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Kamada Y, Umeda C, Mukai Y, Ohtsuka H, Otsubo Y, Yamashita A, Kosugi T. Structure-based engineering of Tor complexes reveals that two types of yeast TORC1 produce distinct phenotypes. J Cell Sci 2024; 137:jcs261625. [PMID: 38415789 PMCID: PMC10941655 DOI: 10.1242/jcs.261625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 01/18/2024] [Indexed: 02/29/2024] Open
Abstract
Certain proteins assemble into diverse complex states, each having a distinct and unique function in the cell. Target of rapamycin (Tor) complex 1 (TORC1) plays a central role in signalling pathways that allow cells to respond to the environment, including nutritional status signalling. TORC1 is widely recognised for its association with various diseases. The budding yeast Saccharomyces cerevisiae has two types of TORC1, Tor1-containing TORC1 and Tor2-containing TORC1, which comprise different constituent proteins but are considered to have the same function. Here, we computationally modelled the relevant complex structures and then, based on the structures, rationally engineered a Tor2 mutant that could form Tor complex 2 (TORC2) but not TORC1, resulting in a redesign of the complex states. Functional analysis of the Tor2 mutant revealed that the two types of TORC1 induce different phenotypes, with changes observed in rapamycin, caffeine and pH dependencies of cell growth, as well as in replicative and chronological lifespan. These findings uncovered by a general approach with huge potential - model structure-based engineering - are expected to provide further insights into various fields such as molecular evolution and lifespan.
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Affiliation(s)
- Yoshiaki Kamada
- Interdisciplinary Research Unit, National Institute for Basic Biology (NIBB), National Institutes of Natural Sciences (NINS), Okazaki, Aichi, 444-8585, Japan
- Basic Biology Program, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa, 240-0193, Japan
| | - Chiharu Umeda
- Department of Frontier Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga, 526-0829, Japan
| | - Yukio Mukai
- Department of Frontier Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga, 526-0829, Japan
| | - Hokuto Ohtsuka
- Laboratory of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Aichi, 464-8601, Japan
| | - Yoko Otsubo
- Interdisciplinary Research Unit, National Institute for Basic Biology (NIBB), National Institutes of Natural Sciences (NINS), Okazaki, Aichi, 444-8585, Japan
| | - Akira Yamashita
- Interdisciplinary Research Unit, National Institute for Basic Biology (NIBB), National Institutes of Natural Sciences (NINS), Okazaki, Aichi, 444-8585, Japan
| | - Takahiro Kosugi
- Research Center of Integrative Molecular Systems (CIMoS), Institute for Molecular Science (IMS), National Institutes of Natural Sciences (NINS), Okazaki, Aichi, 444-8585, Japan
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences (NINS), Okazaki, Aichi, 444-8585, Japan
- Molecular Science Program, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa, 240-0193, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama, 332-0012, Japan
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2
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Zhulyn O, Rosenblatt HD, Shokat L, Dai S, Kuzuoglu-Öztürk D, Zhang Z, Ruggero D, Shokat KM, Barna M. Evolutionarily divergent mTOR remodels translatome for tissue regeneration. Nature 2023; 620:163-171. [PMID: 37495694 DOI: 10.1038/s41586-023-06365-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2021] [Accepted: 06/22/2023] [Indexed: 07/28/2023]
Abstract
An outstanding mystery in biology is why some species, such as the axolotl, can regenerate tissues whereas mammals cannot1. Here, we demonstrate that rapid activation of protein synthesis is a unique feature of the injury response critical for limb regeneration in the axolotl (Ambystoma mexicanum). By applying polysome sequencing, we identify hundreds of transcripts, including antioxidants and ribosome components that are selectively activated at the level of translation from pre-existing messenger RNAs in response to injury. By contrast, protein synthesis is not activated in response to non-regenerative digit amputation in the mouse. We identify the mTORC1 pathway as a key upstream signal that mediates tissue regeneration and translational control in the axolotl. We discover unique expansions in mTOR protein sequence among urodele amphibians. By engineering an axolotl mTOR (axmTOR) in human cells, we show that these changes create a hypersensitive kinase that allows axolotls to maintain this pathway in a highly labile state primed for rapid activation. This change renders axolotl mTOR more sensitive to nutrient sensing, and inhibition of amino acid transport is sufficient to inhibit tissue regeneration. Together, these findings highlight the unanticipated impact of the translatome on orchestrating the early steps of wound healing in a highly regenerative species and provide a missing link in our understanding of vertebrate regenerative potential.
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Affiliation(s)
- Olena Zhulyn
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
- Developmental and Stem Cell Biology Program, SickKids Research Institute, Toronto, Ontario, Canada
| | - Hannah D Rosenblatt
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Leila Shokat
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
| | - Shizhong Dai
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA
| | - Duygu Kuzuoglu-Öztürk
- Department of Urology, University of California, San Francisco, San Francisco, CA, USA
- Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA
| | - Zijian Zhang
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Davide Ruggero
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA
- Department of Urology, University of California, San Francisco, San Francisco, CA, USA
- Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA
| | - Kevan M Shokat
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA
- Howard Hughes Medical Institute, University of California, San Francisco, CA, USA
| | - Maria Barna
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA.
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3
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Gao J, Yao M, Chang D, Liu J. mTOR (Mammalian Target of Rapamycin): Hitting the Bull's Eye for Enhancing Neurogenesis After Cerebral Ischemia? Stroke 2023; 54:279-285. [PMID: 36321454 DOI: 10.1161/strokeaha.122.040376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ischemic stroke remains a leading cause of morbidity and disability around the world. The sequelae of serious neurological damage are irreversible due to body's own limited repair capacity. However, endogenous neurogenesis induced by cerebral ischemia plays a critical role in the repair and regeneration of impaired neural cells after ischemic brain injury. mTOR (mammalian target of rapamycin) kinase has been suggested to regulate neural stem cells ability to self-renew and differentiate into proliferative daughter cells, thus leading to improved cell growth, proliferation, and survival. In this review, we summarized the current evidence to support that mTOR signaling pathways may enhance neurogenesis, angiogenesis, and synaptic plasticity following cerebral ischemia, which could highlight the potential of mTOR to be a viable therapeutic target for the treatment of ischemic brain injury.
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Affiliation(s)
- Jiale Gao
- Beijing Key Laboratory of Pharmacology of Chinese Materia Medica, Institute of Basic Medical Sciences of Xiyuan Hospital, China Academy of Chinese Medical Sciences, China (J.G., M.Y., J.L.)
| | - Mingjiang Yao
- Beijing Key Laboratory of Pharmacology of Chinese Materia Medica, Institute of Basic Medical Sciences of Xiyuan Hospital, China Academy of Chinese Medical Sciences, China (J.G., M.Y., J.L.)
| | - Dennis Chang
- NICM Health Research Institute, Western Sydney University, Penrith, Australia (D.C.)
| | - Jianxun Liu
- Beijing Key Laboratory of Pharmacology of Chinese Materia Medica, Institute of Basic Medical Sciences of Xiyuan Hospital, China Academy of Chinese Medical Sciences, China (J.G., M.Y., J.L.)
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4
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Ma G, Zhang P, Zhou X, Wan Z, Wang S. Label-Free Single-Molecule Pulldown for the Detection of Released Cellular Protein Complexes. ACS CENTRAL SCIENCE 2022; 8:1272-1281. [PMID: 36188347 PMCID: PMC9523780 DOI: 10.1021/acscentsci.2c00602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Indexed: 06/16/2023]
Abstract
Precise and sensitive detection of intracellular proteins and complexes is key to the understanding of signaling pathways and cell functions. Here, we present a label-free single-molecule pulldown (LFSMP) technique for the imaging of released cellular protein and protein complexes with single-molecule sensitivity and low sample consumption down to a few cells per mm2. LFSMP is based on plasmonic scattering imaging and thus can directly image the surface-captured molecules without labels and quantify the binding kinetics. In this paper, we demonstrate the detection principle for LFSMP, study the phosphorylation of protein complexes involved in a signaling pathway, and investigate how kinetic analysis can be used to improve the pulldown specificity. We wish our technique can contribute to uncovering the molecular mechanisms in cells with single-molecule resolution.
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Affiliation(s)
- Guangzhong Ma
- Biodesign
Center for Biosensors and Bioelectronics, Arizona State University, Tempe, Arizona 85287, United States
| | - Pengfei Zhang
- Biodesign
Center for Biosensors and Bioelectronics, Arizona State University, Tempe, Arizona 85287, United States
| | - Xinyu Zhou
- Biodesign
Center for Biosensors and Bioelectronics, Arizona State University, Tempe, Arizona 85287, United States
- School
of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - Zijian Wan
- Biodesign
Center for Biosensors and Bioelectronics, Arizona State University, Tempe, Arizona 85287, United States
- School
of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - Shaopeng Wang
- Biodesign
Center for Biosensors and Bioelectronics, Arizona State University, Tempe, Arizona 85287, United States
- School
of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona 85287, United States
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5
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Selectivity of mTOR-Phosphatidic Acid Interactions Is Driven by Acyl Chain Structure and Cholesterol. Cells 2021; 11:cells11010119. [PMID: 35011681 PMCID: PMC8750377 DOI: 10.3390/cells11010119] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 12/24/2021] [Accepted: 12/27/2021] [Indexed: 11/24/2022] Open
Abstract
The need to gain insights into the molecular details of peripheral membrane proteins’ specificity towards phosphatidic acid (PA) is undeniable. The variety of PA species classified in terms of acyl chain length and saturation translates into a complicated, enigmatic network of functional effects that exert a critical influence on cell physiology. As a consequence, numerous studies on the importance of phosphatidic acid in human diseases have been conducted in recent years. One of the key proteins in this context is mTOR, considered to be the most important cellular sensor of essential nutrients while regulating cell proliferation, and which also appears to require PA to build stable and active complexes. Here, we investigated the specific recognition of three physiologically important PA species by the mTOR FRB domain in the presence or absence of cholesterol in targeted membranes. Using a broad range of methods based on model lipid membrane systems, we elucidated how the length and saturation of PA acyl chains influence specific binding of the mTOR FRB domain to the membrane. We also discovered that cholesterol exerts a strong modulatory effect on PA-FRB recognition. Our data provide insight into the molecular details of some physiological effects reported previously and reveal novel mechanisms of fine-tuning the signaling cascades dependent on PA.
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Moustafa-Kamal M, Kucharski TJ, El-Assaad W, Abbas YM, Gandin V, Nagar B, Pelletier J, Topisirovic I, Teodoro JG. The mTORC1/S6K/PDCD4/eIF4A Axis Determines Outcome of Mitotic Arrest. Cell Rep 2021; 33:108230. [PMID: 33027666 DOI: 10.1016/j.celrep.2020.108230] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Revised: 07/29/2020] [Accepted: 09/14/2020] [Indexed: 12/26/2022] Open
Abstract
mTOR is a serine/threonine kinase and a master regulator of cell growth and proliferation. Raptor, a scaffolding protein that recruits substrates to mTOR complex 1 (mTORC1), is known to be phosphorylated during mitosis, but the significance of this phosphorylation remains largely unknown. Here we show that raptor expression and mTORC1 activity are dramatically reduced in cells arrested in mitosis. Expression of a non-phosphorylatable raptor mutant reactivates mTORC1 and significantly reduces cytotoxicity of the mitotic poison Taxol. This effect is mediated via degradation of PDCD4, a tumor suppressor protein that inhibits eIF4A activity and is negatively regulated by the mTORC1/S6K pathway. Moreover, pharmacological inhibition of eIF4A is able to enhance the effects of Taxol and restore sensitivity in Taxol-resistant cancer cells. These findings indicate that the mTORC1/S6K/PDCD4/eIF4A axis has a pivotal role in the death versus slippage decision during mitotic arrest and may be exploited clinically to treat tumors resistant to anti-mitotic agents.
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Affiliation(s)
- Mohamed Moustafa-Kamal
- Goodman Cancer Research Center, McGill University, Montréal, QC, Canada; Department of Biochemistry, McGill University, Montréal, QC, Canada
| | - Thomas J Kucharski
- Goodman Cancer Research Center, McGill University, Montréal, QC, Canada; Department of Biochemistry, McGill University, Montréal, QC, Canada
| | - Wissal El-Assaad
- Goodman Cancer Research Center, McGill University, Montréal, QC, Canada
| | - Yazan M Abbas
- Department of Biochemistry, McGill University, Montréal, QC, Canada
| | - Valentina Gandin
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Bhushan Nagar
- Department of Biochemistry, McGill University, Montréal, QC, Canada
| | - Jerry Pelletier
- Goodman Cancer Research Center, McGill University, Montréal, QC, Canada; Department of Biochemistry, McGill University, Montréal, QC, Canada
| | - Ivan Topisirovic
- Department of Biochemistry, McGill University, Montréal, QC, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, and Department of Oncology, McGill University, Montréal, QC, Canada.
| | - Jose G Teodoro
- Goodman Cancer Research Center, McGill University, Montréal, QC, Canada; Department of Biochemistry, McGill University, Montréal, QC, Canada.
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7
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Amemiya Y, Nakamura N, Ikeda N, Sugiyama R, Ishii C, Maki M, Shibata H, Takahara T. Amino Acid-Mediated Intracellular Ca 2+ Rise Modulates mTORC1 by Regulating the TSC2-Rheb Axis through Ca 2+/Calmodulin. Int J Mol Sci 2021; 22:ijms22136897. [PMID: 34198993 PMCID: PMC8269083 DOI: 10.3390/ijms22136897] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 06/23/2021] [Indexed: 12/13/2022] Open
Abstract
Mechanistic target of rapamycin complex 1 (mTORC1) is a master growth regulator by controlling protein synthesis and autophagy in response to environmental cues. Amino acids, especially leucine and arginine, are known to be important activators of mTORC1 and to promote lysosomal translocation of mTORC1, where mTORC1 is thought to make contact with its activator Rheb GTPase. Although amino acids are believed to exclusively regulate lysosomal translocation of mTORC1 by Rag GTPases, how amino acids increase mTORC1 activity besides regulation of mTORC1 subcellular localization remains largely unclear. Here we report that amino acids also converge on regulation of the TSC2-Rheb GTPase axis via Ca2+/calmodulin (CaM). We showed that the amino acid-mediated increase of intracellular Ca2+ is important for mTORC1 activation and thereby contributes to the promotion of nascent protein synthesis. We found that Ca2+/CaM interacted with TSC2 at its GTPase activating protein (GAP) domain and that a CaM inhibitor reduced binding of CaM with TSC2. The inhibitory effect of a CaM inhibitor on mTORC1 activity was prevented by loss of TSC2 or by an active mutant of Rheb GTPase, suggesting that a CaM inhibitor acts through the TSC2-Rheb axis to inhibit mTORC1 activity. Taken together, in response to amino acids, Ca2+/CaM-mediated regulation of the TSC2-Rheb axis contributes to proper mTORC1 activation, in addition to the well-known lysosomal translocation of mTORC1 by Rag GTPases.
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8
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Takahara T, Amemiya Y, Sugiyama R, Maki M, Shibata H. Amino acid-dependent control of mTORC1 signaling: a variety of regulatory modes. J Biomed Sci 2020; 27:87. [PMID: 32799865 PMCID: PMC7429791 DOI: 10.1186/s12929-020-00679-2] [Citation(s) in RCA: 116] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 07/30/2020] [Indexed: 01/10/2023] Open
Abstract
The mechanistic target of rapamycin complex 1 (mTORC1) is an essential regulator of cell growth and metabolism through the modulation of protein and lipid synthesis, lysosome biogenesis, and autophagy. The activity of mTORC1 is dynamically regulated by several environmental cues, including amino acid availability, growth factors, energy levels, and stresses, to coordinate cellular status with environmental conditions. Dysregulation of mTORC1 activity is closely associated with various diseases, including diabetes, cancer, and neurodegenerative disorders. The discovery of Rag GTPases has greatly expanded our understanding of the regulation of mTORC1 activity by amino acids, especially leucine and arginine. In addition to Rag GTPases, other factors that also contribute to the modulation of mTORC1 activity have been identified. In this review, we discuss the mechanisms of regulation of mTORC1 activity by particular amino acids.
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Affiliation(s)
- Terunao Takahara
- Department of Applied Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan.
| | - Yuna Amemiya
- Department of Applied Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan
| | - Risa Sugiyama
- Department of Applied Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan
| | - Masatoshi Maki
- Department of Applied Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan
| | - Hideki Shibata
- Department of Applied Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan
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9
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Abstract
Nutrient overload occurs worldwide as a consequence of the modern diet pattern and the physical inactivity that sometimes accompanies it. Cells initiate multiple protective mechanisms to adapt to elevated intracellular metabolites and restore metabolic homeostasis, but irreversible injury to the cells can occur in the event of prolonged nutrient overload. Many studies have advanced the understanding of the different detrimental effects of nutrient overload; however, few reports have made connections and given the full picture of the impact of nutrient overload on cellular metabolism. In this review, detailed changes in metabolic and energy homeostasis caused by chronic nutrient overload, as well as their associations with the development of metabolic disorders, are discussed. Overnutrition-induced changes in key organelles and sensors rewire cellular bioenergetic pathways and facilitate the shift of the metabolic state toward biosynthesis, thereby leading to the onset of various metabolic disorders, which are essentially the downstream manifestations of a misbalanced metabolic equilibrium. Based on these mechanisms, potential therapeutic targets for metabolic disorders and new research directions are proposed.
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Affiliation(s)
- Haowen Qiu
- Department of Nutrition and Health Sciences and Department of Food Science and Technology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Vicki Schlegel
- Department of Nutrition and Health Sciences and Department of Food Science and Technology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
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10
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Abstract
Mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct large multiprotein complexes, referred to as mTOR complex 1 (mTORC1) and mTORC2. mTORC1 and mTORC2 play key physiological roles as they control anabolic and catabolic processes in response to external cues in a variety of tissues and organs. However, mTORC1 and mTORC2 activities are deregulated in widespread human diseases, including cancer. Cancer cells take advantage of mTOR oncogenic signaling to drive their proliferation, survival, metabolic transformation, and metastatic potential. Therefore, mTOR lends itself very well as a therapeutic target for innovative cancer treatment. mTOR was initially identified as the target of the antibiotic rapamycin that displayed remarkable antitumor activity in vitro Promising preclinical studies using rapamycin and its derivatives (rapalogs) demonstrated efficacy in many human cancer types, hence supporting the launch of numerous clinical trials aimed to evaluate the real effectiveness of mTOR-targeted therapies. However, rapamycin and rapalogs have shown very limited activity in most clinical contexts, also when combined with other drugs. Thus, novel classes of mTOR inhibitors with a stronger antineoplastic potency have been developed. Nevertheless, emerging clinical data suggest that also these novel mTOR-targeting drugs may have a weak antitumor activity. Here, we summarize the current status of available mTOR inhibitors and highlight the most relevant results from both preclinical and clinical studies that have provided valuable insights into both their efficacy and failure.
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11
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Moriyama K, Yoshizawa-Sugata N, Masai H. Oligomer formation and G-quadruplex binding by purified murine Rif1 protein, a key organizer of higher-order chromatin architecture. J Biol Chem 2018; 293:3607-3624. [PMID: 29348174 DOI: 10.1074/jbc.ra117.000446] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2017] [Revised: 12/21/2017] [Indexed: 11/06/2022] Open
Abstract
Rap1-interacting protein 1 (Rif1) regulates telomere length in budding yeast. We previously reported that, in metazoans and fission yeast, Rif1 also plays pivotal roles in controlling genome-wide DNA replication timing. We proposed that Rif1 may assemble chromatin compartments that contain specific replication-timing domains by promoting chromatin loop formation. Rif1 also is involved in DNA lesion repair, restart after replication fork collapse, anti-apoptosis activities, replicative senescence, and transcriptional regulation. Although multiple physiological functions of Rif1 have been characterized, biochemical and structural information on mammalian Rif1 is limited, mainly because of difficulties in purifying the full-length protein. Here, we expressed and purified the 2418-amino-acid-long, full-length murine Rif1 as well as its partially truncated variants in human 293T cells. Hydrodynamic analyses indicated that Rif1 forms elongated or extended homo-oligomers in solution, consistent with the presence of a HEAT-type helical repeat segment known to adopt an elongated shape. We also observed that the purified murine Rif1 bound G-quadruplex (G4) DNA with high specificity and affinity, as was previously shown for Rif1 from fission yeast. Both the N-terminal (HEAT-repeat) and C-terminal segments were involved in oligomer formation and specifically bound G4 DNA, and the central intrinsically disordered polypeptide segment increased the affinity for G4. Of note, pulldown assays revealed that Rif1 simultaneously binds multiple G4 molecules. Our findings support a model in which Rif1 modulates chromatin loop structures through binding to multiple G4 assemblies and by holding chromatin fibers together.
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Affiliation(s)
- Kenji Moriyama
- From the Genome Dynamics Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
| | - Naoko Yoshizawa-Sugata
- From the Genome Dynamics Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
| | - Hisao Masai
- From the Genome Dynamics Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
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12
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Takahara T, Inoue K, Arai Y, Kuwata K, Shibata H, Maki M. The calcium-binding protein ALG-2 regulates protein secretion and trafficking via interactions with MISSL and MAP1B proteins. J Biol Chem 2017; 292:17057-17072. [PMID: 28864773 DOI: 10.1074/jbc.m117.800201] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 08/31/2017] [Indexed: 01/12/2023] Open
Abstract
Mobilization of intracellular calcium is essential for a wide range of cellular processes, including signal transduction, apoptosis, and vesicular trafficking. Several lines of evidence have suggested that apoptosis-linked gene 2 (ALG-2, also known as PDCD6), a calcium-binding protein, acts as a calcium sensor linking calcium levels with efficient vesicular trafficking, especially at the endoplasmic reticulum (ER)-to-Golgi transport step. However, how ALG-2 regulates these processes remains largely unclear. Here, we report that MAPK1-interacting and spindle-stabilizing (MISS)-like (MISSL), a previously uncharacterized protein, interacts with ALG-2 in a calcium-dependent manner. Live-cell imaging revealed that upon a rise in intracellular calcium levels, GFP-tagged MISSL (GFP-MISSL) dynamically relocalizes in a punctate pattern and colocalizes with ALG-2. MISSL knockdown caused disorganization of the components of the ER exit site, the ER-Golgi intermediate compartment, and Golgi. Importantly, knockdown of either MISSL or ALG-2 attenuated the secretion of secreted alkaline phosphatase (SEAP), a model secreted cargo protein, with similar reductions in secretion by single- and double-protein knockdowns, suggesting that MISSL and ALG-2 act in the same pathway to regulate the secretion process. Furthermore, ALG-2 or MISSL knockdown delayed ER-to-Golgi transport of procollagen type I. We also found that ALG-2 and MISSL interact with microtubule-associated protein 1B (MAP1B) and that MAP1B knockdown reverts the reduced secretion of SEAP caused by MISSL or ALG-2 depletion. These results suggest that a change in the intracellular calcium level plays a role in regulation of the secretory pathway via interaction of ALG-2 with MISSL and MAP1B.
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Affiliation(s)
- Terunao Takahara
- From the Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, and
| | - Kuniko Inoue
- From the Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, and
| | - Yumika Arai
- From the Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, and
| | - Keiko Kuwata
- the Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
| | - Hideki Shibata
- From the Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, and
| | - Masatoshi Maki
- From the Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, and
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13
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TORC1-Dependent Phosphorylation Targets in Fission Yeast. Biomolecules 2017; 7:biom7030050. [PMID: 28671615 PMCID: PMC5618231 DOI: 10.3390/biom7030050] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 06/27/2017] [Accepted: 06/28/2017] [Indexed: 12/11/2022] Open
Abstract
Target of rapamycin (TOR) kinase controls cell metabolism and growth in response to environmental cues such as nutrients, growth factors, and stress. TOR kinase is widely conserved across eukaryotes. As in other organisms, the fission yeast Schizosaccharomyces pombe has two types of TOR complex, namely TOR complex 1 (TORC1) and TORC2. It is interesting that the two TOR complexes in S. pombe have opposite roles in sexual differentiation, which is induced by nutrient starvation. TORC1, which contains Tor2 as a catalytic subunit, promotes vegetative growth and represses sexual differentiation in nutrient-rich conditions, while TORC2 is required for the initiation of sexual differentiation. Multiple targets of TORC1 have been identified. Some of these, such as S6 kinase and an autophagy regulator Atg13, are known targets in other organisms. In addition, there is a novel group of TORC1 targets involved in the regulation of sexual differentiation. Here, we review recent findings on phosphorylation targets of TORC1 in S. pombe. Furthermore, we briefly report a novel S. pombe target of TORC1.
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14
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Yao CA, Ortiz-Vega S, Sun YY, Chien CT, Chuang JH, Lin Y. Association of mSin1 with mTORC2 Ras and Akt reveals a crucial domain on mSin1 involved in Akt phosphorylation. Oncotarget 2017; 8:63392-63404. [PMID: 28968999 PMCID: PMC5609931 DOI: 10.18632/oncotarget.18818] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 06/02/2017] [Indexed: 12/15/2022] Open
Abstract
mSin1 is a unique component within the mammalian target of rapamycin (mTOR) complex 2 (mTORC2), which is responsible for cellular morphology and glucose metabolism. The association between mSin1 and other mTORC2 components, as well as their functions, has been explored previously; nevertheless, the mapping of the various binding domains of the components is lacking. Based on an evolutionary analysis of the gene, we constructed various fragments and truncated-forms of mSin1. We characterized the individual binding sites of mSin1 with its various partners, including mTOR, Rictor, Ras, and Akt. mTOR and Rictor bind to the amino acid (aa) 100-240 region of mSin1, which is different to the Ras binding site, the aa 260-460 region. A reciprocal examination found that mSin1 associated with the aa 2148-2300 region of mTOR, which is within the kinase domain, and with the carboxyl terminus of Rictor. Interestingly, Akt was found to associate with mSin1 in a region that slightly overlapped with the mTOR/Rictor complex binding site, namely aa 220-260. When only the Akt binding site was deleted from mSin1, phosphorylation of Akt S473 was greatly reduced. Furthermore, the association between Akt and mTOR can be regulated by serum, insulin and LY294002, but not by rapamycin or MAPK kinase inhibitors. Taken together, mSin1 would seem to act as a hub that allows mTORC2 to phosphorylate Akt S473. Our findings should facilitate future proteomic and crystallographic studies, help the development of dominant inhibitors and promote the identification of new drug targets.
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Affiliation(s)
- Chien-An Yao
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.,Department of Family Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Sara Ortiz-Vega
- Diabetes Unit and Medical Services and The Department of Molecular Biology, Massachusetts General Hospital and The Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA
| | - Yun-Ya Sun
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Chiang-Ting Chien
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Jen-Hua Chuang
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Yenshou Lin
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
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15
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Jesus TT, Oliveira PF, Sousa M, Cheng CY, Alves MG. Mammalian target of rapamycin (mTOR): a central regulator of male fertility? Crit Rev Biochem Mol Biol 2017; 52:235-253. [PMID: 28124577 DOI: 10.1080/10409238.2017.1279120] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolic phenotype and is involved in virtually all aspects of cellular function. It integrates not only nutrient and energy-sensing pathways but also actin cytoskeleton organization, in response to environmental cues including growth factors and cellular energy levels. These events are pivotal for spermatogenesis and determine the reproductive potential of males. Yet, the molecular mechanisms by which mTOR signaling acts in male reproductive system remain a matter of debate. Here, we review the current knowledge on physiological and molecular events mediated by mTOR in testis and testicular cells. In recent years, mTOR inhibition has been explored as a prime strategy to develop novel therapeutic approaches to treat cancer, cardiovascular disease, autoimmunity, and metabolic disorders. However, the physiological consequences of mTOR dysregulation and inhibition to male reproductive potential are still not fully understood. Compelling evidence suggests that mTOR is an arising regulator of male fertility and better understanding of this atypical protein kinase coordinated action in testis will provide insightful information concerning its biological significance in other tissues/organs. We also discuss why a new generation of mTOR inhibitors aiming to be used in clinical practice may also need to include an integrative view on the effects in male reproductive system.
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Affiliation(s)
- Tito T Jesus
- a Laboratory of Cell Biology, Department of Microscopy and Unit for Multidisciplinary Research in Biomedicine (UMIB), Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto , Porto , Portugal.,b CICS-UBI - Health Sciences Research Centre, University of Beira Interior , Covilhã , Portugal
| | - Pedro F Oliveira
- a Laboratory of Cell Biology, Department of Microscopy and Unit for Multidisciplinary Research in Biomedicine (UMIB), Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto , Porto , Portugal.,c i3S - Instituto de Investigação e Inovação em Saúde, University of Porto , Porto , Portugal
| | - Mário Sousa
- a Laboratory of Cell Biology, Department of Microscopy and Unit for Multidisciplinary Research in Biomedicine (UMIB), Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto , Porto , Portugal.,d Centre for Reproductive Genetics Prof. Alberto Barros , Porto , Portugal
| | - C Yan Cheng
- e The Mary M. Wohlford Laboratory for Male Contraceptive Research , Center for Biomedical Research, Population Council , New York , NY , USA
| | - Marco G Alves
- a Laboratory of Cell Biology, Department of Microscopy and Unit for Multidisciplinary Research in Biomedicine (UMIB), Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto , Porto , Portugal.,b CICS-UBI - Health Sciences Research Centre, University of Beira Interior , Covilhã , Portugal
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16
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Moriyama K, Lai MS, Masai H. Interaction of Rif1 Protein with G-Quadruplex in Control of Chromosome Transactions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1042:287-310. [PMID: 29357064 DOI: 10.1007/978-981-10-6955-0_14] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Recent studies on G-quadruplex (G4) revealed crucial and conserved functions of G4 in various biological systems. We recently showed that Rif1, a conserved nuclear factor, binds to G4 present in the intergenic regions and plays a major role in spatiotemporal regulation of DNA replication. Rif1 may tether chromatin fibers through binding to G4, generating specific chromatin domains that dictate the replication timing. G4 and its various binding partners are now implicated in many other chromosome regulations, including transcription, replication initiation, recombination, gene rearrangement, and transposition.
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Affiliation(s)
- Kenji Moriyama
- Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan
| | - Mong Sing Lai
- Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan
| | - Hisao Masai
- Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan.
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17
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Sensing the Environment Through Sestrins: Implications for Cellular Metabolism. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 327:1-42. [PMID: 27692174 DOI: 10.1016/bs.ircmb.2016.05.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Sestrins are a family of stress-responsive genes that have evolved to attenuate damage induced by stress caused to the cell. By virtue of their antioxidant activity, protein products of Sestrin genes prevent the accumulation of reactive oxygen species within the cell, thereby attenuating the detrimental effects of oxidative stress. In parallel, Sestrins participate in several signaling pathways that control the activity of the target of rapamycin protein kinase (TOR). TOR is a crucial sensor of intracellular and extracellular conditions that promotes cell growth and anabolism when nutrients and growth factors are abundant. In addition to reacting to stress-inducing insults, Sestrins also monitor the changes in the availability of nutrients, which allows them to serve as a key checkpoint for the TOR-regulated signaling pathways. In this review, we will discuss how Sestrins integrate signals from numerous stress- and nutrient-responsive signaling pathways to orchestrate cellular metabolism and support cell viability.
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18
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Tsokanos FF, Albert MA, Demetriades C, Spirohn K, Boutros M, Teleman AA. eIF4A inactivates TORC1 in response to amino acid starvation. EMBO J 2016; 35:1058-76. [PMID: 26988032 PMCID: PMC4868951 DOI: 10.15252/embj.201593118] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Accepted: 02/19/2016] [Indexed: 12/20/2022] Open
Abstract
Amino acids regulate TOR complex 1 (TORC1) via two counteracting mechanisms, one activating and one inactivating. The presence of amino acids causes TORC1 recruitment to lysosomes where TORC1 is activated by binding Rheb. How the absence of amino acids inactivates TORC1 is less well understood. Amino acid starvation recruits the TSC1/TSC2 complex to the vicinity of TORC1 to inhibit Rheb; however, the upstream mechanisms regulating TSC2 are not known. We identify here the eIF4A-containing eIF4F translation initiation complex as an upstream regulator of TSC2 in response to amino acid withdrawal in Drosophila We find that TORC1 and translation preinitiation complexes bind each other. Cells lacking eIF4F components retain elevated TORC1 activity upon amino acid removal. This effect is specific for eIF4F and not a general consequence of blocked translation. This study identifies specific components of the translation machinery as important mediators of TORC1 inactivation upon amino acid removal.
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Affiliation(s)
- Foivos-Filippos Tsokanos
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Marie-Astrid Albert
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Constantinos Demetriades
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Kerstin Spirohn
- Department of Cell and Molecular Biology, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Division of Signaling and Functional Genomics and Heidelberg University, Heidelberg, Germany
| | - Michael Boutros
- Department of Cell and Molecular Biology, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Division of Signaling and Functional Genomics and Heidelberg University, Heidelberg, Germany
| | - Aurelio A Teleman
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
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19
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An eccentric calpain, CAPN3/p94/calpain-3. Biochimie 2016; 122:169-87. [DOI: 10.1016/j.biochi.2015.09.010] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 09/07/2015] [Indexed: 01/09/2023]
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20
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Pinto A, Mace Y, Drouet F, Bony E, Boidot R, Draoui N, Lobysheva I, Corbet C, Polet F, Martherus R, Deraedt Q, Rodríguez J, Lamy C, Schicke O, Delvaux D, Louis C, Kiss R, Kriegsheim AV, Dessy C, Elias B, Quetin-Leclercq J, Riant O, Feron O. A new ER-specific photosensitizer unravels (1)O2-driven protein oxidation and inhibition of deubiquitinases as a generic mechanism for cancer PDT. Oncogene 2015; 35:3976-85. [PMID: 26686091 DOI: 10.1038/onc.2015.474] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Revised: 10/29/2015] [Accepted: 11/17/2015] [Indexed: 12/19/2022]
Abstract
Photosensitizers (PS) are ideally devoid of any activity in the absence of photoactivation, and rely on molecular oxygen for the formation of singlet oxygen ((1)O2) to produce cellular damage. Off-targets and tumor hypoxia therefore represent obstacles for the use of PS for cancer photodynamic therapy. Herein, we describe the characterization of OR141, a benzophenazine compound identified through a phenotypic screening for its capacity to be strictly activated by light and to kill a large variety of tumor cells under both normoxia and hypoxia. This new class of PS unraveled an unsuspected common mechanism of action for PS that involves the combined inhibition of the mammalian target of rapamycin (mTOR) signaling pathway and proteasomal deubiquitinases (DUBs) USP14 and UCH37. Oxidation of mTOR and other endoplasmic reticulum (ER)-associated proteins drives the early formation of high molecular weight (MW) complexes of multimeric proteins, the concomitant blockade of DUBs preventing their degradation and precipitating cell death. Furthermore, we validated the antitumor effects of OR141 in vivo and documented its highly selective accumulation in the ER, further increasing the ER stress resulting from (1)O2 generation upon light activation.
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Affiliation(s)
- A Pinto
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - Y Mace
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - F Drouet
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - E Bony
- Pharmacognosy Research Group (GNOS), Louvain Drug Research Institute (LDRI), Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - R Boidot
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - N Draoui
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - I Lobysheva
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - C Corbet
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - F Polet
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - R Martherus
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - Q Deraedt
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - J Rodríguez
- Systems Biology Ireland, Conway Institute, Belfield, Dublin 4, Ireland
| | - C Lamy
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - O Schicke
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - D Delvaux
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - C Louis
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - R Kiss
- Laboratoire de Cancérologie et de Toxicologie Expérimentale, Faculté de Pharmacie, Université Libre de Bruxelles, Brussels, Belgium
| | - A V Kriegsheim
- Systems Biology Ireland, Conway Institute, Belfield, Dublin 4, Ireland
| | - C Dessy
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
| | - B Elias
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - J Quetin-Leclercq
- Pharmacognosy Research Group (GNOS), Louvain Drug Research Institute (LDRI), Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - O Riant
- Institute of Condensed Matter and Nanosciences Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - O Feron
- Pole of Pharmacology and Therapeutics (FATH), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Brussels, Belgium
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Jain A, Arauz E, Aggarwal V, Ikon N, Chen J, Ha T. Stoichiometry and assembly of mTOR complexes revealed by single-molecule pulldown. Proc Natl Acad Sci U S A 2014; 111:17833-8. [PMID: 25453101 PMCID: PMC4273350 DOI: 10.1073/pnas.1419425111] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The mammalian target of rapamycin (mTOR) kinase is a master regulator of cellular, developmental, and metabolic processes. Deregulation of mTOR signaling is implicated in numerous human diseases including cancer and diabetes. mTOR functions as part of either of the two multisubunit complexes, mTORC1 and mTORC2, but molecular details about the assembly and oligomerization of mTORCs are currently lacking. We use the single-molecule pulldown (SiMPull) assay that combines principles of conventional pulldown assays with single-molecule fluorescence microscopy to investigate the stoichiometry and assembly of mTORCs. After validating our approach with mTORC1, confirming a dimeric assembly as previously reported, we show that all major components of mTORC2 exist in two copies per complex, indicating that mTORC2 assembles as a homodimer. Interestingly, each mTORC component, when free from the complexes, is present as a monomer and no single subunit serves as the dimerizing component. Instead, our data suggest that dimerization of mTORCs is the result of multiple subunits forming a composite surface. SiMPull also allowed us to distinguish complex disassembly from stoichiometry changes. Physiological conditions that abrogate mTOR signaling such as nutrient deprivation or energy stress did not alter the stoichiometry of mTORCs. On the other hand, rapamycin treatment leads to transient appearance of monomeric mTORC1 before complete disruption of the mTOR-raptor interaction, whereas mTORC2 stoichiometry is unaffected. These insights into assembly of mTORCs may guide future mechanistic studies and exploration of therapeutic potential.
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Affiliation(s)
- Ankur Jain
- Center for Biophysics and Computational Biology, Institute for Genomic Biology
| | - Edwin Arauz
- Department of Cell and Developmental Biology
| | - Vasudha Aggarwal
- Center for Biophysics and Computational Biology, Institute for Genomic Biology
| | - Nikita Ikon
- Department of Cell and Developmental Biology
| | - Jie Chen
- Department of Cell and Developmental Biology,
| | - Taekjip Ha
- Center for Biophysics and Computational Biology, Institute for Genomic Biology, Department of Physics, and Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801
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22
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Abstract
Mammalian target of rapamycin (mTOR) integrates multiple signals, including nutrient status, growth factor availability, and stress, to regulate cellular and organismal growth. How mTOR regulates transcriptional programs in response to these diverse stimuli is poorly understood. MondoA and its obligate transcription partner Mlx are basic helix-loop-helix leucine zipper (bHLHZip) transcription factors that sense and execute a glucose-responsive transcriptional program. MondoA-Mlx complexes activate expression of thioredoxin-interacting protein (TXNIP), which is a potent inhibitor of cellular glucose uptake and aerobic glycolysis. Both mTOR and MondoA are central regulators of glucose metabolism, yet whether they interact physically or functionally is unknown. We show that inhibition of mTOR induces MondoA-dependent expression of TXNIP, coinciding with reduced glucose uptake. Mechanistically, mTOR binds to MondoA in the cytoplasm and prevents MondoA-Mlx complex formation, restricting MondoA's nuclear entry and reducing TXNIP expression. Further, we show that mTOR inhibitors and reactive oxygen species (ROS) regulate interaction between MondoA and mTOR in an opposing manner. Like mTOR's suppression of the MondoA-TXNIP axis, MondoA can also suppress mTOR complex 1 (mTORC1) activity via its direct transcriptional regulation of TXNIP. Collectively, these studies reveal a regulatory relationship between mTOR and the MondoA-TXNIP axis that we propose contributes to glucose homeostasis.
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23
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Goodman CA, Hornberger TA. New roles for Smad signaling and phosphatidic acid in the regulation of skeletal muscle mass. F1000PRIME REPORTS 2014; 6:20. [PMID: 24765525 PMCID: PMC3974568 DOI: 10.12703/p6-20] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Skeletal muscle is essential for normal bodily function and the loss of skeletal muscle (i.e. muscle atrophy/wasting) can have a major impact on mobility, whole-body metabolism, disease resistance, and quality of life. Thus, there is a clear need for the development of therapies that can prevent the loss, or increase, of skeletal muscle mass. However, in order to develop such therapies, we will first have to develop a thorough understanding of the molecular mechanisms that regulate muscle mass. Fortunately, our knowledge is rapidly advancing, and in this review, we will summarize recent studies that have expanded our understanding of the roles that Smad signaling and the synthesis of phosphatidic acid play in the regulation of skeletal muscle mass.
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24
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Jacobs BL, Goodman CA, Hornberger TA. The mechanical activation of mTOR signaling: an emerging role for late endosome/lysosomal targeting. J Muscle Res Cell Motil 2013; 35:11-21. [PMID: 24162376 DOI: 10.1007/s10974-013-9367-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 10/18/2013] [Indexed: 01/03/2023]
Abstract
It is well recognized that mechanical signals play a critical role in the regulation of skeletal muscle mass, and the maintenance of muscle mass is essential for mobility, disease prevention and quality of life. Furthermore, over the last 15 years it has become established that signaling through a protein kinase called the mammalian (or mechanistic) target of rapamycin (mTOR) is essential for mechanically-induced changes in protein synthesis and muscle mass, however, the mechanism(s) via which mechanical stimuli regulate mTOR signaling have not been defined. Nonetheless, advancements are being made, and an emerging body of evidence suggests that the late endosome/lysosomal (LEL) system might play a key role in this process. Therefore, the purpose of this review is to summarize this body of evidence. Specifically, we will first explain why the Ras homologue enriched in brain (Rheb) and phosphatidic acid (PA) are considered to be direct activators of mTOR signaling. We will then describe the process of endocytosis and its involvement in the formation of LEL structures, as well as the evidence which indicates that mTOR and its direct activators (Rheb and PA) are all enriched at the LEL. Finally, we will summarize the evidence that has implicated the LEL in the regulation of mTOR by various growth regulatory inputs such as amino acids, growth factors and mechanical stimuli.
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Affiliation(s)
- Brittany L Jacobs
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI, 53706, USA
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25
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Neural plasticity and proliferation in the generation of antidepressant effects: hippocampal implication. Neural Plast 2013; 2013:537265. [PMID: 23862076 PMCID: PMC3703717 DOI: 10.1155/2013/537265] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/01/2013] [Accepted: 05/08/2013] [Indexed: 12/15/2022] Open
Abstract
It is widely accepted that changes underlying depression and antidepressant-like effects involve not only alterations in the levels of neurotransmitters as monoamines and their receptors in the brain, but also structural and functional changes far beyond. During the last two decades, emerging theories are providing new explanations about the neurobiology of depression and the mechanism of action of antidepressant strategies based on cellular changes at the CNS level. The neurotrophic/plasticity hypothesis of depression, proposed more than a decade ago, is now supported by multiple basic and clinical studies focused on the role of intracellular-signalling cascades that govern neural proliferation and plasticity. Herein, we review the state-of-the-art of the changes in these signalling pathways which appear to underlie both depressive disorders and antidepressant actions. We will especially focus on the hippocampal cellularity and plasticity modulation by serotonin, trophic factors as brain-derived neurotrophic factor (BDNF), and vascular endothelial growth factor (VEGF) through intracellular signalling pathways—cAMP, Wnt/β-catenin, and mTOR. Connecting the classic monoaminergic hypothesis with proliferation/neuroplasticity-related evidence is an appealing and comprehensive attempt for improving our knowledge about the neurobiological events leading to depression and associated to antidepressant therapies.
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26
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Chong ZZ, Yao Q, Li HH. The rationale of targeting mammalian target of rapamycin for ischemic stroke. Cell Signal 2013; 25:1598-607. [PMID: 23563259 DOI: 10.1016/j.cellsig.2013.03.017] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 03/28/2013] [Indexed: 02/06/2023]
Abstract
Given the current limitation of therapeutic approach for ischemic stroke, a leading cause of disability and mortality in the developed countries, to develop new therapeutic strategies for this devastating disease is urgently necessary. As a serine/threonine kinase, mammalian target of rapamycin (mTOR) activation can mediate broad biological activities that include protein synthesis, cytoskeleton organization, and cell survival. mTOR functions through mTORC1 and mTORC2 complexes and their multiple downstream substrates, such as eukaryotic initiation factor 4E-binding protein 1, p70 ribosomal S6 kinase, sterol regulatory element-binding protein 1, hypoxia inducible factor-1, and signal transducer and activator transcription 3, Yin Ying 1, Akt, protein kinase c-alpha, Rho GTPase, serum-and gucocorticoid-induced protein kinase 1, etc. Specially, the role of mTOR in the central nervous system has been attracting considerable attention. Based on the ability of mTOR to prevent neuronal apoptosis, inhibit autophagic cell death, promote neurogenesis, and improve angiogenesis, mTOR may acquire the capability of limiting the ischemic neuronal death and promoting the neurological recovery. Consequently, to regulate the activity of mTOR holds a potential as a novel therapeutic strategy for ischemic stroke.
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Affiliation(s)
- Zhao Zhong Chong
- Department of Neurology and Neurosciences, Cancer Center, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07101, USA.
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27
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Inactivation of the mTORC1-eukaryotic translation initiation factor 4E pathway alters stress granule formation. Mol Cell Biol 2013; 33:2285-301. [PMID: 23547259 DOI: 10.1128/mcb.01517-12] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Stress granules (SG) are cytoplasmic multimeric RNA bodies that form under stress conditions known to inhibit cap-dependent translation. SG contain translation initiation factors, RNA binding proteins, and signaling molecules. SG are known to inhibit apoptotic pathways, thus contributing to chemo- and radioresistance in tumor cells. However, whether stress granule formation involves oncogenic signaling pathways is currently unknown. Here, we report a novel role of the mTORC1-eukaryotic translation initiation factor 4E (eIF4E) pathway, a key regulator of cap-dependent translation initiation of oncogenic factors, in SG formation. mTORC1 specifically drives the eIF4E-mediated formation of SG through the phosphorylation of 4E-BP1, a key factor known to inhibit formation of the mTORC1-dependent eIF4E-eIF4GI interactions. Disrupting formation of SG by inactivation of mTOR with its specific inhibitor pp242 or by depletion of eIF4E or eIF4GI blocks the SG-associated antiapoptotic p21 pathway. Finally, pp242 sensitizes cancer cells to death in vitro and inhibits the growth of chemoresistant tumors in vivo. This work therefore highlights a novel role of the oncogenic mTORC1-eIF4E pathway, namely, the promotion of formation of antiapoptotic SG.
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28
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Chong ZZ, Shang YC, Wang S, Maiese K. A Critical Kinase Cascade in Neurological Disorders: PI 3-K, Akt, and mTOR. FUTURE NEUROLOGY 2012; 7:733-748. [PMID: 23144589 DOI: 10.2217/fnl.12.72] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Neurodegenerative disorders lead to disability and death in a significant proportion of the world's population. However, many disorders of the nervous system remain with limited effective treatments. Kinase pathways in the nervous system that involve phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), and the mammalian target of rapamycin (mTOR) offer exciting prospects for the understanding of neurodegenerative pathways and the development of new avenues of treatment. PI 3-K, Akt, and mTOR pathways are vital cellular components that determine cell fate during acute and chronic disorders, such as Huntington's disease, Alzheimer's disease, Parkinson's disease, epilepsy, stroke, and trauma. Yet, the elaborate relationship among these kinases and the variable control of apoptosis and autophagy can lead to unanticipated biological and clinical outcomes. Crucial for the successful translation of PI 3-K, Akt, and mTOR into robust and safe clinical strategies will be the further elucidation of the complex roles that these kinase pathways hold in the nervous system.
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Affiliation(s)
- Zhao Zhong Chong
- Laboratory of Cellular and Molecular Signaling, Newark, New Jersey 07101 ; New Jersey Health Sciences University, Newark, New Jersey 07101
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Chong ZZ, Shang YC, Wang S, Maiese K. Shedding new light on neurodegenerative diseases through the mammalian target of rapamycin. Prog Neurobiol 2012; 99:128-48. [PMID: 22980037 PMCID: PMC3479314 DOI: 10.1016/j.pneurobio.2012.08.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 08/01/2012] [Accepted: 08/07/2012] [Indexed: 12/13/2022]
Abstract
Neurodegenerative disorders affect a significant portion of the world's population leading to either disability or death for almost 30 million individuals worldwide. One novel therapeutic target that may offer promise for multiple disease entities that involve Alzheimer's disease, Parkinson's disease, epilepsy, trauma, stroke, and tumors of the nervous system is the mammalian target of rapamycin (mTOR). mTOR signaling is dependent upon the mTORC1 and mTORC2 complexes that are composed of mTOR and several regulatory proteins including the tuberous sclerosis complex (TSC1, hamartin/TSC2, tuberin). Through a number of integrated cell signaling pathways that involve those of mTORC1 and mTORC2 as well as more novel signaling tied to cytokines, Wnt, and forkhead, mTOR can foster stem cellular proliferation, tissue repair and longevity, and synaptic growth by modulating mechanisms that foster both apoptosis and autophagy. Yet, mTOR through its proliferative capacity may sometimes be detrimental to central nervous system recovery and even promote tumorigenesis. Further knowledge of mTOR and the critical pathways governed by this serine/threonine protein kinase can bring new light for neurodegeneration and other related diseases that currently require new and robust treatments.
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Affiliation(s)
- Zhao Zhong Chong
- Laboratory of Cellular and Molecular Signaling, New Jersey 07101
- New Jersey Health Sciences University Newark, New Jersey 07101
| | - Yan Chen Shang
- Laboratory of Cellular and Molecular Signaling, New Jersey 07101
- New Jersey Health Sciences University Newark, New Jersey 07101
| | - Shaohui Wang
- Laboratory of Cellular and Molecular Signaling, New Jersey 07101
- New Jersey Health Sciences University Newark, New Jersey 07101
| | - Kenneth Maiese
- Laboratory of Cellular and Molecular Signaling, New Jersey 07101
- Cancer Institute of New Jersey, New Jersey 07101
- New Jersey Health Sciences University Newark, New Jersey 07101
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Hoogeveen-Westerveld M, van Unen L, van den Ouweland A, Halley D, Hoogeveen A, Nellist M. The TSC1-TSC2 complex consists of multiple TSC1 and TSC2 subunits. BMC BIOCHEMISTRY 2012; 13:18. [PMID: 23006675 PMCID: PMC3517901 DOI: 10.1186/1471-2091-13-18] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Accepted: 09/21/2012] [Indexed: 01/05/2023]
Abstract
Background Mutations to the TSC1 and TSC2 genes cause the disease tuberous sclerosis complex. The TSC1 and TSC2 gene products form a protein complex that integrates multiple metabolic signals to regulate the activity of the target of rapamycin (TOR) complex 1 (TORC1) and thereby control cell growth. Here we investigate the quaternary structure of the TSC1-TSC2 complex by gel filtration and coimmunoprecipitation. Results TSC1 and TSC2 co-eluted in high molecular weight fractions by gel filtration. Coimmunoprecipitation of distinct tagged TSC1 and TSC2 isoforms demonstrated that TSC1-TSC2 complexes contain multiple TSC1 and TSC2 subunits. Conclusions TSC1 and TSC2 interact to form large complexes containing multiple TSC1 and TSC2 subunits.
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Nakashima A, Otsubo Y, Yamashita A, Sato T, Yamamoto M, Tamanoi F. Psk1, an AGC kinase family member in fission yeast, is directly phosphorylated and controlled by TORC1 and functions as S6 kinase. J Cell Sci 2012; 125:5840-9. [PMID: 22976295 DOI: 10.1242/jcs.111146] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Target of rapamycin (TOR), an evolutionarily conserved serine/threonine protein kinase, plays pivotal roles in several important cellular processes in eukaryotes. In the fission yeast Schizosaccharomyces pombe, TOR complex 1 (TORC1), which includes Tor2 as a catalytic subunit, manages the switch between cell proliferation and differentiation by sensing nutrient availability. However, little is known about the direct target of TORC1 that plays key roles in nutrient-dependent TORC1 signaling in fission yeast. Here we report that in fission yeast, three AGC kinase family members, named Psk1, Sck1 and Sck2, which exhibit high homology with human S6K1, are phosphorylated under nutrient-rich conditions and are dephosphorylated by starvation conditions. Among these, Psk1 is necessary for phosphorylation of ribosomal protein S6. Furthermore, Psk1 phosphorylation is regulated by TORC1 in nutrient-dependent and rapamycin-sensitive manners in vivo. Three conserved regulatory motifs (the activation loop, the hydrophobic and the turn motifs) in Psk1 are phosphorylated and these modifications are required for Psk1 activity. In particular, phosphorylation of the hydrophobic motif is catalyzed by TORC1 in vivo and in vitro. Ksg1, a homolog of PDK1, is also important for Psk1 phosphorylation in the activation loop and for its activity. The TORC1 components Pop3, Toc1 and Tco89, are dispensable for Psk1 regulation, but disruption of pop3(+) causes an increase in the sensitivity of TORC1 to rapamycin. Taken together, these results provide convincing evidence that TORC1/Psk1/Rps6 constitutes a nutrient-dependent signaling pathway in fission yeast.
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Affiliation(s)
- Akio Nakashima
- Department of Microbiology, Immunology and Molecular Genetics, Molecular Biology Institute, Jonsson Comprehensive Cancer Center, University of California, Los Angeles, CA 90095-1489, USA
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Chong ZZ, Maiese K. Mammalian target of rapamycin signaling in diabetic cardiovascular disease. Cardiovasc Diabetol 2012; 11:45. [PMID: 22545721 PMCID: PMC3398846 DOI: 10.1186/1475-2840-11-45] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 04/30/2012] [Indexed: 12/15/2022] Open
Abstract
Diabetes mellitus currently affects more than 170 million individuals worldwide and is expected to afflict another 200 million individuals in the next 30 years. Complications of diabetes as a result of oxidant stress affect multiple systems throughout the body, but involvement of the cardiovascular system may be one of the most severe in light of the impact upon cardiac and vascular function that can result in rapid morbidity and mortality for individuals. Given these concerns, the signaling pathways of the mammalian target of rapamycin (mTOR) offer exciting prospects for the development of novel therapies for the cardiovascular complications of diabetes. In the cardiovascular and metabolic systems, mTOR and its multi-protein complexes of TORC1 and TORC2 regulate insulin release and signaling, endothelial cell survival and growth, cardiomyocyte proliferation, resistance to β-cell injury, and cell longevity. Yet, mTOR can, at times, alter insulin signaling and lead to insulin resistance in the cardiovascular system during diabetes mellitus. It is therefore vital to understand the complex relationship mTOR and its downstream pathways hold during metabolic disease in order to develop novel strategies for the complications of diabetes mellitus in the cardiovascular system.
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Abstract
The determination of final organ size is a highly coordinated and complex process that relies on the precise regulation of cell number and/or cell size. Perturbation of organ size control contributes to many human diseases, including hypertrophy, degenerative diseases, and cancer. Hippo and TOR are among the key signaling pathways involved in the regulation of organ size through their respective functions in the regulation of cell number and cell size. Here, we review the general mechanisms that regulate organ growth, describe how Hippo and TOR control key aspects of growth, and discuss recent findings that highlight a possible coordination between Hippo and TOR in organ size regulation.
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Lieberthal W, Levine JS. Mammalian target of rapamycin and the kidney. I. The signaling pathway. Am J Physiol Renal Physiol 2012; 303:F1-10. [PMID: 22419691 DOI: 10.1152/ajprenal.00014.2012] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a fundamental role in regulating cellular homeostasis and metabolism. In a two-part review, we examine the complex molecular events involved in the regulation and downstream effects of mTOR, as well as the pivotal role played by this kinase in many renal diseases, particularly acute kidney injury, diabetic nephropathy, and polycystic kidney diseases. Here, in the first part of the review, we provide an overview of the complex signaling events and pathways governing mTOR activity and action. mTOR is a key component of two multiprotein complexes, known as mTOR complex 1 (mTORC1) and 2 (mTORC2). Some proteins are found in both mTORC1 and mTORC2, while others are unique to one or the other complex. Activation of mTORC1 promotes cell growth (increased cellular mass or size) and cell proliferation (increased cell number). mTORC1 acts as a metabolic "sensor," ensuring that conditions are optimal for both cell growth and proliferation. Its activity is tightly regulated by the availability of amino acids, growth factors, energy stores, and oxygen. The effects of mTORC2 activation are distinct from those of mTORC1. Cellular processes modulated by mTORC2 include cell survival, cell polarity, cytoskeletal organization, and activity of the aldosterone-sensitive sodium channel. Upstream events controlling mTORC2 activity are less well understood than those controlling mTORC1, although growth factors appear to stimulate both complexes. Rapamycin and its analogs inhibit the activity of mTORC1 only, and not that of mTORC2, while the newer "catalytic" mTOR inhibitors affect both complexes.
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Affiliation(s)
- Wilfred Lieberthal
- Department of Medicine, Stony Brook University Medical Center, Stony Brook, NY, USA.
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Glatter T, Schittenhelm RB, Rinner O, Roguska K, Wepf A, Jünger MA, Köhler K, Jevtov I, Choi H, Schmidt A, Nesvizhskii AI, Stocker H, Hafen E, Aebersold R, Gstaiger M. Modularity and hormone sensitivity of the Drosophila melanogaster insulin receptor/target of rapamycin interaction proteome. Mol Syst Biol 2011; 7:547. [PMID: 22068330 PMCID: PMC3261712 DOI: 10.1038/msb.2011.79] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 09/09/2011] [Accepted: 09/29/2011] [Indexed: 12/24/2022] Open
Abstract
First systematic analysis of the evolutionary conserved InR/TOR pathway interaction proteome in Drosophila. Quantitative mass spectrometry revealed that 22% of identified protein interactions are regulated by the growth hormone insulin affecting membrane proximal as well as intracellular signaling complexes. Systematic RNA interference linked a significant fraction of network components to the control of dTOR kinase activity. Combined biochemical and genetic data suggest dTTT, a dTOR-containing complex required for cell growth control by dTORC1 and dTORC2 in vivo.
Cellular growth is a fundamental process that requires constant adaptations to changing environmental conditions, like growth factor and nutrient availability, energy levels and more. Over the years, the insulin receptor/target of rapamycin pathway (InR/TOR) emerged as a key signaling system for the control of metazoan cell growth. Genetic screens carried out in the fruit fly Drosophila melanogaster identified key InR/TOR pathway components and their relationships. Phenotypes such as altered cell growth are likely to emerge from perturbed dynamic networks containing InR/TOR pathway components, which stably or transiently interact with other cellular proteins to form complexes and networks thereof. Systematic studies on the topology and dynamics of protein interaction networks become therefore highly relevant to gain systems level understanding of deregulated cell growth. Despite much progress in genetic analysis only few systematic protein interaction studies have been reported for Drosophila, which in most cases lack quantitative information representing the dynamic nature of such networks. Here, we present the first quantitative affinity purification mass spectrometry (AP–MS/MS) analysis on the evolutionary conserved InR/TOR signaling network in Drosophila. Systematic RNAi-based functional analysis of identified network components revealed key components linked to the regulation of the central effector kinase dTOR. This includes also dTTT, a novel dTOR-containing complex required for the control of dTORC1 and dTORC2 in vivo. For systematic AP–MS analysis, we generated Drosophila Kc167 cell lines inducibly expressing affinity-tagged bait proteins previously linked to InR/TOR signaling. Bait expressing Kc167 cell lines were harvested before and after insulin stimulation for subsequent affinity purification. Following LC–MS/MS analysis and probabilistic data filtering using SAINT (Choi et al, 2010), we generated a quantitative network model from 97 high confidence protein–protein interactions and 58 network components (Figure 2). The presented network displayed a high degree of orthologous interactions conserved also in human cells and identified a number of novel molecular interactions with InR/TOR signaling components for future hypothesis driven analysis. To measure insulin-induced changes within the InR/TOR interaction proteome, we applied a recently introduced label-free quantitative MS approach (Rinner et al, 2007). The obtained quantitative data suggest that 22% of all interactions in the network are regulated by insulin. Major changes could be observed within the membrane proximal InR/chico/PI3K signaling complexes, and also in 14-3-3 protein containing signaling complexes and dTORC1, a complex that contains besides dTOR all major orthologous proteins found also in human mTORC1 including the two dTORC1 substrates d4E-BP (Thor) and S6 Kinase (S6K). Insulin triggered both, dissociation and association of dTORC1 proteins. Among the proteins that showed enhanced binding to dTORC1 upon insulin stimulation we found Unkempt, a RING-finger protein with a proposed role in ubiquitin-mediated protein degradation (Lores et al, 2010). Besides dTORC1 our systematic AP–MS analysis also revealed the presence of dTORC2, the second major TOR complex in Drosophila. dTORC2 contains the Drosophila orthologous of human mTORC2 proteins, but in contrast to dTORC1 was not affected upon insulin stimulation. Interestingly, we also found a specific set of proteins that were not linked to the canonical TOR complexes TORC1 and TORC2 in dTOR purifications. These include LqfR (liquid facets related), Pontin, Reptin, Spaghetti and the gene product of CG16908. We found the same set of proteins when we used CG16908 as a bait, suggesting complex formation among the identified proteins. None of the dTORC1/2 components besides dTOR was identified in CG16908 purifications, indicating that these proteins form dTOR complexes distinct from dTORC1 and dTORC2. Based on known interaction information from other species and data obtained from this study we refer to this complex as dTTT (DrosophilaTOR, TELO2, TTI1) (Horejsi et al, 2010; [18]Hurov et al, 2010; [20]Kaizuka et al, 2010). A directed quantitative MS analysis of dTOR complex components suggests that dTORC1 is the most abundant dTOR complex we identified in Kc167 cells. We next studied the potential roles of the identified network components for controlling the activity of the dInR/TOR pathway using systematic RNAi depletion and quantitative western blotting to measure the changes in abundance of phosphorylated substrates of dTORC1 (Thor/d4E-BP, dS6K) and dTORC2 (dPKB) in RNAi-treated cells (Figure 5). Overall, we could identify 16 proteins (out of 58) whose depletion caused an at least 50% increase or decrease in the levels of phosphorylated d4E-BP, S6K and/or PKB compared with control GFP RNAi. Besides established pathway components, we found several novel regulators within the dInR/TOR interaction network. For example, RNAi against the novel insulin-regulated dTORC1 component Unkempt resulted in enhanced phosphorylation of the dTORC1 substrate d4E-BP, which suggests a negative role for Unkempt on dTORC1 activity. In contrast, depletion of CG16908 and LqfR caused hypo-phosphorylation of all dTOR substrates similar to dTOR itself, suggesting a positive role for the dTTT complex on dTOR activity. Subsequently, we tested whether dTTT components also plays a role in dTOR-mediated cell growth in vivo. Depletion of both dTTT components, CG16908 and LqfR, in the Drosophila eye resulted in a substantial decrease in eye size. Likewise, FLP-FRT-mediated mitotic recombination resulted in CG16908 and LqfR mutant clones with a similar reduced growth phenotype as observed in dTOR mutant clones. Hence, the combined biochemical and genetic analysis revealed dTTT as a dTOR-containing complex required for the activity of both dTORC1 and dTORC2 and thus plays a critical role in controlling cell growth. Taken together, these results illustrate how a systematic quantitative AP–MS approach when combined with systematic functional analysis in Drosophila can reveal novel insights into the dynamic organization of regulatory networks for cell growth control in metazoans. Using quantitative mass spectrometry, this study reports how insulin affects the modularity of the interaction proteome of the Drosophila InR/TOR pathway, an evolutionary conserved signaling system for the control of metazoan cell growth. Systematic functional analysis linked a significant number of identified network components to the control of dTOR activity and revealed dTTT, a dTOR complex required for in vivo cell growth control by dTORC1 and dTORC2. Genetic analysis in Drosophila melanogaster has been widely used to identify a system of genes that control cell growth in response to insulin and nutrients. Many of these genes encode components of the insulin receptor/target of rapamycin (InR/TOR) pathway. However, the biochemical context of this regulatory system is still poorly characterized in Drosophila. Here, we present the first quantitative study that systematically characterizes the modularity and hormone sensitivity of the interaction proteome underlying growth control by the dInR/TOR pathway. Applying quantitative affinity purification and mass spectrometry, we identified 97 high confidence protein interactions among 58 network components. In all, 22% of the detected interactions were regulated by insulin affecting membrane proximal as well as intracellular signaling complexes. Systematic functional analysis linked a subset of network components to the control of dTORC1 and dTORC2 activity. Furthermore, our data suggest the presence of three distinct dTOR kinase complexes, including the evolutionary conserved dTTT complex (Drosophila TOR, TELO2, TTI1). Subsequent genetic studies in flies suggest a role for dTTT in controlling cell growth via a dTORC1- and dTORC2-dependent mechanism.
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Affiliation(s)
- Timo Glatter
- Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
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Russell RC, Fang C, Guan KL. An emerging role for TOR signaling in mammalian tissue and stem cell physiology. Development 2011; 138:3343-56. [PMID: 21791526 DOI: 10.1242/dev.058230] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The mammalian target of rapamycin (mTOR) is a kinase that responds to a myriad of signals, ranging from nutrient availability and energy status, to cellular stressors, oxygen sensors and growth factors. The finely tuned response of mTOR to these stimuli results in alterations to cell metabolism and cell growth. Recent studies of conditional knockouts of mTOR pathway components in mice have affirmed the role of mTOR signaling in energy balance, both at the cell and whole organism levels. Such studies have also highlighted a role for mTOR in stem cell homeostasis and lifespan determination. Here, we discuss the molecular mechanisms of TOR signaling and review recent in vitro and in vivo studies of mTOR tissue-specific activities in mammals.
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Affiliation(s)
- Ryan C Russell
- Department of Pharmacology and Moores Cancer Center, University of California at San Diego, La Jolla, CA 92093-0815, USA.
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Abstract
The mechanistic (or mammalian) target of rapamycin (mTOR), an evolutionarily conserved protein kinase, orchestrates cellular responses to growth, metabolic and stress signals. mTOR processes various extracellular and intracellular inputs as part of two mTOR protein complexes, mTORC1 or mTORC2. The mTORCs have numerous cellular targets but members of a family of protein kinases, the protein kinase (PK)A/PKG/PKC (AGC) family are the best characterized direct mTOR substrates. The AGC kinases control multiple cellular functions and deregulation of many members of this family underlies numerous pathological conditions. mTOR phosphorylates conserved motifs in these kinases to allosterically augment their activity, influence substrate specificity, and promote protein maturation and stability. Activation of AGC kinases in turn triggers the phosphorylation of diverse, often overlapping, targets that ultimately control cellular response to a wide spectrum of stimuli. This review will highlight recent findings on how mTOR regulates AGC kinases and how mTOR activity is feedback regulated by these kinases. We will discuss how this regulation can modulate downstream targets in the mTOR pathway that could account for the varied cellular functions of mTOR.
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Affiliation(s)
- Bing Su
- Department of Immunobiology and The Vascular Biology and Therapeutics Program, Yale University School of Medicine, New Haven, CT, USA.
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Abstract
The mechanistic target of rapamycin (mTOR) plays a central role in cellular growth and metabolism. mTOR forms two distinct protein complexes, mTORC1 and mTORC2. Much is known about the regulation and functions of mTORC1 due to availability of a natural compound, rapamycin, that inhibits this complex. Studies that define mTORC2 cellular functions and signaling have lagged behind. The development of pharmacological inhibitors that block mTOR kinase activity, and thereby inhibit both mTOR complexes, along with availability of mice with genetic knockouts in mTOR complex components have now provided new insights on mTORC2 function and regulation. Since prolonged effects of rapamycin can also disrupt mTORC2, it is worth re-evaluating the contribution of this less-studied mTOR complex in cancer, metabolic disorders and aging. In this review, we focus on recent developments on mammalian mTORC2 signaling mechanisms and its cellular and tissue-specific functions.
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Affiliation(s)
- Won Jun Oh
- Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ, USA
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Jaafar R, Zeiller C, Pirola L, Di Grazia A, Naro F, Vidal H, Lefai E, Némoz G. Phospholipase D regulates myogenic differentiation through the activation of both mTORC1 and mTORC2 complexes. J Biol Chem 2011; 286:22609-21. [PMID: 21525000 DOI: 10.1074/jbc.m110.203885] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
How phospholipase D (PLD) is involved in myogenesis remains unclear. At the onset of myogenic differentiation of L6 cells induced by the PLD agonist vasopressin in the absence of serum, mTORC1 complex was rapidly activated, as reflected by phosphorylation of S6 kinase1 (S6K1). Both the long (p85) and short (p70) S6K1 isoforms were phosphorylated in a PLD1-dependent way. Short rapamycin treatment specifically inhibiting mTORC1 suppressed p70 but not p85 phosphorylation, suggesting that p85 might be directly activated by phosphatidic acid. Vasopressin stimulation also induced phosphorylation of Akt on Ser-473 through PLD1-dependent activation of mTORC2 complex. In this model of myogenesis, mTORC2 had a positive role mostly unrelated to Akt activation, whereas mTORC1 had a negative role, associated with S6K1-induced Rictor phosphorylation. The PLD requirement for differentiation can thus be attributed to its ability to trigger via mTORC2 activation the phosphorylation of an effector that could be PKCα. Moreover, PLD is involved in a counter-regulation loop expected to limit the response. This study thus brings new insights in the intricate way PLD and mTOR cooperate to control myogenesis.
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Hardt M, Chantaravisoot N, Tamanoi F. Activating mutations of TOR (target of rapamycin). Genes Cells 2011; 16:141-51. [PMID: 21210909 DOI: 10.1111/j.1365-2443.2010.01482.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Mammalian target of rapamycin (mTOR) is a key regulator of eukaryotic cell growth. In particular, mTORC1, one of the two complexes that contain mTOR, is involved in the regulation of protein synthesis, proliferation, cell cycle and autophagy. Hyperactivation of the mTOR signaling pathway is observed in human cancer. A variety of approaches including deletion analysis, yeast genetic screens and mining of human cancer genome databases were taken that resulted in the identification of activating mutations of TOR. These studies suggest that the FAT, FRB and kinase domains are the three regions of TOR where activating mutations can be identified. Within the kinase domain, the mutations are clustered in three hot spots that are all located in the kinase active site that was deduced by the alignment with PI3K. One of the hot spots corresponds to the region where PI3K oncogenic mutations have been identified. These results are beginning to provide important insights into the mechanism of activation of mTOR.
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Affiliation(s)
- Molly Hardt
- Department of Microbiology, Immunology and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1489, USA
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Sengupta S, Peterson TR, Sabatini DM. Regulation of the mTOR complex 1 pathway by nutrients, growth factors, and stress. Mol Cell 2010; 40:310-22. [PMID: 20965424 DOI: 10.1016/j.molcel.2010.09.026] [Citation(s) in RCA: 938] [Impact Index Per Article: 67.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 09/03/2010] [Accepted: 09/28/2010] [Indexed: 02/06/2023]
Abstract
The large serine/threonine protein kinase mTOR regulates cellular and organismal homeostasis by coordinating anabolic and catabolic processes with nutrient, energy, and oxygen availability and growth factor signaling. Cells and organisms experience a wide variety of insults that perturb the homeostatic systems governed by mTOR and therefore require appropriate stress responses to allow cells to continue to function. Stress can manifest from an excess or lack of upstream signals or as a result of genetic perturbations in upstream effectors of the pathway. mTOR nucleates two large protein complexes that are important nodes in the pathways that help buffer cells from stresses, and are implicated in the progression of stress-associated phenotypes and diseases, such as aging, tumorigenesis, and diabetes. This review focuses on the key components of the mTOR complex 1 pathway and on how various stresses impinge upon them.
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Affiliation(s)
- Shomit Sengupta
- Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA 02142, USA
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Chong ZZ, Shang YC, Zhang L, Wang S, Maiese K. Mammalian target of rapamycin: hitting the bull's-eye for neurological disorders. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2010; 3:374-91. [PMID: 21307646 PMCID: PMC3154047 DOI: 10.4161/oxim.3.6.14787] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The mammalian target of rapamycin (mTOR) and its associated cell signaling pathways have garnered significant attention for their roles in cell biology and oncology. Interestingly,the explosion of information in this field has linked mTOR to neurological diseases with promising initial studies. mTOR, a 289 kDa serine/threonine protein kinase, plays an important role in cell growth and proliferation and is activated through phosphorylation in response to growth factors, mitogens and hormones. Growth factors, amino acids, cellular nutrients and oxygen deficiency can downregulate mTOR activity. The function of mTOR signaling is mediated primarily through two mTOR complexes: mTORC1 and mTORC2. mTORC1 initiates cap-dependent protein translation, a rate-limiting step of protein synthesis, through the phosphorylation of the targets eukaryotic initiation factor 4E-binding protein 1 (4EBP1) and p70 ribosomal S6 kinase (p70S6K). In contrast, mTORC2 regulates development of the cytoskeleton and also controls cell survival. Although closely tied to tumorigenesis, mTOR and the downstream signaling pathways are significantly involved in the central nervous system (CNS) with synaptic plasticity, memory retention, neuroendocrine regulation associated with food intake and puberty and modulation of neuronal repair following injury. The signaling pathways of mTOR also are believed to be a significant component in a number of neurological diseases, such as Alzheimer disease, Parkinson disease and Huntington disease, tuberous sclerosis, neurofibromatosis, fragile X syndrome, epilepsy, traumatic brain injury and ischemic stroke. Here we describe the role of mTOR in the CNS and illustrate the potential for new strategies directed against neurological disorders.
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Affiliation(s)
- Zhao Zhong Chong
- Department of Neurology and Neurosciences, Cancer Center, University of Medicine and Dentistry - New Jersey Medical School, Newark, NJ, USA
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Yip CK, Murata K, Walz T, Sabatini DM, Kang SA. Structure of the human mTOR complex I and its implications for rapamycin inhibition. Mol Cell 2010; 38:768-74. [PMID: 20542007 DOI: 10.1016/j.molcel.2010.05.017] [Citation(s) in RCA: 317] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Revised: 03/25/2010] [Accepted: 04/29/2010] [Indexed: 11/16/2022]
Abstract
The mammalian target of rapamycin complex 1 (mTORC1) regulates cell growth in response to the nutrient and energy status of the cell, and its deregulation is common in human cancers. Little is known about the overall architecture and subunit organization of this essential signaling complex. We have determined the three-dimensional (3D) structure of the fully assembled human mTORC1 by cryo-electron microscopy (cryo-EM). Our analyses reveal that mTORC1 is an obligate dimer with an overall rhomboid shape and a central cavity. The dimeric interfaces are formed by interlocking interactions between the mTOR and raptor subunits. Extended incubation with FKBP12-rapamycin compromises the structural integrity of mTORC1 in a stepwise manner, leading us to propose a model in which rapamycin inhibits mTORC1-mediated phosphorylation of 4E-BP1 and S6K1 through different mechanisms.
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Affiliation(s)
- Calvin K Yip
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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Kaizuka T, Hara T, Oshiro N, Kikkawa U, Yonezawa K, Takehana K, Iemura SI, Natsume T, Mizushima N. Tti1 and Tel2 are critical factors in mammalian target of rapamycin complex assembly. J Biol Chem 2010; 285:20109-16. [PMID: 20427287 DOI: 10.1074/jbc.m110.121699] [Citation(s) in RCA: 187] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Mammalian target of rapamycin (mTOR) is a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family and is a major regulator of translation, cell growth, and autophagy. mTOR exists in two distinct complexes, mTORC1 and mTORC2, that differ in their subunit composition. In this study, we identified KIAA0406 as a novel mTOR-interacting protein. Because it has sequence homology with Schizosaccharomyces pombe Tti1, we named it mammalian Tti1. Tti1 constitutively interacts with mTOR in both mTORC1 and mTORC2. Knockdown of Tti1 suppresses phosphorylation of both mTORC1 substrates (S6K1 and 4E-BP1) and an mTORC2 substrate (Akt) and also induces autophagy. S. pombe Tti1 binds to Tel2, a protein whose mammalian homolog was recently reported to regulate the stability of PIKKs. We confirmed that Tti1 binds to Tel2 also in mammalian cells, and Tti1 interacts with and stabilizes all six members of the PIKK family of proteins (mTOR, ATM, ATR, DNA-PKcs, SMG-1, and TRRAP). Furthermore, using immunoprecipitation and size-exclusion chromatography analyses, we found that knockdown of either Tti1 or Tel2 causes disassembly of mTORC1 and mTORC2. These results indicate that Tti1 and Tel2 are important not only for mTOR stability but also for assembly of the mTOR complexes to maintain their activities.
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Affiliation(s)
- Takeshi Kaizuka
- Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
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The sensing of essential amino acid deficiency in the anterior piriform cortex, that requires the uncharged tRNA/GCN2 pathway, is sensitive to wortmannin but not rapamycin. Pharmacol Biochem Behav 2009; 94:333-40. [PMID: 19800362 DOI: 10.1016/j.pbb.2009.09.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Revised: 09/11/2009] [Accepted: 09/21/2009] [Indexed: 01/20/2023]
Abstract
Animals detect and reject their first essential/indispensable amino acid (IAA) deficient meal within 20min; this IAA sensing requires an intact anterior piriform cortex (APC). In the biochemical responses to IAA deficiency in the APC we have shown that: uncharged tRNA is the primary sensor; IAA transport is increased; and signaling, including the extracellular-regulated kinase (ERK1/2), is activated. The mammalian target of rapamycin (mTOR) is a potential AA sensor and is regulated by AA transport. Previously, the inhibitors, rapamycin for mTOR, wortmannin for phosphoinositide 3 kinase (PI3K) and PD98059 for ERK, each blocked the upregulation of the System A transporter in IAA depleted APC neurons. Here we injected these same inhibitors into the APC and measured intake of an IAA deficient diet. Rapamycin had no effect on the rejection of the IAA deficient diet, but wortmannin increased ERK activation and intake of the deficient diet before 40min and PD98059 acted after 40min to increase the second meal. While the specific wortmannin target involved in blocking the behavioral response remains unclear, we conclude that mTOR is dispensable for sensing IAA deficiency in the APC, and that ERK is associated with the secondary learned responses to IAA deficient diets.
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Panasyuk G, Nemazanyy I, Zhyvoloup A, Filonenko V, Davies D, Robson M, Pedley RB, Waterfield M, Gout I. mTORbeta splicing isoform promotes cell proliferation and tumorigenesis. J Biol Chem 2009; 284:30807-14. [PMID: 19726679 DOI: 10.1074/jbc.m109.056085] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mTOR (mammalian target of rapamycin) promotes growth in response to nutrients and growth factors and is deregulated in numerous pathologies, including cancer. The mechanisms by which mTOR senses and regulates energy metabolism and cell growth are relatively well understood, whereas the molecular events underlining how it mediates survival and proliferation remain to be elucidated. Here, we describe the existence of the mTOR splicing isoform, TOR beta, which, in contrast to the full-length protein (mTOR alpha), has the potential to regulate the G(1) phase of the cell cycle and to stimulate cell proliferation. mTOR beta is an active protein kinase that mediates downstream signaling through complexing with Rictor and Raptor proteins. Remarkably, overexpression of mTOR beta transforms immortal cells and is tumorigenic in nude mice and therefore could be a proto-oncogene.
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Affiliation(s)
- Ganna Panasyuk
- Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, Kyiv-143, Ukraine
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Maehama T, Tanaka M, Nishina H, Murakami M, Kanaho Y, Hanada K. RalA functions as an indispensable signal mediator for the nutrient-sensing system. J Biol Chem 2008; 283:35053-9. [PMID: 18948269 DOI: 10.1074/jbc.m805822200] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Cells sense nutrients present in the extracellular environment and modulate the activities of intracellular signaling systems in response to nutrient availability. This study demonstrates that RalA and its activator RalGDS participate in nutrient sensing and are indispensable for activation of mammalian target of rapamycin complex 1 (mTORC1) induced by extracellular nutrients. Knockdown of RalA or RalGDS abolished amino acid- and glucose-induced mTORC1 activation, as judged by phosphorylation of S6 kinase and eukaryotic translation initiation factor 4E-binding protein 1. The amount of GTP-bound RalA increased in response to increased amino acid availability. In addition, RalA knockdown suppressed Rheb-induced S6 kinase phosphorylation, and the constitutively active form of RalA induced mTORC1 activation in the absence of Rheb. These results collectively suggest that RalGDS and RalA act downstream of Rheb and that RalA activation is a crucial step in nutrient-induced mTORC1 activation.
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Affiliation(s)
- Tomohiko Maehama
- Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Tokyo 162-8640, Japan.
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Ohne Y, Takahara T, Hatakeyama R, Matsuzaki T, Noda M, Mizushima N, Maeda T. Isolation of hyperactive mutants of mammalian target of rapamycin. J Biol Chem 2008; 283:31861-70. [PMID: 18812319 DOI: 10.1074/jbc.m801546200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The mammalian target of rapamycin (mTOR) is a Ser/Thr kinase that plays essential roles in the regulation of a wide array of growth-related processes such as protein synthesis, cell sizing, and autophagy. mTOR forms two functionally distinct complexes, termed the mTOR complex 1 (mTORC1) and 2 (mTORC2); only the former of which is inhibited by rapamycin. Based on the similarity between the cellular responses caused by rapamycin treatment and by nutrient starvation, it has been widely accepted that modulation in the mTORC1 activity in response to nutrient status directs these cellular responses, although direct evidence has been scarce. Here we report isolation of hyperactive mutants of mTOR. The isolated mTOR mutants exhibited enhanced kinase activity in vitro and rendered cells refractory to the dephosphorylation of the mTORC1 substrates upon amino acid starvation. Cells expressing the hyperactive mTOR mutant displayed larger cell size in a normal growing condition and were resistant to cell size reduction and autophagy induction in an amino acid-starved condition. These results indicate that the activity of mTORC1 actually directs these cellular processes in response to nutrient status and confirm the biological functions of mTORC1, which had been proposed solely from loss-of-function analyses using rapamycin and (molecular)genetic techniques. Additionally, the hyperactive mTOR mutant did not induce cellular transformation of NIH/3T3 cells, suggesting that concomitant activation of additional pathways is required for tumorigenesis. This hyperactive mTOR mutant will be a valuable tool for establishing physiological consequences of mTOR activation in cells as well as in organisms.
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Affiliation(s)
- Yoichiro Ohne
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Tokyo 113-0032, Japan
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Abstract
The target of rapamycin (TOR) is a protein kinase with numerous functions in cell growth control. Some of these functions can be potently inhibited by rapamycin, an immunosuppressive and potential anticancer drug. TOR exists as part of two functionally distinct protein complexes. The functions of TOR complex 1 (TORC1) are effectively inhibited by rapamycin, but the mechanism for this inhibition remains elusive. The identification of TORC2 and recent reports that rapamycin can inhibit TORC2 functions, in some cases, challenge current models of TOR regulation. This review discusses the latest findings in yeast and mammals on the possible mechanisms that control TOR activity leading to its many cellular functions
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Affiliation(s)
- Estela Jacinto
- Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
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Sato T, Umetsu A, Tamanoi F. Characterization of the Rheb-mTOR signaling pathway in mammalian cells: constitutive active mutants of Rheb and mTOR. Methods Enzymol 2008; 438:307-20. [PMID: 18413257 DOI: 10.1016/s0076-6879(07)38021-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Rheb (Ras homolog enriched in brain) is a GTPase conserved from yeast to human and belongs to a unique family within the Ras superfamily of GTPases. Rheb plays critical roles in the activation of mTOR, a serine/threonine kinase that is involved in the activation of protein synthesis and growth. mTOR forms two distinct complexes, mTORC1 and mTORC2. While mTORC1 is implicated in the regulation of cell growth, proliferation, and cell size in response to amino acids and growth factors, mTORC2 is involved in actin organization. However, the mechanism of activation is not fully understood. Therefore, studies to elucidate the Rheb-mTOR signaling pathway are of great importance. Here we describe methods to characterize this pathway and to evaluate constitutive active mutants of Rheb and mTOR that we recently identified. Constitutive activity of the mutants can be demonstrated by the phosphorylation of ribosomal protein S6 kinase 1 (S6K1) and eIF4E-binding protein 1 (4E-BP1) both in vivo and in vitro after starving cells for amino acids and growth factors. In addition, formation and activity of mTORC1 and mTORC2 can be measured by immunoprecipitating these complexes and carrying out in vitro kinase assays. We also describe a protocol for rapamycin treatment, which directly inhibits mTOR and can be used to investigate the mTOR signaling pathway in cell growth, cell size, etc.
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Affiliation(s)
- Tatsuhiro Sato
- Department of Microbiology, Immunology and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California, Los Angeles, California, USA
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