scholarly journals Targeted 2′-O Methylation at a Nucleotide within the Pseudoknot of Telomerase RNA Reduces Telomerase Activity In Vivo

2010 ◽  
Vol 30 (18) ◽  
pp. 4368-4378 ◽  
Author(s):  
Chao Huang ◽  
Yi-Tao Yu
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Triple Helix ◽  
Telomerase Activity ◽  
Rna Modification ◽  
Telomerase Rna ◽  
Telomere Shortening ◽  
Pseudoknot Structure ◽  
Novel Approach ◽  
Telomere Lengthening

ABSTRACT Telomerase RNA is an essential component of telomerase, a ribonucleoprotein enzyme that maintains chromosome ends in most eukaryotes. Here we employ a novel approach, namely, RNA-guided RNA modification, to assess whether introducing 2′-O methylation into telomerase RNA can influence telomerase activity in vivo. We generate specific 2′-O methylation sites in and adjacent to the triple helix (within the conserved pseudoknot structure) of Saccharomyces cerevisiae telomerase RNA (TLC1). We show that 2′-O methylation at U809 reduces telomerase activity, resulting in telomere shortening, whereas 2′-O methylation at A804 or A805 leads to moderate telomere lengthening. Importantly, we also show that targeted 2′-O methylation does not affect TLC1 levels and that 2′-O-methylated TLC1 appears to be efficiently assembled into telomerase ribonucleoprotein. Our results demonstrate that RNA-guided RNA modification is a highly useful approach for modulating telomerase activity.

scholarly journals A Triple Helix within a Pseudoknot Is a Conserved and Essential Element of Telomerase RNA

2007 ◽  
Vol 27 (6) ◽  
pp. 2130-2143 ◽  
Author(s):  
Kinneret Shefer ◽  
Yogev Brown ◽  
Valentin Gorkovoy ◽  
Tamar Nussbaum ◽  
Nikolai B. Ulyanov ◽  
...  
Keyword(s):  
Triple Helix ◽  
Kluyveromyces Lactis ◽  
Three Dimensional ◽  
Essential Element ◽  
Proliferative Potential ◽  
Telomerase Rna ◽  
Dependent Manner ◽  
Pseudoknot Structure ◽  
Ph Dependent

ABSTRACT Telomerase copies a short template within its integral telomerase RNA onto eukaryotic chromosome ends, compensating for incomplete replication and degradation. Telomerase action extends the proliferative potential of cells, and thus it is implicated in cancer and aging. Nontemplate regions of telomerase RNA are also crucial for telomerase function. However, they are highly divergent in sequence among species, and their roles are largely unclear. Using in silico three-dimensional modeling, constrained by mutational analysis, we propose a three-dimensional model for a pseudoknot in telomerase RNA of the budding yeast Kluyveromyces lactis. Interestingly, this structure includes a U-A·U major-groove triple helix. We confirmed the triple-helix formation in vitro using oligoribonucleotides and showed that it is essential for telomerase function in vivo. While triplex-disrupting mutations abolished telomerase function, triple compensatory mutations that formed pH-dependent G-C·C+ triples restored the pseudoknot structure in a pH-dependent manner and partly restored telomerase function in vivo. In addition, we identified a novel type of triple helix that is formed by G-C·U triples, which also partly restored the pseudoknot structure and function. We propose that this unusual structure, so far found only in telomerase RNA, provides an essential and conserved telomerase-specific function.

scholarly journals Telomerase activation in mouse mammary tumors: lack of detectable telomere shortening and evidence for regulation of telomerase RNA with cell proliferation.

1996 ◽  
Vol 16 (7) ◽  
pp. 3765-3772 ◽  
Author(s):  
D Broccoli ◽  
L A Godley ◽  
L A Donehower ◽  
H E Varmus ◽  
T de Lange
Keyword(s):  
Cell Proliferation ◽  
Tumor Development ◽  
Mammary Tumorigenesis ◽  
Mammary Tumors ◽  
Mammary Glands ◽  
Telomerase Activity ◽  
Telomerase Rna ◽  
Proliferating Cells ◽  
Telomere Shortening ◽  
Mouse Mammary Tumors

Activation of telomerase in human cancers is thought to be necessary to overcome the progressive loss of telomeric DNA that accompanies proliferation of normal somatic cells. According to this model, telomerase provides a growth advantage to cells in which extensive terminal sequence loss threatens viability. To test these ideas, we have examined telomere dynamics and telomerase activation during mammary tumorigenesis in mice carrying a mouse mammary tumor virus long terminal repeat-driven Wnt-1 transgene. We also analyzed Wnt-1-induced mammary tumors in mice lacking p53 function. Normal mammary glands, hyperplastic mammary glands, and mammary carcinomas all had the long telomeres (20 to 50 kb) typical of Mus musculus and did not show telomere shortening during tumor development. Nevertheless, telomerase activity and the RNA component of the enzyme were consistently upregulated in Wnt-1-induced mammary tumors compared with normal and hyperplastic tissues. The upregulation of telomerase activity and RNA also occurred during tumorigenesis in p53-deficient mice. The expression of telomerase RNA correlated strongly with histone H4 mRNA in all normal tissues and tumors, indicating that the RNA component of telomerase is regulated with cell proliferation. Telomerase activity in the tumors was elevated to a greater extent than telomerase RNA, implying that the enzymatic activity of telomerase is regulated at additional levels. Our data suggest that the mechanism of telomerase activation in mouse mammary tumors is not linked to global loss of telomere function but involves multiple regulatory events including upregulation of telomerase RNA in proliferating cells.

scholarly journals SIRT1 contributes to telomere maintenance and augments global homologous recombination

2010 ◽  
Vol 191 (7) ◽  
pp. 1299-1313 ◽  
Author(s):  
Jose A. Palacios ◽  
Daniel Herranz ◽  
Maria Luigia De Bonis ◽  
Susana Velasco ◽  
Manuel Serrano ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Telomerase Activity ◽  
Histone Deacetylation ◽  
Telomere Maintenance ◽  
Loss Of Function ◽  
Entire Genome ◽  
Telomere Shortening ◽  
Telomere Biology ◽  
Sir Complex

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.

scholarly journals The conserved structure of plant telomerase RNA provides the missing link for an evolutionary pathway from ciliates to humans

2019 ◽  
Vol 116 (49) ◽  
pp. 24542-24550 ◽  
Author(s):  
Jiarui Song ◽  
Dhenugen Logeswaran ◽  
Claudia Castillo-González ◽  
Yang Li ◽  
Sreyashree Bose ◽  
...  
Keyword(s):  
Telomerase Activity ◽  
Telomere Maintenance ◽  
Telomerase Rna ◽  
Telomeric Dna ◽  
Structural Element ◽  
Stem Loop ◽  
Evolutionary Pathway ◽  
Pol Iii

Telomerase is essential for maintaining telomere integrity. Although telomerase function is widely conserved, the integral telomerase RNA (TR) that provides a template for telomeric DNA synthesis has diverged dramatically. Nevertheless, TR molecules retain 2 highly conserved structural domains critical for catalysis: a template-proximal pseudoknot (PK) structure and a downstream stem-loop structure. Here we introduce the authentic TR from the plant Arabidopsis thaliana, called AtTR, identified through next-generation sequencing of RNAs copurifying with Arabidopsis TERT. This RNA is distinct from the RNA previously described as the templating telomerase RNA, AtTER1. AtTR is a 268-nt Pol III transcript necessary for telomere maintenance in vivo and sufficient with TERT to reconstitute telomerase activity in vitro. Bioinformatics analysis identified 85 AtTR orthologs from 3 major clades of plants: angiosperms, gymnosperms, and lycophytes. Through phylogenetic comparisons, a secondary structure model conserved among plant TRs was inferred and verified using in vitro and in vivo chemical probing. The conserved plant TR structure contains a template-PK core domain enclosed by a P1 stem and a 3′ long-stem P4/5/6, both of which resemble a corresponding structural element in ciliate and vertebrate TRs. However, the plant TR contains additional stems and linkers within the template-PK core, allowing for expansion of PK structure from the simple PK in the smaller ciliate TR during evolution. Thus, the plant TR provides an evolutionary bridge that unites the disparate structures of previously characterized TRs from ciliates and vertebrates.

scholarly journals The C Terminus of the Major Yeast Telomere Binding Protein Rap1p Enhances Telomere Formation

1998 ◽  
Vol 18 (3) ◽  
pp. 1284-1295 ◽  
Author(s):  
Alo Ray ◽  
Kurt W. Runge
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Reverse Transcriptase ◽  
Binding Site ◽  
Binding Protein ◽  
Telomerase Activity ◽  
Telomerase Rna ◽  
Constant Length ◽  
C Terminus ◽  
Telomere Binding Protein ◽  
Yeast Telomere

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.

scholarly journals Essential Regions of Saccharomyces cerevisiae Telomerase RNA: Separate Elements for Est1p and Est2p Interaction

2002 ◽  
Vol 22 (7) ◽  
pp. 2366-2374 ◽  
Author(s):  
April J. Livengood ◽  
Arthur J. Zaug ◽  
Thomas R. Cech
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Nucleotide Sequence ◽  
Dna Synthesis ◽  
Active Site ◽  
Telomerase Rna ◽  
Telomeric Dna ◽  
Protein Subunits ◽  
Essential Region ◽  
Selection For

ABSTRACT The Saccharomyces cerevisiae telomerase RNA subunit is encoded by the TLC1 gene. A selection for viable alleles of TLC1 RNA from a large library of random deletion alleles revealed that less than half (∼0.5 kb of the ∼1.3-kb RNA) is required for telomerase function in vivo. The main essential region (430 nucleotides), which contains the template for telomeric DNA synthesis, was required for coimmunoprecipitation with Est1p and Est2p. Furthermore, the subregion required for interaction with Est1p, the telomerase recruitment subunit, differed from those required for interaction with Est2p, the reverse transcriptase subunit. Two regions of the RNA distant from the template in the nucleotide sequence were required for Est2p binding, but the template itself was not. Having the RNA secured to the protein away from the template is proposed to facilitate the translocation of the RNA template through the active site. More generally, our results support a role for the telomerase RNA serving as a scaffold for binding key protein subunits.

scholarly journals Yeast Est2p Affects Telomere Length by Influencing Association of Rap1p with Telomeric Chromatin

2008 ◽  
Vol 28 (7) ◽  
pp. 2380-2390 ◽  
Author(s):  
Hong Ji ◽  
Christopher J. Adkins ◽  
Bethany R. Cartwright ◽  
Katherine L. Friedman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Telomere Length ◽  
Specific Binding ◽  
Telomerase Activity ◽  
Negative Regulator ◽  
Wild Type ◽  
Telomeric Dna ◽  
Telomere Length Homeostasis

ABSTRACT In Saccharomyces cerevisiae, the sequence-specific binding of the negative regulator Rap1p provides a mechanism to measure telomere length: as the telomere length increases, the binding of additional Rap1p inhibits telomerase activity in cis. We provide evidence that the association of Rap1p with telomeric DNA in vivo occurs in part by sequence-independent mechanisms. Specific mutations in EST2 (est2-LT) reduce the association of Rap1p with telomeric DNA in vivo. As a result, telomeres are abnormally long yet bind an amount of Rap1p equivalent to that observed at wild-type telomeres. This behavior contrasts with that of a second mutation in EST2 (est2-up34) that increases bound Rap1p as expected for a strain with long telomeres. Telomere sequences are subtly altered in est2-LT strains, but similar changes in est2-up34 telomeres suggest that sequence abnormalities are a consequence, not a cause, of overelongation. Indeed, est2-LT telomeres bind Rap1p indistinguishably from the wild type in vitro. Taken together, these results suggest that Est2p can directly or indirectly influence the binding of Rap1p to telomeric DNA, implicating telomerase in roles both upstream and downstream of Rap1p in telomere length homeostasis.

Telomerase Activity and Telomere Length of CD4+CD25+ Regulatory T-Cells under Conditions of In Vitro and In Vivo Expansion.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3857-3857
Author(s):  
Dominik G.F. Wolf ◽  
Anna M. Wolf ◽  
Christian Koppelstaetter ◽  
Holger F. Rumpold ◽  
Gert Mayer ◽  
...  
Keyword(s):  
T Cells ◽  
Regulatory T Cells ◽  
Telomere Length ◽  
Cancer Patients ◽  
Telomerase Activity ◽  
Telomere Maintenance ◽  
Healthy Human ◽  
Telomere Shortening

Abstract The expandability of CD4+CD25+ regulatory T-cells (Treg) has been shown in vitro and in vivo. Activation of telomerase activity is a prerequisite for clonal expansion and telomere maintenance in T-cells. There is currently no data available on the expression and function of telomerase in proliferating Treg. Analyses of telomere length by flow-FISH, real-time PCR and Southern blotting revealed that Treg isolated from healthy human volunteers have significantly shortened telomeres when compared to CD4+CD25− T-cells. However, telomere length is not further shortened in Treg isolated from the peripheral blood of cancer patients, despite the observation that the regulatory T-cell pool of these patients was significantly enlarged. To gain further insight into maintenance of telomere length of Treg, we induced in vitro proliferation of Treg by stimulation with anti-CD3 and IL-2. This led to a rapid increase of telomerase activity, as determined by PCR-ELISA. However, when we focused on the proliferating fraction of Treg using a sorting strategy based on the dilution of CFSE, we could show a significant telomere shortening in Treg with high proliferative and immmuno-suppressive capacity. Of note, proliferating CFSElow Treg are characterized by high telomerase activity, which however seems to be insufficient to avoid further telomere shortening under conditions of strong in vitro stimulation. In contrast, under conditions of in vivo expansion of Treg in cancer patients, the induction of telomerase activity is likely to compensate for further telomere erosion. These data might be of importance when considering the application of in vitro expanded Treg for the treatment of GvHD or autoimmune diseases, as telomere shortening might be associated with genomic instability.

Targeting prostate cancer progenitor cells with telomerase interference: A novel therapeutic strategy

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. e22029-e22029
Author(s):  
A. Goldkorn ◽  
T. Xu
Keyword(s):  
Gene Expression ◽  
Prostate Cancer ◽  
Progenitor Cells ◽  
Cancer Progression ◽  
Cell Activation ◽  
Telomerase Activity ◽  
Human Prostate ◽  
Telomerase Rna ◽  
Prostate Tumors

e22029 Background: We investigated whether telomerase, which is critical for benign stem cell activation, also plays a role in prostate cancer progenitor cells (PCPCs), which are thought to mediate therapy resistance and cancer progression, and we tested whether telomerase interference can effectively inhibit PCPC proliferation. Methods: A putative PCPC population was isolated from human prostatectomy specimens via collagen attachment and FACS selection for integrin α2β1 and CD44. PCPCs were characterized for gene expression (RT-PCR), clonogenicity (colony formation), invasiveness (matrigel chamber), and telomerase activity (qPCR-TRAP). PCPC telomerase interference was accomplished by lentiviral expression of 2 constructs: telomerase RNA with an altered template region (MT-Ter) and siRNA targeting wild-type telomerase RNA (anti-Ter siRNA). The effects of these constructs were assessed by measuring PCPC viability (MTS) and apoptosis (TUNEL assay). Results: An integrin α2β1+CD44+ putative PCPC population was isolated from 6 human prostate tumors. This population expressed high levels of “progenitor phenotype” genes (ABCG2, β-catenin, NANOG, Oct3/4) and low levels of “differentiated phenotype” genes (AR and PSA). PCPCs yielded >50 colonies per 1000 cells seeded on collagen after 3 weeks vs. none from FACS- cells, and matrigel chamber assay showed 10% of the PCPC population invading over 24 hours vs. none of the FACS- population. Most importantly, PCPCs possessed at least 20- fold greater telomerase activity than FACS- cells, and induction of telomerase interference in PCPCs via MT-hTer and anti- hTer siRNA expression elicited a brisk apoptotic response (TUNEL) by day 3 in >90% of cells, with concomitant near-complete growth inhibition (MTS). Conclusions: We have shown that human prostate tumors contain a subpopulation of prostate cancer progenitor cells (PCPCs) marked by an undifferentiated gene expression profile, vigorous clonogenicity and invasiveness, and high levels of telomerase activity that can be successfully exploited to neutralize these cells. Ongoing studies are investigating the in vivo effects of telomerase interference on PCPC tumorigenicity in mouse models. No significant financial relationships to disclose.

Mouse prostate tumor inhibition via disruption of murine telomerase: In vivo and in vitro data for a new preclinical cancer model

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. e14631-e14631
Author(s):  
T. Xu ◽  
Y. Xu ◽  
R. Lao ◽  
K. He ◽  
L. Xue ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Dna Damage ◽  
Cancer Cells ◽  
Cancer Cell Line ◽  
Telomerase Activity ◽  
Telomerase Rna ◽  
Prostate Cancer Cells ◽  
Mouse Prostate

e14631 Background: Telomerase-interference (TI), a novel therapeutic strategy, exploits the high telomerase activity in prostate cancer by introducing a mutated telomerase RNA (MT-Ter) that encodes toxic telomeres. Until now, TI has been tested by targeting human telomerase in tumor cells xenografted into immuno-deficient mice, an inadequate model for predicting efficacy and toxicity. We designed and validated 2 new TI gene constructs that specifically target murine telomerase RNA (mTER), enabling the study of TI in preclinical mouse models that are immuno-competent and that develop endogenous prostate tumors. Methods: We designed 2 constructs and cloned them into a lentiviral delivery system: MT-mTER and siRNA against wild type mTer (α-mTer-siRNA). Using a mouse prostate cancer cell line, E4, we tested the 2 constructs for expression (RT-PCR), telomerase activity (TRAP), and biologic activity (53bp1 DNA damage staining, MTS growth assay, TUNEL and caspase apoptosis assays), as well as in vivo efficacy (NOD-SCID allografts). Results: We confirmed MT-mTER expression (∼50-fold) and showed that α-mTer-siRNA specifically depleted WT-mTER (80% reduction) but not MT-mTER when the 2 constructs are co-expressed; thus, the 2 constructs in combination effectively substituted MT-mTer for WT-mTer in the mouse prostate cancer cells. MT-mTER caused mutant telomeric repeats (TTTGGG instead of TTAGGG) to be added to the ends of telomeres, resulting in rapid telomeric uncapping marked by 53bp1 DNA damage foci (an average 7.5 foci/cell vs. 1.4 foci/cell in vector control). This, in turn, led to rapid and significant apoptosis (>90% TUNEL and caspase +) and growth inhibition in vitro (90% reduction by MTS) and in vivo (75% reduction in tumor allograft size). Conclusions: We successfully designed and validated MT-mTer and α-mTer-siRNA, 2 novel gene constructs that specifically target and co-opt murine telomerase activity within mouse prostate cancer cells. These constructs offer a significant advantage, as they can be used to investigate TI in immuno-competent mice that develop prostate cancer, thereby modeling actual human disease and testing TI-based therapies in a much more informative and authentic manner. No significant financial relationships to disclose.

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