151
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Evangelisti C, Cenni V, Lattanzi G. Potential therapeutic effects of the MTOR inhibitors for preventing ageing and progeria-related disorders. Br J Clin Pharmacol 2016; 82:1229-1244. [PMID: 26952863 PMCID: PMC5061804 DOI: 10.1111/bcp.12928] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Revised: 03/02/2016] [Accepted: 03/02/2016] [Indexed: 12/25/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) pathway is an highly conserved signal transduction axis involved in many cellular processes, such as cell growth, survival, transcription, translation, apoptosis, metabolism, motility and autophagy. Recently, this signalling pathway has come to the attention of the scientific community owing to the unexpected finding that inhibition of mTOR by rapamycin, an antibiotic with immunosuppressant and chemotherapeutic properties, extends lifespan in diverse animal models. Moreover, rapamycin has been reported to rescue the cellular phenotype in a progeroid syndrome [Hutchinson–Gilford Progeria syndrome (HGPS)] that recapitulates most of the traits of physiological ageing. The promising perspectives raised by these results warrant a better understanding of mTOR signalling and the potential applications of mTOR inhibitors to counteract ageing‐associated diseases and increase longevity. This review is focused on these issues.
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Affiliation(s)
- Camilla Evangelisti
- CNR Institute for Molecular Genetics, Unit of Bologna, Bologna, Italy.,Rizzoli Orthopedic Institute, Laboratory of Musculoskeletal Cell Biology, Bologna, Italy
| | - Vittoria Cenni
- CNR Institute for Molecular Genetics, Unit of Bologna, Bologna, Italy.,Rizzoli Orthopedic Institute, Laboratory of Musculoskeletal Cell Biology, Bologna, Italy
| | - Giovanna Lattanzi
- CNR Institute for Molecular Genetics, Unit of Bologna, Bologna, Italy. .,Rizzoli Orthopedic Institute, Laboratory of Musculoskeletal Cell Biology, Bologna, Italy.
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152
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Abstract
Cell metabolism and growth are matched to nutrient availability via the amino-acid-regulated mechanistic target of rapamycin complex 1 (mTORC1). Transporters have emerged as important amino acid sensors controlling mTOR recruitment and activation at the surface of multiple intracellular compartments. Classically, this has involved late endosomes and lysosomes, but now, in a recent twist, also the Golgi apparatus. Here we propose a model in which specific amino acids in assorted compartments activate different mTORC1 complexes, which may have distinct drug sensitivities and functions. We will discuss the implications of this for mTORC1 function in health and disease.
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Affiliation(s)
- Deborah C I Goberdhan
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3QX, UK.
| | - Clive Wilson
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3QX, UK
| | - Adrian L Harris
- Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
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153
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Pallis M, Harvey T, Russell N. Phenotypically Dormant and Immature Leukaemia Cells Display Increased Ribosomal Protein S6 Phosphorylation. PLoS One 2016; 11:e0151480. [PMID: 26985829 PMCID: PMC4795744 DOI: 10.1371/journal.pone.0151480] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 02/29/2016] [Indexed: 11/23/2022] Open
Abstract
Mechanistic/mammalian target of rapamycin (mTOR) activity drives a number of key metabolic processes including growth and protein synthesis. Inhibition of the mTOR pathway promotes cellular dormancy. Since cells from patients with acute myeloid leukaemia (AML) can be phenotypically dormant (quiescent), we examined biomarkers of their mTOR pathway activity concurrently with Ki-67 and CD71 (indicators of cycling cells) by quantitative flow cytometry. Using antibodies to phosphorylated epitopes of mTOR (S2448) and its downstream targets ribosomal protein S6 (rpS6, S235/236) and 4E-BP1 (T36/45), we documented that these phosphorylations were negligible in lymphocytes, but evident in dormant as well as proliferating subsets of both mobilised normal stem cell harvest CD34+ cells and AML blasts. Although mTOR phosphorylation in AML blasts was lower than that of the normal CD34+ cells, p-4E-BP1 was 2.6-fold higher and p-rpS6 was 22-fold higher. Moreover, in contrast to 4E-BP1, rpS6 phosphorylation was higher in dormant than proliferating AML blasts, and was also higher in the immature CD34+CD38- blast subset. Data from the Cancer Genome Atlas show that rpS6 expression is associated with that of respiratory chain enzymes in AML. We conclude that phenotypic quiescence markers do not necessarily predict metabolic dormancy and that elevated rpS6 ser235/236 phosphorylation is characteristic of AML.
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Affiliation(s)
- Monica Pallis
- Clinical Haematology, Nottingham University Hospitals, Nottingham, United Kingdom
- * E-mail:
| | - Tamsin Harvey
- Department of Haematology, University of Nottingham, Nottingham, United Kingdom
| | - Nigel Russell
- Clinical Haematology, Nottingham University Hospitals, Nottingham, United Kingdom
- Department of Haematology, University of Nottingham, Nottingham, United Kingdom
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154
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Wittenberg AD, Azar S, Klochendler A, Stolovich-Rain M, Avraham S, Birnbaum L, Binder Gallimidi A, Katz M, Dor Y, Meyuhas O. Phosphorylated Ribosomal Protein S6 Is Required for Akt-Driven Hyperplasia and Malignant Transformation, but Not for Hypertrophy, Aneuploidy and Hyperfunction of Pancreatic β-Cells. PLoS One 2016; 11:e0149995. [PMID: 26919188 PMCID: PMC4769037 DOI: 10.1371/journal.pone.0149995] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 02/08/2016] [Indexed: 12/31/2022] Open
Abstract
Constitutive expression of active Akt (Akttg) drives hyperplasia and hypertrophy of pancreatic β-cells, concomitantly with increased insulin secretion and improved glucose tolerance, and at a later stage the development of insulinoma. To determine which functions of Akt are mediated by ribosomal protein S6 (rpS6), an Akt effector, we generated mice that express constitutive Akt in β-cells in the background of unphosphorylatable ribosomal protein S6 (rpS6P-/-). rpS6 phosphorylation deficiency failed to block Akttg-induced hypertrophy and aneuploidy in β-cells, as well as the improved glucose homeostasis, indicating that Akt carries out these functions independently of rpS6 phosphorylation. In contrast, rpS6 phosphorylation deficiency efficiently restrained the reduction in nuclear localization of the cell cycle inhibitor p27, as well as the development of Akttg-driven hyperplasia and tumor formation in β-cells. In vitro experiments with Akttg and rpS6P-/-;Akttg fibroblasts demonstrated that rpS6 phosphorylation deficiency leads to reduced translation fidelity, which might underlie its anti-tumorigenic effect in the pancreas. However, the role of translation infidelity in tumor suppression cannot simply be inferred from this heterologous experimental model, as rpS6 phosphorylation deficiency unexpectedly elevated the resistance of Akttg fibroblasts to proteotoxic, genotoxic as well as autophagic stresses. In contrast, rpS6P-/- fibroblasts exhibited a higher sensitivity to these stresses upon constitutive expression of oncogenic Kras. The latter result provides a possible mechanistic explanation for the ability of rpS6 phosphorylation deficiency to enhance DNA damage and protect mice from Kras-induced neoplastic transformation in the exocrine pancreas. We propose that Akt1 and Kras exert their oncogenic properties through distinct mechanisms, even though both show addiction to rpS6 phosphorylation.
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Affiliation(s)
- Avigail Dreazen Wittenberg
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Shahar Azar
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Agnes Klochendler
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Miri Stolovich-Rain
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Shlomit Avraham
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Lea Birnbaum
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Adi Binder Gallimidi
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Maximiliano Katz
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Yuval Dor
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Oded Meyuhas
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research-Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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155
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Tee AR, Sampson JR, Pal DK, Bateman JM. The role of mTOR signalling in neurogenesis, insights from tuberous sclerosis complex. Semin Cell Dev Biol 2016; 52:12-20. [PMID: 26849906 DOI: 10.1016/j.semcdb.2016.01.040] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 01/05/2016] [Accepted: 01/25/2016] [Indexed: 11/30/2022]
Abstract
Understanding the development and function of the nervous system is one of the foremost aims of current biomedical research. The nervous system is generated during a relatively short period of intense neurogenesis that is orchestrated by a number of key molecular signalling pathways. Even subtle defects in the activity of these molecules can have serious repercussions resulting in neurological, neurodevelopmental and neurocognitive problems including epilepsy, intellectual disability and autism. Tuberous sclerosis complex (TSC) is a monogenic disease characterised by these problems and by the formation of benign tumours in multiple organs, including the brain. TSC is caused by mutations in the TSC1 or TSC2 gene leading to activation of the mechanistic target of rapamycin (mTOR) signalling pathway. A desire to understand the neurological manifestations of TSC has stimulated research into the role of the mTOR pathway in neurogenesis. In this review we describe TSC neurobiology and how the use of animal model systems has provided insights into the roles of mTOR signalling in neuronal differentiation and migration. Recent progress in this field has identified novel mTOR pathway components regulating neuronal differentiation. The roles of mTOR signalling and aberrant neurogenesis in epilepsy are also discussed. Continuing efforts to understand mTOR neurobiology will help to identify new therapeutic targets for TSC and other neurological diseases.
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Affiliation(s)
- Andrew R Tee
- Institute of Cancer & Genetics, Cardiff University School of Medicine, Institute of Medical Genetics Building, Heath Park, Cardiff CF14 4XN UK
| | - Julian R Sampson
- Institute of Cancer & Genetics, Cardiff University School of Medicine, Institute of Medical Genetics Building, Heath Park, Cardiff CF14 4XN UK
| | - Deb K Pal
- Department of Basic & Clinical Neurosciences, Institute of Psychiatry, Psychology & Neuroscience, King's College, London SE5 8RX UK
| | - Joseph M Bateman
- Wolfson Centre for Age-Related Diseases, King's College London, Guy's Campus, London SE1 1UL UK.
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156
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Impaired Ribosome Biogenesis and Skeletal Muscle Growth in a Murine Model of Inflammatory Bowel Disease. Inflamm Bowel Dis 2016; 22:268-78. [PMID: 26588088 DOI: 10.1097/mib.0000000000000616] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND Inflammation is a factor potentially underpinning skeletal muscle mass. Intestinal-derived inflammation in inflammatory bowel disease (IBD) results in loss of muscle mass; however, the underlying mechanism is unclear. The interleukin 10 gene-deficient (Il10-/-) mouse is a genetically modified animal model of IBD that can be used to study the effect of intestinal-derived inflammation on muscles. METHODS Il10-/- and C57BL/6 wild-type (WT) mice were inoculated with intestinal bacteria to induce colon inflammation at the fifth week of age. Skeletal muscles were collected between 7 and 14 weeks of age for analysis of muscle weight, myofiber cross-sectional area (CSA), and molecular markers of inflammation and anabolism pathways, with a focus on ribosome biogenesis. RESULTS Il10-/- animals that developed colon inflammation had a marked increase in muscle immunoglobulin G (IgG) compared with WT. Inflamed Il10-/- animals had impaired muscle mass gain and smaller myofiber CSA. Intramuscular IgG deposition negatively correlated with muscle mass. After the onset of muscle inflammation, Il10-/- mice had decreased levels of total and ribosomal RNAs (45S, 28S, 18S, and 5.8S rRNAs). Inflammation inversely correlated with muscle levels of total RNA and 28S rRNA which in turn positively correlated with muscle mass. The abundance of growth-related proteins (p70S6K and upstream binding factor, UBF) was decreased in Il10-/- mice. CONCLUSIONS Muscle inflammation and associated decline of ribosome biogenesis lead to muscle growth impairment in Il10-/- mice. This may have implications for maintenance of muscle mass in conditions associated with chronic intestinal-derived inflammation.
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157
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Tuberous sclerosis--A model for tumour growth. Semin Cell Dev Biol 2016; 52:3-11. [PMID: 26816112 DOI: 10.1016/j.semcdb.2016.01.025] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Revised: 12/18/2015] [Accepted: 01/19/2016] [Indexed: 01/06/2023]
Abstract
Tuberous sclerosis complex (TSC) is a rare genetic disorder where patients develop benign tumours in several organ systems. Central to TSC pathology is hyper-activation of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, which is a key controller of cell growth. As a result, TSC model systems are a valuable tool for examining mTORC1-driven cellular processes. The immunosuppressant, rapamycin, is a specific inhibitor of mTORC1 and has shown promise as a therapeutic agent in TSC as well as in malignancy. This review will focus on the cellular processes controlled by mTORC1 and how TSC-deficient cell lines and mouse models have broadened our understanding of the mTORC1 signalling network. It will also discuss how our knowledge of TSC signalling can help us understand sporadic conditions where mTORC1 activity is implicated in disease onset or progression, and the possibility of using rapamycin to treat sporadic disease.
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158
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Autophagy is involved in regulating influenza A virus RNA and protein synthesis associated with both modulation of Hsp90 induction and mTOR/p70S6K signaling pathway. Int J Biochem Cell Biol 2016; 72:100-108. [PMID: 26794463 DOI: 10.1016/j.biocel.2016.01.012] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2015] [Revised: 12/05/2015] [Accepted: 01/15/2016] [Indexed: 11/21/2022]
Abstract
Influenza A virus (IAV) infection triggers autophagosome formation, but inhibits the fusion of autophagosomes with lysosomes. However, the role of autophagy in IAV replication is still largely unclarified. In this study, we aim to reveal the role of autophagy in IAV replication and the molecular mechanisms underlying the regulation. By using autophagy-deficient (Atg7(-/-)) MEFs, we demonstrated that autophagy deficiency significantly reduced the levels of viral proteins, mRNA and genomic RNAs (vRNAs) without affecting viral entry. We further found that autophagy deficiency lead to a transient increase in phosphorylation of mTOR and its downstream targets including 4E-BP1 and S6 at a very early stage of IAV infection, and markedly suppressed p70S6K phosphorylation at the late stage of IAV infection. Furthermore, autophagy deficiency resulted in impairment of Hsp90 induction in response to IAV infection. These results indicate that IAV regulates autophagy to benefit the accumulation of viral elements (synthesis of viral proteins and genomic RNA) during IAV replication. This regulation is associated with modulation of Hsp90 induction and mTOR/p70S6K signaling pathway. Our results provide important evidence for the role of autophagy in IAV replication and the mechanisms underlying the regulation.
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159
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Xu L, Brink M. mTOR, cardiomyocytes and inflammation in cardiac hypertrophy. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:1894-903. [PMID: 26775585 DOI: 10.1016/j.bbamcr.2016.01.003] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 12/30/2015] [Accepted: 01/07/2016] [Indexed: 02/07/2023]
Abstract
Mammalian target of rapamycin (mTOR) is an evolutionary conserved kinase that senses the nutrient and energy status of cells, the availability of growth factors, stress stimuli and other cellular and environmental cues. It responds by regulating a range of cellular processes related to metabolism and growth in accordance with the available resources and intracellular needs. mTOR has distinct functions depending on its assembly in the structurally distinct multiprotein complexes mTORC1 or mTORC2. Active mTORC1 enhances processes including glycolysis, protein, lipid and nucleotide biosynthesis, and it inhibits autophagy. Reported functions for mTORC2 after growth factor stimulation are very diverse, are tissue and cell-type specific, and include insulin-stimulated glucose transport and enhanced glycogen synthesis. In accordance with its cellular functions, mTOR has been demonstrated to regulate cardiac growth in response to pressure overload and is also known to regulate cells of the immune system. The present manuscript presents recently obtained insights into mechanisms whereby mTOR may change anabolic, catabolic and stress response pathways in cardiomocytes and discusses how mTOR may affect inflammatory cells in the heart during hemodynamic stress. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.
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Affiliation(s)
- Lifen Xu
- Department of Biomedicine, University of Basel and University Hospital Basel, Hebelstrasse 20, CH-4031 Basel, Switzerland
| | - Marijke Brink
- Department of Biomedicine, University of Basel and University Hospital Basel, Hebelstrasse 20, CH-4031 Basel, Switzerland.
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160
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Dobrenel T, Mancera-Martínez E, Forzani C, Azzopardi M, Davanture M, Moreau M, Schepetilnikov M, Chicher J, Langella O, Zivy M, Robaglia C, Ryabova LA, Hanson J, Meyer C. The Arabidopsis TOR Kinase Specifically Regulates the Expression of Nuclear Genes Coding for Plastidic Ribosomal Proteins and the Phosphorylation of the Cytosolic Ribosomal Protein S6. FRONTIERS IN PLANT SCIENCE 2016; 7:1611. [PMID: 27877176 PMCID: PMC5100631 DOI: 10.3389/fpls.2016.01611] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 10/12/2016] [Indexed: 05/05/2023]
Abstract
Protein translation is an energy consuming process that has to be fine-tuned at both the cell and organism levels to match the availability of resources. The target of rapamycin kinase (TOR) is a key regulator of a large range of biological processes in response to environmental cues. In this study, we have investigated the effects of TOR inactivation on the expression and regulation of Arabidopsis ribosomal proteins at different levels of analysis, namely from transcriptomic to phosphoproteomic. TOR inactivation resulted in a coordinated down-regulation of the transcription and translation of nuclear-encoded mRNAs coding for plastidic ribosomal proteins, which could explain the chlorotic phenotype of the TOR silenced plants. We have identified in the 5' untranslated regions (UTRs) of this set of genes a conserved sequence related to the 5' terminal oligopyrimidine motif, which is known to confer translational regulation by the TOR kinase in other eukaryotes. Furthermore, the phosphoproteomic analysis of the ribosomal fraction following TOR inactivation revealed a lower phosphorylation of the conserved Ser240 residue in the C-terminal region of the 40S ribosomal protein S6 (RPS6). These results were confirmed by Western blot analysis using an antibody that specifically recognizes phosphorylated Ser240 in RPS6. Finally, this antibody was used to follow TOR activity in plants. Our results thus uncover a multi-level regulation of plant ribosomal genes and proteins by the TOR kinase.
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Affiliation(s)
- Thomas Dobrenel
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- Université Paris-Sud–Université Paris-SaclayOrsay, France
- Umeå Plant Science Center, Department of Plant Physiology, Umeå UniversityUmeå, Sweden
| | - Eder Mancera-Martínez
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Céline Forzani
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
| | - Marianne Azzopardi
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
| | | | - Manon Moreau
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, DSV, IBEB, SBVME, CEA, CNRS, Aix-Marseille Université, Faculté des Sciences de LuminyMarseille, France
| | - Mikhail Schepetilnikov
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Johana Chicher
- Plateforme Protéomique Strasbourg-Esplanade, CNRS FRC1589, Institut de Biologie Moléculaire et CellulaireStrasbourg, France
| | | | - Michel Zivy
- Plateforme PAPPSO, UMR GQE-Le MoulonGif sur Yvette, France
| | - Christophe Robaglia
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, DSV, IBEB, SBVME, CEA, CNRS, Aix-Marseille Université, Faculté des Sciences de LuminyMarseille, France
| | - Lyubov A. Ryabova
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Johannes Hanson
- Umeå Plant Science Center, Department of Plant Physiology, Umeå UniversityUmeå, Sweden
| | - Christian Meyer
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- *Correspondence: Christian Meyer,
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161
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Cargnello M, Tcherkezian J, Roux PP. The expanding role of mTOR in cancer cell growth and proliferation. Mutagenesis 2015; 30:169-76. [PMID: 25688110 DOI: 10.1093/mutage/geu045] [Citation(s) in RCA: 117] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The mechanistic/mammalian target of rapamycin (mTOR) is a conserved protein kinase that controls several anabolic processes required for cell growth and proliferation. As such, mTOR has been implicated in an increasing number of pathological conditions, including cancer, obesity, type 2 diabetes and neurodegeneration. As part of the mTOR complex 1 (mTORC1), mTOR regulates cell growth by promoting the biosynthesis of proteins, lipids and nucleic acids. Several mTORC1 substrates have been shown to regulate protein synthesis, including the eukaryotic initiation factor 4E (eIF4E)-binding proteins (4E-BPs) and the ribosomal S6 kinases (S6Ks) 1 and 2. In this work, we focus on the signalling pathways that lie both upstream and downstream of mTORC1, as well as their relevance to human pathologies. We further discuss pharmacological approaches that target mTOR and their applications for the treatment of cancer.
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Affiliation(s)
- Marie Cargnello
- Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, Québec, Canada
| | - Joseph Tcherkezian
- Laboratory for Therapeutic Development, McGill University, Montréal, Québec, Canada and
| | - Philippe P Roux
- Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, Québec, Canada, Department of Pathology and Cell Biology, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada
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162
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Abstract
Mechanistic target of rapamycin (mTOR, also known as mammalian target of rapamycin) is a ubiquitous serine/threonine kinase that regulates cell growth, proliferation and survival. These effects are cell-type-specific, and are elicited in response to stimulation by growth factors, hormones and cytokines, as well as to internal and external metabolic cues. Rapamycin was initially developed as an inhibitor of T-cell proliferation and allograft rejection in the organ transplant setting. Subsequently, its molecular target (mTOR) was identified as a component of two interacting complexes, mTORC1 and mTORC2, that regulate T-cell lineage specification and macrophage differentiation. mTORC1 drives the proinflammatory expansion of T helper (TH) type 1, TH17, and CD4(-)CD8(-) (double-negative, DN) T cells. Both mTORC1 and mTORC2 inhibit the development of CD4(+)CD25(+)FoxP3(+) T regulatory (TREG) cells and, indirectly, mTORC2 favours the expansion of T follicular helper (TFH) cells which, similarly to DN T cells, promote B-cell activation and autoantibody production. In contrast to this proinflammatory effect of mTORC2, mTORC1 favours, to some extent, an anti-inflammatory macrophage polarization that is protective against infections and tissue inflammation. Outside the immune system, mTORC1 controls fibroblast proliferation and chondrocyte survival, with implications for tissue fibrosis and osteoarthritis, respectively. Rapamycin (which primarily inhibits mTORC1), ATP-competitive, dual mTORC1/mTORC2 inhibitors and upstream regulators of the mTOR pathway are being developed to treat autoimmune, hyperproliferative and degenerative diseases. In this regard, mTOR blockade promises to increase life expectancy through treatment and prevention of rheumatic diseases.
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Affiliation(s)
- Andras Perl
- Division of Rheumatology, Departments of Medicine, Microbiology and Immunology, and Biochemistry and Molecular Biology, State University of New York, Upstate Medical University, College of Medicine, 750 East Adams Street, Syracuse, New York 13210, USA
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163
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Biever A, Valjent E, Puighermanal E. Ribosomal Protein S6 Phosphorylation in the Nervous System: From Regulation to Function. Front Mol Neurosci 2015; 8:75. [PMID: 26733799 PMCID: PMC4679984 DOI: 10.3389/fnmol.2015.00075] [Citation(s) in RCA: 139] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 11/23/2015] [Indexed: 01/31/2023] Open
Abstract
Since the discovery of the phosphorylation of the 40S ribosomal protein S6 (rpS6) about four decades ago, much effort has been made to uncover the molecular mechanisms underlying the regulation of this post-translational modification. In the field of neuroscience, rpS6 phosphorylation is commonly used as a readout of the mammalian target of rapamycin complex 1 signaling activation or as a marker for neuronal activity. Nevertheless, its biological role in neurons still remains puzzling. Here we review the pharmacological and physiological stimuli regulating this modification in the nervous system as well as the pathways that transduce these signals into rpS6 phosphorylation. Altered rpS6 phosphorylation observed in various genetic and pathophysiological mouse models is also discussed. Finally, we examine the current state of knowledge on the physiological role of this post-translational modification and highlight the questions that remain to be addressed.
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Affiliation(s)
- Anne Biever
- Centre National de la Recherche Scientifique, UMR5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale, U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Emmanuel Valjent
- Centre National de la Recherche Scientifique, UMR5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale, U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Emma Puighermanal
- Centre National de la Recherche Scientifique, UMR5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale, U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
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164
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West DWD, Baehr LM, Marcotte GR, Chason CM, Tolento L, Gomes AV, Bodine SC, Baar K. Acute resistance exercise activates rapamycin-sensitive and -insensitive mechanisms that control translational activity and capacity in skeletal muscle. J Physiol 2015; 594:453-68. [PMID: 26548696 DOI: 10.1113/jp271365] [Citation(s) in RCA: 110] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 10/29/2015] [Indexed: 12/19/2022] Open
Abstract
KEY POINTS Ribosome biogenesis is the primary determinant of translational capacity, but its regulation in skeletal muscle following acute resistance exercise is poorly understood. Resistance exercise increases muscle protein synthesis acutely, and muscle mass with training, but the role of translational capacity in these processes is unclear. Here, we show that acute resistance exercise activated pathways controlling translational activity and capacity through both rapamycin-sensitive and -insensitive mechanisms. Transcription factor c-Myc and its downstream targets, which are known to regulate ribosome biogenesis in other cell types, were upregulated after resistance exercise in a rapamycin-independent manner and may play a role in determining translational capacity in skeletal muscle. Local inhibition of myostatin was also not affected by rapamycin and may contribute to the rapamycin-independent effects of resistance exercise. ABSTRACT This study aimed to determine (1) the effect of acute resistance exercise on mechanisms of ribosome biogenesis, and (2) the impact of mammalian target of rapamycin on ribosome biogenesis, and muscle protein synthesis (MPS) and degradation. Female F344BN rats underwent unilateral electrical stimulation of the sciatic nerve to mimic resistance exercise in the tibialis anterior (TA) muscle. TA muscles were collected at intervals over the 36 h of exercise recovery (REx); separate groups of animals were administered rapamycin pre-exercise (REx+Rapamycin). Resistance exercise led to a prolonged (6-36 h) elevation (30-50%) of MPS that was fully blocked by rapamycin at 6 h but only partially at 18 h. REx also altered pathways that regulate protein homeostasis and mRNA translation in a manner that was both rapamycin-sensitive (proteasome activity; phosphorylation of S6K1 and rpS6) and rapamycin-insensitive (phosphorylation of eEF2, ERK1/2 and UBF; gene expression of the myostatin target Mighty as well as c-Myc and its targets involved in ribosome biogenesis). The role of c-Myc was tested in vitro using the inhibitor 10058-F4, which, over time, decreased basal RNA and MPS in a dose-dependent manner (correlation of RNA and MPS, r(2) = 0.98), even though it had no effect on the acute stimulation of protein synthesis. In conclusion, acute resistance exercise stimulated rapamycin-sensitive and -insensitive mechanisms that regulate translation activity and capacity.
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Affiliation(s)
- Daniel W D West
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA
| | - Leslie M Baehr
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA
| | - George R Marcotte
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA
| | - Courtney M Chason
- Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA
| | - Luis Tolento
- Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA
| | - Aldrin V Gomes
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA.,Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA
| | - Sue C Bodine
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA.,Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA.,VA Northern California Health Care System, Mather, CA, USA
| | - Keith Baar
- Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA.,Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA.,VA Northern California Health Care System, Mather, CA, USA
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165
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Yerlikaya S, Meusburger M, Kumari R, Huber A, Anrather D, Costanzo M, Boone C, Ammerer G, Baranov PV, Loewith R. TORC1 and TORC2 work together to regulate ribosomal protein S6 phosphorylation in Saccharomyces cerevisiae. Mol Biol Cell 2015; 27:397-409. [PMID: 26582391 PMCID: PMC4713140 DOI: 10.1091/mbc.e15-08-0594] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 11/09/2015] [Indexed: 11/14/2022] Open
Abstract
Phosphorylation of the S6 protein of the 40S subunit of the eukaryote ribosome downstream of anabolic signals has long been assumed to promote protein synthesis. Both target of rapamycin complexes regulate this modification in yeast, but the use of ribosome profiling shows no role for Rps6 phosphorylation in mRNA translation. Nutrient-sensitive phosphorylation of the S6 protein of the 40S subunit of the eukaryote ribosome is highly conserved. However, despite four decades of research, the functional consequences of this modification remain unknown. Revisiting this enigma in Saccharomyces cerevisiae, we found that the regulation of Rps6 phosphorylation on Ser-232 and Ser-233 is mediated by both TOR complex 1 (TORC1) and TORC2. TORC1 regulates phosphorylation of both sites via the poorly characterized AGC-family kinase Ypk3 and the PP1 phosphatase Glc7, whereas TORC2 regulates phosphorylation of only the N-terminal phosphosite via Ypk1. Cells expressing a nonphosphorylatable variant of Rps6 display a reduced growth rate and a 40S biogenesis defect, but these phenotypes are not observed in cells in which Rps6 kinase activity is compromised. Furthermore, using polysome profiling and ribosome profiling, we failed to uncover a role of Rps6 phosphorylation in either global translation or translation of individual mRNAs. Taking the results together, this work depicts the signaling cascades orchestrating Rps6 phosphorylation in budding yeast, challenges the notion that Rps6 phosphorylation plays a role in translation, and demonstrates that observations made with Rps6 knock-ins must be interpreted cautiously.
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Affiliation(s)
- Seda Yerlikaya
- Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland
| | - Madeleine Meusburger
- Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland
| | - Romika Kumari
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland
| | - Alexandre Huber
- Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland
| | - Dorothea Anrather
- Max F. Perutz Laboratories, Department of Biochemistry, University of Vienna, A1030 Vienna, Austria
| | - Michael Costanzo
- Banting and Best Department of Medical Research, Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Charles Boone
- Banting and Best Department of Medical Research, Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Gustav Ammerer
- Max F. Perutz Laboratories, Department of Biochemistry, University of Vienna, A1030 Vienna, Austria
| | - Pavel V Baranov
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland
| | - Robbie Loewith
- Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland Swiss National Centre for Competence in Research Programme Chemical Biology, 1211 Geneva, Switzerland
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166
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Abstract
Although the eukaryotic TOR (target of rapamycin) kinase signalling pathway has emerged as a key player for integrating nutrient-, energy- and stress-related cues with growth and metabolic outputs, relatively little is known of how this ancient regulatory mechanism has been adapted in higher plants. Drawing comparisons with the substantial knowledge base around TOR kinase signalling in fungal and animal systems, functional aspects of this pathway in plants are reviewed. Both conserved and divergent elements are discussed in relation to unique aspects associated with an autotrophic mode of nutrition and adaptive strategies for multicellular development exhibited by plants.
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167
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Lynch CJ, Kimball SR, Xu Y, Salzberg AC, Kawasawa YI. Global deletion of BCATm increases expression of skeletal muscle genes associated with protein turnover. Physiol Genomics 2015; 47:569-80. [PMID: 26351290 DOI: 10.1152/physiolgenomics.00055.2015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 09/04/2015] [Indexed: 01/04/2023] Open
Abstract
Consumption of a protein-containing meal by a fasted animal promotes protein accretion in skeletal muscle, in part through leucine stimulation of protein synthesis and indirectly through repression of protein degradation mediated by its metabolite, α-ketoisocaproate. Mice lacking the mitochondrial branched-chain aminotransferase (BCATm/Bcat2), which interconverts leucine and α-ketoisocaproate, exhibit elevated protein turnover. Here, the transcriptomes of gastrocnemius muscle from BCATm knockout (KO) and wild-type mice were compared by next-generation RNA sequencing (RNA-Seq) to identify potential adaptations associated with their persistently altered nutrient signaling. Statistically significant changes in the abundance of 1,486/∼39,010 genes were identified. Bioinformatics analysis of the RNA-Seq data indicated that pathways involved in protein synthesis [eukaryotic initiation factor (eIF)-2, mammalian target of rapamycin, eIF4, and p70S6K pathways including 40S and 60S ribosomal proteins], protein breakdown (e.g., ubiquitin mediated), and muscle degeneration (apoptosis, atrophy, myopathy, and cell death) were upregulated. Also in agreement with our previous observations, the abundance of mRNAs associated with reduced body size, glycemia, plasma insulin, and lipid signaling pathways was altered in BCATm KO mice. Consistently, genes encoding anaerobic and/or oxidative metabolism of carbohydrate, fatty acids, and branched chain amino acids were modestly but systematically reduced. Although there was no indication that muscle fiber type was different between KO and wild-type mice, a difference in the abundance of mRNAs associated with a muscular dystrophy phenotype was observed, consistent with the published exercise intolerance of these mice. The results suggest transcriptional adaptations occur in BCATm KO mice that along with altered nutrient signaling may contribute to their previously reported protein turnover, metabolic and exercise phenotypes.
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Affiliation(s)
- Christopher J Lynch
- Department of Cellular and Molecular Physiology, College of Medicine, Penn State University, Hershey, Pennsylvania;
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, College of Medicine, Penn State University, Hershey, Pennsylvania
| | - Yuping Xu
- Department of Cellular and Molecular Physiology, College of Medicine, Penn State University, Hershey, Pennsylvania
| | - Anna C Salzberg
- The Institute for Personalized Medicine, College of Medicine, Penn State University, Hershey, Pennsylvania
| | - Yuka Imamura Kawasawa
- The Institute for Personalized Medicine, College of Medicine, Penn State University, Hershey, Pennsylvania; Department of Pharmacology, College of Medicine, Penn State University, Hershey, Pennsylvania; and Department of Biochemistry and Molecular Biology, College of Medicine, Penn State University, Hershey, Pennsylvania
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168
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Shao J, Stout I, Hendriksen PJM, van Loveren H, Peijnenburg AACM, Volger OL. Protein phosphorylation profiling identifies potential mechanisms for direct immunotoxicity. J Immunotoxicol 2015; 13:97-107. [PMID: 25715851 DOI: 10.3109/1547691x.2015.1016635] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Signaling networks are essential elements that are involved in diverse cellular processes. One group of fundamental components in various signaling pathways concerns protein tyrosine kinases (PTK). Various toxicants have been demonstrated to exert their toxicity via modulation of tyrosine kinase activity. The present study aimed to identify common cellular signaling pathways that are involved in chemical-induced direct immunotoxicity. To this end, an antibody array-based profiling approach was applied to assess effects of five immunotoxicants, two immunosuppressive drugs and two non-immunotoxic control chemicals on the phosphorylation of 28 receptor tyrosine kinases and 11 crucial signaling nodes in Jurkat T-cells. The phosphorylation of ribosomal protein S6 (RPS6) and of kinases Akt, Src and p44/42 were found to be commonly regulated by immunotoxicants and/or immunosuppressive drugs (at least three compounds), with the largest effect observed upon RPS6. Flow cytometry and Western blotting were used to further examine the effect of the model immunotoxicant TBTO on the components of the mTOR-p70S6K-RPS6 pathway. These analyses revealed that both TBTO and the mTOR inhibitor rapamycin inactivate RPS6, but via different mechanisms. Finally, a comparison of the protein phosphorylation data to previously obtained transcriptome data of TBTO-treated Jurkat cells resulted in a good correlation at the pathway level and indicated that TBTO affects ribosome biogenesis and leukocyte migration. The effect of TBTO on the latter process was confirmed using a CXCL12 chemotaxis assay.
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Affiliation(s)
- Jia Shao
- a RIKILT-Institute of Food Safety, Wageningen University and Research Centre , Wageningen , the Netherlands .,b Department of Toxicogenomics , Maastricht University , the Netherlands .,c Netherlands Toxicogenomics Centre , the Netherlands , and
| | - Inge Stout
- a RIKILT-Institute of Food Safety, Wageningen University and Research Centre , Wageningen , the Netherlands
| | - Peter J M Hendriksen
- a RIKILT-Institute of Food Safety, Wageningen University and Research Centre , Wageningen , the Netherlands .,c Netherlands Toxicogenomics Centre , the Netherlands , and
| | - Henk van Loveren
- b Department of Toxicogenomics , Maastricht University , the Netherlands .,c Netherlands Toxicogenomics Centre , the Netherlands , and.,d National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
| | - Ad A C M Peijnenburg
- a RIKILT-Institute of Food Safety, Wageningen University and Research Centre , Wageningen , the Netherlands .,c Netherlands Toxicogenomics Centre , the Netherlands , and
| | - Oscar L Volger
- a RIKILT-Institute of Food Safety, Wageningen University and Research Centre , Wageningen , the Netherlands .,c Netherlands Toxicogenomics Centre , the Netherlands , and
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169
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Esnault S, Kelly EAB, Shen ZJ, Johansson MW, Malter JS, Jarjour NN. IL-3 Maintains Activation of the p90S6K/RPS6 Pathway and Increases Translation in Human Eosinophils. THE JOURNAL OF IMMUNOLOGY 2015; 195:2529-39. [PMID: 26276876 DOI: 10.4049/jimmunol.1500871] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 07/15/2015] [Indexed: 12/12/2022]
Abstract
IL-5 is a major therapeutic target to reduce eosinophilia. However, all of the eosinophil-activating cytokines, such as IL-5, IL-3, and GM-CSF, are typically present in atopic diseases, including allergic asthma. As a result of the functional redundancy of these three cytokines on eosinophils and the loss of IL-5R on airway eosinophils, it is important to take IL-3 and GM-CSF into account to efficiently reduce tissue eosinophil functions. Moreover, these three cytokines signal through a common β-chain receptor but yet differentially affect protein production in eosinophils. Notably, the increased ability of IL-3 to induce the production of proteins, such as semaphorin-7A, without affecting mRNA levels suggests a unique influence of IL-3 on translation. The purpose of this study was to identify the mechanisms by which IL-3 distinctively affects eosinophil function compared with IL-5 and GM-CSF, with a focus on protein translation. Peripheral blood eosinophils were used to study intracellular signaling and protein translation in cells activated with IL-3, GM-CSF, or IL-5. We establish that, unlike GM-CSF or IL-5, IL-3 triggers prolonged signaling through activation of ribosomal protein S6 (RPS6) and the upstream kinase 90-kDa ribosomal S6 kinase (p90S6K). Blockade of p90S6K activation inhibited phosphorylation of RPS6 and IL-3-enhanced semaphorin-7A translation. Furthermore, in an allergen-challenged environment, in vivo phosphorylation of RPS6 and p90S6K was enhanced in human airway compared with circulating eosinophils. Our findings provide new insights into the mechanisms underlying differential activation of eosinophils by IL-3, GM-CSF, and IL-5. These observations identify IL-3 and its downstream intracellular signals as novel targets that should be considered to modulate eosinophil functions.
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Affiliation(s)
- Stephane Esnault
- Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792;
| | - Elizabeth A B Kelly
- Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792
| | - Zhong-Jian Shen
- Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Mats W Johansson
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792
| | - James S Malter
- Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Nizar N Jarjour
- Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792
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170
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Ribosomal Protein S6 Phosphorylation: Four Decades of Research. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 320:41-73. [PMID: 26614871 DOI: 10.1016/bs.ircmb.2015.07.006] [Citation(s) in RCA: 182] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The phosphorylation of ribosomal protein S6 (rpS6) has been described for the first time about four decades ago. Since then, numerous studies have shown that this modification occurs in response to a wide variety of stimuli on five evolutionarily conserved serine residues. However, despite a large body of information on the respective kinases and the signal transduction pathways, the physiological role of rpS6 phosphorylation remained obscure until genetic manipulations were applied in both yeast and mammals in an attempt to block this modification. Thus, studies based on both mice and cultured cells subjected to disruption of the genes encoding rpS6 and the respective kinases, as well as the substitution of the phosphorylatable serine residues in rpS6, have laid the ground for the elucidation of the multiple roles of this protein and its posttranslational modification. This review focuses primarily on newly identified kinases that phosphorylate rpS6, pathways that transduce various signals into rpS6 phosphorylation, and the recently established physiological functions of this modification. It should be noted, however, that despite the significant progress made in the last decade, the molecular mechanism(s) underlying the diverse effects of rpS6 phosphorylation on cellular and organismal physiology are still poorly understood.
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171
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Castillo-Quan JI, Kinghorn KJ, Bjedov I. Genetics and pharmacology of longevity: the road to therapeutics for healthy aging. ADVANCES IN GENETICS 2015; 90:1-101. [PMID: 26296933 DOI: 10.1016/bs.adgen.2015.06.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Aging can be defined as the progressive decline in tissue and organismal function and the ability to respond to stress that occurs in association with homeostatic failure and the accumulation of molecular damage. Aging is the biggest risk factor for human disease and results in a wide range of aging pathologies. Although we do not completely understand the underlying molecular basis that drives the aging process, we have gained exceptional insights into the plasticity of life span and healthspan from the use of model organisms such as the worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster. Single-gene mutations in key cellular pathways that regulate environmental sensing, and the response to stress, have been identified that prolong life span across evolution from yeast to mammals. These genetic manipulations also correlate with a delay in the onset of tissue and organismal dysfunction. While the molecular genetics of aging will remain a prosperous and attractive area of research in biogerontology, we are moving towards an era defined by the search for therapeutic drugs that promote healthy aging. Translational biogerontology will require incorporation of both therapeutic and pharmacological concepts. The use of model organisms will remain central to the quest for drug discovery, but as we uncover molecular processes regulated by repurposed drugs and polypharmacy, studies of pharmacodynamics and pharmacokinetics, drug-drug interactions, drug toxicity, and therapeutic index will slowly become more prevalent in aging research. As we move from genetics to pharmacology and therapeutics, studies will not only require demonstration of life span extension and an underlying molecular mechanism, but also the translational relevance for human health and disease prevention.
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Affiliation(s)
- Jorge Iván Castillo-Quan
- Department of Molecular Neuroscience, Institute of Neurology, University College London, London, UK; Institute of Healthy Ageing, Department of Genetics, Evolution and Environment, University College London, London, UK
| | - Kerri J Kinghorn
- Department of Molecular Neuroscience, Institute of Neurology, University College London, London, UK; Institute of Healthy Ageing, Department of Genetics, Evolution and Environment, University College London, London, UK
| | - Ivana Bjedov
- Cancer Institute, University College London, London, UK
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172
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Casar Tena T, Burkhalter MD, Philipp M. Left-right asymmetry in the light of TOR: An update on what we know so far. Biol Cell 2015; 107:306-18. [PMID: 25943139 PMCID: PMC4744706 DOI: 10.1111/boc.201400094] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 04/29/2015] [Indexed: 01/06/2023]
Abstract
The internal left‐right (LR) asymmetry is a characteristic that exists throughout the animal kingdom from roundworms over flies and fish to mammals. Cilia, which are antenna‐like structures protruding into the extracellular space, are involved in establishing LR asymmetry during early development. Humans who suffer from dysfunctional cilia often develop conditions such as heterotaxy, where internal organs appear to be placed randomly. As a consequence to this failure in asymmetry development, serious complications such as congenital heart defects (CHD) occur. The mammalian (or mechanistic) target of rapamycin (mTOR) pathway has recently emerged as an important regulator regarding symmetry breaking. The mTOR pathway governs fundamental processes such as protein translation or metabolism. Its activity can be transduced by two complexes, which are called TORC1 and TORC2, respectively. So far, only TORC1 has been implicated with asymmetry development and appears to require very precise regulation. A number of recent papers provided evidence that dysregulated TORC1 results in alterations of motile cilia and asymmetry defects. In here, we give an update on what we know so far of mTORC1 in LR asymmetry development.
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Affiliation(s)
- Teresa Casar Tena
- Institute for Biochemistry and Molecular Biology, Ulm University, Ulm, 89081, Germany
| | - Martin D Burkhalter
- Leibniz Institute for Age Research Fritz Lippmann Institute, Jena, 07745, Germany
| | - Melanie Philipp
- Institute for Biochemistry and Molecular Biology, Ulm University, Ulm, 89081, Germany
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173
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Androschuk A, Al-Jabri B, Bolduc FV. From Learning to Memory: What Flies Can Tell Us about Intellectual Disability Treatment. Front Psychiatry 2015; 6:85. [PMID: 26089803 PMCID: PMC4453272 DOI: 10.3389/fpsyt.2015.00085] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2015] [Accepted: 05/19/2015] [Indexed: 01/13/2023] Open
Abstract
Intellectual disability (ID), previously known as mental retardation, affects 3% of the population and remains without pharmacological treatment. ID is characterized by impaired general mental abilities associated with defects in adaptive function in which onset occurs before 18 years of age. Genetic factors are increasing and being recognized as the causes of severe ID due to increased use of genome-wide screening tools. Unfortunately drug discovery for treatment of ID has not followed the same pace as gene discovery, leaving clinicians, patients, and families without the ability to ameliorate symptoms. Despite this, several model organisms have proven valuable in developing and screening candidate drugs. One such model organism is the fruit fly Drosophila. First, we review the current understanding of memory in human and its model in Drosophila. Second, we describe key signaling pathways involved in ID and memory such as the cyclic adenosine 3',5'-monophosphate (cAMP)-cAMP response element binding protein (CREB) pathway, the regulation of protein synthesis, the role of receptors and anchoring proteins, the role of neuronal proliferation, and finally the role of neurotransmitters. Third, we characterize the types of memory defects found in patients with ID. Finally, we discuss how important insights gained from Drosophila learning and memory could be translated in clinical research to lead to better treatment development.
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Affiliation(s)
- Alaura Androschuk
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Basma Al-Jabri
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Francois V. Bolduc
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
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174
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Ho YH, Gasch AP. Exploiting the yeast stress-activated signaling network to inform on stress biology and disease signaling. Curr Genet 2015; 61:503-11. [PMID: 25957506 DOI: 10.1007/s00294-015-0491-0] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 04/23/2015] [Accepted: 04/24/2015] [Indexed: 12/24/2022]
Abstract
Healthy cells utilize intricate systems to monitor their environment and mount robust responses in the event of cellular stress. Whether stress arises from external insults or defects due to mutation and disease, cells must be able to respond precisely to mount the appropriate defenses. Multi-faceted stress responses are generally coupled with arrest of growth and cell-cycle progression, which both limits the transmission of damaged materials and serves to reallocate limited cellular resources toward defense. Therefore, stress defense versus rapid growth represent competing interests in the cell. How eukaryotic cells set the balance between defense versus proliferation, and in particular knowledge of the regulatory networks that control this decision, are poorly understood. In this perspective, we expand upon our recent work inferring the stress-activated signaling network in budding yeast, which captures pathways controlling stress defense and regulators of growth and cell-cycle progression. We highlight similarities between the yeast and mammalian stress responses and explore how stress-activated signaling networks in yeast can inform on signaling defects in human cancers.
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Affiliation(s)
- Yi-Hsuan Ho
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Audrey P Gasch
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI, 53706, USA.
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175
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PKA-dependent phosphorylation of ribosomal protein S6 does not correlate with translation efficiency in striatonigral and striatopallidal medium-sized spiny neurons. J Neurosci 2015; 35:4113-30. [PMID: 25762659 DOI: 10.1523/jneurosci.3288-14.2015] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ribosomal protein S6 (rpS6), a component of the 40S ribosomal subunit, is phosphorylated on several residues in response to numerous stimuli. Although commonly used as a marker for neuronal activity, its upstream mechanisms of regulation are poorly studied and its role in protein synthesis remains largely debated. Here, we demonstrate that the psychostimulant d-amphetamine (d-amph) markedly increases rpS6 phosphorylation at Ser235/236 sites in both crude and synaptoneurosomal preparations of the mouse striatum. This effect occurs selectively in D1R-expressing medium-sized spiny neurons (MSNs) and requires the cAMP/PKA/DARPP-32/PP-1 cascade, whereas it is independent of mTORC1/p70S6K, PKC, and ERK signaling. By developing a novel assay to label nascent peptidic chains, we show that the rpS6 phosphorylation induced in striatonigral MSNs by d-amph, as well as in striatopallidal MSNs by the antipsychotic haloperidol or in both subtypes by papaverine, is not correlated with the translation of global or 5' terminal oligopyrimidine tract mRNAs. Together, these results provide novel mechanistic insights into the in vivo regulation of the post-translational modification of rpS6 in the striatum and point out the lack of a relationship between PKA-dependent rpS6 phosphorylation and translation efficiency.
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176
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Perl A. mTOR activation is a biomarker and a central pathway to autoimmune disorders, cancer, obesity, and aging. Ann N Y Acad Sci 2015; 1346:33-44. [PMID: 25907074 DOI: 10.1111/nyas.12756] [Citation(s) in RCA: 159] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The mechanistic target of rapamycin (mTOR) is a ubiquitous serine/threonine kinase, which plays pivotal roles in integrating growth signals on a cellular level. To support proliferation and survival under stress, two interacting complexes that harbor mTOR, mTORC1 and mTORC2, promote the transcription of genes involved in carbohydrate metabolism and lipogenesis, enhance protein translation, and inhibit autophagy. Although rapamycin was originally developed as an inhibitor of T cell proliferation for preventing organ transplant rejection, its molecular target, mTOR, has been subsequently identified as a central regulator of metabolic cues that drive lineage specification in the immune system. Owing to oxidative stress, the activation of mTORC1 has emerged as a central pathway for the pathogenesis of systemic lupus erythematosus and other autoimmune diseases. Paradoxically, mTORC1 has also been identified as a mediator of the Warburg effect that allows cell survival under hypoxia. Rapamycin and new classes of mTOR inhibitors are being developed to block not only transplant rejection and autoimmunity but also to treat obesity and various forms of cancer. Through preventing these diseases, personalized mTOR blockade holds promise to extend life span.
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Affiliation(s)
- Andras Perl
- Division of Rheumatology, Department of Medicine State University of New York, Upstate Medical University, College of Medicine, Syracuse, New York.,Division of Rheumatology, Department of Microbiology and Immunology, State University of New York, Upstate Medical University, College of Medicine, Syracuse, New York
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177
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Heberle AM, Prentzell MT, van Eunen K, Bakker BM, Grellscheid SN, Thedieck K. Molecular mechanisms of mTOR regulation by stress. Mol Cell Oncol 2015; 2:e970489. [PMID: 27308421 PMCID: PMC4904989 DOI: 10.4161/23723548.2014.970489] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2014] [Revised: 09/12/2014] [Accepted: 09/13/2014] [Indexed: 04/12/2023]
Abstract
Tumors are prime examples of cell growth in unfavorable environments that elicit cellular stress. The high metabolic demand and insufficient vascularization of tumors cause a deficiency of oxygen and nutrients. Oncogenic mutations map to signaling events via mammalian target of rapamycin (mTOR), metabolic pathways, and mitochondrial function. These alterations have been linked with cellular stresses, in particular endoplasmic reticulum (ER) stress, hypoxia, and oxidative stress. Yet tumors survive these challenges and acquire highly energy-demanding traits, such as overgrowth and invasiveness. In this review we focus on stresses that occur in cancer cells and discuss them in the context of mTOR signaling. Of note, many tumor traits require mTOR complex 1 (mTORC1) activity, but mTORC1 hyperactivation eventually sensitizes cells to apoptosis. Thus, mTORC1 activity needs to be balanced in cancer cells. We provide an overview of the mechanisms contributing to mTOR regulation by stress and suggest a model wherein stress granules function as guardians of mTORC1 signaling, allowing cancer cells to escape stress-induced cell death.
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Affiliation(s)
- Alexander Martin Heberle
- Department of Pediatrics and Centre for Systems Biology of Energy Metabolism and Ageing; University of Groningen; University Medical Center Groningen (UMCG); Groningen, The Netherlands
| | - Mirja Tamara Prentzell
- Department of Pediatrics and Centre for Systems Biology of Energy Metabolism and Ageing; University of Groningen; University Medical Center Groningen (UMCG); Groningen, The Netherlands
- Faculty of Biology; Institute for Biology 3; Albert-Ludwigs-University Freiburg; Freiburg, Germany
- Spemann Graduate School of Biology and Medicine (SGBM); University of Freiburg; Freiburg, Germany
| | - Karen van Eunen
- Department of Pediatrics and Centre for Systems Biology of Energy Metabolism and Ageing; University of Groningen; University Medical Center Groningen (UMCG); Groningen, The Netherlands
- Top Institute Food and Nutrition; Wageningen, The Netherlands
| | - Barbara Marleen Bakker
- Department of Pediatrics and Centre for Systems Biology of Energy Metabolism and Ageing; University of Groningen; University Medical Center Groningen (UMCG); Groningen, The Netherlands
| | | | - Kathrin Thedieck
- Department of Pediatrics and Centre for Systems Biology of Energy Metabolism and Ageing; University of Groningen; University Medical Center Groningen (UMCG); Groningen, The Netherlands
- Faculty of Biology; Institute for Biology 3; Albert-Ludwigs-University Freiburg; Freiburg, Germany
- School of Medicine and Health Sciences; Carl von Ossietzky University Oldenburg; Oldenburg, Germany
- BIOSS Centre for Biological Signaling Studies; Albert-Ludwigs-University Freiburg; Freiburg, Germany
- Correspondence to: Kathrin Thedieck; E-mail: ;
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178
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The S6K protein family in health and disease. Life Sci 2015; 131:1-10. [PMID: 25818187 DOI: 10.1016/j.lfs.2015.03.001] [Citation(s) in RCA: 168] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 03/02/2015] [Accepted: 03/05/2015] [Indexed: 02/06/2023]
Abstract
The S6K proteins are mTOR pathway effectors and accumulative evidence suggest that mTOR/S6K signaling contributes to several pathological conditions, such as diabetes, cancer and obesity. The activation of the mTOR/S6K axis stimulates protein synthesis and cell growth. S6K1 has two well-known isoforms, p70-S6K1 and p85-S6K1, generated by alternative translation initiation sites. A third isoform, named p31-S6K1, has been characterized as a truncated type of the protein due to alternative splicing, and reports have shown its important role in cancer. Studies involving S6K2 are scarce. This article aims to review what is new in the literature about these kinases and establish differences regarding their interacting proteins, activation and function, connecting their roles in the homeostasis of the cell and in pathological conditions.
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179
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González A, Shimobayashi M, Eisenberg T, Merle DA, Pendl T, Hall MN, Moustafa T. TORC1 promotes phosphorylation of ribosomal protein S6 via the AGC kinase Ypk3 in Saccharomyces cerevisiae. PLoS One 2015; 10:e0120250. [PMID: 25767889 PMCID: PMC4359079 DOI: 10.1371/journal.pone.0120250] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 01/21/2015] [Indexed: 11/21/2022] Open
Abstract
The target of rapamycin complex 1 (TORC1) is an evolutionarily conserved sensor of nutrient availability. Genetic and pharmacological studies in the yeast Saccharomyces cerevisiae have provided mechanistic insights on the regulation of TORC1 signaling in response to nutrients. Using a highly specific antibody that recognizes phosphorylation of the bona fide TORC1 target ribosomal protein S6 (Rps6) in yeast, we found that nutrients rapidly induce Rps6 phosphorylation in a TORC1-dependent manner. Moreover, we demonstrate that Ypk3, an AGC kinase which exhibits high homology to human S6 kinase (S6K), is required for the phosphorylation of Rps6 in vivo. Rps6 phosphorylation is completely abolished in cells lacking Ypk3 (ypk3Δ), whereas Sch9, previously reported to be the yeast ortholog of S6K, is dispensable for Rps6 phosphorylation. Phosphorylation-deficient mutations in regulatory motifs of Ypk3 abrogate Rps6 phosphorylation, and complementation of ypk3Δ cells with human S6 kinase restores Rps6 phosphorylation in a rapamycin-sensitive manner. Our findings demonstrate that Ypk3 is a critical component of the TORC1 pathway and that the use of a phospho-S6 specific antibody offers a valuable tool to identify new nutrient-dependent and rapamycin-sensitive targets in vivo.
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Affiliation(s)
| | | | - Tobias Eisenberg
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | | | - Tobias Pendl
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | | | - Tarek Moustafa
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
- * E-mail:
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180
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Gentilella A, Kozma SC, Thomas G. A liaison between mTOR signaling, ribosome biogenesis and cancer. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2015; 1849:812-20. [PMID: 25735853 DOI: 10.1016/j.bbagrm.2015.02.005] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 02/20/2015] [Accepted: 02/23/2015] [Indexed: 01/05/2023]
Abstract
The ability to translate genetic information into functional proteins is considered a landmark in evolution. Ribosomes have evolved to take on this responsibility and, although there are some differences in their molecular make-up, both prokaryotes and eukaryotes share a common structural architecture and similar underlying mechanisms of protein synthesis. Understanding ribosome function and biogenesis has been the focus of extensive research since the early days of their discovery. In the last decade however, new and unexpected roles have emerged that place deregulated ribosome biogenesis and protein synthesis at the crossroads of pathological settings, particularly cancer, revealing a set of novel cellular checkpoints. Moreover, it is also becoming evident that mTOR signaling, which regulates an array of anabolic processes, including ribosome biogenesis, is often exploited by cancer cells to sustain proliferation through the upregulation of global protein synthesis. The use of pharmacological agents that interfere with ribosome biogenesis and mTOR signaling has proven to be an effective strategy to control cancer development clinically. Here we discuss the most recent findings concerning the underlying mechanisms by which mTOR signaling controls ribosome production and the potential impact of ribosome biogenesis in tumor development. This article is part of a Special Issue entitled: Translation and Cancer.
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Affiliation(s)
- Antonio Gentilella
- Laboratory of Metabolism and Cancer, Catalan Institute of Oncology, ICO, Bellvitge Biomedical Research Institute, IDIBELL, 08908 Barcelona, Spain.
| | - Sara C Kozma
- Laboratory of Metabolism and Cancer, Catalan Institute of Oncology, ICO, Bellvitge Biomedical Research Institute, IDIBELL, 08908 Barcelona, Spain; Department of Internal Medicine, Division of Hematology/Oncology, University of Cincinnati Medical School, Cincinnati, 45267-0508 OH, USA
| | - George Thomas
- Laboratory of Metabolism and Cancer, Catalan Institute of Oncology, ICO, Bellvitge Biomedical Research Institute, IDIBELL, 08908 Barcelona, Spain; Department of Internal Medicine, Division of Hematology/Oncology, University of Cincinnati Medical School, Cincinnati, 45267-0508 OH, USA.
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181
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Fittschen M, Lastres-Becker I, Halbach MV, Damrath E, Gispert S, Azizov M, Walter M, Müller S, Auburger G. Genetic ablation of ataxin-2 increases several global translation factors in their transcript abundance but decreases translation rate. Neurogenetics 2015; 16:181-92. [PMID: 25721894 PMCID: PMC4475250 DOI: 10.1007/s10048-015-0441-5] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 02/10/2015] [Indexed: 12/12/2022]
Abstract
Spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders, caused or modified by an unstable CAG-repeat expansion in the SCA2 gene, which encodes a polyglutamine (polyQ) domain expansion in ataxin-2 (ATXN2). ATXN2 is an RNA-binding protein and interacts with the poly(A)-binding protein PABPC1, localizing to ribosomes at the rough endoplasmic reticulum. Under cell stress, ATXN2, PABPC1 and small ribosomal subunits are relocated to stress granules, where mRNAs are protected from translation and from degradation. It is unknown whether ATXN2 associates preferentially with specific mRNAs or how it modulates RNA processing. Here, we investigated the RNA profile of the liver and cerebellum from Atxn2 knockout (Atxn2 (-/-)) mice at two adult ages, employing oligonucleotide microarrays. Prominent increases were observed for Lsm12/Paip1 (>2-fold), translation modulators known as protein interactor/competitor of ATXN2 and for Plin3/Mttp (>1.3-fold), known as apolipoprotein modulators in agreement with the hepatosteatosis phenotype of the Atxn2 (-/-) mice. Consistent modest upregulations were also observed for many factors in the ribosome and the translation/secretion apparatus. Quantitative reverse transcriptase PCR in liver tissue validated >1.2-fold upregulations for the ribosomal biogenesis modulator Nop10, the ribosomal components Rps10, Rps18, Rpl14, Rpl18, Gnb2l1, the translation initiation factors Eif2s2, Eif3s6, Eif4b, Pabpc1 and the rER translocase factors Srp14, Ssr1, Sec61b. Quantitative immunoblots substantiated the increased abundance of NOP10, RPS3, RPS6, RPS10, RPS18, GNB2L1 in SDS protein fractions, and of PABPC1. In mouse embryonal fibroblasts, ATXN2 absence also enhanced phosphorylation of the ribosomal protein S6 during growth stimulation, while impairing the rate of overall protein synthesis rates, suggesting a block between the enhanced translation drive and the impaired execution. Thus, the physiological role of ATXN2 subtly modifies the abundance of cellular translation factors as well as global translation.
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Affiliation(s)
- M Fittschen
- Experimental Neurology, Goethe University Medical School, Theodor Stern Kai 7, 60590, Frankfurt am Main, Germany
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182
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Sanij E, Diesch J, Lesmana A, Poortinga G, Hein N, Lidgerwood G, Cameron DP, Ellul J, Goodall GJ, Wong LH, Dhillon AS, Hamdane N, Rothblum LI, Pearson RB, Haviv I, Moss T, Hannan RD. A novel role for the Pol I transcription factor UBTF in maintaining genome stability through the regulation of highly transcribed Pol II genes. Genome Res 2015; 25:201-12. [PMID: 25452314 PMCID: PMC4315294 DOI: 10.1101/gr.176115.114] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 11/26/2014] [Indexed: 12/21/2022]
Abstract
Mechanisms to coordinate programs of highly transcribed genes required for cellular homeostasis and growth are unclear. Upstream binding transcription factor (UBTF, also called UBF) is thought to function exclusively in RNA polymerase I (Pol I)-specific transcription of the ribosomal genes. Here, we report that the two isoforms of UBTF (UBTF1/2) are also enriched at highly expressed Pol II-transcribed genes throughout the mouse genome. Further analysis of UBTF1/2 DNA binding in immortalized human epithelial cells and their isogenically matched transformed counterparts reveals an additional repertoire of UBTF1/2-bound genes involved in the regulation of cell cycle checkpoints and DNA damage response. As proof of a functional role for UBTF1/2 in regulating Pol II transcription, we demonstrate that UBTF1/2 is required for recruiting Pol II to the highly transcribed histone gene clusters and for their optimal expression. Intriguingly, lack of UBTF1/2 does not affect chromatin marks or nucleosome density at histone genes. Instead, it results in increased accessibility of the histone promoters and transcribed regions to micrococcal nuclease, implicating UBTF1/2 in mediating DNA accessibility. Unexpectedly, UBTF2, which does not function in Pol I transcription, is sufficient to regulate histone gene expression in the absence of UBTF1. Moreover, depletion of UBTF1/2 and subsequent reduction in histone gene expression is associated with DNA damage and genomic instability independent of Pol I transcription. Thus, we have uncovered a novel role for UBTF1 and UBTF2 in maintaining genome stability through coordinating the expression of highly transcribed Pol I (UBTF1 activity) and Pol II genes (UBTF2 activity).
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Affiliation(s)
- Elaine Sanij
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia; Department of Pathology, University of Melbourne, Parkville, Victoria 3010, Australia;
| | - Jeannine Diesch
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Analia Lesmana
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Gretchen Poortinga
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia; Department of Medicine, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Nadine Hein
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Grace Lidgerwood
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia
| | - Donald P Cameron
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Jason Ellul
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Gregory J Goodall
- Centre for Cancer Biology, SA Pathology and University of South Australia, Adelaide, South Australia 5000, Australia; Discipline of Medicine, The University of Adelaide, Adelaide, South Australia 5005, Australia; School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Lee H Wong
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia
| | - Amardeep S Dhillon
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia; Department of Pathology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Nourdine Hamdane
- Department of Molecular Biology, Medical Biochemistry and Pathology, Faculty of Medicine, Laval University, Québec, QC, G1V 0A6, Canada; St-Patrick Research Group in Basic Oncology, Québec University Hospital Research Centre, Québec, QC, G1R 3S3, Canada
| | - Lawrence I Rothblum
- Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73104, USA
| | - Richard B Pearson
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Izhak Haviv
- Department of Pathology, University of Melbourne, Parkville, Victoria 3010, Australia; Faculty of Medicine, Bar-Ilan University, Zfat, 13100, Israel
| | - Tom Moss
- Department of Molecular Biology, Medical Biochemistry and Pathology, Faculty of Medicine, Laval University, Québec, QC, G1V 0A6, Canada; St-Patrick Research Group in Basic Oncology, Québec University Hospital Research Centre, Québec, QC, G1R 3S3, Canada
| | - Ross D Hannan
- Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3010, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3010, Australia; Division of Cancer Medicine, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; School of Biomedical Sciences, University of Queensland, Brisbane 4072, Queensland, Australia
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183
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Sun CK, Zhang F, Xiang T, Chen Q, Pandita TK, Huang Y, Hu MCT, Yang Q. Phosphorylation of ribosomal protein S6 confers PARP inhibitor resistance in BRCA1-deficient cancers. Oncotarget 2015; 5:3375-85. [PMID: 24831086 PMCID: PMC4102816 DOI: 10.18632/oncotarget.1952] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Inhibition of poly(ADP-ribose) polymerase (PARP) is a promising therapeutic strategy for BRCA1 deficient cancers, however, the development of drug resistance limits clinical efficacy. Previously we found that the BRCA1-AKT1 pathway contributes to tumorigenesis and that the AKT1/mTOR is a novel therapeutic target for BRCA1-deficient cancers. Here, we report that phosphorylation of ribosomal protein S6, a mTOR downstream effector, is greatly increased in BRCA1 deficient cells resistant to PARP inhibition. Phosphorylation of S6 is associated with DNA damage and repair signaling during PARP inhibitor treatment. In BRCA1 deficient cells, expression of S6 lacking all five phosphorylatable sites renders the cells sensitive to PARP inhibitor and increases DNA damage signals. In addition, the S6 mutations reduce tumor formation induced by Brca1-deficiency in mice. Inhibition of S6 phosphorylation by rapamycin restores PARP sensitivity to resistant cells. Combined treatment with rapamycin and PARP inhibitor effectively suppresses BRCA1-deficient tumor growth in mice. These results provide evidence for a novel mechanism by which BRCA1 deficient cancers acquire drug resistance and suggest a new therapeutic strategy to circumvent resistance.
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Affiliation(s)
- Chong-kui Sun
- Cancer Biology Division, Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, MO 63108
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184
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Albert V, Hall MN. mTOR signaling in cellular and organismal energetics. Curr Opin Cell Biol 2014; 33:55-66. [PMID: 25554914 DOI: 10.1016/j.ceb.2014.12.001] [Citation(s) in RCA: 212] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 12/02/2014] [Accepted: 12/03/2014] [Indexed: 12/20/2022]
Abstract
Mammalian TOR (mTOR) signaling controls growth, metabolism and energy homeostasis in a cell autonomous manner. Recent findings indicate that mTOR signaling in one tissue can also affect other organs thereby affecting whole body metabolism and energy homeostasis in a non-cell autonomous manner. It is thus not surprising that mTOR signaling mediates aging and is often deregulated in metabolic disorders, such as obesity, diabetes and cancer. This review discusses the regulation of cellular and whole body energy metabolism by mTOR, with particular focus on the non-cell autonomous function of mTOR.
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Affiliation(s)
- Verena Albert
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | - Michael N Hall
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
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185
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Chiarini F, Evangelisti C, McCubrey JA, Martelli AM. Current treatment strategies for inhibiting mTOR in cancer. Trends Pharmacol Sci 2014; 36:124-35. [PMID: 25497227 DOI: 10.1016/j.tips.2014.11.004] [Citation(s) in RCA: 209] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 11/07/2014] [Accepted: 11/12/2014] [Indexed: 02/07/2023]
Abstract
Mammalian target of rapamycin (mTOR) is a Ser/Thr kinase that regulates a wide range of functions, including cell growth, proliferation, survival, autophagy, metabolism, and cytoskeletal organization. mTOR activity is dysregulated in several human disorders, including cancer. The crucial role of mTOR in cancer cell biology has stimulated interest in mTOR inhibitors, placing mTOR on the radar of the pharmaceutical industry. Several mTOR inhibitors have already undergone clinical trials for treating tumors, without great success, although mTOR inhibitors are approved for the treatment of some types of cancer, including advanced renal cell carcinoma. However, the role of mTOR inhibitors in cancer treatment continues to evolve as new compounds are continuously being disclosed. Here we review the three classes of mTOR inhibitors currently available for treating cancer patients. Moreover, we highlight efforts to identify markers of resistance and sensitivity to mTOR inhibition that could prove useful in the emerging field of personalized medicine.
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Affiliation(s)
- Francesca Chiarini
- Institute of Molecular Genetics, National Research Council, Bologna, Italy; Rizzoli Orthopedic Institute, Bologna, Italy
| | - Camilla Evangelisti
- Institute of Molecular Genetics, National Research Council, Bologna, Italy; Rizzoli Orthopedic Institute, Bologna, Italy
| | - James A McCubrey
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC, USA
| | - Alberto M Martelli
- Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy.
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186
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Gao B, Roux PP. Translational control by oncogenic signaling pathways. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:753-65. [PMID: 25477072 DOI: 10.1016/j.bbagrm.2014.11.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2014] [Revised: 11/17/2014] [Accepted: 11/19/2014] [Indexed: 01/04/2023]
Abstract
Messenger RNA (mRNA) translation is highly regulated in cells and plays an integral role in the overall process of gene expression. The initiation phase of translation is considered to be the most rate-limiting and is often targeted by oncogenic signaling pathways to promote global protein synthesis and the selective translation of tumor-promoting mRNAs. Translational control is a crucial component of cancer development as it allows cancer cells to adapt to the altered metabolism that is generally associated with the tumor state. The phosphoinositide 3-kinase (PI3K)/Akt and Ras/mitogen-activated protein kinase (MAPK) pathways are strongly implicated in cancer etiology, and they exert their biological effects by modulating both global and specific mRNA translation. In addition to having respective translational targets, these pathways also impinge on the mechanistic/mammalian target of rapamycin (mTOR), which acts as a critical signaling node linking nutrient sensing to the coordinated regulation of cellular metabolism. mTOR is best known as a central regulator of protein synthesis and has been implicated in an increasing number of pathological conditions, including cancer. In this article, we describe the current knowledge on the roles and regulation of mRNA translation by various oncogenic signaling pathways, as well as the relevance of these molecular mechanisms to human malignancies. This article is part of a Special Issue entitled: Translation and cancer.
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Affiliation(s)
- Beichen Gao
- Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, Québec, Canada
| | - Philippe P Roux
- Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, Québec, Canada; Department of Pathology and Cell Biology, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada.
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187
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Regulation of rDNA transcription in response to growth factors, nutrients and energy. Gene 2014; 556:27-34. [PMID: 25447905 DOI: 10.1016/j.gene.2014.11.010] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 11/04/2014] [Accepted: 11/06/2014] [Indexed: 11/21/2022]
Abstract
Exquisite control of ribosome biogenesis is fundamental for the maintenance of cellular growth and proliferation. Importantly, synthesis of ribosomal RNA by RNA polymerase I is a key regulatory step in ribosome biogenesis and a major biosynthetic and energy consuming process. Consequently, ribosomal RNA gene transcription is tightly coupled to the availability of growth factors, nutrients and energy. Thus cells have developed an intricate sensing network to monitor the cellular environment and modulate ribosomal DNA transcription accordingly. Critical controllers in these sensing networks, which mediate growth factor activation of ribosomal DNA transcription, include the PI3K/AKT/mTORC1, RAS/RAF/ERK pathways and MYC transcription factor. mTORC1 also responds to amino acids and energy status, making it a key hub linking all three stimuli to the regulation of ribosomal DNA transcription, although this is achieved via overlapping and distinct mechanisms. This review outlines the current knowledge of how cells respond to environmental cues to control ribosomal RNA synthesis. We also highlight the critical points within this network that are providing new therapeutic opportunities for treating cancers through modulation of RNA polymerase I activity and potential novel imaging strategies.
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188
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Drake JC, Bruns DR, Peelor FF, Biela LM, Miller RA, Hamilton KL, Miller BF. Long-lived crowded-litter mice have an age-dependent increase in protein synthesis to DNA synthesis ratio and mTORC1 substrate phosphorylation. Am J Physiol Endocrinol Metab 2014; 307:E813-21. [PMID: 25205819 PMCID: PMC4216950 DOI: 10.1152/ajpendo.00256.2014] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Increasing mouse litter size [crowded litter (CL)] presumably imposes a transient nutrient stress during suckling and extends lifespan through unknown mechanisms. Chronic calorically restricted and rapamycin-treated mice have decreased DNA synthesis and mTOR complex 1 (mTORC1) signaling but maintained protein synthesis, suggesting maintenance of existing cellular structures. We hypothesized that CL would exhibit similar synthetic and signaling responses to other long-lived models and, by comparing synthesis of new protein to new DNA, that insight may be gained into the potential preservation of existing cellular structures in the CL model. Protein and DNA synthesis was assessed in gastroc complex, heart, and liver of 4- and 7-mo CL mice. We also examined mTORC1 signaling in 3- and 7-mo aged animals. Compared with controls, 4-mo CL had greater DNA synthesis in gastroc complex with no differences in protein synthesis or mTORC1 substrate phosphorylation across tissues. Seven-month CL had less DNA synthesis than controls in heart and greater protein synthesis and mTORC1 substrate phosphorylation across tissues. The increased new protein-to-new DNA synthesis ratio suggests that new proteins are synthesized more so in existing cells at 7 mo, differing from 4 mo, in CL vs. controls. We propose that, in CL, protein synthesis shifts from being directed toward new cells (4 mo) to maintenance of existing cellular structures (7 mo), independently of decreased mTORC1.
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Affiliation(s)
- Joshua C Drake
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
| | - Danielle R Bruns
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
| | - Frederick F Peelor
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
| | - Laurie M Biela
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
| | - Richard A Miller
- Department of Pathology and Geriatrics Center, University of Michigan, Ann Arbor, Michigan
| | - Karyn L Hamilton
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
| | - Benjamin F Miller
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado; and
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189
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Huang K, Fingar DC. Growing knowledge of the mTOR signaling network. Semin Cell Dev Biol 2014; 36:79-90. [PMID: 25242279 DOI: 10.1016/j.semcdb.2014.09.011] [Citation(s) in RCA: 225] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 09/05/2014] [Accepted: 09/10/2014] [Indexed: 12/14/2022]
Abstract
The kinase mTOR (mechanistic target of rapamycin) integrates diverse environmental signals and translates these cues into appropriate cellular responses. mTOR forms the catalytic core of at least two functionally distinct signaling complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 promotes anabolic cellular metabolism in response to growth factors, nutrients, and energy and functions as a master controller of cell growth. While significantly less well understood than mTORC1, mTORC2 responds to growth factors and controls cell metabolism, cell survival, and the organization of the actin cytoskeleton. mTOR plays critical roles in cellular processes related to tumorigenesis, metabolism, immune function, and aging. Consequently, aberrant mTOR signaling contributes to myriad disease states, and physicians employ mTORC1 inhibitors (rapamycin and analogs) for several pathological conditions. The clinical utility of mTOR inhibition underscores the important role of mTOR in organismal physiology. Here we review our growing knowledge of cellular mTOR regulation by diverse upstream signals (e.g. growth factors; amino acids; energy) and how mTORC1 integrates these signals to effect appropriate downstream signaling, with a greater emphasis on mTORC1 over mTORC2. We highlight dynamic subcellular localization of mTORC1 and associated factors as an important mechanism for control of mTORC1 activity and function. We will cover major cellular functions controlled by mTORC1 broadly. While significant advances have been made in the last decade regarding the regulation and function of mTOR within complex cell signaling networks, many important findings remain to be discovered.
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Affiliation(s)
- Kezhen Huang
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109-2200, United States
| | - Diane C Fingar
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109-2200, United States; Division of Metabolism, Endocrinology, and Diabetes (MEND), Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109-2200, United States.
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190
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Phosphorylation of ribosomal protein S6 mediates compensatory renal hypertrophy. Kidney Int 2014; 87:543-56. [PMID: 25229342 PMCID: PMC4344886 DOI: 10.1038/ki.2014.302] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Revised: 07/11/2014] [Accepted: 07/24/2014] [Indexed: 01/15/2023]
Abstract
The molecular mechanism underlying renal hypertrophy and progressive nephron damage remains poorly understood. Here we generated congenic ribosomal protein S6 (rpS6) knockin mice expressing non-phosphorylatable rpS6 and found that uninephrectomy-induced renal hypertrophy was significantly blunted in these knockin mice. Uninephrectomy-induced increases in cyclin D1 and decreases in cyclin E in the remaining kidney were attenuated in the knockin mice compared to their wild-type littermates. Uninephrectomy induced rpS6 phosphorylation in the wild type mice; however, no rpS6 phosphorylation was detected in uninephrectomized or sham-operated knockin mice. Nonetheless, uninephrectomy stimulated comparable 4E-BP1 phosphorylation in both knockin and wild type mice, indicating that mTORC1 was still activated in the knockin mice. Moreover, the mTORC1 inhibitor rapamycin prevented both rpS6 and 4E-BP1 phosphorylation, significantly blunted uninephrectomy-induced renal hypertrophy in wild type mice, but did not prevent residual renal hypertrophy despite inhibiting 4E-BP1 phosphorylation in uninephrectomized knockin mice. Thus, both genetic and pharmacological approaches unequivocally demonstrate that phosphorylated rpS6 is a downstream effector of the mTORC1-S6K1 signaling pathway mediating renal hypertrophy. Hence, rpS6 phosphorylation facilitates the increase in cyclin D1 and decrease in cyclin E1 that underlie the hypertrophic nature of uninephrectomy-induced kidney growth.
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191
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Meyuhas O, Kahan T. The race to decipher the top secrets of TOP mRNAs. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:801-11. [PMID: 25234618 DOI: 10.1016/j.bbagrm.2014.08.015] [Citation(s) in RCA: 164] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 08/18/2014] [Accepted: 08/27/2014] [Indexed: 12/20/2022]
Abstract
Cells encountering hostile growth conditions, like those residing in the middle of a newly developing solid tumor, conserve resources and energy by downregulating protein synthesis. One mechanism in this response is the translational repression of multiple mRNAs that encode components of the translational apparatus. This coordinated translational control is carried through a common cis-regulatory element, the 5' Terminal OligoPyrimidine motif (5'TOP), after which these mRNAs are referred to as TOP mRNAs. Subsequent to the initial structural and functional characterization of members of this family, the research of TOP mRNAs has progressed in three major directions: a) delineating the landscape of the family; b) establishing the pathways that transduce stress cues into selective translational repression; and c) attempting to decipher the most proximal trans-acting factor(s) and defining its mode of action--a repressor or activator. The present chapter critically reviews the development in these three avenues of research with a special emphasis on the two "top secrets" of the TOP mRNA family: the scope of its members and the identity of the proximal cellular regulator(s). This article is part of a Special Issue entitled: Translation and Cancer.
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Affiliation(s)
- Oded Meyuhas
- Department of Biochemistry and Molecular Biology, Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
| | - Tamar Kahan
- Bioinformatics Unit, The Hebrew University, Hadassah Medical School, Jerusalem 91120, Israel
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192
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mTORC1 signaling controls multiple steps in ribosome biogenesis. Semin Cell Dev Biol 2014; 36:113-20. [PMID: 25148809 DOI: 10.1016/j.semcdb.2014.08.004] [Citation(s) in RCA: 180] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/07/2014] [Accepted: 08/11/2014] [Indexed: 02/06/2023]
Abstract
Ribosome biogenesis is critical for cells to generate the ribosomes they need for protein synthesis in order to survive, grow and proliferate. It is a complex process, involving the coordinated production of four different RNA species and about 80 proteins, as well as their assembly into functional ribosomal subunits. Given its high demand for amino acids and nucleotides, it is also a metabolically expensive process for the cell. The mammalian target of rapamycin complex 1 (mTORC1) is a protein kinases which is activated by nutrients, anabolic hormones and oncogenic signaling pathways. mTORC1 positively regulates several steps in ribosome biogenesis, including ribosomal RNA transcription, the synthesis of ribosomal proteins and other components required for ribosome assembly. mTORC1 can thus coordinate stimuli which promote ribosome production with the various steps involved in this process. Although important advances have been made in our understanding of mTORC1 signaling, major questions remain about the molecular mechanisms by which it regulates ribosome biogenesis.
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193
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Shimobayashi M, Hall MN. Making new contacts: the mTOR network in metabolism and signalling crosstalk. Nat Rev Mol Cell Biol 2014; 15:155-62. [PMID: 24556838 DOI: 10.1038/nrm3757] [Citation(s) in RCA: 796] [Impact Index Per Article: 79.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
More than 20 years after its discovery, our understanding of target of rapamycin (TOR) signalling continues to grow. Recent global 'omics' studies have revealed physiological roles of mammalian TOR (mTOR) in protein, nucleotide and lipid synthesis. Furthermore, emerging evidence provides new insight into the control of mTOR by other pathways such as Hippo, WNT and Notch signalling. Together, this progress has expanded the list of downstream effectors and upstream regulators of mTOR signalling.
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Affiliation(s)
| | - Michael N Hall
- Biozentrum, University of Basel, Basel 4056, Switzerland
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194
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Feedback loops blockade potentiates apoptosis induction and antitumor activity of a novel AKT inhibitor DC120 in human liver cancer. Cell Death Dis 2014; 5:e1114. [PMID: 24625973 PMCID: PMC3973233 DOI: 10.1038/cddis.2014.43] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 12/22/2013] [Accepted: 01/17/2014] [Indexed: 12/20/2022]
Abstract
The serine/threonine kinase AKT is generally accepted as a promising anticancer therapeutic target. However, the relief of feedback inhibition and enhancement of other survival pathways often attenuate the anticancer effects of AKT inhibitors. These compensatory mechanisms are very complicated and remain poorly understood. In the present study, we found a novel 2-pyrimidyl-5-amidothiazole compound, DC120, as an ATP competitive AKT kinase inhibitor that suppressed proliferation and induced apoptosis in liver cancer cells both in vitro and in vivo. DC120 blocked the phosphorylation of downstream molecules in the AKT signal pathway in dose- and time-dependent manners both in vitro and in vivo. However, unexpectedly, DC120 activated mammalian target of rapamycin complex 1 (mTORC1) pathway that was suggested by increased phosphorylation of 70KD ribosomal protein S6 kinase (P70S6K) and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1). The activated mTORC1 signal was because of increase of intracellular Ca(2+) via Ca(2+)/calmodulin (CaM)/ signaling to human vacuolar protein sorting 34 (hVps34) upon AKT inhibition. Meanwhile, DC120 attenuated the inhibitory effect of AKT on CRAF by decreasing phosphorylation of CRAF at Ser259 and thus activated the mitogen-activated protein kinase (MAPK) pathway. The activation of the mTORC1 and MAPK pathways by DC120 was not mutually dependent, and the combination of DC120 with mTORC1 inhibitor and/or MEK inhibitor induced significant apoptosis and growth inhibition both in vitro and in vivo. Taken together, the combination of AKT, mTORC1 and/or MEK inhibitors would be a promising therapeutic strategy for liver cancer treatment.
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195
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Patrone M, Carinhas N, Sousa MQ, Peixoto C, Ciferri C, Carfì A, Alves PM. Enhanced expression of full-length human cytomegalovirus fusion protein in non-swelling baculovirus-infected cells with a minimal fed-batch strategy. PLoS One 2014; 9:e90753. [PMID: 24595278 PMCID: PMC3942479 DOI: 10.1371/journal.pone.0090753] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 02/03/2014] [Indexed: 01/22/2023] Open
Abstract
Human cytomegalovirus congenital infection represents an unmet medical issue and attempts are ongoing to develop an effective vaccine. The virion fusion players of this enveloped virus are the natural targets to achieve this goal and to develop novel anti-viral therapies. The secreted ectodomain of the viral fusion factor glycoprotein B (gB) has been exploited so far as an alternative to the cumbersome expression of the wild type trans-membrane protein. In the soluble form, gB showed encouraging but limited potential as antigen candidate calling for further efforts. Here, the exhaustive evaluation of the Baculovirus/insect cell expression system has been coupled to an orthogonal screening for expression additives to produce full-length gB. In detail, rapamycin was found to prolong gB intracellular accumulation while inhibiting the infection-induced cell swelling. Not obvious to predict, this inhibition did not affect Baculovirus growth, revealing that the virus-induced cell size increase is a dispensable side phenotype. In parallel, a feeding strategy for the limiting nutrient cysteine has been set up which improved gB stability. This multi-modal scheme allowed the production of full-length, mutation-free gB in the milligram scale. The recombinant full-length gB obtained was embedded into a stable mono-dispersed particle substantially larger than the protein trimer itself, according to the reported association of this protein with detergent-resistant lipid domains.
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Affiliation(s)
- Marco Patrone
- iBET, Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal
- * E-mail:
| | - Nuno Carinhas
- iBET, Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Marcos Q. Sousa
- iBET, Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal
| | - Cristina Peixoto
- iBET, Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal
| | - Claudio Ciferri
- Novartis Vaccines and Diagnostics, Cambridge, Massachusetts, United States of America
| | - Andrea Carfì
- Novartis Vaccines and Diagnostics, Cambridge, Massachusetts, United States of America
| | - Paula M. Alves
- iBET, Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
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196
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Pende M, Treins C. Ribosomal Protein S6 and S6 Kinases. TRANSLATION AND ITS REGULATION IN CANCER BIOLOGY AND MEDICINE 2014:345-362. [DOI: 10.1007/978-94-017-9078-9_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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197
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Hasty P, Livi CB, Dodds SG, Jones D, Strong R, Javors M, Fischer KE, Sloane L, Murthy K, Hubbard G, Sun L, Hurez V, Curiel TJ, Sharp ZD. eRapa restores a normal life span in a FAP mouse model. Cancer Prev Res (Phila) 2013; 7:169-78. [PMID: 24282255 DOI: 10.1158/1940-6207.capr-13-0299] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Mutation of a single copy of the adenomatous polyposis coli (APC) gene results in familial adenomatous polyposis (FAP), which confers an extremely high risk for colon cancer. Apc(Min/+) mice exhibit multiple intestinal neoplasia (MIN) that causes anemia and death from bleeding by 6 months. Mechanistic target of rapamycin complex 1 (mTORC1) inhibitors were shown to improve Apc(Min/+) mouse survival when administered by oral gavage or added directly to the chow, but these mice still died from neoplasia well short of a natural life span. The National Institute of Aging Intervention Testing Program showed that enterically targeted rapamycin (eRapa) extended life span for wild-type genetically heterogeneous mice in part by inhibiting age-associated cancer. We hypothesized that eRapa would be effective in preventing neoplasia and extend survival of Apc(Min/+) mice. We show that eRapa improved survival of Apc(Min/+) mice in a dose-dependent manner. Remarkably, and in contrast to previous reports, most of the Apc(Min/+) mice fed 42 parts per million eRapa lived beyond the median life span reported for wild-type syngeneic mice. Furthermore, chronic eRapa did not cause detrimental immune effects in mouse models of cancer, infection, or autoimmunity, thus assuaging concerns that chronic rapamycin treatment suppresses immunity. Our studies suggest that a novel formulation (enteric targeting) of a well-known and widely used drug (rapamycin) can dramatically improve its efficacy in targeted settings. eRapa or other mTORC1 inhibitors could serve as effective cancer preventatives for people with FAP without suppressing the immune system, thus reducing the dependency on surgery as standard therapy.
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Affiliation(s)
- Paul Hasty
- 15355 Lambda Drive, San Antonio, TX 78145. Phone: 210-567-7226; Fax: 210-562-4161; E-mail: ; Tyler J. Curiel, E-mail: ; Paul Hasty, ; Carolina B. Livi, Agilent Technologies, 5301 Stevens Creek Boulevard, Santa Clara, CA 95051. ,
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198
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Graber TE, McCamphill PK, Sossin WS. A recollection of mTOR signaling in learning and memory. Learn Mem 2013; 20:518-30. [PMID: 24042848 DOI: 10.1101/lm.027664.112] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mechanistic target of rapamcyin (mTOR) is a central player in cell growth throughout the organism. However, mTOR takes on an additional, more specialized role in the developed neuron, where it regulates the protein synthesis-dependent, plastic changes underlying learning and memory. mTOR is sequestered in two multiprotein complexes (mTORC1 and mTORC2) that have different substrate specificities, thus allowing for distinct functions at synapses. We will examine how learning activates the mTOR complexes, survey the critical effectors of this pathway in the context of synaptic plasticity, and assess whether mTOR plays an instructive or permissive role in generating molecular memory traces.
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Affiliation(s)
- Tyson E Graber
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A-2B4, Canada
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199
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Pardo OE, Seckl MJ. S6K2: The Neglected S6 Kinase Family Member. Front Oncol 2013; 3:191. [PMID: 23898460 PMCID: PMC3721059 DOI: 10.3389/fonc.2013.00191] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 07/08/2013] [Indexed: 01/05/2023] Open
Abstract
S6 kinase 2 (S6K2) is a member of the AGC kinases super-family. Its closest homolog, S6K1, has been extensively studied along the years. However, due to the belief in the community that the high degree of identity between these two isoforms would translate in essentially identical biological functions, S6K2 has been largely neglected. Nevertheless, recent research has clearly highlighted that these two proteins significantly differ in their roles in vitro as well as in vivo. These findings are significant to our understanding of S6 kinase signaling and the development of therapeutic strategies for several diseases including cancer. Here, we will focus on S6K2 and review the protein–protein interactions and specific substrates that determine the selective functions of this kinase.
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Affiliation(s)
- Olivier E Pardo
- Division of Cancer, Department of Surgery and Cancer, Imperial College, Hammersmith Hospital , London , UK
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200
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Loayza-Puch F, Drost J, Rooijers K, Lopes R, Elkon R, Agami R. p53 induces transcriptional and translational programs to suppress cell proliferation and growth. Genome Biol 2013; 14:R32. [PMID: 23594524 PMCID: PMC4053767 DOI: 10.1186/gb-2013-14-4-r32] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Accepted: 04/17/2013] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Cell growth and proliferation are tightly connected to ensure that appropriately sized daughter cells are generated following mitosis. Energy stress blocks cell growth and proliferation, a critical response for survival under extreme conditions. Excessive oncogenic stress leads to p53 activation and the induction of senescence, an irreversible state of cell-cycle arrest and a critical component in the suppression of tumorigenesis. Nutrient-sensing and mitogenic cues converge on a major signaling node, which regulates the activity of the mTOR kinase. Although transcriptional responses to energy and oncogenic stresses have been examined by many gene-expression experiments, a global exploration of the modulation of mRNA translation in response to these conditions is lacking. RESULTS We combine RNA sequencing and ribosomal profiling analyses to systematically delineate modes of transcriptional and translational regulation induced in response to conditions of limited energy, oncogenic stress and cellular transformation. We detect a key role for mTOR and p53 in these distinct physiological states, and provide the first genome-wide demonstration that p53 activation results in mTOR inhibition and a consequent global repression of protein translation. We confirm the role of the direct p53 target genes Sestrin1 and Sestrin2 in this response, as part of the broad modulation of gene expression induced by p53 activation. CONCLUSIONS We delineate a bimodal tumor-suppressive regulatory program activated by p53, in which cell-cycle arrest is imposed mainly at the transcriptional level, whereas cell growth inhibition is enforced by global repression of the translation machinery.
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