Articles de revues : « Telomere protection »

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Hsu, Joseph K., Tao Lin et Robert Y. L. Tsai. « Nucleostemin prevents telomere damage by promoting PML-IV recruitment to SUMOylated TRF1 ». Journal of Cell Biology 197, n^o 5 (28 mai 2012) : 613–24. http://dx.doi.org/10.1083/jcb.201109038.

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Continuously dividing cells must be protected from telomeric and nontelomeric DNA damage in order to maintain their proliferative potential. Here, we report a novel telomere-protecting mechanism regulated by nucleostemin (NS). NS depletion increased the number of telomere damage foci in both telomerase-active (TA+) and alternative lengthening of telomere (ALT) cells and decreased the percentage of damaged telomeres associated with ALT-associated PML bodies (APB) and the number of APB in ALT cells. Mechanistically, NS could promote the recruitment of PML-IV to SUMOylated TRF1 in TA+ and ALT cells. This event was stimulated by DNA damage. Supporting the importance of NS and PML-IV in telomere protection, we demonstrate that loss of NS or PML-IV increased the frequency of telomere damage and aberration, reduced telomeric length, and perturbed the TRF2ΔBΔM-induced telomeric recruitment of RAD51. Conversely, overexpression of either NS or PML-IV protected ALT and TA+ cells from telomere damage. This work reveals a novel mechanism in telomere protection.

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Bunch, Jeremy T., Nancy S. Bae, Jessica Leonardi et Peter Baumann. « Distinct Requirements for Pot1 in Limiting Telomere Length and Maintaining Chromosome Stability ». Molecular and Cellular Biology 25, n^o 13 (1 juillet 2005) : 5567–78. http://dx.doi.org/10.1128/mcb.25.13.5567-5578.2005.

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ABSTRACT The fission yeast Pot1 (protection of telomeres) protein binds to the single-stranded extensions at the ends of telomeres, where its presence is critical for the maintenance of linear chromosomes. Homologs of Pot1 have been identified in a wide variety of eukaryotes, including plants, animals, and humans. We now show that Pot1 plays dual roles in telomere length regulation and chromosome end protection. Using a series of Pot1 truncation mutants, we have defined distinct areas of the protein required for chromosome stability and for limiting access to telomere ends by telomerase. We provide evidence that a large portion of Pot1, including the N-terminal DNA binding domain and amino acids close to the C terminus, is essential for its protective function. C-terminal Pot1 fragments were found to exert a dominant-negative effect by displacing endogenous Pot1 from telomeres. Reducing telomere-bound Pot1 in this manner resulted in dramatic lengthening of the telomere tract. Upon further reduction of Pot1 at telomeres, the opposite phenotype was observed: loss of telomeric DNA and chromosome end fusions. Our results demonstrate that cells must carefully regulate the amount of telomere-bound Pot1 to differentiate between allowing access to telomerase and catastrophic loss of telomeres.

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Mattern, Karin A., Susan J. J. Swiggers, Alex L. Nigg, Bob Löwenberg, Adriaan B. Houtsmuller et J. Mark J. M. Zijlmans. « Dynamics of Protein Binding to Telomeres in Living Cells : Implications for Telomere Structure and Function ». Molecular and Cellular Biology 24, n^o 12 (15 juin 2004) : 5587–94. http://dx.doi.org/10.1128/mcb.24.12.5587-5594.2004.

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ABSTRACT Telomeric proteins have an essential role in the regulation of the length of the telomeric DNA tract and in protection against end-to-end chromosome fusion. Telomere organization and how individual proteins are involved in different telomere functions in living cells is largely unknown. By using green fluorescent protein tagging and photobleaching, we investigated in vivo interactions of human telomeric DNA-binding proteins with telomeric DNA. Our results show that telomeric proteins interact with telomeres in a complex dynamic fashion: TRF2, which has a dual role in chromosome end protection and telomere length homeostasis, resides at telomeres in two distinct pools. One fraction (∼73%) has binding dynamics similar to TRF1 (residence time of ∼44 s). Interestingly, the other fraction of TRF2 binds with similar dynamics as the putative end-protecting factor hPOT1 (residence time of ∼11 min). Our data support a dynamic model of telomeres in which chromosome end-protection and telomere length homeostasis are governed by differential binding of telomeric proteins to telomeric DNA.

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Kelleher, Colleen, Isabel Kurth et Joachim Lingner. « Human Protection of Telomeres 1 (POT1) Is a Negative Regulator of Telomerase Activity In Vitro ». Molecular and Cellular Biology 25, n^o 2 (15 janvier 2005) : 808–18. http://dx.doi.org/10.1128/mcb.25.2.808-818.2005.

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ABSTRACT The telomeric single-strand DNA binding protein protection of telomeres 1 (POT1) protects telomeres from rapid degradation in Schizosaccharomyces pombe and has been implicated in positive and negative telomere length regulation in humans. Human POT1 appears to interact with telomeres both through direct binding to the 3′ overhanging G-strand DNA and through interaction with the TRF1 duplex telomere DNA binding complex. The influence of POT1 on telomerase activity has not been studied at the molecular level. We show here that POT1 negatively effects telomerase activity in vitro. We find that the DNA binding activity of POT1 is required for telomerase inhibition. Furthermore, POT1 is incapable of inhibiting telomeric repeat addition to substrate primers that are defective for POT1 binding, suggesting that in vivo, POT1 likely affects substrate access to telomerase.

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Smogorzewska, Agata, Bas van Steensel, Alessandro Bianchi, Stefan Oelmann, Matthias R. Schaefer, Gisela Schnapp et Titia de Lange. « Control of Human Telomere Length by TRF1 and TRF2 ». Molecular and Cellular Biology 20, n^o 5 (1 mars 2000) : 1659–68. http://dx.doi.org/10.1128/mcb.20.5.1659-1668.2000.

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ABSTRACT Telomere length in human cells is controlled by a homeostasis mechanism that involves telomerase and the negative regulator of telomere length, TRF1 (TTAGGG repeat binding factor 1). Here we report that TRF2, a TRF1-related protein previously implicated in protection of chromosome ends, is a second negative regulator of telomere length. Overexpression of TRF2 results in the progressive shortening of telomere length, similar to the phenotype observed with TRF1. However, while induction of TRF1 could be maintained over more than 300 population doublings and resulted in stable, short telomeres, the expression of exogenous TRF2 was extinguished and the telomeres eventually regained their original length. Consistent with their role in measuring telomere length, indirect immunofluorescence indicated that both TRF1 and TRF2 bind to duplex telomeric DNA in vivo and are more abundant on telomeres with long TTAGGG repeat tracts. Neither TRF1 nor TRF2 affected the expression level of telomerase. Furthermore, the presence of TRF1 or TRF2 on a short linear telomerase substrate did not inhibit the enzymatic activity of telomerase in vitro. These findings are consistent with the recently proposed t loop model of telomere length homeostasis in which telomerase-dependent telomere elongation is blocked by sequestration of the 3′ telomere terminus in TRF1- and TRF2-induced telomeric loops.

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Kibe, Tatsuya, Yuuki Ono, Koichiro Sato et Masaru Ueno. « Fission Yeast Taz1 and RPA Are Synergistically Required to Prevent Rapid Telomere Loss ». Molecular Biology of the Cell 18, n^o 6 (juin 2007) : 2378–87. http://dx.doi.org/10.1091/mbc.e06-12-1084.

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The telomere complex must allow nucleases and helicases to process chromosome ends to make them substrates for telomerase, while preventing these same activities from disrupting chromosome end-protection. Replication protein A (RPA) binds to single-stranded DNA and is required for DNA replication, recombination, repair, and telomere maintenance. In fission yeast, the telomere binding protein Taz1 protects telomeres and negatively regulates telomerase. Here, we show that taz1-d rad11-D223Y double mutants lose their telomeric DNA, indicating that RPA (Rad11) and Taz1 are synergistically required to prevent telomere loss. Telomere loss in the taz1-d rad11-D223Y double mutants was suppressed by additional mutation of the helicase domain in a RecQ helicase (Rqh1), or by overexpression of Pot1, a single-strand telomere binding protein that is essential for protection of chromosome ends. From our results, we propose that in the absence of Taz1 and functional RPA, Pot1 cannot function properly and the helicase activity of Rqh1 promotes telomere loss. Our results suggest that controlling the activity of Rqh1 at telomeres is critical for the prevention of genomic instability.

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Fernandes, Stina George, Rebecca Dsouza, Gouri Pandya, Anuradha Kirtonia, Vinay Tergaonkar, Sook Y. Lee, Manoj Garg et Ekta Khattar. « Role of Telomeres and Telomeric Proteins in Human Malignancies and Their Therapeutic Potential ». Cancers 12, n^o 7 (14 juillet 2020) : 1901. http://dx.doi.org/10.3390/cancers12071901.

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Telomeres are the ends of linear chromosomes comprised of repetitive nucleotide sequences in humans. Telomeres preserve chromosomal stability and genomic integrity. Telomere length shortens with every cell division in somatic cells, eventually resulting in replicative senescence once telomere length becomes critically short. Telomere shortening can be overcome by telomerase enzyme activity that is undetectable in somatic cells, while being active in germline cells, stem cells, and immune cells. Telomeres are bound by a shelterin complex that regulates telomere lengthening as well as protects them from being identified as DNA damage sites. Telomeres are transcribed by RNA polymerase II, and generate a long noncoding RNA called telomeric repeat-containing RNA (TERRA), which plays a key role in regulating subtelomeric gene expression. Replicative immortality and genome instability are hallmarks of cancer and to attain them cancer cells exploit telomere maintenance and telomere protection mechanisms. Thus, understanding the role of telomeres and their associated proteins in cancer initiation, progression and treatment is very important. The present review highlights the critical role of various telomeric components with recently established functions in cancer. Further, current strategies to target various telomeric components including human telomerase reverse transcriptase (hTERT) as a therapeutic approach in human malignancies are discussed.

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Donate, Luis E., et Maria A. Blasco. « Telomeres in cancer and ageing ». Philosophical Transactions of the Royal Society B : Biological Sciences 366, n^o 1561 (12 janvier 2011) : 76–84. http://dx.doi.org/10.1098/rstb.2010.0291.

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Telomeres protect the chromosome ends from unscheduled DNA repair and degradation. Telomeres are heterochromatic domains composed of repetitive DNA (TTAGGG repeats) bound to an array of specialized proteins. The length of telomere repeats and the integrity of telomere-binding proteins are both important for telomere protection. Furthermore, telomere length and integrity are regulated by a number of epigenetic modifications, thus pointing to higher order control of telomere function. In this regard, we have recently discovered that telomeres are transcribed generating long, non-coding RNAs, which remain associated with the telomeric chromatin and are likely to have important roles in telomere regulation. In the past, we showed that telomere length and the catalytic component of telomerase, Tert, are critical determinants for the mobilization of stem cells. These effects of telomerase and telomere length on stem cell behaviour anticipate the premature ageing and cancer phenotypes of telomerase mutant mice. Recently, we have demonstrated the anti-ageing activity of telomerase by forcing telomerase expression in mice with augmented cancer resistance. Shelterin is the major protein complex bound to mammalian telomeres; however, its potential relevance for cancer and ageing remained unaddressed to date. To this end, we have generated mice conditionally deleted for the shelterin proteins TRF1, TPP1 and Rap1. The study of these mice demonstrates that telomere dysfunction, even if telomeres are of a normal length, is sufficient to produce premature tissue degeneration, acquisition of chromosomal aberrations and initiation of neoplastic lesions. These new mouse models, together with the telomerase-deficient mouse model, are valuable tools for understanding human pathologies produced by telomere dysfunction.

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Calado, Rodrigo T. « Telomeres and marrow failure ». Hematology 2009, n^o 1 (1 janvier 2009) : 338–43. http://dx.doi.org/10.1182/asheducation-2009.1.338.

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AbstractTelomeres, repeat sequences at the ends of chromosomes, are protective chromosomal structures highly conserved from primitive organisms to humans. Telomeres inevitably shorten with every cell cycle, and telomere attrition has been hypothesized to be fundamental to normal senescence of cells, tissues, and organisms. Molecular mechanisms have evolved to maintain their length and protective function; telomerase (TERT) is a reverse transcriptase enzyme that uses an RNA molecule (TERC) as the template to elongate the 3′ ends of telomeres. Shelterin is a collection of DNA-binding proteins that cover and protect telomeres. The recent discovery of inherited mutations in genes that function to repair telomeres as etiologic in a range of human diseases, which have clinical manifestations in diverse tissues, including the hematopoietic tissue, suggests that defects in telomere repair and protection can cause organ failure. Dyskeratosis congenita is the prototype of telomere diseases; it is characterized by bone marrow failure, mucocutaneous abnormalities, pulmonary fibrosis, liver cirrhosis, and increased susceptibility to cancer, including acute myeloid leukemia. Aplastic anemia, acute myeloid leukemia, and idiopathic pulmonary fibrosis also are associated with inherited mutations in telomere repair or protection genes. Additionally, telomere defects associate with predisposition to hematologic malignancy and epithelial tumors. Telomere erosion is abnormally rapid in patients with mutations in telomerase genes but also after hematopoietic stem cell transplant, and telomeres are naturally shorter in older individuals—all conditions associated with higher rates of malignant diseases. In human tissue culture, short telomeres produce end-to-end chromosome fusion, nonreciprocal translocations, and aneuploidy.

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Maddar, Haggar, Nir Ratzkovsky et Anat Krauskopf. « Role for Telomere Cap Structure in Meiosis ». Molecular Biology of the Cell 12, n^o 10 (octobre 2001) : 3191–203. http://dx.doi.org/10.1091/mbc.12.10.3191.

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Telomeres, the natural ends of eukaryotic chromosomes, are essential for the protection of chromosomes from end-to-end fusions, recombination, and shortening. Here we explore their role in the process of meiotic division in the budding yeast, Kluyveromyces lactis. Telomerase RNA mutants that cause unusually long telomeres with deregulated structure led to severely defective meiosis. The severity of the meiotic phenotype of two mutants correlated with the degree of loss of binding of the telomere binding protein Rap1p. We show that telomere size and the extent of potential Rap1p binding to the entire telomere are irrelevant to the process of meiosis. Moreover, we demonstrate that extreme difference in telomere size between two homologous chromosomes is compatible with the normal function of telomeres during meiosis. In contrast, the structure of the most terminal telomeric repeats is critical for normal meiosis. Our results demonstrate that telomeres play a critical role during meiotic division and that their terminal cap structure is essential for this role.

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Fan, Hueng-Chuen, Fung-Wei Chang, Jeng-Dau Tsai, Kao-Min Lin, Chuan-Mu Chen, Shinn-Zong Lin, Ching-Ann Liu et Horng-Jyh Harn. « Telomeres and Cancer ». Life 11, n^o 12 (16 décembre 2021) : 1405. http://dx.doi.org/10.3390/life11121405.

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Telomeres cap the ends of eukaryotic chromosomes and are indispensable chromatin structures for genome protection and replication. Telomere length maintenance has been attributed to several functional modulators, including telomerase, the shelterin complex, and the CST complex, synergizing with DNA replication, repair, and the RNA metabolism pathway components. As dysfunctional telomere maintenance and telomerase activation are associated with several human diseases, including cancer, the molecular mechanisms behind telomere length regulation and protection need particular emphasis. Cancer cells exhibit telomerase activation, enabling replicative immortality. Telomerase reverse transcriptase (TERT) activation is involved in cancer development through diverse activities other than mediating telomere elongation. This review describes the telomere functions, the role of functional modulators, the implications in cancer development, and the future therapeutic opportunities.

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DuBois, Michelle L., Zara W. Haimberger, Martin W. McIntosh et Daniel E. Gottschling. « A Quantitative Assay for Telomere Protection in Saccharomyces cerevisiae ». Genetics 161, n^o 3 (1 juillet 2002) : 995–1013. http://dx.doi.org/10.1093/genetics/161.3.995.

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Abstract Telomeres are the protective ends of linear chromosomes. Telomeric components have been identified and described by their abilities to bind telomeric DNA, affect telomere repeat length, participate in telomeric DNA replication, or modulate transcriptional silencing of telomere-adjacent genes; however, their roles in chromosome end protection are not as well defined. We have developed a genetic, quantitative assay in Saccharomyces cerevisiae to measure whether various telomeric components protect chromosome ends from homologous recombination. This “chromosomal cap” assay has revealed that the telomeric end-binding proteins, Cdc13p and Ku, both protect the chromosome end from homologous recombination, as does the ATM-related kinase, Tel1p. We propose that Cdc13p and Ku structurally inhibit recombination at telomeres and that Tel1p regulates the chromosomal cap, acting through Cdc13p. Analysis with recombination mutants indicated that telomeric homologous recombination events proceeded by different mechanisms, depending on which capping component was compromised. Furthermore, we found that neither telomere repeat length nor telomeric silencing correlated with chromosomal capping efficiency. This capping assay provides a sensitive in vivo approach for identifying the components of chromosome ends and the mechanisms by which they are protected.

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Ray, Alo, et Kurt W. Runge. « The C Terminus of the Major Yeast Telomere Binding Protein Rap1p Enhances Telomere Formation ». Molecular and Cellular Biology 18, n^o 3 (1 mars 1998) : 1284–95. http://dx.doi.org/10.1128/mcb.18.3.1284.

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ABSTRACT The telomeres of most organisms consist of short repeated sequences that can be elongated by telomerase, a reverse transcriptase complex that contains its own RNA template for the synthesis of telomere repeats. In Saccharomyces cerevisiae, the RAP1gene encodes the major telomere binding protein Rap1p. Here we use a quantitative telomere formation assay to demonstrate that Rap1p C termini can enhance telomere formation more than 30-fold when they are located at internal sites. This stimulation is distinct from protection from degradation. Enhancement of formation required the gene for telomerase RNA but not Sir1p, Sir2p, Sir3p, Sir4p, Tel1p, or the Rif1p binding site in the Rap1p C terminus. Our data suggest that Rap1p C termini enhance telomere formation by attracting or increasing the activity of telomerase near telomeres. Earlier work suggests that Rap1p molecules at the chromosome terminus inhibit the elongation of long telomeres by blocking the access of telomerase. Our results suggest a model where a balance between internal Rap1p increasing telomerase activity and Rap1p at the termini of long telomeres controlling telomerase access maintains telomeres at a constant length.

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Swiggers, Susan J. J., Marianne A. Kuijpers, Maartje J. de Cort, Berna Beverloo et J. Mark J. M. Zijlmans. « Extensive Chromosome Instability in Acute Myeloid Leukemia Is Associated with Critical Telomere Shortening. » Blood 104, n^o 11 (16 novembre 2004) : 3376. http://dx.doi.org/10.1182/blood.v104.11.3376.3376.

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Abstract Telomeres, the ends of linear chromosomes, have a critical role in protection against chromosome end-to-end fusion. Telomeres shorten in every cell division due to the end replication problem. Telomerase is a reverse transcriptase that adds telomeric DNA repeats to the ultimate chromosome end. In vitro models of long-term fibroblast cultures have identified two sequential mortality stages, senescence (M1) and crisis (M2). Senescence can be bypassed by loss of p53 or Rb function, whereas escape from crisis can only be achieved by activating a telomere maintenance mechanism, mostly telomerase reactivation. Cells that bypass senescence (M1) did not reactivate telomerase, resulting in further telomere shortening to a critical telomere length upon reaching crisis (M2). In these models, critical telomere shortening induces extensive chromosome instability, most likely via chromosome end-to-end fusions. Dicentric chromosomes lead to anaphase breakage-fusion-bridges resulting in multiple chromosomal aberrations. To investigate whether similar mechanisms may be involved in the development of genetic instability in human cancer, we studied telomere length and expression of critical telomeric proteins (TRF2 and POT1) in acute myeloid leukemia (AML) patients. AML is a good model for these studies since distinct subgroups of AML are characterized by either exchanges along chromosome arms (translocation or inversion), or by a complex karyotype with multiple chromosome aberrations. Groups were age-matched. Telomere length was studied in metaphase arrested leukemic cells using quantitative fluorescence in situ hybridization (Q-FISH) using a telomere-specific probe. Subsequently, metaphase spreads were hybridized with a leukemia-specific probe to confirm leukemic origin of each metaphase. Telomeres were significantly shorter in AML samples with multiple chromosomal abnormalities in comparison to AML samples with a reciprocal translocation/inversion or no abnormalities (mean±SEM=16±1.7 AFU, n=12 versus 29±4.3 AFU, n=18; p=0.015). Interestingly, telomerase activity level is significantly higher in AML samples with multiple chromosomal abnormalities, compared to AML samples with a reciprocal translocation or inversion (mean±SEM=330±95, n=11 versus 70±21, n=13; p=0.02). Expression levels of telomeric proteins TRF2 and POT1 were similar in these AML groups. Our observations suggest that, consistent with previous in vitro models in fibroblasts, critical telomere shortening may have a role in the development of genetic instability in human AML. Critically short telomeres in association with high levels of telomerase activity suggest that AML cells with multiple chromosomal abnormalities have bypassed crisis (M2). The longer telomeres and low levels of telomerase activity in AML cells with a reciprocal translocation or inversion suggest that they originate from an earlier stage, preceding crisis. Consequently, telomere length modulation may have a role in cancer prevention.

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Harrington, Lea, et Fabio Pucci. « In medio stat virtus : unanticipated consequences of telomere dysequilibrium ». Philosophical Transactions of the Royal Society B : Biological Sciences 373, n^o 1741 (15 janvier 2018) : 20160444. http://dx.doi.org/10.1098/rstb.2016.0444.

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The integrity of chromosome ends, or telomeres, depends on myriad processes that must balance the need to compact and protect the telomeric, G-rich DNA from detection as a double-stranded DNA break, and yet still permit access to enzymes that process, replicate and maintain a sufficient reserve of telomeric DNA. When unable to maintain this equilibrium, erosion of telomeres leads to perturbations at or near the telomeres themselves, including loss of binding by the telomere protective complex, shelterin, and alterations in transcription and post-translational modifications of histones. Although the catastrophic consequences of full telomere de-protection are well described, recent evidence points to other, less obvious perturbations that arise when telomere length equilibrium is altered. For example, critically short telomeres also perturb DNA methylation and histone post-translational modifications at distal sites throughout the genome. In murine stem cells for example, this dysregulated chromatin leads to inappropriate suppression of pluripotency regulator factors such as Nanog . This review summarizes these recent findings, with an emphasis on how these genome-wide, telomere-induced perturbations can have profound consequences on cell function and fate. This article is part of the theme issue ‘Understanding diversity in telomere dynamics’.

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Malyavko, Alexander N., et Olga A. Dontsova. « The telomeric Cdc13 protein from yeast Hansenula polymorpha ». Acta Naturae 12, n^o 1 (16 avril 2020) : 84–88. http://dx.doi.org/10.32607/actanaturae.10944.

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Telomeres are special structures at the ends of chromosomes that play an important role in the protection of the genetic material. Telomere composition is very diverse; noticeable differences can often be observed even among closely related species. Here, we identify the homolog of telomeric protein Cdc13 in the thermotolerant yeast Hansenula polymorpha. We show that it can specifically bind single-stranded telomeric DNA, as well as interact with the Stn1 protein. In addition, we have uncovered an interaction between Cdc13 and TERT (one of the core components of the telomerase complex), which suggests that Cdc13 is potentially involved in telomerase recruitment to telomeres in H. polymorpha.

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de Lange, Titia. « Shelterin-Mediated Telomere Protection ». Annual Review of Genetics 52, n^o 1 (23 novembre 2018) : 223–47. http://dx.doi.org/10.1146/annurev-genet-032918-021921.

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For more than a decade, it has been known that mammalian cells use shelterin to protect chromosome ends. Much progress has been made on the mechanism by which shelterin prevents telomeres from inadvertently activating DNA damage signaling and double-strand break (DSB) repair pathways. Shelterin averts activation of three DNA damage response enzymes [the ataxia-telangiectasia-mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) kinases and poly(ADP-ribose) polymerase 1 (PARP1)], blocks three DSB repair pathways [classical nonhomologous end joining (c-NHEJ), alternative (alt)-NHEJ, and homology-directed repair (HDR)], and prevents hyper-resection at telomeres. For several of these functions, mechanistic insights have emerged. In addition, much has been learned about how shelterin maintains the telomeric 3′ overhang, forms and protects the t-loop structure, and promotes replication through telomeres. These studies revealed that shelterin is compartmentalized, with individual subunits dedicated to distinct aspects of the end-protection problem. This review focuses on the current knowledge of shelterin-mediated telomere protection, highlights differences between human and mouse shelterin, and discusses some of the questions that remain.

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Palacios, Jose A., Daniel Herranz, Maria Luigia De Bonis, Susana Velasco, Manuel Serrano et Maria A. Blasco. « SIRT1 contributes to telomere maintenance and augments global homologous recombination ». Journal of Cell Biology 191, n^o 7 (27 décembre 2010) : 1299–313. http://dx.doi.org/10.1083/jcb.201005160.

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Yeast Sir2 deacetylase is a component of the silent information regulator (SIR) complex encompassing Sir2/Sir3/Sir4. Sir2 is recruited to telomeres through Rap1, and this complex spreads into subtelomeric DNA via histone deacetylation. However, potential functions at telomeres for SIRT1, the mammalian orthologue of yeast Sir2, are less clear. We studied both loss of function (SIRT1 deficient) and gain of function (SIRT1super) mouse models. Our results indicate that SIRT1 is a positive regulator of telomere length in vivo and attenuates telomere shortening associated with aging, an effect dependent on telomerase activity. Using chromatin immunoprecipitation assays, we find that SIRT1 interacts with telomeric repeats in vivo. In addition, SIRT1 overexpression increases homologous recombination throughout the entire genome, including telomeres, centromeres, and chromosome arms. These findings link SIRT1 to telomere biology and global DNA repair and provide new mechanistic explanations for the known functions of SIRT1 in protection from DNA damage and some age-associated pathologies.

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Shakirov, Eugene V., Yulia V. Surovtseva, Nathan Osbun et Dorothy E. Shippen. « The Arabidopsis Pot1 and Pot2 Proteins Function in Telomere Length Homeostasis and Chromosome End Protection ». Molecular and Cellular Biology 25, n^o 17 (1 septembre 2005) : 7725–33. http://dx.doi.org/10.1128/mcb.25.17.7725-7733.2005.

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ABSTRACT Pot1 (protection of telomeres 1) is a single-stranded telomere binding protein that is essential for chromosome end protection and telomere length homeostasis. Arabidopsis encodes two Pot1-like proteins, dubbed AtPot1 and AtPot2. Here we show that telomeres in transgenic plants expressing a truncated AtPot1 allele lacking the N-terminal oligonucleotide/oligosaccharide binding fold (P1ΔN) are 1 to 1.5 kb shorter than in the wild type, suggesting that AtPot1 contributes to the positive regulation of telomere length control. In contrast, telomere length is unperturbed in plants expressing the analogous region of AtPot2. A strikingly different phenotype is observed in plants overexpressing the AtPot2 N terminus (P2ΔC) but not the corresponding region in AtPot1. Although bulk telomeres in P2ΔC mutants are 1 to 2 kb shorter than in the wild type, these plants resemble late-generation telomerase-deficient mutants with severe growth defects, sterility, and massive genome instability, including bridged chromosomes and aneuploidy. The genome instability associated with P2ΔC mutants implies that AtPot2 contributes to chromosome end protection. Thus, Arabidopsis has evolved two Pot genes that function differently in telomere biology. These findings provide unanticipated information about the evolution of single-stranded telomere binding proteins.

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Webb, Christopher J., et Virginia A. Zakian. « Telomerase RNA stem terminus element affects template boundary element function, telomere sequence, and shelterin binding ». Proceedings of the National Academy of Sciences 112, n^o 36 (24 août 2015) : 11312–17. http://dx.doi.org/10.1073/pnas.1503157112.

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The stem terminus element (STE), which was discovered 13 y ago in human telomerase RNA, is required for telomerase activity, yet its mode of action is unknown. We report that the Schizosaccharomyces pombe telomerase RNA, TER1 (telomerase RNA 1), also contains a STE, which is essential for telomere maintenance. Cells expressing a partial loss-of-function TER1 STE allele maintained short stable telomeres by a recombination-independent mechanism. Remarkably, the mutant telomere sequence was different from that of wild-type cells. Generation of the altered sequence is explained by reverse transcription into the template boundary element, demonstrating that the STE helps maintain template boundary element function. The altered telomeres bound less Pot1 (protection of telomeres 1) and Taz1 (telomere-associated in Schizosaccharomyces pombe 1) in vivo. Thus, the S. pombe STE, although distant from the template, ensures proper telomere sequence, which in turn promotes proper assembly of the shelterin complex.

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Xu, Ling, Ruben C. Petreaca, Hovik J. Gasparyan, Stephanie Vu et Constance I. Nugent. « TEN1 Is Essential for CDC13-Mediated Telomere Capping ». Genetics 183, n^o 3 (14 septembre 2009) : 793–810. http://dx.doi.org/10.1534/genetics.109.108894.

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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 POLα 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.

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McNees, Carolyn J., Agueda M. Tejera, Paula Martínez, Matilde Murga, Francisca Mulero, Oscar Fernandez-Capetillo et Maria A. Blasco. « ATR suppresses telomere fragility and recombination but is dispensable for elongation of short telomeres by telomerase ». Journal of Cell Biology 188, n^o 5 (8 mars 2010) : 639–52. http://dx.doi.org/10.1083/jcb.200908136.

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Telomere shortening caused by incomplete DNA replication is balanced by telomerase-mediated telomere extension, with evidence indicating that the shortest telomeres are preferred substrates in primary cells. Critically short telomeres are detected by the cellular DNA damage response (DDR) system. In budding yeast, the important DDR kinase Tel1 (homologue of ATM [ataxia telangiectasia mutated]) is vital for telomerase recruitment to short telomeres, but mammalian ATM is dispensable for this function. We asked whether closely related ATR (ATM and Rad3 related) kinase, which is important for preventing replicative stress and chromosomal breakage at common fragile sites, might instead fulfill this role. The newly created ATR-deficient Seckel mouse strain was used to examine the function of ATR in telomerase recruitment and telomere function. Telomeres were recently found to resemble fragile sites, and we show in this study that ATR has an important role in the suppression of telomere fragility and recombination. We also find that wild-type ATR levels are important to protect short telomeres from chromosomal fusions but do not appear essential for telomerase recruitment to short telomeres in primary mouse embryonic fibroblasts from the ATR-deficient Seckel mouse model. These results reveal a previously unnoticed role for mammalian ATR in telomere protection and stability.

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Itriago, Humberto, Rishi K. Jaiswal, Susanne Philipp et Marita Cohn. « The telomeric 5′ end nucleotide is regulated in the budding yeast Naumovozyma castellii ». Nucleic Acids Research 50, n^o 1 (15 décembre 2021) : 281–92. http://dx.doi.org/10.1093/nar/gkab1229.

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Abstract The junction between the double-stranded and single-stranded telomeric DNA (ds–ss junction) is fundamental in the maintenance of the telomeric chromatin, as it directs the assembly of the telomere binding proteins. In budding yeast, multiple Rap1 proteins bind the telomeric dsDNA, while ssDNA repeats are bound by the Cdc13 protein. Here, we aimed to determine, for the first time, the telomeric 5′ end nucleotide in a budding yeast. To this end, we developed a permutation-specific PCR-based method directed towards the regular 8-mer telomeric repeats in Naumovozyma castellii. We find that, in logarithmically growing cells, the 320 ± 30 bp long telomeres mainly terminate in either of two specific 5′ end permutations of the repeat, both corresponding to a terminal adenine nucleotide. Strikingly, two permutations are completely absent at the 5′ end, indicating that not all ds-ss junction structures would allow the establishment of the protective telomere chromatin cap structure. Using in vitro DNA end protection assays, we determined that binding of Rap1 and Cdc13 around the most abundant ds–ss junction ensures the protection of both 5′ ends and 3′ overhangs from exonucleolytic degradation. Our results provide mechanistic insights into telomere protection, and reveal that Rap1 and Cdc13 have complementary roles.

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Beier, Fabian, Miguel Foronda, Paula Martinez et Maria A. Blasco. « Conditional TRF1 knockout in the hematopoietic compartment leads to bone marrow failure and recapitulates clinical features of dyskeratosis congenita ». Blood 120, n^o 15 (11 octobre 2012) : 2990–3000. http://dx.doi.org/10.1182/blood-2012-03-418038.

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Abstract TRF1 is part of the shelterin complex, which binds telomeres and it is essential for their protection. Ablation of TRF1 induces sister telomere fusions and aberrant numbers of telomeric signals associated with telomere fragility. Dyskeratosis congenita is characterized by a mucocutaneous triad, bone marrow failure (BMF), and presence of short telomeres because of mutations in telomerase. A subset of patients, however, show mutations in the shelterin component TIN2, a TRF1-interacting protein, presenting a more severe phenotype and presence of very short telomeres despite normal telomerase activity. Allelic variations in TRF1 have been found associated with BMF. To address a possible role for TRF1 dysfunction in BMF, here we generated a mouse model with conditional TRF1 deletion in the hematopoietic system. Chronic TRF1 deletion results in increased DNA damage and cellular senescence, but not increased apoptosis, in BM progenitor cells, leading to severe aplasia. Importantly, increased compensatory proliferation of BM stem cells is associated with rapid telomere shortening and further increase in senescent cells in vivo, providing a mechanism for the very short telomeres of human patients with mutations in the shelterin TIN2. Together, these results represent proof of principle that mutations in TRF1 lead to the main clinical features of BMF.

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Grandin, Nathalie, et Michel Charbonneau. « Telomerase- and Rad52-Independent Immortalization of Budding Yeast by an Inherited-Long-Telomere Pathway of Telomeric Repeat Amplification ». Molecular and Cellular Biology 29, n^o 4 (1 décembre 2008) : 965–85. http://dx.doi.org/10.1128/mcb.00817-08.

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ABSTRACT In the absence of telomerase, telomeres erode, provoking accumulation of DNA damage and death by senescence. Rare survivors arise, however, due to Rad52-based amplification of telomeric sequences by homologous recombination. The present study reveals that in budding yeast cells, postsenescence survival relying on amplification of the TG1-3 telomeric repeats can take place in the absence of Rad52 when overelongated telomeres are present during senescence (hence its designation ILT, for inherited-long-telomere, pathway). By growth competition, the Rad52-independent pathway was almost as efficient as the Rad51- and Rad52-dependent pathway that predominates in telomerase-negative cells. The ILT pathway could also be triggered by increased telomerase accessibility before telomerase removal, combined with loss of telomere protection, indicating that prior accumulation of recombination proteins was not required. The ILT pathway was dependent on Rad50 and Mre11 but not on the Rad51 recombinase and Rad59, thus making it distinct from both the type II (budding yeast ALT [alternative lengthening of telomeres]) and type I pathways amplifying the TG1-3 repeats and subtelomeric sequences, respectively. The ILT pathway also required the Rad1 endonuclease and Elg1, a replication factor C (RFC)-like complex subunit, but not Rad24 or Ctf18 (two subunits of two other RFC-like complexes), the Dnl4 ligase, Yku70, or Nej1. Possible mechanisms for this Rad52-independent pathway of telomeric repeat amplification are discussed. The effects of inherited long telomeres on Rad52-dependent recombination are also reported.

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Kibe, Tatsuya, Gail A. Osawa, Catherine E. Keegan et Titia de Lange. « Telomere Protection by TPP1 Is Mediated by POT1a and POT1b ». Molecular and Cellular Biology 30, n^o 4 (7 décembre 2009) : 1059–66. http://dx.doi.org/10.1128/mcb.01498-09.

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ABSTRACT Mammalian telomeres are protected by the shelterin complex, which contains single-stranded telomeric DNA binding proteins (POT1a and POT1b in rodents, POT1 in other mammals). Mouse POT1a prevents the activation of the ATR kinase and contributes to the repression of the nonhomologous end-joining pathway (NHEJ) at newly replicated telomeres. POT1b represses unscheduled resection of the 5′-ended telomeric DNA strand, resulting in long 3′ overhangs in POT1b KO cells. Both POT1 proteins bind TPP1, forming heterodimers that bind to other proteins in shelterin. Short hairpin RNA (shRNA)-mediated depletion had previously demonstrated that TPP1 contributes to the normal function of POT1a and POT1b. However, these experiments did not establish whether TPP1 has additional functions in shelterin. Here we report on the phenotypes of the conditional deletion of TPP1 from mouse embryo fibroblasts. TPP1 deletion resulted in the release of POT1a and POT1b from chromatin and loss of these proteins from telomeres, indicating that TPP1 is required for the telomere association of POT1a and POT1b but not for their stability. The telomere dysfunction phenotypes associated with deletion of TPP1 were identical to those of POT1a/POT1b DKO cells. No additional telomere dysfunction phenotypes were observed, establishing that the main role of TPP1 is to allow POT1a and POT1b to protect chromosome ends.

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Maser, Richard S., Kwok-Kin Wong, Erguen Sahin, Huili Xia, Maria Naylor, H. Mason Hedberg, Steven E. Artandi et Ronald A. DePinho. « DNA-Dependent Protein Kinase Catalytic Subunit Is Not Required for Dysfunctional Telomere Fusion and Checkpoint Response in the Telomerase-Deficient Mouse ». Molecular and Cellular Biology 27, n^o 6 (4 décembre 2006) : 2253–65. http://dx.doi.org/10.1128/mcb.01354-06.

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ABSTRACT Telomeres are key structural elements for the protection and maintenance of linear chromosomes, and they function to prevent recognition of chromosomal ends as DNA double-stranded breaks. Loss of telomere capping function brought about by telomerase deficiency and gradual erosion of telomere ends or by experimental disruption of higher-order telomere structure culminates in the fusion of defective telomeres and/or the activation of DNA damage checkpoints. Previous work has implicated the nonhomologous end-joining (NHEJ) DNA repair pathway as a critical mediator of these biological processes. Here, employing the telomerase-deficient mouse model, we tested whether the NHEJ component DNA-dependent protein kinase catalytic subunit (DNA-PKcs) was required for fusion of eroded/dysfunctional telomere ends and the telomere checkpoint responses. In late-generation mTerc − / − DNA-PKcs − / − cells and tissues, chromosomal end-to-end fusions and anaphase bridges were readily evident. Notably, nullizygosity for DNA Ligase4 (Lig4)—an additional crucial NHEJ component—was also permissive for chromosome fusions in mTerc − / − cells, indicating that, in contrast to results seen with experimental disruption of telomere structure, telomere dysfunction in the context of gradual telomere erosion can engage additional DNA repair pathways. Furthermore, we found that DNA-PKcs deficiency does not reduce apoptosis, tissue atrophy, or p53 activation in late-generation mTerc − / − tissues but rather moderately exacerbates germ cell apoptosis and testicular degeneration. Thus, our studies indicate that the NHEJ components, DNA-PKcs and Lig4, are not required for fusion of critically shortened telomeric ends and that DNA-PKcs is not required for sensing and executing the telomere checkpoint response, findings consistent with the consensus view of the limited role of DNA-PKcs in DNA damage signaling in general.

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Singh, Sunitha M., Olga Steinberg-Neifach, I. Saira Mian et Neal F. Lue. « Analysis of Telomerase in Candida albicans : Potential Role in Telomere End Protection ». Eukaryotic Cell 1, n^o 6 (décembre 2002) : 967–77. http://dx.doi.org/10.1128/ec.1.6.967-977.2002.

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ABSTRACT Telomerase is a ribonucleoprotein reverse transcriptase responsible for the maintenance of one strand of telomere terminal repeats. Analysis of the telomerase complex in the budding yeast Saccharomyces cerevisiae has revealed the presence of one catalytic protein subunit (Est2p/TERT) and at least two noncatalytic components (Est1p and Est3p). The genome of the pathogenic yeast Candida albicans contains putative orthologues of all three telomerase components. Disruption of each homologue resulted in significant but distinct telomere dysfunction in Candida. Similar to S. cerevisiae, the Candida EST3 disruption strain exhibits progressive telomere loss over many generations, at a rate that is consistent with incomplete replication. In contrast, telomeres in both the Candida TERT and EST1 disruption strains can contract rapidly, followed by partial or nearly complete recovery, suggesting a defect in telomere “capping.” We propose that these two telomerase subunits may participate in the protection of chromosomal ends in Candida. Analysis of telomerase-mediated primer extension in vitro indicates that only the TERT protein is absolutely essential for enzyme activity. Our results support the conservation of telomerase protein components beyond the catalytic subunit but reveal species-specific phenotypic alterations in response to loss of individual telomerase component. We also identify potential homologues of Est1p in phylogenetically diverse organisms. The Est1p sequence family possesses a conserved N-terminal domain predicted to be structurally related to tetratricopeptide repeat-containing proteins.

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Yang, Qin, Yun-Ling Zheng et Curtis C. Harris. « POT1 and TRF2 Cooperate To Maintain Telomeric Integrity ». Molecular and Cellular Biology 25, n^o 3 (1 février 2005) : 1070–80. http://dx.doi.org/10.1128/mcb.25.3.1070-1080.2005.

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ABSTRACT Mammalian telomeric DNA contains duplex TTAGGG repeats and single-stranded overhangs. POT1 (protection of telomeres 1) is a telomere-specific single-stranded DNA-binding protein, highly conserved in eukaryotes. The biological function of human POT1 is not well understood. In the present study, we demonstrate that POT1 plays a key role in telomeric end protection. The reduction of POT1 by RNA interference led to the loss of telomeric single-stranded overhangs and induced apoptosis, chromosomal instability, and senescence in cells. POT1 and TRF2 interacted with each other to form a complex with telomeric DNA. A dominant negative TRF2, TRF2ΔBΔM, bound to POT1 and prevented it from binding to telomeres. POT1 overexpression protected against TRF2ΔBΔM-induced loss of telomeric single-stranded overhangs, chromosomal instability, and senescence. These results demonstrate that POT1 and TRF2 share in part in the same pathway for telomere capping and suggest that POT1 binds to the telomeric single-stranded DNA in the D-loop and cooperates with TRF2 in t-loop maintenance.

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Bettin, Nicole, Claudio Oss Pegorar et Emilio Cusanelli. « The Emerging Roles of TERRA in Telomere Maintenance and Genome Stability ». Cells 8, n^o 3 (15 mars 2019) : 246. http://dx.doi.org/10.3390/cells8030246.

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The finding that transcription occurs at chromosome ends has opened new fields of study on the roles of telomeric transcripts in chromosome end maintenance and genome stability. Indeed, the ends of chromosomes are required to be protected from activation of DNA damage response and DNA repair pathways. Chromosome end protection is achieved by the activity of specific proteins that associate with chromosome ends, forming telomeres. Telomeres need to be constantly maintained as they are in a heterochromatic state and fold into specific structures (T-loops), which may hamper DNA replication. In addition, in the absence of maintenance mechanisms, chromosome ends shorten at every cell division due to limitations in the DNA replication machinery, which is unable to fully replicate the extremities of chromosomes. Altered telomere structure or critically short chromosome ends generate dysfunctional telomeres, ultimately leading to replicative senescence or chromosome instability. Telomere biology is thus implicated in multiple human diseases, including cancer. Emerging evidence indicates that a class of long noncoding RNAs transcribed at telomeres, known as TERRA for “TElomeric Repeat-containing RNA,” actively participates in the mechanisms regulating telomere maintenance and chromosome end protection. However, the molecular details of TERRA activities remain to be elucidated. In this review, we discuss recent findings on the emerging roles of TERRA in telomere maintenance and genome stability and their implications in human diseases.

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Linger, Benjamin R., Gregg B. Morin et Carolyn M. Price. « The Pot1a-associated proteins Tpt1 and Pat1 coordinate telomere protection and length regulation in Tetrahymena ». Molecular Biology of the Cell 22, n^o 21 (novembre 2011) : 4161–70. http://dx.doi.org/10.1091/mbc.e11-06-0551.

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We have identified two new telomere proteins, Tpt1 and Pat1, from the ciliate Tetrahymena thermophila. Although Tetrahymena telomerase is well characterized, only one telomere protein had previously been identified. This was the G-overhang binding-protein Pot1a. Tpt1 and Pat1 were isolated as Pot1a binding partners and shown to localize to telomeres. As Tpt1 and Pat1 were both found to be essential, conditional cell lines were generated to explore their function. Tpt1 depletion caused a rapid growth arrest and telomere elongation in the absence of cell division. The phenotype was similar to that seen after Pot1a depletion suggesting that Tpt1 and Pot1a function together to regulate telomere length and prevent telomere deprotection. In contrast, Pat1 depletion had a modest effect on cell growth but caused progressive telomere shortening similar to that observed upon TERT depletion. Thus Pat1 appears to be needed for telomerase to maintain the chromosome terminus. Analysis of Pot1a-Tpt1-Pat1 complex formation using purified proteins indicated that Tpt1 interacts directly with Pot1a while Pat1 interacts with Tpt1. Our results indicate that Tpt1 is the Tetrahymena equivalent of mammalian TPP1, Schizosaccharomyces pombe Tpz1, and Oxytricha nova TEBPβ.

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Imran, Siti A. M., Muhammad Dain Yazid, Wei Cui et Yogeswaran Lokanathan. « The Intra- and Extra-Telomeric Role of TRF2 in the DNA Damage Response ». International Journal of Molecular Sciences 22, n^o 18 (14 septembre 2021) : 9900. http://dx.doi.org/10.3390/ijms22189900.

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Telomere repeat binding factor 2 (TRF2) has a well-known function at the telomeres, which acts to protect the telomere end from being recognized as a DNA break or from unwanted recombination. This protection mechanism prevents DNA instability from mutation and subsequent severe diseases caused by the changes in DNA, such as cancer. Since TRF2 actively inhibits the DNA damage response factors from recognizing the telomere end as a DNA break, many more studies have also shown its interactions outside of the telomeres. However, very little has been discovered on the mechanisms involved in these interactions. This review aims to discuss the known function of TRF2 and its interaction with the DNA damage response (DDR) factors at both telomeric and non-telomeric regions. In this review, we will summarize recent progress and findings on the interactions between TRF2 and DDR factors at telomeres and outside of telomeres.

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Nakamura, Toru M., Bettina A. Moser et Paul Russell. « Telomere Binding of Checkpoint Sensor and DNA Repair Proteins Contributes to Maintenance of Functional Fission Yeast Telomeres ». Genetics 161, n^o 4 (1 août 2002) : 1437–52. http://dx.doi.org/10.1093/genetics/161.4.1437.

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Abstract Telomeres, the ends of linear chromosomes, are DNA double-strand ends that do not trigger a cell cycle arrest and yet require checkpoint and DNA repair proteins for maintenance. Genetic and biochemical studies in the fission yeast Schizosaccharomyces pombe were undertaken to understand how checkpoint and DNA repair proteins contribute to telomere maintenance. On the basis of telomere lengths of mutant combinations of various checkpoint-related proteins (Rad1, Rad3, Rad9, Rad17, Rad26, Hus1, Crb2, Chk1, Cds1), Tel1, a telomere-binding protein (Taz1), and DNA repair proteins (Ku70, Rad32), we conclude that Rad3/Rad26 and Tel1/Rad32 represent two pathways required to maintain telomeres and prevent chromosome circularization. Rad1/Rad9/Hus1/Rad17 and Ku70 are two additional epistasis groups, which act in the Rad3/Rad26 pathway. However, Rad3/Rad26 must have additional target(s), as cells lacking Tel1/Rad32, Rad1/Rad9/Hus1/Rad17, and Ku70 groups did not circularize chromosomes. Cells lacking Rad3/Rad26 and Tel1/Rad32 senesced faster than a telomerase trt1Δ mutant, suggesting that these pathways may contribute to telomere protection. Deletion of taz1 did not suppress chromosome circularization in cells lacking Rad3/Rad26 and Tel1/Rad32, also suggesting that two pathways protect telomeres. Chromatin immunoprecipitation analyses found that Rad3, Rad1, Rad9, Hus1, Rad17, Rad32, and Ku70 associate with telomeres. Thus, checkpoint sensor and DNA repair proteins contribute to telomere maintenance and protection through their association with telomeres.

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Bi, Xiaolin, Su-Chin D. Wei et Yikang S. Rong. « Telomere Protection without a Telomerase ». Current Biology 14, n^o 15 (août 2004) : 1348–53. http://dx.doi.org/10.1016/j.cub.2004.06.063.

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Stagno D'Alcontres, Martina, Aaron Mendez-Bermudez, Jennifer L. Foxon, Nicola J. Royle et Paolo Salomoni. « Lack of TRF2 in ALT cells causes PML-dependent p53 activation and loss of telomeric DNA ». Journal of Cell Biology 179, n^o 5 (3 décembre 2007) : 855–67. http://dx.doi.org/10.1083/jcb.200703020.

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Alternative lengthening of telomere (ALT) tumors maintain telomeres by a telomerase-independent mechanism and are characterized by a nuclear structure called the ALT-associated PML body (APB). TRF2 is a component of a telomeric DNA/protein complex called shelterin. However, TRF2 function in ALT cells remains elusive. In telomerase-positive tumor cells, TRF2 inactivation results in telomere de-protection, activation of ATM, and consequent induction of p53-dependent apoptosis. We show that in ALT cells this sequence of events is different. First, TRF2 inactivation/silencing does not induce cell death in p53-proficient ALT cells, but rather triggers cellular senescence. Second, ATM is constitutively activated in ALT cells and colocalizes with TRF2 into APBs. However, it is only following TRF2 silencing that the ATM target p53 is activated. In this context, PML is indispensable for p53-dependent p21 induction. Finally, we find a substantial loss of telomeric DNA upon stable TRF2 knockdown in ALT cells. Overall, we provide insight into the functional consequences of shelterin alterations in ALT cells.

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Srinivas, Nalini, Sivaramakrishna Rachakonda et Rajiv Kumar. « Telomeres and Telomere Length : A General Overview ». Cancers 12, n^o 3 (28 février 2020) : 558. http://dx.doi.org/10.3390/cancers12030558.

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Telomeres are highly conserved tandem nucleotide repeats that include proximal double-stranded and distal single-stranded regions that in complex with shelterin proteins afford protection at chromosomal ends to maintain genomic integrity. Due to the inherent limitations of DNA replication and telomerase suppression in most somatic cells, telomeres undergo age-dependent incremental attrition. Short or dysfunctional telomeres are recognized as DNA double-stranded breaks, triggering cells to undergo replicative senescence. Telomere shortening, therefore, acts as a counting mechanism that drives replicative senescence by limiting the mitotic potential of cells. Telomere length, a complex hereditary trait, is associated with aging and age-related diseases. Epidemiological data, in general, support an association with varying magnitudes between constitutive telomere length and several disorders, including cancers. Telomere attrition is also influenced by oxidative damage and replicative stress caused by genetic, epigenetic, and environmental factors. Several single nucleotide polymorphisms at different loci, identified through genome-wide association studies, influence inter-individual variation in telomere length. In addition to genetic factors, environmental factors also influence telomere length during growth and development. Telomeres hold potential as biomarkers that reflect the genetic predisposition together with the impact of environmental conditions and as targets for anti-cancer therapies.

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Baumann, Peter, Elaine Podell et Thomas R. Cech. « Human Pot1 (Protection of Telomeres) Protein : Cytolocalization, Gene Structure, and Alternative Splicing ». Molecular and Cellular Biology 22, n^o 22 (15 novembre 2002) : 8079–87. http://dx.doi.org/10.1128/mcb.22.22.8079-8087.2002.

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ABSTRACT Fission yeast Pot1 (protection of telomeres) is a single-stranded telomeric DNA binding protein with a critical role in ensuring chromosome stability. A putative human homolog (hPot1) was previously identified, based on moderate sequence similarity with fission yeast Pot1 and telomere end-binding proteins from ciliated protozoa. Using indirect immunofluorescence, we show here that epitope-tagged hPot1 localizes to telomeres in interphase nuclei of human cells, consistent with a direct role in telomere end protection. The hPOT1 gene contains 22 exons, most of which are present in all cDNAs examined. However, four exons are subject to exon skipping in some transcripts, giving rise to five splice variants. Four of these are ubiquitously expressed, whereas the fifth appears to be specific to leukocytes. The resultant proteins vary significantly in their ability to form complexes with single-stranded telomeric DNA as judged by electrophoretic mobility shift assays. In addition to these splice variants, the Pot1 family is expanded by the identification of six more genes from diverse species. Pot1-like proteins have now been found in plants, animals, yeasts, and microsporidia.

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Alt, Christina, Menelaos Tsapekos, Diego Perez, Joachim Klode et Ingo Stoffels. « An Open-Label Clinical Trial Analyzing the Efficacy of a Novel Telomere-Protecting Antiaging Face Cream ». Cosmetics 9, n^o 5 (9 septembre 2022) : 95. http://dx.doi.org/10.3390/cosmetics9050095.

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Telomere length, a hallmark of cellular senescence, decreases with age and is associated with age-related diseases. Environmental factors, including dietary and lifestyle factors, can affect the rate at which telomeres shorten, and telomere protection prevents this from happening. The protection of telomeres by natural molecules has been proposed as an antiaging strategy that may play a role in treating age-related diseases. This study investigated the effect of a cycloartane-type triterpene glycoside (astragaloside IV). Astragaloside IV is one of the primary compounds from the aqueous extract of Astragalus membranaceus, and it provides telomere protection both in vitro and in vivo. In a study cohort with 13 participants, telomere length in human skin samples was analyzed after daily treatment for 4 weeks. A comparison of the average median telomere length between the treatment and control groups (5342 bp vs. 4616 bp p = 0.0168) showed significant results. In the second clinical cohort with 20 participants, skin parameters at baseline and after 4 and 8 weeks were measured in vivo. The results show that the product improved hydration by 95%, the skin appeared brighter by 90%, and wrinkle visibility was reduced by 70%. The combination of biologically active compounds in the cream possesses telomere-protecting properties and notable antioxidant activity in vitro and in vivo.

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Wu, Yangxiu, Rebecca C. Poulos et Roger R. Reddel. « Role of POT1 in Human Cancer ». Cancers 12, n^o 10 (24 septembre 2020) : 2739. http://dx.doi.org/10.3390/cancers12102739.

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Telomere abnormalities facilitate cancer development by contributing to genomic instability and cellular immortalization. The Protection of Telomeres 1 (POT1) protein is an essential subunit of the shelterin telomere binding complex. It directly binds to single-stranded telomeric DNA, protecting chromosomal ends from an inappropriate DNA damage response, and plays a role in telomere length regulation. Alterations of POT1 have been detected in a range of cancers. Here, we review the biological functions of POT1, the prevalence of POT1 germline and somatic mutations across cancer predisposition syndromes and tumor types, and the dysregulation of POT1 expression in cancers. We propose a framework for understanding how POT1 abnormalities may contribute to oncogenesis in different cell types. Finally, we summarize the clinical implications of POT1 alterations in the germline and in cancer, and possible approaches for the development of targeted cancer therapies.

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Doksani. « The Response to DNA Damage at Telomeric Repeats and Its Consequences for Telomere Function ». Genes 10, n^o 4 (24 avril 2019) : 318. http://dx.doi.org/10.3390/genes10040318.

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Telomeric repeats, coated by the shelterin complex, prevent inappropriate activation of the DNA damage response at the ends of linear chromosomes. Shelterin has evolved distinct solutions to protect telomeres from different aspects of the DNA damage response. These solutions include formation of t-loops, which can sequester the chromosome terminus from DNA-end sensors and inhibition of key steps in the DNA damage response. While blocking the DNA damage response at chromosome ends, telomeres make wide use of many of its players to deal with exogenous damage and replication stress. This review focuses on the interplay between the end-protection functions and the response to DNA damage occurring inside the telomeric repeats, as well as on the consequences that telomere damage has on telomere structure and function.

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Sánchez-Vázquez, Raúl, Paula Martínez et Maria A. Blasco. « AKT-dependent signaling of extracellular cues through telomeres impact on tumorigenesis ». PLOS Genetics 17, n^o 3 (9 mars 2021) : e1009410. http://dx.doi.org/10.1371/journal.pgen.1009410.

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The telomere-bound shelterin complex is essential for chromosome-end protection and genomic stability. Little is known on the regulation of shelterin components by extracellular signals including developmental and environmental cues. Here, we show that human TRF1 is subjected to AKT-dependent regulation. To study the importance of this modification in vivo, we generate knock-in human cell lines carrying non-phosphorylatable mutants of the AKT-dependent TRF1 phosphorylation sites by CRISPR-Cas9. We find that TRF1 mutant cells show decreased TRF1 binding to telomeres and increased global and telomeric DNA damage. Human cells carrying non-phosphorylatable mutant TRF1 alleles show accelerated telomere shortening, demonstrating that AKT-dependent TRF1 phosphorylation regulates telomere maintenance in vivo. TRF1 mutant cells show an impaired response to proliferative extracellular signals as well as a decreased tumorigenesis potential. These findings indicate that telomere protection and telomere length can be regulated by extracellular signals upstream of PI3K/AKT activation, such as growth factors, nutrients or immune regulators, and this has an impact on tumorigenesis potential.

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Hofr, Ctirad, Pavla Šultesová, Michal Zimmermann, Iva Mozgová, Petra Procházková Schrumpfová, Michaela Wimmerová et Jiří Fajkus. « Single-Myb-histone proteins from Arabidopsis thaliana : a quantitative study of telomere-binding specificity and kinetics ». Biochemical Journal 419, n^o 1 (13 mars 2009) : 221–30. http://dx.doi.org/10.1042/bj20082195.

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Proteins that bind telomeric DNA modulate the structure of chromosome ends and control telomere function and maintenance. It has been shown that AtTRB (Arabidopsis thaliana telomere-repeat-binding factor) proteins from the SMH (single-Myb-histone) family selectively bind double-stranded telomeric DNA and interact with the telomeric protein AtPOT1b (A. thaliana protection of telomeres 1b), which is involved in telomere capping. In the present study, we performed the first quantitative DNA-binding study of this plant-specific family of proteins. Interactions of full-length proteins AtTRB1 and AtTRB3 with telomeric DNA were analysed by electrophoretic mobility-shift assay, fluorescence anisotropy and surface plasmon resonance to reveal their binding stoichiometry and kinetics. Kinetic analyses at different salt conditions enabled us to estimate the electrostatic component of binding and explain different affinities of the two proteins to telomeric DNA. On the basis of available data, a putative model explaining the binding stoichiometry and the protein arrangement on telomeric DNA is presented.

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Cifuentes-Rojas, Catherine, Kalpana Kannan, Lin Tseng et Dorothy E. Shippen. « Two RNA subunits and POT1a are components of Arabidopsis telomerase ». Proceedings of the National Academy of Sciences 108, n^o 1 (16 décembre 2010) : 73–78. http://dx.doi.org/10.1073/pnas.1013021107.

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Telomerase is a ribonucleoprotein (RNP) reverse transcriptase whose essential RNA subunit (TER) functions as a template for telomere repeat synthesis. Here we report the identification of two divergent TER moieties in the flowering plant Arabidopsis thaliana. Although both TER1 and TER2 copurify with telomerase activity and serve as templates for telomerase in vitro, depletion of TER1, but not TER2, leads to decreased telomerase activity and progressive telomere shortening in vivo. Moreover, mutation of the templating domain in TER1 results in the incorporation of mutant telomere repeats on chromosome ends. Thus, TER1 provides the major template for telomerase in vivo. We also show that POT1a binds TER1 with a Kd of 2 × 10-7 M and the two components assemble into an enzymatically active RNP in vivo. In contrast, TER1-POT1b and TER2-POT1a associations were not observed. In other organisms POT1 proteins bind telomeric DNA and provide chromosome end protection. We propose that duplication of TER and POT1 in Arabidopsis fueled the evolution of novel protein–nucleic acid interactions and the migration of POT1 from the telomere to the telomerase RNP.

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Diman, Aurélie, Joanna Boros, Florian Poulain, Julie Rodriguez, Marin Purnelle, Harikleia Episkopou, Luc Bertrand, Marc Francaux, Louise Deldicque et Anabelle Decottignies. « Nuclear respiratory factor 1 and endurance exercise promote human telomere transcription ». Science Advances 2, n^o 7 (juillet 2016) : e1600031. http://dx.doi.org/10.1126/sciadv.1600031.

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DNA breaks activate the DNA damage response and, if left unrepaired, trigger cellular senescence. Telomeres are specialized nucleoprotein structures that protect chromosome ends from persistent DNA damage response activation. Whether protection can be enhanced to counteract the age-dependent decline in telomere integrity is a challenging question. Telomeric repeat–containing RNA (TERRA), which is transcribed from telomeres, emerged as important player in telomere integrity. However, how human telomere transcription is regulated is still largely unknown. We identify nuclear respiratory factor 1 and peroxisome proliferator–activated receptor γ coactivator 1α as regulators of human telomere transcription. In agreement with an upstream regulation of these factors by adenosine 5′-monophosphate (AMP)–activated protein kinase (AMPK), pharmacological activation of AMPK in cancer cell lines or in normal nonproliferating myotubes up-regulated TERRA, thereby linking metabolism to telomere fitness. Cycling endurance exercise, which is associated with AMPK activation, increased TERRA levels in skeletal muscle biopsies obtained from 10 healthy young volunteers. The data support the idea that exercise may protect against aging.

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Sui, Jiang-Dong, Zheng Tang, Benjamin P. C. Chen, Ping Huang, Meng-Qi Yang, Nuo-Han Wang, Hao-Nan Yang et al. « Protein Phosphatase 2A–Dependent Mitotic hnRNPA1 Dephosphorylation and TERRA Formation Facilitate Telomere Capping ». Molecular Cancer Research 20, n^o 4 (21 décembre 2021) : 583–95. http://dx.doi.org/10.1158/1541-7786.mcr-21-0581.

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Abstract The heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), telomeric repeat-containing RNA (TERRA), and protection of telomeres 1 (POT1) have been reported to orchestrate to displace replication protein A (RPA) from telomeric overhangs, ensuring orderly telomere replication and capping. Our previous studies further demonstrated that DNA-dependent protein kinase catalytic subunit (DNA-PKcs)-dependent hnRNPA1 phosphorylation plays a crucial role in the promotion of hnRNPA1 binding to telomeric overhangs and RPA displacement during G2–M phases. However, it is unclear that how the subsequent exchange between hnRNPA1 and POT1 is orchestrated. Here we report that the protein phosphatase 2A (PP2A) depends on its scaffold subunit, which is called PPP2R1A, to interact with and dephosphorylate hnRNPA1 in the late M phase. Furthermore, PP2A-mediated hnRNPA1 dephosphorylation and TERRA accumulation act in concert to promote the hnRNPA1-to-POT1 switch on telomeric single-stranded DNA. Consequently, defective PPP2R1A results in ataxia telangiectasia and Rad3-related (ATR)-mediated DNA damage response at telomeres as well as induction of fragile telomeres. Combined inhibition of ATR and PP2A induces entry into a catastrophic mitosis and leads to synthetic lethality of tumor cells. In addition, PPP2R1A levels correlate with clinical stages and prognosis of multiple types of cancers. Taken together, our results indicate that PP2A is critical for telomere maintenance. Implications: This study demonstrates that the PP2A-dependent hnRNPA1 dephosphorylation and TERRA accumulation facilitates the formation of the protective capping structure of newly replicated telomeres, thus exerting essential oncogenic role in tumorigenesis.

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Fice, Heather, et Bernard Robaire. « Telomere Dynamics Throughout Spermatogenesis ». Genes 10, n^o 7 (12 juillet 2019) : 525. http://dx.doi.org/10.3390/genes10070525.

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Telomeres are repeat regions of DNA that cap either end of each chromosome, thereby providing stability and protection from the degradation of gene-rich regions. Each cell replication causes the loss of telomeric repeats due to incomplete DNA replication, though it is well-established that progressive telomere shortening is evaded in male germ cells by the maintenance of active telomerase. However, germ cell telomeres are still susceptible to disruption or insult by oxidative stress, toxicant exposure, and aging. Our aim was to examine the relative telomere length (rTL) in an outbred Sprague Dawley (SD) and an inbred Brown Norway (BN) rat model for paternal aging. No significant differences were found when comparing pachytene spermatocytes (PS), round spermatids (RS), and sperm obtained from the caput and cauda of the epididymis of young and aged SD rats; this is likely due to the high variance observed among individuals. A significant age-dependent decrease in rTL was observed from 115.6 (±6.5) to 93.3 (±6.3) in caput sperm and from 142.4 (±14.6) to 105.3 (±2.5) in cauda sperm from BN rats. Additionally, an increase in rTL during epididymal maturation was observed in both strains, most strikingly from 115.6 (±6.5) to 142 (±14.6) in young BN rats. These results confirm the decrease in rTL in rodents, but only when an inbred strain is used, and represent the first demonstration that rTL changes as sperm transit through the epididymis.

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Dantzer, Françoise, Marie-Josèphe Giraud-Panis, Isabel Jaco, Jean-Christophe Amé, Inès Schultz, Maria Blasco, Catherine-Elaine Koering et al. « Functional Interaction between Poly(ADP-Ribose) Polymerase 2 (PARP-2) and TRF2 : PARP Activity Negatively Regulates TRF2 ». Molecular and Cellular Biology 24, n^o 4 (15 février 2004) : 1595–607. http://dx.doi.org/10.1128/mcb.24.4.1595-1607.2004.

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ABSTRACT The DNA damage-dependent poly(ADP-ribose) polymerase-2 (PARP-2) is, together with PARP-1, an active player of the base excision repair process, thus defining its key role in genome surveillance and protection. Telomeres are specialized DNA-protein structures that protect chromosome ends from being recognized and processed as DNA strand breaks. In mammals, telomere protection depends on the T2AG3 repeat binding protein TRF2, which has been shown to remodel telomeres into large duplex loops (t-loops). In this work we show that PARP-2 physically binds to TRF2 with high affinity. The association of both proteins requires the N-terminal domain of PARP-2 and the myb domain of TRF2. Both partners colocalize at promyelocytic leukemia bodies in immortalized telomerase-negative cells. In addition, our data show that PARP activity regulates the DNA binding activity of TRF2 via both a covalent heteromodification of the dimerization domain of TRF2 and a noncovalent binding of poly(ADP-ribose) to the myb domain of TRF2. PARP-2−/− primary cells show normal telomere length as well as normal telomerase activity compared to wild-type cells but display a spontaneously increased frequency of chromosome and chromatid breaks and of ends lacking detectable T2AG3 repeats. Altogether, these results suggest a functional role of PARP-2 activity in the maintenance of telomere integrity.

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de la Guardia, Rafael Díaz, Carolina Elosua, Purificación Catalina, Brian A. Walker, David C. Johnson, David Gonzalez, Faith E. Davies, Gareth J. Morgan et Paola Leone. « Expression Profile and up-Regulation of Telomere-Associated Proteins In Multiple Myeloma ». Blood 116, n^o 21 (19 novembre 2010) : 4050. http://dx.doi.org/10.1182/blood.v116.21.4050.4050.

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Abstract Abstract 4050 The role of the telomeres in the mechanisms of ageing and carcinogenesis has generated a considerable interest as a novel approach to the treatment of many cancers. Telomeres are nucleoproteins structures that protect the ends of eukaryotic chromosomes, which are particularly vulnerable due to progressive shortening in almost all dividing cells. The telomere length was observed as a critical factor in the initiation and progression of human cancers, and it is associated to chromosomal instability. Most immortal cells possess enzymatic activity of telomerase. This suggests that telomerase activity and telomere length maintenance may be required for unlimited cell proliferation, tumorigenesis, and protection, allowing the evasion of apoptosis in cancer development. The telomerase activity could also be regulated positively or negatively by post-trancriptional and/or post-translational modification of the enzyme without transcriptional up-regulation of human telomerase reverse transcriptase (hTERT) mRNA. In this work, we analyze the expression data of all genes involved in telomerase activity. Patients with monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM), multiple myeloma (MM) and plasma cell leukemia (PLC) were studied through gene expression profiling analysis (Human Genome U133 Plus 2.0 arrays, Affymetrix). We identify 21 deregulated genes, implicated directly in telomere length maintenance activity in clonal plasma cells compared with normal cells (20 up-regulated and 1 down-regulated). These genes are MYC, KRAS, HSPA9, RB1 and members of the families: Small nucleolar ribonucleoproteins (H/ACA snoRNPs), A/B subfamily of ubiquitously expressed heterogeneous nuclear ribonucleoproteins (hnRNPs), and 14-3 -3 family. In conclusion, the myeloma cells acquire the telomere maintenance capability without deregulation of the human telomerase RNA gene (hTERC) and hTERT gene expression. It is an alternative lengthening of telomeres mechanism that has effect in the regulation of the BAD activity in apoptosis. The mechanism is based on preventing the partially-denatured proteins from aggregating, telomere maintenance through the correct processing and intranuclear trafficking of hTERC, telomerase reactivation and telomere stabilization, and efficient accumulation of hTERT in the nucleus. Thus, the findings of this study may help to improve telomerase-based therapy for multiple myeloma. Disclosures: No relevant conflicts of interest to declare.

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Stoklosa, Tomasz, Anna Deregowska, Katarzyna Pruszczyk, Iwona Solarska, Marcin M. Machnicki, Jagoda Adamczyk, Ilona Seferynska, Anna Lewinska et Maciej Wnuk. « Role of Shelterin Complex and Alternative Telomere Lengthening in Genomic Instability and Disease Progression in Chronic Myeloid Leukemia ». Blood 128, n^o 22 (2 décembre 2016) : 1880. http://dx.doi.org/10.1182/blood.v128.22.1880.1880.

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Abstract Genomic instability has many sources, among others, shortening of telomeres, nucleoprotein complexes located at the ends of chromosomes. Tumor cells have aberrant mechanisms of telomere maintenance: their telomeres are shortened, no longer preventing chromosome end-to-end fusion and recombination, but frequently not short enough to lead to cell senescence. Both telomerase and shelterin complexes are involved in telomere homeostasis. Reduction in the telomere length is considered as one of the features of chronic myeloid leukemia (CML) similar to other human malignancies and telomere shortening is correlated with disease progression from the chronic phase (CML-CP) to the blastic phase (CML-BP)1. However, recent report shows that shorter telomeres can actually be detected in patients who discontinued imatinib and are in treatment-free remission as compared to those who relapsed2. Therefore, there is no agreement on the telomere length dynamics in CML evolution. Moreover, the precise role of telomere-associated proteins, including shelterin complex in BCR-ABL1-mediated genomic instability in CML progression and resistance to TKIs, is not fully elucidated. Initially, we confirmed that the telomere shortening was positively correlated with CML progression (CML-BP in comparison to CML-CP). However, in CD34+ samples from CML-CP TKI-resistant patients in comparison to CML-CP patients, an increase in telomere length was observed. This suggests that shortening of telomeres in CML progression may have a biphasic scenario. This can be explained by alternative telomere lengthening (ALT) mechanisms, since no significant changes in the expression of subunits of the telomerase complex and its enzymatic activity were observed at different phases of the disease; enzymatic activity of telomerase was measured immunoenzymatically, while length of telomeres was determined by Southern blotting. Then we decided to analyze possible involvement of shelterin complex and of ALT mechanisms in CML progression. Importantly, expression of the three members of the shelterin complex, Protection Of Telomeres 1 (POT1), Repressor Activator Protein 1 (RAP1) and Tankyrase 1 (TNKS1) was significantly upregulated in CML-BP (10 samples) as compared to CML-CP (15 samples) and was also positively correlated with BCR-ABL1 expression. Moreover, as determined by TKI treatment of CD34+ CML-BP primary cells, expression of POT1 was BCR-ABL1-dependent. No significant changes were observed in the expression of other members of the shelterin complex, namely TINT1-PTOP-PIP1 (TPP1), TRF1 interactor 2 (TIN2) and Tankyrase 2 (TNKS2). Also telomere repeat-binding factor 1 and 2 (TRF1 and TRF2), which are responsible for anchoring shelterin complex to the double stranded telomeric repeats remain stable in the course of the disease. Expression of subunits of telomerase and shelterin complexes was examined by RT-qPCR and Western blotting. This was confirmed in K562 and K562 imatinib-resistant cell line model. Somatic mutations in POT1 have been recently described in human tumors including chronic lymphocytic leukemia (CLL). In CLL, mutations in POT1 affect telomere stability and are associated with shorter survival in patients receiving chemotherapy as a frontline treatment. We have screened our NGS data from targeted sequencing in a cohort of patients who progressed to CML-BP (paired CP and BP samples, n=10 and BP samples, n=9) but we did not detect any somatic mutations in POT1. This is in accordance with our data on POT1 upregulated expression and suggests that dysregulation of shelterin complex during progression of CML differs significantly from CLL. In conclusion, we present the first comprehensive analysis of the expression of all members of the shelterin complex in the course of CML. We postulate that abnormal expression of selected members such as POT1, RAP1 and TNKS1 may be responsible for the aberrant telomere maintenance mechanisms in CML cells and may play an important role in genomic instability associated with CML progression. References: 1. Brummendorf TH, et al. Blood 2000; 95:1883-1890. 2. Caocci et al. Journal of Hematology & Oncology 2016; 9:63; Disclosures Seferynska: Novartis: Consultancy, Honoraria.

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Ueno, Masaru. « Exploring Genetic Interactions with Telomere Protection Gene pot1 in Fission Yeast ». Biomolecules 13, n^o 2 (15 février 2023) : 370. http://dx.doi.org/10.3390/biom13020370.

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The regulation of telomere length has a significant impact on cancer risk and aging in humans. Circular chromosomes are found in humans and are often unstable during mitosis, resulting in genome instability. Some types of cancer have a high frequency of a circular chromosome. Fission yeast is a good model for studying the formation and stability of circular chromosomes as deletion of pot1 (encoding a telomere protection protein) results in rapid telomere degradation and chromosome fusion. Pot1 binds to single-stranded telomere DNA and is conserved from fission yeast to humans. Loss of pot1 leads to viable strains in which all three fission yeast chromosomes become circular. In this review, I will introduce pot1 genetic interactions as these inform on processes such as the degradation of uncapped telomeres, chromosome fusion, and maintenance of circular chromosomes. Therefore, exploring genes that genetically interact with pot1 contributes to finding new genes and/or new functions of genes related to the maintenance of telomeres and/or circular chromosomes.

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