Whole-Genome Profiling in Liposarcomas Reveals Genetic Alterations Common to Specific Telomere Maintenance Mechanisms
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE8046 | GEO | 2008/05/01
SECONDARY ACCESSION(S): PRJNA100869
REPOSITORIES: GEO
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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. Experiment Overall Design: Goal: To study telomere maintenance and genetic alterations in liposarcoma using Affymetrix Mapping 50K Xba 240 GeneChip. Experiment Overall Design: Brief description: Telomere attrition ultimately leads to the activation of protective cellular responses such as apoptosis or senescence. Impairment of such mechanisms, however, 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. The high-density SNP-based microarrays (e.g., Affymetrix 100K arrays) can detect deletions, amplifications, and loss-of-heterozygosity on a genome in the liposarcoma samples. Chromosomal alterations of liposarcoma should 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. Experiment Overall Design: Quality control steps taken: Experiment Overall Design: a. PCR-based quality assessment of liposarcoma tissue genomic DNA Experiment Overall Design: b. Nanodrop analysis of preprocessed DNA prior to array hybridization Experiment Overall Design: c. Analysis of array call rates following hybridization (array experiments giving call rates of less than 80% were routinely repeated) Experiment Overall Design: Data extraction and processing protocols Experiment Overall Design: a. Image scanning hardware and software, and processing procedures and parameters: SNP array hybridization was detected using a GCS3000 scanner (Affymetrix). SNP calls and signal quantification were obtained with Gene Chip Operating System (GCOS) 1.2 and Affymetrix GDAS 3.0 with Dynamic Model Mapping Analysis by default settings (0.25) for both homozygote and heterozygote call thresholds. Copy number analyses were carried out using Affymetrix Chromosome Copy Number Analysis Tool (CNAT) 2.1 with a default genomic smoothing window setting of 0.5 Mb. Experiment Overall Design: b. Normalization, transformation and data selection procedures and parameters. Array data was normalized by a reference data set with CNAT. Experiment Overall Design: c. Definition of chromosomal aberration, amplification, deletion and LOH used for data interpretation: These definitions and their algorithms were described in detail by Huang, et al: Whole genome DNA copy number changes identified by high density oligonucleotide arrays. Hum Genomics. 2004 May;1(4):287-99.
2008-06-16 | E-GEOD-8046 | biostudies-arrayexpress
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: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: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
Project description:Alternative lengthening of telomeres (ALT) supports telomere maintenance and replicative immortality in around 10-15% of cancers, thus representing a compelling target for therapy.To identify anti-cancer drugs that can be repurposed as ALT-centered therapies, we performed for a compound library screen on isogenic cell lines that rely either on telomerase or ALT mechanisms. We validated candidates on a panel of ALT- vs. telomerase-positive sarcoma cells and assessed levels of extrachromosomal telomeric C-circles after drug treatment, as a bona fide marker of ALT activity. We identified a receptor tyrosine kinase inhibitor ponatinib that deregulated ALT mechanisms, increased telomeric replicative stress and induced telomeric dysfunction in ALT cells. Using a model of ALT sarcoma xenografts, we found that ponatinib targeted ALT-positive cells and mitigated telomere elongation in these tumors. To identify the mode of action of ponatinib on ALT, we performed RNA-sequencing and quantitative proteomic and phosphoproteomic analyses, and shortlisted candidates to test the effect of their loss on telomeric C-circle levels. We identified an ABL1-JNK-JUN signalling circuit to be inhibited by ponatinib and to have a role in suppressing extrachromosomal telomeric C-circle formation. Furthermore, transcriptome and interactome analyses of JUN suggested a role of JUN in DNA damage repair pathways, independently of its capacity as a transcription factor. These results were corroborated by new synergistic drug interactions between ponatinib and either DNA synthesis or repair inhibitors such as triciribine and KU-60019, respectively. Overall, we identified a novel signalling pathway impacting ALT which can be targeted by a clinically approved kinase inhibitor.
2023-02-20 | PXD037501 | Pride
Project description:Alternative lengthening of telomeres (ALT) supports telomere maintenance and replicative immortality in around 10-15% of cancers, thus representing a compelling target for therapy.To identify anti-cancer drugs that can be repurposed as ALT-centered therapies, we performed for a compound library screen on isogenic cell lines that rely either on telomerase or ALT mechanisms. We validated candidates on a panel of ALT- vs. telomerase-positive sarcoma cells and assessed levels of extrachromosomal telomeric C-circles after drug treatment, as a bona fide marker of ALT activity. We identified a receptor tyrosine kinase inhibitor ponatinib that deregulated ALT mechanisms, increased telomeric replicative stress and induced telomeric dysfunction in ALT cells. Using a model of ALT sarcoma xenografts, we found that ponatinib targeted ALT-positive cells and mitigated telomere elongation in these tumors. To identify the mode of action of ponatinib on ALT, we performed RNA-sequencing and quantitative proteomic and phosphoproteomic analyses, and shortlisted candidates to test the effect of their loss on telomeric C-circle levels. We identified an ABL1-JNK-JUN signalling circuit to be inhibited by ponatinib and to have a role in suppressing extrachromosomal telomeric C-circle formation. Furthermore, transcriptome and interactome analyses of JUN suggested a role of JUN in DNA damage repair pathways, independently of its capacity as a transcription factor. These results were corroborated by new synergistic drug interactions between ponatinib and either DNA synthesis or repair inhibitors such as triciribine and KU-60019, respectively. Overall, we identified a novel signalling pathway impacting ALT which can be targeted by a clinically approved kinase inhibitor.
2022-03-14 | PXD032188 | Pride
Project description:Replicative senescence forms a major barrier to tumor progression. Cancer cells bypass this by using one of the two known telomere maintenance mechanisms: telomerase or the recombination-based alternative lengthening of telomeres (ALT) mechanism. The molecular details of ALT are currently poorly understood. We have previously shown that telomerase is actively repressed through complex networks of kinase, gene expression, and chromatin regulation. In this study, we aimed to gain further understanding of the role of kinases in the regulation of telomerase expression in ALT cells. Using a whole human kinome siRNA screen, we highlighted 106 kinases whose expression is linked to hTERT promoter activity. Network modeling of transcriptional regulation implicated c-Myc as a key regulator of the 106 kinase hits. Given our previous observations of lower c-Myc activity in ALT cells, we further explored its potential to regulate telomerase expression in ALT. We found increased c-Myc binding at the hTERT promoter in telomerase-positive compared with ALT cells, although no expression differences in c-Myc, Mad, or Max were observed between ALT and telomerase-positive cells that could explain decreased c-Myc activity in ALT. Instead, we found increased expression of the c-Myc competitive inhibitor TCEAL7 in ALT cells and tumors and that alteration of TCEAL7 expression levels in ALT and telomerase-positive cells affects hTERT expression. Lower c-Myc activity in ALT may therefore be obtained through TCEAL7 regulation. Thus, TCEAL7 may present an interesting novel target for cancer therapy, which warrants further investigation.
2010-05-04 | GSE17118 | GEO