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Gaugel J, Haacke N, Sehgal R, Jähnert M, Jonas W, Hoffmann A, Blüher M, Ghosh A, Noé F, Wolfrum C, Tan J, Schürmann A, Fazakerley DJ, Vogel H. Picalm, a novel regulator of GLUT4-trafficking in adipose tissue. Mol Metab 2024; 88:102014. [PMID: 39182843 PMCID: PMC11402323 DOI: 10.1016/j.molmet.2024.102014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2024] [Revised: 08/13/2024] [Accepted: 08/17/2024] [Indexed: 08/27/2024] Open
Abstract
OBJECTIVE Picalm (phosphatidylinositol-binding clathrin assembly protein), a ubiquitously expressed clathrin-adapter protein, is a well-known susceptibility gene for Alzheimer's disease, but its role in white adipose tissue (WAT) function has not yet been studied. Transcriptome analysis revealed differential expression of Picalm in WAT of diabetes-prone and diabetes-resistant mice, hence we aimed to investigate the potential link between Picalm expression and glucose homeostasis, obesity-related metabolic phenotypes, and its specific role in insulin-regulated GLUT4 trafficking in adipocytes. METHODS Picalm expression and epigenetic regulation by microRNAs (miRNAs) and DNA methylation were analyzed in WAT of diabetes-resistant (DR) and diabetes-prone (DP) female New Zealand Obese (NZO) mice and in male NZO after time-restricted feeding (TRF) and alternate-day fasting (ADF). PICALM expression in human WAT was evaluated in a cross-sectional cohort and assessed before and after weight loss induced by bariatric surgery. siRNA-mediated knockdown of Picalm in 3T3-L1-cells was performed to elucidate functional outcomes on GLUT4-translocation as well as insulin signaling and adipogenesis. RESULTS Picalm expression in WAT was significantly lower in DR compared to DP female mice, as well as in insulin-sensitive vs. resistant NZO males, and was also reduced in NZO males following TRF and ADF. Four miRNAs (let-7c, miR-30c, miR-335, miR-344) were identified as potential mediators of diabetes susceptibility-related differences in Picalm expression, while 11 miRNAs (including miR-23a, miR-29b, and miR-101a) were implicated in TRF and ADF effects. Human PICALM expression in adipose tissue was lower in individuals without obesity vs. with obesity and associated with weight-loss outcomes post-bariatric surgery. siRNA-mediated knockdown of Picalm in mature 3T3-L1-adipocytes resulted in amplified insulin-stimulated translocation of the endogenous glucose transporter GLUT4 to the plasma membrane and increased phosphorylation of Akt and Tbc1d4. Moreover, depleting Picalm before and during 3T3-L1 differentiation significantly suppressed adipogenesis, suggesting that Picalm may have distinct roles in the biology of pre- and mature adipocytes. CONCLUSIONS Picalm is a novel regulator of GLUT4-translocation in WAT, with its expression modulated by both genetic predisposition to diabetes and dietary interventions. These findings suggest a potential role for Picalm in improving glucose homeostasis and highlight its relevance as a therapeutic target for metabolic disorders.
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Affiliation(s)
- Jasmin Gaugel
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany
| | - Neele Haacke
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany
| | - Ratika Sehgal
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany
| | - Markus Jähnert
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany
| | - Wenke Jonas
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany
| | - Anne Hoffmann
- Helmholtz Institute for Metabolic Obesity and Vascular Research (HI-MAG), Helmholtz Zentrum München, University of Leipzig and University Hospital Leipzig, Leipzig, Germany
| | - Matthias Blüher
- German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany; Helmholtz Institute for Metabolic Obesity and Vascular Research (HI-MAG), Helmholtz Zentrum München, University of Leipzig and University Hospital Leipzig, Leipzig, Germany; Medical Department III-Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, Leipzig, Germany
| | - Adhideb Ghosh
- Laboratory of Translational Nutrition Biology, Institute of Food, Nutrition and Health, ETH Zürich, Schwerzenbach, Switzerland
| | - Falko Noé
- Laboratory of Translational Nutrition Biology, Institute of Food, Nutrition and Health, ETH Zürich, Schwerzenbach, Switzerland
| | - Christian Wolfrum
- Laboratory of Translational Nutrition Biology, Institute of Food, Nutrition and Health, ETH Zürich, Schwerzenbach, Switzerland
| | - Joycelyn Tan
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge, CB2 0QQ, United Kingdom
| | - Annette Schürmann
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany; Institute of Nutritional Sciences, University of Potsdam, Nuthetal, Germany
| | - Daniel J Fazakerley
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge, CB2 0QQ, United Kingdom
| | - Heike Vogel
- Research Group Nutrigenomics of Obesity and Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany; German Center for Diabetes Research (DZD e.V.), München, Neuherberg, Germany.
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Ray A, Wen J, Yammine L, Culver J, Parida IS, Garren J, Xue L, Hales K, Xiang Q, Birnbaum MJ, Zhang BB, Monetti M, McGraw TE. Regulated dynamic subcellular GLUT4 localization revealed by proximal proteome mapping in human muscle cells. J Cell Sci 2023; 136:jcs261454. [PMID: 38126809 PMCID: PMC10753500 DOI: 10.1242/jcs.261454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 11/21/2023] [Indexed: 12/23/2023] Open
Abstract
Regulation of glucose transport, which is central for control of whole-body metabolism, is determined by the amount of GLUT4 glucose transporter (also known as SLC2A4) in the plasma membrane (PM) of fat and muscle cells. Physiologic signals [such as activated insulin receptor or AMP-activated protein kinase (AMPK)] increase PM GLUT4. Here, we show that the distribution of GLUT4 between the PM and interior of human muscle cells is dynamically maintained, and that AMPK promotes PM redistribution of GLUT4 by regulating exocytosis and endocytosis. Stimulation of exocytosis by AMPK is mediated by Rab10 and the Rab GTPase-activating protein TBC1D4. APEX2 proximity mapping reveals that GLUT4 traverses both PM-proximal and PM-distal compartments in unstimulated muscle cells, further supporting retention of GLUT4 by a constitutive retrieval mechanism. AMPK-stimulated translocation involves GLUT4 redistribution among the same compartments traversed in unstimulated cells, with a significant recruitment of GLUT4 from the Golgi and trans-Golgi network compartments. Our comprehensive proximal protein mapping provides an integrated, high-density, whole-cell accounting of the localization of GLUT4 at a resolution of ∼20 nm that serves as a structural framework for understanding the molecular mechanisms regulating GLUT4 trafficking downstream of different signaling inputs in a physiologically relevant cell type.
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Affiliation(s)
- Anuttoma Ray
- Department of Biochemistry, Weill Cornell Medicine, New York, NY 10021, USA
| | - Jennifer Wen
- Department of Biochemistry, Weill Cornell Medicine, New York, NY 10021, USA
| | - Lucie Yammine
- Department of Biochemistry, Weill Cornell Medicine, New York, NY 10021, USA
| | - Jeff Culver
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | | | - Jeonifer Garren
- Global Biometrics and Data Management, Global Product Development, Pfizer Inc., Cambridge, MA 02139, USA
| | - Liang Xue
- Early Clinical Development Biomedicine AI, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | - Katherine Hales
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | - Qing Xiang
- Target Sciences, Pfizer Inc., New York, NY 10016, USA
| | - Morris J. Birnbaum
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | - Bei B. Zhang
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | - Mara Monetti
- Internal Medicine Research Unit, Pfizer Worldwide Research, Development and Medical, Cambridge, MA 02139, USA
| | - Timothy E. McGraw
- Department of Biochemistry, Weill Cornell Medicine, New York, NY 10021, USA
- Department of Cardiothoracic Surgery, Weill Cornell Medicine, New York, NY 10021, USA
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3
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Kim H, Kim KS, Na K. Nanoparticle platform comprising lipid-tailed pH-sensitive carbon dots with minimal drug loss. J Control Release 2023; 361:373-384. [PMID: 37558052 DOI: 10.1016/j.jconrel.2023.08.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 07/17/2023] [Accepted: 08/07/2023] [Indexed: 08/11/2023]
Abstract
Herein, we synthesized a lipid-mimicking organic material (PCD_FA) that can surpass the efficacy of lipid-based nanoparticles and demonstrated its potential as a delivery vehicle for various hydrophilic drugs. PCD_FA is a conjugate of pH-sensitive carbon dots (PCDs) and fatty acids (FAs) and has potential applications in several fields owing to various combinations of carbon dots (CDs) and FAs. Similar to phospholipids, PCD-FAs have hydrophilic heads and hydrophobic tails that allow them to self-form nanoparticles (Coposomes) in the aqueous phase. Coposomes can easily combine various hydrophilic head and hydrophobic tail combinations, and several drugs can be encapsulated, or drug release patterns can be controlled according to each property. We analyzed the differences in size, drug loading efficiency, and drug release patterns of Coposomes depending on the type of FAs and characteristics of the encapsulated drugs. Additionally, cell entry and intracellular drug release mechanisms of the Coposomes were identified. The applicability of Coposomes as drug delivery carriers for tumor treatment has been demonstrated in comparison with that of liposomes formulation in tumor-bearing mouse models. Consequently, this study presents possibilities for the synthesis and application of various amphiphilic lipid-mimicking organic materials via the combination of CDs and FAs with various functions.
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Affiliation(s)
- Hongjae Kim
- Department of Biotechnology, The Catholic University of Korea, 43 Jibong-ro, Wonmi-gu, Bucheon-si, Gyeonggi-do 14662, Republic of Korea; Department of BioMedical-Chemical Engineering, The Catholic University of Korea, 43 Jibong-ro, Wonmi-gu, Bucheon-si, Gyeonggi-do 14662, Republic of Korea
| | - Kyoung Sub Kim
- Department of Biotechnology, The Catholic University of Korea, 43 Jibong-ro, Wonmi-gu, Bucheon-si, Gyeonggi-do 14662, Republic of Korea
| | - Kun Na
- Department of Biotechnology, The Catholic University of Korea, 43 Jibong-ro, Wonmi-gu, Bucheon-si, Gyeonggi-do 14662, Republic of Korea; Department of BioMedical-Chemical Engineering, The Catholic University of Korea, 43 Jibong-ro, Wonmi-gu, Bucheon-si, Gyeonggi-do 14662, Republic of Korea.
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4
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Ray A, Wen J, Yammine L, Culver J, Garren J, Xue L, Hales K, Xiang Q, Birnbaum MJ, Zhang BB, Monetti M, McGraw TE. GLUT4 dynamic subcellular localization is controlled by AMP kinase activation as revealed by proximal proteome mapping in human muscle cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543897. [PMID: 37333333 PMCID: PMC10274730 DOI: 10.1101/2023.06.06.543897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Regulation of glucose transport into muscle and adipocytes, central for control of whole-body metabolism, is determined by the amount of GLUT4 glucose transporter in the plasma membrane ( PM ). Physiologic signals (activated insulin receptor or AMP kinase [ AMPK ]), acutely increase PM GLUT4 to enhance glucose uptake. Here we show in kinetic studies that intracellular GLUT4 is in equilibrium with the PM in unstimulated cultured human skeletal muscle cells, and that AMPK promotes GLUT4 redistribution to the PM by regulating both exocytosis and endocytosis. AMPK-stimulation of exocytosis requires Rab10 and Rab GTPase activating protein TBC1D4, requirements shared with insulin control of GLUT4 in adipocytes. Using APEX2 proximity mapping, we identify, at high-density and high-resolution, the GLUT4 proximal proteome, revealing GLUT4 traverses both PM proximal and distal compartments in unstimulated muscle cells. These data support intracellular retention of GLUT4 in unstimulated muscle cells by a dynamic mechanism dependent on the rates of internalization and recycling. AMPK promoted GLUT4 translocation to the PM involves redistribution of GLUT4 among the same compartments traversed in unstimulated cells, with a significant redistribution of GLUT4 from the PM distal Trans Golgi Network Golgi compartments. The comprehensive proximal protein mapping provides an integrated, whole cell accounting of GLUT4's localization at a resolution of ∼20 nm, a structural framework for understanding the molecular mechanisms regulating GLUT4 trafficking downstream of different signaling inputs in physiologically relevant cell type and as such, sheds new light on novel key pathways and molecular components as potential therapeutic approaches to modulate muscle glucose uptake.
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5
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Antonescu CN, Ishikura S, Bilan PJ, Klip A. Measurement of GLUT4 Traffic to and from the Cell Surface in Muscle Cells. Curr Protoc 2023; 3:e803. [PMID: 37367531 DOI: 10.1002/cpz1.803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
Elevated blood glucose following a meal is cleared by insulin-stimulated glucose entry into muscle and fat cells. The hormone increases the amount of the glucose transporter GLUT4 at the plasma membrane in these tissues at the expense of preformed intracellular pools. In addition, muscle contraction also increases glucose uptake via a gain in GLUT4 at the plasma membrane. Regulation of GLUT4 levels at the cell surface could arise from alterations in the rate of its exocytosis, endocytosis, or both. Hence, methods that can independently measure these traffic parameters for GLUT4 are essential to understanding the mechanism of regulation of membrane traffic of the transporter. Here, we describe cell population-based assays to measure the steady-state levels of GLUT4 at the cell surface, as well as to separately measure the rates of GLUT4 endocytosis and endocytosis. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Measuring steady-state cell surface GLUT4myc Basic Protocol 2: Measuring steady-state cell surface GLUT4-HA Basic Protocol 3: Measuring GLUT4myc endocytosis Basic Protocol 4: Measuring GLUT4myc exocytosis.
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Affiliation(s)
- Costin N Antonescu
- Department of Chemistry and Biology, Toronto Metropolitan University, Toronto, Canada
| | | | - Philip J Bilan
- Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Amira Klip
- Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
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6
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Chang YC, Chan MH, Yang YF, Li CH, Hsiao M. Glucose transporter 4: Insulin response mastermind, glycolysis catalyst and treatment direction for cancer progression. Cancer Lett 2023; 563:216179. [PMID: 37061122 DOI: 10.1016/j.canlet.2023.216179] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/27/2023] [Accepted: 04/07/2023] [Indexed: 04/17/2023]
Abstract
The glucose transporter family (GLUT) consists of fourteen members. It is responsible for glucose homeostasis and glucose transport from the extracellular space to the cell cytoplasm to further cascade catalysis. GLUT proteins are encoded by the solute carrier family 2 (SLC2) genes and are members of the major facilitator superfamily of membrane transporters. Moreover, different GLUTs also have their transporter kinetics and distribution, so each GLUT member has its uniqueness and importance to play essential roles in human physiology. Evidence from many studies in the field of diabetes showed that GLUT4 travels between the plasma membrane and intracellular vesicles (GLUT4-storage vesicles, GSVs) and that the PI3K/Akt pathway regulates this activity in an insulin-dependent manner or by the AMPK pathway in response to muscle contraction. Moreover, some published results also pointed out that GLUT4 mediates insulin-dependent glucose uptake. Thus, dysfunction of GLUT4 can induce insulin resistance, metabolic reprogramming in diverse chronic diseases, inflammation, and cancer. In addition to the relationship between GLUT4 and insulin response, recent studies also referred to the potential upstream transcription factors that can bind to the promoter region of GLUT4 to regulating downstream signals. Combined all of the evidence, we conclude that GLUT4 has shown valuable unknown functions and is of clinical significance in cancers, which deserves our in-depth discussion and design compounds by structure basis to achieve therapeutic effects. Thus, we intend to write up a most updated review manuscript to include the most recent and critical research findings elucidating how and why GLUT4 plays an essential role in carcinogenesis, which may have broad interests and impacts on this field.
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Affiliation(s)
- Yu-Chan Chang
- Department of Biomedical Imaging and Radiological Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Ming-Hsien Chan
- Department of Biomedical Imaging and Radiological Science, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yi-Fang Yang
- Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan
| | - Chien-Hsiu Li
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Michael Hsiao
- Genomics Research Center, Academia Sinica, Taipei, Taiwan; Department of Biochemistry, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
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7
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Inhibitors of RNA and protein synthesis cause Glut4 translocation and increase glucose uptake in adipocytes. Sci Rep 2022; 12:15640. [PMID: 36123369 PMCID: PMC9485115 DOI: 10.1038/s41598-022-19534-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 08/30/2022] [Indexed: 12/29/2022] Open
Abstract
Insulin stimulates glucose uptake in adipocytes by triggering translocation of glucose transporter 4-containg vesicles to the plasma membrane. Under basal conditions, these vesicles (IRVs for insulin-responsive vesicles) are retained inside the cell via a “static” or “dynamic” mechanism. We have found that inhibitors of RNA and protein synthesis, actinomycin D and emetine, stimulate Glut4 translocation and glucose uptake in adipocytes without engaging conventional signaling proteins, such as Akt, TBC1D4, or TUG. Actinomycin D does not significantly affect endocytosis of Glut4 or recycling of transferrin, suggesting that it specifically increases exocytosis of the IRVs. Thus, the intracellular retention of the IRVs in adipocytes requires continuous RNA and protein biosynthesis de novo. These results point out to the existence of a short-lived inhibitor of IRV translocation thus supporting the “static” model.
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8
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Kang MA, Rao PP, Matsui H, Mahajan SS. Delivery of mGluR5 siRNAs by Iron Oxide Nanocages by Alternating Magnetic Fields for Blocking Proliferation of Metastatic Osteosarcoma Cells. Int J Mol Sci 2022; 23:7944. [PMID: 35887290 PMCID: PMC9320330 DOI: 10.3390/ijms23147944] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 07/15/2022] [Accepted: 07/18/2022] [Indexed: 02/04/2023] Open
Abstract
Although osteosarcoma is the most common primary malignant bone tumor, chemotherapeutic drugs and treatment have failed to increase the five-year survival rate over the last three decades. We previously demonstrated that type 5 metabotropic glutamate receptor, mGluR5, is required to proliferate metastatic osteosarcoma cells. In this work, we delivered mGluR5 siRNAs in vitro using superparamagnetic iron oxide nanocages (IO-nanocages) as delivery vehicles and applied alternating magnetic fields (AMFs) to improve mGluR5 siRNAs release. We observed functional outcomes when mGluR5 expression is silenced in human and mouse osteosarcoma cell lines. The results elucidated that the mGluR5 siRNAs were successfully delivered by IO-nanocages and their release was enhanced by AMFs, leading to mGluR5 silencing. Moreover, we observed that the proliferation of both human and mouse osteosarcoma cells decreased significantly when mGluR5 expression was silenced in the cells. This novel magnetic siRNA delivery methodology was capable of silencing mGluR5 expression significantly in osteosarcoma cell lines under the AMFs, and our data suggested that this method can be further used in future clinical applications in cancer therapy.
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Affiliation(s)
- Min A Kang
- Ph.D. Program in Biochemistry, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA; (M.A.K.); (P.P.R.); (H.M.)
- Department of Chemistry, Hunter College, City University of New York, 695 Park Ave., New York, NY 10065, USA
| | - Pooja P. Rao
- Ph.D. Program in Biochemistry, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA; (M.A.K.); (P.P.R.); (H.M.)
- Department of Medical Laboratory Science, Hunter College, City University of New York, 425 East 25th Street, New York, NY 10010, USA
| | - Hiroshi Matsui
- Ph.D. Program in Biochemistry, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA; (M.A.K.); (P.P.R.); (H.M.)
- Department of Chemistry, Hunter College, City University of New York, 695 Park Ave., New York, NY 10065, USA
- Ph.D. Program in Chemistry, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA
- Department of Biochemistry, Weill Cornell Medical College, 413 East 69th Street, New York, NY 10021, USA
| | - Shahana S. Mahajan
- Ph.D. Program in Biochemistry, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA; (M.A.K.); (P.P.R.); (H.M.)
- Department of Medical Laboratory Science, Hunter College, City University of New York, 425 East 25th Street, New York, NY 10010, USA
- Ph.D. Program in Biology, The Graduate Center of the City University of New York, 364 5th Ave., New York, NY 10016, USA
- Brain Mind Research Institute, Weill Cornell Medical College, 413 East 69th Street, New York, NY 10021, USA
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9
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Yu W, Wang Z, Yu X, Zhao Y, Xie Z, Zhang K, Chi Z, Chen S, Xu T, Jiang D, Guo X, Li M, Zhang J, Fang H, Yang D, Guo Y, Yang X, Zhang X, Wu Y, Yang W, Wang D. Kir2.1-mediated membrane potential promotes nutrient acquisition and inflammation through regulation of nutrient transporters. Nat Commun 2022; 13:3544. [PMID: 35729093 PMCID: PMC9213538 DOI: 10.1038/s41467-022-31149-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Accepted: 05/26/2022] [Indexed: 12/22/2022] Open
Abstract
Immunometabolism contributes to inflammation, but how activated macrophages acquire extracellular nutrients to fuel inflammation is largely unknown. Here, we show that the plasma membrane potential (Vm) of macrophages mediated by Kir2.1, an inwardly-rectifying K+ channel, is an important determinant of nutrient acquisition and subsequent metabolic reprogramming promoting inflammation. In the absence of Kir2.1 activity, depolarized macrophage Vm lead to a caloric restriction state by limiting nutrient uptake and concomitant adaptations in nutrient conservation inducing autophagy, AMPK (Adenosine 5'-monophosphate-activated protein kinase), and GCN2 (General control nonderepressible 2), which subsequently depletes epigenetic substrates feeding histone methylation at loci of a cluster of metabolism-responsive inflammatory genes, thereby suppressing their transcription. Kir2.1-mediated Vm supports nutrient uptake by facilitating cell-surface retention of nutrient transporters such as 4F2hc and GLUT1 by its modulation of plasma membrane phospholipid dynamics. Pharmacological targeting of Kir2.1 alleviated inflammation triggered by LPS or bacterial infection in a sepsis model and sterile inflammation in human samples. These findings identify an ionic control of macrophage activation and advance our understanding of the immunomodulatory properties of Vm that links nutrient inputs to inflammatory diseases.
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Affiliation(s)
- Weiwei Yu
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China.,Liangzhu Laboratory, Zhejiang University Medical Center, 1369 West Wenyi Road, Hangzhou, P. R. China
| | - Zhen Wang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China.,Liangzhu Laboratory, Zhejiang University Medical Center, 1369 West Wenyi Road, Hangzhou, P. R. China
| | - Xiafei Yu
- Department of Biophysics, and Department of Neurology of the Fourth Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Yonghui Zhao
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, P. R. China
| | - Zili Xie
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, P. R. China
| | - Kailian Zhang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Zhexu Chi
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Sheng Chen
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Ting Xu
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Danlu Jiang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Xingchen Guo
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, P. R. China
| | - Mobai Li
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Jian Zhang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Hui Fang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Dehang Yang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Yuxian Guo
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Xuyan Yang
- Department of Rheumatology of the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Xue Zhang
- Department of Pathology and Pathophysiology, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China
| | - Yingliang Wu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, P. R. China
| | - Wei Yang
- Department of Biophysics, and Department of Neurology of the Fourth Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China.
| | - Di Wang
- Institute of Immunology and Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, P. R. China. .,Liangzhu Laboratory, Zhejiang University Medical Center, 1369 West Wenyi Road, Hangzhou, P. R. China.
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10
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Fazakerley DJ, Koumanov F, Holman GD. GLUT4 On the move. Biochem J 2022; 479:445-462. [PMID: 35147164 PMCID: PMC8883492 DOI: 10.1042/bcj20210073] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 01/11/2022] [Accepted: 01/14/2022] [Indexed: 12/16/2022]
Abstract
Insulin rapidly stimulates GLUT4 translocation and glucose transport in fat and muscle cells. Signals from the occupied insulin receptor are translated into downstream signalling changes in serine/threonine kinases within timescales of seconds, and this is followed by delivery and accumulation of the glucose transporter GLUT4 at the plasma membrane. Kinetic studies have led to realisation that there are distinct phases of this stimulation by insulin. There is a rapid initial burst of GLUT4 delivered to the cell surface from a subcellular reservoir compartment and this is followed by a steady-state level of continuing stimulation in which GLUT4 recycles through a large itinerary of subcellular locations. Here, we provide an overview of the phases of insulin stimulation of GLUT4 translocation and the molecules that are currently considered to activate these trafficking steps. Furthermore, we suggest how use of new experimental approaches together with phospho-proteomic data may help to further identify mechanisms for activation of these trafficking processes.
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Affiliation(s)
- Daniel J Fazakerley
- Metabolic Research Laboratories, Wellcome-Medical Research Council Institute of Metabolic Science, University of Cambridge, Cambridge CB2 0QQ, U.K
| | - Francoise Koumanov
- Department for Health, Centre for Nutrition, Exercise, and Metabolism, University of Bath, Bath, Somerset BA2 7AY, U.K
| | - Geoffrey D Holman
- Department of Biology and Biochemistry, University of Bath, Bath, Somerset BA2 7AY, U.K
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11
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Heckmann M, Klanert G, Sandner G, Lanzerstorfer P, Auer M, Weghuber J. Fluorescence Microscopy-Based Quantitation of GLUT4 Translocation. Methods Appl Fluoresc 2022; 10. [PMID: 35008072 DOI: 10.1088/2050-6120/ac4998] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 01/10/2022] [Indexed: 11/11/2022]
Abstract
Postprandial insulin-stimulated glucose uptake into target tissue is crucial for the maintenance of normal blood glucose homeostasis. This step is rate-limited by the number of facilitative glucose transporters type 4 (GLUT4) present in the plasma membrane. Since insulin resistance and impaired GLUT4 translocation are associated with the development of metabolic disorders such as type 2 diabetes, this transporter has become an important target of antidiabetic drug research. The application of screening approaches that are based on the analysis of GLUT4 translocation to the plasma membrane to identify substances with insulinomimetic properties has gained global research interest in recent years. Here, we review methods that have been implemented to quantitate the translocation of GLUT4 to the plasma membrane. These methods can be broadly divided into two sections: microscopy-based technologies (e.g., immunoelectron, confocal or total internal reflection fluorescence microscopy) and biochemical and spectrometric approaches (e.g., membrane fractionation, photoaffinity labeling or flow cytometry). In this review, we discuss the most relevant approaches applied to GLUT4 thus far, highlighting the advantages and disadvantages of these approaches, and we provide a critical discussion and outlook into new methodological opportunities.
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Affiliation(s)
- Mara Heckmann
- University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, Wels, Oberösterreich, 4600, AUSTRIA
| | - Gerald Klanert
- FFoQSI GmbH-Austrian Competence Centre for Feed and Food Quality, Safety and Innovation, Technopark 1C, Tulln, 3430, AUSTRIA
| | - Georg Sandner
- University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, Wels, Oberösterreich, 4600, AUSTRIA
| | - Peter Lanzerstorfer
- University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, Wels, Oberösterreich, 4600, AUSTRIA
| | - Manfred Auer
- Division of Pathway Medicine, University of Edinburgh, University of Edinburgh Medical School, The Chancellor's Building, 49 Little France Crescent, Edinburgh, EH16 4SB, Edinburgh, EH8 9AB, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Julian Weghuber
- University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, Wels, Oberösterreich, 4600, AUSTRIA
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12
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Black HL, Livingstone R, Mastick CC, Al Tobi M, Taylor H, Geiser A, Stirrat L, Kioumourtzoglou D, Petrie JR, Boyle JG, Bryant NJ, Gould GW. Knockout of Syntaxin-4 in 3T3-L1 adipocytes reveals new insight into GLUT4 trafficking and adiponectin secretion. J Cell Sci 2021; 135:273617. [PMID: 34859814 PMCID: PMC8767277 DOI: 10.1242/jcs.258375] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 11/18/2021] [Indexed: 11/20/2022] Open
Abstract
Adipocytes are key to metabolic regulation, exhibiting insulin-stimulated glucose transport that is underpinned by the insulin-stimulated delivery of glucose transporter type 4 (SLC2A4, also known and hereafter referred to as GLUT4)-containing vesicles to the plasma membrane where they dock and fuse, and increase cell surface GLUT4 levels. Adipocytokines, such as adiponectin, are secreted via a similar mechanism. We used genome editing to knock out syntaxin-4, a protein reported to mediate fusion between GLUT4-containing vesicles and the plasma membrane in 3T3-L1 adipocytes. Syntaxin-4 knockout reduced insulin-stimulated glucose transport and adiponectin secretion by ∼50% and reduced GLUT4 levels. Ectopic expression of haemagglutinin (HA)-tagged GLUT4 conjugated to GFP showed that syntaxin-4-knockout cells retain significant GLUT4 translocation capacity, demonstrating that syntaxin-4 is dispensable for insulin-stimulated GLUT4 translocation. Analysis of recycling kinetics revealed only a modest reduction in the exocytic rate of GLUT4 in knockout cells, and little effect on endocytosis. These analyses demonstrate that syntaxin-4 is not always rate limiting for GLUT4 delivery to the cell surface. In sum, we show that syntaxin-4 knockout results in reduced insulin-stimulated glucose transport, depletion of cellular GLUT4 levels and inhibition of adiponectin secretion but has only modest effects on the translocation capacity of the cells. This article has an associated First Person interview with Hannah L. Black and Rachel Livingstone, joint first authors of the paper. Summary: Syntaxin-4 knockout reduces insulin-stimulated glucose transport, depletes levels of cellular GLUT4 and inhibits secretion of adiponectin but only modestly affects the translocation capacity of the cells.
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Affiliation(s)
- Hannah L Black
- Department of Biology and York Biomedical Research Institute, University of York. Heslington, York, YO10 5DD, UK
| | - Rachel Livingstone
- Henry Welcome Laboratory for Cell Biology, Institute for Molecular, Cellular and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
| | - Cynthia C Mastick
- Henry Welcome Laboratory for Cell Biology, Institute for Molecular, Cellular and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.,Department of Biology, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV 89557, USA
| | - Mohammed Al Tobi
- Henry Welcome Laboratory for Cell Biology, Institute for Molecular, Cellular and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
| | - Holly Taylor
- Strathclyde Institute for Pharmacy and Biomedical Sciences, 161 Cathedral Street, University of Strathclyde, Glasgow G4 0RE, UK
| | - Angéline Geiser
- Strathclyde Institute for Pharmacy and Biomedical Sciences, 161 Cathedral Street, University of Strathclyde, Glasgow G4 0RE, UK
| | - Laura Stirrat
- Strathclyde Institute for Pharmacy and Biomedical Sciences, 161 Cathedral Street, University of Strathclyde, Glasgow G4 0RE, UK
| | - Dimitrios Kioumourtzoglou
- Department of Biology and York Biomedical Research Institute, University of York. Heslington, York, YO10 5DD, UK
| | - John R Petrie
- Institute of Cardiovascular and Medical Sciences, University of Glasgow. Glasgow G12 8QQ, UK
| | - James G Boyle
- Institute of Cardiovascular and Medical Sciences, University of Glasgow. Glasgow G12 8QQ, UK.,School of Medicine, Dentistry and Nursing, University of Glasgow. Glasgow G12 8QQ, UK
| | - Nia J Bryant
- Department of Biology and York Biomedical Research Institute, University of York. Heslington, York, YO10 5DD, UK
| | - Gwyn W Gould
- Strathclyde Institute for Pharmacy and Biomedical Sciences, 161 Cathedral Street, University of Strathclyde, Glasgow G4 0RE, UK
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13
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Brumfield A, Chaudhary N, Molle D, Wen J, Graumann J, McGraw TE. Insulin-promoted mobilization of GLUT4 from a perinuclear storage site requires RAB10. Mol Biol Cell 2021; 32:57-73. [PMID: 33175605 PMCID: PMC8098823 DOI: 10.1091/mbc.e20-06-0356] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 10/30/2020] [Accepted: 11/04/2020] [Indexed: 12/05/2022] Open
Abstract
Insulin controls glucose uptake into muscle and fat cells by inducing a net redistribution of glucose transporter 4 (GLUT4) from intracellular storage to the plasma membrane (PM). The TBC1D4-RAB10 signaling module is required for insulin-stimulated GLUT4 translocation to the PM, although where it intersects GLUT4 traffic was unknown. Here we demonstrate that TBC1D4-RAB10 functions to control GLUT4 mobilization from a trans-Golgi network (TGN) storage compartment, establishing that insulin, in addition to regulating the PM proximal effects of GLUT4-containing vesicles docking to and fusion with the PM, also directly regulates the behavior of GLUT4 deeper within the cell. We also show that GLUT4 is retained in an element/domain of the TGN from which newly synthesized lysosomal proteins are targeted to the late endosomes and the ATP7A copper transporter is translocated to the PM by elevated copper. Insulin does not mobilize ATP7A nor does copper mobilize GLUT4, and RAB10 is not required for copper-elicited ATP7A mobilization. Consequently, GLUT4 intracellular sequestration and mobilization by insulin is achieved, in part, through utilizing a region of the TGN devoted to specialized cargo transport in general rather than being specific for GLUT4. Our results define the GLUT4-containing region of the TGN as a sorting and storage site from which different cargo are mobilized by distinct signals through unique molecular machinery.
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Affiliation(s)
| | - Natasha Chaudhary
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Dorothee Molle
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Jennifer Wen
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Johannes Graumann
- Weill Cornell Medical College in Qatar, Education City, 24144 Doha, State of Qatar
| | - Timothy E. McGraw
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
- Department of Cardiothoracic Surgery, Weill Cornell Medical College, New York, NY 10065
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14
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Szomek M, Reinholdt P, Petersen D, Caci A, Kongsted J, Wüstner D. Direct observation of nystatin binding to the plasma membrane of living cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183528. [PMID: 33279513 DOI: 10.1016/j.bbamem.2020.183528] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 11/24/2020] [Accepted: 11/30/2020] [Indexed: 01/04/2023]
Abstract
Nystatin is an antifungal polyene macrolide which is widely applied to treat yeast infections. Nystatin has also been used as a laboratory tool to inhibit endocytic processes in mammalian cells. The interaction of nystatin with model membranes has been studied thoroughly by various spectroscopic methods, making use of its weak fluorescence in the ultraviolet (UV). Studying its interaction with cells would require direct imaging, which, so far, required attachment of a fluorophore to nystatin. Using UV-sensitive microscopy, we show here how to visualize the interaction of nystatin with the plasma membrane (PM) directly. We find that nystatin forms micron-sized aggregates in buffer, and molecular dynamics simulations confirm that nystatin rapidly self-assembles into aggregates in aqueous solution. Using UV-sensitive microscopy, we find that large nystatin aggregates adhere to the surface of Chinese Hamster Ovarian (CHO) cells, causing slow spreading of nystatin fluorescence into the PM. Binding of nystatin to CHO cells does not interfere with cellular uptake or lateral membrane diffusion of the cholesterol analogue TopFluor-cholesterol (TF-Chol). Nystatin binds extensively to the PM of yeast cells as inferred from a strong UV signal in this membrane. Loading a yeast mutant unable to synthesize ergosterol with cholesterol gave much less nystatin membrane staining compared to loading such cells with ergosterol. These results explain the selective fungicidal effect of nystatin by differential interaction of nystatin with yeast membranes containing ergosterol compared to the mammalian cholesterol. Our combined experimental and computational approach provides a toolset for future design of new polyene macrolides.
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Affiliation(s)
- Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Daniel Petersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Atenisa Caci
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark.
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15
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Wang T, Wang J, Hu X, Huang XJ, Chen GX. Current understanding of glucose transporter 4 expression and functional mechanisms. World J Biol Chem 2020; 11:76-98. [PMID: 33274014 PMCID: PMC7672939 DOI: 10.4331/wjbc.v11.i3.76] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 08/22/2020] [Accepted: 09/22/2020] [Indexed: 02/05/2023] Open
Abstract
Glucose is used aerobically and anaerobically to generate energy for cells. Glucose transporters (GLUTs) are transmembrane proteins that transport glucose across the cell membrane. Insulin promotes glucose utilization in part through promoting glucose entry into the skeletal and adipose tissues. This has been thought to be achieved through insulin-induced GLUT4 translocation from intracellular compartments to the cell membrane, which increases the overall rate of glucose flux into a cell. The insulin-induced GLUT4 translocation has been investigated extensively. Recently, significant progress has been made in our understanding of GLUT4 expression and translocation. Here, we summarized the methods and reagents used to determine the expression levels of Slc2a4 mRNA and GLUT4 protein, and GLUT4 translocation in the skeletal muscle, adipose tissues, heart and brain. Overall, a variety of methods such real-time polymerase chain reaction, immunohistochemistry, fluorescence microscopy, fusion proteins, stable cell line and transgenic animals have been used to answer particular questions related to GLUT4 system and insulin action. It seems that insulin-induced GLUT4 translocation can be observed in the heart and brain in addition to the skeletal muscle and adipocytes. Hormones other than insulin can induce GLUT4 translocation. Clearly, more studies of GLUT4 are warranted in the future to advance of our understanding of glucose homeostasis.
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Affiliation(s)
- Tiannan Wang
- Department of Nutrition, The University of Tennessee, Knoxville, TN 37996, United States
| | - Jing Wang
- College of Pharmacy, South-Central University for Nationalities, Wuhan 430074, Hubei Province, China
| | - Xinge Hu
- Department of Nutrition, The University of Tennessee, Knoxville, TN 37996, United States
| | - Xian-Ju Huang
- College of Pharmacy, South-Central University for Nationalities, Wuhan 430074, Hubei Province, China
| | - Guo-Xun Chen
- Department of Nutrition, The University of Tennessee, Knoxville, TN 37996, United States
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16
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Holman GD. Structure, function and regulation of mammalian glucose transporters of the SLC2 family. Pflugers Arch 2020; 472:1155-1175. [PMID: 32591905 PMCID: PMC7462842 DOI: 10.1007/s00424-020-02411-3] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 05/27/2020] [Accepted: 05/29/2020] [Indexed: 12/12/2022]
Abstract
The SLC2 genes code for a family of GLUT proteins that are part of the major facilitator superfamily (MFS) of membrane transporters. Crystal structures have recently revealed how the unique protein fold of these proteins enables the catalysis of transport. The proteins have 12 transmembrane spans built from a replicated trimer substructure. This enables 4 trimer substructures to move relative to each other, and thereby alternately opening and closing a cleft to either the internal or the external side of the membrane. The physiological substrate for the GLUTs is usually a hexose but substrates for GLUTs can include urate, dehydro-ascorbate and myo-inositol. The GLUT proteins have varied physiological functions that are related to their principal substrates, the cell type in which the GLUTs are expressed and the extent to which the proteins are associated with subcellular compartments. Some of the GLUT proteins translocate between subcellular compartments and this facilitates the control of their function over long- and short-time scales. The control of GLUT function is necessary for a regulated supply of metabolites (mainly glucose) to tissues. Pathophysiological abnormalities in GLUT proteins are responsible for, or associated with, clinical problems including type 2 diabetes and cancer and a range of tissue disorders, related to tissue-specific GLUT protein profiles. The availability of GLUT crystal structures has facilitated the search for inhibitors and substrates and that are specific for each GLUT and that can be used therapeutically. Recent studies are starting to unravel the drug targetable properties of each of the GLUT proteins.
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Affiliation(s)
- Geoffrey D Holman
- Department of Biology and Biochemistry, University of Bath, Bath, BA2 7AY, UK.
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17
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López-Hernández T, Haucke V, Maritzen T. Endocytosis in the adaptation to cellular stress. Cell Stress 2020; 4:230-247. [PMID: 33024932 PMCID: PMC7520666 DOI: 10.15698/cst2020.10.232] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 07/24/2020] [Accepted: 07/29/2020] [Indexed: 12/11/2022] Open
Abstract
Cellular life is challenged by a multitude of stress conditions, triggered for example by alterations in osmolarity, oxygen or nutrient supply. Hence, cells have developed sophisticated stress responses to cope with these challenges. Some of these stress programs such as the heat shock response are understood in great detail, while other aspects remain largely elusive including potential stress-dependent adaptations of the plasma membrane proteome. The plasma membrane is not only the first point of encounter for many types of environmental stress, but given the diversity of receptor proteins and their associated molecules also represents the site at which many cellular signal cascades originate. Since these signaling pathways affect virtually all aspects of cellular life, changes in the plasma membrane proteome appear ideally suited to contribute to the cellular adaptation to stress. The most rapid means to alter the cell surface proteome in response to stress is by alterations in endocytosis. Changes in the overall endocytic flux or in the endocytic regulation of select proteins conceivably can help to counteract adverse environmental conditions. In this review we summarize recent data regarding stress-induced changes in endocytosis and discuss how these changes might contribute to the cellular adaptation to stress in different systems. Future studies will be needed to uncover the underlying mechanisms in detail and to arrive at a coherent picture.
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Affiliation(s)
- Tania López-Hernández
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany
| | - Volker Haucke
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany
- Freie Universität Berlin, Faculty of Biology, Chemistry, Pharmacy, 14195 Berlin, Germany
| | - Tanja Maritzen
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany
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18
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Li DT, Habtemichael EN, Julca O, Sales CI, Westergaard XO, DeVries SG, Ruiz D, Sayal B, Bogan JS. GLUT4 Storage Vesicles: Specialized Organelles for Regulated Trafficking. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 2019; 92:453-470. [PMID: 31543708 PMCID: PMC6747935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Fat and muscle cells contain a specialized, intracellular organelle known as the GLUT4 storage vesicle (GSV). Insulin stimulation mobilizes GSVs, so that these vesicles fuse at the cell surface and insert GLUT4 glucose transporters into the plasma membrane. This example is likely one instance of a broader paradigm for regulated, non-secretory exocytosis, in which intracellular vesicles are translocated in response to diverse extracellular stimuli. GSVs have been studied extensively, yet these vesicles remain enigmatic. Data support the view that in unstimulated cells, GSVs are present as a pool of preformed small vesicles, which are distinct from endosomes and other membrane-bound organelles. In adipocytes, GSVs contain specific cargoes including GLUT4, IRAP, LRP1, and sortilin. They are formed by membrane budding, involving sortilin and probably CHC22 clathrin in humans, but the donor compartment from which these vesicles form remains uncertain. In unstimulated cells, GSVs are trapped by TUG proteins near the endoplasmic reticulum - Golgi intermediate compartment (ERGIC). Insulin signals through two main pathways to mobilize these vesicles. Signaling by the Akt kinase modulates Rab GTPases to target the GSVs to the cell surface. Signaling by the Rho-family GTPase TC10α stimulates Usp25m-mediated TUG cleavage to liberate the vesicles from the Golgi. Cleavage produces a ubiquitin-like protein modifier, TUGUL, that links the GSVs to KIF5B kinesin motors to promote their movement to the cell surface. In obesity, attenuation of these processes results in insulin resistance and contributes to type 2 diabetes and may simultaneously contribute to hypertension and dyslipidemia in the metabolic syndrome.
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Affiliation(s)
- Don T. Li
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT,Department of Cell Biology, Yale University School of Medicine, Yale University, New Haven, CT
| | - Estifanos N. Habtemichael
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Omar Julca
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Chloe I. Sales
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Xavier O. Westergaard
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Stephen G. DeVries
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Diana Ruiz
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Bhavesh Sayal
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT
| | - Jonathan S. Bogan
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, Yale University, New Haven, CT,Department of Cell Biology, Yale University School of Medicine, Yale University, New Haven, CT,To whom all correspondence should be addressed: Jonathan S. Bogan, Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, P.O. Box 208020, New Haven, CT 06520-8020; Tel: 203-785-6319; Fax: 203-785-6462;
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19
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Abstract
A pivotal metabolic function of insulin is the stimulation of glucose uptake into muscle and adipose tissues. The discovery of the insulin-responsive glucose transporter type 4 (GLUT4) protein in 1988 inspired its molecular cloning in the following year. It also spurred numerous cellular mechanistic studies laying the foundations for how insulin regulates glucose uptake by muscle and fat cells. Here, we reflect on the importance of the GLUT4 discovery and chronicle additional key findings made in the past 30 years. That exocytosis of a multispanning membrane protein regulates cellular glucose transport illuminated a novel adaptation of the secretory pathway, which is to transiently modulate the protein composition of the cellular plasma membrane. GLUT4 controls glucose transport into fat and muscle tissues in response to insulin and also into muscle during exercise. Thus, investigation of regulated GLUT4 trafficking provides a major means by which to map the essential signaling components that transmit the effects of insulin and exercise. Manipulation of the expression of GLUT4 or GLUT4-regulating molecules in mice has revealed the impact of glucose uptake on whole-body metabolism. Remaining gaps in our understanding of GLUT4 function and regulation are highlighted here, along with opportunities for future discoveries and for the development of therapeutic approaches to manage metabolic disease.
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Affiliation(s)
- Amira Klip
- Cell Biology Program, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
| | - Timothy E McGraw
- Department of Biochemistry, Weill Medical College of Cornell University, New York, New York 10065
| | - David E James
- Charles Perkins Centre, School of Life and Environmental Sciences, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia
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20
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Arredouani A, Diane A, Khattab N, Bensmail I, Aoude I, Chikri M, Mohammad R, Abou-Samra AB, Dehbi M. DNAJB3 attenuates metabolic stress and promotes glucose uptake by eliciting Glut4 translocation. Sci Rep 2019; 9:4772. [PMID: 30886231 PMCID: PMC6423224 DOI: 10.1038/s41598-019-41244-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 02/14/2019] [Indexed: 12/12/2022] Open
Abstract
Failure of the heat shock response is a key event that leads to insulin resistance and type 2 diabetes. We recently showed that DNAJB3 co-chaperone is downregulated in obese and diabetic patients and that physical exercise restores its normal expression with a significant improvement of the clinical outcomes. In 3T3-L1 adipocytes, DNAJB3 has a role in improving the sensitivity to insulin and glucose uptake. In co-immunoprecipitation assays, DNAJB3 interacts with both JNK1 and IKKβ kinases. However, the functional impact of such interaction on their activities has not been investigated. Here, we assessed the effect of DNAJB3 on the respective activity of JNK1 and IKKβ in cell-based assays. Using JNK1- and IKKβ-dependent luciferase reporters, we show a marked decrease in luciferase activity by DNAJB3 in response to PMA and TNF-α that was consistent with a decrease in the translocation of p65/NF-κB to the nucleus in response to LPS. Furthermore, TNF-α-mediated IL-6 promoter activation and endogenous mRNA expression are significantly abrogated by DNAJB3 both in 3T3-L1 and C2C12 cells. The ability of DNAJB3 to mitigate ER stress and oxidative stress was also investigated and our data show a significant improvement of both forms of stress. Finally, we examined the effect of overexpressing and knocking down the expression of DNAJB3 on glucose uptake in C2C12 as well as the molecular determinants. Accordingly, we provide evidence for a role of DNAJB3 in promoting both basal and insulin-stimulated glucose uptake. Our finding reveals also a novel role of DNAJB3 in eliciting Glut4 translocation to the plasma membrane. These results suggest a physiological role of DNAJB3 in mitigating metabolic stress and improving glucose homeostasis and could therefore represent a novel therapeutic target for type 2 diabetes.
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Affiliation(s)
| | - Abdoulaye Diane
- Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Doha, Qatar
| | - Namat Khattab
- Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Doha, Qatar
| | - Ilham Bensmail
- Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Doha, Qatar
| | - Imad Aoude
- Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Doha, Qatar
| | - Mohamed Chikri
- Faculty of Medicine & Pharmacy, University Sidi Mohamed Ben Abdellah, Fes, Morocco
| | - Ramzi Mohammad
- The Interim Translational Research Institute, Hamad Medical Corporation, Doha, Qatar.,Karmanos Cancer Institute, Department Of Oncology, Wayne State University, Detroit, MI, USA
| | - Abdul Badi Abou-Samra
- Qatar Metabolic Institute, Department of Internal Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Mohammed Dehbi
- Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Doha, Qatar.
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21
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Hinze C, Boucrot E. Endocytosis in proliferating, quiescent and terminally differentiated cells. J Cell Sci 2018; 131:131/23/jcs216804. [PMID: 30504135 DOI: 10.1242/jcs.216804] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Endocytosis mediates nutrient uptake, receptor internalization and the regulation of cell signaling. It is also hijacked by many bacteria, viruses and toxins to mediate their cellular entry. Several endocytic routes exist in parallel, fulfilling different functions. Most studies on endocytosis have used transformed cells in culture. However, as the majority of cells in an adult body have exited the cell cycle, our understanding is biased towards proliferating cells. Here, we review the evidence for the different pathways of endocytosis not only in dividing, but also in quiescent, senescent and terminally differentiated cells. During mitosis, residual endocytosis is dedicated to the internalization of caveolae and specific receptors. In non-dividing cells, clathrin-mediated endocytosis (CME) functions, but the activity of alternative processes, such as caveolae, macropinocytosis and clathrin-independent routes, vary widely depending on cell types and functions. Endocytosis supports the quiescent state by either upregulating cell cycle arrest pathways or downregulating mitogen-induced signaling, thereby inhibiting cell proliferation. Endocytosis in terminally differentiated cells, such as skeletal muscles, adipocytes, kidney podocytes and neurons, supports tissue-specific functions. Finally, uptake is downregulated in senescent cells, making them insensitive to proliferative stimuli by growth factors. Future studies should reveal the molecular basis for the differences in activities between the different cell states.
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Affiliation(s)
- Claudia Hinze
- Institute of Structural and Molecular Biology, Division of Biosciences, University College London, London WC1E 6BT, UK
| | - Emmanuel Boucrot
- Institute of Structural and Molecular Biology, Division of Biosciences, University College London, London WC1E 6BT, UK .,Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, London WC1E 7HX, UK
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22
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Swaminathan SK, Ahlschwede KM, Sarma V, Curran GL, Omtri RS, Decklever T, Lowe VJ, Poduslo JF, Kandimalla KK. Insulin differentially affects the distribution kinetics of amyloid beta 40 and 42 in plasma and brain. J Cereb Blood Flow Metab 2018; 38:904-918. [PMID: 28569090 PMCID: PMC5987944 DOI: 10.1177/0271678x17709709] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Impaired brain clearance of amyloid-beta peptides (Aβ) 40 and 42 across the blood-brain barrier (BBB) is believed to be one of the pathways responsible for Alzheimer's disease (AD) pathogenesis. Hyperinsulinemia prevalent in type II diabetes was shown to damage cerebral vasculature and increase Aβ accumulation in AD brain. However, there is no clarity on how aberrations in peripheral insulin levels affect Aβ accumulation in the brain. This study describes, for the first time, an intricate relation between plasma insulin and Aβ transport at the BBB. Upon peripheral insulin administration in wild-type mice: the plasma clearance of Aβ40 increased, but Aβ42 clearance reduced; the plasma-to-brain influx of Aβ40 increased, and that of Aβ42 reduced; and the clearance of intracerebrally injected Aβ40 decreased, whereas Aβ42 clearance increased. In hCMEC/D3 monolayers (in vitro BBB model) exposed to insulin, the luminal uptake and luminal-to-abluminal permeability of Aβ40 increased and that of Aβ42 reduced; the abluminal-to-luminal permeability of Aβ40 decreased, whereas Aβ42 permeability increased. Moreover, Aβ cellular trafficking machinery was altered. In summary, Aβ40 and Aβ42 demonstrated distinct distribution kinetics in plasma and brain compartments, and insulin differentially modulated their distribution. Cerebrovascular disease and metabolic disorders may disrupt this intricate homeostasis and aggravate AD pathology.
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Affiliation(s)
- Suresh Kumar Swaminathan
- 1 Department of Pharmaceutics and Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, MN, USA.,2 Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Kristen M Ahlschwede
- 1 Department of Pharmaceutics and Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, MN, USA.,3 Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Vidur Sarma
- 1 Department of Pharmaceutics and Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, MN, USA.,2 Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Geoffry L Curran
- 2 Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN, USA.,3 Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Rajesh S Omtri
- 1 Department of Pharmaceutics and Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, MN, USA
| | - Teresa Decklever
- 2 Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Val J Lowe
- 2 Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Joseph F Poduslo
- 3 Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Karunya K Kandimalla
- 1 Department of Pharmaceutics and Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, MN, USA.,3 Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, USA
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23
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Waldhart AN, Dykstra H, Peck AS, Boguslawski EA, Madaj ZB, Wen J, Veldkamp K, Hollowell M, Zheng B, Cantley LC, McGraw TE, Wu N. Phosphorylation of TXNIP by AKT Mediates Acute Influx of Glucose in Response to Insulin. Cell Rep 2018; 19:2005-2013. [PMID: 28591573 DOI: 10.1016/j.celrep.2017.05.041] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 04/22/2017] [Accepted: 05/11/2017] [Indexed: 11/25/2022] Open
Abstract
Growth factors, such as insulin, can induce both acute and long-term glucose uptake into cells. Apart from the rapid, insulin-induced fusion of glucose transporter (GLUT)4 storage vesicles with the cell surface that occurs in muscle and adipose tissues, the mechanism behind acute induction has been unclear in other systems. Thioredoxin interacting protein (TXNIP) has been shown to be a negative regulator of cellular glucose uptake. TXNIP is transcriptionally induced by glucose and reduces glucose influx by promoting GLUT1 endocytosis. Here, we report that TXNIP is a direct substrate of protein kinase B (AKT) and is responsible for mediating AKT-dependent acute glucose influx after growth factor stimulation. Furthermore, TXNIP functions as an adaptor for the basal endocytosis of GLUT4 in vivo, its absence allows excess glucose uptake in muscle and adipose tissues, causing hypoglycemia during fasting. Altogether, TXNIP serves as a key node of signal regulation and response for modulating glucose influx through GLUT1 and GLUT4.
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Affiliation(s)
| | - Holly Dykstra
- Van Andel Research Institute, Grand Rapids, MI 49503, USA
| | | | | | | | - Jennifer Wen
- Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 10065, USA
| | | | | | - Bin Zheng
- Cutaneous Biology Research Center, Massachusetts General Hospital, Boston, MA 02129, USA
| | - Lewis C Cantley
- The Sandra and Edward Meyer Cancer Center, Weill Medical College of Cornell University, New York, NY 10065, USA
| | - Timothy E McGraw
- Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 10065, USA
| | - Ning Wu
- Van Andel Research Institute, Grand Rapids, MI 49503, USA.
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24
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Downregulation of a GPCR by β-Arrestin2-Mediated Switch from an Endosomal to a TGN Recycling Pathway. Cell Rep 2017; 17:2966-2978. [PMID: 27974210 DOI: 10.1016/j.celrep.2016.11.050] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 08/17/2016] [Accepted: 11/14/2016] [Indexed: 01/14/2023] Open
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone involved in nutrient homeostasis. GIP receptor (GIPR) is constitutively internalized and returned to the plasma membrane, atypical behavior for a G-protein-coupled receptor (GPCR). GIP promotes GIPR downregulation from the plasma membrane by inhibiting recycling without affecting internalization. This transient desensitization is achieved by altered intracellular trafficking of activated GIPR. GIP stimulation induces a switch in GIPR recycling from a rapid endosomal to a slow trans-Golgi network (TGN) pathway. GPCR kinases and β-arrestin2 are required for this switch in recycling. A coding sequence variant of GIPR, which has been associated with metabolic alterations, has altered post-activation trafficking characterized by enhanced downregulation and prolonged desensitization. Downregulation of the variant requires β-arrestin2 targeting to the TGN but is independent of GPCR kinases. The single amino acid substitution in the variant biases the receptor to promote GIP-stimulated β-arrestin2 recruitment without receptor phosphorylation, thereby enhancing downregulation.
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25
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Lorenzo DN, Bennett V. Cell-autonomous adiposity through increased cell surface GLUT4 due to ankyrin-B deficiency. Proc Natl Acad Sci U S A 2017; 114:12743-12748. [PMID: 29133412 PMCID: PMC5715754 DOI: 10.1073/pnas.1708865114] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Obesity typically is linked to caloric imbalance as a result of overnutrition. Here we propose a cell-autonomous mechanism for adiposity as a result of persistent cell surface glucose transporter type 4 (GLUT4) in adipocytes resulting from impaired function of ankyrin-B (AnkB) in coupling GLUT4 to clathrin-mediated endocytosis. Adipose tissue-specific AnkB-KO mice develop obesity and progressive pancreatic islet dysfunction with age or high-fat diet (HFD). AnkB-deficient adipocytes exhibit increased lipid accumulation associated with increased glucose uptake and impaired endocytosis of GLUT4. AnkB binds directly to GLUT4 and clathrin and promotes their association in adipocytes. AnkB variants that fail to restore normal lipid accumulation and GLUT4 localization in adipocytes are present in 1.3% of European Americans and 8.4% of African Americans, and are candidates to contribute to obesity susceptibility in humans.
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Affiliation(s)
- Damaris N Lorenzo
- Howard Hughes Medical Institute, Duke University, Durham, NC 27710;
- Department of Biochemistry, Duke University, Durham, NC 27710
| | - Vann Bennett
- Howard Hughes Medical Institute, Duke University, Durham, NC 27710;
- Department of Biochemistry, Duke University, Durham, NC 27710
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26
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Abstract
Cross-presentation of internalized antigens by dendritic cells requires efficient delivery of Major Histocompatibility Complex (MHC) class I molecules to peptide-loading compartments. Strong evidence suggests that such loading can occur outside of the endoplasmic reticulum; however, the trafficking pathways and sources of class I molecules involved are poorly understood. Examination of non-professional, non-phagocytic cells has revealed a clathrin-independent, Arf6-dependent recycling pathway likely traveled by internalized optimally loaded (closed) class I molecules. Some closed and all open MHC class I molecules travel to late endosomes to be degraded but might also partly be re-loaded with peptides and recycled. Studies of viral interference revealed pathways in which class I molecules are directed to degradation in lysosomes upon ubiquitination at the surface, or upon AP-1 and HIV-nef-dependent misrouting from the Golgi network to lysosomes. While many observations made in non-professional cells remain to be re-examined in dendritic cells, available evidence suggests that both recycling and neo-synthesized class I molecules can be loaded with cross-presented peptides. Recycling molecules can be recruited to phagosomes triggered by innate signals such as TLR4 ligands, and may therefore specialize in loading with phagocytosed antigens. In contrast, AP-1-dependent accumulation at, or trafficking through, a Golgi compartment of newly synthesized molecules appears to be important for cross-presentation of soluble proteins and possibly of long peptides that are processed in the so-called vacuolar pathway. However, significant cell biological work will be required to confirm this or any other model and to integrate knowledge on MHC class I biochemistry and trafficking in models of CD8(+) T-cell priming by dendritic cells.
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Affiliation(s)
- Peter van Endert
- Institut National de la Santé et de la Recherche Médicale, Unité 1151, Paris, France.,Université Paris Descartes, Sorbonne Paris Cité, Paris, France.,Centre National de la Recherche Scientifique, Unité 8253, Paris, France
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27
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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: 2.7] [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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28
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Imaging approaches for analysis of cholesterol distribution and dynamics in the plasma membrane. Chem Phys Lipids 2016; 199:106-135. [PMID: 27016337 DOI: 10.1016/j.chemphyslip.2016.03.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 03/04/2016] [Indexed: 11/21/2022]
Abstract
Cholesterol is an important lipid component of the plasma membrane (PM) of mammalian cells, where it is involved in control of many physiological processes, such as endocytosis, cell migration, cell signalling and surface ruffling. In an attempt to explain these functions of cholesterol, several models have been put forward about cholesterol's lateral and transbilayer organization in the PM. In this article, we review imaging techniques developed over the last two decades for assessing the distribution and dynamics of cholesterol in the PM of mammalian cells. Particular focus is on fluorescence techniques to study the lateral and inter-leaflet distribution of suitable cholesterol analogues in the PM of living cells. We describe also several methods for determining lateral cholesterol dynamics in the PM including fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS), single particle tracking (SPT) and spot variation FCS coupled to stimulated emission depletion (STED) microscopy. For proper interpretation of such measurements, we provide some background in probe photophysics and diffusion phenomena occurring in cell membranes. In particular, we show the equivalence of the reaction-diffusion approach, as used in FRAP and FCS, and continuous time random walk (CTRW) models, as often invoked in SPT studies. We also discuss mass spectrometry (MS) based imaging of cholesterol in the PM of fixed cells and compare this method with fluorescence imaging of sterols. We conclude that evidence from many experimental techniques converges towards a model of a homogeneous distribution of cholesterol with largely free and unhindered diffusion in both leaflets of the PM.
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29
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Boal F, Hodgson LR, Reed SE, Yarwood SE, Just VJ, Stephens DJ, McCaffrey MW, Tavaré JM. Insulin promotes Rip11 accumulation at the plasma membrane by inhibiting a dynamin- and PI3-kinase-dependent, but Akt-independent, internalisation event. Cell Signal 2015; 28:74-82. [PMID: 26515129 PMCID: PMC4678287 DOI: 10.1016/j.cellsig.2015.10.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 10/23/2015] [Indexed: 12/11/2022]
Abstract
Rip11 is a Rab11 effector protein that has been shown to be important in controlling the trafficking of several intracellular cargoes, including the fatty acid transporter FAT/CD36, V-ATPase and the glucose transporter GLUT4. We have previously demonstrated that Rip11 translocates to the plasma membrane in response to insulin and here we examine the basis of this regulated phenomenon in more detail. We show that Rip11 rapidly recycles between the cell interior and surface, and that the ability of insulin to increase the appearance of Rip11 at the cell surface involves an inhibition of Rip11 internalisation from the plasma membrane. By contrast the hormone has no effect on the rate of Rip11 translocation towards the plasma membrane. The ability of insulin to inhibit Rip11 internalisation requires dynamin and class I PI3-kinases, but is independent of the activation of the protein kinase Akt; characteristics which are very similar to the mechanism by which insulin inhibits GLUT4 endocytosis.
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Affiliation(s)
- Frédéric Boal
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Lorna R Hodgson
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Sam E Reed
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Sophie E Yarwood
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Victoria J Just
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - David J Stephens
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Mary W McCaffrey
- Molecular Cell Biology Laboratory, School of Biochemistry and Cell Biology, Biosciences Institute, University College Cork, Cork, Ireland
| | - Jeremy M Tavaré
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK.
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30
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TUSC5 regulates insulin-mediated adipose tissue glucose uptake by modulation of GLUT4 recycling. Mol Metab 2015; 4:795-810. [PMID: 26629404 PMCID: PMC4632119 DOI: 10.1016/j.molmet.2015.08.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 08/11/2015] [Accepted: 08/18/2015] [Indexed: 12/26/2022] Open
Abstract
Objective Failure to properly dispose of glucose in response to insulin is a serious health problem, occurring during obesity and is associated with type 2 diabetes development. Insulin-stimulated glucose uptake is facilitated by the translocation and plasma membrane fusion of vesicles containing glucose transporter 4 (GLUT4), the rate-limiting step of post-prandial glucose disposal. Methods We analyzed the role of Tusc5 in the regulation of insulin-stimulated Glut4-mediated glucose uptake in vitro and in vivo. Furthermore, we measured Tusc5 expression in two patient cohorts. Results Herein, we report that TUSC5 controls insulin-stimulated glucose uptake in adipocytes, in vitro and in vivo. TUSC5 facilitates the proper recycling of GLUT4 and other key trafficking proteins during prolonged insulin stimulation, thereby enabling proper protein localization and complete vesicle formation, processes that ultimately enable insulin-stimulated glucose uptake. Tusc5 knockout mice exhibit impaired glucose disposal and TUSC5 expression is predictive of glucose tolerance in obese individuals, independent of body weight. Furthermore, we show that TUSC5 is a PPARγ target and in its absence the anti-diabetic effects of TZDs are significantly blunted. Conclusions Collectively, these findings establish TUSC5 as an adipose tissue-specific protein that enables proper protein recycling, linking the ubiquitous vesicle traffic machinery with tissue-specific insulin-mediated glucose uptake into adipose tissue and the maintenance of a healthy metabolic phenotype in mice and humans. Tusc5 regulates glucose uptake in adipose tissue by modulating the GSV recycling machinery. Tusc5 knockout mice develop insulin resistance due to impaired adipose tissue glucose uptake. Rosiglitazone improves glucose homeostasis in part through the induction of Tusc5. Tusc5 is a novel adipose specific adaptor protein linking Glut4 trafficking to the ubiquitous machinery.
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31
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Lorenzo DN, Healy JA, Hostettler J, Davis J, Yang J, Wang C, Hohmeier HE, Zhang M, Bennett V. Ankyrin-B metabolic syndrome combines age-dependent adiposity with pancreatic β cell insufficiency. J Clin Invest 2015; 125:3087-102. [PMID: 26168218 DOI: 10.1172/jci81317] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 05/27/2015] [Indexed: 12/22/2022] Open
Abstract
Rare functional variants of ankyrin-B have been implicated in human disease, including hereditary cardiac arrhythmia and type 2 diabetes (T2D). Here, we developed murine models to evaluate the metabolic consequences of these alterations in vivo. Specifically, we generated knockin mice that express either the human ankyrin-B variant R1788W, which is present in 0.3% of North Americans of mixed European descent and is associated with T2D, or L1622I, which is present in 7.5% of African Americans. Young AnkbR1788W/R1788W mice displayed primary pancreatic β cell insufficiency that was characterized by reduced insulin secretion in response to muscarinic agonists, combined with increased peripheral glucose uptake and concomitantly increased plasma membrane localization of glucose transporter 4 (GLUT4) in skeletal muscle and adipocytes. In contrast, older AnkbR1788W/R1788W and AnkbL1622I/L1622I mice developed increased adiposity, a phenotype that was reproduced in cultured adipocytes, and insulin resistance. GLUT4 trafficking was altered in animals expressing mutant forms of ankyrin-B, and we propose that increased cell surface expression of GLUT4 in skeletal muscle and fatty tissue of AnkbR1788W/R1788W mice leads to the observed age-dependent adiposity. Together, our data suggest that ankyrin-B deficiency results in a metabolic syndrome that combines primary pancreatic β cell insufficiency with peripheral insulin resistance and is directly relevant to the nearly one million North Americans bearing the R1788W ankyrin-B variant.
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32
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Liao-Chan S, Daine-Matsuoka B, Heald N, Wong T, Lin T, Cai AG, Lai M, D’Alessio JA, Theunissen JW. Quantitative assessment of antibody internalization with novel monoclonal antibodies against Alexa fluorophores. PLoS One 2015; 10:e0124708. [PMID: 25894652 PMCID: PMC4403856 DOI: 10.1371/journal.pone.0124708] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Accepted: 03/04/2015] [Indexed: 12/31/2022] Open
Abstract
Antibodies against cell surface antigens may be internalized through their specific interactions with these proteins and in some cases may induce or perturb antigen internalization. The anti-cancer efficacy of antibody-drug conjugates is thought to rely on their uptake by cancer cells expressing the surface antigen. Numerous techniques, including microscopy and flow cytometry, have been used to identify antibodies with desired cellular uptake rates. To enable quantitative measurements of internalization of labeled antibodies, an assay based on internalized and quenched fluorescence was developed. For this approach, we generated novel anti-Alexa Fluor monoclonal antibodies (mAbs) that effectively and specifically quench cell surface-bound Alexa Fluor 488 or Alexa Fluor 594 fluorescence. Utilizing Alexa Fluor-labeled mAbs against the EphA2 receptor tyrosine kinase, we showed that the anti-Alexa Fluor reagents could be used to monitor internalization quantitatively over time. The anti-Alexa Fluor mAbs were also validated in a proof of concept dual-label internalization assay with simultaneous exposure of cells to two different mAbs. Importantly, the unique anti-Alexa Fluor mAbs described here may also enable other single- and dual-label experiments, including label detection and signal enhancement in macromolecules, trafficking of proteins and microorganisms, and cell migration and morphology.
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Affiliation(s)
- Sindy Liao-Chan
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Barbara Daine-Matsuoka
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Nathan Heald
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Tiffany Wong
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Tracey Lin
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Allen G. Cai
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Michelle Lai
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Joseph A. D’Alessio
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
| | - Jan-Willem Theunissen
- Department of Discovery Research, Igenica Biotherapeutics, Burlingame, California, United States of America
- * E-mail:
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33
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Govers R. Molecular mechanisms of GLUT4 regulation in adipocytes. DIABETES & METABOLISM 2014; 40:400-10. [PMID: 24656589 DOI: 10.1016/j.diabet.2014.01.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/24/2014] [Accepted: 01/26/2014] [Indexed: 01/28/2023]
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34
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Antonescu CN, McGraw TE, Klip A. Reciprocal regulation of endocytosis and metabolism. Cold Spring Harb Perspect Biol 2014; 6:a016964. [PMID: 24984778 DOI: 10.1101/cshperspect.a016964] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The cellular uptake of many nutrients and micronutrients governs both their cellular availability and their systemic homeostasis. The cellular rate of nutrient or ion uptake (e.g., glucose, Fe(3+), K(+)) or efflux (e.g., Na(+)) is governed by a complement of membrane transporters and receptors that show dynamic localization at both the plasma membrane and defined intracellular membrane compartments. Regulation of the rate and mechanism of endocytosis controls the amounts of these proteins on the cell surface, which in many cases determines nutrient uptake or secretion. Moreover, the metabolic action of diverse hormones is initiated upon binding to surface receptors that then undergo regulated endocytosis and show distinct signaling patterns once internalized. Here, we examine how the endocytosis of nutrient transporters and carriers as well as signaling receptors governs cellular metabolism and thereby systemic (whole-body) metabolite homeostasis.
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Affiliation(s)
- Costin N Antonescu
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario M5B 2K3, Canada
| | - Timothy E McGraw
- Department of Biochemistry, Weill Medical College of Cornell University, New York, New York 10065
| | - Amira Klip
- Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
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35
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Brewer PD, Habtemichael EN, Romenskaia I, Mastick CC, Coster ACF. Insulin-regulated Glut4 translocation: membrane protein trafficking with six distinctive steps. J Biol Chem 2014; 289:17280-98. [PMID: 24778187 DOI: 10.1074/jbc.m114.555714] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The trafficking kinetics of Glut4, the transferrin (Tf) receptor, and LRP1 were quantified in adipocytes and undifferentiated fibroblasts. Six steps were identified that determine steady state cell surface Glut4: (i) endocytosis, (ii) degradation, (iii) sorting, (iv) sequestration, (v) release, and (vi) tethering/docking/fusion. Endocytosis of Glut4 is 3 times slower than the Tf receptor in fibroblasts (ken = 0.2 min(-1) versus 0.6 min(-1)). Differentiation decreases Glut4 ken 40% (ken = 0.12 min(-1)). Differentiation also decreases Glut4 degradation, increasing total and cell surface Glut4 3-fold. In fibroblasts, Glut4 is recycled from endosomes through a slow constitutive pathway (kex = 0.025-0.038 min(-1)), not through the fast Tf receptor pathway (kex = 0.2 min(-1)). The kex measured in adipocytes after insulin stimulation is similar (kex = 0.027 min(-1)). Differentiation decreases the rate constant for sorting into the Glut4 recycling pathway (ksort) 3-fold. In adipocytes, Glut4 is also sorted from endosomes into a second exocytic pathway through Glut4 storage vesicles (GSVs). Surprisingly, transfer from endosomes into GSVs is highly regulated; insulin increases the rate constant for sequestration (kseq) 8-fold. Release from sequestration in GSVs is rate-limiting for Glut4 exocytosis in basal adipocytes. AS160 regulates this step. Tethering/docking/fusion of GSVs to the plasma membrane is regulated through an AS160-independent process. Insulin increases the rate of release and fusion of GSVs (kfuseG) 40-fold. LRP1 cycles with the Tf receptor and Glut4 in fibroblasts but predominantly with Glut4 after differentiation. Surprisingly, AS160 knockdown accelerated LRP1 exocytosis in basal and insulin-stimulated adipocytes. These data indicate that AS160 may regulate trafficking into as well as release from GSVs.
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Affiliation(s)
- Paul Duffield Brewer
- From the Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada 89557
| | - Estifanos N Habtemichael
- the Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, and
| | - Irina Romenskaia
- From the Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada 89557
| | - Cynthia Corley Mastick
- From the Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada 89557,
| | - Adelle C F Coster
- the School of Mathematics and Statistics, University of New South Wales, Sydney, New South Wales 2052, Australia
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Fletcher R, Gribben C, Ma X, Burchfield JG, Thomas KC, Krycer JR, James DE, Fazakerley DJ. The role of the Niemann-Pick disease, type C1 protein in adipocyte insulin action. PLoS One 2014; 9:e95598. [PMID: 24752197 PMCID: PMC3994084 DOI: 10.1371/journal.pone.0095598] [Citation(s) in RCA: 17] [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: 12/22/2013] [Accepted: 03/28/2014] [Indexed: 12/12/2022] Open
Abstract
The Niemann-Pick disease, type C1 (NPC1) gene encodes a transmembrane protein involved in cholesterol efflux from the lysosome. SNPs within NPC1 have been associated with obesity and type 2 diabetes, and mice heterozygous or null for NPC1 are insulin resistant. However, the molecular mechanism underpinning this association is currently undefined. This study aimed to investigate the effects of inhibiting NPC1 function on insulin action in adipocytes. Both pharmacological and genetic inhibition of NPC1 impaired insulin action. This impairment was evident at the level of insulin signalling and insulin-mediated glucose transport in the short term and decreased GLUT4 expression due to reduced liver X receptor (LXR) transcriptional activity in the long-term. These data show that cholesterol homeostasis through NPC1 plays a crucial role in maintaining insulin action at multiple levels in adipocytes.
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Affiliation(s)
- Rachael Fletcher
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Christopher Gribben
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Xuiquan Ma
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - James G. Burchfield
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Kristen C. Thomas
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - James R. Krycer
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, New South Wales, Australia
| | - David E. James
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
- Charles Perkins Centre, School of Molecular Bioscience, The University of Sydney, Sydney, Australia
| | - Daniel J. Fazakerley
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
- * E-mail:
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Hodgson L, Tavaré J, Verkade P. Development of a quantitative Correlative Light Electron Microscopy technique to study GLUT4 trafficking. PROTOPLASMA 2014; 251:403-16. [PMID: 24390248 PMCID: PMC3927059 DOI: 10.1007/s00709-013-0597-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 12/12/2013] [Indexed: 05/21/2023]
Abstract
Correlative Light Electron Microscopy (CLEM) combines advantages of light microscopy and electron microscopy in one experiment to deliver information above and beyond the capability of either modality alone. There are many different CLEM techniques, each having its own special advantages but also its technical challenges. It is however the biological question that (should) drive(s) the development and application of a specific CLEM technique in order to provide the answer. Here we describe the development of a CLEM technique that is based on the Tokuyasu cryo immuno-gold labelling technique that has allowed us to quantitatively study GLUT4 trafficking.
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Affiliation(s)
- Lorna Hodgson
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol, BS8 1TD UK
| | - Jeremy Tavaré
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol, BS8 1TD UK
| | - Paul Verkade
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol, BS8 1TD UK
- School of Physiology and Pharmacology, Medical Sciences Building, University Walk, Bristol, BS8 1TD UK
- Wolfson Bioimaging Facility, School of Medical Sciences, University Walk, Bristol, BS8 1TD UK
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Abstract
GLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain.
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Byrne SL, Buckett PD, Kim J, Luo F, Sanford J, Chen J, Enns C, Wessling-Resnick M. Ferristatin II promotes degradation of transferrin receptor-1 in vitro and in vivo. PLoS One 2013; 8:e70199. [PMID: 23894616 PMCID: PMC3720890 DOI: 10.1371/journal.pone.0070199] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Accepted: 06/14/2013] [Indexed: 12/13/2022] Open
Abstract
Previous studies have shown that the small molecule iron transport inhibitor ferristatin (NSC30611) acts by down-regulating transferrin receptor-1 (TfR1) via receptor degradation. In this investigation, we show that another small molecule, ferristatin II (NSC8679), acts in a similar manner to degrade the receptor through a nystatin-sensitive lipid raft pathway. Structural domains of the receptor necessary for interactions with the clathrin pathway do not appear to be necessary for ferristatin II induced degradation of TfR1. While TfR1 constitutively traffics through clathrin-mediated endocytosis, with or without ligand, the presence of Tf blocked ferristatin II induced degradation of TfR1. This effect of Tf was lost in a ligand binding receptor mutant G647A TfR1, suggesting that Tf binding to its receptor interferes with the drug’s activity. Rats treated with ferristatin II have lower TfR1 in liver. These effects are associated with reduced intestinal 59Fe uptake, lower serum iron and transferrin saturation, but no change in liver non-heme iron stores. The observed hypoferremia promoted by degradation of TfR1 by ferristatin II appears to be due to induced hepcidin gene expression.
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Affiliation(s)
- Shaina L. Byrne
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Peter D. Buckett
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Jonghan Kim
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Flora Luo
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Jack Sanford
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Juxing Chen
- Department of Cell Biology, Oregon Health Sciences Center, Portland, Oregon, United States of America
| | - Caroline Enns
- Department of Cell Biology, Oregon Health Sciences Center, Portland, Oregon, United States of America
| | - Marianne Wessling-Resnick
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America
- * E-mail:
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Abstract
GLUT4 is an insulin-regulated glucose transporter that is responsible for insulin-regulated glucose uptake into fat and muscle cells. In the absence of insulin, GLUT4 is mainly found in intracellular vesicles referred to as GLUT4 storage vesicles (GSVs). Here, we summarise evidence for the existence of these specific vesicles, how they are sequestered inside the cell and how they undergo exocytosis in the presence of insulin. In response to insulin stimulation, GSVs fuse with the plasma membrane in a rapid burst and in the continued presence of insulin GLUT4 molecules are internalised and recycled back to the plasma membrane in vesicles that are distinct from GSVs and probably of endosomal origin. In this Commentary we discuss evidence that this delivery process is tightly regulated and involves numerous molecules. Key components include the actin cytoskeleton, myosin motors, several Rab GTPases, the exocyst, SNARE proteins and SNARE regulators. Each step in this process is carefully orchestrated in a sequential and coupled manner and we are beginning to dissect key nodes within this network that determine vesicle-membrane fusion in response to insulin. This regulatory process clearly involves the Ser/Thr kinase AKT and the exquisite manner in which this single metabolic process is regulated makes it a likely target for lesions that might contribute to metabolic disease.
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Affiliation(s)
- Jacqueline Stöckli
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia
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41
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Abstract
Despite daily fasting and feeding, plasma glucose levels are normally maintained within a narrow range owing to the hormones insulin and glucagon. Insulin increases glucose uptake into fat and muscle cells through the regulated trafficking of vesicles that contain glucose transporter type 4 (GLUT4). New insights into insulin signalling reveal that phosphorylation events initiated by the insulin receptor regulate key GLUT4 trafficking proteins, including small GTPases, tethering complexes and the vesicle fusion machinery. These proteins, in turn, control GLUT4 movement through the endosomal system, formation and retention of specialized GLUT4 storage vesicles and targeted exocytosis of these vesicles. Understanding these processes may help to explain the development of insulin resistance in type 2 diabetes and provide new potential therapeutic targets.
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Habegger KM, Hoffman NJ, Ridenour CM, Brozinick JT, Elmendorf JS. AMPK enhances insulin-stimulated GLUT4 regulation via lowering membrane cholesterol. Endocrinology 2012; 153:2130-41. [PMID: 22434076 PMCID: PMC3339638 DOI: 10.1210/en.2011-2099] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
AMP-activated protein kinase (AMPK) enhances glucose transporter GLUT4 regulation. AMPK also suppresses energy-consuming pathways such as cholesterol synthesis. Interestingly, recent in vitro and in vivo data suggest that excess membrane cholesterol impairs GLUT4 regulation. Therefore, this study tested whether a beneficial, GLUT4-regulatory aspect of AMPK stimulation involved cholesterol lowering. Using L6 myotubes stably expressing an exofacial myc-epitope-tagged-GLUT4, AMPK stimulation by 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR; 45 min, 1 mm) or 2,4-dinitrophenol (DNP; 30 min, 200 μm) increased cell surface GLUT4myc labeling by approximately ≈ 25% (P < 0.05). Insulin (20 min, 100 nm) also increased GLUT4myc labeling by about 50% (P < 0.05), which was further enhanced (≈ 25%, P < 0.05) by AICAR or DNP. Consistent with AMPK-mediated suppression of cholesterol synthesis, AICAR and DNP decreased membrane cholesterol by 20-25% (P < 0.05). Whereas AMPK knockdown prevented the enhanced basal and insulin-stimulated GLUT4myc labeling by AICAR and DNP, cholesterol replenishment only blocked the AMPK-associated enhancement in insulin action. Cells cultured in a hyperinsulinemic milieu, resembling conditions in vivo that promote the progression/worsening of insulin resistance, displayed an increase in membrane cholesterol. This occurred concomitantly with a loss of cortical filamentous actin (F-actin) and defects in GLUT4 regulation by insulin. These derangements were prevented by AMPK stimulation. Examination of skeletal muscle from insulin-resistant Zucker rats revealed a similar elevation in membrane cholesterol and loss of F-actin. Lowering cholesterol to control levels restored F-actin structure and insulin sensitivity. In conclusion, these data suggest a novel aspect of GLUT4 regulation by AMPK involves membrane cholesterol lowering. Moreover, this AMPK-mediated process protected against hyperinsulinemia-induced insulin resistance.
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Affiliation(s)
- Kirk M Habegger
- Department of Cellular & Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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Hsu VW, Bai M, Li J. Getting active: protein sorting in endocytic recycling. Nat Rev Mol Cell Biol 2012; 13:323-8. [PMID: 22498832 DOI: 10.1038/nrm3332] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Endocytic recycling returns proteins to the plasma membrane in many physiological contexts. Studies of these events have helped to elucidate fundamental mechanisms that underlie recycling. Recycling was for some time considered to be the exception to a general mechanism of active cargo sorting in multiple intracellular pathways. In recent years, studies have begun to reconcile this seeming disparity and also suggest explanations for why early recycling studies did not detect active sorting. Further articulation of this emerging trend has far-reaching implications for a deeper understanding of many physiological and pathological events that require recycling.
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Affiliation(s)
- Victor W Hsu
- Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachsuetts 02115, USA.
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Abstract
To enhance glucose uptake into muscle and fat cells, insulin stimulates the translocation of GLUT4 glucose transporters from intracellular membranes to the cell surface. This response requires the intersection of insulin signaling and vesicle trafficking pathways, and it is compromised in the setting of overnutrition to cause insulin resistance. Insulin signals through AS160/Tbc1D4 and Tbc1D1 to modulate Rab GTPases and through the Rho GTPase TC10α to act on other targets. In unstimulated cells, GLUT4 is incorporated into specialized storage vesicles containing IRAP, LRP1, sortilin, and VAMP2, which are sequestered by TUG, Ubc9, and other proteins. Insulin mobilizes these vesicles directly to the plasma membrane, and it modulates the trafficking itinerary so that cargo recycles from endosomes during ongoing insulin exposure. Knowledge of how signaling and trafficking pathways are coordinated will be essential to understanding the pathogenesis of diabetes and the metabolic syndrome and may also inform a wide range of other physiologies.
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Affiliation(s)
- Jonathan S Bogan
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8020, USA.
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Habegger KM, Penque BA, Sealls W, Tackett L, Bell LN, Blue EK, Gallagher PJ, Sturek M, Alloosh MA, Steinberg HO, Considine RV, Elmendorf JS. Fat-induced membrane cholesterol accrual provokes cortical filamentous actin destabilisation and glucose transport dysfunction in skeletal muscle. Diabetologia 2012; 55:457-67. [PMID: 22002007 PMCID: PMC3245823 DOI: 10.1007/s00125-011-2334-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Accepted: 09/19/2011] [Indexed: 11/26/2022]
Abstract
AIMS/HYPOTHESIS Diminished cortical filamentous actin (F-actin) has been implicated in skeletal muscle insulin resistance, yet the mechanism(s) is unknown. Here we tested the hypothesis that changes in membrane cholesterol could be a causative factor, as organised F-actin structure emanates from cholesterol-enriched raft microdomains at the plasma membrane. METHODS Skeletal muscle samples from high-fat-fed animals and insulin-sensitive and insulin-resistant human participants were evaluated. The study also used L6 myotubes to directly determine the impact of fatty acids (FAs) on membrane/cytoskeletal variables and insulin action. RESULTS High-fat-fed insulin-resistant animals displayed elevated levels of membrane cholesterol and reduced F-actin structure compared with normal chow-fed animals. Moreover, human muscle biopsies revealed an inverse correlation between membrane cholesterol and whole-body glucose disposal. Palmitate-induced insulin-resistant myotubes displayed membrane cholesterol accrual and F-actin loss. Cholesterol lowering protected against the palmitate-induced defects, whereas characteristically measured defects in insulin signalling were not corrected. Conversely, cholesterol loading of L6 myotube membranes provoked a palmitate-like cytoskeletal/GLUT4 derangement. Mechanistically, we observed a palmitate-induced increase in O-linked glycosylation, an end-product of the hexosamine biosynthesis pathway (HBP). Consistent with HBP activity affecting the transcription of various genes, we observed an increase in Hmgcr, a gene that encodes 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. In line with increased HBP activity transcriptionally provoking a membrane cholesterol-based insulin-resistant state, HBP inhibition attenuated Hmgcr expression and prevented membrane cholesterol accrual, F-actin loss and GLUT4/glucose transport dysfunction. CONCLUSIONS/INTERPRETATION Our results suggest a novel cholesterolgenic-based mechanism of FA-induced membrane/cytoskeletal disorder and insulin resistance.
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Affiliation(s)
- K. M. Habegger
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Membrane Biosciences, Indianapolis, IN USA
| | - B. A. Penque
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Membrane Biosciences, Indianapolis, IN USA
| | - W. Sealls
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Membrane Biosciences, Indianapolis, IN USA
- Indiana University School of Medicine Center for Vascular Biology and Medicine, Indianapolis, IN USA
| | - L. Tackett
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
| | - L. N. Bell
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Department of Medicine, Division of Endocrinology and Metabolism, Indiana University School of Medicine, Indianapolis, IN USA
| | - E. K. Blue
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
| | - P. J. Gallagher
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
| | - M. Sturek
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Vascular Biology and Medicine, Indianapolis, IN USA
| | - M. A. Alloosh
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Vascular Biology and Medicine, Indianapolis, IN USA
| | | | - R. V. Considine
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Department of Medicine, Division of Endocrinology and Metabolism, Indiana University School of Medicine, Indianapolis, IN USA
| | - J. S. Elmendorf
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Rm 308A, 635 Barnhill Drive, Indianapolis, IN 46202-5120 USA
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN USA
- Indiana University School of Medicine Center for Diabetes Research, Indianapolis, IN USA
- Indiana University School of Medicine Center for Membrane Biosciences, Indianapolis, IN USA
- Indiana University School of Medicine Center for Vascular Biology and Medicine, Indianapolis, IN USA
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Strålfors P. Caveolins and Caveolae, Roles in Insulin Signalling and Diabetes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 729:111-26. [DOI: 10.1007/978-1-4614-1222-9_8] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Stöckli J, Fazakerley DJ, Coster ACF, Holman GD, James DE. Muscling in on GLUT4 kinetics. Commun Integr Biol 2011; 3:260-2. [PMID: 20714409 DOI: 10.4161/cib.3.3.11457] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Accepted: 02/10/2010] [Indexed: 01/14/2023] Open
Abstract
Insulin triggers glucose uptake into muscle and adipose tissue by stimulating the translocation of the glucose transporter glut4 from intracellular vesicles to the plasma membrane (pm). insulin leads to a rapid increase in glut4 at the pm from approximately 5% to 40-50%. this effect is time and dose-dependent, reaching a new steady state after 30 min of insulin stimulation. previous kinetic analyses in adipocytes has revealed that this is regulated by two mechanisms-increasing the amount of glut4 in the endosomal recycling system and increasing the exocytosis rate constant. fazakerley et al.1 focuses on GLUT4 kinetics in the L6 skeletal muscle cell line. Despite displaying a similar redistribution of GLUT4 to the cell surface with insulin to that seen in adipocytes, the mechanism for this effect in L6 cells was completely different. Insulin had a modest effect to increase the amount of GLUT4 in the recycling system with the dominant effect being on reduction of the endocytosis rate constant. Similar findings were observed with AMPK agonists. These studies indicate that different cell types are capable of achieving the same cell biological endpoint but using completely distinct mechanisms.
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Berenguer M, Zhang J, Bruce MC, Martinez L, Gonzalez T, Gurtovenko AA, Xu T, Le Marchand-Brustel Y, Govers R. Dimethyl sulfoxide enhances GLUT4 translocation through a reduction in GLUT4 endocytosis in insulin-stimulated 3T3-L1 adipocytes. Biochimie 2011; 93:697-709. [DOI: 10.1016/j.biochi.2010.12.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Accepted: 12/21/2010] [Indexed: 01/14/2023]
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Foley K, Boguslavsky S, Klip A. Endocytosis, recycling, and regulated exocytosis of glucose transporter 4. Biochemistry 2011; 50:3048-61. [PMID: 21405107 DOI: 10.1021/bi2000356] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Glucose transporter 4 (GLUT4) is responsible for the uptake of glucose into muscle and adipose tissues. Under resting conditions, GLUT4 is dynamically retained through idle cycling among selective intracellular compartments, from whence it undergoes slow recycling to the plasma membrane (PM). This dynamic retention can be released by command from intracellular signals elicited by insulin and other stimuli, which result in 2-10-fold increases in the surface level of GLUT4. Insulin-derived signals promote translocation of GLUT4 to the PM from a specialized compartment termed GLUT4 storage vesicles (GSV). Much effort has been devoted to the characterization of the intracellular compartments and dynamics of GLUT4 cycling and to the signals by which GLUT4 is sorted into, and recruited from, GSV. This review summarizes our understanding of intracellular GLUT4 traffic during its internalization from the membrane, its slow, constitutive recycling, and its regulated exocytosis in response to insulin. In spite of specific differences in GLUT4 dynamic behavior in adipose and muscle cells, the generalities of its endocytic and exocytic itineraries are consistent and an array of regulatory proteins that regulate each vesicular traffic event emerges from these cell systems.
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Affiliation(s)
- Kevin Foley
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario M4G 1X8, Canada
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50
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Abstract
One of the most important metabolic actions of insulin is catalysing glucose uptake into skeletal muscle and adipose tissue. This is accomplished via activation of the phosphatidylinositol-3-kinase/Akt signalling pathway and subsequent translocation of GLUT4 from intracellular storage vesicles to the plasma membrane. As such, this represents an ideal system for studying the convergence of signal transduction and protein trafficking. The GLUT4 translocation process is complex, but can be dissected into at least four discrete trafficking steps. This raises the question as to which of these is the major regulated step in insulin-stimulated GLUT4 translocation. Numerous molecules have been reported to regulate GLUT4 trafficking. However, with the exception of TBC1D4, the molecular details of these distal signalling arms of the insulin signalling network and how they modify distinct steps of GLUT4 trafficking have not been established. We discuss the need to adopt a more global approach to expand and deepen our understanding of the molecular processes underpinning this system. Strategies that facilitate the generation of detailed models of the entire insulin signalling network will enable us to identify the critical nodes that control GLUT4 traffic and decipher emergent properties of the system that are not currently apparent.
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Affiliation(s)
- Alexander F Rowland
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia
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