151
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Meijer HJG, Govers F. Genomewide analysis of phospholipid signaling genes in Phytophthora spp.: novelties and a missing link. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2006; 19:1337-47. [PMID: 17153918 DOI: 10.1094/mpmi-19-1337] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Phospholipids are cellular membrane components in eukaryotic cells that execute many important roles in signaling. Genes encoding enzymes required for phospholipid signaling and metabolism have been characterized in several organisms, but only a few have been described for oomycetes. In this study, the genome sequences of Phytophthora sojae and P. ramorum were explored to construct a comprehensive genomewide inventory of genes involved in the most universal phospholipid signaling pathways. Several genes and gene families were annotated, including those encoding phosphatidylinositol synthase (PIS), phosphatidylinositol (phosphate) kinase (PI[P]K), diacylglycerol kinase (DAG), and phospholipase D (PLD). The most obvious missing link is a gene encoding phospholipase C (PLC). In all eukaryotic genomes sequenced to date, PLC genes are annotated based on certain conserved features; however, these genes seem to be absent in Phytophthora spp. Analysis of the structural and regulatory domains and domain organization of the predicted isoforms of PIS, PIK, PIPK, DAG, and PLD revealed many novel features compared with characterized representatives in other eukaryotes. Examples are transmembrane proteins with a C-terminal catalytic PLD domain, secreted PLD-like proteins, and PIPKs that have an N-terminal G-protein-coupled receptor-transmembrane signature. Compared with other sequenced eukaryotes, the genus Phytophthora clearly has several exceptional features in its phospholipid-modifying enzymes.
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Affiliation(s)
- Harold J G Meijer
- Laboratory of Phytopathology, Plant Sciences Group, Wageningen University, Binnenhaven 5, NL-6709 PD Wageningen, The Netherlands.
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152
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Abstract
The story of rapamycin is a pharmaceutical fairytale. Discovered as an antifungal activity in a soil sample collected on Easter Island, this macrocyclic lactone and its derivatives are now billion dollar drugs, used in, and being evaluated for, a number of clinical applications. Taking advantage of its antifungal property, the molecular Target Of Rapamycin, TOR, was first described in the budding yeast Saccharomyces cerevisiae. TORs encode large, Ser/Thr protein kinases that reside in two distinct, structurally and functionally conserved, multi-protein complexes. In yeast, these complexes coordinate many different aspects of cell growth. TOR complex 1, TORC1, promotes protein synthesis and other anabolic processes, while inhibiting macroautophagy and other catabolic and stress-response processes. TORC2 primarily regulates cell polarity, although additional readouts of this complex are beginning to be characterized. TORC1 appears to be activated by nutrient cues and inhibited by stresses and rapamycin; however, detailed mechanisms are not known. In contrast, TORC2 is insensitive to rapamycin and physiological regulators of this complex have yet to be defined. Given the unsurpassed resources available to yeast researchers, this simple eukaryote continues to contribute to our understanding of eukaryotic cell growth in general and TOR function in particular.
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Affiliation(s)
- C De Virgilio
- Département de Microbiologie et Médecine Moléculaire, Université de Genève, CMU, Geneva, Switzerland.
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153
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Abstract
ATM was originally identified by positional cloning as the gene that underlies the autosomal recessive condition ataxia-telangiectasia. The encoded protein plays a central role in the complex processes that repair DNA double-strand breaks. Nearly 20 years ago, epidemiological surveys of relatives of ataxia-telangiectasia cases suggested that female relatives were at modestly increased risk of breast cancer. Subsequently, many studies have tried to clarify the role of ATM in breast cancer susceptibility, but have produced inconclusive and/or inconsistent results. Recently, large epidemiological and molecular studies have finally provided conclusive evidence that ATM mutations that cause ataxia-telangiectasia are breast cancer susceptibility alleles.
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Affiliation(s)
- M Ahmed
- Section of Cancer Genetics, Institute of Cancer Research, Sutton, UK
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154
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Abstract
The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that controls many aspects of cellular physiology, including transcription, translation, cell size, cytoskeletal organization and autophagy. Recent advances in the mTOR signaling field have found that mTOR exists in two heteromeric complexes, mTORC1 and mTORC2. The activity of mTORC1 is regulated by the integration of many signals, including growth factors, insulin, nutrients, energy availability and cellular stressors such as hypoxia, osmotic stress, reactive oxygen species and viral infection. In this review we highlight recent advances in the mTOR signaling field that relate to how the two mTOR complexes are regulated, and we discuss stress conditions linked to the mTOR signaling network that have not been extensively covered in other reviews. Given the diversity of signals that have been shown to impinge on mTOR, we also speculate on other signal-transduction pathways that may be linked to mTOR in the future.
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Affiliation(s)
- M N Corradetti
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
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155
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Kitagawa R, Kastan MB. The ATM-dependent DNA damage signaling pathway. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2006; 70:99-109. [PMID: 16869743 DOI: 10.1101/sqb.2005.70.002] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Many of the insights that we have gained into the mechanisms involved in cellular DNA damage response pathways have come from studies of human cancer susceptibility syndromes that are altered in DNA damage responses. ATM, the gene mutated in the disorder, ataxia-telangiectasia, is a protein kinase that is a central mediator of responses to DNA double-strand breaks in cells. Recent studies have elucidated the mechanism by which DNA damage activates the ATM kinase and initiates these critical cellular signaling pathways. The SMC1 protein appears to be a particularly important target of the ATM kinase, playing critical roles in controlling DNA replication forks and DNA repair after the damage. A major role for the NBS1 and BRCA1 proteins appears to be in the recruitment of an activated ATM kinase molecule to the sites of DNA breaks so that ATM can phosphorylate SMC1. Generation of mice and cells that are unable to phosphorylate SMC1 demonstrated the importance of SMC1 phosphorylation in the DNA-damage-induced S-phase checkpoint, in determining rates of repair of chromosomal breaks, and in determining cell survival after DNA damage. Focusing on ATM and SMC1, the molecular controls of these pathways is discussed.
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Affiliation(s)
- R Kitagawa
- Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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156
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Takahara T, Hara K, Yonezawa K, Sorimachi H, Maeda T. Nutrient-dependent Multimerization of the Mammalian Target of Rapamycin through the N-terminal HEAT Repeat Region. J Biol Chem 2006; 281:28605-14. [PMID: 16870609 DOI: 10.1074/jbc.m606087200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The mammalian target of rapamycin (mTOR) plays a pivotal role in the regulation of cell growth in response to a variety of signals such as nutrients and growth factors. mTOR forms two distinct complexes in vivo. mTORC1 (mTOR complex 1) is rapamycin-sensitive and regulates the rate of protein synthesis in part by phosphorylating two well established effectors, S6K1 (p70 ribosomal S6 kinase 1) and 4E-BP1 (eukaryotic initiation factor 4E-binding protein 1). mTORC2 is rapamycin-insensitive and likely regulates actin organization and activates Akt/protein kinase B. Here, we show that mTOR forms a multimer via its N-terminal HEAT repeat region in mammalian cells. mTOR multimerization is promoted by amino acid sufficiency, although the state of multimerization does not directly correlate with the phosphorylation state of S6K1. mTOR multimerization was insensitive to rapamycin treatment but hindered by butanol treatment, which inhibits phosphatidic acid production by phospholipase D. We also found that mTOR forms a multimer in both mTORC1 and mTORC2. In addition, Saccharomyces cerevisiae TOR proteins Tor1p and Tor2p also exist as homomultimers. These results suggest that TOR multimerization is a conserved mechanism for TOR functioning.
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Affiliation(s)
- Terunao Takahara
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
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157
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Jiang X, Sun Y, Chen S, Roy K, Price BD. The FATC Domains of PIKK Proteins Are Functionally Equivalent and Participate in the Tip60-dependent Activation of DNA-PKcs and ATM. J Biol Chem 2006; 281:15741-6. [PMID: 16603769 DOI: 10.1074/jbc.m513172200] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, including the ATM, DNA-PKcs, Atr, and Trrap proteins, function in signal transduction pathways that activate the DNA damage response. PIKK proteins contain a conserved C-terminal FAT/kinase domain/FATC domain structure. The FATC domain of ATM mediates the interaction between ATM and Tip60, a histone acetyltransferase that regulates activation of ATM. Here, we examined whether the FATC domains of DNA-PKcs, Atr, and Trrap were also able to interact with Tip60. Deletion of the FATC domain of ATM blocked the interaction between ATM and Tip60 and suppressed the activation of ATM kinase activity by DNA damage. Replacement of the FATC domain of ATM with the FATC domains of DNA-PKcs, Atr, or Trrap restored the activation of ATM and its association with Tip60. These results indicate that the FATC domains of DNA-PKcs, Atr, Trrap, and ATM are functionally equivalent. Immunoprecipitation experiments demonstrated that Tip60 is constitutively associated with DNA-PKcs and that the histone acetyltransferase activity associated with DNA-PKcs is up-regulated by DNA damage. When Tip60 expression was suppressed by small interfering RNA, the activation of DNA-PKcs (measured by autophosphorylation of DNA-PKcs at serine 2056 and threonine 2609) was inhibited, demonstrating a key role for Tip60 in the activation of DNA-PKcs by DNA damage. The conserved FATC domain of PIKK proteins may therefore function as a binding domain for the Tip60 histone acetyltransferase. Further, the ability of Tip60 to regulate the activation of both ATM and DNA-PKcs in response to DNA damage demonstrates that Tip60 is a key component of the DNA damage-signaling network.
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Affiliation(s)
- Xiaofeng Jiang
- Division of Genomic Stability and DNA Repair, Department of Radiation Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
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158
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Spagnolo L, Rivera-Calzada A, Pearl LH, Llorca O. Three-Dimensional Structure of the Human DNA-PKcs/Ku70/Ku80 Complex Assembled on DNA and Its Implications for DNA DSB Repair. Mol Cell 2006; 22:511-9. [PMID: 16713581 DOI: 10.1016/j.molcel.2006.04.013] [Citation(s) in RCA: 195] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2006] [Revised: 03/29/2006] [Accepted: 04/11/2006] [Indexed: 11/23/2022]
Abstract
DNA-PKcs is a large (approximately 470 kDa) kinase that plays an essential role in the repair of DNA double-strand breaks (DSBs) by nonhomologous end joining (NHEJ). DNA-PKcs is recruited to DSBs by the Ku70/Ku80 heterodimer, with which it forms the core of a multiprotein complex that promotes synapsis of the broken DNA ends. We have purified the human DNA-PKcs/Ku70/Ku80 holoenzyme assembled on a DNA molecule. Its three-dimensional (3D) structure at approximately 25 Angstroms resolution was determined by single-particle electron microscopy. Binding of Ku and DNA elicits conformational changes in the FAT and FATC domains of DNA-PKcs. Dimeric particles are observed in which two DNA-PKcs/Ku70/Ku80 holoenzymes interact through the N-terminal HEAT repeats. The proximity of the dimer contacts to the likely positions of the DNA ends suggests that these represent synaptic complexes that maintain broken DNA ends in proximity and provide a platform for access of the various enzymes required for end processing and ligation.
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Affiliation(s)
- Laura Spagnolo
- Section of Structural Biology and Cancer Research UK DNA Repair Enzyme Research Group, Institute of Cancer Research, Chester Beatty Laboratories, London
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159
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Chen Z, Robin C, Damiano J, Lydall J, Lumb C, Smith K, Blasetti A, Daborn PJ, Heckel D, McKenzie JA, Batterham P. Positional cloning of a cyromazine resistance gene in Drosophila melanogaster. INSECT MOLECULAR BIOLOGY 2006; 15:181-6. [PMID: 16640728 DOI: 10.1111/j.1365-2583.2006.00622.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Cyromazine is an effective insecticide used to control dipteran insects. Its precise mode of action is yet to be determined, although it has been suggested that it interferes with the hormone system, sclerotization of the cuticle, or nucleic acid metabolism. To understand the way in which cyromazine acts, we have positionally cloned a cyromazine resistance gene from Drosophila melanogaster. Six cyromazine resistance alleles had previously been generated by ethyl methanasulphonate treatment. Two of these failed to complement each other and here we identify them as having independent non-sense mutations in CG32743, which is an ortholog of Smg1 of worms and mammals and encodes a phosphatidylinositol kinase-like kinase (PIKK). RNAi experiments confirm that cyromazine resistance can be achieved by knocking down CG32743. These are the first cyromazine resistant mutations identified at the nucleotide level. In mammals Smg1 phosphorylates P53 in response to DNA damage. This finding supports the hypothesis that cyromazine interferes with nucleic acid metabolism.
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Affiliation(s)
- Z Chen
- Centre for Environmental Stress and Adaptation Research, Department of Genetics, The University of Melbourne, VIC 3010, Australia
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160
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Pinan-Lucarré B, Iraqui I, Clavé C. Podospora anserina target of rapamycin. Curr Genet 2006; 50:23-31. [PMID: 16614869 DOI: 10.1007/s00294-006-0064-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2005] [Revised: 01/30/2006] [Accepted: 02/01/2006] [Indexed: 10/24/2022]
Abstract
We have isolated the Podospora anserina TOR gene. The PaTOR protein displayed strong identities with TOR proteins from other eukaryotes especially in the FRB domain and the kinase domain. Genome analysis suggests that a single TOR gene exists in Podospora. The serine residue known to be one site of missense mutations conferring rapamycin resistance in other organisms is conserved in the PaTOR protein (S1895). A PaTOR-S1895R mutated allele has been constructed and introduced in the wild-type strain, as expected strains expressing the PaTOR-S1895R gene become resistant to rapamycin. The dominance of the PaTOR-S1895R allele indicates that apparently the mutation does not impair the kinase activity. We confirm that all cytological modifications associated with rapamycin treatment in Podospora are indeed mediated by PaTOR. We conclude that the PaTOR gene is likely to be essential and that rapamycin treatment might be useful to further investigate rapamycin-sensitive TOR functions in Podospora and especially newly identified rapamycin-sensitive functions such as the autophagy-independent control of vacuole remodeling and septation.
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Affiliation(s)
- Bérangère Pinan-Lucarré
- Laboratoire de Génétique Moléculaire des Champignons, Institut de Biochimie et de Génétique Cellulaires, UMR 5095 CNRS et Université de Bordeaux 2, France
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161
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Vutskits GV, Salmon P, Mayor L, Vutskits L, Cudré-Mauroux C, Soriano J, Montesano R, Maillet P, Sappino AP. A role for atm in E-cadherin-mediated contact inhibition in epithelial cells. Breast Cancer Res Treat 2006; 99:143-53. [PMID: 16541306 DOI: 10.1007/s10549-006-9195-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2006] [Accepted: 02/07/2006] [Indexed: 10/24/2022]
Abstract
Ataxia telangiectasia is a hereditary pleiomorphic syndrome caused by loss of Atm, a phosphoprotein involved in multiple signaling pathways. Here, we propose a novel role for atm in cultured epithelial cells, namely the regulation of cell growth by contact inhibition. We show that atm is upregulated in epithelial cells reaching confluence. Conditional expression of the PI 3-Kinase domain of atm in non-confluent Tac-2 epithelial cells increases the expression of the anti-proliferative gene Tis-21 and downregulates key cell cycle regulator genes, such as cyclins A, B1, B2, E and E2. Finally, we demonstrate that upregulation of atm, and thus Tis-21, in confluent Tac-2 cells can be inhibited by an E-cadherin antibody blocking specifically homophilic E-cadherin interactions between adjacent cell surfaces. Altogether, these results suggest that atm could participate in a molecular pathway linking extracellular signalling to cell cycle control and may help further clarify the role of Atm in epithelial cell biology and carcinogenesis.
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162
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Abstract
Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.
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Affiliation(s)
- Evan Pisick
- Department of Medicine, Section of Hematology/Oncology, Tufts-New England Medical Center, Boston, MA, USA
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163
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Dip R, Naegeli H. More than just strand breaks: the recognition of structural DNA discontinuities by DNA-dependent protein kinase catalytic subunit. FASEB J 2005; 19:704-15. [PMID: 15857885 DOI: 10.1096/fj.04-3041rev] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The DNA-dependent protein kinase (DNA-PK) is a trimeric factor originally identified as an enzyme that becomes activated upon incubation with DNA. Genetic defects in either the catalytic subunit (DNA-PK(CS)) or the two Ku components of DNA-PK result in immunodeficiency, radiosensitivity, and premature aging. This combined phenotype is generally attributed to the requirement for DNA-PK in the repair of DNA double strand breaks during various biological processes. However, recent studies revealed that DNA-PK(CS), a member of the growing family of phosphatidylinositol 3-kinases, participates in signal transduction cascades related to apoptotic cell death, telomere maintenance and other pathways of genome surveillance. These manifold functions of DNA-PK(CS) have been associated with an increasing number of protein interaction partners and phosphorylation targets. Here we review the DNA binding properties of DNA-PK(CS) and highlight its ability to interact with an astounding diversity of nucleic acid substrates. This survey indicates that the large catalytic subunit of DNA-PK functions as a sensor of not only broken DNA molecules, but of a wider spectrum of aberrant, unusual, or specialized structures that interrupt the standard double helical conformation of DNA.
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Affiliation(s)
- Ramiro Dip
- Institute of Veterinary Pharmacology and Toxicology, University of Zürich, Zürich, Switzerland
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164
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Meier M, den Boer ML, Hall AG, Irving JAE, Passier M, Minto L, van Wering ER, Janka-Schaub GE, Pieters R. Relation between genetic variants of the ataxia telangiectasia-mutated (ATM) gene, drug resistance, clinical outcome and predisposition to childhood T-lineage acute lymphoblastic leukaemia. Leukemia 2005; 19:1887-95. [PMID: 16167060 DOI: 10.1038/sj.leu.2403943] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The T-lineage phenotype in children with acute lymphoblastic leukaemia (ALL) is associated with in vitro drug resistance and a higher relapse-risk compared to a precursor B phenotype. Our study was aimed to investigate whether mutations in the ATM gene occur in childhood T-lineage acute lymphoblastic leukaemia (T-ALL) that are linked to drug resistance and clinical outcome. In all, 20 different single nucleotide substitutions were found in 16 exons of ATM in 62/103 (60%) T-ALL children and 51/99 (52%, P = 0.21) controls. Besides the well-known polymorphism D1853N, five other alterations (S707P, F858L, P1054R, L1472W, Y1475C) in the coding part of ATM were found. These five coding alterations seem to occur more frequently in T-ALL (13%) than controls (5%, P = 0.06), but did not associate with altered expression levels of ATM or in vitro resistance to daunorubicin. However, T-ALL patients carrying these five coding alterations presented with a higher white blood cell count at diagnosis (P = 0.05) and show an increased relapse-risk (5-year probability of disease-free survival (pDFS) = 48%) compared to patients with other alterations or wild-type ATM (5-year pDFS = 76%, P = 0.05). The association between five coding ATM alterations in T-ALL, their germline presence, white blood cell count and unfavourable outcome may point to a role for ATM in the development of T-ALL in these children.
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Affiliation(s)
- M Meier
- Department of Paediatric Oncology/Haematology, Erasmus MC/Sophia Children's Hospital, Erasmus University Medical Centre, Rotterdam, The Netherlands
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165
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Chakhparonian M, Faucher D, Wellinger RJ. A mutation in yeast Tel1p that causes differential effects on the DNA damage checkpoint and telomere maintenance. Curr Genet 2005; 48:310-22. [PMID: 16228207 DOI: 10.1007/s00294-005-0020-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2005] [Revised: 08/02/2005] [Accepted: 08/17/2005] [Indexed: 11/26/2022]
Abstract
ATM/ATR homologs are the central elements of genome surveillance mechanisms in many organisms, including yeasts, flies, and mammals. In Saccharomyces cerevisiae, most checkpoint responses depend on the ATR ortholog Mec1p. The yeast ATM ortholog, Tel1p, so far has been implicated in a specific DNA damage checkpoint during S-phase as well as in telomere homeostasis. In particular, yeast cells lacking only Tel1p harbor short but stable telomeres, while cells lacking both Tel1p and Mec1p are unable to maintain telomeric repeats and senesce. Here, we present the characterization of a new mutation in the TEL1-gene, called tel1-11, which was isolated by virtue of a synthetic lethal interaction at 37 degrees C with a previously described mec1-ts mutation. Interestingly, telomere and checkpoint functions are differentially affected by the mutant protein Tel1-11p. The Tel1p-dependent checkpoint response is undetectable in cells containing Tel1-11p and incubated at 37 degrees C, but basic telomere function is maintained. Further, when the same cells are incubated at 26 degrees C, Tel1-11p confers full proficiency for all telomere functions analyzed, whereas the function for DNA-damage checkpoint activation is clearly affected. The results thus strongly suggest that the different cellular pathways affected by Tel1p do not require the same level of Tel1p activity to be fully functional.
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Affiliation(s)
- Mikhail Chakhparonian
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3001 12e Ave Nord, Sherbrooke, QC, J1H 5N4, Canada
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166
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Hudson JJR, Hsu DW, Guo K, Zhukovskaya N, Liu PH, Williams JG, Pears CJ, Lakin ND. DNA-PKcs-Dependent Signaling of DNA Damage in Dictyostelium discoideum. Curr Biol 2005; 15:1880-5. [PMID: 16243037 DOI: 10.1016/j.cub.2005.09.039] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 09/07/2005] [Accepted: 09/09/2005] [Indexed: 11/17/2022]
Abstract
DNA double-strand breaks (DSBs) can be repaired by either homologous recombination (HR) or nonhomologous end-joining (NHEJ). In vertebrates, the first step in NHEJ is recruitment of the DNA-dependent protein kinase (DNA-PK) to DNA termini. DNA-PK consists of a catalytic subunit (DNA-PKcs) that is recruited to DNA ends by the Ku70/Ku80 heterodimer. Although Ku has been identified in a wide variety of organisms, to date DNA-PKcs has only been identified experimentally in vertebrates. Here, we report the identification of DNA-PK in the nonvertebrate Dictyostelium. Dictyostelium Ku80 contains a conserved domain previously implicated in recruiting DNA-PKcs to DNA and consistent with this observation, we have identified DNA-PKcs in the Dictyostelium genome. Disruption of the gene encoding Dictyostelium DNA-PKcs results in sensitivity to DNA DSBs and defective H2AX phosphorylation in response to this form of DNA damage. However, these phenotypes are only apparent when DNA damage is administered in G(1) phase of the cell cycle. These data illustrate a cell cycle-dependent requirement for Dictyostelium DNA-PK in signaling and combating DNA DSBs and represent the first experimental verification of DNA-PKcs in a nonvertebrate organism.
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Affiliation(s)
- Jessica J R Hudson
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
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167
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Abstract
Target of rapamycin (TOR) functions within the cell as a transducer of information from various sources, including growth factors, energy sensors, and hypoxia sensors, as well as components of the cell regulating growth and division. Blocking TOR function mimics amino acid, and to some extent, growth factor deprivation and has a cytostatic effect on proliferating cells in vivo. Inhibition of TOR in vivo, utilising its namesake rapamycin, leads to immunosuppression. This property has been exploited successfully with the use of rapamycin and its derivatives as a therapeutic agent in the prevention of organ rejection after transplantation with relatively mild side effects when compared to other immunosuppressive agents. The cytostatic effect of TOR on vascular smooth muscle cell proliferation has also recently been exploited in the therapeutic application of rapamycin to drug eluting stents for angioplasty. These stents significantly reduce the amount of arterial reblockage that results from proliferating vascular smooth muscle cells. In cancer, the effect of blocking TOR function on tumour growth and disease progression is currently of major interest and is the basis for a number of ongoing clinical trials. However, different cell types and tumours respond differently to TOR inhibition, and TOR is clearly not cytostatic for all types of cancer cells in vitro or in vivo. As the molecular details of how TOR functions and the targets of TOR activity are further elucidated, tumour and tissue specific functions are being identified that implicate TOR in angiogenesis, apoptosis, and the reversal of some forms of cellular transformation. This review will describe our current understanding of TOR function, describe the current strategies for employing TOR inhibitors in clinical and preclinical development, and outline future strategies for appropriate targets of TOR inhibitors in the treatment of disease.
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Affiliation(s)
- John B Easton
- St. Jude Childrens Research Hospital, Department of Molecular Pharmacology, 332 N. Lauderdale Street, Memphis, TN 38105-2794, USA
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168
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Nakada D, Hirano Y, Tanaka Y, Sugimoto K. Role of the C terminus of Mec1 checkpoint kinase in its localization to sites of DNA damage. Mol Biol Cell 2005; 16:5227-35. [PMID: 16148046 PMCID: PMC1266421 DOI: 10.1091/mbc.e05-05-0405] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The large protein kinases, ataxia-telangiectasia mutated (ATM) and ATM-Rad3-related (ATR), coordinate the cellular response to DNA damage. In budding yeast, ATR homologue Mec1 plays a central role in DNA damage signaling. Mec1 interacts physically with Ddc2 and functions in the form of the Mec1-Ddc2 complex. To identify proteins interacting with the Mec1-Ddc2 complex, we performed a modified two-hybrid screen and isolated RFA1 and RFA2, genes that encode subunits of replication protein A (RPA). Using the two-hybrid system, we found that the extreme C-terminal region of Mec1 is critical for RPA binding. The C-terminal substitution mutation does not affect the Mec1-Ddc2 complex formation, but it does impair the interaction of Mec1 and Ddc2 with RPA as well as their association with DNA lesions. The C-terminal mutation also decreases Mec1 kinase activity. However, the Mec1 kinase-defect by itself does not perturb Mec1 association with sites of DNA damage. We also found that Mec1 and Ddc2 associate with sites of DNA damage in an interdependent manner. Our findings support the model in which Mec1 and Ddc2 localize to sites of DNA damage by interacting with RPA in the form of the Mec1-Ddc2 complex.
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Affiliation(s)
- Daisuke Nakada
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA
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169
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Sun Y, Jiang X, Chen S, Fernandes N, Price BD. A role for the Tip60 histone acetyltransferase in the acetylation and activation of ATM. Proc Natl Acad Sci U S A 2005; 102:13182-7. [PMID: 16141325 PMCID: PMC1197271 DOI: 10.1073/pnas.0504211102] [Citation(s) in RCA: 548] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The ataxia telangiectasia mutant (ATM) protein kinase regulates the cell's response to DNA damage through the phosphorylation of proteins involved in cell-cycle checkpoints and DNA repair. However, the signal-transduction pathway linking DNA strand breaks to activation of ATM's kinase activity is not clearly defined. Here, we demonstrate that DNA damage induces the rapid acetylation of ATM. This acetylation depends on the Tip60 histone acetyltransferase (HAT). Suppression of Tip60 blocks the activation of ATM's kinase activity and prevents the ATM-dependent phosphorylation of p53 and chk2. Further, inactivation of Tip60 sensitizes cells to ionizing radiation. ATM forms a stable complex with Tip60 through the conserved FATC domain of ATM. The interaction between ATM and Tip60 is not regulated in response to DNA damage. Instead, the HAT activity of the ATM-Tip60 complex is specifically activated by DNA damage. Furthermore, this activation of Tip60 by DNA damage and the recruitment of the ATM-Tip60 complex to sites of DNA damage is independent of ATM's kinase activity. The results demonstrate that the Tip60 HAT plays a key role in the activation of ATM's kinase activity in response to DNA damage.
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Affiliation(s)
- Yingli Sun
- Department of Radiation Oncology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA
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170
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Abstract
Ataxia telangiectasia (AT) is a rare human disease characterized by extreme cellular sensitivity to radiation and a predisposition to cancer, with a hallmark of onset in early childhood. Several human diseases also share similar symptoms with AT albeit with different degrees of severity and different associated disorders. While all AT patients contain mutations in the AT-mutated gene (ATM), most other AT-like disorders are defective in genes encoding an MRN protein complex consisting of Mre11, Rad50 and Nbs1. Both ATM and MRN function as cellular sensors to DNA double-strand breaks, which lead to the recruitment and phosphorylation of an array of substrate proteins involved in DNA repair, apoptosis and cell-cycle checkpoints, as well as gene regulation, translation initiation and telomere maintenance. ATM is a member of the family of phosphatidylinositol 3-kinase-like protein kinases (PIKK), and the discovery of many ATM substrates provides the underlying mechanisms of heterologous symptoms among AT patients. This review article focuses on recent findings related to the initial recognition of double-strand breaks by ATM and MRN, as well as a DNA-dependent protein kinase complex consisting of the heterodimer Ku70/Ku80 and its catalytic subunit DNA-PKcs, another member of PIKK. This possible interaction suggests that a much greater complex is involved in sensing, transducing and co-ordinating cellular events in response to genome instability.
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Affiliation(s)
- Lindsay G Ball
- Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, SK Canada, S7N 5E5
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171
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Wullschleger S, Loewith R, Oppliger W, Hall MN. Molecular organization of target of rapamycin complex 2. J Biol Chem 2005; 280:30697-704. [PMID: 16002396 DOI: 10.1074/jbc.m505553200] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The target of rapamycin (TOR), a highly conserved serine/threonine kinase, plays a central role in the control of eukaryotic cell growth. TOR exists in two functionally and structurally distinct complexes, TOR complex 1 (TORC1) and TOR complex 2 (TORC2). TORC1 controls cell growth via a rapamycin-sensitive signaling branch regulating translation, transcription, nutrient uptake, ribosome biogenesis, and autophagy. TORC2 controls the organization of the actin cytoskeleton through a rapamycin-insensitive signaling branch and in yeast consists of the six proteins AVO1, AVO2, AVO3, BIT61, LST8, and TOR2. Here we have focused on the characterization of TORC2. Our studies suggest that TORC2 is oligomeric, likely a TORC2-TORC2 dimer. AVO1 and AVO3 bind cooperatively to the N-terminal HEAT repeat region in TOR2 and are required for TORC2 integrity. AVO2 is a nonessential peripheral protein associated with AVO1 and AVO3. LST8 binds separately to the C-terminal kinase domain region in TOR2 and appears to modulate both the integrity and kinase activity of TORC2. TORC2 autophosphorylates sites in AVO1 and AVO3, but TORC2 kinase activity is not required for TORC2 integrity. We have demonstrated that mammalian TOR is also oligomeric. The architecture of TORC2 is discussed in the context of TORC2 assembly and regulation.
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Affiliation(s)
- Stephan Wullschleger
- Division of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland
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172
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Rivera-Calzada A, Maman JD, Maman JP, Spagnolo L, Pearl LH, Llorca O. Three-dimensional structure and regulation of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Structure 2005; 13:243-55. [PMID: 15698568 DOI: 10.1016/j.str.2004.12.006] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2004] [Revised: 12/15/2004] [Accepted: 12/17/2004] [Indexed: 11/16/2022]
Abstract
DNA-PKcs is a large PI3-kinase-related protein kinase (PIKK) that plays a central role in DNA double-strand break (DSB) repair via nonhomologous end joining. Using cryo-electron microscopy we have now generated an approximately 13 A three-dimensional map of DNA-PKcs, revealing the overall architecture and topology of the 4128 residue polypeptide chain and allowing location of domains. The highly conserved C-terminal PIKK catalytic domain forms a central structure from which FAT and FATC domains protrude. Conformational changes observed in these domains on DNA binding suggest that they transduce DNA-induced conformational changes to the catalytic core and regulate kinase activity. The N-terminal segments form long curved tubular-shaped domains based on helical repeats to create interacting surfaces required for macromolecular assembly. Comparison of DNA-PKcs with another PIKK DNA repair factor, ATM, defines a common architecture for this important protein family.
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Affiliation(s)
- Angel Rivera-Calzada
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maeztu 9, Campus Universidad Complutense, 28040 Madrid, Spain
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173
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Chen Z, Smith KR, Batterham P, Robin C. Smg1 nonsense mutations do not abolish nonsense-mediated mRNA decay in Drosophila melanogaster. Genetics 2005; 171:403-6. [PMID: 15965240 PMCID: PMC1456532 DOI: 10.1534/genetics.105.045674] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Smg1 is a key component of nonsense-mediated decay (NMD) in Caenorhabditis elegans and mammals. Here we report that two nonsense alleles of the ortholog of Smg1 do not affect NMD in Drosophila melanogaster.
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Affiliation(s)
- Zhenzhong Chen
- Centre for Environmental Stress and Adaptation Research, Department of Genetics, University of Melbourne, Melbourne, Victoria 3010, Australia
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174
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Hansen IA, Attardo GM, Roy SG, Raikhel AS. Target of rapamycin-dependent activation of S6 kinase is a central step in the transduction of nutritional signals during egg development in a mosquito. J Biol Chem 2005; 280:20565-72. [PMID: 15788394 DOI: 10.1074/jbc.m500712200] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Female mosquitoes are effective disease vectors, because they take blood from vertebrate hosts to obtain nutrients for egg development. Amino acid signaling via the target of rapamycin (TOR) pathway has been identified as a key requirement for the activation of egg development after a blood meal. We report the characterization of the TOR kinase and one of its major downstream targets, S6 kinase, of the yellow fever mosquito Aedes aegypti during egg development in adult females. Both TOR and S6K mRNA are expressed at high levels in the ovaries and in lower levels in fat body and other tissues. After a blood meal, the subcellular localization of TOR shifts from the cytoplasm to the plasma membrane of fat body cells. By detecting phosphothreonine 388 of mosquito S6 kinase, we show that TOR activity strongly increases in fat body and ovaries after a blood meal in vivo. Furthermore, phosphorylation of S6 kinase increases in in vitro cultured fat bodies after stimulation with amino acids. This increase is sensitive to the TOR inhibitor rapamycin in a concentration-dependent manner but not to the phosphatidylinositol 3-kinase/phosphatidylinositol 3-kinase-related kinase inhibitor LY294002, the MAPK inhibitor PD98059, or the translational inhibitor cycloheximide. RNA interference-mediated reduction of S6 kinase strongly inhibits the amino acid-induced up-regulation of the major yolk protein vitellogenin in vitro and effectively disrupts egg development after a blood meal in vivo. Our data show that TOR-dependent activation of S6 kinase is a central step in the transduction of nutritional information during egg development in mosquitoes.
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Affiliation(s)
- Immo A Hansen
- Department of Entomology and Institute for Integrative Genome Biology, University of California, Riverside, California 92521, USA
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175
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Dames SA, Mulet JM, Rathgeb-Szabo K, Hall MN, Grzesiek S. The solution structure of the FATC domain of the protein kinase target of rapamycin suggests a role for redox-dependent structural and cellular stability. J Biol Chem 2005; 280:20558-64. [PMID: 15772072 DOI: 10.1074/jbc.m501116200] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The target of rapamycin (TOR) is a highly conserved Ser/Thr kinase that plays a central role in the control of cellular growth. TOR has a characteristic multidomain structure. Only the kinase domain has catalytic function; the other domains are assumed to mediate interactions with TOR substrates and regulators. Except for the rapamycin-binding domain, there are no high-resolution structural data available for TOR. Here, we present a structural, biophysical, and mutagenesis study of the extremely conserved COOH-terminal FATC domain. The importance of this domain for TOR function has been highlighted in several publications. We show that the FATC domain, in its oxidized form, exhibits a novel structural motif consisting of an alpha-helix and a COOH-terminal disulfide-bonded loop between two completely conserved cysteine residues. Upon reduction, the flexibility of the loop region increases dramatically. The structural data, the redox potential of the disulfide bridge, and the biochemical data of a cysteine to serine mutant indicate that the intracellular redox potential can affect the cellular amount of the TOR protein via the FATC domain. Because the amount of TOR mRNA is not changed, the redox state of the FATC disulfide bond is probably influencing the degradation of TOR.
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Affiliation(s)
- Sonja A Dames
- Department of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
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176
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Park BJ, Kang JW, Lee SW, Choi SJ, Shin YK, Ahn YH, Choi YH, Choi D, Lee KS, Kim S. The haploinsufficient tumor suppressor p18 upregulates p53 via interactions with ATM/ATR. Cell 2005; 120:209-21. [PMID: 15680327 DOI: 10.1016/j.cell.2004.11.054] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2004] [Revised: 09/07/2004] [Accepted: 11/22/2004] [Indexed: 01/05/2023]
Abstract
p18 was first identified as a factor associated with a macromolecular tRNA synthetase complex. Here we describe the mouse p18 loss-of-function phenotype and a role for p18 in the DNA damage response. Inactivation of both p18 alleles caused embryonic lethality, while heterozygous mice showed high susceptibility to spontaneous tumors. p18 was induced and translocated to the nucleus in response to DNA damage. Expression of p18 resulted in elevated p53 levels, while p18 depletion blocked p53 induction. p18 directly interacted with ATM/ATR in response to DNA damage. The activity of ATM was dependent on the level of p18, suggesting the requirement of p18 for the activation of ATM. Low p18 expression was frequently observed in different human cancer cell lines and tissues. These results suggest that p18 is a haploinsufficient tumor suppressor and a key factor for ATM/ATR-mediated p53 activation.
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Affiliation(s)
- Bum-Joon Park
- National Creative Research Initiatives Center for ARS Network, College of Pharmacy, Seoul National University, Seoul 151-742, South Korea
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177
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Abraham RT. Part-time cop nabs deviant DNA. Nat Med 2005; 11:257-8. [PMID: 15746937 DOI: 10.1038/nm0305-257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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178
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Lavin MF, Birrell G, Chen P, Kozlov S, Scott S, Gueven N. ATM signaling and genomic stability in response to DNA damage. Mutat Res 2005; 569:123-32. [PMID: 15603757 DOI: 10.1016/j.mrfmmm.2004.04.020] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2004] [Accepted: 04/09/2004] [Indexed: 01/10/2023]
Abstract
DNA double strand breaks represent the most threatening lesion to the integrity of the genome in cells exposed to ionizing radiation and radiomimetic chemicals. Those breaks are recognized, signaled to cell cycle checkpoints and repaired by protein complexes. The product of the gene (ATM) mutated in the human genetic disorder ataxia-telangiectasia (A-T) plays a central role in the recognition and signaling of DNA damage. ATM is one of an ever growing number of proteins which when mutated compromise the stability of the genome and predispose to tumour development. Mechanisms for recognising double strand breaks in DNA, maintaining genome stability and minimizing risk of cancer are discussed.
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Affiliation(s)
- Martin F Lavin
- Queensland Cancer Fund Research Unit, The Queensland Institute of Medical Research, PO Box Royal Brisbane Hospital, Herston, Brisbane 4029, Australia.
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179
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Stover CM, Lynch NJ, Hanson SJ, Windbichler M, Gregory SG, Schwaeble WJ. Organization of the MASP2 locus and its expression profile in mouse and rat. Mamm Genome 2005; 15:887-900. [PMID: 15672593 DOI: 10.1007/s00335-004-3006-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The mouse, rat, and human MASP2 loci are situated on syntenic chromosome regions and are highly conserved. They comprise the genes for MASP-2/ MAp19, TAR DNA binding protein of 43 kDa, FRAP kinase, CDT6, Polymyositis-Scleroderma 100-kDa autoantigen, spermidine synthase, and TERE which were analyzed by annotation of available gene transcript data and cross-species comparison of available genomic sequences. The human and rat genes for spermidine synthase have an additional intron compared to the mouse gene. The mouse and rat genes for Polymyositis-Scleroderma 100-kDa autoantigen have an additional exon compared to the human gene. We find support for the hypothesis that the MAp19-specific exon within the MASP2 gene may have originated in a transposable element. Blocks of highly conserved intronic sequences were found in the MASP2 gene and the TARDBP gene. The expression of all genes within the MASP2 locus was analyzed in mouse and rat. The restricted expression of MASP-2 and MAp19 mRNA in liver contrasts with the ubiquitous expression of all neighboring genes studied.
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Affiliation(s)
- Cordula M Stover
- Department of Infection, Immunity and Inflammation, University of Leicester, Leicester LE1 9HN, United Kingdom.
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180
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Abstract
Recent studies have identified, hSMG-1 as the newest member of the phosphoinositide 3-kinase(PI3-kinase)-related kinase (PIKK) family. The protein kinase activity of hSMG-1 resembles that of the related PIKK, ATM, both in terms of substrate specificity and its sensitivity to inhibition by the fungal metabolite wortmannin. hSMG-1 is the ortholog of a Caenorhabditis elegans protein, CeSMG-1, which has been genetically linked to a critical mRNA surveillance pathway termed nonsense-mediated decay (NMD). The function of NMD is to mark for rapid degradation mRNAs that bear a premature termination codon. Compelling evidence now indicates that hSMG-1 is also a central player in the NMD pathway in human cells. In addition, hSMG-1, like ATM, appears to be involved in the recognition and/or repair of damaged DNA in these cells. In this review, we introduce a model in which hSMG-1 teams with ATM and ATR to insure the overall quality of the transcriptome in human cells.
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Affiliation(s)
- Robert T Abraham
- Program in Signal Transduction Research, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92130, USA.
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181
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Abstract
The phosphoinositide 3-kinase related kinases (PIKKs) comprise a family of high molecular mass signaling proteins that play central roles in the control of cell growth, gene expression, and genome surveillance and repair in eukaryotic cells. Mammalian cells express six PIKK family members, five of which-ATM, ATR, mTOR, DNA-PK, and hSMG-1-function as protein serine-threosine kinases. This overview provides some general insights into the pharmacology, biochemistry, and function of this nonconventional group of protein kinases.
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Affiliation(s)
- Robert T Abraham
- Program in Signal Transduction Research, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92130, USA.
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182
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Kurz EU, Lees-Miller SP. DNA damage-induced activation of ATM and ATM-dependent signaling pathways. DNA Repair (Amst) 2005; 3:889-900. [PMID: 15279774 DOI: 10.1016/j.dnarep.2004.03.029] [Citation(s) in RCA: 341] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Ataxia-telangiectasia mutated (ATM) plays a key role in regulating the cellular response to ionizing radiation. Activation of ATM results in phosphorylation of many downstream targets that modulate numerous damage response pathways, most notably cell cycle checkpoints. In this review, we describe recent developments in our understanding of the mechanism of activation of ATM and its downstream signaling pathways, and explore whether DNA double-strand breaks are the sole activators of ATM and ATM-dependent signaling pathways.
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Affiliation(s)
- Ebba U Kurz
- Cancer Biology Research Group, Department of Biochemistry and Molecular Biology, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, Canada
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183
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Abstract
Efficient repair of DNA double-strand breaks is essential for the maintenance of chromosomal integrity. In higher eukaryotes, non-homologous end-joining (NHEJ) DNA is the primary pathway that repairs these breaks. NHEJ also functions in developing lymphocytes to repair strand breaks that occur during V(D)J recombination, the site-specific recombination process that provides for the assembly of functional antigen-receptor genes. If V(D)J recombination is impaired, B- and T-lymphocyte development is blocked resulting in severe combined immunodeficiency disease. In the last decade, an intensive research effort has focused on NHEJ resulting in a reasonable understanding of how double-strand breaks are resolved. Six distinct gene products have been identified that function in this pathway (Ku70, Ku86, XRCC4, DNA ligase IV, Artemis, and DNA-PKcs). Three of these comprise one complex, the DNA-dependent protein kinase (DNA-PK). This protein complex is central during NHEJ, because DNA-PK initially recognizes and binds to the damaged DNA and then targets the other repair activities to the site of DNA damage. In this review, we discuss recent developments that have provided insight into how DNA-PK functions, once bound to DNA ends.
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Affiliation(s)
- Katheryn Meek
- College of Veterinary Medicine and Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, MI 48824, USA
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184
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Abstract
Many human diseases occur when the precise regulation of cell growth (cell mass/size) and proliferation (rates of cell division) is compromised. This review highlights those human disorders that occur as a result of inappropriate cellular signal transduction through the mammalian target of rapamycin (mTOR), a major pathway that coordinates proper cell growth and proliferation by regulating ribosomal biogenesis and protein translation. Recent studies reveal that the tuberous sclerosis complex (TSC)-1/2, PTEN, and LKB1 tumor suppressor proteins tightly control mTOR. Loss of these tumor suppressors leads to an array of hamartoma syndromes as a result of heightened mTOR signaling. Since mTOR plays a pivotal role in maintaining proper cell size and growth, dysregulation of mTOR signaling results in these benign tumor syndromes and an array of other human disorders.
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Affiliation(s)
- Andrew R Tee
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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185
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Brewerton SC, Doré AS, Drake ACB, Leuther KK, Blundell TL. Structural analysis of DNA-PKcs: modelling of the repeat units and insights into the detailed molecular architecture. J Struct Biol 2004; 145:295-306. [PMID: 14960380 DOI: 10.1016/j.jsb.2003.11.024] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2003] [Revised: 11/13/2003] [Indexed: 11/29/2022]
Abstract
DNA-dependent protein kinase (DNA-PK) is part of the eukaryotic DNA double strand break repair pathway and as such is crucial for maintenance of genomic stability, as well as for V(D)J (variable-diversity-joining) recombination. The catalytic subunit of DNA-PK (DNA-PKcs) belongs to the phosphatidylinositol-3 (PI-3) kinase-like kinase (PIKK) superfamily and is comprised of approximately 4100 amino acids. We have used a novel repeat detection method to analyse this enormous protein and have identified two different types of helical repeat motifs in the N-terminal region of the sequence, as well as other previously unreported features in this repeat region. A comparison with the ATMs, ATRs, and TORs show that the features identified are likely to be conserved throughout the PIKK superfamily. Homology modelling of parts of the DNA-PKcs sequence has been undertaken and we have been able to fit the models to previously obtained electron microscopy data. This work provides an insight into the overall architecture of the DNA-PKcs protein and identifies regions of interest for further experimental studies.
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Affiliation(s)
- Suzanne C Brewerton
- Department of Biochemistry, University of Cambridge, Old Addenbrookes site, 80 Tennis Court Road, Cambridge CB2 1GA, UK.
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186
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Ward P, Equinet L, Packer J, Doerig C. Protein kinases of the human malaria parasite Plasmodium falciparum: the kinome of a divergent eukaryote. BMC Genomics 2004; 5:79. [PMID: 15479470 PMCID: PMC526369 DOI: 10.1186/1471-2164-5-79] [Citation(s) in RCA: 376] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2004] [Accepted: 10/12/2004] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND Malaria, caused by the parasitic protist Plasmodium falciparum, represents a major public health problem in the developing world. The P. falciparum genome has been sequenced, which provides new opportunities for the identification of novel drug targets. Eukaryotic protein kinases (ePKs) form a large family of enzymes with crucial roles in most cellular processes; hence malarial ePKS represent potential drug targets. We report an exhaustive analysis of the P. falciparum genomic database (PlasmoDB) aimed at identifying and classifying all ePKs in this organism. RESULTS Using a variety of bioinformatics tools, we identified 65 malarial ePK sequences and constructed a phylogenetic tree to position these sequences relative to the seven established ePK groups. Predominant features of the tree were: (i) that several malarial sequences did not cluster within any of the known ePK groups; (ii) that the CMGC group, whose members are usually involved in the control of cell proliferation, had the highest number of malarial ePKs; and (iii) that no malarial ePK clustered with the tyrosine kinase (TyrK) or STE groups, pointing to the absence of three-component MAPK modules in the parasite. A novel family of 20 ePK-related sequences was identified and called FIKK, on the basis of a conserved amino acid motif. The FIKK family seems restricted to Apicomplexa, with 20 members in P. falciparum and just one member in some other Apicomplexan species. CONCLUSION The considerable phylogenetic distance between Apicomplexa and other Eukaryotes is reflected by profound divergences between the kinome of malaria parasites and that of yeast or mammalian cells.
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Affiliation(s)
- Pauline Ward
- Wellcome Centre for Molecular Parasitology, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK
| | - Leila Equinet
- INSERM U609, Wellcome Centre for Molecular Parasitology, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK
| | - Jeremy Packer
- Division of Advanced Technologies, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, USA
| | - Christian Doerig
- INSERM U609, Wellcome Centre for Molecular Parasitology, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK
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187
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Grimson A, O'Connor S, Newman CL, Anderson P. SMG-1 is a phosphatidylinositol kinase-related protein kinase required for nonsense-mediated mRNA Decay in Caenorhabditis elegans. Mol Cell Biol 2004; 24:7483-90. [PMID: 15314158 PMCID: PMC506987 DOI: 10.1128/mcb.24.17.7483-7490.2004] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Eukaryotic messenger RNAs containing premature stop codons are selectively and rapidly degraded, a phenomenon termed nonsense-mediated mRNA decay (NMD). Previous studies with both Caenohabditis elegans and mammalian cells indicate that SMG-2/human UPF1, a central regulator of NMD, is phosphorylated in an SMG-1-dependent manner. We report here that smg-1, which is required for NMD in C. elegans, encodes a protein kinase of the phosphatidylinositol kinase superfamily of protein kinases. We identify null alleles of smg-1 and demonstrate that SMG-1 kinase activity is required in vivo for NMD and in vitro for SMG-2 phosphorylation. SMG-1 and SMG-2 coimmunoprecipitate from crude extracts, and this interaction is maintained in smg-3 and smg-4 mutants, both of which are required for SMG-2 phosphorylation in vivo and in vitro. SMG-2 is located diffusely through the cytoplasm, and its location is unaltered in mutants that disrupt the cycle of SMG-2 phosphorylation. We discuss the role of SMG-2 phosphorylation in NMD.
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Affiliation(s)
- Andrew Grimson
- Department of Genetics, University of Wisconsin, 445 Henry Mall, Madison, WI 53706, USA
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188
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Abstract
The evolutionarily conserved checkpoint protein kinase, TOR (target of rapamycin), has emerged as a major effector of cell growth and proliferation via the regulation of protein synthesis. Work in the last decade clearly demonstrates that TOR controls protein synthesis through a stunning number of downstream targets. Some of the targets are phosphorylated directly by TOR, but many are phosphorylated indirectly. In this review, we summarize some recent developments in this fast-evolving field. We describe both the upstream components of the signaling pathway(s) that activates mammalian TOR (mTOR) and the downstream targets that affect protein synthesis. We also summarize the roles of mTOR in the control of cell growth and proliferation, as well as its relevance to cancer and synaptic plasticity.
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Affiliation(s)
- Nissim Hay
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 60607, USA.
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189
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Abstract
The phosphoinositide 3-kinase related kinases (PIKKs) mediate responses to diverse stresses, including DNA double-strand breaks (DSBs), abnormal replication fork progression, the recognition of premature termination codons in mRNAs, and inadequate nutrient availability. Rigorous control of these kinases limits cellular damage and promotes cell viability in the presence of stress. Control mechanisms include the localization of PIKKs into multiprotein complexes at the sites of damage and mediation of protein-protein contacts such that substrates are allowed access to the PIKK catalytic domains.
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Affiliation(s)
- Christopher J Bakkenist
- Department of Hematology-Oncology, St. Jude Children's Research Hospital, 332 N. Lauderdale Street, Memphis, TN 38105, USA
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190
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Lavin MF, Scott S, Gueven N, Kozlov S, Peng C, Chen P. Functional consequences of sequence alterations in the ATM gene. DNA Repair (Amst) 2004; 3:1197-205. [PMID: 15279808 DOI: 10.1016/j.dnarep.2004.03.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The product of the gene (ATM) mutated in the human genetic disorder ataxia-telangiectasia (A-T) is a high molecular weight, protein ( approximately 350kDa) containing a C-terminal protein kinase domain and a number of other putative domains not yet functionally defined. The majority of ATM gene mutations in A-T patients are truncating, resulting in prematurely terminated products that are highly unstable. Missense mutations within the kinase domain and elsewhere in the molecule alter the stability of the protein and lead to loss of protein kinase activity. Only rarely are patients observed with two missense mutations and this gives rise to a milder disease phenotype. Evidence for a dominant interfering effect on normal ATM kinase activity has been reported in cell lines transfected with missense mutant ATM and in cell lines from some A-T heterozygotes. The dominant negative effect of mutant ATM is manifested by an enhancement of cellular radiosensitivity and may be responsible for the cancer predisposition observed in carriers of ATM missense mutations. In this review, we explore the domain structure of the ATM molecule, sites of interaction with other proteins and the consequences of specific amino acid changes on function.
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Affiliation(s)
- Martin F Lavin
- The Queensland Cancer Fund Research Unit, The Queensland Institute of Medical Research, P.O. Box Royal Brisbane Hospital, Herston, Brisbane 4029, Qld, Australia.
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191
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Staub E, Fiziev P, Rosenthal A, Hinzmann B. Insights into the evolution of the nucleolus by an analysis of its protein domain repertoire. Bioessays 2004; 26:567-81. [PMID: 15112237 DOI: 10.1002/bies.20032] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Recently, the first investigation of nucleoli using mass spectrometry led to the identification of 271 proteins. This represents a rich resource for a comprehensive investigation of nucleolus evolution. We applied a protocol for the identification of known and novel conserved protein domains of the nucleolus, resulting in the identification of 115 known and 91 novel domain profiles. The phyletic distribution of nucleolar protein domains in a collection of complete proteomes of selected organisms from all domains of life confirms the archaebacterial origin of the core machinery for ribosome maturation and assembly, but also reveals substantial eubacterial and eukaryotic contributions to nucleolus evolution. We predict that, in different phases of nucleolus evolution, protein domains with different biochemical functions were recruited to the nucleolus. We suggest a model for the late and continuous evolution of the nucleolus in early eukaryotes and argue against an endosymbiotic origin of the nucleolus and the nucleus. Supplementary material for this article can be found on the BioEssays website at http://www.interscience.wiley.com/jpages/0265-9247/suppmat/index.html.
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Affiliation(s)
- Eike Staub
- metaGen Pharmaceuticals GmbH, Berlin, Germany.
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192
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Abstract
TOR was discovered and christened 10 years ago. On the occasion of this anniversary, we revisit the discovery of TOR and chronicle subsequent breakthroughs in S. cerevisiae that contributed to an understanding of TOR function in yeast and higher eukaryotes. In particular, we discuss findings that led to the realization that the function of TOR is to control cell growth in response to nutrients.
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Affiliation(s)
- A Lorberg
- Division of Biochemistry, Biozentrum, University of Basel, Klingelbergstr. 70, 4056, Basel, Switzerland
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193
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Drenan RM, Liu X, Bertram PG, Zheng XFS. FKBP12-Rapamycin-associated Protein or Mammalian Target of Rapamycin (FRAP/mTOR) Localization in the Endoplasmic Reticulum and the Golgi Apparatus. J Biol Chem 2004; 279:772-8. [PMID: 14578359 DOI: 10.1074/jbc.m305912200] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FKBP12-rapamycin-associated protein (FRAP) or mammalian target of rapamycin (mTOR) and its effector proteins form a critical signaling pathway that regulates eukaryotic cell growth and proliferation. Although the protein components in this pathway have begun to be identified, little is known about their subcellular localization or the physiological significance of their localization. By immunofluorescence, we find that both endogenous and recombinant FRAP/mTOR proteins show localization predominantly in the endoplasmic reticulum (ER) and the Golgi apparatus. Consistent with this finding, FRAP/mTOR is cofractionated with calnexin, an ER marker protein. Biochemical characterization suggests that FRAP/mTOR is a peripheral ER/Golgi protein with tight membrane association. Finally, we have identified domains of FRAP/mTOR which may mediate its association with the ER and the Golgi apparatus.
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Affiliation(s)
- Ryan M Drenan
- Molecular Cell Biology Graduate Program, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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194
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Abstract
Over the past few years, the target of rapamycin (TOR) pathway has been implicated in the control of translation, both in yeast and in higher eukaryotes. In this review, we provide an overview of translation in eukaryotes, and discuss the mechanisms and advantages of the regulation of translation. We then describe how the TOR pathway can modulate translation in yeast and in mammals, through the modulation of the phosphorylation of key translation components, and the regulation of the abundance of ribosomes and translation factors.
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Affiliation(s)
- A C Gingras
- Department of Biochemistry, McGill Cancer Centre, McGill University, 3655 Promenade Sir-William-Osler, Montréal, Québec, H3G 1Y6, Canada
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195
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Abstract
The mammalian target of rapamycin, mTOR, is a protein Ser-Thr kinase that functions as a central element in a signaling pathway involved in the control of cell growth and proliferation. The activity of mTOR is controlled not only by amino acids, but also by hormones and growth factors that activate the protein kinase Akt. The signaling pathway downstream of Akt leading to mTOR involves the protein products of the genes mutated in tuberous sclerosis, TSC1 and TSC2, and the small guanosine triphosphatase, Rheb. In cells, mTOR is found in a complex with two other proteins, raptor and mLST8. In this review, we describe recent progress in understanding the control of the mTOR signaling pathway and the role of mTOR-interacting proteins.
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Affiliation(s)
- Thurl E Harris
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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196
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Dörk T, Bendix-Waltes R, Wegner RD, Stumm M. Slow progression of ataxia-telangiectasia with double missense and in frame splice mutations. Am J Med Genet A 2003; 126A:272-7. [PMID: 15054841 DOI: 10.1002/ajmg.a.20601] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ataxia-telangiectasia (A-T) is caused by mutations of the ATM gene, the product of which is involved in the regulation of cellular responses to radiation damage. Ataxia usually starts in early childhood but a delayed age at onset and slower rate of neurological deterioration has been found for some patients with variant A-T. Only few patients have been documented to survive into the 4th decade. We report on a patient with an attenuated form of A-T who was diagnosed as having A-T by the age of 52 years and died by the age of 60 years. He was found to be a compound heterozygote for a double missense mutation (D2625E and A2626P) and a novel splicing mutation (496 + 5G --> A) of the ATM gene. Cytogenetic studies of the patient's lymphoblastoid cells revealed modest levels of bleomycin-induced chromosomal instability. Residual ATM protein was found at a level of 10-20% of wildtype. Low residual ATM kinase activity could be demonstrated towards p53, whereas it was poorly detectable towards nibrin. Our results corroborate the view that the clinical variability of A-T is partly determined by the mutation type and indicate that A-T can extend to late adulthood disease.
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Affiliation(s)
- Thilo Dörk
- Clinics of Obstetrics and Gynecology, Medical School Hannover, Hannover, Germany.
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197
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Chen S, Paul P, Price BD. ATM's leucine-rich domain and adjacent sequences are essential for ATM to regulate the DNA damage response. Oncogene 2003; 22:6332-9. [PMID: 14508513 DOI: 10.1038/sj.onc.1206760] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The ATM protein kinase regulates the DNA damage response by phosphorylating proteins involved in cell cycle checkpoints and DNA repair. We report here on the function of the predicted leucine zipper (LZ) motif, and sequences adjacent to this, in regulating ATM activity. The predicted LZ sequence was deleted from ATM, generating ATMDeltaLZ, and expressed in an ATM-negative AT cell line. ATM increased cell survival following exposure to ionizing radiation, whereas expression of ATMDeltaLZ failed to increase cell survival. ATMDeltaLZ retained in vitro kinase activity, but was unable to phosphorylate p53 in vivo. Leucine zippers mediate homo- and heterodimerization of proteins. However, the predicted LZ of ATM did not mediate the formation of ATM dimers. We examined if the predicted LZ of ATM was a dominant-negative inhibitor of ATM function in SW480 cells. Expression of amino acids 769-1436 of ATM, including the predicted LZ, sensitized SW480 cells to ionizing radiation, but did not inhibit ATM's kinase activity or its ability to phosphorylate Brca1. Further, this dominant-negative activity was not dependent on the predicted LZ domain. The central region of the ATM protein therefore contains multiple sequences which regulate cell survival following DNA damage.
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Affiliation(s)
- Shujuan Chen
- Department of Radiation Oncology, JF513, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA
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198
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Laurençon A, Purdy A, Sekelsky J, Hawley RS, Su TT. Phenotypic analysis of separation-of-function alleles of MEI-41, Drosophila ATM/ATR. Genetics 2003; 164:589-601. [PMID: 12807779 PMCID: PMC1462579 DOI: 10.1093/genetics/164.2.589] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
ATM/ATR kinases act as signal transducers in eukaryotic DNA damage and replication checkpoints. Mutations in ATM/ATR homologs have pleiotropic effects that range from sterility to increased killing by genotoxins in humans, mice, and Drosophila. Here we report the generation of a null allele of mei-41, Drosophila ATM/ATR homolog, and the use of it to document a semidominant effect on a larval mitotic checkpoint and methyl methanesulfonate (MMS) sensitivity. We also tested the role of mei-41 in a recently characterized checkpoint that delays metaphase/anaphase transition after DNA damage in cellular embryos. We then compare five existing mei-41 alleles to the null with respect to known phenotypes (female sterility, cell cycle checkpoints, and MMS resistance). We find that not all phenotypes are affected equally by each allele, i.e., the functions of MEI-41 in ensuring fertility, cell cycle regulation, and resistance to genotoxins are genetically separable. We propose that MEI-41 acts not in a single rigid signal transduction pathway, but in multiple molecular contexts to carry out its many functions. Sequence analysis identified mutations, which, for most alleles, fall in the poorly characterized region outside the kinase domain; this allowed us to tentatively identify additional functional domains of MEI-41 that could be subjected to future structure-function studies of this key molecule.
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Affiliation(s)
- Anne Laurençon
- Molecular and Cellular Biology Department, University of California, Davis 95616, USA
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199
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Liu X, Tesfai J, Evrard YA, Dent SYR, Martinez E. c-Myc transformation domain recruits the human STAGA complex and requires TRRAP and GCN5 acetylase activity for transcription activation. J Biol Chem 2003; 278:20405-12. [PMID: 12660246 PMCID: PMC4031917 DOI: 10.1074/jbc.m211795200] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Deregulation of the c-Myc oncoprotein (Myc) is implicated in many types of cancer. Myc is a sequence-specific transcription factor that regulates transcription of genes involved in the control of cell proliferation and apoptosis via mechanisms that are still poorly understood. Cell transformation by Myc involves its association with the transformation-transactivation domain-associated protein (TRRAP) and the human histone acetyltransferase (HAT) GCN5. TRRAP and GCN5 are components of a variety of shared and distinct multiprotein HAT complexes with diverse functions. Myc induces TRRAP recruitment and histone hyperacetylation at specific Myc-activated genes in vivo. However, the identity of the HAT complexes recruited by Myc and the roles of TRRAP and GCN5 in Myc function are still unclear. Here we show that Myc co-recruits TRRAP and GCN5 via direct physical interactions of its N-terminal activation/transformation domain with the human STAGA (SPT3-TAF-GCN5 acetylase) coactivator complex. We demonstrate that GCN5 and TRRAP cooperate to enhance transcription activation by the N-terminal activation domain of Myc in vivo and that this synergy requires both the SPT3/GCN5 interaction domain of TRRAP and the HAT activity of GCN5. Thus, TRRAP might function as an adaptor within the STAGA complex, which helps recruit GCN5 HAT activity to Myc during transcription activation.
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Affiliation(s)
- Xiaohui Liu
- Department of Biochemistry, University of California, Riverside, California 92521
| | - Jerusalem Tesfai
- Department of Biochemistry, University of California, Riverside, California 92521
| | - Yvonne A. Evrard
- Department of Biochemistry and Molecular Biology, University of Texas, M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Sharon Y. R. Dent
- Department of Biochemistry and Molecular Biology, University of Texas, M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Ernest Martinez
- Department of Biochemistry, University of California, Riverside, California 92521
- To whom correspondence should be addressed: Dept. of Biochemistry, University of California, Riverside, CA 92521. Tel.: 909-787-2031; Fax: 909-787-4434;
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200
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Abstract
TOR--a highly conserved atypical protein kinase and the 'target of rapamycin', an immunosuppressant and anti-cancer drug--controls cell growth. TOR controls the growth of proliferating yeast, fly and mammalian cells in response to nutrients. Recent findings, however, indicate that TOR also controls the growth of non-proliferating cells, such as neurons and muscle cells. Furthermore, TOR, by associating with regulatory proteins and inhibiting phosphatases, controls the activity of multiphosphorylated effectors.
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Affiliation(s)
- Estela Jacinto
- Division of Biochemistry, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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