1
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Connelly CJ, Vidal-Cardenas S, Goldsmith S, Greider CW. The Bur1 cyclin-dependent kinase regulates telomere length in Saccharomyces cerevisiae. Yeast 2021; 39:177-192. [PMID: 34781413 PMCID: PMC9299788 DOI: 10.1002/yea.3680] [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: 07/18/2021] [Revised: 10/09/2021] [Accepted: 11/04/2021] [Indexed: 11/26/2022] Open
Abstract
Telomere length regulation is essential for cell viability in eukaryotes. While many pathways that affect telomere length are known, we do not yet have a complete understanding of the mechanism of length regulation. To identify new pathways that might regulate telomere length, we carried out a genetic screen in yeast and identified the cyclin‐dependent kinase complex Bur1/2 as a regulator of telomere length. Mutations in either BUR1 cyclin‐dependent kinase or the associated BUR2 cyclin resulted in short telomeres. This regulation did not function through the known role of BUR1 in regulating histone modification as bur1∆ set2∆ and bur2∆ set2∆ double mutants rescued cell growth but did not rescue the telomere shortening effects. We found that both bur1∆ and bur2∆ set2∆ were also defective in de novo telomere addition, and deletion of SET2 did also not rescue this elongation defect. The Bur1/2 cyclin‐dependent kinase regulates transcription of many genes. We found that TLC1 RNA levels were reduced in bur2∆ set2∆ mutants; however, overexpression of TLC1 restored the transcript levels but did not restore de novo telomere elongation or telomere length. These data suggest that the Bur1/2 kinase plays a role in telomere elongation separate from its role in transcription of telomerase components. Dissecting the role of the Bur1/2 kinase pathway at telomeres will help complete our understanding of the complex network of telomere length regulation. Loss of Bur1/2 cyclin‐dependent kinase activity causes short telomeres. Short telomere phenotype is not due to the role of Bur1/2 in histone modification. Short telomeres are not due to decreased levels of telomerase components Est1, Est2, Est3, or Tlc1. In absence of Bur1/2 activity, TLC1 deleted cells do not form survivors. Bur1/2 kinase directly or indirectly regulates telomere length.
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Affiliation(s)
- Carla J Connelly
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Sofia Vidal-Cardenas
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Exelixis, Inc., Alameda, California, USA
| | - Stephanie Goldsmith
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA
| | - Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, USA
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2
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Abstract
The MRN complex (MRX in Saccharomyces cerevisiae, made of Mre11, Rad50 and Nbs1/Xrs2) initiates double-stranded DNA break repair and activates the Tel1/ATM kinase in the DNA damage response. Telomeres counter both outcomes at chromosome ends, partly by keeping MRN-ATM in check. We show that MRX is disabled by telomeric protein Rif2 through an N-terminal motif (MIN, MRN/X-inhibitory motif). MIN executes suppression of Tel1, DNA end-resection and non-homologous end joining by binding the Rad50 N-terminal region. Our data suggest that MIN promotes a transition within MRX that is not conductive for endonuclease activity, DNA-end tethering or Tel1 kinase activation, highlighting an Achilles' heel in MRN, which we propose is also exploited by the RIF2 paralog ORC4 (Origin Recognition Complex 4) in Kluyveromyces lactis and the Schizosaccharomyces pombe telomeric factor Taz1, which is evolutionarily unrelated to Orc4/Rif2. This raises the possibility that analogous mechanisms might be deployed in other eukaryotes as well.
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3
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Cancer genome datamining and functional genetic analysis implicate mechanisms of ATM/ATR dysfunction underpinning carcinogenesis. Commun Biol 2021; 4:363. [PMID: 33742106 PMCID: PMC7979806 DOI: 10.1038/s42003-021-01884-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Accepted: 02/17/2021] [Indexed: 12/16/2022] Open
Abstract
ATM and ATR are conserved regulators of the DNA damage response linked to cancer. Comprehensive DNA sequencing efforts identified ~4,000 cancer-associated mutations in ATM/ATR; however, their cancer implications remain largely unknown. To gain insights, we identify functionally important conserved residues in ATM, ATR and budding yeast Mec1ATR via cancer genome datamining and a functional genetic analysis, respectively. Surprisingly, only a small fraction of the critical residues is in the active site of the respective enzyme complexes, implying that loss of the intrinsic kinase activity is infrequent in carcinogenesis. A number of residues are solvent accessible, suggestive of their involvement in interacting with a protein-partner(s). The majority, buried inside the respective enzyme complexes, might play a structural or regulatory role. Together, these findings identify evolutionarily conserved ATM, ATR, and Mec1ATR residues involved in diverse aspects of the enzyme function and provide fresh insights into the elusive genotype-phenotype relationships in ATM/ATR and their cancer-associated variants. Waskiewicz et al. identify functionally important and evolutionarily conserved residues of ATM/ATR via data mining and a functional genetic analysis, finding that loss of the intrinsic kinase activity occurs infrequently in carcinogenesis. This study provides insights into the genotype-phenotype relationships in ATM/ATR and their cancer-associated variants.
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4
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He W, Rao HBDP, Tang S, Bhagwat N, Kulkarni DS, Ma Y, Chang MAW, Hall C, Bragg JW, Manasca HS, Baker C, Verhees GF, Ranjha L, Chen X, Hollingsworth NM, Cejka P, Hunter N. Regulated Proteolysis of MutSγ Controls Meiotic Crossing Over. Mol Cell 2020; 78:168-183.e5. [PMID: 32130890 DOI: 10.1016/j.molcel.2020.02.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 01/03/2020] [Accepted: 01/31/2020] [Indexed: 01/04/2023]
Abstract
Crossover recombination is essential for accurate chromosome segregation during meiosis. The MutSγ complex, Msh4-Msh5, facilitates crossing over by binding and stabilizing nascent recombination intermediates. We show that these activities are governed by regulated proteolysis. MutSγ is initially inactive for crossing over due to an N-terminal degron on Msh4 that renders it unstable by directly targeting proteasomal degradation. Activation of MutSγ requires the Dbf4-dependent kinase Cdc7 (DDK), which directly phosphorylates and thereby neutralizes the Msh4 degron. Genetic requirements for Msh4 phosphorylation indicate that DDK targets MutSγ only after it has bound to nascent joint molecules (JMs) in the context of synapsing chromosomes. Overexpression studies confirm that the steady-state level of Msh4, not phosphorylation per se, is the critical determinant for crossing over. At the DNA level, Msh4 phosphorylation enables the formation and crossover-biased resolution of double-Holliday Junction intermediates. Our study establishes regulated protein degradation as a fundamental mechanism underlying meiotic crossing over.
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Affiliation(s)
- Wei He
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - H B D Prasada Rao
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Shangming Tang
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Nikhil Bhagwat
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Dhananjaya S Kulkarni
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Yunmei Ma
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Maria A W Chang
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Christie Hall
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Junxi Wang Bragg
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Harrison S Manasca
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Christa Baker
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Gerrik F Verhees
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA
| | - Lepakshi Ranjha
- Institute for Research in Biomedicine, Università della Svizzera italiana, Bellinzona, Switzerland
| | - Xiangyu Chen
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, USA
| | - Nancy M Hollingsworth
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, USA
| | - Petr Cejka
- Institute for Research in Biomedicine, Università della Svizzera italiana, Bellinzona, Switzerland
| | - Neil Hunter
- Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA; Department of Molecular & Cellular Biology, University of California, Davis, Davis, California, USA; Department of Cell Biology & Human Anatomy, University of California, Davis, Davis, California, USA.
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5
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Keener R, Connelly CJ, Greider CW. Tel1 Activation by the MRX Complex Is Sufficient for Telomere Length Regulation but Not for the DNA Damage Response in Saccharomyces cerevisiae. Genetics 2019; 213:1271-1288. [PMID: 31645360 PMCID: PMC6893380 DOI: 10.1534/genetics.119.302713] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 10/17/2019] [Indexed: 12/26/2022] Open
Abstract
Previous models suggested that regulation of telomere length in Saccharomyces cerevisiae by Tel1(ATM) and Mec1(ATR) would parallel the established pathways regulating the DNA damage response. Here, we provide evidence that telomere length regulation differs from the DNA damage response in both the Tel1 and Mec1 pathways. We found that Rad53 mediates a Mec1 telomere length regulation pathway but is dispensable for Tel1 telomere length regulation, whereas in the DNA damage response, Rad53 is regulated by both Mec1 and Tel1 Using epistasis analysis with a Tel1 hypermorphic allele, Tel1-hy909, we found that the MRX complex is not required downstream of Tel1 for telomere elongation but is required downstream of Tel1 for the DNA damage response. Our data suggest that nucleolytic telomere end processing is not a required step for telomerase to elongate telomeres.
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Affiliation(s)
- Rebecca Keener
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
- Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Carla J Connelly
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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6
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Menin L, Colombo CV, Maestrini G, Longhese MP, Clerici M. Tel1/ATM Signaling to the Checkpoint Contributes to Replicative Senescence in the Absence of Telomerase. Genetics 2019; 213:411-429. [PMID: 31391264 PMCID: PMC6781906 DOI: 10.1534/genetics.119.302391] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 07/27/2019] [Indexed: 11/18/2022] Open
Abstract
Telomeres progressively shorten at every round of DNA replication in the absence of telomerase. When they become critically short, telomeres trigger replicative senescence by activating a DNA damage response that is governed by the Mec1/ATR and Tel1/ATM protein kinases. While Mec1/ATR is known to block cell division when extended single-stranded DNA (ssDNA) accumulates at eroded telomeres, the molecular mechanism by which Tel1/ATM promotes senescence is still unclear. By characterizing a Tel1-hy184 mutant variant that compensates for the lack of Mec1 functions, we provide evidence that Tel1 promotes senescence by signaling to a Rad9-dependent checkpoint. Tel1-hy184 anticipates senescence onset in telomerase-negative cells, while the lack of Tel1 or the expression of a kinase-defective (kd) Tel1 variant delays it. Both Tel1-hy184 and Tel1-kd do not alter ssDNA generation at telomeric DNA ends. Furthermore, Rad9 and (only partially) Mec1 are responsible for the precocious senescence promoted by Tel1-hy184. This precocious senescence is mainly caused by the F1751I, D1985N, and E2133K amino acid substitutions, which are located in the FRAP-ATM-TRAPP domain of Tel1 and also increase Tel1 binding to DNA ends. Altogether, these results indicate that Tel1 induces replicative senescence by directly signaling dysfunctional telomeres to the checkpoint machinery.
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Affiliation(s)
- Luca Menin
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Chiara Vittoria Colombo
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Giorgia Maestrini
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Michela Clerici
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
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7
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Mohibullah N, Keeney S. Numerical and spatial patterning of yeast meiotic DNA breaks by Tel1. Genome Res 2017; 27:278-288. [PMID: 27923845 PMCID: PMC5287233 DOI: 10.1101/gr.213587.116] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 11/30/2016] [Indexed: 01/26/2023]
Abstract
The Spo11-generated double-strand breaks (DSBs) that initiate meiotic recombination are dangerous lesions that can disrupt genome integrity, so meiotic cells regulate their number, timing, and distribution. Mechanisms of this regulation remain poorly understood. Here, we use Spo11-oligonucleotide complexes, a byproduct of DSB formation, to reveal aspects of the contribution of the Saccharomyces cerevisiae DNA damage-responsive kinase Tel1 (ortholog of mammalian ATM). A tel1Δ mutant has globally increased amounts of Spo11-oligonucleotide complexes and altered Spo11-oligonucleotide lengths, consistent with conserved roles for Tel1 in control of DSB number and processing. A kinase-dead tel1 mutation similarly increases Spo11-oligonucleotide levels but mutating known Tel1 phosphotargets on Hop1 and Rec114 does not, implicating Tel1 kinase activity and clarifying roles of Tel1 phosphorylation substrates. Deep sequencing of Spo11 oligonucleotides demonstrates that Tel1 shapes the genome-wide DSB landscape in unexpected ways. Early in meiosis, Tel1 absence causes widespread changes in DSB distributions across large chromosomal domains. Many of these changes are erased as meiosis proceeds, however, illustrating homeostatic behavior of DSB regulatory systems. We further find that effects of Tel1 are distinct but partially overlapping with previously described contributions of the recombination regulator Cst9 (also known as Zip3). Finally, we provide evidence indicating that Tel1-dependent DSB interference influences the population-average DSB landscape but also demonstrate that locally inhibitory effects of an artificial hotspot insertion can be both Tel1-independent and chromosomal context-dependent. Our findings delineate Tel1 roles in regulating number and location of DSBs and illuminate the complex interplay between Tel1 and other pathways for DSB control.
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Affiliation(s)
- Neeman Mohibullah
- Howard Hughes Medical Institute, Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
| | - Scott Keeney
- Howard Hughes Medical Institute, Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
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8
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Iwasaki D, Hayashihara K, Shima H, Higashide M, Terasawa M, Gasser SM, Shinohara M. The MRX Complex Ensures NHEJ Fidelity through Multiple Pathways Including Xrs2-FHA-Dependent Tel1 Activation. PLoS Genet 2016; 12:e1005942. [PMID: 26990569 PMCID: PMC4798412 DOI: 10.1371/journal.pgen.1005942] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 02/25/2016] [Indexed: 12/28/2022] Open
Abstract
Because DNA double-strand breaks (DSBs) are one of the most cytotoxic DNA lesions and often cause genomic instability, precise repair of DSBs is vital for the maintenance of genomic stability. Xrs2/Nbs1 is a multi-functional regulatory subunit of the Mre11-Rad50-Xrs2/Nbs1 (MRX/N) complex, and its function is critical for the primary step of DSB repair, whether by homologous recombination (HR) or non-homologous end joining. In human NBS1, mutations result truncation of the N-terminus region, which contains a forkhead-associated (FHA) domain, cause Nijmegen breakage syndrome. Here we show that the Xrs2 FHA domain of budding yeast is required both to suppress the imprecise repair of DSBs and to promote the robust activation of Tel1 in the DNA damage response pathway. The role of the Xrs2 FHA domain in Tel1 activation was independent of the Tel1-binding activity of the Xrs2 C terminus, which mediates Tel1 recruitment to DSB ends. Both the Xrs2 FHA domain and Tel1 were required for the timely removal of the Ku complex from DSB ends, which correlates with a reduced frequency of imprecise end-joining. Thus, the Xrs2 FHA domain and Tel1 kinase work in a coordinated manner to maintain DSB repair fidelity. Genomic DNA provides the essential blueprint for life, and therefore living organisms have several mechanisms for maintaining the stability of their own genomes. DNA double-strand breaks (DSBs) are one of the most severe forms of DNA damage, which, without precise repair, can provoke a loss of genetic information, leading to tumor formation. DSBs are repaired by two distinct pathways, homologous recombination (HR) and non-homologous end joining (NHEJ), which can be precise or imprecise. In addition, the DNA damage response (DDR) is essential in the cell to integrate multiple events that need to occur after damage: activation of DNA repair enzymes, selection of repair pathway and control of cell cycle progression, transcription, and so on. Here we show that different domains of Xrs2, a central DSB repair protein in budding yeast whose human ortholog, Nbs1, is linked to a human hereditary disorder with a high risk of cancer, is required not only for repair pathway choice but also for full activation of DDR. This result indicates that DSB repair and the DDR are coordinated at multiple levels to ensure precise repair and thus to maintain genomic integrity.
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Affiliation(s)
- Daichi Iwasaki
- Department of Integrated Protein Functions, Institute for Protein Research, Osaka University, Suita, Osaka, Japan
- Department of Biological Science, Graduate School of Science, Osaka University, Suita, Osaka, Japan
| | - Kayoko Hayashihara
- Department of Integrated Protein Functions, Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Hiroki Shima
- Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan
| | - Mika Higashide
- Department of Integrated Protein Functions, Institute for Protein Research, Osaka University, Suita, Osaka, Japan
- Department of Biological Science, Graduate School of Science, Osaka University, Suita, Osaka, Japan
| | - Masahiro Terasawa
- Department of Integrated Protein Functions, Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Susan M. Gasser
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Miki Shinohara
- Department of Integrated Protein Functions, Institute for Protein Research, Osaka University, Suita, Osaka, Japan
- Department of Biological Science, Graduate School of Science, Osaka University, Suita, Osaka, Japan
- Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan
- * E-mail:
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9
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Lee SS, Bohrson C, Pike AM, Wheelan SJ, Greider CW. ATM Kinase Is Required for Telomere Elongation in Mouse and Human Cells. Cell Rep 2015; 13:1623-32. [PMID: 26586427 PMCID: PMC4663052 DOI: 10.1016/j.celrep.2015.10.035] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 09/11/2015] [Accepted: 10/11/2015] [Indexed: 12/26/2022] Open
Abstract
Short telomeres induce a DNA damage response, senescence, and apoptosis, thus maintaining telomere length equilibrium is essential for cell viability. Telomerase addition of telomere repeats is tightly regulated in cells. To probe pathways that regulate telomere addition, we developed the ADDIT assay to measure new telomere addition at a single telomere in vivo. Sequence analysis showed telomerase-specific addition of repeats onto a new telomere occurred in just 48 hr. Using the ADDIT assay, we found that ATM is required for addition of new repeats onto telomeres in mouse cells. Evaluation of bulk telomeres, in both human and mouse cells, showed that blocking ATM inhibited telomere elongation. Finally, the activation of ATM through the inhibition of PARP1 resulted in increased telomere elongation, supporting the central role of the ATM pathway in regulating telomere addition. Understanding this role of ATM may yield new areas for possible therapeutic intervention in telomere-mediated disease.
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Affiliation(s)
- Stella Suyong Lee
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Craig Bohrson
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Alexandra Mims Pike
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Sarah Jo Wheelan
- Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Carol Widney Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
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10
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Regulation of Telomere Length Requires a Conserved N-Terminal Domain of Rif2 in Saccharomyces cerevisiae. Genetics 2015; 201:573-86. [PMID: 26294668 PMCID: PMC4596670 DOI: 10.1534/genetics.115.177899] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 08/19/2015] [Indexed: 12/26/2022] Open
Abstract
The regulation of telomere length equilibrium is essential for cell growth and survival since critically short telomeres signal DNA damage and cell cycle arrest. While the broad principles of length regulation are well established, the molecular mechanism of how these steps occur is not fully understood. We mutagenized the RIF2 gene in Saccharomyces cerevisiae to understand how this protein blocks excess telomere elongation. We identified an N-terminal domain in Rif2 that is essential for length regulation, which we have termed BAT domain for Blocks Addition of Telomeres. Tethering this BAT domain to Rap1 blocked telomere elongation not only in rif2Δ mutants but also in rif1Δ and rap1C-terminal deletion mutants. Mutation of a single amino acid in the BAT domain, phenylalanine at position 8 to alanine, recapitulated the rif2Δ mutant phenotype. Substitution of F8 with tryptophan mimicked the wild-type phenylalanine, suggesting the aromatic amino acid represents a protein interaction site that is essential for telomere length regulation.
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11
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Ogi H, Goto GH, Ghosh A, Zencir S, Henry E, Sugimoto K. Requirement of the FATC domain of protein kinase Tel1 for localization to DNA ends and target protein recognition. Mol Biol Cell 2015; 26:3480-8. [PMID: 26246601 PMCID: PMC4591692 DOI: 10.1091/mbc.e15-05-0259] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 07/29/2015] [Indexed: 02/04/2023] Open
Abstract
Two large phosphatidylinositol 3-kinase-related protein kinases (PIKKs), ATM and ATR, play a central role in the DNA damage response pathway. PIKKs contain a highly conserved extreme C-terminus called the FRAP-ATM-TRRAP-C-terminal (FATC) domain. In budding yeast, ATM and ATR correspond to Tel1 and Mec1, respectively. In this study, we characterized functions of the FATC domain of Tel1 by introducing substitution or truncation mutations. One substitution mutation, termed tel1-21, and a truncation mutation, called tel1-ΔC, did not significantly affect the expression level. The tel1-21 mutation impaired the cellular response to DNA damage and conferred moderate telomere maintenance defect. In contrast, the tel1-ΔC mutation behaved like a null mutation, conferring defects in both DNA damage response and telomere maintenance. Tel1-21 protein localized to DNA ends as effectively as wild-type Tel1 protein, whereas Tel1-ΔC protein failed. Introduction of a hyperactive TEL1-hy mutation suppressed the tel1-21 mutation but not the tel1-ΔC mutation. In vitro analyses revealed that both Tel1-21 and Tel1-ΔC proteins undergo efficient autophosphorylation but exhibit decreased kinase activities toward the exogenous substrate protein, Rad53. Our results show that the FATC domain of Tel1 mediates localization to DNA ends and contributes to phosphorylation of target proteins.
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Affiliation(s)
- Hiroo Ogi
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103
| | - Greicy H Goto
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103
| | - Avik Ghosh
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103
| | - Sevil Zencir
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103
| | - Everett Henry
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103
| | - Katsunori Sugimoto
- Department of Microbiology, Biochemistry and Molecular Genetics, International Center for Public Health, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103 )
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12
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Kirkland JG, Peterson MR, Still CD, Brueggeman L, Dhillon N, Kamakaka RT. Heterochromatin formation via recruitment of DNA repair proteins. Mol Biol Cell 2015; 26:1395-410. [PMID: 25631822 PMCID: PMC4454184 DOI: 10.1091/mbc.e14-09-1413] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Double-strand-break repair proteins interact with and recruit Sir proteins to ectopic sites in the genome. Recruitment results in gene silencing, which depends on Sir proteins, as well as on histone H2A modification. Silencing also results in the localization of the locus to the nuclear periphery. Heterochromatin formation and nuclear organization are important in gene regulation and genome fidelity. Proteins involved in gene silencing localize to sites of damage and some DNA repair proteins localize to heterochromatin, but the biological importance of these correlations remains unclear. In this study, we examined the role of double-strand-break repair proteins in gene silencing and nuclear organization. We find that the ATM kinase Tel1 and the proteins Mre11 and Esc2 can silence a reporter gene dependent on the Sir, as well as on other repair proteins. Furthermore, these proteins aid in the localization of silenced domains to specific compartments in the nucleus. We identify two distinct mechanisms for repair protein–mediated silencing—via direct and indirect interactions with Sir proteins, as well as by tethering loci to the nuclear periphery. This study reveals previously unknown interactions between repair proteins and silencing proteins and suggests insights into the mechanism underlying genome integrity.
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Affiliation(s)
- Jacob G Kirkland
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
| | - Misty R Peterson
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
| | - Christopher D Still
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
| | - Leo Brueggeman
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
| | - Namrita Dhillon
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
| | - Rohinton T Kamakaka
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064
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13
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Al-Ahmadie H, Iyer G, Hohl M, Asthana S, Inagaki A, Schultz N, Hanrahan AJ, Scott SN, Brannon AR, McDermott GC, Pirun M, Ostrovnaya I, Kim P, Socci ND, Viale A, Schwartz GK, Reuter V, Bochner BH, Rosenberg JE, Bajorin DF, Berger MF, Petrini JHJ, Solit DB, Taylor BS. Synthetic lethality in ATM-deficient RAD50-mutant tumors underlies outlier response to cancer therapy. Cancer Discov 2014; 4:1014-21. [PMID: 24934408 PMCID: PMC4155059 DOI: 10.1158/2159-8290.cd-14-0380] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
UNLABELLED Metastatic solid tumors are almost invariably fatal. Patients with disseminated small-cell cancers have a particularly unfavorable prognosis, with most succumbing to their disease within two years. Here, we report on the genetic and functional analysis of an outlier curative response of a patient with metastatic small-cell cancer to combined checkpoint kinase 1 (CHK1) inhibition and DNA-damaging chemotherapy. Whole-genome sequencing revealed a clonal hemizygous mutation in the Mre11 complex gene RAD50 that attenuated ATM signaling which in the context of CHK1 inhibition contributed, via synthetic lethality, to extreme sensitivity to irinotecan. As Mre11 mutations occur in a diversity of human tumors, the results suggest a tumor-specific combination therapy strategy in which checkpoint inhibition in combination with DNA-damaging chemotherapy is synthetically lethal in tumor cells but not normal cells with somatic mutations that impair Mre11 complex function. SIGNIFICANCE Strategies to effect deep and lasting responses to cancer therapy in patients with metastatic disease have remained difficult to attain, especially in early-phase clinical trials. Here, we present an in-depth genomic and functional genetic analysis identifying RAD50 hypomorphism as a contributing factor to a curative response to systemic combination therapy in a patient with recurrent, metastatic small-cell cancer.
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Affiliation(s)
- Hikmat Al-Ahmadie
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Gopa Iyer
- Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York. Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York. Department of Medicine, Weill Cornell Medical College, New York, New York
| | - Marcel Hohl
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Saurabh Asthana
- Department of Medicine, University of California, San Francisco, California. Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, California
| | - Akiko Inagaki
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Nikolaus Schultz
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Aphrothiti J Hanrahan
- Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Sasinya N Scott
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - A Rose Brannon
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Gregory C McDermott
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Mono Pirun
- Bioinformatics Core Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Irina Ostrovnaya
- Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Philip Kim
- Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York. Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Nicholas D Socci
- Bioinformatics Core Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Agnes Viale
- Genomics Core Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Gary K Schwartz
- Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Victor Reuter
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Bernard H Bochner
- Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, New York
| | - Jonathan E Rosenberg
- Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York. Department of Medicine, Weill Cornell Medical College, New York, New York
| | - Dean F Bajorin
- Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York. Department of Medicine, Weill Cornell Medical College, New York, New York
| | - Michael F Berger
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York. Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York
| | - John H J Petrini
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York.
| | - David B Solit
- Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York. Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York. Department of Medicine, Weill Cornell Medical College, New York, New York.
| | - Barry S Taylor
- Department of Medicine, University of California, San Francisco, California. Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, California. Department of Epidemiology and Biostatistics, University of California, San Francisco, California.
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14
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Multifunctional role of ATM/Tel1 kinase in genome stability: from the DNA damage response to telomere maintenance. BIOMED RESEARCH INTERNATIONAL 2014; 2014:787404. [PMID: 25247188 PMCID: PMC4163350 DOI: 10.1155/2014/787404] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 07/28/2014] [Accepted: 08/07/2014] [Indexed: 12/19/2022]
Abstract
The mammalian protein kinase ataxia telangiectasia mutated (ATM) is a key regulator of the DNA double-strand-break response and belongs to the evolutionary conserved phosphatidylinositol-3-kinase-related protein kinases. ATM deficiency causes ataxia telangiectasia (AT), a genetic disorder that is characterized by premature aging, cerebellar neuropathy, immunodeficiency, and predisposition to cancer. AT cells show defects in the DNA damage-response pathway, cell-cycle control, and telomere maintenance and length regulation. Likewise, in Saccharomyces cerevisiae, haploid strains defective in the TEL1 gene, the ATM ortholog, show chromosomal aberrations and short telomeres. In this review, we outline the complex role of ATM/Tel1 in maintaining genomic stability through its control of numerous aspects of cellular survival. In particular, we describe how ATM/Tel1 participates in the signal transduction pathways elicited by DNA damage and in telomere homeostasis and its importance as a barrier to cancer development.
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15
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Hector RE, Ray A, Chen BR, Shtofman R, Berkner KL, Runge KW. Mec1p associates with functionally compromised telomeres. Chromosoma 2012; 121:277-90. [PMID: 22289863 PMCID: PMC3350766 DOI: 10.1007/s00412-011-0359-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 12/30/2011] [Accepted: 12/30/2011] [Indexed: 12/22/2022]
Abstract
In many organisms, telomere DNA consists of simple sequence repeat tracts that are required to protect the chromosome end. In the yeast Saccharomyces cerevisiae, tract maintenance requires two checkpoint kinases of the ATM family, Tel1p and Mec1p. Previous work has shown that Tel1p is recruited to functional telomeres with shorter repeat tracts to promote telomerase-mediated repeat addition, but the role of Mec1p is unknown. We found that Mec1p telomere association was detected as cells senesced when telomere function was compromised by extreme shortening due to either the loss of telomerase or the double-strand break binding protein Ku. Exonuclease I effects the removal of the 5' telomeric strand, and eliminating it prevented both senescence and Mec1p telomere association. Thus, in contrast to Tel1p, Mec1p associates with short, functionally compromised telomeres.
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Affiliation(s)
- Ronald E. Hector
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NE20, Cleveland, OH 44195 USA
- Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4920 USA
- Present Address: NCAUR, ARS, USDA, 1815 N. University St., Peoria, IL 61604 USA
| | - Alo Ray
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NE20, Cleveland, OH 44195 USA
| | - Bo-Ruei Chen
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NE20, Cleveland, OH 44195 USA
- Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4920 USA
| | - Rebecca Shtofman
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NE20, Cleveland, OH 44195 USA
| | - Kathleen L. Berkner
- Department of Molecular Cardiology, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NB50, Cleveland, OH 44195 USA
| | - Kurt W. Runge
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University, Lerner Research Institute, 9500 Euclid Avenue, NE20, Cleveland, OH 44195 USA
- Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4920 USA
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16
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Casein kinase 2 reverses tail-independent inactivation of kinesin-1. Nat Commun 2012; 3:754. [PMID: 22453827 PMCID: PMC3574636 DOI: 10.1038/ncomms1760] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Accepted: 02/24/2012] [Indexed: 11/08/2022] Open
Abstract
Kinesin-1 is a plus-end microtubule-based motor, and defects in kinesin-based transport are linked to diseases including neurodegeneration. Kinesin can auto-inhibit via a head-tail interaction, but is believed to be active otherwise. Here we report a tail-independent inactivation of kinesin, reversible by the disease-relevant signalling protein, casein kinase 2 (CK2). The majority of initially active kinesin (native or tail-less) loses its ability to interact with microtubules in vitro, and CK2 reverses this inactivation (approximately fourfold) without altering kinesin's single motor properties. This activation pathway does not require motor phosphorylation, and is independent of head-tail auto-inhibition. In cultured mammalian cells, reducing CK2 expression, but not its kinase activity, decreases the force required to stall lipid droplet transport, consistent with a decreased number of active kinesin motors. Our results provide the first direct evidence of a protein kinase upregulating kinesin-based transport, and suggest a novel pathway for regulating the activity of cargo-bound kinesin.
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17
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The secret life of kinases: functions beyond catalysis. Cell Commun Signal 2011; 9:23. [PMID: 22035226 PMCID: PMC3215182 DOI: 10.1186/1478-811x-9-23] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 10/28/2011] [Indexed: 02/07/2023] Open
Abstract
Protein phosphorylation participates in the regulation of all fundamental biological processes, and protein kinases have been intensively studied. However, while the focus was on catalytic activities, accumulating evidence suggests that non-catalytic properties of protein kinases are essential, and in some cases even sufficient for their functions. These non-catalytic functions include the scaffolding of protein complexes, the competition for protein interactions, allosteric effects on other enzymes, subcellular targeting, and DNA binding. This rich repertoire often is used to coordinate phosphorylation events and enhance the specificity of substrate phosphorylation, but also can adopt functions that do not rely on kinase activity. Here, we discuss such kinase independent functions of protein and lipid kinases focussing on kinases that play a role in the regulation of cell proliferation, differentiation, apoptosis, and motility.
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18
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Jauhar PP. Genetic control of chromosome behaviour: Implications in evolution, crop improvement, and human biology. THE NUCLEUS 2010. [DOI: 10.1007/s13237-010-0010-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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19
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Subramanian L, Nakamura TM. To fuse or not to fuse: how do checkpoint and DNA repair proteins maintain telomeres? FRONT BIOSCI-LANDMRK 2010; 15:1105-18. [PMID: 20515744 PMCID: PMC2880829 DOI: 10.2741/3664] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
DNA damage checkpoint and DNA repair mechanisms play critical roles in the stable maintenance of genetic information. Various forms of DNA damage that arise inside cells due to common errors in normal cellular processes, such as DNA replication, or due to exposure to various DNA damaging agents, must be quickly detected and repaired by checkpoint signaling and repair factors. Telomeres, the natural ends of linear chromosomes, share many features with undesired "broken" DNA, and are recognized and processed by various DNA damage checkpoint and DNA repair proteins. However, their modes of action at telomeres must be altered from their actions at other DNA damage sites to avoid telomere fusions and permanent cell cycle arrest. Interestingly, accumulating evidence indicates that DNA damage checkpoint and DNA repair proteins are essential for telomere maintenance. In this article, we review our current knowledge on various mechanisms by which DNA damage checkpoint and DNA repair proteins are modulated at telomeres and how they might contribute to telomere maintenance in eukaryotes.
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Affiliation(s)
- Lakxmi Subramanian
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA
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20
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Derheimer FA, Kastan MB. Multiple roles of ATM in monitoring and maintaining DNA integrity. FEBS Lett 2010; 584:3675-81. [PMID: 20580718 DOI: 10.1016/j.febslet.2010.05.031] [Citation(s) in RCA: 180] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2010] [Accepted: 05/14/2010] [Indexed: 01/17/2023]
Abstract
The ability of our cells to maintain genomic integrity is fundamental for protection from cancer development. Central to this process is the ability of cells to recognize and repair DNA damage and progress through the cell cycle in a regulated and orderly manner. In addition, protection of chromosome ends through the proper assembly of telomeres prevents loss of genetic information and aberrant chromosome fusions. Cells derived from patients with ataxia-telangiectasia (A-T) show defects in cell cycle regulation, abnormal responses to DNA breakage, and chromosomal end-to-end fusions. The identification and characterization of the ATM (ataxia-telangiectasia, mutated) gene product has provided an essential tool for researchers in elucidating cellular mechanisms involved in cell cycle control, DNA repair, and chromosomal stability.
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Affiliation(s)
- Frederick A Derheimer
- Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
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21
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A kinase-independent role for the Rad3(ATR)-Rad26(ATRIP) complex in recruitment of Tel1(ATM) to telomeres in fission yeast. PLoS Genet 2010; 6:e1000839. [PMID: 20140190 PMCID: PMC2816689 DOI: 10.1371/journal.pgen.1000839] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Accepted: 01/04/2010] [Indexed: 01/13/2023] Open
Abstract
ATM and ATR are two redundant checkpoint kinases essential for the stable maintenance of telomeres in eukaryotes. Previous studies have established that MRN (Mre11-Rad50-Nbs1) and ATRIP (ATR Interacting Protein) interact with ATM and ATR, respectively, and recruit their partner kinases to sites of DNA damage. Here, we investigated how Tel1ATM and Rad3ATR recruitment to telomeres is regulated in fission yeast. Quantitative chromatin immunoprecipitation (ChIP) assays unexpectedly revealed that the MRN complex could also contribute to the recruitment of Tel1ATM to telomeres independently of the previously established Nbs1 C-terminal Tel1ATM interaction domain. Recruitment of Tel1ATM to telomeres in nbs1-c60Δ cells, which lack the C-terminal 60 amino acid Tel1ATM interaction domain of Nbs1, was dependent on Rad3ATR-Rad26ATRIP, but the kinase domain of Rad3ATR was dispensable. Thus, our results establish that the Rad3ATR-Rad26ATRIP complex contributes to the recruitment of Tel1ATM independently of Rad3ATR kinase activity, by a mechanism redundant with the Tel1ATM interaction domain of Nbs1. Furthermore, we found that the N-terminus of Nbs1 contributes to the recruitment of Rad3ATR-Rad26ATRIP to telomeres. In response to replication stress, mammalian ATR–ATRIP also contributes to ATM activation by a mechanism that is dependent on the MRN complex but independent of the C-terminal ATM interaction domain of Nbs1. Since telomere protection and DNA damage response mechanisms are very well conserved between fission yeast and mammalian cells, mammalian ATR–ATRIP may also contribute to the recruitment of ATM to telomeres and to sites of DNA damage independently of ATR kinase activity. ATM and ATR kinases are two evolutionarily conserved sensors of DNA damage, responsible for maintaining stable genomes in all eukaryotic cells. These two kinases safeguard eukaryotic genomes against undesired double-stranded DNA breaks (DSBs) and errors during duplication of genomic DNA. Furthermore, ATM and ATR are redundantly required for stable maintenance of telomeres, protective structures at ends of linear eukaryotic chromosomes. Our current study in fission yeast demonstrates that the previously defined C-terminal Tel1ATM interaction domain of the DNA repair protein Nbs1, which contributes to recruitment of Tel1ATM to DSBs, is dispensable for recruitment of Tel1ATM to telomeres, due to a previously unrecognized kinase-independent role of ATR in recruitment of Tel1ATM to telomeres. Furthermore, the N-terminus of Nbs1 was found to be critical for recruitment of both ATR and ATM to telomeres. Regulators of telomere maintenance have recently emerged as potentially important therapeutic targets against tumorigenesis and aging in mammalian cells. Since proteins responsible for proper maintenance of telomeres and cellular responses to DNA damage are highly conserved between fission yeast and mammalian cells, a newly uncovered molecular crosstalk between ATM and ATR might also play critical roles in telomere maintenance and DNA damage responses in mammalian cells.
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