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Lin X, Soni A, Hessenow R, Sun Y, Mladenov E, Guberina M, Stuschke M, Iliakis G. Talazoparib enhances resection at DSBs and renders HR-proficient cancer cells susceptible to Polθ inhibition. Radiother Oncol 2024; 200:110475. [PMID: 39147034 DOI: 10.1016/j.radonc.2024.110475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 07/02/2024] [Accepted: 08/12/2024] [Indexed: 08/17/2024]
Abstract
BACKGROUND AND PURPOSE The PARP inhibitor (PARPi), Talazoparib (BMN673), effectively and specifically radiosensitizes cancer cells. Radiosensitization is mediated by a shift in the repair of ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) toward PARP1-independent, alternative end-joining (alt-EJ). DNA polymerase theta (Polθ) is a key component of this PARP1-independent alt-EJ pathway and we show here that its inhibition can further radiosensitize talazoparib-treated cells. The purpose of the present work is to explore mechanisms and dynamics underpinning enhanced talazoparib radiosensitization by Polθ inhibitors in HR-proficient cancer cells. METHODS AND MATERIALS Radiosensitization to PARPis, talazoparib, olaparib, rucaparib and veliparib was assessed by clonogenic survival. Polθ-proficient and -deficient cells were treated with PARPis and/or with the Polθ inhibitors ART558 or novobiocin. The role of DNA end-resection was studied by down-regulating CtIP and MRE11 expression using siRNAs. DSB repair was assessed by scoring γH2AX foci. The formation of chromosomal abnormalities was assessed as evidence of alt-EJ function using G2-specific cytogenetic analysis. RESULTS Talazoparib exerted pronounced radiosensitization that varied among the tested cancer cell lines; however, radiosensitization was undetectable in normal cells. Other commonly used PARPis, olaparib, veliparib, or rucaparib were ineffective radiosensitizers under our experimental conditions. Although genetic ablation or pharmacological inhibition of Polθ only mildly radiosensitized cancer cells, talazoparib-treated cells were markedly further radiosensitized. Mechanistically, talazoparib shunted DSBs to Polθ-dependent alt-EJ by enhancing DNA end-resection in a CtIP- and MRE11-dependent manner - an effect detectable at low, but not high IR doses. Chromosomal translocation analysis in talazoparib-treated cells exposed to Polθ inhibitors suggested that PARP1- and Polθ-dependent alt-EJ pathways may complement, but also back up each other. CONCLUSION We propose that talazoparib promotes low-dose, CtIP/MRE11-dependent resection and increases the reliance of irradiated HR-proficient cancer cells, on Polθ-mediated alt-EJ. The combination of Polθ inhibitors with talazoparib suppresses this option and causes further radiosensitization. The results suggest that Polθ inhibition may be exploited to maximize talazoparib radiosensitization of HR-proficient tumors in the clinic.
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Affiliation(s)
- Xixi Lin
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany
| | - Aashish Soni
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany.
| | - Razan Hessenow
- West German Proton Therapy Center Essen (WPE), University of Duisburg-Essen, 45147, Essen, Germany
| | - Yanjie Sun
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; West German Proton Therapy Center Essen (WPE), University of Duisburg-Essen, 45147, Essen, Germany
| | - Emil Mladenov
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany
| | - Maja Guberina
- Department of Radiation Therapy, West German Cancer Center, University Hospital Essen, University Duisburg-Essen, 45147, Essen, Germany; German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147, Essen, Germany
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; Department of Radiation Therapy, West German Cancer Center, University Hospital Essen, University Duisburg-Essen, 45147, Essen, Germany; German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147, Essen, Germany
| | - George Iliakis
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany; Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147, Essen, Germany.
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2
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Zhang C, Liu J, Wu J, Ranjan K, Cui X, Wang X, Zhang D, Zhu S. Key molecular DNA damage responses of human cells to radiation. Front Cell Dev Biol 2024; 12:1422520. [PMID: 39050891 PMCID: PMC11266142 DOI: 10.3389/fcell.2024.1422520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Accepted: 06/19/2024] [Indexed: 07/27/2024] Open
Abstract
Our understanding of the DNA damage responses of human cells to radiation has increased remarkably over the recent years although some notable signaling events remain to be discovered. Here we provide a brief account of the key molecular events of the responses to reflect the current understanding of the key underlying mechanisms involved.
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Affiliation(s)
- Chencheng Zhang
- Cancer Research Center, Nantong Tumor Hospital, Nantong, China
- Cancer Research Institute, The Affiliated Tumor Hospital of Nantong University, Nantong, China
- Cancer Research Center, Nantong, China
| | - Jibin Liu
- Cancer Research Center, Nantong Tumor Hospital, Nantong, China
- Cancer Research Institute, The Affiliated Tumor Hospital of Nantong University, Nantong, China
- Cancer Research Center, Nantong, China
| | - Jun Wu
- Nantong Tumor Hospital, Nantong, China
| | - Kamakshi Ranjan
- Department of Bio-Medical Sciences, Philadelphia College of Osteopathic Medicine, Philadelphia, PA, United States
| | - Xiaopeng Cui
- Department of General Surgery, The Affiliated Hospital of Nantong University, Nantong, China
| | - Xingdan Wang
- Department of Radiotherapy, Nantong Tumor Hospital, The Affiliated Tumor Hospital of Nantong University, Nantong, China
| | - Dianzheng Zhang
- Department of Bio-Medical Sciences, Philadelphia College of Osteopathic Medicine, Philadelphia, PA, United States
| | - Shudong Zhu
- Cancer Research Center, Nantong Tumor Hospital, Nantong, China
- Cancer Research Institute, The Affiliated Tumor Hospital of Nantong University, Nantong, China
- Cancer Research Center, Nantong, China
- Argus Pharmaceuticals, Changsha, China
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3
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Hu YM, Liu XC, Hu L, Dong ZW, Yao HY, Wang YJ, Zhao WJ, Xiang YK, Liu Y, Wang HB, Yin QK. Inhibition of the ATR-DNAPKcs-RB axis drives G1/S-phase transition and sensitizes triple-negative breast cancer (TNBC) to DNA holliday junctions. Biochem Pharmacol 2024; 225:116310. [PMID: 38788960 DOI: 10.1016/j.bcp.2024.116310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 05/03/2024] [Accepted: 05/21/2024] [Indexed: 05/26/2024]
Abstract
Targeting the DNA damage response (DDR) is a promising strategy in oncotherapy, as most tumor cells are sensitive to excess damage due to their repair defects. Ataxia telangiectasia mutated and RAD3-related protein (ATR) is a damage response signal transduction sensor, and its therapeutic potential in tumor cells needs to be precisely investigated. Herein, we identified a new axis that could be targeted by ATR inhibitors to decrease the DNA-dependent protein kinase catalytic subunit (DNAPKcs), downregulate the expression of the retinoblastoma (RB), and drive G1/S-phase transition. Four-way DNA Holliday junctions (FJs) assembled in this process could trigger S-phase arrest and induce lethal chromosome damage in RB-positive triple-negative breast cancer (TNBC) cells. Furthermore, these unrepaired junctions also exerted toxic effects to RB-deficient TNBC cells when the homologous recombination repair (HRR) was inhibited. This study proposes a precise strategy for treating TNBC by targeting the DDR and extends our understanding of ATR and HJ in tumor treatment.
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Affiliation(s)
- Yue-Miao Hu
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Xue-Cun Liu
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Lei Hu
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Zhi-Wen Dong
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China; Bohai Rim Advanced Research Institute for Drug Discovery, Yantai, China
| | - Hong-Ying Yao
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Ying-Jie Wang
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Wen-Jing Zhao
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China
| | - Yu-Ke Xiang
- Guangzhou Municipal and Guangdong Provincial Key Laboratory of Molecular Target & Clinical Pharmacology, the NMPA and State Key Laboratory of Respiratory Disease, School of Pharmaceutical Sciences and the Fifth Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
| | - Yi Liu
- School of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, China
| | - Hong-Bo Wang
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China.
| | - Qi-Kun Yin
- School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Basic Science Research Center Base (Pharmaceutical Science), Yantai University, Yantai 264005, China.
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Anisenko AN, Nefedova AA, Kireev II, Gottikh MB. Post-Integrational DNA Repair of HIV-1 Is Associated with Activation of the DNA-PK and ATM Cellular Protein Kinases and Phosphorylation of Their Targets. BIOCHEMISTRY. BIOKHIMIIA 2024; 89:1122-1132. [PMID: 38981705 DOI: 10.1134/s0006297924060117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 04/18/2024] [Accepted: 04/25/2024] [Indexed: 07/11/2024]
Abstract
Integration of the DNA copy of HIV-1 genome into the cellular genome results in series of damages, repair of which is critical for successful replication of the virus. We have previously demonstrated that the ATM and DNA-PK kinases, normally responsible for repairing double-strand breaks in the cellular DNA, are required to initiate the HIV-1 DNA postintegrational repair, even though integration does not result in DNA double-strand breaks. In this study, we analyzed changes in phosphorylation status of ATM (pSer1981), DNA-PK (pSer2056), and their related kinase ATR (pSer428), as well as their targets: Chk1 (pSer345), Chk2 (pThr68), H2AX (pSer139), and p53 (pSer15) during the HIV-1 DNA postintegrational repair. We have shown that ATM and DNA-PK, but not ATR, undergo autophosphorylation during postintegrational DNA repair and phosphorylate their target proteins Chk2 and H2AX. These data indicate common signaling mechanisms between the double-strand DNA break repair and postintegrational repair of HIV-1 DNA.
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Affiliation(s)
- Andrey N Anisenko
- Chemistry Department, Lomonosov Moscow State University, Moscow, 119991, Russia.
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, 119991, Russia
| | - Anastasiia A Nefedova
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, 119991, Russia
| | - Igor I Kireev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia
| | - Marina B Gottikh
- Chemistry Department, Lomonosov Moscow State University, Moscow, 119991, Russia
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia
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Rajpurohit YS, Sharma DK, Lal M, Soni I. A perspective on tumor radiation resistance following high-LET radiation treatment. J Cancer Res Clin Oncol 2024; 150:226. [PMID: 38696003 PMCID: PMC11065934 DOI: 10.1007/s00432-024-05757-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2024] [Accepted: 04/22/2024] [Indexed: 05/05/2024]
Abstract
High-linear energy transfer (LET) radiation is a promising alternative to conventional low-LET radiation for therapeutic gain against cancer owing to its ability to induce complex and clustered DNA lesions. However, the development of radiation resistance poses a significant barrier. The potential molecular mechanisms that could confer resistance development are translesion synthesis (TLS), replication gap suppression (RGS) mechanisms, autophagy, epithelial-mesenchymal transition (EMT) activation, release of exosomes, and epigenetic changes. This article will discuss various types of complex clustered DNA damage, their repair mechanisms, mutagenic potential, and the development of radiation resistance strategies. Furthermore, it highlights the importance of careful consideration and patient selection when employing high-LET radiotherapy in clinical settings.
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Affiliation(s)
- Yogendra Singh Rajpurohit
- Molecular Biology Division, Bhabha Atomic Research Centre, 2-46-S, Modular Lab, A-Block, Mumbai, 400085, India.
- Homi Bhabha National Institute, DAE- Deemed University, Mumbai, 400094, India.
| | - Dhirendra Kumar Sharma
- Molecular Biology Division, Bhabha Atomic Research Centre, 2-46-S, Modular Lab, A-Block, Mumbai, 400085, India
| | - Mitu Lal
- Molecular Biology Division, Bhabha Atomic Research Centre, 2-46-S, Modular Lab, A-Block, Mumbai, 400085, India
| | - Ishu Soni
- Homi Bhabha National Institute, DAE- Deemed University, Mumbai, 400094, India
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6
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Dueva R, Krieger LM, Li F, Luo D, Xiao H, Stuschke M, Metzen E, Iliakis G. Chemical Inhibition of RPA by HAMNO Alters Cell Cycle Dynamics by Impeding DNA Replication and G2-to-M Transition but Has Little Effect on the Radiation-Induced DNA Damage Response. Int J Mol Sci 2023; 24:14941. [PMID: 37834389 PMCID: PMC10573259 DOI: 10.3390/ijms241914941] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 09/28/2023] [Accepted: 10/01/2023] [Indexed: 10/15/2023] Open
Abstract
Replication protein A (RPA) is the major single-stranded DNA (ssDNA) binding protein that is essential for DNA replication and processing of DNA double-strand breaks (DSBs) by homology-directed repair pathways. Recently, small molecule inhibitors have been developed targeting the RPA70 subunit and preventing RPA interactions with ssDNA and various DNA repair proteins. The rationale of this development is the potential utility of such compounds as cancer therapeutics, owing to their ability to inhibit DNA replication that sustains tumor growth. Among these compounds, (1Z)-1-[(2-hydroxyanilino) methylidene] naphthalen-2-one (HAMNO) has been more extensively studied and its efficacy against tumor growth was shown to arise from the associated DNA replication stress. Here, we study the effects of HAMNO on cells exposed to ionizing radiation (IR), focusing on the effects on the DNA damage response and the processing of DSBs and explore its potential as a radiosensitizer. We show that HAMNO by itself slows down the progression of cells through the cell cycle by dramatically decreasing DNA synthesis. Notably, HAMNO also attenuates the progression of G2-phase cells into mitosis by a mechanism that remains to be elucidated. Furthermore, HAMNO increases the fraction of chromatin-bound RPA in S-phase but not in G2-phase cells and suppresses DSB repair by homologous recombination. Despite these marked effects on the cell cycle and the DNA damage response, radiosensitization could neither be detected in exponentially growing cultures, nor in cultures enriched in G2-phase cells. Our results complement existing data on RPA inhibitors, specifically HAMNO, and suggest that their antitumor activity by replication stress induction may not extend to radiosensitization. However, it may render cells more vulnerable to other forms of DNA damaging agents through synthetically lethal interactions, which requires further investigation.
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Affiliation(s)
- Rositsa Dueva
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- Institute of Physiology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Lisa Marie Krieger
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- Division of Experimental Radiation Biology, Department of Radiotherapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Fanghua Li
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- West German Proton Therapy Centre Essen (WPE), 45147 Essen, Germany
| | - Daxian Luo
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- Division of Experimental Radiation Biology, Department of Radiotherapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Huaping Xiao
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- Division of Experimental Radiation Biology, Department of Radiotherapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiotherapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, 45147 Essen, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Eric Metzen
- Institute of Physiology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - George Iliakis
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (L.M.K.); (F.L.); (D.L.); (H.X.)
- Division of Experimental Radiation Biology, Department of Radiotherapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
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7
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Mladenov E, Mladenova V, Stuschke M, Iliakis G. New Facets of DNA Double Strand Break Repair: Radiation Dose as Key Determinant of HR versus c-NHEJ Engagement. Int J Mol Sci 2023; 24:14956. [PMID: 37834403 PMCID: PMC10573367 DOI: 10.3390/ijms241914956] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 10/01/2023] [Accepted: 10/03/2023] [Indexed: 10/15/2023] Open
Abstract
Radiation therapy is an essential component of present-day cancer management, utilizing ionizing radiation (IR) of different modalities to mitigate cancer progression. IR functions by generating ionizations in cells that induce a plethora of DNA lesions. The most detrimental among them are the DNA double strand breaks (DSBs). In the course of evolution, cells of higher eukaryotes have evolved four major DSB repair pathways: classical non-homologous end joining (c-NHEJ), homologous recombination (HR), alternative end-joining (alt-EJ), and single strand annealing (SSA). These mechanistically distinct repair pathways have different cell cycle- and homology-dependencies but, surprisingly, they operate with widely different fidelity and kinetics and therefore contribute unequally to cell survival and genome maintenance. It is therefore reasonable to anticipate tight regulation and coordination in the engagement of these DSB repair pathway to achieve the maximum possible genomic stability. Here, we provide a state-of-the-art review of the accumulated knowledge on the molecular mechanisms underpinning these repair pathways, with emphasis on c-NHEJ and HR. We discuss factors and processes that have recently come to the fore. We outline mechanisms steering DSB repair pathway choice throughout the cell cycle, and highlight the critical role of DNA end resection in this process. Most importantly, however, we point out the strong preference for HR at low DSB loads, and thus low IR doses, for cells irradiated in the G2-phase of the cell cycle. We further explore the molecular underpinnings of transitions from high fidelity to low fidelity error-prone repair pathways and analyze the coordination and consequences of this transition on cell viability and genomic stability. Finally, we elaborate on how these advances may help in the development of improved cancer treatment protocols in radiation therapy.
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Affiliation(s)
- Emil Mladenov
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
| | - Veronika Mladenova
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (M.S.)
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, 45147 Essen, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - George Iliakis
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
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8
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Li F, Mladenov E, Sun Y, Soni A, Stuschke M, Timmermann B, Iliakis G. Low CDK Activity and Enhanced Degradation by APC/C CDH1 Abolishes CtIP Activity and Alt-EJ in Quiescent Cells. Cells 2023; 12:1530. [PMID: 37296650 PMCID: PMC10252496 DOI: 10.3390/cells12111530] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Revised: 05/26/2023] [Accepted: 05/27/2023] [Indexed: 06/12/2023] Open
Abstract
Alt-EJ is an error-prone DNA double-strand break (DSBs) repair pathway coming to the fore when first-line repair pathways, c-NHEJ and HR, are defective or fail. It is thought to benefit from DNA end-resection-a process whereby 3' single-stranded DNA-tails are generated-initiated by the CtIP/MRE11-RAD50-NBS1 (MRN) complex and extended by EXO1 or the BLM/DNA2 complex. The connection between alt-EJ and resection remains incompletely characterized. Alt-EJ depends on the cell cycle phase, is at maximum in G2-phase, substantially reduced in G1-phase and almost undetectable in quiescent, G0-phase cells. The mechanism underpinning this regulation remains uncharacterized. Here, we compare alt-EJ in G1- and G0-phase cells exposed to ionizing radiation (IR) and identify CtIP-dependent resection as the key regulator. Low levels of CtIP in G1-phase cells allow modest resection and alt-EJ, as compared to G2-phase cells. Strikingly, CtIP is undetectable in G0-phase cells owing to APC/C-mediated degradation. The suppression of CtIP degradation with bortezomib or CDH1-depletion rescues CtIP and alt-EJ in G0-phase cells. CtIP activation in G0-phase cells also requires CDK-dependent phosphorylation by any available CDK but is restricted to CDK4/6 at the early stages of the normal cell cycle. We suggest that suppression of mutagenic alt-EJ in G0-phase is a mechanism by which cells of higher eukaryotes maintain genomic stability in a large fraction of non-cycling cells in their organisms.
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Affiliation(s)
- Fanghua Li
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (F.L.); (E.M.); (Y.S.); (A.S.)
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, Germany;
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (F.L.); (E.M.); (Y.S.); (A.S.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Yanjie Sun
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (F.L.); (E.M.); (Y.S.); (A.S.)
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, Germany;
| | - Aashish Soni
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (F.L.); (E.M.); (Y.S.); (A.S.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147 Essen, Germany
| | - Beate Timmermann
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, Germany;
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147 Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (F.L.); (E.M.); (Y.S.); (A.S.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
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9
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Luo D, Mladenov E, Soni A, Stuschke M, Iliakis G. The p38/MK2 Pathway Functions as Chk1-Backup Downstream of ATM/ATR in G 2-Checkpoint Activation in Cells Exposed to Ionizing Radiation. Cells 2023; 12:1387. [PMID: 37408221 DOI: 10.3390/cells12101387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 05/06/2023] [Accepted: 05/11/2023] [Indexed: 07/07/2023] Open
Abstract
We have recently reported that in G2-phase cells (but not S-phase cells) sustaining low loads of DNA double-strand break (DSBs), ATM and ATR regulate the G2-checkpoint epistatically, with ATR at the output-node, interfacing with the cell cycle through Chk1. However, although inhibition of ATR nearly completely abrogated the checkpoint, inhibition of Chk1 using UCN-01 generated only partial responses. This suggested that additional kinases downstream of ATR were involved in the transmission of the signal to the cell cycle engine. Additionally, the broad spectrum of kinases inhibited by UCN-01 pointed to uncertainties in the interpretation that warranted further investigations. Here, we show that more specific Chk1 inhibitors exert an even weaker effect on G2-checkpoint, as compared to ATR inhibitors and UCN-01, and identify the MAPK p38α and its downstream target MK2 as checkpoint effectors operating as backup to Chk1. These observations further expand the spectrum of p38/MK2 signaling to G2-checkpoint activation, extend similar studies in cells exposed to other DNA damaging agents and consolidate a role of p38/MK2 as a backup kinase module, adding to similar backup functions exerted in p53 deficient cells. The results extend the spectrum of actionable strategies and targets in current efforts to enhance the radiosensitivity in tumor cells.
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Affiliation(s)
- Daxian Luo
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, 45147 Essen, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
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10
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Mladenova V, Mladenov E, Chaudhary S, Stuschke M, Iliakis G. The high toxicity of DSB-clusters modelling high-LET-DNA damage derives from inhibition of c-NHEJ and promotion of alt-EJ and SSA despite increases in HR. Front Cell Dev Biol 2022; 10:1016951. [PMID: 36263011 PMCID: PMC9574094 DOI: 10.3389/fcell.2022.1016951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 09/14/2022] [Indexed: 11/13/2022] Open
Abstract
Heavy-ion radiotherapy utilizing high linear energy transfer (high-LET) ionizing radiation (IR) is a promising cancer treatment modality owing to advantageous physical properties of energy deposition and associated toxicity over X-rays. Therapies utilizing high-LET radiation will benefit from a better understanding of the molecular mechanisms underpinning their increased biological efficacy. Towards this goal, we investigate here the biological consequences of well-defined clusters of DNA double-strand breaks (DSBs), a form of DNA damage, which on theoretical counts, has often been considered central to the enhanced toxicity of high-LET IR. We test clonal cell lines harboring in their genomes constructs with appropriately engineered I-SceI recognition sites that convert upon I-SceI expression to individual DSBs, or DSB-clusters comprising known numbers of DSBs with defined DNA-ends. We find that, similarly to high-LET IR, DSB-clusters of increasing complexity, i.e. increasing numbers of DSBs, with compatible or incompatible ends, compromise classical non-homologous end-joining, favor DNA end-resection and promote resection-dependent DSB-processing. Analysis of RAD51 foci shows increased engagement of error-free homologous recombination on DSB-clusters. Multicolor fluorescence in situ hybridization analysis shows that complex DSB-clusters markedly increase the incidence of structural chromosomal abnormalities (SCAs). Since RAD51-knockdown further increases SCAs-incidence, we conclude that homologous recombination suppresses SCAs-formation. Strikingly, CtIP-depletion inhibits SCAs-formation, suggesting that it relies on alternative end-joining or single-strand annealing. Indeed, ablation of RAD52 causes a marked reduction in SCAs, as does also inhibition of PARP1. We conclude that increased DSB-cluster formation that accompanies LET-increases, enhances IR-effectiveness by promoting DNA end-resection, which suppresses c-NHEJ and enhances utilization of alt-EJ or SSA. Although increased resection also favors HR, on balance, error-prone processing dominates, causing the generally observed increased toxicity of high-LET radiation. These findings offer new mechanistic insights into high-LET IR-toxicity and have translational potential in the clinical setting that may be harnessed by combining high-LET IR with inhibitors of PARP1 or RAD52.
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Affiliation(s)
- Veronika Mladenova
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Emil Mladenov
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Shipra Chaudhary
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- Institute for Advanced Biosciences, Inserm U 1209 / CNRS UMR 5309 Joint Research Center, Grenoble Alpes University, Grenoble, France
| | - Martin Stuschke
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, Essen, Germany
- German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - George Iliakis
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
- *Correspondence: George Iliakis,
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Huang YJ, Huang MY, Cheng TL, Kuo SH, Ke CC, Chen YT, Hsieh YC, Wang JY, Cheng CM, Chuang CH. ERCC1 Overexpression Increases Radioresistance in Colorectal Cancer Cells. Cancers (Basel) 2022; 14:cancers14194798. [PMID: 36230725 PMCID: PMC9563575 DOI: 10.3390/cancers14194798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 09/24/2022] [Accepted: 09/25/2022] [Indexed: 11/29/2022] Open
Abstract
Simple Summary The 20–30% of locally advanced rectal cancer patients undergoing preoperative concurrent chemoradiotherapy had no expected efficacy, and ERCC1 overexpression was found in these tumor tissue patients. In the interest of confirming and adding details to our understanding of that correlation, The Tet-on gene expression system was used to examine ERCC1 functionality and stability. Our data from regulatable HCT116-Tet-on and COLO205-Tet-on cell lines verified the increased radioresistance in colorectal cancer cells that are associated with ERCC1 overexpression, and they confirmed a high correlation between ERCC1 levels and radiotherapeutic efficiency. Furthermore, overexpression of ERCC1 also increases cell migration under radiation exposure. Additional data from ERCC1 expression regulation in vivo confirmed that the overexpression of increased cancer radiation resistance suggests that ERCC1 expression plays a key role. Abstract Preoperative concurrent chemoradiotherapy (CCRT) is a standard treatment for locally advanced rectal cancer patients, but 20–30% do not benefit from the desired therapeutic effects. Previous reports indicate that high levels of ERCC1 reduce the effectiveness of cisplatin-based CCRT; however, it remains unclear as to whether ERCC1 overexpression increases radiation resistance. To clarify the correlation between ERCC1 levels and radiation (RT) resistance, we established two cell lines (HCT116-Tet-on and COLO205-Tet-on), induced them to overexpress ERCC1, detected cell survival following exposure to radiation, established HCT116-Tet-on and COLO205-Tet-on heterotopic cancer animal models, and detected tumor volume following exposure to radiation. We found that ERCC1 overexpression increased radiation resistance. After regulating ERCC1 levels and radiation exposure to verify the correlation, we noted that increased radiation resistance was dependent on ERCC1 upregulation in both cell lines. For further verification, we exposed HCT116-Tet-on and COLO205-Tet-on heterotopic cancer animal models to radiation and observed that ERCC1 overexpression increased colorectal cancer tumor radioresistance in both. Combined, our results suggest that ERCC1 overexpression may serve as a suitable CCRT prognostic marker for colorectal cancer patients.
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Affiliation(s)
- Yi-Jung Huang
- Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Ming-Yii Huang
- Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Radiation Oncology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Radiation Oncology, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Center for Cancer Research, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Tian-Lu Cheng
- Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Shih-Hsun Kuo
- Department of Radiation Oncology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Chien-Chih Ke
- Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 80708, Taiwan
| | - Yi-Ting Chen
- Department of Pathology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Pathology, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Yuan-Chin Hsieh
- School of Medicine for International Students, I-Shou University, Kaohsiung 84001, Taiwan
| | - Jaw-Yuan Wang
- Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Center for Cancer Research, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Division of Colorectal Surgery, Department of Surgery, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Graduate Institute of Clinical Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Surgery, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Center for Liquid Biopsy and Cohort Research, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Pingtung Hospital, Ministry of Health and Welfare, Pingtung 90054, Taiwan
| | - Chiu-Min Cheng
- Department and Graduate Institute of Aquaculture, National Kaohsiung University of Science and Techology, Kaohsiung 81157, Taiwan
| | - Chih-Hung Chuang
- Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Department of Medical Laboratory Science and Biotechnology, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Correspondence: ; Tel.: +886-7-3121101 (ext. 2353)
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12
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Soni A, Duan X, Stuschke M, Iliakis G. ATR Contributes More Than ATM in Intra-S-Phase Checkpoint Activation after IR, and DNA-PKcs Facilitates Recovery: Evidence for Modular Integration of ATM/ATR/DNA-PKcs Functions. Int J Mol Sci 2022; 23:7506. [PMID: 35886852 PMCID: PMC9316047 DOI: 10.3390/ijms23147506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 06/24/2022] [Accepted: 07/04/2022] [Indexed: 11/25/2022] Open
Abstract
The intra-S-phase checkpoint was among the first reported cell cycle checkpoints in mammalian cells. It transiently slows down the rate of DNA replication after DNA damage to facilitate repair and thus prevents genomic instability. The ionizing radiation (IR)-induced intra-S-phase checkpoint in mammalian cells is thought to be mainly dependent upon the kinase activity of ATM. Defects in the intra-S-phase checkpoint result in radio-resistant DNA synthesis (RDS), which promotes genomic instability. ATM belongs to the PI3K kinase family along with ATR and DNA-PKcs. ATR has been shown to be the key kinase for intra-S-phase checkpoint signaling in yeast and has also been implicated in this checkpoint in higher eukaryotes. Recently, contributions of DNA-PKcs to IR-induced G2-checkpoint could also be established. Whether and how ATR and DNA-PKcs are involved in the IR-induced intra-S-phase checkpoint in mammalian cells is incompletely characterized. Here, we investigated the contributions of ATM, ATR, and DNA-PKcs to intra-S-phase checkpoint activation after exposure to IR of human and hamster cells. The results suggest that the activities of both ATM and ATR are essential for efficient intra-S-phase checkpoint activation. Indeed, in a wild-type genetic background, ATR inhibition generates stronger checkpoint defects than ATM inhibition. Similar to G2 checkpoint, DNA-PKcs contributes to the recovery from the intra-S-phase checkpoint. DNA-PKcs-deficient cells show persistent, mainly ATR-dependent intra-S-phase checkpoints. A correlation between the degree of DSB end resection and the strength of the intra-S-phase checkpoint is observed, which again compares well to the G2 checkpoint response. We conclude that the organization of the intra-S-phase checkpoint has a similar mechanistic organization to that of the G2 checkpoint in cells irradiated in the G2 phase.
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Affiliation(s)
- Aashish Soni
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (A.S.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Xiaolu Duan
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (A.S.); (M.S.)
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, and German Cancer Research Center (DKFZ), 45147 Essen, Germany
| | - George Iliakis
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (A.S.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
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13
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Xiao H, Li F, Mladenov E, Soni A, Mladenova V, Pan B, Dueva R, Stuschke M, Timmermann B, Iliakis G. Increased Resection at DSBs in G2-Phase Is a Unique Phenotype Associated with DNA-PKcs Defects That Is Not Shared by Other Factors of c-NHEJ. Cells 2022; 11:cells11132099. [PMID: 35805183 PMCID: PMC9265841 DOI: 10.3390/cells11132099] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 06/28/2022] [Accepted: 06/30/2022] [Indexed: 01/27/2023] Open
Abstract
The load of DNA double-strand breaks (DSBs) induced in the genome of higher eukaryotes by different doses of ionizing radiation (IR) is a key determinant of DSB repair pathway choice, with homologous recombination (HR) and ATR substantially gaining ground at doses below 0.5 Gy. Increased resection and HR engagement with decreasing DSB-load generate a conundrum in a classical non-homologous end-joining (c-NHEJ)-dominated cell and suggest a mechanism adaptively facilitating resection. We report that ablation of DNA-PKcs causes hyper-resection, implicating DNA-PK in the underpinning mechanism. However, hyper-resection in DNA-PKcs-deficient cells can also be an indirect consequence of their c-NHEJ defect. Here, we report that all tested DNA-PKcs mutants show hyper-resection, while mutants with defects in all other factors of c-NHEJ fail to do so. This result rules out the model of c-NHEJ versus HR competition and the passive shift from c-NHEJ to HR as the causes of the increased resection and suggests the integration of DNA-PKcs into resection regulation. We develop a model, compatible with the results of others, which integrates DNA-PKcs into resection regulation and HR for a subset of DSBs. For these DSBs, we propose that the kinase remains at the break site, rather than the commonly assumed autophosphorylation-mediated removal from DNA ends.
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Affiliation(s)
- Huaping Xiao
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Fanghua Li
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, Germany;
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Aashish Soni
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Veronika Mladenova
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Bing Pan
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
| | - Rositsa Dueva
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Institute of Physiology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147 Essen, Germany
| | - Beate Timmermann
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, Germany;
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, German Cancer Research Center (DKFZ), 45147 Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; (H.X.); (F.L.); (E.M.); (A.S.); (V.M.); (B.P.); (R.D.)
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany;
- Correspondence: ; Tel.: +49-201-723-4152
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14
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Chughtai AA, Pannhausen J, Dinger P, Wirtz J, Knüchel R, Gaisa NT, Eble MJ, Rose M. Effective Radiosensitization of Bladder Cancer Cells by Pharmacological Inhibition of DNA-PK and ATR. Biomedicines 2022; 10:biomedicines10061277. [PMID: 35740300 PMCID: PMC9220184 DOI: 10.3390/biomedicines10061277] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 05/24/2022] [Accepted: 05/27/2022] [Indexed: 12/09/2022] Open
Abstract
This study aims at analyzing the impact of the pharmacological inhibition of DNA damage response (DDR) targets (DNA-PK and ATR) on radiosensitization of bladder cancer cell lines of different molecular/histological subtypes. Applying DNA-PK (AZD7648) and ATR (Ceralasertib) inhibitors on SCaBER, J82 and VMCUB-1 bladder cancer cell lines, we revealed sensitization upon ionizing radiation (IR), i.e., the IC50 for each drug shifted to a lower drug concentration with increased IR doses. In line with this, drug exposure retarded DNA repair after IR-induced DNA damage visualized by a neutral comet assay. Western blot analyses confirmed specific inhibition of targeted DDR pathways in the analyzed bladder cancer cell lines, i.e., drugs blocked DNA-PK phosphorylation at Ser2056 and the ATR downstream mediator CHK1 at Ser317. Interestingly, clonogenic survival assays indicated a cell-line-dependent synergism of combined DDR inhibition upon IR. Calculating combined index (CI) values, with and without IR, according to the Chou–Talalay method, confirmed drug- and IR-dose-specific synergistic CI values. Thus, we provide functional evidence that DNA-PK and ATR inhibitors specifically target corresponding DDR pathways retarding the DNA repair process at nano-molar concentrations. This, in turn, leads to a strong radiosensitizing effect and impairs the survival of bladder cancer cells.
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Affiliation(s)
- Ahmed Ali Chughtai
- Department of Radiation Oncology, RWTH Aachen University, 52074 Aachen, Germany;
- Correspondence: (A.A.C.); (M.R.); Tel.: +49-241-8036863 (A.A.C.); +49-241-8089715 (M.R.); Fax: +49-241-8082425 (A.A.C.); +49-241-8082439 (M.R.)
| | - Julia Pannhausen
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
| | - Pia Dinger
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
| | - Julia Wirtz
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
| | - Ruth Knüchel
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
| | - Nadine T. Gaisa
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
| | - Michael J. Eble
- Department of Radiation Oncology, RWTH Aachen University, 52074 Aachen, Germany;
| | - Michael Rose
- Institute of Pathology, RWTH Aachen University, 52074 Aachen, Germany; (J.P.); (P.D.); (J.W.); (R.K.); (N.T.G.)
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), 52074 Aachen, Germany
- Correspondence: (A.A.C.); (M.R.); Tel.: +49-241-8036863 (A.A.C.); +49-241-8089715 (M.R.); Fax: +49-241-8082425 (A.A.C.); +49-241-8082439 (M.R.)
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15
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Shift in G1-Checkpoint from ATM-Alone to a Cooperative ATM Plus ATR Regulation with Increasing Dose of Radiation. Cells 2021; 11:cells11010063. [PMID: 35011623 PMCID: PMC8750242 DOI: 10.3390/cells11010063] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2021] [Revised: 12/23/2021] [Accepted: 12/24/2021] [Indexed: 12/13/2022] Open
Abstract
The current view of the involvement of PI3-kinases in checkpoint responses after DNA damage is that ATM is the key regulator of G1-, S- or G2-phase checkpoints, that ATR is only partly involved in the regulation of S- and G2-phase checkpoints and that DNA-PKcs is not involved in checkpoint regulation. However, further analysis of the contributions of these kinases to checkpoint responses in cells exposed to ionizing radiation (IR) recently uncovered striking integrations and interplays among ATM, ATR and DNA-PKcs that adapt not only to the phase of the cell cycle in which cells are irradiated, but also to the load of DNA double-strand breaks (DSBs), presumably to optimize their processing. Specifically, we found that low IR doses in G2-phase cells activate a G2-checkpoint that is regulated by epistatically coupled ATM and ATR. Thus, inhibition of either kinase suppresses almost fully its activation. At high IR doses, the epistatic ATM/ATR coupling relaxes, yielding to a cooperative regulation. Thus, single-kinase inhibition suppresses partly, and only combined inhibition suppresses fully G2-checkpoint activation. Interestingly, DNA-PKcs integrates with ATM/ATR in G2-checkpoint control, but functions in its recovery in a dose-independent manner. Strikingly, irradiation during S-phase activates, independently of dose, an exclusively ATR-dependent G2 checkpoint. Here, ATM couples with DNA-PKcs to regulate checkpoint recovery. In the present work, we extend these studies and investigate organization and functions of these PI3-kinases in the activation of the G1 checkpoint in cells irradiated either in the G0 or G1 phase. We report that ATM is the sole regulator of the G1 checkpoint after exposure to low IR doses. At high IR doses, ATM remains dominant, but contributions from ATR also become detectable and are associated with limited ATM/ATR-dependent end resection at DSBs. Under these conditions, only combined ATM + ATR inhibition fully abrogates checkpoint and resection. Contributions of DNA-PKcs and CHK2 to the regulation of the G1 checkpoint are not obvious in these experiments and may be masked by the endpoint employed for checkpoint analysis and perturbations in normal progression through the cell cycle of cells exposed to DNA-PKcs inhibitors. The results broaden our understanding of organization throughout the cell cycle and adaptation with increasing IR dose of the ATM/ATR/DNA-PKcs module to regulate checkpoint responses. They emphasize notable similarities and distinct differences between G1-, G2- and S-phase checkpoint regulation that may guide DSB processing decisions.
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16
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Rossi MJ, DiDomenico SF, Patel M, Mazin AV. RAD52: Paradigm of Synthetic Lethality and New Developments. Front Genet 2021; 12:780293. [PMID: 34887904 PMCID: PMC8650160 DOI: 10.3389/fgene.2021.780293] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 11/05/2021] [Indexed: 12/31/2022] Open
Abstract
DNA double-strand breaks and inter-strand cross-links are the most harmful types of DNA damage that cause genomic instability that lead to cancer development. The highest fidelity pathway for repairing damaged double-stranded DNA is termed Homologous recombination (HR). Rad52 is one of the key HR proteins in eukaryotes. Although it is critical for most DNA repair and recombination events in yeast, knockouts of mammalian RAD52 lack any discernable phenotypes. As a consequence, mammalian RAD52 has been long overlooked. That is changing now, as recent work has shown RAD52 to be critical for backup DNA repair pathways in HR-deficient cancer cells. Novel findings have shed light on RAD52's biochemical activities. RAD52 promotes DNA pairing (D-loop formation), single-strand DNA and DNA:RNA annealing, and inverse strand exchange. These activities contribute to its multiple roles in DNA damage repair including HR, single-strand annealing, break-induced replication, and RNA-mediated repair of DNA. The contributions of RAD52 that are essential to the viability of HR-deficient cancer cells are currently under investigation. These new findings make RAD52 an attractive target for the development of anti-cancer therapies against BRCA-deficient cancers.
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Affiliation(s)
- Matthew J. Rossi
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
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17
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Disruption of Chromatin Dynamics by Hypotonic Stress Suppresses HR and Shifts DSB Processing to Error-Prone SSA. Int J Mol Sci 2021; 22:ijms222010957. [PMID: 34681628 PMCID: PMC8535785 DOI: 10.3390/ijms222010957] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 10/04/2021] [Accepted: 10/05/2021] [Indexed: 11/17/2022] Open
Abstract
The processing of DNA double-strand breaks (DSBs) depends on the dynamic characteristics of chromatin. To investigate how abrupt changes in chromatin compaction alter these dynamics and affect DSB processing and repair, we exposed irradiated cells to hypotonic stress (HypoS). Densitometric and chromosome-length analyses show that HypoS transiently decompacts chromatin without inducing histone modifications known from regulated local chromatin decondensation, or changes in Micrococcal Nuclease (MNase) sensitivity. HypoS leaves undisturbed initial stages of DNA-damage-response (DDR), such as radiation-induced ATM activation and H2AX-phosphorylation. However, detection of ATM-pS1981, γ-H2AX and 53BP1 foci is reduced in a protein, cell cycle phase and cell line dependent manner; likely secondary to chromatin decompaction that disrupts the focal organization of DDR proteins. While HypoS only exerts small effects on classical nonhomologous end-joining (c-NHEJ) and alternative end-joining (alt-EJ), it markedly suppresses homologous recombination (HR) without affecting DNA end-resection at DSBs, and clearly enhances single-strand annealing (SSA). These shifts in pathway engagement are accompanied by decreases in HR-dependent chromatid-break repair in the G2-phase, and by increases in alt-EJ and SSA-dependent chromosomal translocations. Consequently, HypoS sensitizes cells to ionizing radiation (IR)-induced killing. We conclude that HypoS-induced global chromatin decompaction compromises regulated chromatin dynamics and genomic stability by suppressing DSB-processing by HR, and allowing error-prone processing by alt-EJ and SSA.
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18
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Magin S, Meher PK, Iliakis G. Nucleoside Analogs Radiosensitize G0 Cells by Activating DNA End Resection and Alternative End-Joining. Radiat Res 2021; 195:412-426. [PMID: 33755161 DOI: 10.1667/rade-20-00195.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 02/22/2021] [Indexed: 11/03/2022]
Abstract
Alternative end-joining (alt-EJ) is a DNA end resection-dependent, error-prone pathway utilized by vertebrate cells to repair DNA double-strand breaks (DSBs), but its engagement is linked to chromosomal translocations and genomic instability. Here, we report that when proliferating cells are exposed to ionizing radiation, treatment with nucleoside analogs (NAs) causes strong radiosensitization by increasing engagement of alt-EJ, while at the same time suppressing homologous recombination (HR) in S- and G2phase cells. This NA-mediated pathway shift may reflect a passive compensatory engagement of alt-EJ following HR suppression that is specific for S- and G2-phase cells, and/or the direct activation of alt-EJ throughout the cell cycle. To distinguish between these possibilities, we utilize here a cell culture model that exploits genetic and cell cycle-dependent inactivation of DSB repair pathways, to exclusively study alt-EJ and its modulation by NAs in murine and human cell lines. To this end, we allow LIG4-/--deficient cells to accumulate in G1/G0 phase by transfer to serum-deprived media and obtain cells deficient in c-NHEJ owing to the genetic LIG4 knockout, deficient in HR owing to the absence of S- or G2-phase cells, and compromised in their ability to carry out alt-EJ owing to their accumulation in G0. We find that in these cells irradiation and treatment with the NA, β-arabinofuranosyladenine (araA), and to a lesser degree with other NAs, promptly activates suppressed alt-EJ that now functions at levels approximating those of c-NHEJ in wild-type cells. Results at high dose (20 Gy) generated using pulsed-field gel electrophoresis (PFGE) are corroborated by results at low dose (1 Gy) generated by scoring 53BP1 foci. Strikingly, araA treatment activates a normally undetectable DNA-end-resection at DSBs, which requires ATR activity, but proceeds unimpeded after CtIP knockdown. Treatment with araA increases the formation of chromosomal aberrations and enhances radiation-induced cell killing. The results support direct stimulation of resection by NAs and alt-EJ as a mechanism of their documented radiosensitizing potential. We propose that this stimulation also occurs in repair-proficient cells and that it occurs throughout the cell cycle. It may therefore be harnessed to develop protocols combining NAs with radiation to treat human cancer.
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Affiliation(s)
- Simon Magin
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Prabodha Kumar Meher
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
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19
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Mladenova V, Mladenov E, Scholz M, Stuschke M, Iliakis G. Strong Shift to ATR-Dependent Regulation of the G 2-Checkpoint after Exposure to High-LET Radiation. Life (Basel) 2021; 11:life11060560. [PMID: 34198619 PMCID: PMC8232161 DOI: 10.3390/life11060560] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 06/09/2021] [Indexed: 12/29/2022] Open
Abstract
The utilization of high linear-energy-transfer (LET) ionizing radiation (IR) modalities is rapidly growing worldwide, causing excitement but also raising concerns, because our understanding of their biological effects is incomplete. Charged particles such as protons and heavy ions have increasing potential in cancer therapy, due to their advantageous physical properties over X-rays (photons), but are also present in the space environment, adding to the health risks of space missions. Therapy improvements and the protection of humans during space travel will benefit from a better understanding of the mechanisms underpinning the biological effects of high-LET IR. There is evidence that high-LET IR induces DNA double-strand breaks (DSBs) of increasing complexity, causing enhanced cell killing, owing, at least partly, to the frequent engagement of a low-fidelity DSB-repair pathway: alternative end-joining (alt-EJ), which is known to frequently induce severe structural chromosomal abnormalities (SCAs). Here, we evaluate the radiosensitivity of A549 lung adenocarcinoma cells to X-rays, α-particles and 56Fe ions, as well as of HCT116 colorectal cancer cells to X-rays and α-particles. We observe the expected increase in cell killing following high-LET irradiation that correlates with the increased formation of SCAs as detected by mFISH. Furthermore, we report that cells exposed to low doses of α-particles and 56Fe ions show an enhanced G2-checkpoint response which is mainly regulated by ATR, rather than the coordinated ATM/ATR-dependent regulation observed after exposure to low doses of X-rays. These observations advance our understanding of the mechanisms underpinning high-LET IR effects, and suggest the potential utility for ATR inhibitors in high-LET radiation therapy.
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Affiliation(s)
- Veronika Mladenova
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (E.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
| | - Emil Mladenov
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (E.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
| | - Michael Scholz
- Biophysics Division, GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany;
| | - Martin Stuschke
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (E.M.); (M.S.)
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, 45122 Essen, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - George Iliakis
- Department of Radiation Therapy, Division of Experimental Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany; (V.M.); (E.M.); (M.S.)
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45122 Essen, Germany
- Correspondence:
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20
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Nikolakopoulou A, Soni A, Habibi M, Karaiskos P, Pantelias G, Terzoudi GI, Iliakis G. G2/M Checkpoint Abrogation With Selective Inhibitors Results in Increased Chromatid Breaks and Radiosensitization of 82-6 hTERT and RPE Human Cells. Front Public Health 2021; 9:675095. [PMID: 34123995 PMCID: PMC8193504 DOI: 10.3389/fpubh.2021.675095] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 04/26/2021] [Indexed: 11/13/2022] Open
Abstract
While technological advances in radiation oncology have led to a more precise delivery of radiation dose and a decreased risk of side effects, there is still a need to better understand the mechanisms underlying DNA damage response (DDR) at the DNA and cytogenetic levels, and to overcome tumor resistance. To maintain genomic stability, cells have developed sophisticated signaling pathways enabling cell cycle arrest to facilitate DNA repair via the DDR-related kinases and their downstream targets, so that DNA damage or DNA replication stress induced by genotoxic therapies can be resolved. ATM, ATR, and Chk1 kinases are key mediators in DDR activation and crucial factors in treatment resistance. It is of importance, therefore, as an alternative to the conventional clonogenic assay, to establish a cytogenetic assay enabling reliable and time-efficient results in evaluating the potency of DDR inhibitors for radiosensitization. Toward this goal, the present study aims at the development and optimization of a chromosomal radiosensitivity assay using the DDR and G2-checkpoint inhibitors as a novel modification compared to the classical G2-assay. Also, it aims at investigating the strengths of this assay for rapid radiosensitivity assessments in cultured cells, and potentially, in tumor cells obtained from biopsies. Specifically, exponentially growing RPE and 82-6 hTERT human cells are irradiated during the G2/M-phase transition in the presence or absence of Caffeine, VE-821, and UCN-1 inhibitors of ATM/ATR, ATR, and Chk1, respectively, and the induced chromatid breaks are used to evaluate cell radiosensitivity and their potency for radiosensitization. The increased yield of chromatid breaks in the presence of DDR inhibitors, which underpins radiosensitization, is similar to that observed in cells from highly radiosensitive AT-patients, and is considered here as 100% radiosensitive internal control. The results highlight the potential of our modified G2-assay using VE-821 to evaluate cell radiosensitivity, the efficacy of DDR inhibitors in radiosensitization, and reinforce the concept that ATM, ATR, and Chk1 represent attractive anticancer drug targets in radiation oncology.
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Affiliation(s)
- Aggeliki Nikolakopoulou
- Laboratory of Health Physics, Radiobiology and Cytogenetics, Institute of Nuclear and Radiological Sciences and Technology, Energy and Safety, National Centre for Scientific Research "Demokritos", Athens, Greece.,Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Aashish Soni
- Institute of Medical Radiation Biology, Medical School, University of Duisburg-Essen, Essen, Germany
| | - Martha Habibi
- Laboratory of Health Physics, Radiobiology and Cytogenetics, Institute of Nuclear and Radiological Sciences and Technology, Energy and Safety, National Centre for Scientific Research "Demokritos", Athens, Greece.,Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Pantelis Karaiskos
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Gabriel Pantelias
- Laboratory of Health Physics, Radiobiology and Cytogenetics, Institute of Nuclear and Radiological Sciences and Technology, Energy and Safety, National Centre for Scientific Research "Demokritos", Athens, Greece
| | - Georgia I Terzoudi
- Laboratory of Health Physics, Radiobiology and Cytogenetics, Institute of Nuclear and Radiological Sciences and Technology, Energy and Safety, National Centre for Scientific Research "Demokritos", Athens, Greece
| | - George Iliakis
- Institute of Medical Radiation Biology, Medical School, University of Duisburg-Essen, Essen, Germany
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21
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Fedak EA, Adler FR, Abegglen LM, Schiffman JD. ATM and ATR Activation Through Crosstalk Between DNA Damage Response Pathways. Bull Math Biol 2021; 83:38. [PMID: 33704589 DOI: 10.1007/s11538-021-00868-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 02/10/2021] [Indexed: 11/28/2022]
Abstract
Cells losing the ability to self-regulate in response to damage are a hallmark of cancer. When a cell encounters damage, regulatory pathways estimate the severity of damage and promote repair, cell cycle arrest, or apoptosis. This decision-making process would be remarkable if it were based on the total amount of damage in the cell, but because damage detection pathways vary in the rate and intensity with which they promote pro-apoptotic factors, the cell's real challenge is to reconcile dissimilar signals. Crosstalk between repair pathways, crosstalk between pro-apoptotic signaling kinases, and signals induced by damage by-products complicate the process further. The cell's response to [Formula: see text] and UV radiation neatly illustrates this concept. While these forms of radiation produce lesions associated with two different pro-apoptotic signaling kinases, ATM and ATR, recent experiments show that ATM and ATR react to both forms of radiation. To simulate the pro-apoptotic signal induced by [Formula: see text] and UV radiation, we construct a mathematical model that includes three modes of crosstalk between ATM and ATR signaling pathways: positive feedback between ATM/ATR and repair proteins, ATM and ATR mutual upregulation, and changes in lesion topology induced by replication stress or repair. We calibrate the model to agree with 21 experimental claims about ATM and ATR crosstalk. We alter the model by adding or removing specific processes and then examine the effects of each process on ATM/ATR crosstalk by recording which claims the altered model violates. Not only is this the first mathematical model of ATM/ATR crosstalk, it provides a strong argument for treating pro-apoptotic signaling as a holistic effort rather than attributing it to a single dominant kinase.
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Affiliation(s)
- Elizabeth A Fedak
- Department of Mathematics, The University of Utah, 155 Presidents Circle, Salt Lake City, UT, 84112, USA. .,Department of Oncological Sciences, Huntsman Cancer Institute, The University of Utah, 2000 Cir of Hope Dr, Salt Lake City, UT, 84112, USA.
| | - Frederick R Adler
- Department of Mathematics, The University of Utah, 155 Presidents Circle, Salt Lake City, UT, 84112, USA.,Department of Biology, The University of Utah, 257 Presidents Circle, Salt Lake City, UT, 84112, USA
| | - Lisa M Abegglen
- Department of Oncological Sciences, Huntsman Cancer Institute, The University of Utah, 2000 Cir of Hope Dr, Salt Lake City, UT, 84112, USA.,Department of Pediatrics, The University of Utah, 295 Chipeta Way, Salt Lake City, UT, 84108, USA.,PEEL Therapeutics, Inc., Salt Lake City, UT, 84108, USA
| | - Joshua D Schiffman
- Department of Oncological Sciences, Huntsman Cancer Institute, The University of Utah, 2000 Cir of Hope Dr, Salt Lake City, UT, 84112, USA.,Department of Pediatrics, The University of Utah, 295 Chipeta Way, Salt Lake City, UT, 84108, USA.,PEEL Therapeutics, Inc., Salt Lake City, UT, 84108, USA
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22
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Soni A, Mladenov E, Iliakis G. Proficiency in homologous recombination repair is prerequisite for activation of G 2-checkpoint at low radiation doses. DNA Repair (Amst) 2021; 101:103076. [PMID: 33640756 DOI: 10.1016/j.dnarep.2021.103076] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 11/30/2020] [Accepted: 02/13/2021] [Indexed: 10/22/2022]
Abstract
Pathways of repair of DNA double strand breaks (DSBs) cooperate with DNA damage cell cycle checkpoints to safeguard genomic stability when cells are exposed to ionizing radiation (IR). It is widely accepted that checkpoints facilitate the function of DSB repair pathways. Whether DSB repair proficiency feeds back into checkpoint activation is less well investigated. Here, we study activation of the G2-checkpoint in cells deficient in homologous recombination repair (HRR) after exposure to low IR doses (∼1 Gy) in the G2-phase. We report that in the absence of functional HRR, activation of the G2-checkpoint is severely impaired. This response is specific for HRR, as cells deficient in classical non-homologous end joining (c-NHEJ) develop a similar or stronger G2-checkpoint than wild-type (WT) cells. Inhibition of ATM or ATR leaves largely unaffected residual G2-checkpoint in HRR-deficient cells, suggesting that the G2-checkpoint engagement of ATM/ATR is coupled to HRR. HRR-deficient cells show in G2-phase reduced DSB-end-resection, as compared to WT-cells or c-NHEJ mutants, confirming the reported link between resection and G2-checkpoint activation. Strikingly, at higher IR doses (≥4 Gy) HRR-deficient cells irradiated in G2-phase activate a weak but readily detectable ATM/ATR-dependent G2-checkpoint, whereas HRR-deficient cells irradiated in S-phase develop a stronger G2-checkpoint than WT-cells. We conclude that HRR and the ATM/ATR-dependent G2-checkpoint are closely intertwined in cells exposed to low IR-doses in G2-phase, where HRR dominates; they uncouple as HRR becomes suppressed at higher IR doses. Notably, this coupling is specific for cells irradiated in G2-phase, and cells irradiated in S-phase utilize a different mechanistic setup.
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Affiliation(s)
- Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
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23
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Aleksandrov R, Hristova R, Stoynov S, Gospodinov A. The Chromatin Response to Double-Strand DNA Breaks and Their Repair. Cells 2020; 9:cells9081853. [PMID: 32784607 PMCID: PMC7464352 DOI: 10.3390/cells9081853] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 08/03/2020] [Accepted: 08/04/2020] [Indexed: 02/07/2023] Open
Abstract
Cellular DNA is constantly being damaged by numerous internal and external mutagenic factors. Probably the most severe type of insults DNA could suffer are the double-strand DNA breaks (DSBs). They sever both DNA strands and compromise genomic stability, causing deleterious chromosomal aberrations that are implicated in numerous maladies, including cancer. Not surprisingly, cells have evolved several DSB repair pathways encompassing hundreds of different DNA repair proteins to cope with this challenge. In eukaryotic cells, DSB repair is fulfilled in the immensely complex environment of the chromatin. The chromatin is not just a passive background that accommodates the multitude of DNA repair proteins, but it is a highly dynamic and active participant in the repair process. Chromatin alterations, such as changing patterns of histone modifications shaped by numerous histone-modifying enzymes and chromatin remodeling, are pivotal for proficient DSB repair. Dynamic chromatin changes ensure accessibility to the damaged region, recruit DNA repair proteins, and regulate their association and activity, contributing to DSB repair pathway choice and coordination. Given the paramount importance of DSB repair in tumorigenesis and cancer progression, DSB repair has turned into an attractive target for the development of novel anticancer therapies, some of which have already entered the clinic.
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24
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Li F, Mladenov E, Mortoga S, Iliakis G. SCF SKP2 regulates APC/C CDH1-mediated degradation of CTIP to adjust DNA-end resection in G 2-phase. Cell Death Dis 2020; 11:548. [PMID: 32683422 PMCID: PMC7368859 DOI: 10.1038/s41419-020-02755-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 06/22/2020] [Accepted: 06/25/2020] [Indexed: 11/20/2022]
Abstract
The cell cycle-dependent engagement of DNA-end resection at DSBs is regulated by phosphorylation of CTIP by CDKs, the central regulators of cell cycle transitions. Cell cycle transitions are also intimately regulated by protein degradation via two E3 ubiquitin ligases: SCFSKP2 and APC/CCDH1 complex. Although APC/CCDH1 regulates CTIP in G1– and G2-phase, contributions by SCFSKP2 have not been reported. We demonstrate that SCFSKP2 is a strong positive regulator of resection. Knockdown of SKP2, fully suppresses resection in several cell lines. Notably, this suppression is G2-phase specific and is not observed in S-phase or G1–phase cells. Knockdown of SKP2 inactivates SCFSKP2 causing APC/CCDH1 activation, which degrades CTIP. The stabilizing function of SCFSKP2 on CTIP promotes resection and supports gene conversion (GC), alternative end joining (alt-EJ) and cell survival. We propose that CDKs and SCFSKP2-APC/CCDH1 cooperate to regulate resection and repair pathway choice at DSBs in G2-phase.
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Affiliation(s)
- Fanghua Li
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Sharif Mortoga
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
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25
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Gao SS, Guan H, Yan S, Hu S, Song M, Guo ZP, Xie DF, Liu Y, Liu X, Zhang S, Zhou PK. TIP60 K430 SUMOylation attenuates its interaction with DNA-PKcs in S-phase cells: Facilitating homologous recombination and emerging target for cancer therapy. SCIENCE ADVANCES 2020; 6:eaba7822. [PMID: 32832608 PMCID: PMC7439314 DOI: 10.1126/sciadv.aba7822] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Accepted: 06/01/2020] [Indexed: 05/12/2023]
Abstract
Nonhomologous end joining (NHEJ) and homologous recombination (HR) are major repair pathways of DNA double-strand breaks (DSBs). The pathway choice of HR and NHEJ is tightly regulated in cellular response to DNA damage. Here, we demonstrate that the interaction of TIP60 with DNA-PKcs is attenuated specifically in S phase, which facilitates HR pathway activation. SUMO2 modification of TIP60 K430 mediated by PISA4 E3 ligase blocks its interaction with DNA-PKcs, whereas TIP60 K430R mutation recovers its interaction with DNA-PKcs, which results in abnormally increased phosphorylation of DNA-PKcs S2056 in S phase and marked inhibition of HR efficiency, but barely affects NHEJ activity. TIP60 K430R mutant cancer cells are more sensitive to radiation and PARP inhibitors in cancer cell killing and tumor growth inhibition. Collectively, coordinated regulation of TIP60 and DNA-PKcs facilitates HR pathway choice in S-phase cells. TIP60 K430R mutant is a potential target of radiation and PARPi cancer therapy.
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Affiliation(s)
- Shan-Shan Gao
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Hua Guan
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Shuang Yan
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
- Institute for Environmental Medicine and Radiation Hygiene, School of Public Health, University of South China, Hengyang, Hunan Province 421001, P. R. China
| | - Sai Hu
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Man Song
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Zong-Pei Guo
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Da-Fei Xie
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Yike Liu
- Institute for Chemical Carcinogenesis, State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Xinzao, Panyu District, Guangzhou 511436, P. R. China
| | - Xiaodan Liu
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Shimeng Zhang
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
| | - Ping-Kun Zhou
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing 100850, P. R. China
- Institute for Chemical Carcinogenesis, State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Xinzao, Panyu District, Guangzhou 511436, P. R. China
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26
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Forrer Charlier C, Martins RAP. Protective Mechanisms Against DNA Replication Stress in the Nervous System. Genes (Basel) 2020; 11:E730. [PMID: 32630049 PMCID: PMC7397197 DOI: 10.3390/genes11070730] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 06/25/2020] [Accepted: 06/25/2020] [Indexed: 02/06/2023] Open
Abstract
The precise replication of DNA and the successful segregation of chromosomes are essential for the faithful transmission of genetic information during the cell cycle. Alterations in the dynamics of genome replication, also referred to as DNA replication stress, may lead to DNA damage and, consequently, mutations and chromosomal rearrangements. Extensive research has revealed that DNA replication stress drives genome instability during tumorigenesis. Over decades, genetic studies of inherited syndromes have established a connection between the mutations in genes required for proper DNA repair/DNA damage responses and neurological diseases. It is becoming clear that both the prevention and the responses to replication stress are particularly important for nervous system development and function. The accurate regulation of cell proliferation is key for the expansion of progenitor pools during central nervous system (CNS) development, adult neurogenesis, and regeneration. Moreover, DNA replication stress in glial cells regulates CNS tumorigenesis and plays a role in neurodegenerative diseases such as ataxia telangiectasia (A-T). Here, we review how replication stress generation and replication stress response (RSR) contribute to the CNS development, homeostasis, and disease. Both cell-autonomous mechanisms, as well as the evidence of RSR-mediated alterations of the cellular microenvironment in the nervous system, were discussed.
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Affiliation(s)
| | - Rodrigo A. P. Martins
- Programa de Biologia Celular e do Desenvolvimento, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro 21941-902, Brazil;
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27
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Mladenov E, Staudt C, Soni A, Murmann-Konda T, Siemann-Loekes M, Iliakis G. Strong suppression of gene conversion with increasing DNA double-strand break load delimited by 53BP1 and RAD52. Nucleic Acids Res 2020; 48:1905-1924. [PMID: 31832684 PMCID: PMC7038941 DOI: 10.1093/nar/gkz1167] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Revised: 10/30/2019] [Accepted: 12/11/2019] [Indexed: 02/06/2023] Open
Abstract
In vertebrates, genomic DNA double-strand breaks (DSBs) are removed by non-homologous end-joining processes: classical non-homologous end-joining (c-NHEJ) and alternative end-joining (alt-EJ); or by homology-dependent processes: gene-conversion (GC) and single-strand annealing (SSA). Surprisingly, these repair pathways are not real alternative options restoring genome integrity with equal efficiency, but show instead striking differences in speed, accuracy and cell-cycle-phase dependence. As a consequence, engagement of one pathway may be associated with processing-risks for the genome absent from another pathway. Characterization of engagement-parameters and their consequences is, therefore, essential for understanding effects on the genome of DSB-inducing agents, such as ionizing-radiation (IR). Here, by addressing pathway selection in G2-phase, we discover regulatory confinements in GC with consequences for SSA- and c-NHEJ-engagement. We show pronounced suppression of GC with increasing DSB-load that is not due to RAD51 availability and which is delimited but not defined by 53BP1 and RAD52. Strikingly, at low DSB-loads, GC repairs ∼50% of DSBs, whereas at high DSB-loads its contribution is undetectable. Notably, with increasing DSB-load and the associated suppression of GC, SSA gains ground, while alt-EJ is suppressed. These observations explain earlier, apparently contradictory results and advance our understanding of logic and mechanisms underpinning the wiring between DSB repair pathways.
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Affiliation(s)
- Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Christian Staudt
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Tamara Murmann-Konda
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Maria Siemann-Loekes
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
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28
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Soni A, Murmann-Konda T, Siemann-Loekes M, Pantelias GE, Iliakis G. Chromosome breaks generated by low doses of ionizing radiation in G 2-phase are processed exclusively by gene conversion. DNA Repair (Amst) 2020; 89:102828. [PMID: 32143127 DOI: 10.1016/j.dnarep.2020.102828] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 01/31/2020] [Accepted: 02/21/2020] [Indexed: 02/07/2023]
Abstract
Four repair pathways process DNA double-strand breaks (DSBs). Among these pathways the homologous recombination repair (HRR) subpathway of gene conversion (GC) affords error-free processing, but functions only in S- and G2-phases of the cell cycle. Classical non-homologous end-joining (c-NHEJ) operates throughout the cell cycle, but causes small deletions and translocations. Similar deficiencies in exaggerated form, combined with reduced efficiency, are associated with alternative end-joining (alt-EJ). Finally, single-strand annealing (SSA) causes large deletions and possibly translocations. Thus, processing of a DSB by any pathway, except GC, poses significant risks to the genome, making the mechanisms navigating pathway-engagement critical to genome stability. Logically, the cell ought to attempt engagement of the pathway ensuring preservation of the genome, while accommodating necessities generated by the types of DSBs induced. Thereby, inception of DNA end-resection will be key determinant for GC, SSA and alt-EJ engagement. We reported that during G2-phase, where all pathways are active, GC engages in the processing of almost 50 % of DSBs, at low DSB-loads in the genome, and that this contribution rapidly drops to nearly zero with increasing DSB-loads. At the transition between these two extremes, SSA and alt-EJ compensate, but at extremely high DSB-loads resection-dependent pathways are suppressed and c-NHEJ remains mainly active. We inquired whether in this processing framework all DSBs have similar fates. Here, we analyze in G2-phase the processing of a subset of DSBs defined by their ability to break chromosomes. Our results reveal an absolute requirement for GC in the processing of chromatid breaks at doses in the range of 1 Gy. Defects in c-NHEJ delay significantly the inception of processing by GC, but leave processing kinetics unchanged. These results delineate the essential role of GC in chromatid break repair before mitosis and classify DSBs that underpin this breakage as the exclusive substrate of GC.
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Affiliation(s)
- Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Tamara Murmann-Konda
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Maria Siemann-Loekes
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany
| | - Gabriel E Pantelias
- Institute of Nuclear Technology and Radiation Protection, National Centre for Scientific Research "Demokritos,''Aghia Paraskevi Attikis, Athens, Greece
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany.
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