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Rahman M, Nguyen TM, Lee GJ, Kim B, Park MK, Lee CH. Unraveling the Role of Ras Homolog Enriched in Brain (Rheb1 and Rheb2): Bridging Neuronal Dynamics and Cancer Pathogenesis through Mechanistic Target of Rapamycin Signaling. Int J Mol Sci 2024; 25:1489. [PMID: 38338768 PMCID: PMC10855792 DOI: 10.3390/ijms25031489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 01/14/2024] [Accepted: 01/17/2024] [Indexed: 02/12/2024] Open
Abstract
Ras homolog enriched in brain (Rheb1 and Rheb2), small GTPases, play a crucial role in regulating neuronal activity and have gained attention for their implications in cancer development, particularly in breast cancer. This study delves into the intricate connection between the multifaceted functions of Rheb1 in neurons and cancer, with a specific focus on the mTOR pathway. It aims to elucidate Rheb1's involvement in pivotal cellular processes such as proliferation, apoptosis resistance, migration, invasion, metastasis, and inflammatory responses while acknowledging that Rheb2 has not been extensively studied. Despite the recognized associations, a comprehensive understanding of the intricate interplay between Rheb1 and Rheb2 and their roles in both nerve and cancer remains elusive. This review consolidates current knowledge regarding the impact of Rheb1 on cancer hallmarks and explores the potential of Rheb1 as a therapeutic target in cancer treatment. It emphasizes the necessity for a deeper comprehension of the molecular mechanisms underlying Rheb1-mediated oncogenic processes, underscoring the existing gaps in our understanding. Additionally, the review highlights the exploration of Rheb1 inhibitors as a promising avenue for cancer therapy. By shedding light on the complicated roles between Rheb1/Rheb2 and cancer, this study provides valuable insights to the scientific community. These insights are instrumental in guiding the identification of novel targets and advancing the development of effective therapeutic strategies for treating cancer.
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Affiliation(s)
- Mostafizur Rahman
- College of Pharmacy, Dongguk University, Seoul 04620, Republic of Korea; (M.R.); (G.J.L.)
| | - Tuan Minh Nguyen
- College of Pharmacy, Dongguk University, Seoul 04620, Republic of Korea; (M.R.); (G.J.L.)
| | - Gi Jeong Lee
- College of Pharmacy, Dongguk University, Seoul 04620, Republic of Korea; (M.R.); (G.J.L.)
| | - Boram Kim
- College of Pharmacy, Dongguk University, Seoul 04620, Republic of Korea; (M.R.); (G.J.L.)
| | - Mi Kyung Park
- Department of BioHealthcare, Hwasung Medi-Science University, Hwaseong-si 18274, Republic of Korea
| | - Chang Hoon Lee
- College of Pharmacy, Dongguk University, Seoul 04620, Republic of Korea; (M.R.); (G.J.L.)
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2
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Roberson PA, Jefferson LS, Kimball SR. Convergence of signaling pathways in mediating actions of leucine and IGF-1 on mTORC1 in L6 myoblasts. Am J Physiol Cell Physiol 2022; 323:C804-C812. [PMID: 35912992 PMCID: PMC9448342 DOI: 10.1152/ajpcell.00183.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 07/27/2022] [Accepted: 07/28/2022] [Indexed: 11/22/2022]
Abstract
Leucine and insulin-like growth factor-1 (IGF-1) are important regulators of protein synthesis in skeletal muscle. The mechanistic target of rapamycin complex 1 (mTORC1) is of particular importance in their mechanism of action. In the present study, pathways through which leucine and IGF-1 converge to mediate activation of mTORC1 were examined in L6 myoblasts that were deprived of leucine and serum followed by readdition of either leucine or IGF-1. Compared with leucine- and serum-deprived myoblasts, IGF-1, but not leucine, promoted phosphorylation of protein kinase B (AKT), tuberous sclerosis complex 2 (TSC2), and the autophosphorylation site on mTOR (S2481) and also stimulated mTOR kinase activity in mTOR immunoprecipitated samples. Both leucine and IGF-1 promoted phosphorylation of mTOR on S2448. The association of mTOR with the regulatory-associated protein of mTOR (Raptor) was altered by IGF-1 treatment and trended (P = 0.065) to be altered by leucine treatment. Alterations in the association of mTOR with Raptor were proportional to changes in phosphorylation of the mTOR substrates, eIF4E-binding protein 1 (4E-BP1), and ribosomal protein S6 Kinase-β1 (p70S6K1). Surprisingly, leucine, but not IGF-1, stimulated protein synthesis suggesting a unique role for nutrients in regulating protein synthesis. Overall, the results are consistent with a model whereby IGF-1 stimulates phosphorylation of 4E-BP1 and p70S6K1 in L6 myoblasts through an AKT-TSC2-mTORC1 signaling pathway that also involves changes in the interaction between mTOR and Raptor. In contrast, leucine signaling to mTOR results in alterations in certain mTOR phosphorylation sites and the interaction between mTOR and Raptor and stimulates protein synthesis.
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Affiliation(s)
- Paul A Roberson
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania
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3
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Armijo ME, Escalona E, Peña D, Farias A, Morin V, Baumann M, Klebl BM, Pincheira R, Castro AF. Blocking the Farnesyl Pocket of PDEδ Reduces Rheb-Dependent mTORC1 Activation and Survival of Tsc2-Null Cells. Front Pharmacol 2022; 13:912688. [PMID: 35814251 PMCID: PMC9260180 DOI: 10.3389/fphar.2022.912688] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 05/31/2022] [Indexed: 11/22/2022] Open
Abstract
Rheb is a small GTPase member of the Ras superfamily and an activator of mTORC1, a protein complex master regulator of cell metabolism, growth, and proliferation. Rheb/mTORC1 pathway is hyperactivated in proliferative diseases, such as Tuberous Sclerosis Complex syndrome and cancer. Therefore, targeting Rheb-dependent signaling is a rational strategy for developing new drug therapies. Rheb activates mTORC1 in the cytosolic surface of lysosomal membranes. Rheb’s farnesylation allows its anchorage on membranes, while its proper localization depends on the prenyl-binding chaperone PDEδ. Recently, the use of PDEδ inhibitors has been proposed as anticancer agents because they interrupted KRas signaling leading to antiproliferative effects in KRas-dependent pancreatic cancer cells. However, the effect of PDEδ inhibition on the Rheb/mTORC1 pathway has been poorly investigated. Here, we evaluated the impact of a new PDEδ inhibitor, called Deltasonamide 1, in Tsc2-null MEFs, a Rheb-dependent overactivated mTORC1 cell line. By using a yeast two-hybrid assay, we first validated that Deltasonamide 1 disrupts Rheb-PDEδ interaction. Accordingly, we found that Deltasonamide 1 reduces mTORC1 targets activation. In addition, our results showed that Deltasonamide 1 has antiproliferative and cytotoxic effects on Tsc2-null MEFs but has less effect on Tsc2-wild type MEFs viability. This work proposes the pharmacological PDEδ inhibition as a new approach to target the abnormal Rheb/mTORC1 activation in Tuberous Sclerosis Complex cells.
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Affiliation(s)
- Marisol Estrella Armijo
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
- Laboratorio de Investigación en Ciencias Biomédicas, Departamento de Ciencias Básicas y Morfología, Facultad de Medicina, Universidad Católica de la Santísima Concepción, Concepción, Chile
| | - Emilia Escalona
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Daniela Peña
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Alejandro Farias
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Violeta Morin
- Laboratorio de Proteasas y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | | | | | - Roxana Pincheira
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
- *Correspondence: Roxana Pincheira, ; Ariel Fernando Castro,
| | - Ariel Fernando Castro
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
- *Correspondence: Roxana Pincheira, ; Ariel Fernando Castro,
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Small-Molecule RAS Inhibitors as Anticancer Agents: Discovery, Development, and Mechanistic Studies. Int J Mol Sci 2022; 23:ijms23073706. [PMID: 35409064 PMCID: PMC8999084 DOI: 10.3390/ijms23073706] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 03/21/2022] [Accepted: 03/24/2022] [Indexed: 12/11/2022] Open
Abstract
Mutations of RAS oncogenes are responsible for about 30% of all human cancer types, including pancreatic, lung, and colorectal cancers. While KRAS1 is a pseudogene, mutation of KRAS2 (commonly known as KRAS oncogene) is directly or indirectly associated with human cancers. Among the RAS family, KRAS is the most abundant oncogene related to uncontrolled cellular proliferation to generate solid tumors in many types of cancer such as pancreatic carcinoma (over 80%), colon carcinoma (40-50%), lung carcinoma (30-50%), and other types of cancer. Once described as 'undruggable', RAS proteins have become 'druggable', at least to a certain extent, due to the continuous efforts made during the past four decades. In this account, we discuss the chemistry and biology (wherever available) of the small-molecule inhibitors (synthetic, semi-synthetic, and natural) of KRAS proteins that were published in the past decades. Commercial drugs, as well as investigational molecules from preliminary stages to clinical trials, are categorized and discussed in this study. In summary, this study presents an in-depth discussion of RAS proteins, classifies the RAS superfamily, and describes the molecular mechanism of small-molecule RAS inhibitors.
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Zhong Y, Zhou X, Guan KL, Zhang J. Rheb regulates nuclear mTORC1 activity independent of farnesylation. Cell Chem Biol 2022; 29:1037-1045.e4. [PMID: 35294906 DOI: 10.1016/j.chembiol.2022.02.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 10/26/2021] [Accepted: 02/10/2022] [Indexed: 11/26/2022]
Abstract
The small GTPase Ras homolog enriched in brain (Rheb) plays a critical role in activating the mechanistic target of rapamycin complex 1 (mTORC1), a signaling hub that regulates various cellular functions. We recently observed nuclear mTORC1 activity, raising an intriguing question as to how Rheb, which is known to be farnesylated and localized to intracellular membranes, regulates nuclear mTORC1. In this study, we found that active Rheb is present in the nucleus and required for nuclear mTORC1 activity. We showed that inhibition of farnesyltransferase reduced cytosolic, but not nuclear, mTORC1 activity. Furthermore, a farnesylation-deficient Rheb mutant, with preferential nuclear localization and specific lysosome tethering, enables nuclear and cytosolic mTORC1 activities, respectively. These data suggest that non-farnesylated Rheb is capable of interacting with and activating mTORC1, providing mechanistic insights into the molecular functioning of Rheb as well as regulation of the recently observed, active pool of nuclear mTORC1.
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Affiliation(s)
- Yanghao Zhong
- Department of Pharmacology, University of California, San Diego, La Jolla, CA, USA; Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA, USA
| | - Xin Zhou
- Department of Pharmacology, University of California, San Diego, La Jolla, CA, USA
| | - Kun-Liang Guan
- Department of Pharmacology, University of California, San Diego, La Jolla, CA, USA; Moores Cancer Center, University of California, San Diego, La Jolla, CA, USA
| | - Jin Zhang
- Department of Pharmacology, University of California, San Diego, La Jolla, CA, USA; Moores Cancer Center, University of California, San Diego, La Jolla, CA, USA; Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA; Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA.
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6
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Sanvee GM, Hitzfeld L, Bouitbir J, Krähenbühl S. mTORC2 is an important target for simvastatin-associated toxicity in C2C12 cells and mouse skeletal muscle - Roles of Rap1 geranylgeranylation and mitochondrial dysfunction. Biochem Pharmacol 2021; 192:114750. [PMID: 34461118 DOI: 10.1016/j.bcp.2021.114750] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Revised: 08/24/2021] [Accepted: 08/25/2021] [Indexed: 12/25/2022]
Abstract
Statins decrease the serum LDL-cholesterol concentration and reduce the risk for cardiovascular diseases but can cause myopathy, which may be related to mTORC inhibition. In the current study, we investigated which mTORC is inhibited by simvastatin and by which mechanisms. In C2C12 myoblasts and myotubes and mouse gastrocnemius, simvastatin was cytotoxic and inhibited S6rp and Akt Ser473 phosphorylation, indicating inhibition of mTORC1 and mTORC2, respectively. In contrast to simvastatin, the mTORC1 inhibitor rapamycin did not inhibit mTORC2 activity and was not cytotoxic. Like simvastatin, knock-down of Rictor, an essential component of mTORC2, impaired Akt Ser473 and S6rp phosphorylation and was cytotoxic for C2C12 myoblasts, suggesting that mTORC2 inhibition is an important myotoxic mechanism. The investigation of the mechanism of mTORC2 inhibition showed that simvastatin impaired Ras farnesylation, which was prevented by farnesol but without restoring mTORC2 activity. In comparison, Rap1 knock-down reduced mTORC2 activity and was cytotoxic for C2C12 myoblasts. Simvastatin impaired Rap1 geranylgeranylation and function, which was prevented by geranylgeraniol. In addition, simvastatin and the complex III inhibitor antimycin A caused mitochondrial superoxide accumulation and impaired the activity of mTORC2, which could partially be prevented by the antioxidant MitoTEMPO. In conclusion, mTORC2 inhibition is an important mechanism of simvastatin-induced myotoxicity. Simvastatin inhibits mTORC2 by impairing geranylgeranylation of Rap1 and by inducing mitochondrial dysfunction.
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Affiliation(s)
- Gerda M Sanvee
- Division of Clinical Pharmacology & Toxicology, University Hospital, Basel, Switzerland; Department of Biomedicine, University of Basel, Switzerland
| | - Leonie Hitzfeld
- Division of Clinical Pharmacology & Toxicology, University Hospital, Basel, Switzerland
| | - Jamal Bouitbir
- Division of Clinical Pharmacology & Toxicology, University Hospital, Basel, Switzerland; Department of Biomedicine, University of Basel, Switzerland; Division of Molecular and Systemic Toxicology, Department of Pharmaceutical Sciences, University of Basel, Switzerland; Swiss Centre for Applied Human Research (SCAHT), Switzerland
| | - Stephan Krähenbühl
- Division of Clinical Pharmacology & Toxicology, University Hospital, Basel, Switzerland; Department of Biomedicine, University of Basel, Switzerland; Swiss Centre for Applied Human Research (SCAHT), Switzerland.
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7
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Amino Acids in Autophagy: Regulation and Function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1332:51-66. [PMID: 34251638 DOI: 10.1007/978-3-030-74180-8_4] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Autophagy is a dynamic process in which the eukaryotic cells break down intracellular components by lysosomal degradation. Under the normal condition, the basal level of autophagy removes damaged organelles, misfolded proteins, or protein aggregates to keep cells in a homeostatic condition. Deprivation of nutrients (e.g., removal of amino acids) stimulates autophagy activity, promoting lysosomal degradation and the recycling of cellular components for cell survival. Importantly, insulin and amino acids are two main inhibitors of autophagy. They both activate the mTOR complex 1 (mTORC1) signaling pathway to inhibit the autophagy upstream of the uncoordinated-51 like kinase 1/2 (ULK1/2) complex that triggers autophagosome formation. In particular, insulin activates mTORC1 via the PI3K class I-AKT pathway; while amino acids activate mTORC1 either through the PI3K class III (hVps34) pathway or through a variety of amino acid sensors located in the cytosol or lysosomal membrane. These amino acid sensors control the translocation of mTORC1 from the cytosol to the lysosomal surface where mTORC1 is activated by Rheb GTPase, therefore regulating autophagy and the lysosomal protein degradation.
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8
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Abstract
Mechanistic (or mammalian) target of rapamycin complex 1 (mTORC1) is a major signalling kinase in cells that regulates proliferation and metabolism and is controlled by extrinsic and intrinsic signals. The lysosome has received considerable attention as a major hub of mTORC1 activation. However, mTOR has also been located to a variety of other intracellular sites, indicating the possibility of spatial regulation of mTORC1 signalling within cells. In particular, there have been numerous recent reports of mTORC1 activation associated with the Golgi apparatus. Here, we review the evidence for the regulation of mTORC1 signalling at the Golgi in mammalian cells. mTORC1 signalling is closely linked to the morphology of the Golgi architecture; a number of Golgi membrane tethers/scaffolds that influence Golgi architecture in mammalian cells that directly or indirectly regulate mTORC1 activation have been identified. Perturbation of the Golgi mTORC1 pathway arising from fragmentation of the Golgi has been shown to promote oncogenesis. Here, we highlight the potential mechanisms for the activation mTORC1 at the Golgi, which is emerging as a major site for mTORC1 signalling.
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Affiliation(s)
- Christian Makhoul
- The Department of Biochemistry and Pharmacology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia
| | - Paul A Gleeson
- The Department of Biochemistry and Pharmacology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia
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Yin S, Liu L, Gan W. The Roles of Post-Translational Modifications on mTOR Signaling. Int J Mol Sci 2021; 22:ijms22041784. [PMID: 33670113 PMCID: PMC7916890 DOI: 10.3390/ijms22041784] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 02/05/2021] [Accepted: 02/08/2021] [Indexed: 02/06/2023] Open
Abstract
The mechanistic target of rapamycin (mTOR) is a master regulator of cell growth, proliferation, and metabolism by integrating various environmental inputs including growth factors, nutrients, and energy, among others. mTOR signaling has been demonstrated to control almost all fundamental cellular processes, such as nucleotide, protein and lipid synthesis, autophagy, and apoptosis. Over the past fifteen years, mapping the network of the mTOR pathway has dramatically advanced our understanding of its upstream and downstream signaling. Dysregulation of the mTOR pathway is frequently associated with a variety of human diseases, such as cancers, metabolic diseases, and cardiovascular and neurodegenerative disorders. Besides genetic alterations, aberrancies in post-translational modifications (PTMs) of the mTOR components are the major causes of the aberrant mTOR signaling in a number of pathologies. In this review, we summarize current understanding of PTMs-mediated regulation of mTOR signaling, and also update the progress on targeting the mTOR pathway and PTM-related enzymes for treatment of human diseases.
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Ramlaul K, Fu W, Li H, de Martin Garrido N, He L, Trivedi M, Cui W, Aylett CHS, Wu G. Architecture of the Tuberous Sclerosis Protein Complex. J Mol Biol 2020; 433:166743. [PMID: 33307091 PMCID: PMC7840889 DOI: 10.1016/j.jmb.2020.166743] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 11/26/2020] [Accepted: 12/02/2020] [Indexed: 12/11/2022]
Abstract
We report the molecular architecture of the TSC protein complex by single-particle cryo-EM. The TSCC forms an elongated scorpion-like structure, with pincer, body and a barbed tail. The body is TSC2, while TSC1 runs along its surface and makes up the pincer, and TBC1D7 the barb. The TSC2 GAP domain is poised to bind a pair of Rheb molecules at a similar separation to the pair in activated mTORC1.
The Tuberous Sclerosis Complex (TSC) protein complex (TSCC), comprising TSC1, TSC2, and TBC1D7, is widely recognised as a key integration hub for cell growth and intracellular stress signals upstream of the mammalian target of rapamycin complex 1 (mTORC1). The TSCC negatively regulates mTORC1 by acting as a GTPase-activating protein (GAP) towards the small GTPase Rheb. Both human TSC1 and TSC2 are important tumour suppressors, and mutations in them underlie the disease tuberous sclerosis. We used single-particle cryo-EM to reveal the organisation and architecture of the complete human TSCC. We show that TSCC forms an elongated scorpion-like structure, consisting of a central “body”, with a “pincer” and a “tail” at the respective ends. The “body” is composed of a flexible TSC2 HEAT repeat dimer, along the surface of which runs the TSC1 coiled-coil backbone, breaking the symmetry of the dimer. Each end of the body is structurally distinct, representing the N- and C-termini of TSC1; a “pincer” is formed by the highly flexible N-terminal TSC1 core domains and a barbed “tail” makes up the TSC1 coiled-coil-TBC1D7 junction. The TSC2 GAP domain is found abutting the centre of the body on each side of the dimerisation interface, poised to bind a pair of Rheb molecules at a similar separation to the pair in activated mTORC1. Our architectural dissection reveals the mode of association and topology of the complex, casts light on the recruitment of Rheb to the TSCC, and also hints at functional higher order oligomerisation, which has previously been predicted to be important for Rheb-signalling suppression.
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Affiliation(s)
- Kailash Ramlaul
- Section for Structural Biology, Department of Infectious Disease, Imperial College London, Exhibition Road, London SW7 2BB, United Kingdom
| | - Wencheng Fu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, The Joint International Research Laboratory of Metabolic & Developmental Sciences MOE, Shanghai Jiao Tong University, Shanghai, China
| | - Hua Li
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, The Joint International Research Laboratory of Metabolic & Developmental Sciences MOE, Shanghai Jiao Tong University, Shanghai, China
| | - Natàlia de Martin Garrido
- Section for Structural Biology, Department of Infectious Disease, Imperial College London, Exhibition Road, London SW7 2BB, United Kingdom
| | - Lin He
- Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai, China
| | - Manjari Trivedi
- Institute of Reproductive and Developmental Biology, Department of Metabolism, Digestion and Reproduction, Imperial College London, Du Cane Road, London W12 0NN, United Kingdom
| | - Wei Cui
- Institute of Reproductive and Developmental Biology, Department of Metabolism, Digestion and Reproduction, Imperial College London, Du Cane Road, London W12 0NN, United Kingdom
| | - Christopher H S Aylett
- Section for Structural Biology, Department of Infectious Disease, Imperial College London, Exhibition Road, London SW7 2BB, United Kingdom.
| | - Geng Wu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, The Joint International Research Laboratory of Metabolic & Developmental Sciences MOE, Shanghai Jiao Tong University, Shanghai, China.
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Borini Etichetti CM, Arel Zalazar E, Cocordano N, Girardini J. Beyond the Mevalonate Pathway: Control of Post-Prenylation Processing by Mutant p53. Front Oncol 2020; 10:595034. [PMID: 33224889 PMCID: PMC7674641 DOI: 10.3389/fonc.2020.595034] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 10/08/2020] [Indexed: 12/21/2022] Open
Abstract
Missense mutations in the TP53 gene are among the most frequent alterations in human cancer. Consequently, many tumors show high expression of p53 point mutants, which may acquire novel activities that contribute to develop aggressive tumors. An unexpected aspect of mutant p53 function was uncovered by showing that some mutants can increase the malignant phenotype of tumor cells through alteration of the mevalonate pathway. Among metabolites generated through this pathway, isoprenoids are of particular interest, since they participate in a complex process of posttranslational modification known as prenylation. Recent evidence proposes that mutant p53 also enhances this process through transcriptional activation of ICMT, the gene encoding the methyl transferase responsible for the last step of protein prenylation. In this way, mutant p53 may act at different levels to promote prenylation of key proteins in tumorigenesis, including several members of the RAS and RHO families. Instead, wild type p53 acts in the opposite way, downregulating mevalonate pathway genes and ICMT. This oncogenic circuit also allows to establish potential connections with other metabolic pathways. The demand of acetyl-CoA for the mevalonate pathway may pose limitations in cell metabolism. Likewise, the dependence on S-adenosyl methionine for carboxymethylation, may expose cells to methionine stress. The involvement of protein prenylation in tumor progression offers a novel perspective to understand the antitumoral effects of mevalonate pathway inhibitors, such as statins, and to explore novel therapeutic strategies.
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Affiliation(s)
| | - Evelyn Arel Zalazar
- Instituto de Inmunología Clínica y Experimental de Rosario, IDICER, CONICET-UNR, Rosario, Argentina
| | - Nabila Cocordano
- Instituto de Inmunología Clínica y Experimental de Rosario, IDICER, CONICET-UNR, Rosario, Argentina
| | - Javier Girardini
- Instituto de Inmunología Clínica y Experimental de Rosario, IDICER, CONICET-UNR, Rosario, Argentina
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12
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Qian J, Su S, Liu P. Experimental Approaches in Delineating mTOR Signaling. Genes (Basel) 2020; 11:E738. [PMID: 32630768 PMCID: PMC7397015 DOI: 10.3390/genes11070738] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 06/28/2020] [Accepted: 06/30/2020] [Indexed: 11/16/2022] Open
Abstract
The mTOR signaling controls essential biological functions including proliferation, growth, metabolism, autophagy, ageing, and others. Hyperactivation of mTOR signaling leads to a plethora of human disorders; thus, mTOR is an attractive drug target. The discovery of mTOR signaling started from isolation of rapamycin in 1975 and cloning of TOR genes in 1993. In the past 27 years, numerous research groups have contributed significantly to advancing our understanding of mTOR signaling and mTOR biology. Notably, a variety of experimental approaches have been employed in these studies to identify key mTOR pathway members that shape up the mTOR signaling we know today. Technique development drives mTOR research, while canonical biochemical and yeast genetics lay the foundation for mTOR studies. Here in this review, we summarize major experimental approaches used in the past in delineating mTOR signaling, including biochemical immunoprecipitation approaches, genetic approaches, immunofluorescence microscopic approaches, hypothesis-driven studies, protein sequence or motif search driven approaches, and bioinformatic approaches. We hope that revisiting these distinct types of experimental approaches will provide a blueprint for major techniques driving mTOR research. More importantly, we hope that thinking and reasonings behind these experimental designs will inspire future mTOR research as well as studies of other protein kinases beyond mTOR.
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Affiliation(s)
- Jiayi Qian
- Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (J.Q.); (S.S.)
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Siyuan Su
- Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (J.Q.); (S.S.)
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Pengda Liu
- Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (J.Q.); (S.S.)
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Abstract
A complex molecular machinery converges on the surface of lysosomes to ensure that the growth-promoting signaling mediated by mechanistic target of rapamycin complex 1 (mTORC1) is tightly controlled by the availability of nutrients and growth factors. The final step in this activation process is dependent on Rheb, a small GTPase that binds to mTOR and allosterically activates its kinase activity. Here we review the mechanisms that determine the subcellular localization of Rheb (and the closely related RhebL1 protein) as well as the significance of these mechanisms for controlling mTORC1 activation. In particular, we explore how the relatively weak membrane interactions conferred by C-terminal farnesylation are critical for the ability of Rheb to activate mTORC1. In addition to supporting transient membrane interactions, Rheb C-terminal farnesylation also supports an interaction between Rheb and the δ subunit of phosphodiesterase 6 (PDEδ). This interaction provides a potential mechanism for targeting Rheb to membranes that contain Arl2, a small GTPase that triggers the release of prenylated proteins from PDEδ. The minimal membrane targeting conferred by C-terminal farnesylation of Rheb and RhebL1 distinguishes them from other members of the Ras superfamily that possess additional membrane interaction motifs that work with farnesylation for enrichment on the specific subcellular membranes where they engage key effectors. Finally, we highlight diversity in Rheb membrane targeting mechanisms as well as the potential for alternative mTORC1 activation mechanisms across species.
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Affiliation(s)
- Brittany Angarola
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06510, USA.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, 06510, USA
| | - Shawn M Ferguson
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06510, USA.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, 06510, USA
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14
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Carroll B. Spatial regulation of mTORC1 signalling: Beyond the Rag GTPases. Semin Cell Dev Biol 2020; 107:103-111. [PMID: 32122730 DOI: 10.1016/j.semcdb.2020.02.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 02/17/2020] [Accepted: 02/20/2020] [Indexed: 12/15/2022]
Abstract
The mechanistic (or mammalian) Target of Rapamycin Complex 1 (mTORC1) is a central regulator of cell growth and metabolism. By integrating mitogenic signals, mTORC1-dependent phosphorylation of substrates dictates the balance between anabolic, pro-growth and catabolic, recycling processes in the cell. The discovery that amino acids activate mTORC1 by promoting its translocation to the lysosome was a fundamental advance in the understanding of mTORC1 signalling. It has since become clear that the lysosome-cytoplasm shuttling of mTORC1 represents just one layer of spatial control of this signalling pathway. This review will focus on exploring the subcellular localisation of mTORC1 and its regulators to multiple sites within the cell. We will discuss how these spatially distinct regions such as endoplasmic reticulum, plasma membrane and the endosomal pathway co-operate to transduce nutrient availability to mTORC1, allowing for tight control of cell growth.
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Affiliation(s)
- Bernadette Carroll
- School of Biochemistry, Biomedical Sciences Building, University Walk, Bristol, BS8, United Kingdom.
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15
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Rogala KB, Gu X, Kedir JF, Abu-Remaileh M, Bianchi LF, Bottino AMS, Dueholm R, Niehaus A, Overwijn D, Fils ACP, Zhou SX, Leary D, Laqtom NN, Brignole EJ, Sabatini DM. Structural basis for the docking of mTORC1 on the lysosomal surface. Science 2019; 366:468-475. [PMID: 31601708 PMCID: PMC7176403 DOI: 10.1126/science.aay0166] [Citation(s) in RCA: 110] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 10/01/2019] [Indexed: 12/14/2022]
Abstract
The mTORC1 (mechanistic target of rapamycin complex 1) protein kinase regulates growth in response to nutrients and growth factors. Nutrients promote its translocation to the lysosomal surface, where its Raptor subunit interacts with the Rag guanosine triphosphatase (GTPase)-Ragulator complex. Nutrients switch the heterodimeric Rag GTPases among four different nucleotide-binding states, only one of which (RagA/B•GTP-RagC/D•GDP) permits mTORC1 association. We used cryo-electron microscopy to determine the structure of the supercomplex of Raptor with Rag-Ragulator at a resolution of 3.2 angstroms. Our findings indicate that the Raptor α-solenoid directly detects the nucleotide state of RagA while the Raptor "claw" threads between the GTPase domains to detect that of RagC. Mutations that disrupted Rag-Raptor binding inhibited mTORC1 lysosomal localization and signaling. By comparison with a structure of mTORC1 bound to its activator Rheb, we developed a model of active mTORC1 docked on the lysosome.
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Affiliation(s)
- Kacper B Rogala
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Xin Gu
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jibril F Kedir
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Monther Abu-Remaileh
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Laura F Bianchi
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | | | - Rikke Dueholm
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Anna Niehaus
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Daan Overwijn
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | | | - Sherry X Zhou
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Daniel Leary
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
| | - Nouf N Laqtom
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Edward J Brignole
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- MIT.nano, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - David M Sabatini
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA.
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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16
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Angarola B, Ferguson SM. Weak membrane interactions allow Rheb to activate mTORC1 signaling without major lysosome enrichment. Mol Biol Cell 2019; 30:2750-2760. [PMID: 31532697 PMCID: PMC6789162 DOI: 10.1091/mbc.e19-03-0146] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Stable localization of the Rheb GTPase to lysosomes is thought to be required for activation of mTOR complex 1 (mTORC1) signaling. However, the lysosome targeting mechanisms for Rheb remain unclear. We therefore investigated the relationship between Rheb subcellular localization and mTORC1 activation. Surprisingly, we found that Rheb was undetectable at lysosomes. Nonetheless, functional assays in knockout human cells revealed that farnesylation of the C-terminal CaaX motif on Rheb was essential for Rheb-dependent mTORC1 activation. Although farnesylated Rheb exhibited partial endoplasmic reticulum (ER) localization, constitutively targeting Rheb to ER membranes did not support mTORC1 activation. Further systematic analysis of Rheb lipidation revealed that weak, nonselective, membrane interactions support Rheb-dependent mTORC1 activation without the need for a specific lysosome targeting motif. Collectively, these results argue against stable interactions of Rheb with lysosomes and instead that transient membrane interactions optimally allow Rheb to activate mTORC1 signaling.
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Affiliation(s)
- Brittany Angarola
- Departments of Cell Biology and Neuroscience, Yale University School of Medicine, New Haven, CT 06510
| | - Shawn M Ferguson
- Departments of Cell Biology and Neuroscience, Yale University School of Medicine, New Haven, CT 06510
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17
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Abstract
Both acute intoxication and longer-term cumulative ingestion of alcohol negatively impact the metabolic phenotype of both skeletal and cardiac muscle, independent of overt protein calorie malnutrition, resulting in loss of skeletal muscle strength and cardiac contractility. In large part, these alcohol-induced changes are mediated by a decrease in protein synthesis that in turn is governed by impaired activity of a protein kinase, the mechanistic target of rapamycin (mTOR). Herein, we summarize recent advances in understanding mTOR signal transduction, similarities and differences between the effects of alcohol on this central metabolic controller in skeletal muscle and in the heart, and the effects of acute versus chronic alcohol intake. While alcohol-induced alterations in global proteolysis via activation of the ubiquitin-proteasome pathway are equivocal, emerging data suggest alcohol increases autophagy in muscle. Further studies are necessary to define the relative contributions of these bidirectional changes in protein synthesis and autophagy in the etiology of alcoholic myopathy in skeletal muscle and the heart.
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Affiliation(s)
- Scot R Kimball
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA; ,
| | - Charles H Lang
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA; ,
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18
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Choi S, Sadra A, Kang J, Ryu JR, Kim JH, Sun W, Huh SO. Farnesylation-defective Rheb Increases Axonal Length Independently of mTORC1 Activity in Embryonic Primary Neurons. Exp Neurobiol 2019; 28:172-182. [PMID: 31138988 PMCID: PMC6526111 DOI: 10.5607/en.2019.28.2.172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 03/27/2019] [Accepted: 03/28/2019] [Indexed: 02/01/2023] Open
Abstract
Rheb (Ras homolog enriched in the brain) is a small GTPase protein that plays an important role in cell signaling for development of the neocortex through modulation of mTORC1 (mammalian-target-of-rapamycin-complex-1) activity. mTORC1 is known to control various biological processes including axonal growth in forming complexes at the lysosomal membrane compartment. As such, anchoring of Rheb on the lysosomal membrane via the farnesylation of Rheb at its cysteine residue (C180) is required for its promotion of mTOR activity. To test the significance of Rheb farnesylation, we overexpressed a farnesylation mutant form of Rheb, Rheb C180S, in primary rat hippocampal neurons and also in mouse embryonic neurons using in utero electroporation. Interestingly, we found that Rheb C180S maintained promotional effect of axonal elongation similar to the wild-type Rheb in both test systems. On the other hand, Rheb C180S failed to exhibit the multiple axon-promoting effect which is found in wild-type Rheb. The levels of phospho-4EBP1, a downstream target of mTORC1, were surprisingly increased in Rheb C180S transfected neurons, despite the levels of phosphorylated mTOR being significantly decreased compared to control vector transfectants. A specific mTORC1 inhibitor, rapamycin, also could not completely abolish axon elongation characteristics of Rheb C180S in transfected cells. Our data suggests that Rheb in a non-membrane compartment can promote the axonal elongation via phosphorylation of 4EBP1 and through an mTORC1-independent pathway.
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Affiliation(s)
- Seunghyuk Choi
- Department of Pharmacology, College of Medicine, Institute of Natural Medicine, Hallym University, Chuncheon 24252, Korea
| | - Ali Sadra
- Department of Pharmacology, College of Medicine, Institute of Natural Medicine, Hallym University, Chuncheon 24252, Korea
| | - Jieun Kang
- Department of Pharmacology, College of Medicine, Institute of Natural Medicine, Hallym University, Chuncheon 24252, Korea
| | - Jae Ryun Ryu
- Department of Anatomy, Korea University College of Medicine, Brain Korea 21 Plus, Seoul 02841, Korea
| | - June Hoan Kim
- Department of Anatomy, Korea University College of Medicine, Brain Korea 21 Plus, Seoul 02841, Korea
| | - Woong Sun
- Department of Anatomy, Korea University College of Medicine, Brain Korea 21 Plus, Seoul 02841, Korea
| | - Sung-Oh Huh
- Department of Pharmacology, College of Medicine, Institute of Natural Medicine, Hallym University, Chuncheon 24252, Korea
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19
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Abstract
Background The protein kinase Target Of Rapamycin (TOR) is a nexus for the regulation of eukaryotic cell growth. TOR assembles into one of two distinct signalling complexes, TOR complex 1 (TORC1) and TORC2 (mTORC1/2 in mammals), with a set of largely non-overlapping protein partners. (m)TORC1 activation occurs in response to a series of stimuli relevant to cell growth, including nutrient availability, growth factor signals and stress, and regulates much of the cell's biosynthetic activity, from proteins to lipids, and recycling through autophagy. mTORC1 regulation is of great therapeutic significance, since in humans many of these signalling complexes, alongside subunits of mTORC1 itself, are implicated in a wide variety of pathophysiologies, including multiple types of cancer, neurological disorders, neurodegenerative diseases and metabolic disorders including diabetes. Methodology Recent years have seen numerous structures determined of (m)TOR, which have provided mechanistic insight into (m)TORC1 activation in particular, however the integration of cellular signals occurs upstream of the kinase and remains incompletely understood. Here we have collected and analysed in detail as many as possible of the molecular and structural studies which have shed light on (m)TORC1 repression, activation and signal integration. Conclusions A molecular understanding of this signal integration pathway is required to understand how (m)TORC1 activation is reconciled with the many diverse and contradictory stimuli affecting cell growth. We discuss the current level of molecular understanding of the upstream components of the (m)TORC1 signalling pathway, recent progress on this key biochemical frontier, and the future studies necessary to establish a mechanistic understanding of this master-switch for eukaryotic cell growth.
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Affiliation(s)
- Kailash Ramlaul
- Section of Structural Biology, Department of Medicine, Imperial College London, SW7 2AZ, UK
| | - Christopher H S Aylett
- Section of Structural Biology, Department of Medicine, Imperial College London, SW7 2AZ, UK
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20
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Emmanuel N, Ragunathan S, Shan Q, Wang F, Giannakou A, Huser N, Jin G, Myers J, Abraham RT, Unsal-Kacmaz K. Purine Nucleotide Availability Regulates mTORC1 Activity through the Rheb GTPase. Cell Rep 2018; 19:2665-2680. [PMID: 28658616 DOI: 10.1016/j.celrep.2017.05.043] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 04/24/2017] [Accepted: 05/12/2017] [Indexed: 01/05/2023] Open
Abstract
Pharmacologic agents that interfere with nucleotide metabolism constitute an important class of anticancer agents. Recent studies have demonstrated that mTOR complex 1 (mTORC1) inhibitors suppress de novo biosynthesis of pyrimidine and purine nucleotides. Here, we demonstrate that mTORC1 itself is suppressed by drugs that reduce intracellular purine nucleotide pools. Cellular treatment with AG2037, an inhibitor of the purine biosynthetic enzyme GARFT, profoundly inhibits mTORC1 activity via a reduction in the level of GTP-bound Rheb, an obligate upstream activator of mTORC1, because of a reduction in intracellular guanine nucleotides. AG2037 treatment provokes both mTORC1 inhibition and robust tumor growth suppression in mice bearing non-small-cell lung cancer (NSCLC) xenografts. These results indicate that alterations in purine nucleotide availability affect mTORC1 activity and suggest that inhibition of mTORC1 contributes to the therapeutic effects of purine biosynthesis inhibitors.
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Affiliation(s)
- Natasha Emmanuel
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Shoba Ragunathan
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Qin Shan
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Fang Wang
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Andreas Giannakou
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Nanni Huser
- Oncology R&D Group, Pfizer Worldwide Research and Development, 10646 Science Center Drive/CB4, San Diego, CA 92121, USA
| | - Guixian Jin
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Jeremy Myers
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA
| | - Robert T Abraham
- Oncology R&D Group, Pfizer Worldwide Research and Development, 10646 Science Center Drive/CB4, San Diego, CA 92121, USA.
| | - Keziban Unsal-Kacmaz
- Oncology R&D Group, Pfizer Worldwide Research and Development, 401 N. Middletown Road, Pearl River, NY 10965, USA.
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21
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Heard JJ, Phung I, Potes MI, Tamanoi F. An oncogenic mutant of RHEB, RHEB Y35N, exhibits an altered interaction with BRAF resulting in cancer transformation. BMC Cancer 2018; 18:69. [PMID: 29320991 PMCID: PMC5763582 DOI: 10.1186/s12885-017-3938-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 12/19/2017] [Indexed: 12/31/2022] Open
Abstract
Background RHEB is a unique member of the RAS superfamily of small GTPases expressed in all tissues and conserved from yeast to humans. Early studies on RHEB indicated a possible RHEB-RAF interaction, but this has not been fully explored. Recent work on cancer genome databases has revealed a reoccurring mutation in RHEB at the Tyr35 position, and a recent study points to the oncogenic potential of this mutant that involves activation of RAF/MEK/ERK signaling. These developments prompted us to reassess the significance of RHEB effect on RAF, and to compare mutant and wild type RHEB. Methods To study RHEB-RAF interaction, and the effect of the Y35N mutation on this interaction, we used transfection, immunoprecipitation, and Western blotting techniques. We generated cell lines stably expressing RHEB WT, RHEB Y35N, and KRAS G12V, and monitored cellular transforming properties through cell proliferation, anchorage independent growth, cell cycle analysis, and foci formation assays. Results We observe a strong interaction between RHEB and BRAF, but not with CRAF. This interaction is dependent on an intact RHEB effector domain and RHEB-GTP loading status. RHEB overexpression decreases RAF activation of the RAF/MEK/ERK pathway and RHEB knockdown results in an increase in RAF/MEK/ERK activation. RHEB Y35N mutation has decreased interaction with BRAF, and RHEB Y35N cells exhibit greater BRAF/CRAF heterodimerization resulting in increased RAF/MEK/ERK signaling. This leads to cancer transformation of RHEB Y35N stably expressing cell lines, similar to KRAS G12 V expressing cell lines. Conclusions RHEB interaction with BRAF is crucial for inhibiting RAF/MEK/ERK signaling. The RHEB Y35N mutant sustains RAF/MEK/ERK signaling due to a decreased interaction with BRAF, leading to increased BRAF/CRAF heterodimerization. RHEB Y35N expressing cells undergo cancer transformation due to decreased interaction between RHEB and BRAF resulting in overactive RAF/MEK/ERK signaling. Taken together with the previously established function of RHEB to activate mTORC1 signaling, it appears that RHEB performs a dual function; one is to suppress the RAF/MEK/ERK signaling and the other is to activate mTORC1 signaling. Electronic supplementary material The online version of this article (10.1186/s12885-017-3938-5) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Jeffrey J Heard
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, 1602 Molecular Sciences Bldg, 609 Charles E. Young Dr. East, Los Angeles, CA, 90095-1489, USA
| | - Ivy Phung
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, 1602 Molecular Sciences Bldg, 609 Charles E. Young Dr. East, Los Angeles, CA, 90095-1489, USA
| | - Mark I Potes
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, 1602 Molecular Sciences Bldg, 609 Charles E. Young Dr. East, Los Angeles, CA, 90095-1489, USA
| | - Fuyuhiko Tamanoi
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, 1602 Molecular Sciences Bldg, 609 Charles E. Young Dr. East, Los Angeles, CA, 90095-1489, USA. .,Institute for Integrated Cell-Material Sciences, Kyoto University, Kyoto, Japan.
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22
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Nelson N, Clark GJ. Rheb may complex with RASSF1A to coordinate Hippo and TOR signaling. Oncotarget 2017; 7:33821-31. [PMID: 27034171 PMCID: PMC5085121 DOI: 10.18632/oncotarget.8447] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 03/23/2016] [Indexed: 12/19/2022] Open
Abstract
The TOR pathway is a vital component of cellular homeostasis that controls the synthesis of proteins, nucleic acids and lipids. Its core is the TOR kinase. Activation of the TOR pathway suppresses autophagy, which plays a vital but complex role in tumorigenesis. The TOR pathway is regulated by activation of the Ras-related protein Rheb, which can bind mTOR. The Hippo pathway is a major growth control module that regulates cell growth, differentiation and apoptosis. Its core consists of an MST/LATS kinase cascade that can be activated by the RASSF1A tumor suppressor. The TOR and Hippo pathways may be coordinately regulated to promote cellular homeostasis. However, the links between the pathways remain only partially understood. We now demonstrate that in addition to mTOR regulation, Rheb also impacts the Hippo pathway by forming a complex with RASSF1A. Using stable clones of two human lung tumor cell lines (NCI-H1792 and NCI-H1299) with shRNA-mediated silencing or ectopic overexpression of RASSF1A, we show that activated Rheb stimulates the Hippo pathway, but is suppressed in its ability to stimulate the TOR pathway. Moreover, by selectively labeling autophagic vacuoles we show that RASSF1A inhibits the ability of Rheb to suppress autophagy and enhance cell growth. Thus, we identify a new connection that impacts coordination of Hippo and TOR signaling. As RASSF1A expression is frequently lost in human tumors, the RASSF1A status of a tumor may impact not just its Hippo pathway status, but also its TOR pathway status.
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Affiliation(s)
- Nicholas Nelson
- Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY, USA.,Department of Pharmacology and Toxicology, University of Louisville, Louisville, KY, USA
| | - Geoffrey J Clark
- Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY, USA.,Department of Pharmacology and Toxicology, University of Louisville, Louisville, KY, USA
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23
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Li C, Liu X, Liu Y, Zhang E, Medepalli K, Masuda K, Li N, Wikenheiser-Brokamp KA, Osterburg A, Borchers MT, Kopras EJ, Plas DR, Sun J, Franz DN, Capal JK, Mays M, Sun Y, Kwiatkowski DJ, Alayev A, Holz MK, Krueger DA, Siroky BJ, Yu JJ. Tuberin Regulates Prostaglandin Receptor-Mediated Viability, via Rheb, in mTORC1-Hyperactive Cells. Mol Cancer Res 2017; 15:1318-1330. [PMID: 28710231 DOI: 10.1158/1541-7786.mcr-17-0077] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 06/09/2017] [Accepted: 07/10/2017] [Indexed: 11/16/2022]
Abstract
Tuberous sclerosis complex (TSC) is a tumor-suppressor syndrome affecting multiple organs, including the brain, skin, kidneys, heart, and lungs. TSC is associated with mutations in TSC1 or TSC2, resulting in hyperactivation of mTOR complex 1 (mTORC1). Clinical trials demonstrate that mTORC1 inhibitors decrease tumor volume and stabilize lung function in TSC patients; however, mTOR inhibitors are cytostatic not cytocidal, and long-term benefits and toxicities are uncertain. Previously, we identified rapamycin-insensitive upregulation of cyclooxygenase 2 (PTGS2/COX2) and prostaglandin E2 (PGE2) production in TSC2-deficient cells and postulated that the action of excess PGE2 and its cognate receptors (EP) contributes to cell survival. In this study, we identify upregulation of EP3 (PTGER3) expression in TSC2-deficient cells, TSC renal angiomyolipomas, lymphangioleiomyomatosis lung nodules, and epileptic brain tubers. TSC2 negatively regulated EP3 expression via Rheb in a rapamycin-insensitive manner. The EP3 antagonist, L-798106, selectively suppressed the viability of TSC2-deficient cells in vitro and decreased the lung colonization of TSC2-deficient cells. Collectively, these data reveal a novel function of TSC2 and Rheb in the regulation of EP3 expression and cell viability.Implications: Therapeutic targeting of an aberrant PGE2-EP3 signaling axis may have therapeutic benefit for TSC patients and for other mTOR-hyperactive neoplasms. Mol Cancer Res; 15(10); 1318-30. ©2017 AACR.
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Affiliation(s)
- Chenggang Li
- State Key Laboratory of Medicinal Chemical Biology and College of Pharmacy, Nankai University, Tianjin, China.,Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Xiaolei Liu
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Yang Liu
- Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Scientific Research Center for Translational Medicine, Dalian, China
| | - Erik Zhang
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Kantha Medepalli
- Department of Internal Medicine, University of Cincinnati Medical Center, Cincinnati, Ohio
| | - Kouhei Masuda
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Na Li
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio.,Department of Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, China
| | - Kathryn A Wikenheiser-Brokamp
- Pathology and Laboratory Medicine and Pulmonary Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Andrew Osterburg
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Michael T Borchers
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Elizabeth J Kopras
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - David R Plas
- Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Julia Sun
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - David N Franz
- Division of Neurology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Jamie K Capal
- Division of Neurology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Maxwell Mays
- Division of Neurology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Yang Sun
- Cutaneous Biology Research Center, Massachusetts General Hospital, Charlestown, Massachusetts
| | | | - Anya Alayev
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Yeshiva University, New York, New York
| | - Marina K Holz
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Yeshiva University, New York, New York
| | - Darcy A Krueger
- Division of Neurology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Brian J Siroky
- Division of Nephrology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Jane J Yu
- Department of Internal Medicine, Pulmonary, Critical Care and Sleep Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio. .,Department of Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, China
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Yao Y, Jones E, Inoki K. Lysosomal Regulation of mTORC1 by Amino Acids in Mammalian Cells. Biomolecules 2017; 7:biom7030051. [PMID: 28686218 PMCID: PMC5618232 DOI: 10.3390/biom7030051] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 07/03/2017] [Accepted: 07/04/2017] [Indexed: 12/15/2022] Open
Abstract
The mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth in eukaryotic cells. The active mTORC1 promotes cellular anabolic processes including protein, pyrimidine, and lipid biosynthesis, and inhibits catabolic processes such as autophagy. Consistent with its growth-promoting functions, hyper-activation of mTORC1 signaling is one of the important pathomechanisms underlying major human health problems including diabetes, neurodegenerative disorders, and cancer. The mTORC1 receives multiple upstream signals such as an abundance of amino acids and growth factors, thus it regulates a wide range of downstream events relevant to cell growth and proliferation control. The regulation of mTORC1 by amino acids is a fast-evolving field with its detailed mechanisms currently being revealed as the precise picture emerges. In this review, we summarize recent progress with respect to biochemical and biological findings in the regulation of mTORC1 signaling on the lysosomal membrane by amino acids.
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Affiliation(s)
- Yao Yao
- Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109, USA.
| | - Edith Jones
- Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109, USA.
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, 1137 East Catherine Street, Ann Arbor, MI 48109, USA.
| | - Ken Inoki
- Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109, USA.
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, 1137 East Catherine Street, Ann Arbor, MI 48109, USA.
- Department of Internal Medicine, University of Michigan Medical School, 1500 East Medical enter Drive, Ann Arbor, MI 48109, USA.
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Meng W, Liang X, Chen H, Luo H, Bai J, Li G, Zhang Q, Xiao T, He S, Zhang Y, Xu Z, Xiao B, Liu M, Hu F, Liu F. Rheb Inhibits Beiging of White Adipose Tissue via PDE4D5-Dependent Downregulation of the cAMP-PKA Signaling Pathway. Diabetes 2017; 66:1198-1213. [PMID: 28242620 PMCID: PMC5860267 DOI: 10.2337/db16-0886] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 12/14/2016] [Indexed: 12/14/2022]
Abstract
Beiging of white adipose tissue has potential antiobesity and antidiabetes effects, yet the underlying signaling mechanisms remain to be fully elucidated. Here we show that adipose-specific knockout of Rheb, an upstream activator of mechanistic target of rapamycin complex 1 (mTORC1), protects mice from high-fat diet-induced obesity and insulin resistance. On the one hand, Rheb deficiency in adipose tissue reduced mTORC1 signaling, increased lipolysis, and promoted beiging and energy expenditure. On the other hand, overexpression of Rheb in primary adipocytes significantly inhibited CREB phosphorylation and uncoupling protein 1 (UCP1) expression. Mechanistically, fat-specific knockout of Rheb increased cAMP levels, cAMP-dependent protein kinase (PKA) activity, and UCP1 expression in subcutaneous white adipose tissue. Interestingly, treating primary adipocytes with rapamycin only partially alleviated the suppressing effect of Rheb on UCP1 expression, suggesting the presence of a novel mechanism underlying the inhibitory effect of Rheb on thermogenic gene expression. Consistent with this notion, overexpression of Rheb stabilizes the expression of cAMP-specific phosphodiesterase 4D5 (PDE4D5) in adipocytes, whereas knockout of Rheb greatly reduced cellular levels of PDE4D5 concurrently with increased cAMP levels, PKA activation, and UCP1 expression. Taken together, our findings reveal Rheb as an important negative regulator of beige fat development and thermogenesis. In addition, Rheb is able to suppress the beiging effect through an mTORC1-independent mechanism.
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Affiliation(s)
- Wen Meng
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xiuci Liang
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Hongzhi Chen
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Hairong Luo
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Juli Bai
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
- Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX
| | - Guangdi Li
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Qinghai Zhang
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Ting Xiao
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Sijia He
- Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX
| | - Yacheng Zhang
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Zhipeng Xu
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Bo Xiao
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Meilian Liu
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
- Department of Biochemistry and Molecular Biology, University of New Mexico Health Sciences Center, Albuquerque, NM
| | - Fang Hu
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Feng Liu
- Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center of Central South University, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
- Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX
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26
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Tam RCY, Li MWM, Gao YP, Pang YT, Yan S, Ge W, Lau CS, Chan VSF. Human CLEC16A regulates autophagy through modulating mTOR activity. Exp Cell Res 2017; 352:304-312. [PMID: 28223137 DOI: 10.1016/j.yexcr.2017.02.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2016] [Revised: 01/17/2017] [Accepted: 02/11/2017] [Indexed: 12/28/2022]
Abstract
CLEC16A is genetically linked with multiple autoimmune disorders but its functional relevance in autoimmunity remains obscure. Recent evidence has signposted the emerging role of autophagy in autoimmune disease development. Here, by ectopic expression and siRNA silencing, we show that CLEC16A has an inhibitory role in starvation-induced autophagy in human cells. Combining quantitative proteomics and immunoblotting analyses, we found that CLEC16A likely regulates autophagy by activating mTOR pathway. Overexpression of CLEC16A was found to sensitize cells towards the availability of nutrients, resulting in a heightened mTOR activity, which in turn diminished LC3 autophagic activity following nutrient deprivation. CLEC16A deficiency, on the other hand, delayed mTOR activity in response to nutrient sensing, thereby resulted in an augmented autophagic response. CLEC16A was found residing in cytosolic vesicles and the Golgi, and nutrient removal promoted a stronger clustering within the Golgi, where it was possibly in a vantage position to activate mTOR upon nutrient replenishment. These findings suggest that Golgi-associated CLEC16A negatively regulates autophagy via modulation of mTOR activity, and may provide support for a functional link between CLEC16A and autoimmunity.
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Affiliation(s)
- Rachel Chun Yee Tam
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
| | - Michelle Wing Man Li
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
| | - Yan Pan Gao
- National Key Laboratory of Medical Molecular Biology and Department of Immunology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing 100005, China
| | - Yuen Ting Pang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
| | - Sheng Yan
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
| | - Wei Ge
- National Key Laboratory of Medical Molecular Biology and Department of Immunology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing 100005, China
| | - Chak Sing Lau
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
| | - Vera Sau Fong Chan
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR..
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27
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Mechanisms of Chromosome Congression during Mitosis. BIOLOGY 2017; 6:biology6010013. [PMID: 28218637 PMCID: PMC5372006 DOI: 10.3390/biology6010013] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Revised: 01/07/2017] [Accepted: 01/28/2017] [Indexed: 12/13/2022]
Abstract
Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.
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28
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Tsokanos FF, Albert MA, Demetriades C, Spirohn K, Boutros M, Teleman AA. eIF4A inactivates TORC1 in response to amino acid starvation. EMBO J 2016; 35:1058-76. [PMID: 26988032 PMCID: PMC4868951 DOI: 10.15252/embj.201593118] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Accepted: 02/19/2016] [Indexed: 12/20/2022] Open
Abstract
Amino acids regulate TOR complex 1 (TORC1) via two counteracting mechanisms, one activating and one inactivating. The presence of amino acids causes TORC1 recruitment to lysosomes where TORC1 is activated by binding Rheb. How the absence of amino acids inactivates TORC1 is less well understood. Amino acid starvation recruits the TSC1/TSC2 complex to the vicinity of TORC1 to inhibit Rheb; however, the upstream mechanisms regulating TSC2 are not known. We identify here the eIF4A-containing eIF4F translation initiation complex as an upstream regulator of TSC2 in response to amino acid withdrawal in Drosophila We find that TORC1 and translation preinitiation complexes bind each other. Cells lacking eIF4F components retain elevated TORC1 activity upon amino acid removal. This effect is specific for eIF4F and not a general consequence of blocked translation. This study identifies specific components of the translation machinery as important mediators of TORC1 inactivation upon amino acid removal.
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Affiliation(s)
- Foivos-Filippos Tsokanos
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Marie-Astrid Albert
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Constantinos Demetriades
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Kerstin Spirohn
- Department of Cell and Molecular Biology, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Division of Signaling and Functional Genomics and Heidelberg University, Heidelberg, Germany
| | - Michael Boutros
- Department of Cell and Molecular Biology, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Division of Signaling and Functional Genomics and Heidelberg University, Heidelberg, Germany
| | - Aurelio A Teleman
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), Heidelberg, Germany
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29
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Demetriades C, Plescher M, Teleman AA. Lysosomal recruitment of TSC2 is a universal response to cellular stress. Nat Commun 2016; 7:10662. [PMID: 26868506 PMCID: PMC4754342 DOI: 10.1038/ncomms10662] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Accepted: 01/08/2016] [Indexed: 02/06/2023] Open
Abstract
mTORC1 promotes cell growth and is therefore inactivated upon unfavourable growth conditions. Signalling pathways downstream of most cellular stresses converge on TSC1/2, which serves as an integration point that inhibits mTORC1. The TSC1/2 complex was shown to translocate to lysosomes to inactivate mTORC1 in response to two stresses: amino-acid starvation and growth factor removal. Whether other stresses also regulate TSC2 localization is not known. How TSC2 localization responds to combinations of stresses and other stimuli is also unknown. We show that both amino acids and growth factors are required simultaneously to maintain TSC2 cytoplasmic; when one of the two is missing, TSC2 relocalizes to lysosomes. Furthermore, multiple different stresses that inhibit mTORC1 also drive TSC2 lysosomal accumulation. Our findings indicate that lysosomal recruitment of TSC2 is a universal response to stimuli that inactivate mTORC1, and that the presence of any single stress is sufficient to cause TSC2 lysosomal localization.
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Affiliation(s)
- Constantinos Demetriades
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Monika Plescher
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Aurelio A. Teleman
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
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30
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Plescher M, Teleman AA, Demetriades C. TSC2 mediates hyperosmotic stress-induced inactivation of mTORC1. Sci Rep 2015; 5:13828. [PMID: 26345496 PMCID: PMC4642562 DOI: 10.1038/srep13828] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 08/06/2015] [Indexed: 02/07/2023] Open
Abstract
mTOR complex 1 (mTORC1) regulates cell growth and metabolism. mTORC1 activity is regulated via integration of positive growth-promoting stimuli and negative stress stimuli. One stress cells confront in physiological and pathophysiological contexts is hyperosmotic stress. The mechanism by which hyperosmotic stress regulates mTORC1 activity is not well understood. We show here that mild hyperosmotic stress induces a rapid and reversible inactivation of mTORC1 via a mechanism involving multiple upstream signaling pathways. We find that hyperosmotic stress causes dynamic changes in TSC2 phosphorylation by upstream kinases, such as Akt, thereby recruiting TSC2 from the cytoplasm to lysosomes where it acts on Rheb, the direct activator of mTORC1. This work puts together a signaling pathway whereby hyperosmotic stress inactivates mTORC1.
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Affiliation(s)
- Monika Plescher
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
| | - Aurelio A Teleman
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
| | - Constantinos Demetriades
- Division of Signal Transduction in Cancer and Metabolism, German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
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31
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Armijo ME, Campos T, Fuentes-Villalobos F, Palma ME, Pincheira R, Castro AF. Rheb signaling and tumorigenesis: mTORC1 and new horizons. Int J Cancer 2015; 138:1815-23. [PMID: 26234902 DOI: 10.1002/ijc.29707] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 07/22/2015] [Indexed: 01/05/2023]
Abstract
Rheb is a conserved small GTPase that belongs to the Ras superfamily, and is mainly involved in activation of cell growth through stimulation of mTORC1 activity. Because deregulation of the Rheb/mTORC1 signaling is associated with proliferative disorders and cancer, inhibition of mTORC1 has been therapeutically approached. Although this therapy has proven antitumor activity, its efficacy is not as expected. Here, we will review the main work on the identification of the role of Rheb in cell growth, and on the relevance of Rheb in proliferative disorders, including cancer. We will also review the Rheb functions that could explain tumor resistance to therapies with mTORC1 inhibitors, and will mainly focus our discussion on mTORC1-independent Rheb functions that could also be implicated in cancer cell survival and tumorigenesis. The current progress on the understanding of the noncanonical Rheb functions prompts future studies to establish their relevance in cancer and in the context of current cancer therapies.
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Affiliation(s)
- Marisol E Armijo
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
| | - Tania Campos
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
| | - Francisco Fuentes-Villalobos
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
| | - Mario E Palma
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
| | - Roxana Pincheira
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
| | - Ariel F Castro
- Laboratorio de Transducción de Señales y Cáncer, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad De Concepción, Concepción, Chile
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32
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Dibble CC, Cantley LC. Regulation of mTORC1 by PI3K signaling. Trends Cell Biol 2015; 25:545-55. [PMID: 26159692 DOI: 10.1016/j.tcb.2015.06.002] [Citation(s) in RCA: 544] [Impact Index Per Article: 60.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Revised: 06/08/2015] [Accepted: 06/08/2015] [Indexed: 11/29/2022]
Abstract
The class I phosphoinositide 3-kinase (PI3K)-mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signaling network directs cellular metabolism and growth. Activation of mTORC1 [composed of mTOR, regulatory-associated protein of mTOR (Raptor), mammalian lethal with SEC13 protein 8(mLST8), 40-kDa proline-rich Akt substrate (PRAS40), and DEP domain-containing mTOR-interacting protein (DEPTOR)] depends on the Ras-related GTPases (Rags) and Ras homolog enriched in brain (Rheb) GTPase and requires signals from amino acids, glucose, oxygen, energy (ATP), and growth factors (including cytokines and hormones such as insulin). Here we discuss the signal transduction mechanisms through which growth factor-responsive PI3K signaling activates mTORC1. We focus on how PI3K-dependent activation of Akt and spatial regulation of the tuberous sclerosis complex (TSC) complex (TSC complex) [composed of TSC1, TSC2, and Tre2-Bub2-Cdc16-1 domain family member 7 (TBC1D7)] switches on Rheb at the lysosome, where mTORC1 is activated. Integration of PI3K- and amino acid-dependent signals upstream of mTORC1 at the lysosome is detailed in a working model. A coherent understanding of the PI3K-mTORC1 network is imperative as its dysregulation has been implicated in diverse pathologies including cancer, diabetes, autism, and aging.
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Affiliation(s)
- Christian C Dibble
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
| | - Lewis C Cantley
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medical College, New York, NY 10065, USA.
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33
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Zhou X, Clister TL, Lowry PR, Seldin MM, Wong GW, Zhang J. Dynamic Visualization of mTORC1 Activity in Living Cells. Cell Rep 2015; 10:1767-1777. [PMID: 25772363 DOI: 10.1016/j.celrep.2015.02.031] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 01/15/2015] [Accepted: 02/09/2015] [Indexed: 12/18/2022] Open
Abstract
The mechanistic target of rapamycin complex 1 (mTORC1) senses diverse signals to regulate cell growth and metabolism. It has become increasingly clear that mTORC1 activity is regulated in time and space inside the cell, but direct interrogation of such spatiotemporal regulation is challenging. Here, we describe a genetically encoded mTORC1 activity reporter (TORCAR) that exhibits a change in FRET in response to phosphorylation by mTORC1. Co-imaging mTORC1 activity and calcium dynamics revealed that a growth-factor-induced calcium transient contributes to mTORC1 activity. Dynamic activity maps generated with the use of subcellularly targeted TORCAR uncovered mTORC1 activity not only in cytosol and at the lysosome but also in the nucleus and at the plasma membrane. Furthermore, a wide distribution of activities was observed upon growth factor stimulation, whereas leucine ester, an amino acid surrogate, induces more compartmentalized activities at the lysosome and in the nucleus. Thus, mTORC1 activities are spatiotemporally regulated in a signal-specific manner.
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Affiliation(s)
- Xin Zhou
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Terri L Clister
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Pamela R Lowry
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Marcus M Seldin
- Department of Physiology and Center for Metabolism and Obesity Research, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - G William Wong
- Department of Physiology and Center for Metabolism and Obesity Research, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jin Zhang
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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34
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Al Abdallah Q, Fortwendel JR. Exploration of Aspergillus fumigatus Ras pathways for novel antifungal drug targets. Front Microbiol 2015; 6:128. [PMID: 25767465 PMCID: PMC4341556 DOI: 10.3389/fmicb.2015.00128] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 02/03/2015] [Indexed: 01/05/2023] Open
Abstract
Ras pathway signaling is a critical virulence determinant for pathogenic fungi. Localization of Ras to the plasma membrane (PM) is required for Ras network interactions supporting fungal growth and virulence. For example, loss of Aspergillus fumigatus RasA signaling at the PM via inhibition of palmitoylation leads to decreased growth, altered hyphal morphogenesis, decreased cell wall integrity and loss of virulence. In order to be properly localized and activated, Ras proteins must transit a series of post-translational modification (PTM) steps. These steps include farnesylation, proteolytic cleavage of terminal amino acids, carboxymethylation, and palmitoylation. Because Ras activation drives tumor development, Ras pathways have been extensively studied in mammalian cells as a potential target for anti-cancer therapy. Inhibitors of mammalian Ras interactions and PTM components have been, or are actively being, developed. This review will focus on the potential for building upon existing scaffolds to exploit fungal Ras proteins for therapy, synthesizing data from studies employing both mammalian and fungal systems.
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Affiliation(s)
- Qusai Al Abdallah
- Department of Microbiology and Immunology, University of South Alabama , Mobile, AL, USA
| | - Jarrod R Fortwendel
- Department of Microbiology and Immunology, University of South Alabama , Mobile, AL, USA
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35
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Sato T, Akasu H, Shimono W, Matsu C, Fujiwara Y, Shibagaki Y, Heard JJ, Tamanoi F, Hattori S. Rheb protein binds CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase) protein in a GTP- and effector domain-dependent manner and influences its cellular localization and carbamoyl-phosphate synthetase (CPSase) activity. J Biol Chem 2014; 290:1096-105. [PMID: 25422319 DOI: 10.1074/jbc.m114.592402] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Rheb small GTPases, which consist of Rheb1 and Rheb2 (also known as RhebL1) in mammalian cells, are unique members of the Ras superfamily and play central roles in regulating protein synthesis and cell growth by activating mTOR. To gain further insight into the function of Rheb, we carried out a search for Rheb-binding proteins and found that Rheb binds to CAD protein (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase), a multifunctional enzyme required for the de novo synthesis of pyrimidine nucleotides. CAD binding is more pronounced with Rheb2 than with Rheb1. Rheb binds CAD in a GTP- and effector domain-dependent manner. The region of CAD where Rheb binds is located at the C-terminal region of the carbamoyl-phosphate synthetase domain and not in the dihydroorotase and aspartate transcarbamoylase domains. Rheb stimulated carbamoyl-phosphate synthetase activity of CAD in vitro. In addition, an elevated level of intracellular UTP pyrimidine nucleotide was observed in Tsc2-deficient cells, which was attenuated by knocking down of Rheb. Immunostaining analysis showed that expression of Rheb leads to increased accumulation of CAD on lysosomes. Both a farnesyltransferase inhibitor that blocks membrane association of Rheb and knockdown of Rheb mislocalized CAD. These results establish CAD as a downstream effector of Rheb and suggest a possible role of Rheb in regulating de novo pyrimidine nucleotide synthesis.
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Affiliation(s)
- Tatsuhiro Sato
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Hitomi Akasu
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Wataru Shimono
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Chisa Matsu
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Yuki Fujiwara
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Yoshio Shibagaki
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
| | - Jeffrey J Heard
- Department of Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, Jonsson Comprehensive Cancer Center, University of California, Los Angeles, California, 90095
| | - Fuyuhiko Tamanoi
- Department of Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, Jonsson Comprehensive Cancer Center, University of California, Los Angeles, California, 90095
| | - Seisuke Hattori
- From the Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo 108-8641, Japan and
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36
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Swer PB, Bhadoriya P, Saran S. Analysis of Rheb in the cellular slime mold Dictyostelium discoideum: cellular localization, spatial expression and overexpression. J Biosci 2014; 39:75-84. [PMID: 24499792 DOI: 10.1007/s12038-013-9405-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Dictyostelium discoideum encodes a single Rheb protein showing sequence similarity to human homologues of Rheb. The DdRheb protein shares 52 percent identity and 100 percent similarity with the human Rheb1 protein. Fluorescence of Rheb yellow fluorescent protein fusion was detected in the D. discoideum cytoplasm. Reverse transcription-polymerase chain reaction and whole-mount in situ hybridization analyses showed that rheb is expressed at all stages of development and in prestalk cells in the multicellular structures developed. When the expression of rheb as a fusion with lacZ was driven under its own promoter, the beta-galactosidase activity was seen in the prestalk cells. D. discoideum overexpressing Rheb shows an increase in the size of the cell. Treatment of the overexpressing Rheb cells with rapamycin confirms its involvement in the TOR signalling pathway.
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Affiliation(s)
- Pynskhem Bok Swer
- School of Life Science, Jawaharlal Nehru University, New Delhi 110 067, India
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37
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Yasuda S, Sugiura H, Katsurabayashi S, Shimada T, Tanaka H, Takasaki K, Iwasaki K, Kobayashi T, Hino O, Yamagata K. Activation of Rheb, but not of mTORC1, impairs spine synapse morphogenesis in tuberous sclerosis complex. Sci Rep 2014; 4:5155. [PMID: 24889507 PMCID: PMC4042127 DOI: 10.1038/srep05155] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 05/15/2014] [Indexed: 12/30/2022] Open
Abstract
Mutations in the Tsc1 or Tsc2 genes cause tuberous sclerosis complex (TSC). Tsc1 and Tsc2 proteins form a complex that inhibits mammalian target of rapamycin complex 1 (mTORC1) signalling through Rheb-GTPase. We found that Tsc2+/− neurons showed impaired spine synapse formation, which was resistant to an mTORC1 inhibitor. Knockdown of mTOR also failed to restore these abnormalities, suggesting mTORC may not participate in impaired spinogenesis in Tsc2+/− neurons. To address whether Rheb activation impairs spine synapse formation, we expressed active and inactive forms of Rheb in WT and Tsc2+/− neurons, respectively. Expression of active Rheb abolished dendritic spine formation in WT neurons, whereas inactive Rheb restored spine synapse formation in Tsc2+/− neurons. Moreover, inactivation of Rheb with farnesyl transferase inhibitors recovered spine synapse morphogenesis in Tsc2+/− neurons. In conclusion, dendritic spine abnormalities in TSC neurons may be caused through activation of Rheb, but not through of mTORC1.
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Affiliation(s)
- Shin Yasuda
- 1] Neural Plasticity Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan [2]
| | - Hiroko Sugiura
- 1] Neural Plasticity Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan [2]
| | - Shutaro Katsurabayashi
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan
| | - Tadayuki Shimada
- Neural Plasticity Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Hidekazu Tanaka
- Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Kotaro Takasaki
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan
| | - Katsunori Iwasaki
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan
| | - Toshiyuki Kobayashi
- Department of Pathology and Oncology, Juntendo University, School of Medicine, Tokyo, Japan
| | - Okio Hino
- Department of Pathology and Oncology, Juntendo University, School of Medicine, Tokyo, Japan
| | - Kanato Yamagata
- Neural Plasticity Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
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38
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Recent progress in the study of the Rheb family GTPases. Cell Signal 2014; 26:1950-7. [PMID: 24863881 DOI: 10.1016/j.cellsig.2014.05.011] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 05/15/2014] [Indexed: 11/20/2022]
Abstract
In this review we highlight recent progress in the study of Rheb family GTPases. Structural studies using X-ray crystallography and NMR have given us insight into unique features of this GTPase. Combined with mutagenesis studies, these works have expanded our understanding of residues that affect Rheb GTP/GDP bound ratios, effector protein interactions, and stimulation of mTORC1 signaling. Analysis of cancer genome databases has revealed that several human carcinomas contain activating mutations of the protein. Rheb's role in activating mTORC1 signaling at the lysosome in response to stimuli has been further elucidated. Rheb has also been suggested to play roles in other cellular pathways including mitophagy and peroxisomal ROS response. A number of studies in mice have demonstrated the importance of Rheb in development, as well as in a variety of functions including cardiac protection and myelination. We conclude with a discussion of future prospects in the study of Rheb family GTPases.
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Menon S, Dibble CC, Talbott G, Hoxhaj G, Valvezan AJ, Takahashi H, Cantley LC, Manning BD. Spatial control of the TSC complex integrates insulin and nutrient regulation of mTORC1 at the lysosome. Cell 2014; 156:771-85. [PMID: 24529379 DOI: 10.1016/j.cell.2013.11.049] [Citation(s) in RCA: 567] [Impact Index Per Article: 56.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 11/14/2013] [Accepted: 12/24/2013] [Indexed: 12/22/2022]
Abstract
mTORC1 promotes cell growth in response to nutrients and growth factors. Insulin activates mTORC1 through the PI3K-Akt pathway, which inhibits the TSC1-TSC2-TBC1D7 complex (the TSC complex) to turn on Rheb, an essential activator of mTORC1. However, the mechanistic basis of how this pathway integrates with nutrient-sensing pathways is unknown. We demonstrate that insulin stimulates acute dissociation of the TSC complex from the lysosomal surface, where subpopulations of Rheb and mTORC1 reside. The TSC complex associates with the lysosome in a Rheb-dependent manner, and its dissociation in response to insulin requires Akt-mediated TSC2 phosphorylation. Loss of the PTEN tumor suppressor results in constitutive activation of mTORC1 through the Akt-dependent dissociation of the TSC complex from the lysosome. These findings provide a unifying mechanism by which independent pathways affecting the spatial recruitment of mTORC1 and the TSC complex to Rheb at the lysosomal surface serve to integrate diverse growth signals.
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Affiliation(s)
- Suchithra Menon
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA
| | - Christian C Dibble
- Department of Systems Biology, Harvard Medical School and Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
| | - George Talbott
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA
| | - Gerta Hoxhaj
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA
| | - Alexander J Valvezan
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA
| | - Hidenori Takahashi
- Department of Systems Biology, Harvard Medical School and Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
| | - Lewis C Cantley
- Department of Systems Biology, Harvard Medical School and Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA; Department of Medicine, Weill Cornell Medical College, New York, NY 10065, USA
| | - Brendan D Manning
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA.
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Shahani N, Pryor W, Swarnkar S, Kholodilov N, Thinakaran G, Burke RE, Subramaniam S. Rheb GTPase regulates β-secretase levels and amyloid β generation. J Biol Chem 2013; 289:5799-808. [PMID: 24368770 DOI: 10.1074/jbc.m113.532713] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The β-site amyloid precursor protein (APP)-cleaving enzyme 1 (β-secretase, BACE1) initiates amyloidogenic processing of APP to generate amyloid β (Aβ), which is a hallmark of Alzheimer disease (AD) pathology. Cerebral levels of BACE1 are elevated in individuals with AD, but the molecular mechanisms are not completely understood. We demonstrate that Rheb GTPase (Ras homolog enriched in brain), which induces mammalian target of rapamycin (mTOR) activity, is a physiological regulator of BACE1 stability and activity. Rheb overexpression depletes BACE1 protein levels and reduces Aβ generation, whereas the RNAi knockdown of endogenous Rheb promotes BACE1 accumulation, and this effect by Rheb is independent of its mTOR signaling. Moreover, GTP-bound Rheb interacts with BACE1 and degrades it through proteasomal and lysosomal pathways. Finally, we demonstrate that Rheb levels are down-regulated in the AD brain, which is consistent with an increased BACE1 expression. Altogether, our study defines Rheb as a novel physiological regulator of BACE1 levels and Aβ generation, and the Rheb-BACE1 circuitry may have a role in brain biology and disease.
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Affiliation(s)
- Neelam Shahani
- From the Department of Neuroscience, The Scripps Research Institute, Florida, Jupiter, Florida 33458
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41
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Ding H, McDonald JS, Yun S, Schneider PA, Peterson KL, Flatten KS, Loegering DA, Oberg AL, Riska SM, Huang S, Sinicrope FA, Adjei AA, Karp JE, Meng XW, Kaufmann SH. Farnesyltransferase inhibitor tipifarnib inhibits Rheb prenylation and stabilizes Bax in acute myelogenous leukemia cells. Haematologica 2013; 99:60-9. [PMID: 23996484 DOI: 10.3324/haematol.2013.087734] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Although farnesyltransferase inhibitors have shown promising activity in relapsed lymphoma and sporadic activity in acute myelogenous leukemia, their mechanism of cytotoxicity is incompletely understood, making development of predictive biomarkers difficult. In the present study, we examined the action of tipifarnib in human acute myelogenous leukemia cell lines and clinical samples. In contrast to the Ras/MEK/ERK pathway-mediated Bim upregulation that is responsible for tipifarnib-induced killing of malignant lymphoid cells, inhibition of Rheb-induced mTOR signaling followed by dose-dependent upregulation of Bax and Puma occurred in acute myelogenous leukemia cell lines undergoing tipifarnib-induced apoptosis. Similar Bax and Puma upregulation occurred in serial bone marrow samples harvested from a subset of acute myelogenous leukemia patients during tipifarnib treatment. Expression of FTI-resistant Rheb M184L, like knockdown of Bax or Puma, diminished tipifarnib-induced killing. Further analysis demonstrated that increased Bax and Puma levels reflect protein stabilization rather than increased gene expression. In U937 cells selected for tipifarnib resistance, neither inhibition of signaling downstream of Rheb nor Bax and Puma stabilization occurred. Collectively, these results not only identify a pathway downstream from Rheb that contributes to tipifarnib cytotoxicity in human acute myelogenous leukemia cells, but also demonstrate that FTI-induced killing of lymphoid versus myeloid cells reflects distinct biochemical mechanisms downstream of different farnesylated substrates. (ClinicalTrials.gov identifier NCT00602771).
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42
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Dibble CC, Manning BD. Signal integration by mTORC1 coordinates nutrient input with biosynthetic output. Nat Cell Biol 2013; 15:555-64. [PMID: 23728461 DOI: 10.1038/ncb2763] [Citation(s) in RCA: 539] [Impact Index Per Article: 49.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Flux through metabolic pathways is inherently sensitive to the levels of specific substrates and products, but cellular metabolism is also managed by integrated control mechanisms that sense the nutrient and energy status of a cell or organism. The mechanistic target of rapamycin complex 1 (mTORC1), a protein kinase complex ubiquitous to eukaryotic cells, has emerged as a critical signalling node that links nutrient sensing to the coordinated regulation of cellular metabolism. Here, we discuss the role of mTORC1 as a conduit between cellular growth conditions and the anabolic processes that promote cell growth. The emerging network of signalling pathways through which mTORC1 integrates systemic signals (secreted growth factors) with local signals (cellular nutrients - amino acids, glucose and oxygen - and energy, ATP) is detailed. Our expanding understanding of the regulatory network upstream of mTORC1 provides molecular insights into the integrated sensing mechanisms by which diverse cellular signals converge to control cell physiology.
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Affiliation(s)
- Christian C Dibble
- Division of Signal Transduction, Beth Israel Deaconess Medical Center, Systems Biology Department, Harvard Medical School, Boston, Massachusetts 02115, USA
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Melser S, Chatelain EH, Lavie J, Mahfouf W, Jose C, Obre E, Goorden S, Priault M, Elgersma Y, Rezvani HR, Rossignol R, Bénard G. Rheb regulates mitophagy induced by mitochondrial energetic status. Cell Metab 2013; 17:719-30. [PMID: 23602449 DOI: 10.1016/j.cmet.2013.03.014] [Citation(s) in RCA: 202] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Revised: 02/09/2013] [Accepted: 03/13/2013] [Indexed: 12/18/2022]
Abstract
Mitophagy has been recently described as a mechanism of elimination of damaged organelles. Although the regulation of the amount of mitochondria is a core issue concerning cellular energy homeostasis, the relationship between mitochondrial degradation and energetic activity has not yet been considered. Here, we report that the stimulation of mitochondrial oxidative phosphorylation enhances mitochondrial renewal by increasing its degradation rate. Upon high oxidative phosphorylation activity, we found that the small GTPase Rheb is recruited to the mitochondrial outer membrane. This mitochondrial localization of Rheb promotes mitophagy through a physical interaction with the mitochondrial autophagic receptor Nix and the autophagosomal protein LC3-II. Thus, Rheb-dependent mitophagy contributes to the maintenance of optimal mitochondrial energy production. Our data suggest that mitochondrial degradation contributes to a bulk renewal of the organelle in order to prevent mitochondrial aging and to maintain the efficiency of oxidative phosphorylation.
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Affiliation(s)
- Su Melser
- EA4576, Maladies Rares: Génétique et Métabolisme, 33000 Bordeaux Cedex, France
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Mazhab-Jafari MT, Marshall CB, Stathopulos PB, Kobashigawa Y, Stambolic V, Kay LE, Inagaki F, Ikura M. Membrane-dependent modulation of the mTOR activator Rheb: NMR observations of a GTPase tethered to a lipid-bilayer nanodisc. J Am Chem Soc 2013; 135:3367-70. [PMID: 23409921 DOI: 10.1021/ja312508w] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Like most Ras superfamily proteins, the GTPase domain of Ras homologue enriched in brain (Rheb) is tethered to cellular membranes through a prenylated cysteine in a flexible C-terminal region; however, little is known about how Rheb or other GTPases interact with the membrane or how this environment may affect their GTPase functions. We used NMR methods to characterize Rheb tethered to nanodiscs, monodisperse protein-encapsulated lipid bilayers with a diameter of 10 nm. Membrane conjugation markedly reduced the rate of intrinsic nucleotide exchange, while GTP hydrolysis was unchanged. NMR measurements revealed that the GTPase domain interacts transiently with the surface of the bilayer in two distinct preferred orientations, which are determined by the bound nucleotide. We propose models of membrane-dependent signal regulation by Rheb that shed light on previously unexplained in vivo properties of this GTPase. The study presented provides a general approach for direct experimental investigation of membrane-dependent properties of other Ras-superfamily GTPases.
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Affiliation(s)
- Mohammad T Mazhab-Jafari
- Department of Medical Biophysics, Campbell Family Cancer Research Institute, Princess Margaret Cancer Center, University Health Network, University of Toronto, Toronto, Ontario M5G 2M9, Canada
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45
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Eom M, Han A, Lee MJ, Park KH. Expressional Difference of RHEB, HDAC1, and WEE1 Proteins in the Stromal Tumors of the Breast and Their Significance in Tumorigenesis. KOREAN JOURNAL OF PATHOLOGY 2012; 46:324-30. [PMID: 23110024 PMCID: PMC3479826 DOI: 10.4132/koreanjpathol.2012.46.4.324] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Revised: 06/19/2012] [Accepted: 06/26/2012] [Indexed: 12/15/2022]
Abstract
Background Fibroadenoma (FA) and phyllodes tumor (PT) are stromal tumors of breast and are histologically similar. There are no established differences in tumorigenesis and oncogene expression among them. Ras homolog enriched in brain (RHEB) plays an important role in cell growth and cell-cycle control, histone deacetylase 1 (HDAC1) is an important factor in breast tumor progression and prognosis, and WEE1 homolog (WEE1) functions as a tumor suppressor. No studies on the expressional differences of these proteins in FA and PT have been reported to date. Methods The expression of these proteins in FA, PT, and normal breast was compared. We used 102 cases of FA and 25 cases of benign PT. Results In epithelial cells, the expression of RHEB, HDAC1, and WEE1 was lowest in PT, higher in FA, and most enhanced in normal breast. In addition, the expression of RHEB and HDAC1 was higher in the stromal cells of PT than in FA and normal breast. Conclusions Both epithelial and stromal cells of FA and PT express these proteins, which indicates that epithelial cells play an important role in the development of stromal tumors. In addition, the expressional differences of these proteins may be associated with the tumorigenesis of breast stromal tumors.
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Affiliation(s)
- Minseob Eom
- Department of Pathology, Yonsei University Wonju College of Medicine, Wonju, Korea
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46
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Karassek S, Berghaus C, Schwarten M, Goemans CG, Ohse N, Kock G, Jockers K, Neumann S, Gottfried S, Herrmann C, Heumann R, Stoll R. Ras homolog enriched in brain (Rheb) enhances apoptotic signaling. J Biol Chem 2010; 285:33979-91. [PMID: 20685651 PMCID: PMC2962498 DOI: 10.1074/jbc.m109.095968] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2009] [Revised: 07/19/2010] [Indexed: 12/18/2022] Open
Abstract
Rheb is a homolog of Ras GTPase that regulates cell growth, proliferation, and regeneration via mammalian target of rapamycin (mTOR). Because of the well established potential of activated Ras to promote survival, we sought to investigate the ability of Rheb signaling to phenocopy Ras. We found that overexpression of lipid-anchored Rheb enhanced the apoptotic effects induced by UV light, TNFα, or tunicamycin in an mTOR complex 1 (mTORC1)-dependent manner. Knocking down endogenous Rheb or applying rapamycin led to partial protection, identifying Rheb as a mediator of cell death. Ras and c-Raf kinase opposed the apoptotic effects induced by UV light or TNFα but did not prevent Rheb-mediated apoptosis. To gain structural insight into the signaling mechanisms, we determined the structure of Rheb-GDP by NMR. The complex adopts the typical canonical fold of RasGTPases and displays the characteristic GDP-dependent picosecond to nanosecond backbone dynamics of the switch I and switch II regions. NMR revealed Ras effector-like binding of activated Rheb to the c-Raf-Ras-binding domain (RBD), but the affinity was 1000-fold lower than the Ras/RBD interaction, suggesting a lack of functional interaction. shRNA-mediated knockdown of apoptosis signal-regulating kinase 1 (ASK-1) strongly reduced UV or TNFα-induced apoptosis and suppressed enhancement by Rheb overexpression. In conclusion, Rheb-mTOR activation not only promotes normal cell growth but also enhances apoptosis in response to diverse toxic stimuli via an ASK-1-mediated mechanism. Pharmacological regulation of the Rheb/mTORC1 pathway using rapamycin should take the presence of cellular stress into consideration, as this may have clinical implications.
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Affiliation(s)
| | | | | | | | - Nadine Ohse
- Physical Chemistry I, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, 44780 Bochum, Germany
| | | | | | | | | | - Christian Herrmann
- Physical Chemistry I, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, 44780 Bochum, Germany
| | - Rolf Heumann
- From the Departments of Molecular Neurobiochemistry
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Sancak Y, Bar-Peled L, Zoncu R, Markhard AL, Nada S, Sabatini DM. Ragulator-Rag complex targets mTORC1 to the lysosomal surface and is necessary for its activation by amino acids. Cell 2010; 141:290-303. [PMID: 20381137 PMCID: PMC3024592 DOI: 10.1016/j.cell.2010.02.024] [Citation(s) in RCA: 1781] [Impact Index Per Article: 127.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 12/28/2009] [Accepted: 02/05/2010] [Indexed: 12/11/2022]
Abstract
The mTORC1 kinase promotes growth in response to growth factors, energy levels, and amino acids, and its activity is often deregulated in disease. The Rag GTPases interact with mTORC1 and are proposed to activate it in response to amino acids by promoting mTORC1 translocation to a membrane-bound compartment that contains the mTORC1 activator, Rheb. We show that amino acids induce the movement of mTORC1 to lysosomal membranes, where the Rag proteins reside. A complex encoded by the MAPKSP1, ROBLD3, and c11orf59 genes, which we term Ragulator, interacts with the Rag GTPases, recruits them to lysosomes, and is essential for mTORC1 activation. Constitutive targeting of mTORC1 to the lysosomal surface is sufficient to render the mTORC1 pathway amino acid insensitive and independent of Rag and Ragulator, but not Rheb, function. Thus, Rag-Ragulator-mediated translocation of mTORC1 to lysosomal membranes is the key event in amino acid signaling to mTORC1.
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Affiliation(s)
- Yasemin Sancak
- Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
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48
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Weatherill DB, Dyer J, Sossin WS. Ribosomal protein S6 kinase is a critical downstream effector of the target of rapamycin complex 1 for long-term facilitation in Aplysia. J Biol Chem 2010; 285:12255-67. [PMID: 20177060 DOI: 10.1074/jbc.m109.071142] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Long-term facilitation (LTF) in Aplysia is a leading cellular model for elucidating the biochemical mechanisms of synaptic plasticity underlying learning. In Aplysia, LTF requires translational control downstream of the target of rapamycin (TOR) complex 1 (TORC1). The major known downstream targets of TORC1 are 4E binding protein (4E-BP) and S6 kinase (S6K). By removing the site within these regulators required for their interaction with TORC1, we have generated dominant negative proteins that disrupt specific pathways downstream of TORC1. Expression of dominant negative S6K, but not dominant negative 4E-BP, in Aplysia sensory neurons (SNs) blocked 24-h LTF. TORC1 is directly activated by the small GTP-binding protein, Ras homologue enriched in brain (Rheb). To determine the effects of TORC1 activation on translation in Aplysia neurons, we have examined the effects of expressing a constitutively active form of the Aplysia orthologue of Rheb, ApRheb (ApRheb(Q63L)). Expression of ApRheb(Q63L) increased 4E-BP phosphorylation and the level of general, cap-dependent translation within the SN cell soma in a rapamycin-sensitive manner. This increase in cap-dependent translation was blocked neither by dominant negative 4E-BP nor dominant negative S6K. Thus, we demonstrate that S6K is an important downstream target of TORC1 in Aplysia and that it is necessary for 24-h LTF, but not for TORC1-mediated increases in somatic cap-dependent translation.
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Affiliation(s)
- Daniel B Weatherill
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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49
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Abstract
Rheb belongs to a unique family within the Ras superfamily of G-proteins. Although initially identified in rat brain, this G-protein is highly conserved from yeast to human. While only one Rheb is present in lower eukaryotes, two Rheb proteins exist in mammalian cells. A number of studies establish that one of the functions of Rheb is to activate mTOR leading to growth. In particular, the ability of Rheb to activate mTORC1 in vitro points to direct interaction of Rheb with the mTORC1 complex. Additional functions of Rheb that are independent of mTOR have also been suggested.
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Affiliation(s)
- Nitika Parmar
- Biology Program, California State University Channel Islands, 1 University Drive, Camarillo, California, USA
| | - Fuyuhiko Tamanoi
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, California, USA
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50
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Phase II trial and prediction of response of single agent tipifarnib in patients with relapsed/refractory mantle cell lymphoma: a Groupe d’Etude des Lymphomes de l’Adulte trial. Cancer Chemother Pharmacol 2009; 65:781-90. [DOI: 10.1007/s00280-009-1185-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2009] [Accepted: 11/11/2009] [Indexed: 01/28/2023]
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