Reliable assessment of telomere maintenance mechanisms in neuroblastoma
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PROVIDER: EGAS00001006510 | EGA |
REPOSITORIES: EGA
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Project description:Telomere maintenance mechanisms (TMM) are a hallmark of high-risk neuroblastoma, and are conferred by activation of telomerase or alternative lengthening of telomeres (ALT). However, detection of TMM is not yet part of the clinical routine, and consensus on TMM detection, especially on ALT assessment, remains to be achieved. Based on our results we here propose a workflow to reliably detect TMM in neuroblastoma. We show that unambiguous classification is feasible following a stepwise approach that determines both, activation of telomerase and ALT. The workflow proposed in this study can be used in clinical routine and provides a framework to systematically evaluate telomere maintenance mechanisms in risk stratification and treatment allocation of neuroblastoma patients.
2022-09-19 | GSE211653 | GEO
Project description:The aim of this study is to determine the clinical relevance of telomerase activation versus ALT as biomarkers in pre-treatment neuroblastoma, and to assess the potential value of telomerase as a therapeutic target. Therefore, the genomic status of TERT and MYCN was assessed in 457 pretreatment neuroblastomas by fluorescence-in-situ-hybridization. ALT was examined in 273/457 tumors by detection of ALT-associated promyelocytic leukemia nuclear bodies, and TERT expression was determined by 4x44k microarrays in 223 of these. The presence of activated telomerase, i.e., TERT rearrangements, MYCN amplification, or high TERT expression without these alterations, was associated with poorest overall survival, and was an independent prognostic marker in multivariable analyses.
2019-09-16 | E-MTAB-8248 | biostudies-arrayexpress
Project description:Telomerase-negative tumors can maintain telomere length by alternative lengthening of telomeres (ALT) but the mechanism of telomere maintenance in ALT cells is not well understood. A significant portion of the relapse Neuroblastoma (NB) tumors are positive for ALT which suggests better dissecting the ALT mechanism could provide novel therapeutic opportunities. TERRA RNA which is derived from the telomere ends is localized to telomeres in R-loop dependent manner and is essential for telomere maintenance. In the present study, we provide evidence that RNA modification at the N6 position of internal adenosine (m6A) in TERRA RNA by methyl transferase METTL3 is essential for telomere maintenance in ALT cells and loss of TERRA m6A/METTL3 leads to accumulation of DNA damage over telomere. Our data suggest that m6A modification in TERRA RNA is required for R-loop formation and telomere targeting of TERRA. We observed that R-loop enriched TERRA is abundantly m6A modified and m6A mediated recruitment of hnRNPA2B1 to TERRA RNA is essential for R-loop formation. Together our study suggests that m6A-mediated R-loop formation could be a widespread mechanism utilized by other chromatin-interacting lncRNAs. We also show treating ALT positive NB cells with small molecule METTL3 inhibitor leads to compromised telomere targeting of TERRA and accumulation of DNA damage over telomere, suggesting METTL3 inhibition could be a therapeutic opportunity for ALT positive NB.
2023-12-13 | GSE240690 | GEO
Project description:Telomerase-negative tumors can maintain telomere length by alternative lengthening of telomeres (ALT) but the mechanism of telomere maintenance in ALT cells is not well understood. A significant portion of the relapse Neuroblastoma (NB) tumors are positive for ALT which suggests better dissecting the ALT mechanism could provide novel therapeutic opportunities. TERRA RNA which is derived from the telomere ends is localized to telomeres in R-loop dependent manner and is essential for telomere maintenance. In the present study, we provide evidence that RNA modification at the N6 position of internal adenosine (m6A) in TERRA RNA by methyl transferase METTL3 is essential for telomere maintenance in ALT cells and loss of TERRA m6A/METTL3 leads to accumulation of DNA damage over telomere. Our data suggest that m6A modification in TERRA RNA is required for R-loop formation and telomere targeting of TERRA. We observed that R-loop enriched TERRA is abundantly m6A modified and m6A mediated recruitment of hnRNPA2B1 to TERRA RNA is essential for R-loop formation. Together our study suggests that m6A-mediated R-loop formation could be a widespread mechanism utilized by other chromatin-interacting lncRNAs. We also show treating ALT positive NB cells with small molecule METTL3 inhibitor leads to compromised telomere targeting of TERRA and accumulation of DNA damage over telomere, suggesting METTL3 inhibition could be a therapeutic opportunity for ALT positive NB.
2023-12-13 | GSE219212 | GEO
Project description:Telomerase-negative tumors can maintain telomere length by alternative lengthening of telomeres (ALT) but the mechanism of telomere maintenance in ALT cells is not well understood. A significant portion of the relapse Neuroblastoma (NB) tumors are positive for ALT which suggests better dissecting the ALT mechanism could provide novel therapeutic opportunities. TERRA RNA which is derived from the telomere ends is localized to telomeres in R-loop dependent manner and is essential for telomere maintenance. In the present study, we provide evidence that RNA modification at the N6 position of internal adenosine (m6A) in TERRA RNA by methyl transferase METTL3 is essential for telomere maintenance in ALT cells and loss of TERRA m6A/METTL3 leads to accumulation of DNA damage over telomere. Our data suggest that m6A modification in TERRA RNA is required for R-loop formation and telomere targeting of TERRA. We observed that R-loop enriched TERRA is abundantly m6A modified and m6A mediated recruitment of hnRNPA2B1 to TERRA RNA is essential for R-loop formation. Together our study suggests that m6A-mediated R-loop formation could be a widespread mechanism utilized by other chromatin-interacting lncRNAs. We also show treating ALT positive NB cells with small molecule METTL3 inhibitor leads to compromised telomere targeting of TERRA and accumulation of DNA damage over telomere, suggesting METTL3 inhibition could be a therapeutic opportunity for ALT positive NB.
2023-12-13 | GSE219146 | GEO
Project description:The up-regulation of a telomere maintenance mechanism (TMM) is an essential step in cancer progression to escape dysfunctional telomeres, 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. Comparative analysis of gene expression after the rescue of ALT with telomerase and analysis of telomerase positive paediatric brain cancers showed normalization of telomeric heterochromatin and maintenance of telomere length, with reduced expression of genes of the pre-replicative complex as hallmark. Thus our study identifies telomere maintenance mechanisms as major drivers of DNA replication and chromatin status at telomeres in brain cancers.
2022-07-01 | GSE134135 | GEO
Project description:Telomere attrition ultimately leads to the activation of protective cellular responses such as apoptosis or senescence. Impairment of such mechanisms can allow continued proliferation despite the presence of dysfunctional telomeres. Under such conditions, high levels of genome instability are often engendered. Data from both mouse and human model systems indicate that a period of genome instability might facilitate tumorigenesis. Here, we employ a liposarcoma model system to assay telomere maintenance mechanism-specific genetic alterations. A multiassay approach was used to assess the telomere maintenance mechanism(s) active in tumors. Genomic DNA from these samples was then analyzed by high resolution DNA mapping array in order to identify genetic alterations. Our data reveal a higher level of genome instability in ALT-positive tumors as compared with telomerase-positive tumors, whereas tumors lacking both mechanisms have relatively low levels of genome instability. The bulk of the genetic changes are amplifications, regardless of the mode of telomere maintenance employed. We also identified genetic changes specific to the ALT mechanism, e.g., deletion of chromosome 1q32.2-q44, as well as changes that are underrepresented amongst ALT-positive tumors, such as amplification of chromosome 12q14.3-q21.2. Taken together, these studies provide insight into the molecular pathways involved in the regulation of ALT and reveal several loci that might be exploited either as prognostic markers or targets of chemotherapeutic intervention. Keywords: genotype, genome instability, copy number alteration, liposarcoma, ALT, telomerase, telomere
2008-05-01 | GSE8046 | GEO
Project description:Telomere is a highly refined system for maintaining the stability of linear chromosomes. Most telomeres rely on simple repetitive sequences and telomerase enzymes, but in some species or telomerase-defective situations, alternative telomere lengthening (ALT) mechanism is utilized to protect chromosomal ends. Telomere loss can induce telomere recombination by which specific sequences can be recruited into telomeres. However, canonical telomeric repeat-based telomeres have been found in mammals. Here, we show that mammalian telomeres can also be completely reconstituted using a non-telomeric unique sequence. We found that a specific subtelomeric element, named as mouse template for ALT (mTALT), is utilized for repairing telomeric DNA damage and composing new telomeric sequences in mouse embryonic stem cells. We found a high-level of non-coding mTALT transcript despite the heterochromatic nature of mTALT-based telomere. After ALT activation, the increased HMGN1, a non-histone chromosomal protein, contributed to maintaining telomere stability by regulating telomeric transcriptions. Our findings reveal novel molecular features of potential telomeric sequences which can reconstitute telomeres during cancer formation and evolution.
2020-07-17 | MSV000085772 | MassIVE
Project description:A gene expression signature classifying telomerase and ALT immortalisation reveals an hTERT regulatory network and suggests a mesenchymal stem cell origin for ALT Telomere length is maintained by 2 known mechanisms, activation of telomerase or alternative lengthening of telomeres (ALT). The molecular mechanisms regulating the ALT phenotype are poorly understood and it is unknown how the decision of which pathway to activate is made at the cellular level. We have shown previously that active repression of telomerase gene expression by chromatin remodelling of the promoters is one mechanism of regulation, however other genes and signalling networks are likely to be required to regulate telomerase and maintain the ALT phenotype. Using gene expression profiling we have uncovered a signature of 1305 genes to distinguish telomerase positive and ALT cell lines. By combining this with gene expression profiles of liposarcoma tissue samples we refined this signature to 297 genes significantly associated with telomere maintenance mechanism. Network analysis of known direct interactions between genes within this signature revealed a regulatory signalling network consistent with a model of hTERT repression in ALT cell lines and liposarcomas. This network expands on our existing knowledge of hTERT regulation and provides a platform to understand differential regulation of hTERT in different tumour types and normal tissues. In addition we show evidence to suggest a novel mesenchymal stem cell origin for ALT immortalisation in cell lines and mesenchymal tissues. Keywords: cell type comparison, gene expression
2009-11-02 | GSE14529 | GEO
Project description:A gene expression signature classifying telomerase and ALT immortalisation reveals an hTERT regulatory network and suggests a mesenchymal stem cell origin for ALT Telomere length is maintained by 2 known mechanisms, activation of telomerase or alternative lengthening of telomeres (ALT). The molecular mechanisms regulating the ALT phenotype are poorly understood and it is unknown how the decision of which pathway to activate is made at the cellular level. We have shown previously that active repression of telomerase gene expression by chromatin remodelling of the promoters is one mechanism of regulation, however other genes and signalling networks are likely to be required to regulate telomerase and maintain the ALT phenotype. Using gene expression profiling we have uncovered a signature of 1305 genes to distinguish telomerase positive and ALT cell lines. By combining this with gene expression profiles of liposarcoma tissue samples we refined this signature to 297 genes significantly associated with telomere maintenance mechanism. Network analysis of known direct interactions between genes within this signature revealed a regulatory signalling network consistent with a model of hTERT repression in ALT cell lines and liposarcomas. This network expands on our existing knowledge of hTERT regulation and provides a platform to understand differential regulation of hTERT in different tumour types and normal tissues. In addition we show evidence to suggest a novel mesenchymal stem cell origin for ALT immortalisation in cell lines and mesenchymal tissues. Keywords: cell type comparison, gene expression
2009-11-02 | GSE14487 | GEO