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Tropomodulin3 is a novel Akt2 effector regulating insulin-stimulated GLUT4 exocytosis through cortical actin remodeling. Nat Commun 2015; 6:5951. [PMID: 25575350 PMCID: PMC4354152 DOI: 10.1038/ncomms6951] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 11/25/2014] [Indexed: 12/19/2022] Open
Abstract
Akt2 and its downstream effectors mediate insulin-stimulated GLUT4-storage vesicle (GSV) translocation and fusion with the plasma membrane (PM). Using mass spectrometry, we identify actin-capping protein Tropomodulin 3 (Tmod3) as an Akt2-interacting partner in 3T3-L1 adipocytes. We demonstrate that Tmod3 is phosphorylated at Ser71 on insulin-stimulated Akt2 activation, and Ser71 phosphorylation is required for insulin-stimulated GLUT4 PM insertion and glucose uptake. Phosphorylated Tmod3 regulates insulin-induced actin remodelling, an essential step for GSV fusion with the PM. Furthermore, the interaction of Tmod3 with its cognate tropomyosin partner, Tm5NM1 is necessary for GSV exocytosis and glucose uptake. Together these results establish Tmod3 as a novel Akt2 effector that mediates insulin-induced cortical actin remodelling and subsequent GLUT4 membrane insertion. Our findings suggest that defects in cytoskeletal remodelling may contribute to impaired GLUT4 exocytosis and glucose uptake.
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52
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Govers R. Molecular mechanisms of GLUT4 regulation in adipocytes. DIABETES & METABOLISM 2014; 40:400-10. [DOI: 10.1016/j.diabet.2014.01.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [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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Abstract
Protein palmitoylation, by modulating the dynamic interaction between protein and cellular membrane, is involved in a wide range of biological processes, including protein trafficking, sorting, sub-membrane partitioning, protein-protein interaction and cell signaling. To explore the role of protein palmitoylation in adipocytes, we have performed proteomic analysis of palmitoylated proteins in adipose tissue and 3T3-L1 adipocytes and identified more than 800 putative palmitoylated proteins. These include various transporters, enzymes required for lipid and glucose metabolism, regulators of protein trafficking and signaling molecules. Of note, key proteins involved in membrane translocation of the glucose-transporter Glut4 including IRAP, Munc18c, AS160 and Glut4, and signaling proteins in the JAK-STAT pathway including JAK1 and 2, STAT1, 3 and 5A and SHP2 in JAK-STAT, were palmitoylated in cultured adipocytes and primary adipose tissue. Further characterization showed that palmitoylation of Glut4 and IRAP was altered in obesity, and palmitoylation of JAK1 played a regulatory role in JAK1 intracellular localization. Overall, our studies provide evidence to suggest a novel and potentially regulatory role for protein palmitoylation in adipocyte function.
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Zorman S, Rebane AA, Ma L, Yang G, Molski MA, Coleman J, Pincet F, Rothman JE, Zhang Y. Common intermediates and kinetics, but different energetics, in the assembly of SNARE proteins. eLife 2014; 3:e03348. [PMID: 25180101 PMCID: PMC4166003 DOI: 10.7554/elife.03348] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 08/29/2014] [Indexed: 01/10/2023] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are evolutionarily conserved machines that couple their folding/assembly to membrane fusion. However, it is unclear how these processes are regulated and function. To determine these mechanisms, we characterized the folding energy and kinetics of four representative SNARE complexes at a single-molecule level using high-resolution optical tweezers. We found that all SNARE complexes assemble by the same step-wise zippering mechanism: slow N-terminal domain (NTD) association, a pause in a force-dependent half-zippered intermediate, and fast C-terminal domain (CTD) zippering. The energy release from CTD zippering differs for yeast (13 kBT) and neuronal SNARE complexes (27 kBT), and is concentrated at the C-terminal part of CTD zippering. Thus, SNARE complexes share a conserved zippering pathway and polarized energy release to efficiently drive membrane fusion, but generate different amounts of zippering energy to regulate fusion kinetics. DOI:http://dx.doi.org/10.7554/eLife.03348.001 Many processes in living things need molecules to be transported within, or between, cells. For example, damaged or waste molecules are transported within a cell to structures that can break the molecules down, while nerve impulses are transmitted from one neuron to the next via the release of signaling molecules. Cells—and the compartments within cells—are surrounded by membranes that act as barriers to certain molecules. Vesicles are small, membrane-enclosed packages that are used to transport molecules between different membranes; and in order to release its cargo, a vesicle must fuse with its target membrane. To fuse like this, the forces that act to push membranes away from one another need to be overcome. Proteins called SNARES, which are embedded in both membranes, are the molecular engines that power the fusion process. Once the SNARE proteins from the vesicle and the target membrane bind, they assemble into a more compact complex that pulls the two membranes close together and allows fusion to take place. The final shape of an assembled SNARE complex is essentially the same for all SNARE complexes; however, it is not known whether all of these complexes fold using the same method. Now Zorman et al. have used optical tweezers—an instrument that uses a highly focused laser beam to hold and manipulate microscopic objects—to observe the folding and unfolding of four different types of SNARE complex. All four SNARE complexes followed the same step-by-step process: the leading ends of the SNARE proteins slowly bound to each other; the process paused; then the rest of the proteins rapidly ‘zippered’ together. Zorman et al. revealed that, although the steps in the processes were the same, the energy released in the last step was different when different complexes assembled. This suggests that the energy released by the ‘zippering’ of different SNARE proteins is optimized to match the required speed of different membrane fusion events. Furthermore, Zorman et al. propose that the reason why the majority of energy is released in the later stages of complex assembly is because this is when the repulsion between the two membranes is strongest. The discoveries of Zorman et al. will now aid future efforts aimed at understanding better how the numerous other proteins that interact with SNARE proteins regulate the process of membrane fusion. DOI:http://dx.doi.org/10.7554/eLife.03348.002
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Affiliation(s)
- Sylvain Zorman
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | | | - Lu Ma
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Guangcan Yang
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Matthew A Molski
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Jeff Coleman
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Frederic Pincet
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
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Foley KP, Klip A. Dynamic GLUT4 sorting through a syntaxin-6 compartment in muscle cells is derailed by insulin resistance-causing ceramide. Biol Open 2014; 3:314-25. [PMID: 24705014 PMCID: PMC4021353 DOI: 10.1242/bio.20147898] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
GLUT4 constitutively recycles between the plasma membrane and intracellular depots. Insulin shifts this dynamic equilibrium towards the plasma membrane by recruiting GLUT4 to the plasma membrane from insulin-responsive vesicles. Muscle is the primary site for dietary glucose deposition; however, how GLUT4 sorts into insulin-responsive vesicles, and if and how insulin resistance affects this process, is unknown. In L6 myoblasts stably expressing myc-tagged GLUT4, we analyzed the intracellular itinerary of GLUT4 as it internalizes from the cell surface and examined if such sorting is perturbed by C2-ceramide, a lipid metabolite causing insulin resistance. Surface-labeled GLUT4myc that internalized for 30 min accumulated in a Syntaxin-6 (Stx6)- and Stx16-positive perinuclear sub-compartment devoid of furin or internalized transferrin, and displayed insulin-responsive re-exocytosis. C2-ceramide dispersed the Stx6-positive sub-compartment and prevented insulin-responsive re-exocytosis of internalized GLUT4myc, even under conditions not affecting insulin-stimulated signaling towards Akt. Microtubule disruption with nocodazole prevented pre-internalized GLUT4myc from reaching the Stx6-positive perinuclear sub-compartment and from undergoing insulin-responsive exocytosis. Removing nocodazole allowed both parameters to recover, suggesting that the Stx6-positive perinuclear sub-compartment was required for GLUT4 insulin-responsiveness. Accordingly, Stx6 knockdown inhibited by ∼50% the ability of internalized GLUT4myc to undergo insulin-responsive re-exocytosis without altering its overall perinuclear accumulation. We propose that Stx6 defines the insulin-responsive compartment in muscle cells. Our data are consistent with a model where ceramide could cause insulin resistance by altering intracellular GLUT4 sorting.
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Affiliation(s)
- Kevin P Foley
- Program in Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Amira Klip
- Program in Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada
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Matz M, Schumacher K, Hatlapatka K, Lorenz D, Baumann K, Rustenbeck I. Observer-independent quantification of insulin granule exocytosis and pre-exocytotic mobility by TIRF microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:206-218. [PMID: 24230985 DOI: 10.1017/s1431927613013767] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Total internal reflection fluorescence microscopy of fluorescently labeled secretory granules permits monitoring of exocytosis and the preceding granule behavior in one experiment. While observer-dependent evaluation may be sufficient to quantify exocytosis, most of the other information contained in the video files cannot be accessed this way. The present program performs observer-independent detection of exocytosis and tracking of the entire submembrane population of insulin granules. A precondition is the exact localization of the peak of the granule fluorescence. Tracking is based on the peak base radius, peak intensity, and the precrossing itineraries. Robustness of the tracking was shown by simulated tracks of original granule patterns. Mobility in the X-Y dimension is described by the caging diameter which in contrast to the widely used mean square displacement has an inherent time resolution. Observer-independent detection of exocytosis in MIN6 cells labeled with insulin-EGFP is based on the maximal decrease in fluorescence intensity and position of the centroid of the dissipating cloud of released material. Combining the quantification of KCl-induced insulin exocytosis with the analysis of prefusion mobility showed that during the last 3 s pre-exocytotic granules had a smaller caging diameter than control granules and that it increased significantly immediately before fusion.
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Affiliation(s)
- Magnus Matz
- Institute of Medicinal and Pharmaceutical Chemistry, University of Braunschweig, Braunschweig D38106, Germany
| | - Kirstin Schumacher
- Institute of Pharmacology and Toxicology, University of Braunschweig, Braunschweig D38106, Germany
| | - Kathrin Hatlapatka
- Institute of Pharmacology and Toxicology, University of Braunschweig, Braunschweig D38106, Germany
| | - Dirk Lorenz
- Institute of Analysis and Algebra, University of Braunschweig, Braunschweig D38106, Germany
| | - Knut Baumann
- Institute of Medicinal and Pharmaceutical Chemistry, University of Braunschweig, Braunschweig D38106, Germany
| | - Ingo Rustenbeck
- Institute of Pharmacology and Toxicology, University of Braunschweig, Braunschweig D38106, Germany
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57
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Insulin stimulates syntaxin4 SNARE complex assembly via a novel regulatory mechanism. Mol Cell Biol 2014; 34:1271-9. [PMID: 24469400 DOI: 10.1128/mcb.01203-13] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Insulin stimulates glucose transport into fat and muscle cells by increasing the exocytic trafficking rate of the GLUT4 facilitative glucose transporter from intracellular stores to the plasma membrane. Delivery of GLUT4 to the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for the first time that insulin stimulation causes an increase in syntaxin4-containing SNARE complex formation in adipocytes. Furthermore, we demonstrate that insulin brings about this increase in SNARE complex formation by mobilizing a pool of syntaxin4 held in an inactive state under basal conditions. Finally, we have identified phosphorylation of the regulatory protein Munc18c, a direct target of the insulin receptor, as a molecular switch to coordinate this process. Hence, this report provides molecular detail of how the cell alters membrane traffic in response to an external stimulus, in this case, insulin.
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58
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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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Crivat G, Lizunov VA, Li CR, Stenkula KG, Zimmerberg J, Cushman SW, Pick L. Insulin stimulates translocation of human GLUT4 to the membrane in fat bodies of transgenic Drosophila melanogaster. PLoS One 2013; 8:e77953. [PMID: 24223128 PMCID: PMC3819322 DOI: 10.1371/journal.pone.0077953] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 09/05/2013] [Indexed: 12/23/2022] Open
Abstract
The fruit fly Drosophila melanogaster is an excellent model system for studies of genes controlling development and disease. However, its applicability to physiological systems is less clear because of metabolic differences between insects and mammals. Insulin signaling has been studied in mammals because of relevance to diabetes and other diseases but there are many parallels between mammalian and insect pathways. For example, deletion of Drosophila Insulin-Like Peptides resulted in 'diabetic' flies with elevated circulating sugar levels. Whether this situation reflects failure of sugar uptake into peripheral tissues as seen in mammals is unclear and depends upon whether flies harbor the machinery to mount mammalian-like insulin-dependent sugar uptake responses. Here we asked whether Drosophila fat cells are competent to respond to insulin with mammalian-like regulated trafficking of sugar transporters. Transgenic Drosophila expressing human glucose transporter-4 (GLUT4), the sugar transporter expressed primarily in insulin-responsive tissues, were generated. After expression in fat bodies, GLUT4 intracellular trafficking and localization were monitored by confocal and total internal reflection fluorescence microscopy (TIRFM). We found that fat body cells responded to insulin with increased GLUT4 trafficking and translocation to the plasma membrane. While the amplitude of these responses was relatively weak in animals reared on a standard diet, it was greatly enhanced in animals reared on sugar-restricted diets, suggesting that flies fed standard diets are insulin resistant. Our findings demonstrate that flies are competent to mobilize translocation of sugar transporters to the cell surface in response to insulin. They suggest that Drosophila fat cells are primed for a response to insulin and that these pathways are down-regulated when animals are exposed to constant, high levels of sugar. Finally, these studies are the first to use TIRFM to monitor insulin-signaling pathways in Drosophila, demonstrating the utility of TIRFM of tagged sugar transporters to monitor signaling pathways in insects.
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Affiliation(s)
- Georgeta Crivat
- Department of Entomology, University of Maryland, College Park, Maryland, United States of America
| | - Vladimir A. Lizunov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Caroline R. Li
- Department of Entomology, University of Maryland, College Park, Maryland, United States of America
| | - Karin G. Stenkula
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Joshua Zimmerberg
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Samuel W. Cushman
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Leslie Pick
- Department of Entomology, University of Maryland, College Park, Maryland, United States of America
- * E-mail:
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60
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Chen Y, Lippincott-Schwartz J. Insulin triggers surface-directed trafficking of sequestered GLUT4 storage vesicles marked by Rab10. Small GTPases 2013; 4:193-7. [PMID: 24030635 PMCID: PMC3976978 DOI: 10.4161/sgtp.26471] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Understanding how glucose transporter isoform 4 (GLUT4) redistributes to the plasma membrane during insulin stimulation is a major goal of glucose transporter research. GLUT4 molecules normally reside in numerous intracellular compartments, including specialized storage vesicles and early/recycling endosomes. It is unclear how these diverse compartments respond to insulin stimulation to deliver GLUT4 molecules to the plasma membrane. For example, do they fuse with each other first or remain as separate compartments with different trafficking characteristics? Our recent live cell imaging studies are helping to clarify these issues. Using Rab proteins as specific markers to distinguish between storage vesicles and endosomes containing GLUT4, we demonstrate that it is primarily internal GLUT4 storage vesicles (GSVs) marked by Rab10 that approach and fuse at the plasma membrane and GSVs don’t interact with endosomes on their way to the plasma membrane. These new findings add strong support to the model that GSV release from intracellular retention plays a major role in supplying GLUT4 molecules onto the PM under insulin stimulation.
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Affiliation(s)
- Yu Chen
- The Eugene Kennedy Shriver National Institute of Child Health and Human Development; National Institutes of Health; Bethesda, MD USA
| | - Jennifer Lippincott-Schwartz
- The Eugene Kennedy Shriver National Institute of Child Health and Human Development; National Institutes of Health; Bethesda, MD USA
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61
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Lizunov VA, Lee JP, Skarulis MC, Zimmerberg J, Cushman SW, Stenkula KG. Impaired tethering and fusion of GLUT4 vesicles in insulin-resistant human adipose cells. Diabetes 2013; 62:3114-9. [PMID: 23801575 PMCID: PMC3749349 DOI: 10.2337/db12-1741] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Systemic glucose homeostasis is profoundly influenced by adipose cell function. Here we investigated GLUT4 dynamics in living adipose cells from human subjects with varying BMI and insulin sensitivity index (Si) values. Cells were transfected with hemagglutinin (HA)-GLUT4-green fluorescent protein (GFP)/mCherry (red fluorescence), and were imaged live using total internal reflection fluorescence and confocal microscopy. HA-GLUT4-GFP redistribution to the plasma membrane (PM) was quantified by surface-exposed HA epitope. In the basal state, GLUT4 storage vesicle (GSV) trafficking to and fusion with the PM were invariant with donor subject Si, as was total cell-surface GLUT4. In cells from insulin-sensitive subjects, insulin augmented GSV tethering and fusion approximately threefold, resulting in a corresponding increase in total PM GLUT4. However, with decreasing Si, these effects diminished progressively. All insulin-induced effects on GLUT4 redistribution and trafficking correlated strongly with Si and only weakly with BMI. Thus, while basal GLUT4 dynamics and total cell-surface GLUT4 are intact in human adipose cells, independent of donor Si, cells from insulin-resistant donors show markedly impaired GSV tethering and fusion responses to insulin, even after overnight culture. This altered insulin responsiveness is consistent with the hypothesis that adipose cellular dysfunction is a primary contributor to systemic metabolic dysfunction.
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Affiliation(s)
- Vladimir A. Lizunov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Jo-Ping Lee
- Experimental Diabetes, Metabolism, and Nutrition Section, National Institutes of Health, Bethesda, Maryland
- Corresponding author: Joshua Zimmerberg,
| | - Monica C. Skarulis
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Joshua Zimmerberg
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Samuel W. Cushman
- Experimental Diabetes, Metabolism, and Nutrition Section, National Institutes of Health, Bethesda, Maryland
| | - Karin G. Stenkula
- Experimental Diabetes, Metabolism, and Nutrition Section, National Institutes of Health, Bethesda, Maryland
- Experimental Medical Sciences, Lund University, Lund, Sweden
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Huang G, Buckler-Pena D, Nauta T, Singh M, Asmar A, Shi J, Kim JY, Kandror KV. Insulin responsiveness of glucose transporter 4 in 3T3-L1 cells depends on the presence of sortilin. Mol Biol Cell 2013; 24:3115-22. [PMID: 23966466 PMCID: PMC3784384 DOI: 10.1091/mbc.e12-10-0765] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Insulin-dependent translocation of Glut4 to the plasma membrane of fat and skeletal muscle cells plays the key role in postprandial clearance of blood glucose. In undifferentiated cells, insulin responsiveness of Glut4 depends on the presence of sortilin, whereas sortilin responds to insulin regardless of Glut4 expression. Insulin-dependent translocation of glucose transporter 4 (Glut4) to the plasma membrane of fat and skeletal muscle cells plays the key role in postprandial clearance of blood glucose. Glut4 represents the major cell-specific component of the insulin-responsive vesicles (IRVs). It is not clear, however, whether the presence of Glut4 in the IRVs is essential for their ability to respond to insulin stimulation. We prepared two lines of 3T3-L1 cells with low and high expression of myc7-Glut4 and studied its translocation to the plasma membrane upon insulin stimulation, using fluorescence-assisted cell sorting and cell surface biotinylation. In undifferentiated 3T3-L1 preadipocytes, translocation of myc7-Glut4 was low regardless of its expression levels. Coexpression of sortilin increased targeting of myc7-Glut4 to the IRVs, and its insulin responsiveness rose to the maximal levels observed in fully differentiated adipocytes. Sortilin ectopically expressed in undifferentiated cells was translocated to the plasma membrane regardless of the presence or absence of myc7-Glut4. AS160/TBC1D4 is expressed at low levels in preadipocytes but is induced in differentiation and provides an additional mechanism for the intracellular retention and insulin-stimulated release of Glut4.
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Affiliation(s)
- Guanrong Huang
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
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63
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Sadacca LA, Bruno J, Wen J, Xiong W, McGraw TE. Specialized sorting of GLUT4 and its recruitment to the cell surface are independently regulated by distinct Rabs. Mol Biol Cell 2013; 24:2544-57. [PMID: 23804653 PMCID: PMC3744946 DOI: 10.1091/mbc.e13-02-0103] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
RAB10 and RAB14 function at sequential steps of insulin-stimulated GLUT4 translocation to the plasma membrane. RAB14 functions upstream of RAB10 in GLUT4 sorting to the specialized transport vesicles, and RAB10 and its GAP protein comprise the main signaling module that regulates the accumulation of GLUT4 transport vesicles at the plasma membrane. Adipocyte glucose uptake in response to insulin is essential for physiological glucose homeostasis: stimulation of adipocytes with insulin results in insertion of the glucose transporter GLUT4 into the plasma membrane and subsequent glucose uptake. Here we establish that RAB10 and RAB14 are key regulators of GLUT4 trafficking that function at independent, sequential steps of GLUT4 translocation. RAB14 functions upstream of RAB10 in the sorting of GLUT4 to the specialized transport vesicles that ferry GLUT4 to the plasma membrane. RAB10 and its GTPase-activating protein (GAP) AS160 comprise the principal signaling module downstream of insulin receptor activation that regulates the accumulation of GLUT4 transport vesicles at the plasma membrane. Although both RAB10 and RAB14 are regulated by the GAP activity of AS160 in vitro, only RAB10 is under the control of AS160 in vivo. Insulin regulation of the pool of RAB10 required for GLUT4 translocation occurs through regulation of AS160, since activation of RAB10 by DENND4C, its GTP exchange factor, does not require insulin stimulation.
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Affiliation(s)
- L Amanda Sadacca
- Department of Biochemistry, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
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64
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Chen Y, Lippincott-Schwartz J. Rab10 delivers GLUT4 storage vesicles to the plasma membrane. Commun Integr Biol 2013; 6:e23779. [PMID: 23713133 PMCID: PMC3656013 DOI: 10.4161/cib.23779] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 01/25/2013] [Indexed: 12/25/2022] Open
Abstract
The glucose transporter, GLUT4, redistributes to the plasma membrane (PM) upon insulin stimulation, but also recycles through endosomal compartments. Different Rab proteins control these transport itineraries of GLUT4. However, the specific roles played by different Rab proteins in GLUT4 trafficking has been difficult to assess, primarily due to the complexity of endomembrane organization and trafficking. To address this problem, we recently performed advanced live cell imaging using total internal reflection fluorescence (TIRF) microscopy, which images objects ~150 nm from the PM, directly visualizing GLUT4 trafficking in response to insulin stimulation. Using IRAP-pHluorin to selectively label GSVs undergoing PM fusion in response to insulin, we identified Rab10 as the only Rab protein that binds this compartment. Rab14 was found to label transferrin-positive, endosomal compartments containing GLUT4. These also could fuse with the PM in response to insulin, albeit more slowly. Several other Rab proteins, including Rab4A, 4B and 8A, were found to mediate GLUT4 intra-endosomal recycling, serving to internalize surface-bound GLUT4 into endosomal compartments for ultimate delivery to GSVs. Thus, multiple Rab proteins regulate the circulation of GLUT4 molecules within the endomembrane system, maintaining optimal insulin responsiveness within cells.
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Affiliation(s)
- Yu Chen
- The Eugene Kennedy Shriver National Institute of Child Health and Human Development; National Institutes of Health; Bethesda, MD USA
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Yu H, Rathore SS, Shen J. Synip arrests soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent membrane fusion as a selective target membrane SNARE-binding inhibitor. J Biol Chem 2013; 288:18885-93. [PMID: 23665562 DOI: 10.1074/jbc.m113.465450] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The vesicle fusion reaction in regulated exocytosis requires the concerted action of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) core fusion engine and a group of SNARE-binding regulatory factors. The regulatory mechanisms of vesicle fusion remain poorly understood in most exocytic pathways. Here, we reconstituted the SNARE-dependent vesicle fusion reaction of GLUT4 exocytosis in vitro using purified components. Using this defined fusion system, we discovered that the regulatory factor synip binds to GLUT4 exocytic SNAREs and inhibits the docking, lipid mixing, and content mixing of the fusion reaction. Synip arrests fusion by binding the target membrane SNARE (t-SNARE) complex and preventing the initiation of ternary SNARE complex assembly. Although synip also interacts with the syntaxin-4 monomer, it does not inhibit the pairing of syntaxin-4 with SNAP-23. Interestingly, synip selectively arrests the fusion reactions reconstituted with its cognate SNAREs, suggesting that the defined system recapitulates the biological functions of the vesicle fusion proteins. We further showed that the inhibitory function of synip is dominant over the stimulatory activity of Sec1/Munc18 proteins. Importantly, the inhibitory function of synip is distinct from how other fusion inhibitors arrest SNARE-dependent membrane fusion and therefore likely represents a novel regulatory mechanism of vesicle fusion.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA
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Lizunov VA, Stenkula K, Troy A, Cushman SW, Zimmerberg J. Insulin regulates Glut4 confinement in plasma membrane clusters in adipose cells. PLoS One 2013; 8:e57559. [PMID: 23520472 PMCID: PMC3592853 DOI: 10.1371/journal.pone.0057559] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 01/22/2013] [Indexed: 01/12/2023] Open
Abstract
Insulin-stimulated delivery of glucose transporter-4 (GLUT4) to the plasma membrane (PM) is the hallmark of glucose metabolism. In this study we examined insulin’s effects on GLUT4 organization in PM of adipose cells by direct microscopic observation of single monomers tagged with photoswitchable fluorescent protein. In the basal state, after exocytotic delivery only a fraction of GLUT4 is dispersed into the PM as monomers, while most of the GLUT4 stays at the site of fusion and forms elongated clusters (60–240 nm). GLUT4 monomers outside clusters diffuse freely and do not aggregate with other monomers. In contrast, GLUT4 molecule collision with an existing cluster can lead to immediate confinement and association with that cluster. Insulin has three effects: it shifts the fraction of dispersed GLUT4 upon delivery, it augments the dissociation of GLUT4 monomers from clusters ∼3-fold and it decreases the rate of endocytic uptake. All together these three effects of insulin shift most of the PM GLUT4 from clustered to dispersed states. GLUT4 confinement in clusters represents a novel kinetic mechanism for insulin regulation of glucose homeostasis.
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Affiliation(s)
- Vladimir A. Lizunov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Karin Stenkula
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Aaron Troy
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Samuel W. Cushman
- Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Joshua Zimmerberg
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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Otterstrom J, van Oijen AM. Visualization of membrane fusion, one particle at a time. Biochemistry 2013; 52:1654-68. [PMID: 23421412 DOI: 10.1021/bi301573w] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Protein-mediated fusion between phospholipid bilayers is a fundamental and necessary mechanism for many cellular processes. The short-lived nature of the intermediate states visited during fusion makes it challenging to capture precise kinetic information using classical, ensemble-averaging biophysical techniques. Recently, a number of single-particle fluorescence microscopy-based assays that allow researchers to obtain highly quantitative data about the fusion process by observing individual fusion events in real time have been developed. These assays depend upon changes in the acquired fluorescence signal to provide a direct readout for transitions between the various fusion intermediates. The resulting data yield meaningful and detailed kinetic information about the transitory states en route to productive membrane fusion. In this review, we highlight recent in vitro and in vivo studies of membrane fusion at the single-particle level in the contexts of viral membrane fusion and SNARE-mediated synaptic vesicle fusion. These studies afford insight into mechanisms of coordination between fusion-mediating proteins as well as coordination of the overall fusion process with other cellular processes. The development of single-particle approaches to investigate membrane fusion and their successful application to a number of model systems have resulted in a new experimental paradigm and open up considerable opportunities to extend these methods to other biological processes that involve membrane fusion.
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Affiliation(s)
- Jason Otterstrom
- Harvard Biophysics Program, Harvard Medical School , 240 Longwood Avenue, Boston, Massachusetts 02115, United States
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Burchfield JG, Lu J, Fazakerley DJ, Tan SX, Ng Y, Mele K, Buckley MJ, Han W, Hughes WE, James DE. Novel systems for dynamically assessing insulin action in live cells reveals heterogeneity in the insulin response. Traffic 2013; 14:259-73. [PMID: 23252720 DOI: 10.1111/tra.12035] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 12/13/2012] [Accepted: 12/18/2012] [Indexed: 12/23/2022]
Abstract
Regulated GLUT4 trafficking is a key action of insulin. Quantitative stepwise analysis of this process provides a powerful tool for pinpointing regulatory nodes that contribute to insulin regulation and insulin resistance. We describe a novel GLUT4 construct and workflow for the streamlined dissection of GLUT4 trafficking; from simple high throughput screens to high resolution analyses of individual vesicles. We reveal single cell heterogeneity in insulin action highlighting the utility of this approach - each cell displayed a unique and highly reproducible insulin response, implying that each cell is hard-wired to produce a specific output in response to a given stimulus. These data highlight that the response of a cell population to insulin is underpinned by extensive heterogeneity at the single cell level. This heterogeneity is pre-programmed within each cell and is not the result of intracellular stochastic events.
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Affiliation(s)
- James G Burchfield
- Diabetes and Obesity Research Program, The Garvan Institute of Medical Research, Sydney, NSW, 2010, Australia
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Wang H, Ducommun S, Quan C, Xie B, Li M, Wasserman D, Sakamoto K, Mackintosh C, Chen S. AS160 deficiency causes whole-body insulin resistance via composite effects in multiple tissues. Biochem J 2013; 449:479-89. [PMID: 23078342 PMCID: PMC3685216 DOI: 10.1042/bj20120702] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Revised: 10/02/2012] [Accepted: 10/19/2012] [Indexed: 11/17/2022]
Abstract
AS160 (Akt substrate of 160 kDa) is a Rab GTPase-activating protein implicated in insulin control of GLUT4 (glucose transporter 4) trafficking. In humans, a truncation mutation (R363X) in one allele of AS160 decreased the expression of the protein and caused severe postprandial hyperinsulinaemia during puberty. To complement the limited studies possible in humans, we generated an AS160-knockout mouse. In wild-type mice, AS160 expression is relatively high in adipose tissue and soleus muscle, low in EDL (extensor digitorum longus) muscle and detectable in liver only after enrichment. Despite having lower blood glucose levels under both fasted and random-fed conditions, the AS160-knockout mice exhibited insulin resistance in both muscle and liver in a euglycaemic clamp study. Consistent with this paradoxical phenotype, basal glucose uptake was higher in AS160-knockout primary adipocytes and normal in isolated soleus muscle, but their insulin-stimulated glucose uptake and overall GLUT4 levels were markedly decreased. In contrast, insulin-stimulated glucose uptake and GLUT4 levels were normal in EDL muscle. The liver also contributes to the AS160-knockout phenotype via hepatic insulin resistance, elevated hepatic expression of phosphoenolpyruvate carboxykinase isoforms and pyruvate intolerance, which are indicative of increased gluconeogenesis. Overall, as well as its catalytic function, AS160 influences expression of other proteins, and its loss deregulates basal and insulin-regulated glucose homoeostasis, not only in tissues that normally express AS160, but also by influencing liver function.
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Key Words
- akt substrate of 160 kda (as160)
- glucose transport
- insulin resistance
- liver
- muscle
- as160, akt substrate of 160 kda
- edl, extensor digitorum longus
- fbp-1, fructose-1,6-bisphosphatase 1
- gap, gtpase-activating protein
- gapdh, glyceraldehyde-3-phosphate dehydrogenase
- gir, glucose infusion rate
- glut, glucose transporter
- gsk3, glycogen synthase kinase 3
- mbp, myelin basic protein
- pck/pepck, phosphoenolpyruvate carboxykinase
- pkb, protein kinase b
- pm, plasma membrane
- rer, respiratory exchange ratio
- ta, tibialis anterior
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Affiliation(s)
- Hong Yu Wang
- *MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Pukou District, Nanjing 210061, China
| | - Serge Ducommun
- †MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
- ‡Nestlé Institute of Health Sciences SA, Campus EPFL, Quartier de l'Innovation, Bâtiment G, 1015 Lausanne, Switzerland
| | - Chao Quan
- *MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Pukou District, Nanjing 210061, China
| | - Bingxian Xie
- *MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Pukou District, Nanjing 210061, China
| | - Min Li
- *MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Pukou District, Nanjing 210061, China
| | - David H. Wasserman
- §Department of Molecular Physiology and Biophysics, Vanderbilt University, School of Medicine, 2200 Pierce Ave, Nashville, TN 37232, U.S.A
| | - Kei Sakamoto
- †MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
- ‡Nestlé Institute of Health Sciences SA, Campus EPFL, Quartier de l'Innovation, Bâtiment G, 1015 Lausanne, Switzerland
| | - Carol Mackintosh
- †MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
- ‖Division of Cell and Developmental Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K
| | - Shuai Chen
- *MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Pukou District, Nanjing 210061, China
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A diffusion model for detecting and classifying vesicle fusion and undocking events. MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION : MICCAI ... INTERNATIONAL CONFERENCE ON MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION 2013. [PMID: 23286147 DOI: 10.1007/978-3-642-33454-2_41] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register]
Abstract
Fluorescently-tagged proteins located on vesicles can fuse with the surface membrane (visualised as a 'puff') or undock and return back into the bulk of the cell. Detection and quantitative measurement of these events from time-lapse videos has proven difficult. We propose a novel approach to detect fusion and undocking events by first searching for docked vesicles that 'disappear' from the field of view, and then using a diffusion model to classify them as either fusion or undocking events. We can also use the same searching method to identify docking events. We present comparative results against existing algorithms.
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71
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Jambaldorj B, Terada E, Hosaka T, Kishuku Y, Tomioka Y, Iwashima K, Hirata Y, Teshigawara K, Thi Kim Le C, Nakagawa T, Harada N, Sakai T, Sakaue H, Matsumoto T, Funaki M, Takahashi A, Nakaya Y. Cysteine string protein 1 (CSP1) modulates insulin sensitivity by attenuating glucose transporter 4 (GLUT4) vesicle docking with the plasma membrane. THE JOURNAL OF MEDICAL INVESTIGATION 2013; 60:197-204. [DOI: 10.2152/jmi.60.197] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Bayasgalan Jambaldorj
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Eri Terada
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Toshio Hosaka
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Yuka Kishuku
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Yukiko Tomioka
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Kaori Iwashima
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Yohko Hirata
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Kiyoshi Teshigawara
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Chung Thi Kim Le
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Tadahiko Nakagawa
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Nagakatsu Harada
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Tohru Sakai
- Department of Public Health and Applied Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Hiroshi Sakaue
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Toshio Matsumoto
- Department of Medicine and Bioregulatory Sciences, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Makoto Funaki
- Clinical Research Center for Diabetes, Tokushima University Hospital
| | - Akira Takahashi
- Department of Preventive Environment and Nutrition, Institute of Health Biosciences, the University of Tokushima Graduate School
| | - Yutaka Nakaya
- Department of Nutrition and Metabolism, Institute of Health Biosciences, the University of Tokushima Graduate School
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72
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Acute regulation of 5'-AMP-activated protein kinase by long-chain fatty acid, glucose and insulin in rat primary adipocytes. Biosci Rep 2012; 33:71-82. [PMID: 23095119 PMCID: PMC3522478 DOI: 10.1042/bsr20120031] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Palmitate increased AMPK (5'-AMP-activated protein kinase) activity, glucose utilization and 2-DOG (2-deoxyglucose) transport in rat adipocytes. All three effects were blocked by the AMPK inhibitor Compound C, leading to the conclusion that in response to an increase in long-chain NEFA (non-esterified fatty acid) concentration AMPK mediated an enhancement of adipocyte glucose transport, thereby providing increased glycerol 3-phosphate for FA (fatty acid) esterification to TAG (triacylglycerol). Activation of AMPK in response to palmitate was not due to an increase in the adipocyte AMP:ATP ratio. Glucose decreased AMPK activity and effects of palmitate and glucose on AMPK activity were antagonistic. While insulin had no effect on basal AMPK activity insulin did decrease AMPK activity in the presence of palmitate and also decreased the percentage effectiveness of palmitate to increase the transport of 2-DOG. It is suggested that activation of adipocyte AMPK by NEFA, as well as decreasing the activity of hormone-sensitive lipase, could modulate adipose tissue dynamics by increasing FA esterification and, under certain circumstances, FA synthesis.
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73
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Lansey MN, Walker NN, Hargett SR, Stevens JR, Keller SR. Deletion of Rab GAP AS160 modifies glucose uptake and GLUT4 translocation in primary skeletal muscles and adipocytes and impairs glucose homeostasis. Am J Physiol Endocrinol Metab 2012; 303:E1273-86. [PMID: 23011063 PMCID: PMC3517634 DOI: 10.1152/ajpendo.00316.2012] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Tight control of glucose uptake in skeletal muscles and adipocytes is crucial to glucose homeostasis and is mediated by regulating glucose transporter GLUT4 subcellular distribution. In cultured cells, Rab GAP AS160 controls GLUT4 intracellular retention and release to the cell surface and consequently regulates glucose uptake into cells. To determine AS160 function in GLUT4 trafficking in primary skeletal muscles and adipocytes and investigate its role in glucose homeostasis, we characterized AS160 knockout (AS160(-/-)) mice. We observed increased and normal basal glucose uptake in isolated AS160(-/-) adipocytes and soleus, respectively, while insulin-stimulated glucose uptake was impaired and GLUT4 expression decreased in both. No such abnormalities were found in isolated AS160(-/-) extensor digitorum longus muscles. In plasma membranes isolated from AS160(-/-) adipose tissue and gastrocnemius/quadriceps, relative GLUT4 levels were increased under basal conditions and remained the same after insulin treatment. Concomitantly, relative levels of cell surface-exposed GLUT4, determined with a glucose transporter photoaffinity label, were increased in AS160(-/-) adipocytes and normal in AS160(-/-) soleus under basal conditions. Insulin augmented cell surface-exposed GLUT4 in both. These observations suggest that AS160 is essential for GLUT4 intracellular retention and regulation of glucose uptake in adipocytes and skeletal muscles in which it is normally expressed. In vivo studies revealed impaired insulin tolerance in the presence of normal (male) and impaired (female) glucose tolerance. Concurrently, insulin-elicited increases in glucose disposal were abolished in all AS160(-/-) skeletal muscles and liver but not in AS160(-/-) adipose tissues. This suggests AS160 as a target for differential manipulation of glucose homeostasis.
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Affiliation(s)
- Melissa N Lansey
- Dept. of Medicine/Division of Endocrinology, Univ. of Virginia, Charlottesville, VA 22908, USA.
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74
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A novel PKB/Akt inhibitor, MK-2206, effectively inhibits insulin-stimulated glucose metabolism and protein synthesis in isolated rat skeletal muscle. Biochem J 2012; 447:137-47. [PMID: 22793019 DOI: 10.1042/bj20120772] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PKB (protein kinase B), also known as Akt, is a key component of insulin signalling. Defects in PKB activation lead to insulin resistance and metabolic disorders, whereas PKB overactivation has been linked to tumour growth. Small-molecule PKB inhibitors have thus been developed for cancer treatment, but also represent useful tools to probe the roles of PKB in insulin action. In the present study, we examined the acute effects of two allosteric PKB inhibitors, MK-2206 and Akti 1/2 (Akti) on PKB signalling in incubated rat soleus muscles. We also assessed the effects of the compounds on insulin-stimulated glucose uptake, glycogen and protein synthesis. MK-2206 dose-dependently inhibited insulin-stimulated PKB phosphorylation, PKBβ activity and phosphorylation of PKB downstream targets (including glycogen synthase kinase-3α/β, proline-rich Akt substrate of 40 kDa and Akt substrate of 160 kDa). Insulin-stimulated glucose uptake, glycogen synthesis and glycogen synthase activity were also decreased by MK-2206 in a dose-dependent manner. Incubation with high doses of MK-2206 (10 μM) inhibited insulin-induced p70 ribosomal protein S6 kinase and 4E-BP1 (eukaryotic initiation factor 4E-binding protein-1) phosphorylation associated with increased eEF2 (eukaryotic elongation factor 2) phosphorylation. In contrast, Akti only modestly inhibited insulin-induced PKB and mTOR (mammalian target of rapamycin) signalling, with little or no effect on glucose uptake and protein synthesis. MK-2206, rather than Akti, would thus be the tool of choice for studying the role of PKB in insulin action in skeletal muscle. The results point to a key role for PKB in mediating insulin-stimulated glucose uptake, glycogen synthesis and protein synthesis in skeletal muscle.
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75
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Chen Y, Wang Y, Zhang J, Deng Y, Jiang L, Song E, Wu XS, Hammer JA, Xu T, Lippincott-Schwartz J. Rab10 and myosin-Va mediate insulin-stimulated GLUT4 storage vesicle translocation in adipocytes. ACTA ACUST UNITED AC 2012; 198:545-60. [PMID: 22908308 PMCID: PMC3514028 DOI: 10.1083/jcb.201111091] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rab proteins are important regulators of insulin-stimulated GLUT4 translocation to the plasma membrane (PM), but the precise steps in GLUT4 trafficking modulated by particular Rab proteins remain unclear. Here, we systematically investigate the involvement of Rab proteins in GLUT4 trafficking, focusing on Rab proteins directly mediating GLUT4 storage vesicle (GSV) delivery to the PM. Using dual-color total internal reflection fluorescence (TIRF) microscopy and an insulin-responsive aminopeptidase (IRAP)-pHluorin fusion assay, we demonstrated that Rab10 directly facilitated GSV translocation to and docking at the PM. Rab14 mediated GLUT4 delivery to the PM via endosomal compartments containing transferrin receptor (TfR), whereas Rab4A, Rab4B, and Rab8A recycled GLUT4 through the endosomal system. Myosin-Va associated with GSVs by interacting with Rab10, positioning peripherally recruited GSVs for ultimate fusion. Thus, multiple Rab proteins regulate the trafficking of GLUT4, with Rab10 coordinating with myosin-Va to mediate the final steps of insulin-stimulated GSV translocation to the PM.
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Affiliation(s)
- Yu Chen
- Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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76
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Olson AL. Regulation of GLUT4 and Insulin-Dependent Glucose Flux. ISRN MOLECULAR BIOLOGY 2012; 2012:856987. [PMID: 27335671 PMCID: PMC4890881 DOI: 10.5402/2012/856987] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2012] [Accepted: 09/24/2012] [Indexed: 12/21/2022]
Abstract
GLUT4 has long been known to be an insulin responsive glucose transporter. Regulation of GLUT4 has been a major focus of research on the cause and prevention of type 2 diabetes. Understanding how insulin signaling alters the intracellular trafficking of GLUT4 as well as understanding the fate of glucose transported into the cell by GLUT4 will be critically important for seeking solutions to the current rise in diabetes and metabolic disease.
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Affiliation(s)
- Ann Louise Olson
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, P.O. Box 26901, BMSB 964, Oklahoma City, OK 73190, USA
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77
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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78
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Godinez WJ, Lampe M, Koch P, Eils R, Müller B, Rohr K. Identifying virus-cell fusion in two-channel fluorescence microscopy image sequences based on a layered probabilistic approach. IEEE TRANSACTIONS ON MEDICAL IMAGING 2012; 31:1786-1808. [PMID: 22692902 DOI: 10.1109/tmi.2012.2203142] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The entry process of virus particles into cells is decisive for infection. In this work, we investigate fusion of virus particles with the cell membrane via time-lapse fluorescence microscopy. To automatically identify fusion for single particles based on their intensity over time, we have developed a layered probabilistic approach. The approach decomposes the action of a single particle into three abstractions: the intensity over time, the underlying temporal intensity model, as well as a high level behavior. Each abstraction corresponds to a layer and these layers are represented via stochastic hybrid systems and hidden Markov models. We use a maxbelief strategy to efficiently combine both representations. To compute estimates for the abstractions we use a hybrid particle filter and the Viterbi algorithm. Based on synthetic image sequences, we characterize the performance of the approach as a function of the image noise. We also characterize the performance as a function of the tracking error. We have also successfully applied the approach to real image sequences displaying pseudotyped HIV-1 particles in contact with host cells and compared the experimental results with ground truth obtained by manual analysis.
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Affiliation(s)
- William J Godinez
- Department Bioinformatics and Functional Genomics, University of Heidelberg, Heidelberg, Germany.
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79
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Barker G, Lim R, Georgiou HM, Lappas M. Omentin-1 is decreased in maternal plasma, placenta and adipose tissue of women with pre-existing obesity. PLoS One 2012; 7:e42943. [PMID: 22952622 PMCID: PMC3429479 DOI: 10.1371/journal.pone.0042943] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2011] [Accepted: 07/15/2012] [Indexed: 11/18/2022] Open
Abstract
OBJECTIVE The aim of this study was to determine (i) the effect of maternal obesity and gestational diabetes mellitus (GDM) on (i) the circulating levels of omentin-1 in cord and maternal plasma, and (ii) gene expression and release of omentin-1 from human placenta and adipose tissue. The effect of pregnancy on circulating omentin-1 levels was also determined. DESIGN Omentin-1 levels were measured in maternal and cord plasma from obese and non-obese normal glucose tolerant women (NGT; n = 44) and women with GDM (n = 39) at the time of term elective Caesarean section. Placenta and adipose tissue expression and release of omentin-1 was measured from 22 NGT and 22 GDM women collected at the time of term elective Caesarean section. Omentin-1 levels were also measured in maternal plasma from 13 NGT women at 11 and 28 weeks gestation and 7 weeks postpartum. RESULTS Maternal obesity was associated with significantly lower omentin-1 levels in maternal plasma; however, there was no effect of maternal obesity on cord omentin levels. Omentin-1 gene expression was lower in placenta and adipose tissue obtained from women with pre-existing obesity. In addition to this, adipose tissue release of omentin-1 was significantly lower from obese pregnant women. Omentin-1 levels were significantly lower in non-obese GDM compared to non-obese NGT women. However, there was no difference in omentin-1 levels between obese NGT and obese GDM women. There was no effect of GDM on cord omentin levels, and placental and adipose tissue omentin-1 expression. Maternal omentin-1 levels were negatively correlated with fetal birthweight and fetal ponderal index. CONCLUSIONS The data presented in this study demonstrate that pre-existing maternal obesity is associated with lower omentin-1 expression in placenta, adipose tissue and maternal plasma. Alteration in omentin-1 in pregnancy may influence the development of metabolic disorders in offspring later in life.
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Affiliation(s)
| | | | | | - Martha Lappas
- Department of Obstetrics and Gynaecology, University of Melbourne, Victoria, Australia Mercy Perinatal Research Centre, Mercy Hospital for Women, Heidelberg, Victoria, Australia
- * E-mail:
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Sites of glucose transporter-4 vesicle fusion with the plasma membrane correlate spatially with microtubules. PLoS One 2012; 7:e43662. [PMID: 22916292 PMCID: PMC3423385 DOI: 10.1371/journal.pone.0043662] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 07/23/2012] [Indexed: 12/25/2022] Open
Abstract
In adipocytes, vesicles containing glucose transporter-4 (GLUT4) redistribute from intracellular stores to the cell periphery in response to insulin stimulation. Vesicles then fuse with the plasma membrane, facilitating glucose transport into the cell. To gain insight into the details of microtubule involvement, we examined the spatial organization and dynamics of microtubules in relation to GLUT4 vesicle trafficking in living 3T3-L1 adipocytes using total internal reflection fluorescence (TIRF) microscopy. Insulin stimulated an increase in microtubule density and curvature within the TIRF-illuminated region of the cell. The high degree of curvature and abrupt displacements of microtubules indicate that substantial forces act on microtubules. The time course of the microtubule density increase precedes that of the increase in intensity of fluorescently-tagged GLUT4 in this same region of the cell. In addition, portions of the microtubules are highly curved and are pulled closer to the cell cortex, as confirmed by Parallax microscopy. Microtubule disruption delayed and modestly reduced GLUT4 accumulation at the plasma membrane. Quantitative analysis revealed that fusions of GLUT4-containing vesicles with the plasma membrane, detected using insulin-regulated aminopeptidase with a pH-sensitive GFP tag (pHluorin), preferentially occur near microtubules. Interestingly, long-distance vesicle movement along microtubules visible at the cell surface prior to fusion does not appear to account for this proximity. We conclude that microtubules may be important in providing spatial information for GLUT4 vesicle fusion.
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81
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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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82
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Haga Y, Ishii K, Hibino K, Sako Y, Ito Y, Taniguchi N, Suzuki T. Visualizing specific protein glycoforms by transmembrane fluorescence resonance energy transfer. Nat Commun 2012; 3:907. [DOI: 10.1038/ncomms1906] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Accepted: 05/14/2012] [Indexed: 11/09/2022] Open
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83
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Ren W, Cheema S, Du K. The association of ClipR-59 protein with AS160 modulates AS160 protein phosphorylation and adipocyte Glut4 protein membrane translocation. J Biol Chem 2012; 287:26890-900. [PMID: 22689584 DOI: 10.1074/jbc.m112.357699] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
ClipR-59 is a membrane-associated protein and has been implicated in membrane signaling and vesicle trafficking. Recently, we have identified ClipR-59 as an Akt-interacting protein, and we have found that, by interacting with Akt, ClipR-59 modulates Akt subcellular compartmentalization and Akt substrate AS160 phosphorylation, thereby promoting Glut4 membrane translocation. Here, we have further investigated the regulatory effects of ClipR-59 on AS160 phosphorylation and subsequent adipocyte glucose transport. Our data showed that ClipR-59 interacted with AS160, which was mediated by the ankyrin repeats of ClipR-59 and regulated by insulin signaling. Moreover, the data also demonstrated that the interaction of ClipR-59 with AS160 was required for ClipR-59 to modulate Glut4 membrane translocation as ΔANK-ClipR-59, an AS160 interaction-defective mutant, failed to promote AS160 phosphorylation, Glut4 membrane translocation, and glucose transport induced by insulin in 3T3-L1 adipocytes. Because ClipR-59 also interacts with Akt and enhances the interaction between Akt and AS160, we suggest that ClipR-59 functions as a scaffold protein to facilitate Akt-mediated AS160 phosphorylation, thereby regulating glucose transport.
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Affiliation(s)
- Wenying Ren
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111, USA
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84
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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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85
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Wu ZY, Zhu LJ, Zou N, Bombek LK, Shao CY, Wang N, Wang XX, Liang L, Xia J, Rupnik M, Shen Y. AMPA receptors regulate exocytosis and insulin release in pancreatic β cells. Traffic 2012; 13:1124-39. [PMID: 22540213 DOI: 10.1111/j.1600-0854.2012.01373.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Revised: 04/25/2012] [Accepted: 04/27/2012] [Indexed: 01/06/2023]
Abstract
Ionotropic glutamate receptors (iGluRs) are expressed in islets and insulinoma cells and involved in insulin secretion. However, the exact roles that iGluRs play in β cells remain unclear. Here, we demonstrated that GluR2-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) were expressed in mouse β cells. Glutamate application increased both cytosolic calcium and the number of docked insulin-containing granules, which resulted in augmentation of depolarization-induced exocytosis and high-glucose-stimulated insulin release. While glutamate application directly depolarized β cells, it also induced an enormous depolarization when K(ATP) channels were available. Glutamate application reduced the conductance of K(ATP) channels and increased voltage oscillations. Moreover, actions of AMPARs were absent in Kir6.2 knock-out mice. The effects of AMPARs on K(ATP) channels were mediated by cytosolic cGMP. Taken together, our experiments uncovered a novel mechanism by which AMPARs participate in insulin release.
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Affiliation(s)
- Zhen-Yong Wu
- Department of Neurobiology, Key Laboratory of Medical Neurobiology of Ministry of Health, Zhejiang Province Key Laboratory of Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310058, P. R. China
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86
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Li J, Malaby AW, Famulok M, Sabe H, Lambright DG, Hsu VW. Grp1 plays a key role in linking insulin signaling to glut4 recycling. Dev Cell 2012; 22:1286-98. [PMID: 22609160 DOI: 10.1016/j.devcel.2012.03.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Revised: 01/31/2012] [Accepted: 03/13/2012] [Indexed: 11/29/2022]
Abstract
The glucose transporter type 4 (glut4) is critical for metabolic homeostasis. Insulin regulates glut4 by modulating its expression on the cell surface. This regulation is mainly achieved by targeting the endocytic recycling of glut4. We identify general receptor for 3-phosphoinositides 1 (Grp1) as a guanine nucleotide exchange factor for ADP-ribosylation factor 6 (ARF6) that promotes glut4 vesicle formation. Grp1 also promotes the later steps of glut4 recycling through ARF6. Insulin signaling regulates Grp1 through phosphorylation by Akt. We also find that mutations that mimic constitutive phosphorylation of Grp1 can bypass upstream insulin signaling to induce glut4 recycling. Thus, we have uncovered a major mechanism by which insulin regulates glut4 recycling. Our findings also reveal the complexity by which a single small GTPase in vesicular transport can coordinate its multiple steps to accomplish a round of transport.
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Affiliation(s)
- Jian Li
- Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, MA 02115, USA
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87
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Zhang M, Chang H, Zhang Y, Yu J, Wu L, Ji W, Chen J, Liu B, Lu J, Liu Y, Zhang J, Xu P, Xu T. Rational design of true monomeric and bright photoactivatable fluorescent proteins. Nat Methods 2012; 9:727-9. [PMID: 22581370 DOI: 10.1038/nmeth.2021] [Citation(s) in RCA: 333] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 04/18/2012] [Indexed: 12/12/2022]
Abstract
Monomeric (m)Eos2 is an engineered photoactivatable fluorescent protein widely used for super-resolution microscopy. We show that mEos2 forms oligomers at high concentrations and forms aggregates when labeling membrane proteins, limiting its application as a fusion partner. We solved the crystal structure of tetrameric mEos2 and rationally designed improved versions, mEos3.1 and mEos3.2, that are truly monomeric, are brighter, mature faster and exhibit higher photon budget and label density.
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Affiliation(s)
- Mingshu Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
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88
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Abstract
Insulin resistance is a key pathological feature of type 2 diabetes and is characterized by defects in signaling by the insulin receptor (IR) protein tyrosine kinase. The inhibition of protein tyrosine phosphatases (PTPs) that antagonize IR signaling may provide a means for enhancing the insulin response and alleviating insulin resistance. The prototypic phosphotyrosine-specific phosphatase PTP1B dephosphorylates the IR and attenuates insulin signaling in muscle and liver. Mice that are deficient for PTP1B exhibit improved glucose homeostasis in diet and genetic models of insulin resistance and type 2 diabetes. The phosphatase TCPTP shares 72% catalytic domain sequence identity with PTP1B and has also been implicated in IR regulation. Despite their high degree of similarity, PTP1B and TCPTP act together in vitro and in vivo to regulate insulin signaling and glucose homeostasis. This review highlights their capacity to act specifically and nonredundantly in cellular signaling, describes their roles in IR regulation and glucose homeostasis, and discusses their potential as drug targets for the enhancement of IR phosphorylation and insulin sensitivity in type 2 diabetes.
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Affiliation(s)
- Tony Tiganis
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Australia.
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89
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Lizunov VA, Stenkula KG, Lisinski I, Gavrilova O, Yver DR, Chadt A, Al-Hasani H, Zimmerberg J, Cushman SW. Insulin stimulates fusion, but not tethering, of GLUT4 vesicles in skeletal muscle of HA-GLUT4-GFP transgenic mice. Am J Physiol Endocrinol Metab 2012; 302:E950-60. [PMID: 22297303 PMCID: PMC3330721 DOI: 10.1152/ajpendo.00466.2011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Insulin regulates glucose uptake into fat and muscle by modulating the subcellular distribution of GLUT4 between the cell surface and intracellular compartments. However, quantification of these translocation processes in muscle by classical subcellular fractionation techniques is confounded by contaminating microfibrillar protein; dynamic studies at the molecular level are almost impossible. In this study, we introduce a muscle-specific transgenic mouse model in which HA-GLUT4-GFP is expressed under the control of the MCK promoter. HA-GLUT4-GFP was found to translocate to the plasma membrane and T-tubules after insulin stimulation, thus mimicking endogenous GLUT4. To investigate the dynamics of GLUT4 trafficking in skeletal muscle, we quantified vesicles containing HA-GLUT4-GFP near the sarcolemma and T-tubules and analyzed insulin-stimulated exocytosis at the single vesicle level by total internal reflection fluorescence and confocal microscopy. We found that only 10% of the intracellular GLUT4 pool comprised mobile vesicles, whereas most of the GLUT4 structures remained stationary or tethered at the sarcolemma or T-tubules. In fact, most of the insulin-stimulated exocytosis emanated from pretethered vesicles, whereas the small pool of mobile GLUT4 vesicles was not significantly affected by insulin. Our data strongly suggest that the mobile pool of GLUT4 vesicles is not a major site of insulin action but rather locally distributed. Most likely, pretethered GLUT4 structures are responsible for the initial phase of insulin-stimulated exocytosis.
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Affiliation(s)
- Vladimir A Lizunov
- Program in Physical Biology, National Institute of Child Health and Human Development/National Institutes of Health, Bethesda, MD, USA
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90
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Loh K, Merry TL, Galic S, Wu BJ, Watt MJ, Zhang S, Zhang ZY, Neel BG, Tiganis T. T cell protein tyrosine phosphatase (TCPTP) deficiency in muscle does not alter insulin signalling and glucose homeostasis in mice. Diabetologia 2012; 55:468-78. [PMID: 22124607 PMCID: PMC5057388 DOI: 10.1007/s00125-011-2386-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 10/25/2011] [Indexed: 12/17/2022]
Abstract
AIMS/HYPOTHESIS Insulin activates insulin receptor protein tyrosine kinase and downstream phosphatidylinositol-3-kinase (PI3K)/Akt signalling in muscle to promote glucose uptake. The insulin receptor can serve as a substrate for the protein tyrosine phosphatase (PTP) 1B and T cell protein tyrosine phosphatase (TCPTP), which share a striking 74% sequence identity in their catalytic domains. PTP1B is a validated therapeutic target for the alleviation of insulin resistance in type 2 diabetes. PTP1B dephosphorylates the insulin receptor in liver and muscle to regulate glucose homeostasis, whereas TCPTP regulates insulin receptor signalling and gluconeogenesis in the liver. In this study we assessed for the first time the role of TCPTP in the regulation of insulin receptor signalling in muscle. METHODS We generated muscle-specific TCPTP-deficient (Mck-Cre;Ptpn2(lox/lox)) mice (Mck, also known as Ckm) and assessed the impact on glucose homeostasis and muscle insulin receptor signalling in chow-fed versus high-fat-fed mice. RESULTS Blood glucose and insulin levels, insulin and glucose tolerance, and insulin-induced muscle insulin receptor activation and downstream PI3K/Akt signalling remained unaltered in chow-fed Mck-Cre;Ptpn2(lox/lox) versus Ptpn2(lox/lox) mice. In addition, body weight, adiposity, energy expenditure, insulin sensitivity and glucose homeostasis were not altered in high-fat-fed Mck-Cre;Ptpn2(lox/lox) versus Ptpn2(lox/lox) mice. CONCLUSIONS/INTERPRETATION These results indicate that TCPTP deficiency in muscle has no effect on insulin signalling and glucose homeostasis, and does not prevent high-fat diet-induced insulin resistance. Thus, despite their high degree of sequence identity, PTP1B and TCPTP contribute differentially to insulin receptor regulation in muscle. Our results are consistent with the notion that these two highly related PTPs make distinct contributions to insulin receptor regulation in different tissues.
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Affiliation(s)
- Kim Loh
- Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia
| | - Troy L. Merry
- Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia
| | - Sandra Galic
- Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia
| | - Ben J. Wu
- Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia
| | - Matthew J. Watt
- Department of Physiology, Monash University, Victoria 3800, Australia
| | - Sheng Zhang
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Zhong-Yin Zhang
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Benjamin G. Neel
- Campbell Family Cancer Research Institute, Ontario Cancer Institute, Princess Margaret Hospital and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Tony Tiganis
- Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia
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91
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Abstract
In the last decade, the availability of genetically modified animals has revealed interesting roles for phosphoinositide 3-kinases (PI3Ks) as signaling platforms orchestrating multiple cellular responses, both in health and pathology. By acting downstream distinct receptor types, PI3Ks nucleate complex signaling assemblies controlling several biological process, ranging from cell proliferation and survival to immunity, cancer, metabolism and cardiovascular control. While the involvement of these kinases in modulating immune reactions and neoplastic transformation has long been accepted, recent progress from our group and others has highlighted new and unforeseen roles of PI3Ks in controlling cardiovascular function. Hence, the view is emerging that pharmacological targeting of distinct PI3K isoforms could be successful in treating disorders such as myocardial infarction and heart failure, besides inflammatory diseases and cancer. Currently, PI3Ks represent attractive drug targets for companies interested in the development of novel and safe treatments for such diseases. Numerous hit and lead compounds are now becoming available and, for some of them, clinical trials can be envisaged in the near future. In the following sections, we will outline the impact of specific PI3K isoforms in regulating different cellular contexts, including immunity, metabolism, cancer and cardiovascular system, both in physiological and disease conditions.
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92
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Lane RF, Shineman DW, Steele JW, Lee LBH, Fillit HM. Beyond amyloid: the future of therapeutics for Alzheimer's disease. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2012; 64:213-71. [PMID: 22840749 DOI: 10.1016/b978-0-12-394816-8.00007-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Currently, the field is awaiting the results of several pivotal Phase III clinical Alzheimer's disease (AD) trials that target amyloid-β (Aβ). In light of the recent biomarker studies that indicate Aβ levels are at their most dynamic 5-10 years before the onset of clinical symptoms, it is becoming uncertain whether direct approaches to target Aβ will achieve desired clinical efficacy. AD is a complex neurodegenerative disease caused by dysregulation of numerous neurobiological networks and cellular functions, resulting in synaptic loss, neuronal loss, and ultimately impaired memory. While it is clear that Aβ plays a key role in the pathogenesis of AD, it may be a challenging and inefficient target for mid-to-late stage AD intervention. Throughout the course of AD, multiple pathways become perturbed, presenting a multitude of possible therapeutic avenues for design of AD intervention and prophylactic therapies. In this chapter, we sought to first provide an overview of Aβ-directed strategies that are currently in development, and the pivotal Aβ-targeted trials that are currently underway. Next, we delve into the biology and therapeutic designs associated with other key areas of research in the field including tau, protein trafficking and degradation pathways, ApoE, synaptic function, neurotrophic/neuroprotective strategies, and inflammation and energy utilization. For each area we have provided a comprehensive and balanced overview of the therapeutic strategies currently in preclinical and clinical development, which will shape the future therapeutic landscape of AD.
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Affiliation(s)
- Rachel F Lane
- Alzheimer's Drug Discovery Foundation, New York, NY, USA
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93
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Chiu TT, Jensen TE, Sylow L, Richter EA, Klip A. Rac1 signalling towards GLUT4/glucose uptake in skeletal muscle. Cell Signal 2011; 23:1546-54. [DOI: 10.1016/j.cellsig.2011.05.022] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Accepted: 05/31/2011] [Indexed: 12/27/2022]
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94
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Xie X, Gong Z, Mansuy-Aubert V, Zhou QL, Tatulian SA, Sehrt D, Gnad F, Brill LM, Motamedchaboki K, Chen Y, Czech MP, Mann M, KrÜger M, Jiang ZY. C2 domain-containing phosphoprotein CDP138 regulates GLUT4 insertion into the plasma membrane. Cell Metab 2011; 14:378-89. [PMID: 21907143 PMCID: PMC3172579 DOI: 10.1016/j.cmet.2011.06.015] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 05/03/2011] [Accepted: 06/09/2011] [Indexed: 10/17/2022]
Abstract
The protein kinase B(β) (Akt2) pathway is known to mediate insulin-stimulated glucose transport through increasing glucose transporter GLUT4 translocation from intracellular stores to the plasma membrane (PM). Combining quantitative phosphoproteomics with RNAi-based functional analyses, we show that a previously uncharacterized 138 kDa C2 domain-containing phosphoprotein (CDP138) is a substrate for Akt2, and is required for optimal insulin-stimulated glucose transport, GLUT4 translocation, and fusion of GLUT4 vesicles with the PM in live adipocytes. The purified C2 domain is capable of binding Ca(2+) and lipid membranes. CDP138 mutants lacking the Ca(2+)-binding sites in the C2 domain or Akt2 phosphorylation site S197 inhibit insulin-stimulated GLUT4 insertion into the PM, a rate-limiting step of GLUT4 translocation. Interestingly, CDP138 is dynamically associated with the PM and GLUT4-containing vesicles in response to insulin stimulation. Together, these results suggest that CDP138 is a key molecule linking the Akt2 pathway to the regulation of GLUT4 vesicle-PM fusion.
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Affiliation(s)
- Xiangyang Xie
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL 32827, USA
| | - Zhenwei Gong
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL 32827, USA
| | - Virginie Mansuy-Aubert
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL 32827, USA
| | - Qiong L. Zhou
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Suren A. Tatulian
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Daniel Sehrt
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL 32827, USA
| | - Florian Gnad
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Laurence M. Brill
- Proteomic Core Facility, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA
| | - Khatereh Motamedchaboki
- Proteomic Core Facility, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA
| | - Yu Chen
- Cell Biology and Metabolism Program, NICHD, NIH, Bethesda, MD 20892, USA
| | - Michael P. Czech
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Matthias Mann
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Marcus KrÜger
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried, Germany
- Biomolecular Mass Spectrometry, Max-Planck-Institute for Heart and Lung Research, Bad Nauheim, Germany
| | - Zhen Y. Jiang
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL 32827, USA
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95
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Abstract
Delivery of the glucose transporter type 4 (GLUT4) from an intracellular location to the cell surface in response to insulin represents a specialized form of membrane traffic, known to be impaired in the disease states of insulin resistance and type 2 diabetes. Like all membrane trafficking events, this translocation of GLUT4 requires members of the SNARE family of proteins. Here, we discuss two SNARE complexes that have been implicated in insulin-regulated GLUT4 traffic: one regulating the final delivery of GLUT4 to the cell surface in response to insulin and the other controlling GLUT4's intracellular trafficking.
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Affiliation(s)
- Nia J Bryant
- Henry Wellcome Laboratory of Cell Biology, Institute of Molecular, Cell and Systems Biology, Davidson Building, College of Medicine, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
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96
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Yan P, Li L, Yang M, Liu D, Liu H, Boden G, Yang G. Effects of the long-acting human glucagon-like peptide-1 analog liraglutide on plasma omentin-1 levels in patients with type 2 diabetes mellitus. Diabetes Res Clin Pract 2011; 92:368-74. [PMID: 21458097 DOI: 10.1016/j.diabres.2011.02.030] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Revised: 12/02/2010] [Accepted: 02/28/2011] [Indexed: 11/27/2022]
Abstract
OBJECTIVE Omentin is a protein expressed and secreted from visceral but not subcutaneous adipose tissue, which increases insulin sensitivity in human adipocytes. However, its pathophysiologic role in humans remains largely unknown. The objective of this study is to assess plasma omentin-1 levels in patients with type 2 diabetes mellitus (T2DM) and matched control subjects and to investigate the effects of liraglutide on plasma omentin-1 levels in patients with T2DM. PATIENTS AND METHODS Thirty T2DM patients with poor glycemic control after more than 3 months of treatment with one or two OHA(s) (T2DM), and 30 matched normal glycaemic controls (NGT) participated in the study. The T2DM group was given an injection of liraglutide once-daily for 16 weeks. Plasma omentin-1 levels were measured by enzyme-linked immunosorbent assay and the relationship between plasma omentin-1 levels and metabolic parameters was also analyzed. RESULTS Plasma omentin-1 levels were lower in T2DM than in the control (19.3 ± 4.0 μg/L vs. 26.4 ± 6.0 μg/L, P < 0.01). Plasma omentin-1 levels increased significantly in T2DM patients after treatment with liraglutide compared with pre-treatment (19.3 ± 4.0 μg/L vs. 21.2 ± 3. 9 μg/L, P < 0.01). In all diabetic patients, multiple regression analysis showed that FINS and HOMA-IR were independently associated with plasma omentin-1 levels. CONCLUSIONS In T2DM patients, plasma omentin-1 levels decreased, but significantly increased after the treatment with liraglutide and metformin. These data suggest that liraglutide may play a role in increasing omentin-1 levels in T2DM patients.
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Affiliation(s)
- Pijun Yan
- Department of Endocrinology, the Second Affiliated Hospital, Chongqing Medical University, 400010 Chongqing, China
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97
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Brewer PD, Romenskaia I, Kanow MA, Mastick CC. Loss of AS160 Akt substrate causes Glut4 protein to accumulate in compartments that are primed for fusion in basal adipocytes. J Biol Chem 2011; 286:26287-97. [PMID: 21613213 DOI: 10.1074/jbc.m111.253880] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The Akt substrate AS160 (TCB1D4) regulates Glut4 exocytosis; shRNA knockdown of AS160 increases surface Glut4 in basal adipocytes. AS160 knockdown is only partially insulin-mimetic; insulin further stimulates Glut4 translocation in these cells. Insulin regulates translocation as follows: 1) by releasing Glut4 from retention in a slowly cycling/noncycling storage pool, increasing the actively cycling Glut4 pool, and 2) by increasing the intrinsic rate constant for exocytosis of the actively cycling pool (k(ex)). Kinetic studies were performed in 3T3-L1 adipocytes to measure the effects of AS160 knockdown on the rate constants of exocytosis (k(ex)), endocytosis (k(en)), and release from retention into the cycling pool. AS160 knockdown released Glut4 into the actively cycling pool without affecting k(ex) or k(en). Insulin increased k(ex) in the knockdown cells, further increasing cell surface Glut4. Inhibition of phosphatidylinositol 3-kinase or Akt affected both k(ex) and release from retention in control cells but only k(ex) in AS160 knockdown cells. Glut4 vesicles accumulate in a primed pre-fusion pool in basal AS160 knockdown cells. Akt regulates the rate of exocytosis of the primed vesicles through an AS160-independent mechanism. Therefore, there is an additional Akt substrate that regulates the fusion of Glut4 vesicles that remain to be identified. Mathematical modeling was used to test the hypothesis that this substrate regulates vesicle priming (release from retention), whereas AS160 regulates the reverse step by stimulating GTP turnover of a Rab protein required for vesicle tethering/docking/fusion. Our analysis indicates that fusion of the primed vesicles with the plasma membrane is an additional non-Akt-dependent insulin-regulated step.
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Affiliation(s)
- Paul Duffield Brewer
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA
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98
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Koumanov F, Richardson JD, Murrow BA, Holman GD. AS160 phosphotyrosine-binding domain constructs inhibit insulin-stimulated GLUT4 vesicle fusion with the plasma membrane. J Biol Chem 2011; 286:16574-82. [PMID: 21454690 PMCID: PMC3089500 DOI: 10.1074/jbc.m111.226092] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 03/16/2011] [Indexed: 01/14/2023] Open
Abstract
AS160 (TBC1D4) is a known Akt substrate that is phosphorylated downstream of insulin action and that leads to regulated traffic of GLUT4. As GLUT4 vesicle fusion with the plasma membrane is a highly regulated step in GLUT4 traffic, we investigated whether AS160 and 14-3-3 interactions are involved in this process. Fusion was inhibited by a human truncated AS160 variant that encompasses the first N-terminal phosphotyrosine-binding (PTB) domain, by either of the two N-terminal PTB domains, and by a tandem construct of both PTB domains of rat AS160. We also found that in vitro GLUT4 vesicle fusion was strongly inhibited by the 14-3-3-quenching inhibitors R18 and fusicoccin. To investigate the mode of interaction of AS160 and 14-3-3, we examined insulin-dependent increases in the levels of these proteins on GLUT4 vesicles. 14-3-3γ was enriched on insulin-stimulated vesicles, and its binding to AS160 on GLUT4 vesicles was inhibited by the AS160 tandem PTB domain construct. These data suggest a model for PTB domain action on GLUT4 vesicle fusion in which these constructs inhibit insulin-stimulated 14-3-3γ interaction with AS160 rather than AS160 phosphorylation.
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Affiliation(s)
- Françoise Koumanov
- From the Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
| | - Judith D. Richardson
- From the Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
| | - Beverley A. Murrow
- From the Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
| | - Geoffrey D. Holman
- From the Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
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99
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Xu Y, Rubin BR, Orme CM, Karpikov A, Yu C, Bogan JS, Toomre DK. Dual-mode of insulin action controls GLUT4 vesicle exocytosis. ACTA ACUST UNITED AC 2011; 193:643-53. [PMID: 21555461 PMCID: PMC3166865 DOI: 10.1083/jcb.201008135] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Insulin releases an intracellular brake and promotes fusion pore expansion to translocate GLUT4 vesicles, and switches vesicle trafficking between distinct exocytic circuits. Insulin stimulates translocation of GLUT4 storage vesicles (GSVs) to the surface of adipocytes, but precisely where insulin acts is controversial. Here we quantify the size, dynamics, and frequency of single vesicle exocytosis in 3T3-L1 adipocytes. We use a new GSV reporter, VAMP2-pHluorin, and bypass insulin signaling by disrupting the GLUT4-retention protein TUG. Remarkably, in unstimulated TUG-depleted cells, the exocytic rate is similar to that in insulin-stimulated control cells. In TUG-depleted cells, insulin triggers a transient, twofold burst of exocytosis. Surprisingly, insulin promotes fusion pore expansion, blocked by acute perturbation of phospholipase D, which reflects both properties intrinsic to the mobilized vesicles and a novel regulatory site at the fusion pore itself. Prolonged stimulation causes cargo to switch from ∼60 nm GSVs to larger exocytic vesicles characteristic of endosomes. Our results support a model whereby insulin promotes exocytic flux primarily by releasing an intracellular brake, but also by accelerating plasma membrane fusion and switching vesicle traffic between two distinct circuits.
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Affiliation(s)
- Yingke Xu
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
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100
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Liu D, Martina JA, Wu XS, Hammer JA, Long EO. Two modes of lytic granule fusion during degranulation by natural killer cells. Immunol Cell Biol 2011; 89:728-38. [PMID: 21483445 PMCID: PMC3257049 DOI: 10.1038/icb.2010.167] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Lytic granules in cytotoxic lymphocytes, which include T cells and natural killer (NK) cells, are secretory lysosomes that release their content upon fusion with the plasma membrane (PM), a process known as degranulation. Although vesicle exocytosis has been extensively studied in endocrine and neuronal cells, much less is known about the fusion of lytic granules in cytotoxic lymphocytes. Here, we used total internal reflection fluorescence microscopy to examine lytic granules labeled with fluorescently tagged Fas ligand (FasL) in the NK cell line NKL stimulated with phorbol ester and ionomycin and in primary NK cells activated by physiological receptor–ligand interactions. Two fusion modes were observed: complete fusion, characterized by loss of granule content and rapid diffusion of FasL at the PM; and incomplete fusion, characterized by transient fusion pore opening and retention of FasL at the fusion site. The pH-sensitive green fluorescence protein (pHluorin) fused to the lumenal domain of FasL was used to visualize fusion pore opening with a time resolution of 30 ms. Upon incomplete fusion, pHluorin emission lasted several seconds in the absence of noticeable diffusion. Thus, we conclude that lytic granules in NK cells undergo both complete and incomplete fusion with the PM, and propose that incomplete fusion may promote efficient recycling of lytic granule membrane after the release of cytotoxic effector molecules.
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Affiliation(s)
- Dongfang Liu
- Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
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