scholarly journals Nuclear receptors regulate alternative lengthening of telomeres through a novel noncanonical FANCD2 pathway

2019 ◽  
Vol 5 (10) ◽  
pp. eaax6366 ◽  
Author(s):  
Mafei Xu ◽  
Jun Qin ◽  
Leiming Wang ◽  
Hui-Ju Lee ◽  
Chung-Yang Kao ◽  
...  
Keyword(s):  
Nuclear Receptors ◽  
Direct Interaction ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Core Complex ◽  
Alternative Lengthening Of Telomeres ◽  
Independent Manner ◽  
Replication Complex ◽  
Alternative Lengthening ◽  
Key Steps

Alternative lengthening of telomeres (ALT) is known to use homologous recombination (HR) to replicate telomeric DNA in a telomerase-independent manner. However, the detailed process remains largely undefined. It was reported that nuclear receptors COUP-TFII and TR4 are recruited to the enriched GGGTCA variant repeats embedded within ALT telomeres, implicating nuclear receptors in regulating ALT activity. Here, we identified a function of nuclear receptors in ALT telomere maintenance that involves a direct interaction between COUP-TFII/TR4 and FANCD2, the key protein in the Fanconi anemia (FA) DNA repair pathway. The COUP-TFII/TR4-FANCD2 complex actively induces the DNA damage response by recruiting endonuclease MUS81 and promoting the loading of the PCNA-POLD3 replication complex in ALT telomeres. Furthermore, the COUP-TFII/TR4-mediated ALT telomere pathway does not require the FA core complex or the monoubiquitylation of FANCD2, key steps in the canonical FA pathway. Thus, our findings reveal that COUP-TFII/TR4 regulates ALT telomere maintenance through a novel noncanonical FANCD2 pathway.

scholarly journals Alternative Lengthening of Telomeres Mediated by Mitotic DNA Synthesis Engages Break-Induced Replication Processes

2017 ◽  
Vol 37 (20) ◽  
Author(s):  
Jaewon Min ◽  
Woodring E. Wright ◽  
Jerry W. Shay
Keyword(s):  
Dna Synthesis ◽  
Telomere Maintenance ◽  
Synthesis Process ◽  
Loop Formation ◽  
Alternative Lengthening Of Telomeres ◽  
Independent Manner ◽  
Content Type ◽  
Alternative Lengthening ◽  
Telomere Replication ◽  
Break Induced Replication

ABSTRACT Alternative lengthening of telomeres (ALT) is a telomerase-independent telomere maintenance mechanism that occurs in a subset of cancers. By analyzing telomerase-positive cells and their human TERC knockout-derived ALT human cell lines, we show that ALT cells harbor more fragile telomeres representing telomere replication problems. ALT-associated replication defects trigger mitotic DNA synthesis (MiDAS) at telomeres in a RAD52-dependent, but RAD51-independent, manner. Telomeric MiDAS is a conservative DNA synthesis process, potentially mediated by break-induced replication, similar to type II ALT survivors in Saccharomyces cerevisiae. Replication stresses induced by ectopic oncogenic expression of cyclin E, G-quadruplexes, or R-loop formation facilitate the ALT pathway and lead to telomere clustering, a hallmark of ALT cancers. The TIMELESS/TIPIN complex suppresses telomere clustering and telomeric MiDAS, whereas the SMC5/6 complex promotes them. In summary, ALT cells exhibit more telomere replication defects that result in persistent DNA damage responses at telomeres, leading to the engagement of telomeric MiDAS (spontaneous mitotic telomere synthesis) that is triggered by DNA replication stress, a potential driver of genomic duplications in cancer.

scholarly journals Detection of alternative lengthening of telomeres mechanism on tumor sections

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Eloïse Claude ◽  
Guillaume de Lhoneux ◽  
Christophe E. Pierreux ◽  
Etienne Marbaix ◽  
Maëlle de Ville de Goyet ◽  
...  
Keyword(s):  
Xenograft Model ◽  
Telomere Maintenance ◽  
Cancer Therapies ◽  
Telomeric Dna ◽  
Alternative Lengthening Of Telomeres ◽  
Alternative Lengthening ◽  
Mouse Xenograft Model ◽  
Targeted Cancer Therapies ◽  
Amplification Assay ◽  
Set Up

AbstractThe vast majority of adult cancer cells achieve cellular immortality by activating a telomere maintenance mechanism (TMM). While this is mostly achieved by the de-silencing of hTERT telomerase gene expression, an alternative homologous recombination-based and telomerase-independent mechanism, known as ALT (Alternative Lengthening of Telomeres), is frequently activated in a subset of tumors, including paediatric cancers. Being absent from normal cells, the ALT mechanism offers interesting perspectives for new targeted cancer therapies. To date, however, the development of better translationally applicable tools for ALT detection in tumor sections is still needed. Here, using a newly derived ALT-positive cancer cell mouse xenograft model, we extensively examined how the previously known ALT markers could be used as reliable tools for ALT diagnosis in tumor sections. We found that, together with the detection of ultra-bright telomeric signals (UBS), an ALT hallmark, native telomeric FISH, that detects single-stranded C-rich telomeric DNA, provides a very sensitive and robust tool for ALT diagnosis in tissues. We applied these assays to paediatric tumor samples and readily identified three ALT-positive tumors for which the TMM was confirmed by the gold-standard C-circle amplification assay. Although the latter offers a robust assay for ALT detection in the context of research laboratories, it is more difficult to set up in histopathological laboratories and could therefore be conveniently replaced by the combination of UBS detection and native telomeric FISH.

scholarly journals Alternative lengthening of telomeres in childhood neuroblastoma from genome to proteome

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sabine A. Hartlieb ◽  
Lina Sieverling ◽  
Michal Nadler-Holly ◽  
Matthias Ziehm ◽  
Umut H. Toprak ◽  
...  
Keyword(s):  
High Frequency ◽  
Clinical Course ◽  
Population Based ◽  
Telomeric Repeat ◽  
Telomere Maintenance ◽  
Study Cohort ◽  
Alternative Lengthening Of Telomeres ◽  
Course Of Disease ◽  
Low Protein ◽  
Alternative Lengthening

AbstractTelomere maintenance by telomerase activation or alternative lengthening of telomeres (ALT) is a major determinant of poor outcome in neuroblastoma. Here, we screen for ALT in primary and relapsed neuroblastomas (n = 760) and characterize its features using multi-omics profiling. ALT-positive tumors are molecularly distinct from other neuroblastoma subtypes and enriched in a population-based clinical sequencing study cohort for relapsed cases. They display reduced ATRX/DAXX complex abundance, due to either ATRX mutations (55%) or low protein expression. The heterochromatic histone mark H3K9me3 recognized by ATRX is enriched at the telomeres of ALT-positive tumors. Notably, we find a high frequency of telomeric repeat loci with a neuroblastoma ALT-specific hotspot on chr1q42.2 and loss of the adjacent chromosomal segment forming a neo-telomere. ALT-positive neuroblastomas proliferate slowly, which is reflected by a protracted clinical course of disease. Nevertheless, children with an ALT-positive neuroblastoma have dismal outcome.

scholarly journals G-quadruplex Stabilization Fuels the ALT Pathway in ALT-positive Osteosarcoma Cells

Genes ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 304 ◽  
Author(s):  
Roberta Amato ◽  
Martina Valenzuela ◽  
Francesco Berardinelli ◽  
Erica Salvati ◽  
Carmen Maresca ◽  
...  
Keyword(s):  
Dna Damage ◽  
Sister Chromatid Exchanges ◽  
Telomere Maintenance ◽  
Osteosarcoma Cell ◽  
Telomeric Dna ◽  
Replicative Stress ◽  
Alternative Lengthening ◽  
G Quadruplex ◽  
Reduce Cell Proliferation ◽  
The Impact

Most human tumors maintain telomere lengths by telomerase, whereas a portion of them (10–15%) uses a mechanism named alternative lengthening of telomeres (ALT). The telomeric G-quadruplex (G4) ligand RHPS4 is known for its potent antiproliferative effect, as shown in telomerase-positive cancer models. Moreover, RHPS4 is also able to reduce cell proliferation in ALT cells, although the influence of G4 stabilization on the ALT mechanism has so far been poorly investigated. Here we show that sensitivity to RHPS4 is comparable in ALT-positive (U2OS; SAOS-2) and telomerase-positive (HOS) osteosarcoma cell lines, unlinking the telomere maintenance mechanism and RHPS4 responsiveness. To investigate the impact of G4 stabilization on ALT, the cardinal ALT hallmarks were analyzed. A significant induction of telomeric doublets, telomeric clusterized DNA damage, ALT-associated Promyelocytic Leukaemia-bodies (APBs), telomere sister chromatid exchanges (T-SCE) and c-circles was found exclusively in RHPS4-treated ALT cells. We surmise that RHPS4 affects ALT mechanisms through the induction of replicative stress that in turn is converted in DNA damage at telomeres, fueling recombination. In conclusion, our work indicates that RHPS4-induced telomeric DNA damage promotes overactivation of telomeric recombination in ALT cells, opening new questions on the therapeutic employment of G4 ligands in the treatment of ALT positive tumors.

scholarly journals Alternative lengthening of telomeres is the major telomere maintenance mechanism in astrocytoma with isocitrate dehydrogenase 1 mutation

2020 ◽  
Vol 147 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Monica Sofia Ventura Ferreira ◽  
Mia Dahl Sørensen ◽  
Stefan Pusch ◽  
Dagmar Beier ◽  
Anne-Sophie Bouillon ◽  
...  
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Telomere Maintenance ◽  
Alternative Lengthening Of Telomeres ◽  
Isocitrate Dehydrogenase 1 ◽  
Maintenance Mechanism ◽  
Alternative Lengthening

scholarly journals Genetic Inactivation ofATRXLeads to a Decrease in the Amount of Telomeric Cohesin and Level of Telomere Transcription in Human Glioma Cells

2015 ◽  
Vol 35 (16) ◽  
pp. 2818-2830 ◽  
Author(s):  
Rita Eid ◽  
Marie-Véronique Demattei ◽  
Harikleia Episkopou ◽  
Corinne Augé-Gouillou ◽  
Anabelle Decottignies ◽  
...  
Keyword(s):  
Rna Polymerase Ii ◽  
Chromatin Immunoprecipitation ◽  
Glioma Cells ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Hairpin Rna ◽  
Genetic Inactivation ◽  
Alternative Lengthening ◽  
Rnap Ii ◽  
Subtelomeric Regions

Mutations in ATRX (alphathalassemia/mentalretardation syndromeX-linked), a chromatin-remodeling protein, are associated with the telomerase-independent ALT (alternative lengthening of telomeres) pathway of telomere maintenance in several types of cancer, including human gliomas. In telomerase-positive glioma cells, we found by immunofluorescence that ATRX localized not far from the chromosome ends but not exactly at the telomere termini. Chromatin immunoprecipitation (ChIP) experiments confirmed a subtelomeric localization for ATRX, yet short hairpin RNA (shRNA)-mediated genetic inactivation ofATRXfailed to trigger the ALT pathway. Cohesin has been recently shown to be part of telomeric chromatin. Here, using ChIP, we showed that genetic inactivation ofATRXprovoked diminution in the amount of cohesin in subtelomeric regions of telomerase-positive glioma cells. Inactivation ofATRXalso led to diminution in the amount of TERRAs, noncoding RNAs resulting from transcription of telomeric DNA, as well as to a decrease in RNA polymerase II (RNAP II) levels at the telomeres. Our data suggest that ATRX might establish functional interactions with cohesin on telomeric chromatin in order to control TERRA levels and that one or the other or both of these events might be relevant to the triggering of the ALT pathway in cancer cells that exhibit genetic inactivation ofATRX.

Chaperones and Their Role in Telomerase Ribonucleoprotein Biogenesis and Telomere Maintenance

2018 ◽  
Vol 16 (1) ◽  
pp. 31-43
Author(s):  
Maria Alejandra Viviescas ◽  
Maria Isabel Nogueira Cano ◽  
Marcela Segatto
Keyword(s):  
Telomere Length ◽  
Molecular Chaperones ◽  
Genome Stability ◽  
Direct Interaction ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Rnp Complex ◽  
And Migration ◽  
Human Telomerase ◽  
Rna Chaperones

Telomere length maintenance is important for genome stability and cell division. In most eukaryotes, telomeres are maintained by the telomerase ribonucleoprotein (RNP) complex, minimally composed of the Telomerase Reverse Transcriptase (TERT) and the telomerase RNA (TER) components. In addition to TERT and TER, other protein subunits are part of the complex and are involved in telomerase regulation, assembly, disassembly, and degradation. Among them are some molecular chaperones such as Hsp90 and its co-chaperone p23 which are found associated with the telomerase RNP complex in humans, yeast and probably in protozoa. Hsp90 and p23 are necessary for the telomerase RNP assembly and enzyme activity. In budding yeast, the Hsp90 homolog (Hsp82) is also responsible for the association and dissociation of telomerase from the telomeric DNA by its direct interaction with a telomere end-binding protein (Cdc13), responsible for regulating telomerase access to telomeres. In addition, AAA+ ATPases, such as Pontin and Reptin, which are also considered chaperone- like proteins, associate with the human telomerase complex by the direct interaction of Pontin with TERT and dyskerin. They are probably responsible for telomerase RNP assembly since their depletion impairs the accumulation of the complex. Moreover, various RNA chaperones, are also pivotal in the assembly and migration of the mature telomerase complex and complex intermediates. In this review, we will focus on the importance of molecular chaperones for telomerase RNP biogenesis and how they impact telomere length maintenance and cellular homeostasis.

Evidence for Alternative Lengthening of Telomeres in Chronic Lymphocytic Leukemia Patients.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1179-1179
Author(s):  
Rajendra N. Damle ◽  
Taraneh Banapour ◽  
Cristina Sison ◽  
Steven L. Allen ◽  
Kanti R. Rai ◽  
...  
Keyword(s):  
Chronic Lymphocytic Leukemia ◽  
Telomerase Activity ◽  
Lymphocytic Leukemia ◽  
Nuclear Bodies ◽  
Telomere Maintenance ◽  
Osteosarcoma Cell ◽  
Clonal Deletion ◽  
Alternative Lengthening Of Telomeres ◽  
Alternative Lengthening ◽  
V Genes

Abstract Telomere shortening is a consequence of repetitive clonal replication and leads to clonal deletion unless DNA extension and repair occur. All tumors must circumvent this problem by up-regulating mechanisms that lead to chromosomal lengthening. Two mechanisms have been identified that maintain chromosome ends- telomerase that does so by reverse transcription and alternative lengthening of telomeres (ALT) that occurs by homologous recombination. The latter function is characterized by the presence of promyelocytic leukemia protein-associated nuclear bodies (PML-NBs) and the presence of PML-NB is used to mark cells that use this process. B cell Chronic lymphocytic leukemia (B-CLL) cells with unmutated Ig V genes have shorter mean telomere lengths compared with those exhibiting mutated Ig V genes. In addition, cells with unmutated Ig V genes demonstrate more telomerase activity than their mutated counterparts. The mutated cases show long and heterogeneously elongated telomeres in spite of the absence, in most cases, of detectable telomerase activity. Therefore we determined whether the ALT pathway plays a role in telomere maintenance in B-CLL, using a monoclonal anti-PML antibody and a flow-cytometric assay for assessment of PML protein. Telomerase-expressing Jurkat T cells and murine fibroblasts-L cells served as negative controls for PML staining, whereas the ALT positive Osteosarcoma cell line U2-OS served as a positive control. In a cohort of 20 B-CLL cases, PML protein was detected in all cases regardless of Ig V mutation status. In addition, a similar percentage of cells within the clones contained PML (10 - 90% of the members of unmutated clones and 11–96% of mutated clones), whereas peripheral blood B cells from 6/6 elderly normal donors did not show any PML staining. PML expression was compared with telomere length and telomerase activity in the same cases. The percentage of cells showing PML expression inversely correlated with telomerase activity (r= −0.58; p=0.029). Although in most published reports telomere maintenance by ALT occurs in the absence of telomerase activity, we found ALT (as suggested by PML positive cells) in cells with telomerase activity (detected by the standard TRAP assay). Thus, B-CLL cases can express PML bodies and some B-CLL cells can contain both PML-NB and express telomerase activity. These findings suggest that B-CLL cells can use two distinct mechanisms to assure telomere maintenance and perpetuate clonal survival and expansion.

scholarly journals Oncogenic herpesvirus KSHV triggers hallmarks of alternative lengthening of telomeres

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Timothy P. Lippert ◽  
Paulina Marzec ◽  
Aurora I. Idilli ◽  
Grzegorz Sarek ◽  
Aleksandra Vancevska ◽  
...  
Keyword(s):  
Cancer Cells ◽  
Cell Lines ◽  
Telomere Maintenance ◽  
Alternative Lengthening Of Telomeres ◽  
Telomere Shortening ◽  
Alternative Lengthening ◽  
A Cell ◽  
Infected Cells ◽  
Break Induced Replication ◽  
Alt Activity

AbstractTo achieve replicative immortality, cancer cells must activate telomere maintenance mechanisms to prevent telomere shortening. ~85% of cancers circumvent telomeric attrition by re-expressing telomerase, while the remaining ~15% of cancers induce alternative lengthening of telomeres (ALT), which relies on break-induced replication (BIR) and telomere recombination. Although ALT tumours were first reported over 20 years ago, the mechanism of ALT induction remains unclear and no study to date has described a cell-based model that permits the induction of ALT. Here, we demonstrate that infection with Kaposi’s sarcoma herpesvirus (KSHV) induces sustained acquisition of ALT-like features in previously non-ALT cell lines. KSHV-infected cells acquire hallmarks of ALT activity that are also observed in KSHV-associated tumour biopsies. Down-regulating BIR impairs KSHV latency, suggesting that KSHV co-opts ALT for viral functionality. This study uncovers KSHV infection as a means to study telomere maintenance by ALT and reveals features of ALT in KSHV-associated tumours.

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