Effect of TERT and ATM on Gene Expression Profiles in Human Fibroblasts
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: E-GEOD-953 | BioStudies |
REPOSITORIES: biostudies
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Project description:Gene expression profiling was performed by use of serial analysis of gene expression (SAGE) on BJ normal human skin fibroblasts, A-T cells, and BJ and A-T cells transduced with hTERT cDNA and expressing telomerase activity. Keywords = telomere Keywords = telomerase Keywords = TERT Keywords = ataxia telangiectasia mutated Keywords = ATM Keywords = serial analysis of gene expression Keywords = SAGE Keywords = fibroblast Keywords: parallel sample
2004-01-16 | E-GEOD-953 | ArrayExpress
Project description:The complexity and heterogeneity of cancer cells are under-represented by the current experimental models which revolve around primary tumor cells, cancer cell lines, and rodent models. We used the transformed cell model in our studies. IMR90 and BJ fibroblast cells were transformed by three oncogenic genetic factors, SV40 Large-T antigen, H-Ras and human telomerase (hTERT). These transformed cells can grow under anchorage independent conditions, are self-sufficient in growth signals, have decreased sensitivity to apoptosis, and showed recurrent chromosomal abnormalities. Further characterization of transformed cells through cell cycle profiling and mass spectrometry analysis also revealed an increased fraction in the G2/M phase, and an up-regulation of Ku70. Furthermore, transformed cells exhibited increased telomerase activity that was not accountable by hTERT overexpression alone. Microarray results revealed that hTERT overexpression promoted cell migration and the initiation of DNA damage responses; two cellular processes that are important in cancer progression. Collectively, these data imply that IMR90 transformed cell model is an invaluable tool for cancer studies. Our results in the systematic study of this model helped us identify possible early events in cancer transformation and reveal the extra-telomeric effects of telomerase in cell migration and DNA damage initiation. IMR90 and BJ fibroblast cells were transformed by three oncogenic genetic factors, SV40 Large-T antigen, H-Ras and human telomerase (hTERT). Through microarray analysis, gene expression of transformed cells were compared against control cells.
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Project description:Senescence is a highly regulated process that limits cellular replication by enforcing a G1 arrest in response to various stimuli. Replicative senescence occurs in response to telomeric DNA erosion, and telomerase expression can offset replicative senescence leading to immortalization of many human cells. Limited data exists regarding changes of microRNA (miRNA) expression during senescence in human cells and no reports correlate telomerase expression with regulation of senescence-related miRNAs. We used miRNA microarrays to provide a detailed account of miRNA profiles for early passage and senescent human foreskin (BJ) fibroblasts as well as early and late passage immortalized fibroblasts (BJ-hTERT) that stably express the human telomerase reverse transcriptase subunit hTERT. Selected miRNAs that were differentially expressed in senescence were assayed for expression in quiescent cells to identify miRNAs that are specifically associated with senescence-associated growth arrest. From this group of senescence-associated miRNAs, we confirmed the ability of miR-143 to induce growth arrest after ectopic expression in young fibroblasts. Remarkably, miR-143 failed to induce growth arrest in BJ-hTERT cells. Importantly, the comparison of late passage immortalized fibroblasts to senescent wild type fibroblasts reveals that miR-146a, a miRNA with a validated role in regulating the senescence associated secretory pathway, is also regulated during extended cell culture independently of senescence. The discovery that miRNA expression is impacted by expression of ectopic hTERT as well as extended passaging in immortalized fibroblasts contributes to a comprehensive understanding of the connections between telomerase expression, senescence and processes of cellular aging.
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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.
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Project description:In vivo expression of human telomerase is significantly different from that of mouse telomerase. To assess the basis for this difference, a bacterial artificial chromosome clone containing the entire hTERT (human telomerase reverse transcriptase) gene was introduced in mice. In these transgenic mice, expression of the hTERT transgene was similar to that of endogenous hTERT in humans, rather than endogenous mTERT (mouse telomerase reverse transcriptase). In tissues and cells showing a striking difference in expression levels between hTERT in humans and mTERT in mice (i.e., liver, kidney, lung, uterus, and fibroblasts), expression of the hTERT transgene in transgenic mice was repressed, mimicking hTERT in humans. The transcriptional activity of the hTERT promoter was much lower than that of the mTERT promoter in mouse embryonic fibroblasts or human fibroblasts. Mutational analysis of the hTERT and mTERT promoters revealed that a nonconserved GC-box within the hTERT promoter was responsible for the human-specific repression. These results reveal that a difference in cis-regulation of transcription, rather than transacting transcription factors, is critical to species differences in tissue-specific TERT expression. Our data also suggest that the GC-box-mediated, human-specific mechanism for TERT repression is impaired in human cancers. This study represents a detailed characterization of the functional difference in a gene promoter of mice versus humans and provides not only important insight into species-specific regulation of telomerase and telomeres but also an experimental basis for generating mice humanized for telomerase enzyme and its pattern of expression.
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Project description:Dysregulation of alternative splicing of hTERT gene to generate full-length Htert (hTERT-FL) that reactivate telomerase has been recognized as a major pathological alteration in pancreatic cancer (PrCa). Mechanism about the factors that regulate hTERT-FL splicing is lacking. Through bioinformatics approach, we focus on a candidate splicing factor RBM10, which leads to a switch in hTERT transcripts to generate a function-less isoform hTERT-s in PrCa, suppressed both telomerase activity and subsequent telomere shortening. RBM10 expression is negatively associated with PrCa progression. Gain or loss of RBM10 also significantly changed PrCa cell proliferation in vitro and in xenografts. RNA-IP and RNA pull-down assays reveal that RBM10 promotes the exclusion of exons7 and 8 which results in the production of TERT-s transcripts. This study may increase knowledge about potentially targetable cancer associated splicing factors and provide novel insights into therapeutic approach in PrCa.
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Project description:Given the involvement of telomerase activation and dysregulated metabolism in glioma progression, the connection between these two critical players was investigated. Pharmacological inhibition of human Telomerase reverse transcriptase (hTERT) by Costunolide induced glioma cell apoptosis in a reactive oxygen species (ROS)-dependent manner. Costunolide induced an ROS-dependent increase in p53 abrogated telomerase activity. Costunolide decreased Nrf2 level; and ectopic Nrf2 expression decreased Costunolide-induced ROS generation. While TERT knock-down abrogated Nrf2 levels, overexpression of Nrf2 increased TERT expression. Inhibition of hTERT either by Costunolide, or by siRNA or dominant-negative hTERT (DN-hTERT) abrogated (i) expression of Glucose-6-phosphate dehydrogenase (G6PD) and Transketolase (TKT) - two major nodes in the pentose phosphate (PPP) pathway; and (ii) phosphorylation of glycogen synthase (GS). hTERT knock-down decreased TKT activity and increased glycogen accumulation. Interestingly, siRNA-mediated knock-down of TKT elevated glycogen accumulation. Coherent with the in vitro findings, Costunolide reduced tumor burden in heterotypic xenograft glioma mouse model. Costunolide-treated tumors exhibited diminished TKT activity, heightened glycogen accumulation, and increased senescence. Importantly, glioblastoma multiforme (GBM) patient tumors bearing TERT promoter mutations (C228T and C250T) known to be associated with increased telomerase activity; exhibited elevated Nrf2 and TKT expression and decreased glycogen accumulation. Taken together, our findings highlight the previously unknown (i) role of telomerase in the regulation of PPP and glycogen accumulation and (ii) the involvement of Nrf2-TERT loop in maintaining oxidative defense responses in glioma cells.
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Project description:Human retinal and RPE SAGE libraries. Profile of the genes expressed in the human peripheral retina, macula, and retinal pigment epithelium determined through serial analysis of gene expression (SAGE). Keywords: other
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Project description:The transcriptional regulation of the human telomerase catalytic subunit (hTERT) plays a critical role in telomerase activity. Approximately 200 bp of the proximal core promoter is responsible for basic hTERT expression; however, the function of the distal regulatory elements remains unclear. The transcription factor activator protein 1 (AP-1) is involved in cellular proliferation, differentiation, carcinogenesis, and apoptosis and is expressed broadly in both cancer and normal cells. There are several putative AP-1 sites in the hTERT promoter, but their functions are unknown. The present study examined the regulatory role of AP-1 in hTERT gene transcription. Overexpression of AP-1 leads to transcriptional suppression of hTERT in cancer cells. The combination of c-Fos and c-Jun or c-Fos and JunD strongly suppresses hTERT promoter activity in transient-expression analyses. The hTERT promoter region between -2000 and -378 is responsible for this function. Gel shift and supershift analyses, as well as ChIP, show binding of JunD and c-Jun on two putative AP-1 sites within this region. Mutations in the AP-1 binding sites rescued suppressions caused by AP-1, suggesting this is a direct regulation of the hTERT promoter. In contrast, there was no effect on mTERT expression or mTERT promoter activity by AP-1 overexpression in mouse fibroblasts. The species-specific function of AP-1 in TERT expression may in part help explain the difference in telomerase activity between normal human and mouse cells.
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Project description:Telomerase, a ribonucleoprotein enzyme that maintains telomere length, is crucial for cellular immortalization and cancer progression. Telomerase activity is attributed primarily to the expression of telomerase reverse transcriptase (TERT). Using microcell-mediated chromosome transfer (MMCT) into the mouse melanoma cell line B16F10, we previously found that human chromosome 5 carries a gene, or genes, that can negatively regulate TERT expression (H. Kugoh, K. Shigenami, K. Funaki, J. Barrett, and M. Oshimura, Genes Chromosome Cancer 36:37-47, 2003). 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 expression 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 show that three and one binding site within the hTERT and mtert promoters, respectively, 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.
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