE, Lemak A, Yun HY, Houliston S, Patel A, Arrowsmith CH, Sharpe S, Wyatt HD. Phosphorylation of the DNA repair scaffold SLX4 drives folding of the SAP domain and activation of the MUS81-EME1 endonuclease. Cell Rep 2022; 41:111537. [DOI: 10.1016/j.celrep.2022.111537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2022] [Revised: 08/11/2022] [Accepted: 09/29/2022] [Indexed: 11/03/2022] Open
|
6
|
Extended DNA binding interfaces beyond the canonical SAP domain contribute to the function of replication stress regulator SDE2 at DNA replication forks. J Biol Chem 2022; 298:102268. [PMID: 35850305 PMCID: PMC9399289 DOI: 10.1016/j.jbc.2022.102268] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 07/05/2022] [Accepted: 07/07/2022] [Indexed: 11/25/2022] Open
Abstract
Elevated DNA replication stress causes instability of the DNA replication fork and increased DNA mutations, which underlies tumorigenesis. The DNA replication stress regulator silencing-defective 2 (SDE2) is known to bind to TIMELESS (TIM), a protein of the fork protection complex, and enhances its stability, thereby supporting replisome activity at DNA replication forks. However, the DNA-binding activity of SDE2 is not well defined. Here, we structurally and functionally characterize a new conserved DNA-binding motif related to the SAP (SAF-A/B, Acinus, PIAS) domain in human SDE2 and establish its preference for ssDNA. Our NMR solution structure of the SDE2SAP domain reveals a helix-extended loop-helix core with the helices aligned parallel to each other, consistent with known canonical SAP folds. Notably, we have shown that the DNA interaction of this SAP domain extends beyond the core SAP domain and is augmented by two lysine residues in the C-terminal tail, which is uniquely positioned adjacent to the SAP motif and conserved in the pre-mRNA splicing factor SF3A3. Furthermore, we found that mutation in the SAP domain and extended C terminus not only disrupts ssDNA binding but also impairs TIM localization at replication forks, thus inhibiting efficient fork progression. Taken together, our results establish SDE2SAP as an essential element for SDE2 to exert its role in preserving replication fork integrity via fork protection complex regulation and highlight the structural diversity of the DNA–protein interactions achieved by a specialized DNA-binding motif.
Collapse
|
7
|
Wang Y, Liu B, Lu H, Liu J, Romanienko PJ, Montelione GT, Shen Z. SETD4-mediated KU70 methylation suppresses apoptosis. Cell Rep 2022; 39:110794. [PMID: 35545041 PMCID: PMC9201767 DOI: 10.1016/j.celrep.2022.110794] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 12/28/2021] [Accepted: 04/15/2022] [Indexed: 12/12/2022] Open
Abstract
The mammalian KU70 is a pleiotropic protein functioning in DNA repair and cytoplasmic suppression of apoptosis. We report a regulatory mechanism by which KU70’s cytoplasmic function is enabled due to a methylation at K570 of KU70 by SET-domain-containing protein 4 (SETD4). While SETD4 silencing reduces the level of methylated KU70, over-expression of SETD4 enhances methylation of KU70. Mutations of Y272 and Y284 of SETD4 abrogate methylation of KU70. Although SETD4 is predominantly a nuclear protein, the methylated KU70 is enriched in the cytoplasm. SETD4 knockdown enhances staurosporine (STS)-induced apoptosis and cell killing. Over-expression of the wild-type (WT) SETD4, but not the SETD4-Y272/Y284F mutant, suppresses STS-induced apoptosis. The KU70-K570R (mouse Ku70-K568R) mutation dampens the anti-apoptosis activity of KU70. Our study identifies KU70 as a non-histone substrate of SETD4, discovers a post-translational modification of KU70, and uncovers a role for SETD4 and KU70-K570 methylation in the suppression of apoptosis. Wang et al. identify the methylation of mammalian KU70 by SETD4. This post-translational modification is critical for KU70 localization to the cytoplasm and subsequent suppression of apoptosis.
Collapse
Affiliation(s)
- Yuan Wang
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA
| | - Bochao Liu
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA
| | - Huimei Lu
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA
| | - Jingmei Liu
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA
| | - Peter J Romanienko
- Genome Editing Shared Resource, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA
| | - Gaetano T Montelione
- Department of Chemistry and Chemical Biology, and Center for Biotechnology and Interdisciplinary Sciences, Rensselaer Polytechnic Institute, 110 8th St, Troy, NY 12180, USA
| | - Zhiyuan Shen
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA.
| |
Collapse
|
8
|
Liang S, Chaplin AK, Stavridi AK, Appleby R, Hnizda A, Blundell TL. Stages, scaffolds and strings in the spatial organisation of non-homologous end joining: Insights from X-ray diffraction and Cryo-EM. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2021; 163:60-73. [PMID: 33285184 PMCID: PMC8224183 DOI: 10.1016/j.pbiomolbio.2020.11.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Accepted: 11/26/2020] [Indexed: 01/10/2023]
Abstract
Non-homologous end joining (NHEJ) is the preferred pathway for the repair of DNA double-strand breaks in humans. Here we describe three structural aspects of the repair pathway: stages, scaffolds and strings. We discuss the orchestration of DNA repair to guarantee robust and efficient NHEJ. We focus on structural studies over the past two decades, not only using X-ray diffraction, but also increasingly exploiting cryo-EM to investigate the macromolecular assemblies.
Collapse
Affiliation(s)
- Shikang Liang
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK
| | - Amanda K Chaplin
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK
| | - Antonia Kefala Stavridi
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK
| | - Robert Appleby
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK
| | - Ales Hnizda
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK
| | - Tom L Blundell
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1GA, Cambridgeshire, UK.
| |
Collapse
|
9
|
Abbasi S, Parmar G, Kelly RD, Balasuriya N, Schild-Poulter C. The Ku complex: recent advances and emerging roles outside of non-homologous end-joining. Cell Mol Life Sci 2021; 78:4589-4613. [PMID: 33855626 PMCID: PMC11071882 DOI: 10.1007/s00018-021-03801-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 01/29/2021] [Accepted: 02/24/2021] [Indexed: 12/15/2022]
Abstract
Since its discovery in 1981, the Ku complex has been extensively studied under multiple cellular contexts, with most work focusing on Ku in terms of its essential role in non-homologous end-joining (NHEJ). In this process, Ku is well-known as the DNA-binding subunit for DNA-PK, which is central to the NHEJ repair process. However, in addition to the extensive study of Ku's role in DNA repair, Ku has also been implicated in various other cellular processes including transcription, the DNA damage response, DNA replication, telomere maintenance, and has since been studied in multiple contexts, growing into a multidisciplinary point of research across various fields. Some advances have been driven by clarification of Ku's structure, including the original Ku crystal structure and the more recent Ku-DNA-PKcs crystallography, cryogenic electron microscopy (cryoEM) studies, and the identification of various post-translational modifications. Here, we focus on the advances made in understanding the Ku heterodimer outside of non-homologous end-joining, and across a variety of model organisms. We explore unique structural and functional aspects, detail Ku expression, conservation, and essentiality in different species, discuss the evidence for its involvement in a diverse range of cellular functions, highlight Ku protein interactions and recent work concerning Ku-binding motifs, and finally, we summarize the clinical Ku-related research to date.
Collapse
Affiliation(s)
- Sanna Abbasi
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Gursimran Parmar
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Rachel D Kelly
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Nileeka Balasuriya
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Caroline Schild-Poulter
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada.
| |
Collapse
|
10
|
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: 43] [Impact Index Per Article: 14.3] [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
|
11
|
Hnízda A, Tesina P, Nguyen TB, Kukačka Z, Kater L, Chaplin AK, Beckmann R, Ascher DB, Novák P, Blundell TL. SAP domain forms a flexible part of DNA aperture in Ku70/80. FEBS J 2021; 288:4382-4393. [PMID: 33511782 PMCID: PMC8653891 DOI: 10.1111/febs.15732] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 01/19/2021] [Accepted: 01/26/2021] [Indexed: 12/26/2022]
Abstract
Nonhomologous end joining (NHEJ) is a DNA repair mechanism that religates double-strand DNA breaks to maintain genomic integrity during the entire cell cycle. The Ku70/80 complex recognizes DNA breaks and serves as an essential hub for recruitment of NHEJ components. Here, we describe intramolecular interactions of the Ku70 C-terminal domain, known as the SAP domain. Using single-particle cryo-electron microscopy, mass spectrometric analysis of intermolecular cross-linking and molecular modelling simulations, we captured variable positions of the SAP domain depending on DNA binding. The first position was localized at the DNA aperture in the Ku70/80 apo form but was not observed in the DNA-bound state. The second position, which was observed in both apo and DNA-bound states, was found below the DNA aperture, close to the helical arm of Ku70. The localization of the SAP domain in the DNA aperture suggests a function as a flexible entry gate for broken DNA. DATABASES: EM maps have been deposited in EMDB (EMD-11933). Coordinates have been deposited in Protein Data Bank (PDB 7AXZ). Other data are available from corresponding authors upon a request.
Collapse
Affiliation(s)
- Aleš Hnízda
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Petr Tesina
- Gene Center and Department of Biochemistry, University of Munich, Germany
| | - Thanh-Binh Nguyen
- Computational and Systems Biology, Bio21 Institute, University of Melbourne, Parkville, VIC, Australia.,Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, Melbourne, VIC, Australia
| | - Zdeněk Kukačka
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Lukas Kater
- Gene Center and Department of Biochemistry, University of Munich, Germany
| | - Amanda K Chaplin
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Roland Beckmann
- Gene Center and Department of Biochemistry, University of Munich, Germany
| | - David B Ascher
- Department of Biochemistry, University of Cambridge, Cambridge, UK.,Computational and Systems Biology, Bio21 Institute, University of Melbourne, Parkville, VIC, Australia.,Computational Biology and Clinical Informatics, Baker Heart and Diabetes Institute, Melbourne, VIC, Australia.,Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, VIC, Australia
| | - Petr Novák
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Tom L Blundell
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| |
Collapse
|
12
|
Hepburn M, Saltzberg DJ, Lee L, Fang S, Atkinson C, Strynadka NCJ, Sali A, Lees-Miller SP, Schriemer DC. The active DNA-PK holoenzyme occupies a tensed state in a staggered synaptic complex. Structure 2021; 29:467-478.e6. [PMID: 33412091 DOI: 10.1016/j.str.2020.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Revised: 11/14/2020] [Accepted: 12/09/2020] [Indexed: 01/06/2023]
Abstract
In the non-homologous end-joining (NHEJ) of a DNA double-strand break, DNA ends are bound and protected by DNA-PK, which synapses across the break to tether the broken ends and initiate repair. There is little clarity surrounding the nature of the synaptic complex and the mechanism governing the transition to repair. We report an integrative structure of the synaptic complex at a precision of 13.5 Å, revealing a symmetric head-to-head arrangement with a large offset in the DNA ends and an extensive end-protection mechanism involving a previously uncharacterized plug domain. Hydrogen/deuterium exchange mass spectrometry identifies an allosteric pathway connecting DNA end-binding with the kinase domain that places DNA-PK under tension in the kinase-active state. We present a model for the transition from end-protection to repair, where the synaptic complex supports hierarchical processing of the ends and scaffold assembly, requiring displacement of the catalytic subunit and tension release through kinase activity.
Collapse
Affiliation(s)
- Morgan Hepburn
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada
| | - Daniel J Saltzberg
- Department of Bioengineering and Therapeutic Sciences, Department of Pharmaceutical Sciences, and California Institute for Quantitative Biomedical Sciences, University of California, San Francisco, CA 94158, USA
| | - Linda Lee
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada
| | - Shujuan Fang
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada
| | - Claire Atkinson
- Department of Biochemistry and Molecular Biology and High-Resolution Macromolecular Electron Microscopy Facility, The University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology and High-Resolution Macromolecular Electron Microscopy Facility, The University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, Department of Pharmaceutical Sciences, and California Institute for Quantitative Biomedical Sciences, University of California, San Francisco, CA 94158, USA
| | - Susan P Lees-Miller
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada; Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, University of Calgary, Calgary, AB, Canada
| | - David C Schriemer
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada; Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, University of Calgary, Calgary, AB, Canada; Department of Chemistry, University of Calgary, Calgary, AB, Canada.
| |
Collapse
|
13
|
Structural mechanism of DNA-end synapsis in the non-homologous end joining pathway for repairing double-strand breaks: bridge over troubled ends. Biochem Soc Trans 2020; 47:1609-1619. [PMID: 31829407 DOI: 10.1042/bst20180518] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 11/25/2019] [Accepted: 11/27/2019] [Indexed: 12/18/2022]
Abstract
Non-homologous end joining (NHEJ) is a major repair pathway for DNA double-strand breaks (DSBs), which is the most toxic DNA damage in cells. Unrepaired DSBs can cause genome instability, tumorigenesis or cell death. DNA end synapsis is the first and probably the most important step of the NHEJ pathway, aiming to bring two broken DNA ends close together and provide structural stability for end processing and ligation. This process is mediated through a group of NHEJ proteins forming higher-order complexes, to recognise and bridge two DNA ends. Spatial and temporal understanding of the structural mechanism of DNA-end synapsis has been largely advanced through recent structural and single-molecule studies of NHEJ proteins. This review focuses on core NHEJ proteins that mediate DNA end synapsis through their unique structures and interaction properties, as well as how they play roles as anchor and linker proteins during the process of 'bridge over troubled ends'.
Collapse
|
14
|
Shadrina O, Garanina I, Korolev S, Zatsepin T, Van Assche J, Daouad F, Wallet C, Rohr O, Gottikh M. Analysis of RNA binding properties of human Ku protein reveals its interactions with 7SK snRNA and protein components of 7SK snRNP complex. Biochimie 2020; 171-172:110-123. [PMID: 32105815 DOI: 10.1016/j.biochi.2020.02.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Accepted: 02/21/2020] [Indexed: 12/21/2022]
Abstract
Human Ku heterodimeric protein composed of Ku70 and Ku80 subunits plays an important role in the non-homologous end-joining DNA repair pathway as a sensor of double strand DNA breaks. Ku is also involved in numerous cellular processes, and in some of them it acts in an RNA-dependent manner. However, RNA binding properties of the human Ku have not been well studied. Here we have analyzed interactions of a recombinant Ku heterodimer with a set of RNAs of various structure as well as eCLIP (enhanced crosslinking and immunoprecipitation) data for human Ku70. As a result, we have proposed a consensus RNA structure preferable for the Ku binding that is a hairpin possessing a bulge just near GpG sequence-containing terminal loop. 7SK snRNA is a scaffold for a ribonucleoprotein complex (7SK snRNP), which is known to participate in transcription regulation. We have shown that the recombinant Ku specifically binds a G-rich loop of hairpin 1 within 7SK snRNA. Moreover, Ku protein has been co-precipitated from HEK 293T cells with endogenous 7SK snRNA and such proteins included in 7SK snRNP as HEXIM1, Cdk9 and CTIP2. Ku and Cdk9 binding is found to be RNA-independent, meanwhile HEXIM1 and Ku co-precipitation depended on the presence of intact 7SK snRNA. The latter result has been confirmed using recombinant HEXIM1 and Ku proteins. Colocalization of Ku and CTIP2 was additionally confirmed by confocal microscopy. These results allow us to propose human Ku as a new component of the 7SK snRNP complex.
Collapse
Affiliation(s)
- Olga Shadrina
- Chemistry Department, Lomonosov Moscow State University, Moscow, 199991, Russia; Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992, Moscow, Russia.
| | - Irina Garanina
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Sergey Korolev
- Chemistry Department, Lomonosov Moscow State University, Moscow, 199991, Russia; Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992, Moscow, Russia
| | - Timofei Zatsepin
- Chemistry Department, Lomonosov Moscow State University, Moscow, 199991, Russia; Skolkovo Institute of Science and Technology, Skolkovo, 121205, Russia
| | - Jeanne Van Assche
- Université de Strasbourg, EA7292, FMTS, IUT Louis Pasteur, Schiltigheim, France
| | - Fadoua Daouad
- Université de Strasbourg, EA7292, FMTS, IUT Louis Pasteur, Schiltigheim, France
| | - Clementine Wallet
- Université de Strasbourg, EA7292, FMTS, IUT Louis Pasteur, Schiltigheim, France
| | - Olivier Rohr
- Université de Strasbourg, EA7292, FMTS, IUT Louis Pasteur, Schiltigheim, France
| | - Marina Gottikh
- Chemistry Department, Lomonosov Moscow State University, Moscow, 199991, Russia; Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992, Moscow, Russia
| |
Collapse
|
15
|
Choul-Li S, Legrand AJ, Bidon B, Vicogne D, Villeret V, Aumercier M. Ets-1 interacts through a similar binding interface with Ku70 and Poly (ADP-Ribose) Polymerase-1. Biosci Biotechnol Biochem 2018; 82:1753-1759. [PMID: 29912634 DOI: 10.1080/09168451.2018.1484276] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Abstract
The Ets-1 transcription factor plays an important role in various physiological and pathological processes. These diverse roles of Ets-1 are likely to depend on its interaction proteins. We have previously showed that Ets-1 interacted with DNA-dependent protein kinase (DNA-PK) complex including its regulatory subunits, Ku70 and Ku86 and with poly (ADP-ribose) polymerase-1 (PARP-1). In this study, the binding domains for the interaction between Ets-1 and these proteins were reported. We demonstrated that the interaction of Ets-1 with DNA-PK was mediated through the Ku70 subunit and was mapped to the C-terminal region of Ets-1 and the C-terminal part of Ku70 including SAP domain. The interactive domains between Ets-1 and PARP-1 have been mapped to the C-terminal region of Ets-1 and the BRCA1 carboxy-terminal (BRCT) domain of PARP-1. The results presented in this study may advance our understanding of the functional link between Ets-1 and its interaction partners, DNA-PK and PARP-1.
Collapse
Affiliation(s)
- Souhaila Choul-Li
- Faculté des Sciences, Département de Biologie , Université Chouaib Doukkali , El Jadida , Maroc
| | | | - Baptiste Bidon
- Groupe d’Etude des Interactions Hôte-Pathogéne (GEIHP - EA 3142), Institut de Biologie en Santé, Université d’Angers, Angers, France
| | - Dorothée Vicogne
- Univ. Lille, CNRS, INRA, UMR8576-UGSF-Unité de Biologie Structurale et Fonctionnelle , Lille , France
| | - Vincent Villeret
- Univ. Lille, CNRS, INRA, UMR8576-UGSF-Unité de Biologie Structurale et Fonctionnelle , Lille , France
| | - Marc Aumercier
- Univ. Lille, CNRS, INRA, UMR8576-UGSF-Unité de Biologie Structurale et Fonctionnelle , Lille , France
| |
Collapse
|
16
|
Brosey CA, Ahmed Z, Lees-Miller SP, Tainer JA. What Combined Measurements From Structures and Imaging Tell Us About DNA Damage Responses. Methods Enzymol 2017; 592:417-455. [PMID: 28668129 DOI: 10.1016/bs.mie.2017.04.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
DNA damage outcomes depend upon the efficiency and fidelity of DNA damage responses (DDRs) for different cells and damage. As such, DDRs represent tightly regulated prototypical systems for linking nanoscale biomolecular structure and assembly to the biology of genomic regulation and cell signaling. However, the dynamic and multifunctional nature of DDR assemblies can render elusive the correlation between the structures of DDR factors and specific biological disruptions to the DDR when these structures are altered. In this chapter, we discuss concepts and strategies for combining structural, biophysical, and imaging techniques to investigate DDR recognition and regulation, and thus bridge sequence-level structural biochemistry to quantitative biological outcomes visualized in cells. We focus on representative DDR responses from PARP/PARG/AIF damage signaling in DNA single-strand break repair and nonhomologous end joining complexes in double-strand break repair. Methods with exemplary experimental results are considered with a focus on strategies for probing flexibility, conformational changes, and assembly processes that shape a predictive understanding of DDR mechanisms in a cellular context. Integration of structural and imaging measurements promises to provide foundational knowledge to rationally control and optimize DNA damage outcomes for synthetic lethality and for immune activation with resulting insights for biology and cancer interventions.
Collapse
Affiliation(s)
- Chris A Brosey
- The University of Texas, M.D. Anderson Cancer Center, Houston, TX, United States
| | - Zamal Ahmed
- The University of Texas, M.D. Anderson Cancer Center, Houston, TX, United States
| | - Susan P Lees-Miller
- Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, University of Calgary, Calgary, AB, Canada.
| | - John A Tainer
- The University of Texas, M.D. Anderson Cancer Center, Houston, TX, United States; Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States.
| |
Collapse
|
17
|
Anisenko AN, Knyazhanskaya ES, Zatsepin TS, Gottikh MB. Human Ku70 protein binds hairpin RNA and double stranded DNA through two different sites. Biochimie 2016; 132:85-93. [PMID: 27825805 DOI: 10.1016/j.biochi.2016.11.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2016] [Accepted: 11/02/2016] [Indexed: 02/07/2023]
Abstract
Human protein Ku usually functions in the cell as a complex of two subunits, Ku70 and Ku80. The Ku heterodimer plays a key role in the non-homologous end joining DNA repair pathway by specifically recognizing the DNA ends at the site of the lesion. The binding of the Ku heterodimer to DNA has been well-studied, and its interactions with RNA have been also described. However, Ku70 subunit is known to have independent DNA binding capability, which is less characterized. RNA binding properties of Ku70 have not been yet specially studied. We have prepared recombinant full-length Ku70 and a set of its truncated mutants in E. coli, and studied their interactions with nucleic acids of various structures: linear single- and double-stranded DNA and RNA, as well as closed circular DNA and hairpin RNA. Ku70 has demonstrated a high affinity binding to double stranded DNA and hairpin RNA with a certain structure only. Interestingly, in contrast to the Ku heterodimer, Ku70 is found to interact with closed circular DNA. We also show for the first time that Ku70 employs two different sites for DNA and RNA binding. The double-stranded DNA is recognized by the C-terminal part of Ku70 including SAP domain as it has been earlier demonstrated, whereas hairpin RNA binding is provided by amino acids 251-438.
Collapse
Affiliation(s)
- Andrey N Anisenko
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, Russia.
| | | | - Timofey S Zatsepin
- Chemistry Department, Lomonosov Moscow State University, Moscow, Russia; Skolkovo Institute of Science and Technology, Skolkovo, Russia.
| | - Marina B Gottikh
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.
| |
Collapse
|
18
|
Grundy GJ, Moulding HA, Caldecott KW, Rulten SL. One ring to bring them all--the role of Ku in mammalian non-homologous end joining. DNA Repair (Amst) 2014; 17:30-8. [PMID: 24680220 DOI: 10.1016/j.dnarep.2014.02.019] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 02/25/2014] [Indexed: 12/26/2022]
Abstract
The repair of DNA double strand breaks is essential for cell survival and several conserved pathways have evolved to ensure their rapid and efficient repair. The non-homologous end joining pathway is initiated when Ku binds to the DNA break site. Ku is an abundant nuclear heterodimer of Ku70 and Ku80 with a toroidal structure that allows the protein to slide over the broken DNA end and bind with high affinity. Once locked into placed, Ku acts as a tool-belt to recruit multiple interacting proteins, forming one or more non-homologous end joining complexes that act in a regulated manner to ensure efficient repair of DNA ends. Here we review the structure and functions of Ku and the proteins with which it interacts during non-homologous end joining.
Collapse
Affiliation(s)
- Gabrielle J Grundy
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Hayley A Moulding
- School of Biochemistry, Medical Sciences, University Walk, Bristol BS8 1TD, UK
| | - Keith W Caldecott
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Stuart L Rulten
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| |
Collapse
|
19
|
Williams GJ, Hammel M, Radhakrishnan SK, Ramsden D, Lees-Miller SP, Tainer JA. Structural insights into NHEJ: building up an integrated picture of the dynamic DSB repair super complex, one component and interaction at a time. DNA Repair (Amst) 2014; 17:110-20. [PMID: 24656613 PMCID: PMC4102006 DOI: 10.1016/j.dnarep.2014.02.009] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Revised: 01/27/2014] [Accepted: 02/10/2014] [Indexed: 10/25/2022]
Abstract
Non-homologous end joining (NHEJ) is the major pathway for repair of DNA double-strand breaks (DSBs) in human cells. NHEJ is also needed for V(D)J recombination and the development of T and B cells in vertebrate immune systems, and acts in both the generation and prevention of non-homologous chromosomal translocations, a hallmark of genomic instability and many human cancers. X-ray crystal structures, cryo-electron microscopy envelopes, and small angle X-ray scattering (SAXS) solution conformations and assemblies are defining most of the core protein components for NHEJ: Ku70/Ku80 heterodimer; the DNA dependent protein kinase catalytic subunit (DNA-PKcs); the structure-specific endonuclease Artemis along with polynucleotide kinase/phosphatase (PNKP), aprataxin and PNKP related protein (APLF); the scaffolding proteins XRCC4 and XLF (XRCC4-like factor); DNA polymerases, and DNA ligase IV (Lig IV). The dynamic assembly of multi-protein NHEJ complexes at DSBs is regulated in part by protein phosphorylation. The basic steps of NHEJ have been biochemically defined to require: (1) DSB detection by the Ku heterodimer with subsequent DNA-PKcs tethering to form the DNA-PKcs-Ku-DNA complex (termed DNA-PK), (2) lesion processing, and (3) DNA end ligation by Lig IV, which functions in complex with XRCC4 and XLF. The current integration of structures by combined methods is resolving puzzles regarding the mechanisms, coordination and regulation of these three basic steps. Overall, structural results suggest the NHEJ system forms a flexing scaffold with the DNA-PKcs HEAT repeats acting as compressible macromolecular springs suitable to store and release conformational energy to apply forces to regulate NHEJ complexes and the DNA substrate for DNA end protection, processing, and ligation.
Collapse
Affiliation(s)
- Gareth J Williams
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
| | - Michal Hammel
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
| | - Sarvan Kumar Radhakrishnan
- Department of Biochemistry & Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada
| | - Dale Ramsden
- Lineberger Comprehensive Cancer Center, Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 2759, United States
| | - Susan P Lees-Miller
- Department of Biochemistry & Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada; Department of Oncology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada.
| | - John A Tainer
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States; Department of Molecular Biology, Skaggs Institute of Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, United States.
| |
Collapse
|
20
|
Balestrini A, Ristic D, Dionne I, Liu XZ, Wyman C, Wellinger RJ, Petrini JHJ. The Ku heterodimer and the metabolism of single-ended DNA double-strand breaks. Cell Rep 2013; 3:2033-45. [PMID: 23770241 DOI: 10.1016/j.celrep.2013.05.026] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 03/25/2013] [Accepted: 05/14/2013] [Indexed: 11/16/2022] Open
Abstract
Single-ended double-strand breaks (DSBs) are a common form of spontaneous DNA break, generated when the replisome encounters a discontinuity in the DNA template. Given their prevalence, understanding the mechanisms governing the fate(s) of single-ended DSBs is important. We describe the influence of the Ku heterodimer and Mre11 nuclease activity on processing of single-ended DSBs. Separation-of-function alleles of yku70 were derived that phenocopy Ku deficiency with respect to single-ended DSBs but remain proficient for NHEJ. The Ku mutants fail to regulate Exo1 activity, and bypass the requirement for Mre11 nuclease activity in the repair of camptothecin-induced single-ended DSBs. Ku mutants exhibited reduced affinity for DNA ends, manifest as both reduced end engagement and enhanced probability of diffusing inward on linear DNA. This study reveals an interplay between Ku and Mre11 in the metabolism of single-ended DSBs that is distinct from repair pathway choice at double-ended DSBs.
Collapse
Affiliation(s)
- Alessia Balestrini
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
| | | | | | | | | | | | | |
Collapse
|
21
|
Chiruvella KK, Liang Z, Wilson TE. Repair of double-strand breaks by end joining. Cold Spring Harb Perspect Biol 2013; 5:a012757. [PMID: 23637284 DOI: 10.1101/cshperspect.a012757] [Citation(s) in RCA: 279] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Nonhomologous end joining (NHEJ) refers to a set of genome maintenance pathways in which two DNA double-strand break (DSB) ends are (re)joined by apposition, processing, and ligation without the use of extended homology to guide repair. Canonical NHEJ (c-NHEJ) is a well-defined pathway with clear roles in protecting the integrity of chromosomes when DSBs arise. Recent advances have revealed much about the identity, structure, and function of c-NHEJ proteins, but many questions exist regarding their concerted action in the context of chromatin. Alternative NHEJ (alt-NHEJ) refers to more recently described mechanism(s) that repair DSBs in less-efficient backup reactions. There is great interest in defining alt-NHEJ more precisely, including its regulation relative to c-NHEJ, in light of evidence that alt-NHEJ can execute chromosome rearrangements. Progress toward these goals is reviewed.
Collapse
|
22
|
Jensik PJ, Huggenvik JI, Collard MW. Deformed epidermal autoregulatory factor-1 (DEAF1) interacts with the Ku70 subunit of the DNA-dependent protein kinase complex. PLoS One 2012; 7:e33404. [PMID: 22442688 PMCID: PMC3307728 DOI: 10.1371/journal.pone.0033404] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 02/14/2012] [Indexed: 11/19/2022] Open
Abstract
Deformed Epidermal Autoregulatory Factor 1 (DEAF1) is a transcription factor linked to suicide, cancer, autoimmune disorders and neural tube defects. To better understand the role of DEAF1 in protein interaction networks, a GST-DEAF1 fusion protein was used to isolate interacting proteins in mammalian cell lysates, and the XRCC6 (Ku70) and the XRCC5 (Ku80) subunits of DNA dependent protein kinase (DNA-PK) complex were identified by mass spectrometry, and the DNA-PK catalytic subunit was identified by immunoblotting. Interaction of DEAF1 with Ku70 and Ku80 was confirmed to occur within cells by co-immunoprecipitation of epitope-tagged proteins, and was mediated through interaction with the Ku70 subunit. Using in vitro GST-pulldowns, interaction between DEAF1 and the Ku70 subunit was mapped to the DEAF1 DNA binding domain and the C-terminal Bax-binding region of Ku70. In transfected cells, DEAF1 and Ku70 colocalized to the nucleus, but Ku70 could not relocalize a mutant cytoplasmic form of DEAF1 to the nucleus. Using an in vitro kinase assay, DEAF1 was phosphorylated by DNA-PK in a DNA-independent manner. Electrophoretic mobility shift assays showed that DEAF1 or Ku70/Ku80 did not interfere with the DNA binding of each other, but DNA containing DEAF1 binding sites inhibited the DEAF1-Ku70 interaction. The data demonstrates that DEAF1 can interact with the DNA-PK complex through interactions of its DNA binding domain with the carboxy-terminal region of Ku70 that contains the Bax binding domain, and that DEAF1 is a potential substrate for DNA-PK.
Collapse
Affiliation(s)
| | | | - Michael W. Collard
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
- * E-mail:
| |
Collapse
|
23
|
WONG WINGCHEONG, MAURER-STROH SEBASTIAN, EISENHABER FRANK. THE JANUS-FACED E-VALUES OF HMMER2: EXTREME VALUE DISTRIBUTION OR LOGISTIC FUNCTION? J Bioinform Comput Biol 2011. [DOI: 10.1142/s0219720011005264] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
E-value guided extrapolation of protein domain annotation from libraries such as Pfam with the HMMER suite is indispensable for hypothesizing about the function of experimentally uncharacterized protein sequences. Since the recent release of HMMER3 does not supersede all functions of HMMER2, the latter will remain relevant for ongoing research as well as for the evaluation of annotations that reside in databases and in the literature. In HMMER2, the E-value is computed from the score via a logistic function or via a domain model-specific extreme value distribution (EVD); the lower of the two is returned as E-value for the domain hit in the query sequence. We find that, for thousands of domain models, this treatment results in switching from the EVD to the statistical model with the logistic function when scores grow (for Pfam release 23, 99% in the global mode and 75% in the fragment mode). If the score corresponding to the breakpoint results in an E-value above a user-defined threshold (e.g. 0.1), a critical score region with conflicting E-values from the logistic function (below the threshold) and from EVD (above the threshold) does exist. Thus, this switch will affect E-value guided annotation decisions in an automated mode. To emphasize, switching in the fragment mode is of no practical relevance since it occurs only at E-values far below 0.1. Unfortunately, a critical score region does exist for 185 domain models in the hmmpfam and 1,748 domain models in the hmmsearch global-search mode. For 145 out the respective 185 models, the critical score region is indeed populated by actual sequences. In total, 24.4% of their hits have a logistic function-derived E-value < 0.1 when the EVD provides an E-value > 0.1. We provide examples of false annotations and critically discuss the appropriateness of a logistic function as alternative to the EVD.
Collapse
Affiliation(s)
- WING-CHEONG WONG
- Bioinformatics Institute (BII), Agency for Science, Technology and Research (A *STAR), 30 Biopolis Street, #07-01, Matrix, Singapore 138671, Singapore
| | - SEBASTIAN MAURER-STROH
- Bioinformatics Institute (BII), Agency for Science, Technology and Research (A *STAR), 30 Biopolis Street, #07-01, Matrix, Singapore 138671, Singapore
- School of Biological Sciences (SBS), Nanyang Technological University (NTU), 60 Nanyang Drive, Singapore 63755, Singapore
| | - FRANK EISENHABER
- Bioinformatics Institute (BII), Agency for Science, Technology and Research (A *STAR), 30 Biopolis Street, #07-01, Matrix, Singapore 138671, Singapore
- Department of Biological Sciences (DBS), National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- School of Computer Engineering (SCE), Nanyang Technological University (NTU), 50 Nanyang Drive, Singapore 637553, Singapore
| |
Collapse
|
24
|
Hu S, Pluth JM, Cucinotta FA. Putative binding modes of Ku70-SAP domain with double strand DNA: a molecular modeling study. J Mol Model 2011; 18:2163-74. [PMID: 21947447 DOI: 10.1007/s00894-011-1234-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 08/26/2011] [Indexed: 01/31/2023]
Abstract
The channel structure of the Ku protein elegantly reveals the mechanistic basis of sequence-independent DNA-end binding, which is essential to genome integrity after exposure to ionizing radiation or in V(D)J recombination. However, contradicting evidence indicates that this protein is also involved in the regulation of gene expression and in other regulatory processes with intact chromosomes. This computational study predicts that a putative DNA binding domain of this protein, the SAP domain, can form DNA-bound complexes with relatively high affinities (ΔG ≈ -20 kcal mol(-1)). The binding modes are searched by low frequency vibration modes driven by the fully flexible docking method while binding affinities are calculated by the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method. We find this well defined 5 kDa domain with a helix-extended loop-helix structure is suitable to form favorable electrostatic and hydrophobic interactions with either the major groove or the minor groove of DNA. The calculation also reveals the sequence specified binding preference which may relate to the observed pause sites when Ku translocates along DNA and the perplex binding of Ku with circular DNA.
Collapse
Affiliation(s)
- Shaowen Hu
- Division of Space Life Sciences, Universities Space Research Association, Houston, TX 77058, USA.
| | | | | |
Collapse
|
25
|
Hu S, Cucinotta FA. Computational studies on full-length Ku70 with DNA duplexes: base interactions and a helical path. J Mol Model 2011; 18:1935-49. [DOI: 10.1007/s00894-011-1220-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 08/09/2011] [Indexed: 11/30/2022]
|
26
|
Takeda AAS, de Barros AC, Chang CW, Kobe B, Fontes MRM. Structural basis of importin-α-mediated nuclear transport for Ku70 and Ku80. J Mol Biol 2011; 412:226-34. [PMID: 21806995 DOI: 10.1016/j.jmb.2011.07.038] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 07/15/2011] [Accepted: 07/19/2011] [Indexed: 10/18/2022]
Abstract
Ku70 and Ku80 form a heterodimeric complex involved in multiple nuclear processes. This complex plays a key role in DNA repair due to its ability to bind DNA double-strand breaks and facilitate repair by the nonhomologous end-joining pathway. Ku70 and Ku80 have been proposed to contain bipartite and monopartite nuclear localization sequences (NLSs), respectively, that allow them to be translocated to the nucleus independently of each other via the classical importin-α (Impα)/importin-β-mediated nuclear import pathway. To determine the structural basis of the recognition of Ku70 and Ku80 proteins by Impα, we solved the crystal structures of the complexes of Impα with the peptides corresponding to the Ku70 and Ku80 NLSs. Our structural studies confirm the binding of the Ku80 NLS as a classical monopartite NLS but reveal an unexpected binding mode for Ku70 NLS with only one basic cluster bound to the receptor. Both Ku70 and Ku80 therefore contain monopartite NLSs, and sequences outside the basic cluster make favorable interactions with Impα, suggesting that this may be a general feature in monopartite NLSs. We show that the Ku70 NLS has a higher affinity for Impα than the Ku80 NLS, consistent with more extensive interactions in its N-terminal region. The prospect of nuclear import of Ku70 and Ku80 independently of each other provides a powerful regulatory mechanism for the function of the Ku70/Ku80 heterodimer and independent functions of the two proteins.
Collapse
Affiliation(s)
- Agnes A S Takeda
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, Botucatu, SP 18618-970, Brazil
| | | | | | | | | |
Collapse
|
27
|
Bau DT, Tsai CW, Wu CN. Role of the XRCC5/XRCC6 dimer in carcinogenesis and pharmacogenomics. Pharmacogenomics 2011; 12:515-34. [PMID: 21521024 DOI: 10.2217/pgs.10.209] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Over the past few decades, the incidence of cancer has rapidly increased all over the world and cancer remains a major threat to public health. It is believed that cancer results from a series of genetic alterations that lead to the progressive disorder of the normal mechanisms controlling cell proliferation, differentiation, death and/or genomic stability. The response of the cell to genetic injury and its ability to maintain genomic stability by means of a variety of DNA repair mechanisms are therefore essential in preventing tumor initiation and progression. From the same viewpoint, the relative role of DNA repair as a biomarker for prognosis, predictor of drug and therapy responses or indeed as a target for novel gene therapy, is very promising. In this article, we have summarized the studies investigating the association between the XRCC5/XRCC6 dimer and the susceptibility to multiple cancers and discuss its role in carcinogenesis and its potential application to anticancer drug discovery.
Collapse
Affiliation(s)
| | - Chia-Wen Tsai
- Terry Fox Cancer Research Laboratory, China Medical University Hospital, 2 Yuh-Der Road, Taichung, 404 Taiwan, Republic of China
| | - Cheng-Nan Wu
- Terry Fox Cancer Research Laboratory, China Medical University Hospital, 2 Yuh-Der Road, Taichung, 404 Taiwan, Republic of China
- Department of Medical Laboratory Science & Biotechnology, Central-Taiwan University of Science & Technology, Taichung, Taiwan, Republic of China
| |
Collapse
|
28
|
Yano KI, Morotomi-Yano K, Lee KJ, Chen DJ. Functional significance of the interaction with Ku in DNA double-strand break recognition of XLF. FEBS Lett 2011; 585:841-6. [PMID: 21349273 DOI: 10.1016/j.febslet.2011.02.020] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 01/28/2011] [Accepted: 02/14/2011] [Indexed: 11/25/2022]
Abstract
Ku heterodimer is essential for the repair of DNA double-strand breaks (DSBs) by non-homologous end-joining (NHEJ). Ku recruits XLF, also known as Cernunnos, to DSBs. Here we report domain analyses of Ku-XLF interaction. The heterodimeric domain of Ku was found to be sufficient for the recruitment of XLF to DSBs and for the interaction of Ku with XLF. A small C-terminal deletion of XLF completely abolished recruitment of XLF to DSBs and Ku-XLF interaction. This deletion also led to marked reduction of XLF-XRCC4 interaction although the XRCC4-binding site on the XLF N-terminal domain remained intact. These results demonstrate the significance of Ku-XLF interaction in the molecular assembly of NHEJ factors.
Collapse
Affiliation(s)
- Ken-ichi Yano
- Bioelectrics Research Center, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
| | | | | | | |
Collapse
|
29
|
Abstract
Ku plays a crucial role in the non-homologous end joining pathway to repair DNA double-strand breaks. In this study, we modelled the full-length Ku heterodimer from the truncated crystal structure and NMR structure, and conducted a series of docking and molecular dynamics simulations in an effort to probe the structural, dynamical and energetic features of each domain in free Ku and Ku-DNA complexes.
Collapse
Affiliation(s)
- Shaowen Hu
- Universities Space Research Association, Division of Space Life Sciences, Houston, TX 77058, USA.
| | | |
Collapse
|
30
|
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
|
31
|
Pace P, Mosedale G, Hodskinson MR, Rosado IV, Sivasubramaniam M, Patel KJ. Ku70 corrupts DNA repair in the absence of the Fanconi anemia pathway. Science 2010; 329:219-23. [PMID: 20538911 DOI: 10.1126/science.1192277] [Citation(s) in RCA: 191] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
A conserved DNA repair response is defective in the human genetic illness Fanconi anemia (FA). Mutation of some FA genes impairs homologous recombination and error-prone DNA repair, rendering FA cells sensitive to DNA cross-linking agents. We found a genetic interaction between the FA gene FANCC and the nonhomologous end joining (NHEJ) factor Ku70. Disruption of both FANCC and Ku70 suppresses sensitivity to cross-linking agents, diminishes chromosome breaks, and reverses defective homologous recombination. Ku70 binds directly to free DNA ends, committing them to NHEJ repair. We show that purified FANCD2, a downstream effector of the FA pathway, might antagonize Ku70 activity by modifying such DNA substrates. These results reveal a function for the FA pathway in processing DNA ends, thereby diverting double-strand break repair away from abortive NHEJ and toward homologous recombination.
Collapse
Affiliation(s)
- Paul Pace
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | | | | | | | | | | |
Collapse
|
32
|
Hammel M, Yu Y, Mahaney BL, Cai B, Ye R, Phipps BM, Rambo RP, Hura GL, Pelikan M, So S, Abolfath RM, Chen DJ, Lees-Miller SP, Tainer JA. Ku and DNA-dependent protein kinase dynamic conformations and assembly regulate DNA binding and the initial non-homologous end joining complex. J Biol Chem 2009; 285:1414-23. [PMID: 19893054 PMCID: PMC2801267 DOI: 10.1074/jbc.m109.065615] [Citation(s) in RCA: 175] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
DNA double strand break (DSB) repair by non-homologous end joining (NHEJ) is initiated by DSB detection by Ku70/80 (Ku) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) recruitment, which promotes pathway progression through poorly defined mechanisms. Here, Ku and DNA-PKcs solution structures alone and in complex with DNA, defined by x-ray scattering, reveal major structural reorganizations that choreograph NHEJ initiation. The Ku80 C-terminal region forms a flexible arm that extends from the DNA-binding core to recruit and retain DNA-PKcs at DSBs. Furthermore, Ku- and DNA-promoted assembly of a DNA-PKcs dimer facilitates trans-autophosphorylation at the DSB. The resulting site-specific autophosphorylation induces a large conformational change that opens DNA-PKcs and promotes its release from DNA ends. These results show how protein and DNA interactions initiate large Ku and DNA-PKcs rearrangements to control DNA-PK biological functions as a macromolecular machine orchestrating assembly and disassembly of the initial NHEJ complex on DNA.
Collapse
Affiliation(s)
- Michal Hammel
- Physical Biosciences Division, Department of Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Suzuki R, Shindo H, Tase A, Kikuchi Y, Shimizu M, Yamazaki T. Solution structures and DNA binding properties of the N-terminal SAP domains of SUMO E3 ligases from Saccharomyces cerevisiae and Oryza sativa. Proteins 2009; 75:336-47. [PMID: 18831036 DOI: 10.1002/prot.22243] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
SUMO E3 ligase of the Siz/PIAS family that promotes sumoylation of target proteins contains SAP motif in its N-terminal region. The SAP motif with a consensus sequence of 35 residues was first proposed to be as a new DNA binding motif found in diverse nuclear proteins involved in chromosomal organization. We have determined solution structures of the SAP domains of SUMO ligases Siz1 from yeast and rice by NMR spectroscopy, showing that the structure of the SAP domain (residues 2-105) of rice Siz1 is a four-helix bundle with an up-down-extended loop-down-up topology, whereas the SAP domain (residues 1-111) of yeast Siz1 is comprised of five helices where the fifth helix alpha5 causes a significant change in the alignment of the four-helix bundle characteristic to the SAP domains of the Siz/PIAS family. We have also demonstrated that both SAP domains have binding ability to an A/T-rich DNA, but that binding affinity of yeast Siz1 SAP is at least by an order of magnitude higher than that of rice Siz1 SAP. Our NMR titration experiments clearly showed that yeast Siz1 SAP uses alpha2-helix for DNA binding more effectively than rice Siz1 SAP, which would result from the dislocation of this helix due to the existence of the extra helix alpha5. In addition, based on the structures of the SAP domains determined here and registered in Protein Data Bank, general features of structures of the SAP domains are discussed in conjunction with equivocal nature of their DNA binding.
Collapse
Affiliation(s)
- Rintaro Suzuki
- Protein Research Unit, National Institute of Agrobiological Sciences, Ibaraki 305-8602, Japan
| | | | | | | | | | | |
Collapse
|
34
|
Yu Y, Mahaney BL, Yano KI, Ye R, Fang S, Douglas P, Chen DJ, Lees-Miller SP. DNA-PK and ATM phosphorylation sites in XLF/Cernunnos are not required for repair of DNA double strand breaks. DNA Repair (Amst) 2008; 7:1680-92. [PMID: 18644470 DOI: 10.1016/j.dnarep.2008.06.015] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Revised: 06/21/2008] [Accepted: 06/23/2008] [Indexed: 11/30/2022]
Abstract
Nonhomologous end joining (NHEJ) is the major pathway for the repair of DNA double strand breaks (DSBs) in human cells. NHEJ requires the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), Ku70, Ku80, XRCC4, DNA ligase IV and Artemis, as well as DNA polymerases mu and lambda and polynucleotide kinase. Recent studies have identified an additional participant, XLF, for XRCC4-like factor (also called Cernunnos), which interacts with the XRCC4-DNA ligase IV complex and stimulates its activity in vitro, however, its precise role in the DNA damage response is not fully understood. Since the protein kinase activity of DNA-PKcs is required for NHEJ, we asked whether XLF might be a physiological target of DNA-PK. Here, we have identified two major in vitro DNA-PK phosphorylation sites in the C-terminal region of XLF, serines 245 and 251. We show that these represent the major phosphorylation sites in XLF in vivo and that serine 245 is phosphorylated in vivo by DNA-PK, while serine 251 is phosphorylated by Ataxia-Telangiectasia Mutated (ATM). However, phosphorylation of XLF did not have a significant effect on the ability of XLF to interact with DNA in vitro or its recruitment to laser-induced DSBs in vivo. Similarly, XLF in which the identified in vivo phosphorylation sites were mutated to alanine was able to complement the DSB repair defect as well as radiation sensitivity in XLF-deficient 2BN cells. We conclude that phosphorylation of XLF at these sites does not play a major role in the repair of IR-induced DSBs in vivo.
Collapse
Affiliation(s)
- Yaping Yu
- Department of Biochemistry and Molecular Biology, and The Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, Canada
| | | | | | | | | | | | | | | |
Collapse
|
35
|
Urano M, Huang Y, He F, Minami A, Ling CC, Li GC. Response to multiple radiation doses of fibroblasts over-expressing dominant negative Ku70. Int J Radiat Oncol Biol Phys 2008; 71:533-41. [PMID: 18374502 DOI: 10.1016/j.ijrobp.2007.12.061] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2006] [Revised: 11/21/2007] [Accepted: 12/22/2007] [Indexed: 11/30/2022]
Abstract
PURPOSE To evaluate the response of cells over-expressing dominant negative (DN) Ku70 to single and multiple small radiation doses. METHODS AND MATERIALS Clones of fibroblasts over-expressing DNKu70, DNKu70-7, DNKu70-11, and parental Rat-1 cells were irradiated under oxic or hypoxic conditions with single or multiple doses. Cells were trypsinized 0 or 6 h after irradiation to determine surviving fraction (SF). RESULTS Oxic DNKu70-7 or -11 cells trypsinized 6 h after irradiation were 1.52 or 1.25 and 1.28 or 1.15 times more sensitive than oxic Rat-1 at SF of 0.5 and 0.1, respectively. Hypoxic DNKu70-7 or -11 cells trypsinized 6 h after irradiation were 1.44 or 1.70 and 1.33 or 1.51 times more sensitive than hypoxic Rat-1 at SF of 0.5 and 0.1, respectively. To the multiple doses, oxic and hypoxic DNKu70-7 or -11 cells were 1.35 or 1.37 and 2.23 or 4.61 times more sensitive than oxic and hypoxic Rat-1, respectively, resulting in very small oxygen enhancement ratios. Namely, enhancement caused by DNKu70 under hypoxia after multiple doses was greater than that under oxic conditions and greater than that after single dose. CONCLUSIONS Over-expression of DNKu70 enhances cells' response to radiation given as a single dose and as multiple small doses. The enhancement after multiple doses was stronger under hypoxic than under oxic conditions. These results encourage the use of DNKu70 fragment in a gene-radiotherapy.
Collapse
Affiliation(s)
- Muneyasu Urano
- Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
| | | | | | | | | | | |
Collapse
|
36
|
Tsuji Y, Watanabe K, Araki K, Shinohara M, Yamagata Y, Tsurimoto T, Hanaoka F, Yamamura KI, Yamaizumi M, Tateishi S. Recognition of forked and single-stranded DNA structures by human RAD18 complexed with RAD6B protein triggers its recruitment to stalled replication forks. Genes Cells 2008; 13:343-54. [PMID: 18363965 DOI: 10.1111/j.1365-2443.2008.01176.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Post-replication DNA repair facilitates the resumption of DNA synthesis upon replication fork stalling at DNA damage sites. Despite the importance of RAD18 and polymerase eta (Poleta) for post-replication repair (PRR), the molecular mechanisms by which these factors are recruited to stalled replication forks are not well understood. We present evidence that human RAD18 complexed with RAD6B protein preferentially binds to forked and single-stranded DNA (ssDNA) structures, which are known to be localized at stalled replication forks. The SAP domain of RAD18 (residues 248-282) is crucial for binding of RAD18 complexed with RAD6B to DNA substrates. RAD18 mutated in the SAP domain fails to accumulate at DNA damage sites in vivo and does not guide DNA Poleta to stalled replication forks. The SAP domain is also required for the efficient mono-ubiquitination of PCNA. The SAP domain mutant fails to suppress the ultraviolet (UV)-sensitivity of Rad18-knockout cells. These results suggest that RAD18 complexed with RAD6B is recruited to stalled replication forks via interactions with forked DNA or long ssDNA structures, a process that is required for initiating PRR.
Collapse
Affiliation(s)
- Yuri Tsuji
- Cell Genetics, Institute of Molecular Embryology and Genetics, Kumamoto University, Kumamoto, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
37
|
Lehman JA, Hoelz DJ, Turchi JJ. DNA-dependent conformational changes in the Ku heterodimer. Biochemistry 2008; 47:4359-68. [PMID: 18355052 DOI: 10.1021/bi702284c] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Ionizing radiation induces DNA double-strand breaks which are repaired by the nonhomologous end joining (NHEJ) pathway. NHEJ is initiated upon Ku binding to the DNA ends and facilitating an interaction with the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). This heterotrimeric DNA-PK complex is then active as a serine/threonine protein kinase. The molecular mechanisms involved in DNA-PK activation are unknown. Considering the crucial role of Ku in this process, we therefore determined the influence of DNA binding on the structure of the Ku heterodimer. Chemical modification with NHS-biotin and mass spectrometry were used to identify sites of modification. Biotinylation of free Ku revealed several reactive lysines on Ku70 and Ku80 which were reduced or eliminated upon DNA binding. Interestingly, in the predicted C-terminal SAP domain of Ku70, biotinylation patterns were observed which suggest a structural change in this region of the protein induced by DNA binding. Limited proteolytic digests of free and DNA-bound Ku revealed a series of unique peptides, again, indicative of a change in the accessibility of the Ku70 and Ku80 C-terminal domains. A 10 kDa peptide was also identified which was preferentially generated under non-DNA-bound conditions and mapped to the C-terminus of Ku70. These results indicate a DNA-dependent movement or structural change in the C-terminal domains of Ku70 and Ku80 that may contribute to DNA-PKcs binding and activation. These results represent the first demonstration of DNA-induced changes in Ku structure and provide a framework for analysis of DNA-PKcs and the mechanism of DNA-PK activation.
Collapse
Affiliation(s)
- Jason A Lehman
- Biomedical Sciences Graduate Program, Wright State University, Dayton, Ohio 45435, USA
| | | | | |
Collapse
|
38
|
Devany M, Kappes F, Chen KM, Markovitz DM, Matsuo H. Solution NMR structure of the N-terminal domain of the human DEK protein. Protein Sci 2008; 17:205-15. [PMID: 18227428 PMCID: PMC2222715 DOI: 10.1110/ps.073244108] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2007] [Revised: 11/09/2007] [Accepted: 11/15/2007] [Indexed: 10/22/2022]
Abstract
The human DEK protein has a long-standing association with carcinogenesis since the DEK gene was originally identified in the t(6:9) chromosomal translocation in a subtype of patients with acute myelogenous leukemia (AML). Recent studies have partly unveiled DEK's cellular functions including apoptosis inhibition in primary cells as well as cancer cells, determination of 3' splice site of transcribed RNA, and suppression of transcription initiation by polymerase II. It has been previously shown that the N-terminal region of DEK, spanning residues 68-226, confers important in vitro and in vivo functions of DEK, which include double-stranded DNA (ds-DNA) binding, introduction of constrained positive supercoils into closed dsDNA, and apoptosis inhibition. In this paper, we describe the three-dimensional structure of the N-terminal domain of DEK (DEKntd) as determined using solution NMR. The C-terminal part of DEKntd, which contains a putative DNA-binding motif (SAF/SAP motif), folds into a helix-loop-helix structure. Interestingly, the N-terminal part of DEKntd shows a very similar structure to the C-terminal part, although the N-terminal and the C-terminal part differ distinctively in their amino acid sequences. As a consequence, the structure of DEKntd has a pseudo twofold plane symmetry. In addition, we tested dsDNA binding of DEKntd by monitoring changes of NMR chemical shifts upon addition of dsDNAs. We found that not only the C-terminal part containing the SAF/SAP motif but the N-terminal part is also involved in DEKntd's dsDNA binding. Our study illustrates a new structural variant and reveals novel dsDNA-binding properties for proteins containing the SAP/SAF motif.
Collapse
Affiliation(s)
- Matthew Devany
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | | | | | | | | |
Collapse
|
39
|
He F, Li L, Kim D, Wen B, Deng X, Gutin PH, Ling CC, Li GC. Adenovirus-mediated expression of a dominant negative Ku70 fragment radiosensitizes human tumor cells under aerobic and hypoxic conditions. Cancer Res 2007; 67:634-42. [PMID: 17234773 DOI: 10.1158/0008-5472.can-06-1860] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ku70 is one component of a protein complex, the Ku70/Ku80 heterodimer, which binds to DNA double-strand breaks and activates DNA-dependent protein kinase (DNA-PK), leading to DNA damage repair. Our previous work has confirmed that Ku70 is important for DNA damage repair in that Ku70 deficiency compromises the ability of cells to repair DNA double-strand breaks, increases the radiosensitivity of cells, and enhances radiation-induced apoptosis. Because of the radioresistance of some human cancers, particularly glioblastoma, we examined the use of a radio-gene therapy paradigm to sensitize cells to ionizing radiation. Based on the analysis of the structure-function of Ku70 and the crystal structure of Ku70/Ku80 heterodimer, we designed and identified a candidate dominant negative fragment involving an NH(2)-terminal deletion, and designated it as DNKu70. We generated this mutant construct, stably overexpressed it in Rat-1 cells, and showed that it has a dominant negative effect (i.e., DNKu70 overexpression results in decreased Ku-DNA end-binding activity, and increases radiosensitivity). We then constructed and generated recombinant replication-defective adenovirus, with DNKu70 controlled by the cytomegalovirus promoter, and infected human glioma U-87 MG cells and human colorectal tumor HCT-8 cells. We show that the infected cells significantly express DNKu70 and are greatly radiosensitized under both aerobic and hypoxic conditions. The functional ramification of DNKu70 was further shown in vivo: expression of DNKu70 inhibits radiation-induced DNA-PK catalytic subunit autophosphorylation and prolongs the persistence of gamma-H2AX foci. If radiation-resistant tumor cells could be sensitized by down-regulating the cellular level/activity of Ku/DNA-PK, this approach could be evaluated as an adjuvant to radiation therapy.
Collapse
Affiliation(s)
- Fuqiu He
- Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Rivera-Calzada A, Spagnolo L, Pearl LH, Llorca O. Structural model of full-length human Ku70-Ku80 heterodimer and its recognition of DNA and DNA-PKcs. EMBO Rep 2006; 8:56-62. [PMID: 17159921 PMCID: PMC1796749 DOI: 10.1038/sj.embor.7400847] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2006] [Revised: 09/11/2006] [Accepted: 10/02/2006] [Indexed: 11/10/2022] Open
Abstract
Recognition of DNA double-strand breaks during non-homologous end joining is carried out by the Ku70-Ku80 protein, a 150 kDa heterodimer that recruits the DNA repair kinase DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to the lesion. The atomic structure of a truncated Ku70-Ku80 was determined; however, the subunit-specific carboxy-terminal domain of Ku80--essential for binding to DNA-PKcs--was determined only in isolation, and the C-terminal domain of Ku70 was not resolved in its DNA-bound conformation. Both regions are conserved and mediate protein-protein interactions specific to mammals. Here, we reconstruct the three-dimensional structure of the human full-length Ku70-Ku80 dimer at 25 A resolution, alone and in complex with DNA, by using single-particle electron microscopy. We map the C-terminal regions of both subunits, and their conformational changes after DNA and DNA-PKcs binding to define a molecular model of the functions of these domains during DNA repair in the context of full-length Ku70-Ku80 protein.
Collapse
Affiliation(s)
- Angel Rivera-Calzada
- Centro de Investigaciones Biológicas (CIB), Spanish National Research Council (CSIC), Ramiro de Maeztu 9, Campus Complutense University, Madrid 28040, Spain
| | - Laura Spagnolo
- Section of Structural Biology and Cancer Research UK DNA Repair Enzyme Research Group, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK
| | - Laurence H Pearl
- Section of Structural Biology and Cancer Research UK DNA Repair Enzyme Research Group, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK
- Tel: +44 20 7153 5422; Fax: +44 20 7153 5457; E-mail:
| | - Oscar Llorca
- Centro de Investigaciones Biológicas (CIB), Spanish National Research Council (CSIC), Ramiro de Maeztu 9, Campus Complutense University, Madrid 28040, Spain
- Tel: +34 91 837 3112 ext 4446; Fax: +34 91 5360432; E-mail:
| |
Collapse
|
41
|
Zhang Z, Hu W, Cano L, Lee TD, Chen DJ, Chen Y. Solution structure of the C-terminal domain of Ku80 suggests important sites for protein-protein interactions. Structure 2004; 12:495-502. [PMID: 15016365 DOI: 10.1016/j.str.2004.02.007] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Accepted: 11/14/2003] [Indexed: 10/26/2022]
Abstract
The solution structure of Ku80 CTD from residue 566 to 732 has been solved in order to gain insights into the mechanisms of its interactions with other proteins. The structure reveals a topology similar to several common scaffolds for protein-protein interactions, in the absence of significant sequence similarity to these proteins. Conserved surface amino acid residues are clustered on two main surface areas, which are likely involved in mediating interactions between Ku80 and other proteins. The Ku70/Ku80 heterodimer has been shown to be involved in at least three processes, nonhomologous end joining, transcription, and telomere maintenance, and thus it needs to interact with different proteins involved in these different processes. The three-dimensional structure of the Ku80 C-terminal domain and the availability of NMR chemical shift assignments provide a basis for further investigation of the interactions between Ku80 and other proteins in these Ku-dependent cellular functions.
Collapse
Affiliation(s)
- Ziming Zhang
- Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | | | | | | | | | | |
Collapse
|
42
|
Okubo S, Hara F, Tsuchida Y, Shimotakahara S, Suzuki S, Hatanaka H, Yokoyama S, Tanaka H, Yasuda H, Shindo H. NMR structure of the N-terminal domain of SUMO ligase PIAS1 and its interaction with tumor suppressor p53 and A/T-rich DNA oligomers. J Biol Chem 2004; 279:31455-61. [PMID: 15133049 DOI: 10.1074/jbc.m403561200] [Citation(s) in RCA: 73] [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
A member of the PIAS (protein inhibitor of activated STAT) family of proteins, PIAS1, have been reported to serve as an E3-type SUMO ligase for tumor suppressor p53 and its own. It also was proposed that the N-terminal domain of PIAS1 interacts with DNA as well as p53. Extensive biochemical studies have been devoted recently to understand sumoylations and its biological implications, whereas the structural aspects of the PIAS family and the mechanism of its interactions with various factors are less well known to date. In this study, the three-dimensional structure of the N-terminal domain (residues 1-65) of SUMO ligase PIAS1 was determined by NMR spectroscopy. The structure revealed a unique four-helix bundle with a topology of an up-down-extended loop-down-up, a part of which the helix-extended loop-helix represented the SAP (SAF-A/B, Acinus, and PIAS) motif. Thus, this N-terminal domain may be referred to as a four-helix SAP domain. The glutathione S-transferase pull-down assay demonstrated that this domain possesses a binding ability to tumor suppressor p53, a target protein for sumoylation by PIAS1, whereas gel mobility assays showed that it has a strong affinity toward A/T-rich DNA. An NMR analysis of the four-helix SAP domain complexed with the 16-bp-long DNA demonstrated that one end of the four-helix bundle is the binding site and may fit into the minor groove of DNA. The three-dimensional structure and its binding duality are discussed in conjunction with the biological functions of PIAS1 as a SUMO ligase.
Collapse
Affiliation(s)
- Seiji Okubo
- School of Pharmacy, Tokyo University of Pharmacy & Life Science, Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
43
|
Affiliation(s)
- Jessica A Downs
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK.
| | | |
Collapse
|
44
|
Cohen HY, Lavu S, Bitterman KJ, Hekking B, Imahiyerobo TA, Miller C, Frye R, Ploegh H, Kessler BM, Sinclair DA. Acetylation of the C terminus of Ku70 by CBP and PCAF controls Bax-mediated apoptosis. Mol Cell 2004; 13:627-38. [PMID: 15023334 DOI: 10.1016/s1097-2765(04)00094-2] [Citation(s) in RCA: 445] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2003] [Revised: 12/30/2003] [Accepted: 12/30/2003] [Indexed: 10/26/2022]
Abstract
Apoptosis is a key tumor suppression mechanism that can be initiated by activation of the proapoptotic factor Bax. The Ku70 DNA end-joining protein has recently been shown to suppress apoptosis by sequestering Bax from mitochondria. The mechanism by which Bax is regulated remains unknown. Here, we identify eight lysines in Ku70 that are targets for acetylation in vivo. Five of these, K539, K542, K544, K533, and K556, lie in the C-terminal linker domain of Ku70 adjacent to the Bax interaction domain. We show that CBP and PCAF efficiently acetylate K542 in vitro and associate with Ku70 in vivo. Mimicking acetylation of K539 or K542 or treating cells with deacetylase inhibitors abolishes the ability of Ku70 to suppress Bax-mediated apoptosis. We demonstrate that increased acetylation of Ku70 disrupts the Ku70-Bax interaction and coincides with cytoplasmic accumulation of CBP. These results shed light on the role of acetyltransferases as tumor suppressors.
Collapse
Affiliation(s)
- Haim Y Cohen
- Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115 USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Harris R, Esposito D, Sankar A, Maman JD, Hinks JA, Pearl LH, Driscoll PC. The 3D solution structure of the C-terminal region of Ku86 (Ku86CTR). J Mol Biol 2004; 335:573-82. [PMID: 14672664 DOI: 10.1016/j.jmb.2003.10.047] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In eukaryotes the non-homologous end-joining repair of double strand breaks in DNA is executed by a series of proteins that bring about the synapsis, preparation and ligation of the broken DNA ends. The mechanism of this process appears to be initiated by the obligate heterodimer (Ku70/Ku86) protein complex Ku that has affinity for DNA ends. Ku then recruits the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The three-dimensional structures of the major part of the Ku heterodimer, representing the DNA-binding core, both free and bound to DNA are known from X-ray crystallography. However, these structures lack a region of ca 190 residues from the C-terminal region (CTR) of the Ku86 subunit (also known as Lupus Ku autoantigen p86, Ku80, or XRCC5) that includes the extreme C-terminal tail that is reported to be sufficient for DNA-PKcs-binding. We have examined the structural characteristics of the Ku86CTR protein expressed in bacteria. By deletion mutagenesis and heteronuclear NMR spectroscopy we localised a globular domain consisting of residues 592-709. Constructs comprising additional residues either to the N-terminal side (residues 543-709), or the C-terminal side (residues 592-732), which includes the putative DNA-PKcs-binding motif, yielded NMR spectra consistent with these extra regions lacking ordered structure. The three-dimensional solution structure of the core globular domain of the C-terminal region of Ku86 (Ku86CTR(592-709)) has been determined using heteronuclear NMR spectroscopy and dynamical simulated annealing using structural restraints from nuclear Overhauser effect spectroscopy, and scalar and residual dipolar couplings. The polypeptide fold comprises six regions of alpha-helical secondary structure that has an overall superhelical topology remotely homologous to the MIF4G homology domain of the human nuclear cap binding protein 80 kDa subunit and the VHS domain of the Drosophila protein Hrs, though strict analysis of the structures suggests that these domains are not functionally related. Two prominent hydrophobic pockets in the gap between helices alpha2 and alpha4 suggest a potential ligand-binding characteristic for this globular domain.
Collapse
Affiliation(s)
- Richard Harris
- Bloomsbury Centre for Structural Biology, University College London, Gower Street, London WC1E 6BT, UK
| | | | | | | | | | | | | |
Collapse
|
46
|
Sawada M, Hayes P, Matsuyama S. Cytoprotective membrane-permeable peptides designed from the Bax-binding domain of Ku70. Nat Cell Biol 2003; 5:352-7. [PMID: 12652309 DOI: 10.1038/ncb955] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2002] [Revised: 12/02/2002] [Accepted: 02/21/2003] [Indexed: 12/31/2022]
Abstract
Bax is a pro-apoptotic member of Bcl-2 family proteins and is central to mitochondria-dependent apoptosis. Bax resides in the cytosol as a quiescent protein and translocates into mitochondria after apoptotic stimuli. Ku70 is a 70K subunit of the Ku complex, which has an important role in DNA double-strand break (DSB) repair in the nucleus. In another article in this issue, we reported that Ku70 interacts with pro-apoptotic protein Bax in the cytosol and prevents its mitochondrial translocation, suggesting that Ku70 suppresses Bax-mediated apoptosis. Here, we describe the development of a new membrane-permeable peptide, Bax-inhibiting peptide (BIP) that inhibits Bax-mediated apoptosis, on the basis of the previous finding that showed an interaction between Ku70 and Bax. BIP is comprised of five amino acids designed from the Bax-binding domain of Ku70, and suppresses the mitochondrial translocation of Bax. BIP inhibited Bax-mediated apoptosis induced by staurosporine, UVC irradiation and anti-cancer drugs in several types of cells. BIP may provide valuable information in the development of therapeutics that control apoptosis-related diseases.
Collapse
Affiliation(s)
- Motoshi Sawada
- Blood Research Institute, The Blood Center of South Eastern Wisconsin and Department of Biochemistry, Medical College of Wisconsin 8727 Watertown Plank Rd, Milwaukee WI 53226, USA
| | | | | |
Collapse
|
47
|
Mo X, Dynan WS. Subnuclear localization of Ku protein: functional association with RNA polymerase II elongation sites. Mol Cell Biol 2002; 22:8088-99. [PMID: 12391174 PMCID: PMC134733 DOI: 10.1128/mcb.22.22.8088-8099.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ku is an abundant nuclear protein with an essential function in the repair of DNA double-strand breaks. Various observations suggest that Ku also interacts with the cellular transcription machinery, although the mechanism and significance of this interaction are not well understood. In the present study, we investigated the subnuclear distribution of Ku in normally growing human cells by using confocal microscopy, chromatin immunoprecipitation, and protein immunoprecipitation. All three approaches indicated association of Ku with RNA polymerase II (RNAP II) elongation sites. This association occurred independently of the DNA-dependent protein kinase catalytic subunit and was highly selective. There was no detectable association with the initiating isoform of RNAP II or with the general transcription initiation factors. In vitro protein-protein interaction assays demonstrated that the association of Ku with elongation proteins is mediated, in part, by a discrete C-terminal domain in the Ku80 subunit. Functional disruption of this interaction with a dominant-negative mutant inhibited transcription in vitro and in vivo and suppressed cell growth. These results suggest that association of Ku with transcription sites is important for maintenance of global transcription levels. Tethering of double-strand break repair proteins to defined subnuclear structures may also be advantageous in maintenance of genome stability.
Collapse
Affiliation(s)
- Xianming Mo
- Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912, USA
| | | |
Collapse
|
48
|
Willis DM, Loewy AP, Charlton-Kachigian N, Shao JS, Ornitz DM, Towler DA. Regulation of osteocalcin gene expression by a novel Ku antigen transcription factor complex. J Biol Chem 2002; 277:37280-91. [PMID: 12145306 DOI: 10.1074/jbc.m206482200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously described an osteocalcin (OC) fibroblast growth factor (FGF) response element (FRE) DNA binding activity as a target of Msx2 transcriptional regulation. We now identify Ku70, Ku80, and Tbdn100, a variant of Tubedown-1, as constituents of the purified OCFRE-binding complex. Northern and Western blot analyses demonstrate expression of Ku and Tbdn100 in MC3T3E1 osteoblasts. FGF2 treatment regulates Ku, but not Tbdn100, protein accumulation. Gel supershift studies confirm sequence-specific DNA binding of Ku in the OCFRE complex; chromatin immunoprecipitation assays confirm association of Ku and Tbdn100 with the endogenous OC promoter. In the promoter region -154 to -113, the OCFRE is juxtaposed to OSE2, an osteoblast-specific element that binds Runx2 (Osf2, Cbfa1). Expression of the Ku.Tbdn100 complex up-regulates both the basal and Runx2-dependent transcription driven by this 42-bp OC promoter element, reconstituted in CV-1 cells. Synergistic transactivation occurs in the presence of activated FGF receptor 2 signaling. Msx2 suppresses Ku- and Runx2-dependent transcription; suppression is dependent upon the Msx2 homeodomain NH(2)-terminal arm and extension. Pull-down assays confirm physical interactions between Ku and these co-regulatory transcription factors, consistent with the functional interactions identified. Finally, cultured Ku70 -/- calvarial cells exhibit a profound, selective deficiency in OC expression as compared with wild-type calvarial cells, confirming the biochemical data showing a role for Ku in OC transcription. In toto, these data indicate that a novel Ku antigen complex assembles on the OC promoter, functioning in concert with Msx2 and Runx2 to regulate OC gene expression.
Collapse
Affiliation(s)
- David M Willis
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | | | | | | | | | | |
Collapse
|
49
|
Abstract
DNA double-strand break repair is a complex process that requires multiple enzymatic and structural activities to rejoin or repair the broken DNA ends using one of several repair pathways. These enzymatic and structural activities include end detection, end processing and alignment of DNA ends. Recent structural and functional studies of the DNA double-strand break repair factors Mre11/Rad50, Ku70/80 and Xrcc4 show how these enzymes combine and assemble both enzymatic and structural activities in DNA double-strand break repair.
Collapse
|