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The Role of p53 Protein in the Realization of the Exogenous Heat Shock Protein 70 Anti-Apoptotic Effect during Axotomy. Cells 2021; 11:cells11010093. [PMID: 35011655 PMCID: PMC8750896 DOI: 10.3390/cells11010093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/20/2021] [Accepted: 12/24/2021] [Indexed: 11/17/2022] Open
Abstract
The search for effective neuroprotective agents for the treatment of neurotrauma has always been of great interest to researchers around the world. Extracellular heat shock protein 70 (eHsp70) is considered a promising agent to study, as it has been demonstrated to exert a significant neuroprotective activity against various neurodegenerative diseases. We showed that eHsp70 can penetrate neurons and glial cells when added to the incubation medium, and can accumulate in the nuclei of neurons and satellite glial cells after axotomy. eHsp70 reduces apoptosis and necrosis of the glial cells, but not the neurons. At the same time, co-localization of eHsp70 with p53 protein, one of the key regulators of apoptosis, was noted. eHsp70 reduces the level of the p53 protein apoptosis promoter both in glial cells and in the nuclei and cytoplasm of neurons, which indicates its neuroprotective effect. The ability of eHsp70 to reverse the proapoptotic effect of the p53 activator WR1065 may indicate its ability to regulate p53 activity or its proteosome-dependent degradation.
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2
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Toussi A, Mans N, Welborn J, Kiuru M. Germline mutations predisposing to melanoma. J Cutan Pathol 2020; 47:606-616. [PMID: 32249949 DOI: 10.1111/cup.13689] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 03/03/2020] [Accepted: 03/06/2020] [Indexed: 12/11/2022]
Abstract
Nearly 15% of melanomas occur in patients with a family history and a subset of these patients have a germline mutation in a melanoma predisposing gene. CDKN2A mutations are responsible for the majority of hereditary melanoma, but many other susceptibility genes have been discovered in recent years, including CDK4, TERT, ACD, TERF2IP, POT1, MITF, MC1R, and BAP1. Additionally, melanoma risk is increased in mixed cancer syndromes caused by mutations in PTEN, BRCA2, BRCA1, RB1, and TP53. While early onset, multiple tumors, and family cancer history remain the most valuable clinical clues for hereditary melanoma, characteristic epithelioid cytology of melanocytic tumors may suggest an underlying BAP1 mutation. Herein, we review the clinical and histopathologic characteristics of melanocytic tumors associated with these germline mutations and discuss the role of genetic counseling.
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Affiliation(s)
- Atrin Toussi
- Department of Dermatology, University of California, Davis, Sacramento, California, USA
| | - Nicole Mans
- Hereditary Cancer Program, Comprehensive Cancer Center, University of California, Davis, Sacramento, California, USA
| | - Jeanna Welborn
- Hereditary Cancer Program, Comprehensive Cancer Center, University of California, Davis, Sacramento, California, USA
| | - Maija Kiuru
- Department of Dermatology, University of California, Davis, Sacramento, California, USA.,Department of Pathology and Laboratory Medicine, University of California, Davis, Sacramento, California, USA
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3
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Tian S, Siu FM, Lok CN, Fung YME, Che CM. Anticancer auranofin engages 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) as a target. Metallomics 2019; 11:1925-1936. [PMID: 31631207 DOI: 10.1039/c9mt00185a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Auranofin (AuRF) has been reported to display anticancer activity and has entered several clinical trials; however, its mechanism of action remains largely unknown. In this work, the anticancer mechanism of auranofin was investigated using a proteomics strategy entailing subcellular fractionation prior to mass spectrometric analysis. Bioinformatics analysis of the nuclear sub-proteomes revealed that tumor suppressor p14ARF is a key regulator of transcription. Through independent analysis, we validated that up-regulation of p14ARF is associated with E2F-dependent transcription and increased p53 expression. Our analyses further reveal that 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), which is the rate-determining enzyme of the mevalonate pathway, is a novel target of auranofin with half maximal inhibitory concentration at micromolar levels. The auranofin-induced cancer cell death could be partially reverted by the addition of downstream products of the mevalonate pathway (mevalonolactone or geranyleranyl pyrophosphate (GGPP)), implying that auranofin may target the mevalonate pathway to exert its anticancer effect.
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Affiliation(s)
- Songhai Tian
- Department of Chemistry, The University of Hong Kong, Chemical Biology Centre, The Hong Kong Jockey Club Building for Interdisciplinary Research, Sassoon Road, Hong Kong SAR, China.
| | - Fung-Ming Siu
- Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
| | - Chun-Nam Lok
- Department of Chemistry, The University of Hong Kong, Chemical Biology Centre, The Hong Kong Jockey Club Building for Interdisciplinary Research, Sassoon Road, Hong Kong SAR, China.
| | - Yi Man Eva Fung
- Department of Chemistry, The University of Hong Kong, Chemical Biology Centre, The Hong Kong Jockey Club Building for Interdisciplinary Research, Sassoon Road, Hong Kong SAR, China.
| | - Chi-Ming Che
- Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
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4
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García-Gutiérrez L, Delgado MD, León J. MYC Oncogene Contributions to Release of Cell Cycle Brakes. Genes (Basel) 2019; 10:E244. [PMID: 30909496 PMCID: PMC6470592 DOI: 10.3390/genes10030244] [Citation(s) in RCA: 113] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Revised: 03/16/2019] [Accepted: 03/18/2019] [Indexed: 12/12/2022] Open
Abstract
Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.
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Affiliation(s)
- Lucía García-Gutiérrez
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) CSIC-Universidad de Cantabria and Department of Biología Molecular, Universidad de Cantabria, 39011 Santander, Spain.
- Current address: Systems Biology Ireland, University College Dublin, Belfield, Dublin 4, Ireland.
| | - María Dolores Delgado
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) CSIC-Universidad de Cantabria and Department of Biología Molecular, Universidad de Cantabria, 39011 Santander, Spain.
| | - Javier León
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) CSIC-Universidad de Cantabria and Department of Biología Molecular, Universidad de Cantabria, 39011 Santander, Spain.
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5
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Gadahi JA, Ehsan M, Wang S, Zhang Z, Yan R, Song X, Xu L, Li X. Recombinant protein of Haemonchus contortus small GTPase ADP-ribosylation factor 1 (HcARF1) modulate the cell mediated immune response in vitro. Oncotarget 2017; 8:112211-112221. [PMID: 29348819 PMCID: PMC5762504 DOI: 10.18632/oncotarget.22662] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Accepted: 11/03/2017] [Indexed: 01/08/2023] Open
Abstract
ADP-ribosylation factors (ARFs) are members of the Ras-related small GTPase family involved in the vesicular trafficking regulation. Immunomodulatory effects of these proteinson host cell arenot being addressed yet. H. contortus small GTPase ADP-ribosylation 1 gene (HcARF1) was cloned and recombinant protein of HcARF1 (rHcARF1) was successfully expressed in Escherichia coli. Binding activity of rHcARF1 to goat PBMCs was confirmed by immunofluorescence assay (IFA) and its immunomudulatory effects on cytokine secretion, cell proliferation, cell migration and nitric oxide production (NO) were observed by co-incubation of rHcARF1. IFA results revealed that rHcARF1 could bind to the PBMCs. The interaction of rHcARF1 modulated the cytokine production, the production of IL-4, IL-10 and IL-17 was increased in a dose dependent manner, however, the IFN-γ production was significantly decreased. Cell migration and NO production were significantly increased by rHcARF1, whereas, rHcARF1 treatment significantly suppressed the proliferation of the PBMC in a dose dependent manner. Our findings showed that the rHcARF1 play important roles on the goat PBMCs.
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Affiliation(s)
- Javaid Ali Gadahi
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China.,Department of Veterinary Parasitology, Sindh Agriculture University, Tando Jam, Pakistan
| | - Muhammad Ehsan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Shuai Wang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Zhenchao Zhang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Ruofeng Yan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Xiaokai Song
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Lixin Xu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
| | - Xiangrui Li
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, PR China
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Baeza-Raja B, Eckel-Mahan K, Zhang L, Vagena E, Tsigelny IF, Sassone-Corsi P, Ptáček LJ, Akassoglou K. p75 neurotrophin receptor is a clock gene that regulates oscillatory components of circadian and metabolic networks. J Neurosci 2013; 33:10221-34. [PMID: 23785138 PMCID: PMC3685830 DOI: 10.1523/jneurosci.2757-12.2013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 04/01/2013] [Accepted: 05/01/2013] [Indexed: 01/09/2023] Open
Abstract
The p75 neurotrophin receptor (p75(NTR)) is a member of the tumor necrosis factor receptor superfamily with a widespread pattern of expression in tissues such as the brain, liver, lung, and muscle. The mechanisms that regulate p75(NTR) transcription in the nervous system and its expression in other tissues remain largely unknown. Here we show that p75(NTR) is an oscillating gene regulated by the helix-loop-helix transcription factors CLOCK and BMAL1. The p75(NTR) promoter contains evolutionarily conserved noncanonical E-box enhancers. Deletion mutagenesis of the p75(NTR)-luciferase reporter identified the -1039 conserved E-box necessary for the regulation of p75(NTR) by CLOCK and BMAL1. Accordingly, gel-shift assays confirmed the binding of CLOCK and BMAL1 to the p75(NTR-)1039 E-box. Studies in mice revealed that p75(NTR) transcription oscillates during dark and light cycles not only in the suprachiasmatic nucleus (SCN), but also in peripheral tissues including the liver. Oscillation of p75(NTR) is disrupted in Clock-deficient and mutant mice, is E-box dependent, and is in phase with clock genes, such as Per1 and Per2. Intriguingly, p75(NTR) is required for circadian clock oscillation, since loss of p75(NTR) alters the circadian oscillation of clock genes in the SCN, liver, and fibroblasts. Consistent with this, Per2::Luc/p75(NTR-/-) liver explants showed reduced circadian oscillation amplitude compared with those of Per2::Luc/p75(NTR+/+). Moreover, deletion of p75(NTR) also alters the circadian oscillation of glucose and lipid homeostasis genes. Overall, our findings reveal that the transcriptional activation of p75(NTR) is under circadian regulation in the nervous system and peripheral tissues, and plays an important role in the maintenance of clock and metabolic gene oscillation.
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Affiliation(s)
| | - Kristin Eckel-Mahan
- Center for Epigenetics and Metabolism, Department of Biological Chemistry, University of California, Irvine, Irvine, California 92697, and
| | | | | | - Igor F. Tsigelny
- San Diego Supercomputer Center and Department of Neurosciences, University of California, San Diego, La Jolla, California 92093
| | - Paolo Sassone-Corsi
- Center for Epigenetics and Metabolism, Department of Biological Chemistry, University of California, Irvine, Irvine, California 92697, and
| | - Louis J. Ptáček
- Department of Neurology, and
- Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94158
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7
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Shi X, Zhao Y, Jiao Y, Shi T, Yang X. ROS-dependent mitochondria molecular mechanisms underlying antitumor activity of Pleurotus abalonus acidic polysaccharides in human breast cancer MCF-7 cells. PLoS One 2013; 8:e64266. [PMID: 23691187 PMCID: PMC3653930 DOI: 10.1371/journal.pone.0064266] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Accepted: 04/08/2013] [Indexed: 12/29/2022] Open
Abstract
Background A greater reduction in cancer risk associated with mushroom diet rich in fungus polysaccharides is generally accepted. Meanwhile, edible Pleurotus abalonus as a member of Abalone mushroom family is a popular nutritional supplement that purportedly prevents cancer occurrence. However, these anecdotal claims are supported by limited studies describing tumor-inhibitory responses to the promising polysaccharides, and the molecular mechanisms underlying these properties have not yet been elucidated. Methodology/Principal Findings We here fractionated the crude polysaccharide preparation from the fruiting bodies of P. abalonus into three fractions, namely PAP-1, PAP-2 and PAP-3, and tested these fractions for antiproliferative activity in human breast cancer MCF-7 cells. The largest PAP-3, an acidic polysaccharide fraction with a molecular mass of 3.68×105 Da, was the most active in inhibiting MCF-7 cancer cells with an IC50 of 193 µg/mL. The changes in cell normal morphology were observed by DAPI staining and the PAP-3-induced apoptosis was confirmed by annexin V/propidium iodide staining. The apoptosis was involved in mitochondria-mediated pathway including the loss of mitochondrial membrane potential (Δψm), the increase of Bax/Bcl-2 ratio, caspase-9/3 activation, and poly(ADP-ribose) polymerase (PARP) degradation, as well as intracellular ROS production. PAP-3 also induced up-regulation of p53, and cell cycle arrest at the S phase. The incubation of MCF-7 cells with antioxidant superoxide dismutase (SOD) and N-acetylcysteine (NAC) significantly attenuated the ROS generation and apoptosis caused by PAP-3, indicating that intracellular ROS plays a pivotal role in cell death. Conclusions/Significance These findings suggest that the polysaccharides, especially acidic PAP-3, are very important nutritional ingredients responsible for, at least in part, the anticancer health benefits of P. abalonus via ROS-mediated mitochondrial apoptotic pathway. It is a major breakthrough bringing new insight of the potential use of the polysaccharides as health-care food or medicine to provide significant natural defense against human cancer.
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Affiliation(s)
- Xiaolong Shi
- Key Laboratory of Medicinal Resources and Natural Pharmaceutical Chemistry, Ministry of Education, and National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an, China
| | - Yan Zhao
- School of Pharmacy, Fourth Military Medical University, Xi’an, China
| | - Yadong Jiao
- Key Laboratory of Medicinal Resources and Natural Pharmaceutical Chemistry, Ministry of Education, and National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an, China
| | - Tengrui Shi
- Key Laboratory of Medicinal Resources and Natural Pharmaceutical Chemistry, Ministry of Education, and National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an, China
| | - Xingbin Yang
- Key Laboratory of Medicinal Resources and Natural Pharmaceutical Chemistry, Ministry of Education, and National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an, China
- * E-mail:
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8
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Udayakumar T, Shareef MM, Diaz DA, Ahmed MM, Pollack A. The E2F1/Rb and p53/MDM2 pathways in DNA repair and apoptosis: understanding the crosstalk to develop novel strategies for prostate cancer radiotherapy. Semin Radiat Oncol 2011; 20:258-66. [PMID: 20832018 DOI: 10.1016/j.semradonc.2010.05.007] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Both the p53- and E2F1-signaling pathways are defective in almost all types of tumors, suggesting very important roles for their signaling networks in regulating the process of tumorigenesis and therapy response. Studies on Radiation Therapy Oncology Group tissue samples have identified aberrant expression of p53, MDM2 (an E3 ubiquitin ligase that targets p53 for proteosomal degradation), and p16 (an upstream regulator of retinoblastoma and hence E2F1 in prostate cancer); abnormal expression of these biomarkers has been associated with clinical outcome after radiotherapy ± androgen deprivation therapy. Although the proapoptotic properties of p53 are well documented, a relatively new aspect of p53 function as an active mediator of prosurvival signaling pathways is now emerging. E2F1 is a transcription factor that possesses both proapoptotic and prosurvival properties. Thus, the role of E2F1 in the process of tumorigenesis versus apoptosis is a contested issue that needs to be resolved. Furthermore, the role of E2F1 in DNA repair is being increasingly recognized. Thus, novel approaches to curb the prosurvival and DNA repair capability of E2F1 while promoting apoptotic function are of interest. In this review, we discuss the challenges involved in targeting the p53/E2F1 pathways and the crosstalk networks, and further propose potential therapeutic strategies for prostate cancer management.
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Affiliation(s)
- Thirupandiyur Udayakumar
- Department of Radiation Oncology, Sylvester Comprehensive Cancer Center, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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9
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Abstract
During tumour development cells sustain mutations that disrupt normal mechanisms controlling proliferation. Remarkably, the Rb-E2f and MDM2-p53 pathways are both defective in most, if not all, human tumours, which underscores the crucial role of these pathways in regulating cell cycle progression and viability. A simple interpretation of the observation that both pathways are deregulated is that they function independently in the control of cell fate. However, a large body of evidence indicates that, in addition to their independent effects on cell fate, there is extensive crosstalk between these two pathways, and specifically between the transcription factors E2F1 and p53, which influences vital cellular decisions. This Review discusses the molecular mechanisms that underlie the intricate interactions between E2f and p53.
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Affiliation(s)
- Shirley Polager
- The Mina and Everard Goodman Faculty of Life Science, Bar Ilan University, Ramat Gan 52900, Israel
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10
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Paulson QX, Pusapati RV, Hong S, Weaks RL, Conti CJ, Johnson DG. Transgenic expression of E2F3a causes DNA damage leading to ATM-dependent apoptosis. Oncogene 2008; 27:4954-61. [PMID: 18469863 DOI: 10.1038/onc.2008.138] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Many early stage human tumors display markers of a DNA-damage response (DDR), including ataxia telangiectasia mutated (ATM) kinase activation. This suggests that DNA damage accumulates during the process of carcinogenesis and that the ATM-dependent response to this damage may function to suppress cancer progression. The E2F3a transcription factor plays an important role in regulating cell proliferation and is amplified in a subset of human cancers. Similar to human premalignant lesions, we find activated ATM and other markers of the DDR in the hyperplastic epidermis of transgenic mice expressing E2F3a through a keratin 5 (K5) promoter. Primary keratinocytes from K5 E2F3a transgenic mice contain increased levels of DNA breaks compared to wild-type cells. E2F3a overexpression also induced DNA damage in primary human fibroblasts that was inhibited by blocking DNA replication. The absence of ATM impaired apoptosis induced by E2F3a and treating K5 E2F3a transgenic mice with caffeine, an inhibitor of ATM and Rad3-related (ATR), promoted skin tumor development. These findings demonstrate that the deregulated expression of E2F3a causes DNA damage under physiological conditions and indicate that the ATM-dependent response to this damage is important for the induction of apoptosis and tumor suppression.
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Affiliation(s)
- Q X Paulson
- Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, TX 78957, USA
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11
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Li J, Ran C, Li E, Gordon F, Comstock G, Siddiqui H, Cleghorn W, Chen HZ, Kornacker K, Liu CG, Pandit SK, Khanizadeh M, Weinstein M, Leone G, de Bruin A. Synergistic function of E2F7 and E2F8 is essential for cell survival and embryonic development. Dev Cell 2008; 14:62-75. [PMID: 18194653 DOI: 10.1016/j.devcel.2007.10.017] [Citation(s) in RCA: 159] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Revised: 10/01/2007] [Accepted: 10/30/2007] [Indexed: 12/22/2022]
Abstract
The E2f7 and E2f8 family members are thought to function as transcriptional repressors important for the control of cell proliferation. Here, we have analyzed the consequences of inactivating E2f7 and E2f8 in mice and show that their individual loss had no significant effect on development. Their combined ablation, however, resulted in massive apoptosis and dilation of blood vessels, culminating in lethality by embryonic day E11.5. A deficiency in E2f7 and E2f8 led to an increase in E2f1 and p53, as well as in many stress-related genes. Homo- and heterodimers of E2F7 and E2F8 were found on target promoters, including E2f1. Importantly, loss of either E2f1 or p53 suppressed the massive apoptosis in double-mutant embryos. These results identify E2F7 and E2F8 as a unique repressive arm of the E2F transcriptional network that is critical for embryonic development and control of the E2F1-p53 apoptotic axis.
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Affiliation(s)
- Jing Li
- Department of Molecular Virology, The Ohio State University, Columbus, OH 43210, USA
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12
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Martínez-Cruz AB, Santos M, Lara MF, Segrelles C, Ruiz S, Moral M, Lorz C, García-Escudero R, Paramio JM. Spontaneous Squamous Cell Carcinoma Induced by the Somatic Inactivation of Retinoblastoma and Trp53 Tumor Suppressors. Cancer Res 2008; 68:683-92. [DOI: 10.1158/0008-5472.can-07-3049] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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Abstract
In contrast with the low frequency of alterations found in the Rb gene, the pRb pathway is inactivated in the vast majority of human tumors. A similar situation takes place in mouse models of cancer, including two-stage skin tumorigenesis. This might be explained if the Rb functions are carried out, in its absence, by other proteins that are also controlled by the same upstream regulators and display similar effectors. The other Rb family members, p107 and or p130, are plausible candidates. The embryonic lethality of pRb-deficient animals, which precludes the analysis of the roles of Rb gene in mouse models, has been avoided using tissue-specific deletion of pRb. In epidermis, pRb deletion leads to altered proliferation and differentiation. However, these deficient mice do not develop spontaneous tumors, and chemical carcinogenesis experiments revealed that the absence of pRb renders fewer and smaller tumors than control animals, but showing increased malignant conversion to squamous cell carcinomas (SCC). Detailed biochemical analyses have indicated that, in the absence of pRb, multiple pathways, including the aberrant p53 activation mediated by E2F/p19(ARF), are activated leading to increased tumor apoptosis. As Rb loss in epidermis is functionally compensated by Rbl1 (p107), this might also suggest that p107 could behave as a tumor suppressor. We summarize here our findings in support of this hypothesis. The pRb-;p107-/- epidermis form spontaneous tumors, and the reduction of p107 levels restores the susceptibility of pRb-mice to chemical skin carcinogenesis experiments. Moreover, Rb-deficient keratinocytes are highly susceptible to Ha-ras-induced transformation, and this susceptibility is enhanced by p107 loss. Further functional studies have indicated that the loss of p107 in the absence of pRb produces the reduction of p53-dependent proapoptotic signals through the modulation of p63 and p73 isoforms. In addition, expression profiling analysis has revealed multiple oncogenic alterations that can contribute to tumor susceptibility in epidermis in the absence of pRb and p107.
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Abstract
Defects in apoptotic programs contribute to a number of human diseases, ranging from neurodegenerative disorders to malignancy, and treatment failure. The genetic basis for apoptosis implies that cell death can be disrupted by mutations, raising the intriguing possibility that cell numbers can be regulated by factors that influence cell survival. It is well documented that the E2F1 transcription factor is a key regulator of apoptotic programs. E2F1-induced cell death occurs via multiple pathways, some of which involve the tumour suppressor p53, and autonomous of p53. This has led to the opinion that E2F1 functions as a tumour surveillance factor, detecting aberrant proliferation and engaging apoptotic pathways to protect the organism from developing tumours. Frequently, novel players are discovered that expand the interpretation of apoptosis control by E2F1. This information will help to produce new strategies to exploit E2F1-induced apoptosis for therapeutic benefit.
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Affiliation(s)
- B M Pützer
- Department of Vectorology and Experimental Gene Therapy, University of Rostock, Biomedical Research Center, Schillingallee 69, D-18055 Rostock, Germany.
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15
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Jiang X, Tsang YH, Yu Q. c-Myc overexpression sensitizes Bim-mediated Bax activation for apoptosis induced by histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) through regulating Bcl-2/Bcl-xL expression. Int J Biochem Cell Biol 2007; 39:1016-25. [PMID: 17331788 DOI: 10.1016/j.biocel.2007.01.024] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 01/23/2007] [Accepted: 01/23/2007] [Indexed: 11/18/2022]
Abstract
Overexpression of the oncogene c-Myc sensitizes many apoptotic signals through the activation of mitochondrial apoptosis pathway. However, the underling mechanism has not been clearly defined. Here, we investigated the effect of c-Myc expression on histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)-induced apoptosis in rat fibroblast cells possessing various c-Myc levels. In Rat 1a cells overexpressing c-Myc, SAHA-induced enhanced the cell death response relative to the parental cells; whereas Rat 1a cells lacking c-Myc were refractory to SAHA treatment. We demonstrated that SAHA selectively induced the expression of pro-apoptotic BH3-only protein Bim, leading to Bax activation in c-Myc-expressing cells. Where c-Myc was absent, Bim, despite its induction by SAHA, failed to activate Bax and was unable to induce apoptosis. These results indicate that c-Myc is dispensable for Bim induction by SAHA, but is required for subsequent Bax activation. We further show that the expression levels of anti-apoptotic Bcl-2/Bcl2-xL were much elevated in Myc-null cells compared with the c-Myc-expressing cells; furthermore, depletion of Bcl-2/Bcl-xL in these cells restored the ability of SAHA to induce apoptosis by enhancing Bax activation. These data indicate that SAHA induces apoptosis through Bim-triggered Bax activation and that c-Myc regulates this process by modulating Bcl-2/Bcl-xL. Our results provide novel insight into the mechanism whereby Myc sensitizes the apoptotic signals; furthermore, our data suggest that cancer cells with deregulated Myc might be more sensitive to SAHA treatment.
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Affiliation(s)
- Xia Jiang
- Laboratory of Molecular Pharmacology, Genome Institute of Singapore, Genome Building, #02-01, 60 Biopolis Street, Singapore 138672, Singapore
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16
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Frame FM, Rogoff HA, Pickering MT, Cress WD, Kowalik TF. E2F1 induces MRN foci formation and a cell cycle checkpoint response in human fibroblasts. Oncogene 2006; 25:3258-66. [PMID: 16434972 DOI: 10.1038/sj.onc.1209352] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2005] [Revised: 11/07/2005] [Accepted: 11/07/2005] [Indexed: 11/09/2022]
Abstract
Deregulation of the Rb/E2F pathway in human fibroblasts results in an E2F1-mediated apoptosis dependent on Atm, Nbs1, Chk2 and p53. Here, we show that E2F1 expression results in MRN foci formation, which is independent of the Nbs1 interacting region and the DNA-binding domain of E2F1. E2F1-induced MRN foci are similar to irradiation-induced foci (IRIF) that result from double-strand DNA breaks because they correlate with 53BP1 and gammaH2AX foci, do not form in NBS cells, do form in AT cells and do not correlate with cell cycle entry. In fact, we find that in human fibroblasts deregulated E2F1 causes a G1 arrest, blocking serum-induced cell cycle progression, in part through an Nbs1/53BP1/p53/p21(WAF1/CIP1) checkpoint pathway. This checkpoint protects against apoptosis because depletion of 53BP1 or p21(WAF1/CIP1) increases both the rate and extent of apoptosis. Nbs1 and p53 contribute to both checkpoint and apoptosis pathways. These results suggest that E2F1-induced foci generate a cell cycle checkpoint that, with sustained E2F1 activity, eventually yields to apoptosis. Uncontrolled proliferation due to Rb/E2F deregulation as well as inactivation of both checkpoint and apoptosis programs would then be required for transformation of normal cells to tumor cells.
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Affiliation(s)
- F M Frame
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, 01655, USA
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17
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Bell LA, O'Prey J, Ryan KM. DNA-binding independent cell death from a minimal proapoptotic region of E2F-1. Oncogene 2006; 25:5656-63. [PMID: 16652153 DOI: 10.1038/sj.onc.1209580] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The ability to induce cell cycle progression while evading cell death is a defining characteristic of cancer. Deregulation of E2F is a common event in most human cancers. Paradoxically, this can lead to both cell cycle progression and apoptosis. Although the way in which E2F causes cell cycle progression is well characterized, the pathways by which E2F induces cell death are less well defined. Many of the known mechanisms through which E2F induces apoptosis occur through regulation of E2F target genes. However, mutants of E2F-1 that lack the transactivation domain are still able to induce cell death. To further investigate this activity, we refined a transactivation independent mutant to identify a minimal apoptotic domain. This revealed that only 75 amino acids from within the DNA-binding domain of E2F-1 is sufficient for cell death and that this activity is also present in the DNA-binding domains of E2F-2 and E2F-3. However, analysis of this domain from E2F-1 revealed it does not bind DNA and is consequently unable to transactivate, repress or de-repress E2F target genes. This provocative observation therefore defines a potential new mechanism of death from E2F and opens up new opportunities for inducing cell death in tumours for therapeutic gain.
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Affiliation(s)
- L A Bell
- Tumour Cell Death Laboratory, Beatson Institute for Cancer Research, Cancer Research UK Beatson Laboratories, Garscube Estate, Glasgow, UK
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18
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Stanelle J, Pützer BM. E2F1-induced apoptosis: turning killers into therapeutics. Trends Mol Med 2006; 12:177-85. [PMID: 16530485 DOI: 10.1016/j.molmed.2006.02.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2005] [Revised: 01/30/2006] [Accepted: 02/17/2006] [Indexed: 01/04/2023]
Abstract
The cellular transcription factor E2F1 is part of an anti-tumor safeguard mechanism: it engages cell-death pathways either alone or in cooperation with p53 to protect organisms from the development of tumors. E2F1 activates downstream factors, which in turn produce secondary changes in gene expression that trigger apoptosis. Although the mechanisms are incompletely understood, several studies have demonstrated that E2F1 is involved in many different aspects of programmed cell death depending on the cellular background. Here, these findings are highlighted in the context of the most recent follow-up studies that have used apoptotic E2F1 genes as new therapeutics or drug targets, thereby providing insight into the basic mechanisms of E2F1-induced apoptosis and its possible clinical implications.
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Affiliation(s)
- Jens Stanelle
- Department of Vectorology and Experimental Gene Therapy, University of Rostock, Schillingallee 70, 18057 Rostock, Germany
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19
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Russell JL, Weaks RL, Berton TR, Johnson DG. E2F1 suppresses skin carcinogenesis via the ARF-p53 pathway. Oncogene 2006; 25:867-76. [PMID: 16205640 DOI: 10.1038/sj.onc.1209120] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The E2F1 transcription factor, which is deregulated in most human cancers by mutations in the p16-cyclin D-Rb pathway, has both oncogenic and tumor-suppressive properties. This is dramatically illustrated by the phenotype of an E2F1 transgenic mouse model that spontaneously develops tumors in the skin and other epithelial tissues but is resistant to papilloma formation when subjected to a two-stage carcinogenesis protocol. Here, this E2F1 transgenic model was used to further explore the tumor-suppressive property of E2F1. Transgenic expression of E2F1 was found to inhibit ras-driven skin carcinogenesis at the promotion stage independent of the type of promoting agent used. E2F1 transgenic epidermis displayed increased expression of p19(ARF), p53, and p21(Cip1). Inactivation of either p53 or Arf in E2F1 transgenic mice restored sensitivity to two-stage skin carcinogenesis. While Arf inactivation impaired tumor suppression and p21 induction by E2F1, it did not reduce the level of apoptosis observed in E2F1 transgenic mice. Based on these findings, we propose that E2F1 suppresses ras-driven skin carcinogenesis through a nonapoptotic mechanism involving ARF and p53.
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Affiliation(s)
- J L Russell
- Department of Carcinogenesis, The University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, TX 78957, USA
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20
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Pusapati RV, Rounbehler RJ, Hong S, Powers JT, Yan M, Kiguchi K, McArthur MJ, Wong PK, Johnson DG. ATM promotes apoptosis and suppresses tumorigenesis in response to Myc. Proc Natl Acad Sci U S A 2006; 103:1446-51. [PMID: 16432227 PMCID: PMC1345703 DOI: 10.1073/pnas.0507367103] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2005] [Accepted: 12/09/2005] [Indexed: 01/24/2023] Open
Abstract
Overexpression of the c-myc oncogene contributes to the development of a significant number of human cancers. In response to deregulated Myc activity, the p53 tumor suppressor is activated to promote apoptosis and inhibit tumor formation. Here we demonstrate that p53 induction in response to Myc overexpression requires the ataxia-telangiectasia mutated (ATM) kinase, a major regulator of the cellular response to DNA double-strand breaks. In a transgenic mouse model overexpressing Myc in squamous epithelial tissues, inactivation of Atm suppresses apoptosis and accelerates tumorigenesis. Deregulated Myc expression induces DNA damage in primary transgenic keratinocytes and the formation of gammaH2AX and phospho-SMC1 foci in transgenic tissue. These findings suggest that Myc overexpression causes DNA damage in vivo and that the ATM-dependent response to this damage is critical for p53 activation, apoptosis, and the suppression of tumor development.
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Affiliation(s)
- Raju V Pusapati
- Department of Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Science Park Research Division, 1808 Park Road 1C, Smithville, TX 78957, USA
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21
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Dannenberg JH, te Riele HPJ. The retinoblastoma gene family in cell cycle regulation and suppression of tumorigenesis. Results Probl Cell Differ 2006; 42:183-225. [PMID: 16903212 DOI: 10.1007/400_002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Since its discovery in 1986, as the first tumor suppressor gene, the retinoblastoma gene (Rb) has been extensively studied. Numerous biochemical and genetic studies have elucidated in great detail the function of the Rb gene and placed it at the heart of the molecular machinery controlling the cell cycle. As more insight was gained into the genetic events required for oncogenic transformation, it became clear that the retinoblastoma gene is connected to biochemical pathways that are dysfunctional in virtually all tumor types. Besides regulating the E2F transcription factors, pRb is involved in numerous biological processes such as apoptosis, DNA repair, chromatin modification, and differentiation. Further complexity was added to the system with the discovery of p107 and p130, two close homologs of Rb. Although the three family members share similar functions, it is becoming clear that these proteins also have unique functions in differentiation and regulation of transcription. In contrast to Rb, p107 and p130 are rarely found inactivated in human tumors. Yet, evidence is accumulating that these proteins are part of a "tumor-surveillance" mechanism and can suppress tumorigenesis. Here we provide an overview of the knowledge obtained from studies involving the retinoblastoma gene family with particular focus on its role in suppressing tumorigenesis.
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Affiliation(s)
- Jan-Hermen Dannenberg
- Department of Medical Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts, USA.
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22
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Pauklin S, Kristjuhan A, Maimets T, Jaks V. ARF and ATM/ATR cooperate in p53-mediated apoptosis upon oncogenic stress. Biochem Biophys Res Commun 2005; 334:386-94. [PMID: 16004968 DOI: 10.1016/j.bbrc.2005.06.097] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Accepted: 06/16/2005] [Indexed: 11/30/2022]
Abstract
Induction of apoptosis is pivotal for eliminating cells with damaged DNA or deregulated proliferation. We show that tumor suppressor ARF and ATM/ATR kinase pathways cooperate in the induction of apoptosis in response to elevated expression of c-myc, beta-catenin or human papilloma virus E7 oncogenes. Overexpression of oncogenes leads to the formation of phosphorylated H2AX foci, induction of Rad51 protein levels and ATM/ATR-dependent phosphorylation of p53. Inhibition of ATM/ATR kinases abolishes both induction of Rad51 and phosphorylation of p53, and remarkably reduces the level of apoptosis induced by co-expression of oncogenes and ARF. However, the induction of apoptosis is downregulated in p53-/- cells and does not depend on activities of ATM/ATR kinases, indicating that efficient induction of apoptosis by oncogene activation depends on coordinated action of ARF and ATM/ATR pathways in the regulation of p53.
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Affiliation(s)
- Siim Pauklin
- Department of Cell Biology, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, Tartu 51010, Estonia.
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23
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Stanelle J, Tu-Rapp H, Pützer BM. A novel mitochondrial protein DIP mediates E2F1-induced apoptosis independently of p53. Cell Death Differ 2005; 12:347-57. [PMID: 15565177 DOI: 10.1038/sj.cdd.4401532] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The transcription factor E2F1 does not only induce cell proliferation but also shows the strongest proapoptotic effect of all E2F family members as part of an antitumor safeguard mechanism. We have recently identified KIAA0767 as a novel p53-independent target of E2F1. Here, we investigated the biological function of interaction. Overexpression studies of KIAA0767, termed D(eath)-I(nducing)-P(rotein), revealed its strong proapoptotic effect. DIP greatly reduced cell viability in several in vitro systems accompanied by typical apoptotic features such as caspase-3 activation and cleavage of poly(ADP-ribose)-polymerase. Endogenous DIP levels increased following E2F1 activation. Yet, inhibition of endogenous DIP function by small interfering RNA rescued p53-negative cells from E2F1-induced apoptosis, indicating that DIP is an essential mediator of the p53-independent E2F1 death pathway. Localization studies showed that DIP localizes to the mitochondria, where endogenous DIP is upregulated following E2F1 induction. These results provide new insights to the incompletely understood regulatory mechanisms of E2F1-induced apoptosis.
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Affiliation(s)
- J Stanelle
- Department of Vectorology and Experimental Gene Therapy, Rostock University, Schillingallee 70, Rostock, Germany
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24
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Hershko T, Chaussepied M, Oren M, Ginsberg D. Novel link between E2F and p53: proapoptotic cofactors of p53 are transcriptionally upregulated by E2F. Cell Death Differ 2005; 12:377-83. [PMID: 15706352 DOI: 10.1038/sj.cdd.4401575] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The E2F1 transcription factor is a critical downstream target of the tumor suppressor RB. When activated, E2F1 induces cell proliferation. In addition, E2F1 can induce apoptosis via both p53-dependent and p53-independent pathways. A number of E2F-regulated genes, including ARF, ATM and Chk2, contribute to E2F-induced p53 stabilization. However, it is not known how E2F directs p53 activity towards apoptosis rather than growth arrest. We show that E2F1 upregulates the expression of four proapoptotic cofactors of p53--ASPP1, ASPP2, JMY and TP53INP1--through a direct transcriptional mechanism. Adenovirus E1A protein also induces upregulation of these genes, implicating endogenous E2F in this effect. TP53INP1 was shown to mediate phosphorylation of p53 on serine 46. We demonstrate that activation of E2F1 leads to phosphorylation of p53 on serine 46 and this modification is important for E2F1-p53 cooperation in apoptosis. Overall, these data provide novel functional links between RB/E2F pathway and p53-induced apoptosis.
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Affiliation(s)
- T Hershko
- Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel
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25
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Fogal V, Hsieh JK, Royer C, Zhong S, Lu X. Cell cycle-dependent nuclear retention of p53 by E2F1 requires phosphorylation of p53 at Ser315. EMBO J 2005; 24:2768-82. [PMID: 16037820 PMCID: PMC1182237 DOI: 10.1038/sj.emboj.7600735] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2004] [Accepted: 06/08/2005] [Indexed: 11/08/2022] Open
Abstract
We show here that the cell cycle-dependent DNA-binding and transcriptional activity of p53 correlates with E2F expression in human primary fibroblasts. E2F1 binds and stimulates DNA-binding, transactivation and apoptotic functions of p53 but not p63 and p73. E2F1 binds residues 347-370 of p53 and enhances nuclear retention of Ser315 phosphorylated p53. This regulation of p53 by E2F1 is cell cycle dependent, as the cellular distribution of Ser315 phosphorylated p53 is associated with the periodic expression of E2F and cyclin A throughout the cell cycle. This is the first demonstration that the activities of p53 are regulated during the cell cycle by E2F/p53 interactions and that phosphorylation of p53 at Ser315 is required for this regulation.
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Affiliation(s)
- Valentina Fogal
- Ludwig Institute for Cancer Research, University College London Branch, London, UK
| | - Jung-Kuang Hsieh
- Ludwig Institute for Cancer Research, University College London Branch, London, UK
| | - Christophe Royer
- Ludwig Institute for Cancer Research, University College London Branch, London, UK
| | - Shan Zhong
- Ludwig Institute for Cancer Research, University College London Branch, London, UK
| | - Xin Lu
- Ludwig Institute for Cancer Research, University College London Branch, London, UK
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26
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Li Z, Stanelle J, Leurs C, Hanenberg H, Pützer BM. Selection of novel mediators of E2F1-induced apoptosis through retroviral expression of an antisense cDNA library. Nucleic Acids Res 2005; 33:2813-21. [PMID: 15897325 PMCID: PMC1129028 DOI: 10.1093/nar/gki581] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The E2F1 transcription factor is an essential mediator of p53-dependent and p53-independent apoptosis as part of an anti-tumour safeguard mechanism. In this study, a functional so-called technical knockout (TKO) approach was applied to Saos-2ERE2F1 cells that conditionally activate E2F1 by the addition of 4-hydroxytamoxifen to search for p53-independent pro-apoptotic E2F1 targets. The approach was based on random inactivation of genes after retroviral transfer of an antisense cDNA library enriched of E2F1-induced genes, followed by the selection of Saos-2ERE2F1 cells that survive in the presence of the apoptotic stimulus. We identified 13 novel E2F1 target genes encoding proteins of known cellular function, including apoptosis and RNA binding. FACS analysis revealed that E2F1-induced apoptosis was significantly attenuated in cell clones containing the antisense cDNA fragments of these genes, demonstrating their participation in E2F1 death pathways. Moreover, inactivation of the target genes resulted in a clear increase of cell viability (>80%) in response to E2F1 activation compared with controls (∼30%). Four genes showed an increase in expression intensity in the presence of cycloheximide, suggesting a direct effect of E2F1 on gene transcription, whereas one gene was identified as an indirect target. Our data provide new insight in the regulation of E2F1-induced apoptosis.
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Affiliation(s)
| | | | - C. Leurs
- Department of Pediatric Oncology, Hematology and Immunology, Children's Hospital, Heinrich Heine University Medical CenterMoorenstr. 5, 40225 Dusseldorf, Germany
| | - H. Hanenberg
- Department of Pediatric Oncology, Hematology and Immunology, Children's Hospital, Heinrich Heine University Medical CenterMoorenstr. 5, 40225 Dusseldorf, Germany
| | - B. M. Pützer
- To whom correspondence should be addressed. Tel: +49 381 4945066; Fax: +49 381 4945062;
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27
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Stevens C, La Thangue NB. The emerging role of E2F-1 in the DNA damage response and checkpoint control. DNA Repair (Amst) 2005; 3:1071-9. [PMID: 15279795 DOI: 10.1016/j.dnarep.2004.03.034] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Genotoxic stress triggers a myriad of cellular responses including cell cycle arrest, stimulation of DNA repair and apoptosis. A central role for the E2F-1 transcription factor in the DNA damage response pathway is gaining support. E2F-1 is phosphorylated by DNA damage responsive protein kinases, which leads to E2F-1 accumulation and the induction of apoptosis. In addition, emerging information suggests that E2F-1 may play a role in the detection and subsequent repair of damaged DNA.
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Affiliation(s)
- Craig Stevens
- Division of Biochemistry and Molecular Biology, Davidson Building, University of Glasgow, Glasgow G12 8QQ, UK
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28
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Berton TR, Mitchell DL, Guo R, Johnson DG. Regulation of epidermal apoptosis and DNA repair by E2F1 in response to ultraviolet B radiation. Oncogene 2005; 24:2449-60. [PMID: 15735727 DOI: 10.1038/sj.onc.1208462] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The E2F1 transcription factor regulates the expression of genes involved in cell proliferation, apoptosis and DNA repair. Following DNA damage, E2F1 is phosphorylated and stabilized, but the physiological role of E2F1 in the response to DNA damage is unclear. We find that mice lacking E2F1 have increased levels of epidermal apoptosis compared to wild-type mice following exposure to ultraviolet B (UVB) radiation. Moreover, transgenic overexpression of E2F1 in basal layer keratinocytes suppresses apoptosis induced by UVB. Inhibition of UVB-induced apoptosis by E2F1 is unexpected given that most studies have demonstrated a proapoptotic function for E2F1. E2F1-mediated suppression of apoptosis does not involve alterations in mitogen-activated protein kinase activation or Bcl-2 downregulation in response to UVB and is independent of p53. Instead, inhibition of UVB-induced apoptosis by E2F1 correlates with a stimulation of DNA repair. Mice lacking E2F1 are impaired for the removal of DNA photoproducts, while E2F1 transgenic mice repair UVB-induced DNA damage at an accelerated rate compared to wild-type mice. These findings suggest that E2F1 participates in the response to UVB by promoting DNA repair and suppressing apoptosis.
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Affiliation(s)
- Thomas R Berton
- Department of Carcinogenesis, Science Park Research Division, The University of Texas MD Anderson Cancer Center, PO Box 389, 1808 Park Road 1C, Smithville, TX 78957, USA
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29
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Slack A, Chen Z, Tonelli R, Pule M, Hunt L, Pession A, Shohet JM. The p53 regulatory gene MDM2 is a direct transcriptional target of MYCN in neuroblastoma. Proc Natl Acad Sci U S A 2005; 102:731-6. [PMID: 15644444 PMCID: PMC545522 DOI: 10.1073/pnas.0405495102] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2004] [Accepted: 11/19/2004] [Indexed: 02/02/2023] Open
Abstract
The MYCN oncogene is the major negative prognostic marker in neuroblastoma with important roles in both the pathogenesis and clinical behavior of this aggressive malignancy. MYC oncogenes activate both proliferative and apoptotic cellular pathways and, accordingly, inhibition of p53-mediated apoptosis is a prerequisite for MYC-driven tumorigenesis. To identify novel transcriptional targets mediating the MYCN-dependent phenotype, we screened a MYCN-amplified neuroblastoma cell line by using chromatin immunoprecipitation (ChIP) cloning. We identified the essential p53 inhibitor and protooncogene MDM2 as a putative target. MDM2 has multiple p53-independent functions modulating cell cycle and transcriptional events. Standard ChIP with MYCN antibodies established the binding of MYCN to a consensus E-box within the human MDM2 promoter. Oligonucleotide pull-down assays further established the capacity of MYCN to bind to this promoter region, confirming the ChIP results. Luciferase reporter assays confirmed the E-box-specific, MYCN-dependent regulation of the MDM2 promoter in MYCN-inducible neuroblastoma cell lines. Real-time quantitative PCR and Western blot analysis demonstrated a rapid increase in endogenous MDM2 mRNA and MDM2 protein upon induction of MYCN. Targeted inhibition of MYCN in a MYCN-amplified neuroblastoma cell line resulted in decreased MDM2 expression levels with concomitant stabilization of p53 and induction of apoptosis. Our finding that MYCN directly modulates baseline MDM2 levels suggests a mechanism contributing to the pathogenesis of neuroblastoma and other MYC-driven malignancies through inhibition of MYC-stimulated apoptosis.
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Affiliation(s)
- Andrew Slack
- Center for Cell and Gene Therapy, Texas Children's Cancer Center, Baylor College of Medicine, 1102 Bates Street, Houston, TX 77030, USA
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30
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Yi Y, Shepard A, Kittrell F, Mulac-Jericevic B, Medina D, Said TK. p19ARF determines the balance between normal cell proliferation rate and apoptosis during mammary gland development. Mol Biol Cell 2005; 15:2302-11. [PMID: 15105443 PMCID: PMC404024 DOI: 10.1091/mbc.e03-11-0785] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
This study demonstrated, for the first time, the following events related to p19(ARF) involvement in mammary gland development: 1) Progesterone appears to regulate p19(ARF) in normal mammary gland during pregnancy. 2) p19(ARF) expression levels increased sixfold during pregnancy, and the protein level plateaus during lactation. 3) During involution, p19(ARF) protein level remained at high levels at 2 and 8 days of involution and then, declined sharply at day 15. Absence of p19(ARF) in mammary epithelial cells leads to two major changes, 1) a delay in the early phase of involution concomitant with downregulation of p21(Cip1) and decrease in apoptosis, and 2) p19(ARF) null cells are immortal in vivo measured by serial transplantion, which is partly attributed to complete absence of p21(Cip1) compared with WT cells. Although, p19(ARF) is dispensable in mammary alveologenesis, as evidenced by normal differentiation in the mammary gland of pregnant p19(ARF) null mice, the upregulation of p19(ARF) by progesterone in the WT cells and the weakness of p21(Cip1) in mammary epithelial cells lacking p19(ARF) strongly suggest that the functional role(s) of p19(ARF) in mammary gland development is critical to sustain normal cell proliferation rate during pregnancy and normal apoptosis in involution possibly through the p53-dependent pathway.
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Affiliation(s)
- Yijun Yi
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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31
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del Arroyo AG, Peters G. The Ink4a/Arf network--cell cycle checkpoint or emergency brake? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2005; 570:227-47. [PMID: 18727503 DOI: 10.1007/1-4020-3764-3_8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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32
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Abstract
Mutations that drive uncontrolled cell-cycle progression are requisite events in tumorigenesis. But evolution has installed in the proliferative programmes of mammalian cells a variety of innate tumour-suppressive mechanisms that trigger apoptosis or senescence, should proliferation become aberrant. These contingent processes rely on a series of sensors and transducers that act in a coordinated network to target the machinery responsible for apoptosis and cell-cycle arrest at different points. Although oncogenic mutations that disable such networks can have profound and varied effects on tumour evolution, they may leave intact latent tumour-suppressive potential that can be harnessed therapeutically.
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Affiliation(s)
- Scott W Lowe
- Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, New York 11724, USA.
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33
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Chen D, Padiernos E, Ding F, Lossos IS, Lopez CD. Apoptosis-stimulating protein of p53-2 (ASPP2/53BP2L) is an E2F target gene. Cell Death Differ 2004; 12:358-68. [PMID: 15592436 DOI: 10.1038/sj.cdd.4401536] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The p53 pathway is a central apoptotic regulator. Deregulation of the Rb/E2F pathway occurs in a majority of tumors, resulting in both unrestrained proliferation and enhanced apoptosis sensitivity via p53-dependent and independent mechanisms. However, the mechanisms coupling the p53 and Rb/E2F pathways remain incompletely understood. We report that ASPP2/53BP2L, a p53/p73-binding protein that promotes p53/p73-dependent apoptosis, is an E2F target gene. The ASPP2/53BP2L promoter was identified and ectopic expression of transcription-competent E2F-1 (E2F-2 and E2F-3) stimulated an ASPP2/53BP2L promoter-luciferase reporter. Mutational analysis of the ASPP2/53BP2L promoter identified E2F-binding sites that cooperate for E2F-1 induction and basal repression of ASPP2/53BP2L. Moreover, endogenous ASPP2/53BP2L levels increased after E2F-1 expression, and E2F-1 bound the endogenous ASPP2/53BP2L promoter after chromatin immunoprecipitation. Typical for an E2F target, ASPP2/53BP2L expression was maximal in early S-phase. Thus, ASPP2/53BP2L is downstream of E2F, suggesting that it functions as a common link between the p53/p73 and Rb/E2F apoptotic pathways.
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Affiliation(s)
- D Chen
- Department of Medicine, Division of Hematology and Medical Oncology, L586B, Oregon Health & Science University, Portland, OR 97239, USA
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34
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Hipfner DR, Cohen SM. Connecting proliferation and apoptosis in development and disease. Nat Rev Mol Cell Biol 2004; 5:805-15. [PMID: 15459661 DOI: 10.1038/nrm1491] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Cells grow and divide rapidly during embryonic and postnatal development. Net tissue growth reflects the balance between the addition of new cells and the elimination of existing cells by programmed cell death. Cells compete for growth and survival factors to ensure an appropriate balance between the addition and elimination of cells. Elaborate mechanisms ensure that cells do not evade these constraints, and thereby prevent uncontrolled proliferation.
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Affiliation(s)
- David R Hipfner
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 169117, Heidelberg, Germany.
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35
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Eischen CM, Alt JR, Wang P. Loss of one allele of ARF rescues Mdm2 haploinsufficiency effects on apoptosis and lymphoma development. Oncogene 2004; 23:8931-40. [PMID: 15467748 DOI: 10.1038/sj.onc.1208052] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The tumor suppressor p19ARF inhibits Mdm2, which restricts the activity of p53. Complicated feedback and control mechanisms regulate ARF, Mdm2, and p53 interactions. Here we report that ARF haploinsufficiency completely rescued the p53-dependent effects of Mdm2 haploinsufficiency on B-cell development, survival, and transformation. In contrast to Mdm2+/- B cells, Mdm2+/- B cells deficient in ARF were similar to wild-type B cells in their rates of growth and apoptosis and activation of p53. Consequently, the profoundly reduced numbers of B cells in Mdm2+/-Emu-myc transgenic mice were restored to normal levels in ARF+/-Mdm2+/-Emu-myc transgenics. Additionally, ARF+/-Mdm2+/-Emu-myc transgenics developed lymphomas at rates analogous to those observed for wild-type Emu-myc transgenics, demonstrating that loss of one allele of ARF rescued the protracted lymphoma latency in Mdm2+/-Emu-myc transgenics. Importantly, in ARF+/-Mdm2+/-Emu-myc transgenic lymphomas, p53 was inactivated at the frequency observed in lymphomas of wild-type Emu-myc transgenics. Collectively, these results support a model whereby the stoichiometry of Mdm2 and ARF controls apoptosis and tumor development, which should have significant implications in the treatment of malignancies that have inactivated ARF.
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Affiliation(s)
- Christine M Eischen
- Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, NE 68198, USA.
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36
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Li Y, Wu D, Chen B, Ingram A, He L, Liu L, Zhu D, Kapoor A, Tang D. ATM activity contributes to the tumor-suppressing functions of p14ARF. Oncogene 2004; 23:7355-65. [PMID: 15258567 DOI: 10.1038/sj.onc.1207957] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
P14/p19ARF (ARF) plays a major role in the activation of p53 by oncogenic signals. The biochemical basis of this has not been fully elucidated. We report here that forced expression of p14ARF enhances phosphorylation of p53 serine 15 (p53S15) in NIH3T3, IMR90 and MCF7 cells. Ectopic expression of the oncogenes c-myc, E2F1 and E1A, all of which activate p53 at least partially via ARF, lead to p53S15 phosphorylation in IMR90 cells. In addition, ectopic expression of p53 also results in p53S15 phosphorylation, suggesting that this is a common event in the ARF-p53 tumor suppression system. Furthermore, p53-, p14ARF-, c-myc- and E2F1-, but not E1A-, induced p53S15 phosphorylation was substantially reduced in AT fibroblasts (GM05823). Downregulation of ATM in MCF7 cells using RNA interference (RNAi) technology significantly attenuated p14ARF- and p53-induced phosphorylation of p53S15. Ectopically expressed ARF in NIH3T3 cells induced ATM nuclear foci and activated ATM kinase. Functionally, ectopic expression of p14ARF and c-myc inhibited the proliferation of IMR90 but not ATM null GM05823 cells, and p14ARF-induced inhibition of MCF7 cell proliferation was significantly attenuated by downregulation of ATM by RNAi. Taken together, these data show a functional role for ATM in ARF-mediated tumor suppression.
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Affiliation(s)
- Yanxia Li
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, ON, Canada
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37
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Aslanian A, Iaquinta PJ, Verona R, Lees JA. Repression of the Arf tumor suppressor by E2F3 is required for normal cell cycle kinetics. Genes Dev 2004; 18:1413-22. [PMID: 15175242 PMCID: PMC423192 DOI: 10.1101/gad.1196704] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Tumor development is dependent upon the inactivation of two key tumor-suppressor networks, p16(Ink4a)-cycD/cdk4-pRB-E2F and p19(Arf)-mdm2-p53, that regulate cellular proliferation and the tumor surveillance response. These networks are known to intersect with one another, but the mechanisms are poorly understood. Here, we show that E2F directly participates in the transcriptional control of Arf in both normal and transformed cells. This occurs in a manner that is significantly different from the regulation of classic E2F-responsive targets. In wild-type mouse embryonic fibroblasts (MEFs), the Arf promoter is occupied by E2F3 and not other E2F family members. In quiescent cells, this role is largely fulfilled by E2F3b, an E2F3 isoform whose function was previously undetermined. E2f3 loss is sufficient to derepress Arf, triggering activation of p53 and expression of p21(Cip1). Thus, E2F3 is a key repressor of the p19(Arf)-p53 pathway in normal cells. Consistent with this notion, Arf mutation suppresses the activation of p53 and p21(Cip1) in E2f3-deficient MEFs. Arf loss also rescues the known cell cycle re-entry defect of E2f3(-/-) cells, and this correlates with restoration of appropriate activation of classic E2F-responsive genes. Our data also demonstrate a direct role for E2F in the oncogenic activation of Arf. Specifically, we observe recruitment of the endogenous activating E2Fs, E2F1, and E2F3a, to the Arf promoter. Thus, distinct E2F complexes directly contribute to the normal repression and oncogenic activation of Arf. We propose that monitoring of E2F levels and/or activity is a key component of Arf's ability to respond to inappropriate, but not normal cellular proliferation.
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Affiliation(s)
- Aaron Aslanian
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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38
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Rogoff HA, Pickering MT, Frame FM, Debatis ME, Sanchez Y, Jones S, Kowalik TF. Apoptosis associated with deregulated E2F activity is dependent on E2F1 and Atm/Nbs1/Chk2. Mol Cell Biol 2004; 24:2968-77. [PMID: 15024084 PMCID: PMC371110 DOI: 10.1128/mcb.24.7.2968-2977.2004] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The retinoblastoma protein (Rb)/E2F pathway links cellular proliferation control to apoptosis and is critical for normal development and cancer prevention. Here we define a transcription-mediated pathway in which deregulation of E2F1 by ectopic E2F expression or Rb inactivation by E7 of human papillomavirus type 16 signals apoptosis by inducing the expression of Chk2, a component of the DNA damage response. E2F1- and E7-mediated apoptosis are compromised in cells from patients with the related disorders ataxia telangiectasia and Nijmegen breakage syndrome lacking functional Atm and Nbs1 gene products, respectively. Both Atm and Nbs1 contribute to Chk2 activation and p53 phosphorylation following deregulation of normal Rb growth control. E2F2, a related E2F family member that does not induce apoptosis, also activates Atm, resulting in phosphorylation of p53. However, we found that the key commitment step in apoptosis induction is the ability of E2F1, and not E2F2, to upregulate Chk2 expression. Our results suggest that E2F1 plays a central role in signaling disturbances in the Rb growth control pathway and, by upregulation of Chk2, may sensitize cells to undergo apoptosis.
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Affiliation(s)
- Harry A Rogoff
- Program in Immunology and Virology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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39
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Powers JT, Hong S, Mayhew CN, Rogers PM, Knudsen ES, Johnson DG. E2F1 Uses the ATM Signaling Pathway to Induce p53 and Chk2 Phosphorylation and Apoptosis. Mol Cancer Res 2004. [DOI: 10.1158/1541-7786.203.2.4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
The p53 tumor suppressor protein is phosphorylated and activated by several DNA damage-inducible kinases, such as ATM, and is a key effector of the DNA damage response by promoting cell cycle arrest or apoptosis. Deregulation of the Rb-E2F1 pathway also results in the activation of p53 and the promotion of apoptosis, and this contributes to the suppression of tumor development. Here, we describe a novel connection between E2F1 and the ATM DNA damage response pathway. In primary human fibroblasts lacking functional ATM, the ability of E2F1 to induce the phosphorylation of p53 and apoptosis is impaired. In contrast, ATM status has no effect on transcriptional activation of target genes or the stimulation of DNA synthesis by E2F1. Cells containing mutant Nijmegen breakage syndrome protein (NBS1), a component of the Mre11-Rad50 DNA repair complex, also have attenuated p53 phosphorylation and apoptosis in response to E2F1 expression. Moreover, E2F1 induces ATM- and NBS1-dependent phosphorylation of the checkpoint kinase Chk2 at Thr68, a phosphorylation site that stimulates Chk2 activity. Delayed γH2AX phosphorylation and absence of ATM autophosphorylation at Ser1981 suggest that E2F1 stimulates ATM through a unique mechanism that is distinct from agents that cause DNA double-strand breaks. These findings identify new roles for several DNA damage response factors by demonstrating that they also participate in the oncogenic stress signaling pathway between E2F1 and p53.
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Affiliation(s)
- John T. Powers
- 1Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, Texas
- 2Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, Texas; and
| | - SungKi Hong
- 1Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, Texas
| | - Christopher N. Mayhew
- 3Department of Cell Biology, College of Medicine, University of Cincinnati, Cincinnati, Ohio
| | - Pamela M. Rogers
- 1Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, Texas
| | - Erik S. Knudsen
- 3Department of Cell Biology, College of Medicine, University of Cincinnati, Cincinnati, Ohio
| | - David G. Johnson
- 1Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, Texas
- 2Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, Texas; and
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Sheahan S, Bellamy COC, Treanor L, Harrison DJ, Prost S. Additive effect of p53, p21 and Rb deletion in triple knockout primary hepatocytes. Oncogene 2004; 23:1489-97. [PMID: 14647424 DOI: 10.1038/sj.onc.1207280] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Using Cre-Lox technology to inducibly delete Rb from wild-type, p21- and/or p53-deficient primary hepatocytes, we investigated the role of p53, p21 and pRb in the regulation of liver cell proliferation, polyploidization and death. These cellular decisions are critical to maintaining liver cell replacement in disease, and in determining the likelihood of carcinogenesis in chronic liver injury. Clearly, the present study shows a complex interplay between p53, p21 and pRb, which regulates the likelihood of hepatocytes stimulated from quiescence, to proliferate, undergo polyploidy or die. It reveals that these proteins act both in concert and independently, demonstrating that a small set of key cellular players is common to diverse cell decisions of fundamental importance to disease.
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Affiliation(s)
- Sharon Sheahan
- School of Molecular & Clinical Medicine, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, UK
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41
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O'Leary KA, Mendrysa SM, Vaccaro A, Perry ME. Mdm2 regulates p53 independently of p19(ARF) in homeostatic tissues. Mol Cell Biol 2004; 24:186-91. [PMID: 14673154 PMCID: PMC303350 DOI: 10.1128/mcb.24.1.186-191.2004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Tumor suppressor proteins must be exquisitely regulated since they can induce cell death while preventing cancer. For example, the p19(ARF) tumor suppressor (p14(ARF) in humans) appears to stimulate the apoptotic function of the p53 tumor suppressor to prevent lymphomagenesis and carcinogenesis induced by oncogene overexpression. Here we present a genetic approach to defining the role of p19(ARF) in regulating the apoptotic function of p53 in highly proliferating, homeostatic tissues. In contrast to our expectation, p19(ARF) did not activate the apoptotic function of p53 in lymphocytes or epithelial cells. These results demonstrate that the mechanisms that control p53 function during homeostasis differ from those that are critical for tumor suppression. Moreover, the Mdm2/p53/p19(ARF) pathway appears to exist only under very restricted conditions.
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Affiliation(s)
- Kathleen A O'Leary
- Department of Oncology, University of Wisconsin, Madison, Wisconsin 53706, USA
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42
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Abstract
A paradox for the cancer biology field has been the revelation that oncogenes, once thought to simply provide advantages to a cancer cell, actually put it at dire risk of cell suicide. Myc is the quintessential oncogene in this respect, as in normal cells it is required for cell cycle traverse, whereas in cancers it is overexpressed and functions as the angiogenic switch. Nonetheless, Myc overexpression kills normal cells dead in their tracks. Here we review Myc-induced pathways that contribute to the apoptotic response. Molecular analysis of Myc-induced tumors has established that some of these apoptotic pathways are essential checkpoints that guard the cell from cancer, as they are selectively bypassed during tumorigenesis. The precise mechanism(s) by which Myc targets these pathways are largely unresolved, but we propose that they involve crosstalk and feedback regulatory loops between arbiters of cell death.
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Affiliation(s)
- Jonas A Nilsson
- Department of Biochemistry, St Jude Children's Research Hospital, 332 N Lauderdale, Memphis, TN 38105, USA
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43
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Hurlin PJ, Dezfouli S. Functions of myc:max in the control of cell proliferation and tumorigenesis. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 238:183-226. [PMID: 15364199 DOI: 10.1016/s0074-7696(04)38004-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Deregulation and elevated expression of members of the Myc family of bHLHZip transcription factors are observed in a high percentage of tumors. This close association with human cancers has led to a tremendous effort to define their biological and biochemical activities. Although Myc family proteins have the capacity to elicit a wide range of cell behaviors, their principal function appears to be to drive cells into the cell cycle and to keep them there. However, forced expression of Myc profoundly sensitizes normal cells to apoptosis. Therefore, tumor formation caused by deregulated Myc expression requires cooperating events that disrupt pathways that mediate apoptosis. Myc-dependent tumor formation may also be impeded by a set of related bHLHZip proteins with the demonstrated potential to act as Myc antagonists in cell culture experiments. In this review, we examine the complex activities of Myc family proteins and how their actions might be regulated in the context of a network of bHLHZip proteins.
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Affiliation(s)
- Peter J Hurlin
- Portland Shriners Hospitals for Children and Department of Cell and Developmental Biology Oregon Health Sciences University, Portland, Oregon 97201, USA
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44
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Lindström MS, Wiman KG. Myc and E2F1 induce p53 through p14ARF-independent mechanisms in human fibroblasts. Oncogene 2003; 22:4993-5005. [PMID: 12902982 DOI: 10.1038/sj.onc.1206659] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
p19ARF is induced in response to oncogene activation or during cellular senescence in mouse embryo fibroblasts, triggering p53-dependent and p53-independent cell cycle arrest and apoptosis. We have studied the involvement of human p14ARF as a regulator of p53 activity in normal human skin fibroblasts (NHFs) or WI38 lung embryonic fibroblasts expressing conditional Myc or E2F1 estrogen receptor fusion proteins. Both Myc and E2F1 activation rapidly induced p53 phosphorylation at Ser-15, p53 protein accumulation, and upregulation of the p53 target genes MDM2 and p21. Activation of E2F1 induced p14ARF mRNA and protein levels. In contrast, Myc activation did not induce any significant increase in p14ARF mRNA or protein levels in neither NHFs nor WI38 fibroblasts within 48 h. Myc and E2F1 induced p53 and cell cycle arrest even after silencing of p14ARF using short-interfering RNA. Treatment with the ATM/ATR kinase inhibitor caffeine prevented p53 accumulation upon activation of Myc or E2F1. Our results indicate that p53 phosphorylation, but not p14ARF, plays a major role for the induction of p53 in response to Myc and E2F1 activation in normal human fibroblasts.
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Affiliation(s)
- Mikael S Lindström
- Department of Oncology-Pathology, Cancer Center Karolinska (CCK), R8:04, Karolinska Institutet, SE-171 76 Stockholm, Sweden
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45
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Wong CF, Barnes LM, Dahler AL, Smith L, Serewko-Auret MM, Popa C, Abdul-Jabbar I, Saunders NA. E2F modulates keratinocyte squamous differentiation: implications for E2F inhibition in squamous cell carcinoma. J Biol Chem 2003; 278:28516-22. [PMID: 12754218 DOI: 10.1074/jbc.m301246200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
E2F regulation is essential for normal cell cycle progression. Therefore, it is not surprising that squamous cell carcinoma cell lines (SCC) overexpress E2F1 and exhibit deregulated E2F activity when compared with normal keratinocytes. Indeed, deliberate E2F1 deregulation has been shown to induce hyperplasia and skin tumor formation. In this study, we report on a dual role for E2F as a mediator of keratinocyte proliferation and modulator of squamous differentiation. Overexpression of E2F isoforms in confluent primary keratinocyte cultures resulted in suppression of differentiation-associated markers. Moreover, we found that the DNA binding domain and the trans-activation domain of E2F1 are important in mediating suppression of differentiation. Use of a dominant/negative form of E2F1 (E2F d/n) found that E2F inhibition alone is sufficient to suppress the activity of proliferation-associated markers but is not capable of inducing differentiation markers. However, if the E2F d/n is expressed in differentiated keratinocytes, differentiation marker activity is further induced, suggesting that E2F may act as a modulator of squamous differentiation. We therefore examined the effects of E2F d/n in a differentiation-insensitive SCC cell line. We found that treatment with the differentiating agent, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), or expression of E2F d/n alone had no effect on differentiation markers. However, a combination of E2F d/n + TPA induced the expression of differentiation markers. Combined, these data indicate that E2F may play a key role in keratinocyte differentiation. These data also illustrate the unique potential of anti-E2F therapies in arresting proliferation and inducing differentiation of SCCs.
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Affiliation(s)
- Chung Fai Wong
- Epithelial Pathobiology Group, Cancer Biology Programme, Centre for Immunology and Cancer Research, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Australia 4102
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46
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Affiliation(s)
- Timothy F Burns
- Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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47
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48
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Wikonkal NM, Remenyik E, Knezevic D, Zhang W, Liu M, Zhao H, Berton TR, Johnson DG, Brash DE. Inactivating E2f1 reverts apoptosis resistance and cancer sensitivity in Trp53-deficient mice. Nat Cell Biol 2003; 5:655-60. [PMID: 12833065 DOI: 10.1038/ncb1001] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2003] [Accepted: 05/22/2003] [Indexed: 12/12/2022]
Abstract
The E2f1 transcription factor, which regulates genes required for S-phase entry, also induces apoptosis by transcriptional and post-translational mechanisms. As E2f1 is inducible by DNA damage we investigated its importance in vivo in ultraviolet (UV)-induced apoptosis, a protective mechanism that prevents the epidermis from accumulating UV-induced mutations. Contrary to expectation, E2f1-/- mice demonstrated enhanced keratinocyte apoptosis after UVB exposure, whereas apoptosis was suppressed by epidermis-specific overexpression of human E2F1. Apoptosis induced by -radiation was also repressed by E2f1. E2f1-/-;Trp53-/- double knockout mice exhibited the elevated UVB-induced apoptosis of E2f1-/- alone, rather than the profound apoptosis defect seen in Trp53-/- mice, indicating that Trp53 (p53) lies functionally upstream of E2f1. Transfecting E2F1 into E2f1-/-;Trp53-/- primary fibroblasts suppressed UVB-induced apoptosis and this suppression was relieved by Trp53. The double knockout also reverted the abnormal sex ratio and early-onset tumours of Trp53-/- mice. These results imply that E2f1 functions as a suppressor of an apoptosis pathway that is initiated by DNA photoproducts and perhaps genetic abnormalities; p53 relieves this suppression.
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Affiliation(s)
- Norbert M Wikonkal
- Department of Therapeutic Radiology, Yale School of Medicine, New Haven, CT 06520 USA
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49
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Baudino TA, Maclean KH, Brennan J, Parganas E, Yang C, Aslanian A, Lees JA, Sherr CJ, Roussel MF, Cleveland JL. Myc-Mediated Proliferation and Lymphomagenesis, but Not Apoptosis, Are Compromised by E2f1 Loss. Mol Cell 2003; 11:905-14. [PMID: 12718877 DOI: 10.1016/s1097-2765(03)00102-3] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Myc and E2f1 promote cell cycle progression, but overexpression of either can trigger p53-dependent apoptosis. Mice expressing an Emu-Myc transgene in B lymphocytes develop lymphomas, the majority of which sustain mutations of either the Arf or p53 tumor suppressors. Emu-Myc transgenic mice lacking one or both E2f1 alleles exhibited a slower onset of lymphoma development associated with increased expression of the cyclin-dependent kinase inhibitor p27(Kip1) and a reduced S phase fraction in precancerous B cells. In contrast, Myc-induced apoptosis and the frequency of Arf and p53 mutations in lymphomas were unaffected by E2f1 loss. Therefore, Myc does not require E2f1 to induce Arf, p53, or apoptosis in B cells, but depends upon E2f1 to accelerate cell cycle progression and downregulate p27(Kip1).
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Affiliation(s)
- Troy A Baudino
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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50
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Abstract
The p53 tumor-suppressor plays a critical role in the prevention of human cancer. In the absence of cellular stress, the p53 protein is maintained at low steady-state levels and exerts very little, if any, effect on cell fate. However, in response to various types of stress, p53 becomes activated; this is reflected in elevated protein levels, as well as augmented biochemical capabilities. As a consequence of p53 activation, cells can undergo marked phenotypic changes, ranging from increased DNA repair to senescence and apoptosis. This review deals with the mechanisms that underlie the apoptotic activities of p53, as well as the complex interactions between p53 and central regulatory signaling networks. In p53-mediated apoptosis, the major role is played by the ability of p53 to transactivate specific target genes. The choice of particular subsets of target genes, dictated by covalent p53 modifications and protein-protein interactions, can make the difference between life and apoptotic death of a cell. In addition, transcriptional repression of antiapoptotic genes, as well as transcription-independent activities of p53, can also contribute to the apoptotic effects of p53. Regarding the crosstalk between p53 and signaling networks, this review focuses on the interplay between p53 and two pivotal regulatory proteins: beta-catenin and Akt/PKB. Both proteins can regulate p53 as well as be regulated by it. In addition, p53 interacts with the GSK-3beta kinase, which serves as a link between Akt and beta-catenin. This review discusses how the functional balance between these different interactions might dictate the likelihood of a given cell to become cancerous or be eliminated from the replicative pool, resulting in suppression of cancer.
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Affiliation(s)
- M Oren
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
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