<i>Plasmodium falciparum</i> Telomerase: De Novo Telomere Addition to Telomeric and Nontelomeric Sequences and Role in Chromosome Healing

Bottius, Emmanuel; Bakhsis, Nassera; Scherf, Artur

doi:10.1128/mcb.18.2.919

Cited by 74 publications

(75 citation statements)

References 36 publications

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“…2 Furthermore, telomerase is able to initiate de novo telomere formation on artificially generated chromosome ends, although most of the data regarding this function were obtained from experiments with non-human cells. [35][36][37][38][39] Nevertheless, human telomerase can be considered to be an enzyme with DNA-repair function. Consequently, telomerase-inhibited cancer cells show two alterations: (i) cell proliferation dependent, slow telomere shortening that finally leads to senescence, 7,40 and (ii) increased sensitivity to DNA-damaging agents and to apoptosis.…”

Section: Discussionmentioning

confidence: 99%

DNA damage transiently increases TRF2 mRNA expression and telomerase activity

et al. 2003

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Telomerase activity transiently increases when HL60 cells are treated with the topoisomerase II inhibitor etoposide. A quantitative assessment revealed that telomerase is activated by etoposide treatment in a number of cell lines and that the increase is reversible after withdrawal of etoposide from the cell culture. Telomerase activation correlated with the occurrence of DNA damage but not with cell cycle arrest. We did not detect any transcriptional upregulation of hTERT mRNA, suggesting a post-transcriptional mechanism of telomerase activation. Furthermore, the mRNA expression of the telomere binding protein TRF2 was upregulated early and reversibly after etoposide treatment. TRF1 mRNA expression levels were unchanged after DNA damage, but increased when the cells accumulated in the G2/M phase. The data show that the telosome reacts after DNA damage by upregulating telomerase activity and TRF2 expression in malignant cells. It has previously been shown that overexpression of TRF2 can repress senescence signals arising from critically shortened telomeres. We show here that TRF2 is upregulated by undirected DNA damage that also affects the telomeric DNA. These data suggest that upregulation of telomerase activity and TRF2 expression might act as antiapoptotic mechanisms in the DNA-damage response of malignant cells. Leukemia (2003Leukemia ( ) 17, 2007Leukemia ( -2015 IntroductionThe chromosomal ends are composed of short repetitive DNA sequences and specialized telomere binding proteins. 1 The function of this 'telosome' is to protect the natural ends of the chromosomes from being recognized as artificial DNA breaks and to mediate chromosomal pairing and movement during cell division. 2 Immortal cells, such as germ line cells, stem cells and cancer cells, express the ribonucleoprotein telomerase, a reverse transcriptase, that synthesizes new telomeric repeats onto the chromosome ends and compensates for the loss occurring during cell division. 3 In most conditions analyzed so far, the limiting component of an active telomerase enzyme is the catalytic subunit hTERT. Upregulation of telomerase activity by enhanced proliferation of tumor cell lines or of sporadic tumors with high proliferation in vivo is virtually always mediated by a transcriptional overexpression of hTERT mRNA. 4 Although the predominant function of telomerase is maintenance of telomere length, some data indicate that the catalytic subunit hTERT additionally mediates a survival promoting function that is independent of its catalytic activity. 5,6 Inhibition of telomerase by targeting the catalytic subunit hTERT induces slow, proliferation-associated telomere shortening and finally senescence. 7,8 However, even before a critical telomere length is reached, the telomerase-inhibited cell lines show an increased sensitivity to DNA-damaging agents like etoposide. 8,9 Therefore, targeting telomerase simultaneously with DNA-damage-inducing agents might potentiate the effect of both therapeutic approaches.The telomere binding proteins TRF1 and TRF2 are...

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Section: Discussionmentioning

confidence: 99%

DNA damage transiently increases TRF2 mRNA expression and telomerase activity

et al. 2003

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“…The telomerase RNA is an integral component of telomerase that dictates the RNA template-dependent telomere synthesis [4,5]. Lack of telomerase activity leads to telomere shortening in a number of eukaryotic organisms, including human [6], mouse [7], plant [8], worm [9], budding [10] and fission yeasts [11], and protozoan parasites such as Plasmodium falciparum [12] and Trypanosoma brucei [13].…”

Section: Introductionmentioning

confidence: 99%

A trans-spliced telomerase RNA dictates telomere synthesis in Trypanosoma brucei

et al. 2013

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Telomerase is a ribonucleoprotein enzyme typically required for sustained cell proliferation. Although both telomerase activity and the telomerase catalytic protein component, TbTERT, have been identified in the eukaryotic pathogen Trypanosoma brucei, the RNA molecule that dictates telomere synthesis remains unknown. Here, we identify the RNA component of Trypanosoma brucei telomerase, TbTR, and provide phylogenetic and in vivo evidence for TbTR's native folding and activity. We show that TbTR is processed through trans-splicing, and is a capped transcript that interacts and copurifies with TbTERT in vivo. Deletion of TbTR caused progressive shortening of telomeres at a rate of 3-5 bp/population doubling (PD), which can be rescued by ectopic expression of a wild-type allele of TbTR in an apparent dose-dependent manner. Remarkably, introduction of mutations in the TbTR template domain resulted in corresponding mutant telomere sequences, demonstrating that telomere synthesis in T. brucei is dependent on TbTR. We also propose a secondary structure model for TbTR based on phylogenetic analysis and chemical probing experiments, thus defining TbTR domains that may have important functional implications in telomere synthesis. Identification and characterization of TbTR not only provide important insights into T. brucei telomere functions, which have been shown to play important roles in T. brucei pathogenesis, but also offer T. brucei as an attractive model system for studying telomerase biology in pathogenic protozoa and for comparative analysis of telomerase function with higher eukaryotes.

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“…Aunque en este organismo se ha reportado actividad de telomerasa (9)(10)(11), no existe a la fecha información alguna sobre los componentes de la enzima. Sumado a esto, llama la atención el hecho de que P. falciparum presenta repeticiones teloméricas variables en la secuencia GGGTTT/ CA mayor del 80%, a diferencia de la mayoría de los organismos estudiados donde la telomerasa sintetiza repeticiones invariables (12).…”

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Identificación de la secuencia del gen de la subunidad catalítica de la telomerasa en Plasmodium falciparum.

Rubiano¹,

Wasserman²

2005

biomedica

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Introducción. La enzima telomerasa participa en la regulación de la longitud de los telómeros al sintetizar nuevas repeticiones teloméricas que compensan las pérdidas en cada ronda de replicación del ADN. Por esta razón, el bloqueo de su actividad se plantea como un posible blanco de acción para detener el crecimiento de células con altas tasas de crecimiento. Tal es el caso de Plasmodium falciparum, parásito causante de la forma más grave de paludismo humano, en el cual se sabe que hay actividad de telomerasa pero no se tiene información sobre la enzima misma. Metodología. Para hacer un acercamiento al estudio de la telomerasa en P. falciparum, se realizó un alineamiento múltiple de las secuencias de la subunidad catalítica de la telomerasa disponibles en bases de datos y se obtuvo una secuencia consenso, la cual se comparó con las secuencias generadas en el proyecto de genoma de P. falciparum. Se encontró una secuencia que podría corresponder a parte del gen de la telomerasa de P. falciparum. Para comprobarlo, se diseñaron iniciadores que se utilizaron en ensayos de amplificación sobre el ADN y el ARN del parásito. Resultados. Se amplificaron fragmentos de ADN correspondientes a motivos conservados en las telomerasas y se detectó la presencia del ARNm mediante trascripción reversa y PCR sobre el ADNc generado. De esta manera, al combinar la utilización de herramientas de bioinformática y su posterior comprobación mediante técnicas de biología molecular, se obtuvo la secuencia del gen de la subunidad catalítica de la telomerasa en P. falciparum y se comprobó su presencia y trascripción en el parásito.Palabras clave: telomerasa, telómero, Plasmodium falciparum, biología computacional, paludismo. Identification of the gene sequence of telomerase catalytic subunit in Plasmodium falciparumIntroduction. The enzyme telomerase regulates telomere length by synthesis of telomeric repeats to compensate for telomeric loss in each DNA replication cycle. Therefore, telomerase is a potential target to block growth of cells with high replication rates. In Plasmodium falciparum, telomerase activity has been documented, but little information on its structure and role. Methods. Herein, alignment of multiple sequences was undertaken comparing telomerase catalytic subunit sequences as found in existing databases. A consensus sequence was compared with the sequences in the P. falciparum genome project and as a result, a candidate sequence for a portion of the telomerase gene was recovered. Primer sets were designed for DNA and RNA amplifications. Results. DNA fragments corresponding to telomerase conserved domains were amplified by using reverse transcription and PCR of cDNA. With a combination of bioinformatics and sequencing methods, the sequence of telomerase catalytic subunit gene (TERT) in P. falciparum was discovered, and its presence and transcription demonstrated.

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Plasmodium falciparum Telomerase: De Novo Telomere Addition to Telomeric and Nontelomeric Sequences and Role in Chromosome Healing

Cited by 74 publications

References 36 publications

DNA damage transiently increases TRF2 mRNA expression and telomerase activity

DNA damage transiently increases TRF2 mRNA expression and telomerase activity

A trans-spliced telomerase RNA dictates telomere synthesis in Trypanosoma brucei

Identificación de la secuencia del gen de la subunidad catalítica de la telomerasa en Plasmodium falciparum.

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