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Discovery of TERT isoforms by Long read RNA seq

ABSTRACT: All cancer cells must adopt a telomere maintenance mechanism to achieve replicative immortality. Most human cancer cells utilize the enzyme telomerase to maintain telomeres. Alternative splicing of TERT regulates the amount and function of telomerase, however many alternative splicing isoforms of TERT have unknown functions. Single molecule long read RNA/cDNA sequencing of TERT revealed 45 TERT mRNA variants including 13 known and 32 novel variants. Among the variants, TERT Delta 2-4, which lacks exons 2-4 but retains the original open reading frame, was selected for further study. Induced pluripotent stem cells and cancer cells express higher levels of TERT Delta 2-4 compared to primary human bronchial epithelial cells. Overexpression of TERT Delta 2-4 enhanced clonogenicity and resistance to cisplatin- induced apoptosis. Knockdown of endogenous TERT Delta 2-4 in Calu-6 cells reduced clonogenicity and resistance to cisplatin. Our results suggest that TERT Delta 2-4 enhances cancer cells’ resistance to intrinsic apoptosis. RNA sequencing following knockdown of Delta 2-4 TERT indicates that translation is downregulated and that mitochondrial related proteins are upregulated compared to controls. Overall, our data indicate that TERT produces many isoforms that influence the function TERT and the abundance and activity of telomerase.

ORGANISM(S): Homo sapiens

PROVIDER: GSE279325 | GEO | 2025/03/05

REPOSITORIES: GEO

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Identification of TERT Delta 2-4 knockdown effect by Long read RNA seq.

Project description:All cancer cells must adopt a telomere maintenance mechanism to achieve replicative immortality. Most human cancer cells utilize the enzyme telomerase to maintain telomeres. Alternative splicing of TERT regulates the amount and function of telomerase, however many alternative splicing isoforms of TERT have unknown functions. Single molecule long read RNA/cDNA sequencing of TERT revealed 45 TERT mRNA variants including 13 known and 32 novel variants. Among the variants, TERT Delta 2-4, which lacks exons 2-4 but retains the original open reading frame, was selected for further study. Induced pluripotent stem cells and cancer cells express higher levels of TERT Delta 2-4 compared to primary human bronchial epithelial cells. Overexpression of TERT Delta 2-4 enhanced clonogenicity and resistance to cisplatin- induced apoptosis. Knockdown of endogenous TERT Delta 2-4 in Calu-6 cells reduced clonogenicity and resistance to cisplatin. Our results suggest that TERT Delta 2-4 enhances cancer cells’ resistance to intrinsic apoptosis. RNA sequencing following knockdown of Delta 2-4 TERT indicates that translation is downregulated and that mitochondrial related proteins are upregulated compared to controls. Overall, our data indicate that TERT produces many isoforms that influence the function TERT and the abundance and activity of telomerase.

2025-03-05 | GSE279438 | GEO

GABP determines the epigenetic status of mutant TERT promoter

Project description:Blocking telomerase is recognized as a key anti-cancer mechanism. Unlike in stem cells, levels of telomerase catalytic subunit TERT are limiting in reconstituting telomerase activity in somatic cells. However in some cancers, Tert is transcriptionally reactivated by mutations in its promoter. Given that Tert in stem cells is driven by WT Tert promoter, if we can selectively target Tert reactivation through mutant Tert promoters we can block telomerase activity specifically in cancer cells without toxicity in stem cells. Here we report the epigenetic regulation of Tert promoter comparing WT and mutant promoters. We showed that GABPA homodimerization through long-range interaction stabilizes Gabpa to drive Tert expression. Furthermore, BRD4 specifically activates the C250T mutant promoter via dual mechanism involving GABPA, thereby setting the stage for future therapeutics.

2017-02-27 | GSE77265 | GEO

Chemical genomic screen identifies SP2509, WT hTERT specific repressor in colorectal cancer

Project description:Telomerase is necessary for cell immortality in cancer. Hence, during tumerognesis cancer cells reactivates telomerase to attain uncotrolled proliferation. There are no clinically approved drugs available to inhibit telomerase in cancer. We performed a chemical screen using a novel endogenous hTERT reported cell line and identified a compound, SP2509 which acts specifically in cancer cells immortalised by WT TERT activity. Further we identified that Pirin is a molecular target of the compund and it regulate the level of SP1, an important transcriptional activator of WT TERT gene. We finally show iron dependency of pirin to activate TERT in CRC cell lines.

2022-12-01 | GSE203120 | GEO

Genomic copy number profiling of different generations of Atm-/-TERT-ER T-cell lymphomas and associated resistant tumors following telomerase inhibition

Project description:Genomic copy numbers of various generations of Atm-/-TERT-ER mice treated with 4-OHT or vehicle were profiled. Genomic copy numbers of transplanted G3 Atm-/-TERT-ER T-cell lymphomas with telomerase or ALT T-cell lymphomas were developed in various generations of Atm-/-TERT-ER mice with 4-OHT or vehicle treatment. These tumors were profiled with aCGH. G3 Atm-/-TERT-ER tumors were transplanted into SCID mice treated with 4-OHT or vehicle. Cells maintained on vehicle eventually developed ALT-dependent resistance. We used aCGH to profile telomerase+ tumors vs. ALT+ tumors from the same parental lines.

2012-01-17 | E-GEOD-35045 | biostudies-arrayexpress

Expression profiles of Telomerase+ vs. ALT+ G3 Atm-/-TERT-ER T-cell lymphomas

Project description:We used microarray profiling to document the difference between telomerase+ vs. ALT+ T-cell lymphomas developed on G3 Atm-/-TERT-ER genetic background. T-cell lymphomas were developed in G3 Atm-/-TERT-ER mice with 4-OHT treatment. These cells were either maintained on SCID mice treated with 4-OHT or vehicle. Cells maintained on vehicle eventually developed ALT-dependent resistance. We used microarray to profile telomerase+ tumors vs. ALT+ tumors from the same parental lines.

2012-01-17 | E-GEOD-35044 | biostudies-arrayexpress

Telomerase subunit TERT regulates MYC stability independent of its role on telomeres (ChIP-Seq)

Project description:Constitutively active MYC and reactivated telomerase often co-exist in cancers. While the reactivation of telomerase is thought to be essential for replicative immortality, MYC, in conjunction with co-factors, confers several growth advantages to cancer cells. However, it is unclear which co-factors sustain elevated MYC activity in tumours . Here, we identify TERT, the catalytic subunit of telomerase, as a novel regulator of MYC stability in cancers. Binding of TERT to MYC stabilizes its levels on chromatin, contributing to either activation or repression of its target genes. Mechanistically, TERT regulates MYC ubiquitination and stability, and this effect of TERT is independent of its role on telomeres. Genetic inhibition and knocking out of TERT phenocopied the loss of MYC, resulting in reduced disease burden of early- and late-stage MYC-driven murine lymphomas. Conversly, the ectopic expression of TERT could substitute for reduced MYC in these functions. Finally we show that TERT null mice, unlike Terc null mice, show delayed onset of MYC induced lymphomagenesis. Accordingly, inhibiting TERT function in primary human leukemia cells blocked the expression of MYC targets, while Terc depletion had no effects . Based on our data, we conclude that the re-expression of TERT, a direct MYC target in tumors, provides a feed-forward mechanism to potentiate MYC-dependent oncogenesis. ChIP was performed using anti-MYC (sc-764) in primary lymphoma cells from Eµ-Myc;Tert -/- mice, Eµ-Myc;Tert +/+ mice, or in P493 cells treated with shTert, P493 shTerc and shControl.

2015-04-23 | E-GEOD-60223 | biostudies-arrayexpress

Telomerase subunit TERT regulates MYC stability independent of its role on telomeres (array)

Project description:Constitutively active MYC and reactivated telomerase often co-exist in cancers. While the reactivation of telomerase is thought to be essential for replicative immortality, MYC, in conjunction with co-factors, confers several growth advantages to cancer cells. However, it is unclear which co-factors sustain elevated MYC activity in tumors . Here, we identify TERT, the catalytic subunit of telomerase, as a novel regulator of MYC stability in cancers. Binding of TERT to MYC stabilizes its levels on chromatin, contributing to either activation or repression of its target genes. Mechanistically, TERT regulates MYC ubiquitination and stability, and this effect of TERT is independent of its role on telomeres. Genetic inhibition and knocking out of TERT phenocopied the loss of MYC, resulting in reduced disease burden of early- and late-stage MYC-driven murine lymphomas. Conversly, the ectopic expression of TERT could substitute for reduced MYC in these functions. Finally we show that TERT null mice, unlike Terc null mice, show delayed onset of MYC induced lymphomagenesis. Accordingly, inhibiting TERT function in primary human leukemia cells blocked the expression of MYC targets, while Terc depletion had no effects . Based on our data, we conclude that the re-expression of TERT, a direct MYC target in tumors, provides a feed-forward mechanism to potentiate MYC-dependent oncogenesis. P493 cells were stably infected with the following viruses: pLKO shControl and pLKO shTERT.

2015-04-23 | E-GEOD-60175 | biostudies-arrayexpress

PITX1 suppresses TERT transcription

Project description:Using microcell-mediated chromosome transfer (MMCT) into the mouse melanoma cell line, B16F10, we have previously found that human chromosome 5 carries a gene, or genes, that can negatively regulate TERT expression. To identify the gene responsible for the regulation of TERT transcription, we performed cDNA microarray analysis using parental B16F10 cells, telomerase negative B16F10 microcell hybrids with a human chromosome 5 (B16F10MH5), and its revertant clones (MH5R) with reactivated telomerase. Here we report the identification of PITX1, whose restoration leads to the downregulation of mouse tert (mtert) transcription, as a TERT suppressor gene. Additionally, both human TERT (hTERT) and mouse TERT (mtert) promoter activity can be suppressed by PITX1. We showed that three and one binding sites, respectively, within the hTERT and mtert promoters that express a unique conserved region are responsible for the transcriptional activation of TERT. Furthermore, we showed that PITX1 binds to the TERT promoter both in vitro and in vivo. Thus, PITX1 suppresses TERT transcription through direct binding to the TERT promoter, which ultimately regulates telomerase activity. We transferred intact human chromosome 5 into mouse melanoma B16F10 cells by microcell fusion. The microcell hybrids (MH5) exhibited suppression of telomerase, we also obtained revertant clones (MH5R) in which telomerase is reactivated. To identify the differentially expressed genes on human chromosome 5, we performed expression microarray analysis using these two clones and parental B16F10 cells.

2010-09-10 | E-GEOD-23216 | biostudies-arrayexpress

Telomerase subunit TERT regulates MYC stability independent of its role on telomeres (ChIP-Seq)

2015-04-23 | GSE60223 | GEO

Telomerase subunit TERT regulates MYC stability independent of its role on telomeres (array)

Project description:Constitutively active MYC and reactivated telomerase often co-exist in cancers. While the reactivation of telomerase is thought to be essential for replicative immortality, MYC, in conjunction with co-factors, confers several growth advantages to cancer cells. However, it is unclear which co-factors sustain elevated MYC activity in tumors . Here, we identify TERT, the catalytic subunit of telomerase, as a novel regulator of MYC stability in cancers. Binding of TERT to MYC stabilizes its levels on chromatin, contributing to either activation or repression of its target genes. Mechanistically, TERT regulates MYC ubiquitination and stability, and this effect of TERT is independent of its role on telomeres. Genetic inhibition and knocking out of TERT phenocopied the loss of MYC, resulting in reduced disease burden of early- and late-stage MYC-driven murine lymphomas. Conversly, the ectopic expression of TERT could substitute for reduced MYC in these functions. Finally we show that TERT null mice, unlike Terc null mice, show delayed onset of MYC induced lymphomagenesis. Accordingly, inhibiting TERT function in primary human leukemia cells blocked the expression of MYC targets, while Terc depletion had no effects . Based on our data, we conclude that the re-expression of TERT, a direct MYC target in tumors, provides a feed-forward mechanism to potentiate MYC-dependent oncogenesis.

2015-04-23 | GSE60175 | GEO

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