1
|
Holland CL, Sanderson BA, Titus JK, Weis MF, Riojas AM, Malczewskyj E, Wasko BM, Lewis LK. Suppression of telomere capping defects of Saccharomyces cerevisiae yku70 and yku80 mutants by telomerase. G3-GENES GENOMES GENETICS 2021; 11:6395363. [PMID: 34718547 PMCID: PMC8664480 DOI: 10.1093/g3journal/jkab359] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 09/27/2021] [Indexed: 11/18/2022]
Abstract
The Ku complex performs multiple functions inside eukaryotic cells, including protection of chromosomal DNA ends from degradation and fusion events, recruitment of telomerase, and repair of double-strand breaks (DSBs). Inactivation of Ku complex genes YKU70 or YKU80 in cells of the yeast Saccharomyces cerevisiae gives rise to mutants that exhibit shortened telomeres and temperature-sensitive growth. In this study, we have investigated the mechanism by which overexpression of telomerase suppresses the temperature sensitivity of yku mutants. Viability of yku cells was restored by overexpression of the Est2 reverse transcriptase and TLC1 RNA template subunits of telomerase, but not the Est1 or Est3 proteins. Overexpression of other telomerase- and telomere-associated proteins (Cdc13, Stn1, Ten1, Rif1, Rif2, Sir3, and Sir4) did not suppress the growth defects of yku70 cells. Mechanistic features of suppression were assessed using several TLC1 RNA deletion derivatives and Est2 enzyme mutants. Supraphysiological levels of three catalytically inactive reverse transcriptase mutants (Est2-D530A, Est2-D670A, and Est2-D671A) suppressed the loss of viability as efficiently as the wild-type Est2 protein, without inducing cell senescence. Roles of proteins regulating telomere length were also determined. The results support a model in which chromosomes in yku mutants are stabilized via a replication-independent mechanism involving structural reinforcement of protective telomere cap structures.
Collapse
Affiliation(s)
- Cory L Holland
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Brian A Sanderson
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - James K Titus
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Monica F Weis
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Angelica M Riojas
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Eric Malczewskyj
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| | - Brian M Wasko
- Department of Biology and Biotechnology, University of Houston-Clear Lake, Houston, TX, 77058, USA
| | - L Kevin Lewis
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
| |
Collapse
|
2
|
Carballar R, Martínez-Láinez JM, Samper B, Bru S, Bállega E, Mirallas O, Ricco N, Clotet J, Jiménez J. CDK-mediated Yku80 Phosphorylation Regulates the Balance Between Non-homologous End Joining (NHEJ) and Homologous Directed Recombination (HDR). J Mol Biol 2020; 432:166715. [PMID: 33217428 DOI: 10.1016/j.jmb.2020.11.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 11/04/2020] [Accepted: 11/11/2020] [Indexed: 11/28/2022]
Abstract
There are two major pathways for repairing DNA double-strand breaks (DSBs): homologous directed recombination (HDR) and non-homologous end-joining (NHEJ). While NHEJ functions throughout the cell cycle, HDR is only possible during S/G2 phases, suggesting that there are cell cycle-specific mechanisms regulating the balance between the two repair systems. The regulation exerted by CDKs on HDR has been extensively demonstrated, and here we present evidence that the CDK Pho85, in association with the G1 cyclin Pcl1, phosphorylates Yku80 on Ser 623 to regulate NHEJ activity. Cells bearing a non-phosphorylatable version of Yku80 show increased NHEJ and reduced HDR activity. Accordingly, yku80S623A cells present diminished viability upon treatment with the DSB-producer bleomycin, specifically in the G2 phase of the cell cycle. Interestingly, the mutation of the equivalent residue in human Ku80 increases sensitivity to bleomycin in several cancer cell lines, suggesting that this mechanism is conserved in humans. Altogether, our results reveal a new mechanism whereby G1-CDKs mediate the choice between HDR and NHEJ repair pathways, putting the error prone NHEJ on a leash and enabling error free HDR in G2 when homologous sequences are available.
Collapse
Affiliation(s)
- Reyes Carballar
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Joan M Martínez-Láinez
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Bàrbara Samper
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Samuel Bru
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Elisabet Bállega
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Oriol Mirallas
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Natalia Ricco
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain
| | - Josep Clotet
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain.
| | - Javier Jiménez
- Basic Sciences Department, Faculty of Medicine and Health Sciences, Universitat Internacional de Catalunya, Barcelona, Spain.
| |
Collapse
|
3
|
Barbero Barcenilla B, Shippen DE. Back to the future: The intimate and evolving connection between telomere-related factors and genotoxic stress. J Biol Chem 2019; 294:14803-14813. [PMID: 31434740 DOI: 10.1074/jbc.aw119.008145] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The conversion of circular genomes to linear chromosomes during molecular evolution required the invention of telomeres. This entailed the acquisition of factors necessary to fulfill two new requirements: the need to fully replicate terminal DNA sequences and the ability to distinguish chromosome ends from damaged DNA. Here we consider the multifaceted functions of factors recruited to perpetuate and stabilize telomeres. We discuss recent theories for how telomere factors evolved from existing cellular machineries and examine their engagement in nontelomeric functions such as DNA repair, replication, and transcriptional regulation. We highlight the remarkable versatility of protection of telomeres 1 (POT1) proteins that was fueled by gene duplication and divergence events that occurred independently across several eukaryotic lineages. Finally, we consider the relationship between oxidative stress and telomeres and the enigmatic role of telomere-associated proteins in mitochondria. These findings point to an evolving and intimate connection between telomeres and cellular physiology and the strong drive to maintain chromosome integrity.
Collapse
Affiliation(s)
- Borja Barbero Barcenilla
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
| | - Dorothy E Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
| |
Collapse
|
4
|
Wang J, Zhang H, Al Shibar M, Willard B, Ray A, Runge KW. Rif1 phosphorylation site analysis in telomere length regulation and the response to damaged telomeres. DNA Repair (Amst) 2018; 65:26-33. [PMID: 29544213 PMCID: PMC5911405 DOI: 10.1016/j.dnarep.2018.03.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 03/02/2018] [Accepted: 03/05/2018] [Indexed: 12/11/2022]
Abstract
Telomeres, the ends of eukaryotic chromosomes, consist of repetitive DNA sequences and their bound proteins that protect the end from the DNA damage response. Short telomeres with fewer repeats are preferentially elongated by telomerase. Tel1, the yeast homolog of human ATM kinase, is preferentially recruited to short telomeres and Tel1 kinase activity is required for telomere elongation. Rif1, a telomere-binding protein, negatively regulates telomere length by forming a complex with two other telomere binding proteins, Rap1 and Rif2, to block telomerase recruitment. Rif1 has 14 SQ/TQ consensus phosphorylation sites for ATM kinases, including 6 in a SQ/TQ Cluster Domain (SCD) similar to other DNA damage response proteins. These 14 sites were analyzed as N-terminal, SCD and C-terminal domains. Mutating some sites to non-phosphorylatable residues increased telomere length in cells lacking Tel1 while a different set of phosphomimetic mutants increased telomere length in cells lacking Rif2, suggesting that Rif1 phosphorylation has both positive and negative effects on length regulation. While these mutations did not alter the sensitivity to DNA damaging agents, inducing telomere-specific damage by growing cells lacking YKU70 at high temperature revealed a role for the SCD. Mass spectrometry of Rif1 from wild type cells or those induced for telomere-specific DNA damage revealed increased phosphorylation in cells with telomere damage at an ATM consensus site in the SCD, S1351, and non-ATM sites S181 and S1637. A phosphomimetic rif1-S1351E mutation caused an increase in telomere length at synthetic telomeres but not natural telomeres. These results indicate that the Rif1 SCD can modulate Rif1 function. As all Rif1 orthologs have one or more SCD domains, these results for yeast Rif1 have implications for the regulation of Rif1 function in humans and other organisms.
Collapse
Affiliation(s)
- Jinyu Wang
- Department of Genetics and Genome Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, United States; Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States; Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States
| | - Haitao Zhang
- Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States
| | - Mohammed Al Shibar
- Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States
| | - Belinda Willard
- Lerner Research Institute Proteomics and Metabolomics Core, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, United States
| | - Alo Ray
- Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States
| | - Kurt W Runge
- Department of Genetics and Genome Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, United States; Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States; Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, United States.
| |
Collapse
|
5
|
Ivanova IG, Maringele L. Polymerases ε and ∂ repair dysfunctional telomeres facilitated by salt. Nucleic Acids Res 2016; 44:3728-38. [PMID: 26883631 PMCID: PMC4856982 DOI: 10.1093/nar/gkw071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 02/01/2016] [Indexed: 12/19/2022] Open
Abstract
Damaged DNA can be repaired by removal and re-synthesis of up to 30 nucleotides during base or nucleotide excision repair. An important question is what happens when many more nucleotides are removed, resulting in long single-stranded DNA (ssDNA) lesions. Such lesions appear on chromosomes during telomere damage, double strand break repair or after the UV damage of stationary phase cells. Here, we show that long single-stranded lesions, formed at dysfunctional telomeres in budding yeast, are re-synthesized when cells are removed from the telomere-damaging environment. This process requires Pol32, an accessory factor of Polymerase δ. However, re-synthesis takes place even when the telomere-damaging conditions persist, in which case the accessory factors of both polymerases δ and ε are required, and surprisingly, salt. Salt added to the medium facilitates the DNA synthesis, independently of the osmotic stress responses. These results provide unexpected insights into the DNA metabolism and challenge the current view on cellular responses to telomere dysfunction.
Collapse
Affiliation(s)
- Iglika G Ivanova
- Institute for Cell and Molecular Biosciences (ICaMB), Newcastle University, Newcastle upon Tyne, NE2 44H, UK
| | - Laura Maringele
- Institute for Cell and Molecular Biosciences (ICaMB), Newcastle University, Newcastle upon Tyne, NE2 44H, UK
| |
Collapse
|
6
|
Gandía M, Xu S, Font C, Marcos JF. Disruption of ku70 involved in non-homologous end-joining facilitates homologous recombination but increases temperature sensitivity in the phytopathogenic fungus Penicillium digitatum. Fungal Biol 2015; 120:317-23. [PMID: 26895860 DOI: 10.1016/j.funbio.2015.11.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 11/04/2015] [Accepted: 11/05/2015] [Indexed: 12/22/2022]
Abstract
The dominant mechanism to repair double-stranded DNA breaks in filamentous fungi is the non-homologous end joining (NHEJ) pathway, and not the homologous recombination (HR) pathway that operates in the mutation of genes by replacement of target DNA for selection cassettes. The key to improve HR frequency is the inactivation of the NHEJ pathway by eliminating components of its Ku70/80 heterodimeric complex. We have obtained ku70 mutants of Penicillium digitatum, the main citrus postharvest pathogen. The increased efficiency of HR in Δku70 strains was demonstrated by the generation of mutants in two different chitin synthase genes (PdchsII and PdchsV). P. digitatum Δku70 strains showed no differences from the parental strain in vegetative growth, asexual development or virulence to citrus fruit, when experiments were conducted at the optimal temperature of 24°C. However, growth of Δku70 strains at temperatures higher than 24°C demonstrated a detrimental effect in axenic growth and conidia production. These observations are in agreement with previous studies describing differences between ku70 mutants and their parental strains in some fungal species, and must be taken into account for future applications of the Δku approach to increase HR efficiency in fungi.
Collapse
Affiliation(s)
- Mónica Gandía
- Food Science Department, Instituto de Agroquímica y Tecnología de Alimentos (IATA), Consejo Superior de Investigaciones Científicas (CSIC), Avda Agustín Escardino 7, 46980 Paterna, Valencia, Spain.
| | - Shaomei Xu
- Food Science Department, Instituto de Agroquímica y Tecnología de Alimentos (IATA), Consejo Superior de Investigaciones Científicas (CSIC), Avda Agustín Escardino 7, 46980 Paterna, Valencia, Spain.
| | - Cristina Font
- Food Science Department, Instituto de Agroquímica y Tecnología de Alimentos (IATA), Consejo Superior de Investigaciones Científicas (CSIC), Avda Agustín Escardino 7, 46980 Paterna, Valencia, Spain.
| | - Jose F Marcos
- Food Science Department, Instituto de Agroquímica y Tecnología de Alimentos (IATA), Consejo Superior de Investigaciones Científicas (CSIC), Avda Agustín Escardino 7, 46980 Paterna, Valencia, Spain.
| |
Collapse
|
7
|
de Sena-Tomás C, Yu EY, Calzada A, Holloman WK, Lue NF, Pérez-Martín J. Fungal Ku prevents permanent cell cycle arrest by suppressing DNA damage signaling at telomeres. Nucleic Acids Res 2015; 43:2138-51. [PMID: 25653166 PMCID: PMC4344518 DOI: 10.1093/nar/gkv082] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The Ku heterodimer serves in the initial step in repairing DNA double-strand breaks by the non-homologous end-joining pathway. Besides this key function, Ku also plays a role in other cellular processes including telomere maintenance. Inactivation of Ku can lead to DNA repair defects and telomere aberrations. In model organisms where Ku has been studied, inactivation can lead to DNA repair defects and telomere aberrations. In general Ku deficient mutants are viable, but a notable exception to this is human where Ku has been found to be essential. Here we report that similar to the situation in human Ku is required for cell proliferation in the fungus Ustilago maydis. Using conditional strains for Ku expression, we found that cells arrest permanently in G2 phase when Ku expression is turned off. Arrest results from cell cycle checkpoint activation due to persistent signaling via the DNA damage response (DDR). Our results point to the telomeres as the most likely source of the DNA damage signal. Inactivation of the DDR makes the Ku complex dispensable for proliferation in this organism. Our findings suggest that in U. maydis, unprotected telomeres arising from Ku depletion are the source of the signal that activates the DDR leading to cell cycle arrest.
Collapse
Affiliation(s)
- Carmen de Sena-Tomás
- Instituto de Biología Funcional y Genómica (CSIC), Zacarías González 2, 37007 Salamanca, Spain
| | - Eun Young Yu
- Department of Microbiology and Immunology, Weill Cornell Cancer Center, Weill Medical College of Cornell University, New York, 10021 NY, USA
| | - Arturo Calzada
- Centro Nacional de Biotecnología (CSIC), 28049 Madrid, Spain
| | - William K Holloman
- Department of Microbiology and Immunology, Weill Cornell Cancer Center, Weill Medical College of Cornell University, New York, 10021 NY, USA
| | - Neal F Lue
- Department of Microbiology and Immunology, Weill Cornell Cancer Center, Weill Medical College of Cornell University, New York, 10021 NY, USA
| | - José Pérez-Martín
- Instituto de Biología Funcional y Genómica (CSIC), Zacarías González 2, 37007 Salamanca, Spain
| |
Collapse
|
8
|
Laterreur N, Eschbach SH, Lafontaine DA, Wellinger RJ. A new telomerase RNA element that is critical for telomere elongation. Nucleic Acids Res 2013; 41:7713-24. [PMID: 23783570 PMCID: PMC3763530 DOI: 10.1093/nar/gkt514] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The stability of chromosome ends, the telomeres, is dependent on the ribonucleoprotein telomerase. In vitro, telomerase requires at least one RNA molecule and a reverse transcriptase-like protein. However, for telomere homeostasis in vivo, additional proteins are required. Telomerase RNAs of different species vary in size and sequence and only few features common to all telomerases are known. Here we show that stem-loop IVc of the Saccharomyces cerevisiae telomerase RNA contains a structural element that is required for telomerase function in vivo. Indeed, the distal portion of stem-loop IVc stimulates telomerase activity in vitro in a way that is independent of Est1 binding on more proximal portions of this stem-loop. Functional analyses of the RNA in vivo reveal that this distal element we call telomerase-stimulating structure (TeSS) must contain a bulged area in single stranded form and also show that Est1-dependent functions such as telomerase import or recruitment are not affected by TeSS. This study thus uncovers a new structural telomerase RNA element implicated in catalytic activity. Given previous evidence for TeSS elements in ciliate and mammalian RNAs, we speculate that this substructure is a conserved feature that is required for optimal telomerase holoenzyme function.
Collapse
Affiliation(s)
- Nancy Laterreur
- Department of Microbiology and Infectious Diseases and Department of Biology, RNA Group, Université de Sherbrooke, 3201, rue Jean-Mignault, Sherbrooke J1E 4K8, Canada
| | | | | | | |
Collapse
|
9
|
Abstract
The mechanisms that maintain the stability of chromosome ends have broad impact on genome integrity in all eukaryotes. Budding yeast is a premier organism for telomere studies. Many fundamental concepts of telomere and telomerase function were first established in yeast and then extended to other organisms. We present a comprehensive review of yeast telomere biology that covers capping, replication, recombination, and transcription. We think of it as yeast telomeres—soup to nuts.
Collapse
|
10
|
Gallardo F, Laterreur N, Wellinger RJ, Chartrand P. Telomerase caught in the act: united we stand, divided we fall. RNA Biol 2012; 9:1139-43. [PMID: 22951592 DOI: 10.4161/rna.21498] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The stable linearity of eukaryotic chromosomes depends on special characteristics of their ends, the telomeres. Accurate telomere function in turn requires a sustained presence of repeated DNA elements, which are maintained by the enzyme telomerase. The telomerase holoenzyme is composed of both protein and RNA, and its functions rely on proper expression, maturation, trafficking and assembly of these components. Conflicting models for the recruitment of telomerase at telomeres have been proposed; one suggests a local activation of telomerase at short telomeres, while the other proposes that telomerase is recruited only at short telomeres. To discriminate between these models and investigate the cell cycle-dependent regulation of telomerase in living cells, a GFP reporter system to visualize the yeast telomerase RNA has been recently developed. This assay shed new light on the mechanism of recruitment of telomerase to telomeres, and it uncovered a hitherto unrecognized mechanism for restricting telomerase access to telomeres.
Collapse
Affiliation(s)
- Franck Gallardo
- Université Paul Sabatier, Laboratoire de Biologie Moléculaire Eucaryote, Toulouse, France.
| | | | | | | |
Collapse
|
11
|
Deletion of the Pichia pastoris KU70 homologue facilitates platform strain generation for gene expression and synthetic biology. PLoS One 2012; 7:e39720. [PMID: 22768112 PMCID: PMC3387205 DOI: 10.1371/journal.pone.0039720] [Citation(s) in RCA: 178] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Accepted: 05/25/2012] [Indexed: 12/16/2022] Open
Abstract
Targeted gene replacement to generate knock-outs and knock-ins is a commonly used method to study the function of unknown genes. In the methylotrophic yeast Pichia pastoris, the importance of specific gene targeting has increased since the genome sequencing projects of the most commonly used strains have been accomplished, but rapid progress in the field has been impeded by inefficient mechanisms for accurate integration. To improve gene targeting efficiency in P. pastoris, we identified and deleted the P. pastoris KU70 homologue. We observed a substantial increase in the targeting efficiency using the two commonly known and used integration loci HIS4 and ADE1, reaching over 90% targeting efficiencies with only 250-bp flanking homologous DNA. Although the ku70 deletion strain was noted to be more sensitive to UV rays than the corresponding wild-type strain, no lethality, severe growth retardation or loss of gene copy numbers could be detected during repetitive rounds of cultivation and induction of heterologous protein production. Furthermore, we demonstrated the use of the ku70 deletion strain for fast and simple screening of genes in the search of new auxotrophic markers by targeting dihydroxyacetone synthase and glycerol kinase genes. Precise knock-out strains for the well-known P. pastoris AOX1, ARG4 and HIS4 genes and a whole series of expression vectors were generated based on the wild-type platform strain, providing a broad spectrum of precise tools for both intracellular and secreted production of heterologous proteins utilizing various selection markers and integration strategies for targeted or random integration of single and multiple genes. The simplicity of targeted integration in the ku70 deletion strain will further support protein production strain generation and synthetic biology using P. pastoris strains as platform hosts.
Collapse
|
12
|
A naturally thermolabile activity compromises genetic analysis of telomere function in Saccharomyces cerevisiae. Genetics 2012; 191:79-93. [PMID: 22377634 DOI: 10.1534/genetics.111.137869] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The core assumption driving the use of conditional loss-of-function reagents such as temperature-sensitive mutations is that the resulting phenotype(s) are solely due to depletion of the mutant protein under nonpermissive conditions. However, prior published data, combined with observations presented here, challenge the generality of this assumption at least for telomere biology: for both wild-type yeast and strains bearing null mutations in telomere protein complexes, there is an additional phenotypic consequence when cells are grown above 34°. We propose that this synthetic phenotype is due to a naturally thermolabile activity that confers a telomere-specific defect, which we call the Tmp(-) phenotype. This prompted a re-examination of commonly used cdc13-ts and stn1-ts mutations, which indicates that these alleles are instead hypomorphic mutations that behave as apparent temperature-sensitive mutations due to the additive effects of the Tmp(-) phenotype. We therefore generated new cdc13-ts reagents, which are nonpermissive below 34°, to allow examination of cdc13-depleted phenotypes in the absence of this temperature-dependent defect. A return-to-viability experiment following prolonged incubation at 32°, 34°, and 36° with one of these new cdc13-ts alleles argues that the accelerated inviability previously observed at 36° in cdc13-1 rad9-Δ mutant strains is a consequence of the Tmp(-) phenotype. Although this study focused on telomere biology, viable null mutations that confer inviability at 36° have been identified for multiple cellular pathways. Thus, phenotypic analysis of other aspects of yeast biology may similarly be compromised at high temperatures by pathway-specific versions of the Tmp(-) phenotype.
Collapse
|
13
|
Live cell imaging of telomerase RNA dynamics reveals cell cycle-dependent clustering of telomerase at elongating telomeres. Mol Cell 2012; 44:819-27. [PMID: 22152484 DOI: 10.1016/j.molcel.2011.09.020] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/21/2011] [Accepted: 09/12/2011] [Indexed: 11/22/2022]
Abstract
The telomerase, which is composed of both protein and RNA, maintains genome stability by replenishing telomeric repeats at the ends of chromosomes. Here, we use live-cell imaging to follow yeast telomerase RNA dynamics and recruitment to telomeres in single cells. Tracking of single telomerase particles revealed a diffusive behavior and transient association with telomeres in G1 and G2 phases of the cell cycle. Interestingly, concurrent with telomere elongation in late S phase, a subset of telomerase enzyme clusters and stably associates with few telomeres. Our data show that this clustering represents elongating telomerase and it depends on regulators of telomerase at telomeres (MRX, Tel1, Rif1/2, and Cdc13). Furthermore, the assay revealed premature telomere elongation in G1 in a rif1/2 strains, suggesting that Rif1/2 act as cell-cycle dependent negative regulators of telomerase. We propose that telomere elongation is organized around a local and transient accumulation of several telomerases on a few telomeres.
Collapse
|
14
|
Harrington L. Haploinsufficiency and telomere length homeostasis. Mutat Res 2012; 730:37-42. [PMID: 22100521 DOI: 10.1016/j.mrfmmm.2011.11.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 11/01/2011] [Indexed: 05/22/2023]
Abstract
In humans, autosomal dominant or X-linked disease can arise through a phenomenon termed haploinsufficiency, where one remaining wild-type allele is insufficient for function. In model organisms, the impact of heterozygosity can be tested directly with engineered mutant alleles or in a hemizygous state where the expression of one allele is abrogated completely. This review will focus on haploinsufficiency as it relates to telomerase and telomere length maintenance and, citing selected examples in various model organisms, it will discuss how the problem of gene dosage relates to telomere function in normal and diseased states.
Collapse
|
15
|
The Candida albicans Ku70 modulates telomere length and structure by regulating both telomerase and recombination. PLoS One 2011; 6:e23732. [PMID: 21886818 PMCID: PMC3160324 DOI: 10.1371/journal.pone.0023732] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 07/25/2011] [Indexed: 12/18/2022] Open
Abstract
The heterodimeric Ku complex has been shown to participate in DNA repair and telomere regulation in a variety of organisms. Here we report a detailed characterization of the function of Ku70 in the diploid fungal pathogen Candida albicans. Both ku70 heterozygous and homozygous deletion mutants have a wild-type colony and cellular morphology, and are not sensitive to MMS or UV light. Interestingly, we observed complex effects of KU70 gene dosage on telomere lengths, with the KU70/ku70 heterozygotes exhibiting slightly shorter telomeres, and the ku70 null strain exhibiting long and heterogeneous telomeres. Analysis of combination mutants suggests that the telomere elongation in the ku70 null mutant is due mostly to unregulated telomerase action. In addition, elevated levels of extrachromosomal telomeric circles were detected in the null mutant, consistent with activation of aberrant telomeric recombination. Altogether, our observations point to multiple mechanisms of the Ku complex in telomerase regulation and telomere protection in C. albicans, and reveal interesting similarities and differences in the mechanisms of the Ku complex in disparate systems.
Collapse
|
16
|
Anbalagan S, Bonetti D, Lucchini G, Longhese MP. Rif1 supports the function of the CST complex in yeast telomere capping. PLoS Genet 2011; 7:e1002024. [PMID: 21437267 PMCID: PMC3060071 DOI: 10.1371/journal.pgen.1002024] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2010] [Accepted: 01/26/2011] [Indexed: 12/28/2022] Open
Abstract
Telomere integrity in budding yeast depends on the CST (Cdc13-Stn1-Ten1) and shelterin-like (Rap1-Rif1-Rif2) complexes, which are thought to act independently from each other. Here we show that a specific functional interaction indeed exists among components of the two complexes. In particular, unlike RIF2 deletion, the lack of Rif1 is lethal for stn1ΔC cells and causes a dramatic reduction in viability of cdc13-1 and cdc13-5 mutants. This synthetic interaction between Rif1 and the CST complex occurs independently of rif1Δ-induced alterations in telomere length. Both cdc13-1 rif1Δ and cdc13-5 rif1Δ cells display very high amounts of telomeric single-stranded DNA and DNA damage checkpoint activation, indicating that severe defects in telomere integrity cause their loss of viability. In agreement with this hypothesis, both DNA damage checkpoint activation and lethality in cdc13 rif1Δ cells are partially counteracted by the lack of the Exo1 nuclease, which is involved in telomeric single-stranded DNA generation. The functional interaction between Rif1 and the CST complex is specific, because RIF1 deletion does not enhance checkpoint activation in case of CST-independent telomere capping deficiencies, such as those caused by the absence of Yku or telomerase. Thus, these data highlight a novel role for Rif1 in assisting the essential telomere protection function of the CST complex. Protection of chromosome ends is crucial for maintaining chromosome stability and genome integrity, and its failure leads to genome rearrangements that may facilitate carcinogenesis. This protection is achieved by the packaging of chromosome ends into protective structures called telomeres that prevent DNA repair/recombination activities. Telomeric DNA is bound and stabilized by two protein complexes named CST and shelterin, which are present in a wide range of multicellular organisms. Whether structural and functional connections exist between these two capping complexes is an important issue in telomere biology. Here, we investigate this topic by analyzing the consequences of disabling the two Saccharomyces cerevisiae shelterin-like components, Rif1 and Rif2, in different hypomorphic mutants defective in CST components. We demonstrate that Rif1 plays a previously unanticipated role in assisting the essential telomere protection function of the CST complex, indicating a tight coupling between CST and Rif1. As CST complexes have been recently identified also in other organisms, including humans, which all rely on shelterin for telomere protection, this functional link between CST and shelterin might be an evolutionarily conserved common feature to ensure telomere integrity.
Collapse
Affiliation(s)
- Savani Anbalagan
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy
| | - Diego Bonetti
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy
| | - Giovanna Lucchini
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy
| | - Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy
- * E-mail:
| |
Collapse
|
17
|
Telomere capping in non-dividing yeast cells requires Yku and Rap1. EMBO J 2010; 29:3007-19. [PMID: 20628356 DOI: 10.1038/emboj.2010.155] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 06/18/2010] [Indexed: 01/13/2023] Open
Abstract
The assembly of a protective cap onto the telomeres of eukaryotic chromosomes suppresses genomic instability through inhibition of DNA repair activities that normally process accidental DNA breaks. We show here that the essential Cdc13-Stn1-Ten1 complex is entirely dispensable for telomere protection in non-dividing cells. However, Yku and Rap1 become crucially important for this function in these cells. After inactivation of Yku70 in G1-arrested cells, moderate but significant telomere degradation occurs. As the activity of cyclin-dependent kinases (CDK) promotes degradation, these results suggest that Yku stabilizes G1 telomeres by blocking the access of CDK1-independent nucleases to telomeres. The results indeed show that both Exo1 and the Mre11/Rad50/Xrs2 complex are required for telomeric resection after Yku loss in non-dividing cells. Unexpectedly, both asynchronously growing and quiescent G0 cells lacking Rap1 display readily detectable telomere degradation, suggesting an earlier unanticipated function for this protein in suppression of nuclease activities at telomeres. Together, our results show a high flexibility of the telomeric cap and suggest that distinct configurations may provide for efficient capping in dividing versus non-dividing cells.
Collapse
|
18
|
Abstract
Telomere binding proteins protect chromosome ends from degradation and mask chromosome termini from checkpoint surveillance. In Saccharomyces cerevisiae, Cdc13 binds single-stranded G-rich telomere repeats, maintaining telomere integrity and length. Two additional proteins, Ten1 and Stn1, interact with Cdc13 but their contributions to telomere integrity are not well defined. Ten1 is known to prevent accumulation of aberrant single-stranded telomere DNA; whether this results from defective end protection or defective telomere replication is unclear. Here we report our analysis of a new group of ten1 temperature-sensitive (ts) mutants. At permissive temperatures, ten1-ts strains display greatly elongated telomeres. After shift to nonpermissive conditions, however, ten1-ts mutants accumulate extensive telomeric single-stranded DNA. Cdk1 activity is required to generate these single-stranded regions, and deleting the EXO1 nuclease partially suppresses ten1-ts growth defects. This is similar to cdc13-1 mutants, suggesting ten1-ts strains are defective for end protection. Moreover, like Cdc13, our analysis reveals Ten1 promotes de novo telomere addition. Interestingly, in ten1-ts strains at high temperatures, telomeric single-stranded DNA and Rad52-YFP repair foci are strongly induced despite Cdc13 remaining associated with telomeres, revealing Cdc13 telomere binding is not sufficient for end protection. Finally, unlike cdc13-1 mutants, ten1-ts strains display strong synthetic interactions with mutations in the POLalpha complex. These results emphasize that Cdc13 relies on Ten1 to execute its essential function, but leave open the possibility that Ten1 has a Cdc13-independent role in DNA replication.
Collapse
|
19
|
Ku86 represses lethal telomere deletion events in human somatic cells. Proc Natl Acad Sci U S A 2009; 106:12430-5. [PMID: 19581589 DOI: 10.1073/pnas.0903362106] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Nonhomologous end joining (NHEJ), a form of DNA double-strand break (DSB) repair, is conserved from bacteria to humans. One essential NHEJ factor is Ku, which consists of a heterodimer of Ku70 and Ku86. In a plethora of model systems, null mutations for Ku70 or Ku86 present with defects in DNA DSB repair, variable(diversity)joining [V(D)J] recombination, and/or telomere maintenance. The complete loss of Ku from bacteria to mice is, however, compatible with viability. In striking contrast, human patients with mutations of either Ku subunit have never been described. Here, we have used recombinant adeno-associated virus-mediated gene targeting to produce a human somatic cell line that expresses a conditionally null allele of Ku86. The induced loss of Ku86 results in cell death accompanied by massive telomere loss in the form of t-circles. Thus, Ku86 is an essential gene in human somatic cells because of its requirement, not in NHEJ or V(D)J recombination, but in telomere maintenance.
Collapse
|
20
|
Gunisova S, Elboher E, Nosek J, Gorkovoy V, Brown Y, Lucier JF, Laterreur N, Wellinger RJ, Tzfati Y, Tomaska L. Identification and comparative analysis of telomerase RNAs from Candida species reveal conservation of functional elements. RNA (NEW YORK, N.Y.) 2009; 15:546-559. [PMID: 19223441 PMCID: PMC2661832 DOI: 10.1261/rna.1194009] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 12/16/2008] [Indexed: 05/27/2023]
Abstract
The RNA component of telomerase (telomerase RNA; TER) varies substantially both in sequence composition and size (from approximately 150 nucleotides [nt] to >1500 nt) across species. This dramatic divergence has hampered the identification of TER genes and a large-scale comparative analysis of TER sequences and structures among distantly related species. To identify by phylogenetic analysis conserved sequences and structural features of TER that are of general importance, it is essential to obtain TER sequences from evolutionarily distant groups of species, providing enough conservation within each group and enough variation among the groups. To this end, we identified TER genes in several yeast species with relatively large (>20 base pairs) and nonvariant telomeric repeats, mostly from the genus Candida. Interestingly, several of the TERs reported here are longer than all other yeast TERs known to date. Within these TERs, we predicted a pseudoknot containing U-A.U base triples (conserved in vertebrates, budding yeasts, and ciliates) and a three-way junction element (conserved in vertebrates and budding yeasts). In addition, we identified a novel conserved sequence (CS2a) predicted to reside within an internal-loop structure, in all the budding yeast TERs examined. CS2a is located near the Est1p-binding bulge-stem previously identified in Saccharomyces cerevisiae. Mutational analyses in both budding yeasts S. cerevisiae and Kluyveromyces lactis demonstrate that CS2a is essential for in vivo telomerase function. The comparative and mutational analyses of conserved TER elements reported here provide novel insights into the structure and function of the telomerase ribonucleoprotein complex.
Collapse
|
21
|
Jeggo PA. Genomic instability in cancer development. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 570:175-97. [PMID: 18727501 DOI: 10.1007/1-4020-3764-3_6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Penny A Jeggo
- Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, UK
| |
Collapse
|
22
|
The role of Stn1p in Saccharomyces cerevisiae telomere capping can be separated from its interaction with Cdc13p. Genetics 2007; 177:1459-74. [PMID: 17947422 DOI: 10.1534/genetics.107.078840] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The function of telomeres is twofold: to facilitate complete chromosome replication and to protect chromosome ends against fusions and illegitimate recombination. In the budding yeast Saccharomyces cerevisiae, interactions among Cdc13p, Stn1p, and Ten1p are thought to be critical for promoting these processes. We have identified distinct Stn1p domains that mediate interaction with either Ten1p or Cdc13p, allowing analysis of whether the interaction between Cdc13p and Stn1p is indeed essential for telomere capping or length regulation. Consistent with the model that the Stn1p essential function is to promote telomere end protection through Cdc13p, stn1 alleles that truncate the C-terminal 123 residues fail to interact with Cdc13p and do not support viability when expressed at endogenous levels. Remarkably, more extensive deletions that remove an additional 185 C-terminal residues from Stn1p now allow cell growth at endogenous expression levels. The viability of these stn1-t alleles improves with increasing expression level, indicating that increased stn1-t dosage can compensate for the loss of Cdc13p-Stn1p interaction. However, telomere length is misregulated at all expression levels. Thus, an amino-terminal region of Stn1p is sufficient for its essential function, while a central region of Stn1p either negatively regulates the STN1 essential function or destabilizes the mutant Stn1 protein.
Collapse
|
23
|
Riha K, Heacock ML, Shippen DE. The role of the nonhomologous end-joining DNA double-strand break repair pathway in telomere biology. Annu Rev Genet 2007; 40:237-77. [PMID: 16822175 DOI: 10.1146/annurev.genet.39.110304.095755] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Double-strand breaks are a cataclysmic threat to genome integrity. In higher eukaryotes the predominant recourse is the nonhomologous end-joining (NHEJ) double-strand break repair pathway. NHEJ is a versatile mechanism employing the Ku heterodimer, ligase IV/XRCC4 and a host of other proteins that juxtapose two free DNA ends for ligation. A critical function of telomeres is their ability to distinguish the ends of linear chromosomes from double-strand breaks, and avoid NHEJ. Telomeres accomplish this feat by forming a unique higher order nucleoprotein structure. Paradoxically, key components of NHEJ associate with normal telomeres and are required for proper length regulation and end protection. Here we review the biochemical mechanism of NHEJ in double-strand break repair, and in the response to dysfunctional telomeres. We discuss the ways in which NHEJ proteins contribute to telomere biology, and highlight how the NHEJ machinery and the telomere complex are evolving to maintain genome stability.
Collapse
Affiliation(s)
- Karel Riha
- Gregor Mendel Institute of Plant Molecular Biology, Austrian Academy of Sciences, A-1030 Vienna, Austria.
| | | | | |
Collapse
|
24
|
Pöggeler S, Kück U. Highly efficient generation of signal transduction knockout mutants using a fungal strain deficient in the mammalian ku70 ortholog. Gene 2006; 378:1-10. [PMID: 16814491 DOI: 10.1016/j.gene.2006.03.020] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Revised: 03/17/2006] [Accepted: 03/17/2006] [Indexed: 10/24/2022]
Abstract
Targeted gene replacement via homologous recombination is a routinely used approach to elucidate the function of unknown genes. Integration of exogenous DNA in the genomic DNA requires the action of double-strand repair mechanisms. The filamentous ascomycete Sordaria macrospora is a model system for studying fruiting body development in fungi. In contrast to the budding yeast Saccharomyces cerevisiae, but similar to many filamentous fungi, plants and animals, transformed DNA is ectopically integrated into the genome of S. macrospora. Most probably this occurs by non-homologous end joining (NHEJ), a mechanism that involves the binding of the Ku heterodimer (Ku70/Ku80) at the ends of a DNA double-strand break (DSB). Phylogenetic analysis of Ku70 orthologs of fungal, plant, and animal origin reveals that the Ku70 protein is well conserved among eukaryotes. To improve gene targeting efficiency in S. macrospora, we identified and deleted the S. macrospora ku70 gene. No impairment of the Deltaku70 mutant in vegetative or fruiting body nor ascospore development was observed making this strain an ideal recipient for gene targeting of developmental genes. As a case study, the S. macrospora Deltaku70 strain was used for targeted deletion of the pheromone gene ppg2 and the pheromone receptor gene pre2. PCR generated deletion constructs containing 1000 bp of homologous flanking sequence resulted in a drastically increased gene targeting efficiency. As a consequence, almost all transformants generated carried a disrupted target gene.
Collapse
Affiliation(s)
- Stefanie Pöggeler
- Ruhr-Universität Bochum, Lehrstuhl für Allgemeine und Molekulare Botanik, 44780 Bochum, Germany
| | | |
Collapse
|
25
|
Corda Y, Lee SE, Guillot S, Walther A, Sollier J, Arbel-Eden A, Haber JE, Géli V. Inactivation of Ku-mediated end joining suppresses mec1Delta lethality by depleting the ribonucleotide reductase inhibitor Sml1 through a pathway controlled by Tel1 kinase and the Mre11 complex. Mol Cell Biol 2005; 25:10652-64. [PMID: 16287875 PMCID: PMC1291227 DOI: 10.1128/mcb.25.23.10652-10664.2005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
RAD53 and MEC1 are essential Saccharomyces cerevisiae genes required for the DNA replication and DNA damage checkpoint responses. Their lethality can be suppressed by increasing the intracellular pool of deoxynucleotide triphosphates. We report that deletion of YKU70 or YKU80 suppresses mec1Delta, but not rad53Delta, lethality. We show that suppression of mec1Delta lethality is not due to Ku--associated telomeric defects but rather results from the inability of Ku- cells to efficiently repair DNA double strand breaks by nonhomologous end joining. Consistent with these results, mec1Delta lethality is also suppressed by lif1Delta, which like yku70Delta and yku80Delta, prevents nonhomologous end joining. The viability of yku70Delta mec1Delta and yku80Delta mec1Delta cells depends on the ATM-related Tel1 kinase, the Mre11-Rad50-Xrs2 complex, and the DNA damage checkpoint protein Rad9. We further report that this Mec1-independent pathway converges with the Rad53/Dun1-regulated checkpoint kinase cascade and leads to the degradation of the ribonucleotide reductase inhibitor Sml1.
Collapse
Affiliation(s)
- Yves Corda
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, IBSM, CNRS, 31 chemin Joseph Aiguier, 13402 Marseille, Cedex 20, France
| | | | | | | | | | | | | | | |
Collapse
|
26
|
Fisher TS, Zakian VA. Ku: A multifunctional protein involved in telomere maintenance. DNA Repair (Amst) 2005; 4:1215-26. [PMID: 15979949 DOI: 10.1016/j.dnarep.2005.04.021] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2004] [Accepted: 04/08/2005] [Indexed: 10/25/2022]
Abstract
The DNA-binding protein Ku plays a critical role in a variety of cellular processes, including the repair of double-stranded DNA breaks and V(D)J recombination. Paradoxically, while Ku is required for double-stranded break repair by non-homologous end-joining, in many organisms, Ku is also associated with telomeres. Although telomeres are naturally occurring double-stranded DNA breaks, one of their first identified functions is to protect chromosomes from end-to-end fusions, a process that is promoted by non-homologous end-joining. While located at telomeres, Ku appears to play several important roles, including: (1) regulating telomere addition, (2) protecting telomeres from recombination and nucleolytic degradation, (3) promoting transcriptional silencing of telomere-proximal genes and (4) nuclear positioning of telomeres. Here, we review the role of Ku at telomeres in the model organism, Saccharomyces cerevisiae and compare and contrast it to the roles of Ku at telomeres in other organisms.
Collapse
Affiliation(s)
- Timothy S Fisher
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | | |
Collapse
|
27
|
Bates SE, Zhou NY, Federico LE, Xia L, O'Connor TR. Repair of cyclobutane pyrimidine dimers or dimethylsulfate damage in DNA is identical in normal or telomerase-immortalized human skin fibroblasts. Nucleic Acids Res 2005; 33:2475-85. [PMID: 15863724 PMCID: PMC1087900 DOI: 10.1093/nar/gki542] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The progression of a normal cell to senescence in vivo and in vitro is accompanied by a reduction in the length of the telomeres, the chromosome capping segments at the end of each linkage group. However, overexpression of the reverse transcriptase subunit (HTERT) of the ribonucleoprotein telomerase restores telomere length and delays cellular senescence. Although some data exist in the literature with respect to survival, no molecular data have shown that DNA repair in telomerase-immortalized cells is normal. Several telomerase-immortalized human skin fibroblast cell lines were constructed from a primary human fibroblast cell line. The primary line and the telomerase-immortalized cell lines were treated with either ultraviolet (UV) radiation or dimethylsulfate (DMS). UV radiation principally produces cyclobutane pyrimidine dimers that are repaired by nucleotide excision repair, whereas DMS introduces mainly N-methylpurines repaired by base excision repair. Here, we show that repair of both types of damage in the telomerase-immortalized human skin fibroblast cell lines is identical to repair observed in normal skin fibroblasts. Thus, telomerase expression and consequent immortalization of skin fibroblasts do not alter nucleotide or base excision repair in human cells.
Collapse
Affiliation(s)
| | | | | | | | - Timothy R. O'Connor
- To whom correspondence should be addressed. Tel: +1 626 301 8220; Fax: +1 626 930 5366;
| |
Collapse
|
28
|
Rog O, Smolikov S, Krauskopf A, Kupiec M. The yeast VPS genes affect telomere length regulation. Curr Genet 2004; 47:18-28. [PMID: 15551135 DOI: 10.1007/s00294-004-0548-y] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2004] [Revised: 10/14/2004] [Accepted: 10/14/2004] [Indexed: 10/26/2022]
Abstract
Eukaryotic cells invest a large proportion of their genome in maintaining telomere length homeostasis. Among the 173 non-essential yeast genes found to affect telomere length, a large proportion is involved in vacuolar traffic. When mutated, these vacuolar protein-sorting (VPS) genes lead to telomeres shorter than those observed in the wild type. Using genetic analysis, we characterized the pathway by which VPS15, VPS34, VPS22, VPS23 and VPS28 affect the telomeres. Our results indicate that these VPS genes affect telomere length through a single pathway and that this effect requires the activity of telomerase and the Ku heterodimer, but not the activity of Tel1p or Rif2p. We present models to explain the link between vacuolar traffic and telomere length homeostasis.
Collapse
Affiliation(s)
- Ofer Rog
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, 69978, Israel
| | | | | | | |
Collapse
|
29
|
d'Adda di Fagagna F, Teo SH, Jackson SP. Functional links between telomeres and proteins of the DNA-damage response. Genes Dev 2004; 18:1781-99. [PMID: 15289453 DOI: 10.1101/gad.1214504] [Citation(s) in RCA: 210] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In response to DNA damage, cells engage a complex set of events that together comprise the DNA-damage response (DDR). These events bring about the repair of the damage and also slow down or halt cell cycle progression until the damage has been removed. In stark contrast, the ends of linear chromosomes, telomeres, are generally not perceived as DNA damage by the cell even though they terminate the DNA double-helix. Nevertheless, it has become clear over the past few years that many proteins involved in the DDR, particularly those involved in responding to DNA double-strand breaks, also play key roles in telomere maintenance. In this review, we discuss the current knowledge of both the telomere and the DDR, and then propose an integrated model for the events associated with the metabolism of DNA ends in these two distinct physiological contexts.
Collapse
|
30
|
Myung K, Ghosh G, Fattah FJ, Li G, Kim H, Dutia A, Pak E, Smith S, Hendrickson EA. Regulation of telomere length and suppression of genomic instability in human somatic cells by Ku86. Mol Cell Biol 2004; 24:5050-9. [PMID: 15143195 PMCID: PMC416406 DOI: 10.1128/mcb.24.11.5050-5059.2004] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ku86 plays a key role in nonhomologous end joining in organisms as evolutionarily disparate as bacteria and humans. In eukaryotic cells, Ku86 has also been implicated in the regulation of telomere length although the effect of Ku86 mutations varies considerably between species. Indeed, telomeres either shorten significantly, shorten slightly, remain unchanged, or lengthen significantly in budding yeast, fission yeast, chicken cells, or plants, respectively, that are null for Ku86 expression. Thus, it has been unclear which model system is most relevant for humans. We demonstrate here that the functional inactivation of even a single allele of Ku86 in human somatic cells results in profound telomere loss, which is accompanied by an increase in chromosomal fusions, translocations, and genomic instability. Together, these experiments demonstrate that Ku86, separate from its role in nonhomologous end joining, performs the additional function in human somatic cells of suppressing genomic instability through the regulation of telomere length.
Collapse
Affiliation(s)
- Kyungjae Myung
- 6-155 Jackson Hall, Department of Biochemistry, Molecular Biology, and Biophysics, 321 Church St. SE, University of Minnesota Medical School, Minneapolis, MN 55355, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Affiliation(s)
- Jessica A Downs
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK.
| | | |
Collapse
|
32
|
Abstract
Telomere integrity plays a crucial role in the capacity for continuous cell proliferation. In some circumstances, shortened telomeres contribute to cell arrest or death, but in others, shortened telomeres may actually enhance the incidence and spectrum of tumors. Resolution of this apparent paradox requires a more detailed understanding of a non-functional telomere. Recent evidence reveals that critically shortened or uncapped telomeres share molecular hallmarks of damaged DNA. It is likely that the cellular response to this DNA damage, influenced by the nature of the damage itself, affects the outcome of loss of telomere function.
Collapse
Affiliation(s)
- Lea Harrington
- Department of Medical Biophysics, University of Toronto, Ontario Cancer Institute, 620 University Avenue, Toronto, Ontario M5G 2C1, Canada.
| |
Collapse
|
33
|
Bertuch AA, Lundblad V. The Ku heterodimer performs separable activities at double-strand breaks and chromosome termini. Mol Cell Biol 2003; 23:8202-15. [PMID: 14585978 PMCID: PMC262345 DOI: 10.1128/mcb.23.22.8202-8215.2003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Ku heterodimer functions at two kinds of DNA ends: telomeres and double-strand breaks. The role that Ku plays at these two classes of termini must be distinct, because Ku is required for accurate and efficient joining of double-strand breaks while similar DNA repair events are normally prohibited at chromosome ends. Toward defining these functional differences, we have identified eight mutations in the large subunit of the Saccharomyces cerevisiae Ku heterodimer (YKU80) which retain the ability to repair double-strand breaks but are severely impaired for chromosome end protection. Detailed characterization of these mutations, referred to as yku80(tel) alleles, has revealed that Ku performs functionally distinct activities at subtelomeric chromatin versus the end of the chromosome, and these activities are separable from Ku's role in telomere length regulation. While at the chromosome terminus, we propose that Ku participates in two different activities: it facilitates telomerase-mediated G-strand synthesis, thereby contributing to telomere length regulation, and it separately protects against resection of the C-strand, thereby contributing to protection of chromosome termini. Furthermore, we propose that the Ku heterodimer performs discrete sets of functions at chromosome termini and at duplex subtelomeric chromatin, via separate interactions with these two locations. Based on homology modeling with the human Ku structure, five of the yku80(tel) alleles mutate residues that are conserved between the yeast and human Ku80 proteins, suggesting that these mutations probe activities that are shared between yeast and humans.
Collapse
Affiliation(s)
- Alison A Bertuch
- Department of Pediatrics, Hematology/Oncology Section, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
| | | |
Collapse
|
34
|
Stellwagen AE, Haimberger ZW, Veatch JR, Gottschling DE. Ku interacts with telomerase RNA to promote telomere addition at native and broken chromosome ends. Genes Dev 2003; 17:2384-95. [PMID: 12975323 PMCID: PMC218076 DOI: 10.1101/gad.1125903] [Citation(s) in RCA: 227] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Ku is a conserved DNA end-binding protein that plays various roles at different kinds of DNA ends. At telomeres, Ku is part of the structure that protects the chromosome end, whereas at broken DNA ends, Ku promotes DNA repair as part of the nonhomologous end-joining (NHEJ) pathway. Here, we present evidence of a new role for Ku that impacts both telomere-length maintenance and DNA repair in Saccharomyces cerevisiae. We show that Ku binds TLC1, the RNA component of telomerase. We also describe a novel separation-of-function allele of Ku that is specifically defective in TLC1 binding. In this mutant, telomeres are short and the kinetics of telomere addition are slow, but other Ku-dependent activities, such as chromosome end protection and NHEJ, are unaffected. At low frequency, yeast will use telomerase to heal DNA damage by capping the broken chromosome with telomeric DNA sequences. We show that when Ku's ability to bind TLC1 is disrupted, DNA repair via telomere healing is reduced 10- to 100-fold, and the spectrum of sequences that can acquire a telomere changes. Thus, the interaction between Ku and TLC1 RNA enables telomerase to act at both broken and normal chromosome ends.
Collapse
Affiliation(s)
- Anne E Stellwagen
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
| | | | | | | |
Collapse
|
35
|
Grandin N, Charbonneau M. The Rad51 pathway of telomerase-independent maintenance of telomeres can amplify TG1-3 sequences in yku and cdc13 mutants of Saccharomyces cerevisiae. Mol Cell Biol 2003; 23:3721-34. [PMID: 12748277 PMCID: PMC155211 DOI: 10.1128/mcb.23.11.3721-3734.2003] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the yeast Saccharomyces cerevisiae, Cdc13, Yku, and telomerase define three parallel pathways for telomere end protection that prevent chromosome instability and death by senescence. We report here that cdc13-1 yku70delta mutants generated telomere deprotection-resistant cells that, in contrast with telomerase-negative senescent cells, did not display classical crisis events. cdc13-1 yku70delta cells survived telomere deprotection by exclusively amplifying TG(1-3) repeats (type II recombination). In a background lacking telomerase (tlc1delta), this process predominated over type I recombination (amplification of subtelomeric Y' sequences). Strikingly, inactivation of the Rad50/Rad59 pathway (which is normally required for type II recombination) in cdc13-1 yku70delta or yku70delta tlc1delta mutants, but also in cdc13-1 YKU70(+) tlc1delta mutants, still permitted type II recombination, but this process was now entirely dependent on the Rad51 pathway. In addition, delayed senescence was observed in cdc13-1 yku70delta rad51delta and cdc13-1 tlc1delta rad51delta cells. These results demonstrate that in wild-type cells, masking by Cdc13 and Yku prevents the Rad51 pathway from amplifying telomeric TG(1-3) sequences. They also suggest that Rad51 is more efficient than Rad50 in amplifying the sequences left uncovered by the absence of Cdc13 or Yku70.
Collapse
Affiliation(s)
- Nathalie Grandin
- Ecole Normale Supérieure de Lyon, UMR CNRS 5665, 69364 Lyon, France
| | | |
Collapse
|
36
|
Downs JA, Kosmidou E, Morgan A, Jackson SP. Suppression of homologous recombination by the Saccharomyces cerevisiae linker histone. Mol Cell 2003; 11:1685-92. [PMID: 12820979 DOI: 10.1016/s1097-2765(03)00197-7] [Citation(s) in RCA: 139] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The basic unit of chromatin in eukaryotes is the nucleosome, comprising 146 bp of DNA wound around two copies of each of four core histones. Chromatin is further condensed by association with linker histones. Saccharomyces cerevisiae Hho1p has sequence homology to other known linker histones and interacts with nucleosomes in vitro. However, disruption of HHO1 results in no significant changes in the phenotypes examined thus far. Here, we show that Hho1p is inhibitory to DNA repair by homologous recombination (HR). We find Hho1p is abundant and associated with the genome, consistent with a global role in DNA repair. Furthermore, we establish that Hho1p is required for a full life span and propose that this is mechanistically linked to its role in HR. Finally, we show that Hho1p is inhibitory to the recombination-dependent mechanism of telomere maintenance. The role of linker histones in genome stability, aging, and tumorigenesis is discussed.
Collapse
Affiliation(s)
- Jessica A Downs
- The Wellcome Trust/Cancer Research UK Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, United Kingdom
| | | | | | | |
Collapse
|
37
|
Abstract
Arthur Kornberg "never met a dull enzyme" (For the Love of Enzymes: The Odyssey of a Biochemist, Harvard University Press, 1989) and telomerase is no exception. Telomerase is a remarkable polymerase that uses an internal RNA template to reverse-transcribe telomere DNA, one nucleotide at a time, onto telomeric, G-rich single-stranded DNA. In the 17 years since its discovery, the characterization of telomerase enzyme components has uncovered a highly conserved family of telomerase reverse transcriptases that, together with the telomerase RNA, appear to comprise the enzymatic core of telomerase. While not as comprehensively understood as yet, some telomerase-associated proteins also serve crucial roles in telomerase function in vivo, such as telomerase ribonudeoprotein (RNP) assembly, recruitment to the telomere, and the coordination of DNA replication at the telomere. A selected overview of the biochemical properties of this unique enzyme, in vitro and in vivo, will be presented.
Collapse
|
38
|
Riha K, Shippen DE. Ku is required for telomeric C-rich strand maintenance but not for end-to-end chromosome fusions in Arabidopsis. Proc Natl Acad Sci U S A 2003; 100:611-5. [PMID: 12511598 PMCID: PMC141044 DOI: 10.1073/pnas.0236128100] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Telomere dysfunction arising from mutations in telomerase or in telomere capping proteins leads to end-to-end chromosome fusions. Paradoxically, the Ku7080 heterodimer, essential for nonhomologous end-joining double-strand break repair, is also found at telomeres, and in mammals it is required to prevent telomere fusion. Previously, we showed that inactivation of Ku70 in Arabidopsis results in telomere lengthening. Here, we have demonstrated that this telomere elongation is telomerase dependent. Further, we found that the terminal 3' G overhang was significantly extended in ku70 mutants and in plants deficient in both Ku70 and the catalytic subunit of telomerase (TERT), implying that Ku is needed for proper maintenance of the telomeric C-rich strand. Consistent with inefficient C-strand maintenance, telomere shortening was accelerated in ku70 tert double mutants, and the onset of a terminal sterile phenotype was reached two to three times faster than in tert single mutants. Unexpectedly, abundant anaphase bridges were found in terminal plants harboring critically shortened telomeres, indicating that Ku is not required for the formation of end-to-end chromosome fusions in telomerase-deficient Arabidopsis. Together, these findings define Ku70 as a gene in higher eukaryotes required for maintenance of the telomeric C-rich strand and underscore the complexity and diversity of molecular interactions at telomeres.
Collapse
Affiliation(s)
- Karel Riha
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA
| | | |
Collapse
|
39
|
Current awareness. Yeast 2002; 19:903-8. [PMID: 12112243 DOI: 10.1002/yea.826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
|