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Inhibition of Casein kinase-2 induces p53-dependent cell cycle arrest and sensitizes glioblastoma cells to tumor necrosis factor (TNFα)-induced apoptosis through SIRT1 inhibition. Cell Death Dis 2012; 3:e271. [PMID: 22318540 PMCID: PMC3288342 DOI: 10.1038/cddis.2012.10] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Glioblastoma multiforme (GBM) are resistant to TNFα-induced apoptosis and blockade of TNFα-induced NF-κB activation sensitizes glioma cells to apoptosis. As Casein kinase-2 (CK2) induces aberrant NF-κB activation and as we observed elevated CK2 levels in GBM tumors, we investigated the potential of CK2 inhibitors (CK2-Is) - DRB and Apigenin in sensitizing glioma cells to TNFα-induced apoptosis. CK2-Is and CK2 small interfering RNA (siRNA) reduced glioma cell viability, inhibited TNFα-mediated NF-κB activation, and sensitized cell to TNFα-induced apoptosis. Importantly, CK2-Is activated p53 function in wild-type but not in p53 mutant cells. Activation of p53 function involved its increased transcriptional activation, DNA-binding ability, increased expression of p53 target genes associated with cell cycle progression and apoptosis. Moreover, CK2-Is decreased telomerase activity and increased senescence in a p53-dependent manner. Apoptotic gene profiling indicated that CK2-Is differentially affect p53 and TNFα targets in p53 wild-type and mutant glioma cells. CK2-I decreased MDM2-p53 association and p53 ubiquitination to enhance p53 levels. Interestingly, CK2-Is downregulated SIRT1 activity and over-expression of SIRT1 decreased p53 transcriptional activity and rescued cells from CK2-I-induced apoptosis. This ability of CK2-Is to sensitize glioma to TNFα-induced death via multiple mechanisms involving abrogation of NF-κB activation, reactivation of wild-type p53 function and SIRT1 inhibition warrants investigation.
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52
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Cifuentes-Rojas C, Shippen DE. Telomerase regulation. Mutat Res 2012; 730:20-7. [PMID: 22032831 PMCID: PMC3256259 DOI: 10.1016/j.mrfmmm.2011.10.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 09/15/2011] [Accepted: 10/12/2011] [Indexed: 02/05/2023]
Abstract
The intimate connection between telomerase regulation and human disease is now well established. The molecular basis for telomerase regulation is highly complex and entails multiple layers of control. While the major target of enzyme regulation is the catalytic subunit TERT, the RNA subunit of telomerase is also implicated in telomerase control. In addition, alterations in gene dosage and alternative isoforms of core telomerase components have been described. Finally, telomerase localization, recruitment to the telomere and enzymology at the chromosome terminus are all subject to modulation. In this review we summarize recent advances in understanding fundamental mechanisms of telomerase regulation.
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Affiliation(s)
| | - Dorothy E. Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
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53
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Golomb L, Bublik DR, Wilder S, Nevo R, Kiss V, Grabusic K, Oren M. Importin 7 and exportin 1 link c-Myc and p53 to regulation of ribosomal biogenesis. Mol Cell 2012; 45:222-32. [PMID: 22284678 PMCID: PMC3270374 DOI: 10.1016/j.molcel.2011.11.022] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 07/13/2011] [Accepted: 11/04/2011] [Indexed: 11/22/2022]
Abstract
Members of the β-karyopherin family mediate nuclear import of ribosomal proteins and export of ribosomal subunits, both required for ribosome biogenesis. We report that transcription of the β-karyopherin genes importin 7 (IPO7) and exportin 1 (XPO1), and several additional nuclear import receptors, is regulated positively by c-Myc and negatively by p53. Partial IPO7 depletion triggers p53 activation and p53-dependent growth arrest. Activation of p53 by IPO7 knockdown has distinct features of ribosomal biogenesis stress, with increased binding of Mdm2 to ribosomal proteins L5 and L11 (RPL5 and RPL11). Furthermore, p53 activation is dependent on RPL5 and RPL11. Of note, IPO7 and XPO1 are frequently overexpressed in cancer. Altogether, we propose that c-Myc and p53 counter each other in the regulation of elements within the nuclear transport machinery, thereby exerting opposing effects on the rate of ribosome biogenesis. Perturbation of this balance may play a significant role in promoting cancer.
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Affiliation(s)
- Lior Golomb
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Debora Rosa Bublik
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Sylvia Wilder
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Reinat Nevo
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Vladimir Kiss
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Kristina Grabusic
- Department of Molecular medicine and Biotechnology, University of Rijeka, School of Medicine, Rijeka 51000, Croatia
| | - Moshe Oren
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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Yamasaki Y, Tazawa H, Hashimoto Y, Kojima T, Kuroda S, Yano S, Yoshida R, Uno F, Mizuguchi H, Ohtsuru A, Urata Y, Kagawa S, Fujiwara T. A novel apoptotic mechanism of genetically engineered adenovirus-mediated tumour-specific p53 overexpression through E1A-dependent p21 and MDM2 suppression. Eur J Cancer 2012; 48:2282-91. [PMID: 22244827 DOI: 10.1016/j.ejca.2011.12.020] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 12/15/2011] [Accepted: 12/17/2011] [Indexed: 10/14/2022]
Abstract
Oncolytic viruses engineered to replicate in tumour cells but not in normal cells could be used as tumour-specific vectors carrying the therapeutic genes. We previously developed a telomerase-specific oncolytic adenovirus, OBP-301, that causes cell death in human cancer cells with telomerase activities. Here, we further modified OBP-301 to express the wild-type p53 tumour suppressor gene (OBP-702), and investigated whether OBP-702 induces stronger antitumour activity than OBP-301. The antitumour effect of OBP-702 was compared to that of OBP-301 on OBP-301-sensitive (H358 and H460) and OBP-301-resistant (T.Tn and HSC4) human cancer cells. OBP-702 suppressed the viability of both OBP-301-sensitive and OBP-301-resistant cancer cells more efficiently than OBP-301. OBP-702 caused increased apoptosis compared to OBP-301 or a replication-deficient adenovirus expressing the p53 gene (Ad-p53) in H358 and T.Tn cells. Adenovirus E1A-mediated p21 and MDM2 downregulation was involved in the apoptosis caused by OBP-702. Moreover, OBP-702 significantly suppressed tumour growth in subcutaneous tumour xenograft models compared to monotherapy with OBP-301 or Ad-p53. Our data demonstrated that OBP-702 infection expressed adenovirus E1A and then inhibited p21 and MDM2 expression, which in turn efficiently induced apoptotic cell death. This novel apoptotic mechanism suggests that the p53-expressing OBP-702 is a promising antitumour reagent for human cancer and could improve the clinical outcome.
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Affiliation(s)
- Yasumoto Yamasaki
- Department of Gastroenterological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan
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55
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The NF-Y/p53 liaison: well beyond repression. Biochim Biophys Acta Rev Cancer 2011; 1825:131-9. [PMID: 22138487 DOI: 10.1016/j.bbcan.2011.11.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 11/09/2011] [Accepted: 11/12/2011] [Indexed: 12/15/2022]
Abstract
NF-Y is a sequence-specific transcription factor - TF - targeting the common CCAAT promoter element. p53 is a master TF controlling the response to stress signals endangering genome integrity, often mutated in human cancers. The NF-Y/p53 - and p63, p73 - interaction results in transcriptional repression of a subset of genes within the vast NF-Y regulome under DNA-damage conditions. Recent data shows that NF-Y is also involved in pro-apoptotic activities, either directly, by mediating p53 transcriptional activation, or indirectly, by being targeted by a non coding RNA, PANDA. The picture is subverted in cells carrying Gain-of-function mutant p53, through interactions with TopBP1, a protein also involved in DNA repair and replication. In summary, the connection between p53 and NF-Y is crucial in determining cell survival or death.
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56
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Gladych M, Wojtyla A, Rubis B. Human telomerase expression regulation. Biochem Cell Biol 2011; 89:359-76. [DOI: 10.1139/o11-037] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Since telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells, it has become a very promising target for anti-cancer therapy. A correlation between short telomere length and increased mortality was revealed in many studies. The telomerase expression/activity appears to be one of the most crucial factors to study to improve cancer therapy and prevention. However, this multisubunit enzymatic complex can be regulated at various levels. Thus, several strategies have been proposed to control telomerase in cancer cells such as anti-sense technology against TR and TERT, ribozymes against TERT, anti-estrogens, progesterone, vitamin D, retinoic acid, quadruplex stabilizers, telomere and telomerase targeting agents, modulation of interaction with other proteins involved in the regulation of telomerase and telomeres, etc. However, the transcription control of key telomerase subunits seems to play the crucial role in whole complexes activity and cancer cells immortality. Thus, the research of telomerase regulation can bring significant insight into the knowledge concerning stem cells metabolism but also ageing. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms at the transcription level in human that might become attractive anti-cancer therapy targets.
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Affiliation(s)
- Marta Gladych
- Poznan University of Medical Sciences, Department of Clinical Chemistry and Molecular Diagnostics, Przybyszewskiego 49 St., 60-355 Poznan, Poland
| | - Aneta Wojtyla
- Poznan University of Medical Sciences, Department of Clinical Chemistry and Molecular Diagnostics, Przybyszewskiego 49 St., 60-355 Poznan, Poland
| | - Blazej Rubis
- Poznan University of Medical Sciences, Department of Clinical Chemistry and Molecular Diagnostics, Przybyszewskiego 49 St., 60-355 Poznan, Poland
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57
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RuvBl2 cooperates with Ets2 to transcriptionally regulate hTERT in colon cancer. FEBS Lett 2011; 585:2537-44. [DOI: 10.1016/j.febslet.2011.07.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Revised: 07/01/2011] [Accepted: 07/05/2011] [Indexed: 01/26/2023]
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58
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Yoon AR, Gao R, Kaul Z, Choi IK, Ryu J, Noble JR, Kato Y, Saito S, Hirano T, Ishii T, Reddel RR, Yun CO, Kaul SC, Wadhwa R. MicroRNA-296 is enriched in cancer cells and downregulates p21WAF1 mRNA expression via interaction with its 3' untranslated region. Nucleic Acids Res 2011; 39:8078-91. [PMID: 21724611 PMCID: PMC3185413 DOI: 10.1093/nar/gkr492] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
MicroRNAs (miRNAs) are a class of noncoding small RNAs that act as negative regulators of gene expression. To identify miRNAs that may regulate human cell immortalization and carcinogenesis, we performed comparative miRNA array profiling of human normal and SV40-T antigen immortalized cells. We found that miR-296 was upregulated in immortalized cells that also had activation of telomerase. By an independent experiment on genomic analysis of cancer cells we found that chromosome region (20q13.32), where miR-296 is located, was amplified in 28/36 cell lines, and most of these showed enriched miR-296 expression. Overexpression of miR-296 in human cancer cells, with and without telomerase activity, had no effect on their telomerase function. Instead, it suppressed p53 function that is frequently downregulated during human cell immortalization and carcinogenesis. By monitoring the activity of a luciferase reporter connected to p53 and p21WAF1 (p21) untranslated regions (UTRs), we demonstrate that miR-296 interacts with the p21-3′UTR, and the Hu binding site of p21-3′UTR was identified as a potential miR-296 target site. We demonstrate for the first time that miR-296 is frequently upregulated during immortalization of human cells and contributes to carcinogenesis by downregulation of p53-p21WAF1 pathway.
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Affiliation(s)
- A-rum Yoon
- National Institute of Advanced Industrial Science & Technology, Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki - 305 8562, Japan
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59
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Bayne S, Li H, Jones MEE, Pinto AR, van Sinderen M, Drummond A, Simpson ER, Liu JP. Estrogen deficiency reversibly induces telomere shortening in mouse granulosa cells and ovarian aging in vivo. Protein Cell 2011; 2:333-46. [PMID: 21574023 DOI: 10.1007/s13238-011-1033-2] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 03/21/2011] [Indexed: 12/31/2022] Open
Abstract
Estrogen is implicated as playing an important role in aging and tumorigenesis of estrogen responsive tissues; however the mechanisms underlying the mitogenic actions of estrogen are not fully understood. Here we report that estrogen deficiency in mice caused by targeted disruption of the aromatase gene results in a significant inhibition of telomerase maintenance of telomeres in mouse ovaries in a tissue-specific manner. The inhibition entails a significant shortening of telomeres and compromised proliferation in the follicular granulosa cell compartment of ovary. Gene expression analysis showed decreased levels of proto-oncogene c-Myc and the telomerase catalytic subunit, telomerase reverse transcriptase (TERT), in response to estrogen deficiency. Estrogen replacement therapy led to increases in TERT gene expression, telomerase activity, telomere length and ovarian tissue growth, thereby reinstating ovary development to normal in four weeks. Our data demonstrate for the first time that telomere maintenance is the primary mechanism mediating the mitogenic effect of estrogen on ovarian granulosa cell proliferation by upregulating the genes of c-Myc and TERT in vivo. Estrogen deficiency or over-activity may cause ovarian tissue aging or tumorigenesis, respectively, through estrogen regulation of telomere remodeling.
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Affiliation(s)
- Sharyn Bayne
- Department of Immunology, Central Eastern Clinical School, Monash University, Victoria 3800, Australia
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60
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Yew TL, Chiu FY, Tsai CC, Chen HL, Lee WP, Chen YJ, Chang MC, Hung SC. Knockdown of p21(Cip1/Waf1) enhances proliferation, the expression of stemness markers, and osteogenic potential in human mesenchymal stem cells. Aging Cell 2011; 10:349-61. [PMID: 21342417 DOI: 10.1111/j.1474-9726.2011.00676.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Mammalian aging of many tissues is associated with a decline in the replicative and functional capacity of somatic stem cells. Understanding the basis of this decline is a major goal of aging research. Human bone marrow-derived multipotent stromal cells (MSCs) have been applied in the treatment of fracture nonunion. Clinical application of MSCs requires abundant cells that can be overcome by ex vivo expansion of cells, but often at the expense of stemness and differentiation potentiality. We first demonstrated that late-passage MSCs exhibited decreased proliferation capacity, reduced expression of stemness markers such as Oct-4 and Nanog, and deterioration of osteogenic potential. Further, late-passage MSCs showed increased expression of p21(Cip1/Waf1) (p21), an inhibitor of the cyclin-dependent kinase. Knockdown of p21 by lentivirus-mediated shRNAs against p21 in late-passage MSCs increased the proliferation capacity, the expression of Oct-4 and Nanog, and osteogenic potential compared with cells transduced with control shRNA. More importantly, reduction in p21 expression in MSCs enhanced the bone repair capacity of MSCs in a rodent calvarial defect model. Knockdown of p21 in MSCs also increased the telomerase activity and telomere length, and did not show chromosomal abnormalities or acquire transformation ability. Therefore, these data successfully demonstrate the involvement of senescence gene in the expression of stemness markers and osteogenic potential of MSCs.
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Affiliation(s)
- Tu-Lai Yew
- Department of Dentistry, Institute of Oral Biology, National Yang-Ming University, Taipei 112, Taiwan
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61
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One function--multiple mechanisms: the manifold activities of p53 as a transcriptional repressor. J Biomed Biotechnol 2011; 2011:464916. [PMID: 21436991 PMCID: PMC3062963 DOI: 10.1155/2011/464916] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Accepted: 01/17/2011] [Indexed: 12/31/2022] Open
Abstract
Maintenance of genome integrity is a dynamic process involving complex regulation systems. Defects in one or more of these pathways could result in cancer. The most important tumor-suppressor is the transcription factor p53, and its functional inactivation is frequently observed in many tumor types. The tumor suppressive function of p53 is mainly attributed to its ability to regulate numerous target genes at the transcriptional level. While the mechanism of transcriptional induction by p53 is well characterized, p53-dependent repression is not understood in detail. Here, we review the manifold mechanisms of p53 as a transcriptional repressor. We classify two different categories of repressed genes based on the underlying mechanism, and novel mechanisms which involve regulation through noncoding RNAs are discussed. The complete elucidation of p53 functions is important for our understanding of its tumor-suppressor activity and, therefore, represents the key for the development of novel therapeutic approaches.
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62
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Gopalan V, Smith RA, Ho YH, Lam AKY. Signet-ring cell carcinoma of colorectum--current perspectives and molecular biology. Int J Colorectal Dis 2011; 26:127-33. [PMID: 20686774 DOI: 10.1007/s00384-010-1037-z] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/26/2010] [Indexed: 02/08/2023]
Abstract
PURPOSE Colorectal signet-ring cell carcinoma (SRCC) is rare, and very little detailed information on the molecular biology of the disease is available. METHODS The literature on the clinical, pathological and, in particular, the molecular biology of this rare entity was critically reviewed. The reviewed articles take into account a total of 1,817 cases of SRCC, but only 143 cases have molecular data available. The characteristics of two patients with colorectal SRCC were also discussed. RESULTS Colorectal SRCC mostly occurs in younger patients, is larger and has different site predilection compared with conventional colorectal adenocarcinoma. It can occur as one of the synchronous cancers in the colorectum. The cancer is usually diagnosed at advanced stages because of the late manifestation of symptoms, and aggressive treatment strategy is required. Limited reports in the literature have shown that the variant of colorectal cancer demonstrated a different pattern of genetic alterations of common growth kinase-related oncogenes (K-ras, BRAF), tumour suppressor genes (p53, p16), gene methylation and cell adhesion-related genes related to the Wingless signalling pathway (E-cadherin and beta-catenin) from conventional colorectal adenocarcinoma. Colorectal SRCC also showed high expression of mucin-related genes and genes related to the gastrointestinal system. There was also a higher prevalence of microsatellite instability-high tumours and low Cox-2 expression in colorectal SRCC as opposed to conventional adenocarcinoma. CONCLUSIONS Colorectal SRCC has unique molecular pathological features. The unique molecular profiles in SRCC may provide molecular-based improvements to patient management in colorectal SRCC.
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Affiliation(s)
- Vinod Gopalan
- School of Medicine, Griffith Health Institute, Gold Coast, QLD, Australia
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63
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Zheltukhin AO, Chumakov PM. Constitutive and induced functions of the p53 gene. BIOCHEMISTRY (MOSCOW) 2011; 75:1692-721. [DOI: 10.1134/s0006297910130110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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64
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Islam MR, Jimenez T, Pelham C, Rodova M, Puri S, Magenheimer BS, Maser RL, Widmann C, Calvet JP. MAP/ERK kinase kinase 1 (MEKK1) mediates transcriptional repression by interacting with polycystic kidney disease-1 (PKD1) promoter-bound p53 tumor suppressor protein. J Biol Chem 2010; 285:38818-31. [PMID: 20923779 DOI: 10.1074/jbc.m110.145284] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitogen-activated protein kinase (MAPK) cascades regulate a wide variety of cellular processes that ultimately depend on changes in gene expression. We have found a novel mechanism whereby one of the key MAP3 kinases, Mekk1, regulates transcriptional activity through an interaction with p53. The tumor suppressor protein p53 down-regulates a number of genes, including the gene most frequently mutated in autosomal dominant polycystic kidney disease (PKD1). We have discovered that Mekk1 translocates to the nucleus and acts as a co-repressor with p53 to down-regulate PKD1 transcriptional activity. This repression does not require Mekk1 kinase activity, excluding the need for an Mekk1 phosphorylation cascade. However, this PKD1 repression can also be induced by the stress-pathway stimuli, including TNFα, suggesting that Mekk1 activation induces both JNK-dependent and JNK-independent pathways that target the PKD1 gene. An Mekk1-p53 interaction at the PKD1 promoter suggests a new mechanism by which abnormally elevated stress-pathway stimuli might directly down-regulate the PKD1 gene, possibly causing haploinsufficiency and cyst formation.
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Affiliation(s)
- M Rafiq Islam
- Department of Chemistry/Physics, Northwest Missouri State University, Maryville, Missouri 64468, USA.
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65
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Lee JH, Lee SY, Lee JH, Lee SH. p21 WAF1 is involved in interferon-β-induced attenuation of telomerase activity and human telomerase reverse transcriptase (hTERT) expression in ovarian cancer. Mol Cells 2010; 30:327-33. [PMID: 20814747 DOI: 10.1007/s10059-010-0131-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 07/21/2010] [Accepted: 07/30/2010] [Indexed: 10/19/2022] Open
Abstract
Telomerase activation is a key step in the development of human cancers. Interferon-β (IFN-β) signaling induces growth arrest in many tumors but the anticancer mechanism of IFN-β is poorly understood. In the present study, we show that IFN-β signaling represses telomerase activity and human telomerase reverse transcriptase (hTERT) transcription in ovarian cancer and suggest that this signaling is mediated by p21(WAF1). IFN-β triggered down-regulation of telomerase activity and hTERT mRNA expression and also induced p21 expression, independently of p53 induction. Ectopic expression of p21 attenuated hTERT promoter activity. Murine embryonic fibroblasts (MEFs) genetically deficient in p21 (p21-/-) showed elevated (> 15 times) hTERT promoter activity compared to wild-type MEFs. Overexpression of p21 reduced the hTERT promoter activity of p21-/- MEFs and hTERT mRNA expression in HCT119 p21(WAF1) null cell. These findings provide evidence that p21 is a potential mediator of IFN-β-induced attenuation of telomerase activity and tumor suppression.
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Affiliation(s)
- Ji-Hae Lee
- Department of Life Science, Yongin University, Yongin, 449-714, Korea
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66
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Heminger K, Markey M, Mpagi M, Berberich SJ. Alterations in gene expression and sensitivity to genotoxic stress following HdmX or Hdm2 knockdown in human tumor cells harboring wild-type p53. Aging (Albany NY) 2010; 1:89-108. [PMID: 19946469 PMCID: PMC2783638 DOI: 10.18632/aging.100008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
While half of all human tumors possess p53 mutations, inactivation of wild-type p53 can also occur through a variety of mechanisms that do not involve p53 gene mutation or deletion. Our laboratory has been interested in tumor cells possessing wild-type p53 protein and elevated levels of HdmX and/or Hdm2, two critical negative regulators of p53 function. In this study we utilized RNAi to knockdown HdmX or Hdm2 in MCF7 human breast cancer cells, which harbor wild-type p53 and elevated levels of HdmX and Hdm2 then examined gene expression changes and effects on cell growth.Cell cycle and growth assays confirmed that the loss of either HdmX or Hdm2 led to a significant growth inhibition and G1cell cycle arrest. Although the removal of overexpressed HdmX/2 appears limited to an anti-proliferative effect in MCF7cells, the loss of HdmX and/or Hdm2 enhanced cytotoxicity in these same cells exposed to DNA damage. Through the use of Affymetrix GeneChips and subsequent RT-qPCR validations, we uncovered a subset of anti-proliferative p53 target genes activated upon HdmX/2 knockdown. Interestingly, a second set of genes, normally transactivated by E2F1 as cells transverse the G1-S phase boundary, were found repressed in a p21-dependent manner following HdmX/2 knockdown.Taken together, these results provide novel insights into the reactivation of p53 in cells overexpressing HdmX and Hdm2.
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Affiliation(s)
- Katherine Heminger
- Wright State University Boonshoft School of Medicine Biochemistry & Molecular Biology Department, Dayton, OH 45435, USA
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67
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Mingaleeva RN, Chernov IP, Kopantzev EP, Zavalova LL, Sass AV, Sverdlov ED. Comparative analysis of herpes simplex virus thymidine kinase gene expression potentiation via HIV-1 Tat-TAR system and cancer-specific promoters in P53(+) and P53(-) cells. Mol Biol 2010. [DOI: 10.1134/s0026893310030131] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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68
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Qian Y, Chen X. Tumor suppression by p53: making cells senescent. Histol Histopathol 2010; 25:515-26. [PMID: 20183804 DOI: 10.14670/hh-25.515] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Cellular senescence is a permanent cell cycle arrest and a potent tumor suppression mechanism. The p53 tumor suppressor is a sequence-specific transcription factor and acts as a central hub sensing various stress signals and activating an array of target genes to induce cell cycle arrest, apoptosis, and senescence. Recent reports showed that restoration of p53 induces premature senescence and tumor regression in mice with hepatocarcinomas or sarcomas. Thus, p53-mediated senescence is capable of eliminating cancer cells in vivo. p63 and p73, two homologues of p53, have similar function in cell cycle arrest and apoptosis. However, the role of p63 and p73 in cellular senescence is elusive. In this review, we will discuss how p53 regulates senescence and future studies about p53 family members in senescence.
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Affiliation(s)
- Yingjuan Qian
- Center for Comparative Oncology, University of California, Davis, California 95616, USA
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69
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Oh W, Lee EW, Lee D, Yang MR, Ko A, Yoon CH, Lee HW, Bae YS, Choi CY, Song J. Hdm2 negatively regulates telomerase activity by functioning as an E3 ligase of hTERT. Oncogene 2010; 29:4101-12. [PMID: 20453884 DOI: 10.1038/onc.2010.160] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In this study, we identified posttranslational regulation of human telomerase reverse-transcriptase (hTERT) by the E3 ligase Hdm2. The telomerase activity generated by exogenous hTERT in U2OS cells was reduced on adriamycin treatment. The overexpressed levels of hTERT were also decreased under the same conditions. These processes were reversed by treatment with a proteasome inhibitor or depletion of Hdm2. Furthermore, intrinsic telomerase activity was increased in HCT116 cells with ablation of Hdm2. Immunoprecipitation analyses showed that hTERT and Hdm2 bound to each other in multiple domains. Ubiquitination analyses showed that Hdm2 could polyubiquitinate hTERT principally at the N-terminus, which was further degraded in a proteasome-dependent manner. An hTERT mutant with all five lysine residues at the N-terminus of hTERT that mutated to arginine became resistant to Hdm2-mediated ubiquitination and degradation. In U2OS cells, depletion of Hdm2 or addition of the Hdm2-resistant hTERT mutant strengthened the cellular protective effects against apoptosis. Similar results were obtained with the Hdm2-stable H1299 cell line. These observations indicate that Hdm2 is an E3 ligase of hTERT.
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Affiliation(s)
- W Oh
- Department of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Korea
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70
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Souček K, Gajdušková P, Brázdová M, Hýžd'alová M, Kočí L, Vydra D, Trojanec R, Pernicová Z, Lentvorská L, Hajdúch M, Hofmanová J, Kozubík A. Fetal colon cell line FHC exhibits tumorigenic phenotype, complex karyotype, and TP53 gene mutation. ACTA ACUST UNITED AC 2010; 197:107-16. [DOI: 10.1016/j.cancergencyto.2009.11.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2009] [Revised: 11/02/2009] [Accepted: 11/13/2009] [Indexed: 11/29/2022]
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71
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Brosh R, Rotter V. Transcriptional control of the proliferation cluster by the tumor suppressor p53. ACTA ACUST UNITED AC 2010; 6:17-29. [DOI: 10.1039/b911416e] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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72
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Daniel-Carmi V, Makovitzki-Avraham E, Reuven EM, Goldstein I, Zilkha N, Rotter V, Tzehoval E, Eisenbach L. The human 1-8D gene (IFITM2) is a novel p53 independent pro-apoptotic gene. Int J Cancer 2009; 125:2810-9. [PMID: 19544527 DOI: 10.1002/ijc.24669] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The human 1-8 interferon inducible gene family consists of at least 3 functional genes; 9-27, 1-8D and 1-8U, which are all linked on an 18-kb fragment of chromosome 11 and are highly homologous. It has recently been shown by us and others that the 1-8D gene is overexpressed in colon carcinoma. Here, we show, by sequence comparison of the 1-8D in pairs of tumor/normal colon tissues, the existence of 6 different alleles, containing single-nucleotide polymorphisms with no mutations. Transformation assays revealed a possible role for the 1-8D gene as a transformation inhibitor. Further, transient expression of the human 1-8D gene in multiple mammalian cell lines showed accumulation of cells in the G1 phase followed by elevation in the subG1 phase. SubG1 elevation was confirmed as apoptosis by Annexin-V binding assays and transferase-mediated dUTP nick end labeling assays. Moreover, knock-down of 1-8D provided partial protection from Etoposide and UV-induced apoptosis. The induction of apoptosis by 1-8D is dependent on caspase activities but not on p53 expression. Although 1-8D induces apoptosis independently of p53, p53 expression downregulates 1-8D protein expression. Our data suggest a role for the 1-8D gene as a novel pro-apoptotic gene that will provide new insights into the regulated cellular pathways to death.
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Affiliation(s)
- Vered Daniel-Carmi
- Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel
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Barsotti AM, Prives C. Pro-proliferative FoxM1 is a target of p53-mediated repression. Oncogene 2009; 28:4295-305. [PMID: 19749794 DOI: 10.1038/onc.2009.282] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The p53 tumor suppressor protein acts as a transcription factor to modulate cellular responses to a wide variety of stresses. In this study we show that p53 is required for the downregulation of FoxM1, an essential transcription factor that regulates many G2/M-specific genes and is overexpressed in a multitude of solid tumors. After DNA damage, p53 facilitates the repression of FoxM1 mRNA, which is accompanied by a decrease in FoxM1 protein levels. In cells with reduced p53 expression, FoxM1 is upregulated after DNA damage. Nutlin, a small-molecule activator of p53, suppresses FoxM1 levels in two cell lines in which DNA damage facilitates only mild repression. Mechanistically, p53-mediated inhibition of FoxM1 is partially p21 and retinoblastoma (Rb) family dependent, although in some cases p21-independent repression of FoxM1 was also observed. The importance of FoxM1 to cell fate was indicated by the observation that G2/M arrest follows FoxM1 ablation. Finally, our results indicate a potential contribution of p53-mediated repression of FoxM1 for maintenance of a stable G2 arrest.
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Affiliation(s)
- A M Barsotti
- Department of Biological Sciences, Columbia University, New York, NY, USA
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74
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Sanduja S, Kaza V, Dixon DA. The mRNA decay factor tristetraprolin (TTP) induces senescence in human papillomavirus-transformed cervical cancer cells by targeting E6-AP ubiquitin ligase. Aging (Albany NY) 2009; 1:803-17. [PMID: 20157568 PMCID: PMC2815738 DOI: 10.18632/aging.100086] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2009] [Accepted: 09/08/2009] [Indexed: 12/31/2022]
Abstract
The RNA-binding
protein tristetraprolin (TTP) regulates expression of many
cancer-associated and proinflammatory factors through binding AU-rich
elements (ARE) in the 3'-untranslated region (3'UTR) and facilitating rapid
mRNA decay. Here we report on the ability of TTP to act in an
anti-proliferative capacity in HPV18-positive HeLa cells by inducing
senescence. HeLa cells maintain a dormant p53 pathway and elevated
telomerase activity resulting from HPV-mediated transformation, whereas TTP
expression counteracted this effect by stabilizing p53 protein and
inhibiting hTERT expression. Presence of TTP did not alter E6 and E7 viral
mRNA levels indicating that these are not TTP targets. It was found that
TTP promoted rapid mRNA decay of the cellular
ubiquitin ligase E6-associated protein (E6-AP). RNA-binding studies
demonstrated TTP and E6-AP mRNA interaction and deletion of the E6-AP mRNA
ARE-containing 3'UTR imparts resistance to TTP-mediated downregulation.
Similar results were obtained with high-risk HPV16-positive cells that
employ the E6-AP pathway to control p53 and hTERT levels. Furthermore, loss
of TTP expression was consistently observed in cervical cancer tissue
compared to normal tissue. These findings demonstrate the ability of TTP to
act as a tumor suppressor by inhibiting the E6-AP pathway
and indicate TTP loss to be a critical event during HPV-mediated
carcinogenesis.
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Affiliation(s)
- Sandhya Sanduja
- Department of Biological Sciences and Cancer Research Center, University of South Carolina, Columbia, SC 29203, USA
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Abstract
While the tumor suppressor functions of p53 have long been recognized, the contribution of p53 to numerous other aspects of disease and normal life is only now being appreciated. This burgeoning range of responses to p53 is reflected by an increasing variety of mechanisms through which p53 can function, although the ability to activate transcription remains key to p53's modus operandi. Control of p53's transcriptional activity is crucial for determining which p53 response is activated, a decision we must understand if we are to exploit efficiently the next generation of drugs that selectively activate or inhibit p53.
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Affiliation(s)
- Karen H Vousden
- The Beatson Institute for Cancer Research, Garscube Estate, Glasgow, UK.
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Abstract
1. Oestrogen plays an important role in ageing and ageing-related development. Lack of oestrogen prompts endocrine cell ageing of the ovary, whereas oestrogen overflow impacts on epithelial cell neoplastic development. 2. Recent studies indicate that oestrogen regulates cell proliferative fates by a mechanism of reprogramming the size of telomeres (ends of chromosomes) in the oestrogen target cells. This is achieved by upregulating the telomerase reverse transcriptase (TERT) gene in a temporal and spatial manner. 3. Currently, the relationship between oestrogen and telomerase activity in regulating productive cell development and function remains elusive. A number of lines of evidence suggest that telomerase is a downstream target of oestrogen in oestrogen-dependent reproductive ageing and neoplastic development. 4. The present minireview discusses our current understanding of the mechanisms by which telomerase maintenance of telomere homeostasis mediates oestrogen-induced ageing and tumourigenesis in the ovary under physiological and pathological conditions.
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Affiliation(s)
- He Li
- Department of Immunology, Molecular Signalling Laboratory, Monash University Central Clinical School, AMREP, Melbourne, Victoria 3004, Australia.
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Abstract
One of the main engines that drives cellular transformation is the loss of proper control of the mammalian cell cycle. The cyclin-dependent kinase inhibitor p21 (also known as p21WAF1/Cip1) promotes cell cycle arrest in response to many stimuli. It is well positioned to function as both a sensor and an effector of multiple anti-proliferative signals. This Review focuses on recent advances in our understanding of the regulation of p21 and its biological functions with emphasis on its p53-independent tumour suppressor activities and paradoxical tumour-promoting activities, and their implications in cancer.
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Affiliation(s)
- Tarek Abbas
- Department of Biochemistry and Molecular Genetics, University of Virginia, School of Medicine, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA.
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78
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Deville L, Hillion J, Ségal-Bendirdjian E. Telomerase regulation in hematological cancers: a matter of stemness? Biochim Biophys Acta Mol Basis Dis 2009; 1792:229-39. [PMID: 19419697 DOI: 10.1016/j.bbadis.2009.01.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2008] [Revised: 01/30/2009] [Accepted: 01/30/2009] [Indexed: 01/02/2023]
Abstract
Human telomerase is a nuclear ribonucleoprotein enzyme complex that catalyzes the synthesis and extension of telomeric DNA. This enzyme is highly expressed and active in most malignant tumors while it is usually not or transiently detectable in normal somatic cells, suggesting that it plays an important role in cellular immortalization and tumorigenesis. As most leukemic cells are generally telomerase-positive and have often shortened telomeres, our understanding of how telomerase is deregulated in these diseases could help to define novel therapies targeting the telomere/telomerase complex. Nonetheless, considering that normal hematopoietic stem cells and some of their progeny do express a functional telomerase, it is tempting to consider such an activity in leukemias as a sustained stemness feature and important to understand how telomere length and telomerase activity are regulated in the various forms of leukemias.
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Affiliation(s)
- Laure Deville
- INSERM UMR-S 685, Institut d'Hématologie, Hôpital Saint-Louis, 75475 Paris cedex 10, France
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79
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Wilson PM, Fazzone W, LaBonte MJ, Lenz HJ, Ladner RD. Regulation of human dUTPase gene expression and p53-mediated transcriptional repression in response to oxaliplatin-induced DNA damage. Nucleic Acids Res 2008; 37:78-95. [PMID: 19015155 PMCID: PMC2615606 DOI: 10.1093/nar/gkn910] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Deoxyuridine triphosphate nucleotidohydrolase (dUTPase) catalyzes the hydrolysis of dUTP to dUMP and PPi. Although dUTP is a normal intermediate in DNA synthesis, its accumulation and misincorporation into DNA is lethal. Importantly, uracil misincorporation is a mechanism of cytotoxicity induced by fluoropyrimidine chemotherapeutic agents including 5-fluorouracil (5-FU) and elevated expression of dUTPase is negatively correlated with clinical response to 5-FU-therapy. In this study we performed the first functional characterization of the dUTPase promoter and demonstrate a role for E2F-1 and Sp1 in driving dUTPase expression. We establish a direct role for both mutant and wild-type forms of p53 in modulating dUTPase promoter activity. Treatment of HCT116 p53(+/+) cells with the DNA-damaging agent oxaliplatin induced a p53-dependent transcriptional downregulation of dUTPase not observed in the isogenic null cell line. Oxaliplatin treatment induced enrichment of p53 at the dUTPase promoter with a concomitant reduction in Sp1. The suppression of dUTPase by oxaliplatin promoted increased levels of dUTP that was enhanced by subsequent addition of fluoropyrimidines. The novel observation that oxaliplatin downregulates dUTPase expression may provide a mechanistic basis contributing to the synergy observed between 5-FU and oxaliplatin in the clinic. Furthermore, these studies provide the first evidence of a direct transcriptional link between the essential enzyme dUTPase and the tumor suppressor p53.
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Affiliation(s)
- Peter M Wilson
- Department of Pathology, Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
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80
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Zhang C, Guo X, Zhang L, Lu Z, Ma N, Cheng Y, Shen F, Zhang B, Wu M, Wei L. Methylation-Related silencing of p14ARF gene correlates with telomerase activity and mRNA expression of human telomerase reverse transcriptase in hepatocellular carcinoma. J Surg Oncol 2008; 98:462-8. [DOI: 10.1002/jso.21131] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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81
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Zhang C, Guo X, Jiang G, Zhang L, Yang Y, Shen F, Wu M, Wei L. CpG island methylator phenotype association with upregulated telomerase activity in hepatocellular carcinoma. Int J Cancer 2008; 123:998-1004. [PMID: 18546260 DOI: 10.1002/ijc.23650] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
CpG island methylator phenotype (CIMP) involves the targeting of multiple genes by promoter hypermethylation. Telomerase plays an important role in the development of cellular immortality and oncogenesis. To gain insight into the role of epigenetic aberration of telomerase-related genes in hepatocarcinogenesis, we determined a hypermethylation profile in HCC. We examined the promoter methylation status of 9 genes associated with telomerase activity in 120 HCC, 120 cirrhosis tissues and 10 normal liver tissues by methylation-specific PCR. Assay of telomerase activity was by TRAP-ELISA. The frequency of promoter methylation of each gene was P21 63.3%, P15 42.5%, P16 62.5%, P53 14.2%, RB 32.5%, P27 48.3%, WTI 54.2%, E2F-1 70.8% and P300 65.8% of 120 HCC. Methylation status of P21, P15, P16, WTI and E2F-1 was significantly associated with HCC and nontumor tissues (p < 0.05). CIMP+ was detected in 61.7% (74/120) HCC and 15% (18/120) cirrhosis tissues, no CIMP+ was present in normal liver tissues (p < 0.001). A significant difference between CIMP status and metastasis was been found in HCC (p < 0.001). Results showed that 94.6% (70/74) HCC and 55.6% (10/18) cirrhosis patients with CIMP+ show expression of high telomerase activity than 45.5% (10/22) HCC and 6.25% (1/16) cirrhosis patients with CIMP- (p < 0.001). CIMP lead to high levels of expression of telomerase activity through the simultaneous inactivation of multiple genes associated with telomerase activity by concordant methylation.
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Affiliation(s)
- Changsong Zhang
- Tumor Immunology and Gene Therapy Center, Eastern Hepatobiliary Surgery Hospital, the Second Military Medical University, Shanghai, China
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82
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Chen YJ, Campbell HG, Wiles AK, Eccles MR, Reddel RR, Braithwaite AW, Royds JA. PAX8 Regulates Telomerase Reverse Transcriptase and Telomerase RNA Component in Glioma. Cancer Res 2008; 68:5724-32. [DOI: 10.1158/0008-5472.can-08-0058] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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83
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hTERT expression in colorectal adenocarcinoma: correlations with p21, p53 expressions and clinicopathological features. Int J Colorectal Dis 2008; 23:587-94. [PMID: 18322660 DOI: 10.1007/s00384-008-0455-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/12/2008] [Indexed: 02/04/2023]
Abstract
BACKGROUND The clinicopathological roles and relationships of hTERT, p21 and p53 proteins have not been studied in depth in colorectal cancer. The aim of the present study is to investigate the clinicopathological roles of expression of hTERT protein expression and its relationship with the expression of p21 and p53 proteins in a large cohort of patients with colorectal adenocarcinoma. MATERIALS AND METHODS Expressions of hTERT, p21 and p53 proteins were investigated in 188 patients with colorectal adenocarcinomas by immunohistochemistry. The findings were correlated with the clinicopathological features and survival data of colorectal adenocarcinomas. RESULTS hTERT, p53 and p21 proteins were detected in 63%, 100% and 62% of the patients with colorectal carcinoma. High level of hTERT protein expression was noted in patients with metastases (p = 0.038) and in patients with rectal cancer (p = 0.046). Loss or low level of p21 protein was often noted in non-mucinous colorectal adenocarcinoma when compared with mucinous adenocarcinoma (p = 0.001). Furthermore, p53 expression was more frequently noted in non-mucinous adenocarcinoma (p = 0.001). The level of expression of p21 protein was positively correlated with expression of level of hTERT protein (p = 0.00001). The survival of the patients was related to staging (p = 0.001) and p53 protein expression (p = 0.038) of the tumours. CONCLUSIONS hTERT protein expression is an indicator of the biological aggressiveness of the cancer. The level of expression of the protein was also related to the distal location and level of p21 expression of the tumours.
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84
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Buhlmann S, Racek T, Schwarz A, Schaefer S, Pützer BM. Molecular mechanism of p73-mediated regulation of hepatitis B virus core promoter/enhancer II: implications for hepatocarcinogenesis. J Mol Biol 2008; 378:20-30. [PMID: 18342333 DOI: 10.1016/j.jmb.2008.02.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Revised: 02/05/2008] [Accepted: 02/12/2008] [Indexed: 12/16/2022]
Abstract
Hepatitis B virus (HBV) is a causative agent of chronic hepatitis and hepatocellular carcinoma. Recent findings demonstrating p73 and specifically N-terminally truncated p73 (DeltaTAp73) accumulation in hepatocellular carcinoma suggest that p73 plays a role in the malignant phenotype. Here, we investigated the mechanism of HBV pregenomic core promoter/enhancer II (cp/EII) regulation by full-length TAp73 and its oncogenic counterpart DeltaTAp73. Ectopic and endogenous expression of TAp73 leads to a significant downregulation of cp/EII activity in p53-deficient hepatoma cell lines. In contrast, overexpression of DeltaTAp73 results in significant cp/EII activation and increased HBV core (HBc) expression. TAp73-mediated repression of HBV transcription was substantially abolished by DeltaTAp73. We show that both TAp73 and DeltaTAp73 proteins directly bind to the Sp1 transcription factor, a key stimulator of HBV gene expression. However, only TAp73 abolishes Sp1 binding to cp/EII, whereas the DeltaTAp73-Sp1 complex further persists on the DNA. The inhibitory effect of p53/p73 on HBc expression is associated with the inhibition of viral replication, while DeltaTAp73 is not. These data strongly support the fact that the p73-isoform-related interaction with Sp1 is the underlying mechanism of the diverse outcome on HBc expression, suggesting a new mechanism by which oncogenic DeltaTAp73 could enhance the carcinogenic process in liver cells.
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Affiliation(s)
- Sven Buhlmann
- Department of Vectorology and Experimental Gene Therapy, Biomedical Research Center, University of Rostock, Schillingallee 69, D-18057 Rostock, Germany
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85
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Voghel G, Thorin-Trescases N, Farhat N, Mamarbachi AM, Villeneuve L, Fortier A, Perrault LP, Carrier M, Thorin E. Chronic treatment with N-acetyl-cystein delays cellular senescence in endothelial cells isolated from a subgroup of atherosclerotic patients. Mech Ageing Dev 2008; 129:261-70. [PMID: 18302967 DOI: 10.1016/j.mad.2008.01.004] [Citation(s) in RCA: 246] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Revised: 01/08/2008] [Accepted: 01/16/2008] [Indexed: 10/22/2022]
Abstract
Endothelial senescence may contribute to the pathogenesis of age-related vascular disorders. Furthermore, chronic exposure to risk factors for cardiovascular disease (CVD) accelerates the effects of chronological aging by generating stress-dependent damages, including oxidative stress, therefore promoting stress-induced premature senescence. Our objective was to determine whether a chronic treatment with an antioxidant (N-acetyl-cystein, NAC) could delay senescence of endothelial cells (EC) isolated and cultured from arterial segments of patients with severe coronary artery disease. If EC were considered as one population (n=26), chronic NAC treatment slightly shortened telomere attrition rate associated with senescence but did not significantly delay the onset of endothelial senescence. However, in a subgroup of NAC-treated EC (n=15) cellular senescence was significantly delayed, NAC decreased lipid peroxidation (HNE), activated the catalytic subunit of telomerase (hTERT) and inhibited telomere attrition. In contrast, in another subgroup of EC (n=11) characterized by initial short telomeres, no effect of NAC on HNE and high levels of DNA damages, the antioxidant was not beneficial on senescence, suggesting an irreversible stress-dependent damage. In conclusion, chronic exposure to NAC can delay senescence of diseased EC via hTERT activation and transient telomere stabilization, unless oxidative stress-associated cell damage has become irreversible.
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Affiliation(s)
- Guillaume Voghel
- Department of Surgery, Research Center, Montreal Heart Institute, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada
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86
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Shirako E, Hirayama N, Tsukada YI, Tanaka T, Kitamura N. Up-regulation of p21CIP1 expression mediated by ERK-dependent and -independent pathways contributes to hepatocyte growth factor-induced inhibition of HepG2 hepatoma cell proliferation. J Cell Biochem 2008; 104:176-88. [DOI: 10.1002/jcb.21614] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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87
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Trkova M, Prochazkova K, Krutilkova V, Sumerauer D, Sedlacek Z. Telomere length in peripheral blood cells of germline TP53 mutation carriers is shorter than that of normal individuals of corresponding age. Cancer 2007; 110:694-702. [PMID: 17567834 DOI: 10.1002/cncr.22834] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND A decrease in the age at cancer onset and increase in cancer incidence in successive generations in Li-Fraumeni syndrome (LFS) families with germline TP53 mutations have been previously described. In the current study a possible relation was analyzed between telomere length and cancer onset in TP53 mutation carriers. METHODS Telomere length was measured using real-time quantitative polymerase chain reaction (PCR) in 20 carriers of germline TP53 mutations and in 83 unrelated healthy individuals. According to the age at blood sampling, patients and controls were divided into 2 age groups, children and adults. Telomere length was correlated to TP53 mutation status and telomere shortening in patients to the age at cancer onset. A t-test and linear regression were used to analyze the data. RESULTS Compared with healthy controls, telomere length was significantly shorter both in the child (P = .001) and adult (P = .034) germline T53 mutation carriers. Although a statistically significant correlation between telomere shortening and the age at cancer onset was not observed, there was a trend of shorter telomeres in mutation carriers affected in childhood compared with those affected later in life. Neither cancer therapy nor sex differences were likely to affect the results. CONCLUSIONS The findings suggest a possible link between the carriership of a germline TP53 mutation, telomere length, predisposition to early-onset cancer, and anticipation in LFS.
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Affiliation(s)
- Marie Trkova
- Department of Biology and Medical Genetics, Charles University 2nd Medical School and University Hospital Motol, Prague, Czech Republic.
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88
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Scian MJ, Carchman EH, Mohanraj L, Stagliano KER, Anderson MAE, Deb D, Crane BM, Kiyono T, Windle B, Deb SP, Deb S. Wild-type p53 and p73 negatively regulate expression of proliferation related genes. Oncogene 2007; 27:2583-93. [PMID: 17982488 DOI: 10.1038/sj.onc.1210898] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
When normal cells come under stress, the wild-type (WT) p53 level increases resulting in the regulation of gene expression responsible for growth arrest or apoptosis. Here we show that elevated levels of WT p53 or its homologue, p73, inhibit expression of a number of cell cycle regulatory and growth promoting genes. Our analysis also identified a group of genes whose expression is differentially regulated by WT p53 and p73. We have infected p53-null H1299 human lung carcinoma cells with recombinant adenoviruses expressing WT p53, p73 or beta-galactosidase, and have undertaken microarray hybridization analyses to identify genes whose expression profile is altered by p53 or p73. Quantitative real-time PCR verified the repression of E2F-5, centromere protein A and E, minichromosome maintenance proteins (MCM)-2, -3, -5, -6 and -7 and human CDC25B after p53 expression. 5-Fluorouracil treatment of colon carcinoma HCT116 cells expressing WT p53 results in a reduction of the cyclin B2 protein level suggesting that DNA damage may indeed cause repression of these genes. Transient transcriptional assays verified that WT p53 repressed promoters of a number of these genes. Interestingly, a gain-of-function p53 mutant instead upregulated a number of these promoters in transient transfection. Using promoter deletion mutants of MCM-7 we have found that WT p53-mediated repression needs a minimal promoter that contains a single E2F site and surrounding sequences. However, a single E2F site cannot be significantly repressed by WT p53. Many of the genes identified are also repressed by p21. Thus, our work shows that WT p53 and p73 repress a number of growth-related genes and that in many instances this repression may be through the induction of p21.
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Affiliation(s)
- M J Scian
- Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA
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89
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Lacerte A, Korah J, Roy M, Yang XJ, Lemay S, Lebrun JJ. Transforming growth factor-beta inhibits telomerase through SMAD3 and E2F transcription factors. Cell Signal 2007; 20:50-9. [PMID: 17881189 DOI: 10.1016/j.cellsig.2007.08.012] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Accepted: 08/14/2007] [Indexed: 11/30/2022]
Abstract
Cancer arises from multiple genetic changes within the cell, among which constitutive telomerase activity and attainment of immortality are central. Expression of hTERT, the protein component of telomerase, is increased in most cancer cells. Transforming growth factor-beta (TGFbeta), a potent tumor suppressor, has been reported to regulate hTERT expression. We found that TGFbeta represses hTERT expression in normal and cancer cells and that this effect is mediated through Smad3 but also requires Erk1/2, p38 kinase and histone deacetylase activity. Furthermore, we identified four critical E2F transcription factor binding sites within the hTERT gene promoter that confer the TGFbeta response. Finally, using the E2F-1 knockout model, we showed that loss of E2F-1 abolishes TGFbeta inhibition of telomerase expression. These findings highlight the prominent role of TGFbeta in regulating telomerase expression and identify Smad3 and E2F-1 as critical mediators of TGFbeta effects in both normal and cancer cells.
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Affiliation(s)
- Annie Lacerte
- Hormones and Cancer Research Unit, Department of Medicine, Royal Victoria Hospital, McGill University, 687 Pine Avenue West, H3A 1A1, Montreal, Quebec, Canada
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90
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Chen M, Gu J, Xing J, Spitz MR, Wu X. Irradiation-induced telomerase activity and the risk of lung cancer: a pilot case-control study. Cancer 2007; 109:1157-63. [PMID: 17265522 DOI: 10.1002/cncr.22493] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Telomerase activity is undetectable in most normal somatic cells, but is up-regulated by various mechanisms during tumorigenesis. Telomerase activation enables cells to overcome replicative senescence and maintain telomere stability during cell proliferation. The aim of the study was to evaluate the association between irradiation-induced telomerase activity and the risk of lung cancer. METHODS A case-control design was used that measured the baseline and gamma-radiation-induced telomerase activity in cultured peripheral blood lymphocytes from 44 lung cancer patients and 44 healthy controls. The associations between gamma-radiation-inducible telomerase activity and the risk of lung cancer were then analyzed. RESULTS The baseline telomerase activity was lower in cases than in controls (0.956 vs 1.222, P = .126). After gamma-radiation the telomerase activity in cases experienced a significant increase over baseline (1.480 vs 0.956, P < .001); the telomerase activity in controls also increased, but on a smaller scale (1.485 vs 1.222, P = .0025). The relative gamma-radiation-induced telomerase activity, defined as the ratio of the net increase of telomerase activity (gamma-radiation induced minus baseline) to the baseline telomerase activity, was significantly higher in cases than in controls (0.730 vs 0.224, P = .0003). When dichotomized, the subjects at the 75th percentile of the relative gamma-radiation-induced telomerase activity in controls, a higher ratio was associated with a significantly increased lung cancer risk (odds ratio [OR], 4.71, 95% confidence interval [CI]: 1.37, 16.21). Moreover, a dose response was observed between the relative gamma-radiation-induced telomerase activity and lung cancer risk. Compared with individuals with the lowest tertile of the relative gamma-radiation-induced telomerase activity, individuals with the second and the highest tertiles of the relative telomerase activity exhibited significantly elevated risks of lung cancer, with adjusted ORs of 12.58 (95% CI: 1.08, 146.86) and 31.08 (95% CI: 2.71, 356.81), respectively (P for trend <.001). CONCLUSIONS The pilot-case control study suggested that the gamma-radiation-induced telomerase activation is associated with a significantly increased risk of developing lung cancer. Larger case-control studies and prospective studies are needed to confirm the findings.
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Affiliation(s)
- Meng Chen
- Department of Epidemiology, University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA
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91
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Xing J, Zhu Y, Zhao H, Yang H, Chen M, Spitz MR, Wu X. Differential induction in telomerase activity among bladder cancer patients and controls on gamma-radiation. Cancer Epidemiol Biomarkers Prev 2007; 16:606-9. [PMID: 17372259 DOI: 10.1158/1055-9965.epi-06-0615] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Expression of telomerase is one of the hallmarks of tumor cells and has been used as a diagnostic biomarker and a therapeutic target in cancer. Novel findings have shown that telomerase activation in normal human epithelial cells may affect expression of several cancer-related genes, such as growth-related genes and c-myc gene, suggesting a possible role of telomerase in tumor initiation. Therefore, we hypothesized that individuals who are sensitive to mutagen challenge in terms of induced telomerase activity might have increased cancer risk. We tested this hypothesis in a bladder cancer case-control study (51 cases and 51 matched controls) by measuring baseline and gamma-radiation-induced telomerase activities in peripheral blood lymphocytes. We found a significantly higher gamma-radiation-induced telomerase activity in bladder cancer cases compared with the controls (1.34 versus 1.23; P = 0.044). A similar finding was also observed using the normalized telomerase activity (ratio of gamma-radiation induced versus baseline; 1.49 versus 1.19; P < 0.001). In further categorizing the telomerase activity using 75% of the normalized value in the controls as a cutoff point, we found a significantly increased risk for bladder cancer associated with higher induced telomerase activity (adjusted odds ratio, 3.62; 95% confidence interval, 1.38-9.51). In quartile analysis, a dose-response association was noted between the induced telomerase activity and increased bladder cancer risk (P(trend) = 0.005). Our findings provide the first evidence linking the mutagen-induced telomerase activity in peripheral blood lymphocytes to the risk of bladder cancer, which warrants further investigation in large-sized studies and other cancer types.
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Affiliation(s)
- Jinliang Xing
- Department of Epidemiology, The University of Texas M. D. Anderson Cancer Center, Unit 1304, 1155 Pressler Boulevard, Houston, TX 77030, USA
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92
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Katzenellenbogen RA, Egelkrout EM, Vliet-Gregg P, Gewin LC, Gafken PR, Galloway DA. NFX1-123 and poly(A) binding proteins synergistically augment activation of telomerase in human papillomavirus type 16 E6-expressing cells. J Virol 2007; 81:3786-96. [PMID: 17267499 PMCID: PMC1866132 DOI: 10.1128/jvi.02007-06] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Overcoming senescence signals in somatic cells is critical to cellular immortalization and carcinogenesis. High-risk human papillomavirus (HPV) can immortalize epithelial cells in culture through degradation of the retinoblastoma protein by HPV E7 and activation of hTERT transcription, the catalytic subunit of telomerase, by the heterodimer HPV E6/E6-associated protein (E6AP). Recent work in our laboratory identified a novel repressor of hTERT transcription, NFX1-91, which is targeted for ubiquitin-mediated degradation by HPV type 16 (HPV16) E6/E6AP. In contrast, NFX1-123, a splice variant NFX1, increased expression from an hTERT promoter that was activated by HPV16 E6/E6AP. Here, we show that HPV16 E6 bound both NFX1-91 and NFX1-123 through the common central domain of NFX1 in the absence of E6AP. NFX1-123 positively regulated hTERT expression, as its knockdown decreased hTERT mRNA levels and telomerase activity and its overexpression increased telomerase activity. We identified new protein partners of NFX1-123, including several cytoplasmic poly(A) binding proteins (PABPCs) that interacted with NFX1-123 through its N-terminal PAM2 motif, a protein domain characteristic of other PABPC protein partners. Furthermore, NFX1-123 and PABPCs together had a synergistic stimulatory effect on hTERT-regulated reporter assays. The data suggest that NFX1-123 is integral to hTERT regulation in HPV16 E6-expressing epithelial cells and that the interaction between NFX1-123 and PABPCs is critical to hTERT activity.
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Affiliation(s)
- Rachel A Katzenellenbogen
- Fred Hutchinson Cancer Research Center, and Department of Pediatrics, University of Washington, Seattle, WA 98109, USA.
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93
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Agarwal MK, Ruhul Amin ARM, Agarwal ML. DNA replication licensing factor minichromosome maintenance deficient 5 rescues p53-mediated growth arrest. Cancer Res 2007; 67:116-21. [PMID: 17210690 DOI: 10.1158/0008-5472.can-06-2835] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Inactivation of p53 signaling by mutation of p53 itself or abrogation of its normal function by other transfactors, such as MDM2, is a key event in the development of most human cancers. To identify novel regulators of p53, we have used a phenotype-based selection in which a total cDNA library in a retroviral vector has been introduced into TR9-7ER cells, which arrest when p53 is expressed from a tetracycline-regulated promoter. We have isolated several clones derived from cells that are not growth-arrested when p53 is overexpressed. In one clone, the levels of p53, p21, and MDM2 are comparable with those in TR9-7ER cells and, therefore, the abrogation of growth arrest by an exogenous cDNA is likely to be distal to p21. Using reverse transcription-PCR, we were able to isolate a cDNA of approximately 2.2 kb, which was found to have 99% identity to the nucleotides between about 80 and 2,288 of the open reading frame of a gene encoding DNA replication licensing factor. It encodes complete peptide of 734 residues of this protein also called minichromosome maintenance deficient 5 (MCM5) or cell division cycle 46 (Saccharomyces cerevisiae). Northern and Western blot analyses revealed that the expression of MCM5 and its transcriptional regulator, E2F1, is negatively regulated by p53. When MCM5 cDNA was reintroduced into fresh TR9-7ER cells, numerous colonies that grow in the absence of tetracycline were formed. This novel observation establishes a role for MCM5 in negating the growth arrest function of p53.
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Affiliation(s)
- Mukesh K Agarwal
- Department of Genetics, Case Western Reserve University, Cleveland, OH 44106, USA
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94
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Anderson L, Burnstein RM, He X, Luce R, Furlong R, Foltynie T, Sykacek P, Menon DK, Caldwell MA. Gene expression changes in long term expanded human neural progenitor cells passaged by chopping lead to loss of neurogenic potential in vivo. Exp Neurol 2007; 204:512-24. [PMID: 17306795 DOI: 10.1016/j.expneurol.2006.12.025] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Revised: 12/22/2006] [Accepted: 12/26/2006] [Indexed: 12/19/2022]
Abstract
Numerous cell culture protocols have been described for the proliferation of multipotent human neural progenitor cells (HNPCs). The mitogen combinations used to expand HNPCs vary, and it is not clear to what extent this may affect the subsequent differentiation of these cells. In this study human foetal cortical tissue was cultured in the presence of either EGF, or FGF-2, or a combination of both using a unique chopping method in which cell to cell contact is maintained. The differentiation potential of neurospheres following mitogen withdrawal was assessed at early (8 weeks) and late (20 weeks) times of expansion, both in vitro and in vivo. In addition, changes in gene expression with time were analysed by microarray experiments. Results show that the presence of FGF-2 was highly predictive of neuronal differentiation after short term culture both in vitro and in vivo. In addition, time in culture had a significant effect on transplant size and neural constituents suggesting that cells have a limited life span and restricted lineage potential. Array analysis confirms that following extensive time in culture cells are entering growth arrest with fundamental expression changes in genes associated with cell cycle regulation, apoptosis and immune functions.
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Affiliation(s)
- Lucy Anderson
- Centre for Brain Repair and Department of Clinical Neurosciences, University Forvie Site, Robinson Way, Cambridge CB2 2PY, UK
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95
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Lai SR, Cunningham AP, Huynh VQ, Andrews LG, Tollefsbol TO. Evidence of extra-telomeric effects of hTERT and its regulation involving a feedback loop. Exp Cell Res 2007; 313:322-30. [PMID: 17134697 PMCID: PMC1829489 DOI: 10.1016/j.yexcr.2006.10.014] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Revised: 09/29/2006] [Accepted: 10/16/2006] [Indexed: 10/24/2022]
Abstract
The human telomerase reverse transcriptase (hTERT) is the catalytic subunit of the enzyme telomerase which is responsible for telomeric maintenance and extension. Using RNA interference to knock down hTERT mRNA expression, we provide evidence that hTERT exerts extra-telomeric effects on the cell cycle and on its own regulatory proteins, specifically: p53 and p21. We tested our hypothesis that hTERT regulates its own expression through effects on upstream regulatory genes using transformed human embryonic kidney (HEK 293) cells, p53 and p16(INK4a) null human ovarian cancer SKOV-3 cells, and p53-null MDA-MB-157 human mammary cancer cells. In HEK 293 cells, hTERT knockdown resulted in elevated p53 and p21 transcription and a decrease in cellular proliferation. Similar results were observed in the MDA-MB-157 cell line where p21 was upregulated, correlating with cell growth inhibition. In contrast, we observed a decrease in expression of p21 in SKOV-3 cells with hTERT knockdown and cell growth appeared to be unaffected. These findings suggest that hTERT may be involved in a feedback loop system, thereby playing a role in its own regulation.
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Affiliation(s)
- Serene R. Lai
- Department of Biology, University of Alabama at Birmingham, AL 35294, USA
| | | | - Vu Q. Huynh
- Department of Biology, University of Alabama at Birmingham, AL 35294, USA
- Center for Aging, University of Alabama at Birmingham, AL 35294, USA
- Comprehensive Cancer Center, University of Alabama at Birmingham, AL 25294, USA
| | - Lucy G. Andrews
- Department of Biology, University of Alabama at Birmingham, AL 35294, USA
| | - Trygve O. Tollefsbol
- Department of Biology, University of Alabama at Birmingham, AL 35294, USA
- Center for Aging, University of Alabama at Birmingham, AL 35294, USA
- Comprehensive Cancer Center, University of Alabama at Birmingham, AL 25294, USA
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96
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Liu JP, Cassar L, Pinto A, Li H. Mechanisms of cell immortalization mediated by EB viral activation of telomerase in nasopharyngeal carcinoma. Cell Res 2006; 16:809-17. [PMID: 17016469 DOI: 10.1038/sj.cr.7310098] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Nasopharyngeal carcinoma (NPC) is a common cancer in Southern China and Southeast Asia. The disease is a poorly differentiated carcinoma without effective cure, and the mechanism underlying its development remains largely unknown. Of several factors identified in NPC aetiology in recent years, Epstein-Barr virus (EBV) infection has emerged to be most important. In almost all NPC cells, EBV uses several intracellular mechanisms to cause oncogenic evolution of the infected cells. One such mechanism by which EBV infection induces cellular immortalization is believed to be through the activation of telomerase, an enzyme that is normally repressed but becomes activated during cancer development. Studies show that greater than 85% of primary NPC display high telomerase activity by mechanisms involving EBV infection, consistent with the notion that EBV is commonly involved in inducing cell immortalization. More recently, different EBV proteins have been shown to activate or inhibit the human telomerase reverse transcriptase gene, by modulating intracellular signalling pathways. These findings suggest a new model with a number of challenges towards our understanding, molecular targeting and therapeutic intervention in NPC.
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Affiliation(s)
- Jun-Ping Liu
- Department of Immunology, Central Eastern Clinical School, Monash University, AMREP, Commercial Road, Prahran, Melbourne, Victoria 3181, Australia.
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97
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Van Bodegom D, Saifudeen Z, Dipp S, Puri S, Magenheimer BS, Calvet JP, El-Dahr SS. The Polycystic Kidney Disease-1 Gene Is a Target for p53-mediated Transcriptional Repression. J Biol Chem 2006. [DOI: 10.1016/s0021-9258(19)84036-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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98
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Van Bodegom D, Saifudeen Z, Dipp S, Puri S, Magenheimer BS, Calvet JP, El-Dahr SS. The polycystic kidney disease-1 gene is a target for p53-mediated transcriptional repression. J Biol Chem 2006; 281:31234-44. [PMID: 16931520 DOI: 10.1074/jbc.m606510200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
This study provides evidence that the tumor suppressor protein, p53, is a transcriptional repressor of PKD1. Kidneys of p53-null mice expressed higher Pkd1 mRNA levels than wild-type littermates; gamma-irradiation suppressed PKD1 gene expression in p53+/+ but not p53-/- cells; and chromatin immunoprecipitation assays demonstrated the binding of p53 to the PKD1 promoter in vivo. In transient transfection assays, p53 repressed PKD1 promoter activity independently of endogenous p21. Deletion analysis mapped p53-mediated repression to the proximal promoter region of PKD1. Mutations of the DNA binding or C-terminal minimal repression domains of p53 abolished its ability to repress PKD1. Moreover, trichostatin A, an inhibitor of histone deacetylase activity, attenuated p53-induced repression of the PKD1 promoter. These findings, together with previous reports showing that dedifferentiated Pkd1-deficient cells express lower p53 and p21 levels, suggest a model whereby PKD1 signaling activates the p53-p21 differentiation pathway. In turn, p53 cooperates with histone deacetylases to repress PKD1 gene transcription. Loss of a p53-mediated negative feedback loop in PKD1 mutant cells may therefore contribute to deregulated PKD1 expression and cystogenesis.
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Affiliation(s)
- Diederik Van Bodegom
- Department of Pediatrics, Section of Pediatric Nephrology, Tulane University Health Sciences Center, New Orleans, Louisiana 70112, USA
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99
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Pizzimenti S, Briatore F, Laurora S, Toaldo C, Maggio M, De Grandi M, Meaglia L, Menegatti E, Giglioni B, Dianzani MU, Barrera G. 4-Hydroxynonenal inhibits telomerase activity and hTERT expression in human leukemic cell lines. Free Radic Biol Med 2006; 40:1578-91. [PMID: 16632118 DOI: 10.1016/j.freeradbiomed.2005.12.024] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Revised: 10/28/2005] [Accepted: 12/23/2005] [Indexed: 11/28/2022]
Abstract
4-Hydroxynonenal (HNE), produced during oxidative stress, has an antiproliferative/differentiative effect in several tumor cells. Recently, it has been observed that oxidative stress accelerates telomere loss. The length of telomeres depends on the telomerase activity, and the catalytic subunit of telomerase (hTERT) is strongly up-regulated in most human cancers and inhibited by differentiating agents. In this paper the inhibitory effect of HNE on telomerase activity and hTERT expression in three human leukemic cell lines (HL-60, U937, ML-1) is reported. To investigate the molecular mechanism involved in hTERT down-regulation by HNE, the expression of several transcription factors was also studied: in all these cell lines, c-Myc was inhibited, Mad-1 was up-regulated, and Sp-1 was not affected. Moreover, in p53 wild-type ML-1 cells, HNE up-regulated p53 expression. In HL-60 cells, DNA binding activity of c-Myc and Mad-1 to the E-box sequence of the hTERT promoter was inhibited and up-regulated, respectively. In summary, HNE inhibits telomerase activity via decreased hTERT promoter activity, by modulating c-Myc/Mad-1 transcription factor expression.
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Affiliation(s)
- Stefania Pizzimenti
- Section of General Pathology, Department of Experimental Medicine and Oncology, University of Turin, Corso Raffaello 30, 10125 Turin, Italy.
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100
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Wright LS, Prowse KR, Wallace K, Linskens MHK, Svendsen CN. Human progenitor cells isolated from the developing cortex undergo decreased neurogenesis and eventual senescence following expansion in vitro. Exp Cell Res 2006; 312:2107-20. [PMID: 16631163 DOI: 10.1016/j.yexcr.2006.03.012] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Revised: 03/08/2006] [Accepted: 03/10/2006] [Indexed: 12/11/2022]
Abstract
Isolation of a true self-renewing stem cell from the human brain would be of great interest as a reliable source of neural tissue. Here, we report that human fetal cortical cells grown in epidermal growth factor expressed low levels of telomerase and telomeres in these cultures shortened over time leading to growth arrest after 30 weeks. Following leukemia inhibitory factor (LIF) supplementation, growth rates and telomerase expression increased. This was best demonstrated following cell cycle synchronization and staining for telomerase using immunocytochemistry. This increase in activity resulted in the maintenance of telomeres at approximately 7 kb for more than 60 weeks in vitro. However, all cultures displayed a lack of oligodendrotye production, decreases in neurogenesis over time and underwent replicative senescence associated with increased expression of p21 before 70 weeks in vitro. Thus, under our culture conditions, these cells are not stable, multipotent, telomerase expressing self-renewing stem cells. They may be more accurately described as human neural progenitor cells (hNPC) with limited lifespan and bi-potent potential (neurons/astrocytes). Interestingly, hNPC follow a course of proliferation, neuronal production and growth arrest similar to that seen during expansion and development of the human cortex, thus providing a possible model neural system. Furthermore, due to their high expansion potential and lack of tumorogenicity, these cells remain a unique and safe source of tissue for clinical transplantation.
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Affiliation(s)
- Lynda S Wright
- Waisman Center and Departments of Neurology and Anatomy University of Wisconsin-Madison, WI 53705-2280, USA
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