751
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Parks SK, Cormerais Y, Pouysségur J. Hypoxia and cellular metabolism in tumour pathophysiology. J Physiol 2017; 595:2439-2450. [PMID: 28074546 DOI: 10.1113/jp273309] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 12/01/2016] [Indexed: 12/17/2022] Open
Abstract
Cancer cells are optimised for growth and survival via an ability to outcompete normal cells in their microenvironment. Many of these advantageous cellular adaptations are promoted by the pathophysiological hypoxia that arises in solid tumours due to incomplete vascularisation. Tumour cells are thus faced with the challenge of an increased need for nutrients to support the drive for proliferation in the face of a diminished extracellular supply. Among the many modifications occurring in tumour cells, hypoxia inducible factors (HIFs) act as essential drivers of key pro-survival pathways via the promotion of numerous membrane and cytosolic proteins. Here we focus our attention on two areas: the role of amino acid uptake and the handling of metabolic acid (CO2 /H+ ) production. We provide evidence for a number of hypoxia-induced proteins that promote cellular anabolism and regulation of metabolic acid-base levels in tumour cells including amino-acid transporters (LAT1), monocarboxylate transporters, and acid-base regulating carbonic anhydrases (CAs) and bicarbonate transporters (NBCs). Emphasis is placed on current work manipulating multiple CA isoforms and NBCs, which is at an interesting crossroads of gas physiology as they are regulated by hypoxia to contribute to the cellular handling of CO2 and pHi regulation. Our research combined with others indicates that targeting of HIF-regulated membrane proteins in tumour cells will provide promising future anti-cancer therapeutic approaches and we suggest strategies that could be potentially used to enhance these tactics.
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Affiliation(s)
- Scott K Parks
- Medical Biology Department, Centre Scientifique de Monaco, 8 Quai Antoine 1er, MC-98000, Monaco, Principality of Monaco
| | - Yann Cormerais
- Medical Biology Department, Centre Scientifique de Monaco, 8 Quai Antoine 1er, MC-98000, Monaco, Principality of Monaco
| | - Jacques Pouysségur
- Medical Biology Department, Centre Scientifique de Monaco, 8 Quai Antoine 1er, MC-98000, Monaco, Principality of Monaco.,Institute for Research on Cancer and Aging (IRCAN), CNRS, INSERM, Centre A. Lacassagne, University of Nice-Sophia Antipolis, Nice, France
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752
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Peng M, Yin N, Li MO. SZT2 dictates GATOR control of mTORC1 signalling. Nature 2017; 543:433-437. [PMID: 28199315 DOI: 10.1038/nature21378] [Citation(s) in RCA: 122] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 12/22/2016] [Indexed: 12/28/2022]
Abstract
Mechanistic target of rapamycin complex 1 (TORC1) integrates nutrient signals to control cell growth and organismal homeostasis across eukaryotes. The evolutionarily conserved GATOR complex regulates mTORC1 signalling through Rag GTPases, and GATOR1 displays GTPase activating protein (GAP) activity for RAGA and RAGB (RAGA/B) and GATOR2 has been proposed to be an inhibitor of GATOR1. Furthermore, the metazoan-specific SESN proteins function as guanine nucleotide dissociation inhibitors (GDIs) for RAGA/B, and interact with GATOR2 with unknown effects. Here we show that SZT2 (seizure threshold 2), a metazoan-specific protein mutated in epilepsy, recruits a fraction of mammalian GATOR1 and GATOR2 to form a SZT2-orchestrated GATOR (SOG) complex with an essential role in GATOR- and SESN-dependent nutrient sensing and mTORC1 regulation. The interaction of SZT2 with GATOR1 and GATOR2 was synergistic, and an intact SOG complex was required for its localization at the lysosome. SZT2 deficiency resulted in constitutive mTORC1 signalling in cells under nutrient-deprived conditions and neonatal lethality in mice, which was associated with failure to inactivate mTORC1 during fasting. Hyperactivation of mTORC1 in SZT2-deficient cells could be partially corrected by overexpression of the GATOR1 component DEPDC5, and by the lysosome-targeted GATOR2 component WDR59 or lysosome-targeted SESN2. These findings demonstrate that SZT2 has a central role in dictating GATOR-dependent nutrient sensing by promoting lysosomal localization of SOG, and reveal an unexpected function of lysosome-located GATOR2 in suppressing mTORC1 signalling through SESN recruitment.
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Affiliation(s)
- Min Peng
- Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
| | - Na Yin
- Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
| | - Ming O Li
- Immunology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
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753
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Maynard TM, Manzini MC. Balancing Act: Maintaining Amino Acid Levels in the Autistic Brain. Neuron 2017; 93:476-479. [DOI: 10.1016/j.neuron.2017.01.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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754
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Phillips SM, Dickerson RN, Moore FA, Paddon-Jones D, Weijs PJM. Protein Turnover and Metabolism in the Elderly Intensive Care Unit Patient. Nutr Clin Pract 2017; 32:112S-120S. [PMID: 28388378 DOI: 10.1177/0884533616686719] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Many intensive care unit (ICU) patients do not achieve target protein intakes particularly in the early days following admittance. This period of iatrogenic protein undernutrition contributes to a rapid loss of lean, in particular muscle, mass in the ICU. The loss of muscle in older (aged >60 years) patients in the ICU may be particularly rapid due to a perfect storm of increased catabolic factors, including systemic inflammation, disuse, protein malnutrition, and reduced anabolic stimuli. This loss of muscle mass has marked consequences. It is likely that the older patient is already experiencing muscle loss due to sarcopenia; however, the period of stay in the ICU represents a greatly accelerated period of muscle loss. Thus, on discharge, the older ICU patient is now on a steeper downward trajectory of muscle loss, more likely to have ICU-acquired muscle weakness, and at risk of becoming sarcopenic and/or frail. One practice that has been shown to have benefit during ICU stays is early ambulation and physical therapy (PT), and it is likely that both are potent stimuli to induce a sensitivity of protein anabolism. Thus, recommendations for the older ICU patient would be provision of at least 1.2-1.5 g protein/kg usual body weight/d, regular and early utilization of ambulation (if possible) and/or PT, and follow-up rehabilitation for the older discharged ICU patient that includes rehabilitation, physical activity, and higher habitual dietary protein to change the trajectory of ICU-mediated muscle mass loss and weakness.
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Affiliation(s)
- Stuart M Phillips
- 1 McMaster University, Department of Kinesiology, Hamilton, Ontario, Canada
| | - Roland N Dickerson
- 2 Department of Clinical Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee, USA
| | - Frederick A Moore
- 3 Department of Surgery, Division of Acute Care Surgery, and Center for Sepsis and Critical Illness Research, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Douglas Paddon-Jones
- 4 Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas, USA
| | - Peter J M Weijs
- 5 Nutrition and Dietetics, Department of Internal Medicine, Department of Intensive Care Medicine, and Amsterdam Public Health Research Institute, VU University Medical Center, Amsterdam, The Netherlands.,6 Nutrition and Dietetics, Faculty of Sports and Nutrition, Amsterdam University of Applied Sciences, Amsterdam, The Netherlands
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755
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Kissing S, Rudnik S, Damme M, Lüllmann-Rauch R, Ichihara A, Kornak U, Eskelinen EL, Jabs S, Heeren J, De Brabander JK, Haas A, Saftig P. Disruption of the vacuolar-type H +-ATPase complex in liver causes MTORC1-independent accumulation of autophagic vacuoles and lysosomes. Autophagy 2017; 13:670-685. [PMID: 28129027 DOI: 10.1080/15548627.2017.1280216] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The vacuolar-type H+-translocating ATPase (v-H+-ATPase) has been implicated in the amino acid-dependent activation of the mechanistic target of rapamycin complex 1 (MTORC1), an important regulator of macroautophagy. To reveal the mechanistic links between the v-H+-ATPase and MTORC1, we destablilized v-H+-ATPase complexes in mouse liver cells by induced deletion of the essential chaperone ATP6AP2. ATP6AP2-mutants are characterized by massive accumulation of endocytic and autophagic vacuoles in hepatocytes. This cellular phenotype was not caused by a block in endocytic maturation or an impaired acidification. However, the degradation of LC3-II in the knockout hepatocytes appeared to be reduced. When v-H+-ATPase levels were decreased, we observed lysosome association of MTOR and normal signaling of MTORC1 despite an increase in autophagic marker proteins. To better understand why MTORC1 can be active when v-H+-ATPase is depleted, the activation of MTORC1 was analyzed in ATP6AP2-deficient fibroblasts. In these cells, very little amino acid-elicited activation of MTORC1 was observed. In contrast, insulin did induce MTORC1 activation, which still required intracellular amino acid stores. These results suggest that in vivo the regulation of macroautophagy depends not only on v-H+-ATPase-mediated regulation of MTORC1.
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Affiliation(s)
- Sandra Kissing
- a Institut für Biochemie, Christian-Albrechts-Universität zu Kiel , Germany
| | - Sönke Rudnik
- a Institut für Biochemie, Christian-Albrechts-Universität zu Kiel , Germany
| | - Markus Damme
- a Institut für Biochemie, Christian-Albrechts-Universität zu Kiel , Germany
| | | | - Atsuhiro Ichihara
- c Department of Medicine II , Tokyo Women´s Medical University , Japan
| | - Uwe Kornak
- d Institut für Medizinische Genetik und Humangenetik, Charité-Universitaetsmedizin , Berlin , Germany
| | - Eeva-Liisa Eskelinen
- e Department of Biosciences , Division of Biochemistry and Biotechnology, University of Helsinki , Finland
| | - Sabrina Jabs
- f Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC) , Berlin , Germany
| | - Jörg Heeren
- g Institut für Biochemie und Molekulare Zellbiologie, Zentrum für Experimentelle Medizin, Universitätsklinikum Hamburg-Eppendorf , Germany
| | - Jef K De Brabander
- h Department of Biochemistry , University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Albert Haas
- i Institut für Zellbiologie, Friedrich-Wilhelms Universität Bonn , Germany
| | - Paul Saftig
- a Institut für Biochemie, Christian-Albrechts-Universität zu Kiel , Germany
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756
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González A, Hall MN. Nutrient sensing and TOR signaling in yeast and mammals. EMBO J 2017; 36:397-408. [PMID: 28096180 DOI: 10.15252/embj.201696010] [Citation(s) in RCA: 485] [Impact Index Per Article: 69.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 12/12/2016] [Accepted: 12/15/2016] [Indexed: 01/13/2023] Open
Abstract
Coordinating cell growth with nutrient availability is critical for cell survival. The evolutionarily conserved TOR (target of rapamycin) controls cell growth in response to nutrients, in particular amino acids. As a central controller of cell growth, mTOR (mammalian TOR) is implicated in several disorders, including cancer, obesity, and diabetes. Here, we review how nutrient availability is sensed and transduced to TOR in budding yeast and mammals. A better understanding of how nutrient availability is transduced to TOR may allow novel strategies in the treatment for mTOR-related diseases.
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757
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Hayashi K, Anzai N. Novel therapeutic approaches targeting L-type amino acid transporters for cancer treatment. World J Gastrointest Oncol 2017; 9:21-29. [PMID: 28144396 PMCID: PMC5241523 DOI: 10.4251/wjgo.v9.i1.21] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 10/08/2016] [Accepted: 11/02/2016] [Indexed: 02/05/2023] Open
Abstract
L-type amino acid transporters (LATs) mainly assist the uptake of neutral amino acids into cells. Four LATs (LAT1, LAT2, LAT3 and LAT4) have so far been identified. LAT1 (SLC7A5) has been attracting much attention in the field of cancer research since it is commonly up-regulated in various cancers. Basic research has made it increasingly clear that LAT1 plays a predominant role in malignancy. The functional significance of LAT1 in cancer and the potential therapeutic application of the features of LAT1 to cancer management are described in this review.
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758
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Kamada Y. Novel tRNA function in amino acid sensing of yeast Tor complex1. Genes Cells 2017; 22:135-147. [DOI: 10.1111/gtc.12462] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Accepted: 11/24/2016] [Indexed: 12/20/2022]
Affiliation(s)
- Yoshiaki Kamada
- Laboratory of Biological Diversity; National Institute for Basic Biology; Okazaki 444-8585 Japan
- Department of Basic Biology; School of Life Science; The Graduate University for Advanced Studies (SOKENDAI); Okazaki 444-8585 Japan
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759
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Ishikawa T, Kitaura Y, Kadota Y, Morishita Y, Ota M, Yamanaka F, Xu M, Ikawa M, Inoue N, Kawano F, Nakai N, Murakami T, Miura S, Hatazawa Y, Kamei Y, Shimomura Y. Muscle-specific deletion of BDK amplifies loss of myofibrillar protein during protein undernutrition. Sci Rep 2017; 7:39825. [PMID: 28051178 PMCID: PMC5209746 DOI: 10.1038/srep39825] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 11/28/2016] [Indexed: 12/30/2022] Open
Abstract
Branched-chain amino acids (BCAAs) are essential amino acids for mammals and play key roles in the regulation of protein metabolism. However, the effect of BCAA deficiency on protein metabolism in skeletal muscle in vivo remains unclear. Here we generated mice with lower BCAA concentrations by specifically accelerating BCAA catabolism in skeletal muscle and heart (BDK-mKO mice). The mice appeared to be healthy without any obvious defects when fed a protein-rich diet; however, bolus ingestion of BCAAs showed that mTORC1 sensitivity in skeletal muscle was enhanced in BDK-mKO mice compared to the corresponding control mice. When these mice were fed a low protein diet, the concentration of myofibrillar protein was significantly decreased (but not soluble protein) and mTORC1 activity was reduced without significant change in autophagy. BCAA supplementation in drinking water attenuated the decreases in myofibrillar protein levels and mTORC1 activity. These results suggest that BCAAs are essential for maintaining myofibrillar proteins during protein undernutrition by keeping mTORC1 activity rather than by inhibiting autophagy and translation. This is the first report to reveal the importance of BCAAs for protein metabolism of skeletal muscle in vivo.
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Affiliation(s)
- Takuya Ishikawa
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Yasuyuki Kitaura
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Yoshihiro Kadota
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Yukako Morishita
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Miki Ota
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Fumiya Yamanaka
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Minjun Xu
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Masahito Ikawa
- Animal Resource Center for Infectious Diseases, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Naokazu Inoue
- Department of Experimental Genome Research, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Fuminori Kawano
- Graduate School of Health Sciences, Matsumoto University, Matsumoto, Nagano, Japan
| | - Naoya Nakai
- School of Human Cultures, University of Shiga Prefecture, Hikone, Shiga, Japan
| | - Taro Murakami
- Department of Nutrition, Shigakkan University, Obu, Aichi, Japan
| | - Shinji Miura
- Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan
| | - Yukino Hatazawa
- Graduate School of Environmental and Life Science, Kyoto Prefectural University, Kyoto, Japan
| | - Yasutomi Kamei
- Graduate School of Environmental and Life Science, Kyoto Prefectural University, Kyoto, Japan
| | - Yoshiharu Shimomura
- Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
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760
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Abstract
Signaling breakthroughs of 2016 clustered mainly in the areas of neuroscience, immunology, and metabolism, with excursions into plant hormone signaling and bacterial manipulation of host signaling pathways. Perhaps reflecting the growing maturity of the discipline of cell signaling, many of this year's breakthroughs have implications for the pathogenesis or treatment of human disease.
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761
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Abstract
Mammalian/mechanistic target of rapamycin (mTOR) is an evolutionarily conserved genuine protein kinase, which phosphorylates serine/threonine in response to growth factors and nutrients. It functions as a catalytic core in two distinct multiprotein complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 promotes cell growth and proliferation by positively regulating translation, transcription, and lipid biosynthesis in response to growth factors and amino acids, whereas it inhibits autophagy, an essential degradation and recycling pathway. mTORC2 regulates cell survival and cytoskeleton organization. Mechanistic insights into the function and regulation of mTOR complexes have been provided in various experimental settings and monitoring mTOR activity has been a most valuable way to judge whether levels of environmental cues such nutrients and growth factors can satisfy cellular needs for cell growth, proliferation, and autophagic response. Here, we describe useful methods to access mTOR activity in different experimental settings.
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Affiliation(s)
- S Hong
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, United States
| | - K Inoki
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, United States; University of Michigan Medical School, Ann Arbor, MI, United States.
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762
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Gai Z, Wang Q, Yang C, Wang L, Deng W, Wu G. Structural mechanism for the arginine sensing and regulation of CASTOR1 in the mTORC1 signaling pathway. Cell Discov 2016; 2:16051. [PMID: 28066558 PMCID: PMC5187391 DOI: 10.1038/celldisc.2016.51] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 12/12/2016] [Indexed: 12/12/2022] Open
Abstract
The mTOR complex I (mTORC1) signaling pathway controls many metabolic processes and is regulated by amino acid signals, especially arginine. CASTOR1 has been identified as the cytosolic arginine sensor for the mTORC1 pathway, but the molecular mechanism of how it senses arginine is elusive. Here, by determining the crystal structure of human CASTOR1 in complex with arginine, we found that an exquisitely tailored pocket, carved between the NTD and the CTD domains of CASTOR1, is employed to recognize arginine. Mutation of critical residues in this pocket abolished or diminished arginine binding. By comparison with structurally similar aspartate kinases, a surface patch of CASTOR1-NTD on the opposite side of the arginine-binding site was identified to mediate direct physical interaction with its downstream effector GATOR2, via GATOR2 subunit Mios. Mutation of this surface patch disrupted CASTOR1’s recognition and inhibition of GATOR2, revealed by in vitro pull-down assay. Normal mode (NM) analysis revealed an ‘open’-to-‘closed’ conformational change for CASTOR1, which is correlated to the switching between the exposing and concealing of its GATOR2-binding residues, and is most likely related to arginine binding. Interestingly, the GATOR2-binding sites on the two protomers of CASTOR1 dimer face the same direction, which prompted us to propose a model for how dimerization of CASTOR1 relieves the inhibition of GATOR1 by GATOR2. Our study thus provides a thorough analysis on how CASTOR1 recognizes arginine, and describes a possible mechanism of how arginine binding induces the inter-domain movement of CASTOR1 to affect its association with GATOR2.
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Affiliation(s)
- Zhongchao Gai
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University , Shanghai, China
| | - Qian Wang
- National Center for Protein Science Shanghai , Shanghai, China
| | - Can Yang
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University , Shanghai, China
| | - Lei Wang
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University , Shanghai, China
| | - Wei Deng
- National Center for Protein Science Shanghai , Shanghai, China
| | - Geng Wu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University , Shanghai, China
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763
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De Bandt JP. Leucine and Mammalian Target of Rapamycin-Dependent Activation of Muscle Protein Synthesis in Aging. J Nutr 2016; 146:2616S-2624S. [PMID: 27934653 DOI: 10.3945/jn.116.234518] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 05/11/2016] [Accepted: 06/15/2016] [Indexed: 12/17/2022] Open
Abstract
The preservation or restoration of muscle mass is of prime importance for healthy aging. However, aging has been repeatedly shown to be associated with resistance of muscle to the anabolic effects of feeding. Leucine supplementation has been proposed as a possible strategy because of its regulatory role on protein homeostasis. Indeed, it acts independently of growth factors and leads to enhanced cap-dependent mRNA translation initiation and increased protein synthesis. Leucine acts as a signaling molecule directly at the muscle level via the activation of mammalian/mechanistic target of rapamycin complex 1 (mTORC1). However, in aged muscle, mTORC1 activation seems to be impaired, with decreased sensitivity and responsiveness of muscle protein synthesis to amino acids, whereas the phosphorylation state of several components of this signaling pathway appears to be higher in the basal state. This may stem from specific age-related impairment of muscle signaling and from decreased nutrient and growth factor delivery to the muscle. Whether aging per se affects mTORC1 signaling remains to be established, because aging is frequently associated with inadequate protein intake, decreased insulin sensitivity, inactivity, inflammatory processes, etc. Whatever its origin, this anabolic resistance to feeding can be mitigated by quantitative and qualitative manipulation of protein supply, such as leucine supplementation; however, there remains the question of possible adverse effects of long-term, high-dose leucine supplementation in terms of insulin resistance and tumorigenesis.
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Affiliation(s)
- Jean-Pascal De Bandt
- EA4466 PRETRAM, Nutrition Biology Laboratory, Faculty of Pharmacy, Paris Descartes University, Sorbonne Paris Cité, Paris, France
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764
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A systems study reveals concurrent activation of AMPK and mTOR by amino acids. Nat Commun 2016; 7:13254. [PMID: 27869123 PMCID: PMC5121333 DOI: 10.1038/ncomms13254] [Citation(s) in RCA: 95] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 09/13/2016] [Indexed: 12/17/2022] Open
Abstract
Amino acids (aa) are not only building blocks for proteins, but also signalling molecules, with the mammalian target of rapamycin complex 1 (mTORC1) acting as a key mediator. However, little is known about whether aa, independently of mTORC1, activate other kinases of the mTOR signalling network. To delineate aa-stimulated mTOR network dynamics, we here combine a computational–experimental approach with text mining-enhanced quantitative proteomics. We report that AMP-activated protein kinase (AMPK), phosphatidylinositide 3-kinase (PI3K) and mTOR complex 2 (mTORC2) are acutely activated by aa-readdition in an mTORC1-independent manner. AMPK activation by aa is mediated by Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ). In response, AMPK impinges on the autophagy regulators Unc-51-like kinase-1 (ULK1) and c-Jun. AMPK is widely recognized as an mTORC1 antagonist that is activated by starvation. We find that aa acutely activate AMPK concurrently with mTOR. We show that AMPK under aa sufficiency acts to sustain autophagy. This may be required to maintain protein homoeostasis and deliver metabolite intermediates for biosynthetic processes. mTORC1 is known to mediate the signalling activity of amino acids. Here, the authors combine modelling with experiments and find that amino acids acutely stimulate mTORC2, IRS/PI3K and AMPK, independently of mTORC1. AMPK activation through CaMKKβ sustains autophagy under non-starvation conditions.
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765
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Eliopoulos AG, Havaki S, Gorgoulis VG. DNA Damage Response and Autophagy: A Meaningful Partnership. Front Genet 2016; 7:204. [PMID: 27917193 PMCID: PMC5116470 DOI: 10.3389/fgene.2016.00204] [Citation(s) in RCA: 124] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Accepted: 11/02/2016] [Indexed: 01/07/2023] Open
Abstract
Autophagy and the DNA damage response (DDR) are biological processes essential for cellular and organismal homeostasis. Herein, we summarize and discuss emerging evidence linking DDR to autophagy. We highlight published data suggesting that autophagy is activated by DNA damage and is required for several functional outcomes of DDR signaling, including repair of DNA lesions, senescence, cell death, and cytokine secretion. Uncovering the mechanisms by which autophagy and DDR are intertwined provides novel insight into the pathobiology of conditions associated with accumulation of DNA damage, including cancer and aging, and novel concepts for the development of improved therapeutic strategies against these pathologies.
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Affiliation(s)
- Aristides G Eliopoulos
- Molecular and Cellular Biology Laboratory, Division of Basic Sciences, Medical School, University of CreteHeraklion, Greece; Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology HellasHeraklion, Greece
| | - Sophia Havaki
- Molecular Carcinogenesis Group, Department of Histology and Embryology, Medical School, National and Kapodistrian University of Athens Athens, Greece
| | - Vassilis G Gorgoulis
- Molecular Carcinogenesis Group, Department of Histology and Embryology, Medical School, National and Kapodistrian University of AthensAthens, Greece; Faculty Institute of Cancer Sciences, Manchester Academic Health Sciences Centre, University of ManchesterManchester, UK; Biomedical Research Foundation of the Academy of AthensAthens, Greece
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766
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Mlitz V, Gendronneau G, Berlin I, Buchberger M, Eckhart L, Tschachler E. The Expression of the Endogenous mTORC1 Inhibitor Sestrin 2 Is Induced by UVB and Balanced with the Expression Level of Sestrin 1. PLoS One 2016; 11:e0166832. [PMID: 27861561 PMCID: PMC5115827 DOI: 10.1371/journal.pone.0166832] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 11/05/2016] [Indexed: 01/28/2023] Open
Abstract
Sestrin 2 (SESN2) is an evolutionarily conserved regulator of mechanistic target of rapamycin complex 1 (mTORC1) which controls central cellular processes such as protein translation and autophagy. Previous studies have suggested that SESN2 itself is subjected to regulation at multiple levels. Here, we investigated the expression of SESN2 in the skin and in isolated skin cells. SESN2 was detected by immunofluorescence analysis in fibroblasts and keratinocytes of human skin. Differentiation of epidermal keratinocytes was not associated with altered SESN2 expression and siRNA-mediated knockdown of SESN2 did not impair stratum corneum formation in vitro. However, SESN2 was increased in both cell types when the expression of its paralog SESN1 was blocked by siRNA-mediated knock down, indicating a compensatory mechanism for the control of expression. Irradiation with UVB but not with UVA significantly increased SESN2 expression in both keratinocytes and fibroblasts. Upregulation of SESN2 expression could be completely blocked by suppression of p53. These results suggest that SESN2 is dispensable for normal epidermal keratinization but involved in the UVB stress response of skin cells.
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Affiliation(s)
- Veronika Mlitz
- Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria
| | | | - Irina Berlin
- Department of Biology and Women Beauty, Chanel R&T, Pantin, France
| | - Maria Buchberger
- Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria
| | - Leopold Eckhart
- Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria
- * E-mail: (ET); (LE)
| | - Erwin Tschachler
- Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria
- * E-mail: (ET); (LE)
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767
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Moro T, Ebert SM, Adams CM, Rasmussen BB. Amino Acid Sensing in Skeletal Muscle. Trends Endocrinol Metab 2016; 27:796-806. [PMID: 27444066 PMCID: PMC5075248 DOI: 10.1016/j.tem.2016.06.010] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Revised: 06/23/2016] [Accepted: 06/27/2016] [Indexed: 12/19/2022]
Abstract
Aging impairs skeletal muscle protein synthesis, leading to muscle weakness and atrophy. However, the underlying molecular mechanisms remain poorly understood. Here, we review evidence that mammalian/mechanistic target of rapamycin complex 1 (mTORC1)-mediated and activating transcription factor 4 (ATF4)-mediated amino acid (AA) sensing pathways, triggered by impaired AA delivery to aged skeletal muscle, may play important roles in skeletal muscle aging. Interventions that alleviate age-related impairments in muscle protein synthesis, strength, and/or muscle mass appear to do so by reversing age-related changes in skeletal muscle AA delivery, mTORC1 activity, and/or ATF4 activity. An improved understanding of the mechanisms and roles of AA sensing pathways in skeletal muscle may lead to evidence-based strategies to attenuate sarcopenia.
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Affiliation(s)
- Tatiana Moro
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX, USA; Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX, USA
| | - Scott M Ebert
- Department of Internal Medicine, University of Iowa, Iowa City, IA, USA; Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, USA; Iowa City Veterans Affairs Medical Center, Iowa City, IA, USA
| | - Christopher M Adams
- Department of Internal Medicine, University of Iowa, Iowa City, IA, USA; Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, USA; Iowa City Veterans Affairs Medical Center, Iowa City, IA, USA
| | - Blake B Rasmussen
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX, USA; Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX, USA.
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768
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Van de Velde LA, Murray PJ. Proliferating Helper T Cells Require Rictor/mTORC2 Complex to Integrate Signals from Limiting Environmental Amino Acids. J Biol Chem 2016; 291:25815-25822. [PMID: 27799302 DOI: 10.1074/jbc.c116.763623] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Indexed: 11/06/2022] Open
Abstract
Antigen-stimulated T cells require elevated importation of essential and non-essential amino acids to generate large numbers of daughter cells necessary for effective immunity to pathogens. When amino acids are limiting, T cells arrest in the G1 phase of the cell cycle, suggesting that they have specific sensing mechanisms to ensure sufficient amino acids are available for multiple rounds of daughter generation. We found that activation of mTORC1, which is regulated by amino acid amounts, was uncoupled from limiting amino acids in the G1 phase of the cell cycle. Instead, we found that Rictor/mTORC2 has an essential role in T cell amino acid sensing. In the absence of Rictor, CD4+ T cells proliferate normally in limiting arginine or leucine. Our data suggest that Rictor/mTORC2 controls an amino acid-sensitive checkpoint that allows T cells to determine whether the microenvironment contains sufficient resources for daughter cell generation.
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Affiliation(s)
- Lee-Ann Van de Velde
- From the Departments of Infectious Diseases and.,Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Peter J Murray
- From the Departments of Infectious Diseases and .,Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
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769
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Khayati K, Antikainen H, Bonder EM, Weber GF, Kruger WD, Jakubowski H, Dobrowolski R. The amino acid metabolite homocysteine activates mTORC1 to inhibit autophagy and form abnormal proteins in human neurons and mice. FASEB J 2016; 31:598-609. [PMID: 28148781 DOI: 10.1096/fj.201600915r] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 10/11/2016] [Indexed: 11/11/2022]
Abstract
The molecular mechanisms leading to and responsible for age-related, sporadic Alzheimer's disease (AD) remain largely unknown. It is well documented that aging patients with elevated levels of the amino acid metabolite homocysteine (Hcy) are at high risk of developing AD. We investigated the impact of Hcy on molecular clearance pathways in mammalian cells, including in vitro cultured induced pluripotent stem cell-derived forebrain neurons and in vivo neurons in mouse brains. Exposure to Hcy resulted in up-regulation of the mechanistic target of rapamycin complex 1 (mTORC1) activity, one of the major kinases in cells that is tightly linked to anabolic and catabolic pathways. Hcy is sensed by a constitutive protein complex composed of leucyl-tRNA-synthetase and folliculin, which regulates mTOR tethering to lysosomal membranes. In hyperhomocysteinemic human cells and cystathionine β-synthase-deficient mouse brains, we find an acute and chronic inhibition of the molecular clearance of protein products resulting in a buildup of abnormal proteins, including β-amyloid and phospho-Tau. Formation of these protein aggregates leads to AD-like neurodegeneration. This pathology can be prevented by inhibition of mTORC1 or by induction of autophagy. We conclude that an increase of intracellular Hcy levels predisposes neurons to develop abnormal protein aggregates, which are hallmarks of AD and its associated onset and pathophysiology with age.-Khayati, K., Antikainen, H., Bonder, E. M., Weber, G. F., Kruger, W. D., Jakubowski, H., Dobrowolski, R. The amino acid metabolite homocysteine activates mTORC1 to inhibit autophagy and form abnormal proteins in human neurons and mice.
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Affiliation(s)
- Khoosheh Khayati
- Federated Department of Biological Sciences, Rutgers University/New Jersey Institute of Technology, Newark, New Jersey, USA
| | - Henri Antikainen
- Federated Department of Biological Sciences, Rutgers University/New Jersey Institute of Technology, Newark, New Jersey, USA
| | - Edward M Bonder
- Federated Department of Biological Sciences, Rutgers University/New Jersey Institute of Technology, Newark, New Jersey, USA
| | - Gregory F Weber
- Federated Department of Biological Sciences, Rutgers University/New Jersey Institute of Technology, Newark, New Jersey, USA
| | | | - Hieronim Jakubowski
- Department of Microbiology, Biochemistry, and Molecular Genetics, International Center for Public Health, Rutgers-New Jersey Medical School, Newark, New Jersey, USA.,Institute of Bioorganic Chemistry, Poznań, Poland; and.,Department of Biochemistry and Biotechnology, University of Life Sciences, Poznań, Poland
| | - Radek Dobrowolski
- Federated Department of Biological Sciences, Rutgers University/New Jersey Institute of Technology, Newark, New Jersey, USA;
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770
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Abstract
Lysosomes (or lytic bodies) were so named because they contain high levels of hydrolytic enzymes. Lysosome function and dysfunction have been found to play important roles in human disease, including cancer; however, the ways in which lysosomes contribute to tumorigenesis and cancer progression are still being uncovered. Beyond serving as a cellular recycling center, recent evidence suggests that the lysosome is involved in energy homeostasis, generating building blocks for cell growth, mitogenic signaling, priming tissues for angiogenesis and metastasis formation, and activating transcriptional programs. This review examines emerging knowledge of how lysosomal processes contribute to the hallmarks of cancer and highlights vulnerabilities that might be exploited for cancer therapy.
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Affiliation(s)
- Shawn M Davidson
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; , .,Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Matthew G Vander Heiden
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; , .,Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.,Dana-Farber Cancer Institute, Boston, Massachusetts 02215
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771
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Manifava M, Smith M, Rotondo S, Walker S, Niewczas I, Zoncu R, Clark J, Ktistakis NT. Dynamics of mTORC1 activation in response to amino acids. eLife 2016; 5. [PMID: 27725083 PMCID: PMC5059141 DOI: 10.7554/elife.19960] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2016] [Accepted: 09/07/2016] [Indexed: 12/12/2022] Open
Abstract
Amino acids are essential activators of mTORC1 via a complex containing RAG GTPases, RAGULATOR and the vacuolar ATPase. Sensing of amino acids causes translocation of mTORC1 to lysosomes, an obligate step for activation. To examine the spatial and temporal dynamics of this translocation, we used live imaging of the mTORC1 component RAPTOR and a cell permeant fluorescent analogue of di-leucine methyl ester. Translocation to lysosomes is a transient event, occurring within 2 min of aa addition and peaking within 5 min. It is temporally coupled with fluorescent leucine appearance in lysosomes and is sustained in comparison to aa stimulation. Sestrin2 and the vacuolar ATPase are negative and positive regulators of mTORC1 activity in our experimental system. Of note, phosphorylation of canonical mTORC1 targets is delayed compared to lysosomal translocation suggesting a dynamic and transient passage of mTORC1 from the lysosomal surface before targetting its substrates elsewhere. DOI:http://dx.doi.org/10.7554/eLife.19960.001 Cells in all organisms must constantly measure the amount of nutrients available to them in order to be healthy and grow properly. For example, cells use a complex sensing system to measure how many amino acids – the building blocks of proteins – are available to them. One enzyme called mTOR alerts the cell to amino acid levels. When amino acids are available, mTOR springs into action and turns on the production of proteins in the cell. However, when amino acids are scarce, mTOR turns off, which slows down protein production and causes the cell to begin scavenging amino acids by digesting parts of itself. Studies of mTOR have shown that the protein cannot turn on until it visits the surface of small sacks in the cell called lysosomes. These are the major sites within cell where proteins and other molecules are broken down. Scientists know how mTOR gets to the lysosomes, but not how quickly the process occurs. Now, Manifava, Smith et al. have used microscopes to record live video of the mTOR enzyme as it interacts with amino acids revealing the whole process takes place in just a few minutes. In the experiments, a fluorescent tag was added to part of mTOR to make the protein visible under a microscope. The video showed that, in human cells supplied with amino acids, mTOR reaches the lysosomes within 2 minutes of the amino acids becoming available. Then, within 3-4 minutes the mTOR turns on and leaves the lysosome. Even though the mTOR has left the lysosome, it somehow remembers that amino acids are available and stays active. The experiments show that mTOR’s brief interaction with the lysosome switches it on and keeps it on even after mTOR leaves. Future studies will be needed to determine exactly how mTOR remembers its interaction with the lysosome and stays active afterwards. DOI:http://dx.doi.org/10.7554/eLife.19960.002
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Affiliation(s)
- Maria Manifava
- Signalling Programme, Babraham Institute, Cambridge, United Kingdom
| | - Matthew Smith
- Signalling Programme, Babraham Institute, Cambridge, United Kingdom
| | - Sergio Rotondo
- Signalling Programme, Babraham Institute, Cambridge, United Kingdom
| | - Simon Walker
- Signalling Programme, Babraham Institute, Cambridge, United Kingdom
| | | | - Roberto Zoncu
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Jonathan Clark
- Signalling Programme, Babraham Institute, Cambridge, United Kingdom
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772
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Abstract
The lysosome has long been viewed as the recycling center of the cell. However, recent discoveries have challenged this simple view and have established a central role of the lysosome in nutrient-dependent signal transduction. The degradative role of the lysosome and its newly discovered signaling functions are not in conflict but rather cooperate extensively to mediate fundamental cellular activities such as nutrient sensing, metabolic adaptation, and quality control of proteins and organelles. Moreover, lysosome-based signaling and degradation are subject to reciprocal regulation. Transcriptional programs of increasing complexity control the biogenesis, composition, and abundance of lysosomes and fine-tune their activity to match the evolving needs of the cell. Alterations in these essential activities are, not surprisingly, central to the pathophysiology of an ever-expanding spectrum of conditions, including storage disorders, neurodegenerative diseases, and cancer. Thus, unraveling the functions of this fascinating organelle will contribute to our understanding of the fundamental logic of metabolic organization and will point to novel therapeutic avenues in several human diseases.
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Affiliation(s)
- Rushika M Perera
- Department of Anatomy and Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, California 94143;
| | - Roberto Zoncu
- Department of Molecular and Cellular Biology and Paul F. Glenn Center for Aging Research, University of California, Berkeley, California 94720;
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773
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Roohi A, Hojjat-Farsangi M. Recent advances in targeting mTOR signaling pathway using small molecule inhibitors. J Drug Target 2016; 25:189-201. [PMID: 27632356 DOI: 10.1080/1061186x.2016.1236112] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Targeted-based cancer therapy (TBCT) or personalized medicine is one of the main treatment modalities for cancer that has been developed to decrease the undesirable effects of chemotherapy. Targeted therapy inhibits the growth of tumor cells by interrupting with particular molecules required for tumorigenesis and proliferation of tumor cells rather than interfering with dividing normal cells. Therefore, targeted therapies are anticipated to be more efficient than former tumor treatment agents with minimal side effects on non-tumor cells. Small molecule inhibitors (SMIs) are currently one of the most investigated anti-tumor agents of TBCT. These small organic agents target several vital molecules involved in cell biological processes and induce target cells apoptosis and necrosis. Mechanistic (mammalian) target of rapamycin (mTOR) complexes (mTORC1/2) control different intracellular processes, including growth, proliferation, angiogenesis and metabolism. Signaling pathways, in which mTOR complexes are involved in are usually dysregulated in various tumors and have been shown to be ideal targets for SMIs. Currently, different mTOR-SMIs are in the clinic for the treatment of cancer patients, and several others are in preclinical or clinical settings. In this review, we summarize recent advances in developing different mTOR inhibitors, which are currently in preclinical and clinical investigations or have been approved for cancer treatment.
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Affiliation(s)
- Azam Roohi
- a Department of Immunology, School of Public Health , Tehran University of Medical Sciences , Tehran , Iran
| | - Mohammad Hojjat-Farsangi
- b Department of Oncology-Pathology, Immune and Gene therapy Lab , Cancer Center Karolinska (CCK), Karolinska University Hospital Solna and Karolinska Institute , Stockholm , Sweden.,c Department of Immunology, School of Medicine , Bushehr University of Medical Sciences , Bushehr , Iran
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774
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Kamiński MM, Liedmann S, Milasta S, Green DR. Polarization and asymmetry in T cell metabolism. Semin Immunol 2016; 28:525-534. [DOI: 10.1016/j.smim.2016.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 10/06/2016] [Accepted: 10/06/2016] [Indexed: 12/31/2022]
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775
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Walls J, Sinclair L, Finlay D. Nutrient sensing, signal transduction and immune responses. Semin Immunol 2016; 28:396-407. [DOI: 10.1016/j.smim.2016.09.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Accepted: 09/13/2016] [Indexed: 12/11/2022]
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776
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Brady OA, Diab HI, Puertollano R. Rags to riches: Amino acid sensing by the Rag GTPases in health and disease. Small GTPases 2016; 7:197-206. [PMID: 27580159 PMCID: PMC5129890 DOI: 10.1080/21541248.2016.1218990] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Revised: 07/26/2016] [Accepted: 07/27/2016] [Indexed: 02/06/2023] Open
Abstract
The Rags represent a unique family of evolutionarily conserved, heterodimeric, lysosome-localized small GTPases that play an indispensible role in regulating cellular metabolism in response to various amino acid signaling mechanisms. Rapid progress in the field has begun to unveil a picture in which Rags act as central players in translating information regarding cellular amino acid levels by modulating their nucleotide binding status through an ensemble of support proteins localized in and around the lysosomes. By cooperating with other signaling pathways that converge on the lysosomes, Rags promote anabolic processes through positively affecting mTORC1 signaling in the presence of abundant amino acids. Conversely, Rag inactivation plays an indispensible role in switching cellular metabolism into a catabolic paradigm by promoting the activity of the master lysosomal/autophagic transcription factors TFEB and TFE3. Precise control of Rag signaling is necessary for cells to adapt to constantly changing cellular demands and emerging evidence has highlighted their importance in a wide variety of developmental and pathological conditions.
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Affiliation(s)
- Owen A. Brady
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Heba I. Diab
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Rosa Puertollano
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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777
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Abstract
The resurgence of research into cancer metabolism has recently broadened interests beyond glucose and the Warburg effect to other nutrients, including glutamine. Because oncogenic alterations of metabolism render cancer cells addicted to nutrients, pathways involved in glycolysis or glutaminolysis could be exploited for therapeutic purposes. In this Review, we provide an updated overview of glutamine metabolism and its involvement in tumorigenesis in vitro and in vivo, and explore the recent potential applications of basic science discoveries in the clinical setting.
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Affiliation(s)
- Brian J. Altman
- Abramson Family Cancer Research Institute, Perelman School of
Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Abramson Cancer Center, Perelman School of Medicine, University of
Pennsylvania, Philadelphia, PA, 19104, USA
- Division of Hematology-Oncology, Department of Medicine, Perelman
School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Zachary E. Stine
- Abramson Family Cancer Research Institute, Perelman School of
Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Abramson Cancer Center, Perelman School of Medicine, University of
Pennsylvania, Philadelphia, PA, 19104, USA
- Division of Hematology-Oncology, Department of Medicine, Perelman
School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Chi V. Dang
- Abramson Family Cancer Research Institute, Perelman School of
Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Abramson Cancer Center, Perelman School of Medicine, University of
Pennsylvania, Philadelphia, PA, 19104, USA
- Division of Hematology-Oncology, Department of Medicine, Perelman
School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
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778
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Guo X, Huang C, Lian K, Wang S, Zhao H, Yan F, Zhang X, Zhang J, Xie H, An R, Tao L. BCKA down-regulates mTORC2-Akt signal and enhances apoptosis susceptibility in cardiomyocytes. Biochem Biophys Res Commun 2016; 480:106-113. [PMID: 27697526 DOI: 10.1016/j.bbrc.2016.09.162] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 09/29/2016] [Indexed: 12/15/2022]
Abstract
Diabetic mellitus (DM) portends poor prognosis concerning pressure overloaded heart disease. Branched-chain amino acids (BCAAs), elements of essential amino acids, have been found altered in its catabolism in diabetes decades ago. However, the relationship between BCAAs and DM induced deterioration of pressure overloaded heart disease remains controversial. This study is aimed to investigate the particular effect of BCKA, a metabolite of BCAA, on myocardial injury induced by pressure overloaded. Primary cardiomyocytes were incubated with or without BCKA and followed by treatment with isoproterenol (ISO); then cell viability was detected by CCK8 and apoptosis was examined by TUNNEL stain and caspase-3 activity analysis. Compared to non-BCKA incubated group, BCKA incubation decreased cell survival and increased apoptosis concentration dependently. Furthermore, Western blot assay showed that mTORC2-Akt pathway was significantly inactivated by BCKA incubation. Moreover, overexpression of rictor, a vital component of mTORC2, significantly abolished the adverse effects of BCKA on apoptosis susceptibility of cardiomyocytes. These results indicate that BCKA contribute to vulnerability of cardiomyocytes in stimulated stress via inactivation of mTORC2-Akt pathway.
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Affiliation(s)
- Xiong Guo
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Chong Huang
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Kun Lian
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Shan Wang
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Huishou Zhao
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Feng Yan
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Xiaomeng Zhang
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Jinglong Zhang
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Huaning Xie
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Rui An
- Department of Radiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China
| | - Ling Tao
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an, 710032, China.
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779
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Recent Advances in Understanding Amino Acid Sensing Mechanisms that Regulate mTORC1. Int J Mol Sci 2016; 17:ijms17101636. [PMID: 27690010 PMCID: PMC5085669 DOI: 10.3390/ijms17101636] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Revised: 09/19/2016] [Accepted: 09/21/2016] [Indexed: 11/25/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is the central regulator of mammalian cell growth, and is essential for the formation of two structurally and functionally distinct complexes: mTORC1 and mTORC2. mTORC1 can sense multiple cues such as nutrients, energy status, growth factors and hormones to control cell growth and proliferation, angiogenesis, autophagy, and metabolism. As one of the key environmental stimuli, amino acids (AAs), especially leucine, glutamine and arginine, play a crucial role in mTORC1 activation, but where and how AAs are sensed and signal to mTORC1 are not fully understood. Classically, AAs activate mTORC1 by Rag GTPases which recruit mTORC1 to lysosomes, where AA signaling initiates. Plasma membrane transceptor L amino acid transporter 1 (LAT1)-4F2hc has dual transporter-receptor function that can sense extracellular AA availability upstream of mTORC1. The lysosomal AA sensors (PAT1 and SLC38A9) and cytoplasmic AA sensors (LRS, Sestrin2 and CASTOR1) also participate in regulating mTORC1 activation. Importantly, AAs can be sensed by plasma membrane receptors, like G protein-coupled receptor (GPCR) T1R1/T1R3, and regulate mTORC1 without being transported into the cells. Furthermore, AA-dependent mTORC1 activation also initiates within Golgi, which is regulated by Golgi-localized AA transporter PAT4. This review provides an overview of the research progress of the AA sensing mechanisms that regulate mTORC1 activity.
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780
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Phillips SM. The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass. Nutr Metab (Lond) 2016; 13:64. [PMID: 27708684 PMCID: PMC5041535 DOI: 10.1186/s12986-016-0124-8] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 09/21/2016] [Indexed: 12/20/2022] Open
Abstract
Protein supplementation during resistance exercise training augments hypertrophic gains. Protein ingestion and the resultant hyperaminoacidemia provides the building blocks (indispensable amino acids - IAA) for, and also triggers an increase in, muscle protein synthesis (MPS), suppression of muscle protein breakdown (MPB), and net positive protein balance (i.e., MPS > MPB). The key amino acid triggering the rise in MPS is leucine, which stimulates the mechanistic target of rapamycin complex-1, a key signalling protein, and triggers a rise in MPS. As such, ingested proteins with a high leucine content would be advantageous in triggering a rise in MPS. Thus, protein quality (reflected in IAA content and protein digestibility) has an impact on changes in MPS and could ultimately affect skeletal muscle mass. Protein quality has been measured by the protein digestibility-corrected amino acid score (PDCAAS); however, the digestible indispensable amino acid score (DIAAS) has been recommended as a better method for protein quality scoring. Under DIAAS there is the recognition that amino acids are individual nutrients and that protein quality is contingent on IAA content and ileal (as opposed to fecal) digestibility. Differences in protein quality may have important ramifications for exercise-induced changes in muscle mass gains made with resistance exercise as well as muscle remodelling. Thus, the purpose of this review is a critical appraisal of studies examining the effects of protein quality in supplementation on changes in muscle mass and strength as well as body composition during resistance training.
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Affiliation(s)
- Stuart M. Phillips
- Department of Kinesiology, McMaster University, 1280 Main St., West Hamilton, ON L8S 4K1 Canada
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781
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Yoshikawa N, Shimizu N, Uehara M, Oda A, Matsumiya R, Matsubara E, Kobayashi H, Hosono O, Kuribara-Souta A, Baba H, Nagamura F, Kiryu S, Tanaka H. The effects of bolus supplementation of branched-chain amino acids on skeletal muscle mass, strength, and function in patients with rheumatic disorders during glucocorticoid treatment. Mod Rheumatol 2016; 27:508-517. [PMID: 27678151 DOI: 10.1080/14397595.2016.1213480] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVES To test the effects of bolus supplementation of branched-chain amino acids (BCAA) on skeletal muscle mass, strength, and function in patients with rheumatic disorders taking glucocorticoid (GC). METHODS Patients with rheumatic disorders treated with prednisolone (≥10 mg/day) were randomized to ingest additional daily 12 g of BCAA (n = 9) or not (n = 9) for 12 weeks. At baseline, and 4, 8, and 12 weeks, they underwent bioelectrical impedance analysis, muscle strength and functional tests, and computed tomography analysis for cross-sectional area of mid-thigh muscle. RESULTS Disease activities of the patients were well controlled and daily GC dose was similarly reduced in both groups. Limb muscle mass was recovered in both groups. Whole-body muscle mass and muscle strength and functional mobility were increased only in BCAA (+) group. The effects of BCAA supplementation on recovering skeletal muscle mass were prominent in particular muscles including biceps femoris muscle. CONCLUSIONS This trial is the first-in-man clinical trial to demonstrate that BCAA supplementation might be safe and, at least in part, improve skeletal muscle mass, strength, and function in patients with rheumatic disorders treated with GC.
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Affiliation(s)
| | - Noriaki Shimizu
- a Department of Rheumatology and Allergy.,b Division of Rheumatology, Center for Antibody and Vaccine Therapy
| | | | - Aya Oda
- a Department of Rheumatology and Allergy
| | | | | | | | | | | | | | | | - Shigeru Kiryu
- d Department of Radiology , IMSUT Hospital, Institute of Medical Science, the University of Tokyo , Shirokanedai , Minato-ku , Tokyo , Japan
| | - Hirotoshi Tanaka
- a Department of Rheumatology and Allergy.,b Division of Rheumatology, Center for Antibody and Vaccine Therapy
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782
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Saxton RA, Knockenhauer KE, Schwartz TU, Sabatini DM. The apo-structure of the leucine sensor Sestrin2 is still elusive. Sci Signal 2016; 9:ra92. [PMID: 27649739 DOI: 10.1126/scisignal.aah4497] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Sestrin2 is a GATOR2-interacting protein that directly binds leucine and is required for the inhibition of mTORC1 under leucine deprivation, indicating that it is a leucine sensor for the mTORC1 pathway. We recently reported the structure of Sestrin2 in complex with leucine [Protein Data Bank (PDB) ID, 5DJ4] and demonstrated that mutations in the leucine-binding pocket that alter the affinity of Sestrin2 for leucine result in a corresponding change in the leucine sensitivity of mTORC1 in cells. A lower resolution structure of human Sestrin2 (PDB ID, 5CUF), which was crystallized in the absence of exogenous leucine, showed Sestrin2 to be in a nearly identical conformation as the leucine-bound structure. On the basis of this observation, it has been argued that leucine binding does not affect the conformation of Sestrin2 and that Sestrin2 may not be a sensor for leucine. We show that simple analysis of the reported "apo"-Sestrin2 structure reveals the clear presence of prominent, unmodeled electron density in the leucine-binding pocket that exactly accommodates the leucine observed in the higher resolution structure. Refining the reported apo-structure with leucine eliminated the large Fobs-Fcalc difference density at this position and improved the working and free R factors of the model. Consistent with this result, our own structure of Sestrin2 crystallized in the absence of exogenous leucine also contained electron density that is best explained by leucine. Thus, the structure of apo-Sestrin2 remains elusive.
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Affiliation(s)
- Robert A Saxton
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA. Howard Hughes Medical Institute, Cambridge, MA 02139, USA. Koch Institute for Integrative Cancer Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. Broad Institute of Harvard and Massachusetts Institute of Technology, 415 Main Street, Cambridge, MA 02142, USA
| | - Kevin E Knockenhauer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Thomas U Schwartz
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - David M Sabatini
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA. Howard Hughes Medical Institute, Cambridge, MA 02139, USA. Koch Institute for Integrative Cancer Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. Broad Institute of Harvard and Massachusetts Institute of Technology, 415 Main Street, Cambridge, MA 02142, USA.
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783
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Abstract
The heart is a biological pump that converts chemical to mechanical energy. This process of energy conversion is highly regulated to the extent that energy substrate metabolism matches energy use for contraction on a beat-to-beat basis. The biochemistry of cardiac metabolism includes the biochemistry of energy transfer, metabolic regulation, and transcriptional, translational as well as posttranslational control of enzymatic activities. Pathways of energy substrate metabolism in the heart are complex and dynamic, but all of them conform to the First Law of Thermodynamics. The perspectives expand on the overall idea that cardiac metabolism is inextricably linked to both physiology and molecular biology of the heart. The article ends with an outlook on emerging concepts of cardiac metabolism based on new molecular models and new analytical tools. © 2016 American Physiological Society. Compr Physiol 6:1675-1699, 2016.
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Affiliation(s)
- Heinrich Taegtmeyer
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
| | - Truong Lam
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
| | - Giovanni Davogustto
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
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784
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Xia J, Wang R, Zhang T, Ding J. Structural insight into the arginine-binding specificity of CASTOR1 in amino acid-dependent mTORC1 signaling. Cell Discov 2016; 2:16035. [PMID: 27648300 PMCID: PMC5020642 DOI: 10.1038/celldisc.2016.35] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 08/30/2016] [Indexed: 12/25/2022] Open
Abstract
The mechanistic Target Of Rapamycin Complex 1 (mTORC1) is central to the cellular response to changes in nutrient signals such as amino acids. CASTOR1 is shown to be an arginine sensor, which plays an important role in the activation of the mTORC1 pathway. In the deficiency of arginine, CASTOR1 interacts with GATOR2, which together with GATOR1 and Rag GTPases controls the relocalization of mTORC1 to lysosomes. The binding of arginine to CASTOR1 disrupts its association with GATOR2 and hence activates the mTORC1 signaling. Here, we report the crystal structure of CASTOR1 in complex with arginine at 2.5 Å resolution. CASTOR1 comprises of four tandem ACT domains with an architecture resembling the C-terminal allosteric domains of aspartate kinases. ACT1 and ACT3 adopt the typical βαββαβ topology and function in dimerization via the conserved residues from helices α1 of ACT1 and α5 of ACT3; whereas ACT 2 and ACT4, both comprising of two non-sequential regions, assume the unusual ββαββα topology and contribute an arginine-binding pocket at the interface. The bound arginine makes a number of hydrogen-bonding interactions and extensive hydrophobic contacts with the surrounding residues of the binding pocket. The functional roles of the key residues are validated by mutagenesis and biochemical assays. Our structural and functional data together reveal the molecular basis for the arginine-binding specificity of CASTOR1 in the arginine-dependent activation of the mTORC1 signaling.
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Affiliation(s)
- Jing Xia
- School of Life Sciences, Shanghai University , Shanghai, China
| | - Rong Wang
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai, China
| | - Tianlong Zhang
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai, China
| | - Jianping Ding
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; Shanghai Science Research Center, Chinese Academy of Sciences, Shanghai, China
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785
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Lim CY, Zoncu R. The lysosome as a command-and-control center for cellular metabolism. J Cell Biol 2016; 214:653-64. [PMID: 27621362 PMCID: PMC5021098 DOI: 10.1083/jcb.201607005] [Citation(s) in RCA: 196] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 08/22/2016] [Indexed: 12/25/2022] Open
Abstract
Lysosomes are membrane-bound organelles found in every eukaryotic cell. They are widely known as terminal catabolic stations that rid cells of waste products and scavenge metabolic building blocks that sustain essential biosynthetic reactions during starvation. In recent years, this classical view has been dramatically expanded by the discovery of new roles of the lysosome in nutrient sensing, transcriptional regulation, and metabolic homeostasis. These discoveries have elevated the lysosome to a decision-making center involved in the control of cellular growth and survival. Here we review these recently discovered properties of the lysosome, with a focus on how lysosomal signaling pathways respond to external and internal cues and how they ultimately enable metabolic homeostasis and cellular adaptation.
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Affiliation(s)
- Chun-Yan Lim
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720
| | - Roberto Zoncu
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720
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786
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Ali M, Devkota S, Roh JI, Lee J, Lee HW. Telomerase reverse transcriptase induces basal and amino acid starvation-induced autophagy through mTORC1. Biochem Biophys Res Commun 2016; 478:1198-204. [DOI: 10.1016/j.bbrc.2016.08.094] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 08/16/2016] [Indexed: 01/06/2023]
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787
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Dyachok J, Earnest S, Iturraran EN, Cobb MH, Ross EM. Amino Acids Regulate mTORC1 by an Obligate Two-step Mechanism. J Biol Chem 2016; 291:22414-22426. [PMID: 27587390 DOI: 10.1074/jbc.m116.732511] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 08/30/2016] [Indexed: 12/21/2022] Open
Abstract
The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cell growth with its nutritional, hormonal, energy, and stress status. Amino acids are critical regulators of mTORC1 that permit other inputs to mTORC1 activity. However, the roles of individual amino acids and their interactions in mTORC1 activation are not well understood. Here we demonstrate that activation of mTORC1 by amino acids includes two discrete and separable steps: priming and activation. Sensitizing mTORC1 activation by priming amino acids is a prerequisite for subsequent stimulation of mTORC1 by activating amino acids. Priming is achieved by a group of amino acids that includes l-asparagine, l-glutamine, l-threonine, l-arginine, l-glycine, l-proline, l-serine, l-alanine, and l-glutamic acid. The group of activating amino acids is dominated by l-leucine but also includes l-methionine, l-isoleucine, and l-valine. l-Cysteine predominantly inhibits priming but not the activating step. Priming and activating steps differ in their requirements for amino acid concentration and duration of treatment. Priming and activating amino acids use mechanisms that are distinct both from each other and from growth factor signaling. Neither step requires intact tuberous sclerosis complex of proteins to activate mTORC1. Concerted action of priming and activating amino acids is required to localize mTORC1 to lysosomes and achieve its activation.
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Affiliation(s)
- Julia Dyachok
- From the Department of Pharmacology.,Green Center for Systems Biology, and.,McDermott Center for Growth and Development, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041
| | | | - Erica N Iturraran
- From the Department of Pharmacology.,Green Center for Systems Biology, and
| | | | - Elliott M Ross
- From the Department of Pharmacology, .,Green Center for Systems Biology, and
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788
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Semba RD, Trehan I, Gonzalez-Freire M, Kraemer K, Moaddel R, Ordiz MI, Ferrucci L, Manary MJ. Perspective: The Potential Role of Essential Amino Acids and the Mechanistic Target of Rapamycin Complex 1 (mTORC1) Pathway in the Pathogenesis of Child Stunting. Adv Nutr 2016; 7:853-65. [PMID: 27633102 PMCID: PMC5015042 DOI: 10.3945/an.116.013276] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Stunting is the best summary measure of chronic malnutrition in children. Approximately one-quarter of children under age 5 worldwide are stunted. Lipid-based or micronutrient supplementation has little to no impact in reducing stunting, which suggests that other critical dietary nutrients are missing. A dietary pattern of poor-quality protein is associated with stunting. Stunted children have significantly lower circulating essential amino acids than do nonstunted children. Inadequate dietary intakes of essential amino acids could adversely affect growth, because amino acids are required for synthesis of proteins. The master growth regulation pathway, the mechanistic target of rapamycin complex 1 (mTORC1) pathway, is exquisitely sensitive to amino acid availability. mTORC1 integrates cues such as nutrients, growth factors, oxygen, and energy to regulate growth of bone, skeletal muscle, nervous system, gastrointestinal tract, hematopoietic cells, immune effector cells, organ size, and whole-body energy balance. mTORC1 represses protein and lipid synthesis and cell and organismal growth when amino acids are deficient. Over the past 4 decades, the main paradigm for child nutrition in developing countries has been micronutrient malnutrition, with relatively less attention paid to protein. In this Perspective, we present the view that essential amino acids and the mTORC1 pathway play a key role in child growth. The current assumption that total dietary protein intake is adequate for growth among most children in developing countries needs re-evaluation.
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Affiliation(s)
- Richard D Semba
- Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD;
| | - Indi Trehan
- Department of Pediatrics, Washington University in St. Louis, St. Louis, MO
| | | | - Klaus Kraemer
- Sight and Life, Basel, Switzerland; and Johns Hopkins Bloomberg School of Public Health, Baltimore, MD
| | | | - M Isabel Ordiz
- Department of Pediatrics, Washington University in St. Louis, St. Louis, MO
| | | | - Mark J Manary
- Department of Pediatrics, Washington University in St. Louis, St. Louis, MO
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789
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Amick J, Roczniak-Ferguson A, Ferguson SM. C9orf72 binds SMCR8, localizes to lysosomes, and regulates mTORC1 signaling. Mol Biol Cell 2016; 27:3040-3051. [PMID: 27559131 PMCID: PMC5063613 DOI: 10.1091/mbc.e16-01-0003] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 08/19/2016] [Indexed: 12/18/2022] Open
Abstract
C9orf72 interacts strongly with SMCR8 and depends on this interaction for its stability. Lysosomes are major sites of C9orf72 subcellular localization, and abnormal lysosome morphology is seen in its absence. Defects are found in the regulation of the lysosome-localized mTORC1 signaling pathway in C9orf72 KO cells. Hexanucleotide expansion in an intron of the C9orf72 gene causes amyotrophic lateral sclerosis and frontotemporal dementia. However, beyond bioinformatics predictions that suggested structural similarity to folliculin, the Birt-Hogg-Dubé syndrome tumor suppressor, little is known about the normal functions of the C9orf72 protein. To address this problem, we used genome-editing strategies to investigate C9orf72 interactions, subcellular localization, and knockout (KO) phenotypes. We found that C9orf72 robustly interacts with SMCR8 (a protein of previously unknown function). We also observed that C9orf72 localizes to lysosomes and that such localization is negatively regulated by amino acid availability. Analysis of C9orf72 KO, SMCR8 KO, and double-KO cell lines revealed phenotypes that are consistent with a function for C9orf72 at lysosomes. These include abnormally swollen lysosomes in the absence of C9orf72 and impaired responses of mTORC1 signaling to changes in amino acid availability (a lysosome-dependent process) after depletion of either C9orf72 or SMCR8. Collectively these results identify strong physical and functional interactions between C9orf72 and SMCR8 and support a lysosomal site of action for this protein complex.
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Affiliation(s)
- Joseph Amick
- Department of Cell Biology and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510
| | - Agnes Roczniak-Ferguson
- Department of Cell Biology and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510
| | - Shawn M Ferguson
- Department of Cell Biology and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510
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790
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Abstract
The activation state of mTORC1, a master regulator of cell growth, is particularly sensitive to changes in the intracellular levels of the amino acid arginine, but the sensing mechanisms are poorly understood. In this issue of Cell, Chantranupong et al. identify CASTOR1 as a direct arginine sensor that acts through the GATOR2 complex to regulate mTORC1.
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Affiliation(s)
- James E Hughes Hallett
- Department of Genetics and Complex Diseases, Harvard T.H. Chan School of Public Health, Boston MA, USA
| | - Brendan D Manning
- Department of Genetics and Complex Diseases, Harvard T.H. Chan School of Public Health, Boston MA, USA.
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791
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Abstract
Altered cellular metabolism is an emerging hallmark of cancer. Accumulating recent evidence links long non-coding RNAs (lncRNAs), a still poorly understood class of non-coding RNAs, to cancer metabolism. Here we review the emerging findings on the functions of lncRNAs in cancer metabolism, with particular emphasis on how lncRNAs regulate glucose and glutamine metabolism in cancer cells, discuss how lncRNAs regulate various aspects of cancer metabolism through their cross-talk with other macromolecules, explore the mechanistic conceptual framework of lncRNAs in reprogramming metabolism in cancers, and highlight the challenges in this field. A more in-depth understanding of lncRNAs in cancer metabolism may enable the development of novel and effective therapeutic strategies targeting cancer metabolism.
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Affiliation(s)
- Zhen-Dong Xiao
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Li Zhuang
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Boyi Gan
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
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792
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Dimeloe S, Burgener AV, Grählert J, Hess C. T-cell metabolism governing activation, proliferation and differentiation; a modular view. Immunology 2016; 150:35-44. [PMID: 27479920 DOI: 10.1111/imm.12655] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 07/27/2016] [Accepted: 07/28/2016] [Indexed: 12/14/2022] Open
Abstract
T lymphocytes are a critical component of the adaptive immune system mediating protection against infection and malignancy, but also implicated in many immune pathologies. Upon recognition of specific antigens T cells clonally expand, traffic to inflamed sites and acquire effector functions, such as the capacity to kill infected and malignantly transformed cells and secrete cytokines to coordinate the immune response. These processes have significant bioenergetic and biosynthetic demands, which are met by dynamic changes in T-cell metabolism, specifically increases in glucose uptake and metabolism; mitochondrial function; amino acid uptake, and cholesterol and lipid synthesis. These metabolic changes are coordinate by key cellular kinases and transcription factors. Dysregulated T-cell metabolism is associated with impaired immunity in chronic infection and cancer and conversely with excessive T-cell activity in autoimmune and inflammatory pathologies. Here we review the key aspects of T-cell metabolism relevant to their immune function, and discuss evidence for the potential to therapeutically modulate T-cell metabolism in disease.
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Affiliation(s)
- Sarah Dimeloe
- Immunobiology Laboratory, Department of Biomedicine, University of Basel, Basel, Switzerland
| | - Anne-Valérie Burgener
- Immunobiology Laboratory, Department of Biomedicine, University of Basel, Basel, Switzerland
| | - Jasmin Grählert
- Immunobiology Laboratory, Department of Biomedicine, University of Basel, Basel, Switzerland
| | - Christoph Hess
- Immunobiology Laboratory, Department of Biomedicine, University of Basel, Basel, Switzerland
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793
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Kitakaze T, Sakamoto T, Kitano T, Inoue N, Sugihara F, Harada N, Yamaji R. The collagen derived dipeptide hydroxyprolyl-glycine promotes C2C12 myoblast differentiation and myotube hypertrophy. Biochem Biophys Res Commun 2016; 478:1292-7. [PMID: 27553280 DOI: 10.1016/j.bbrc.2016.08.114] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 08/19/2016] [Indexed: 01/21/2023]
Abstract
The majority of studies on possible roles for collagen hydrolysates in human health have focused on their effects on bone and skin. Hydroxyprolyl-glycine (Hyp-Gly) was recently identified as a novel collagen hydrolysate-derived dipeptide in human blood. However, any possible health benefits of Hyp-Gly remain unclear. Here, we report the effects of Hyp-Gly on differentiation and hypertrophy of murine skeletal muscle C2C12 cells. Hyp-Gly increased the fusion index, the myotube size, and the expression of the myotube-specific myosin heavy chain (MyHC) and tropomyosin structural proteins. Hyp-Gly increased the phosphorylation of Akt, mTOR, and p70S6K in myoblasts, whereas the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 inhibited their phosphorylation by Hyp-Gly. LY294002 and the mammalian target of rapamycin (mTOR) inhibitor rapamycin repressed the enhancing effects of Hyp-Gly on MyHC and tropomyosin expression. The peptide/histidine transporter 1 (PHT1) was highly expressed in both myoblasts and myotubes, and co-administration of histidine inhibited Hyp-Gly-induced phosphorylation of p70S6K in myoblasts and myotubes. These results indicate that Hyp-Gly can induce myogenic differentiation and myotube hypertrophy and suggest that Hyp-Gly promotes myogenic differentiation by activating the PI3K/Akt/mTOR signaling pathway, perhaps depending on PHT1 for entry into cells.
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Affiliation(s)
- Tomoya Kitakaze
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan
| | - Tomotaka Sakamoto
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan
| | - Takehiro Kitano
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan
| | - Naoki Inoue
- Nitta Gelatin Inc., Peptide Division, 2-22 Futamata, Yao, Osaka, 5810024, Japan
| | - Fumihito Sugihara
- Nitta Gelatin Inc., Peptide Division, 2-22 Futamata, Yao, Osaka, 5810024, Japan
| | - Naoki Harada
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan
| | - Ryoichi Yamaji
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan.
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794
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Amino acids regulate mTOR pathway and milk protein synthesis in a mouse mammary epithelial cell line is partly mediated by T1R1/T1R3. Eur J Nutr 2016; 56:2467-2474. [DOI: 10.1007/s00394-016-1282-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Accepted: 07/20/2016] [Indexed: 12/18/2022]
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795
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Saxton RA, Chantranupong L, Knockenhauer KE, Schwartz TU, Sabatini DM. Mechanism of arginine sensing by CASTOR1 upstream of mTORC1. Nature 2016; 536:229-33. [PMID: 27487210 PMCID: PMC4988899 DOI: 10.1038/nature19079] [Citation(s) in RCA: 206] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 07/05/2016] [Indexed: 12/25/2022]
Abstract
The mechanistic Target of Rapamycin Complex 1 (mTORC1) is a major regulator of eukaryotic growth that coordinates anabolic and catabolic cellular processes with inputs such as growth factors and nutrients, including amino acids. In mammals arginine is particularly important, promoting diverse physiological effects such as immune cell activation, insulin secretion, and muscle growth, largely mediated through activation of mTORC1 (refs 4, 5, 6, 7). Arginine activates mTORC1 upstream of the Rag family of GTPases, through either the lysosomal amino acid transporter SLC38A9 or the GATOR2-interacting Cellular Arginine Sensor for mTORC1 (CASTOR1). However, the mechanism by which the mTORC1 pathway detects and transmits this arginine signal has been elusive. Here, we present the 1.8 Å crystal structure of arginine-bound CASTOR1. Homodimeric CASTOR1 binds arginine at the interface of two Aspartate kinase, Chorismate mutase, TyrA (ACT) domains, enabling allosteric control of the adjacent GATOR2-binding site to trigger dissociation from GATOR2 and downstream activation of mTORC1. Our data reveal that CASTOR1 shares substantial structural homology with the lysine-binding regulatory domain of prokaryotic aspartate kinases, suggesting that the mTORC1 pathway exploited an ancient, amino-acid-dependent allosteric mechanism to acquire arginine sensitivity. Together, these results establish a structural basis for arginine sensing by the mTORC1 pathway and provide insights into the evolution of a mammalian nutrient sensor.
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Affiliation(s)
- Robert A. Saxton
- Department of Biology, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
- Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Broad Institute of Harvard and Massachusetts Institute of Technology, 415 Main Street, Cambridge MA 02142, USA
| | - Lynne Chantranupong
- Department of Biology, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
- Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Broad Institute of Harvard and Massachusetts Institute of Technology, 415 Main Street, Cambridge MA 02142, USA
| | - Kevin E. Knockenhauer
- Department of Biology, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
| | - Thomas U. Schwartz
- Department of Biology, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
| | - David M. Sabatini
- Department of Biology, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
- Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Broad Institute of Harvard and Massachusetts Institute of Technology, 415 Main Street, Cambridge MA 02142, USA
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796
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Fultang L, Vardon A, De Santo C, Mussai F. Molecular basis and current strategies of therapeutic arginine depletion for cancer. Int J Cancer 2016; 139:501-9. [PMID: 26913960 DOI: 10.1002/ijc.30051] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 02/11/2016] [Accepted: 02/16/2016] [Indexed: 12/12/2022]
Abstract
Renewed interest in the use of therapeutic enzymes combined with an improved knowledge of cancer cell metabolism, has led to the translation of several arginine depletion strategies into early phase clinical trials. Arginine auxotrophic tumors are reliant on extracellular arginine, due to the downregulation of arginosuccinate synthetase or ornithine transcarbamylase-key enzymes for intracellular arginine recycling. Engineered arginine catabolic enzymes such as recombinant human arginase (rh-Arg1-PEG) and arginine deiminase (ADI-PEG) have demonstrated cytotoxicity against arginine auxotrophic tumors. In this review, we discuss the molecular events triggered by extracellular arginine depletion that contribute to tumor cell death.
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Affiliation(s)
- Livingstone Fultang
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
| | - Ashley Vardon
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
| | - Carmela De Santo
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
| | - Francis Mussai
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
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797
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Metabolic Control of Longevity. Cell 2016; 166:802-821. [DOI: 10.1016/j.cell.2016.07.031] [Citation(s) in RCA: 482] [Impact Index Per Article: 60.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 05/15/2016] [Accepted: 07/20/2016] [Indexed: 12/19/2022]
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798
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Yoon MS, Son K, Arauz E, Han JM, Kim S, Chen J. Leucyl-tRNA Synthetase Activates Vps34 in Amino Acid-Sensing mTORC1 Signaling. Cell Rep 2016; 16:1510-1517. [PMID: 27477288 DOI: 10.1016/j.celrep.2016.07.008] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 06/08/2016] [Accepted: 07/01/2016] [Indexed: 11/16/2022] Open
Abstract
Amino acid availability activates signaling by the mammalian target of rapamycin (mTOR) complex 1, mTORC1, a master regulator of cell growth. The class III PI-3-kinase Vps34 mediates amino acid signaling to mTORC1 by regulating lysosomal translocation and activation of the phospholipase PLD1. Here, we identify leucyl-tRNA synthetase (LRS) as a leucine sensor for the activation of Vps34-PLD1 upstream of mTORC1. LRS is necessary for amino acid-induced Vps34 activation, cellular PI(3)P level increase, PLD1 activation, and PLD1 lysosomal translocation. Leucine binding, but not tRNA charging activity of LRS, is required for this regulation. Moreover, LRS physically interacts with Vps34 in amino acid-stimulatable non-autophagic complexes. Finally, purified LRS protein activates Vps34 kinase in vitro in a leucine-dependent manner. Collectively, our findings provide compelling evidence for a direct role of LRS in amino acid activation of Vps34 via a non-canonical mechanism and fill a gap in the amino acid-sensing mTORC1 signaling network.
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Affiliation(s)
- Mee-Sup Yoon
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue B107, Urbana, IL 61801, USA; Department of Molecular Medicine, School of Medicine, Gachon University, Incheon 406-840, Republic of Korea.
| | - Kook Son
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue B107, Urbana, IL 61801, USA
| | - Edwin Arauz
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue B107, Urbana, IL 61801, USA
| | - Jung Min Han
- Department of Integrated OMICS for Biomedical Science, Yonsei University, Seoul 120-749, Republic of Korea; College of Pharmacy, Yonsei University, Incheon 406-840, Republic of Korea
| | - Sunghoon Kim
- Medicinal Bioconvergence Research Center, Seoul National University, Seoul 151-742, Republic of Korea
| | - Jie Chen
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue B107, Urbana, IL 61801, USA.
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799
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Deng W, Cha J, Yuan J, Haraguchi H, Bartos A, Leishman E, Viollet B, Bradshaw HB, Hirota Y, Dey SK. p53 coordinates decidual sestrin 2/AMPK/mTORC1 signaling to govern parturition timing. J Clin Invest 2016; 126:2941-54. [PMID: 27454290 DOI: 10.1172/jci87715] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 05/24/2016] [Indexed: 12/15/2022] Open
Abstract
Inflammation and oxidative stress are known risk factors for preterm birth (PTB); however, the mechanisms and pathways that influence this condition are not fully described. Previously, we showed that mTORC1 signaling is increased in mice harboring a uterine-specific deletion of transformation-related protein 53 (p53d/d mice), which exhibit premature decidual senescence that triggers spontaneous and inflammation-induced PTB. Treatment with the mTORC1 inhibitor rapamycin reduced the incidence of PTB in the p53d/d mice. Decidual senescence with heightened mTORC1 signaling is also a signature of human PTB. Here, we have identified an underlying mechanism for PTB and a potential therapeutic strategy for treating the condition. Treatment of pregnant p53d/d mice with either the antidiabetic drug metformin or the antioxidant resveratrol activated AMPK signaling and inhibited mTORC1 signaling in decidual cells. Both metformin and resveratrol protected against spontaneous and inflammation-induced PTB in p53d/d females. Using multiple approaches, we determined that p53 interacts with sestrins to coordinate an inverse relationship between AMPK and mTORC1 signaling that determines parturition timing. This signature was also observed in human decidual cells. Together, these results reveal that p53-dependent coordination of AMPK and mTORC1 signaling controls parturition timing and suggest that metformin and resveratrol have therapeutic potential to prevent PTB.
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800
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Yoon MS. The Emerging Role of Branched-Chain Amino Acids in Insulin Resistance and Metabolism. Nutrients 2016; 8:nu8070405. [PMID: 27376324 PMCID: PMC4963881 DOI: 10.3390/nu8070405] [Citation(s) in RCA: 264] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 06/01/2016] [Accepted: 06/27/2016] [Indexed: 12/12/2022] Open
Abstract
Insulin is required for maintenance of glucose homeostasis. Despite the importance of insulin sensitivity to metabolic health, the mechanisms that induce insulin resistance remain unclear. Branched-chain amino acids (BCAAs) belong to the essential amino acids, which are both direct and indirect nutrient signals. Even though BCAAs have been reported to improve metabolic health, an increased BCAA plasma level is associated with a high risk of metabolic disorder and future insulin resistance, or type 2 diabetes mellitus (T2DM). The activation of mammalian target of rapamycin complex 1 (mTORC1) by BCAAs has been suggested to cause insulin resistance. In addition, defective BCAA oxidative metabolism might occur in obesity, leading to a further accumulation of BCAAs and toxic intermediates. This review provides the current understanding of the mechanism of BCAA-induced mTORC1 activation, as well as the effect of mTOR activation on metabolic health in terms of insulin sensitivity. Furthermore, the effects of impaired BCAA metabolism will be discussed in detail.
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Affiliation(s)
- Mee-Sup Yoon
- Department of Molecular Medicine, School of Medicine, Gachon University, Incheon 406-840, Korea.
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