151
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Schmutz V, Wagner J, Janel-Bintz R, Fuchs RPP, Cordonnier AM. Requirements for PCNA monoubiquitination in human cell-free extracts. DNA Repair (Amst) 2007; 6:1726-31. [PMID: 17669698 DOI: 10.1016/j.dnarep.2007.06.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Revised: 06/11/2007] [Accepted: 06/13/2007] [Indexed: 10/23/2022]
Abstract
The Rad6/Rad18-dependent monoubiquitination of PCNA plays a crucial role in regulating replication past DNA damage in eukaryotic cells. We show here that in human cell-free extracts, efficient PCNA monoubiquitination requires both the synthesis of relatively long DNA tracts and polymerase idling or stalling at sites of DNA modification or DNA secondary structures. This dual dependency suggests a dynamic process in which, following initiation, the DNA synthesizing complex undergoes modifications that make it competent as a mediator for the activation of the Rad6/Rad18 pathway.
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Affiliation(s)
- Valérie Schmutz
- Institut Gilbert Laustriat, Biomolécules, Biotechnologie, Innovations thérapeutiques,UMR 7175 - LC1 - CNRS/ULP, ESBS, Bld Sébastien Brandt, BP 10413, Illkirch 67412, France
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152
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Langerak P, Nygren AOH, Krijger PHL, van den Berk PCM, Jacobs H. A/T mutagenesis in hypermutated immunoglobulin genes strongly depends on PCNAK164 modification. ACTA ACUST UNITED AC 2007; 204:1989-98. [PMID: 17664295 PMCID: PMC2118671 DOI: 10.1084/jem.20070902] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
B cells use translesion DNA synthesis (TLS) to introduce somatic mutations around genetic lesions caused by activation-induced cytidine deaminase. Monoubiquitination at lysine164 of proliferating cell nuclear antigen (PCNAK164) stimulates TLS. To determine the role of PCNAK164 modifications in somatic hypermutation, PCNAK164R knock-in mice were generated. PCNAK164R/K164R mutants are born at a sub-Mendelian frequency. Although PCNAK164R/K164R B cells proliferate and class switch normally, the mutation spectrum of hypermutated immunoglobulin (Ig) genes alters dramatically. A strong reduction of mutations at template A/T is associated with a compensatory increase at G/C, which is a phenotype similar to polymerase η (Polη) and mismatch repair–deficient B cells. Mismatch recognition, monoubiquitinated PCNA, and Polη likely cooperate in establishing mutations at template A/T during replication of Ig genes.
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Affiliation(s)
- Petra Langerak
- The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands
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153
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Bish RA, Myers MP. Werner helicase-interacting protein 1 binds polyubiquitin via its zinc finger domain. J Biol Chem 2007; 282:23184-93. [PMID: 17550899 DOI: 10.1074/jbc.m701042200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA repair is regulated on many levels by ubiquitination. In order to identify novel connections between DNA repair pathways and ubiquitin signaling, we used mass spectrometry to identify proteins that interact with lysine 6-linked polyubiquitin chains. From this proteomic screen, we identified the DNA repair protein WRNIP1 (Werner helicase-interacting protein 1), along with nucleosome assembly protein 1, as novel ubiquitin-interacting proteins. We found that a small zinc finger domain at the N terminus of WRNIP1 is sufficient and necessary for noncovalent ubiquitin binding. This ubiquitin-binding zinc finger (UBZ) domain binds polyubiquitin but not monoubiquitin and appears to show no specificity for polyubiquitin chain linkage. A homologous zinc finger domain in RAD18 also binds polyubiquitin, suggesting a wider role for the UBZ domain in DNA repair. The WRNIP1 ubiquitin-binding function, along with its previously established ATPase activity, suggests that WRNIP1 plays a role in the metabolism of ubiquitinated proteins. Supporting this model, deletion of MGS1, the yeast homolog of WRNIP1, slows the rate of ubiquitin turnover, rendering yeast resistant to cycloheximide. We also find that WRNIP1 is heavily modified with ubiquitin and SUMO, revealing complex layers in the involvement of ubiquitin pathway proteins in the regulation of DNA repair. The novel ubiquitin-binding ability of WRNIP1 sheds light on the role of UBZ domain-containing proteins in postreplication DNA repair.
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Affiliation(s)
- Rebecca A Bish
- Watson School of Biological Sciences, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
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154
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García-Ortiz MV, Roldán-Arjona T, Ariza RR. The noncatalytic C-terminus of AtPOLK Y-family DNA polymerase affects synthesis fidelity, mismatch extension and translesion replication. FEBS J 2007; 274:3340-50. [PMID: 17550419 DOI: 10.1111/j.1742-4658.2007.05868.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Cell survival depends not only on the ability to repair damaged DNA but also on the capability to perform DNA replication on unrepaired or imperfect templates. Crucial to this process are specialized DNA polymerases belonging to the Y family. These enzymes share a similar catalytic fold in their N-terminal region, and most of them have a less-well-conserved C-terminus which is not required for catalytic activity. Although this region is essential for appropriate localization and recruitment in vivo, its precise role during DNA synthesis remains unclear. Here we have compared the catalytic properties of AtPOLK, an Arabidopsis orthologue of mammalian pol kappa, and a truncated version lacking 193 amino acids from its C-terminus. We found that C-terminally truncated AtPOLK is a high-efficiency mutant protein, the DNA-binding capacity of which is not affected but it has higher catalytic efficiency and fidelity than the full-length enzyme. The truncated protein shows increased propensity to extend mispaired primer termini through misalignment and enhanced error-free bypass activity on DNA templates containing 7,8-dihydro-8-oxoGuanine. These results suggest that, in addition to facilitating recruitment to the replication fork, the C-terminus of Y-family DNA polymerases may also play a role in the kinetic control of their enzymatic activity.
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155
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Abstract
Inheritance requires genome duplication, reproduction of chromatin and its epigenetic information, mechanisms to ensure genome integrity, and faithful transmission of the information to progeny. Proliferating cell nuclear antigen (PCNA)-a cofactor of DNA polymerases that encircles DNA-orchestrates several of these functions by recruiting crucial players to the replication fork. Remarkably, many factors that are involved in replication-linked processes interact with a particular face of PCNA and through the same interaction domain, indicating that these interactions do not occur simultaneously during replication. Switching of PCNA partners may be triggered by affinity-driven competition, phosphorylation, proteolysis, and modification of PCNA by ubiquitin and SUMO.
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Affiliation(s)
- George-Lucian Moldovan
- Department of Molecular Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18 82152 Martinsried, Germany
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156
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Woelk T, Sigismund S, Penengo L, Polo S. The ubiquitination code: a signalling problem. Cell Div 2007; 2:11. [PMID: 17355622 PMCID: PMC1832185 DOI: 10.1186/1747-1028-2-11] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Accepted: 03/13/2007] [Indexed: 11/10/2022] Open
Abstract
Ubiquitin is a highly versatile post-translational modification that controls virtually all types of cellular events. Over the past ten years we have learned that diverse forms of ubiquitin modifications and of ubiquitin binding modules co-exist in the cell, giving rise to complex networks of protein:protein interactions. A central problem that continues to puzzle ubiquitinologists is how cells translate this myriad of stimuli into highly specific responses. This is a classical signalling problem. Here, we draw parallels with the phosphorylation signalling pathway and we discuss the expanding repertoire of ubiquitin signals, signal tranducers and signalling-regulated E3 enzymes. We examine recent advances in the field, including a new mechanism of regulation of E3 ligases that relies on ubiquitination.
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Affiliation(s)
- Tanja Woelk
- IFOM, Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139, Milan, Italy
| | - Sara Sigismund
- IFOM, Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139, Milan, Italy
| | - Lorenza Penengo
- IFOM, Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139, Milan, Italy
| | - Simona Polo
- IFOM, Istituto FIRC di Oncologia Molecolare, Via Adamello 16, 20139, Milan, Italy
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157
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Bomar MG, Pai MT, Tzeng SR, Li SSC, Zhou P. Structure of the ubiquitin-binding zinc finger domain of human DNA Y-polymerase eta. EMBO Rep 2007; 8:247-51. [PMID: 17304240 PMCID: PMC1808033 DOI: 10.1038/sj.embor.7400901] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 12/04/2006] [Accepted: 12/07/2006] [Indexed: 11/08/2022] Open
Abstract
The ubiquitin-binding zinc finger (UBZ) domain of human DNA Y-family polymerase (pol) eta is important in the recruitment of the polymerase to the stalled replication machinery in translesion synthesis. Here, we report the solution structure of the pol eta UBZ domain and its interaction with ubiquitin. We show that the UBZ domain adopts a classical C(2)H(2) zinc-finger structure characterized by a betabetaalpha fold. Nuclear magnetic resonance titration maps the binding interfaces between UBZ and ubiquitin to the alpha-helix of the UBZ domain and the canonical hydrophobic surface of ubiquitin defined by residues L8, I44 and V70. Although the UBZ domain binds ubiquitin through a single alpha-helix, in a manner similar to the inverted ubiquitin-interacting motif, its structure is distinct from previously characterized ubiquitin-binding domains. The pol eta UBZ domain represents a novel member of the C(2)H(2) zinc finger family that interacts with ubiquitin to regulate translesion synthesis.
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Affiliation(s)
- Martha G Bomar
- Department of Biochemistry, Duke University Medical Center, Research Drive, 242 Nanaline Duke Building, Durham, North Carolina 27710, USA
| | - Ming-Tao Pai
- Department of Biochemistry, Duke University Medical Center, Research Drive, 242 Nanaline Duke Building, Durham, North Carolina 27710, USA
| | - Shiou-Ru Tzeng
- Department of Biochemistry and the Siebens–Drake Medical Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario N6G 2V4, Canada
| | - Shawn Shun-Cheng Li
- Department of Biochemistry and the Siebens–Drake Medical Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario N6G 2V4, Canada
| | - Pei Zhou
- Department of Biochemistry, Duke University Medical Center, Research Drive, 242 Nanaline Duke Building, Durham, North Carolina 27710, USA
- Tel: +1 919 668 6409; Fax: +1 919 684 8885; E-mail:
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158
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Kirkin V, Dikic I. Role of ubiquitin- and Ubl-binding proteins in cell signaling. Curr Opin Cell Biol 2007; 19:199-205. [PMID: 17303403 DOI: 10.1016/j.ceb.2007.02.002] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Accepted: 02/05/2007] [Indexed: 12/15/2022]
Abstract
Besides tagging proteins for degradation, ubiquitin is now recognized as a signaling module for diverse cellular processes, including progression through the cell cycle, DNA repair, gene transcription, receptor trafficking and endocytosis. Recent advances have indicated the existence of a wide variety of ubiquitin-binding proteins that, upon recognition of conjugated ubiquitin moieties, can control assembly of complex signaling networks. Small ubiquitin-like proteins, like SUMO, emerge to play biological roles distinct from ubiquitin, and require specific recognition by a dedicated set of proteins. Identification and characterization of recognition motifs and domains for ubiquitin-like proteins have just begun, promising new insights into the diversity of functions ubiquitin family proteins have in physiological and pathological settings.
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Affiliation(s)
- Vladimir Kirkin
- Institute of Biochemistry II, Goethe University Hospital, Theodor-Stern-Kai 7, D-60590 Frankfurt (Main), Germany
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159
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Parker JL, Bielen AB, Dikic I, Ulrich HD. Contributions of ubiquitin- and PCNA-binding domains to the activity of Polymerase eta in Saccharomyces cerevisiae. Nucleic Acids Res 2007; 35:881-9. [PMID: 17251197 PMCID: PMC1807963 DOI: 10.1093/nar/gkl1102] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Bypassing of DNA lesions by damage-tolerant DNA polymerases depends on the interaction of these enzymes with the monoubiquitylated form of the replicative clamp protein, PCNA. We have analyzed the contributions of ubiquitin and PCNA binding to damage bypass and damage-induced mutagenesis in Polymerase η (encoded by RAD30) from the budding yeast Saccharomyces cerevisiae. We report here that a ubiquitin-binding domain provides enhanced affinity for the ubiquitylated form of PCNA and is essential for in vivo function of the polymerase, but only in conjunction with a basal affinity for the unmodified clamp, mediated by a conserved PCNA interaction motif. We show that enhancement of the interaction and function in damage tolerance does not depend on the ubiquitin attachment site within PCNA. Like its mammalian homolog, budding yeast Polymerase η itself is ubiquitylated in a manner dependent on its ubiquitin-binding domain.
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Affiliation(s)
- Joanne L. Parker
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, EN6 3LD, United Kingdom Max Planck Insitute for Terrestrial Microbiology, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Goethe University Medical School, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany
| | - Aleksandra B. Bielen
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, EN6 3LD, United Kingdom Max Planck Insitute for Terrestrial Microbiology, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Goethe University Medical School, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany
| | - Ivan Dikic
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, EN6 3LD, United Kingdom Max Planck Insitute for Terrestrial Microbiology, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Goethe University Medical School, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany
| | - Helle D. Ulrich
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, EN6 3LD, United Kingdom Max Planck Insitute for Terrestrial Microbiology, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Goethe University Medical School, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany
- *To whom the correspondence should be addressed. Tel: +44 1707 625821; Fax: +44 1707 625550; E-mail:
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160
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Barkley LR, Ohmori H, Vaziri C. Integrating S-phase checkpoint signaling with trans-lesion synthesis of bulky DNA adducts. Cell Biochem Biophys 2007; 47:392-408. [PMID: 17652783 PMCID: PMC3103048 DOI: 10.1007/s12013-007-0032-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 01/12/2023]
Abstract
Bulky adducts are DNA lesions generated in response to environmental agents including benzo[a]pyrene (a combustion product) and solar ultraviolet radiation. Error-prone replication of adducted DNA can cause mutations, which may result in cancer. To minimize the detrimental effects of bulky adducts and other DNA lesions, S-phase checkpoint mechanisms sense DNA damage and integrate DNA repair with ongoing DNA replication. The essential protein kinase Chk1 mediates the S-phase checkpoint, inhibiting initiation of new DNA synthesis and promoting stabilization and recovery of stalled replication forks. Here we review the mechanisms by which Chk1 is activated in response to bulky adducts and potential mechanisms by which Chk1 signaling inhibits the initiation stage of DNA synthesis. Additionally, we discuss mechanisms by which Chk1 signaling facilitates bypass of bulky lesions by specialized Y-family DNA polymerases, thereby attenuating checkpoint signaling and allowing resumption of normal cell cycle progression.
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Affiliation(s)
- Laura R Barkley
- Department of Genetics and Genomics, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA
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161
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Abstract
Ubiquitin and ubiquitin-like proteins (Ubls) are signalling messengers that control many cellular functions, such as cell proliferation, apoptosis, the cell cycle and DNA repair. It is becoming apparent that the deregulation of ubiquitin pathways results in the development of human diseases, including many types of tumours. Here we summarize the common principles and specific features of ubiquitin and Ubls in the regulation of cancer-relevant pathways, and discuss new strategies to target ubiquitin signalling in drug discovery.
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Affiliation(s)
- Daniela Hoeller
- Institute of Biochemistry II, Goethe University School of Medicine, University Hospital, Building 75, Theodour-Stern-Kai 7, D-60590 Frankfurt, Germany
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162
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Northam MR, Garg P, Baitin DM, Burgers PMJ, Shcherbakova PV. A novel function of DNA polymerase zeta regulated by PCNA. EMBO J 2006; 25:4316-25. [PMID: 16957771 PMCID: PMC1570441 DOI: 10.1038/sj.emboj.7601320] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2006] [Accepted: 08/09/2006] [Indexed: 11/09/2022] Open
Abstract
DNA polymerase zeta (Polzeta) participates in translesion DNA synthesis and is involved in the generation of the majority of mutations induced by DNA damage. The mechanisms that license access of Polzeta to the primer terminus and regulate the extent of its participation in genome replication are poorly understood. The Polzeta-dependent damage-induced mutagenesis requires monoubiquitination of proliferating cell nuclear antigen (PCNA) that is triggered by exposure to mutagens. We show that Polzeta contributes to DNA replication and causes mutagenesis not only in response to DNA damage but also in response to malfunction of normal replicative machinery due to mutations in replication genes. These replication defects lead to ubiquitination of PCNA even in the absence of DNA damage. Unlike damage-induced mutagenesis, the Polzeta-dependent spontaneous mutagenesis in replication mutants is reduced in strains defective in both ubiquitination and sumoylation of Lys164 of PCNA. Additionally, studies of a PCNA mutant defective for functional interactions with Polzeta, but not for monoubiquitination by the Rad6/Rad18 complex demonstrate a role for PCNA in regulating the mutagenic activity of Polzeta separate from its modification at Lys164.
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Affiliation(s)
- Matthew R Northam
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
| | - Parie Garg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, MO, USA
| | - Dmitri M Baitin
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
| | - Peter M J Burgers
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, MO, USA
| | - Polina V Shcherbakova
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198, USA. Tel.: +1 402 559 7694; Fax: +1 402 559 8270; E-mail:
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163
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Chiu RK, Brun J, Ramaekers C, Theys J, Weng L, Lambin P, Gray DA, Wouters BG. Lysine 63-polyubiquitination guards against translesion synthesis-induced mutations. PLoS Genet 2006; 2:e116. [PMID: 16789823 PMCID: PMC1513265 DOI: 10.1371/journal.pgen.0020116] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Accepted: 06/12/2006] [Indexed: 12/23/2022] Open
Abstract
Eukaryotic cells possess several mechanisms to protect the integrity of their DNA against damage. These include cell-cycle checkpoints, DNA-repair pathways, and also a distinct DNA damage–tolerance system that allows recovery of replication forks blocked at sites of DNA damage. In both humans and yeast, lesion bypass and restart of DNA synthesis can occur through an error-prone pathway activated following mono-ubiquitination of proliferating cell nuclear antigen (PCNA), a protein found at sites of replication, and recruitment of specialized translesion synthesis polymerases. In yeast, there is evidence for a second, error-free, pathway that requires modification of PCNA with non-proteolytic lysine 63-linked polyubiquitin (K63-polyUb) chains. Here we demonstrate that formation of K63-polyUb chains protects human cells against translesion synthesis–induced mutations by promoting recovery of blocked replication forks through an alternative error-free mechanism. Furthermore, we show that polyubiquitination of PCNA occurs in UV-irradiated human cells. Our findings indicate that K63-polyubiquitination guards against environmental carcinogenesis and contributes to genomic stability. Genome instability is associated with increased cancer risk, and thus considerable effort has been put into unraveling the mechanisms underlying genome surveillance. Guarding the integrity of DNA are a number of DNA-repair and cell cycle–control systems. Insight into how these pathways become activated is crucially important to the understanding of carcinogenesis and in the development of cancer treatments. This study concerns a distinct pathway that promotes the tolerance of DNA damage during its replication phase. Prior attempts to investigate this pathway in human cells have been difficult due to extensive redundancy in the genes that carry out this process. Previous knowledge from lower organisms suggested the requirement for enzymes capable of constructing a chain of ubiquitin molecules linked in a specific manner. The authors used a novel approach to disrupt the formation of these ubiquitin chains in human cells and found that this caused a significant increase in mutations after exposure to UV light. Several lines of evidence implicate a family of error-prone enzymes, called translesion synthesis polymerases, in the formation of these mutations. Furthermore, they provide evidence suggesting that proliferating cell nuclear antigen (PCNA), a protein found at sites of replication, is the relevant target of these chains in human cells. These findings indicate that polyubiquitination guards against environmental carcinogenesis and contributes to genomic stability.
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Affiliation(s)
- Roland K Chiu
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
| | - Jan Brun
- Ottawa Health Research Institute, Ottawa, Ontario, Canada
| | - Chantal Ramaekers
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
| | - Jan Theys
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
| | - Lin Weng
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
| | - Philippe Lambin
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
| | - Douglas A Gray
- Ottawa Health Research Institute, Ottawa, Ontario, Canada
- * To whom correspondence should be addressed. E-mail: (DAG); (BGW)
| | - Bradly G Wouters
- Department of Radiation Oncology, GROW Research Institute, University of Maastricht, Maastricht, Netherlands
- * To whom correspondence should be addressed. E-mail: (DAG); (BGW)
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