Human telomerase catalytic subunit (hTERT) suppresses p53-mediated anti-apoptotic response via induction of basic fibroblast growth factor.
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ABSTRACT:
SUBMITTER: Jin X
PROVIDER: S-EPMC2928930 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:We have mapped the 5' and 3' boundaries of the region of the human telomerase RNA (hTR) that is required to produce activity with the human protein catalytic subunit (hTERT) by using in vitro assembly systems derived from rabbit reticulocyte lysates and human cell extracts. The region spanning nucleotides +33 to +325 of the 451-base hTR is the minimal sequence required to produce levels of telomerase activity that are comparable with that made with full-length hTR. Our results suggest that the sequence approximately 270 bases downstream of the template is required for efficient assembly of active telomerase in vitro; this sequence encompasses a substantially larger portion of the 3' end of hTR than previously thought necessary. In addition, we identified two fragments of hTR (nucleotides +33 to +147 and +164 to +325) that cannot produce telomerase activity when combined separately with hTERT but can function together to assemble active telomerase. These results suggest that the minimal sequence of hTR can be divided into two sections, both of which are required for de novo assembly of active telomerase in vitro.
| S-EPMC84565 | biostudies-literature
Project description:Failures to arrest growth in response to senescence or transforming growth factor beta (TGF-beta) are key derangements associated with carcinoma progression. We report that activation of telomerase activity may overcome both inhibitory pathways. Ectopic expression of the human telomerase catalytic subunit, hTERT, in cultured human mammary epithelial cells (HMEC) lacking both telomerase activity and p16(INK4A) resulted in gaining the ability to maintain indefinite growth in the absence and presence of TGF-beta. The ability to maintain growth in TGF-beta was independent of telomere length and required catalytically active telomerase capable of telomere maintenance in vivo. The capacity of ectopic hTERT to induce TGF-beta resistance may explain our previously described gain of TGF-beta resistance after reactivation of endogenous telomerase activity in rare carcinogen-treated HMEC. In those HMEC that overcame senescence, both telomerase activity and TGF-beta resistance were acquired gradually during a process we have termed conversion. This effect of hTERT may model a key change occurring during in vivo human breast carcinogenesis.
| S-EPMC31863 | biostudies-literature
Project description:Telomerase, a cellular reverse transcriptase, adds telomeric repeats to chromosome ends. In normal human somatic cells, telomerase is repressed and telomeres progressively shorten, leading to proliferative senescence. Introduction of the telomerase (hTERT) cDNA is sufficient to produce telomerase activity and immortalize normal human cells, suggesting that the repression of telomerase activity is transcriptional. The telomerase transcript has been shown to have at least six alternate splicing sites (four insertion sites and two deletion sites), and variants containing both or either of the deletion sites are present during development and in a panel of cancer cell lines we surveyed. One deletion (beta site) and all four insertions cause premature translation terminations, whereas the other deletion (alpha site) is 36 bp and lies within reverse transcriptase (RT) motif A, suggesting that this deletion variant may be a candidate as a dominant-negative inhibitor of telomerase. We have cloned three alternately spliced hTERT variants that contain the alpha, beta or both alpha and beta deletion sites. These alternate splicing variants along with empty vector and wild-type hTERT were introduced into normal human fibroblasts and several telomerase-positive immortal and tumor cell lines. Expression of the alpha site deletion variant (hTERT alpha-) construct was confirmed by Western blotting. We found that none of the three alternate splicing variants reconstitutes telomerase activity in fibroblasts. However, hTERT alpha- inhibits telomerase activities in telomerase-positive cells, causes telomere shortening and eventually cell death. This alternately spliced dominant-negative variant may be important in understanding telomerase regulation during development, differentiation and in cancer progression.
| S-EPMC1507981 | biostudies-literature
Project description:Telomerase, a ribonucleoprotein complex that includes the telomerase RNA component (hTR) and the telomerase catalytic subunit gene (hTERT) product, has been shown to be activated in the majority of cancer tissues and immortalized cells. To study telomerase activation during the progression of cervical cancer, the expression of hTR and hTERT RNAs in tissues of various stages of cervical cancer was analyzed using the in situ hybridization method and compared with proliferative activity as estimated by Ki-67 immunostaining. To test whether expression of these components is reflected in enzyme activity, we determined the levels of the RNAs in cervical cancer and normal tissues and in primary and immortal keratinocytes by reverse transcription-polymerase chain reaction and RNase protection assays and compared the results to telomerase activities as detected by telomeric repeat amplification protocol assay. In situ hybridization signals of hTR and hTERT were present not only in carcinoma tissues but also in normal epidermal layers. In many adenocarcinoma and fewer squamous cell carcinoma tissues, both signals were focally increased where high proliferative activity was present at the stages of dysplasia/metaplasia, in situ carcinoma, and invasive carcinoma. The level of bTERT, as quantitated by RNase protection assay, was not different between cancer and control tissues or immortal and a subset of primary keratinocytes and did not correlate with telomerase activity. These results indicate that expression of hTR and bTERT is up-regulated in at least a subset of neoplastic cells at an early stage of carcinogenesis and that unidentified factors, such as the modulation or coordination of its protein level with other products, may contribute to the activation of telomerase in cervical cancer.
| S-EPMC1853016 | biostudies-literature
Project description:BackgroundTargeting angiogenesis has been considered a promising treatment of choice for a large number of malignancies, including gastrointestinal cancers. Bevacizumab is an anti-vascular endothelial growth factor (anti-VEGF) being used for this purpose. However, treatment efficacy is largely questioned. Telomerase activity, responsible for cancer cell immortality, is detected in 85-95% of human cancers and is considered a potential regulator of VEGF. The aim of our study was to investigate the interrelationship between VEGF and hTERT in gastrointestinal cancers and to explore cell response to a combined inhibition of telomerase and VEGF.MethodsAGS (gastric cancer), Caco-2 (colorectal cancer) and HepG2/C3A (hepatocellular carcinoma), were treated with telomerase inhibitors BIBR-1232 (10μM) and costunolide (10μM), with bevacizumab (Avastin® at 5 ng/ml or 100μg/ml) or with a combination of both types of inhibitors. VEGF and hTERT mRNA levels, and telomerase activity were detected by RT-PCR. VEGF levels were quantified by ELISA. Telomerase was knocked down using hTERT siRNA and hTERT was overexpressed in the telomerase negative cell line, Saos-2 (osteosarcoma), using constructs expressing either wild type hTERT (hTERT-WT) or dominant negative hTERT (hTERT-DN). Tube formation by HUVECs was assessed using ECMatrix™ (EMD Millipore).ResultsOur results showed that telomerase regulates VEGF expression and secretion through its catalytic subunit hTERT in AGS, Caco2, and HepG2/C3A, independent of its catalytic activity. Interestingly, VEGF inhibition with bevacizumab (100μg/ml) increased hTERT expression 42.3% in AGS, 94.1% in Caco2, and 52.5% in HepG2/C3A, and increased telomerase activity 30-fold in AGS, 10.3-fold in Caco2 and 8-fold in HepG2/C3A. A further investigation showed that VEGF upregulates hTERT expression in a mechanism that implicates the PI3K/AKT/mTOR pathway and HIF-1α. Moreover, bevacizumab treatment increased VEGFR1 and VEGFR2 expression in cancer cells and human umbilical vein endothelial cells (HUVECs) through hTERT. Thus, the combination of bevacizumab with telomerase inhibitors decreased VEGF expression and secretion by cancer cells, inhibited VEGFR1 and VEGFR2 upregulation, and reduced tube formation by HUVECs.ConclusionsTaken together, our results suggest that bevacizumab treatment activates a VEGF autoregulatory mechanism involving hTERT and VEGF receptors and that an inhibition of this pathway could improve tumor cell response to anti-VEGF treatment.
| S-EPMC5466359 | biostudies-literature
Project description:Mutants of trt-1, the Caenorhabditis elegans telomerase reverse transcriptase, reproduce normally for several generations but eventually become sterile as a consequence of telomere erosion and end-to-end chromosome fusions. Telomere erosion and uncapping do not cause an increase in apoptosis in the germlines of trt-1 mutants. Instead, late-generation trt-1 mutants display chromosome segregation defects that are likely to be the direct cause of sterility. trt-1 functions in the same telomere replication pathway as mrt-2, a component of the Rad9/Rad1/Hus1 (9-1-1) proliferating cell nuclear antigen-like sliding clamp. Thus, the 9-1-1 complex may be required for telomerase to act at chromosome ends in C. elegans. Although telomere erosion limits replicative life span in human somatic cells, neither trt-1 nor telomere shortening affects postmitotic aging in C. elegans. These findings illustrate effects of telomere dysfunction in C. elegans mutants lacking the catalytic subunit of telomerase, trt-1.
| S-EPMC1361356 | biostudies-literature
Project description:Telomerase, the enzyme that elongates telomeres, is essential to maintain telomere length and to immortalize most cancer cells. However, little is known about the regulation of this enzyme in higher eukaryotes. We previously described a domain in the hTERT telomerase catalytic subunit that is essential for telomere elongation and cell immortalization in vivo but dispensable for catalytic activity in vitro. Here, we show that fusions of hTERT containing different mutations in this domain to the telomere binding protein hTRF2 redirected the mutated hTERT to telomeres and rescued its in vivo functions. We suggest that this domain posttranscriptionally regulates telomerase function by targeting the enzyme to telomeres.
| S-EPMC153184 | biostudies-literature
Project description:Telomerase is a ribonucleoprotein complex that elongates telomeres, allowing the stable maintenance of chromosomes during multiple cell divisions. Here, we describe the isolation and characterization of the catalytic subunit of mouse telomerase, mTERT (mouse telomerase reverse transcriptase), an essential protein component of the telomerase complex. During embryonic development, mTERT mRNA is abundantly expressed in the whole embryo, especially in regions of intense proliferation. We found that the mTERT mRNA expression in both embryonic and adult tissues is independent of the essential RNA component of telomerase, mTR, and therefore, of the formation of active telomerase complexes. mTERT protein is present exclusively in tissues with telomerase activity, such as testis, spleen, and thymus. mTERT protein is barely detectable in the thymus of mTR-/- mice, suggesting that mTERT protein stability in this tissue may depend on the actual assembly of active telomerase complexes. Finally, we found that mouse and human telomerase catalytic subunit is located in the cell nucleus, and its localization is not regulated during cell cycle progression.
| S-EPMC27918 | biostudies-literature
Project description:Our previous studies have implicated CHIP (carboxyl terminus of Hsp70-interacting protein) as a co-chaperone/ubiquitin ligase whose activities yield protection against stress-induced apoptotic events. In this report, we demonstrate a stress-dependent interaction between CHIP and Daxx (death domain-associated protein). This interaction interferes with the stress-dependent association of HIPK2 with Daxx, blocking phosphorylation of serine 46 in p53 and inhibiting the p53-dependent apoptotic program. Microarray analysis confirmed suppression of the p53-dependent transcriptional portrait in CHIP(+/+) but not in CHIP(-/-) heat shocked mouse embryonic fibroblasts. The interaction between CHIP and Daxx results in ubiquitination of Daxx, which is then partitioned to an insoluble compartment of the cell. In vitro ubiquitination of Daxx by CHIP revealed that ubiquitin chain formation utilizes non-canonical lysine linkages associated with resistance to proteasomal degradation. The ubiquitination of Daxx by CHIP utilizes lysines 630 and 631 and competes with the sumoylation machinery of the cell at these residues. These studies implicate CHIP as a stress-dependent regulator of Daxx that counters the pro-apoptotic influence of Daxx in the cell. By abrogating p53-dependent apoptotic pathways and by ubiquitination competitive with Daxx sumoylation, CHIP integrates the proteotoxic stress response of the cell with cell cycle pathways that influence cell survival.
| S-EPMC2742829 | biostudies-literature
Project description:Our previous studies have implicated CHIP as a co-chaperone/ubiquitin ligase, whose activities yield protection against stress-induced apoptotic events. In this report, we demonstrate a stress-dependent interaction between CHIP (carboxyl terminus of Hsp70-interacting protein) and Daxx, death domain-associated protein. This interaction interferes with the stress-dependent association of HIPK2 with Daxx, blocking phosphorylation of serine 46 in p53 and inhibiting the p53-dependent apoptotic program. Microarray analysis confirmed suppression of the p53-dependent transcriptional portrait in CHIP (+/+) but not in CHIP (-/-) heat shocked MEFs. The interaction between CHIP and Daxx results in ubiquitination of Daxx which is then partitioned to an insoluble compartment of the cell. In vitro ubiquitination of Daxx by CHIP revealed that Ub chain formation utilizes non canonical lysine linkages associated with resistance to proteasomal degradation. CHIP's ubiquitination of Daxx utilizes lysines 630 and 631 and competes with the cell's sumoylation machinery at these residues. These studies implicate CHIP as a stress-dependent regulator of Daxx that counters Daxx's pro-apoptotic influence in the cell. By abrogating p53-dependent apoptotic pathways and by ubiquitination competitive with Daxx sumoylation, CHIP integrates the cell's proteotoxic stress response with cell cycle pathways that influence cell survival. Keywords: p53, apoptosis, cell stress, ubiquitination We utilized a âsample x referenceâ experimental design strategy in which RNA extracted from mouse embryonic fibroblasts was hybridized to the microarray slide in the presence of labeled Universal Mouse Reference RNA (UMRR, Stratagene, LaJolla, CA). A total of 24 RNA samples were used in this analysis. Briefly, five hundred nanograms of total RNA were used for gene expression profiling following reverse transcription and T-7 polymerase-mediated amplification/labeling with Cyanine-5 CTP. Labeled subject cRNA was co-hybridized to Agilent G4112F Whole Mouse Genome 4x44K oligonucleotide arrays with equimolar amounts of Cyanine-3 labeled UHRR. Slides were hybridized, washed, and scanned on an Axon 4000b microarray scanner. The data were processed using Feature Extaction software (Agilent, Santa Clara, CA).
2010-04-03 | E-GEOD-14339 | biostudies-arrayexpress