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1.
Nat Commun ; 11(1): 5288, 2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-33082336

RESUMO

Telomerase is a specialized reverse transcriptase that adds GGTTAG repeats to chromosome ends and is upregulated in most human cancers to enable limitless proliferation. Here, we uncover two distinct mechanisms by which naturally occurring oxidized dNTPs and therapeutic dNTPs inhibit telomerase-mediated telomere elongation. We conduct a series of direct telomerase extension assays in the presence of modified dNTPs on various telomeric substrates. We provide direct evidence that telomerase can add the nucleotide reverse transcriptase inhibitors ddITP and AZT-TP to the telomeric end, causing chain termination. In contrast, telomerase continues elongation after inserting oxidized 2-OH-dATP or therapeutic 6-thio-dGTP, but insertion disrupts translocation and inhibits further repeat addition. Kinetics reveal that telomerase poorly selects against 6-thio-dGTP, inserting with similar catalytic efficiency as dGTP. Furthermore, telomerase processivity factor POT1-TPP1 fails to restore processive elongation in the presence of inhibitory dNTPs. These findings reveal mechanisms for targeting telomerase with modified dNTPs in cancer therapy.


Assuntos
Inibidores Enzimáticos/metabolismo , Telomerase/antagonistas & inibidores , Telomerase/metabolismo , Nucleotídeos de Desoxiadenina/química , Nucleotídeos de Desoxiadenina/metabolismo , Nucleotídeos de Desoxiguanina/química , Nucleotídeos de Desoxiguanina/metabolismo , Inibidores Enzimáticos/química , Humanos , Cinética , Modelos Moleculares , Oxirredução , Telomerase/química , Telomerase/genética , Telômero/metabolismo
2.
Nat Commun ; 11(1): 5297, 2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-33082350

RESUMO

Extrachromosomal telomeric circles are commonly invoked as important players in telomere maintenance, but their origin has remained elusive. Using electron microscopy analysis on purified telomeres we show that, apart from known structures, telomeric repeats accumulate internal loops (i-loops) that occur in the proximity of nicks and single-stranded DNA gaps. I-loops are induced by single-stranded damage at normal telomeres and represent the majority of telomeric structures detected in ALT (Alternative Lengthening of Telomeres) tumor cells. Our data indicate that i-loops form as a consequence of the exposure of single-stranded DNA at telomeric repeats. Finally, we show that these damage-induced i-loops can be excised to generate extrachromosomal telomeric circles resulting in loss of telomeric repeats. Our results identify damage-induced i-loops as a new intermediate in telomere metabolism and reveal a simple mechanism that links telomere damage to the accumulation of extrachromosomal telomeric circles and to telomere erosion.


Assuntos
Telômero/química , Telômero/metabolismo , Animais , DNA de Cadeia Simples/química , DNA de Cadeia Simples/genética , DNA de Cadeia Simples/metabolismo , Humanos , Camundongos , Telômero/genética , Homeostase do Telômero
3.
Nucleic Acids Res ; 48(17): 9660-9680, 2020 09 25.
Artigo em Inglês | MEDLINE | ID: mdl-32890403

RESUMO

Maintenance of genome integrity is critical to guarantee transfer of an intact genome from parent to offspring during cell division. DNA polymerases (Pols) provide roles in both replication of the genome and the repair of a wide range of lesions. Amongst replicative DNA Pols, translesion DNA Pols play a particular role: replication to bypass DNA damage. All cells express a range of translesion Pols, but little work has examined their function in parasites, including whether the enzymes might contribute to host-parasite interactions. Here, we describe a dual function of one putative translesion Pol in African trypanosomes, which we now name TbPolIE. Previously, we demonstrated that TbPolIE is associated with telomeric sequences and here we show that RNAi-mediated depletion of TbPolIE transcripts results in slowed growth, altered DNA content, changes in cell morphology, and increased sensitivity to DNA damaging agents. We also show that TbPolIE displays pronounced localization at the nuclear periphery, and that its depletion leads to chromosome segregation defects and increased levels of endogenous DNA damage. Finally, we demonstrate that TbPolIE depletion leads to deregulation of telomeric variant surface glycoprotein genes, linking the function of this putative translesion DNA polymerase to host immune evasion by antigenic variation.


Assuntos
Variação Antigênica , DNA Polimerase Dirigida por DNA/metabolismo , Telômero/genética , Trypanosoma brucei brucei/genética , Linhagem Celular , Núcleo Celular/enzimologia , Núcleo Celular/genética , Segregação de Cromossomos , Replicação do DNA , DNA Polimerase Dirigida por DNA/genética , Regulação da Expressão Gênica , Genoma de Protozoário , Humanos , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Interferência de RNA , Telômero/metabolismo , Trypanosoma brucei brucei/metabolismo , Trypanosoma brucei brucei/patogenicidade , Glicoproteínas Variantes de Superfície de Trypanosoma/genética
5.
Oncogene ; 39(36): 5811-5824, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32733068

RESUMO

Telomere maintenance via telomerase reactivation is a nearly universal hallmark of cancer cells which enables replicative immortality. In contrast, telomerase activity is silenced in most adult somatic cells. Thus, telomerase represents an attractive target for highly selective cancer therapeutics. However, development of telomerase inhibitors has been challenging and thus far there are no clinically approved strategies exploiting this cancer target. The discovery of prevalent mutations in the TERT promoter region in many cancers and recent advances in telomerase biology has led to a renewed interest in targeting this enzyme. Here we discuss recent efforts targeting telomerase, including immunotherapies and direct telomerase inhibitors, as well as emerging approaches such as targeting TERT gene expression driven by TERT promoter mutations. We also address some of the challenges to telomerase-directed therapies including potential therapeutic resistance and considerations for future therapeutic applications and translation into the clinical setting. Although much work remains to be done, effective strategies targeting telomerase will have a transformative impact for cancer therapy and the prospect of clinically effective drugs is boosted by recent advances in structural models of human telomerase.


Assuntos
Inibidores Enzimáticos/farmacologia , Inibidores Enzimáticos/uso terapêutico , Terapia de Alvo Molecular , Neoplasias/tratamento farmacológico , Neoplasias/enzimologia , Telomerase/antagonistas & inibidores , Animais , Biomarcadores Tumorais , Estudos Clínicos como Assunto , Avaliação Pré-Clínica de Medicamentos , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Neoplasias/diagnóstico , Neoplasias/etiologia , Telômero/genética , Telômero/metabolismo , Homeostase do Telômero , Resultado do Tratamento
6.
Nat Commun ; 11(1): 3321, 2020 07 03.
Artigo em Inglês | MEDLINE | ID: mdl-32620872

RESUMO

Human telomeres are bound by the telomere repeat binding proteins TRF1 and TRF2. Telomere shortening in human cells leads to a DNA damage response that signals replicative senescence. While insufficient loading of TRF2 at shortened telomeres contributes to the DNA damage response in senescence, the contribution of TRF1 to senescence induction has not been determined. Here we show that counter to TRF2 deficiency-mediated induction of DNA damage, TRF1 deficiency serves a protective role to limit induction of DNA damage induced by subtelomere recombination. Shortened telomeres recruit insufficient TRF1 and as a consequence inadequate tankyrase 1 to resolve sister telomere cohesion. Our findings suggest that the persistent cohesion protects short telomeres from inappropriate recombination. Ultimately, in the final division, telomeres are no longer able to maintain cohesion and subtelomere copying ensues. Thus, the gradual loss of TRF1 and concomitant persistent cohesion that occurs with telomere shortening ensures a measured approach to replicative senescence.


Assuntos
Encurtamento do Telômero/genética , Telômero/genética , Proteína 1 de Ligação a Repetições Teloméricas/genética , Proteína 2 de Ligação a Repetições Teloméricas/genética , Sequência de Bases , Linhagem Celular , Linhagem Celular Tumoral , Senescência Celular/genética , Dano ao DNA , Células HEK293 , Heterocromatina/genética , Heterocromatina/metabolismo , Humanos , Hibridização in Situ Fluorescente , Mutação , Interferência de RNA , Tanquirases/metabolismo , Telômero/metabolismo , Proteína 1 de Ligação a Repetições Teloméricas/deficiência , Proteína 1 de Ligação a Repetições Teloméricas/metabolismo , Proteína 2 de Ligação a Repetições Teloméricas/deficiência , Proteína 2 de Ligação a Repetições Teloméricas/metabolismo
7.
Nat Struct Mol Biol ; 27(8): 752-762, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32661422

RESUMO

Budding yeast Cdc13-Stn1-Ten1 (CST) complex plays an essential role in telomere protection and maintenance. Despite extensive studies, only structural information of individual domains of CST is available; the architecture of CST still remains unclear. Here, we report crystal structures of Kluyveromyces lactis Cdc13-telomeric-DNA, Cdc13-Stn1 and Stn1-Ten1 complexes and propose an integrated model depicting how CST assembles and plays its roles at telomeres. Surprisingly, two oligonucleotide/oligosaccharide-binding (OB) folds of Cdc13 (OB2 and OB4), previously believed to mediate Cdc13 homodimerization, actually form a stable intramolecular interaction. This OB2-OB4 module of Cdc13 is required for the Cdc13-Stn1 interaction that assembles CST into an architecture with a central ring-like core and multiple peripheral modules in a 2:2:2 stoichiometry. Functional analyses indicate that this unique CST architecture is essential for both telomere capping and homeostasis regulation. Overall, our results provide fundamentally valuable structural information regarding the CST complex and its roles in telomere biology.


Assuntos
Proteínas Fúngicas/metabolismo , Kluyveromyces/metabolismo , Proteínas de Ligação a Telômeros/metabolismo , Telômero/metabolismo , Cristalografia por Raios X , DNA Fúngico/química , DNA Fúngico/metabolismo , Proteínas Fúngicas/química , Kluyveromyces/química , Modelos Moleculares , Conformação Proteica , Multimerização Proteica , Telômero/química , Homeostase do Telômero , Proteínas de Ligação a Telômeros/química
8.
Mol Cell ; 79(1): 115-126.e6, 2020 07 02.
Artigo em Inglês | MEDLINE | ID: mdl-32497497

RESUMO

Extension of telomeres is a critical step in the immortalization of cancer cells. This complex reaction requires proper spatiotemporal coordination of telomerase and telomeres and remains poorly understood at the cellular level. To understand how cancer cells execute this process, we combine CRISPR genome editing and MS2 RNA tagging to image single molecules of telomerase RNA (hTR). Real-time dynamics and photoactivation experiments of hTR in Cajal bodies (CBs) reveal that hTERT controls the exit of hTR from CBs. Single-molecule tracking of hTR at telomeres shows that TPP1-mediated recruitment results in short telomere-telomerase scanning interactions, and then base pairing between hTR and telomere ssDNA promotes long interactions required for stable telomerase retention. Interestingly, POT1 OB-fold mutations that result in abnormally long telomeres in cancers act by enhancing this retention step. In summary, single-molecule imaging unveils the life cycle of telomerase RNA and provides a framework to reveal how cancer-associated mutations mechanistically drive defects in telomere homeostasis.


Assuntos
Corpos Enovelados/metabolismo , DNA de Cadeia Simples/metabolismo , RNA/metabolismo , Imagem Individual de Molécula/métodos , Telomerase/metabolismo , Homeostase do Telômero , Telômero/metabolismo , Repetições Palindrômicas Curtas Agrupadas e Regularmente Espaçadas , DNA de Cadeia Simples/genética , Edição de Genes , Células HeLa , Humanos , Mutação , RNA/genética , Telomerase/genética , Telômero/genética , Proteínas de Ligação a Telômeros/genética , Proteínas de Ligação a Telômeros/metabolismo
9.
Clin Interv Aging ; 15: 827-839, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32581523

RESUMO

Different factors influence the development and control of ageing. It is well known that progressive telomere shorting is one of the molecular mechanisms underlying ageing. The shelterin complex consists of six telomere-specific proteins which are involved in the protection of chromosome ends. More particularly, this vital complex protects the telomeres from degradation, prevents from activation of unwanted repair systems, regulates the activity of telomerase, and has a crucial role in cellular senescent and ageing-related pathologies. This review explores the organization and function of telomeric DNA along with the mechanism of telomeres during ageing, followed by a discussion of the critical role of shelterin components and their changes during ageing.


Assuntos
Envelhecimento/metabolismo , Estresse Oxidativo , Telomerase/metabolismo , Proteínas de Ligação a Telômeros/metabolismo , Telômero/metabolismo , Envelhecimento/genética , Replicação do DNA , Humanos , Proteínas de Ligação a Telômeros/genética
10.
Trends Pharmacol Sci ; 41(8): 506-508, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32482456

RESUMO

Genetic defects in telomere maintenance result in stem cell exhaustion and a spectrum of telomere biology diseases. Systemic treatments beyond organ transplantation are lacking for these diseases. Nagpal and colleagues identified small molecules that restore telomere maintenance in patient-derived stem cells, offering a promising therapy for telomere biology diseases.


Assuntos
Disceratose Congênita , Telomerase , Humanos , RNA , Células-Tronco/metabolismo , Telomerase/genética , Telomerase/metabolismo , Telômero/metabolismo
11.
Cell Stem Cell ; 26(6): 804-805, 2020 06 04.
Artigo em Inglês | MEDLINE | ID: mdl-32502401

RESUMO

Most rare inherited telomere biology disorders and some common aging-related diseases are associated with shortened telomeres. In this issue of Cell Stem Cell, insights into one of the rarest genetic causes of these disorders led to the discovery (Nagpal et al., 2020) of small molecules that lengthen telomeres.


Assuntos
Telomerase , Telômero , Humanos , Células-Tronco/metabolismo , Telomerase/metabolismo , Telômero/genética , Telômero/metabolismo , Encurtamento do Telômero
12.
Proc Natl Acad Sci U S A ; 117(26): 15066-15074, 2020 06 30.
Artigo em Inglês | MEDLINE | ID: mdl-32554492

RESUMO

Cancer incidence increases exponentially with age when human telomeres are shorter. Similarly, telomerase reverse transcriptase (tert) mutant zebrafish have premature short telomeres and anticipate cancer incidence to younger ages. However, because short telomeres constitute a road block to cell proliferation, telomere shortening is currently viewed as a tumor suppressor mechanism and should protect from cancer. This conundrum is not fully understood. In our current study, we report that telomere shortening promotes cancer in a noncell autonomous manner. Using zebrafish chimeras, we show increased incidence of invasive melanoma when wild-type (WT) tumors are generated in tert mutant zebrafish. Tissues adjacent to melanoma lesions (skin) and distant organs (intestine) in tert mutants exhibited higher levels of senescence and inflammation. In addition, we transferred second generation (G2) tert blastula cells into WT to produce embryo chimeras. Cells with very short telomeres induced increased tumor necrosis factor1-α (TNF1-α) expression and senescence in larval tissues in a noncell autonomous manner, creating an inflammatory environment. Considering that inflammation is protumorigenic, we transplanted melanoma-derived cells into G2 tert zebrafish embryos and observed that tissue environment with short telomeres leads to increased tumor development. To test if inflammation was necessary for this effect, we treated melanoma transplants with nonsteroid anti-inflammatory drugs and show that higher melanoma dissemination can be averted. Thus, apart from the cell autonomous role of short telomeres in contributing to genome instability, we propose that telomere shortening with age causes systemic chronic inflammation leading to increased tumor incidence.


Assuntos
Melanoma/metabolismo , Telômero/metabolismo , Peixe-Zebra/metabolismo , Animais , Modelos Animais de Doenças , Humanos , Melanoma/genética , Melanoma/imunologia , Telomerase/genética , Telomerase/metabolismo , Telômero/genética , Encurtamento do Telômero , Fator de Necrose Tumoral alfa/genética , Fator de Necrose Tumoral alfa/imunologia , Peixe-Zebra/genética , Peixe-Zebra/imunologia , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismo
13.
Proc Natl Acad Sci U S A ; 117(24): 13647-13658, 2020 06 16.
Artigo em Inglês | MEDLINE | ID: mdl-32499315

RESUMO

During meiosis, interhomolog recombination produces crossovers and noncrossovers to create genetic diversity. Meiotic recombination frequency varies at multiple scales, with high subtelomeric recombination and suppressed centromeric recombination typical in many eukaryotes. During recombination, sister chromatids are tethered as loops to a polymerized chromosome axis, which, in plants, includes the ASY1 HORMA domain protein and REC8-cohesin complexes. Using chromatin immunoprecipitation, we show an ascending telomere-to-centromere gradient of ASY1 enrichment, which correlates strongly with REC8-cohesin ChIP-seq data. We mapped crossovers genome-wide in the absence of ASY1 and observe that telomere-led recombination becomes dominant. Surprisingly, asy1/+ heterozygotes also remodel crossovers toward subtelomeric regions at the expense of the pericentromeres. Telomeric recombination increases in asy1/+ occur in distal regions where ASY1 and REC8 ChIP enrichment are lowest in wild type. In wild type, the majority of crossovers show interference, meaning that they are more widely spaced along the chromosomes than expected by chance. To measure interference, we analyzed double crossover distances, MLH1 foci, and fluorescent pollen tetrads. Interestingly, while crossover interference is normal in asy1/+, it is undetectable in asy1 mutants, indicating that ASY1 is required to mediate crossover interference. Together, this is consistent with ASY1 antagonizing telomere-led recombination and promoting spaced crossover formation along the chromosomes via interference. These findings provide insight into the role of the meiotic axis in patterning recombination frequency within plant genomes.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Troca Genética , Proteínas de Ligação a DNA/metabolismo , Recombinação Genética , Telômero/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/genética , Telômero/metabolismo
14.
PLoS Genet ; 16(6): e1008799, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32502208

RESUMO

TRF2 and TRF1 are a key component in shelterin complex that associates with telomeric DNA and protects chromosome ends. BRM is a core ATPase subunit of SWI/SNF chromatin remodeling complex. Whether and how BRM-SWI/SNF complex is engaged in chromatin end protection by telomeres is unknown. Here, we report that depletion of BRM does not affect heterochromatin state of telomeres, but results in telomere dysfunctional phenomena including telomere uncapping and replication defect. Mechanistically, expression of TRF2 and TRF1 is jointly regulated by BRM-SWI/SNF complex, which is localized to promoter region of both genes and facilitates their transcription. BRM-deficient cells bear increased TRF2-free or TRF1-free telomeres due to insufficient expression. Importantly, BRM depletion-induced telomere uncapping or replication defect can be rescued by compensatory expression of exogenous TRF2 or TRF1, respectively. Together, these results identify a new function of BRM-SWI/SNF complex in enabling functional telomeres for maintaining genome stability.


Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Telômero/metabolismo , Proteína 1 de Ligação a Repetições Teloméricas/genética , Proteína 2 de Ligação a Repetições Teloméricas/genética , Fatores de Transcrição/metabolismo , Instabilidade Genômica , Células HEK293 , Células HeLa , Células Hep G2 , Heterocromatina/metabolismo , Humanos , Regiões Promotoras Genéticas , Proteína 1 de Ligação a Repetições Teloméricas/metabolismo , Proteína 2 de Ligação a Repetições Teloméricas/metabolismo , Fatores de Transcrição/genética
15.
Nat Commun ; 11(1): 2320, 2020 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-32385320

RESUMO

Chromothripsis is a recently identified mutational phenomenon, by which a presumably single catastrophic event generates extensive genomic rearrangements of one or a few chromosome(s). Considered as an early event in tumour development, this form of genome instability plays a prominent role in tumour onset. Chromothripsis prevalence might have been underestimated when using low-resolution methods, and pan-cancer studies based on sequencing are rare. Here we analyse chromothripsis in 28 tumour types covering all major adult cancers (634 tumours, 316 whole-genome and 318 whole-exome sequences). We show that chromothripsis affects a substantial proportion of human cancers, with a prevalence of 49% across all cases. Chromothripsis generates entity-specific genomic alterations driving tumour development, including clinically relevant druggable fusions. Chromothripsis is linked with specific telomere patterns and univocal mutational signatures in distinct tumour entities. Longitudinal analysis of chromothriptic patterns in 24 matched tumour pairs reveals insights in the clonal evolution of tumours with chromothripsis.


Assuntos
Cromotripsia , Neoplasias/genética , Adulto , Genoma Humano/genética , Instabilidade Genômica/genética , Humanos , Telômero/genética , Telômero/metabolismo
16.
Nat Commun ; 11(1): 2173, 2020 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-32358529

RESUMO

RNase P and MRP are highly conserved, multi-protein/RNA complexes with essential roles in processing ribosomal and tRNAs. Three proteins found in both complexes, Pop1, Pop6, and Pop7 are also telomerase-associated. Here, we determine how temperature sensitive POP1 and POP6 alleles affect yeast telomerase. At permissive temperatures, mutant Pop1/6 have little or no effect on cell growth, global protein levels, the abundance of Est1 and Est2 (telomerase proteins), and the processing of TLC1 (telomerase RNA). However, in pop mutants, TLC1 is more abundant, telomeres are short, and TLC1 accumulates in the cytoplasm. Although Est1/2 binding to TLC1 occurs at normal levels, Est1 (and hence Est3) binding is highly unstable. We propose that Pop-mediated stabilization of Est1 binding to TLC1 is a pre-requisite for formation and nuclear localization of the telomerase holoenzyme. Furthermore, Pop proteins affect TLC1 and the RNA subunits of RNase P/MRP in very different ways.


Assuntos
Ribonuclease P/metabolismo , Ribonucleoproteínas/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Telomerase/metabolismo , Telômero/metabolismo , Núcleo Celular/genética , Núcleo Celular/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Metilação , Ligação Proteica , RNA/metabolismo , Processamento de Terminações 3' de RNA/genética , Ribonuclease P/genética , Ribonucleoproteínas/genética , Proteínas de Saccharomyces cerevisiae/genética , Telomerase/genética , Telômero/química
17.
Nucleic Acids Res ; 48(11): 6019-6031, 2020 06 19.
Artigo em Inglês | MEDLINE | ID: mdl-32379321

RESUMO

ALT tumor cells often contain abundant DNA damage foci at telomeres and rely on the alternative lengthening of telomeres (ALT) mechanism to maintain their telomeres. How the telomere chromatin is regulated and maintained in these cells remains largely unknown. In this study, we present evidence that heterochromatin protein 1 binding protein 3 (HP1BP3) can localize to telomeres and is particularly enriched on telomeres in ALT cells. HP1BP3 inhibition led to preferential growth inhibition of ALT cells, which was accompanied by telomere chromatin decompaction, increased presence of C-circles, more pronounced ALT-associated phenotypes and elongated telomeres. Furthermore, HP1BP3 appeared to participate in regulating telomere histone H3K9me3 epigenetic marks. Taken together, our data suggest that HP1BP3 functions on telomeres to maintain telomere chromatin and represents a novel target for inhibiting ALT cancer cells.


Assuntos
Proliferação de Células , Montagem e Desmontagem da Cromatina , Heterocromatina/metabolismo , Histonas/metabolismo , Telômero/metabolismo , Linhagem Celular Tumoral , Dano ao DNA , Eucromatina/genética , Eucromatina/metabolismo , Técnicas de Silenciamento de Genes , Heterocromatina/genética , Código das Histonas , Histonas/química , Humanos , Metilação , Proteínas Nucleares/antagonistas & inibidores , Proteínas Nucleares/deficiência , Proteínas Nucleares/metabolismo , Multimerização Proteica , Homeostase do Telômero
18.
Nat Commun ; 11(1): 2267, 2020 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-32385287

RESUMO

To faithfully transmit genetic information, cells must replicate their entire genome before division. This is thought to be ensured by the temporal separation of replication and chromosome segregation. Here we show that in 20-40% of unperturbed yeast cells, DNA synthesis continues during anaphase, late in mitosis. High cyclin-Cdk activity inhibits DNA synthesis in metaphase, and the decrease in cyclin-Cdk activity during mitotic exit allows DNA synthesis to finish at subtelomeric and some difficult-to-replicate regions. DNA synthesis during late mitosis correlates with elevated mutation rates at subtelomeric regions, including copy number variation. Thus, yeast cells temporally overlap DNA synthesis and chromosome segregation during normal growth, possibly allowing cells to maximize population-level growth rate while simultaneously exploring greater genetic space.


Assuntos
Segregação de Cromossomos , Cromossomos Fúngicos/metabolismo , DNA Fúngico/metabolismo , Saccharomycetales/metabolismo , Anáfase/genética , Núcleo Celular/metabolismo , Cromatina/metabolismo , Quinases Ciclina-Dependentes/metabolismo , Replicação do DNA , Genes Fúngicos , Metáfase , Mitose , Taxa de Mutação , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomycetales/genética , Telômero/metabolismo
19.
PLoS Genet ; 16(5): e1008816, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32469862

RESUMO

Alternative lengthening of telomeres (ALT) in human cells is a conserved process that is often activated in telomerase-deficient human cancers. This process exploits components of the recombination machinery to extend telomere ends, thus allowing for increased proliferative potential. Human MUS81 (Mus81 in Saccharomyces cerevisiae) is the catalytic subunit of structure-selective endonucleases involved in recombination and has been implicated in the ALT mechanism. However, it is unclear whether MUS81 activity at the telomere is specific to ALT cells or if it is required for more general aspects of telomere stability. In this study, we use S. cerevisiae to evaluate the contribution of the conserved Mus81-Mms4 endonuclease in telomerase-deficient yeast cells that maintain their telomeres by mechanisms akin to human ALT. Similar to human cells, we find that yeast Mus81 readily localizes to telomeres and its activity is important for viability after initial loss of telomerase. Interestingly, our analysis reveals that yeast Mus81 is not required for the survival of cells undergoing recombination-mediated telomere lengthening, i.e. for ALT itself. Rather we infer from genetic analysis that Mus81-Mms4 facilitates telomere replication during times of telomere instability. Furthermore, combining mus81 mutants with mutants of a yeast telomere replication factor, Rrm3, reveals that the two proteins function in parallel to promote normal growth during times of telomere stress. Combined with previous reports, our data can be interpreted in a consistent model in which both yeast and human MUS81-dependent nucleases participate in the recovery of stalled replication forks within telomeric DNA. Furthermore, this process becomes crucial under conditions of additional replication stress, such as telomere replication in telomerase-deficient cells.


Assuntos
Proteínas de Ligação a DNA/metabolismo , Endonucleases/metabolismo , Endonucleases Flap/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/crescimento & desenvolvimento , Telomerase/deficiência , Replicação do DNA , Proteínas de Ligação a DNA/genética , Endonucleases/genética , Endonucleases Flap/genética , Viabilidade Microbiana , Recombinação Genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Telômero/metabolismo , Homeostase do Telômero
20.
Cancer Res ; 80(12): 2663-2675, 2020 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-32291317

RESUMO

Neuroblastoma is a childhood cancer with heterogeneous clinical outcomes. To comprehensively assess the impact of telomere maintenance mechanism (TMM) on clinical outcomes in high-risk neuroblastoma, we integrated the C-circle assay [a marker for alternative lengthening of telomeres (ALT)], TERT mRNA expression by RNA-sequencing, whole-genome/exome sequencing, and clinical covariates in 134 neuroblastoma patient samples at diagnosis. In addition, we assessed TMM in neuroblastoma cell lines (n = 104) and patient-derived xenografts (n = 28). ALT was identified in 23.4% of high-risk neuroblastoma tumors and genomic alterations in ATRX were detected in 60% of ALT tumors; 40% of ALT tumors lacked genomic alterations in known ALT-associated genes. Patients with high-risk neuroblastoma were classified into three subgroups (TERT-high, ALT+, and TERT-low/non-ALT) based on presence of C-circles and TERT mRNA expression (above or below median TERT expression). Event-free survival was similar among TERT-high, ALT+, or TERT-low/non-ALT patients. However, overall survival (OS) for TERT-low/non-ALT patients was significantly higher relative to TERT-high or ALT patients (log-rank test; P < 0.01) independent of current clinical and molecular prognostic markers. Consistent with the observed higher OS in patients with TERT-low/non-ALT tumors, continuous shortening of telomeres and decreasing viability occurred in low TERT-expressing, non-ALT patient-derived high-risk neuroblastoma cell lines. These findings demonstrate that assaying TMM with TERT mRNA expression and C-circles provides precise stratification of high-risk neuroblastoma into three subgroups with substantially different OS: a previously undescribed TERT-low/non-ALT cohort with superior OS (even after relapse) and two cohorts of patients with poor survival that have distinct molecular therapeutic targets. SIGNIFICANCE: These findings assess telomere maintenance mechanisms with TERT mRNA and the ALT DNA biomarker C-circles to stratify neuroblastoma into three groups, with distinct overall survival independent of currently used clinical risk classifiers.


Assuntos
Regulação Neoplásica da Expressão Gênica , Neuroblastoma/genética , Telomerase/metabolismo , Homeostase do Telômero , Telômero/metabolismo , Linhagem Celular Tumoral , Criança , Pré-Escolar , Intervalo Livre de Doença , Feminino , Seguimentos , Humanos , Lactente , Masculino , Recidiva Local de Neoplasia , Neuroblastoma/mortalidade , Neuroblastoma/patologia , RNA Mensageiro/isolamento & purificação , RNA Mensageiro/metabolismo , RNA-Seq , Telomerase/genética , Telomerase/isolamento & purificação , Sequenciamento Completo do Genoma , Proteína Nuclear Ligada ao X/genética , Ensaios Antitumorais Modelo de Xenoenxerto
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