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Al-Gazally ME, Khan R, Imran M, Ramírez-Coronel AA, Alshahrani SH, Altalbawy FMA, Turki Jalil A, Romero-Parra RM, Zabibah RS, Shahid Iqbal M, Karampoor S, Mirzaei R. The role and mechanism of action of microRNA-122 in cancer: Focusing on the liver. Int Immunopharmacol 2023; 123:110713. [PMID: 37523968 DOI: 10.1016/j.intimp.2023.110713] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 07/08/2023] [Accepted: 07/24/2023] [Indexed: 08/02/2023]
Abstract
microRNA-122 (miR-122) is a highly conserved microRNA that is predominantly expressed in the liver and plays a critical role in the regulation of liver metabolism. Recent studies have shown that miR-122 is involved in the pathogenesis of various types of cancer, particularly liver cancer. In this sense, The current findings highlighted the potential role of miR-122 in regulating many vital processes in cancer pathophysiology, including apoptosis, signaling pathway, cell metabolism, immune system response, migration, and invasion. These results imply that miR-122, which has been extensively studied for its biological functions and potential therapeutic applications, acts as a tumor suppressor or oncogene in cancer development. We first provide an overview and summary of the physiological function and mode of action of miR-122 in liver cancer. We will examine the various signaling pathways and molecular mechanisms through which miR-122 exerts its effects on cancer cells, including the regulation of oncogenic and tumor suppressor genes, the modulation of cell proliferation and apoptosis, and the regulation of metastasis. Most importantly, we will also discuss the potential diagnostic and therapeutic applications of miR-122 in cancer, including the development of miRNA-based biomarkers for cancer diagnosis and prognosis, and the potential use of miR-122 as a therapeutic target for cancer treatment.
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Affiliation(s)
| | - Ramsha Khan
- MBBS, Nawaz Sharif Medical College, Gujrat, Pakistan
| | - Muhammad Imran
- MBBS, Multan Medical and Dental College, Multan, Pakistan
| | | | | | - Farag M A Altalbawy
- National Institute of Laser Enhanced Sciences (NILES), University of Cairo, Giza 12613, Egypt; Department of Chemistry, University College of Duba, University of Tabuk, Tabuk, Saudi Arabia
| | - Abduladheem Turki Jalil
- Medical Laboratories Techniques Department, Al-Mustaqbal University College, Babylon, Hilla 51001, Iraq
| | | | - Rahman S Zabibah
- Medical Laboratory Technology Department, College of Medical Technology, The Islamic University, Najaf, Iraq
| | - Muhammad Shahid Iqbal
- Department of Clinical Pharmacy, College of Pharmacy, Prince Sattam bin Abdulaziz University, 11942 Alkharj, Saudi Arabia
| | - Sajad Karampoor
- Gastrointestinal and Liver Diseases Research Center, Iran University of Medical Sciences, Tehran, Iran.
| | - Rasoul Mirzaei
- Venom and Biotherapeutics Molecules Lab, Medical Biotechnology Department, Biotechnology Research Center, Pasteur Institute of Iran, Tehran, Iran.
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2
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Liu B, Lin L, Riazuddin S, Zubair A, Wang L, Di LJ, Li R, Dong TT, Deng CX, Tong WM. RETRACTED: PP2ACα deficiency impairs early cortical development through inducing DNA damage in neuroprojenitor cells. Int J Biochem Cell Biol 2019; 109:40-58. [PMID: 30710753 DOI: 10.1016/j.biocel.2019.01.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 01/25/2019] [Accepted: 01/29/2019] [Indexed: 01/09/2023]
Abstract
This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor in Chief due to objections raised by persons identified as co-authors of corresponding author Bo Liu. The University of Macau states that Bo Liu is not affiliated with the University of Macau. The purported co-authors who are only affiliated with University of Macau report their names have been misappropriated for use on this paper without notice or prior permission. These co-authors deny any involvement in the study, preparation or submission of the manuscript, or review of any supporting data. The purported co-authors who are affiliated with the University of Maryland, Baltimore report their names and credentials have been misappropriated for use on this paper without notice or permission. These co-authors deny any involvement in the study, preparation or submission of the manuscript, or review of any supporting data. The National Institute of Health also states that none of the co-authors are affiliated with the institution. The University of Maryland, Baltimore states that Bo Liu is not affiliated with the university. Bo Liu has been non-responsive to approaches from the Publisher. Rui Li and Ting-Ting Dong were not reachable by the Publisher. Lin Lin confirmed the affiliation with The University of California Riverside; Chu-Xia Deng confirmed the affiliation with the University of Macau; Wei-Min Tong confirmed the affiliation with the Chinese Academy of Medical Sciences.
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Affiliation(s)
- Bo Liu
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA; University of Macau, Macau, China.
| | - Lin Lin
- University of Macau, Macau, China; Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China
| | - Saima Riazuddin
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA
| | - Ahmed Zubair
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA
| | - Li Wang
- Branch of Cancer Research, Jones Hopkins University, Baltimore, USA
| | - Li-Jun Di
- Branch of Cancer Research, Jones Hopkins University, Baltimore, USA
| | - Rui Li
- Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China.
| | - Ting-Ting Dong
- Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China; China Agricultural University, Beijing, China
| | - Chu-Xia Deng
- National Institute of Neurological Disorders and Stroke, National Institute of Heath, Bethesda, USA.
| | - Wei-Min Tong
- National Institute of Neurological Disorders and Stroke, National Institute of Heath, Bethesda, USA.
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Gordon EM, Ravicz JR, Liu S, Chawla SP, Hall FL. Cell cycle checkpoint control: The cyclin G1/Mdm2/p53 axis emerges as a strategic target for broad-spectrum cancer gene therapy - A review of molecular mechanisms for oncologists. Mol Clin Oncol 2018; 9:115-134. [PMID: 30101008 PMCID: PMC6083405 DOI: 10.3892/mco.2018.1657] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 06/14/2018] [Indexed: 12/13/2022] Open
Abstract
Basic research in genetics, biochemistry and cell biology has identified the executive enzymes and protein kinase activities that regulate the cell division cycle of all eukaryotic organisms, thereby elucidating the importance of site-specific protein phosphorylation events that govern cell cycle progression. Research in cancer genomics and virology has provided meaningful links to mammalian checkpoint control elements with the characterization of growth-promoting proto-oncogenes encoding c-Myc, Mdm2, cyclins A, D1 and G1, and opposing tumor suppressor proteins, such as p53, pRb, p16INK4A and p21WAF1, which are commonly dysregulated in cancer. While progress has been made in identifying numerous enzymes and molecular interactions associated with cell cycle checkpoint control, the marked complexity, particularly the functional redundancy, of these cell cycle control enzymes in mammalian systems, presents a major challenge in discerning an optimal locus for therapeutic intervention in the clinical management of cancer. Recent advances in genetic engineering, functional genomics and clinical oncology converged in identifying cyclin G1 (CCNG1 gene) as a pivotal component of a commanding cyclin G1/Mdm2/p53 axis and a strategic locus for re-establishing cell cycle control by means of therapeutic gene transfer. The purpose of the present study is to provide a focused review of cycle checkpoint control as a practicum for clinical oncologists with an interest in applied molecular medicine. The aim is to present a unifying model that: i) clarifies the function of cyclin G1 in establishing proliferative competence, overriding p53 checkpoints and advancing cell cycle progression; ii) is supported by studies of inhibitory microRNAs linking CCNG1 expression to the mechanisms of carcinogenesis and viral subversion; and iii) provides a mechanistic basis for understanding the broad-spectrum anticancer activity and single-agent efficacy observed with dominant-negative cyclin G1, whose cytocidal mechanism of action triggers programmed cell death. Clinically, the utility of companion diagnostics for cyclin G1 pathways is anticipated in the staging, prognosis and treatment of cancers, including the potential for rational combinatorial therapies.
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Affiliation(s)
- Erlinda M Gordon
- Cancer Center of Southern California/Sarcoma Oncology Center, Santa Monica, CA 90403, USA.,Aveni Foundation, Santa Monica, CA 90405, USA.,DELTA Next-Gen, LLC, Santa Monica, CA 90405, USA
| | - Joshua R Ravicz
- Cancer Center of Southern California/Sarcoma Oncology Center, Santa Monica, CA 90403, USA
| | - Seiya Liu
- Department of Cell Biology, Harvard University, Cambridge, MA 02138, USA
| | - Sant P Chawla
- Cancer Center of Southern California/Sarcoma Oncology Center, Santa Monica, CA 90403, USA
| | - Frederick L Hall
- Aveni Foundation, Santa Monica, CA 90405, USA.,DELTA Next-Gen, LLC, Santa Monica, CA 90405, USA
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4
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Yang X, Sun Y, Li H, Shao Y, Zhao D, Yu W, Fu J. C-terminal binding protein-2 promotes cell proliferation and migration in breast cancer via suppression of p16INK4A. Oncotarget 2018; 8:26154-26168. [PMID: 28412731 PMCID: PMC5432247 DOI: 10.18632/oncotarget.15402] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 02/01/2017] [Indexed: 01/27/2023] Open
Abstract
C-terminal binding protein-2 (CtBP2) enhances cancer proliferation and metastasis. The role and mechanism of CtBP2 in breast cancer remains to be elucidated. Western blot and immunochemistry were employed to evaluate the level of CtBP2 and p16INK4A in breast cancer. Genetic manipulation was used to study the expression of p16INK4A and its downstream genes regulated by CtBP2. Functional assays, including colony formation, wound healing, transwell invasion, anchorage-independent growth assay and a xenograft tumor model were used to determine the oncogenic role of CtBP2 in breast cancer progression. The expression of CtBP2 was increased in breast cancer tissues and cell lines. The expression of p16INK4A were inversely correlated CtBP2 (r2 = 0.43, P < 0.01). The expression of both CtBP2 and p16INK4A were significantly related to histological differentiation (P < 0.01 and P = 0.004, respectively) and metastasis (P = 0.046 and 0.047, respectively). The overall survival rate was lower in patients with increased CtBP2 expression and lower p16INK4A expression. Knockdown of CtBP2 resulted in the activation of p16INK4A and down–regulation of cell cycle regulators cyclin D, cyclin E and cyclin-dependent kinase 2 and 4. This down-regulation also led to a decreased transition of the G1-S phase in breast cancer cells. Moreover, gain-of-function experiments showed that CtBP2 suppressed p16INK4A and matrix metalloproteinase-2, subsequently enhancing the migration in breast cancer. However, the silence of CtBP2 abrogated this effect. Collectively, these findings provide insight into the role CtBP2 plays in promoting proliferation and migration in breast cancer by the inhibition of p16INK4A.
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Affiliation(s)
- Xiaojing Yang
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Yi Sun
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Hongling Li
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Yuhui Shao
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Depeng Zhao
- Department of Obstetrics, Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai 200040, P.R. China
| | - Weiwei Yu
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Jie Fu
- Department of Radiation Oncology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
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5
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Mao Z, Liu C, Lin X, Sun B, Su C. PPP2R5A: A multirole protein phosphatase subunit in regulating cancer development. Cancer Lett 2018; 414:222-229. [DOI: 10.1016/j.canlet.2017.11.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 11/20/2017] [Accepted: 11/21/2017] [Indexed: 12/21/2022]
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6
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Protein Phosphatase 2A: a Double-Faced Phosphatase of Cellular System and Its Role in Neurodegenerative Disorders. Mol Neurobiol 2017; 55:1750-1761. [PMID: 28224476 DOI: 10.1007/s12035-017-0444-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 02/03/2017] [Indexed: 12/17/2022]
Abstract
Protein phosphatase 2A (PP2A), a ubiquitously expressed serine/threonine phosphatase, is a vitally important phosphatase for the cellular system. Structurally, it is constituted of three different subunits, namely catalytic subunit (PP2Ac), structural scaffold subunit (PP2A-A), and regulatory subunit (PP2A-B). All subunits have various isoforms, and catalytic and scaffold subunits are ubiquitously expressed, whereas regulatory subunits are more specific to tissue and cell type. It is the numerous possibilities of PP2A holoenzyme assembly with varying isoform components that make it possess a dual nature of activator or the inhibitory character in different signaling pathways, namely neural developmental pathways, Akt/protein kinase B pathway, NF-kB pathway, MAPK pathway, apoptosis pathway, and cell cycle progression to name a few. Importantly, the expression of PP2A in the brain is highest among the serine phosphatases and is known to actively participate in the neural development process. However, the exact mechanism of action of PP2A is still debated and enunciating the holoenzyme components, especially the regulatory subunit of PP2A involved in regulating neural developmental process is still poorly understood. In this review, we try to throw some light on the involvement of various PP2A holoenzyme forms in the process of neurogenesis and progression of neurodegenerative diseases.
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7
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Lazo PA. Reverting p53 activation after recovery of cellular stress to resume with cell cycle progression. Cell Signal 2017; 33:49-58. [PMID: 28189587 DOI: 10.1016/j.cellsig.2017.02.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2016] [Revised: 01/23/2017] [Accepted: 02/06/2017] [Indexed: 11/17/2022]
Abstract
The activation of p53 in response to different types of cellular stress induces several protective reactions including cell cycle arrest, senescence or cell death. These protective effects are a consequence of the activation of p53 by specific phosphorylation performed by several kinases. The reversion of the cell cycle arrest, induced by p53, is a consequence of the phosphorylated and activated p53, which triggers its own downregulation and that of its positive regulators. The different down-regulatory processes have a sequential and temporal order of events. The mechanisms implicated in p53 down-regulation include phosphatases, deacetylases, and protein degradation by the proteasome or autophagy, which also affect different p53 protein targets and functions. The necessary first step is the dephosphorylation of p53 to make it available for interaction with mdm2 ubiquitin-ligase, which requires the activation of phosphatases targeting both p53 and p53-activating kinases. In addition, deacetylation of p53 is required to make lysine residues accessible to ubiquitin ligases. The combined action of these downregulatory mechanisms brings p53 protein back to its basal levels, and cell cycle progression can resume if cells have overcome the stress or damage situation. The specific targeting of these down-regulatory mechanisms can be exploited for therapeutic purposes in cancers harbouring wild-type p53.
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Affiliation(s)
- Pedro A Lazo
- Experimental Therapeutics and Translational Oncology Program, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas (CSIC), Universidad de Salamanca, Salamanca, Spain; Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain.
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8
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Comprehensive phenotypic analysis of knockout mice deficient in cyclin G1 and cyclin G2. Sci Rep 2016; 6:39091. [PMID: 27982046 PMCID: PMC5159814 DOI: 10.1038/srep39091] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Accepted: 11/17/2016] [Indexed: 01/12/2023] Open
Abstract
Cyclin G1 (CycG1) and Cyclin G2 (CycG2) play similar roles during the DNA damage response (DDR), but their detailed roles remain elusive. To investigate their distinct roles, we generated knockout mice deficient in CycG1 (G1KO) or CycG2 (G2KO), as well as double knockout mice (DKO) deficient in both proteins. All knockouts developed normally and were fertile. Generation of mouse embryonic fibroblasts (MEFs) from these mice revealed that G2KO MEFs, but not G1KO or DKO MEFs, were resistant to DNA damage insults caused by camptothecin and ionizing radiation (IR) and underwent cell cycle arrest. CycG2, but not CycG1, co-localized with γH2AX foci in the nucleus after γ-IR, and γH2AX-mediated DNA repair and dephosphorylation of CHK2 were delayed in G2KO MEFs. H2AX associated with CycG1, CycG2, and protein phosphatase 2A (PP2A), suggesting that γH2AX affects the function of PP2A via direct interaction with its B'γ subunit. Furthermore, expression of CycG2, but not CycG1, was abnormal in various cancer cell lines. Kaplan-Meier curves based on TCGA data disclosed that head and neck cancer patients with reduced CycG2 expression have poorer clinical prognoses. Taken together, our data suggest that reduced CycG2 expression could be useful as a novel prognostic marker of cancer.
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9
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Abstract
Protein phosphatase 2A (PP2A) plays a critical multi-faceted role in the regulation of the cell cycle. It is known to dephosphorylate over 300 substrates involved in the cell cycle, regulating almost all major pathways and cell cycle checkpoints. PP2A is involved in such diverse processes by the formation of structurally distinct families of holoenzymes, which are regulated spatially and temporally by specific regulators. Here, we review the involvement of PP2A in the regulation of three cell signaling pathways: wnt, mTOR and MAP kinase, as well as the G1→S transition, DNA synthesis and mitotic initiation. These processes are all crucial for proper cell survival and proliferation and are often deregulated in cancer and other diseases.
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Affiliation(s)
- Nathan Wlodarchak
- a McArdle Laboratory for Cancer Research, University of Wisconsin-Madison , Madison , WI , USA
| | - Yongna Xing
- a McArdle Laboratory for Cancer Research, University of Wisconsin-Madison , Madison , WI , USA
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10
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Ohno S, Naito Y, Mukai S, Yabuta N, Nojima H. ELAS1-mediated inhibition of the cyclin G1-B'γ interaction promotes cancer cell apoptosis via stabilization and activation of p53. Oncogene 2015; 34:5983-96. [PMID: 25915850 DOI: 10.1038/onc.2015.47] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 01/09/2015] [Accepted: 01/27/2015] [Indexed: 12/16/2022]
Abstract
Radiation therapy (RT) is useful for selectively killing cancer cells. However, because high levels of ionizing radiation (IR) are toxic to normal cells, RT cannot be applied repeatedly to cancer patients. Therefore, novel chemicals that enhance the efficacy of chemoradiotherapy (CRT) would be valuable. Here, we report that ELAS1, a peptide corresponding to the protein phosphatase 2A (PP2A) association domain of cyclin G1 (CycG1), can enhance the efficacy of CRT. ELAS1 interacts with the PP2A B'γ-subunit and competitively inhibits association with CycG1, thereby preventing the PP2A holoenzyme from dephosphorylating target proteins, Mdm2 (pT218) and p53 (pS46), following DNA double-strand break (DSB) insults. Doxycycline (Dox)-induced overexpression of Myc-ELAS1 caused γ-irradiation to induce apoptosis in human osteosarcoma (U2OS) cells, at 1/10th the effective dosage of γ-irradiation required for apoptosis in Myc-vector-expressing cells; ELAS1 peptide incorporation into U2OS cells also showed similar apoptotic effects. Moreover, administration of DSB-inducing chemicals, camptothecin (CPT) or irinotecan, to Myc-ELAS1-expressing U2OS cells also induced efficient apoptosis with only 1/100th (CPT) or 1/5th (irinotecan) of the amounts of drugs required for this effect in Myc-vector-expressing cells. Taken together, ELAS1 may be important for the design of ELAS1-mimetic compounds to improve CRT efficacy.
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Affiliation(s)
- S Ohno
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Y Naito
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - S Mukai
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - N Yabuta
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - H Nojima
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
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11
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Hong CS, Ho W, Zhang C, Yang C, Elder JB, Zhuang Z. LB100, a small molecule inhibitor of PP2A with potent chemo- and radio-sensitizing potential. Cancer Biol Ther 2015; 16:821-33. [PMID: 25897893 DOI: 10.1080/15384047.2015.1040961] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that plays a significant role in mitotic progression and cellular responses to DNA damage. While traditionally viewed as a tumor suppressor, inhibition of PP2A has recently come to attention as a novel therapeutic means of driving senescent cancer cells into mitosis and promoting cell death via mitotic catastrophe. These findings have been corroborated in numerous studies utilizing naturally produced compounds that selectively inhibit PP2A. To overcome the known human toxicities associated with these compounds, a water-soluble small molecule inhibitor, LB100, was recently developed to competitively inhibit the PP2A protein. This review summarizes the pre-clinical studies to date that have demonstrated the anti-cancer activity of LB100 via its chemo- and radio-sensitizing properties. These studies demonstrate the tremendous therapeutic potential of LB100 in a variety of cancer types. The results of an ongoing phase 1 trial are eagerly anticipated.
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Key Words
- ABC, ATP-binding cassette.
- APC, adenomatous polyposis coli
- ARPP19, cyclic AMP-regulated phosphoprotein 19
- ATM, ataxia-telangiectasia mutated
- CIP2A, cancerous inhibitor of PP2A
- CNTF, ciliary neurotrophic factor
- DISC, death-inducing signaling complex
- DVL, dishevelled
- ENSA, α-endosulphine
- GBM, glioblastoma
- GFAP, glial fibrillary acidic protein
- HCC, hepatocellular carcinoma
- HDACs, histone deacetylase complexes
- HIF-1a, hypoxia-inducible factor-1a
- HRR, homologous recombination repair
- MDM2, mouse double minute 2 homolog
- MRI, magnetic resonance imaging
- NPC, nasopharyngeal carcinoma
- PP2A, protein phosphatase 2A
- Plk1, polo-like kinase 1
- TCTP, translationally-controlled tumor protein
- TMZ, temozolomide
- TRAIL, TNF-related apoptosis-inducing ligand
- VEGF, vascular endothelial growth factor
- cell cycle
- chemosensitization
- mitotic catastrophe
- protein phosphatase 2A
- radiosensitizationreview
- small molecule inhibitor
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Affiliation(s)
- Christopher S Hong
- a The Ohio State University Wexner Medical Center ; Department of Neurological Surgery ; Columbus , OH USA
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12
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Al-Ansari MM, Hendrayani SF, Tulbah A, Al-Tweigeri T, Shehata AI, Aboussekhra A. p16INK4A represses breast stromal fibroblasts migration/invasion and their VEGF-A-dependent promotion of angiogenesis through Akt inhibition. Neoplasia 2012; 14:1269-77. [PMID: 23308058 PMCID: PMC3540951 DOI: 10.1593/neo.121632] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2012] [Revised: 10/24/2012] [Accepted: 10/29/2012] [Indexed: 01/09/2023]
Abstract
Stromal fibroblasts, the most abundant and probably the most active cellular component of breast cancer-associated stroma, become active and promote angiogenesis through paracrine effects. However, it still unclear how these processes are regulated. Here, we have shown that down-regulation of the tumor suppressor p16(INK4A) protein enhances the migration/invasion abilities of breast stromal fibroblasts, which form dendritic network of extensions into matrigel. Furthermore, we present clear evidence that p16(INK4A) represses the expression/secretion of the proangiogenesis protein vascular endothelial growth factor A (VEGF-A). Consequently, p16(INK4A)-deficient breast stromal fibroblasts and mouse embryonic fibroblasts enhanced endothelial cell differentiation into capillary-like structures in a paracrine manner. This effect was suppressed by adding bevacizumab, a specific VEGF-A inhibitor. Additionally, p16(INK4A)-defective mouse embryonic fibroblasts enhanced angiogenesis in breast cancer xenografts in mice. Furthermore, we have shown that p16(INK4A) suppresses the Akt/mammalian target of rapamycin (mTOR) signaling pathway and its downstream effector hypoxia-inducible factor 1-alpha (HIF-1α), which transactivates VEGF-A. Consequently, Akt inactivation suppressed both the p16(INK4A)-dependent autocrine effect on fibroblast migration/invasion and the paracrine effect on angiogenesis, showing the important role of this protein kinase in mediating the various effects related to p16(INK4A) deficiency. These results indicate that p16(INK4A) is an efficient inhibitor of the migration/invasion abilities of breast stromal fibroblasts and also their paracrine proangiogenic effects, through inhibition of Akt. Therefore, pharmacologic restoration of p16(INK4A) level in stromal fibroblasts may be exploited as therapeutic strategy to help eradicate tumor cells and/or prevent their recurrence, through suppressing cell non-autonomous procarcinogenic mediators.
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Affiliation(s)
- Mysoon M Al-Ansari
- Department of Molecular Oncology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Siti-Fauziah Hendrayani
- Department of Molecular Oncology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Asma Tulbah
- Department of Pathology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Taher Al-Tweigeri
- Department of Oncology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Afaf I Shehata
- Department of Microbiology, King Saud University, Riyadh, Saudi Arabia
| | - Abdelilah Aboussekhra
- Department of Molecular Oncology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
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13
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Wen W, Ding J, Sun W, Fu J, Chen Y, Wu K, Ning B, Han T, Huang L, Chen C, Xie D, Li Z, Feng G, Wu M, Xie W, Wang H. Cyclin G1-mediated epithelial-mesenchymal transition via phosphoinositide 3-kinase/Akt signaling facilitates liver cancer progression. Hepatology 2012; 55:1787-98. [PMID: 22271581 DOI: 10.1002/hep.25596] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Accepted: 12/02/2011] [Indexed: 12/07/2022]
Abstract
UNLABELLED Cyclin G1 deficiency is associated with reduced incidence of carcinogen-induced hepatocellular carcinoma (HCC), but its function in HCC progression remains obscure. We report a critical role of cyclin G1 in HCC metastasis. Elevated expression of cyclin G1 was detected in HCCs (60.6%), and its expression levels were even higher in portal vein tumor thrombus. Clinicopathological analysis revealed a close correlation of cyclin G1 expression with distant metastasis and poor prognosis of HCC. Forced expression of cyclin G1 promoted epithelial-mesenchymal transition (EMT) and metastasis of HCC cells in vitro and in vivo. Cyclin G1 overexpression enhanced Akt activation through interaction with p85 (regulatory subunit of phosphoinositide 3-kinase [PI3K]), which led to subsequent phosphorylation of glycogen synthase kinase-3β (GSK-3β) and stabilization of Snail, a critical EMT mediator. These results suggest that elevated cyclin G1 facilitates HCC metastasis by promoting EMT via PI3K/Akt/GSK-3β/Snail-dependent pathway. Consistently, we have observed a significant correlation between cyclin G1 expression and p-Akt levels in a cohort of HCC patients, and found that combination of these two parameters is a more powerful predictor of poor prognosis. CONCLUSIONS Cyclin G1 plays a pivotal role in HCC metastasis and may serve as a novel prognostic biomarker and therapeutic target.
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Affiliation(s)
- Wen Wen
- International Cooperation Laboratory on Signal Transduction of Eastern Hepatobiliary Surgery Institute, Shanghai, China
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14
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Gopinathan L, Ratnacaram CK, Kaldis P. Established and novel Cdk/cyclin complexes regulating the cell cycle and development. Results Probl Cell Differ 2011; 53:365-89. [PMID: 21630153 DOI: 10.1007/978-3-642-19065-0_16] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The identification of new members in the Cdk and cyclin families, functions for many of which are still emerging, has added new facets to the cell cycle regulatory network. With roles extending beyond the classical regulation of cell cycle progression, these new players are involved in diverse processes such as transcription, neuronal function, and ion transport. Members closely related to Cdks and cyclins such as the Speedy/RINGO proteins offer fresh insights and hope for filling in the missing gaps in our understanding of cell division. This chapter will present a broad outlook on the cell cycle and its key regulators with special emphasis on the less-studied members and their emerging roles.
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Affiliation(s)
- Lakshmi Gopinathan
- Cell Division and Cancer Laboratory (PRK), Institute of Molecular and Cell Biology (IMCB), 61 Biopolis Drive, Proteos #03-09, Singapore
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15
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Guergnon J, Godet AN, Galioot A, Falanga PB, Colle JH, Cayla X, Garcia A. PP2A targeting by viral proteins: a widespread biological strategy from DNA/RNA tumor viruses to HIV-1. Biochim Biophys Acta Mol Basis Dis 2011; 1812:1498-507. [PMID: 21856415 DOI: 10.1016/j.bbadis.2011.07.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 06/22/2011] [Accepted: 07/05/2011] [Indexed: 12/27/2022]
Abstract
Protein phosphatase 2A (PP2A) is a large family of holoenzymes that comprises 1% of total cellular proteins and accounts for the majority of Ser/Thr phosphatase activity in eukaryotic cells. Although initially viewed as constitutive housekeeping enzymes, it is now well established that PP2A proteins represent a family of highly and sophistically regulated phosphatases. The past decade, multiple complementary studies have improved our knowledge about structural and functional regulation of PP2A holoenzymes. In this regard, after summarizing major cellular regulation, this review will mainly focus on discussing a particulate biological strategy, used by various viruses, which is based on the targeting of PP2A enzymes by viral proteins in order to specifically deregulate, for their own benefit, cellular pathways of their hosts. The impact of such PP2A targeting for research in human diseases, and in further therapeutic developments, is also discussed.
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Affiliation(s)
- Julien Guergnon
- Laboratoire E3 Phosphatases-Unité Signalisation Moléculaire et Activation Cellulaire, Institut Pasteur 25, rue du Dr Roux, 75015 Paris, France
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16
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Yang J, Phiel C. Functions of B56-containing PP2As in major developmental and cancer signaling pathways. Life Sci 2010; 87:659-66. [PMID: 20934435 PMCID: PMC2993835 DOI: 10.1016/j.lfs.2010.10.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/08/2010] [Accepted: 09/23/2010] [Indexed: 12/20/2022]
Abstract
Members of the B'/B56/PR61 family regulatory subunits of PP2A determine the subcellular localization, substrate specificity, and catalytic activity of PP2A in a wide range of biological processes. Here, we summarize the structure and intracellular localization of B56-containing PP2As and review functions of B56-containing PP2As in several major developmental/cancer signaling pathways.
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Affiliation(s)
- Jing Yang
- The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, the Ohio State University, 700 Children's Dr., Columbus, OH, 43205, United States.
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17
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Gharbi-Ayachi A, Labbé JC, Burgess A, Vigneron S, Strub JM, Brioudes E, Van-Dorsselaer A, Castro A, Lorca T. The substrate of Greatwall kinase, Arpp19, controls mitosis by inhibiting protein phosphatase 2A. Science 2010; 330:1673-1677. [PMID: 21164014 DOI: 10.1016/b978-0-12-374145-5.00168-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Initiation and maintenance of mitosis require the activation of protein kinase cyclin B-Cdc2 and the inhibition of protein phosphatase 2A (PP2A), which, respectively, phosphorylate and dephosphorylate mitotic substrates. The protein kinase Greatwall (Gwl) is required to maintain mitosis through PP2A inhibition. We describe how Gwl activation results in PP2A inhibition. We identified cyclic adenosine monophosphate-regulated phosphoprotein 19 (Arpp19) and α-Endosulfine as two substrates of Gwl that, when phosphorylated by this kinase, associate with and inhibit PP2A, thus promoting mitotic entry. Conversely, in the absence of Gwl activity, Arpp19 and α-Endosulfine are dephosphorylated and lose their capacity to bind and inhibit PP2A. Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts.
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Affiliation(s)
- Aicha Gharbi-Ayachi
- Universités Montpellier 2 et 1, Centre de Recherche de Biochimie Macromoléculaire, CNRS UMR 5237, IFR 122, 1919 Route de Mende, 34293 Montpellier cedex 5, France
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18
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Jin Z, Wallace L, Harper SQ, Yang J. PP2A:B56{epsilon}, a substrate of caspase-3, regulates p53-dependent and p53-independent apoptosis during development. J Biol Chem 2010; 285:34493-502. [PMID: 20807766 DOI: 10.1074/jbc.m110.169581] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is one of the most abundantly expressed serine/threonine protein phosphatases. A large body of evidence suggests that PP2A is a tumor suppressor and plays critical roles in regulating apoptosis. PP2A is a heterotrimeric protein complex. Its substrate specificity, localization, and activity are regulated by regulatory subunits of PP2A. A recent study has demonstrated that single nucleotide polymorphism in B56ε (PPP2R5E), a B56 family regulatory subunit of PP2A, is associated with human soft tissue sarcoma. This raises the possibility that B56ε is involved in tumorigenesis and plays important roles in regulating apoptosis. However, this hypothesis has not been tested experimentally. Our previous studies revealed that B56ε regulates a number of developmental signaling pathways during early embryonic patterning. Here we report novel functions of B56ε in regulating apoptosis. We provide evidence that B56ε has both anti- and pro-apoptotic functions. B56ε suppresses p53-independent apoptosis during neural development, but triggers p53-dependent apoptosis. Mechanistically, B56ε regulates the p53-dependent apoptotic pathway solely through controlling the stability of p53 protein. In addition to its function in regulating apoptosis, we show that B56ε undergoes proteolytic cleavage. The cleavage of B56ε is mediated by caspase-3 and occurs on the carboxyl side of an evolutionarily conserved N-terminal "DKXD" motif. These results demonstrate that B56ε, a substrate of caspase-3, is an essential regulator of apoptosis. So far, we have identified an alternative translation isoform and a caspase cleavage product of B56ε. The significance of post-transcriptional regulation of B56ε is discussed.
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Affiliation(s)
- Zhigang Jin
- Department of Pediatrics, Research Institute at Nationwide Children's Hospital, Ohio State University, Columbus, Ohio 43205, USA
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19
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Fornari F, Gramantieri L, Giovannini C, Veronese A, Ferracin M, Sabbioni S, Calin GA, Grazi GL, Croce CM, Tavolari S, Chieco P, Negrini M, Bolondi L. MiR-122/cyclin G1 interaction modulates p53 activity and affects doxorubicin sensitivity of human hepatocarcinoma cells. Cancer Res 2009; 69:5761-7. [PMID: 19584283 DOI: 10.1158/0008-5472.can-08-4797] [Citation(s) in RCA: 318] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The identification of target genes is a key step for assessing the role of aberrantly expressed microRNAs (miRNA) in human cancer and for the further development of miRNA-based gene therapy. MiR-122 is a liver-specific miRNA accounting for 70% of the total miRNA population. Its down-regulation is a common feature of both human and mouse hepatocellular carcinoma (HCC). We have previously shown that miR-122 can regulate the expression of cyclin G1, whose high levels have been reported in several human cancers. We evaluated the role of miR-122 and cyclin G1 expression in hepatocarcinogenesis and in response to treatment with doxorubicin and their relevance on survival and time to recurrence (TTR) of HCC patients. We proved that, by modulating cyclin G1, miR-122 influences p53 protein stability and transcriptional activity and reduces invasion capability of HCC-derived cell lines. In addition, in a therapeutic perspective, we assayed the effects of a restored miR-122 expression in triggering doxorubicin-induced apoptosis and we proved that miR-122, as well as cyclin G1 silencing, increases sensitivity to doxorubicin challenge. In patients resected for HCC, lower miR-122 levels were associated with a shorter TTR, whereas higher cyclin G1 expression was related to a lower survival, suggesting that miR-122 might represent an effective molecular target for HCC. Our findings establish a basis toward the development of combined chemo- and miRNA-based therapy for HCC treatment.
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Affiliation(s)
- Francesca Fornari
- Dipartimento di Medicina Clinica e CRBA, Policlinico S.Orsola-Malpighi, Bologna, Italy
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20
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Sato J, Shimizu H, Kasama T, Yabuta N, Nojima H. GAK, a regulator of clathrin-mediated membrane trafficking, localizes not only in the cytoplasm but also in the nucleus. Genes Cells 2009; 14:627-41. [PMID: 19371378 DOI: 10.1111/j.1365-2443.2009.01296.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The ubiquitously expressed Cyclin G-associated kinase (GAK) regulates clathrin-mediated membrane trafficking in the cytoplasm. However, the association of GAK with a nuclear protein Cyclin G1 that is unrelated to membrane trafficking suggests an unidentified role of GAK in the nucleus. Indeed, we report here that GAK localizes in both cytoplasm and nucleus by immunostaining, ectopic expression of GFP-GAK and pull-down assays using dissected GAK fragments. GAK forms complexes not only with cyclin G1 but also with other nuclear proteins such as p53, clathrin heavy chain (CHC) and protein phosphatase 2A (PP2A) B'alpha1. Moreover, CHC associates with GAK via a different domain depending on whether it is in the cytoplasm or nucleus. Immunostaining revealed that about 20-30% of B'alpha1, cyclin G1 and p53 complex with nuclear GAK. CHC also displayed dots in the nucleus and almost all nuclear CHC signals colocalized with GAK. These observations together suggest an important function of GAK in the nucleus.
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Affiliation(s)
- Jun Sato
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita City, Osaka 565-0871, Japan
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21
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Oscillations by the p53-Mdm2 feedback loop. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 641:28-38. [PMID: 18783169 DOI: 10.1007/978-0-387-09794-7_2] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
The p53 network is perhaps the most important pathway involved in preventing the initiation of cancer, p53 levels and activity are upregulated in response to various stresses including DNA damage, hypoxia, and oncogene activation. Active p53 initiates different transcriptional programs that result in cell cycle arrest, cellular senescence or apoptosis. p53 also activates the transcription of Mdm2, which in turns target p53 for degradation, therefore creating a negative feedback loop on p53. Previous studies showed that the level of p53 increased dramatically after exposure to damaging radiation, then declined in a series of damped oscillations. Recent quantitative studies examined p53 responses in individual living cells, using time-lapse fluorescent microscopy and showed that-on an individual cell level-the oscillations are not damped. Instead, one cell may have only one pulse of p53, while its neighbor may show several repeated pulses. As the amount of irradiation increased, the percentage of cells showing a high number of p53 pulses also increased. The mean height and width of the pulses was constant and did not depend on the damage level. These observations opened new questions regarding the mechanism and function of p53 oscillatory dynamics. In this chapter I will review the different models that have been suggested for p53 oscillations, including proposed reasons for variation between cells, and will discuss potential functions for oscillatory dynamics in the p53 signaling pathway and in stress responses in general.
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22
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Lysine-independent turnover of cyclin G1 can be stabilized by B'alpha subunits of protein phosphatase 2A. Mol Cell Biol 2008; 29:919-28. [PMID: 18981217 DOI: 10.1128/mcb.00907-08] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Although the cyclin G1 gene is known to be regulated at the transcriptional level by p53, less is understood about the turnover of its protein product. We found that ectopically and endogenously expressed cyclin G1 protein is highly unstable and is degraded by a proteasome-mediated pathway. The N-terminal 137 amino acids of cyclin G1 (cyclin G(1-137)) are necessary and sufficient for both cyclin G1 ubiquitination and turnover. Interestingly, a mutant cyclin G1 (8KR) in which all lysine residues in this region have been replaced with arginine can be both ubiquitinated in cells and stabilized by a proteasome inhibitor to a similar extent as wild-type cyclin G(1-137). Furthermore, the presence of a six-Myc tag at the N terminus of cyclin G(1-137) significantly inhibits the protein's turnover, suggesting a role for the extreme N terminus of the protein in ubiquitin-mediated proteolysis. Although we and others previously showed that cyclin G1 protein can bind to MDM2, which functions as an E3 ubiquitin ligase to p53 and itself, cyclin G1 protein can be degraded in cells without MDM2 and p53. Interestingly, the B'alpha1 subunit of the serine/threonine protein phosphatase 2A, which binds to cyclin G1, can stabilize cyclin G1 under unstressed conditions and upon DNA damage, as well as inhibit the ability of cyclin G1 to be ubiquitinated. Our results thus indicate that proteasomal turnover of cyclin G1 is regulated by noncanonical processes.
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23
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Abstract
Cyclin G1 was identified as a transcriptional target of p53 that encodes a protein with strong homology to the cyclin family of cell cycle regulators. We show that either ectopically expressed or endogenous cyclin G1 protein is very unstable, undergoes modification with ubiquitin, and is likely degraded by the proteasome. Ectopic cyclin G1 protein stability is increased by cyclin box mutation or by association with inactive cyclin-dependent kinase (CDK) subunits, suggesting that a function of cyclin G1 as a CDK regulator may be required for its rapid turnover. Furthermore, cyclin G1 and the cyclin box mutant interact with and are ubiquitinated by MDM2, another transcriptional target of p53 that acts as a negative regulator of p53 stability. These data suggest that the cyclin box has a role in the proteasome-mediated degradation of cyclin G1 and thus suggest a putative role for a CDK in cyclin G1 metabolism and function.
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Affiliation(s)
- Denise M. Piscopo
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111 USA
| | - Philip W. Hinds
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111 USA
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24
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Kwon SH, Park JC, Ramachandran S, Cha SD, Kwon KY, Park JK, Park JW, Bae I, Cho CH. Loss of cyclin g1 expression in human uterine leiomyoma cells induces apoptosis. Reprod Sci 2008; 15:400-10. [PMID: 18497347 DOI: 10.1177/1933719107314063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Observations from the authors' laboratory suggest a physiological role for increased cyclin G1 protein levels in human uterine leiomyoma. The hypothesis of the present study is that the strategic modulation of cyclin G1 by antisense technology will inhibit the survival of in vitro-grown uterine leiomyoma cells. Cultured uterine leiomyoma cells were transfected with cyclin G1 ribbon-type antisense oligonucleotide (cyclin G1 RiAS) to effectively reduce cyclin G1 expression. Cell viability, in situ terminal deoxyuridine nick end-labeling (TUNEL) assay, flow cytometry, DNA fragmentation, and expression of cell cycle regulatory-related proteins were evaluated by Western blot. Antisense oligonucleotides compromised uterine leiomyoma cell viability and inducted apoptosis in a caspase-independent mechanism. In situ TUNEL and DNA fragmentation revealed apoptosis induction, and fluorescent-activated cell sorting analysis showed increased sub-G1-phase cells. Furthermore, abrogation of cyclin G1 enhanced p53 accumulation, phosphorylation of p53 at Ser-15 residue, and increased expression of cyclin-dependent kinase inhibitors p21 and p27. These data imply that cyclin G1 expression is associated with growth promotion and the potential utility and novelty of using ribbon-type antisense oligonucleotides as a gene therapy strategy to treat human uterine leiomyoma.
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Affiliation(s)
- Sang-Hoon Kwon
- Department of Obstetrics and Gynecology, School of Medicine, Keimyung University, Daegu, Korea
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25
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Seo HR, Kim J, Bae S, Soh JW, Lee YS. Cdk5-mediated phosphorylation of c-Myc on Ser-62 is essential in transcriptional activation of cyclin B1 by cyclin G1. J Biol Chem 2008; 283:15601-10. [PMID: 18408012 PMCID: PMC2414302 DOI: 10.1074/jbc.m800987200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Revised: 04/08/2008] [Indexed: 01/16/2023] Open
Abstract
It has been reported previously that cyclin G1 enables cells to overcome radiation-induced G(2) arrest and increased cell death and that these effects are mediated by transcriptional activation of cyclin B1. In this study, we further investigated the mechanism by which cyclin G1 transcriptionally activates cyclin B1. Deletion or point mutations within the cyclin B1 promoter region revealed that the c-Myc binding site (E-box) is necessary for cyclin G1-mediated transcriptional activation of cyclin B1 to occur. In addition, the kinase activity of Cdk5 was increased by cyclin G1 overexpression, and Cdk5 directly phosphorylated c-Myc on Ser-62. Furthermore, cyclin G1 mediated increased radiosensitivity, and radiation-induced M phase arrest was attenuated when RNA interference of Cdk5 was treated. Taken together, the results of this study indicate that Cdk5 activation in cells that overexpress cyclin G1 leads to c-Myc phosphorylation on Ser-62, which is responsible for cyclin G1-mediated transcriptional activation of cyclin B1.
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Affiliation(s)
- Haeng Ran Seo
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Joon Kim
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Sangwoo Bae
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Jae-Won Soh
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Yun-Sil Lee
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
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26
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Eichhorn PJA, Creyghton MP, Bernards R. Protein phosphatase 2A regulatory subunits and cancer. Biochim Biophys Acta Rev Cancer 2008; 1795:1-15. [PMID: 18588945 DOI: 10.1016/j.bbcan.2008.05.005] [Citation(s) in RCA: 274] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Revised: 05/20/2008] [Accepted: 05/21/2008] [Indexed: 01/06/2023]
Abstract
The serine/threonine protein phosphatase (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of a number of major signaling pathways whose deregulation can contribute to cancer. The specificity and activity of PP2A are highly regulated through the interaction of a family of regulatory B subunits with the substrates. Accumulating evidence indicates that PP2A acts as a tumor suppressor. In this review we summarize the known effects of specific PP2A holoenzymes and their roles in cancer relevant pathways. In particular we highlight PP2A function in the regulation of MAPK and Wnt signaling.
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Affiliation(s)
- Pieter J A Eichhorn
- Division of Molecular Carcinogenesis, Center for Cancer Genomics and Center for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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27
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Batchelor E, Mock C, Bhan I, Loewer A, Lahav G. Recurrent initiation: a mechanism for triggering p53 pulses in response to DNA damage. Mol Cell 2008; 30:277-89. [PMID: 18471974 PMCID: PMC2579769 DOI: 10.1016/j.molcel.2008.03.016] [Citation(s) in RCA: 298] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Revised: 11/20/2007] [Accepted: 03/30/2008] [Indexed: 01/26/2023]
Abstract
DNA damage initiates a series of p53 pulses. Although much is known about the interactions surrounding p53, little is known about which interactions contribute to p53's dynamical behavior. The simplest explanation is that these pulses are oscillations intrinsic to the p53/Mdm2 negative feedback loop. Here we present evidence that this simple mechanism is insufficient to explain p53 pulses; we show that p53 pulses are externally driven by pulses in the upstream signaling kinases, ATM and Chk2, and that the negative feedback between p53 and ATM, via Wip1, is essential for maintaining the uniform shape of p53 pulses. We propose that p53 pulses result from repeated initiation by ATM, which is reactivated by persistent DNA damage. Our study emphasizes the importance of collecting quantitative dynamic information at high temporal resolution for understanding the regulation of signaling pathways and opens new ways to manipulate p53 pulses to ask questions about their function in response to DNA damage.
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Affiliation(s)
- Eric Batchelor
- Department of Systems Biology, Harvard Medical School, Boston MA 02115, USA
| | - Caroline Mock
- Department of Systems Biology, Harvard Medical School, Boston MA 02115, USA
| | - Irun Bhan
- Department of Systems Biology, Harvard Medical School, Boston MA 02115, USA
- Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Boston, MA 02115, USA
| | - Alexander Loewer
- Department of Systems Biology, Harvard Medical School, Boston MA 02115, USA
| | - Galit Lahav
- Department of Systems Biology, Harvard Medical School, Boston MA 02115, USA
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28
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Xie H, Vucetic S, Iakoucheva LM, Oldfield CJ, Dunker AK, Uversky VN, Obradovic Z. Functional anthology of intrinsic disorder. 1. Biological processes and functions of proteins with long disordered regions. J Proteome Res 2007; 6:1882-98. [PMID: 17391014 PMCID: PMC2543138 DOI: 10.1021/pr060392u] [Citation(s) in RCA: 438] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Identifying relationships between function, amino acid sequence, and protein structure represents a major challenge. In this study, we propose a bioinformatics approach that identifies functional keywords in the Swiss-Prot database that correlate with intrinsic disorder. A statistical evaluation is employed to rank the significance of these correlations. Protein sequence data redundancy and the relationship between protein length and protein structure were taken into consideration to ensure the quality of the statistical inferences. Over 200,000 proteins from the Swiss-Prot database were analyzed using this approach. The predictions of intrinsic disorder were carried out using PONDR VL3E predictor of long disordered regions that achieves an accuracy of above 86%. Overall, out of the 710 Swiss-Prot functional keywords that were each associated with at least 20 proteins, 238 were found to be strongly positively correlated with predicted long intrinsically disordered regions, whereas 302 were strongly negatively correlated with such regions. The remaining 170 keywords were ambiguous without strong positive or negative correlation with the disorder predictions. These functions cover a large variety of biological activities and imply that disordered regions are characterized by a wide functional repertoire. Our results agree well with literature findings, as we were able to find at least one illustrative example of functional disorder or order shown experimentally for the vast majority of keywords showing the strongest positive or negative correlation with intrinsic disorder. This work opens a series of three papers, which enriches the current view of protein structure-function relationships, especially with regards to functionalities of intrinsically disordered proteins, and provides researchers with a novel tool that could be used to improve the understanding of the relationships between protein structure and function. The first paper of the series describes our statistical approach, outlines the major findings, and provides illustrative examples of biological processes and functions positively and negatively correlated with intrinsic disorder.
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Affiliation(s)
- Hongbo Xie
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
| | - Slobodan Vucetic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
| | - Lilia M. Iakoucheva
- Laboratory of Statistical Genetics, The Rockefeller University, New York, NY 10021, USA
| | - Christopher J. Oldfield
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
| | - A. Keith Dunker
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
| | - Vladimir N. Uversky
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
- Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia
| | - Zoran Obradovic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
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29
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Arnold HK, Sears RC. Protein phosphatase 2A regulatory subunit B56alpha associates with c-myc and negatively regulates c-myc accumulation. Mol Cell Biol 2006; 26:2832-44. [PMID: 16537924 PMCID: PMC1430332 DOI: 10.1128/mcb.26.7.2832-2844.2006] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 10/07/2005] [Accepted: 01/10/2006] [Indexed: 01/05/2023] Open
Abstract
Protein phosphatase 2A (PP2A) plays a prominent role in controlling accumulation of the proto-oncoprotein c-Myc. PP2A mediates its effects on c-Myc by dephosphorylating a conserved residue that normally stabilizes c-Myc, and in this way, PP2A enhances c-Myc ubiquitin-mediated degradation. Stringent regulation of c-Myc levels is essential for normal cell function, as c-Myc overexpression can lead to cell transformation. Conversely, PP2A has tumor suppressor activity. Uncovering relevant PP2A holoenzymes for a particular target has been limited by the fact that cellular PP2A represents a large heterogeneous population of trimeric holoenzymes, composed of a conserved catalytic subunit and a structural subunit along with a variable regulatory subunit which directs the holoenzyme to a specific target. We now report the identification of a specific PP2A regulatory subunit, B56alpha, that selectively associates with the N terminus of c-Myc. B56alpha directs intact PP2A holoenzymes to c-Myc, resulting in a dramatic reduction in c-Myc levels. Inhibition of PP2A-B56alpha holoenzymes, using small hairpin RNA to knock down B56alpha, results in c-Myc overexpression, elevated levels of c-Myc serine 62 phosphorylation, and increased c-Myc function. These results uncover a new protein involved in regulating c-Myc expression and reveal a critical interconnection between a potent oncoprotein, c-Myc, and a well-documented tumor suppressor, PP2A.
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Affiliation(s)
- Hugh K Arnold
- Department of Molecular and Medical Genetics, Oregon Health & Sciences University, 3181 S.W. Sam Jackson Park Rd., L103A, Portland, Oregon 97239, USA
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30
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Abstract
Genetic and biochemical evidence have demonstrated a direct link between Mdm2 and cancer development. Elevated expression of Mdm2 is observed in a significant proportion of different types of cancer. The major contribution of Mdm2 to the development of cancer is through a tight inhibition of the activities and stability of the tumor suppressor p53. However, extensive studies over the past few years have identified p53-independent functions of Mdm2, in the regulation of several important cellular processes and multiple signaling pathways. The promotion of cell cycle progression by Mdm2 is mediated via p53 inhibition, and by regulating the pRb/E2F complex. Mdm2 is an important mediator of growth and survival signaling in the PI3K/Akt pathway, an activator of certain steroid hormone receptors, and an inhibitor of the TGF-beta growth restrictive pathway. Thus, the impact on these pathways by deregulated Mdm2, as often observed in cancer, can be oncogenic in a permissible environment. This renders Mdm2 as an important target for the development of anti-cancer drugs.
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Affiliation(s)
- Yaara Levav-Cohen
- The Hebrew University Hadassah Medical School, Lautenberg Center for General and Tumor Immunology, Jerusalem, Israel
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31
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Chen Y, Perry D, Boackle SA, Sobel ES, Molina H, Croker BP, Morel L. Several Genes Contribute to the Production of Autoreactive B and T Cells in the Murine Lupus Susceptibility Locus Sle1c. THE JOURNAL OF IMMUNOLOGY 2005; 175:1080-9. [PMID: 16002709 DOI: 10.4049/jimmunol.175.2.1080] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The systemic lupus erythematosus 1 (Sle1) locus mediates the loss of tolerance to nuclear Ags in the NZM2410 mouse model of lupus through intrinsic defects in both B and T cells. Congenic analysis has shown that Sle1 corresponds to at least three genetic loci, Sle1a, Sle1b, and Sle1c. Telomeric Sle1c is associated with abnormal B cell responses to subthreshold stimulation with anti-IgM and C3d and with decreased T-dependent humoral immune responses. We have proposed that these phenotypes resulted from polymorphisms in the C3 complement receptor Cr2 gene. We have also found that Sle1c was associated with the production of histone-specific autoreactive CD4(+) T cells, which correlated with higher activation and proliferative responses, and a reduction in the CD4(+)CD25(+)CD62L(+)forkhead/winged helix transcription factor gene (Foxp3(+)) compartment. In this study we showed, using congenic recombinants, that the decreased humoral immune response and impaired GC formation map to the NZM2410 Cr2 allele. A chronic graft-vs-host disease model also showed that Sle1c produces significantly more autoreactive B cells than B6 controls, and that this phenotype maps to two regions excluding the Cr2 gene. Mixed bone marrow chimera demonstrated that the increased activation, proliferative response, and reduced regulatory T cell compartment were intrinsic to Sle1c-expressing CD4(+) T cells. These phenotypes mapped to the same two loci identified with the chronic graft-vs-host disease model, excluding the Cr2 region. Overall, these results show that Sle1c results in the production of autoreactive B and T cells through the expression of three different genes, one of which is consistent with Cr2, based on the phenotypes of the Cr2-deficient mice, and the other two corresponding to as yet unidentified genes.
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MESH Headings
- Animals
- B-Lymphocyte Subsets/immunology
- B-Lymphocyte Subsets/pathology
- B-Lymphocyte Subsets/radiation effects
- Cell Differentiation/genetics
- Cell Differentiation/immunology
- Chromosome Mapping
- Female
- Genetic Markers/immunology
- Genetic Predisposition to Disease
- Germinal Center/immunology
- Germinal Center/pathology
- Graft vs Host Disease/genetics
- Graft vs Host Disease/immunology
- Immunoglobulin G/biosynthesis
- Immunoglobulin M/biosynthesis
- Immunophenotyping
- Lupus Erythematosus, Systemic/genetics
- Lupus Erythematosus, Systemic/immunology
- Lupus Erythematosus, Systemic/pathology
- Male
- Mice
- Mice, Congenic
- Mice, Inbred C57BL
- Mice, Inbred NZB
- Radiation Chimera
- Receptors, Complement 3d/biosynthesis
- Receptors, Complement 3d/deficiency
- Receptors, Complement 3d/genetics
- Recombination, Genetic/immunology
- T-Lymphocyte Subsets/immunology
- T-Lymphocyte Subsets/pathology
- T-Lymphocyte Subsets/radiation effects
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Affiliation(s)
- Yifang Chen
- Department of Pathology, Immunology, and Laboratory Medicine, Department of Medicine, University of Florida, Gainesville, FL 32610, USA
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32
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Abstract
PP2A is one of the few serine/threonine-specific phosphatases in the cell, and its complex structure and regulation guarantees its many different functions. Some viruses have chosen to target this enzyme system in order to manage the host cell machinery for their own profit and to program cells into a malignant state. Suppression of PR61/B'gamma, a specific third regulatory subunit of PP2A, can substitute for the viral SV40 protein small t antigen in causing tumorigenic transformation of several human cell lines -- provided that telomerase, SV40 large T antigen and oncogenic Ras are also present. Accumulation of c-Myc seems to be the common denominator.
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Affiliation(s)
- Veerle Janssens
- Afdeling Biochemie, KU Leuven, Faculteit Geneeskunde, Campus Gasthuisberg, Herestraat 49 Bus 901, B-3000 Leuven, Belgium
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33
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Yue L, Daikoku T, Hou X, Li M, Wang H, Nojima H, Dey SK, Das SK. Cyclin G1 and cyclin G2 are expressed in the periimplantation mouse uterus in a cell-specific and progesterone-dependent manner: evidence for aberrant regulation with Hoxa-10 deficiency. Endocrinology 2005; 146:2424-33. [PMID: 15661853 PMCID: PMC4274954 DOI: 10.1210/en.2004-1605] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Because uterine cell-specific proliferation, differentiation, and apoptosis are differentially regulated during the periimplantation period, we speculated that negative cell cycle regulators are also operative in the uterus during this period. This prompted us to examine the roles of two negative growth-regulatory genes, cyclin G1 and cyclin G2, in the periimplantation mouse uterus. We show that cyclin G1 and cyclin G2 genes are differentially regulated in the uterus during this period (d 1-8 of pregnancy) in a spatiotemporal manner. The results suggest that cyclin G1 is primarily associated with epithelial cell differentiation before implantation and stromal cell proliferation and differentiation during decidualization, whereas cyclin G2 is associated with terminal differentiation and apoptosis of the luminal epithelial and stromal cells at the site of blastocyst after implantation. Pharmacological and genetic studies provide evidence that the expression of cyclin G1, not cyclin G2, is regulated by progesterone via its nuclear receptor. Furthermore, the expression of these genes is aberrantly up-regulated in homeo box A-10 mutant uteri, suggesting that cyclin G1 and cyclin G2 genes act as downstream targets of homeobox A-10 and negatively impact uterine cell proliferation. Collectively, our present and previous studies suggest that negative cell cycle regulators collaborate with growth-promoting regulators in regulating uterine cell-specific proliferation, differentiation, and apoptosis relevant to implantation and decidualization.
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Affiliation(s)
- Limin Yue
- Division of Reproductive and Developmental Biology, Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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34
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Ohtsuka T, Jensen MR, Kim HG, Kim KT, Lee SW. The negative role of cyclin G in ATM-dependent p53 activation. Oncogene 2004; 23:5405-8. [PMID: 15077171 DOI: 10.1038/sj.onc.1207693] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cyclin G is one of the earliest p53 target genes to be identified, but its function in the p53 pathway has been elusive. Although the precise mechanisms of cyclin G in this novel network have not been explored, recent studies have demonstrated that cyclin G is a key regulator of the p53-Mdm2 network. Here we present evidence that cyclin G-mediated p53 regulation is dependent upon the status of ataxia-telangiectasia mutated (ATM) protein, which activates p53 in response to DNA damage. Abrogation of cyclin G enhances p53 accumulation and phosphorylation of p53 at the Ser-15 residue, resulting in cell cycle arrest. Ectopically expressed cyclin G significantly reduces the steady-state levels of p53 as well as that of phosphorylated p53 at Ser-15 after DNA damage in normal human dermal fibroblasts containing normal ATM. However, cyclin G does not cause similar reductions in p53 levels in ATM-mutated cells. We also show that translocation of cyclin G to the nucleus requires functional ATM. Thus, our findings identify a new role of cyclin G in ATM-dependent p53 regulation and in cell cycle regulation during DNA damage.
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Affiliation(s)
- Takao Ohtsuka
- Cancer Biology Program, Hematology/Oncology Division, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02115, USA
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35
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Martínez-Gac L, Marqués M, García Z, Campanero MR, Carrera AC. Control of cyclin G2 mRNA expression by forkhead transcription factors: novel mechanism for cell cycle control by phosphoinositide 3-kinase and forkhead. Mol Cell Biol 2004; 24:2181-9. [PMID: 14966295 PMCID: PMC350549 DOI: 10.1128/mcb.24.5.2181-2189.2004] [Citation(s) in RCA: 153] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Revised: 08/29/2003] [Accepted: 12/04/2003] [Indexed: 11/20/2022] Open
Abstract
Cyclin G2 is an unconventional cyclin highly expressed in postmitotic cells. Unlike classical cyclins that promote cell cycle progression, cyclin G2 blocks cell cycle entry. Here we studied the mechanisms that regulate cyclin G2 mRNA expression during the cell cycle. Analysis of synchronized NIH 3T3 cell cultures showed elevated cyclin G2 mRNA expression levels at G(0), with a considerable reduction as cells enter cell cycle. Downregulation of cyclin G2 mRNA levels requires activation of phosphoinositide 3-kinase, suggesting that this enzyme controls cyclin G2 mRNA expression. Because the phosphoinositide 3-kinase pathway inhibits the FoxO family of forkhead transcription factors, we examined the involvement of these factors in the regulation of cyclin G2 expression. We show that active forms of the forkhead transcription factor FoxO3a (FKHRL1) increase cyclin G2 mRNA levels. Cyclin G2 has forkhead consensus motifs in its promoter, which are transactivated by constitutive active FoxO3a forms. Finally, interference with forkhead-mediated transcription by overexpression of an inactive form decreases cyclin G2 mRNA expression levels. These results show that FoxO genes regulate cyclin G2 expression, illustrating a new role for phosphoinositide 3-kinase and FoxO transcription factors in the control of cell cycle entry.
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Affiliation(s)
- Lorena Martínez-Gac
- Department of Immunology and Oncology, Centro Nacional de Biotecnología/CSIC, Universidad Autónoma de Madrid, Cantoblanco, Madrid E-28049, Spain
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36
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Chen W, Possemato R, Campbell KT, Plattner CA, Pallas DC, Hahn WC. Identification of specific PP2A complexes involved in human cell transformation. Cancer Cell 2004; 5:127-36. [PMID: 14998489 DOI: 10.1016/s1535-6108(04)00026-1] [Citation(s) in RCA: 262] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2003] [Revised: 12/03/2003] [Accepted: 12/23/2003] [Indexed: 12/30/2022]
Abstract
The SV40 small t antigen (ST) interacts with the serine-threonine protein phosphatase 2A (PP2A). To investigate the role of this interaction in transformation, we suppressed the expression of the PP2A B56gamma subunit in human embryonic kidney (HEK) epithelial cells expressing SV40 large T antigen, hTERT, and H-RAS. Suppression of PP2A B56gamma expression inhibited PP2A-specific phosphatase activity similar to that achieved by ST and conferred the ability to grow in an anchorage-independent fashion and to form tumors. Overexpression of PP2A B56gamma3 in tumorigenic HEK cells expressing ST or human lung cancer cell lines partially reversed the tumorigenicity of these cells. These observations identify specific PP2A complexes involved in human cell transformation.
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Affiliation(s)
- Wen Chen
- Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA
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37
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Dohoney KM, Guillerm C, Whiteford C, Elbi C, Lambert PF, Hager GL, Brady JN. Phosphorylation of p53 at serine 37 is important for transcriptional activity and regulation in response to DNA damage. Oncogene 2004; 23:49-57. [PMID: 14712210 DOI: 10.1038/sj.onc.1207005] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The p53 tumor suppressor protein plays a critical role in mediating cellular response to stress. Upon DNA damage, post-translational modifications stabilize and activate this nuclear phosphoprotein. To determine the effect of phosphorylation site mutants in the context of the whole p53 protein, we performed reporter assays in p53 and MDM2 knockout mouse embryonic fibroblasts transfected with full-length p53 constructs. We show that mutation of S37 causes a decrease in p53 transcriptional activity compared to wild-type p53. Our data further suggest that the dephosphorylation of p53 at S37 is a regulated event involving protein phosphatase 2A (PP2A). Coimmunoprecipitation and immunofluorescence microscopy studies demonstrate that PP2A and p53 associate with one another in vivo following gamma-irradiation. Consistent with these observations, phosphorylated S37 accumulates in cell extracts prepared from gamma-irradiated Molt-4 cells in the presence of okadaic acid. Furthermore, in vitro phosphatase assays show that PP2A dephosphorylates p53 at S37. These results suggest that dephosphorylation of p53 at S37 plays a role in the transcriptional regulation of the p53 protein in response to DNA damage.
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Affiliation(s)
- Kathleen M Dohoney
- Basic Research Laboratory, Virus Tumor Biology Section, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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38
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Van Hoof C, Goris J. Phosphatases in apoptosis: to be or not to be, PP2A is in the heart of the question. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1640:97-104. [PMID: 12729918 DOI: 10.1016/s0167-4889(03)00029-6] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Protein phosphatase type 2A (PP2A) is a major Ser/Thr phosphatase involved in several cellular signal transduction pathways. In this review, we will focus on recent progress concerning the role of PP2A in apoptotic signalling. Since PP2A activates pro-apoptotic and inhibits anti-apoptotic proteins of the Bcl-2 family, we conclude that PP2A has a positive regulatory function in apoptosis. However, in Drosophila, a specific subset of the PP2A holoenzyme family, containing B'/PR61 as third regulatory subunit, is inhibitory for apoptosis, suggesting different regulatory mechanisms and substrates in different species. Moreover, PP2A acts not only upstream as a regulator of the apoptotic signal transduction pathway but also downstream as a substrate of effector caspases. Hence, PP2A is involved in the regulation as well as in the cellular response of apoptosis. Probably, various PP2A holoenzymes with distinct regulatory subunits specifically target different apoptotic substrates. This could explain the implication of PP2A at several levels of the apoptotic signal transduction pathway. Finally, some viral proteins such as adenovirus E4orf4 and simian virus small t target PP2A to alter its activity, resulting in induction of apoptosis as a regulatory mechanism to enhance virus spread.
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Affiliation(s)
- Christine Van Hoof
- Afdeling Biochemie, Faculteit Geneeskunde, Campus Gasthuisberg O&N, Katholieke Universiteit Leuven, Herestraat 49, B-3000 Leuven, Belgium
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39
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Jensen MR, Factor VM, Fantozzi A, Helin K, Huh CG, Thorgeirsson SS. Reduced hepatic tumor incidence in cyclin G1-deficient mice. Hepatology 2003; 37:862-70. [PMID: 12668979 DOI: 10.1053/jhep.2003.50137] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Cyclin G1 is a transcriptional target of the tumor suppressor p53, and its expression is increased after DNA damage. Recent data show that cyclin G1 can regulate the levels of p53 by a mechanism that involves dephosphorylation of Mdm2 by protein phosphatase 2A. To understand the biologic role of cyclin G1, we have generated cyclin G1-deficient mice. In agreement with previous results, we showed that these mice develop normally, and that proliferation and induction of cellular senescence in cyclin G1-deficient mouse embryo fibroblasts are indistinguishable from wild-type fibroblasts. However, we found that the p53 levels in the cyclin G1-deficient mice are 2-fold higher that in wild-type mice. Moreover, we showed that treatment of mice with the alkylating agent 1,4-bis[N,N'-di(ethylene)-phosphamide]piperazine (Dipin), followed by partial hepatectomy, decreased G1-S transition in cyclin G1-null hepatocytes as compared with wild type. Finally, we found a significant decrease in tumor incidence, mass, and malignancy in both male and female cyclin G1-null mice after treatment with the potent hepatocarcinogen N-diethylnitrosamine. Taken with recent published data, our results suggest that cyclin G1, together with Mdm2, constitute a part of a negative feedback system that attenuates the activity of p53. In conclusion, our data suggest that the decreased tumor susceptibility after loss of cyclin G1 function is caused by the increased tumor suppressor action of p53.
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Affiliation(s)
- Michael Rugaard Jensen
- Laboratory of Experimental Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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40
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Baek WK, Kim D, Jung N, Yi YW, Kim JM, Cha SD, Bae I, Cho CH. Increased expression of cyclin G1 in leiomyoma compared with normal myometrium. Am J Obstet Gynecol 2003; 188:634-9. [PMID: 12634633 DOI: 10.1067/mob.2003.140] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE The purpose of this study was to detect the expression of cyclin G1 in leiomyoma and to investigate the alteration of its expression compared with normal myometrial tissue that was obtained from the same patient. STUDY DESIGN With the use of Northern blot analysis, Western blot analysis, and immunohistochemistry, we analyzed the expression of cyclin G1 in 24 patients who underwent hysterectomies. RESULTS We found that messenger RNA levels of cyclin G1 were elevated in human leiomyomas compared with their adjacent normal myometrial tissues. Consistent with elevated messenger RNA levels, high levels of cyclin G1 protein expression were detected by immunoblot analysis in all leiomyoma samples. Immunohistochemistry revealed that cyclin G1 is located mainly in the nucleus in both normal myometrium and leiomyoma. However, higher levels of cyclin G1 were apparent in tumor regions compared with adjacent normal myometrial regions. In addition, we found the expression levels of other cyclins (A and E) and CDK2 were elevated in leiomyomas compared with normal myometrium. Because cyclin G1 is a transcriptional target of the p53 tumor suppressor, we examined the p53 status of all eight leiomyoma samples and found no p53 mutations. CONCLUSION These results suggest that cyclin G1 is frequently overexpressed in uterine leiomyoma in a p53-independent manner and that this abnormality could be attributed to the severe proliferation of human uterine leiomyomas.
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Affiliation(s)
- Won-Ki Baek
- Department of Microbiology, School of Medicine, Keimyung University, Daegu, Korea
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41
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Brown BM, Carlson BL, Zhu X, Lolley RN, Craft CM. Light-driven translocation of the protein phosphatase 2A complex regulates light/dark dephosphorylation of phosducin and rhodopsin. Biochemistry 2002; 41:13526-38. [PMID: 12427013 DOI: 10.1021/bi0204490] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In steps of protein purification of bovine retinal protein phosphatase 2A (PP2A), phosducin dephosphorylation activity peaks coelute with a PP2A enzyme complex, shown by peptide sequence analysis to contain a B' subunit, B56 epsilon. Other PP2A complexes with a slightly larger (56.5 kDa) B' subunit (sequenced to be B56 alpha) or with the B alpha regulatory subunit have no phosducin dephosphorylation activity. Upon exposure to light, a significant increase in the immunoreactive protein level of the A, C, and B56 epsilon PP2A subunits is observed in the cytosolic fraction of mouse retina, the phosducin dephosphorylation of which occurs rapidly. During dark exposure, these subunits translocate to the membrane fraction where rhodopsin is slowly dephosphorylated. This PP2A redistribution occurs in less than 1.5 min and is dependent upon light and not upon an intrinsic circadian rhythm. Forty times more of the A subunit (approximately 20 ng/mouse retina) and 9 times more of the C subunit (approximately 4 ng/mouse retina) than of the B56 epsilon subunit (approximately 0.45 ng/mouse retina) redistribute, which suggests that the predominant form of the PP2A enzyme complex on the membrane in the dark is a dimer, consisting of only A and C subunits. We observe that the dimer favors phosphorylated opsin as a substrate, while the trimer, particularly the enzyme complex with the B56 epsilon subunit, greatly prefers phosphorylated phosducin, with an activity several hundred times those of other substrates that were tested. This light-driven PP2A translocation provides a potential mechanism for efficient dephosphorylation of two critical photoreceptor transduction proteins, cytosolic phosducin and membrane-bound rhodopsin, by the same enzyme.
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Affiliation(s)
- Bruce M Brown
- The Mary D. Allen Laboratory for Vision Research, Doheny Eye Institute, and Department of Cell and Neurobiology, Keck School of Medicine of the University of Southern California, Los Angeles, California 90089-9112, USA
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Strack S. Overexpression of the protein phosphatase 2A regulatory subunit Bgamma promotes neuronal differentiation by activating the MAP kinase (MAPK) cascade. J Biol Chem 2002; 277:41525-32. [PMID: 12191994 DOI: 10.1074/jbc.m203767200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Protein serine/threonine phosphatase 2A (PP2A) is a multifunctional regulator of cellular signaling. Variable regulatory subunits associate with a core dimer of scaffolding and catalytic subunits and are postulated to dictate substrate specificity and subcellular location of the heterotrimeric PP2A holoenzyme. The role of brain-specific regulatory subunits in neuronal differentiation and signaling was investigated in the PC6-3 subline of PC12 cells. Endogenous Bbeta, Bgamma, and B'beta protein expression was induced during nerve growth factor (NGF)-mediated neuronal differentiation. Transient expression of Bgamma, but not other PP2A regulatory subunits, facilitated neurite outgrowth in the absence and presence of NGF. Tetracycline-inducible expression of Bgamma caused growth arrest and neurofilament expression, further evidence that PP2A/Bgamma can promote differentiation. In PC6-3 cells, but not non-neuronal cell lines, Bgamma specifically promoted long lasting activation of the mitogen-activated protein (MAP) kinase cascade, a key mediator of neuronal differentiation. Pharmacological and dominant-negative inhibition and kinase assays indicate that Bgamma promotes neuritogenesis by stimulating the MAP kinase cascade downstream of the TrkA NGF receptor but upstream or at the level of the B-Raf kinase. Mutational analyses demonstrate that the divergent N terminus is critical for Bgamma activity. These studies implicate PP2A/Bgamma as a positive regulator of MAP kinase signaling in neurons.
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Affiliation(s)
- Stefan Strack
- Department of Pharmacology, University of Iowa, College of Medicine, Iowa City 52242, USA.
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43
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Abstract
SR proteins constitute a family of pre-mRNA splicing factors that play important roles in both constitutive and regulated splicing. Here, we describe one member of the family, which we call SRp38, with unexpected properties. Unlike other SR proteins, SRp38 cannot activate splicing and is essentially inactive in splicing assays. However, dephosphorylation converts SRp38 to a potent, general repressor that inhibits splicing at an early step. To investigate the cellular function of SRp38, we examined its possible role in cell cycle control. We show first that splicing, like other steps in gene expression, is inhibited in extracts of mitotic cells. Strikingly, SRp38 was found to be dephosphorylated specifically in mitotic cells, and we show that dephosphorylated SRp38 is required for the observed splicing repression.
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Affiliation(s)
- Chanseok Shin
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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44
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Kimura SH, Nojima H. Cyclin G1 associates with MDM2 and regulates accumulation and degradation of p53 protein. Genes Cells 2002; 7:869-80. [PMID: 12167164 DOI: 10.1046/j.1365-2443.2002.00564.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Cyclin G1 is a transcriptional target of p53 and is induced by DNA damage in a p53 dependent manner. Analysis of cyclin G1 disrupted mice demonstrated that cyclin G1 is involved in many of the functions regulated by p53 such as apoptosis, growth control and check point regulation in response to DNA damage. The results suggest that the main role of cyclin G1 is to mediate or regulate the function of p53. RESULTS Western blot analysis revealed that the accumulation of p53 protein during the initial 24 h period following DNA damage is reduced in cyclin G1-/- cells compared to wild-type cells. This decrease in p53 accumulation could be recovered by introducing a cDNA expressing cyclin G1. Cyclin G1 interacted directly with MDM2 and promoted the formation of the ARF/MDM2 complex within the initial 24 h period following DNA damage. Furthermore, 48 h after irradiation, accumulation of p53 protein was enhanced in cyclin G1-/- cells compared to wild-type cells. In contrast, in 48 h postirradiated wild-type cells, the cyclin G1-MDM2 complex was found not to be associated with ARF but with the B'alpha subunit of protein phosphatase A. CONCLUSION These results suggest that cyclin G1 stabilizes and promotes the degradation of p53 protein by associating, respectively, with MDM2 complexes containing ARF and PP2A.
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Affiliation(s)
- Shinya H Kimura
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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45
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Bennin DA, Don ASA, Brake T, McKenzie JL, Rosenbaum H, Ortiz L, DePaoli-Roach AA, Horne MC. Cyclin G2 associates with protein phosphatase 2A catalytic and regulatory B' subunits in active complexes and induces nuclear aberrations and a G1/S phase cell cycle arrest. J Biol Chem 2002; 277:27449-67. [PMID: 11956189 DOI: 10.1074/jbc.m111693200] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cyclin G2, together with cyclin G1 and cyclin I, defines a novel cyclin family expressed in terminally differentiated tissues including brain and muscle. Cyclin G2 expression is up-regulated as cells undergo cell cycle arrest or apoptosis in response to inhibitory stimuli independent of p53 (Horne, M., Donaldson, K., Goolsby, G., Tran, D., Mulheisen, M., Hell, J. and Wahl, A. (1997) J. Biol. Chem. 272, 12650-12661). We tested the hypothesis that cyclin G2 may be a negative regulator of cell cycle progression and found that ectopic expression of cyclin G2 induces the formation of aberrant nuclei and cell cycle arrest in HEK293 and Chinese hamster ovary cells. Cyclin G2 is primarily partitioned to a detergent-resistant compartment, suggesting an association with cytoskeletal elements. We determined that cyclin G2 and its homolog cyclin G1 directly interact with the catalytic subunit of protein phosphatase 2A (PP2A). An okadaic acid-sensitive (<2 nm) phosphatase activity coprecipitates with endogenous and ectopic cyclin G2. We found that cyclin G2 also associates with various PP2A B' regulatory subunits, as previously shown for cyclin G1. The PP2A/A subunit is not detectable in cyclin G2-PP2A-B'-C complexes. Notably, cyclin G2 colocalizes with both PP2A/C and B' subunits in detergent-resistant cellular compartments, suggesting that these complexes form in living cells. The ability of cyclin G2 to inhibit cell cycle progression correlates with its ability to bind PP2A/B' and C subunits. Together, our findings suggest that cyclin G2-PP2A complexes inhibit cell cycle progression.
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Affiliation(s)
- David A Bennin
- Department of Pharmacology, University of Wisconsin, Madison, WI 53706-1532, USA
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46
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Abstract
A recent study published in the April issue of Molecular Cell has shown that cyclin G, a p53 target, is a regulatory component of the active PP2A holoenzyme, which activates Mdm2 through dephosphorylation. These findings suggest that cyclin G is a key regulator of the p53-Mdm2 network.
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Affiliation(s)
- Xinbin Chen
- Department of Cell Biology, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Okamoto K, Li H, Jensen MR, Zhang T, Taya Y, Thorgeirsson SS, Prives C. Cyclin G recruits PP2A to dephosphorylate Mdm2. Mol Cell 2002; 9:761-71. [PMID: 11983168 DOI: 10.1016/s1097-2765(02)00504-x] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The function of cyclin G, a commonly induced p53 target, has remained elusive. We show that cyclin G forms a quaternary complex in vivo and in vitro with enzymatically active phosphatase 2A (PP2A) holoenzymes containing B' subunits. Interestingly, cyclin G also binds in vivo and in vitro to Mdm2 and markedly stimulates the ability of PP2A to dephosphorylate Mdm2 at T216. Consistent with these data, cyclin G null cells have both Mdm2 that is hyperphosphorylated at T216 and markedly higher levels of p53 protein when compared to wild-type cells. Cyclin G expression also results in reduced phosphorylation of human Hdm2 at S166. Thus, our data suggest that cyclin G recruits PP2A in order to modulate the phosphorylation of Mdm2 and thereby to regulate both Mdm2 and p53.
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Affiliation(s)
- Koji Okamoto
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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McCluskey A, Sim ATR, Sakoff JA. Serine-threonine protein phosphatase inhibitors: development of potential therapeutic strategies. J Med Chem 2002; 45:1151-75. [PMID: 11881984 DOI: 10.1021/jm010066k] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Adam McCluskey
- School of Biological & Chemical Science, Medicinal Chemistry Group, The University of Newcastle, Callaghan, NSW 2308, Australia.
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Abstract
The product of the MDM2 gene interacts with and regulates a number of proteins, in particular the tumor suppressor p53. The MDM2 protein is likely to be extensively modified in vivo, and such modification may regulate its functions in cells. We identified a potential cyclin-dependent kinase (CDK) site in murine MDM2, and found the protein to be efficiently phosphorylated in vitro by cyclin A-containing complexes (cyclin A-CDK2 and cyclin A-CDK1), but MDM2 was either weakly or not phosphorylated by other cyclin-containing complexes. Moreover, a peptide containing a putative MDM2 cyclin recognition motif specifically inhibited phosphorylation by cyclin A-CDK2. The site of cyclin A-CDK2 phosphorylation was identified as Thr-216 by two-dimensional phosphopeptide mapping and mutational analysis. Phosphorylation of MDM2 at Thr-216 both weakens its interaction with p53 and modestly augments its binding to p19(ARF). Interestingly, an MDM2-specific monoclonal antibody, SMP14, cannot recognize MDM2 phosphorylated at Thr-216. Changes in SMP14 reactivity of MDM2 in staged cell extracts indicate that phosphorylation of MDM2 at Thr-216 in vivo is most prevalent at the onset of S phase when cyclin A first becomes detectable.
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Affiliation(s)
- T Zhang
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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Forsyth CJ, Dounay AB, Sabes SF, Urbanek RA. Biotherapeutic potential and synthesis of okadaic acid. ERNST SCHERING RESEARCH FOUNDATION WORKSHOP 2001:57-102. [PMID: 11077606 DOI: 10.1007/978-3-662-04042-3_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- C J Forsyth
- Department of Chemistry, University of Minnesota, Minneapolis 55455-0431, USA
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