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1.
Genes Dev ; 33(13-14): 814-827, 2019 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-31171703

RESUMO

Alternative lengthening of telomeres (ALT) is a telomerase-independent telomere maintenance mechanism that occurs in a subset of cancers. One of the hallmarks of ALT cancer is the excessively clustered telomeres in promyelocytic leukemia (PML) bodies, represented as large bright telomere foci. Here, we present a model system that generates telomere clustering in nuclear polySUMO (small ubiquitin-like modification)/polySIM (SUMO-interacting motif) condensates, analogous to PML bodies, and thus artificially engineered ALT-associated PML body (APB)-like condensates in vivo. We observed that the ALT-like phenotypes (i.e., a small fraction of heterogeneous telomere lengths and formation of C circles) are rapidly induced by introducing the APB-like condensates together with BLM through its helicase domain, accompanied by ssDNA generation and RPA accumulation at telomeres. Moreover, these events lead to mitotic DNA synthesis (MiDAS) at telomeres mediated by RAD52 through its highly conserved N-terminal domain. We propose that the clustering of large amounts of telomeres in human cancers promotes ALT that is mediated by MiDAS, analogous to Saccharomyces cerevisiae type II ALT survivors.


Assuntos
Núcleo Celular/metabolismo , DNA/biossíntese , Leucemia Promielocítica Aguda/fisiopatologia , Mitose , Proteína Rad52 de Recombinação e Reparo de DNA/metabolismo , RecQ Helicases/metabolismo , Homeostase do Telômero/genética , Motivos de Aminoácidos , Linhagem Celular Tumoral , Expressão Gênica , Humanos , Leucemia Promielocítica Aguda/genética , Fenótipo , Transporte Proteico , Proteína SUMO-1/metabolismo , Telômero/genética , Telômero/metabolismo
2.
Nat Commun ; 10(1): 2491, 2019 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-31171785

RESUMO

Genetic factors underlying leukocyte telomere length (LTL) may provide insights into telomere homeostasis, with direct links to disease susceptibility. Genetic evaluation of 23,096 Singaporean Chinese samples identifies 10 genome-wide loci (P < 5 × 10-8). Several of these contain candidate genes (TINF2, PARP1, TERF1, ATM and POT1) with potential roles in telomere biology and DNA repair mechanisms. Meta-analyses with additional 37,505 European individuals reveals six more genome-wide loci, including associations at MPHOSPH6, NKX2-3 and TYMS. We demonstrate that longer LTL associates with protection against respiratory disease mortality [HR = 0.854(0.804-0.906), P = 1.88 × 10-7] in the Singaporean Chinese samples. We further show that the LTL reducing SNP rs7253490 associates with respiratory infections (P = 7.44 × 10-4) although this effect may not be strongly mediated through LTL. Our data expands on the genetic basis of LTL and may indicate on a potential role of LTL in immune competence.


Assuntos
Grupo com Ancestrais do Continente Asiático/genética , Reparo do DNA/genética , Leucócitos/metabolismo , Homeostase do Telômero/genética , Telômero/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Estudos de Coortes , Grupo com Ancestrais do Continente Europeu/genética , Feminino , Estudo de Associação Genômica Ampla , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Infecções Respiratórias/genética , Singapura , Adulto Jovem
3.
Plant Cell Rep ; 38(9): 1081-1097, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31134349

RESUMO

KEY MESSAGE: Duplicate POT1 genes must rapidly diverge or be inactivated. Protection of telomeres 1 (POT1) encodes a conserved telomere binding protein implicated in both chromosome end protection and telomere length maintenance. Most organisms harbor a single POT1 gene, but in the few lineages where the POT1 family has expanded, the duplicate genes have diversified. Arabidopsis thaliana bears three POT1-like loci, POT1a, POT1b and POT1c. POT1a retains the ancestral function of telomerase regulation, while POT1b is implicated in chromosome end protection. Here we examine the function and evolution of the third POT1 paralog, POT1c. POT1c is a new gene, unique to A. thaliana, and was derived from a duplication event involving the POT1a locus and a neighboring gene encoding ribosomal protein S17. The duplicate S17 locus (dS17) is highly conserved across A. thaliana accessions, while POT1c is highly divergent, harboring multiple deletions within the gene body and two transposable elements within the promoter. The POT1c locus is transcribed at very low to non-detectable levels under standard growth conditions. In addition, no discernable molecular or developmental defects are associated with plants bearing a CRISPR mutation in the POT1c locus. However, forced expression of POT1c leads to decreased telomerase enzyme activity and shortened telomeres. Evolutionary reconstruction indicates that transposons invaded the POT1c promoter soon after the locus was formed, permanently silencing the gene. Altogether, these findings argue that POT1 dosage is critically important for viability and duplicate gene copies are retained only upon functional divergence.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Dosagem de Genes , Homeostase do Telômero/genética , Proteínas de Ligação a Telômeros/metabolismo , Telômero/genética , Arabidopsis/enzimologia , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Elementos de DNA Transponíveis/genética , Evolução Molecular , Duplicação Gênica , Mutação , Regiões Promotoras Genéticas/genética , Telomerase/genética , Telomerase/metabolismo , Proteínas de Ligação a Telômeros/genética
4.
Nat Commun ; 10(1): 2253, 2019 05 28.
Artigo em Inglês | MEDLINE | ID: mdl-31138795

RESUMO

Telomerase negative immortal cancer cells elongate telomeres through the Alternative Lengthening of Telomeres (ALT) pathway. While sustained telomeric replicative stress is required to maintain ALT, it might also lead to cell death when excessive. Here, we show that the ATPase/translocase activity of FANCM keeps telomeric replicative stress in check specifically in ALT cells. When FANCM is depleted in ALT cells, telomeres become dysfunctional, and cells stop proliferating and die. FANCM depletion also increases ALT-associated marks and de novo synthesis of telomeric DNA. Depletion of the BLM helicase reduces the telomeric replication stress and cell proliferation defects induced by FANCM inactivation. Finally, FANCM unwinds telomeric R-loops in vitro and suppresses their accumulation in cells. Overexpression of RNaseH1 completely abolishes the replication stress remaining in cells codepleted for FANCM and BLM. Thus, FANCM allows controlled ALT activity and ALT cell proliferation by limiting the toxicity of uncontrolled BLM and telomeric R-loops.


Assuntos
DNA Helicases/genética , Replicação do DNA/genética , RecQ Helicases/genética , Homeostase do Telômero/genética , Telômero/metabolismo , Morte Celular/genética , Linhagem Celular Tumoral , Proliferação de Células/genética , DNA Helicases/metabolismo , Células HEK293 , Células HeLa , Humanos , RecQ Helicases/metabolismo , Ribonuclease H/genética , Ribonuclease H/metabolismo
5.
Lipids Health Dis ; 18(1): 80, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-30935416

RESUMO

BACKGROUND: Evidence regarding the correlation between lipoproteins and telomere length in US adults is limited. We aimed to investigate whether lipoproteins was associated with telomere length using US National Health and Nutrition Examination Survey (NHANES) database. METHODS: A total of 6468 selected participants were identified in the NHANES Data Base (1999-2002). The independent and dependent variables were lipoproteins and telomere length, respectively. The covariates included demographic data, dietary data, physical examination data, and comorbidities. RESULTS: In fully-adjusted model, we found that 0.1 differences of telomere length were positively associated with HDL-C [0.19 (95% CI 0.07, 0.31)], while the associations between LDL-C [0.19 (95% CI -0.27, 0.65)], TG [- 1.00 (95% CI -2.09, 0.07) and telomere length were not detected. By nonlinearity test, only the relationship between HDL-C and telomere length was nonlinear. The inflection point we got was 1.25. On the left side of the inflection point (telomere length ≤ 1.25), a difference in 0.1 of telomere length was associated with 0.50 difference in HDL-C. CONCLUSION: After adjusting for demographic data, dietary data, physical examination data, and comorbidities, telomere length is not associated with LDL-C and TG, but is positively associated with HDL-C when telomere length is less than 1.25.


Assuntos
Hiperlipoproteinemia Tipo II/epidemiologia , Lipoproteínas/genética , Homeostase do Telômero/genética , Telômero/genética , Adulto , Idoso , HDL-Colesterol/sangue , LDL-Colesterol/sangue , Dieta , Feminino , Humanos , Hiperlipoproteinemia Tipo II/sangue , Hiperlipoproteinemia Tipo II/genética , Hiperlipoproteinemia Tipo II/patologia , Leucócitos/citologia , Leucócitos/metabolismo , Lipoproteínas/sangue , Masculino , Pessoa de Meia-Idade , Inquéritos Nutricionais , Fatores de Risco , Triglicerídeos/sangue
6.
PLoS Genet ; 15(4): e1008039, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30970016

RESUMO

The SWI/SNF-family chromatin remodeling protein ATRX is a tumor suppressor in sarcomas, gliomas and other malignancies. Its loss of function facilitates the alternative lengthening of telomeres (ALT) pathway in tumor cells, while it also affects Polycomb repressive complex 2 (PRC2) silencing of its target genes. To further define the role of inactivating ATRX mutations in carcinogenesis, we knocked out atrx in our previously reported p53/nf1-deficient zebrafish line that develops malignant peripheral nerve sheath tumors and gliomas. Complete inactivation of atrx using CRISPR/Cas9 was lethal in developing fish and resulted in an alpha-thalassemia-like phenotype including reduced alpha-globin expression. In p53/nf1-deficient zebrafish neither peripheral nerve sheath tumors nor gliomas showed accelerated onset in atrx+/- fish, but these fish developed various tumors that were not observed in their atrx+/+ siblings, including epithelioid sarcoma, angiosarcoma, undifferentiated pleomorphic sarcoma and rare types of carcinoma. These cancer types are included in the AACR Genie database of human tumors associated with mutant ATRX, indicating that our zebrafish model reliably mimics a role for ATRX-loss in the early pathogenesis of these human cancer types. RNA-seq of p53/nf1- and p53/nf1/atrx-deficient tumors revealed that down-regulation of telomerase accompanied ALT-mediated lengthening of the telomeres in atrx-mutant samples. Moreover, inactivating mutations in atrx disturbed PRC2-target gene silencing, indicating a connection between ATRX loss and PRC2 dysfunction in cancer development.


Assuntos
Sarcoma Experimental/etiologia , Proteína Supressora de Tumor p53/deficiência , Proteína Supressora de Tumor p53/genética , Proteína Nuclear Ligada ao X/deficiência , Proteína Nuclear Ligada ao X/genética , Proteínas de Peixe-Zebra/deficiência , Proteínas de Peixe-Zebra/genética , Animais , Animais Geneticamente Modificados , Sistemas CRISPR-Cas , Carcinogênese/genética , Carcinogênese/metabolismo , Modelos Animais de Doenças , Eritropoese , Feminino , Técnicas de Inativação de Genes , Globinas/genética , Humanos , Mutação com Perda de Função , Masculino , Neurofibromina 1/deficiência , Neurofibromina 1/genética , Sarcoma Experimental/genética , Sarcoma Experimental/metabolismo , Homeostase do Telômero/genética , Peixe-Zebra/embriologia , Peixe-Zebra/genética , Peixe-Zebra/metabolismo
7.
Int J Mol Sci ; 20(5)2019 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-30870992

RESUMO

Mammalian telomere lengths are primarily regulated by telomerase, consisting of a reverse transcriptase protein (TERT) and an RNA subunit (TERC). We previously reported the generation of mouse Terc+/- and Terc-/- embryonic stem cells (ntESCs) by somatic cell nuclear transfer. In the present work, we investigated the germ layer development competence of Terc-/-, Terc+/- and wild-type (Terc+/+) ntESCs. The telomere lengths are longest in wild-type but shortest in Terc-/- ntESCs, and correlate reversely with the population doubling time. Interestingly, while in vitro embryoid body (EB) differentiation assay reveals EB size difference among ntESCs of different genotypes, the more stringent in vivo teratoma assay demonstrates that Terc-/- ntESCs are severely defective in differentiating into the mesodermal lineage cartilage. Consistently, in a directed in vitro chondrocyte differentiation assay, the Terc-/- cells failed in forming Collagen II expressing cells. These findings underscore the significance in maintaining proper telomere lengths in stem cells and their derivatives for regenerative medicine.


Assuntos
Diferenciação Celular/fisiologia , Núcleo Celular/fisiologia , Condrócitos/fisiologia , Células-Tronco Embrionárias Murinas/fisiologia , RNA/genética , Telomerase/genética , Animais , Cartilagem/fisiologia , Diferenciação Celular/genética , Núcleo Celular/genética , Células Cultivadas , Condrogênese/genética , Condrogênese/fisiologia , Células HEK293 , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Técnicas de Transferência Nuclear , Telômero/genética , Homeostase do Telômero/genética , Homeostase do Telômero/fisiologia
8.
Pancreas ; 48(3): 396-399, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30747827

RESUMO

OBJECTIVES: DAXX immunohistochemistry (IHC) is often used as a surrogate for sequencing. We aimed to elucidate the sensitivity of IHC for DAXX mutation. METHODS: All pancreatic neuroendocrine tumors (PanNETs) with DAXX mutations detected by sequencing and a subset of DAXX wild-type PanNETs were analyzed for DAXX expression by IHC. RESULTS: Of 154 PanNETs with MSK-IMPACT testing, 36 (30%) harbored DAXX mutations. DAXX mutations were associated with TSC2 mutations (46% vs 10%, P < 0.0001), tended to co-occur with MEN1 mutations (63% vs 49%, P = 0.11), and tended to be mutually exclusive with ATRX mutations (11% vs 25%, P = 0.053). Of 27 available DAXX mutant PanNETs, 23 lost DAXX expression (85.2%). All 4 DAXX mutants with retained expression harbored DAXX mutations within the SUMO-interacting motif of the last exon. Telomere-specific fluorescence in situ hybridization demonstrated alternative lengthening of telomeres in all 4 cases. Of 20 PanNETs with wild-type DAXX, 19 retained DAXX IHC expression (95%). CONCLUSIONS: The sensitivity and specificity of IHC for DAXX mutation are 85% and 95%, respectively. Last exon DAXX mutant PanNETs often show alternative lengthening of telomeres despite retained DAXX expression, likely due to escape of nonmediated decay.


Assuntos
Proteínas Adaptadoras de Transdução de Sinal/biossíntese , Biomarcadores Tumorais/biossíntese , Mutação , Tumores Neuroendócrinos/metabolismo , Proteínas Nucleares/biossíntese , Neoplasias Pancreáticas/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Biomarcadores Tumorais/genética , Análise Mutacional de DNA , Humanos , Imuno-Histoquímica , Hibridização in Situ Fluorescente , Tumores Neuroendócrinos/diagnóstico , Tumores Neuroendócrinos/genética , Proteínas Nucleares/genética , Neoplasias Pancreáticas/diagnóstico , Neoplasias Pancreáticas/genética , Estudos Retrospectivos , Homeostase do Telômero/genética , Proteína Nuclear Ligada ao X/biossíntese , Proteína Nuclear Ligada ao X/genética
9.
PLoS Genet ; 15(2): e1007925, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30716077

RESUMO

Telomerase-independent ALT (alternative lengthening of telomeres) cells are characterized by high frequency of telomeric homologous recombination (HR), C-rich extrachromosomal circles (C-circles) and C-rich terminal 5' overhangs (C-overhangs). However, underlying mechanism is poorly understood. Here, we show that both C-circle and C-overhang form when replication fork collapse is induced by strand break at telomeres. We find that endogenous DNA break predominantly occur on C-rich strand of telomeres in ALT cells, resulting in high frequency of replication fork collapse. While collapsed forks could be rescued by replication fork regression leading to telomeric homologous recombination, those unresolved are converted to C-circles and C-overhang at lagging and leading synthesized strand, respectively. Meanwhile, multiple hallmarks of ALT are provoked, suggesting that strand break-induced replication stress underlies ALT. These findings provide a molecular basis underlying telomeric HR and biogenesis of C-circle and C-overhang, thus implicating the specific mechanism to resolve strand break-induced replication defect at telomeres in ALT cells.


Assuntos
Replicação do DNA/genética , Recombinação Genética/genética , Telômero/genética , Linhagem Celular , Estruturas Cromossômicas/genética , DNA/genética , Reparo do DNA/genética , Humanos , Telomerase/genética , Homeostase do Telômero/genética
10.
Gene ; 694: 97-101, 2019 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-30738962

RESUMO

BACKGROUND: Previous studies indicate that low birth weight and exposure to maternal stress during pregnancy may result in shortened telomeres in infants. Shorter telomere length has in turn been linked with accelerated ageing and with age-related diseases. This study aimed to investigate the association between pregnancy and birth factors and relative telomere length in offspring at 11 years of age. METHODS: Participants were aged 11 years enrolled in the Auckland Birthweight Collaborative Study at birth (n = 380). Half of the children were born small for gestational age (SGA = birthweight ≤ 10th percentile) and half were appropriate for gestational age (AGA = birthweight > 10th percentile). Maternal stress during pregnancy was assessed using the Perceived Stress Scale. Relative leukocyte telomere length (RTL) in leukocytes was measured at 11 years of age using quantitative real-time PCR. RESULTS: RTL was normally distributed (mean = 3.78, SD = 1.05). There were no significant associations between RTL at age 11 years and birthweight, sex, maternal smoking, maternal stress during pregnancy or maternal pre-pregnancy body mass index. CONCLUSION: At age 11 years, RTL did not differ between children by birthweight or pregnancy-related stressors. Further telomere-related studies in newborns, children and adolescents are merited to increase knowledge of potential telomere modulating factors.


Assuntos
Peso ao Nascer/genética , Estresse Psicológico/genética , Homeostase do Telômero/genética , Adulto , Peso ao Nascer/fisiologia , Índice de Massa Corporal , Criança , Feminino , Idade Gestacional , Humanos , Recém-Nascido , Recém-Nascido Pequeno para a Idade Gestacional/metabolismo , Leucócitos , Masculino , Herança Materna/genética , Gravidez , Efeitos Tardios da Exposição Pré-Natal/genética , Estresse Psicológico/metabolismo , Telômero/genética , Encurtamento do Telômero/genética
11.
Nucleic Acids Res ; 47(4): 1896-1907, 2019 02 28.
Artigo em Inglês | MEDLINE | ID: mdl-30629181

RESUMO

Telomeres are nucleoprotein structures at the ends of linear chromosomes and present an essential feature for genome integrity. Vertebrate telomeres usually consist of hexameric TTAGGG repeats, however, in cells that use the alternative lengthening of telomeres (ALT) mechanism, variant repeat sequences are interspersed throughout telomeres. Previously, it was shown that NR2C/F transcription factors bind to TCAGGG variant repeats and contribute to telomere maintenance in ALT cells. While specific binders to other variant repeat sequences have been lacking to date, we here identify ZBTB10 as the first TTGGGG-binding protein and demonstrate direct binding via the two zinc fingers with affinity in the nanomolar range. Concomitantly, ZBTB10 co-localizes with a subset of telomeres in ALT-positive U2OS cells and interacts with TRF2/RAP1 via the N-terminal region of TRF2. Our data establishes ZBTB10 as a novel variant repeat binding protein at ALT telomeres.


Assuntos
Proteínas Repressoras/genética , Homeostase do Telômero/genética , Telômero/genética , Proteína 2 de Ligação a Repetições Teloméricas/genética , Sítios de Ligação/genética , Cromossomos/genética , Proteínas de Ligação a DNA/genética , Genoma/genética , Humanos , Ligação Proteica/genética , Sequências Repetitivas de Ácido Nucleico/genética , Proteínas de Ligação a Telômeros/genética
12.
Genes Dev ; 33(3-4): 221-235, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30692206

RESUMO

Approximately 15% of cancers use homologous recombination for alternative lengthening of telomeres (ALT). How the initiating genomic lesions invoke homology-directed telomere synthesis remains enigmatic. Here, we show that distinct dependencies exist for telomere synthesis in response to replication stress or DNA double-strand breaks (DSBs). RAD52 deficiency reduced spontaneous telomeric DNA synthesis and replication stress-associated recombination in G2, concomitant with telomere shortening and damage. However, viability and proliferation remained unaffected, suggesting that alternative telomere recombination mechanisms compensate in the absence of RAD52. In agreement, RAD52 was dispensable for DSB-induced telomere synthesis. Moreover, a targeted CRISPR screen revealed that loss of the structure-specific endonuclease scaffold SLX4 reduced the proliferation of RAD52-null ALT cells. While SLX4 was dispensable for RAD52-mediated ALT telomere synthesis in G2, combined SLX4 and RAD52 loss resulted in elevated telomere loss, unresolved telomere recombination intermediates, and mitotic infidelity. These findings establish that RAD52 and SLX4 mediate distinct postreplicative DNA repair processes that maintain ALT telomere stability and cancer cell viability.


Assuntos
Proteína Rad52 de Recombinação e Reparo de DNA/metabolismo , Recombinases/metabolismo , Homeostase do Telômero/genética , Linhagem Celular Tumoral , Quebras de DNA de Cadeia Dupla , Técnicas de Inativação de Genes , Instabilidade Genômica/genética , Células HEK293 , Células HeLa , Humanos , Interfase , Proteína Rad52 de Recombinação e Reparo de DNA/genética , Recombinases/genética
13.
J Exp Clin Cancer Res ; 38(1): 21, 2019 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-30654820

RESUMO

Telomeres, the nucleoprotein structures that cap the ends of eukaryotic chromosomes, play important and multiple roles in tumorigenesis. Functional telomeres need the establishment of a protective chromatin structure based on the interplay between the specific complex named shelterin and a tight nucleosomal organization. Telomere shortening in duplicating somatic cells leads eventually to the destabilization of the telomere capping structure and to the activation of a DNA damage response (DDR) signaling. The final outcome of this process is cell replicative senescence, which constitute a protective barrier against unlimited proliferation. Cells that can bypass senescence checkpoint continue to divide until a second replicative checkpoint, crisis, characterized by chromosome fusions and rearrangements leading to massive cell death by apoptosis. During crisis telomere dysfunctions can either inhibit cell replication or favor tumorigenesis by the accumulation of chromosomal rearrangements and neoplastic mutations. The acquirement of a telomere maintenance mechanism allows fixing the aberrant phenotype, and gives the neoplastic cell unlimited replicative potential, one of the main hallmarks of cancer.Despite the crucial role that telomeres play in cancer development, little is known about the epigenetic alterations of telomeric chromatin that affect telomere protection and are associated with tumorigenesis. Here we discuss the current knowledge on the role of telomeric chromatin in neoplastic transformation, with a particular focus on H3.3 mutations in alternative lengthening of telomeres (ALT) cancers and sirtuin deacetylases dysfunctions.


Assuntos
Cromatina/genética , Variação Genética , Neoplasias/genética , Telômero/genética , Animais , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Cromatina/metabolismo , Dano ao DNA , Epigênese Genética , Heterocromatina/genética , Heterocromatina/metabolismo , Humanos , Neoplasias/metabolismo , Neoplasias/patologia , Neoplasias/terapia , Sirtuínas/metabolismo , Homeostase do Telômero/genética
14.
Psychoneuroendocrinology ; 99: 271-278, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30343983

RESUMO

Research in the last decade has explored the length of telomeres, the protective ends of eukaryotic chromosomes, as a biomarker for the cumulative effects of environmental exposures and life experiences as well as a risk factor for major diseases. With a growing interest in telomere biology across biomedical, epidemiological and public health research, it is critical to ensure that the measurement of telomere length is performed with high precision and accuracy. Of the several major methods utilized to determine telomere length, quantitative PCR (qPCR) remains the most cost-effective and suitable method for large-scale epidemiological and population studies. However, inconsistencies in recent reports utilizing the qPCR method highlight the need for a careful methodological analysis of each step of this process. In this review, we summarize each critical step in qPCR telomere length assay, including sample type selection, sample collection, storage, processing issues and assay procedures. We provide guidance and recommendations for each step based on current knowledge. It is clear that a collaborative and rigorous effort is needed to characterize and resolve existing issues related to sample storage, both before and after DNA extraction, as well as the impact of different extraction protocols, reagents and post extraction processing across all tissue types (e.g. blood, saliva, buccal swabs, etc.) to provide the needed data upon which best practices for TL analyses can be agreed upon. Additionally, we suggest that the whole telomere research community be invited to collaborate on the development and implementation of standardized protocols for the assay itself as well as for reporting in scientific journals. The existing evidence provides substantial support for the continuation of telomere research across a range of different exposures and health outcomes. However, as with any technological or methodologic advance in science, reproducibility, reliability and rigor need to be established to ensure the highest quality research.


Assuntos
Reação em Cadeia da Polimerase em Tempo Real/métodos , Manejo de Espécimes/métodos , Homeostase do Telômero/fisiologia , Humanos , Reação em Cadeia da Polimerase em Tempo Real/normas , Padrões de Referência , Reprodutibilidade dos Testes , Manejo de Espécimes/normas , Telômero/fisiologia , Homeostase do Telômero/genética
15.
Genes Dev ; 32(9-10): 658-669, 2018 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-29773556

RESUMO

Telomerase counteracts telomere shortening and cellular senescence in germ, stem, and cancer cells by adding repetitive DNA sequences to the ends of chromosomes. Telomeres are susceptible to damage by reactive oxygen species (ROS), but the consequences of oxidation of telomeres on telomere length and the mechanisms that protect from ROS-mediated telomere damage are not well understood. In particular, 8-oxoguanine nucleotides at 3' ends of telomeric substrates inhibit telomerase in vitro, whereas, at internal positions, they suppress G-quadruplex formation and were therefore proposed to promote telomerase activity. Here, we disrupt the peroxiredoxin 1 (PRDX1) and 7,8-dihydro-8-oxoguanine triphosphatase (MTH1) genes in cancer cells and demonstrate that PRDX1 and MTH1 cooperate to prevent accumulation of oxidized guanine in the genome. Concomitant disruption of PRDX1 and MTH1 leads to ROS concentration-dependent continuous shortening of telomeres, which is due to efficient inhibition of telomere extension by telomerase. Our results identify antioxidant systems that are required to protect telomeres from oxidation and are necessary to allow telomere maintenance by telomerase conferring immortality to cancer cells.


Assuntos
Enzimas Reparadoras do DNA/metabolismo , Peroxirredoxinas/metabolismo , Monoéster Fosfórico Hidrolases/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Telomerase/metabolismo , Encurtamento do Telômero/genética , Dano ao DNA/genética , Enzimas Reparadoras do DNA/genética , Ativação Enzimática/genética , Técnicas de Inativação de Genes , Genoma , Guanina/metabolismo , Células HCT116 , Humanos , Oxirredução , Estresse Oxidativo/genética , Monoéster Fosfórico Hidrolases/genética , Telomerase/antagonistas & inibidores , Homeostase do Telômero/genética
16.
Artigo em Inglês | MEDLINE | ID: mdl-29694602

RESUMO

OBJECTIVE: We evaluated the association between cognitive deficits and leukocyte telomere length (LTL) in HIV-1-infected individuals. DESIGN: 73 HIV-1-infected patients undergoing neuropsychological evaluation and 91 healthy controls were included in this study. Fifteen HIV-1 positive patients did not have cognitive disorders whereas 26 had asymptomatic neurocognitive disorder (ANI), 13 presented mild to moderate neurocognitive disorder (MND), and 10 had HIV-associated dementia (HAD). METHODS: DNA from the peripheral blood of HIV-1-infected patients was used for measurement of telomere length by real-time PCR. HIV-1 viral load was determined in blood. RESULTS: LTL decreased with age in healthy controls (p=0.0001). Regardless of the HIV status, age-matched LTL from HIV patients, including those with ANI and MND, were shortened in comparison to the healthy control group (p=0.0073); however, no association was found among the HIV-1-infected individuals with cognitive deficits (p=0.01). In addition, no gender-related association with LTL was observed (p=0.80), smoking, physical exercise, and plasma viral load were not correlated to telomere length (p=0.66). CONCLUSIONS: We concluded that leukocyte telomere length may not be a marker of cellular senescence in individuals with HIV infection and neurocognitive disorders.


Assuntos
Infecções por HIV/genética , Infecções por HIV/psicologia , HIV-1 , Transtornos Neurocognitivos/genética , Transtornos Neurocognitivos/virologia , Homeostase do Telômero/genética , Telômero/genética , Fatores Etários , Análise de Variância , Estudos de Casos e Controles , Feminino , Humanos , Leucócitos/virologia , Masculino , Pessoa de Meia-Idade , Testes Neuropsicológicos , Reação em Cadeia da Polimerase em Tempo Real , Valores de Referência , Estatísticas não Paramétricas , Inquéritos e Questionários , Carga Viral
17.
Plant Cell Rep ; 37(3): 501-513, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29392401

RESUMO

KEY MESSAGE: Prolonged hypomethylation of DNA leads to telomere truncation correlated with increased telomere recombination, transposon mobilization and stem cell death. Epigenetic pathways, including DNA methylation, are crucial for telomere maintenance. Deficient in DNA Methylation 1 (DDM1) encodes a nucleosome remodeling protein, required to maintain DNA methylation in Arabidopsis thaliana. Plants lacking DDM1 can be self-propagated, but in the sixth generation (G6) hypomethylation leads to rampant transposon activation and infertility. Here we examine the role of DDM1 in telomere length homeostasis through a longitudinal study of successive generations of ddm1-2 mutants. We report that bulk telomere length remains within the wild-type range for the first five generations (G1-G5), and then precipitously drops in G6. While telomerase activity becomes more variable in later generation ddm1-2 mutants, there is no correlation between enzyme activity and telomere length. Plants lacking DDM1 also exhibit no dysregulation of several known telomere-associated transcripts, including TERRA. Instead, telomere shortening coincides with increased G-overhangs and extra-chromosomal circles, consistent with deletional recombination. Telomere shortening also correlates with transcriptional activation of retrotransposons, and a hypersensitive DNA damage response in root apical meristems. Since abiotic stresses, including DNA damage, stimulate homologous recombination, we hypothesize that telomere deletion in G6 ddm1-2 mutants is a by-product of elevated genome-wide recombination in response to transposon mobilization. Further, we speculate that telomere truncation may be beneficial in adverse environmental conditions by accelerating the elimination of stem cells with aberrant genomes.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Proteínas de Ligação a DNA/genética , Mutação , Telômero/genética , Fatores de Transcrição/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Dano ao DNA , Metilação de DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica de Plantas , Retroelementos/genética , Telômero/metabolismo , Homeostase do Telômero/genética , Fatores de Tempo , Fatores de Transcrição/metabolismo
18.
Curr Genet ; 64(4): 901-905, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-29392410

RESUMO

Telomere maintenance mechanism is poorly studied in quiescence, a reversible non-proliferative state. We previously described in fission yeast a new mode of repair of telomeres named STEEx, that specifically operates in post-mitotic cells harboring eroded telomeres. This mechanism, promoted by transcription-induced telomeric recombination, prevents cells to exit properly from quiescence, suggesting that STEEx act as an anti-proliferative barrier. Here, we further showed that STEEx are genetically controlled by the Tel1ATM- and Rad3ATR- dependent DDR pathways. We discussed the possibility that STEEx represent a boundary between quiescence and vegetative cycle.


Assuntos
Ciclo Celular/genética , Schizosaccharomyces/genética , Homeostase do Telômero/genética , Telômero/genética , Proteínas de Ciclo Celular/genética , Divisão Celular/genética , Mutação , Fosforilação , Proteínas Quinases/genética , Telomerase/genética
19.
Pancreas ; 47(3): 265-271, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29424808

RESUMO

Many risk factors have been firmly established for pancreatic cancer (PC), but the molecular processes by which known risk factors influence susceptibility to PC are not clear. There has been a recent upsurge of interest in the role of telomere length (TL), the protective DNA sequence repeats at chromosome ends, in pancreatic carcinogenesis. Given this heightened interest, we performed an in-depth, focused, and up-to-date review of the epidemiological evidence linking leukocyte TL (LTL) with PC risk. We searched MEDLINE, Embase, and the Cochrane Library databases for all published studies on LTL and PC risk, up to May 2017. Five studies were identified for review: 4 nested case-control studies and 1 retrospective case-control study. Two studies found opposite associations between LTL and PC risk: 1 found a dose-response positive association and the other found a dose-response inverse association. Two studies also found a "U-shaped" association, whereas another reported a weak nonlinear relationship. We offer potential reasons for the conflicting findings including variation in study design, biospecimen characteristics, and differences in interlaboratory measurements of TL. Future studies should carefully control for risk factors of PC that are associated also with telomere attrition and investigate the role of genetic variation in TL maintenance.


Assuntos
Leucócitos/metabolismo , Neoplasias Pancreáticas/genética , Homeostase do Telômero/genética , Telômero/genética , Humanos , Neoplasias Pancreáticas/epidemiologia , Medição de Risco/métodos , Medição de Risco/estatística & dados numéricos , Fatores de Risco
20.
Int J Mol Sci ; 19(1)2018 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-29351238

RESUMO

Telomeres facilitate the protection of natural ends of chromosomes from constitutive exposure to the DNA damage response (DDR). This is most likely achieved by a lariat structure that hides the linear telomeric DNA through protein-protein and protein-DNA interactions. The telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in unmasked telomeres. Then, the subsequent activation of the DDR will define the fate of cells according to the functionality of cell cycle checkpoints. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptotic pathways, but they can also promote tumour initiation. Studies in telomere dynamics and karyotype analysis underpin telomere crisis as a key event driving genomic instability. Significant attainment of telomerase or alternative lengthening of telomeres (ALT)-pathway to maintain telomere length may be permissive and required for clonal evolution of genomically-unstable cells during progression to malignancy. We summarise current knowledge of the role of telomeres in the maintenance of chromosomal stability and carcinogenesis.


Assuntos
Carcinogênese/genética , Neoplasias/genética , Telômero/genética , Apoptose/genética , Senescência Celular/genética , Instabilidade Cromossômica/genética , Instabilidade Genômica/genética , Humanos , Telomerase/genética , Homeostase do Telômero/genética
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