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Zhao X, Wan B, Guan D, Li S, Chwat-Edelstein T. The Mms22-Rtt107 axis dampens the DNA damage checkpoint by reducing the stability of the Rad9 checkpoint mediator. RESEARCH SQUARE 2024:rs.3.rs-4417144. [PMID: 38826278 PMCID: PMC11142307 DOI: 10.21203/rs.3.rs-4417144/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
The DNA damage checkpoint is a highly conserved signaling pathway induced by genotoxin exposure or endogenous genome stress. It alters many cellular processes such as arresting the cell cycle progression and increasing DNA repair capacities. However, cells can downregulate the checkpoint after prolonged stress exposure to allow continued growth and alternative repair. Strategies that can dampen the DNA damage checkpoint are not well understood. Here, we report that budding yeast employs a pathway composed of the scaffold protein Rtt107, its binding partner Mms22, and an Mms22-associated ubiquitin ligase complex to downregulate the DNA damage checkpoint. Mechanistically, this pathway promotes the proteasomal degradation of a key checkpoint factor, Rad9. Furthermore, Rtt107 binding to Mms22 helps to enrich the ubiquitin ligase complex on chromatin and target the chromatin-bound form of Rad9. Finally, we provide evidence that the Rtt107-Mms22 axis operates in parallel with the Rtt107-Slx4 axis, which displaces Rad9 from chromatin. We thus propose that Rtt107 enables a bifurcated "anti-Rad9" strategy to optimally downregulate the DNA damage checkpoint.
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Affiliation(s)
| | | | | | - Shibai Li
- Memorial Sloan Kettering Cancer Center
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2
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Fan J, Dhingra N, Yang T, Yang V, Zhao X. Srs2 binding to PCNA and its sumoylation contribute to RPA antagonism during the DNA damage response. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.28.587206. [PMID: 38586001 PMCID: PMC10996639 DOI: 10.1101/2024.03.28.587206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
Activation of the DNA damage checkpoint upon genotoxin treatment induces a multitude of cellular changes, such as cell cycle arrest, to cope with genome stress. After prolonged genotoxin treatment, the checkpoint can be downregulated to allow cell cycle and growth resumption. In yeast, downregulation of the DNA damage checkpoint requires the Srs2 DNA helicase, which removes the ssDNA binding complex RPA and the associated Mec1 checkpoint kinase from DNA, thus dampening Mec1 activation. However, it is unclear whether the 'anti-checkpoint' role of Srs2 is temporally and spatially regulated to both allow timely checkpoint termination and to prevent superfluous RPA removal. Here we address this question by examining regulatory elements of Srs2, including its phosphorylation, sumoylation, and protein-interaction sites. Our genetic analyses and checkpoint level assessment suggest that the RPA countering role of Srs2 is promoted by Srs2 binding to PCNA, which is known to recruit Srs2 to subsets of ssDNA regions. RPA antagonism is further fostered by Srs2 sumoylation, which we found depends on the Srs2-PCNA interaction. Srs2 sumoylation is additionally reliant on Mec1 and peaks after Mec1 activity reaches maximal levels. Collectively, our data provide evidence for a two-step model wherein checkpoint downregulation is facilitated by PCNA-mediated Srs2 recruitment to ssDNA-RPA filaments and the subsequent Srs2 sumoylation stimulated upon Mec1 hyperactivation. We propose that this mechanism allows Mec1 hyperactivation to trigger checkpoint recovery.
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Affiliation(s)
- Jiayi Fan
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065
| | - Nalini Dhingra
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065
| | - Tammy Yang
- City University of New York Hunter College, New York, NY 10065
| | - Vicki Yang
- City University of New York Hunter College, New York, NY 10065
| | - Xiaolan Zhao
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065
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3
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Marshall S, Navarro MV, Ascenҫão CF, Smolka MB. IN-DEPTH MAPPING OF DNA-PKcs SIGNALING UNCOVERS CONSERVED FEATURES OF ITS KINASE SPECIFICITY. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.17.576037. [PMID: 38293078 PMCID: PMC10827184 DOI: 10.1101/2024.01.17.576037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
DNA-PKcs is a DNA damage sensor kinase with established roles in DNA double-strand break repair via non-homologous end joining. Recent studies have revealed additional roles of DNA-PKcs in the regulation of transcription, translation and DNA replication. However, the substrates through which DNA-PKcs regulates these processes remain largely undefined. Here we utilized quantitative phosphoproteomics to generate a high coverage map of DNA-PKcs signaling in response to ionizing radiation and mapped its interplay with the ATM kinase. Beyond the detection of the canonical S/T-Q phosphorylation motif, we uncovered a non-canonical mode of DNA-PKcs signaling targeting S/T-ψ-D/E motifs. Cross-species analysis in mouse pre-B and human HCT116 cell lines revealed splicing factors and transcriptional regulators phosphorylated at this novel motif, several of which contain SAP domains. These findings expand the list of DNA-PKcs and ATM substrates and establish a novel preferential phosphorylation motif for DNA-PKcs that connects it to proteins involved in nucleotide processes and interactions.
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Affiliation(s)
- Shannon Marshall
- 1. Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Marcos V.A.S. Navarro
- 1. Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
- 2. IFSC Institute of Physics of São Carlos, University of São Paulo, São Carlos - SP, 13566-590, Brazil
| | - Carolline F.R. Ascenҫão
- 1. Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Marcus B. Smolka
- 1. Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
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4
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Xiao D, Chen C, Yang P. Computational systems approach towards phosphoproteomics and their downstream regulation. Proteomics 2023; 23:e2200068. [PMID: 35580145 DOI: 10.1002/pmic.202200068] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 04/26/2022] [Accepted: 05/03/2022] [Indexed: 11/07/2022]
Abstract
Protein phosphorylation plays an essential role in modulating cell signalling and its downstream transcriptional and translational regulations. Until recently, protein phosphorylation has been studied mostly using low-throughput biochemical assays. The advancement of mass spectrometry (MS)-based phosphoproteomics transformed the field by enabling measurement of proteome-wide phosphorylation events, where tens of thousands of phosphosites are routinely identified and quantified in an experiment. This has brought a significant challenge in analysing large-scale phosphoproteomic data, making computational methods and systems approaches integral parts of phosphoproteomics. Previous works have primarily focused on reviewing the experimental techniques in MS-based phosphoproteomics, yet a systematic survey of the computational landscape in this field is still missing. Here, we review computational methods and tools, and systems approaches that have been developed for phosphoproteomics data analysis. We categorise them into four aspects including data processing, functional analysis, phosphoproteome annotation and their integration with other omics, and in each aspect, we discuss the key methods and example studies. Lastly, we highlight some of the potential research directions on which future work would make a significant contribution to this fast-growing field. We hope this review provides a useful snapshot of the field of computational systems phosphoproteomics and stimulates new research that drives future development.
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Affiliation(s)
- Di Xiao
- Computational Systems Biology Group, Children's Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia.,Charles Perkins Centre, The University of Sydney, Sydney, New South Wales, Australia
| | - Carissa Chen
- Computational Systems Biology Group, Children's Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia.,Charles Perkins Centre, The University of Sydney, Sydney, New South Wales, Australia
| | - Pengyi Yang
- Computational Systems Biology Group, Children's Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia.,Charles Perkins Centre, The University of Sydney, Sydney, New South Wales, Australia.,School of Mathematics and Statistics, The University of Sydney, Sydney, New South Wales, Australia
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5
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James Sanford E, Bustamante Smolka M. A field guide to the proteomics of post-translational modifications in DNA repair. Proteomics 2022; 22:e2200064. [PMID: 35695711 PMCID: PMC9950963 DOI: 10.1002/pmic.202200064] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 05/19/2022] [Accepted: 05/30/2022] [Indexed: 12/15/2022]
Abstract
All cells incur DNA damage from exogenous and endogenous sources and possess pathways to detect and repair DNA damage. Post-translational modifications (PTMs), in the past 20 years, have risen to ineluctable importance in the study of the regulation of DNA repair mechanisms. For example, DNA damage response kinases are critical in both the initial sensing of DNA damage as well as in orchestrating downstream activities of DNA repair factors. Mass spectrometry-based proteomics revolutionized the study of the role of PTMs in the DNA damage response and has canonized PTMs as central modulators of nearly all aspects of DNA damage signaling and repair. This review provides a biologist-friendly guide for the mass spectrometry analysis of PTMs in the context of DNA repair and DNA damage responses. We reflect on the current state of proteomics for exploring new mechanisms of PTM-based regulation and outline a roadmap for designing PTM mapping experiments that focus on the DNA repair and DNA damage responses.
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Key Words
- LC-MS/MS, technology, bottom-up proteomics, technology, signal transduction, cell biology
- phosphoproteomics, technology, post-translational modification analysis, technology, post-translational modifications, cell biology, mass spectrometry
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Affiliation(s)
- Ethan James Sanford
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853
| | - Marcus Bustamante Smolka
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853,Corresponding author:
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6
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Sims JR, Faça VM, Pereira C, Ascenção C, Comstock W, Badar J, Arroyo-Martinez GA, Freire R, Cohen PE, Weiss RS, Smolka MB. Phosphoproteomics of ATR signaling in mouse testes. eLife 2022; 11:e68648. [PMID: 35133275 PMCID: PMC8824463 DOI: 10.7554/elife.68648] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 12/22/2021] [Indexed: 11/13/2022] Open
Abstract
The phosphatidylinositol 3' kinase (PI3K)-related kinase ATR is crucial for mammalian meiosis. ATR promotes meiotic progression by coordinating key events in DNA repair, meiotic sex chromosome inactivation (MSCI), and checkpoint-dependent quality control during meiotic prophase I. Despite its central roles in meiosis, the ATR-dependent meiotic signaling network remains largely unknown. Here, we used phosphoproteomics to define ATR signaling events in testes from mice following chemical and genetic ablation of ATR signaling. Quantitative analysis of phosphoproteomes obtained after germ cell-specific genetic ablation of the ATR activating 9-1-1 complex or treatment with ATR inhibitor identified over 14,000 phosphorylation sites from testes samples, of which 401 phosphorylation sites were found to be dependent on both the 9-1-1 complex and ATR. Our analyses identified ATR-dependent phosphorylation events in crucial DNA damage signaling and DNA repair proteins including TOPBP1, SMC3, MDC1, RAD50, and SLX4. Importantly, we identified ATR and RAD1-dependent phosphorylation events in proteins involved in mRNA regulatory processes, including SETX and RANBP3, whose localization to the sex body was lost upon ATR inhibition. In addition to identifying the expected ATR-targeted S/T-Q motif, we identified enrichment of an S/T-P-X-K motif in the set of ATR-dependent events, suggesting that ATR promotes signaling via proline-directed kinase(s) during meiosis. Indeed, we found that ATR signaling is important for the proper localization of CDK2 in spermatocytes. Overall, our analysis establishes a map of ATR signaling in mouse testes and highlights potential meiotic-specific actions of ATR during prophase I progression.
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Affiliation(s)
- Jennie R Sims
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - Vitor M Faça
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
- Department of Biochemistry and Immunology, Ribeirão Preto Medical School, University of São PauloRibeirão PretoBrazil
| | - Catalina Pereira
- Department of Biomedical Sciences, Cornell UniversityIthacaUnited States
| | - Carolline Ascenção
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - William Comstock
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - Jumana Badar
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | | | - Raimundo Freire
- Unidad de Investigación, Hospital Universitario de CanariasTenerifeSpain
- Instituto de Tecnologías Biomédicas, Universidad de La LagunaLa LagunaSpain
- Universidad Fernando Pessoa CanariasLas Palmas de Gran CanariaSpain
| | - Paula E Cohen
- Department of Biomedical Sciences, Cornell UniversityIthacaUnited States
| | - Robert S Weiss
- Department of Biomedical Sciences, Cornell UniversityIthacaUnited States
| | - Marcus B Smolka
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
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7
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Iannetta AA, Minton NE, Uitenbroek AA, Little JL, Stanton CR, Kristich CJ, Hicks LM. IreK-Mediated, Cell Wall-Protective Phosphorylation in Enterococcus faecalis. J Proteome Res 2021; 20:5131-5144. [PMID: 34672600 PMCID: PMC10037947 DOI: 10.1021/acs.jproteome.1c00635] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Enterococcus faecalis is a Gram-positive bacterium that is a major cause of hospital-acquired infections due, in part, to its intrinsic resistance to cell wall-active antimicrobials. One critical determinant of this resistance is the transmembrane kinase IreK, which belongs to the penicillin-binding protein and serine/threonine kinase-associated kinase family of bacterial signaling proteins involved with the regulation of cell wall homeostasis. The activity of IreK is enhanced in response to cell wall stress, but direct substrates of IreK phosphorylation, leading to antimicrobial resistance, are largely unknown. To better understand stress-modulated phosphorylation events contributing to antimicrobial resistance, wild type E. faecalis cells treated with cell wall-active antimicrobials, chlorhexidine or ceftriaxone, were examined via phosphoproteomics. Among the most prominent changes was increased phosphorylation of divisome components after both treatments, suggesting that E. faecalis modulates cell division in response to cell wall stress. Phosphorylation mediated by IreK was then determined via a similar analysis with a E. faecalis ΔireK mutant strain, revealing potential IreK substrates involved with the regulation of peptidoglycan biosynthesis and within the E. faecalis CroS/R two-component system, another signal transduction pathway that promotes antimicrobial resistance. These results reveal critical insights into the biological functions of IreK.
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Affiliation(s)
- Anthony A. Iannetta
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Nicole E. Minton
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Alexis A. Uitenbroek
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Jaime L. Little
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Caroline R. Stanton
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Christopher J. Kristich
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Leslie M. Hicks
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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8
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Sanford EJ, Smolka MB. Fe-NTA Microcolumn Purification of Phosphopeptides from Immunoprecipitation (IP) Eluates for Mass Spectrometry Analysis. Bio Protoc 2021; 11:e4113. [PMID: 34458407 DOI: 10.21769/bioprotoc.4113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 04/18/2021] [Accepted: 04/30/2021] [Indexed: 11/02/2022] Open
Abstract
Protein phosphorylation is a nearly universal signaling mechanism. To date, a number of proteomics tools have been developed to analyze phosphorylation. Phosphoproteome-wide analyses using whole cell extracts suffer from incomplete coverage, often missing phosphorylation events from low-abundance proteins. In order to increase coverage of phosphorylation sites on individual proteins of interest ("phospho-mapping"), immunoprecipitation (IP) followed by phosphoenrichment is necessary. Unfortunately, most commercially available phosphoenrichment kits are not readily scalable to the low-microgram quantities of protein present in IP eluates. Here, we describe a simple method specifically optimized for the enrichment of phosphopeptides from IP samples using an Fe-NTA based method. This method can be added downstream of any standard immunoprecipitation protocol and upstream of any MS analysis pipeline. The protocol described herein is cost effective, uses commonly available laboratory reagents, and can be used to obtain deep coverage of individual protein phosphorylation patterns, supplementary to phosphoproteomics data. Graphical abstract: Phospho-mapping workflow for a hypothetical protein of interest.
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Affiliation(s)
- Ethan J Sanford
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Marcus B Smolka
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
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9
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Sanford EJ, Comstock WJ, Faça VM, Vega SC, Gnügge R, Symington LS, Smolka MB. Phosphoproteomics reveals a distinctive Mec1/ATR signaling response upon DNA end hyper-resection. EMBO J 2021; 40:e104566. [PMID: 33764556 DOI: 10.15252/embj.2020104566] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 02/16/2021] [Accepted: 02/22/2021] [Indexed: 01/27/2023] Open
Abstract
The Mec1/ATR kinase is crucial for genome maintenance in response to a range of genotoxic insults, but it remains unclear how it promotes context-dependent signaling and DNA repair. Using phosphoproteomic analyses, we uncovered a distinctive Mec1/ATR signaling response triggered by extensive nucleolytic processing (resection) of DNA ends. Budding yeast cells lacking Rad9, a checkpoint adaptor and an inhibitor of resection, exhibit a selective increase in Mec1-dependent phosphorylation of proteins associated with single-strand DNA (ssDNA) transactions, including the ssDNA-binding protein Rfa2, the translocase/ubiquitin ligase Uls1, and the Sgs1-Top3-Rmi1 (STR) complex that regulates homologous recombination (HR). Extensive Mec1-dependent phosphorylation of the STR complex, mostly on the Sgs1 helicase subunit, promotes an interaction between STR and the DNA repair scaffolding protein Dpb11. Fusion of Sgs1 to phosphopeptide-binding domains of Dpb11 strongly impairs HR-mediated repair, supporting a model whereby Mec1 signaling regulates STR upon hyper-resection to influence recombination outcomes. Overall, the identification of a distinct Mec1 signaling response triggered by hyper-resection highlights the multi-faceted action of this kinase in the coordination of checkpoint signaling and HR-mediated DNA repair.
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Affiliation(s)
- Ethan J Sanford
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - William J Comstock
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Vitor M Faça
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA.,Department of Biochemistry and Immunology and Cell-Based Therapy Center, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, Brazil
| | - Stephanie C Vega
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Robert Gnügge
- Department of Microbiology and Immunology, Columbia University Irving Medical Center, New York, NY, USA
| | - Lorraine S Symington
- Department of Microbiology and Immunology, Columbia University Irving Medical Center, New York, NY, USA
| | - Marcus B Smolka
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
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The Srs2 helicase dampens DNA damage checkpoint by recycling RPA from chromatin. Proc Natl Acad Sci U S A 2021; 118:2020185118. [PMID: 33602817 DOI: 10.1073/pnas.2020185118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The DNA damage checkpoint induces many cellular changes to cope with genotoxic stress. However, persistent checkpoint signaling can be detrimental to growth partly due to blockage of cell cycle resumption. Checkpoint dampening is essential to counter such harmful effects, but its mechanisms remain to be understood. Here, we show that the DNA helicase Srs2 removes a key checkpoint sensor complex, RPA, from chromatin to down-regulate checkpoint signaling in budding yeast. The Srs2 and RPA antagonism is supported by their numerous suppressive genetic interactions. Importantly, moderate reduction of RPA binding to single-strand DNA (ssDNA) rescues hypercheckpoint signaling caused by the loss of Srs2 or its helicase activity. This rescue correlates with a reduction in the accumulated RPA and the associated checkpoint kinase on chromatin in srs2 mutants. Moreover, our data suggest that Srs2 regulation of RPA is separable from its roles in recombinational repair and critically contributes to genotoxin resistance. We conclude that dampening checkpoint by Srs2-mediated RPA recycling from chromatin aids cellular survival of genotoxic stress and has potential implications in other types of DNA transactions.
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