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Jia JJ, Lahr RM, Solgaard MT, Moraes BJ, Pointet R, Yang AD, Celucci G, Graber TE, Hoang HD, Niklaus M, Pena IA, Hollensen AK, Smith EM, Chaker-Margot M, Anton L, Dajadian C, Livingstone M, Hearnden J, Wang XD, Yu Y, Maier T, Damgaard CK, Berman AJ, Alain T, Fonseca BD. mTORC1 promotes TOP mRNA translation through site-specific phosphorylation of LARP1. Nucleic Acids Res 2021; 49:3461-3489. [PMID: 33398329 PMCID: PMC8034618 DOI: 10.1093/nar/gkaa1239] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 11/29/2020] [Accepted: 12/15/2020] [Indexed: 02/06/2023] Open
Abstract
LARP1 is a key repressor of TOP mRNA translation. It binds the m7Gppp cap moiety and the adjacent 5'TOP motif of TOP mRNAs, thus impeding the assembly of the eIF4F complex on these transcripts. mTORC1 controls TOP mRNA translation via LARP1, but the details of the mechanism are unclear. Herein we elucidate the mechanism by which mTORC1 controls LARP1's translation repression activity. We demonstrate that mTORC1 phosphorylates LARP1 in vitro and in vivo, activities that are efficiently inhibited by rapamycin and torin1. We uncover 26 rapamycin-sensitive phospho-serine and -threonine residues on LARP1 that are distributed in 7 clusters. Our data show that phosphorylation of a cluster of residues located proximally to the m7Gppp cap-binding DM15 region is particularly sensitive to rapamycin and regulates both the RNA-binding and the translation inhibitory activities of LARP1. Our results unravel a new model of translation control in which the La module (LaMod) and DM15 region of LARP1, both of which can directly interact with TOP mRNA, are differentially regulated: the LaMod remains constitutively bound to PABP (irrespective of the activation status of mTORC1), while the C-terminal DM15 'pendular hook' engages the TOP mRNA 5'-end to repress translation, but only in conditions of mTORC1 inhibition.
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Affiliation(s)
- Jian-Jun Jia
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Roni M Lahr
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Michael T Solgaard
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Bruno J Moraes
- GABBA PhD Program, Abel Salazar Biomedical Sciences Institute, University of Porto, Porto, Portugal
- PrimerGen Ltd, Viseu, Portugal
| | - Roberta Pointet
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - An-Dao Yang
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Giovanna Celucci
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Tyson E Graber
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Huy-Dung Hoang
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Marius R Niklaus
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Izabella A Pena
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Anne K Hollensen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Ewan M Smith
- Cancer Research UK Beatson Institute, Glasgow, UK
| | | | - Leonie Anton
- Biozentrum, University of Basel, Basel, Switzerland
| | - Christopher Dajadian
- Department of Biochemistry, Rosalind and Morris Goodman Cancer Centre, McGill University, Montréal, Canada
| | - Mark Livingstone
- Department of Biochemistry, Rosalind and Morris Goodman Cancer Centre, McGill University, Montréal, Canada
| | - Jaclyn Hearnden
- Department of Biochemistry, Rosalind and Morris Goodman Cancer Centre, McGill University, Montréal, Canada
| | - Xu-Dong Wang
- Department of Biochemistry, UT Southwestern Medical Center, Dallas, TX, USA
| | - Yonghao Yu
- Department of Biochemistry, UT Southwestern Medical Center, Dallas, TX, USA
| | - Timm Maier
- Biozentrum, University of Basel, Basel, Switzerland
| | - Christian K Damgaard
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Andrea J Berman
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Tommy Alain
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
| | - Bruno D Fonseca
- Children's Hospital of Eastern Ontario (CHEO) Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Canada
- PrimerGen Ltd, Viseu, Portugal
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Knudsen JR, Li Z, Persson KW, Li J, Henriquez-Olguin C, Jensen TE. Contraction-regulated mTORC1 and protein synthesis: Influence of AMPK and glycogen. J Physiol 2020; 598:2637-2649. [PMID: 32372406 DOI: 10.1113/jp279780] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Accepted: 04/14/2020] [Indexed: 12/18/2022] Open
Abstract
KEY POINTS AMP-activated protein kinase (AMPK)-dependent Raptor Ser792 phosphorylation does not influence mechanistic target of rapamycin complex 1 (mTORC1)-S6K1 activation by intense muscle contraction. α2 -AMPK activity-deficient mice have lower contraction-stimulated protein synthesis. Increasing glycogen activates mTORC1-S6K1. Normalizing muscle glycogen content rescues reduced protein synthesis in AMPK-deficient mice. ABSTRACT The mechansitic target of rapamycin complex 1 (mTORC1)-S6K1 signalling pathway regulates muscle growth-related protein synthesis and is antagonized by AMP-activated protein kinase (AMPK) in multiple cell types. Resistance exercise stimulates skeletal muscle mTORC1-S6K1 and AMPK signalling and post-contraction protein synthesis. Glycogen inhibits AMPK and has been proposed as a pro-anabolic stimulus. The present study aimed to investigate how muscle mTORC1-S6K1 signalling and protein synthesis respond to resistance exercise-mimicking contraction in the absence of AMPK and with glycogen manipulation. Resistance exercise-mimicking unilateral in situ contraction of musculus quadriceps femoris in anaesthetized wild-type and dominant negative α2 AMPK kinase dead transgenic (KD-AMPK) mice, measuring muscle mTORC1 and AMPK signalling immediately (0 h) and 4 h post-contraction, and protein-synthesis at 4 h. Muscle glycogen manipulation by 5 day oral gavage of the glycogen phosphorylase inhibitor CP316819 and sucrose (80 g L-1 ) in the drinking water prior to in situ contraction. The mTORC1-S6K1 and AMPK signalling axes were coactivated immediately post-contraction, despite potent AMPK-dependent Ser792 phosphorylation on the mTORC1 subunit raptor. KD-AMPK muscles displayed normal mTORC1-S6K1 activation at 0 h and 4 h post-exercise, although there was impaired contraction-stimulated protein synthesis 4 h post-contraction. Pharmacological/dietary elevation of muscle glycogen content augmented contraction-stimulated mTORC1-S6K1-S6 signalling and rescued the reduced protein synthesis-response in KD-AMPK to wild-type levels. mTORC-S6K1 signalling is not influenced by α2 -AMPK during or after intense muscle contraction. Elevated glycogen augments mTORC1-S6K1 signalling. α2 -AMPK-deficient KD-AMPK mice display impaired contraction-induced muscle protein synthesis, which can be rescued by normalizing muscle glycogen content.
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Affiliation(s)
- Jonas R Knudsen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Zhencheng Li
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Kaspar W Persson
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Jingwen Li
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Carlos Henriquez-Olguin
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Thomas E Jensen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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3
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Sun R, Cheng E, Velásquez C, Chang Y, Moore PS. Mitosis-related phosphorylation of the eukaryotic translation suppressor 4E-BP1 and its interaction with eukaryotic translation initiation factor 4E (eIF4E). J Biol Chem 2019; 294:11840-11852. [PMID: 31201269 PMCID: PMC6682726 DOI: 10.1074/jbc.ra119.008512] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 06/10/2019] [Indexed: 11/22/2022] Open
Abstract
Eukaryotic translation initiation factor 4E (eIF4E)–binding protein 1 (4E-BP1) inhibits cap-dependent translation in eukaryotes by competing with eIF4G for an interaction with eIF4E. Phosphorylation at Ser-83 of 4E-BP1 occurs during mitosis through the activity of cyclin-dependent kinase 1 (CDK1)/cyclin B rather than through canonical mTOR kinase activity. Here, we investigated the interaction of eIF4E with 4E-BP1 or eIF4G during interphase and mitosis. We observed that 4E-BP1 and eIF4G bind eIF4E at similar levels during interphase and mitosis. The most highly phosphorylated mitotic 4E-BP1 isoform (δ) did not interact with eIF4E, whereas a distinct 4E-BP1 phospho-isoform, EB-γ, phosphorylated at Thr-70, Ser-83, and Ser-101, bound to eIF4E during mitosis. Two-dimensional gel electrophoretic analysis corroborated the identity of the phosphorylation marks on the eIF4E-bound 4E-BP1 isoforms and uncovered a population of phosphorylated 4E-BP1 molecules lacking Thr-37/Thr-46–priming phosphorylation. Moreover, proximity ligation assays for phospho-4E-BP1 and eIF4E revealed different in situ interactions during interphase and mitosis. The eIF4E:eIF4G interaction was not inhibited but rather increased in mitotic cells, consistent with active translation initiation during mitosis. Phosphodefective substitution of 4E-BP1 at Ser-83 did not change global translation or individual mRNA translation profiles as measured by single-cell nascent protein synthesis and eIF4G RNA immunoprecipitation sequencing. Mitotic 5′-terminal oligopyrimidine RNA translation was active and, unlike interphase translation, resistant to mTOR inhibition. Our findings reveal the phosphorylation profiles of 4E-BP1 isoforms and their interactions with eIF4E throughout the cell cycle and indicate that 4E-BP1 does not specifically inhibit translation initiation during mitosis.
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Affiliation(s)
- Rui Sun
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.,Cancer Virology Program, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania 15213
| | - Erdong Cheng
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.,Cancer Virology Program, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania 15213
| | - Celestino Velásquez
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.,Cancer Virology Program, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania 15213
| | - Yuan Chang
- Cancer Virology Program, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania 15213 .,Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Patrick S Moore
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 .,Cancer Virology Program, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania 15213
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4
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Ogasawara R, Fujita S, Hornberger TA, Kitaoka Y, Makanae Y, Nakazato K, Naokata I. The role of mTOR signalling in the regulation of skeletal muscle mass in a rodent model of resistance exercise. Sci Rep 2016; 6:31142. [PMID: 27502839 PMCID: PMC4977552 DOI: 10.1038/srep31142] [Citation(s) in RCA: 124] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 07/14/2016] [Indexed: 12/13/2022] Open
Abstract
Resistance exercise (RE) activates signalling by the mammalian target of rapamycin (mTOR), and it has been suggested that rapamycin-sensitive mTOR signalling controls RE-induced changes in protein synthesis, ribosome biogenesis, autophagy, and the expression of peroxisome proliferator gamma coactivator 1 alpha (PGC-1α). However, direct evidence to support the aforementioned relationships is lacking. Therefore, in this study, we investigated the role of rapamycin-sensitive mTOR in the RE-induced activation of muscle protein synthesis, ribosome biogenesis, PGC-1α expression and hypertrophy. The results indicated that the inhibition of rapamycin-sensitive mTOR could prevent the induction of ribosome biogenesis by RE, but it only partially inhibited the activation of muscle protein synthesis. Likewise, the inhibition of rapamycin-sensitive mTOR only partially blocked the hypertrophic effects of chronic RE. Furthermore, both acute and chronic RE promoted an increase in PGC-1α expression and these alterations were not affected by the inhibition of rapamycin-sensitive mTOR. Combined, the results from this study not only establish that rapamycin-sensitive mTOR plays an important role in the RE-induced activation of protein synthesis and the induction of hypertrophy, but they also demonstrate that additional (rapamycin-sensitive mTOR-independent) mechanisms contribute to these fundamentally important events.
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Affiliation(s)
- Riki Ogasawara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
- Department of Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Satoshi Fujita
- Department of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| | - Troy A. Hornberger
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Yu Kitaoka
- Department of Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Yuhei Makanae
- Department of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| | - Koichi Nakazato
- Department of exercise physiology, Nippon Sport Science University, Tokyo, Japan
| | - Ishii Naokata
- Department of Life Sciences, The University of Tokyo, Tokyo, Japan
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5
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Moberg M, Apró W, Ekblom B, van Hall G, Holmberg HC, Blomstrand E. Activation of mTORC1 by leucine is potentiated by branched-chain amino acids and even more so by essential amino acids following resistance exercise. Am J Physiol Cell Physiol 2016; 310:C874-84. [PMID: 27053525 DOI: 10.1152/ajpcell.00374.2015] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Accepted: 03/31/2016] [Indexed: 12/31/2022]
Abstract
Protein synthesis is stimulated by resistance exercise and intake of amino acids, in particular leucine. Moreover, activation of mammalian target of rapamycin complex 1 (mTORC1) signaling by leucine is potentiated by the presence of other essential amino acids (EAA). However, the contribution of the branched-chain amino acids (BCAA) to this effect is yet unknown. Here we compare the stimulatory role of leucine, BCAA, and EAA ingestion on anabolic signaling following exercise. Accordingly, eight trained volunteers completed four sessions of resistance exercise during which they ingested either placebo, leucine, BCAA, or EAA (including the BCAA) in random order. Muscle biopsies were taken at rest, immediately after exercise, and following 90 and 180 min of recovery. Following 90 min of recovery the activity of S6 kinase 1 (S6K1) was greater than at rest in all four trials (Placebo<Leucine<BCAA<EAA; P < 0.05 time × supplement), with a ninefold increase in the EAA trial. At this same time point, phosphorylation of eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) at Thr(37/46) was unaffected by supplementation, while that of Thr(46) alone exhibited a pattern similar to that of S6K1, being 18% higher with EAA than BCAA. However, after 180 min of recovery this difference between EAA and BCAA had disappeared, although with both these supplements the increases were still higher than with leucine (40%, P < 0.05) and placebo (100%, P < 0.05). In summary, EAA ingestion appears to stimulate translation initiation more effectively than the other supplements, although the results also suggest that this effect is primarily attributable to the BCAA.
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Affiliation(s)
- Marcus Moberg
- Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden;
| | - William Apró
- Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Björn Ekblom
- Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Gerrit van Hall
- Clinical Metabolomics Core Facility, Rigshopitalet and Department of Biomedical Sciences, Rigshospitalet, University of Copenhagen, Copenhagen Denmark
| | - Hans-Christer Holmberg
- Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Östersund, Sweden; and
| | - Eva Blomstrand
- Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
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6
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Kanno T, Furukawa K, Horigome T. Exploring the phosphoproteome profiles during Xenopus egg activation by calcium stimulation using a fully automated phosphopeptide purification system. J Biochem 2015; 159:407-19. [PMID: 26530081 DOI: 10.1093/jb/mvv109] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2015] [Accepted: 10/01/2015] [Indexed: 12/18/2022] Open
Abstract
To explore the phosphoproteome profiles duringXenopusegg activation by Ca(2+)-stimulation, an automated phosphopeptide purification system involving a titania column was improved by introducing 4-step elution with phosphate buffers. The number of detected phosphopeptides in the tryptic digest of aXenopusegg cytosol fraction on mass spectrometry (MS) was increased 1.5-fold and the percentage of multiply phosphorylated peptides increased from 17 to 24% with introduction of the 4-step elution method. Phosphopeptides were purified by the improved method from tryptic digests of cytosol fractions ofXenopuseggs without and with a Ca(2+)-stimulus, and then, analysed by MS. One thousand three hundred and seventy-five and 994 phosphopeptides were reproducibly detected on duplicate MS, respectively. They included 818 and 437 phosphopeptides specific to each digest, respectively. A method involving isobaric tags for relative and absolute quantitation (iTRAQ) was also applied to compare the phosphorylation levels inXenopuseggs without and with a Ca(2+)-stimulus, the ratios for 112 phosphopeptides in tryptic digests of these egg cytosol fractions being obtained. It was suggested from all the results that the phosphorylation sites and levels change duringXenopusegg activation for many known and unknown sites on structural proteins, signalling related proteins, cell cycle-related proteins and others.
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Affiliation(s)
- Takuma Kanno
- Graduate School of Science and Technology, Niigata University, Igarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Kazuhiro Furukawa
- Graduate School of Science and Technology, Niigata University, Igarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Tsuneyoshi Horigome
- Graduate School of Science and Technology, Niigata University, Igarashi-2, Nishi-ku, Niigata 950-2181, Japan
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7
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Fonseca BD, Smith EM, Yelle N, Alain T, Bushell M, Pause A. The ever-evolving role of mTOR in translation. Semin Cell Dev Biol 2014; 36:102-12. [PMID: 25263010 DOI: 10.1016/j.semcdb.2014.09.014] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 09/12/2014] [Accepted: 09/15/2014] [Indexed: 02/06/2023]
Abstract
Control of translation allows for the production of stoichiometric levels of each protein in the cell. Attaining such a level of fine-tuned regulation of protein production requires the coordinated temporal and spatial control of numerous cellular signalling cascades impinging on the various components of the translational machinery. Foremost among these is the mTOR signalling pathway. The mTOR pathway regulates both the initiation and elongation steps of protein synthesis through the phosphorylation of numerous translation factors, while simultaneously ensuring adequate folding of nascent polypeptides through co-translational degradation of misfolded proteins. Perhaps most remarkably, mTOR is also a key regulator of the synthesis of ribosomal proteins and translation factors themselves. Two seminal studies have recently shown in translatome analysis that the mTOR pathway preferentially regulates the translation of mRNAs encoding ribosomal proteins and translation factors. Therefore, the role of the mTOR pathway in the control of protein synthesis extends far beyond immediate translational control. By controlling ribosome production (and ultimately ribosome availability), mTOR is a master long-term controller of protein synthesis. Herein, we review the literature spanning the early discoveries of mTOR on translation to the latest advances in our understanding of how the mTOR pathway controls the synthesis of ribosomal proteins.
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Affiliation(s)
- Bruno D Fonseca
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
| | - Ewan M Smith
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Nicolas Yelle
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada
| | - Tommy Alain
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada
| | - Martin Bushell
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Arnim Pause
- Goodman Cancer Research Centre, Department of Biochemistry, McGill University, Montreal, QC H3A 1A3, Canada.
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8
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Liu Y, Vertommen D, Rider MH, Lai YC. Mammalian target of rapamycin-independent S6K1 and 4E-BP1 phosphorylation during contraction in rat skeletal muscle. Cell Signal 2013; 25:1877-86. [PMID: 23707523 DOI: 10.1016/j.cellsig.2013.05.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Accepted: 05/07/2013] [Indexed: 11/18/2022]
Abstract
Muscle protein synthesis rates decrease during contraction/exercise, but rapidly increase post-exercise. Previous studies mainly focused on signaling pathways that control protein synthesis during post-exercise recovery, such as mTOR and its downstream targets S6K1 and 4E-BP1. In this study, we investigated the effect of high-frequency electrical stimulation on the phosphorylation state of signaling components controlling protein synthesis in rat skeletal muscle. Electrical stimulation increased S6K1 Thr389 phosphorylation, which was unaffected by Torin1, a selective mTOR inhibitor, suggesting that S6K1 phosphorylation by contraction was mTOR-independent. Phosphorylation of eIF4B Ser422 was also increased during electrical stimulation, which was abrogated by inhibition of MEK/ERK/RSK1 activation. Moreover, although phosphorylation of conventional mTOR sites in 4E-BP1 decreased during contraction, mTOR-independent phosphorylation was also apparent, which was associated with the release of 4E-BP1 from eIF4E. The results indicate mTOR-independent phosphorylation of S6K1 and 4E-BP1 and suggest MEK/ERK/RSK1-dependent phosphorylation of eIF4B during skeletal muscle contraction. These phosphorylation events would keep the translation initiation machinery "primed" in an active state so that protein synthesis could quickly resume post-exercise.
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Affiliation(s)
- Yang Liu
- Université catholique de Louvain and de Duve Institute, Avenue Hippocrate 75, B-1200 Brussels, Belgium
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9
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Kume A, Boldbaatar D, Takazawa Y, Umemiya-Shirafuji R, Tanaka T, Fujisaki K. RNAi of the translation inhibition gene 4E-BP identified from the hard tick, Haemaphysalis longicornis, affects lipid storage during the off-host starvation period of ticks. Parasitol Res 2012; 111:889-96. [PMID: 22618568 DOI: 10.1007/s00436-012-2915-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 03/22/2012] [Indexed: 10/28/2022]
Abstract
4E-BP, an eIF4E-binding protein, is well known as a cap-dependent translation inhibitor. Here, the 4E-BP homolog, Hl4E-BP, was isolated and identified from the hard tick Haemaphysalis longicornis. Hl4E-BP transcripts were ubiquitously expressed in the active stages, including the larvae, nymphs, and female adults, and the transcription levels were found to be higher in unfed than engorged ticks. In contrast, the expression levels of non-phosphorylated Hl4E-BP, which is a 13.4-kDa protein detected by the anti-recombinant Hl4E-BP antibody, were the highest in engorged ticks and significantly decreased progressively during the unfed starvation period of ticks. The functional role of Hl4E-BP as a metabolic brake was verified by histochemical observations on the lipid storage in midguts and fat bodies during the starvation period using ticks injected with dsHl4E-BP. The results indicate that Hl4E-BP is highly relevant to the lipid storage of ticks during the non-feeding starvation period. Our results suggest, for the first time, that Hl4E-BP may have a crucial role in the starvation resistance of ticks in an off-host condition via lipid metabolism control, although it was unclear whether Hl4E-BP might be involved in lipid synthesis regulation and/or lipid consumption inhibition.
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Affiliation(s)
- Aiko Kume
- Department of Frontier Veterinary Medicine, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan
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10
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Ayuso MI, Hernández-Jiménez M, Martín ME, Salinas M, Alcázar A. New hierarchical phosphorylation pathway of the translational repressor eIF4E-binding protein 1 (4E-BP1) in ischemia-reperfusion stress. J Biol Chem 2010; 285:34355-63. [PMID: 20736160 PMCID: PMC2966049 DOI: 10.1074/jbc.m110.135103] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) is a translational repressor that is characterized by its capacity to bind specifically to eIF4E and inhibit its interaction with eIF4G. Phosphorylation of 4E-BP1 regulates eIF4E availability, and therefore, cap-dependent translation, in cell stress. This study reports a physiological study of 4E-BP1 regulation by phosphorylation using control conditions and a stress-induced translational repression condition, ischemia-reperfusion (IR) stress, in brain tissue. In control conditions, 4E-BP1 was found in four phosphorylation states that were detected by two-dimensional gel electrophoresis and Western blotting, which corresponded to Thr69-phosphorylated alone, Thr69- and Thr36/Thr45-phosphorylated, all these plus Ser64 phosphorylation, and dephosphorylation of the sites analyzed. In control or IR conditions, no Thr36/Thr45 phosphorylation alone was detected without Thr69 phosphorylation, and neither was Ser64 phosphorylation without Thr36/Thr45/Thr69 phosphorylation detected. Ischemic stress induced 4E-BP1 dephosphorylation at Thr69, Thr36/Thr45, and Ser64 residues, with 4E-BP1 remaining phosphorylated at Thr69 alone or dephosphorylated. In the subsequent reperfusion, 4E-BP1 phosphorylation was induced at Thr36/Thr45 and Ser64, in addition to Thr69. Changes in 4E-BP1 phosphorylation after IR were according to those found for Akt and mammalian target of rapamycin (mTOR) kinases. These results demonstrate a new hierarchical phosphorylation for 4E-BP1 regulation in which Thr69 is phosphorylated first followed by Thr36/Thr45 phosphorylation, and Ser64 is phosphorylated last. Thr69 phosphorylation alone allows binding to eIF4E, and subsequent Thr36/Thr45 phosphorylation was sufficient to dissociate 4E-BP1 from eIF4E, which led to eIF4E-4G interaction. These data help to elucidate the physiological role of 4E-BP1 phosphorylation in controlling protein synthesis.
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Affiliation(s)
- María I Ayuso
- Department of Investigation, Hospital Ramón y Cajal, 28034 Madrid, Spain
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11
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Feldman ME, Apsel B, Uotila A, Loewith R, Knight ZA, Ruggero D, Shokat KM. Active-site inhibitors of mTOR target rapamycin-resistant outputs of mTORC1 and mTORC2. PLoS Biol 2009; 7:e38. [PMID: 19209957 PMCID: PMC2637922 DOI: 10.1371/journal.pbio.1000038] [Citation(s) in RCA: 879] [Impact Index Per Article: 58.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Accepted: 01/12/2009] [Indexed: 12/14/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) regulates cell growth and survival by integrating nutrient and hormonal signals. These signaling functions are distributed between at least two distinct mTOR protein complexes: mTORC1 and mTORC2. mTORC1 is sensitive to the selective inhibitor rapamycin and activated by growth factor stimulation via the canonical phosphoinositide 3-kinase (PI3K)→Akt→mTOR pathway. Activated mTORC1 kinase up-regulates protein synthesis by phosphorylating key regulators of mRNA translation. By contrast, mTORC2 is resistant to rapamycin. Genetic studies have suggested that mTORC2 may phosphorylate Akt at S473, one of two phosphorylation sites required for Akt activation; this has been controversial, in part because RNA interference and gene knockouts produce distinct Akt phospho-isoforms. The central role of mTOR in controlling key cellular growth and survival pathways has sparked interest in discovering mTOR inhibitors that bind to the ATP site and therefore target both mTORC2 and mTORC1. We investigated mTOR signaling in cells and animals with two novel and specific mTOR kinase domain inhibitors (TORKinibs). Unlike rapamycin, these TORKinibs (PP242 and PP30) inhibit mTORC2, and we use them to show that pharmacological inhibition of mTOR blocks the phosphorylation of Akt at S473 and prevents its full activation. Furthermore, we show that TORKinibs inhibit proliferation of primary cells more completely than rapamycin. Surprisingly, we find that mTORC2 is not the basis for this enhanced activity, and we show that the TORKinib PP242 is a more effective mTORC1 inhibitor than rapamycin. Importantly, at the molecular level, PP242 inhibits cap-dependent translation under conditions in which rapamycin has no effect. Our findings identify new functional features of mTORC1 that are resistant to rapamycin but are effectively targeted by TORKinibs. These potent new pharmacological agents complement rapamycin in the study of mTOR and its role in normal physiology and human disease. Growth factor pathways are required for normal development but are often inappropriately activated in many cancers. One growth-factor–sensitive pathway of increasing interest to cancer researchers relies on the mammalian target of rapamycin (mTOR), a kinase that (like all kinases) delivers phosphate groups from ATP to amino acid residues of downstream proteins. TOR proteins were first discovered in yeast as the cellular targets of rapamycin, a small, naturally occurring molecule derived from bacteria that is widely used as an immunosuppressant and more recently in some cancer therapies. The study of TOR proteins has relied heavily on the use of rapamycin, but rapamycin does not directly inhibit TOR kinase activity; rather, rapamycin influences TOR's enzymatic activities by binding to a domain far from the kinase's active site. Some mTOR functions are resistant to rapamycin, as a result of the kinase activity of one kind of multiprotein complex, the mTOR complex 2 (mTORC2), whereas rapamycin-sensitive functions of mTOR are due to the mTOR complex 1 (mTORC1). We have developed new inhibitors of mTOR that bind to the ATP-binding site of mTOR and inhibit the catalytic activity of both mTORC1 and mTORC2 without inhibiting other kinases. Unexpectedly, these inhibitors had profound effects on protein synthesis and cell proliferation due to their inhibition of mTORC1 rather than mTORC2. We found that the phosphorylation of a protein that controls protein synthesis, the mTORC1 substrate 4E binding protein (4EBP) is partially resistant to rapamycin but fully inhibited by our new inhibitors. The finding that 4EBP phosphorylation is resistant to rapamycin suggests that active-site inhibitors may be more effective than rapamycin in the treatment of cancer and may explain why rapamycin is so well tolerated when taken for immunosuppression. Cells rely on the mammalian target of rapamycin kinase (mTOR) to sense growth factors. Inhibition of all forms of mTOR using newly developed inhibitors of its active site reveals new insights into the function of two mTOR-containing protein complexes and their potential as therapeutic targets.
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Affiliation(s)
- Morris E Feldman
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, United States of America
| | - Beth Apsel
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, United States of America
| | - Aino Uotila
- Department of Molecular Biology, University of Geneva, Switzerland
| | - Robbie Loewith
- Department of Molecular Biology, University of Geneva, Switzerland
| | - Zachary A Knight
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, United States of America
| | - Davide Ruggero
- School of Medicine and Department of Urology, Helen Diller Family Comprehensive Cancer Center, University of California San Francisco, San Francisco, United States of America
| | - Kevan M Shokat
- Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, United States of America
- * To whom correspondence should be addressed. E-mail:
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12
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Proud CG. Signalling to translation: how signal transduction pathways control the protein synthetic machinery. Biochem J 2007; 403:217-34. [PMID: 17376031 DOI: 10.1042/bj20070024] [Citation(s) in RCA: 380] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Recent advances in our understanding of both the regulation of components of the translational machinery and the upstream signalling pathways that modulate them have provided important new insights into the mechanisms by which hormones, growth factors, nutrients and cellular energy status control protein synthesis in mammalian cells. The importance of proper control of mRNA translation is strikingly illustrated by the fact that defects in this process or its control are implicated in a number of disease states, such as cancer, tissue hypertrophy and neurodegeneration. Signalling pathways such as those involving mTOR (mammalian target of rapamycin) and mitogen-activated protein kinases modulate the phosphorylation of translation factors, the activities of the protein kinases that act upon them and the association of RNA-binding proteins with specific mRNAs. These effects contribute both to the overall control of protein synthesis (which is linked to cell growth) and to the modulation of the translation or stability of specific mRNAs. However, important questions remain about both the contributions of individual regulatory events to the control of general protein synthesis and the mechanisms by which the translation of specific mRNAs is controlled.
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Affiliation(s)
- Christopher G Proud
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3.
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13
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Abstract
There is currently a high level of interest in signalling through the mammalian target of rapamycin (mTOR). This reflects both its key role in many cell functions and its involvement in disease states such as cancers. The best understood targets for mTOR signalling are proteins involved in controlling the translational machinery, including the ribosomal protein S6 kinases and proteins that regulate the initiation and elongation phases of translation. Indeed, there is compelling evidence that at least one of these targets of mTOR (eukaryotic initiation factor eIF4E) plays a key role in tumorigenesis. It is regulated through the mTOR-dependent phosphorylation of inhibitory proteins such as eIF4E-binding protein 1. Thus, targeting mTOR signalling may be an effective anticancer strategy, in at least a significant subset of tumours. Not all effects of mTOR are sensitive to the classical anti-mTOR drug rapamycin, and this compound also interferes with other processes besides eIF4E function. Developing new approaches to targeting mTOR for cancer therapy requires more detailed knowledge of signalling downstream of mTOR. Such advances are likely to come from further work to understand the regulation of mTOR targets such as components of the translational apparatus.
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Affiliation(s)
- J Averous
- Unité de Nutrition Humaine, INRA de Theix, Saint Genès Champanelle, France
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Kasinath BS, Mariappan MM, Sataranatarajan K, Lee MJ, Feliers D. mRNA translation: unexplored territory in renal science. J Am Soc Nephrol 2006; 17:3281-92. [PMID: 16959824 DOI: 10.1681/asn.2006050488] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Ambient protein levels are under coordinated control of transcription, mRNA translation, and degradation. Whereas transcription and degradation mechanisms have been studied in depth in renal science, the role of mRNA translation, the process by which peptide synthesis occurs according to the genetic code that is present in the mRNA, has not received much attention. mRNA translation occurs in three phases: Initiation, elongation, and termination. Each phase is controlled by unique eukaryotic factors. In the initiation phase, mRNA and ribosomal subunits are brought together. During the elongation phase, amino acids are added to the nascent peptide chain in accordance with codon sequences in the mRNA. During the termination phase, the fully synthesized peptide is released from the ribosome for posttranslational processing. Signaling pathways figure prominently in regulation of mRNA translation, particularly the phosphatidylinositol 3 kinase-Akt-mammalian target of rapamycin pathway, the AMP-activated protein kinase-tuberous sclerosis complex protein 1/tuberous sclerosis complex protein 2-Rheb pathway, and the extracellular signal-regulated kinase 1/2 type mitogen-activated protein kinase signaling pathway; there is significant cross-talk among these pathways. Regulation by mRNA translation is suggested when changes in mRNA and protein levels do not correlate and in the setting of rapid protein synthesis. Ongoing work suggests an important role for mRNA translation in compensatory renal growth, hypertrophy and extracellular matrix synthesis in diabetic nephropathy, growth factor synthesis by kidney cells, and glomerulonephritis. Considering that mRNA translation plays an important role in cell growth, development, malignancy, apoptosis, and response to stress, its study should provide novel insights in renal physiology and pathology.
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Affiliation(s)
- Balakuntalam S Kasinath
- O'Brien Kidney Research Center, Division of Nephrology, University of Texas Health Science Center, South Texas Veterans Healthcare System, San Antonio, TX 78229, USA.
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15
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Lu J, Zhang J, Block ER, Patel JM. Angiotensin IV enhances phosphorylation of 4EBP1 by multiple signaling events in lung endothelial cells. Mol Cell Biochem 2006; 275:181-8. [PMID: 16342424 DOI: 10.1007/s11010-005-1487-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Angiotensin IV (Ang IV)-stimulated cell proliferation is regulated through activation of multiple signaling modules in lung endothelial cells (EC). Because eukaryotic intitiation factor 4E (eIF4E) binding protein 1 (4EBP1) plays a critical role in the RNA translation and the regulation of cell growth, we examined whether Ang IV modulates expression and/or phosphorylation of eIF4E and 4EBP1 as well as the role of multiple signaling events associated with 4EBP1 phosphorylation in EC. Ang IV stimulation increased phosphorylation but not expression of eIF4E and 4EBP1 proteins. Ang IV stimulation selectively phosphorylated Thr46 > Thr70 > Ser65 but not Thr37 residues in 4EBP1. Pretreatment of cells with PD-98059 and rapamycin, inhibitors of mitogen-activated protein kinase (ERK1/2) and mammalian target for rapamycin (mTOR), respectively, partially blocked Ang IV-mediated phosphorylation of 4EBP1. In contrast, overexpression of p70 ribosomal S6 kinase (p70S6K) and protein kinase B (Akt) enhanced phosphorylation of 4EBP1 and eIF4E binding affinity to the cap region of mRNA. These results support critical roles of multiple signaling and phosphorylation of 4EBP1 by Ang IV in translation process and protein synthesis.
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Affiliation(s)
- Jianghua Lu
- Department of Medicine, University of Florida
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16
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Lisik W, Kahan BD. Proliferation signal inhibitors: chemical, biologic, and clinical properties. Transplant Rev (Orlando) 2005. [DOI: 10.1016/j.trre.2005.11.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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17
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Constantinou C, Clemens MJ. Regulation of the phosphorylation and integrity of protein synthesis initiation factor eIF4GI and the translational repressor 4E-BP1 by p53. Oncogene 2005; 24:4839-50. [PMID: 15897901 DOI: 10.1038/sj.onc.1208648] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Activation of a temperature-sensitive form of mouse p53 in murine erythroleukaemia cells rapidly inhibits protein synthesis and causes early dephosphorylation and cleavage of protein synthesis initiation factor eIF4GI and the eIF4E-binding protein 4E-BP1. Dephosphorylated 4E-BP1 and the cleaved products of 4E-BP1 and eIF4GI associate with eIF4E under these conditions, concomitant with decreased interaction of full-length eIF4GI with eIF4E. These changes may play an important role in preventing formation of the eIF4F complex and thus the initiation of protein synthesis. As observed previously for eIF4GI, the cleavage of 4E-BP1 is insensitive to the general caspase inhibitor z-VAD.FMK, consistent with a caspase-independent mechanism of factor modification and regulation of protein synthesis. Comparison of the p53-induced patterns of eIF4GI and 4E-BP1 dephosphorylation and cleavage with those caused by the mTOR inhibitor rapamycin indicates that p53 activation and rapamycin have distinct but additive effects. Moreover, p53 activation inhibits rapamycin-insensitive protein kinase activity against 4E-BP1. P53 and rapamycin have additive effects on the inhibition of overall protein synthesis. These data suggest that the inhibition of protein synthesis by p53 is largely independent of the regulation of rapamycin-sensitive mTOR in the system under investigation.
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Affiliation(s)
- Constantina Constantinou
- Translational Control Group, Department of Basic Medical Sciences (Biochemistry and Immunology), St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK
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18
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Wang X, Beugnet A, Murakami M, Yamanaka S, Proud CG. Distinct signaling events downstream of mTOR cooperate to mediate the effects of amino acids and insulin on initiation factor 4E-binding proteins. Mol Cell Biol 2005; 25:2558-72. [PMID: 15767663 PMCID: PMC1061630 DOI: 10.1128/mcb.25.7.2558-2572.2005] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Signaling through the mammalian target of rapamycin (mTOR) controls cell size and growth as well as other functions, and it is a potential therapeutic target for graft rejection, certain cancers, and disorders characterized by inappropriate cell or tissue growth. mTOR signaling is positively regulated by hormones or growth factors and amino acids. mTOR signaling regulates the phosphorylation of several proteins, the best characterized being ones that control mRNA translation. Eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) undergoes phosphorylation at multiple sites. Here we show that amino acids regulate the N-terminal phosphorylation sites in 4E-BP1 through the RAIP motif in a rapamycin-insensitive manner. Several criteria indicate this reflects a rapamycin-insensitive output from mTOR. In contrast, the insulin-stimulated phosphorylation of the C-terminal site Ser64/65 is generally sensitive to rapamycin, as is phosphorylation of another well-characterized target for mTOR signaling, S6K1. Our data imply that it is unlikely that mTOR directly phosphorylates Thr69/70 in 4E-BP1. Although 4E-BP1 and S6K1 bind the mTOR partner, raptor, our data indicate that the outputs from mTOR to 4E-BP1 and S6K1 are distinct. In cells, efficient phosphorylation of 4E-BP1 requires it to be able to bind to eIF4E, whereas phosphorylation of 4E-BP1 by mTOR in vitro shows no such preference. These data have important implications for understanding signaling downstream of mTOR and the development of new strategies to impair mTOR signaling.
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Affiliation(s)
- Xuemin Wang
- Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, United Kingdom
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19
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Feliers D, Duraisamy S, Barnes JL, Ghosh-Choudhury G, Kasinath BS. Translational regulation of vascular endothelial growth factor expression in renal epithelial cells by angiotensin II. Am J Physiol Renal Physiol 2005; 288:F521-9. [PMID: 15572520 DOI: 10.1152/ajprenal.00271.2004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
ANG II regulates growth factor expression in the kidney. We investigated whether ANG II regulated vascular endothelial growth factor (VEGF) synthesis in proximal tubular epithelial (MCT) cells. ANG II (1 nM) increased VEGF protein expression within 5 min, the effect lasting for 30 min. There was no change in VEGF mRNA levels or mRNA stability, and transcription inhibitors did not affect ANG II-induced VEGF expression. Regulation of VEGF translation was investigated. Polyribosomal analysis revealed selective enrichment of heavy ribosomes (polysomes) with VEGF mRNA transcripts compared with light ribosomes in ANG II-treated cells, although distribution of GAPDH was unaltered. In vitro translation of total RNA from polysomal fractions showed selective increase in VEGF protein synthesis in ANG II-treated cells. Preincubation with LY-294002, a PI 3-kinase inhibitor, or expression of dominant-negative Akt prevented ANG II-stimulated increase in VEGF translation. ANG II increased phosphorylation of eukaryotic initiation factor 4E and its binding protein 4E-BP1, critical events that regulate the initiation phase of protein translation. ANG II failed to increase VEGF mRNA translation in cells stably expressing the phosphorylation mutant of 4E-BP1. Our data illustrate that a rapid increase in VEGF protein expression by ANG II is regulated at the initiation phase of translation of VEGF mRNA in renal epithelial cells. Regulation of VEGF translation by ANG II represents a novel pathway of renal response to injury.
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Affiliation(s)
- Denis Feliers
- Dept. of Medicine, Mail Code 7882, Univ. of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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20
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Lisik W, Kahan BD. Inhibitors of mammalian target of rapamycin: mechanism of action explains efficacy and toxicity. Curr Opin Organ Transplant 2004. [DOI: 10.1097/01.mot.0000146725.34815.ea] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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21
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Abstract
The evolutionarily conserved checkpoint protein kinase, TOR (target of rapamycin), has emerged as a major effector of cell growth and proliferation via the regulation of protein synthesis. Work in the last decade clearly demonstrates that TOR controls protein synthesis through a stunning number of downstream targets. Some of the targets are phosphorylated directly by TOR, but many are phosphorylated indirectly. In this review, we summarize some recent developments in this fast-evolving field. We describe both the upstream components of the signaling pathway(s) that activates mammalian TOR (mTOR) and the downstream targets that affect protein synthesis. We also summarize the roles of mTOR in the control of cell growth and proliferation, as well as its relevance to cancer and synaptic plasticity.
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Affiliation(s)
- Nissim Hay
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 60607, USA.
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22
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Abstract
The mammalian target of rapamycin, mTOR, is a protein Ser-Thr kinase that functions as a central element in a signaling pathway involved in the control of cell growth and proliferation. The activity of mTOR is controlled not only by amino acids, but also by hormones and growth factors that activate the protein kinase Akt. The signaling pathway downstream of Akt leading to mTOR involves the protein products of the genes mutated in tuberous sclerosis, TSC1 and TSC2, and the small guanosine triphosphatase, Rheb. In cells, mTOR is found in a complex with two other proteins, raptor and mLST8. In this review, we describe recent progress in understanding the control of the mTOR signaling pathway and the role of mTOR-interacting proteins.
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Affiliation(s)
- Thurl E Harris
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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