1
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Huang X, Wang B, Shen H, Huang D, Shi G. Farnesoid X receptor functions in cervical cancer via the p14 ARF-mouse double minute 2-p53 pathway. Mol Biol Rep 2022; 49:3617-3625. [PMID: 35347542 PMCID: PMC9174312 DOI: 10.1007/s11033-022-07201-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Accepted: 01/25/2022] [Indexed: 02/05/2023]
Abstract
BACKGROUND Cervical cancer is the second most common cancer among women living in developing countries. Farnesoid X receptor (FXR) is a member of the nuclear receptor family, which regulates the development and proliferation of cancer. However, the role of and molecular mechanism by which FXR acts in cervical cancer are still unknown. METHODS AND RESULTS The relationship between FXR and the proliferation of cervical cancer cell lines was detected by MTT and colony formation assays. Immunohistochemistry was used to detect the expression of FXR in cervical cancer tissue slides. Western blotting was used to detect the expression of p14ARF, mouse double minute 2 (MDM2) and p53 when FXR was overexpressed or siRNA was applied. Western blotting was used to detect the expression of MDM2 and p53 when pifithrin-α (PFT-α) was applied. FXR activation inhibited the proliferation of cervical cancer cell lines. FXR was significantly decreased in cervical squamous cell carcinoma, which was correlated with TNM stage, but not with metastasis. Overexpression of FXR activated the p14ARF-MDM2-p53 pathway. As a p53 inhibitor, PFT-α increased MDM2 in Lenti-vector cells, but had no effect on MDM2 in Lenti-FXR cells. CONCLUSIONS FXR inhibits cervical cancer by upregulating the p14ARF-MDM2-p53 pathway. Activation of FXR may be a potential strategy for the treatment of cervical cancer.
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Affiliation(s)
- Xiaohua Huang
- Department of Pediatrics, Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Bin Wang
- Department of Pharmacology, Shantou University Medical College, Shantou, China
| | - Huimin Shen
- Department of Neurology, Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Danmei Huang
- Department of Pharmacology, Shantou University Medical College, Shantou, China
| | - Ganggang Shi
- Department of Pharmacology, Shantou University Medical College, Shantou, China
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2
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Kung CP, Weber JD. It’s Getting Complicated—A Fresh Look at p53-MDM2-ARF Triangle in Tumorigenesis and Cancer Therapy. Front Cell Dev Biol 2022; 10:818744. [PMID: 35155432 PMCID: PMC8833255 DOI: 10.3389/fcell.2022.818744] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 01/07/2022] [Indexed: 01/31/2023] Open
Abstract
Anti-tumorigenic mechanisms mediated by the tumor suppressor p53, upon oncogenic stresses, are our bodies’ greatest weapons to battle against cancer onset and development. Consequently, factors that possess significant p53-regulating activities have been subjects of serious interest from the cancer research community. Among them, MDM2 and ARF are considered the most influential p53 regulators due to their abilities to inhibit and activate p53 functions, respectively. MDM2 inhibits p53 by promoting ubiquitination and proteasome-mediated degradation of p53, while ARF activates p53 by physically interacting with MDM2 to block its access to p53. This conventional understanding of p53-MDM2-ARF functional triangle have guided the direction of p53 research, as well as the development of p53-based therapeutic strategies for the last 30 years. Our increasing knowledge of this triangle during this time, especially through identification of p53-independent functions of MDM2 and ARF, have uncovered many under-appreciated molecular mechanisms connecting these three proteins. Through recognizing both antagonizing and synergizing relationships among them, our consideration for harnessing these relationships to develop effective cancer therapies needs an update accordingly. In this review, we will re-visit the conventional wisdom regarding p53-MDM2-ARF tumor-regulating mechanisms, highlight impactful studies contributing to the modern look of their relationships, and summarize ongoing efforts to target this pathway for effective cancer treatments. A refreshed appreciation of p53-MDM2-ARF network can bring innovative approaches to develop new generations of genetically-informed and clinically-effective cancer therapies.
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Affiliation(s)
- Che-Pei Kung
- ICCE Institute, St. Louis, MO, United States
- Division of Molecular Oncology, Department of Medicine, St. Louis, MO, United States
- *Correspondence: Che-Pei Kung, ; Jason D. Weber,
| | - Jason D. Weber
- ICCE Institute, St. Louis, MO, United States
- Division of Molecular Oncology, Department of Medicine, St. Louis, MO, United States
- Alvin J. Siteman Cancer Center, Washington University School of Medicine, St. Louis, MO, United States
- *Correspondence: Che-Pei Kung, ; Jason D. Weber,
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3
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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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4
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Umesalma S, Kaemmer CA, Kohlmeyer JL, Letney B, Schab AM, Reilly JA, Sheehy RM, Hagen J, Tiwari N, Zhan F, Leidinger MR, O'Dorisio TM, Dillon J, Merrill RA, Meyerholz DK, Perl AL, Brown BJ, Braun TA, Scott AT, Ginader T, Taghiyev AF, Zamba GK, Howe JR, Strack S, Bellizzi AM, Narla G, Darbro BW, Quelle FW, Quelle DE. RABL6A inhibits tumor-suppressive PP2A/AKT signaling to drive pancreatic neuroendocrine tumor growth. J Clin Invest 2019; 129:1641-1653. [PMID: 30721156 DOI: 10.1172/jci123049] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 01/24/2019] [Indexed: 12/15/2022] Open
Abstract
Hyperactivated AKT/mTOR signaling is a hallmark of pancreatic neuroendocrine tumors (PNETs). Drugs targeting this pathway are used clinically, but tumor resistance invariably develops. A better understanding of factors regulating AKT/mTOR signaling and PNET pathogenesis is needed to improve current therapies. We discovered that RABL6A, a new oncogenic driver of PNET proliferation, is required for AKT activity. Silencing RABL6A caused PNET cell-cycle arrest that coincided with selective loss of AKT-S473 (not T308) phosphorylation and AKT/mTOR inactivation. Restoration of AKT phosphorylation rescued the G1 phase block triggered by RABL6A silencing. Mechanistically, loss of AKT-S473 phosphorylation in RABL6A-depleted cells was the result of increased protein phosphatase 2A (PP2A) activity. Inhibition of PP2A restored phosphorylation of AKT-S473 in RABL6A-depleted cells, whereas PP2A reactivation using a specific small-molecule activator of PP2A (SMAP) abolished that phosphorylation. Moreover, SMAP treatment effectively killed PNET cells in a RABL6A-dependent manner and suppressed PNET growth in vivo. The present work identifies RABL6A as a new inhibitor of the PP2A tumor suppressor and an essential activator of AKT in PNET cells. Our findings offer what we believe is a novel strategy of PP2A reactivation for treatment of PNETs as well as other human cancers driven by RABL6A overexpression and PP2A inactivation.
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Affiliation(s)
| | | | | | | | | | | | - Ryan M Sheehy
- Department of Pharmacology.,Free Radical & Radiation Biology Training Program
| | | | | | | | - Mariah R Leidinger
- Department of Pathology, in the College of Medicine, Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa, USA
| | | | | | | | - David K Meyerholz
- Department of Pathology, in the College of Medicine, Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa, USA
| | - Abbey L Perl
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
| | | | | | | | | | - Agshin F Taghiyev
- Pediatrics, Colleges of Medicine, Engineering, or Public Health, University of Iowa, Iowa City, Iowa, USA
| | | | | | | | - Andrew M Bellizzi
- Department of Pathology, in the College of Medicine, Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa, USA
| | - Goutham Narla
- Department of Medicine, University of Michigan, Ann Arbor, Michigan, USA
| | - Benjamin W Darbro
- Pediatrics, Colleges of Medicine, Engineering, or Public Health, University of Iowa, Iowa City, Iowa, USA
| | | | - Dawn E Quelle
- Department of Pharmacology.,Molecular Medicine Graduate Program.,Free Radical & Radiation Biology Training Program.,Department of Pathology, in the College of Medicine, Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa, USA
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5
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Fontana R, Ranieri M, La Mantia G, Vivo M. Dual Role of the Alternative Reading Frame ARF Protein in Cancer. Biomolecules 2019; 9:E87. [PMID: 30836703 PMCID: PMC6468759 DOI: 10.3390/biom9030087] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 02/20/2019] [Accepted: 02/22/2019] [Indexed: 02/07/2023] Open
Abstract
The CDKN2a/ARF locus expresses two partially overlapping transcripts that encode two distinct proteins, namely p14ARF (p19Arf in mouse) and p16INK4a, which present no sequence identity. Initial data obtained in mice showed that both proteins are potent tumor suppressors. In line with a tumor-suppressive role, ARF-deficient mice develop lymphomas, sarcomas, and adenocarcinomas, with a median survival rate of one year of age. In humans, the importance of ARF inactivation in cancer is less clear whereas a more obvious role has been documented for p16INK4a. Indeed, many alterations in human tumors result in the elimination of the entire locus, while the majority of point mutations affect p16INK4a. Nevertheless, specific mutations of p14ARF have been described in different types of human cancers such as colorectal and gastric carcinomas, melanoma and glioblastoma. The activity of the tumor suppressor ARF has been shown to rely on both p53-dependent and independent functions. However, novel data collected in the last years has challenged the traditional and established role of this protein as a tumor suppressor. In particular, tumors retaining ARF expression evolve to metastatic and invasive phenotypes and in humans are associated with a poor prognosis. In this review, the recent evidence and the molecular mechanisms of a novel role played by ARF will be presented and discussed, both in pathological and physiological contexts.
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Affiliation(s)
- Rosa Fontana
- Department of Pharmacology, Moores Cancer Center, University of California, San Diego, La Jolla, CA 92093, USA.
| | - Michela Ranieri
- Division of Hematology and Medical Oncology, Laura and Isaac Perlmutter Cancer Center, NYU Langone Medical Center, New York, NY 10016, USA.
| | - Girolama La Mantia
- Department of Biology, University of Naples Federico II, 80126 Naples, Italy.
| | - Maria Vivo
- Department of Biology, University of Naples Federico II, 80126 Naples, Italy.
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6
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Stępiński D. Nucleolus-derived mediators in oncogenic stress response and activation of p53-dependent pathways. Histochem Cell Biol 2016; 146:119-39. [PMID: 27142852 DOI: 10.1007/s00418-016-1443-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2016] [Indexed: 12/12/2022]
Abstract
Rapid growth and division of cells, including tumor ones, is correlated with intensive protein biosynthesis. The output of nucleoli, organelles where translational machineries are formed, depends on a rate of particular stages of ribosome production and on accessibility of elements crucial for their effective functioning, including substrates, enzymes as well as energy resources. Different factors that induce cellular stress also often lead to nucleolar dysfunction which results in ribosome biogenesis impairment. Such nucleolar disorders, called nucleolar or ribosomal stress, usually affect cellular functioning which in fact is a result of p53-dependent pathway activation, elicited as a response to stress. These pathways direct cells to new destinations such as cell cycle arrest, damage repair, differentiation, autophagy, programmed cell death or aging. In the case of impaired nucleolar functioning, nucleolar and ribosomal proteins mediate activation of the p53 pathways. They are also triggered as a response to oncogenic factor overexpression to protect tissues and organs against extensive proliferation of abnormal cells. Intentional impairment of any step of ribosome biosynthesis which would direct the cells to these destinations could be a strategy used in anticancer therapy. This review presents current knowledge on a nucleolus, mainly in relation to cancer biology, which is an important and extremely sensitive element of the mechanism participating in cellular stress reaction mediating activation of the p53 pathways in order to counteract stress effects, especially cancer development.
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Affiliation(s)
- Dariusz Stępiński
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland.
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7
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Vivo M, Matarese M, Sepe M, Di Martino R, Festa L, Calabrò V, Mantia GL, Pollice A. MDM2-mediated degradation of p14ARF: a novel mechanism to control ARF levels in cancer cells. PLoS One 2015; 10:e0117252. [PMID: 25723571 PMCID: PMC4344200 DOI: 10.1371/journal.pone.0117252] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Accepted: 12/19/2014] [Indexed: 01/22/2023] Open
Abstract
We here show a new relationship between the human p14ARF oncosuppressor and the MDM2 oncoprotein. MDM2 overexpression in various cancer cell lines causes p14ARF reduction inducing its degradation through the proteasome. The effect does not require the ubiquitin ligase activity of MDM2 and preferentially occurs in the cytoplasm. Interestingly, treatment with inhibitors of the PKC (Protein Kinase C) pathway and use of p14ARF phosphorylation mutants indicate that ARF phosphorylation could play a role in MDM2 mediated ARF degradation reinforcing our previous observations that ARF phosphorylation influences its stability and biological activity. Our study uncovers a new potentially important mechanism through which ARF and MDM2 can counterbalance each other during the tumorigenic process.
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Affiliation(s)
- Maria Vivo
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
| | - Maria Matarese
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
- Istituto di Genetica e Biofisica (IGB)—Consiglio Nazionale delle Ricerche (CNR), Naples, Italy
| | - Maria Sepe
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
- Dipartimento di Medicina Molecolare e Biotecnologie Mediche- Università di Napoli Federico II, Naples, Italy
| | - Rosaria Di Martino
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
- Istituto di Biochimica delle Proteine (IBP)—Consiglio Nazionale delle Ricerche (CNR), Naples, Italy
| | - Luisa Festa
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
- Diagnostica e Farmaceutica Molecolare- Consiglio Nazionale delle Ricerche (CNR), Naples, Italy
| | - Viola Calabrò
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
| | - Girolama La Mantia
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
| | - Alessandra Pollice
- Dipartimento di Biologia, Università di Napoli Federico II, Naples, Italy
- * E-mail:
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8
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Hagen J, Muniz VP, Falls KC, Reed SM, Taghiyev AF, Quelle FW, Gourronc FA, Klingelhutz AJ, Major HJ, Askeland RW, Sherman SK, O'Dorisio TM, Bellizzi AM, Howe JR, Darbro BW, Quelle DE. RABL6A promotes G1-S phase progression and pancreatic neuroendocrine tumor cell proliferation in an Rb1-dependent manner. Cancer Res 2014; 74:6661-70. [PMID: 25273089 DOI: 10.1158/0008-5472.can-13-3742] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Mechanisms of neuroendocrine tumor (NET) proliferation are poorly understood, and therapies that effectively control NET progression and metastatic disease are limited. We found amplification of a putative oncogene, RABL6A, in primary human pancreatic NETs (PNET) that correlated with high-level RABL6A protein expression. Consistent with those results, stable silencing of RABL6A in cultured BON-1 PNET cells revealed that it is essential for their proliferation and survival. Cells lacking RABL6A predominantly arrested in G1 phase with a moderate mitotic block. Pathway analysis of microarray data suggested activation of the p53 and retinoblastoma (Rb1) tumor-suppressor pathways in the arrested cells. Loss of p53 had no effect on the RABL6A knockdown phenotype, indicating that RABL6A functions independent of p53 in this setting. By comparison, Rb1 inactivation partially restored G1 to S phase progression in RABL6A-knockdown cells, although it was insufficient to override the mitotic arrest and cell death caused by RABL6A loss. Thus, RABL6A promotes G1 progression in PNET cells by inactivating Rb1, an established suppressor of PNET proliferation and development. This work identifies RABL6A as a novel negative regulator of Rb1 that is essential for PNET proliferation and survival. We suggest RABL6A is a new potential biomarker and target for anticancer therapy in PNET patients.
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Affiliation(s)
- Jussara Hagen
- Department of Pharmacology, University of Iowa, Iowa City, Iowa
| | - Viviane P Muniz
- Department of Pharmacology, University of Iowa, Iowa City, Iowa. Molecular and Cellular Biology Graduate Program, University of Iowa, Iowa City, Iowa
| | - Kelly C Falls
- Medical Scientist Training Program, University of Iowa, Iowa City, Iowa
| | - Sara M Reed
- Department of Pharmacology, University of Iowa, Iowa City, Iowa. Medical Scientist Training Program, University of Iowa, Iowa City, Iowa
| | - Agshin F Taghiyev
- Department of Pediatrics, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Frederick W Quelle
- Department of Pharmacology, University of Iowa, Iowa City, Iowa. The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa
| | - Francoise A Gourronc
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Aloysius J Klingelhutz
- Molecular and Cellular Biology Graduate Program, University of Iowa, Iowa City, Iowa. The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa. Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Heather J Major
- Department of Pediatrics, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Ryan W Askeland
- Department of Pathology, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Scott K Sherman
- Department of Surgery, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Thomas M O'Dorisio
- The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa. Department of Internal Medicine, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Andrew M Bellizzi
- The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa. Department of Pathology, College of Medicine, University of Iowa, Iowa City, Iowa
| | - James R Howe
- The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa. Department of Surgery, College of Medicine, University of Iowa, Iowa City, Iowa
| | - Benjamin W Darbro
- Department of Pediatrics, College of Medicine, University of Iowa, Iowa City, Iowa. The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa
| | - Dawn E Quelle
- Department of Pharmacology, University of Iowa, Iowa City, Iowa. Molecular and Cellular Biology Graduate Program, University of Iowa, Iowa City, Iowa. Medical Scientist Training Program, University of Iowa, Iowa City, Iowa. The Holden Comprehensive Cancer Center, University of Iowa, Iowa City, Iowa. Department of Pathology, College of Medicine, University of Iowa, Iowa City, Iowa.
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9
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Britigan EMC, Wan J, Zasadil LM, Ryan SD, Weaver BA. The ARF tumor suppressor prevents chromosomal instability and ensures mitotic checkpoint fidelity through regulation of Aurora B. Mol Biol Cell 2014; 25:2761-73. [PMID: 25057018 PMCID: PMC4161511 DOI: 10.1091/mbc.e14-05-0966] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The ARF tumor suppressor is best known for its role in stabilizing p53. This study identifies p53-independent functions of ARF in chromosome segregation and the mitotic checkpoint. Mitotic defects caused by loss of ARF are recapitulated by Aurora B overexpression and rescued by partial depletion of Aurora B. The ARF tumor suppressor is part of the CDKN2A locus and is mutated or undetectable in numerous cancers. The best-characterized role for ARF is in stabilizing p53 in response to cellular stress. However, ARF has tumor suppressive functions outside this pathway that have not been fully defined. Primary mouse embryonic fibroblasts (MEFs) lacking the ARF tumor suppressor contain abnormal numbers of chromosomes. However, no role for ARF in cell division has previously been proposed. Here we demonstrate a novel, p53-independent role for ARF in the mitotic checkpoint. Consistent with this, loss of ARF results in aneuploidy in vitro and in vivo. ARF−/− MEFs exhibit mitotic defects including misaligned and lagging chromosomes, multipolar spindles, and increased tetraploidy. ARF−/− cells exhibit overexpression of Mad2, BubR1, and Aurora B, but only overexpression of Aurora B phenocopies mitotic defects observed in ARF−/− MEFs. Restoring Aurora B to near-normal levels rescues mitotic phenotypes in cells lacking ARF. Our results define an unexpected role for ARF in chromosome segregation and mitotic checkpoint function. They further establish maintenance of chromosomal stability as one of the additional tumor-suppressive functions of ARF and offer a molecular explanation for the common up-regulation of Aurora B in human cancers.
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Affiliation(s)
- Eric M C Britigan
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53705 Molecular and Cellular Pharmacology Training Program, University of Wisconsin, Madison, WI 53705
| | - Jun Wan
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53705 Physiology Training Program, University of Wisconsin, Madison, WI 53705
| | - Lauren M Zasadil
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53705 Molecular and Cellular Pharmacology Training Program, University of Wisconsin, Madison, WI 53705
| | - Sean D Ryan
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53705
| | - Beth A Weaver
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53705 Carbone Cancer Center, University of Wisconsin, Madison, WI 53705
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10
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Wang Y, Huang JW, Castella M, Huntsman DG, Taniguchi T. p53 is positively regulated by miR-542-3p. Cancer Res 2014; 74:3218-27. [PMID: 24762395 DOI: 10.1158/0008-5472.can-13-1706] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The tumor suppressor p53 and miRNAs are linked through a complex network. Several miRNAs modulate p53 expression, while p53 regulates the transcription and/or biogenesis of several other miRNAs. Here, we report the development of a cell-based assay used with a library of human miRNA mimics in a high-throughput screen for miRNAs that modulate p53 expression. Overexpression of miRNA (miR)-542-3p in cancer cells elevated p53 expression, stimulated the expression of p53 targets, and inhibited cell proliferation. Mechanistically, miR-542-3p increased p53 protein stability by weakening interactions between p53 and its negative regulator MDM2. Furthermore, miR-542-3p suppressed ribosome biogenesis by downregulating a subset of ribosomal proteins such as RPS23, leading to upregulation of RPL11 and stabilization of p53. The 3'untranslated region in the RPS23 transcript contained a miR-542-3p-binding site, suggesting that RPS23 is a direct target of miR-542-3p. Our results define miR-542-3p as an important new positive regulator of p53 with potential applications in cancer treatment.
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Affiliation(s)
- Yemin Wang
- Authors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, CanadaAuthors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, Canada
| | - Jen-Wei Huang
- Authors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, CanadaAuthors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, Canada
| | - Maria Castella
- Authors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, Canada
| | - David George Huntsman
- Authors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, Canada
| | - Toshiyasu Taniguchi
- Authors' Affiliations: Divisions of Human Biology and Public Health Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center; Molecular & Cellular Biology Program, University of Washington, Seattle, Washington; and Department of Pathology and Laboratory Medicine, Center for Translational and Applied Genomics, British Columbia Cancer Agency, University of British Columbia, Vancouver BC, Canada
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11
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Zhang X, Hagen J, Muniz VP, Smith T, Coombs GS, Eischen CM, Mackie DI, Roman DL, Van Rheeden R, Darbro B, Tompkins VS, Quelle DE. RABL6A, a novel RAB-like protein, controls centrosome amplification and chromosome instability in primary fibroblasts. PLoS One 2013; 8:e80228. [PMID: 24282525 PMCID: PMC3839920 DOI: 10.1371/journal.pone.0080228] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 10/01/2013] [Indexed: 12/18/2022] Open
Abstract
RABL6A (RAB-like 6 isoform A) is a novel protein that was originally identified based on its association with the Alternative Reading Frame (ARF) tumor suppressor. ARF acts through multiple p53-dependent and p53-independent pathways to prevent cancer. How RABL6A functions, to what extent it depends on ARF and p53 activity, and its importance in normal cell biology are entirely unknown. We examined the biological consequences of RABL6A silencing in primary mouse embryo fibroblasts (MEFs) that express or lack ARF, p53 or both proteins. We found that RABL6A depletion caused centrosome amplification, aneuploidy and multinucleation in MEFs regardless of ARF and p53 status. The centrosome amplification in RABL6A depleted p53−/− MEFs resulted from centrosome reduplication via Cdk2-mediated hyperphosphorylation of nucleophosmin (NPM) at threonine-199. Thus, RABL6A prevents centrosome amplification through an ARF/p53-independent mechanism that restricts NPM-T199 phosphorylation. These findings demonstrate an essential role for RABL6A in centrosome regulation and maintenance of chromosome stability in non-transformed cells, key processes that ensure genomic integrity and prevent tumorigenesis.
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Affiliation(s)
- Xuefeng Zhang
- Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America
| | - Jussara Hagen
- Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America
| | - Viviane P. Muniz
- The Molecular and Cellular Biology Graduate Program, University of Iowa, Iowa City, Iowa, United States of America
| | - Tarik Smith
- Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America
| | - Gary S. Coombs
- Department of Biology, Waldorf College, Forest City, Iowa, United States of America
| | - Christine M. Eischen
- Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America
| | - Duncan I. Mackie
- Division of Medicinal and Natural Products Chemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - David L. Roman
- Division of Medicinal and Natural Products Chemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Richard Van Rheeden
- Department of Pediatrics, University of Iowa, Iowa City, Iowa, United States of America
| | - Benjamin Darbro
- Department of Pediatrics, University of Iowa, Iowa City, Iowa, United States of America
| | - Van S. Tompkins
- Department of Pathology, University of Iowa, Iowa City, Iowa, United States of America
| | - Dawn E. Quelle
- Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America
- The Molecular and Cellular Biology Graduate Program, University of Iowa, Iowa City, Iowa, United States of America
- Department of Pathology, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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12
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Down-regulation of c9orf86 in human breast cancer cells inhibits cell proliferation, invasion and tumor growth and correlates with survival of breast cancer patients. PLoS One 2013; 8:e71764. [PMID: 23977139 PMCID: PMC3743754 DOI: 10.1371/journal.pone.0071764] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2011] [Accepted: 07/06/2013] [Indexed: 11/29/2022] Open
Abstract
C9orf86 which is a novel subfamily within the Ras superfamily of GTPases, is overexpressed in the majority of primary breast tumors. Few functional studies have focused on the C9orf86 protein; therefore, in this study, we explored the role of C9orf86 in breast carcinogenesis. In our study, we found that silencing of C9orf86 by siRNA in MCF-7 and SK-BR-3 cells resulted in suppressed cell proliferation as well as in vitro cell invasion capabilities. Moreover, knockdown of C9orf86 inhibited tumor growth in nude mice. Cell cycle and apoptotic assays showed that the anti-proliferative effect of C9orf86-siRNA was mediated by arresting cells in the G1 phase and promoting apoptosis. In addition, we found that patients with high levels of C9orf86 expression showed a significant trend towards worse survival compared to patients with low C9orf86 expression (P = 0.002). These results provide evidence that C9orf86 represents a novel and clinically useful biomarker for BC patients and plays an important role during the progression of BC.
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Milojkovic A, Hemmati PG, Müer A, Overkamp T, Chumduri C, Jänicke RU, Gillissen B, Daniel PT. p14ARF induces apoptosis via an entirely caspase-3-dependent mitochondrial amplification loop. Int J Cancer 2013; 133:2551-62. [PMID: 23686572 DOI: 10.1002/ijc.28279] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 02/28/2013] [Indexed: 11/12/2022]
Abstract
The p14(ARF) tumor suppressor triggers cell death or cell cycle arrest upon oncogenic stress. In MCF-7 breast carcinoma cells, expression of the tumor suppressor gene p14(ARF) fails to trigger apoptosis but induces an arrest in the G1 and, to a lesser extent, in the G2 phase in the cell division cycle. Here, inhibition of cell cycle arrest resulted in apoptosis induction in caspase-3 proficient MCF-7 cells upon expression of p14(ARF) . This occurred in the absence of S-phase progression or mitotic entry. In contrast, syngeneic, caspase-3-deficient MCF-7 cells remained entirely resistant to p14(ARF) -induced apoptosis. Thus, cell cycle checkpoint abrogation overcomes resistance to p14(ARF) -induced cell death and promotes cell death via a caspase-3-dependent pathway. Cell death coincided with dissipation of the mitochondrial membrane potential, release of cytochrome c, and was inhibitable by pan-caspase inhibitors and the caspase-3/7 inhibitor zDEVD-fmk. Of note, mitochondrial events of apoptosis execution depended entirely on caspase-3 proficiency indicating that caspase-3 either acts "up-stream" of the mitochondria in a "non-canonical" pathway or mediates a mitochondrial feedback loop to amplify the apoptotic caspase signal in p14(ARF) -induced stress signaling.
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Affiliation(s)
- Ana Milojkovic
- Clinical and Molecular Oncology, Max Delbrück Centrum für Molekulare Medizin, Berlin-Buch, Germany
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Vivo M, Ranieri M, Sansone F, Santoriello C, Calogero RA, Calabrò V, Pollice A, La Mantia G. Mimicking p14ARF phosphorylation influences its ability to restrain cell proliferation. PLoS One 2013; 8:e53631. [PMID: 23308265 PMCID: PMC3538741 DOI: 10.1371/journal.pone.0053631] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Accepted: 12/03/2012] [Indexed: 11/29/2022] Open
Abstract
The INK4a/ARF locus on the short arm of chromosome 9 is one of the most frequently altered loci in human cancer. It is generally accepted that ARF is involved in oncogenic checkpoint pathways by sensitizing incipient cancer cells to undergo growth arrest or apoptosis through both p53-dependent and independent pathways. While intensive studies have been focused on ARF activation at the transcriptional level, only recently mechanisms governing ARF turnover have been identified. Here, we show for the first time that p14ARF is a PKC target. Prediction analysis showed many potential phosphorylation sites in PKC consensus sequences within ARF protein, and, among them, the threonine at position 8 was the most conserved. Substitution of this threonine influences both ARF stability and localization. Furthermore, a phosphomimetic ARF mutation reduces the ability to arrest cell growth although the ability to bind MDM2 and stabilize p53 result unaffected. Thus we propose that phosphorylation of ARF in both immortalized and tumor cell lines could be a mechanism to escape ARF surveillance following proliferative and oncogenic stress.
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Affiliation(s)
- Maria Vivo
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
- * E-mail: (MV); (GLM)
| | - Michela Ranieri
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
| | - Federica Sansone
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
| | - Cristina Santoriello
- Harvard Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | | | - Viola Calabrò
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
| | - Alessandra Pollice
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
| | - Girolama La Mantia
- Department of Structural and Functional Biology, University of Naples “Federico II”, Naples, Italy
- * E-mail: (MV); (GLM)
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15
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Li Z, Hou J, Sun L, Wen T, Wang L, Zhao X, Xie Q, Zhang SQ. NMI mediates transcription-independent ARF regulation in response to cellular stresses. Mol Biol Cell 2012; 23:4635-46. [PMID: 23034180 PMCID: PMC3510024 DOI: 10.1091/mbc.e12-04-0304] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
ETOC: NMI is a novel ARF-interacting protein identified in a yeast two-hybrid screen. NMI inhibits ULF-induced ubiquitin degradation of ARF protein. It mediates transcription-independent ARF regulation and is required for the stabilization and up-regulation of ARF in response to cellular stresses. The ARF tumor suppressor is a product of the INK4a/ARF locus, which is frequently mutated in human cancer. The expression of ARF is up-regulated in response to certain types of DNA damage, oncogene activation, and interferon stimuli. Through interaction with the p53 negative regulator MDM2, ARF controls a well-described p53/MDM2-dependent checkpoint. However, the mechanism of ARF induction is poorly understood. Using a yeast two-hybrid screen, we identify a novel ARF-interacting protein, N-Myc and STATs interactor (NMI). Previously, NMI was known to be a c-Myc–interacting protein. Here we demonstrate that through competitive binding to the ARF ubiquitin E3 ligase (ubiquitin ligase for ARF [ULF]), NMI protects ARF from ULF-mediated ubiquitin degradation. In response to cellular stresses, NMI is induced, and a fraction of NMI is translocated to the nucleus to stabilize ARF. Thus our work reveals a novel NMI-mediated, transcription-independent ARF induction pathway in response to cellular stresses.
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Affiliation(s)
- Zengpeng Li
- State Key Laboratory of Cellular Stress Biology and School of Life Sciences, Xiamen University, Xiamen, Fujian 361005, China
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16
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Nucleophosmin is essential for c-Myc nucleolar localization and c-Myc-mediated rDNA transcription. Oncogene 2012; 32:1988-94. [PMID: 22665062 DOI: 10.1038/onc.2012.227] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The transcription factor c-Myc has a critical role in cell proliferation and growth. The control of ribosome biogenesis by c-Myc through the regulation of transcription mediated by all three RNA polymerases is essential for c-Myc-driven proliferation. Specifically, in the nucleolus, c-Myc has been shown to be recruited to ribosomal DNA and activate RNA polymerase (pol) I-mediated transcription of ribosomal RNA (rRNA) genes. In addition, c-Myc accumulates in nucleoli upon inhibition of the proteasome, suggesting nucleolar localization also has a role in c-Myc proteolysis. Nucleophosmin (NPM), a predominantly nucleolar protein, is also critical in ribosome biogenesis and, like c-Myc, is found overexpressed in many types of tumors. Previously, we demonstrated that NPM directly interacts with c-Myc and controls c-Myc-induced hyperproliferation and transformation. Here, we show that NPM is necessary for the localization of c-Myc protein to nucleoli, whereas c-Myc nucleolar localization is independent of p53, Mdm2 and ARF. Conversely, high transient NPM expression enhances c-Myc nucleolar localization, leading to increased c-Myc proteolysis. In addition, NPM is necessary for the ability of c-Myc to induce rRNA synthesis in the nucleolus, and constitutive NPM overexpression stimulates c-Myc-mediated rRNA synthesis. Taken together, these results demonstrate an essential role for NPM in c-Myc nucleolar localization and c-Myc-mediated rDNA transcription.
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17
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Chen G, Ghosh P, O'Farrell T, Munk R, Rezanka LJ, Sasaki CY, Longo DL. Transforming growth factor β1 (TGF-β1) suppresses growth of B-cell lymphoma cells by p14(ARF)-dependent regulation of mutant p53. J Biol Chem 2012; 287:23184-95. [PMID: 22621932 DOI: 10.1074/jbc.m112.351411] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Previously we reported that TGF-β1-induced growth suppression was associated with a decrease in mutant p53 levels in B-cell lymphoma cells. The goal of the present study was to understand the mechanism involved in TGF-β1-mediated down-regulation of mutant p53. In RL and CA46, two B-cell lymphoma cell lines, TGF-β1 treatment caused down-regulation of E2F-1 transcription factor resulting in the down-regulation of both p14(ARF) and mutant p53, leading to growth arrest. Experimental overexpression of E2F-1 increased p14(ARF) level and blocked TGF-β1-induced down-regulation of p14(ARF). Overexpression of p14(ARF) blocked the down-regulation of mutant p53 and prevented growth arrest. p14(ARF) also attenuated TGF-β1-induced p21(Cip1/WAF1) induction, which was reversible by p53 siRNA, indicating the involvement of mutant p53 in controlling the TGF-β1-induced expression of p21(Cip1/WAF1). The interaction observed between phospho-Smad2 and mutant p53 in the nucleus could be the mechanism responsible for blocking the growth-suppressive effects of TGF-β1. In RL cells, p14(ARF) is present in a trimer consisting of mutant p53-Mdm2-p14(ARF) and in a dimer consisting of Mdm2-p14(ARF). Because it is known that Mdm2 can degrade p53, it is possible that, in its trimeric form, p14(ARF) is able to stabilize mutant p53 by inhibiting Mdm2. In its dimeric form, p14(ARF) may be sequestering Mdm2, limiting its ability to degrade p53. Collectively, these data demonstrate a unique mechanism in which the inhibition of TGF-β1-mediated growth suppression by mutant p53 can be reversed by the down-regulation of its stabilizing protein p14(ARF). This work suggests that the high levels of p14(ARF) often found in tumor cells could be a potential therapeutic target.
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Affiliation(s)
- Gang Chen
- Lymphocyte Cell Biology Unit, Laboratory of Molecular Biology and Immunology, Intramural Research Program, NIA, National Institutes of Health, Baltimore, Maryland 21224, USA
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18
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Suh YA, Post SM, Elizondo-Fraire AC, Maccio DR, Jackson JG, El-Naggar AK, Van Pelt C, Terzian T, Lozano G. Multiple stress signals activate mutant p53 in vivo. Cancer Res 2011; 71:7168-75. [PMID: 21983037 DOI: 10.1158/0008-5472.can-11-0459] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
p53 levels are tightly regulated in normal cells, and thus, the wild-type p53 protein is nearly undetectable until stimulated through a variety of stresses. In response to stress, p53 is released from its negative regulators, mainly murine double minute 2 (Mdm2), allowing p53 to be stabilized to activate cell-cycle arrest, senescence, and apoptosis programs. Many of the upstream signals that regulate wild-type p53 are known; however, limited information for the regulation of mutant p53 exists. Previously, we showed that wild-type and mutant p53R172H are regulated in a similar manner in the absence of Mdm2 or p16. In addition, this stabilization of mutant p53 is responsible for the gain-of-function metastatic phenotype observed in the mouse. In this report, we examined the role of oncogenes, DNA damage, and reactive oxygen species, signals that stabilize wild-type p53, on the stabilization of mutant p53 in vivo and the consequences of this expression on tumor formation and survival. These factors stabilized mutant p53 protein which oftentimes contributed to exacerbated tumor phenotypes. These findings, coupled with the fact that patients carry p53 mutations without stabilization of p53, suggest that personalized therapeutic schemes may be needed for individual patients depending on their p53 status.
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Affiliation(s)
- Young-Ah Suh
- Department of Genetics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA
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19
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Colombo E, Alcalay M, Pelicci PG. Nucleophosmin and its complex network: a possible therapeutic target in hematological diseases. Oncogene 2011; 30:2595-609. [PMID: 21278791 DOI: 10.1038/onc.2010.646] [Citation(s) in RCA: 165] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nucleophosmin (NPM, also known as B23, numatrin or NO38) is a ubiquitously expressed phosphoprotein belonging to the nucleoplasmin family of chaperones. NPM is mainly localized in the nucleolus where it exerts many of its functions, but a proportion of the protein continuously shuttles between the nucleus and the cytoplasm. A growing number of cellular proteins have been described as physical interactors of NPM, and consequently, NPM is thought to have a relevant role in diverse cellular functions, including ribosome biogenesis, centrosome duplication, DNA repair and response to stress. NPM has been implicated in the pathogenesis of several human malignancies and intriguingly, it has been described both as an activating oncogene and a tumor suppressor, depending on cell type and protein levels. In fact, increased NPM expression is associated with different types of solid tumors whereas an impairment of NPM function is characteristic of a subgroup of hematolologic malignancies. A large body of experimental evidence links the deregulation of specific NPM functions to cellular transformation, yet the molecular mechanisms through which NPM contributes to tumorigenesis remain elusive. In this review, we have summarized current knowledge concerning NPM functions, and attempted to interpret its multifaceted and sometimes apparently contradictory activities in the context of both normal cellular homeostasis and neoplastic transformation.
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Affiliation(s)
- E Colombo
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy.
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20
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Solodushko V, Alvarez DF, Viator R, Messerall T, Fouty B. Heterogeneous activation of p19Arf in pulmonary artery smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 2011; 300:L642-7. [PMID: 21216978 DOI: 10.1152/ajplung.00117.2010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
p19(ARF) is a tumor suppressor that leads to cell cycle arrest or apoptosis by stabilizing p53. p19(ARF) is not critical for cell cycle regulation under normal conditions, but loss of p19(ARF) is seen in many human cancers, and a murine p19(Arf) knockout model leads to malignant proliferation and tumor formation; its role in controlling nonmalignant proliferation is less defined. To examine this question, pulmonary artery smooth muscle cells (PASMC) were expanded in culture from a transgenic mouse in which the coding sequence of the p19(Arf) gene was replaced with a cDNA encoding green fluorescent protein (GFP), leaving the promoter intact. During the first 10 days in culture, wild-type, heterozygous, and knockout PASMC grew similarly, but, by day 14, p19(Arf)-deficient PASMC proliferated faster than p19(Arf) heterozygous or wild-type cells; reexpression of p19(Arf) prevented the increased proliferation. This time course correlated with activation of the p19(Arf) promoter, as indicated by the appearance of GFP positivity in p19(Arf)-deficient PASMC. By day 42, ∼80% of p19(Arf)-deficient cells were GFP-positive. When GFP-positive, p19(Arf)-deficient cells were sorted and subcultured separately, they remained GFP-positive, indicating that once cells had activated the p19(Arf) promoter, the promoter remained active in those and all subsequent daughter cells. In contrast, GFP-negative p19(Arf)-deficient cells gave rise to a combination of GFP-positive and -negative daughter cells over time. These results suggest that a subpopulation of PASMC are resistant to the signals that activate the p19(Arf) promoter, an event that would normally target these cells for arrest or cell death.
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Affiliation(s)
- Victor Solodushko
- Center for Lung Biology and Department of Pharmacology, University of South Alabama School of Medicine, Mobile, Alabama 36688, USA
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21
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Shcherbik N, Pestov DG. Ubiquitin and ubiquitin-like proteins in the nucleolus: multitasking tools for a ribosome factory. Genes Cancer 2010; 1:681-689. [PMID: 21113400 DOI: 10.1177/1947601910381382] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Synthesis of new ribosomes is an essential process upregulated during cell growth and proliferation. Here, we review our current understanding of the role that ubiquitin and ubiquitin-like proteins (UBLs) play in ribosome biogenesis, with a focus on mammalian cells. One important function of the nuclear ubiquitin-proteasome system is to control the supply of ribosomal proteins for the assembly of new ribosomal subunits in the nucleolus. Mutations in ribosomal proteins or ribosome assembly factors, stress, and many anticancer drugs have been shown to disrupt normal ribosome biogenesis, triggering a p53-dependent response. We discuss how p53 can be activated by the aberrant ribosome formation, centering on the current models of the interaction between ribosomal proteins released from the nucleolus and the ubiquitin ligase Mdm2. Recent studies also revealed multiple ubiquitin- and UBL-conjugated forms of nucleolar proteins with largely unknown functions, indicating that many new details about the role of these modifications in the nucleolus await to be discovered.
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Affiliation(s)
- Natalia Shcherbik
- Department of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford, NJ 08084
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22
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Ozenne P, Eymin B, Brambilla E, Gazzeri S. The ARF tumor suppressor: Structure, functions and status in cancer. Int J Cancer 2010; 127:2239-47. [DOI: 10.1002/ijc.25511] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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23
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Bloethner S, Scherer D, Drechsel M, Hemminki K, Kumar R. Malignant Melanoma–a Genetic Overview. ACTAS DERMO-SIFILIOGRAFICAS 2009. [DOI: 10.1016/s0001-7310(09)73167-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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Abstract
The multifunctional nucleolar proteins, nucleophosmin (NPM) and the tumor suppressor ARF, have been assigned numerous roles in diverse cellular processes impacting cellular proliferation, tumorigenesis and apoptosis. In addition, both proteins have been linked to the oncogenic function of c-Myc, a transcription factor that drives the majority of human cancers. Both proteins are induced by oncogenic c-Myc, but have opposing outcomes. Whereas loss of ARF accelerates c-Myc-induced tumorigenesis, NPM overexpression enhances c-Myc transformation. Accordingly, ARF expression is lost in many tumors, while NPM expression is elevated. Previously, we demonstrated that ARF interacts directly with c-Myc, leading to inhibition of its transforming activity while enhancing its apoptotic activity, independently of p53. We have recently shown that NPM also binds directly to c-Myc, but with opposite effects compared to ARF. NPM dramatically enhances the oncogenic activity of c-Myc, independently of ARF and p53. In tumor cells, the ARF-p53 pathway is often inactivated while NPM is elevated. However, when NPM and ARF are both expressed with oncogenic c-Myc the outcome of the interactions becomes more complex, since NPM and ARF also interact directly and NPM controls ARF localization. In this report we demonstrate that in the presence of ARF, NPM overexpression dramatically inhibits c-Myc-induced p53-independent apoptosis, while enhancing proliferation and transformation. We find that NPM sequesters ARF in nucleoli, blocking the relocalization of ARF to the nucleoplasm caused by activation of c-Myc. Therefore, the fate of a cell to undergo apoptosis or become transformed is dependent on this complex interacting network of oncogenic and tumor suppressor proteins.
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Affiliation(s)
- Zhaoliang Li
- Department of Cell and Developmental Biology, Vanderbilt University, School of Medicine, Nashville, TN 37232, USA
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25
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Aguirre-Hernández J, Milne BS, Queen C, O'Brien PCM, Hoather T, Haugland S, Ferguson-Smith MA, Dobson JM, Sargan DR. Disruption of chromosome 11 in canine fibrosarcomas highlights an unusual variability of CDKN2B in dogs. BMC Vet Res 2009; 5:27. [PMID: 19643034 PMCID: PMC2732616 DOI: 10.1186/1746-6148-5-27] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Accepted: 07/31/2009] [Indexed: 01/07/2023] Open
Abstract
Background In dogs in the western world neoplasia constitutes the most frequently diagnosed cause of death. Although there appear to be similarities between canine and human cancers, rather little is known about the cytogenetic and molecular alterations in canine tumours. Different dog breeds are susceptible to different types of cancer, but the genetic basis of the great majority of these predispositions has yet to be discovered. In some retriever breeds there is a high incidence of soft tissue sarcomas and we have previously reported alterations of chromosomes 11 and 30 in two poorly differentiated fibrosarcomas. Here we extend our observations and present a case report on detail rearrangements on chromosome 11 as well as genetic variations in a tumour suppressor gene in normal dogs. Results BAC hybridisations on metaphases of two fibrosarcomas showed complex rearrangements on chromosome 11, and loss of parts of this chromosome. Microsatellite markers on a paired tumour and blood DNA pointed to loss of heterozygosity on chromosome 11 in the CDKN2B-CDKN2A tumour suppressor gene cluster region. PCR and sequencing revealed the homozygous loss of coding sequences for these genes, except for exon 1β of CDKN2A, which codes for the N-terminus of p14ARF. For CDKN2B exon 1, two alleles were observed in DNA from blood; one of them identical to the sequence in the dog reference genome and containing 4 copies of a 12 bp repeat found only in the canine gene amongst all species so far sequenced; the other allele was shorter due to a missing copy of the repeat. Sequencing of this exon in 141 dogs from 18 different breeds revealed a polymorphic region involving a GGC triplet repeat and a GGGGACGGCGGC repeat. Seven alleles were recorded and sixteen of the eighteen breeds showed heterozygosity. Conclusion Complex chromosome rearrangements were observed on chromosome 11 in two Labrador retriever fibrosarcomas. The chromosome alterations were reflected in the loss of sequences corresponding to two tumour suppressor genes involved in cell-cycle progression. Sequencing of CDKN2B across many different breeds revealed a widespread polymorphism within the first exon of the gene, immediately before the ankyrin coding sequences.
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26
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di Tommaso A, Hagen J, Tompkins V, Muniz V, Dudakovic A, Kitzis A, Ladeveze V, Quelle DE. Residues in the alternative reading frame tumor suppressor that influence its stability and p53-independent activities. Exp Cell Res 2009; 315:1326-35. [PMID: 19331830 DOI: 10.1016/j.yexcr.2009.01.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Revised: 01/19/2009] [Accepted: 01/20/2009] [Indexed: 02/02/2023]
Abstract
The Alternative Reading Frame (ARF) protein suppresses tumorigenesis through p53-dependent and p53-independent pathways. Most of ARF's anti-proliferative activity is conferred by sequences in its first exon. Previous work showed specific amino acid changes occurred in that region during primate evolution, so we programmed those changes into human p14ARF to assay their functional impact. Two human p14ARF residues (Ala(14) and Thr(31)) were found to destabilize the protein while two others (Val(24) and Ala(41)) promoted more efficient p53 stabilization and activation. Despite those effects, all modified p14ARF forms displayed robust p53-dependent anti-proliferative activity demonstrating there are no significant biological differences in p53-mediated growth suppression associated with simian versus human p14ARF residues. In contrast, p53-independent p14ARF function was considerably altered by several residue changes. Val(24) was required for p53-independent growth suppression whereas multiple residues (Val(24), Thr(31), Ala(41) and His(60)) enabled p14ARF to block or reverse the inherent chromosomal instability of p53-null MEFs. Together, these data pinpoint specific residues outside of established p14ARF functional domains that influence its expression and signaling activities. Most intriguingly, this work reveals a novel and direct role for p14ARF in the p53-independent maintenance of genomic stability.
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Affiliation(s)
- Anne di Tommaso
- Pole Biologie Sante, UMR 6187 CNRS, Pathologies Moléculaire de l'Adressage et de la Signalisation, Université de Poitiers, Poitiers, France
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27
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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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28
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Changes in p19Arf localization accompany apoptotic crisis during pre-B-cell transformation by Abelson murine leukemia virus. J Virol 2008; 82:8383-91. [PMID: 18579612 DOI: 10.1128/jvi.00348-08] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Transformation by Abelson murine leukemia virus (Ab-MLV) is a multistep process in which growth-stimulatory signals from the v-Abl oncoprotein and growth-suppressive signals from the p19(Arf)-p53 tumor suppressor pathway oppose each other and influence the outcome of infection. The process involves a proliferative phase during which highly viable primary transformants expand, followed by a period of marked apoptosis (called "crisis") that is dependent on the presence of p19(Arf) and p53; rare cells that survive this phase emerge as fully transformed and malignant. To understand the way in which v-Abl expression affects p19(Arf) expression, we examined changes in expression of Arf during all stages of Ab-MLV transformation process. As is consistent with the ability of v-Abl to stimulate Myc, a transcription factor known to induce p19(Arf), Myc and Arf are induced soon after infection and p19(Arf) is expressed. At these early time points, the infected cells remain highly viable. The onset of crisis is marked by an increase in p19(Arf) expression and a change in localization of the protein from the nucleoplasm to the nucleolus. These data together suggest that the localization and expression levels of p19(Arf) modulate the effects of the protein during oncogenesis and reveal that the p19(Arf)-mediated response is subject to multiple layers of regulation that influence its function during Ab-MLV-mediated transformation.
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29
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Ueda Y, Koya T, Yoneda-Kato N, Kato JY. Small mitochondrial ARF (smARF) is located in both the nucleus and cytoplasm, induces cell death, and activates p53 in mouse fibroblasts. FEBS Lett 2008; 582:1459-64. [PMID: 18381074 DOI: 10.1016/j.febslet.2008.03.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2008] [Revised: 03/10/2008] [Accepted: 03/19/2008] [Indexed: 11/30/2022]
Abstract
The ARF transcript produces two proteins, the full-length ARF, p19(ARF), and a short mitochondrial version, smARF. To explore the functional difference between the two, we generated GFP-fused expression vectors for each protein and introduced them into NIH3T3 murine fibroblasts, which sustains a global deletion in the INK4a locus but contains a functional p53 gene. GFP-p19ARF was located within the nucleolus as previously reported, whereas GFP-smARF was detected mainly in the nucleoplasm. GFP-smARF induced cell death although to a slightly lesser extent than p19ARF. GFP-smARF stabilized p53 thereby inducing expression of the target genes, MDM2 and p21. We suggest that smARF has functions other than mitochondria-mediated autophagy, and induces p53 expression and cell death via a novel mechanism.
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Affiliation(s)
- Yuko Ueda
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
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30
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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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31
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Dias CS, Liu Y, Yau A, Westrick L, Evans SC. Regulation of hdm2 by stress-induced hdm2alt1 in tumor and nontumorigenic cell lines correlating with p53 stability. Cancer Res 2007; 66:9467-73. [PMID: 17018602 DOI: 10.1158/0008-5472.can-05-3013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Alternative and aberrant splicing of hdm2 occurs in tumor and normal tissues. However, the factors that induce these splice variants and whether they are translated to protein products in vivo is unknown, making it difficult to decipher which of these hdm2 transcripts have a normal physiologic function or contribute to carcinogenesis. We investigated the conditions that induce this post-transcriptional modification of hdm2 in tumor and nontumorigenic cell lines. We showed that UV and gamma radiation as well as cisplatin treatment induced alternative splicing of hdm2, which resulted in a single splice variant, hdm2(alt1), irrespective of the cell type. Interestingly, the mechanism of UV-induced splicing is independent of p53 status. Immunoanalysis revealed that, after UV radiation, HDM2(ALT1) protein was expressed and interacted with HDM2 that correlated to increased p53 protein levels and its accumulation in the nucleus, whereas HDM2 localized more to the cytoplasm with a decrease in its RNA and protein level. We propose that stress-induced HDM2(ALT1) regulates HDM2 at two levels, RNA and protein, further modulating the p53-HDM2 interaction or interactions of HDM2 with other cell cycle regulatory proteins. This kind of regulation may possibly restrict oncogenic functions of HDM2 and contribute to the many protective responses triggered by certain stress signals. Our data imply that HDM2(ALT1) possesses a normal physiologic function in damaged cells, perhaps facilitating cellular defense.
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MESH Headings
- Alternative Splicing/drug effects
- Alternative Splicing/radiation effects
- Carcinoma/genetics
- Carcinoma/metabolism
- Cell Line, Transformed/drug effects
- Cell Line, Transformed/metabolism
- Cell Line, Transformed/radiation effects
- Cell Line, Tumor/drug effects
- Cell Line, Tumor/metabolism
- Cell Line, Tumor/radiation effects
- Cisplatin/pharmacology
- DNA/drug effects
- DNA/radiation effects
- DNA Damage
- Epithelial Cells/drug effects
- Epithelial Cells/metabolism
- Epithelial Cells/radiation effects
- Female
- Gamma Rays
- Homeostasis
- Humans
- Neoplasm Proteins/genetics
- Neoplasm Proteins/physiology
- Protein Isoforms/genetics
- Protein Isoforms/physiology
- Proto-Oncogene Proteins c-mdm2/genetics
- Proto-Oncogene Proteins c-mdm2/physiology
- RNA, Messenger/metabolism
- RNA, Neoplasm/metabolism
- Subcellular Fractions/metabolism
- Transcription, Genetic/drug effects
- Transcription, Genetic/radiation effects
- Tumor Suppressor Protein p53/deficiency
- Tumor Suppressor Protein p53/genetics
- Tumor Suppressor Protein p53/metabolism
- Ultraviolet Rays
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Affiliation(s)
- Chrisanne S Dias
- Department of Chemistry and Biochemistry, Edison Biotechnology Institute, Ohio University, Athens, OH 45701, USA
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32
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Platonova N, Scotti M, Babich P, Bertoli G, Mento E, Meneghini V, Egeo A, Zucchi I, Merlo GR. TBX3, the gene mutated in ulnar-mammary syndrome, promotes growth of mammary epithelial cells via repression of p19ARF, independently of p53. Cell Tissue Res 2007; 328:301-16. [PMID: 17265068 DOI: 10.1007/s00441-006-0364-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2006] [Accepted: 11/27/2006] [Indexed: 01/10/2023]
Abstract
TBX3, the gene mutated in ulnar-mammary syndrome (UMS), is involved in the production of a transcription factor of the T-box family, known to inhibit transcription from the p14ARF (p19ARF in mouse) promoter in fibroblasts and to contribute to cell immortalization. One of the main features of the UMS phenotype is the severe hypoplasia of the breast, associated with haploinsufficiency of the TBX3 gene product. In mice homozygous for the targeted disruption of Tbx3, the mammary glands (MGs) are nearly absent from early stages of embryogenesis, whereas in heterozygous adults, the MGs show reduced ductal branching. All these data strongly suggest a specific role of TBX3 in promoting the growth of mammary epithelial cells (MECs), although direct evidence of this is lacking. Here, we provide data showing the growth-promoting function of Tbx3 in several models of MECs, in association with its ability to repress the ARF promoter. However, no effect of Tbx3 on cell differentiation or apoptosis has been observed. The growth promoting function also entails the down-regulation of p21 ( CIP1/WAF ) and an increase in cyclin D1 but is independent of p53 and Mdm2 cell-cycle regulatory proteins, as p53-null MECs show similar growth responses associated with the up- or down-regulation of Tbx3. This is the first direct evidence that the level of Tbx3 expression positively controls the proliferation of MECs via pathways alternative to Mdm2-p53.
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Affiliation(s)
- Natalia Platonova
- Dulbecco Telethon Institute/CNR-ITB, Via F lli Cervi 93 Segrate, Milano, Italy
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33
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Abstract
Loss of the INK4a/ARF/INK4b locus on chromosome 9p21 is among the most frequent cytogenetic events in human cancer. The products of the locus--p15(INK4b), p16(INK4a), and ARF--play widespread and independent roles in tumor suppression. Recent data also suggest that expression of p16(INK4a) induces an age-dependent decrease in the proliferative capacity of certain tissue-specific stem cells and unipotent progenitors. Here, we discuss the regulation and role of p16(INK4a), ARF, and p15(INK4b) in cancer and aging.
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Affiliation(s)
- William Y Kim
- Department of Medicine, The University of North Carolina School of Medicine, Chapel Hill, 27599, USA
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34
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Saxena A, Rorie CJ, Dimitrova D, Daniely Y, Borowiec JA. Nucleolin inhibits Hdm2 by multiple pathways leading to p53 stabilization. Oncogene 2006; 25:7274-88. [PMID: 16751805 DOI: 10.1038/sj.onc.1209714] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 04/17/2006] [Accepted: 04/17/2006] [Indexed: 12/27/2022]
Abstract
Nucleolin is a c-Myc-induced gene product with defined roles in ribosomal RNA processing and the inhibition of chromosomal DNA replication following stress. Here we find that changes in nucleolin protein levels in unstressed cells cause parallel changes in the amount of p53 protein. Alterations in p53 levels arise from nucleolin binding to the p53 antagonist Hdm2, resulting in the inhibition of both p53 ubiquitination and Hdm2 auto-ubiquitination. Nucleolin does not alter p53 ubiquitination by human papillomavirus E6, indicating that the effect is specific for Hdm2. Although the inhibition of ligase activity would be expected to stabilize Hdm2, we instead find that nucleolin also reduces Hdm2 protein levels, demonstrating that nucleolin inhibits Hdm2 using multiple mechanisms. Increases in nucleolin levels in unstressed cells led to higher expression of p21(cip1/waf1), a reduced rate of cellular proliferation, and an increase in apoptosis. Thus, nucleolin has a number of properties in common with the tumor suppressor ARF (alternate reading frame). We propose that nucleolin, like ARF, responds to hyperproliferative signals by upregulation of p53 through Hdm2 inhibition.
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Affiliation(s)
- A Saxena
- Department of Biochemistry and New York University Cancer Institute, New York University School of Medicine, New York, NY 10016, USA
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35
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Tompkins VS, Hagen J, Frazier AA, Lushnikova T, Fitzgerald MP, di Tommaso A, Ladeveze V, Domann FE, Eischen CM, Quelle DE. A novel nuclear interactor of ARF and MDM2 (NIAM) that maintains chromosomal stability. J Biol Chem 2006; 282:1322-33. [PMID: 17110379 DOI: 10.1074/jbc.m609612200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The ARF tumor suppressor signals through p53 and other poorly defined anti-proliferative pathways to block carcinogenesis. In a search for new regulators of ARF signaling, we discovered a novel nuclear protein that we named NIAM (nuclear interactor of ARF and MDM2) for its ability to bind both ARF and the p53 antagonist MDM2. NIAM protein is normally expressed at low to undetectable levels in cells because of, at least in part, MDM2-mediated ubiquitination and proteasomal degradation. When reintroduced into cells, NIAM activated p53, caused a G1 phase cell cycle arrest, and collaborated with ARF in an additive fashion to suppress proliferation. Notably, NIAM retains growth inhibitory activity in cells lacking ARF and/or p53, and knockdown experiments revealed that it is not essential for ARF-mediated growth inhibition. Thus, NIAM and ARF act in separate anti-proliferative pathways that intersect mechanistically and suppress growth more effectively when jointly activated. Intriguingly, silencing of NIAM accelerated chromosomal instability, and microarray analyses showed reduced NIAM mRNA expression in numerous primary human tumors. This study identifies a novel protein with tumor suppressor-like behaviors and functional links to ARF-MDM2-p53 signaling.
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Affiliation(s)
- Van S Tompkins
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, 52242-1109, USA, and the Laboratoire de Genetique Cellulaire et Moleculaire, UPRES EA2622, Centre Hospitalier Universitaire de Poitiers, France
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36
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Rizos H, McKenzie HA, Ayub AL, Woodruff S, Becker TM, Scurr LL, Stahl J, Kefford RF. Physical and functional interaction of the p14ARF tumor suppressor with ribosomes. J Biol Chem 2006; 281:38080-8. [PMID: 17035234 DOI: 10.1074/jbc.m609405200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Alterations in the p14(ARF) tumor suppressor are frequent in many human cancers and are associated with susceptibility to melanoma, pancreatic cancer, and nervous system tumors. In addition to its p53-regulatory functions, p14(ARF) has been shown to influence ribosome biogenesis and to regulate the endoribonuclease B23, but there remains considerable controversy about its nucleolar role. We sought to clarify the activities of p14(ARF) by studying its interaction with ribosomes. We show that p14(ARF) and B23 interact within the nucleolar 60 S preribosomal particle and that this interaction does not require rRNA. In contrast to previous reports, we found that expression of p14(ARF) does not significantly alter ribosome biogenesis but inhibits polysome formation and protein translation in vivo. These results suggest a ribosome-dependent p14(ARF) pathway that regulates cell growth and thus complements p53-dependent p14(ARF) functions.
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Affiliation(s)
- Helen Rizos
- Westmead Institute for Cancer Research, University of Sydney at Westmead Millennium Institute, Westmead Hospital, Westmead, New South Wales 2145, Australia.
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37
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Abstract
In this review, we discuss the recent identification of ARF-BP1 (also known as Mule, UREB1, E3histone, LASU1, and HectH9). ARF-BP1, a HECT domain-containing E3 ubiquitin ligase, interacts with ARF and p53. Its ubiquitin ligase activity is inhibited by ARF. Inactivation of ARF-BP1 stabilised p53 and induced apoptosis. Notably, inactivation of ARF-BP1 also caused cell growth repression in p53-null cells and breast cancer cells with mutant p53. Thus, ARF-BP1 emerges as a novel therapeutic target against cancer regardless of p53 status.
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Affiliation(s)
- D Chen
- Institute for Cancer Genetics, Department of Pathology, College of Physicians & Surgeons, Columbia University, 1150 St Nicholas Ave, New York, NY 10032, USA
| | - C L Brooks
- Institute for Cancer Genetics, Department of Pathology, College of Physicians & Surgeons, Columbia University, 1150 St Nicholas Ave, New York, NY 10032, USA
| | - W Gu
- Institute for Cancer Genetics, Department of Pathology, College of Physicians & Surgeons, Columbia University, 1150 St Nicholas Ave, New York, NY 10032, USA
- E-mail:
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38
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Hemmati PG, Güner D, Gillissen B, Wendt J, von Haefen C, Chinnadurai G, Dörken B, Daniel PT. Bak functionally complements for loss of Bax during p14ARF-induced mitochondrial apoptosis in human cancer cells. Oncogene 2006; 25:6582-94. [PMID: 16847458 DOI: 10.1038/sj.onc.1209668] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In contrast to the initial notion that the biological activity of p14(ARF) strictly depends on a functional mdm-2/p53 signaling axis, we recently demonstrated that p14(ARF) mediates apoptosis in a p53/Bax-independent manner. Here, we show that p14(ARF) induces breakdown of the mitochondrial membrane potential and cytochrome c release before triggering caspase-9- and caspase-3/7-like activities in p53/Bax-deficient DU145 prostate cancer cells expressing wild-type Bak. Re-expression of Bax in these cells failed to further enhance p14(ARF)-induced apoptosis, suggesting that p14(ARF)-induced apoptosis primarily depends on Bak but not Bax in these cells. To further define the role of Bak and Bax in p14(ARF)-induced mitochondrial apoptosis, we employed short interference RNA for the knockdown of bak in isogeneic, p53 wild-type HCT116 colon cancer cells either proficient or deficient for Bax. There, combined loss of Bax and Bak attenuated p14(ARF)-induced apoptosis whereas single loss of Bax or Bak was only marginally effective, as in the case of DU145. Notably, HCT116 cells deficient for Bax and Bak failed to release cytochrome c and showed attenuated activation of caspase-9 (LEHDase) and caspase-3/caspase-7 (DEVDase) upon p14(ARF) expression. These data indicate that p14(ARF) triggers apoptosis via a Bax/Bak-dependent pathway in p53-proficient HCT116, whereas Bax is dispensable in p53-deficient DU145 cells. Nevertheless, a substantial proportion of p14(ARF)-induced cell death proceeds in a Bax/Bak-independent manner. This is also the case for inhibition of clonogenic growth that occurs, at least in part, through an entirely Bax/Bak-independent mechanism.
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Affiliation(s)
- P G Hemmati
- Department of Hematology, Oncology and Tumor Immunology, University Medical Center Charité, Berlin-Buch, Germany
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39
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Surjit M, Liu B, Chow VTK, Lal SK. The nucleocapsid protein of severe acute respiratory syndrome-coronavirus inhibits the activity of cyclin-cyclin-dependent kinase complex and blocks S phase progression in mammalian cells. J Biol Chem 2006; 281:10669-81. [PMID: 16431923 PMCID: PMC7995956 DOI: 10.1074/jbc.m509233200] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 01/17/2006] [Indexed: 11/15/2022] Open
Abstract
Deregulation of the cell cycle is a common strategy employed by many DNA and RNA viruses to trap and exploit the host cell machinery toward their own benefit. In many coronaviruses, the nucleocapsid protein (N protein) has been shown to inhibit cell cycle progression although the mechanism behind this is poorly understood. The N protein of severe acute respiratory syndrome-coronavirus (SARS-CoV) bears signature motifs for binding to cyclin and phosphorylation by cyclin-dependent kinase (CDK) and has recently been reported by us to get phosphorylated by the cyclin-CDK complex (Surjit, M., Kumar, R., Mishra, R. N., Reddy, M. K., Chow, V. T., and Lal, S. K. (2005) J. Virol. 79, 11476-11486). In the present study, we prove that the N protein of SARS-CoV can inhibit S phase progression in mammalian cell lines. N protein expression was found to directly inhibit the activity of the cyclin-CDK complex, resulting in hypophosphorylation of retinoblastoma protein with a concomitant down-regulation in E2F1-mediated transactivation. Coexpression of E2F1 under such conditions could restore the expression of S phase genes. Analysis of RXL and CDK phosphorylation mutant N protein identified the mechanism of inhibition of CDK4 and CDK2 activity to be different. Whereas N protein could directly bind to cyclin D and inhibit the activity of CDK4-cyclin D complex; inhibition of CDK2 activity appeared to be achieved in two different ways: indirectly by down-regulation of protein levels of CDK2, cyclin E, and cyclin A and by direct binding of N protein to CDK2-cyclin complex. Down-regulation of E2F1 targets was also observed in SARS-CoV-infected VeroE6 cells. These data suggest that the S phase inhibitory activity of the N protein may have major significance during viral pathogenesis.
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Affiliation(s)
- Milan Surjit
- Virology Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Rd., New Delhi 110067, India
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40
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González L, Freije JMP, Cal S, López-Otín C, Serrano M, Palmero I. A functional link between the tumour suppressors ARF and p33ING1. Oncogene 2006; 25:5173-9. [PMID: 16607280 DOI: 10.1038/sj.onc.1209526] [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: 11/08/2022]
Abstract
The ARF tumour suppressor protein plays a critical role in the activation of p53 in response to oncogenic stress. ARF can activate p53 through nucleolar sequestration of Mdm2. However, several lines of evidence indicate that this is not the only way of action of ARF, and alternative mechanisms must exist. p33ING1 is a putative tumour suppresor, which induces cell-cycle arrest and apoptosis in a p53-dependent manner. Here, we describe that ARF and p33ING1 can interact in vivo. We also show that the subcellular localization of ING1 can be modulated by ARF protein levels, causing a displacement from nuclear to nucleolar localization. Finally, the ability of p33ING1 to cause cell-cycle arrest and induction of p21CIP1, or Mdm2, is impaired in ARF-deficient primary mouse fibroblasts. Based on these observations, we propose that the interaction with p33ING1 represents a novel mechanism for the tumour suppression function of ARF.
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Affiliation(s)
- L González
- Institute of Biomedical Research, CSIC-UAM, Arturo Duperier 4, Madrid, Spain
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41
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Wang P, Greiner TC, Lushnikova T, Eischen CM. Decreased Mdm2 expression inhibits tumor development induced by loss of ARF. Oncogene 2006; 25:3708-18. [PMID: 16491126 DOI: 10.1038/sj.onc.1209411] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The tumor suppressor p14/p19(ARF) regulates Mdm2, which is known for controlling the p53 tumor suppressor. Here we report that loss of one allele of Mdm2 in cells that lack ARF resulted in a decreased rate of proliferation, fewer chromosomal aberrations, and suppression of Ras-induced transformation. Moreover, a haploinsufficiency of Mdm2 inhibited spontaneous tumor development in ARF-null mice. Remarkably, Mdm2(+/-)ARF(-/-) mice survived an average of 6 months longer than Mdm2(+/+)ARF(-/-) mice. The spectrum of tumors that arose in Mdm2(+/-)ARF(-/-) mice did not significantly differ from those that developed in mice lacking only ARF. However, the extended tumor latency allowed for the emergence of multiple primary tumors in a third of the Mdm2(+/-)ARF(-/-) mice, as compared to the single tumor type that arose in ARF-null only mice. Therefore, a decrease in Mdm2 levels restored regulation of critical cellular processes that are altered during transformation and that occur in the absence of ARF. Our findings also indicate that Mdm2 can function independently from ARF and imply that targeting Mdm2 in tumors that lack ARF expression should be an effective therapeutic approach.
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Affiliation(s)
- P Wang
- Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, 68198, USA
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42
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Qiu J, Wong J, Tweardy DJ, Dong S. Decreased intranuclear mobility of acute myeloid leukemia 1-containing fusion proteins is accompanied by reduced mobility and compartmentalization of core binding factor beta. Oncogene 2006; 25:3982-93. [PMID: 16474840 DOI: 10.1038/sj.onc.1209431] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Acute myeloid leukemia 1 (AML1) gene on chromosome 21 is involved in several chromosomal translocations, including t(8;21) and t(16;21), that produce chimeric fusion proteins AML1-eight twenty-one (ETO) and AML-myeloid transforming gene chromosome 16 (MTG16), which contribute to leukemogenesis. The molecular basis for the leukemogenic effects of these fusion proteins is incompletely understood. Using gel-shift assay, we showed that AML1-ETO and AML1-MTG16 bound to a series of AML1 consensus DNA-binding sites with different affinities. Using fluorescence recovery after photobleaching (FRAP), we demonstrated that a fusion of AML1 with ETO or MTG16 exhibits reduced intranuclear mobility compared with wild-type AML1 or either fusion partner. The dimerization domain (nervy homology region 2) of ETO is responsible for the reduced mobility of AML1-ETO. Dual FRAP studies revealed that CBFbeta colocalized with AML1-ETO within the nucleus, resulting in reduced mobility of CBFbeta. Therefore, AML1 fusion proteins may interfere with normal AML1 function due to aberrant nuclear dynamics, which leads to spatial and temporal sequestration of CBFbeta and perhaps other coregulators critical for myeloid differentiation.
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Affiliation(s)
- J Qiu
- Department of Medicine, Section of Infectious Diseases, Baylor College of Medicine, Houston, TX 77030, USA
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Wsierska-Gadek J, Horky M. How the Nucleolar Sequestration of p53 Protein or Its Interplayers Contributes to Its (Re)-Activation. Ann N Y Acad Sci 2006; 1010:266-72. [PMID: 15033732 DOI: 10.1196/annals.1299.046] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The tumor suppressor p53 is a short-lived protein that under normal conditions is reduced to a barely detectable level. The stability of p53 protein is primarily regulated in normal non-transformed cells by two interplayers: Mdm2 and p14(ARF). Relocation of p53, Mdm2, and p14(ARF) to the nucleolus seems to regulate, at least partially, the steady-state of p53. Moreover, there are alternative pathways of the regulation of p53 stability in unstressed cells. Jun-N(amino)-terminal kinase (JNK) and poly(ADP-ribose) polymerase-1 (PARP-1) are involved in the regulation of the steady-state of wild-type (wt) p53 protein. However, in most human cervical carcinomas, which express the high-risk human papilloma viruses (HPVs) E6 protein, a complete switch from Mdm2 to HPV E6-mediated degradation of p53 occurs. Virally encoded E6 protein utilizes the cellular ubiquitin-protein ligase termed E6-associated protein (E6-AP) to target p53 protein for proteolytic degradation. We recently addressed the question of whether p53 protein can be generally reactivated by chemotherapy in HeLa cells despite the E6 activity. We observed an increase of cellular p53 after cisplatin (CP) treatment. p53 protein accumulated preferentially in the nucleoli. We checked the cellular level of E6 during CP therapy. Six hours after application of CP the expression of E6 protein was markedly reduced. This coincided with the increase of cellular p53 level and preceded the nucleolar accumulation of p53 protein, thereby indicating that repression of virally coded E6 protein by CP contributes to the restoration of p53 expression.
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Affiliation(s)
- Józefa Wsierska-Gadek
- Cell Cycle Regulation Group, Institute of Cancer Research, Faculty of Medicine, University of Vienna, Vienna, Austria.
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Lee C, Smith BA, Bandyopadhyay K, Gjerset RA. DNA damage disrupts the p14ARF-B23(nucleophosmin) interaction and triggers a transient subnuclear redistribution of p14ARF. Cancer Res 2005; 65:9834-42. [PMID: 16267006 DOI: 10.1158/0008-5472.can-05-1759] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The p14 alternate reading frame (ARF) tumor suppressor plays a central role in cancer by binding to mdm2 (Hdm2 in humans) and enhancing p53-mediated apoptosis following DNA damage and oncogene activation. It is unclear, however, how ARF initiates its involvement in the p53/mdm2 pathway, as p53 and mdm2 are located in the nucleoplasm, whereas ARF is largely nucleolar in tumor cells. We have used immunofluorescence and coimmunoprecipitation to examine how the subnuclear distribution and protein-protein interactions of ARF change immediately after DNA damage and over the time course of the DNA damage response in human tumor cells. We find that DNA damage disrupts the interaction of ARF with the nucleolar protein B23(nucleophosmin) and promotes a transient p53-independent translocation of ARF to the nucleoplasm, resulting in a masking of the ARF NH2 terminus that correlates with the appearance of ARF-Hdm2 complexes. The translocation also results in an unmasking of the ARF COOH terminus, suggesting that redistribution disrupts a nucleolar interaction of ARF involving this region. By 24 hours after irradiation, DNA repair has ceased and the pretreatment immunofluorescence patterns and complexes of ARF have been restored. Although the redistribution of ARF is independent of p53 and likely to be regulated by interactions other than Hdm2, ARF does not promote UV sensitization unless p53 is expressed. The results implicate the nucleolus and nucleolar interactions of the ARF, including potentially novel interactions involving its COOH terminus as sites for early DNA damage and stress-mediated cellular events.
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Affiliation(s)
- Casey Lee
- Department of Cancer Cell Biology, Sidney Kimmel Cancer Center, San Diego, California 92121, USA
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Datta A, Sen J, Hagen J, Korgaonkar CK, Caffrey M, Quelle DE, Hughes DE, Ackerson TJ, Costa RH, Raychaudhuri P. ARF directly binds DP1: interaction with DP1 coincides with the G1 arrest function of ARF. Mol Cell Biol 2005; 25:8024-36. [PMID: 16135794 PMCID: PMC1234342 DOI: 10.1128/mcb.25.18.8024-8036.2005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The tumor suppressor ARF inhibits cell growth in response to oncogenic stress in a p53-dependent manner. Also, there is an increasing appreciation of ARF's ability to inhibit cell growth via multiple p53-independent mechanisms, including its ability to regulate the E2F pathway. We have investigated the interaction between the tumor suppressor ARF and DP1, the DNA binding partner of the E2F family of factors (E2Fs). We show that ARF directly binds to DP1. Interestingly, binding of ARF to DP1 results in an inhibition of the interaction between DP1 and E2F1. Moreover, ARF regulates the association of DP1 with its target gene, as evidenced by a chromatin immunoprecipitation assay with the dhfr promoter. By analyzing a series of ARF mutants, we demonstrate a strong correlation between ARF's ability to regulate DP1 and its ability to cause cell cycle arrest. S-phase inhibition by ARF is preceded by an inhibition of the E2F-activated genes. Moreover, we provide evidence that ARF inhibits the E2F-activated genes independently of p53 and Mdm2. Also, the interaction between ARF and DP1 is enhanced during oncogenic stress and "culture shock." Taken together, our results show that DP1 is a critical direct target of ARF.
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Affiliation(s)
- Abhishek Datta
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S. Ashland Ave., Chicago, IL 60607, USA
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Sharpless NE. INK4a/ARF: a multifunctional tumor suppressor locus. Mutat Res 2005; 576:22-38. [PMID: 15878778 DOI: 10.1016/j.mrfmmm.2004.08.021] [Citation(s) in RCA: 290] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2004] [Revised: 07/12/2004] [Accepted: 08/12/2004] [Indexed: 02/02/2023]
Abstract
The INK4a/ARF locus encodes two physically linked tumor suppressor proteins, p16(INK4a) and ARF, which regulate the RB and p53 pathways, respectively. The unusual genomic relationship of the open reading frames of these proteins initially fueled speculation that only one of the two was the true tumor suppressor, and loss of the other merely coincidental in cancer. Recent human and mouse genetic data, however, have firmly established that both proteins possess significant in vivo tumor suppressor activity, although there appear to be species- and cell-type specific differences between the two. For example, ARF plays a clear role in preventing Myc-induced lymphomagenesis in mice, whereas the role for p16(INK4a) is human carcinomas is more firmly established. In this review, I discuss the evolutionary history of the locus, the relative importance of these tumor suppressor genes in human cancer, and recent information suggesting novel biochemical and physiologic functions of these proteins in vivo.
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Affiliation(s)
- Norman E Sharpless
- Department of Medicine, The Lineberger Comprehensive Cancer Center, The University of North Carolina School of Medicine, Chapel Hill, 27599-7295, USA.
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Chen D, Kon N, Li M, Zhang W, Qin J, Gu W. ARF-BP1/Mule is a critical mediator of the ARF tumor suppressor. Cell 2005; 121:1071-83. [PMID: 15989956 DOI: 10.1016/j.cell.2005.03.037] [Citation(s) in RCA: 404] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Revised: 02/24/2005] [Accepted: 03/30/2005] [Indexed: 10/25/2022]
Abstract
Although the importance of the ARF tumor suppressor in p53 regulation is well established, numerous studies indicate that ARF also suppresses cell growth in a p53/Mdm2-independent manner. To understand the mechanism of ARF-mediated tumor suppression, we identified a ubiquitin ligase, ARF-BP1, as a key factor associated with ARF in vivo. ARF-BP1 harbors a signature HECT motif, and its ubiquitin ligase activity is inhibited by ARF. Notably, inactivation of ARF-BP1, but not Mdm2, suppresses the growth of p53 null cells in a manner reminiscent of ARF induction. Surprisingly, in p53 wild-type cells, ARF-BP1 directly binds and ubiquitinates p53, and inactivation of endogenous ARF-BP1 is crucial for ARF-mediated p53 stabilization. Thus, our study modifies the current view of ARF-mediated p53 activation and reveals that ARF-BP1 is a critical mediator of both the p53-independent and p53-dependent tumor suppressor functions of ARF. As such, ARF-BP1 may serve as a potential target for therapeutic intervention in tumors regardless of p53 status.
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Affiliation(s)
- Delin Chen
- Institute for Cancer Genetics, Department of Pathology, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, New York 10032
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Song YJ, Stinski MF. Inhibition of cell division by the human cytomegalovirus IE86 protein: role of the p53 pathway or cyclin-dependent kinase 1/cyclin B1. J Virol 2005; 79:2597-603. [PMID: 15681459 PMCID: PMC546562 DOI: 10.1128/jvi.79.4.2597-2603.2005] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (HCMV) IE86 protein induces the human fibroblast cell cycle from G(0)/G(1) to G(1)/S, where cell cycle progression stops. Cells with a wild-type, mutated, or null p53 or cells with null p21 protein were transduced with replication-deficient adenoviruses expressing HCMV IE86 protein or cellular p53 or p21. Even though S-phase genes were activated in a p53 wild-type cell, IE86 protein also induced phospho-Ser(15) p53 and p21 independent of p14ARF but dependent on ATM kinase. These cells did not enter the S phase. In human p53 mutant, p53 null, or p21 null cells, IE86 protein did not up-regulate p21, cellular DNA synthesis was not inhibited, but cell division was inhibited. Cells accumulated in the G(2)/M phase, and there was increased cyclin-dependent kinase 1/cyclin B1 activity. Although the HCMV IE86 protein increases cellular E2F activity, it also blocks cell division in both p53(+/+) and p53(-/-) cells.
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Affiliation(s)
- Yoon-Jae Song
- Department of Microbiology, Carver College of Medicine, The University of Iowa, Iowa City, IA 52242, USA
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Kwong RA, Kalish LH, Nguyen TV, Kench JG, Bova RJ, Cole IE, Musgrove EA, Sutherland RL. p14ARF Protein Expression Is a Predictor of Both Relapse and Survival in Squamous Cell Carcinoma of the Anterior Tongue. Clin Cancer Res 2005; 11:4107-16. [PMID: 15930346 DOI: 10.1158/1078-0432.ccr-04-2036] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE The INK4A-ARF locus at chromosome 9p21 is frequently altered in head and neck squamous cell carcinoma (SCC) and encodes two distinct tumor suppressors, p16(INK4A) and p14(ARF). This study addressed the role of p14(ARF) as a potential prognostic marker in this disease. EXPERIMENTAL DESIGN p14(ARF) protein expression was assessed by immunohistochemistry in a cohort of 140 patients with SCC of the anterior tongue. Using univariate and multivariate Cox's proportional hazards models, the outcomes examined were time to disease recurrence or death, with or without clinicopathologic covariates, including nodal status, disease stage, treatment status, Ki-67 staining, and molecular markers with known functional or genetic relationships with p14(ARF) (p16(INK4A), p53, pRb, p21(WAF1/CIP1), E2F-1). RESULTS On multivariate analysis, p14(ARF) positivity (nucleolar p14(ARF) staining and/or nuclear p14(ARF) staining in >/=30% of tumor cells) was an independent predictor of improved disease-free survival (DFS; P = 0.002) and overall survival (OS; P = 0.002). This was further enhanced when p14(ARF) positivity was cosegregated with positive (>/=1%) p16(INK4A) staining (DFS, P < 0.001; OS, P < 0.001). Patients whose cancers were p14(ARF) negative and p53 positive (>50%) had the poorest outcome (DFS, P < 0.001; OS, P < 0.001) of any patient subgroup analyzed. CONCLUSIONS These data show that in patients with SCC of the tongue, combined nuclear and nucleolar expression of p14(ARF) protein predicts for improved DFS and OS independent of established prognostic markers.
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Affiliation(s)
- Rhonda A Kwong
- Cancer Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
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Inoue R, Shiraishi T. PKCα is involved in phorbol ester TPA-mediated stabilization of p14ARF. Biochem Biophys Res Commun 2005; 330:1314-8. [PMID: 15823586 DOI: 10.1016/j.bbrc.2005.03.117] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Indexed: 11/28/2022]
Abstract
We generated A21-13 cells expressing p14(ARF) in the presence of doxycycline in order to examine the stability of p14(ARF) protein. The effects of proteasome inhibitor MG132 on p14(ARF) protein stabilization were detectable using our experimental procedure. Introduction of mutant p53 did not affect MG132-mediated p14(ARF) protein stabilization. We found that phorbol ester TPA (12-o-tetradecanoyl-phorbol 13-acetate) stabilized p14(ARF) protein and that p53 status had no effect on TPA-mediated stabilization. TPA-mediated stabilization was abolished by staurosporine but not by lovastatin or U0126. We further investigated which isoforms of PKC were involved in TPA-mediated p14(ARF) stabilization using short-interference RNA. Knockdown of PKCalpha, but not PKCdelta, attenuated TPA-mediated p14(ARF) stabilization. These findings suggest that PKCalpha is involved in TPA-mediated stabilization of p14(ARF) protein, and this effect of TPA was not affected by the Ras/MAPK pathway or p53 status. Our results are indicative of a novel role of PKC in p14(ARF) protein stability.
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Affiliation(s)
- Rie Inoue
- Second Department of Pathology, Mie University School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan.
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