Dyskerin Is a Component of the Arabidopsis Telomerase RNP Required for Telomere Maintenance

ABSTRACT Dyskerin binds the H/ACA box of human telomerase RNA and is a core telomerase subunit required for RNP biogenesis and enzyme function in vivo. Missense mutations in dyskerin result in dyskeratosis congenita, a complex syndrome characterized by bone marrow failure, telomerase enzyme deficiency, and progressive telomere shortening. Here we demonstrate that dyskerin also contributes to telomere maintenance in Arabidopsis thaliana. We report that both AtNAP57, the Arabidopsis dyskerin homolog, and AtTERT, the telomerase catalytic subunit, accumulate in the plant nucleolus, and AtNAP57 associates with active telomerase RNP particles in an RNA-dependent manner. Furthermore, AtNAP57 interacts in vitro with AtPOT1a, a novel component of Arabidopsis telomerase. Although a null mutation in AtNAP57 is lethal, AtNAP57, like AtTERT, is not haploinsufficient for telomere maintenance in Arabidopsis. However, introduction of an AtNAP57 allele containing a T66A mutation decreased telomerase activity in vitro, disrupted telomere length regulation on individual chromosome ends in vivo, and established a new, shorter telomere length set point. These results imply that T66A NAP57 behaves as a dominant-negative inhibitor of telomerase. We conclude that dyskerin is a conserved component of the telomerase RNP complex in higher eukaryotes that is required for maximal enzyme activity in vivo.

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

Blood ◽

10.1182/blood.v104.11.3857.3857 ◽

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.

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Extracellular Signal-Regulated Kinase Binds to TFII-I and Regulates Its Activation of the c-fosPromoter

Molecular and Cellular Biology ◽

10.1128/mcb.20.4.1140-1148.2000 ◽

2000 ◽

Vol 20 (4) ◽

pp. 1140-1148 ◽

Cited By ~ 37

Author(s):

Dae-Won Kim ◽

Brent H. Cochran

Keyword(s):

Map Kinase ◽

Transcriptional Activation ◽

Dominant Negative ◽

Binding Motif ◽

Dependent Manner ◽

Consensus Map ◽

Interaction Domain ◽

Extracellular Signal

ABSTRACT We have previously shown that TFII-I enhances transcriptional activation of the c-fos promoter through interactions with upstream elements in a signal-dependent manner. Here we demonstrate that activated Ras and RhoA synergize with TFII-I for c-fospromoter activation, whereas dominant-negative Ras and RhoA inhibit these effects of TFII-I. The Mek1 inhibitor, PD98059 abrogates the enhancement of the c-fos promoter by TFII-I, indicating that TFII-I function is dependent on an active mitogen-activated protein (MAP) kinase pathway. Analysis of the TFII-I protein sequence revealed that TFII-I contains a consensus MAP kinase interaction domain (D box). Consistent with this, we have found that TFII-I forms an in vivo complex with extracellular signal-related kinase (ERK). Point mutations within the consensus MAP kinase binding motif of TFII-I inhibit its ability to bind ERK and its ability to enhance the c-fos promoter. Therefore, the D box of TFII-I is required for its activity on the c-fos promoter. Moreover, the interaction between TFII-I and ERK can be regulated. Serum stimulation enhances complex formation between TFII-I and ERK, and dominant-negative Ras abrogates this interaction. In addition, TFII-I can be phosphorylated in vitro by ERK and mutation of consensus MAP kinase substrate sites at serines 627 and 633 impairs the phosphorylation of TFII-I by ERK and its activity on the c-fos promoter. These results suggest that ERK regulates the activity of TFII-I by direct phosphorylation.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1915312116 ◽

2019 ◽

Vol 116 (49) ◽

pp. 24542-24550 ◽

Cited By ~ 8

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.

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TIN2 Functions with TPP1/POT1 To Stimulate Telomerase Processivity

Molecular and Cellular Biology ◽

10.1128/mcb.00593-18 ◽

2019 ◽

Vol 39 (21) ◽

Cited By ~ 6

Author(s):

Alexandra M. Pike ◽

Margaret A. Strong ◽

John Paul T. Ouyang ◽

Carol W. Greider

Keyword(s):

Telomere Length ◽

Telomerase Activity ◽

Human Cells ◽

Short Telomere ◽

Gene Encoding ◽

Important Regulator

ABSTRACT TIN2 is an important regulator of telomere length, and mutations in TINF2, the gene encoding TIN2, cause short-telomere syndromes. While the genetics underscore the importance of TIN2, the mechanism through which TIN2 regulates telomere length remains unclear. Here, we tested the effects of human TIN2 on telomerase activity. We identified a new isoform in human cells, TIN2M, that is expressed at levels similar to those of previously studied TIN2 isoforms. All three TIN2 isoforms localized to and maintained telomere integrity in vivo, and localization was not disrupted by telomere syndrome mutations. Using direct telomerase activity assays, we discovered that TIN2 stimulated telomerase processivity in vitro. All of the TIN2 isoforms stimulated telomerase to similar extents. Mutations in the TPP1 TEL patch abrogated this stimulation, suggesting that TIN2 functions with TPP1/POT1 to stimulate telomerase processivity. We conclude from our data and previously published work that TIN2/TPP1/POT1 is a functional shelterin subcomplex.

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Phosphorylation and SCF-mediated degradation regulate CREB-H transcription of metabolic targets

Molecular Biology of the Cell ◽

10.1091/mbc.e15-04-0247 ◽

2015 ◽

Vol 26 (16) ◽

pp. 2939-2954 ◽

Cited By ~ 8

Author(s):

Sónia Barbosa ◽

Suzanne Carreira ◽

Daniel Bailey ◽

Fernando Abaitua ◽

Peter O'Hare

Keyword(s):

Target Gene ◽

Active Form ◽

Dominant Negative ◽

Dependent Manner ◽

Critical Determinant ◽

Phosphatase Treatment ◽

Steady State Levels ◽

Treatment Use

CREB‑H, an endoplasmic reticulum–anchored transcription factor, plays a key role in regulating secretion and in metabolic and inflammatory pathways, but how its activity is modulated remains unclear. We examined processing of the nuclear active form and identified a motif around S87–S90 with homology to DSG-type phosphodegrons. We show that this region is subject to multiple phosphorylations, which regulate CREB-H stability by targeting it to the SCFFbw1aE3 ubiquitin ligase. Data from phosphatase treatment, use of phosophospecific antibody, and substitution of serine residues demonstrate phosphorylation of candidate serines in the region, with the core S87/S90 motif representing a critical determinant promoting proteasome-mediated degradation. Candidate kinases CKII and GSK-3b phosphorylate CREB-H in vitro with specificities for different serines. Prior phosphorylation with GSK-3 at one or more of the adjacent serines substantially increases S87/S90-dependent phosphorylation by CKII. In vivo expression of a dominant-negative Cul1 enhances steady-state levels of CREB‑H, an effect augmented by Fbw1a. CREB-H directly interacts with Fbw1a in a phosphorylation-dependent manner. Finally, mutations within the phosphodegron, when incorporated into the full-length protein, result in increased levels of constitutively cleaved nuclear protein and increased transcription and secretion of a key endogenous target gene, apolipoprotein A IV.

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

Molecular and Cellular Biology ◽

10.1128/mcb.01648-07 ◽

2008 ◽

Vol 28 (7) ◽

pp. 2380-2390 ◽

Cited By ~ 11

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.

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Effective Telomerase Inhibition Via Expression of Dominant-Negative HTERT Leads to Altered Growth Kinetics, Elevated Apoptosis and Increased Radiosensitivity of Bcr-Abl-Positive K562 Cells In Vitro.

Blood ◽

10.1182/blood.v110.11.2935.2935 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2935-2935

Author(s):

Ute Brassat ◽

Stefan Balabanov ◽

Henning Wege ◽

Daniel Roessler ◽

Kerstin Borgmann ◽

...

Keyword(s):

Growth Kinetics ◽

K562 Cells ◽

Telomerase Activity ◽

Double Strand Breaks ◽

Dominant Negative ◽

Telomere Maintenance ◽

Telomere Shortening ◽

Telomerase Inhibition ◽

Strand Breaks

Abstract Disease progression in CML is associated with accelerated telomere shortening caused by increased turnover of Bcr-Abl positive cells. We have recently proposed a model in which continuous telomere shortening is correlated with increasing genetic instability in Bcr-Abl-positive cells thus facilitating the acquisition of secondary genetic abnormalities and, as a consequence clonal succession and eventually clinical progression of the disease. Based on this hypothesis, telomerase upregulation in late stage disease is a prerequisite for prevention of replication-induced senescence in Bcr-Abl positive cells. As a consequence, treatment of CML with Telomerase inhibitors (TI) represents an attractive strategy aiming at the potential eradication of cycling CML stem cells. Therefore, we have exploited both pharmacological (small molecule inhibitor) and genetic strategies (dominant negative hTERT mutants, DN-hTERT) of telomerase inhibition in CML cells in vitro We first treated K562 cells with the pharmacological telomerase inhibitor BIBR1532 in vitro. After around 400 population doublings (PD), no differences in growth kinetics nor signs of senescence or apoptosis were observed in BIBR1532 treated cells despite of significant telomere shortening (22 base pairs (bp) per PD) compared to control cells. Furthermore, neither significant differences in mRNA expression of telomere/telomerase-associated proteins, nor accumulation of double strand breaks (DSBs) under irradiation was observed in treated cells with short telomeres as opposed to untreated control cells. The very slow shortening rate of 22bp/PD plus the lack of stigmata pointing to induction of senescence in K562 cells lead to the assumption that telomerase activity is not complete inhibited by the compound. In order to verify the potency of telomerase directed treatments in CML, we therefore expressed DN-hTERT in K562 cells. Integration of DN-hTERT led to a significant decrease in telomerase activity (measured by RQ-TRAP). Furthermore, DN-hTERT expressing cells underwent accelerated telomere shortening at a substantially higher rate (>100 bp/PD) from 15kb to around 4kb within 110 days of culture. In contrast to BIBR1532-treated cells, DN-hTERT expressing K562 cells slowed down growth kinetic in comparison to control cells after 80 days of culture. By using Annexin 5 staining, 25% of apoptotic cells could be detected in cells with critically short telomeres as compared to control cells (<3%). Finally, a significantly increased accumulation of double strand breaks (DSBs) detected by gammaH2AX foci after exposure to irradiation was observed in DN-hTERT K562 cells as compared to control cells pointing to an impaired DNA repair machinery in Bcr-Abl positive cells with disrupted telomere maintenance. In summary, the data suggest that pharmacological telomerase inhibition by BIBR1532 is insufficient to induce telomere-mediated senescence in Bcr-Abl-positive cells. However, accelerated telomere shortening, slowing down of growth kinetics, elevated apoptosis and increased radiosensitivity induced by expression of DN-hTERT indicate a therapeutic potential for telomerase-directed treatment strategies in CML.

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Conditional TRF1 knockout in the hematopoietic compartment leads to bone marrow failure and recapitulates clinical features of dyskeratosis congenita

Blood ◽

10.1182/blood-2012-03-418038 ◽

2012 ◽

Vol 120 (15) ◽

pp. 2990-3000 ◽

Cited By ~ 41

Author(s):

Fabian Beier ◽

Miguel Foronda ◽

Paula Martinez ◽

Maria A. Blasco

Keyword(s):

Bone Marrow ◽

Clinical Features ◽

Bone Marrow Failure ◽

Telomerase Activity ◽

Dyskeratosis Congenita ◽

Telomere Shortening ◽

Interacting Protein ◽

Compensatory Proliferation ◽

Allelic Variations

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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Diagnostic utility of telomere length measurement in a hospital setting

10.1101/225797 ◽

2017 ◽

Author(s):

Jonathan K. Alder ◽

Vidya Sagar Hanumanthu ◽

Margaret A. Strong ◽

Amy E. DeZern ◽

Susan E. Stanley ◽

...

Keyword(s):

Bone Marrow ◽

Telomere Length ◽

Predictive Value ◽

Bone Marrow Failure ◽

Hospital Setting ◽

Treatment Decisions ◽

Telomere Maintenance ◽

Short Telomere ◽

Hematopoietic Stem

AbstractVery short telomere length (TL) provokes cellular senescence in vitro, but the clinical utility of TL measurement in a hospital-based setting has not been determined. We tested the diagnostic and prognostic value of TL measurement by flow cytometry and fluorescence in situ hybridization (flowFISH) in individuals with mutations in telomerase and telomere maintenance genes, and examined prospectively whether TL altered treatment decisions for patients with bone marrow failure. TL had a definable normal range across populations with discrete lower and upper boundaries. TL above the 50th age-adjusted percentile had a 100% negative predictive value for clinically relevant mutations in telomere maintenance genes, but the lower threshold for diagnosis was age-dependent. The extent of deviation from the age-adjusted median correlated with the age at diagnosis of a telomere syndrome as well as the predominant complication. Mild short telomere defects manifested in adults as pulmonary fibrosis-emphysema, while severely short TL manifested in children as bone marrow failure and immunodeficiency. Among 38 newly diagnosed patients with bone marrow failure, TL shorter than the 1st age-adjusted percentile enriched for patients with germline mutations in inherited bone marrow failure genes, such as RUNX1, in addition to telomere maintenance genes. The TL result modified the hematopoietic stem cell donor choice and/or treatment regimen in one-fourth of the cases (9 of 38,24%). TL testing by flowFISH has diagnostic and predictive value in definable clinical settings. In patients with bone marrow failure, it altered treatment decisions for a significant subset.

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Significance of Telomere Length Measurement in the Diagnosis of Dyskeratosis Congenita.

Blood ◽

10.1182/blood.v110.11.836.836 ◽

2007 ◽

Vol 110 (11) ◽

pp. 836-836

Author(s):

Hong-Yan Du ◽

Elena Pumbo ◽

Akiko Shimamura ◽

Adrianna Vlachos ◽

Jeffrey M. Lipton ◽

...

Keyword(s):

Bone Marrow ◽

Aplastic Anemia ◽

Telomere Length ◽

Bone Marrow Failure ◽

Skin Pigmentation ◽

Screening Method ◽

Dyskeratosis Congenita ◽

Telomere Maintenance ◽

Healthy Controls ◽

Mutation Carriers

Abstract Dyskeratosis congenita (DC) is a rare inherited bone marrow failure (BMF) syndrome. The classical features of DC include nail dystrophy, abnormal skin pigmentation, and mucosal leukoplakia. The diagnosis of DC can be difficult. Originally, the diagnosis was based on the presence of the classical mucocutaneous features. However, the identification of four genes responsible for DC (DKC1, TERC, TERT, and NOP10) showed that these mucocutaneous features are only present in a proportion of patients with DC. Additionally, screening for mutations in the affected genes is expensive and is negative in about 50% of patients with classical features of DC. The products of the genes mutated in DC are the components of the telomerase ribonucleoprotein complex, which is essential for telomere maintenance. Therefore it has been postulated that DC is a disease arising from excessive telomere shortening. Here we examined whether the measurement of telomeres could be used as a screening test to identify individuals with DC. For this purpose we examined telomere length in peripheral blood mononuclear cells from 169 patients who presented with bone marrow failure including 17 patients with DC, diagnosed by the presence of classical cutaneous features or the identification of mutations in DKC1, TERC or TERT, 28 patients with paroxysmal nocturnal hemoglobinuria, 25 patients with Diamond Blackfan anemia, 5 patients with Shwachman-Diamond syndrome, 8 patients with myelodysplastic syndrome, and 74 patients with aplastic anemia of unknown cause classified as idiopathic aplastic anemia. In addition we measured telomere length in 12 patients with idiopathic pulmonary fibrosis and in 45 individuals with a de novo deletion of chromosome 5p including the TERT gene. Their telomere lengths were compared with those of 202 age-matched healthy controls. Moreover, mutations were screened in the genes associated with DC. In cases where a mutation was identified, telomere length and mutations were also examined in all the family members. Our results show that all patients with DC and bone marrow failure have very short telomeres far below the first percentile of healthy controls. Not all mutation carriers, including some carriers of apparently dominant mutations, have very short telomeres. What is more, very short telomeres could be found in healthy individuals in these families, some of whom were not mutation carriers. These findings indicate that in patients with BMF the measurement of telomere length is a sensitive screening method for DC, whether very short telomeres in this setting are also specific for DC remains to be determined. However, in contrast to a previous study, we find that telomere length does not always identify mutation carriers in the families of DC.

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