351
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Bassett EA, Wang W, Rastinejad F, El-Deiry WS. Structural and functional basis for therapeutic modulation of p53 signaling. Clin Cancer Res 2008; 14:6376-86. [PMID: 18927276 DOI: 10.1158/1078-0432.ccr-08-1526] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Effective modulation of structural features and/or functional properties of the major tumor suppressor p53 as a wild-type or cancer-associated mutant protein represents a major challenge in drug development for cancer. p53 is an attractive target for therapeutic design because of its involvement as a mediator of growth arrest and apoptosis after exposure to chemoradiotherapy and/or radiotherapy. Although most clinically used cytotoxic agents target stabilization of wild-type p53, there are a number of approaches that hold promise for reactivation of mutant p53. On the other hand, brief blockade of p53 may reduce toxicity from systemic cytotoxic therapy. Screens for restoration of p53 transcriptional responses in p53-deficient cells may provide a functional means to develop anticancer therapeutics. Structure-based modulation continues to hold promise for development of peptides or small molecules capable of modulation of either wild-type or mutant p53 proteins.
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Affiliation(s)
- Emily A Bassett
- Department of Medicine, The Abramson Comprehensive Cancer Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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352
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Raina D, Ahmad R, Chen D, Kumar S, Kharbanda S, Kufe D. MUC1 oncoprotein suppresses activation of the ARF-MDM2-p53 pathway. Cancer Biol Ther 2008; 7:1959-67. [PMID: 18981727 DOI: 10.4161/cbt.7.12.6956] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The MUC1 oncoprotein interacts with the c-Abl tyrosine kinase and blocks nuclear targeting of c-Abl in the apoptotic response to DNA damage. Mutation of the MUC1 cytoplasmic domain at Tyr-60 disrupts the MUC1-c-Abl interaction. The present results demonstrate that the MUC1(Y60F) mutant is a potent inducer of the ARF tumor suppressor. MUC1(Y60F) induces transcription of the ARF locus by a c-Abl-dependent mechanism that promotes CUL-4A-mediated nuclear export of the replication protein Cdc6. The functional significance of these findings is that MUC1(Y60F)-induced ARF expression and thereby inhibition of MDM2 results in the upregulation of p53 and the homeodomain interacting protein kinase 2 (HIPK2) serine/threonine kinase. HIPK2-mediated phosphorylation of p53 on Ser-46 was further associated with a shift from expression of the cell cycle arrest-related p21 gene to the apoptosis-related PUMA gene. We also show that the MUC1(Y60F) mutant functions as dominant negative inhibitor of tumorigenicity. These findings indicate that the oncogenic function of MUC1 is conferred by suppressing activation of the ARF-MDM2-p53 pathway.
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Affiliation(s)
- Deepak Raina
- Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts, USA
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353
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Damiani LA, Yingling CM, Leng S, Romo PE, Nakamura J, Belinsky SA. Carcinogen-induced gene promoter hypermethylation is mediated by DNMT1 and causal for transformation of immortalized bronchial epithelial cells. Cancer Res 2008; 68:9005-14. [PMID: 18974146 DOI: 10.1158/0008-5472.can-08-1276] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A better understanding of key molecular changes during transformation of lung epithelial cells could affect strategies to reduce mortality from lung cancer. This study uses an in vitro model to identify key molecular changes that drive cell transformation and the likely clonal outgrowth of preneoplastic lung epithelial cells that occurs in the chronic smoker. Here, we show differences in transformation efficiency associated with DNA repair capacity for two hTERT/cyclin-dependent kinase 4, immortalized bronchial epithelial cell lines after low-dose treatment with the carcinogens methylnitrosourea, benzo(a)pyrene-diolepoxide 1, or both for 12 weeks. Levels of cytosine-DNA methyltransferase 1 (DNMT1) protein increased significantly during carcinogen exposure and were associated with the detection of promoter hypermethylation of 5 to 10 genes in each transformed cell line. Multiple members of the cadherin gene family were commonly methylated during transformation. Stable knockdown of DNMT1 reversed transformation and gene silencing. Moreover, stable knockdown of DNMT1 protein before carcinogen treatment prevented transformation and methylation of cadherin genes. These studies provide a mechanistic link between increased DNMT1 protein, de novo methylation of tumor suppressor genes, and reduced DNA repair capacity that together seem causal for transformation of lung epithelial cells. This finding supports the development of demethylation strategies for primary prevention of lung cancer in smokers.
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Affiliation(s)
- Leah A Damiani
- Lung Cancer Program, Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108, USA
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354
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Yu J, Zhang SS, Saito K, Williams S, Arimura Y, Ma Y, Ke Y, Baron V, Mercola D, Feng GS, Adamson E, Mustelin T. PTEN regulation by Akt-EGR1-ARF-PTEN axis. EMBO J 2008; 28:21-33. [PMID: 19057511 DOI: 10.1038/emboj.2008.238] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2008] [Accepted: 10/22/2008] [Indexed: 11/09/2022] Open
Abstract
The PTEN tumour suppressor gene is induced by the early growth response 1 (EGR1) transcription factor, which also transactivates p53, p73, and p300/CBP as well as other proapoptotic and anti-cancer genes. Here, we describe a novel Akt-EGR1-alternate reading frame (ARF)-PTEN axis, in which PTEN activation in vivo requires p14ARF-mediated sumoylation of EGR1. This modification is dependent on the phosphorylation of EGR1 at S350 and T309 by Akt, which promotes interaction of EGR1 with ARF at K272 in its repressor domain by the ARF/Ubc9/SUMO system. EGR1 sumoylation is decreased by ARF reduction, and no EGR1 sumoylation is detected in ARF(-/-) mice, which also exhibit reduced amounts of PTEN. Our model predicts that perturbation of any of the clinically important tumour suppressors, PTEN, EGR1, and ARF, will cause some degree of dysfunction of the others. These results also explain the known negative feedback regulation by PTEN on its own synthesis through PI3 kinase inhibition.
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Affiliation(s)
- Jianxiu Yu
- The Burnham Institute for Medical Research, La Jolla, CA 92037, USA.
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355
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Gsponer J, Futschik ME, Teichmann SA, Babu MM. Tight regulation of unstructured proteins: from transcript synthesis to protein degradation. Science 2008; 322:1365-8. [PMID: 19039133 PMCID: PMC2803065 DOI: 10.1126/science.1163581] [Citation(s) in RCA: 366] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Altered abundance of several intrinsically unstructured proteins (IUPs) has been associated with perturbed cellular signaling that may lead to pathological conditions such as cancer. Therefore, it is important to understand how cells precisely regulate the availability of IUPs. We observed that regulation of transcript clearance, proteolytic degradation, and translational rate contribute to controlling the abundance of IUPs, some of which are present in low amounts and for short periods of time. Abundant phosphorylation and low stochasticity in transcription and translation indicate that the availability of IUPs can be finely tuned. Fidelity in signaling may require that most IUPs be available in appropriate amounts and not present longer than needed.
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Affiliation(s)
- Jörg Gsponer
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, United Kingdom
| | - Matthias E. Futschik
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, United Kingdom
- Institute for Theoretical Biology, Charité, Humboldt-University, Berlin, Germany
- Centre of Molecular and Structural Biomedicine, University of Algarve, Faro, Portugal
| | - Sarah A. Teichmann
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, United Kingdom
| | - M. Madan Babu
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, United Kingdom
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356
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Yun C, Wang Y, Mukhopadhyay D, Backlund P, Kolli N, Yergey A, Wilkinson KD, Dasso M. Nucleolar protein B23/nucleophosmin regulates the vertebrate SUMO pathway through SENP3 and SENP5 proteases. J Cell Biol 2008; 183:589-95. [PMID: 19015314 PMCID: PMC2582899 DOI: 10.1083/jcb.200807185] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Accepted: 10/20/2008] [Indexed: 11/22/2022] Open
Abstract
Ubiquitin-like protein/sentrin-specific proteases (Ulp/SENPs) mediate both processing and deconjugation of small ubiquitin-like modifier proteins (SUMOs). Here, we show that Ulp/SENP family members SENP3 and SENP5 localize within the granular component of the nucleolus, a subnucleolar compartment that contains B23/nucleophosmin. B23/nucleophosmin is an abundant shuttling phosphoprotein, which plays important roles in ribosome biogenesis and which has been strongly implicated in hematopoietic malignancies. Moreover, we found that B23/nucleophosmin binds SENP3 and SENP5 in Xenopus laevis egg extracts and that it is essential for stable accumulation of SENP3 and SENP5 in mammalian tissue culture cells. After either codepletion of SENP3 and SENP5 or depletion of B23/nucleophosmin, we observed accumulation of SUMO proteins within nucleoli. Finally, depletion of these Ulp/SENPs causes defects in ribosome biogenesis reminiscent of phenotypes observed in the absence of B23/nucleophosmin. Together, these results suggest that regulation of SUMO deconjugation may be a major facet of B23/nucleophosmin function in vivo.
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Affiliation(s)
- Chawon Yun
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA
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357
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A dose-dependent tug of war involving the NPM1 leukaemic mutant, nucleophosmin, and ARF. Leukemia 2008; 23:501-9. [DOI: 10.1038/leu.2008.326] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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358
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A retroviral mutagenesis screen reveals strong cooperation between Bcl11a overexpression and loss of the Nf1 tumor suppressor gene. Blood 2008; 113:1075-85. [PMID: 18948576 DOI: 10.1182/blood-2008-03-144436] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
NF1 inactivation occurs in specific human cancers, including juvenile myelomonocytic leukemia, an aggressive myeloproliferative disorder of childhood. However, evidence suggests that Nf1 loss alone does not cause leukemia. We therefore hypothesized that inactivation of the Nf1 tumor suppressor gene requires cooperating mutations to cause acute leukemia. To search for candidate genes that cooperate with Nf1 deficiency in leukemogenesis, we performed a forward genetic screen using retroviral insertion mutagenesis in Nf1 mutant mice. We identified 43 common proviral insertion sites that contain candidate genes involved in leukemogenesis. One of these genes, Bcl11a, confers a growth advantage in cultured Nf1 mutant hematopoietic cells and causes early onset of leukemia of either myeloid or lymphoid lineage in mice when expressed in Nf1-deficient bone marrow. Bcl11a-expressing cells display compromised p21(Cip1) induction, suggesting that Bcl11a's oncogenic effects are mediated, in part, through suppression of p21(Cip1). Importantly, Bcl11a is expressed in human chronic myelomonocytic leukemia and juvenile myelomonocytic leukemia samples. A subset of AML patients, who had poor outcomes, of 16 clusters, displayed high levels of BCL11A in leukemic cells. These findings suggest that deregulated Bcl11a cooperates with Nf1 in leukemogenesis, and a therapeutic strategy targeting the BCL11A pathway may prove beneficial in the treatment of leukemia.
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359
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Wade M, Rodewald LW, Espinosa JM, Wahl GM. BH3 activation blocks Hdmx suppression of apoptosis and cooperates with Nutlin to induce cell death. Cell Cycle 2008; 7:1973-82. [PMID: 18604177 DOI: 10.4161/cc.7.13.6072] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The Hdmx protein restricts p53 activity in vivo and is overexpressed in a significant fraction of human tumors that retain the wild type p53 allele. An understanding of how Hdmx limits p53 activation and blocks apoptosis could therefore lead to development of novel therapeutic agents. We previously showed that Hdmx modulates tumor cell sensitivity to Nutlin-3a, a potent antagonist of the p53/Hdm2 interaction. In this report, we demonstrate that this also applies to MI-219, another Hdm2 antagonist. Thus, the inability to disrupt Hdmx/p53 complexes is a potential barrier to the efficacy of these compounds as single agents. We show that sensitivity to apoptosis in cells with high Hdmx levels is restored by combined treatment with Nutlin and a Bcl-2 family member antagonist to activate Bax. The data are consistent with a model in which Hdmx attenuates p53-dependent activation of the intrinsic apoptotic pathway, and that this occurs upstream of Bax activation. Thus, selectively inhibiting Hdm2 and activating Bax is one effective strategy to induce apoptosis in tumors with high Hdmx levels. Our findings also indicate that preferential induction of apoptosis in tumor versus normal cells occurs using appropriate drug doses.
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Affiliation(s)
- Mark Wade
- Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037, USA
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360
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Pollice A, Vivo M, La Mantia G. The promiscuity of ARF interactions with the proteasome. FEBS Lett 2008; 582:3257-62. [PMID: 18805416 DOI: 10.1016/j.febslet.2008.09.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Revised: 09/03/2008] [Accepted: 09/06/2008] [Indexed: 11/30/2022]
Abstract
The tumor suppressor ARF is one of the most important oncogenic stress sensors in mammalian cells. Its effect is exerted through the interaction with different cellular partners, often resulting in their functional inactivation. This review focuses on the role played by the proteasome in ARF regulation of protein turnover and the function of most of its interacting partners. Specific proteasome components appear to be involved in the regulation of ARF turnover, bringing to light a complex network of interactions between ARF and the proteasome.
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Affiliation(s)
- Alessandra Pollice
- Department of Structural and Functional Biology, University of Naples Federico II, Naples, Italy.
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361
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Sivakolundu SG, Nourse A, Moshiach S, Bothner B, Ashley C, Satumba J, Lahti J, Kriwacki RW. Intrinsically unstructured domains of Arf and Hdm2 form bimolecular oligomeric structures in vitro and in vivo. J Mol Biol 2008; 384:240-54. [PMID: 18809412 DOI: 10.1016/j.jmb.2008.09.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Revised: 09/04/2008] [Accepted: 09/10/2008] [Indexed: 12/31/2022]
Abstract
Arf, Hdm2, and p53 regulate the tumor-suppressor pathway that is most frequently disrupted in human cancer. In the absence of tumorigenic stress, Hdm2 actively attenuates p53-dependent cell cycle arrest and apoptosis by mediating ubiquitination-dependent degradation of p53. Mitogenic stress activates Arf, which indirectly activates p53 by binding to and nullifying the anti-p53 activities of Hdm2. Small conserved domains within Arf and Hdm2 mediate their direct interaction. Individually, these domains are intrinsically unstructured and, when combined in vitro, cofold into bimolecular oligomeric structures that resemble amyloid fibrils in some features. Detailed structural characterization of Hdm2/Arf complexes has previously been hampered by their heterogeneity and large size. Here, we report that a nine-residue fragment of the N-terminus of mouse Arf (termed "A1-mini") cofolds specifically with the Arf-binding domain of Hdm2 to form bimolecular oligomers. We characterized these unprecedented structures using analytical ultracentrifugation and NMR spectroscopy, providing insights into their structural organization. The A1-mini peptide not only binds specifically to Hdm2 in vitro but also recapitulates the nucleolar localization features of full-length Arf in cells. Furthermore, larger fragments of Arf that contain the A1-mini segment have previously been shown to activate p53 in mouse and human cells. Our studies provide the first insights into the molecular basis through which Arf nullifies the p53-inhibiting activity of Hdm2, indirectly activating the tumor-suppressor function of p53 in mammalian cells.
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Affiliation(s)
- Sivashankar G Sivakolundu
- Department of Structural Biology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105, USA
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362
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Abstract
Arf and p53 are regarded among the most relevant tumor suppressors based on their ubiquitous and frequent inactivation in human cancer. The Arf/p53 pathway protects cells against several types of damage and this is the basis of its tumor suppressor activity. Interestingly, aging is a process associated with the accumulation of damage derived from chronic stresses of small magnitude. In agreement with its damage protection role, it has been recently described that the Arf/p53 pathway not only protects mammalian organisms from cancer but also from aging. However, there is also evidence that p53, under certain circumstances, such as when constitutively active, can induce aging. We discuss here the current evidence linking the Arf/p53 pathway to the process of aging and present a unified model.
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Affiliation(s)
- Ander Matheu
- Tumor Suppression Group, Spanish National Cancer Research Center, Madrid, Spain
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363
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364
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In vitro genetic screen identifies a cooperative role for LPA signaling and c-Myc in cell transformation. Oncogene 2008; 27:6806-16. [PMID: 18762810 DOI: 10.1038/onc.2008.294] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
c-Myc drives uncontrolled cell proliferation in various human cancers. However, in mouse embryo fibroblasts (MEFs), c-Myc also induces apoptosis by activating the p19Arf tumor suppressor pathway. Tbx2, a transcriptional repressor of p19Arf, can collaborate with c-Myc by suppressing apoptosis. MEFs overexpressing c-Myc and Tbx2 are immortal but not transformed. We have performed an unbiased genetic screen, which identified 12 oncogenes that collaborate with c-Myc and Tbx2 to transform MEFs in vitro. One of them encodes the LPA2 receptor for the lipid growth factor lysophosphatidic acid (LPA). We find that LPA1 and LPA4, but not LPA3, can reproduce the transforming effect of LPA2. Using pharmacological inhibitors, we show that the in vitro cell transformation induced by LPA receptors is dependent on the Gi-linked ERK and PI3K signaling pathways. The transforming ability of LPA1, LPA2 and LPA4 was confirmed by tumor formation assays in vivo and correlated with prolonged ERK1/2 activation in response to LPA. Our results reveal a direct role for LPA receptor signaling in cell transformation and tumorigenesis in conjunction with c-Myc and reduced p19Arf expression.
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365
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Hagen J, Tompkins V, Dudakovic A, Weydert JA, Quelle DE. Generation and characterization of monoclonal antibodies to NIAM: a nuclear interactor of ARF and Mdm2. Hybridoma (Larchmt) 2008; 27:159-66. [PMID: 18582208 DOI: 10.1089/hyb.2007.0533] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Nuclear interactor of ARF and Mdm2 (NIAM) is a newly discovered growth inhibitor that helps maintain chromosomal stability. It is functionally linked to the ARF-Mdm2-p53 tumor suppressor pathway and is predicted to be a tumor suppressor, but the lack of antibodies capable of detecting the endogenous human protein has delayed efforts to define its role in human tumorigenesis. This study reports the development, screening, and characterization of several monoclonal antibodies (MAbs) that specifically recognize endogenous human NIAM protein by Western blotting, immunoprecipitation, immunofluorescence, and immunohistochemistry. These MAbs are predicted to be important tools for evaluating the expression and physiological function of NIAM in normal versus neoplastic human cells and tissues.
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Affiliation(s)
- Jussara Hagen
- Department of Pharmacology, The University of Iowa, College of Medicine, Iowa City, Iowa, USA
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366
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Abstract
The Ras-activated transcription factor DMP1 can stimulate Arf transcription to promote p53-dependent cell arrest. One recent study deepens the pathophysiologic significance of this pathway in cancer, first, by identifying DMP1 losses in human lung cancers that lack ARF/p53 mutations, and second, by demonstrating that Dmp1 deletions in the mouse are sufficient to promote K-ras-induced lung tumorigenesis via mechanisms consistent with a disruption of Arf/p53 suppressor function. These findings prompt further investigations of the prognostic value of DMP1 alterations in human cancers and the oncogenic events that can cooperate with DMP1 inactivation to drive tumorigenesis.
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Affiliation(s)
- Kazushi Inoue
- Departments of Pathology and Cancer Biology, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, North Carolina, USA.
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367
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Sugiyama T, Frazier DP, Taneja P, Morgan RL, Willingham MC, Inoue K. Role of DMP1 and its future in lung cancer diagnostics. Expert Rev Mol Diagn 2008; 8:435-47. [PMID: 18598225 DOI: 10.1586/14737159.8.4.435] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Lung cancer is the most lethal carcinoma worldwide. Mutations of p53, inactivation of p16(INK4a), and overexpression of cyclins E, A and B are independently associated with poor prognoses of patients, while the prognostic value of cyclin D1 or RB expression is inconclusive. Cyclin D binding myb-like protein 1 (Dmp1) encodes a DNA binding protein that receives signals from oncogenic Ras and functions as a tumor suppressor by activating the Arf-p53 [corrected] pathway. Dmp1 has been shown to be haplo-insufficient for tumor suppression in mouse models including K-ras-mediated lung carcinogenesis. The human DMP1 gene is located on chromosome 7q21, and our recent results revealed that the hDMP1 gene is deleted, but not mutated or silenced, in approximately 40 % of human non-small-cell lung carcinomas. These cases typically retained wild-type ARF and p53 and expressed very low levels of the hDMP1 protein. Thus, hDMP1 loss could be a novel diagnostic marker for non-small-cell lung carcinomas.
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Affiliation(s)
- Takayuki Sugiyama
- The Department of Pathology & Cancer Biology, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, NC 27157-0001, USA.
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368
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Piscopo DM, Hinds PW. A role for the cyclin box in the ubiquitin-mediated degradation of cyclin G1. Cancer Res 2008; 68:5581-90. [PMID: 18632610 DOI: 10.1158/0008-5472.can-07-6346] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cyclin G1 was identified as a transcriptional target of p53 that encodes a protein with strong homology to the cyclin family of cell cycle regulators. We show that either ectopically expressed or endogenous cyclin G1 protein is very unstable, undergoes modification with ubiquitin, and is likely degraded by the proteasome. Ectopic cyclin G1 protein stability is increased by cyclin box mutation or by association with inactive cyclin-dependent kinase (CDK) subunits, suggesting that a function of cyclin G1 as a CDK regulator may be required for its rapid turnover. Furthermore, cyclin G1 and the cyclin box mutant interact with and are ubiquitinated by MDM2, another transcriptional target of p53 that acts as a negative regulator of p53 stability. These data suggest that the cyclin box has a role in the proteasome-mediated degradation of cyclin G1 and thus suggest a putative role for a CDK in cyclin G1 metabolism and function.
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Affiliation(s)
- Denise M Piscopo
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111, USA
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369
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Spechler SJ, Souza RF. Biomarkers and photodynamic therapy for Barrett's esophagus: time to FISH or cut bait? Gastroenterology 2008; 135:354-7. [PMID: 18619447 DOI: 10.1053/j.gastro.2008.06.065] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
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370
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Guo Y, Pajovic S, Gallie BL. Expression of p14ARF, MDM2, and MDM4 in human retinoblastoma. Biochem Biophys Res Commun 2008; 375:1-5. [PMID: 18644346 DOI: 10.1016/j.bbrc.2008.07.055] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Accepted: 07/09/2008] [Indexed: 12/19/2022]
Abstract
It is still not clear whether the p53 pathway is altered in retinoblastoma development. We assessed the expression of the p53 pathway genes p14(ARF), mouse double minute 2 (MDM2), and mouse double minute 4 (MDM4) in human retinoblastoma compared to normal retina. Primary human retinoblastomas, retinoblastoma cell lines and normal retinas were assessed for p14(ARF) and MDM4 mRNA by quantitative RT-PCR. p14(ARF), MDM2, and MDM4 protein were measured by immunoblot and immunohistochemistry. Compared to retina, p14(ARF) mRNA expression was notably increased in retinoblastoma but p14(ARF) protein was undetectable. MDM2 and MDM4 proteins were expressed in 22/22 retinoblastomas. MDM2 was expressed in 3/10 retinas tested, and MDM4 in 10/10 retinas. The expression level of MDM2 protein in retinoblastomas and retina was comparable, while MDM4 protein was overexpressed in one retinoblastoma cell line Y79 and two primary retinoblastomas. We observe that overexpression of MDM2 and MDM4 is not a necessary step in retinoblastoma development. However, loss of detectable p14(ARF) protein and resultant lack of functional inactivation of these p53 inhibitors may contribute to retinoblastoma development by constitutive inhibition of p53.
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Affiliation(s)
- Ying Guo
- Division of Applied Molecular Oncology, Ontario Cancer Institute/Princess Margaret Hospital, University Health Network, Room 8-415, 610 University Avenue, Toronto, ON, Canada
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371
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Ewing SJ, Zhu S, Zhu F, House JS, Smart RC. C/EBPbeta represses p53 to promote cell survival downstream of DNA damage independent of oncogenic Ras and p19(Arf). Cell Death Differ 2008; 15:1734-44. [PMID: 18636078 DOI: 10.1038/cdd.2008.105] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
CCAAT/enhancer-binding protein-beta (C/EBPbeta) is a mediator of cell survival and tumorigenesis. When C/EBPbeta(-/-) mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19(Arf) and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19(Arf) is dramatically elevated in C/EBPbeta(-/-) epidermis and that C/EBPbeta represses a p19(Arf) promoter reporter. To determine whether p19(Arf) is responsible for the proapoptotic phenotype in C/EBPbeta(-/-) mice, C/EBPbeta(-/-);p19(Arf-/-) mice were generated. C/EBPbeta(-/-);p19(Arf-/-) mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19(Arf) is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPbeta(-/-) epidermis, we generated K14-ER:Ras;C/EBPbeta(-/-) mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPbeta(-/-) mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPbeta represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPbeta may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.
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Affiliation(s)
- S J Ewing
- Cell Signaling and Cancer Group, Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695-7633, USA
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372
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Abstract
Oncogenes can induce p53 through a signaling pathway involving p19/Arf. It was recently proposed that oncogenes can also induce DNA damage, and this can induce p53 through the Atm DNA damage pathway. To assess the relative roles of Atm, Arf, and p53 in the suppression of Ras-driven tumors, we examined susceptibility to skin carcinogenesis in 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate (TPA)-treated Atm- and p53-deficient mice and compared these results to previous studies on Arf-deficient mice. Mice with epidermal-specific deletion of p53 showed increased papilloma number and progression to malignant invasive carcinomas compared with wild-type littermates. In contrast, Atm-deficient mice showed no increase in papilloma number, growth, or malignant progression. gamma-H2AX and p53 levels were increased in both Atm(+/+) and Atm(-/-) papillomas, whereas Arf(-/-) papillomas showed much lower p53 expression. Thus, although there is evidence of DNA damage, signaling through Arf seems to regulate p53 in these Ras-driven tumors. In spontaneous and radiation-induced lymphoma models, tumor latency was accelerated in Atm(-/-)p53(-/-) compound mutant mice compared with the single mutant Atm(-/-) or p53(-/-) mice, indicating cooperation between loss of Atm and loss of p53. Although p53-mediated apoptosis was impaired in irradiated Atm(-/-) lymphocytes, p53 loss was still selected for during lymphomagenesis in Atm(-/-) mice. In conclusion, in these models of oncogene- or DNA damage-induced tumors, p53 retains tumor suppressor activity in the absence of Atm.
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Affiliation(s)
- S. Lawrence Bailey
- Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N. Seattle WA, 90109-1024, USA
| | - Kay E. Gurley
- Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N. Seattle WA, 90109-1024, USA
| | | | - Karen S. Kelly-Spratt
- Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N. Seattle WA, 90109-1024, USA
| | - Christopher J. Kemp
- Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N. Seattle WA, 90109-1024, USA
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373
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Abstract
Cellular senescence is associated with ageing and cancer in vivo and has a proven tumour-suppressive function. Common to both ageing and cancer is the generation of DNA damage and the engagement of the DNA-damage response pathways. In this Review, the diverse mechanisms that lead to DNA-damage generation and the activation of DNA-damage-response signalling pathways are discussed, together with the evidence for their contribution to the establishment and maintenance of cellular senescence in the context of organismal ageing and cancer development.
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374
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Ha L, Merlino G, Sviderskaya EV. Melanomagenesis: overcoming the barrier of melanocyte senescence. Cell Cycle 2008; 7:1944-8. [PMID: 18604170 PMCID: PMC2678050 DOI: 10.4161/cc.7.13.6230] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Although melanoma ultimately progresses to a highly aggressive and metastatic disease that is typically resistant to currently available therapy, it often begins as a benign nevus consisting of a clonal population of hyperplastic melanocytes that cannot progress because they are locked in a state of cellular senescence. Once senescence is overcome, the nevus can exhibit dysplastic features and readily progress to more lethal stages. Recent advances have convincingly demonstrated that senescence represents a true barrier to the progression of many types of cancer, including melanoma. Thus, understanding the mechanism(s) by which melanoma evades senescence has become a priority in the melanoma research community. Senescence in most cells is regulated through some combination of activities within the RB and p53 pathways. However, differences discovered among various tumor types, some subtle and others quite profound, have revealed that senescence frequently operates in a context-dependent manner. Here we review what is known about melanocyte senescence, and how such knowledge may provide a much-needed edge in our struggles to contain or perhaps vanquish this often-fatal malignancy.
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Affiliation(s)
- Linan Ha
- Division of Monoclonal Antibody, Center of Drug Evaluation and Research, Food and Drug Administration, Bethesda, Maryland, USA
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375
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Basak S, Jacobs SBR, Krieg AJ, Pathak N, Zeng Q, Kaldis P, Giaccia AJ, Attardi LD. The metastasis-associated gene Prl-3 is a p53 target involved in cell-cycle regulation. Mol Cell 2008; 30:303-14. [PMID: 18471976 DOI: 10.1016/j.molcel.2008.04.002] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Revised: 12/04/2007] [Accepted: 04/04/2008] [Indexed: 10/22/2022]
Abstract
The p53 tumor suppressor restricts tumorigenesis through the transcriptional activation of target genes involved in cell-cycle arrest and apoptosis. Here, we identify Prl-3 (phosphatase of regenerating liver-3) as a p53-inducible gene. Whereas previous studies implicated Prl-3 in metastasis because of its overexpression in metastatic human colorectal cancer and its ability to promote invasiveness and motility, we demonstrate here that Prl-3 is an important cell-cycle regulator. Consistent with a role in DNA damage-induced cell-cycle arrest, Prl-3 overexpression induces G(1) arrest downstream of p53 by triggering a PI3K-Akt-activated negative feedback loop. Surprisingly, attenuation of Prl-3 expression also elicits an arrest response, suggesting that basal level Prl-3 expression is pivotal for normal cell-cycle progression. Our findings highlight key dose-dependent functions of Prl-3 in both positive and negative regulation of cell-cycle progression and provide insight into Prl-3's role in cancer progression.
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Affiliation(s)
- Shashwati Basak
- Division of Radiation and Cancer Biology, Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA
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376
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Uren AG, Kool J, Matentzoglu K, de Ridder J, Mattison J, van Uitert M, Lagcher W, Sie D, Tanger E, Cox T, Reinders M, Hubbard TJ, Rogers J, Jonkers J, Wessels L, Adams DJ, van Lohuizen M, Berns A. Large-scale mutagenesis in p19(ARF)- and p53-deficient mice identifies cancer genes and their collaborative networks. Cell 2008; 133:727-41. [PMID: 18485879 PMCID: PMC2405818 DOI: 10.1016/j.cell.2008.03.021] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Revised: 01/21/2008] [Accepted: 03/10/2008] [Indexed: 01/25/2023]
Abstract
p53 and p19(ARF) are tumor suppressors frequently mutated in human tumors. In a high-throughput screen in mice for mutations collaborating with either p53 or p19(ARF) deficiency, we identified 10,806 retroviral insertion sites, implicating over 300 loci in tumorigenesis. This dataset reveals 20 genes that are specifically mutated in either p19(ARF)-deficient, p53-deficient or wild-type mice (including Flt3, mmu-mir-106a-363, Smg6, and Ccnd3), as well as networks of significant collaborative and mutually exclusive interactions between cancer genes. Furthermore, we found candidate tumor suppressor genes, as well as distinct clusters of insertions within genes like Flt3 and Notch1 that induce mutants with different spectra of genetic interactions. Cross species comparative analysis with aCGH data of human cancer cell lines revealed known and candidate oncogenes (Mmp13, Slamf6, and Rreb1) and tumor suppressors (Wwox and Arfrp2). This dataset should prove to be a rich resource for the study of genetic interactions that underlie tumorigenesis.
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Affiliation(s)
- Anthony G Uren
- Division of Molecular Genetics and Cancer Genomics Centre, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX, Amsterdam, The Netherlands
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377
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Itahana K, Zhang Y. Mitochondrial p32 is a critical mediator of ARF-induced apoptosis. Cancer Cell 2008; 13:542-53. [PMID: 18538737 PMCID: PMC4504427 DOI: 10.1016/j.ccr.2008.04.002] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 01/16/2008] [Accepted: 04/09/2008] [Indexed: 11/30/2022]
Abstract
The shared exon 2 of the p14ARF-p16INK4a locus is frequently mutated in human cancers. However, in contrast to the exon 1beta-encoded N-terminal half of ARF, the function of the exon 2-encoded C-terminal half of ARF has been elusive. Here, we report that the mitochondrial protein p32/C1QBP binds the ARF C terminus. We show that p32 is required for ARF to localize to mitochondria and induce apoptosis, and that ARF mutations specifically disrupting p32 binding can impair both of these functions. Wild-type ARF, but not a p32-binding-deficient ARF mutant, localizes to mitochondria, reduces mitochondrial membrane potential, and sensitizes cells to p53-induced apoptosis. These findings provide a potential explanation for the frequent human cancer mutations targeting the ARF C terminus.
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Affiliation(s)
- Koji Itahana
- Department of Radiation Oncology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7512, USA
- Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7512, USA
| | - Yanping Zhang
- Department of Radiation Oncology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7512, USA
- Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7512, USA
- Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7512, USA
- Correspondence:
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378
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Peters G. Tumor Suppression for ARFicionados: The Relative Contributions of p16INK4a and p14ARF in Melanoma. J Natl Cancer Inst 2008; 100:757-9. [DOI: 10.1093/jnci/djn156] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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379
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Abstract
The cell-fate determinant Numb has recently been shown to help activate the tumor suppressor protein p53. Loss of Numb in breast cancers would result, therefore, in both the activation of the potential oncogene Notch and the diminution of tumor suppression by p53.
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Affiliation(s)
- Stephanie Carter
- The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow G61 1BD, UK
| | - Karen H Vousden
- The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow G61 1BD, UK
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380
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Cheung CTY, Hasan MK, Widodo N, Kaul SC, Wadhwa R. CARF: an emerging regulator of p53 tumor suppressor and senescence pathway. Mech Ageing Dev 2008; 130:18-23. [PMID: 18555516 DOI: 10.1016/j.mad.2008.05.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2008] [Revised: 04/08/2008] [Accepted: 05/02/2008] [Indexed: 10/22/2022]
Abstract
Replicative senescence, a major outcome of normal cells with finite lifespan, is a widely accepted in vitro model for ageing studies. Limited repair and defense mechanisms of normal cells, in addition to DNA alterations and oncogene inductions under stress, are believed to result in senescence as a protective mechanism to prevent undesirable proliferation of cells. The ARF/p53/p21(cip1/waf1) tumor suppression pathway acts as a molecular sensor and regulator of cellular stress, senescence, and immortalization. Understanding the molecular regulation of this pathway by intrinsic and extrinsic signals is extremely important to address unsolved questions in senescence and cancer. CARF was first discovered as a binding partner of ARF and has since been shown to have both ARF-dependent and -independent functions that converge to regulate p53 pathway. CARF directly binds to p53 and HDM2, and functions in a negative feedback pathway. Whereas CARF transcriptionally represses HDM2 to increase p53 activity, HDM2 in return degrades CARF. Thus, CARF may act as a novel key regulator of the p53 pathway at multiple checkpoints. The aim of this article is to discuss the current knowledge about functions of CARF and its impact on p53 pathway in regulation of senescence and carcinogenesis.
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Affiliation(s)
- Caroline T Y Cheung
- National Institute of Advanced Industrial Science & Technology, Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
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381
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Hogan C, Hutchison C, Marcar L, Milne D, Saville M, Goodlad J, Kernohan N, Meek D. Elevated levels of oncogenic protein kinase Pim-1 induce the p53 pathway in cultured cells and correlate with increased Mdm2 in mantle cell lymphoma. J Biol Chem 2008; 283:18012-23. [PMID: 18467333 DOI: 10.1074/jbc.m709695200] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Mutation of the p53 gene is a common event during tumor pathogenesis. Other mechanisms, such as mdm2 amplification, provide alternative routes through which dysfunction of the p53 pathway is promoted. Here, we address the hypothesis that elevated expression of pim oncogenes might suppress p53 by regulating Mdm2. At a physiological level, we show that endogenous Pim-1 and Pim-2 interact with endogenous Mdm2. Additionally, the Pim kinases phosphorylate Mdm2 in vitro and in cultured cells at Ser(166) and Ser(186), two previously identified targets of other signaling pathways, including Akt. Surprisingly, at high levels of Pim expression, as would occur in tumors, active, but not inactive, Pim-1 or Pim-2 blocks the degradation of both p53 and Mdm2 in a manner that is independent of Mdm2 phosphorylation, leading to increased p53 levels and, proportionately, p53-dependent transactivation. Additionally, Pim-1 induces endogenous ARF, p53, Mdm2, and p21 in primary murine embryo fibroblasts and stimulates senescence-associated beta-galactosidase levels, consistent with the induction of senescence. Immunohistochemical analysis of a cohort of 33 human mantle cell lymphomas shows that elevated expression of Pim-1 occurs in 42% of cases, with elevated Pim-2 occurring in 9% of cases, all of which also express Pim-1. Notably, elevated Pim-1 correlates with elevated Mdm2 in MCL with a p value of 0.003. Taken together, our data are consistent with the idea that Pim normally interacts with the p53 pathway but, when expressed at pathological levels, behaves as a classic dominant oncogene that stimulates a protective response through induction of the p53 pathway.
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Affiliation(s)
- Carol Hogan
- Biomedical Research Centre, Division of Pathology and Neuroscience, Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK
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382
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Lain S, Hollick JJ, Campbell J, Staples OD, Higgins M, Aoubala M, McCarthy A, Appleyard V, Murray KE, Baker L, Thompson A, Mathers J, Holland SJ, Stark MJR, Pass G, Woods J, Lane DP, Westwood NJ. Discovery, in vivo activity, and mechanism of action of a small-molecule p53 activator. Cancer Cell 2008; 13:454-63. [PMID: 18455128 PMCID: PMC2742717 DOI: 10.1016/j.ccr.2008.03.004] [Citation(s) in RCA: 382] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 12/05/2007] [Accepted: 03/06/2008] [Indexed: 12/20/2022]
Abstract
We have carried out a cell-based screen aimed at discovering small molecules that activate p53 and have the potential to decrease tumor growth. Here, we describe one of our hit compounds, tenovin-1, along with a more water-soluble analog, tenovin-6. Via a yeast genetic screen, biochemical assays, and target validation studies in mammalian cells, we show that tenovins act through inhibition of the protein-deacetylating activities of SirT1 and SirT2, two important members of the sirtuin family. Tenovins are active on mammalian cells at one-digit micromolar concentrations and decrease tumor growth in vivo as single agents. This underscores the utility of these compounds as biological tools for the study of sirtuin function as well as their potential therapeutic interest.
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Affiliation(s)
- Sonia Lain
- Department of Surgery and Molecular Oncology, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY Scotland, UK.
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383
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Ushijima R, Matsuyama T, Nagata I, Yamamoto K. Nucleolar targeting of proteins by the tandem array of basic amino acid stretches identified in the RNA polymerase I-associated factor PAF49. Biochem Biophys Res Commun 2008; 369:1017-21. [DOI: 10.1016/j.bbrc.2008.02.138] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2008] [Accepted: 02/26/2008] [Indexed: 10/22/2022]
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384
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Fukasawa K. P53, cyclin-dependent kinase and abnormal amplification of centrosomes. Biochim Biophys Acta Rev Cancer 2008; 1786:15-23. [PMID: 18472015 DOI: 10.1016/j.bbcan.2008.04.002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2007] [Revised: 03/13/2008] [Accepted: 04/08/2008] [Indexed: 01/10/2023]
Abstract
Centrosomes play a critical role in formation of bipolar mitotic spindles, an essential event for accurate chromosome segregation into daughter cells. Numeral abnormalities of centrosomes (centrosome amplification) occur frequently in cancers, and are considered to be the major cause of chromosome instability, which accelerates acquisition of malignant phenotypes during tumor progression. Loss or mutational inactivation of p53 tumor suppressor protein, one of the most common mutations found in cancers, results in a high frequency of centrosome amplification in part via allowing the activation of the cyclin-dependent kinase (CDK) 2-cyclin E (as well as CDK2-cyclin A) which is a key factor for the initiation of centrosome duplication. In this review, the role of centrosome amplification in tumor progression, and mechanistic view of how centrosomes are amplified in cells through focusing on loss of p53 and aberrant activities of CDK2-cyclins will be discussed.
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Affiliation(s)
- Kenji Fukasawa
- Molecular Oncology Program, H. Lee Moffitt Cancer Center & Research Institute, Tampa, FL 33612, USA.
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385
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Yogev O, Saadon K, Anzi S, Inoue K, Shaulian E. DNA damage-dependent translocation of B23 and p19 ARF is regulated by the Jun N-terminal kinase pathway. Cancer Res 2008; 68:1398-406. [PMID: 18316603 DOI: 10.1158/0008-5472.can-07-2865] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The dynamic behavior of the nucleolus plays a role in the detection of and response to DNA damage of cells. Two nucleolar proteins, p14(ARF)/p19(ARF) and B23, were shown to translocate out of the nucleolus after exposure of cells to DNA-damaging agents. This translocation affects multiple cellular functions, such as DNA repair, proliferation, and survival. In this study, we identify a pathway and scrutinize the mechanisms leading to the translocation of these proteins after exposure of cells to DNA-damaging agents. We show that redistribution of B23 and p19(ARF) after the exposure to genotoxic stress occurs preferentially when the c-Jun-NH(2)-kinase (JNK) pathway is activated and is inhibited when the JNK pathway is impaired. The stress-induced translocation of alternative reading frame (ARF) is JNK dependent and mediated by two activator proteins, c-Jun and JunB. Thr(91) and Thr(93) of c-Jun are required for the translocation, but the transcriptional activity of c-Jun is dispensable. Instead, c-Jun interacts with B23 in a dose-dependent manner. c-Jun itself is excluded from the nucleolus in a JNK-dependent manner. Hence, we suggest that c-Jun translocates B23 and ARF from the nucleolus after JNK activation by means of protein interactions. In senescent cells, JNK activity and c-Jun levels are reduced concomitantly with ARF nucleolar accumulation, and UV radiation does not cause the translocation of ARF.
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Affiliation(s)
- Orli Yogev
- Department of Experimental Medicine and Cancer Research, Hebrew University Medical School, Jerusalem, Israel
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386
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Miyazaki M, Miyazaki K, Itoi M, Katoh Y, Guo Y, Kanno R, Katoh-Fukui Y, Honda H, Amagai T, van Lohuizen M, Kawamoto H, Kanno M. Thymocyte proliferation induced by pre-T cell receptor signaling is maintained through polycomb gene product Bmi-1-mediated Cdkn2a repression. Immunity 2008; 28:231-45. [PMID: 18275833 DOI: 10.1016/j.immuni.2007.12.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2007] [Revised: 11/15/2007] [Accepted: 12/07/2007] [Indexed: 11/16/2022]
Abstract
Thymocytes undergo massive proliferation before T cell receptor (TCR) gene rearrangement, ensuring the diversification of the TCR repertoire. Because activated cells are more susceptible to damage, cell-death restraint as well as promotion of cell-cycle progression is considered important for adequate cell growth. Although the molecular mechanism of pre-TCR-induced proliferation has been examined, the mechanisms of protection against cell death during the proliferation phase remain unknown. Here we show that the survival of activated pre-T cells induced by pre-TCR signaling required the Polycomb group (PcG) gene product Bmi-1-mediated repression of Cdkn2A, and that p19Arf expression resulted in thymocyte cell death and inhibited the transition from CD4(-)CD8(-) (DN) to CD4(+)CD8(+) (DP) stage upstream of the transcriptional factor p53 pathway. The expression of Cdkn2A (the gene encoding p19Arf) in immature thymocytes was directly regulated by PcG complex containing Bmi-1 and M33 through the maintenance of local trimethylated histone H3K27. Our results indicate that this epigenetic regulation critically contributes to the survival of the activated pre-T cells, thereby supporting their proliferation during the DN-DP transition.
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Affiliation(s)
- Masaki Miyazaki
- Department of Immunology, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
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387
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Sugiyama T, Frazier DP, Taneja P, Kendig RD, Morgan RL, Matise LA, Lagedrost SJ, Inoue K. Signal transduction involving the dmp1 transcription factor and its alteration in human cancer. Clin Med Oncol 2008; 2:209-19. [PMID: 21892281 PMCID: PMC3161675 DOI: 10.4137/cmo.s548] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Dmp1 (cyclin D-interacting myb-like protein 1; also called Dmtf1) is a transcription factor that has been isolated in a yeast two-hybrid screen through its binding property to cyclin D2. Dmp1 directly binds to and activates the Arf promoter and induces Arf-p53-dependent cell cycle arrest in primary cells. D-type cyclins usually inhibit Dmp1-mediated transcription in a Cdk-independent fashion; however, Dmp1 shows synergistic effects with D-cyclins on the Arf promoter. Ras or Myc oncogene-induced tumor formation is accelerated in both Dmp1+/− and Dmp1−/− mice with no significant differences between Dmp1+/− and Dmp1−/−. Thus, Dmp1 is haplo-insufficient for tumor suppression. Tumors from Dmp1−/− or Dmp1+/− mice often retain wild-type Arf and p53, suggesting that Dmp1 is a physiological regulator of the Arf-p53 pathway. The Dmp1 promoter is activated by oncogenic Ras-Raf signaling, while it is repressed by physiological mitogenic stimuli, overexpression of E2F proteins, and genotoxic stimuli mediated by NF-κB. The human DMP1 gene (hDMP1) is located on chromosome 7q21 and is hemizygously deleted in approximately 40% of human lung cancers, especially those that retain normal INK4a/ARF and P53 loci. Thus, hDMP1 is clearly involved in human carcinogenesis, and tumors with hDMP1 deletion may constitute a discrete disease entity.
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Affiliation(s)
- Takayuki Sugiyama
- The Department of Pathology, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, N.C. 27157-0001, U.S.A
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388
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Chu LH, Chen BS. Comparisons of robustness and sensitivity between cancer and normal cells by microarray data. Cancer Inform 2008; 6:165-81. [PMID: 19259409 PMCID: PMC2623309 DOI: 10.4137/cin.s386] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Robustness is defined as the ability to uphold performance in face of perturbations and uncertainties, and sensitivity is a measure of the system deviations generated by perturbations to the system. While cancer appears as a robust but fragile system, few computational and quantitative evidences demonstrate robustness tradeoffs in cancer. Microarrays have been widely applied to decipher gene expression signatures in human cancer research, and quantification of global gene expression profiles facilitates precise prediction and modeling of cancer in systems biology. We provide several efficient computational methods based on system and control theory to compare robustness and sensitivity between cancer and normal cells by microarray data. Measurement of robustness and sensitivity by linear stochastic model is introduced in this study, which shows oscillations in feedback loops of p53 and demonstrates robustness tradeoffs that cancer is a robust system with some extreme fragilities. In addition, we measure sensitivity of gene expression to perturbations in other gene expression and kinetic parameters, discuss nonlinear effects in feedback loops of p53 and extend our method to robustness-based cancer drug design.
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Affiliation(s)
- Liang-Hui Chu
- Lab of Control and Systems Biology, National Tsing Hua University, Hsinchu, Taiwan
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389
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Abstract
The ARF tumor suppressor is a crucial component of the cellular response to hyperproliferative signals, including oncogene activation, and functions by inducing a p53-dependent cell growth arrest and apoptosis program. It has recently been reported that the ARF mRNA can produce a smARF isoform that lacks the NH(2)-terminal region required for p53 activation. Overexpression of this isoform can induce autophagy, a cellular process characterized by the formation of cytoplasmic vesicles and the digestion of cellular content, independently of p53. However, the level of this isoform is extremely low in cells, and it remains unclear whether the predominant form of ARF, the full-length protein, is able to activate autophagy. Here, we show that full-length ARF can induce autophagy in 293T cells where p53 is inactivated by viral proteins, and, notably, expression of the NH(2)-terminal region alone, which is required for nucleolar localization, is sufficient for autophagy activation, independently of p53. Given the reported ability of p53 to induce autophagy, we also investigated the role of p53 in ARF-mediated autophagy induction. We found that full-length ARF expression induces p53 activation and promotes autophagy in a p53-positive cell line, and that ARF-mediated autophagy can be abrogated, at least in part, by RNAi-mediated knockdown of p53 in this cellular context. Thus, our findings modify the current view regarding the mechanism of autophagy induction by ARF and suggest an important role for autophagy in tumor suppression via full-length ARF in both p53-dependent and p53-independent manners, depending on cellular context.
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Affiliation(s)
- Wassim M Abida
- Institute for Cancer Genetics and Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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390
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Chen YW, Paliwal S, Draheim K, Grossman SR, Lewis BC. p19Arf inhibits the invasion of hepatocellular carcinoma cells by binding to C-terminal binding protein. Cancer Res 2008; 68:476-82. [PMID: 18199542 DOI: 10.1158/0008-5472.can-07-1960] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The INK4A/ARF tumor suppressor locus is frequently inactivated in hepatocellular carcinoma (HCC), yet the consequences of this remain unknown. We recently described a HCC mouse model in which loss of the Ink4a/Arf locus accelerates the development of metastasis and enhances tumor cell migration and invasion in cell culture assays. We show here that knockdown of p19Arf in an HCC cell line increases invasion in cell culture assays. Furthermore, reintroduction of p19(Arf) into HCC cell lines lacking Ink4a/Arf inhibits tumor cell invasion, without affecting cell proliferation, or cell transformation as measured by soft agar colony formation. Inhibition of cell invasion by p19(Arf) was dependent on its C-terminal binding protein (CtBP) interaction domain but independent of Mdm2 binding and nucleolar localization. Indeed, RNA interference-mediated knockdown of CtBP1 or CtBP2 decreased cell invasion, and ectopic expression of CtBP2 enhanced tumor cell migration and invasion. Thus, our data indicate a novel role for the Arf tumor suppressor protein in regulating phenotypes associated with tumor progression and metastasis in HCC cells.
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Affiliation(s)
- Ya-Wen Chen
- Program in Gene Function and Expression, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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391
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The nucleolar SUMO-specific protease SENP3 reverses SUMO modification of nucleophosmin and is required for rRNA processing. EMBO Rep 2008; 9:273-9. [PMID: 18259216 DOI: 10.1038/embor.2008.3] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 12/21/2007] [Accepted: 12/31/2007] [Indexed: 01/10/2023] Open
Abstract
The ubiquitin-like SUMO system functions by a cyclic process of modification and demodification, and recent data suggest that the nucleolus is a site of sumoylation-desumoylation cycles. For example, the tumour suppressor ARF stimulates sumoylation of nucleolar proteins. Here, we show that the nucleolar SUMO-specific protease SENP3 is associated with nucleophosmin (NPM1), a crucial factor in ribosome biogenesis. SENP3 catalyses desumoylation of NPM1-SUMO2 conjugates in vitro and counteracts ARF-induced modification of NPM1 by SUMO2 in vivo. Intriguingly, depletion of SENP3 by short interfering RNA interferes with nucleolar ribosomal RNA processing and inhibits the conversion of the 32S rRNA species to the 28S form, thus phenocopying the processing defect observed on depletion of NPM1. Moreover, mimicking constitutive modification of NPM1 by SUMO2 interferes with 28S rRNA maturation. These results define SENP3 as an essential factor for ribosome biogenesis and suggest that deconjugation of SUMO2 from NPM1 by SENP3 is critically involved in 28S rRNA maturation.
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392
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hAda3 degradation by papillomavirus type 16 E6 correlates with abrogation of the p14ARF-p53 pathway and efficient immortalization of human mammary epithelial cells. J Virol 2008; 82:3912-20. [PMID: 18256148 DOI: 10.1128/jvi.02466-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Two activities of human papillomavirus type 16 E6 (HPV16 E6) are proposed to contribute to the efficient immortalization of human epithelial cells: the degradation of p53 protein and the induction of telomerase. However, the requirement for p53 inactivation has been debated. Another E6 target is the hAda3 protein, a p53 coactivator and a component of histone acetyltransferase complexes. We have previously described the role of hAda3 and p53 acetylation in p14ARF-induced human mammary epithelial cell (MEC) senescence (P. Sekaric, V. A. Shamanin, J. Luo, and E. J. Androphy, Oncogene 26:6261-6268, 2007). In this study, we analyzed a set of HPV16 E6 mutants for the ability to induce hAda3 degradation. E6 mutants that degrade hAda3 but not p53 could abrogate p14ARF-induced growth arrest despite the presence of normal levels of p53 and efficiently immortalized MECs. However, two E6 mutants that previously were reported to immortalize MECs with low efficiency were found to be defective for both p53 and hAda3 degradation. We found that these immortal MECs select for reduced p53 protein levels through a proteasome-dependent mechanism. The findings strongly imply that the inactivation of the p14ARF-p53 pathway, either by the E6-mediated degradation of p53 or hAda3 or by cellular adaptation, is required for MEC immortalization.
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393
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Abstract
The p53 tumor suppressor-signaling pathway is inactivated in most human cancers. Depending on how p53 is targeted during tumorigenesis impacts whether partial or full tumor suppressor activity is lost. The degree of remaining p53 activity, if any, intuitively impacts the tumor phenotype. This review focuses on recent findings from human cancer studies and genetically engineered mouse models to highlight a p53 functional "gradient effect" and its clinical implications.
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Affiliation(s)
- Gerard P Zambetti
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
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394
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Bouchard C, Lee S, Paulus-Hock V, Loddenkemper C, Eilers M, Schmitt CA. FoxO transcription factors suppress Myc-driven lymphomagenesis via direct activation of Arf. Genes Dev 2008; 21:2775-87. [PMID: 17974917 DOI: 10.1101/gad.453107] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
FoxO transcription factors play critical roles in cell cycle control and cellular stress responses, and abrogation of FoxO function promotes focus formation by Myc in vitro. Here we show that stable introduction of a dominant-negative FoxO moiety (dnFoxO) into Emu-myc transgenic hematopoietic stem cells accelerates lymphoma development in recipient mice by attenuating Myc-induced apoptosis. When expressed in Emu-myc; p53(+/-) progenitor cells, dnFoxO alleviates the pressure to inactivate the remaining p53 allele in upcoming lymphomas. Expression of the p53 upstream regulator p19(Arf) is virtually undetectable in most dnFoxO-positive Myc-driven lymphomas. We find that FoxO proteins bind to a distinct site within the Ink4a/Arf locus and activate Arf expression. Moreover, constitutive Myc signaling induces a marked increase in nuclear FoxO levels and stimulates binding of FoxO proteins to the Arf locus. These data demonstrate that FoxO factors mediate Myc-induced Arf expression and provide direct genetic evidence for their tumor-suppressive capacity.
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Affiliation(s)
- Caroline Bouchard
- Institute of Molecular Biology and Tumor Research, 35033 Marburg, Germany
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395
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Defect in Ser46 Phosphorylation of p53 Protein : A Resistance Mechanism against p53 Gene Transfer in Oral Squamous Cell Carcinoma Cells. J Oral Biosci 2008. [DOI: 10.1016/s1349-0079(08)80023-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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396
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A non-tumor suppressor role for basal p19ARF in maintaining nucleolar structure and function. Mol Cell Biol 2007; 28:1068-80. [PMID: 18070929 DOI: 10.1128/mcb.00484-07] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The nucleolus is the center of ribosome synthesis, with the nucleophosmin (NPM) and p19(ARF) proteins antagonizing one another to either promote or inhibit growth. However, basal NPM and ARF proteins form nucleolar complexes whose functions remain unknown. Nucleoli from Arf(-/)(-) cells displayed increased nucleolar area, suggesting that basal ARF might regulate key nucleolar functions. Concordantly, ribosome biogenesis and protein synthesis were dramatically elevated in the absence of Arf, causing these cells to exhibit tremendous gains in protein amounts and increases in cell volume. The transcription of ribosomal DNA (rDNA), the processing of nascent rRNA molecules, and the nuclear export of ribosomes were all increased in the absence of ARF. Similar results were obtained using targeted lentiviral RNA interference of ARF in wild-type MEFs. Postmitotic osteoclasts from Arf-null mice exhibited hyperactivity in vitro and in vivo, demonstrating a physiological function for basal ARF. Moreover, the knockdown of NPM blocked the increases in Arf(-/-) ribosome output and osteoclast activity, demonstrating that these gains require NPM. Thus, basal ARF proteins act as a monitor of steady-state ribosome biogenesis and growth independent of their ability to prevent unwarranted hyperproliferation.
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397
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Abstract
Chromosome instability, which is equated to mitotic defects and consequential chromosome segregation errors, provides a formidable basis for the acquisition of further malignant phenotypes during tumour progression. Centrosomes have a crucial role in the formation of bipolar mitotic spindles, which are essential for accurate chromosome segregation. Mutations of certain oncogenic and tumour-suppressor proteins directly induce chromosome instability by disrupting the normal function and numeral integrity of centrosomes. How these proteins control centrosome duplication and function, and how their mutational activation and/or inactivation results in numeral and functional centrosome abnormalities, is discussed in this Review.
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Affiliation(s)
- Kenji Fukasawa
- Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
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398
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Widlund HR, Fisher DE. Potent p53-independent tumor suppressor activity of ARF in melanoma-genesis. ACTA ACUST UNITED AC 2007; 20:339-40. [PMID: 17850505 DOI: 10.1111/j.1600-0749.2007.00401.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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399
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Di Micco R, Fumagalli M, d'Adda di Fagagna F. Breaking news: high-speed race ends in arrest--how oncogenes induce senescence. Trends Cell Biol 2007; 17:529-36. [PMID: 17980599 DOI: 10.1016/j.tcb.2007.07.012] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Revised: 07/27/2007] [Accepted: 07/27/2007] [Indexed: 12/30/2022]
Abstract
Oncogene activation in normal cells induces a permanent proliferative arrest known as cellular senescence. This phenomenon restrains the expansion of cells that bear an activated oncogene and acts as a powerful tumor-suppressive process. Although the full molecular mechanisms are still being elucidated, it has been observed recently that some oncogenes alter the DNA-replication process and cause DNA-damage accumulation. DNA-damage checkpoint-response activation together with the increased appearance of heterochromatin formation that leads to transcriptional silencing of proliferative genes are, presently, the two main mechanisms known that establish and maintain oncogene-induced senescence. Here, we discuss the most recent advancements in understanding the molecular and cellular mechanisms that control cellular senescence caused by oncogene activation and their impact on cancer studies.
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Affiliation(s)
- Raffaella Di Micco
- IFOM Foundation - FIRC Institute of Molecular Oncology Foundation, via Adamello 16, 20139 Milan, Italy
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400
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Garcia MA, Muñoz-Fontela C, Collado M, Marcos-Villar L, Esteban M, Rivas C. Novel and unexpected role for the tumor suppressor ARF in viral infection surveillance. Future Virol 2007. [DOI: 10.2217/17460794.2.6.625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Virus infection induces the synthesis of interferons which, in turn, stimulate the expression of hundreds of cellular genes, any of those denominated viral-stress-inducible genes. Among interferon-upregulated genes, also triggered by oncogenic viruses, several tumor-suppressor genes can also be listed. A correlation between the tumor suppressor alternative reading frame (ARF) and virus replication was noted some time ago. Yang and colleagues in 2001 demonstrated that p14ARF modulated the cytolytic effect of the E1B-deleted adenovirus ONYX-015 in mesothelioma cells with wild-type p53, and expression of p14ARF attenuated the cytolytic effect of the virus. Later, in 2006, Garcia and colleagues identified ARF as a gene product with a role in reducing the sensitivity of cells to infection by several viruses, showing an inverse relationship between doses of ARF and levels of virus replication. Additionally, the same authors presented a number of experiments designed to illustrate the molecular mechanisms underlying the decrease of virus replication upon ARF overexpression, demonstrating a p53-independent ARF function. ARF is the latest tumor suppressor added to the list of the cellular genes upregulated by type I interferon that possesses antiviral activity. The antiviral role of other tumor suppressor pathways targeted by both interferons and oncogenic viruses requires further investigation.
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Affiliation(s)
- Maria Angel Garcia
- Centro Nacional de Biotecnología CSIC, Campus Universidad Autónoma, Madrid 28049, Spain
| | - Cesar Muñoz-Fontela
- Mount Sinai School of Medicine, Dept of Oncological Sciences, One Gustave L. Levy Place. Box 1130, NY 10029, USA
| | - Manuel Collado
- Spanish National Cancer Centre (CNIO), 3 Melchor Fernández Almagro, Madrid 28029, Spain
| | - Laura Marcos-Villar
- Universidad Complutense de Madrid, Departamento de Microbiología II, Plaza Ramón y Cajal s/n, Madrid 28040, Spain
| | - Mariano Esteban
- Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma, Madrid 28049, Spain
| | - Carmen Rivas
- Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma, Madrid 28049, Spain
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