Project description:Promoter rearrangement of the telomerase reverse transcriptase (TERT) gene juxtaposes the coding sequence to strong enhancer elements, leading to TERT overexpression and poor prognosis. TERT associated oncogenic signaling in neuroblastoma remains unclear. Gene set enrichment analysis of RNA-seq data from 498 neuroblastoma patients revealed a coordinated activation of oncogenic signaling pathways and differentially overexpressed gene signature in a subgroup of MycN non-amplified neuroblastomas with TERT overexpression. ChIP-seq analysis of human neuroblastoma cell line CLB-GA harboring TERT rearrangement uncovered genome-wide chromatin co-occupancy of Brd4 and H3K27Ac and robust enrichment of H3K36me3 in TERT and multiple TERT-associated genes. We demonstrated a critical regulatory role of Brd4 and cyclin-dependent kinases in the expression and chromatin activation. Inhibition of both with AZD5153 and dinaciclib proved most effective in tumor growth suppression of neuroblastoma cell lines, primary cells, and xenograft. Our study provides a therapeutic strategy utilizing epigenetic targeting of neuroblastoma with TERT overexpression.
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.
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.
Project description:Whole genome sequencing detected structural rearrangements of TERT in 17/75 high stage neuroblastoma with 5 cases resulting from chromothripsis. Rearrangements were associated with increased TERT expression and targeted immediate up- and down-stream regions of TERT, placing in 7 cases a super-enhancer close to the breakpoints. TERT rearrangements (23%), ATRX deletions (11%) and MYCN amplifications (37%) identify three almost non-overlapping groups of high stage neuroblastoma, each associated with very poor prognosis
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.
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.
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.