scholarly journals Expression of telomerase prevents ALT and maintains telomeric heterochromatin in juvenile brain tumors

2019 ◽  
Author(s):  
Aurora Irene Idilli ◽  
Emilio Cusanelli ◽  
Francesca Pagani ◽  
Emanuela Kerschbamer ◽  
Francesco Berardinelli ◽  
...  
Keyword(s):  
Brain Tumor ◽  
Brain Tumors ◽  
Cancer Progression ◽  
Replicative Senescence ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Expression Of Genes ◽  
Alternative Lengthening ◽  
Brain Tumor Cells ◽  
Telomeric Heterochromatin

ABSTRACTThe activation of a telomere maintenance mechanism (TMM) is an essential step in cancer progression to escape replicative senescence and apoptosis. Paediatric brain tumors frequently exhibit Alternative Lengthening of Telomere (ALT) as active TMM, but the mechanisms involved in the induction of ALT in brain tumor cells are not clear.Here, we report a model of juvenile zebrafish brain tumor that progressively develops ALT. We discovered that reduced expression of tert and increase in Terra expression precedes ALT development. Additionally, tumors show persistent telomeric DNA damage and loss of heterochromatin marks at chromosome ends. Surprisingly, expression of telomerase reverts ALT features. Comparative analysis of gene expression after the rescue of ALT with telomerase and analysis of telomerase positive paediatric brain cancers showed increase of telomeric heterochromatin and maintenance of telomere length compared to ALT tumors, with reduced expression of genes of the pre-replicative complex as hallmark. Thus our study identifies telomere maintenance mechanisms as major drivers of telomeric DNA replication and chromatin status in brain cancers.

scholarly journals Changes in the Expression of Pre-Replicative Complex Genes in hTERT and ALT Pediatric Brain Tumors

Cancers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 1028 ◽  
Author(s):  
Aurora Irene Idilli ◽  
Francesca Pagani ◽  
Emanuela Kerschbamer ◽  
Francesco Berardinelli ◽  
Manuel Bernabé ◽  
...  
Keyword(s):  
Gene Expression ◽  
Brain Tumors ◽  
Cancer Cells ◽  
Pediatric Brain Tumors ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Maintenance Mechanism ◽  
Alternative Lengthening ◽  
Differential Gene ◽  
Pediatric Brain

Background: The up-regulation of a telomere maintenance mechanism (TMM) is a common feature of cancer cells and a hallmark of cancer. Routine methods for detecting TMMs in tumor samples are still missing, whereas telomerase targeting treatments are becoming available. In paediatric cancers, alternative lengthening of telomeres (ALT) is found in a subset of sarcomas and malignant brain tumors. ALT is a non-canonical mechanism of telomere maintenance developed by cancer cells with no-functional telomerase. Methods: To identify drivers and/or markers of ALT, we performed a differential gene expression analysis between two zebrafish models of juvenile brain tumors, that differ only for the telomere maintenance mechanism adopted by tumor cells: one is ALT while the other is telomerase-dependent. Results: Comparative analysis of gene expression identified five genes of the pre-replicative complex, ORC4, ORC6, MCM2, CDC45 and RPA3 as upregulated in ALT. We searched for a correlation between telomerase levels and expression of the pre-replicative complex genes in a cohort of paediatric brain cancers and identified a counter-correlation between telomerase expression and the genes of the pre-replicative complex. Moreover, the analysis of ALT markers in a group of 20 patients confirmed the association between ALT and increased RPA and decreased H3K9me3 localization at telomeres. Conclusions: Our study suggests that telomere maintenance mechanisms may act as a driver of telomeric DNA replication and chromatin status in brain cancers and identifies markers of ALT that could be exploited for precise prognostic and therapeutic purposes.

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 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 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.

scholarly journals Rad21 Haploinsufficiency Prevents ALT-Associated Phenotypes in Zebrafish Brain Tumors

Genes ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1442
Author(s):  
Aurora Irene Idilli ◽  
Cecilia Pazzi ◽  
Francesca dal Pozzolo ◽  
Michela Roccuzzo ◽  
Maria Caterina Mione
Keyword(s):  
Brain Tumors ◽  
Telomere Maintenance ◽  
Long Distance ◽  
Zebrafish Model ◽  
Strand Breaks ◽  
Zebrafish Brain ◽  
3D Genome ◽  
Alternative Lengthening ◽  
Repair Efficiency

Cohesin is a protein complex consisting of four core subunits responsible for sister chromatid cohesion in mitosis and meiosis, and for 3D genome organization and gene expression through the establishment of long distance interactions regulating transcriptional activity in the interphase. Both roles are important for telomere integrity, but the role of cohesin in telomere maintenance mechanisms in highly replicating cancer cells in vivo is poorly studied. Here we used a zebrafish model of brain tumor, which uses alternative lengthening of telomeres (ALT) as primary telomere maintenance mechanism to test whether haploinsufficiency for Rad21, a member of the cohesin ring, affects ALT development. We found that a reduction in Rad21 levels prevents ALT-associated phenotypes in zebrafish brain tumors and triggers an increase in tert expression. Despite the rescue of ALT phenotypes, tumor cells in rad21+/− fish exhibit an increase in DNA damage foci, probably due to a reduction in double-strand breaks repair efficiency.

scholarly journals The Methanol Extract ofAngelica sinensisInduces Cell Apoptosis and Suppresses Tumor Growth in Human Malignant Brain Tumors

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Yu-Ling Lin ◽  
Wen-Lin Lai ◽  
Horng-jyh Harn ◽  
Pei-Hsiu Hung ◽  
Ming-Chang Hsieh ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Brain Tumor ◽  
Brain Tumors ◽  
Cell Cycle Arrest ◽  
Tumor Cells ◽  
Methanol Extract ◽  
Cycle Arrest ◽  
Anticancer Effects ◽  
Brain Tumor Cells

Glioblastoma multiforme (GBM) is a highly vascularized and invasive neoplasm. The methanol extract ofAngelica sinensis(AS-M) is commonly used in traditional Chinese medicine to treat several diseases, such as gastric mucosal damage, hepatic injury, menopausal symptoms, and chronic glomerulonephritis. AS-M also displays potency in suppressing the growth of malignant brain tumor cells. The growth suppression of malignant brain tumor cells by AS-M results from cell cycle arrest and apoptosis. AS-M upregulates expression of cyclin kinase inhibitors, including p16, to decrease the phosphorylation of Rb proteins, resulting in arrest at the G0-G1phase. The expression of the p53 protein is increased by AS-M and correlates with activation of apoptosis-associated proteins. Therefore, the apoptosis of cancer cells induced by AS-M may be triggered through the p53 pathway. Inin vivostudies, AS-M not only suppresses the growth of human malignant brain tumors but also significantly prolongs patient survival. In addition, AS-M has potent anticancer effects involving cell cycle arrest, apoptosis, and antiangiogenesis. Thein vitroandin vivoanticancer effects of AS-M indicate that this extract warrants further investigation and potential development as a new antibrain tumor agent, providing new hope for the chemotherapy of malignant brain cancer.

scholarly journals Telomerase-Independent Proliferation Is Influenced by Cell Type in Saccharomyces cerevisiae

Genetics ◽  
2003 ◽  
Vol 164 (3) ◽  
pp. 909-921
Author(s):  
Joanna E Lowell ◽  
Alexander I Roughton ◽  
Victoria Lundblad ◽  
Lorraine Pillus
Keyword(s):  
Replicative Senescence ◽  
Telomere Maintenance ◽  
Cell Type ◽  
Telomeric Dna ◽  
Yeast Strains ◽  
Cell Type Specific ◽  
Specific Regulation ◽  
Mat Locus ◽  
Dependent Pathway

Abstract Yeast strains harboring mutations in genes required for telomerase function (TLC1 and the EST genes) exhibit progressive shortening of telomeric DNA and replicative senescence. A minority of cells withstands loss of telomerase through RAD52-dependent amplification of telomeric and subtelomeric sequences; such survivors are now capable of long-term propagation with telomeres maintained by recombination rather than by telomerase. Here we report that simultaneous expression in haploid cells of both MATa and MATα information suppresses the senescence of telomerase-deficient mutants, with suppression occurring via the RAD52-dependent survivor pathway(s). Such suppression can be mimicked by deletion of SIR1-SIR4, genes that function in transcriptional silencing of several loci including the silent mating-type loci. Furthermore, telomerase-defective diploid strains that express only MATa or MATα information senesce at a faster rate than telomerase-defective diploids that are heterozygous at the MAT locus. This suggests that the RAD52-dependent pathway(s) for telomere maintenance respond to changes in the levels of recombination, a process regulated in part by the hierarchy of gene control that includes MAT regulation. We propose that cell-type-specific regulation of recombination at human telomeres may similarly contribute to the tissue-specific patterns of disease found in telomerase-deficient tumors.

scholarly journals Suppression of cdc13-2-associated senescence by pif1-m2 requires Ku-mediated telomerase recruitment

2021 ◽  
Author(s):  
Enikő Fekete-Szücs ◽  
Fernando Rodrigo Rosas Bringas ◽  
Sonia Stinus ◽  
Michael Chang
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Replicative Senescence ◽  
Telomere Maintenance ◽  
Telomerase Rna ◽  
Telomeric Dna ◽  
Insight Into

In Saccharomyces cerevisiae, recruitment of telomerase to telomeres requires an interaction between Cdc13, which binds single-stranded telomeric DNA, and the Est1 subunit of telomerase. A second pathway involving an interaction between the yKu complex and telomerase RNA (TLC1) contributes to telomerase recruitment, but cannot sufficiently recruit telomerase on its own to prevent replicative senescence when the primary Cdc13-Est1 pathway is abolished—for example, in the cdc13-2 mutant. In this study, we find that mutation of PIF1, which encodes a helicase that inhibits telomerase, suppresses the replicative senescence of cdc13-2 by increasing reliance on the yKu-TLC1 pathway for telomerase recruitment. Our findings reveal new insight into telomerase-mediated telomere maintenance.

scholarly journals Analysis of two mechanisms of telomere maintenance based on the theory of g-Networks and stochastic automata networks

BMC Genomics ◽  
2020 ◽  
Vol 21 (S9) ◽  
Author(s):  
Kyung Hyun Lee ◽  
Marek Kimmel
Keyword(s):  
Queueing Theory ◽  
Physiological Condition ◽  
Replicative Senescence ◽  
Transient State ◽  
Telomere Maintenance ◽  
Stochastic Automata ◽  
Automata Networks ◽  
Alternative Lengthening ◽  
Normal Physiological Condition ◽  
The Given

Abstract * Background Telomeres, which are composed of repetitive nucleotide sequences at the end of chromosomes, behave as a division clock that measures replicative senescence. Under the normal physiological condition, telomeres shorten with each cell division, and cells use the telomere lengths to sense the number of divisions. Replicative senescence has been shown to occur at approximately 50–70 cell divisions, which is termed the Hayflick’s limit. However, in cancer cells telomere lengths are stabilized, thereby allowing continual cell replication by two known mechanisms: activation of telomerase and Alternative Lengthening of Telomeres (ALT). The connections between the two mechanisms are complicated and still poorly understood. * Results In this research, we propose that two different approaches, G-Networks and Stochastic Automata Networks, which are stochastic models motivated by queueing theory, are useful to identify a set of genes that play an important role in the state of interest and to infer their previously unknown correlation by obtaining both stationary and joint transient distributions of the given system. Our analysis using G-Network detects five statistically significant genes (CEBPA, FOXM1, E2F1, c-MYC, hTERT) with either mechanism, contrasted to normal cells. A new algorithm is introduced to show how the correlation between two genes of interest varies in the transient state according not only to each mechanism but also to each cell condition. * Conclusions This study expands our existing knowledge of genes associated with mechanisms of telomere maintenance and provides a platform to understand similarities and differences between telomerase and ALT in terms of the correlation between two genes in the system. This is particularly important because telomere dynamics plays a major role in many physiological and disease processes, including hematopoiesis.

scholarly journals Telomerase as a new target for the treatment of hormone-refractory prostate cancer

2004 ◽  
Vol 11 (3) ◽  
pp. 407-421 ◽  
Author(s):  
Annamaria Biroccio ◽  
Carlo Leonetti
Keyword(s):  
Prostate Cancer ◽  
Reverse Transcriptase ◽  
Tumor Cells ◽  
Cancer Progression ◽  
Telomere Maintenance ◽  
Telomeric Dna ◽  
Human Telomerase Reverse Transcriptase ◽  
Htert Gene ◽  
Reverse Transcriptase Enzyme ◽  
Androgen Ablation

Prostate cancer is the leading cause of cancer-related deaths in men. Androgen ablation is the mainstay of treatment for advanced prostate cancer. This therapy is very effective in androgen-dependent cancer; however, these cancers eventually become androgen independent, rendering anti-androgen therapy ineffective. The exploration of novel modalities of treatment is therefore essential to improve the prognosis of this neoplasia. Telomeres are specialized heterochromatin structures that act as protective caps at the ends of chromosomes. Telomere maintenance in the majority of tumor cells is achieved by telomerase, a reverse transcriptase enzyme that catalyzes the synthesis of further telomeric DNA. Telomerase is detected in the majority of prostate cancers, but not in normal or benign prostatic hyperplasia tissue. Moreover, the human telomerase reverse transcriptase (hTERT) gene, the catalytic subunit of telomerase, is regulated by androgens as well as by different oncogenes including Her-2, Ras, c-Myc and Bcl-2, which seem to play an important role in prostate cancer progression. Thus, telomerase may represent a very good candidate for targeted therapy in prostate tumors. To inhibit telomere maintenance by telomerase, approaches that directly target either telomerase and telomeres or the telomerase regulatory mechanisms have been used. Moreover, strategies targeting telomerase-positive cells as a means to directly kill the tumor cells have been tested. This review summarizes the most promising results achieved by anti-telomerase strategy in different solid tumors. Most of the telomeraseassociated therapies described here have proved very promising for the treatment of prostate cancer. On the basis of the good results obtained and considering the multigenic defects of human tumors, including prostate cancer, the combination of anti-telomerase strategies with conventional drugs and/or molecules capable of interfering with oncogenic pathways could efficiently improve the response of this neoplasia.

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