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The telomerase reverse transcriptase regulates chromatin state and DNA damage responses.

ABSTRACT: Constitutive expression of telomerase prevents senescence and crisis by maintaining telomere homeostasis. However, recent evidence suggests that telomerase is dynamically regulated in normal cells and also contributes to transformation independently of net telomere elongation. Here, we show that suppression of the telomerase catalytic subunit [human telomerase reverse transcriptase (hTERT)] expression abrogates the cellular response to DNA double strand breaks. Loss of hTERT does not alter short-term telomere integrity but instead affects the overall configuration of chromatin. Cells lacking hTERT exhibit increased radiosensitivity, diminished capacity for DNA repair, and fragmented chromosomes, demonstrating that loss of hTERT impairs the DNA damage response.

SUBMITTER: Masutomi K

PROVIDER: S-EPMC1149439 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature

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The telomerase reverse transcriptase regulates chromatin state and DNA damage responses.

Masutomi Kenkichi K Possemato Richard R Wong Judy M Y JM Currier Jennifer L JL Tothova Zuzana Z Manola Judith B JB Ganesan Shridar S Lansdorp Peter M PM Collins Kathleen K Hahn William C WC

Proceedings of the National Academy of Sciences of the United States of America 20050531 23

Constitutive expression of telomerase prevents senescence and crisis by maintaining telomere homeostasis. However, recent evidence suggests that telomerase is dynamically regulated in normal cells and also contributes to transformation independently of net telomere elongation. Here, we show that suppression of the telomerase catalytic subunit [human telomerase reverse transcriptase (hTERT)] expression abrogates the cellular response to DNA double strand breaks. Loss of hTERT does not alter short ...[more]

PMID: 15928077

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Project description:The Hedgehog (HH) signaling pathway is critical for normal embryonic development, tissue patterning and cell differentiation. Aberrant HH signaling is involved in multiple human cancers. HH signaling involves a multi-protein cascade activating the GLI proteins that transcriptionally regulate HH target genes. We have previously reported that HH signaling is essential for human colon cancer cell survival and inhibition of this signal induces DNA damage and extensive cell death. Here we report that the HH/GLI axis regulates human telomerase reverse transcriptase (hTERT), which determines the replication potential of cancer cells. Suppression of GLI1/GLI2 functions by a C-terminus truncated GLI3 repressor mutant (GLI3R), or by GANT61, a pharmacological inhibitor of GLI1/GLI2, reduced hTERT protein expression in human colon cancer, prostate cancer and Glioblastoma multiforme (GBM) cell lines. Expression of an N-terminus deleted constitutively active mutant of GLI2 (GLI2?N) increased hTERT mRNA and protein expression and hTERT promoter driven luciferase activity in human colon cancer cells while GANT61 inhibited hTERT mRNA expression and hTERT promoter driven luciferase activity. Chromatin immunoprecipitation with GLI1 or GLI2 antibodies precipitated fragments of the hTERT promoter in human colon cancer cells, which was reduced upon exposure to GANT61. In contrast, expression of GLI1 or GLI2?N in non-malignant 293T cells failed to alter the levels of hTERT mRNA and protein, or hTERT promoter driven luciferase activity. Further, expression of GLI2?N increased the telomerase enzyme activity, which was reduced by GANT61 administration in human colon cancer, prostate cancer, and GBM cells. These results identify hTERT as a direct target of the HH signaling pathway, and reveal a previously unknown role of the HH/GLI axis in regulating the replication potential of cancer cells. These findings are of significance in understanding the important regulatory mechanisms that determine the functions of HH/GLI signaling in cancer cells.

Project description:BackgroundAngiogenesis is an endogenous repair mechanism following hypoxic-ischemic brain damage (HIBD). Interestingly, recent studies have shown that angiogenesis can be regulated by telomerase reverse transcriptase (TERT), a critical component of telomerase. As telomerase reverse transcriptase can promote angiogenesis after stroke, we hypothesized that it could also promote angiogenesis after HIBD. To test this hypothesis, we developed in vivo and in vitro HIBD models in neonatal rats.MethodsTERT was overexpressed by lentivirus and adenovirus infection, and levels were measured using quantitative real-time polymerase chain reaction. We used a cell counting kit to quantify the proliferation rate of brain microvascular endothelial cells (BMECs), and immunofluorescence staining to measure CD34 expression levels. A microvessel formation assay was used to evaluate angiogenesis. Blood-brain barrier (BBB) integrity was assessed using immunohistochemical staining for ZO-1 and Evans Blue staining. Lastly, the expression level of Notch-1 was measured by western blotting.ResultsOverexpression of TERT promoted the proliferation of BMECs after hypoxic-ischemic damage in vitro. TERT overexpression increased the formation of microvessels in the neonatal brain after HIBD both in vivo and in vitro. Overexpression of TERT improved BBB integrity in the brains of neonatal rats after HIBD. In addition, the expression level of Notch-1 was increased in BMECs following oxygen glucose deprivation, and overexpression of TERT further increased Notch-1 expression levels in BMECs following oxygen glucose deprivation.DiscussionOur results reveal that telomerase reverse transcriptase promotes angiogenesis and maintains the integrity of the blood-brain barrier after neonatal hypoxic-ischemic brain damage. Furthermore, the Notch-1 signaling pathway appears to contribute to the angiogenic function of telomerase reverse transcriptase. This protective effect of telomerase reverse transcriptase opens new horizons for future investigations aimed at uncovering the full potential of telomerase reverse transcriptase as a promising new target for the treatment of hypoxic-ischemic encephalopathy.

Project description:Helicobacter pylori infection causes chronic gastritis and is the major risk factor of gastric cancer. H. pylori induces a chronic inflammation-producing reactive oxygen species (ROS) which is a source of chromosome instabilities and contributes to the development of malignancy. H. pylori also promotes DNA hypermethylation, known to dysregulate essential genes that maintain genetic stability. The maintenance of telomere length by telomerase is essential for chromosome integrity. Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase activity and an important target during host-pathogen interaction. We aimed to investigate the consequences of H. pylori on the regulation of TERT gene expression and telomerase activity. In vitro, hTERT mRNA levels and telomerase activity were analysed in H. pylori-infected human gastric epithelial cells. In addition, C57BL/6 and INS-GAS mice were used to investigate the influence of H. pylori-induced inflammation on TERT levels. Our data demonstrated that, in vitro, H. pylori inhibits TERT gene expression and decreases the telomerase activity. The exposure of cells to lycopene, an antioxidant compound, restores TERT levels in infected cells, indicating that ROS are implicated in this downregulation. In vivo, fewer TERT-positive cells are observed in gastric tissues of infected mice compared to uninfected, more predominantly in the vicinity of large aggregates of lymphocytes, suggesting an inflammation-mediated regulation. Furthermore, H. pylori appears to downregulate TERT gene expression through DNA hypermethylation as shown by the restoration of TERT transcript levels in cells treated with 5'-azacytidine, an inhibitor of DNA methylation. This was confirmed in infected mice, by PCR-methylation assay of the TERT gene promoter. Our data unraveled a novel way for H. pylori to promote genome instabilities through the inhibition of TERT levels and telomerase activity. This mechanism could play an important role in the early steps of gastric carcinogenesis.

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The telomerase reverse transcriptase regulates chromatin state and DNA damage responses.

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The telomerase reverse transcriptase regulates chromatin state and DNA damage responses.

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