1
|
Aksan B, Kenkel AK, Yan J, Sánchez Romero J, Missirlis D, Mauceri D. VEGFD signaling balances stability and activity-dependent structural plasticity of dendrites. Cell Mol Life Sci 2024; 81:354. [PMID: 39158743 DOI: 10.1007/s00018-024-05357-2] [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: 05/24/2024] [Revised: 07/08/2024] [Accepted: 07/09/2024] [Indexed: 08/20/2024]
Abstract
Mature neurons have stable dendritic architecture, which is essential for the nervous system to operate correctly. The ability to undergo structural plasticity, required to support adaptive processes like memory formation, is still present in mature neurons. It is unclear what molecular and cellular processes control this delicate balance between dendritic structural plasticity and stabilization. Failures in the preservation of optimal dendrite structure due to atrophy or maladaptive plasticity result in abnormal connectivity and are associated with various neurological diseases. Vascular endothelial growth factor D (VEGFD) is critical for the maintenance of mature dendritic trees. Here, we describe how VEGFD affects the neuronal cytoskeleton and demonstrate that VEGFD exerts its effects on dendrite stabilization by influencing the actin cortex and reducing microtubule dynamics. Further, we found that during synaptic activity-induced structural plasticity VEGFD is downregulated. Our findings revealed that VEGFD, acting on its cognate receptor VEGFR3, opposes structural changes by negatively regulating dendrite growth in cultured hippocampal neurons and in vivo in the adult mouse hippocampus with consequences on memory formation. A phosphoproteomic screening identified several regulatory proteins of the cytoskeleton modulated by VEGFD. Among the actin cortex-associated proteins, we found that VEGFD induces dephosphorylation of ezrin at tyrosine 478 via activation of the striatal-enriched protein tyrosine phosphatase (STEP). Activity-triggered structural plasticity of dendrites was impaired by expression of a phospho-deficient mutant ezrin in vitro and in vivo. Thus, VEGFD governs the equilibrium between stabilization and plasticity of dendrites by acting as a molecular brake of structural remodeling.
Collapse
Affiliation(s)
- Bahar Aksan
- Department of Neurobiology, Interdisciplinary Centre for Neurosciences (IZN), Heidelberg University, INF 366, 69120, Heidelberg, Germany
| | - Ann-Kristin Kenkel
- Department of Neurobiology, Interdisciplinary Centre for Neurosciences (IZN), Heidelberg University, INF 366, 69120, Heidelberg, Germany
| | - Jing Yan
- Department of Neurobiology, Interdisciplinary Centre for Neurosciences (IZN), Heidelberg University, INF 366, 69120, Heidelberg, Germany
| | - Javier Sánchez Romero
- Department of Neurobiology, Interdisciplinary Centre for Neurosciences (IZN), Heidelberg University, INF 366, 69120, Heidelberg, Germany
| | - Dimitris Missirlis
- Department of Cellular Biophysics, Max-Planck-Institute for Medical Research, Jahnstraße 29, 69120, Heidelberg, Germany
| | - Daniela Mauceri
- Department of Neurobiology, Interdisciplinary Centre for Neurosciences (IZN), Heidelberg University, INF 366, 69120, Heidelberg, Germany.
- Department Molecular and Cellular Neuroscience, Institute of Anatomy and Cell Biology, University of Marburg, Robert-Koch-Str. 8, 35032, Marburg, Germany.
| |
Collapse
|
2
|
Abudu YP, Kournoutis A, Brenne HB, Lamark T, Johansen T. MORG1 limits mTORC1 signaling by inhibiting Rag GTPases. Mol Cell 2024; 84:552-569.e11. [PMID: 38103557 DOI: 10.1016/j.molcel.2023.11.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 10/02/2023] [Accepted: 11/17/2023] [Indexed: 12/19/2023]
Abstract
Autophagy, an important quality control and recycling process vital for cellular homeostasis, is tightly regulated. The mTORC1 signaling pathway regulates autophagy under conditions of nutrient availability and scarcity. However, how mTORC1 activity is fine-tuned during nutrient availability to allow basal autophagy is unclear. Here, we report that the WD-domain repeat protein MORG1 facilitates basal constitutive autophagy by inhibiting mTORC1 signaling through Rag GTPases. Mechanistically, MORG1 interacts with active Rag GTPase complex inhibiting the Rag GTPase-mediated recruitment of mTORC1 to the lysosome. MORG1 depletion in HeLa cells increases mTORC1 activity and decreases autophagy. The autophagy receptor p62/SQSTM1 binds to MORG1, but MORG1 is not an autophagy substrate. However, p62/SQSTM1 binding to MORG1 upon re-addition of amino acids following amino acid's depletion precludes MORG1 from inhibiting the Rag GTPases, allowing mTORC1 activation. MORG1 depletion increases cell proliferation and migration. Low expression of MORG1 correlates with poor survival in several important cancers.
Collapse
Affiliation(s)
- Yakubu Princely Abudu
- Autophagy Research Group, Department of Medical Biology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway; Nanoscopy Group, Department of Physics and Technology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway.
| | - Athanasios Kournoutis
- Autophagy Research Group, Department of Medical Biology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway
| | - Hanne Britt Brenne
- Autophagy Research Group, Department of Medical Biology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway
| | - Trond Lamark
- Autophagy Research Group, Department of Medical Biology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway
| | - Terje Johansen
- Autophagy Research Group, Department of Medical Biology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway.
| |
Collapse
|
3
|
Kincheloe GN, Roberson PA, Jefferson LS, Kimball SR. Tissue-specific expression differences in Ras-related GTP-binding proteins in male rats. Physiol Rep 2024; 12:e15928. [PMID: 38296461 PMCID: PMC10830385 DOI: 10.14814/phy2.15928] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 12/30/2023] [Accepted: 01/14/2024] [Indexed: 02/05/2024] Open
Abstract
The protein kinase Mechanistic Target of Rapamycin (mTOR) in Complex 1 (mTORC1) is regulated in part by the Ras-related GTP-binding proteins (Rag GTPases). Rag GTPases form a heterodimeric complex consisting of either RagA or RagB associated with either RagC or RagD and act to localize mTORC1 to the lysosomal membrane. Until recently, RagA and RagB were thought to be functionally redundant, as were RagC and RagD. However, recent research suggests that the various isoforms differentially activate mTORC1. Here, the mRNA expression and protein abundance of the Rag GTPases was compared across male rat skeletal muscle, heart, liver, kidney, and brain. Whereas mRNA expression of RagA was higher than RagB in nearly all tissues studied, RagB protein abundance was higher than RagA in all tissues besides skeletal muscle. RagC mRNA expression was more abundant or equal to RagD mRNA, and RagD protein was more abundant than RagC protein in all tissues. Moreover, the proportion of RagB in the short isoform was greater than the long in liver, whereas the opposite was true in brain. These results serve to further elucidate Rag GTPase expression and offer potential explanations for the differential responses to amino acids that are observed in different tissues.
Collapse
Affiliation(s)
- Gregory N. Kincheloe
- Department of Cellular and Molecular PhysiologyPenn State College of MedicineHersheyPennsylvaniaUSA
- Present address:
Department of AnatomyUCSF College of MedicineSan FranciscoCaliforniaUSA
| | - Paul A. Roberson
- Department of Cellular and Molecular PhysiologyPenn State College of MedicineHersheyPennsylvaniaUSA
- Present address:
Division of Endocrinology, Metabolism, Diabetes, Department of MedicineUniversity of Colorado – Anschutz Medical CampusAuroraColoradoUSA
| | - Leonard S. Jefferson
- Department of Cellular and Molecular PhysiologyPenn State College of MedicineHersheyPennsylvaniaUSA
| | - Scot R. Kimball
- Department of Cellular and Molecular PhysiologyPenn State College of MedicineHersheyPennsylvaniaUSA
| |
Collapse
|
4
|
Goul C, Peruzzo R, Zoncu R. The molecular basis of nutrient sensing and signalling by mTORC1 in metabolism regulation and disease. Nat Rev Mol Cell Biol 2023; 24:857-875. [PMID: 37612414 DOI: 10.1038/s41580-023-00641-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/06/2023] [Indexed: 08/25/2023]
Abstract
The Ser/Thr kinase mechanistic target of rapamycin (mTOR) is a central regulator of cellular metabolism. As part of mTOR complex 1 (mTORC1), mTOR integrates signals such as the levels of nutrients, growth factors, energy sources and oxygen, and triggers responses that either boost anabolism or suppress catabolism. mTORC1 signalling has wide-ranging consequences for the growth and homeostasis of key tissues and organs, and its dysregulated activity promotes cancer, type 2 diabetes, neurodegeneration and other age-related disorders. How mTORC1 integrates numerous upstream cues and translates them into specific downstream responses is an outstanding question with major implications for our understanding of physiology and disease mechanisms. In this Review, we discuss recent structural and functional insights into the molecular architecture of mTORC1 and its lysosomal partners, which have greatly increased our mechanistic understanding of nutrient-dependent mTORC1 regulation. We also discuss the emerging involvement of aberrant nutrient-mTORC1 signalling in multiple diseases.
Collapse
Affiliation(s)
- Claire Goul
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
| | - Roberta Peruzzo
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
| | - Roberto Zoncu
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
| |
Collapse
|
5
|
Kao HY, Yao Y, Yang T, Ziobro J, Zylinski M, Mir MY, Hu S, Cao R, Borna NN, Banerjee R, Parent JM, Wang S, Leventhal DK, Li P, Wang Y. Sudden Unexpected Death in Epilepsy and Respiratory Defects in a Mouse Model of DEPDC5-Related Epilepsy. Ann Neurol 2023; 94:812-824. [PMID: 37606181 PMCID: PMC10592102 DOI: 10.1002/ana.26773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 08/07/2023] [Accepted: 08/09/2023] [Indexed: 08/23/2023]
Abstract
OBJECTIVES DEPDC5 is a common causative gene in familial focal epilepsy with or without malformations of cortical development. Its pathogenic variants also confer a significantly higher risk for sudden unexpected death in epilepsy (SUDEP), providing opportunities to investigate the pathophysiology intersecting neurodevelopment, epilepsy, and cardiorespiratory function. There is an urgent need to gain a mechanistic understanding of DEPDC5-related epilepsy and SUDEP, identify biomarkers for patients at high risk, and develop preventive interventions. METHODS Depdc5 was specifically deleted in excitatory or inhibitory neurons in the mouse brain to determine neuronal subtypes that drive epileptogenesis and SUDEP. Electroencephalogram (EEG), cardiac, and respiratory recordings were performed to determine cardiorespiratory phenotypes associated with SUDEP. Baseline respiratory function and the response to hypoxia challenge were also studied in these mice. RESULTS Depdc5 deletion in excitatory neurons in cortical layer 5 and dentate gyrus caused frequent generalized tonic-clonic seizures and SUDEP in young adult mice, but Depdc5 deletion in cortical interneurons did not. EEG suppression immediately following ictal offset was observed in fatal and non-fatal seizures, but low amplitude rhythmic theta frequency activity was lost only in fatal seizures. In addition, these mice developed baseline respiratory dysfunction prior to SUDEP, during which ictal apnea occurred long before terminal cardiac asystole. INTERPRETATION Depdc5 deletion in excitatory neurons is sufficient to cause DEPDC5-related epilepsy and SUDEP. Ictal apnea and respiratory dysregulation play critical roles in SUDEP. Our study also provides a novel mouse model to investigate the underlying mechanisms of DEPDC5-related epilepsy and SUDEP. ANN NEUROL 2023;94:812-824.
Collapse
Affiliation(s)
- Hsin-Yi Kao
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Yilong Yao
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
| | - Tao Yang
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Julie Ziobro
- Department of Pediatrics, University of Michigan, Ann Arbor, MI, USA
| | - Mary Zylinski
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
| | - Mohd Yaqub Mir
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
| | - Shuntong Hu
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Runnan Cao
- Department of Radiology, Washington University in St. Louis, St. Louis, MO, USA
| | | | - Rajat Banerjee
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Jack M. Parent
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
- VA Ann Arbor Healthcare System, Ann Arbor, MI 48105, USA
- Michgian Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA
| | - Shuo Wang
- Department of Radiology, Washington University in St. Louis, St. Louis, MO, USA
| | - Daniel K. Leventhal
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
- VA Ann Arbor Healthcare System, Ann Arbor, MI 48105, USA
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Parkinson Disease Foundation Research Center of Excellence, University of Michigan, Ann Arbor, MI, USA
| | - Peng Li
- Michgian Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Biologic and Material Sciences, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
| | - Yu Wang
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
- VA Ann Arbor Healthcare System, Ann Arbor, MI 48105, USA
- Michgian Neuroscience Institute, University of Michigan, Ann Arbor, MI, USA
| |
Collapse
|
6
|
Liu Y, Zhu Y, Chen H, Zhou J, Niu P, Shi D. Raptor mediates the selective inhibitory effect of cardamonin on RRAGC-mutant B cell lymphoma. BMC Complement Med Ther 2023; 23:336. [PMID: 37749558 PMCID: PMC10521446 DOI: 10.1186/s12906-023-04166-7] [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: 04/14/2023] [Accepted: 09/12/2023] [Indexed: 09/27/2023] Open
Abstract
BACKGROUND mTORC1 (mechanistic target of rapamycin complex 1) is associated with lymphoma progression. Oncogenic RRAGC (Rag guanosine triphosphatase C) mutations identified in patients with follicular lymphoma facilitate the interaction between Raptor (regulatory protein associated with mTOR) and Rag GTPase. It promotes the activation of mTORC1 and accelerates lymphomagenesis. Cardamonin inhibits mTORC1 by decreasing the protein level of Raptor. In the present study, we investigated the inhibitory effect and possible mechanism of action of cardamonin in RRAGC-mutant lymphoma. This could provide a precise targeted therapy for lymphoma with RRAGC mutations. METHODS Cell viability was measured using a cell counting kit-8 (CCK-8) assay. Protein expression and phosphorylation levels were determined using western blotting. The interactions of mTOR and Raptor with RagC were determined by co-immunoprecipitation. Cells overexpressing RagC wild-type (RagCWT) and RagC Thr90Asn (RagCT90N) were generated by lentiviral infection. Raptor knockdown was performed by lentivirus-mediated shRNA transduction. The in vivo anti-tumour effect of cardamonin was assessed in a xenograft model. RESULTS Cardamonin disrupted mTOR complex interactions by decreasing Raptor protein levels. RagCT90N overexpression via lentiviral infection increased cell proliferation and mTORC1 activation. The viability and tumour growth rate of RagCT90N-mutant cells were more sensitive to cardamonin treatment than those of normal and RagCWT cells. Cardamonin also exhibited a stronger inhibitory effect on the phosphorylation of mTOR and p70 S6 kinase 1 in RagCT90N-mutant cells. Raptor knockdown abolishes the inhibitory effects of cardamonin on mTOR. An in vivo xenograft model demonstrated that the RagCT90N-mutant showed significantly higher sensitivity to cardamonin treatment. CONCLUSIONS Cardamonin exerts selective therapeutic effects on RagCT90N-mutant cells. Cardamonin can serve as a drug for individualised therapy for follicular lymphoma with RRAGC mutations.
Collapse
Affiliation(s)
- Ying Liu
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China
| | - Yanting Zhu
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China
| | - Huajiao Chen
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China
| | - Jintuo Zhou
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China
| | - Peiguang Niu
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China.
| | - Daohua Shi
- Department of Pharmacy, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University Fujian Maternity and Child Health Hospital, 18 Daoshan Road, Fuzhou, 350001, Fujian, China.
| |
Collapse
|
7
|
Nicastro R, Brohée L, Alba J, Nüchel J, Figlia G, Kipschull S, Gollwitzer P, Romero-Pozuelo J, Fernandes SA, Lamprakis A, Vanni S, Teleman AA, De Virgilio C, Demetriades C. Malonyl-CoA is a conserved endogenous ATP-competitive mTORC1 inhibitor. Nat Cell Biol 2023; 25:1303-1318. [PMID: 37563253 PMCID: PMC10495264 DOI: 10.1038/s41556-023-01198-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 06/29/2023] [Indexed: 08/12/2023]
Abstract
Cell growth is regulated by the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which functions both as a nutrient sensor and a master controller of virtually all biosynthetic pathways. This ensures that cells are metabolically active only when conditions are optimal for growth. Notably, although mTORC1 is known to regulate fatty acid biosynthesis, how and whether the cellular lipid biosynthetic capacity signals back to fine-tune mTORC1 activity remains poorly understood. Here we show that mTORC1 senses the capacity of a cell to synthesise fatty acids by detecting the levels of malonyl-CoA, an intermediate of this biosynthetic pathway. We find that, in both yeast and mammalian cells, this regulation is direct, with malonyl-CoA binding to the mTOR catalytic pocket and acting as a specific ATP-competitive inhibitor. When fatty acid synthase (FASN) is downregulated/inhibited, elevated malonyl-CoA levels are channelled to proximal mTOR molecules that form direct protein-protein interactions with acetyl-CoA carboxylase 1 (ACC1) and FASN. Our findings represent a conserved and unique homeostatic mechanism whereby impaired fatty acid biogenesis leads to reduced mTORC1 activity to coordinately link this metabolic pathway to the overall cellular biosynthetic output. Moreover, they reveal the existence of a physiological metabolite that directly inhibits the activity of a signalling kinase in mammalian cells by competing with ATP for binding.
Collapse
Affiliation(s)
- Raffaele Nicastro
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Laura Brohée
- Max Planck Institute for Biology of Ageing (MPI-AGE), Cologne, Germany
| | - Josephine Alba
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Julian Nüchel
- Max Planck Institute for Biology of Ageing (MPI-AGE), Cologne, Germany
| | - Gianluca Figlia
- German Cancer Research Center (DKFZ), Heidelberg, Germany
- Heidelberg University, Heidelberg, Germany
| | | | - Peter Gollwitzer
- Max Planck Institute for Biology of Ageing (MPI-AGE), Cologne, Germany
| | - Jesus Romero-Pozuelo
- German Cancer Research Center (DKFZ), Heidelberg, Germany
- Heidelberg University, Heidelberg, Germany
- Unidad de Investigación Biomedica, Universidad Alfonso X El Sabio (UAX), Madrid, Spain
| | | | - Andreas Lamprakis
- Max Planck Institute for Biology of Ageing (MPI-AGE), Cologne, Germany
| | - Stefano Vanni
- Department of Biology, University of Fribourg, Fribourg, Switzerland.
| | - Aurelio A Teleman
- German Cancer Research Center (DKFZ), Heidelberg, Germany.
- Heidelberg University, Heidelberg, Germany.
| | | | - Constantinos Demetriades
- Max Planck Institute for Biology of Ageing (MPI-AGE), Cologne, Germany.
- University of Cologne, Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), Cologne, Germany.
| |
Collapse
|
8
|
Regulation of mTORC1 by the Rag GTPases. Biochem Soc Trans 2023; 51:655-664. [PMID: 36929165 DOI: 10.1042/bst20210038] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Revised: 02/21/2023] [Accepted: 02/23/2023] [Indexed: 03/18/2023]
Abstract
The Rag GTPases are an evolutionarily conserved family that play a crucial role in amino acid sensing by the mammalian target of rapamycin complex 1 (mTORC1). mTORC1 is often referred to as the master regulator of cell growth. mTORC1 hyperactivation is observed in multiple diseases such as cancer, obesity, metabolic disorders, and neurodegeneration. The Rag GTPases sense amino acid levels and form heterodimers, where RagA or RagB binds to RagC or RagD, to recruit mTORC1 to the lysosome where it becomes activated. Here, we review amino acid signaling to mTORC1 through the Rag GTPases.
Collapse
|
9
|
A Rag GTPase dimer code defines the regulation of mTORC1 by amino acids. Nat Cell Biol 2022; 24:1394-1406. [PMID: 36097072 PMCID: PMC9481461 DOI: 10.1038/s41556-022-00976-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 07/13/2022] [Indexed: 12/14/2022]
Abstract
Amino acid availability controls mTORC1 activity via a heterodimeric Rag GTPase complex that functions as a scaffold at the lysosomal surface, bringing together mTORC1 with its activators and effectors. Mammalian cells express four Rag proteins (RagA–D) that form dimers composed of RagA/B bound to RagC/D. Traditionally, the Rag paralogue pairs (RagA/B and RagC/D) are referred to as functionally redundant, with the four dimer combinations used interchangeably in most studies. Here, by using genetically modified cell lines that express single Rag heterodimers, we uncover a Rag dimer code that determines how amino acids regulate mTORC1. First, RagC/D differentially define the substrate specificity downstream of mTORC1, with RagD promoting phosphorylation of its lysosomal substrates TFEB/TFE3, while both Rags are involved in the phosphorylation of non-lysosomal substrates such as S6K. Mechanistically, RagD recruits mTORC1 more potently to lysosomes through increased affinity to the anchoring LAMTOR complex. Furthermore, RagA/B specify the signalling response to amino acid removal, with RagB-expressing cells maintaining lysosomal and active mTORC1 even upon starvation. Overall, our findings reveal key qualitative differences between Rag paralogues in the regulation of mTORC1, and underscore Rag gene duplication and diversification as a potentially impactful event in mammalian evolution. Gollwitzer, Grützmacher et al. and Figlia et al. establish that the various Rag GTPase genes and isoforms differentially regulate mTORC1 activity and distinctly modulate the responsiveness of mammalian cells to amino acid availability.
Collapse
|
10
|
|