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Bogan JS. Ubiquitin-like processing of TUG proteins as a mechanism to regulate glucose uptake and energy metabolism in fat and muscle. Front Endocrinol (Lausanne) 2022; 13:1019405. [PMID: 36246906 PMCID: PMC9556833 DOI: 10.3389/fendo.2022.1019405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 09/06/2022] [Indexed: 12/02/2022] Open
Abstract
In response to insulin stimulation, fat and muscle cells mobilize GLUT4 glucose transporters to the cell surface to enhance glucose uptake. Ubiquitin-like processing of TUG (Aspscr1, UBXD9) proteins is a central mechanism to regulate this process. Here, recent advances in this area are reviewed. The data support a model in which intact TUG traps insulin-responsive "GLUT4 storage vesicles" at the Golgi matrix by binding vesicle cargoes with its N-terminus and matrix proteins with its C-terminus. Insulin stimulation liberates these vesicles by triggering endoproteolytic cleavage of TUG, mediated by the Usp25m protease. Cleavage occurs in fat and muscle cells, but not in fibroblasts or other cell types. Proteolytic processing of intact TUG generates TUGUL, a ubiquitin-like protein modifier, as the N-terminal cleavage product. In adipocytes, TUGUL modifies a single protein, the KIF5B kinesin motor, which carries GLUT4 and other vesicle cargoes to the cell surface. In muscle, this or another motor may be modified. After cleavage of intact TUG, the TUG C-terminal product is extracted from the Golgi matrix by the p97 (VCP) ATPase. In both muscle and fat, this cleavage product enters the nucleus, binds PPARγ and PGC-1α, and regulates gene expression to promote fatty acid oxidation and thermogenesis. The stability of the TUG C-terminal product is regulated by an Ate1 arginyltransferase-dependent N-degron pathway, which may create a feedback mechanism to control oxidative metabolism. Although it is now clear that TUG processing coordinates glucose uptake with other aspects of physiology and metabolism, many questions remain about how this pathway is regulated and how it is altered in metabolic disease in humans.
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Affiliation(s)
- Jonathan S. Bogan
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale School of Medicine, New Haven, CT, United States
- Department of Cell Biology, Yale School of Medicine, New Haven, CT, United States
- Yale Center for Molecular and Systems Metabolism, Yale School of Medicine, New Haven, CT, United States
- *Correspondence: Jonathan S. Bogan,
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Bridges E, Sheldon H, Kleibeuker E, Ramberger E, Zois C, Barnard A, Harjes U, Li JL, Masiero M, MacLaren R, Harris A. RHOQ is induced by DLL4 and regulates angiogenesis by determining the intracellular route of the Notch intracellular domain. Angiogenesis 2020; 23:493-513. [PMID: 32506201 PMCID: PMC7311507 DOI: 10.1007/s10456-020-09726-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Accepted: 04/27/2020] [Indexed: 02/04/2023]
Abstract
Angiogenesis, the formation of new blood vessels by endothelial cells, is a finely tuned process relying on the balance between promoting and repressing signalling pathways. Among these, Notch signalling is critical in ensuring appropriate response of endothelial cells to pro-angiogenic stimuli. However, the downstream targets and pathways effected by Delta-like 4 (DLL4)/Notch signalling and their subsequent contribution to angiogenesis are not fully understood. We found that the Rho GTPase, RHOQ, is induced by DLL4 signalling and that silencing RHOQ results in abnormal sprouting and blood vessel formation both in vitro and in vivo. Loss of RHOQ greatly decreased the level of Notch signalling, conversely overexpression of RHOQ promoted Notch signalling. We describe a new feed-forward mechanism regulating DLL4/Notch signalling, whereby RHOQ is induced by DLL4/Notch and is essential for the NICD nuclear translocation. In the absence of RHOQ, Notch1 becomes targeted for degradation in the autophagy pathway and NICD is sequestered from the nucleus and targeted for degradation in lysosomes.
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Affiliation(s)
- Esther Bridges
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Helen Sheldon
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Esther Kleibeuker
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Evelyn Ramberger
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Christos Zois
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Alun Barnard
- Oxford Eye Hospital, University of Oxford, Oxford, OX3 9DS, UK
| | - Ulrike Harjes
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Ji-Liang Li
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
| | - Massimo Masiero
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK
- Radcliffe Department of Medicine, NDCLS, Oxford, OX3 9DU, UK
| | - Robert MacLaren
- Oxford Eye Hospital, University of Oxford, Oxford, OX3 9DS, UK
| | - Adrian Harris
- Cancer Research UK Department of Medical Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK.
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Kilisch M, Mayer S, Mitkovski M, Roehse H, Hentrich J, Schwappach B, Papadopoulos T. A GTPase-induced switch in phospholipid affinity of collybistin contributes to synaptic gephyrin clustering. J Cell Sci 2020; 133:jcs.232835. [PMID: 31932505 DOI: 10.1242/jcs.232835] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 12/19/2019] [Indexed: 11/20/2022] Open
Abstract
Synaptic transmission between neurons relies on the exact spatial organization of postsynaptic transmitter receptors, which are recruited and positioned by dedicated scaffolding and regulatory proteins. At GABAergic synapses, the regulatory protein collybistin (Cb, also known as ARHGEF9) interacts with small GTPases, cell adhesion proteins and phosphoinositides to recruit the scaffolding protein gephyrin and GABAA receptors to nascent synapses. We dissected the interaction of Cb with the small Rho-like GTPase TC10 (also known as RhoQ) and phospholipids. Our data define a protein-lipid interaction network that controls the clustering of gephyrin at synapses. Within this network, TC10 and monophosphorylated phosphoinositides, particulary phosphatidylinositol 3-phosphate (PI3P), provide a coincidence detection platform that allows the accumulation and activation of Cb in endomembranes. Upon activation, TC10 induces a phospholipid affinity switch in Cb, which allows Cb to specifically interact with phosphoinositide species present at the plasma membrane. We propose that this GTPase-based regulatory switch mechanism represents an important step in the process of tethering of Cb-dependent scaffolds and receptors at nascent postsynapses.
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Affiliation(s)
- Markus Kilisch
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | - Simone Mayer
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Hermann-Rein Str. 3, Göttingen 37075, Germany
| | - Miso Mitkovski
- MPI-EM Light Microscopy Facility, Max Planck Institute of Experimental Medicine, Hermann-Rein Str. 3, Göttingen 37075, Germany
| | - Heiko Roehse
- MPI-EM Light Microscopy Facility, Max Planck Institute of Experimental Medicine, Hermann-Rein Str. 3, Göttingen 37075, Germany
| | - Jennifer Hentrich
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | - Theofilos Papadopoulos
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
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Møller LLV, Klip A, Sylow L. Rho GTPases-Emerging Regulators of Glucose Homeostasis and Metabolic Health. Cells 2019; 8:E434. [PMID: 31075957 PMCID: PMC6562660 DOI: 10.3390/cells8050434] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/02/2019] [Accepted: 05/06/2019] [Indexed: 12/11/2022] Open
Abstract
Rho guanosine triphosphatases (GTPases) are key regulators in a number of cellular functions, including actin cytoskeleton remodeling and vesicle traffic. Traditionally, Rho GTPases are studied because of their function in cell migration and cancer, while their roles in metabolism are less documented. However, emerging evidence implicates Rho GTPases as regulators of processes of crucial importance for maintaining metabolic homeostasis. Thus, the time is now ripe for reviewing Rho GTPases in the context of metabolic health. Rho GTPase-mediated key processes include the release of insulin from pancreatic β cells, glucose uptake into skeletal muscle and adipose tissue, and muscle mass regulation. Through the current review, we cast light on the important roles of Rho GTPases in skeletal muscle, adipose tissue, and the pancreas and discuss the proposed mechanisms by which Rho GTPases act to regulate glucose metabolism in health and disease. We also describe challenges and goals for future research.
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Affiliation(s)
- Lisbeth Liliendal Valbjørn Møller
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, 2100 Copenhagen Oe, Denmark.
| | - Amira Klip
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada.
| | - Lykke Sylow
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, 2100 Copenhagen Oe, Denmark.
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Perona JS. Membrane lipid alterations in the metabolic syndrome and the role of dietary oils. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1690-1703. [PMID: 28428072 DOI: 10.1016/j.bbamem.2017.04.015] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Revised: 04/12/2017] [Accepted: 04/15/2017] [Indexed: 12/13/2022]
Abstract
The metabolic syndrome is a cluster of pathological conditions, including hypertension, hyperglycemia, hypertriglyceridemia, obesity and low HDL levels that is of great concern worldwide, as individuals with metabolic syndrome have an increased risk of type-2 diabetes and cardiovascular disease. Insulin resistance, the key feature of the metabolic syndrome, might be at the same time cause and consequence of impaired lipid composition in plasma membranes of insulin-sensitive tissues like liver, muscle and adipose tissue. Diet intervention has been proposed as a powerful tool to prevent the development of the metabolic syndrome, since healthy diets have been shown to have a protective role against the components of the metabolic syndrome. Particularly, dietary fatty acids are capable of modulating the deleterious effects of these conditions, among other mechanisms, by modifications of the lipid composition of the membranes in insulin-sensitive tissues. However, there is still scarce data based of high-level evidence on the effects of dietary oils on the effects of the metabolic syndrome and its components. This review summarizes the current knowledge on the effects of dietary oils on improving alterations of the components of the metabolic syndrome. It also examines their influence in the modulation of plasma membrane lipid composition and in the functionality of membrane proteins involved in insulin activity, like the insulin receptor, GLUT-4, CD36/FAT and ABCA-1, and their effect in the metabolism of glucose, fatty acids and cholesterol, and, in turn, the key features of the metabolic syndrome. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
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Affiliation(s)
- Javier S Perona
- Bioactive Compunds, Nutrition and Health, Instituto de la Grasa-CSIC, Campus Universidad Pablo de Olavide, Ctra. Utrera km 1, Building 46, 41013 Seville, (Spain)
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Moreno-Castellanos N, Rodríguez A, Rabanal-Ruiz Y, Fernández-Vega A, López-Miranda J, Vázquez-Martínez R, Frühbeck G, Malagón MM. The cytoskeletal protein septin 11 is associated with human obesity and is involved in adipocyte lipid storage and metabolism. Diabetologia 2017; 60:324-335. [PMID: 27866222 DOI: 10.1007/s00125-016-4155-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 10/25/2016] [Indexed: 11/28/2022]
Abstract
AIMS/HYPOTHESIS Septins are newly identified members of the cytoskeleton that have been proposed as biomarkers of a number of diseases. However, septins have not been characterised in adipose tissue and their relationship with obesity and insulin resistance remains unknown. Herein, we characterised a member of this family, septin 11 (SEPT11), in human adipose tissue and analysed its potential involvement in the regulation of adipocyte metabolism. METHODS Gene and protein expression levels of SEPT11 were analysed in human adipose tissue. SEPT11 distribution was evaluated by immunocytochemistry, electron microscopy and subcellular fractionation techniques. Glutathione S-transferase (GST) pull-down, immunoprecipitation and yeast two-hybrid screening were used to identify the SEPT11 interactome. Gene silencing was used to assess the role of SEPT11 in the regulation of insulin signalling and lipid metabolism in adipocytes. RESULTS We demonstrate the expression of SEPT11 in human adipocytes and its upregulation in obese individuals, with SEPT11 mRNA content positively correlating with variables of insulin resistance in subcutaneous adipose tissue. SEPT11 content was regulated by lipogenic, lipolytic and proinflammatory stimuli in human adipocytes. SEPT11 associated with caveolae in mature adipocytes and interacted with both caveolin-1 and the intracellular fatty acid chaperone, fatty acid binding protein 5 (FABP5). Lipid loading of adipocytes caused the association of the three proteins with the surface of lipid droplets. SEPT11 silencing impaired insulin signalling and insulin-induced lipid accumulation in adipocytes. CONCLUSIONS/INTERPRETATION Our findings support a role for SEPT11 in lipid traffic and metabolism in adipocytes and open new avenues for research on the control of lipid storage in obesity and insulin resistance.
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Affiliation(s)
- Natalia Moreno-Castellanos
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC)/University of Córdoba/Reina Sofia University Hospital, Edificio IMIBIC, Avda. Menéndez Pidal s/n, 14004, Córdoba, Spain
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Córdoba, Spain
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
| | - Amaia Rodríguez
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
- Metabolic Research Laboratory, Clínica Universidad de Navarra, IdiSNA, Pamplona, Spain
| | - Yoana Rabanal-Ruiz
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC)/University of Córdoba/Reina Sofia University Hospital, Edificio IMIBIC, Avda. Menéndez Pidal s/n, 14004, Córdoba, Spain
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Córdoba, Spain
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
| | - Alejandro Fernández-Vega
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC)/University of Córdoba/Reina Sofia University Hospital, Edificio IMIBIC, Avda. Menéndez Pidal s/n, 14004, Córdoba, Spain
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Córdoba, Spain
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
| | - José López-Miranda
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
- Lipids and Atherosclerosis Unit, IMIBIC/Reina Sofia University Hospital/University of Córdoba, Córdoba, Spain
| | - Rafael Vázquez-Martínez
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC)/University of Córdoba/Reina Sofia University Hospital, Edificio IMIBIC, Avda. Menéndez Pidal s/n, 14004, Córdoba, Spain
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Córdoba, Spain
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain
| | - Gema Frühbeck
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain, .
- Metabolic Research Laboratory, Clínica Universidad de Navarra, IdiSNA, Pamplona, Spain.
- Department of Endocrinology & Nutrition, Clínica Universidad de Navarra, Avda. Pío XII 36, 31008, Pamplona, Spain.
| | - María M Malagón
- Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC)/University of Córdoba/Reina Sofia University Hospital, Edificio IMIBIC, Avda. Menéndez Pidal s/n, 14004, Córdoba, Spain.
- Department of Cell Biology, Physiology and Immunology, University of Cordoba, Córdoba, Spain.
- CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Spain, .
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Lu JC, Chiang YT, Lin YC, Chang YT, Lu CY, Chen TY, Yeh CS. Disruption of Lipid Raft Function Increases Expression and Secretion of Monocyte Chemoattractant Protein-1 in 3T3-L1 Adipocytes. PLoS One 2016; 11:e0169005. [PMID: 28030645 PMCID: PMC5193455 DOI: 10.1371/journal.pone.0169005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 12/11/2016] [Indexed: 12/13/2022] Open
Abstract
The adipocyte is unique in its capacity to store lipids. In addition to triglycerides, the adipocyte stores a significant amount of cholesterol. Moreover, obese adipocytes are characterized by a redistribution of cholesterol with depleted cholesterol in the plasma membrane, suggesting that cholesterol perturbation may play a role in adipocyte dysfunction. We used methyl-β-cyclodextrin (MβCD), a molecule with high affinity for cholesterol, to rapidly deplete cholesterol level in differentiated 3T3-L1 adipocytes. We tested whether this perturbation altered adipocyte secretion of monocyte chemoattractant protein-1 (MCP-1), a chemokine that is elevated in obesity and is linked to obesity-associated chronic diseases. Depletion of cholesterol by MβCD increased MCP-1 secretion as well as the mRNA and protein levels, suggesting perturbation at biosynthesis and secretion. Pharmacological inhibition revealed that NF-κB, but not MEK, p38 and JNK, was involved in MβCD-stimulated MCP-1 biosynthesis and secretion in adipocytes. Finally, another cholesterol-binding drug, filipin, also induced MCP-1 secretion without altering membrane cholesterol level. Interestingly, both MβCD and filipin disturbed the integrity of lipid rafts, the membrane microdomains enriched in cholesterol. Thus, the depletion of membrane cholesterol in obese adipocytes may result in dysfunction of lipid rafts, leading to the elevation of proinflammatory signaling and MCP-1 secretion in adipocytes.
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Affiliation(s)
- Juu-Chin Lu
- Department of Physiology and Pharmacology, Chang Gung University, Taoyuan, Taiwan
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Chang Gung Memorial Hospital, Linkou, Taiwan
- * E-mail:
| | - Yu-Ting Chiang
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
| | - Yu-Chun Lin
- Department of Physiology and Pharmacology, Chang Gung University, Taoyuan, Taiwan
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
| | - Yu-Tzu Chang
- Department of Physiology and Pharmacology, Chang Gung University, Taoyuan, Taiwan
| | - Chia-Yun Lu
- Department of Physiology and Pharmacology, Chang Gung University, Taoyuan, Taiwan
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
| | - Tzu-Yu Chen
- Department of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Chia-Shan Yeh
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
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Gao L, Chen J, Gao J, Wang H, Xiong W. Super-resolution microscopy reveals the insulin-resistance-regulated reorganization of GLUT4 on plasma membranes. J Cell Sci 2016; 130:396-405. [PMID: 27888215 DOI: 10.1242/jcs.192450] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 11/11/2016] [Indexed: 02/01/2023] Open
Abstract
GLUT4 (also known as SLC2A4) is essential for glucose uptake in skeletal muscles and adipocytes, which play central roles in whole-body glucose metabolism. Here, using direct stochastic optical reconstruction microscopy (dSTORM) to investigate the characteristics of plasma-membrane-fused GLUT4 at the single-molecule level, we have demonstrated that insulin and insulin resistance regulate the spatial organization of GLUT4 in adipocytes. Stimulation with insulin shifted the balance of GLUT4 on the plasma membrane toward a more dispersed configuration. In contrast, insulin resistance induced a more clustered distribution of GLUT4 and increased the mean number of molecules per cluster. Furthermore, our data demonstrate that the F5QQI motif and lipid rafts mediate the maintenance of GLUT4 clusters on the plasma membrane. Mutation of F5QQI (F5QQA-GLUT4) induced a more clustered distribution of GLUT4; moreover, destruction of lipid rafts in adipocytes expressing F5QQA-GLUT4 dramatically decreased the percentage of large clusters and the mean number of molecules per cluster. In conclusion, our data clarify the effects of insulin stimulation or insulin resistance on GLUT4 reorganization on the plasma membrane and reveal new pathogenic mechanisms of insulin resistance.
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Affiliation(s)
- Lan Gao
- State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, P.R. China.,Graduate University of Chinese Academy of Sciences, Beijing 100049, P.R. China
| | - Junling Chen
- Graduate University of Chinese Academy of Sciences, Beijing 100049, P.R. China.,State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilil 130022, P.R. China
| | - Jing Gao
- Graduate University of Chinese Academy of Sciences, Beijing 100049, P.R. China.,State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilil 130022, P.R. China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilil 130022, P.R. China
| | - Wenyong Xiong
- State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, P.R. China
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Fairbridge NA, Southall TM, Ayre DC, Komatsu Y, Raquet PI, Brown RJ, Randell E, Kovacs CS, Christian SL. Loss of CD24 in Mice Leads to Metabolic Dysfunctions and a Reduction in White Adipocyte Tissue. PLoS One 2015; 10:e0141966. [PMID: 26536476 PMCID: PMC4633231 DOI: 10.1371/journal.pone.0141966] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 10/15/2015] [Indexed: 12/21/2022] Open
Abstract
CD24 is a glycophosphatidylinositol (GPI)-linked cell surface receptor that is involved in regulating the survival or differentiation of several different cell types. CD24 has been used to identify pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Moreover, we recently found that the dynamic upregulation of CD24 in vitro during early phases of adipogenesis is necessary for mature adipocyte development. To determine the role of CD24 in adipocyte development in vivo, we evaluated the development of the inguinal and interscapular subcutaneous WAT and the epididymal visceral WAT in mice with a homozygous deletion of CD24 (CD24KO). We observed a significant decrease in WAT mass of 40% to 74% in WAT mass from both visceral and subcutaneous depots in male mice, with no significant effect in female mice, compared to wild-type (WT) sex- and age-matched controls. We also found that CD24KO mice had increased fasting glucose and free fatty acids, decreased fasting insulin, and plasma leptin. No major differences were observed in the sensitivity to insulin or glucose, or in circulating triglycerides, total cholesterol, HDL-cholesterol, or LDL-cholesterol levels between WT and CD24KO mice. Challenging the CD24KO mice with either high sucrose (35%) or high fat (45%) diets that promote increased adiposity, increased WAT mass and fasting insulin, adiponectin and leptin levels, as well as reduced the sensitivity to insulin and glucose, to the levels of WT mice on the same diets. The CD24-mediated reduction in fat pad size was due to a reduction in adipocyte cell size in all depots with no significant reduction pre-adipocyte or adipocyte cell number. Thus, we have clearly demonstrated that the global absence of CD24 affects adipocyte cell size in vivo in a sex- and diet-dependent manner, as well as causing metabolic disturbances in glucose homeostasis and free fatty acid levels.
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Affiliation(s)
- Nicholas A. Fairbridge
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Thomas M. Southall
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - D. Craig Ayre
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Yumiko Komatsu
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Paula I. Raquet
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Robert J. Brown
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Edward Randell
- Department of Laboratory Medicine, Faculty of Medicine, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Christopher S. Kovacs
- Division of Medicine-Endocrinology, Faculty of Medicine, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
| | - Sherri L. Christian
- Department of Biochemistry, Faculty of Science, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
- * E-mail:
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10
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Charming neighborhoods on the cell surface: plasma membrane microdomains regulate receptor tyrosine kinase signaling. Cell Signal 2015; 27:1963-76. [PMID: 26163824 DOI: 10.1016/j.cellsig.2015.07.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 07/07/2015] [Indexed: 12/14/2022]
Abstract
Receptor tyrosine kinases (RTK) are an important family of growth factor and hormone receptors that regulate many aspects of cellular physiology. Ligand binding by RTKs at the plasma membrane elicits activation of many signaling intermediates. The spatial and temporal regulation of RTK signaling within cells is an important determinant of receptor signaling outcome. In particular, the compartmentalization of the plasma membrane into a number of microdomains allows context-specific control of RTK signaling. Indeed various RTKs are recruited to and enriched within specific plasma membrane microdomains under various conditions, including lipid-ordered domains such as caveolae and lipid rafts, clathrin-coated structures, tetraspanin-enriched microdomains, and actin-dependent protrusive membrane microdomains such as dorsal ruffles and invadosomes. We examine the evidence for control of RTK signaling by each of these plasma membrane microdomains, as well as molecular mechanisms for how this spatial organization controls receptor signaling.
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Shah A, Chen D, Boda AR, Foster LJ, Davis MJ, Hill MM. RaftProt: mammalian lipid raft proteome database. Nucleic Acids Res 2014; 43:D335-8. [PMID: 25392410 PMCID: PMC4383944 DOI: 10.1093/nar/gku1131] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
RaftProt (http://lipid-raft-database.di.uq.edu.au/) is a database of mammalian lipid raft-associated proteins as reported in high-throughput mass spectrometry studies. Lipid rafts are specialized membrane microdomains enriched in cholesterol and sphingolipids thought to act as dynamic signalling and sorting platforms. Given their fundamental roles in cellular regulation, there is a plethora of information on the size, composition and regulation of these membrane microdomains, including a large number of proteomics studies. To facilitate the mining and analysis of published lipid raft proteomics studies, we have developed a searchable database RaftProt. In addition to browsing the studies, performing basic queries by protein and gene names, searching experiments by cell, tissue and organisms; we have implemented several advanced features to facilitate data mining. To address the issue of potential bias due to biochemical preparation procedures used, we have captured the lipid raft preparation methods and implemented advanced search option for methodology and sample treatment conditions, such as cholesterol depletion. Furthermore, we have identified a list of high confidence proteins, and enabled searching only from this list of likely bona fide lipid raft proteins. Given the apparent biological importance of lipid raft and their associated proteins, this database would constitute a key resource for the scientific community.
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Affiliation(s)
- Anup Shah
- The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia
| | - David Chen
- School of Information and Communication Technology, Griffith University, Brisbane, QLD, Australia
| | - Akash R Boda
- The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia
| | - Leonard J Foster
- Centre for High-Throughput Biology, University of British Columbia, British Columbia, Canada
| | - Melissa J Davis
- Systems Biology Laboratory, Melbourne School of Engineering, The University of Melbourne, Parkville, VIC, Australia
| | - Michelle M Hill
- The University of Queensland Diamantina Institute, The University of Queensland, Translational Research Institute, Brisbane, QLD, Australia
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Abstract
Insulin regulates glucose uptake by controlling the subcellular location of GLUT4 glucose transporters. GLUT4 is sequestered within fat and muscle cells during low-insulin states, and is translocated to the cell surface upon insulin stimulation. The TUG protein is a functional tether that sequesters GLUT4 at the Golgi matrix. To stimulate glucose uptake, insulin triggers TUG endoproteolytic cleavage. Cleavage accounts for a large proportion of the acute effect of insulin to mobilize GLUT4 to the cell surface. During ongoing insulin exposure, endocytosed GLUT4 recycles to the plasma membrane directly from endosomes, and bypasses a TUG-regulated trafficking step. Insulin acts through the TC10α GTPase and its effector protein, PIST, to stimulate TUG cleavage. This action is coordinated with insulin signals through AS160/Tbc1D4 and Tbc1D1 to modulate Rab GTPases, and with other signals to direct overall GLUT4 targeting. Data support the idea that the N-terminal TUG cleavage product, TUGUL, functions as a novel ubiquitin-like protein modifier to facilitate GLUT4 movement to the cell surface. The C-terminal TUG cleavage product is extracted from the Golgi matrix, which vacates an "anchoring" site to permit subsequent cycles of GLUT4 retention and release. Together, GLUT4 vesicle translocation and TUG cleavage may coordinate glucose uptake with physiologic effects of other proteins present in the GLUT4-containing vesicles, and with potential additional effects of the TUG C-terminal product. Understanding this TUG pathway for GLUT4 retention and release will shed light on the regulation of glucose uptake and the pathogenesis of type 2 diabetes.
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Affiliation(s)
- Jonathan P Belman
- Section of Endocrinology and Metabolism, Department of Internal Medicine, and Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, Box 208020, New Haven, CT, 06520-8020, USA
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13
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Ramalingam L, Oh E, Thurmond DC. Novel roles for insulin receptor (IR) in adipocytes and skeletal muscle cells via new and unexpected substrates. Cell Mol Life Sci 2013; 70:2815-34. [PMID: 23052216 PMCID: PMC3556358 DOI: 10.1007/s00018-012-1176-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 08/21/2012] [Accepted: 09/18/2012] [Indexed: 01/30/2023]
Abstract
The insulin signaling pathway regulates whole-body glucose homeostasis by transducing extracellular signals from the insulin receptor (IR) to downstream intracellular targets, thus coordinating a multitude of biological functions. Dysregulation of IR or its signal transduction is associated with insulin resistance, which may culminate in type 2 diabetes. Following initial stimulation of IR, insulin signaling diverges into different pathways, activating multiple substrates that have roles in various metabolic and cellular processes. The integration of multiple pathways arising from IR activation continues to expand as new IR substrates are identified and characterized. Accordingly, our review will focus on roles for IR substrates as they pertain to three primary areas: metabolism/glucose uptake, mitogenesis/growth, and aging/longevity. While IR functions in a seemingly pleiotropic manner in many cell types, through these three main roles in fat and skeletal muscle cells, IR multi-tasks to regulate whole-body glucose homeostasis to impact healthspan and lifespan.
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Affiliation(s)
- Latha Ramalingam
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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14
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Das >UN. Lipoxins, resolvins, protectins, maresins and nitrolipids, and their clinical implications with specific reference to diabetes mellitus and other diseases: part II. ACTA ACUST UNITED AC 2013. [DOI: 10.2217/clp.13.32] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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15
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Lizunov VA, Stenkula K, Troy A, Cushman SW, Zimmerberg J. Insulin regulates Glut4 confinement in plasma membrane clusters in adipose cells. PLoS One 2013; 8:e57559. [PMID: 23520472 PMCID: PMC3592853 DOI: 10.1371/journal.pone.0057559] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 01/22/2013] [Indexed: 01/12/2023] Open
Abstract
Insulin-stimulated delivery of glucose transporter-4 (GLUT4) to the plasma membrane (PM) is the hallmark of glucose metabolism. In this study we examined insulin’s effects on GLUT4 organization in PM of adipose cells by direct microscopic observation of single monomers tagged with photoswitchable fluorescent protein. In the basal state, after exocytotic delivery only a fraction of GLUT4 is dispersed into the PM as monomers, while most of the GLUT4 stays at the site of fusion and forms elongated clusters (60–240 nm). GLUT4 monomers outside clusters diffuse freely and do not aggregate with other monomers. In contrast, GLUT4 molecule collision with an existing cluster can lead to immediate confinement and association with that cluster. Insulin has three effects: it shifts the fraction of dispersed GLUT4 upon delivery, it augments the dissociation of GLUT4 monomers from clusters ∼3-fold and it decreases the rate of endocytic uptake. All together these three effects of insulin shift most of the PM GLUT4 from clustered to dispersed states. GLUT4 confinement in clusters represents a novel kinetic mechanism for insulin regulation of glucose homeostasis.
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Affiliation(s)
- Vladimir A. Lizunov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Karin Stenkula
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Aaron Troy
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Samuel W. Cushman
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Joshua Zimmerberg
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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16
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Morino-Koga S, Yano S, Kondo T, Shimauchi Y, Matsuyama S, Okamoto Y, Suico MA, Koga T, Sato T, Shuto T, Arima H, Wada I, Araki E, Kai H. Insulin receptor activation through its accumulation in lipid rafts by mild electrical stress. J Cell Physiol 2013; 228:439-46. [PMID: 22740366 DOI: 10.1002/jcp.24149] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Insulin resistance is due to the reduced cellular response to insulin in peripheral tissues. The interaction of insulin with its receptor is the first step in insulin action and thus the identified target of insulin resistance. It has been well established that defects or mutations in the insulin receptor (IR) cause insulin resistance. Therefore, an IR activator might be a novel therapeutic approach for insulin resistance. Our previous report showed that mild electrical stress (MES) enhanced the insulin-induced signaling pathway. However, the molecular mechanism of the effect of MES remains unclear. We assessed the effect of MES, which is characterized by low-intensity direct current, on insulin signaling in vitro and in vivo. Here, we showed that MES activated the insulin signaling in an insulin-independent manner and improved insulin resistance in peripheral tissues of high fat-fed mice. Moreover, we found that MES increased the localization of IR in lipid rafts and enhanced the level of phosphorylated Akt in insulin-resistant hepatic cells. Ablation of lipid rafts disrupted the effect of MES on Akt activation. Our findings indicate that MES has potential as an activator of IR in an insulin-independent manner, and might be beneficial for insulin resistance in type 2 diabetes.
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Affiliation(s)
- Saori Morino-Koga
- Department of Molecular Medicine, Global COE Cell Fate Regulation Research and Education Unit, Kumamoto University, Kumamoto, Japan
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17
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Bridges D, Chang L, Lodhi IJ, Clark NA, Saltiel AR. TC10 is regulated by caveolin in 3T3-L1 adipocytes. PLoS One 2012; 7:e42451. [PMID: 22900022 PMCID: PMC3416860 DOI: 10.1371/journal.pone.0042451] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 07/05/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND TC10 is a small GTPase found in lipid raft microdomains of adipocytes. The protein undergoes activation in response to insulin, and plays a key role in the regulation of glucose uptake by the hormone. METHODOLOGY/PRINCIPAL FINDINGS TC10 requires high concentrations of magnesium in order to stabilize guanine nucleotide binding. Kinetic analysis of this process revealed that magnesium acutely decreased the nucleotide release and exchange rates of TC10, suggesting that the G protein may behave as a rapidly exchanging, and therefore active protein in vivo. However, in adipocytes, the activity of TC10 is not constitutive, indicating that mechanisms must exist to maintain the G protein in a low activity state in untreated cells. Thus, we searched for proteins that might bind to and stabilize TC10 in the inactive state. We found that Caveolin interacts with TC10 only when GDP-bound and stabilizes GDP binding. Moreover, knockdown of Caveolin 1 in 3T3-L1 adipocytes increased the basal activity state of TC10. CONCLUSIONS/SIGNIFICANCE Together these data suggest that TC10 is intrinsically active in vivo, but is maintained in the inactive state by binding to Caveolin 1 in 3T3-L1 adipocytes under basal conditions, permitting its activation by insulin.
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Affiliation(s)
- Dave Bridges
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Louise Chang
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Irfan J. Lodhi
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Natalie A. Clark
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Alan R. Saltiel
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail:
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18
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Oinuma I, Kawada K, Tsukagoshi K, Negishi M. Rnd1 and Rnd3 targeting to lipid raft is required for p190 RhoGAP activation. Mol Biol Cell 2012; 23:1593-604. [PMID: 22357615 PMCID: PMC3327318 DOI: 10.1091/mbc.e11-11-0900] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The N-terminal region is the lipid raft–targeting determinant. A novel regulatory mechanism is found by which Rnd proteins function as RhoA antagonists, as is a striking mechanism by which differential membrane targeting governs activities of G proteins having similarities in effector interaction. The Rnd proteins Rnd1, Rnd2, and Rnd3/RhoE are well known as key regulators of the actin cytoskeleton in various cell types, but they comprise a distinct subgroup of the Rho family in that they are GTP bound and constitutively active. Functional differences of the Rnd proteins in RhoA inhibition signaling have been reported in various cell types. Rnd1 and Rnd3 antagonize RhoA signaling by activating p190 RhoGAP, whereas Rnd2 does not. However, all the members of the Rnd family have been reported to bind directly to p190 RhoGAP and equally induce activation of p190 RhoGAP in vitro, and there is no evidence that accounts for the functional difference of the Rnd proteins in RhoA inhibition signaling. Here we report the role of the N-terminal region in signaling. Rnd1 and Rnd3, but not Rnd2, have a KERRA (Lys-Glu-Arg-Arg-Ala) sequence of amino acids in their N-terminus, which functions as the lipid raft-targeting determinant. The sequence mediates the lipid raft targeting of p190 RhoGAP correlated with its activation. Overall, our results demonstrate a novel regulatory mechanism by which differential membrane targeting governs activities of Rnd proteins to function as RhoA antagonists.
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Affiliation(s)
- Izumi Oinuma
- Laboratory of Molecular Neurobiology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
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19
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Chambaut-Guérin AM, Pairault J. Tumour necrosis factor α-induced adipose-related protein (TIARP): co-localization with caveolin-1. Biol Cell 2012; 97:339-47. [PMID: 15836432 DOI: 10.1042/bc20040062] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We previously identified TIARP (TNF(alpha)-induced adipose-related protein, where TNF(alpha) stands for tumour necrosis factor alpha), a novel plasma-membrane protein that is induced during 3T3-L1 preadipocytes differentiation by TNF(alpha). Whereas the biological function of TIARP is currently unknown, its protein sequence is reminiscent of transporter protein and/or NAD(P)/NAD(P)H-dependent oxidoreductase activities. We hypothesized that TIARP could be associated with the 3T3-L1 adipocyte plasma-membrane caveolae domains that contain many proteins involved in cellular trafficking and signalling processes. Studies by confocal microscopy showed that TIARP and caveolin-1, a major protein of caveolae, co-localized as patches at the plasma membrane. Immunoblot analysis of cell extracts indicated that TIARP was completely detergent-extractible from membranes, whereas caveolin-1 was present as both detergent-extractible and -insoluble pools. Since TIARP is compartmentalized with caveolin-1 within caveolae domains, we suggest this protein to be part of a signalling complex in association with caveolin-1 and regulatory proteins.
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Affiliation(s)
- Anne-Marie Chambaut-Guérin
- Laboratoire de Physiologie et Physiopathologie, Centre de Recherche Biomédicale des Cordeliers, UMR 7079 CNRS-Université Paris VI, 15 rue de l'Ecole de Médecine, 75270 Paris Cedex 06, France.
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20
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Nohara A, Okada S, Ohshima K, Pessin JE, Mori M. Cyclin-dependent kinase-5 is a key molecule in tumor necrosis factor-α-induced insulin resistance. J Biol Chem 2011; 286:33457-65. [PMID: 21813649 DOI: 10.1074/jbc.m111.231431] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism of TNF-α-induced insulin resistance has remained unresolved with evidence for down-regulation of insulin effector targets effects or blockade of proximal as well as distal insulin signaling events depending upon the dose, time, and cell type examined. To address this issue we examined the acute actions of TNF-α in differentiated 3T3L1 adipocytes. Acute (5-15 min) treatment with 20 ng/ml (~0.8 nm) TNF-α had no significant effect on IRS1-associated phosphatidylinositol 3-kinase. In contrast, TNF-α increased insulin-stimulated cyclin-dependent kinase-5 (CDK5) phosphorylation on tyrosine residue 15 through an Erk-dependent pathway and up-regulated the expression of the CDK5 regulator protein p35. In parallel, TNF-α stimulation also resulted in the phosphorylation and GTP loading of the Rho family GTP-binding protein, TC10α. TNF-α enhanced the depolymerization of cortical F-actin and inhibited insulin-stimulated glucose transporter-4 (GLUT4) translocation. Treatment with the MEK inhibitor, PD98059, blocked the TNF-α-induced increase in CDK5 phosphorylation and the depolymerization of cortical F-actin. Conversely, siRNA-mediated knockdown of CDK5 or treatment with the MEK inhibitor restored the impaired insulin-stimulated GLUT4 translocation induced by TNF-α. Furthermore, siRNA-mediated knockdown of p44/42 Erk also rescued the TNF-α inhibition of insulin-stimulated GLUT4 translocation. Together, these data demonstrate that TNF-α-mediated insulin resistance of glucose uptake can occur through a MEK/Erk-dependent activation of CDK5.
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Affiliation(s)
- Atsushi Nohara
- Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, 3-39-15 Showa-machi, Maebashi, Japan
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21
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Zhao FQ, Keating AF. Functional properties and genomics of glucose transporters. Curr Genomics 2011; 8:113-28. [PMID: 18660845 DOI: 10.2174/138920207780368187] [Citation(s) in RCA: 363] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 12/08/2006] [Accepted: 12/17/2007] [Indexed: 12/17/2022] Open
Abstract
Glucose is the major energy source for mammalian cells as well as an important substrate for protein and lipid synthesis. Mammalian cells take up glucose from extracellular fluid into the cell through two families of structurallyrelated glucose transporters. The facilitative glucose transporter family (solute carriers SLC2A, protein symbol GLUT) mediates a bidirectional and energy-independent process of glucose transport in most tissues and cells, while the NaM(+)/glucose cotransporter family (solute carriers SLC5A, protein symbol SGLT) mediates an active, Na(+)-linked transport process against an electrochemical gradient. The GLUT family consists of thirteen members (GLUT1-12 and HMIT). Phylogenetically, the members of the GLUT family are split into three classes based on protein similarities. Up to now, at least six members of the SGLT family have been cloned (SGLT1-6). In this review, we report both the genomic structure and function of each transporter as well as intra-species comparative genomic analysis of some of these transporters. The affinity for glucose and transport kinetics of each transporter differs and ranges from 0.2 to 17mM. The ability of each protein to transport alternative substrates also differs and includes substrates such as fructose and galactose. In addition, the tissue distribution pattern varies between species. There are different regulation mechanisms of these transporters. Characterization of transcriptional control of some of the gene promoters has been investigated and alternative promoter usage to generate different protein isoforms has been demonstrated. We also introduce some pathophysiological roles of these transporters in human.
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Affiliation(s)
- Feng-Qi Zhao
- Lactation and Mammary Gland Biology Group, Department of Animal Science, University of Vermont, Burlington, VT, USA
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22
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Osawa Y, Seki E, Kodama Y, Suetsugu A, Miura K, Adachi M, Ito H, Shiratori Y, Banno Y, Olefsky JM, Nagaki M, Moriwaki H, Brenner DA, Seishima M. Acid sphingomyelinase regulates glucose and lipid metabolism in hepatocytes through AKT activation and AMP-activated protein kinase suppression. FASEB J 2010; 25:1133-44. [PMID: 21163859 PMCID: PMC3058702 DOI: 10.1096/fj.10-168351] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Acid sphingomyelinase (ASM) regulates the homeostasis of sphingolipids, including ceramides and sphingosine-1-phosphate (S1P). Because sphingolipids regulate AKT activation, we investigated the role of ASM in hepatic glucose and lipid metabolism. Initially, we overexpressed ASM in the livers of wild-type and diabetic db/db mice by adenovirus vector (Ad5ASM). In these mice, glucose tolerance was improved, and glycogen and lipid accumulation in the liver were increased. Using primary cultured hepatocytes, we confirmed that ASM increased glucose uptake, glycogen deposition, and lipid accumulation through activation of AKT and glycogen synthase kinase-3β. In addition, ASM induced up-regulation of glucose transporter 2 accompanied by suppression of AMP-activated protein kinase (AMPK) phosphorylation. Loss of sphingosine kinase-1 (SphK1) diminished ASM-mediated AKT phosphorylation, but exogenous S1P induced AKT activation in hepatocytes. In contrast, SphK1 deficiency did not affect AMPK activation. These results suggest that the SphK/S1P pathway is required for ASM-mediated AKT activation but not for AMPK inactivation. Finally, we found that treatment with high-dose glucose increased glycogen deposition and lipid accumulation in wild-type hepatocytes but not in ASM(-/-) cells. This result is consistent with glucose intolerance in ASM(-/-) mice. In conclusion, ASM modulates AKT activation and AMPK inactivation, thus regulating glucose and lipid metabolism in the liver.
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Affiliation(s)
- Yosuke Osawa
- Department of Informative Clinical Medicine, Gifu University Graduate School of Medicine, Gifu, Japan.
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Wada T, Hori S, Sugiyama M, Fujisawa E, Nakano T, Tsuneki H, Nagira K, Saito S, Sasaoka T. Progesterone inhibits glucose uptake by affecting diverse steps of insulin signaling in 3T3-L1 adipocytes. Am J Physiol Endocrinol Metab 2010; 298:E881-8. [PMID: 20071559 DOI: 10.1152/ajpendo.00649.2009] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Maternal insulin resistance is essential for efficient provision of glucose to the fetus. Although elevation of placental hormones is known to relate to the development of insulin resistance, the precise underlying mechanism of maternal insulin resistance is unknown. Therefore, we examined the molecular mechanisms of progesterone causing insulin resistance in 3T3-L1 adipocytes. Progesterone at 10(-4) M, but not 10(-5) M, reduced the amount of IRS-1. As a result, insulin-induced phosphorylation of IRS-1, the association of IRS-1 with p85alpha, and subsequent phosphorylation of Akt1 and -2 was decreased moderately by 10(-4) M progesterone. Subsequently, insulin-induced translocation of GLUT4 to the plasma membrane evaluated by immunostaining on the plasma membrane sheet by confocal laser microscope was also decreased by 10(-4) M progesterone. In contrast, 2-[(3)H]deoxyglucose (2DG) uptake was markedly inhibited by both 10(-5) and 10(-4) M progesterone in a dose-dependent manner. Surprisingly, 2DG uptake elicited by adenovirus-mediated expression of constitutive-active mutant of PI 3-kinase (myr-p110) and Akt (myr-Akt) was suppressed by progesterone. Interestingly, insulin-induced tyrosine phosphorylation of Cbl and activation of TC10 were inhibited by progesterone at 10(-5) M. These results indicate that progesterone is implicated in insulin resistance during pregnancy by inhibiting the PI 3-kinase pathway at the step of 1) IRS-1 expression and 2) distal to Akt and 3) by suppressing the PI 3-kinase-independent pathway of TC10 activation by affecting Cbl phosphorylation.
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Affiliation(s)
- Tsutomu Wada
- Dept. of Clinical Pharmacology, Univ. of Toyama, Japan
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24
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Gómez-Ruiz A, de Miguel C, Campión J, Martínez JA, Milagro FI. Time-dependent regulation of muscle caveolin activation and insulin signalling in response to high-fat diet. FEBS Lett 2009; 583:3259-64. [PMID: 19751730 DOI: 10.1016/j.febslet.2009.09.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Revised: 09/04/2009] [Accepted: 09/07/2009] [Indexed: 11/25/2022]
Abstract
We studied the effect of high-fat diet on the expression and activation of the three caveolins in rat skeletal muscle and their association with the insulin signalling cascade. Initial response was characterized by increased signalling through Cav-1 and Cav-3 phosphorylation, suggesting that both participate in an initial acute response to the calorie surplus. Afterwards, Cav-1 signalling was slightly reduced, whereas Cav-3 remained active. Late chronic phase signalling through both proteins was impaired inducing a prediabetic state. Summarizing, caveolins seem to mediate a time-dependent regulation of insulin cascade in response to high-fat diet in muscle.
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Affiliation(s)
- Ana Gómez-Ruiz
- Department of Biochemistry and Molecular Biology, University of Navarra, Pamplona, Spain
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25
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Abstract
Type 2 diabetes affects approximately 7% of the population in the United States and is characterized by decreased disposal of glucose in peripheral tissues due to insulin resistance and overproduction of glucose by the liver, defects in pancreatic beta-cell function, and decreased beta-cell mass. Obesity, decreased physical exercise, and consumption of foods with a high glycemic index (GI) and load are major predisposing factors in the development of type 2 diabetes. The GI is used to evaluate the rise in blood glucose levels in response to food. The GI provides an indication of the quality of carbohydrate in a food. The glycemic load (GL) is used to provide information about the quantity of carbohydrates in a food and the insulin demand. Individuals with diabetes are advised to maintain a diet of low-GL foods, because low-GL diets improve diabetes symptoms. Grapes have a mean GI and GL in the low range. Little research has been performed with grapes and/or grape products to determine the glycemic response either alone or with a meal. Grapes and other fruits contain numerous polyphenols, including the stilbene resveratrol, the flavanol quercetin, catechins, and anthocyanins that have shown potential for reducing hyperglycemia, improving beta-cell function, and protecting against beta-cell loss. Therefore, with a low mean GI and GL, grapes or grape products may provide health benefits to type 2 diabetics.
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Affiliation(s)
- Susanj Zunino
- USDA, Agricultural Research Service, Western Human Nutrition Research Center, University of California, Davis, CA 95616, USA.
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26
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González-Muñoz E, López-Iglesias C, Calvo M, Palacín M, Zorzano A, Camps M. Caveolin-1 loss of function accelerates glucose transporter 4 and insulin receptor degradation in 3T3-L1 adipocytes. Endocrinology 2009; 150:3493-502. [PMID: 19406948 DOI: 10.1210/en.2008-1520] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Caveolae are a specialized type of lipid rafts that are stabilized by oligomers of caveolin protein. Caveolae are particularly enriched in adipocytes. Here we analyzed the effects of caveolin-1 knockdown and caveolae ablation on adipocyte function. To this end, we obtained several multiclonal mouse 3T3-L1 cell lines with a reduced expression of caveolin-1 (95% reduction) by a small interfering RNA approach using lentiviral vectors. Control cell lines were obtained by lentiviral infection with lentiviral vectors encoding appropriate scrambled RNAs. Caveolin-1 knockdown adipocytes showed a drastic reduction in the number of caveolae (95% decrease) and cholera toxin labeling was reorganized in dynamic plasma membrane microdomains. Caveolin-1 depletion caused a specific decrease in glucose transporter 4 (GLUT4) and insulin receptor protein levels. This reduction was not the result of a generalized defect in adipocyte differentiation or altered gene expression but was explained by faster degradation of these proteins. Caveolin-1 knockdown adipocytes showed reductions in insulin-stimulated glucose transport, insulin-triggered GLUT4 recruitment to the cell surface, and insulin receptor activation. In all, our data indicate that caveolin-1 loss of function reduces maximal insulin response through lowered stability and diminished expression of insulin receptors and GLUT4. We propose that caveolin-1/caveolae control insulin action in adipose cells.
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Affiliation(s)
- Elena González-Muñoz
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Institute for Research in Biomedicine (IRB Barcelona), Serveis Cientifico-Tècnics, Universitat de Barcelona, 08028 Barcelona, Spain
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Seong J, Lu S, Ouyang M, Huang H, Zhang J, Frame MC, Wang Y. Visualization of Src activity at different compartments of the plasma membrane by FRET imaging. ACTA ACUST UNITED AC 2009; 16:48-57. [PMID: 19171305 DOI: 10.1016/j.chembiol.2008.11.007] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 11/10/2008] [Accepted: 11/18/2008] [Indexed: 12/11/2022]
Abstract
Membrane compartments function as segregated signaling platforms for different cellular functions. It is not clear how Src is regulated at different membrane compartments. To visualize local Src activity in live cells, a FRET-based Src biosensor was targeted in or outside of lipid rafts at the plasma membrane, via acylation or prenylation modifications on targeting tags either directly fused to the biosensor or coupled to the biosensor through an inducible heterodimerization system. In response to growth factors and pervanadate, the induction of Src activity in rafts was slower and weaker, dependent on actin and possibly its mediated transportation of Src from perinuclear regions to the plasma membrane. In contrast, the induction of Src activity in nonrafts was faster and stronger, dependent on microtubules. Hence, Src activity is differentially regulated via cytoskeleton at different membrane compartments.
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Affiliation(s)
- Jihye Seong
- Neuroscience Program, Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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28
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Korol’ TY, Korol’ SV, Kostyuk EP, Kostyuk PG. Disruption of Calcium Homeostasis in Alzheimer’s Disease. NEUROPHYSIOLOGY+ 2009. [DOI: 10.1007/s11062-009-9064-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Coisy-Quivy M, Touzet O, Bourret A, Hipskind RA, Mercier J, Fort P, Philips A. TC10 controls human myofibril organization and is activated by the sarcomeric RhoGEF obscurin. J Cell Sci 2009; 122:947-56. [PMID: 19258391 DOI: 10.1242/jcs.040121] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The contractile activity of striated muscle depends on myofibrils that are highly ordered macromolecular complexes. The protein components of myofibrils are well characterized, but it remains largely unclear how signaling at the molecular level within the sarcomere and the control of assembly are coordinated. We show that the Rho GTPase TC10 appears during differentiation of human primary skeletal myoblasts and it is active in differentiated myotubes. We identify obscurin, a sarcomere-associated protein, as a specific activator of TC10. Indeed, TC10 binds directly to obscurin via its predicted RhoGEF motif. Importantly, we demonstrate that obscurin is a specific activator of TC10 but not the Rho GTPases Rac and Cdc42. Finally, we show that inhibition of TC10 activity by expression of a dominant-negative mutant or its knockdown by expression of specific shRNA block myofibril assembly. Our findings reveal a novel signaling pathway in human skeletal muscle that involves obscurin and the Rho GTPase TC10 and implicate this pathway in new sarcomere formation.
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30
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Okada S, Yamada E, Saito T, Ohshima K, Hashimoto K, Yamada M, Uehara Y, Tsuchiya T, Shimizu H, Tatei K, Izumi T, Yamauchi K, Hisanaga SI, Pessin JE, Mori M. CDK5-dependent phosphorylation of the Rho family GTPase TC10(alpha) regulates insulin-stimulated GLUT4 translocation. J Biol Chem 2008; 283:35455-63. [PMID: 18948252 DOI: 10.1074/jbc.m806531200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Insulin stimulation results in the activation of cyclin-dependent kinase-5 (CDK5) in lipid raft domains via a Fyn-dependent phosphorylation on tyrosine residue 15. In turn, activated CDK5 phosphorylates the Rho family GTP-binding protein TC10alpha on threonine 197 that is sensitive to the CDK5 inhibitor olomoucine and blocked by small interfering RNA-mediated knockdown of CDK5. The phosphorylation deficient mutant T197A-TC10alpha was not phosphorylated and excluded from the lipid raft domain, whereas the phosphorylation mimetic mutant (T197D-TC10alpha) was lipid raft localized. Insulin resulted in the GTP loading of T197D-TC10alpha but not T197A-TC10alpha and in parallel, T197D-TC10alpha but not T197A-TC10alpha depolymerized cortical actin and inhibited insulin-stimulated GLUT4 translocation. These data demonstrate that CDK5-dependent phosphorylation maintains TC10alpha in lipid raft compartments thereby disrupting cortical actin, whereas subsequent dephosphorylation of TC10alpha through inactivation of CDK5 allows for the re-assembly of F-actin. Because cortical actin reorganization is required for insulin-stimulated GLUT4 translocation, these data are consistent with a CDK5-dependent TC10alpha cycling between lipid raft and non-lipid raft compartments.
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Affiliation(s)
- Shuichi Okada
- Department of Medicine, Gunma University Graduate School of Medicine, Showa-machi, Maebashi, Gunma 371-0034, Japan.
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31
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Jin S, Yi F, Zhang F, Poklis JL, Li PL. Lysosomal targeting and trafficking of acid sphingomyelinase to lipid raft platforms in coronary endothelial cells. Arterioscler Thromb Vasc Biol 2008; 28:2056-62. [PMID: 18772496 DOI: 10.1161/atvbaha.108.172478] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The purpose of this study was to determine whether lysosome trafficking and targeting of acid sphingomyelinase (ASMase) to this organelle contribute to the formation of lipid raft (LR) signaling platforms in the membrane of coronary arterial endothelial cells (CAECs). METHODS AND RESULTS By measurement of fluorescent resonance energy transfer (FRET), it was found that in FasL-stimulated CAECs, membrane lamp1 (a lysosome marker protein) or Fas and GM1 (a LR marker) were trafficking together. Cofocal colocalization assay showed that ceramide was enriched in these LR platforms. Further studies demonstrated that these ceramide molecules in LR platforms were colocalized with ASMase, a ceramide producing enzyme. Fluorescence imaging of living CAECs loaded with lysosomal specific dyes demonstrated that lysosomes fused with membrane on FasL stimulation. In the presence of lysosome function inhibitors, bafilomycin (Baf) or glycyl-L-phenylalanine-beta-naphthylamide (GPN), these FasL-induced changes were abolished. Moreover, this FasL-induced formation of LR platforms was also blocked in ECs transfected with siRNA of sortilin, an intracellular transporter for targeting of ASMase to lysosomes. Functionally, FasL-induced impairment of vasodilator response was reversed by lysosomal inhibitors or sortilin gene silencing. CONCLUSIONS Lysosomal trafficking and targeting of ASMase are importantly involved in LRs clustering in ECs membrane, leading to the formation of signaling platforms or signalosomes.
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Affiliation(s)
- Si Jin
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA
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32
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Saito M, Lessard SJ, Rivas DA, Reeder DW, Hawley JA, Yaspelkis BB. Activation of atypical protein kinase Czeta toward TC10 is regulated by high-fat diet and aerobic exercise in skeletal muscle. Metabolism 2008; 57:1173-80. [PMID: 18702941 PMCID: PMC2597576 DOI: 10.1016/j.metabol.2008.03.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Accepted: 03/04/2008] [Indexed: 12/29/2022]
Abstract
We determined whether sustained aerobic exercise reverses high-fat diet-induced impairments in the c-Cbl associated protein (CAP)/Casitas b-lineage lymphoma (c-Cbl) signaling cascade in rodent skeletal muscle. Sprague-Dawley rats were placed into either control (n = 16) or high-fat-fed (n = 32) diet groups for 4 weeks. During a subsequent 4-week experimental period, 16 high-fat-fed rats remained sedentary, 16 high-fat-fed rats completed 4 weeks of exercise training, and control animals were sedentary and remained on the control diet. After the intervention period, animals were subjected to hind limb perfusions in the presence (n = 8 per group) or absence (n = 8 per group) of insulin. In the plasma membrane fractions, neither high-fat feeding nor exercise training altered adaptor protein with PH and SH2 domains, (APS), c-Cbl, or TC10 protein concentrations. In contrast, CAP protein concentration and insulin-stimulated plasma membrane c-Cbl tyrosine phosphorylation were reduced by high-fat feeding; but exercise training reversed these impairments. Of note was that insulin-stimulated atypical protein kinase Czeta kinase activity toward TC10 was reduced by high-fat feeding but normalized by exercise training. We conclude that sustained (4 weeks) exercise training can reverse high-fat diet-induced impairments on the CAP/c-Cbl pathway in high-fat-fed rodent skeletal muscle. We also provide the first evidence that the CAP/c-Cbl insulin signaling cascade in skeletal muscle may directly interact with components of the classic (phosphoinositide 3-kinase dependent) insulin signaling cascade.
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Affiliation(s)
- Misato Saito
- Exercise Biochemistry Laboratory, Department of Kinesiology, California State University Northridge, CA 91330-8287, USA
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33
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Lodhi IJ, Bridges D, Chiang SH, Zhang Y, Cheng A, Geletka LM, Weisman LS, Saltiel AR. Insulin stimulates phosphatidylinositol 3-phosphate production via the activation of Rab5. Mol Biol Cell 2008; 19:2718-28. [PMID: 18434594 DOI: 10.1091/mbc.e08-01-0105] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylinositol 3-phosphate (PI(3)P) plays an important role in insulin-stimulated glucose uptake. Insulin promotes the production of PI(3)P at the plasma membrane by a process dependent on TC10 activation. Here, we report that insulin-stimulated PI(3)P production requires the activation of Rab5, a small GTPase that plays a critical role in phosphoinositide synthesis and turnover. This activation occurs at the plasma membrane and is downstream of TC10. TC10 stimulates Rab5 activity via the recruitment of GAPEX-5, a VPS9 domain-containing guanyl nucleotide exchange factor that forms a complex with TC10. Although overexpression of plasma membrane-localized GAPEX-5 or constitutively active Rab5 promotes PI(3)P formation, knockdown of GAPEX-5 or overexpression of a dominant negative Rab5 mutant blocks the effects of insulin or TC10 on this process. Concomitant with its effect on PI(3)P levels, the knockdown of GAPEX-5 blocks insulin-stimulated Glut4 translocation and glucose uptake. Together, these studies suggest that the TC10/GAPEX-5/Rab5 axis mediates insulin-stimulated production of PI(3)P, which regulates trafficking of Glut4 vesicles.
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Affiliation(s)
- Irfan J Lodhi
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA
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34
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Yuan T, Hong S, Yao Y, Liao K. Glut-4 is translocated to both caveolae and non-caveolar lipid rafts, but is partially internalized through caveolae in insulin-stimulated adipocytes. Cell Res 2008; 17:772-82. [PMID: 17846641 DOI: 10.1038/cr.2007.73] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Caveolae and non-caveolar lipid rafts are two types of membrane lipid microdomains that play important roles in insulin-stimulated glucose uptake in adipocytes. In order to ascertain their specific functions in this process, caveolae were ablated by caveolin-1 RNA interference. In Cav-1 RNAi adipocytes, neither insulin-stimulated glucose uptake nor Glut-4 (glucose transporter 4) translocation to membrane lipid microdomains was affected by the ablation of caveolae. With a modified sucrose density gradient, caveolae and non-caveolar lipid rafts could be separated. In the wild-type 3T3-L1 adipocytes, Glut-4 was found to be translocated into both caveolae and non-caveolar lipid rafts. However, in Cav-1 RNAi adipocytes, Glut-4 was localized predominantly in non-caveolar lipid rafts. After the removal of insulin, caveolae-localized Glut-4 was internalized faster than non-caveolar lipid raft-associated Glut-4. The internalization of Glut-4 from plasma membrane was significantly decreased in Cav-1 RNAi adipocytes. These results suggest that insulin-stimulated Glut-4 translocation and glucose uptake are caveolae-independent events. Caveolae play a role in the internalization of Glut-4 from plasma membrane after the removal of insulin.
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Affiliation(s)
- Taichang Yuan
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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35
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Robin E, Cognié J, Foulon-Gauze F, Fontaine J, Cayla X. Disruption of lipid rafts induces gonadotropin release in ovine pituitary and LbetaT2 gonadotroph cells. Biol Reprod 2008; 79:17-25. [PMID: 18322272 DOI: 10.1095/biolreprod.107.064881] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
In order to better understand the cellular mechanisms underlying LH and FSH secretion, we have addressed the contribution of lipid rafts to the secretion of gonadotropins. We used methyl-beta-cyclodextrin (MbetaCD), a cholesterol-sequestering agent, on an LbetaT2 murine gonadotroph cell line and on primary cultures of ovine pituitary cells. We found that in both systems, cholesterol depletion by MbetaCD induced a fast and substantial release of LH in the absence of natural stimulation by GnRH. In ovine pituitary cells, MbetaCD-mediated LH release was shown to be independent of protein synthesis. Twenty-four hours after MbetaCD treatment, there was no loss of cell viability and full recovery of LH secretory capabilities, as determined by GnRH or MbetaCD treatment. In addition, our data suggest the existence of a pool of LH that is not released by GnRH treatment but that is released by MbetaCD treatment. Finally, in ovine pituitary cells, MbetaCD treatment induced FSH secretion. Importantly, these in vitro data are supported by in vivo studies, because MbetaCD injected into the pituitary glands of anaesthetized sheep reproducibly induced a peak of LH release.
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Affiliation(s)
- E Robin
- UMR Physiologie de la Reproduction et des Comportements, INRA/CNRS/Université Tours/Haras Nationaux, 37380 Nouzilly, France
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36
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Horvath EM, Tackett L, McCarthy AM, Raman P, Brozinick JT, Elmendorf JS. Antidiabetogenic effects of chromium mitigate hyperinsulinemia-induced cellular insulin resistance via correction of plasma membrane cholesterol imbalance. Mol Endocrinol 2007; 22:937-50. [PMID: 18165437 DOI: 10.1210/me.2007-0410] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Previously, we found that a loss of plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate (PIP2)-regulated filamentous actin (F-actin) structure contributes to insulin-induced insulin resistance. Interestingly, we also demonstrated that chromium picolinate (CrPic), a dietary supplement thought to improve glycemic status in insulin-resistant individuals, augments insulin-regulated glucose transport in insulin-sensitive 3T3-L1 adipocytes by lowering PM cholesterol. Here, to gain mechanistic understanding of these separate observations, we tested the prediction that CrPic would protect against insulin-induced insulin resistance by improving PM features important in cytoskeletal structure and insulin sensitivity. We found that insulin-induced insulin-resistant adipocytes display elevated PM cholesterol with a reciprocal decrease in PM PIP2. This lipid imbalance and insulin resistance was corrected by the cholesterol-lowering action of CrPic. The PM lipid imbalance did not impair insulin signaling, nor did CrPic amplify insulin signal transduction. In contrast, PM analyses corroborated cholesterol and PIP2 interactions influencing cytoskeletal structure. Because extensive in vitro study documents an essential role for cytoskeletal capacity in insulin-regulated glucose transport, we next evaluated intact skeletal muscle from obese, insulin-resistant Zucker (fa/fa) rats. Because insulin resistance in these animals likely involves multiple mechanisms, findings that cholesterol-lowering restored F-actin cytoskeletal structure and insulin sensitivity to that witnessed in lean control muscle were striking. Also, experiments using methyl-beta-cyclodextrin to shuttle cholesterol into or out of membranes respectively recapitulated the insulin-induced insulin-resistance and protective effects of CrPic on membrane/cytoskeletal interactions and insulin sensitivity. These data predict a PM cholesterol basis for hyperinsulinemia-associated insulin resistance and importantly highlight the reversible nature of this abnormality.
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Affiliation(s)
- Emily M Horvath
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202, USA
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37
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Hill WG, Butterworth MB, Wang H, Edinger RS, Lebowitz J, Peters KW, Frizzell RA, Johnson JP. The epithelial sodium channel (ENaC) traffics to apical membrane in lipid rafts in mouse cortical collecting duct cells. J Biol Chem 2007; 282:37402-11. [PMID: 17932048 DOI: 10.1074/jbc.m704084200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously showed that ENaC is present in lipid rafts in A6 cells, a Xenopus kidney cell line. We now demonstrate that ENaC can be detected in lipid rafts in mouse cortical collecting duct ((MPK)CCD(14)) cells by detergent insolubility, buoyancy on density gradients using two distinct approaches, and colocalization with caveolin 1. Less than 30% of ENaC subunits were found in raft fractions. The channel subunits also colocalized on sucrose gradients with known vesicle targeting and fusion proteins syntaxin 1A, Vamp 2, and SNAP23. Hormonal stimulation of ENaC activity by either forskolin or aldosterone, short or long term, did not alter the lipid raft distribution of ENaC. Methyl-beta-cyclodextrin added apically to (MPK)CCD(14) cells resulted in a slow decline in amiloride-sensitive sodium transport with short circuit current reductions of 38.1 +/- 9.6% after 60 min. The slow decline in ENaC activity in response to apical cyclodextrin was identical to the rate of decline seen when protein synthesis was inhibited by cycloheximide. Apical biotinylation of (MPK)CCD(14) cells confirmed the loss of ENaC at the cell surface following cyclodextrin treatment. Acute stimulation of the recycling pool of ENaC was unaffected by apical cyclodextrin application. Expression of dominant negative caveolin isoforms (CAV1-eGFP and CAV3-DGV) which disrupt caveolae, reduced basal ENaC currents by 72.3 and 78.2%, respectively; but, as with cyclodextrin, the acute response to forskolin was unaffected. We conclude that ENaC is present in and regulated by lipid rafts. The data are consistent with a model in which rafts mediate the constitutive apical delivery of ENaC.
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Affiliation(s)
- Warren G Hill
- Division of Matrix Biology, Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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38
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Abstract
NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.
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Affiliation(s)
- Mark Donowitz
- Department of Medicine, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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39
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Eriksson JW. Metabolic stress in insulin's target cells leads to ROS accumulation - A hypothetical common pathway causing insulin resistance. FEBS Lett 2007; 581:3734-42. [PMID: 17628546 DOI: 10.1016/j.febslet.2007.06.044] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Revised: 06/16/2007] [Accepted: 06/18/2007] [Indexed: 01/04/2023]
Abstract
The metabolic syndrome is a cluster of cardiovascular risk factors, and visceral adiposity is a central component that is also strongly associated with insulin resistance. Both visceral obesity and insulin resistance are important risk factors for the development of type 2 diabetes. It is likely that adipose tissue, particularly in the intra-abdominal depot, is part of a complex interplay involving several tissues and that dysregulated hormonal, metabolic and neural signalling within and between organs can trigger development of metabolic disease. One attractive hypothesis is that many factors leading to insulin resistance are mediated via the generation of abnormal amounts of reactive oxygen species (ROS). There is much evidence supporting that detrimental effects of glucose, fatty acids, hormones and cytokines leading to insulin resistance can be exerted via such a common pathway. This review paper mainly focuses on metabolic and other 'stress' factors that affect insulin's target cells, in particular adipocytes, and it will highlight oxidative stress as a potential unifying mechanism by which these stress factors promote insulin resistance and the development and progression of type 2 diabetes.
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Affiliation(s)
- Jan W Eriksson
- The Lundberg Laboratory for Diabetes Research, Institute of Medicine, Sahlgrenska University Hospital, SE 41345 Gothenburg, Sweden.
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40
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Abstract
The dissection of mechanisms that regulate glucose transport by insulin has revealed an intricate network of signaling molecules scattered from the insulin receptor to the intracellular glucose transporter GLUT4. It is also appreciated that some insulin receptor signals jaunt in different directions to regulate events essential for the efficient redistribution of GLUT4 to the plasma membrane. Moreover key assists in the process appear to be arranged by membrane lipids and cytoskeletal proteins. Following current considerations of insulin signals regulating GLUT4, this review will focus on in vitro and in vivo evidence that supports an essential role for phosphoinositides and actin filaments in the control of glucose transport. The discussion will visit recent cell culture, whole animal, and human data highlighting membrane and cytoskeletal aspects of insulin resistance.
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Affiliation(s)
- Joseph T Brozinick
- Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA.
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41
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Cayouette S, Boulay G. Intracellular trafficking of TRP channels. Cell Calcium 2007; 42:225-32. [PMID: 17368756 DOI: 10.1016/j.ceca.2007.01.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Revised: 01/30/2007] [Accepted: 01/31/2007] [Indexed: 11/18/2022]
Abstract
Thirteen years ago, it was suggested that exocytotic insertion of store-operated channels into the plasma membrane lead to increased Ca(2+) entry in non-excitable cells upon G protein-coupled or tyrosine kinase receptor stimulation. Since the discovery of the TRP channel superfamily and their involvement in receptor-induced Ca(2+) entry, many studies have shown that different members of the TRP superfamily translocate into the plasma membrane upon stimulation. While the exact molecular mechanism by which TRP channels insert into the plasma membrane is unknown, TRP-binding proteins have been shown to directly regulate this trafficking. This review summarizes recent advances related to the mechanism of TRP channel trafficking, focusing on the role of TRP-binding proteins.
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Affiliation(s)
- Sylvie Cayouette
- Department of Pharmacology, Université de Sherbrooke, Sherbrooke, Quebec, Canada
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42
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Lodhi IJ, Chiang SH, Chang L, Vollenweider D, Watson RT, Inoue M, Pessin JE, Saltiel AR. Gapex-5, a Rab31 guanine nucleotide exchange factor that regulates Glut4 trafficking in adipocytes. Cell Metab 2007; 5:59-72. [PMID: 17189207 PMCID: PMC1779820 DOI: 10.1016/j.cmet.2006.12.006] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Revised: 10/27/2006] [Accepted: 12/11/2006] [Indexed: 10/23/2022]
Abstract
Insulin stimulates glucose uptake by promoting translocation of the Glut4 glucose transporter from intracellular storage compartments to the plasma membrane. In the absence of insulin, Glut4 is retained intracellularly; the mechanism underlying this process remains uncertain. Using the TC10-interacting protein CIP4 as bait in a yeast two-hybrid screen, we cloned a RasGAP and VPS9 domain-containing protein, Gapex-5/RME-6. The VPS9 domain is a guanine nucleotide exchange factor for Rab31, a Rab5 subfamily GTPase implicated in trans-Golgi network (TGN)-to-endosome trafficking. Overexpression of Rab31 blocks insulin-stimulated Glut4 translocation, whereas knockdown of Rab31 potentiates insulin-stimulated Glut4 translocation and glucose uptake. Gapex-5 is predominantly cytosolic in untreated cells; its overexpression promotes intracellular retention of Glut4 in adipocytes. Insulin recruits the CIP4/Gapex-5 complex to the plasma membrane, thus reducing Rab31 activity and permitting Glut4 vesicles to translocate to the cell surface, where Glut4 docks and fuses to transport glucose into the cell.
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Affiliation(s)
- Irfan J. Lodhi
- Life Sciences Institute
- Cellular and Molecular Biology Program University of Michigan Ann Arbor, MI 48109
| | | | | | - Daniel Vollenweider
- Department of Pharmacological Sciences Stony Brook University Stony Brook, NY 11794
| | - Robert T. Watson
- Department of Pharmacological Sciences Stony Brook University Stony Brook, NY 11794
| | | | - Jeffrey E. Pessin
- Department of Pharmacological Sciences Stony Brook University Stony Brook, NY 11794
| | - Alan R. Saltiel
- Life Sciences Institute
- Departments of Internal Medicine and Molecular and Integrative Physiology
- Cellular and Molecular Biology Program University of Michigan Ann Arbor, MI 48109
- *Corresponding author: Alan R. Saltiel Life Sciences Institute University of Michigan 210 Washtenaw Ave. Ann Arbor, MI 48109
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43
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Abstract
Previous studies have suggested that activation of the Rho family member GTPase TC10 is necessary but not sufficient for the stimulation of glucose transport by insulin. We show here that endogenous TC10alpha is rapidly activated in response to insulin in 3T3L1 adipocytes in a phosphatidylinositol 3-kinase-independent manner, whereas platelet-derived growth factor was without effect. Knockdown of TC10alpha but not TC10beta by RNA interference inhibited insulin-stimulated glucose uptake as well as the translocation of the insulin-sensitive glucose transporter GLUT4 from intracellular sites to the plasma membrane. In contrast, loss of TC10alpha had no effect on the stimulation of Akt by insulin. Additionally, knockdown of TC10alpha inhibited insulin-stimulated translocation of its effector CIP4. These data indicate that TC10alpha is specifically required for insulin-stimulated glucose uptake in adipocytes.
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Affiliation(s)
- Louise Chang
- Life Sciences Institute, University of Michigan Medical Center, Ann Arbor, Michigan 48109-2216, USA
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44
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Liu XJ, He AB, Chang YS, Fang FD. Atypical protein kinase C in glucose metabolism. Cell Signal 2006; 18:2071-6. [PMID: 16787739 DOI: 10.1016/j.cellsig.2006.04.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Accepted: 04/28/2006] [Indexed: 01/17/2023]
Abstract
Type 2 diabetes mellitus is a multigenic disease with evident genetic predisposition, and complex pathogenesis in which environmental and genetic factors interact. The disorder of body utilization glucose is a crucial reason for causing diabetes. Atypical PKCs, belonging to Ser/Thr protein kinase, have many important biological functions in vivo, and may be involved in the pathogenesis of diabetes mellitus. APKCs participate in glucose metabolism by regulating glucose transport and absorption, glycogen synthesis, and insulin secretion. The exact mechanism by which aPKCs participate in glucose metabolism remains unclear. So far, the clarification of which will be helpful for the prevention and cure of type 2 diabetes.
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Affiliation(s)
- Xiao-Jun Liu
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences Chinese Academy of Medical Sciences and School of Basic Medicine Peking Union Medical College, Beijing 100005, China
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45
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Williams D, Hicks SW, Machamer CE, Pessin JE. Golgin-160 is required for the Golgi membrane sorting of the insulin-responsive glucose transporter GLUT4 in adipocytes. Mol Biol Cell 2006; 17:5346-55. [PMID: 17050738 PMCID: PMC1679696 DOI: 10.1091/mbc.e06-05-0386] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The peripheral Golgi protein golgin-160 is induced during 3T3L1 adipogenesis and is primarily localized to the Golgi cisternae distinct from the trans-Golgi network (TGN) in a general distribution similar to p115. Small interfering RNA (siRNA)-mediated reduction in golgin-160 protein resulted in an increase accumulation of the insulin-responsive amino peptidase (IRAP) and the insulin-regulated glucose transporter (GLUT4) at the plasma membrane concomitant with enhanced glucose uptake in the basal state. The redistribution of GLUT4 was rescued by expression of a siRNA-resistant golgin-160 cDNA. The basal state accumulation of plasma membrane GLUT4 occurred due to an increased rate of exocytosis without any significant effect on the rate of endocytosis. This GLUT4 trafficking to the plasma membrane in the absence of golgin-160 was independent of TGN/Golgi sorting, because it was no longer inhibited by the expression of a dominant-interfering Golgi-localized, gamma-ear-containing ARF-binding protein mutant and displayed reduced binding to the lectin wheat germ agglutinin. Moreover, expression of the amino terminal head domain (amino acids 1-393) had no significant effect on the distribution or insulin-regulated trafficking of GLUT4 or IRAP. In contrast, expression of carboxyl alpha helical region (393-1498) inhibited insulin-stimulated GLUT4 and IRAP translocation, but it had no effect on the sorting of constitutive membrane trafficking proteins, the transferrin receptor, or vesicular stomatitis virus G protein. Together, these data demonstrate that golgin-160 plays an important role in directing insulin-regulated trafficking proteins toward the insulin-responsive compartment in adipocytes.
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Affiliation(s)
- Dumaine Williams
- *Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794
| | - Stuart W. Hicks
- Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06536; and
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Carolyn E. Machamer
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Jeffrey E. Pessin
- *Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794
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Fuster DG, Bobulescu IA, Zhang J, Wade J, Moe OW. Characterization of the regulation of renal Na+/H+ exchanger NHE3 by insulin. Am J Physiol Renal Physiol 2006; 292:F577-85. [PMID: 17018843 PMCID: PMC2861556 DOI: 10.1152/ajprenal.00240.2006] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Insulin receptors are widely distributed in the kidney and affect multiple aspects of renal function. In the proximal tubule, insulin regulates volume and acid-base regulation through stimulation of the Na(+)/H(+) exchanger NHE3. This paper characterizes the signaling pathway by which insulin stimulates NHE3 in a cell culture model [opossum kidney (OK) cell]. Insulin has two distinct phases of action on NHE3. Chronic insulin (24 h) activates NHE3 through the classic phosphatidylinositol 3-kinase-serum- and glucocorticoid-dependent kinase 1 (PI3K-SGK1) pathway as insulin stimulates SGK1 phosphorylation and the insulin effect can be blocked by the PI3K inhibitor wortmannin or a dominant-negative SGK1. We showed that SGK1 transcript and protein are expressed in rat proximal tubule and OK cells. We previously showed that glucocorticoids augment the effect of insulin on NHE3 (Klisic J, Hu MC, Nief V, Reyes L, Fuster D, Moe OW, Ambuhl PM. Am J Physiol Renal Physiol 283: F532-F539, 2002). Part of this can be mediated via induction of SGK1 by glucocorticoids, and indeed the insulin effect on NHE3 can also be amplified by overexpression of SGK1. We next addressed the acute effect of insulin (1-2 h) on NHE3 by systematically examining the candidate signaling cascades and activation mechanisms of NHE3. We ruled out the PI3K-SGK1-Akt and TC10 pathways, increased surface NHE3, NHE3 phosphorylation, NHE3 association with calcineurin homologous protein 1 or megalin as mechanisms of acute activation of NHE3 by insulin. In summary, insulin stimulates NHE3 acutely via yet undefined pathways and mechanisms. The chronic effect of insulin is mediated by the classic PI3K-SGK1 route.
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Affiliation(s)
- Daniel G Fuster
- Department of Internal Medicine, University of Texas Southwestern Medical Ctr., Dallas, TX 75390-8856, USA
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Tong S, Liss AS, You M, Bose HR. The activation of TC10, a Rho small GTPase, contributes to v-Rel-mediated transformation. Oncogene 2006; 26:2318-29. [PMID: 17016434 DOI: 10.1038/sj.onc.1210023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
v-Rel is the oncogenic member of the Rel/NF-kappaB family of transcription factors and transforms hematopoietic cells and fibroblasts. Differential display was employed to identify target genes that exhibit altered expression in v-Rel transformed cells. One of the cDNAs identified encodes the chicken ortholog of TC10, a member of the Rho small GTPase family. The expression of TC10 was increased in v-Rel-transformed chicken embryonic fibroblasts (CEFs) 3 to 6-fold relative to control cells at both the RNA and protein levels. An elevated level of active, GTP-bound TC10 was also detected in v-Rel-transformed cells relative to control cells. Expression of a dominant-negative TC10 mutant (TC10T32N) decreased the colony formation potential of v-Rel-transformed cells. Furthermore, overexpression of wild-type TC10 or a gain-of-function mutant (TC10Q76L) greatly enhanced the ability of v-Rel transformed CEFs to form colonies in soft agar. In addition to enhance the transformation potential of v-Rel, the overexpression of wild-type TC10 or the gain-of-function mutant alone enhanced the saturation density of CEFs and was sufficient for their anchorage-independent growth in vitro. These results indicate that elevated TC10 activity contributes to v-Rel-mediated transformation of CEFs and demonstrate for the first time that a Rho factor alone is capable of inducing the in vitro transformation of primary cells.
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Affiliation(s)
- S Tong
- Section of Molecular Genetics and Microbiology and the Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712-1095, USA
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48
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Nedachi T, Kanzaki M. Regulation of glucose transporters by insulin and extracellular glucose in C2C12 myotubes. Am J Physiol Endocrinol Metab 2006; 291:E817-28. [PMID: 16735448 DOI: 10.1152/ajpendo.00194.2006] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
It is well established that insulin stimulation of glucose uptake in skeletal muscle cells is mediated through translocation of GLUT4 from intracellular storage sites to the cell surface. However, the established skeletal muscle cell lines, with the exception of L6 myocytes, reportedly show minimal insulin-dependent glucose uptake and GLUT4 translocation. Using C(2)C(12) myocytes expressing exofacial-Myc-GLUT4-enhanced cyan fluorescent protein, we herein show that differentiated C(2)C(12) myotubes are equipped with basic GLUT4 translocation machinery that can be activated by insulin stimulation ( approximately 3-fold increase as assessed by anti-Myc antibody uptake and immunostaining assay). However, this insulin stimulation of GLUT4 translocation was difficult to demonstrate with a conventional 2-deoxyglucose uptake assay because of markedly elevated basal glucose uptake via other glucose transporter(s). Intriguingly, the basal glucose transport activity in C(2)C(12) myotubes appeared to be acutely suppressed within 5 min by preincubation with a pathophysiologically high level of extracellular glucose (25 mM). In contrast, this activity was augmented by acute glucose deprivation via an unidentified mechanism that is independent of GLUT4 translocation but is dependent on phosphatidylinositol 3-kinase activity. Taken together, these findings indicate that regulation of the facilitative glucose transport system in differentiated C(2)C(12) myotubes can be achieved through surprisingly acute glucose-dependent modulation of the activity of glucose transporter(s), which apparently contributes to obscuring the insulin augmentation of glucose uptake elicited by GLUT4 translocation. We herein also describe several methods of monitoring insulin-dependent glucose uptake in C(2)C(12) myotubes and propose this cell line to be a useful model for analyzing GLUT4 translocation in skeletal muscle.
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Affiliation(s)
- Taku Nedachi
- TUBERO/Tohoku University Biomedical Engineering Research Organization, Tohoku University 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan
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Babiychuk EB, Draeger A. Regulation of ecto-5'-nucleotidase activity via Ca2+-dependent, annexin 2-mediated membrane rearrangement? Biochem Soc Trans 2006; 34:374-6. [PMID: 16709165 DOI: 10.1042/bst0340374] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The spatial segregation of the plasma membrane plays a prominent role in distinguishing and sorting a large number of signals a cell receives simultaneously. The plasma membrane comprises regions known as lipid rafts, which serve as signal-transduction hubs and platforms for sorting membrane-associated proteins. Ca(2+)-binding proteins of the annexin family have been ascribed a role in the regulation of raft dynamics. Glycosylphosphatidylinositol-anchored 5'-nucleotidase is an extracellular, raft-associated enzyme responsible for conversion of extracellular ATP into adenosine. Our results point to a regulation of ecto-5'-nucleotidase activity by Ca(2+)-dependent, annexin-mediated stabilization of membrane rafts.
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Affiliation(s)
- E B Babiychuk
- Department of Cell Biology, Institute of Anatomy, University of Bern, Switzerland
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50
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Liu B, Yu J, Taylor L, Zhou X, Polgar P. Microarray and phosphokinase screenings leading to studies on ERK and JNK regulation of connective tissue growth factor expression by angiotensin II 1a and bradykinin B2 receptors in Rat1 fibroblasts. J Cell Biochem 2006; 97:1104-20. [PMID: 16294326 DOI: 10.1002/jcb.20709] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Rat1 fibroblasts stably transfected with the rat angiotensin II (AngII) AT1a and bradykinin (BK) B2 receptor cDNAs gained the ability to bind Ang II and BK. Wild-type Rat1 cells bound neither ligand. Exposure to either effector led to characteristic Galphai and Galphaq signal cascades, the release of arachidonic acid (ARA), and the intracellular accumulation of inositol phosphates (IP). Microarray analyses in response to BK or AngII showed that both receptors markedly induce the CCN family genes, CTGF (CCN2) and Cyr61 (CCN1), as well as the vasculature-related genes, Cnn1 and Egr1. Real time PCR confirmed the increased expression of connective tissue growth factor (CTGF) mRNA. Combined sequence-based analysis of gene promoter regions with statistical prevalence analyses identified CREB, SRF, and ATF-1, downstream targets of ERK, and JNK, as prominent products of genes that are regulated by ligand binding to the BK or AngII receptors. The binding of AngII or BK markedly stimulated the phosphorylation and thus the activation of ERK2, JNK, and p38MAPK. A BKB2R and an AT1aR chimera which displayed only negligible G-protein-related signaling were constructed. Both mutant receptors continued to activate these kinases and stimulate CTGF expression. Inhibitors of ERK1/2 and JNK but not p38MAPK inhibited the BK- and AngII-stimulated expression of CTGF in cells expressing either the WT or mutant receptors, illustrating that ERK and JNK participate in the control of CTGF expression in a manner that appears to be independent of G-protein. Conversely, addition of BK or AngII to the cell line expressing WT AT1aR and BKB2R downregulated the expression of collagen alpha1(I) (COL1A1) mRNA. However, these effectors did not have this effect in cells expressing the mutant receptors. Thus, a robust G-protein related response is necessary for BK or AngII to affect COL1A1 expression.
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Affiliation(s)
- B Liu
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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