Control of TSC2-Rheb signaling axis by arginine regulates mTORC1 activity

The mammalian target of rapamycin complex 1 (mTORC1) is the key signaling hub that regulates cellular protein homeostasis, growth, and proliferation in health and disease. As a prerequisite for activation of mTORC1 by hormones and mitogens, there first has to be an available pool of intracellular amino acids. Arginine, an amino acid essential during mammalian embryogenesis and early development is one of the key activators of mTORC1. Herein, we demonstrate that arginine acts independently of its metabolism to allow maximal activation of mTORC1 by growth factors via a mechanism that does not involve regulation of mTORC1 localization to lysosomes. Instead, arginine specifically suppresses lysosomal localization of the TSC complex and interaction with its target small GTPase protein, Rheb. By interfering with TSC-Rheb complex, arginine relieves allosteric inhibition of Rheb by TSC. Arginine cooperates with growth factor signaling which further promotes dissociation of TSC2 from lysosomes and activation of mTORC1. Arginine is the main amino acid sensed by the mTORC1 pathway in several cell types including human embryonic stem cells (hESCs). Dependence on arginine is maintained once hESCs are differentiated to fibroblasts, neurons, and hepatocytes, highlighting the fundamental importance of arginine-sensing to mTORC1 signaling. Together, our data provide evidence that different growth promoting cues cooperate to a greater extent than previously recognized to achieve tight spatial and temporal regulation of mTORC1 signaling.

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Persistent mTORC1 signaling in cell senescence results from defects in amino acid and growth factor sensing

The Journal of Cell Biology ◽

10.1083/jcb.201610113 ◽

2017 ◽

Vol 216 (7) ◽

pp. 1949-1957 ◽

Cited By ~ 31

Author(s):

Bernadette Carroll ◽

Glyn Nelson ◽

Yoana Rabanal-Ruiz ◽

Olena Kucheryavenko ◽

Natasha A. Dunhill-Turner ◽

...

Keyword(s):

Amino Acid ◽

Growth Factor ◽

Primary Cilia ◽

Human Fibroblasts ◽

Mammalian Target Of Rapamycin ◽

Senescent Cell ◽

Cell Senescence ◽

Growth Factor Signaling ◽

Mtorc1 Signaling ◽

Underlying Mechanisms

Mammalian target of rapamycin complex 1 (mTORC1) and cell senescence are intimately linked to each other and to organismal aging. Inhibition of mTORC1 is the best-known intervention to extend lifespan, and recent evidence suggests that clearance of senescent cells can also improve health and lifespan. Enhanced mTORC1 activity drives characteristic phenotypes of senescence, although the underlying mechanisms responsible for increased activity are not well understood. We have identified that in human fibroblasts rendered senescent by stress, replicative exhaustion, or oncogene activation, mTORC1 is constitutively active and resistant to serum and amino acid starvation. This is driven in part by depolarization of senescent cell plasma membrane, which leads to primary cilia defects and a resultant failure to inhibit growth factor signaling. Further, increased autophagy and high levels of intracellular amino acids may act to support mTORC1 activity in starvation conditions. Interventions to correct these phenotypes restore sensitivity to the mTORC1 signaling pathway and cause death, indicating that persistent signaling supports senescent cell survival.

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Aminoacyl-tRNA synthetase inhibition activates a pathway that branches from the canonical amino acid response in mammalian cells

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1913788117 ◽

2020 ◽

Vol 117 (16) ◽

pp. 8900-8911 ◽

Cited By ~ 1

Author(s):

Yeonjin Kim ◽

Mark S. Sundrud ◽

Changqian Zhou ◽

Maja Edenius ◽

Davide Zocco ◽

...

Keyword(s):

Amino Acid ◽

Mammalian Cells ◽

Inflammatory Responses ◽

Mammalian Target Of Rapamycin ◽

Cell Types ◽

Trna Synthetase ◽

Aminoacyl Trna Synthetase ◽

Therapeutic Benefits ◽

Fibroblast Like Synoviocytes ◽

Amino Acid Response

Signaling pathways that sense amino acid abundance are integral to tissue homeostasis and cellular defense. Our laboratory has previously shown that halofuginone (HF) inhibits the prolyl-tRNA synthetase catalytic activity of glutamyl-prolyl-tRNA synthetase (EPRS), thereby activating the amino acid response (AAR). We now show that HF treatment selectively inhibits inflammatory responses in diverse cell types and that these therapeutic benefits occur in cells that lack GCN2, the signature effector of the AAR. Depletion of arginine, histidine, or lysine from cultured fibroblast-like synoviocytes recapitulates key aspects of HF treatment, without utilizing GCN2 or mammalian target of rapamycin complex 1 pathway signaling. Like HF, the threonyl-tRNA synthetase inhibitor borrelidin suppresses the induction of tissue remodeling and inflammatory mediators in cytokine-stimulated fibroblast-like synoviocytes without GCN2, but both aminoacyl-tRNA synthetase (aaRS) inhibitors are sensitive to the removal of GCN1. GCN1, an upstream component of the AAR pathway, binds to ribosomes and is required for GCN2 activation. These observations indicate that aaRS inhibitors, like HF, can modulate inflammatory response without the AAR/GCN2 signaling cassette, and that GCN1 has a role that is distinct from its activation of GCN2. We propose that GCN1 participates in a previously unrecognized amino acid sensor pathway that branches from the canonical AAR.

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Persistent Rheb-induced mTORC1 activation in spinal cord neurons induces hypersensitivity in neuropathic pain

Cell Death and Disease ◽

10.1038/s41419-020-02966-0 ◽

2020 ◽

Vol 11 (9) ◽

Author(s):

Xiaqing Ma ◽

Wenjie Du ◽

Wenying Wang ◽

Limin Luo ◽

Min Huang ◽

...

Keyword(s):

Neuropathic Pain ◽

Cell Cycle Progression ◽

Mammalian Target Of Rapamycin ◽

Firing Frequency ◽

Small Gtpase ◽

Hcn Channels ◽

Spinal Cord Neurons ◽

Mtorc1 Signaling ◽

New Strategy ◽

Cci Model

Abstract The small GTPase Ras homolog enriched in the brain (Rheb) can activate mammalian target of rapamycin (mTOR) and regulate the growth and cell cycle progression. We investigated the role of Rheb-mediated mTORC1 signaling in neuropathic pain. A chronic constriction injury (CCI) model was dopted. CCI induced obvious spinal Rheb expression and phosphorylation of mTOR, S6, and 4-E-BP1. Blocking mTORC1 signal with rapamycin alleviated the neuropathic pain and restored morphine efficacy in CCI model. Immunofluoresence showed a neuronal co-localization of CCI-induced Rheb and pS6. Rheb knockin mouse showed a similar behavioral phenotype as CCI. In spinal slice recording, CCI increased the firing frequency of neurons expressing HCN channels; inhibition of mTORC1 with rapamycin could reverse the increased spinal neuronal activity in neuropathic pain. Spinal Rheb is induced in neuropathic pain, which in turn active the mTORC1 signaling in CCI. Spinal Rheb-mTOR signal plays an important role in regulation of spinal sensitization in neuropathic pain, and targeting mTOR may give a new strategy for pain management.

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Amino acids and mTOR signalling in anabolic function

Biochemical Society Transactions ◽

10.1042/bst0351187 ◽

2007 ◽

Vol 35 (5) ◽

pp. 1187-1190 ◽

Cited By ~ 93

Author(s):

C.G. Proud

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Tuberous Sclerosis ◽

Tuberous Sclerosis Complex ◽

Ribosome Biogenesis ◽

Mammalian Target Of Rapamycin ◽

Single Amino Acid ◽

Translational Machinery ◽

Intracellular Amino Acids ◽

Mtor Signalling

Amino acids regulate signalling through the mTORC1 (mammalian target of rapamycin, complex 1) and thereby control a number of components of the translational machinery, including initiation and elongation factors. mTORC1 also positively regulates other anabolic processes, in particular ribosome biogenesis. The most effective single amino acid is leucine. A key issue is how intracellular amino acids regulate mTORC1. This does not require the TSC1/2 (tuberous sclerosis complex 1/2) complex, which is involved in the activation of mTORC1, for example, by insulin. Progress in understanding the mechanisms responsible for this will be reviewed.

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Insights into the Interaction of Lysosomal Amino Acid Transporters SLC38A9 and SLC36A1 Involved in mTORC1 Signaling in C2C12 Cells

Biomolecules ◽

10.3390/biom11091314 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1314

Author(s):

Dan Wang ◽

Xuebin Wan ◽

Xiaoli Du ◽

Zhuxia Zhong ◽

Jian Peng ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Skeletal Muscle Mass ◽

Mammalian Target Of Rapamycin ◽

C2c12 Cells ◽

Amino Acid Transporters ◽

Interacting Proteins ◽

Mtorc1 Signaling ◽

Amino Acid Sensing ◽

Mtorc1 Activation

Amino acids are critical for mammalian target of rapamycin complex 1 (mTORC1) activation on the lysosomal surface. Amino acid transporters SLC38A9 and SLC36A1 are the members of the lysosomal amino acid sensing machinery that activates mTORC1. The current study aims to clarify the interaction of SLC38A9 and SLC36A1. Here, we discovered that leucine increased expressions of SLC38A9 and SLC36A1, leading to mTORC1 activation. SLC38A9 interacted with SLC36A1 and they enhanced each other’s expression levels and locations on the lysosomal surface. Additionally, the interacting proteins of SLC38A9 in C2C12 cells were identified to participate in amino acid sensing mechanism, mTORC1 signaling pathway, and protein synthesis, which provided a resource for future investigations of skeletal muscle mass.

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Targeting the mTOR Signaling Pathway Utilizing Nanoparticles: A Critical Overview

Cancers ◽

10.3390/cancers11010082 ◽

2019 ◽

Vol 11 (1) ◽

pp. 82 ◽

Cited By ~ 18

Author(s):

Mariia Lunova ◽

Barbora Smolková ◽

Anna Lynnyk ◽

Mariia Uzhytchak ◽

Milan Jirsa ◽

...

Keyword(s):

Structural Changes ◽

Molecular Mechanisms ◽

Therapeutic Option ◽

Mammalian Target Of Rapamycin ◽

Mtor Signaling ◽

Therapeutic Effects ◽

Mtorc1 Signaling ◽

Challenges And Opportunities ◽

Signaling Axis ◽

Mtor Modulation

Proteins of the mammalian target of rapamycin (mTOR) signaling axis are overexpressed or mutated in cancers. However, clinical inhibition of mTOR signaling as a therapeutic strategy in oncology shows rather limited progress. Nanoparticle-based mTOR targeted therapy proposes an attractive therapeutic option for various types of cancers. Along with the progress in the biomedical applications of nanoparticles, we start to realize the challenges and opportunities that lie ahead. Here, we critically analyze the current literature on the modulation of mTOR activity by nanoparticles, demonstrate the complexity of cellular responses to functionalized nanoparticles, and underline challenges lying in the identification of the molecular mechanisms of mTOR signaling affected by nanoparticles. We propose the idea that subcytotoxic doses of nanoparticles could be relevant for the induction of subcellular structural changes with possible involvement of mTORC1 signaling. The evaluation of the mechanisms and therapeutic effects of nanoparticle-based mTOR modulation will provide fundamental knowledge which could help in developing safe and efficient nano-therapeutics.

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Metabolism of Amino Acids in Cancer

Frontiers in Cell and Developmental Biology ◽

10.3389/fcell.2020.603837 ◽

2021 ◽

Vol 8 ◽

Author(s):

Zhen Wei ◽

Xiaoyi Liu ◽

Chunming Cheng ◽

Wei Yu ◽

Ping Yi

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Amino Acid Metabolism ◽

Therapeutic Strategy ◽

Acid Metabolism ◽

Epigenetic Modification ◽

Mammalian Target Of Rapamycin ◽

Metabolic Reprogramming ◽

Mtorc1 Signaling ◽

Uptake And Metabolism

Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.

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ASCT2 silencing regulates mammalian target-of-rapamycin growth and survival signaling in human hepatoma cells

AJP Cell Physiology ◽

10.1152/ajpcell.00330.2006 ◽

2007 ◽

Vol 293 (1) ◽

pp. C55-C63 ◽

Cited By ~ 87

Author(s):

Bryan C. Fuchs ◽

Richard E. Finger ◽

Marie C. Onan ◽

Barrie P. Bode

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Ribosomal Protein ◽

Binding Protein ◽

Mammalian Target Of Rapamycin ◽

Amino Acid Transporter ◽

Human Hepatoma ◽

Growth And Survival ◽

Mtorc1 Signaling ◽

Survival Signaling

System ASC amino acid transporter-2 (ASCT2) was previously demonstrated to be essential for human hepatoma cell growth and survival, as its silencing via inducible antisense RNA expression results in complete apoptosis within 48 h by a mechanism that transcends its role in amino acid delivery. To gain mechanistic insights into the reliance of cancerous liver cells on ASCT2, the aim of this study was to determine the early consequences of its silencing on the growth and survival signaling that presage apoptosis. Induced antisense ASCT2 RNA in SK-Hep1 cells led to >90% suppression of ASCT2 mRNA by 6 h and inhibition of mammalian target-of-rapamycin (mTOR)/raptor (mTOR complex-1; mTORC1) signaling by 8 h, as manifested by diminished p70 ribosomal protein S6 kinase-1 and eukaryotic initiation factor-4E (eIF4E) binding protein-1 phosphorylation, while protein synthesis rates declined by nearly 50% despite no measurable decreases in the cap binding protein eIF4G or cellular ribosomal protein content. Depressed mTORC1 signaling occurred before detectable reduction in ASCT2 activity but coincided with a 30% decline in total cellular ASCT2 protein. By 12 h after ASCT2 silencing, further decrements were observed in protein synthesis rates and ASCT2 protein and activity, each by ∼50%, while signaling from mTOR/rictor (mTOR complex-2; mTORC2) was stimulated as indexed by enhanced phosphorylation of the Akt/PKB kinase on serine-473 and of its proapoptotic substrate Bad on serine-136. These results suggest that ASCT2 silencing inhibits mTORC1 signaling to the translational machinery followed by an mTORC2-initiated survival response, establishing a link between amino acid transporter expression and mTOR function.

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A Special Amino-Acid Formula Tailored to Boosting Cell Respiration Prevents Mitochondrial Dysfunction and Oxidative Stress Caused by Doxorubicin in Mouse Cardiomyocytes

Nutrients ◽

10.3390/nu12020282 ◽

2020 ◽

Vol 12 (2) ◽

pp. 282 ◽

Cited By ~ 4

Author(s):

Laura Tedesco ◽

Fabio Rossi ◽

Maurizio Ragni ◽

Chiara Ruocco ◽

Dario Brunetti ◽

...

Keyword(s):

Oxidative Stress ◽

Amino Acid ◽

Mitochondrial Biogenesis ◽

Cardiac Tissue ◽

Tricarboxylic Acid Cycle ◽

Mammalian Target Of Rapamycin ◽

Essential Amino Acids ◽

Mitochondrial Damage ◽

Mtorc1 Signaling ◽

And Oxidative Stress

Anthracycline anticancer drugs, such as doxorubicin (DOX), can induce cardiotoxicity supposed to be related to mitochondrial damage. We have recently demonstrated that a branched-chain amino acid (BCAA)-enriched mixture (BCAAem), supplemented with drinking water to middle-aged mice, was able to promote mitochondrial biogenesis in cardiac and skeletal muscle. To maximally favor and increase oxidative metabolism and mitochondrial function, here we tested a new original formula, composed of essential amino acids, tricarboxylic acid cycle precursors and co-factors (named α5), in HL-1 cardiomyocytes and mice treated with DOX. We measured mitochondrial biogenesis, oxidative stress, and BCAA catabolic pathway. Moreover, the molecular relevance of endothelial nitric oxide synthase (eNOS) and mechanistic/mammalian target of rapamycin complex 1 (mTORC1) was studied in both cardiac tissue and HL-1 cardiomyocytes. Finally, the role of Krüppel-like factor 15 (KLF15), a critical transcriptional regulator of BCAA oxidation and eNOS-mTORC1 signal, was investigated. Our results demonstrate that the α5 mixture prevents the DOX-dependent mitochondrial damage and oxidative stress better than the previous BCAAem, implying a KLF15/eNOS/mTORC1 signaling axis. These results could be relevant for the prevention of cardiotoxicity in the DOX-treated patients.

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mTORC1-Activated S6K1 Phosphorylates Rictor on Threonine 1135 and Regulates mTORC2 Signaling

Molecular and Cellular Biology ◽

10.1128/mcb.00601-09 ◽

2009 ◽

Vol 30 (4) ◽

pp. 908-921 ◽

Cited By ~ 255

Author(s):

Louis-Andre Julien ◽

Audrey Carriere ◽

Julie Moreau ◽

Philippe P. Roux

Keyword(s):

Ribosome Biogenesis ◽

Cellular Localization ◽

Glycogen Synthase ◽

Mammalian Target Of Rapamycin ◽

Mrna Translation ◽

Growth Factor Signaling ◽

Mtorc1 Signaling ◽

Ribosomal S6 Kinase

ABSTRACT The mammalian target of rapamycin (mTOR) is a conserved Ser/Thr kinase that forms two functionally distinct complexes important for nutrient and growth factor signaling. While mTOR complex 1 (mTORC1) regulates mRNA translation and ribosome biogenesis, mTORC2 plays an important role in the phosphorylation and subsequent activation of Akt. Interestingly, mTORC1 negatively regulates Akt activation, but whether mTORC1 signaling directly targets mTORC2 remains unknown. Here we show that growth factors promote the phosphorylation of Rictor (rapamycin-insensitive companion of mTOR), an essential subunit of mTORC2. We found that Rictor phosphorylation requires mTORC1 activity and, more specifically, the p70 ribosomal S6 kinase 1 (S6K1). We identified several phosphorylation sites in Rictor and found that Thr1135 is directly phosphorylated by S6K1 in vitro and in vivo, in a rapamycin-sensitive manner. Phosphorylation of Rictor on Thr1135 did not affect mTORC2 assembly, kinase activity, or cellular localization. However, cells expressing a Rictor T1135A mutant were found to have increased mTORC2-dependent phosphorylation of Akt. In addition, phosphorylation of the Akt substrates FoxO1/3a and glycogen synthase kinase 3α/β (GSK3α/β) was found to be increased in these cells, indicating that S6K1-mediated phosphorylation of Rictor inhibits mTORC2 and Akt signaling. Together, our results uncover a new regulatory link between the two mTOR complexes, whereby Rictor integrates mTORC1-dependent signaling.

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