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Building GLUT4 Vesicles: CHC22 Clathrin's Human Touch. Trends Cell Biol 2020; 30:705-719. [PMID: 32620516 DOI: 10.1016/j.tcb.2020.05.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 05/24/2020] [Accepted: 05/27/2020] [Indexed: 12/18/2022]
Abstract
Insulin stimulates glucose transport by triggering regulated delivery of intracellular vesicles containing the GLUT4 glucose transporter to the plasma membrane. This process is defective in diseases such as type 2 diabetes (T2DM). While studies in rodent cells have been invaluable in understanding GLUT4 traffic, evolutionary plasticity must be considered when extrapolating these findings to humans. Recent work has identified species-specific distinctions in GLUT4 traffic, notably the participation of a novel clathrin isoform, CHC22, in humans but not rodents. Here, we discuss GLUT4 sorting in different species and how studies of CHC22 have identified new routes for GLUT4 trafficking. We further consider how different sorting-protein complexes relate to these routes and discuss other implications of these pathways in cell biology and disease.
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2
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Cerebellar neurons possess a vesicular compartment structurally and functionally similar to Glut4-storage vesicles from peripheral insulin-sensitive tissues. J Neurosci 2009; 29:5193-201. [PMID: 19386915 DOI: 10.1523/jneurosci.0858-09.2009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The insulin-sensitive isoform of the glucose transporting protein, Glut4, is expressed in fat as well as in skeletal and cardiac muscle and is responsible for the effect of insulin on blood glucose clearance. Recent studies have revealed that Glut4 is also expressed in the brain, although the intracellular compartmentalization and regulation of Glut4 in neurons remains unknown. Using sucrose gradient centrifugation, immunoadsorption and immunofluorescence staining, we have shown that Glut4 in the cerebellum is localized in intracellular vesicles that have the sedimentation coefficient, the buoyant density, and the protein composition similar to the insulin-responsive Glut4-storage vesicles from fat and skeletal muscle cells. In cultured cerebellar neurons, insulin stimulates glucose uptake and causes translocation of Glut4 to the cell surface. Using 18FDG (18fluoro-2-deoxyglucose) positron emission tomography, we found that physical exercise acutely increases glucose uptake in the cerebellum in vivo. Prolonged physical exercise increases expression of the Glut4 protein in the cerebellum. Our results suggest that neurons have a novel type of translocation-competent vesicular compartment which is regulated by insulin and physical exercise similar to Glut4-storage vesicles in peripheral insulin target tissues.
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Alderman JM, Flurkey K, Brooks NL, Naik SB, Gutierrez JM, Srinivas U, Ziara KB, Jing L, Boysen G, Bronson R, Klebanov S, Chen X, Swenberg JA, Stridsberg M, Parker CE, Harrison DE, Combs TP. Neuroendocrine inhibition of glucose production and resistance to cancer in dwarf mice. Exp Gerontol 2008; 44:26-33. [PMID: 18582556 DOI: 10.1016/j.exger.2008.05.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 05/23/2008] [Accepted: 05/27/2008] [Indexed: 10/22/2022]
Abstract
Pit1 null (Snell dwarf) and Proph1 null (Ames dwarf) mutant mice lack GH, PRL and TSH. Snell and Ames dwarf mice also exhibit reduced IGF-I, resistance to cancer and a longer lifespan than control mice. Endogenous glucose production during fasting is reduced in Snell dwarf mice compared to fasting control mice. In view of cancer cell dependence on glucose for energy, low endogenous glucose production may provide Snell dwarf mice with resistance to cancer. We investigated whether endogenous glucose production is lower in Snell dwarf mice during feeding. Inhibition of endogenous glucose production by glucose injection was enhanced in 12 to 14 month-old female Snell dwarf mice. Thus, we hypothesize that lower endogenous glucose production during feeding and fasting reduces cancer cell glucose utilization providing Snell dwarf mice with resistance to cancer. The elevation of circulating adiponectin, a hormone produced by adipose tissue, may contribute to the suppression of endogenous glucose production in 12 to 14 month-old Snell dwarf mice. We compared the incidence of cancer at time of death between old Snell dwarf and control mice. Only 18% of old Snell dwarf mice had malignant lesions at the time of death compared to 82% of control mice. The median ages at death for old Snell dwarf and control mice were 33 and 26 months, respectively. By contrast, previous studies showed a high incidence of cancer in old Ames dwarf mice at the time of death. Hence, resistance to cancer in old Snell dwarf mice may be mediated by neuroendocrine factors that reduce glucose utilization besides elevated adiponectin, reduced IGF-I and a lack of GH, PRL and TSH, seen in both Snell and Ames dwarf mice. Proteomics analysis of pituitary secretions from Snell dwarf mice confirmed the absence of GH and PRL, the secretion of ACTH and elevated secretion of Chromogranin B and Secretogranin II. Radioimmune assays confirmed that circulating Chromogranin B and Secretogranin II were elevated in 12 to 14 month-old Snell dwarf mice. In summary, our results in Snell dwarf mice suggest that the pituitary gland and adipose tissue are part of a neuroendocrine loop that lowers the risk of cancer during aging by reducing the availability of glucose.
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Fernando RN, Luff SE, Albiston AL, Chai SY. Sub-cellular localization of insulin-regulated membrane aminopeptidase, IRAP to vesicles in neurons. J Neurochem 2007; 102:967-76. [PMID: 17504262 DOI: 10.1111/j.1471-4159.2007.04659.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Angiotensin IV and LVV-hemorphin 7 promote robust enhancing effects on learning and memory. These peptides are also competitive inhibitors of the insulin-regulated membrane aminopeptidase, suggesting that the biological actions of these peptides may result from inhibition of IRAP activity. However, the normal function of IRAP in the brain is yet to be determined. The present study investigated the sub-cellular distribution of IRAP in four neuronal cell lines and in the mouse brain. Using sub-cellular fractionation, IRAP was found to be enriched in low density microsomes, while lower levels of IRAP were also present in high density microsomes, plasma membrane and mitochondrial fractions. Dual-label immunohistochemistry confirmed the presence of IRAP in vesicles co-localized with the vesicular maker VAMP2, in the trans Golgi network co-localized with TGN 38 and in endosomes co-localized with EEA1. Finally using electron microscopy, IRAP specific immunoreactivity was predominantly associated with large 100-200 nm vesicles in hippocampal neurons. The location, appearance and size of these vesicles are consistent with neurosecretory vesicles. IRAP precipitate was also detected in intracellular structures including the rough endoplasmic reticulum, Golgi stack and mitochondrial membranes. The sub-cellular localization of IRAP in neurons demonstrated in the present study bears striking parallels with distribution of IRAP in insulin responsive cells, where the enzyme plays a role in insulin-regulated glucose uptake. Therefore, we propose that the function of IRAP in neurons may be similar to that in insulin responsive cells.
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Affiliation(s)
- Ruani N Fernando
- Howard Florey Institute, The University of Melbourne, Parkville, Victoria, Australia
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5
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Watson RT, Kanzaki M, Pessin JE. Regulated membrane trafficking of the insulin-responsive glucose transporter 4 in adipocytes. Endocr Rev 2004; 25:177-204. [PMID: 15082519 DOI: 10.1210/er.2003-0011] [Citation(s) in RCA: 309] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Since the discovery of insulin roughly 80 yr ago, much has been learned about how target cells receive, interpret, and respond to this peptide hormone. For example, we now know that insulin activates the tyrosine kinase activity of its cell surface receptor, thereby triggering intracellular signaling cascades that regulate many cellular processes. With respect to glucose homeostasis, these include the function of insulin to suppress hepatic glucose production and to increase glucose uptake in muscle and adipose tissues, the latter resulting from the translocation of the glucose transporter 4 (GLUT4) to the cell surface membrane. Although simple in broad outline, elucidating the molecular intricacies of these receptor-signaling pathways and membrane-trafficking processes continues to challenge the creative ingenuity of scientists, and many questions remain unresolved, or even perhaps unasked. The identification and functional characterization of specific molecules required for both insulin signaling and GLUT4 vesicle trafficking remain key issues in our pursuit of developing specific therapeutic agents to treat and/or prevent this debilitating disease process. To this end, the combined efforts of numerous research groups employing a range of experimental approaches has led to a clearer molecular picture of how insulin regulates the membrane trafficking of GLUT4.
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Affiliation(s)
- Robert T Watson
- Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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6
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Carvalho E, Schellhorn SE, Zabolotny JM, Martin S, Tozzo E, Peroni OD, Houseknecht KL, Mundt A, James DE, Kahn BB. GLUT4 overexpression or deficiency in adipocytes of transgenic mice alters the composition of GLUT4 vesicles and the subcellular localization of GLUT4 and insulin-responsive aminopeptidase. J Biol Chem 2004; 279:21598-605. [PMID: 14985357 DOI: 10.1074/jbc.m312269200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The majority of GLUT4 is sequestered in unique intracellular vesicles in the absence of insulin. Upon insulin stimulation GLUT4 vesicles translocate to, and fuse with, the plasma membrane. To determine the effect of GLUT4 content on the distribution and subcellular trafficking of GLUT4 and other vesicle proteins, adipocytes of adipose-specific, GLUT4-deficient (aP2-GLUT4-/-) mice and adipose-specific, GLUT4-overexpressing (aP2-GLUT4-Tg) mice were studied. GLUT4 amount was reduced by 80-95% in aP2-GLUT4-/- adipocytes and increased approximately 10-fold in aP2-GLUT4-Tg adipocytes compared with controls. Insulin-responsive aminopeptidase (IRAP) protein amount was decreased 35% in aP2-GLUT4-/- adipocytes and increased 45% in aP2-GLUT4-Tg adipocytes. VAMP2 protein was also decreased by 60% in aP2-GLUT4-/- adipocytes and increased 2-fold in aP2-GLUT4-Tg adipocytes. IRAP and VAMP2 mRNA levels were unaffected in aP2-GLUT4-Tg, suggesting that overexpression of GLUT4 affects IRAP and VAMP2 protein stability. The amount and subcellular distribution of syntaxin4, SNAP23, Munc-18c, and GLUT1 were unchanged in either aP2-GLUT4-/- or aP2-GLUT4-Tg adipocytes, but transferrin receptor was partially redistributed to the plasma membrane in aP2-GLUT4-Tg adipocytes. Immunogold electron microscopy revealed that overexpression of GLUT4 in adipocytes increased the number of GLUT4 molecules per vesicle nearly 2-fold and the number of GLUT4 and IRAP-containing vesicles per cell 3-fold. In addition, the proportion of cellular GLUT4 and IRAP at the plasma membrane in unstimulated aP2-GLUT4-Tg adipocytes was increased 4- and 2-fold, respectively, suggesting that sequestration of GLUT4 and IRAP is saturable. Our results show that GLUT4 overexpression or deficiency affects the amount of other GLUT4-vesicle proteins including IRAP and VAMP2 and that GLUT4 sequestration is saturable.
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Affiliation(s)
- Eugenia Carvalho
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 99 Brookline Avenue, Boston, MA 02215, USA
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7
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James DE, Piper RC, Slot JW. Insulin stimulation of GLUT-4 translocation: a model for regulated recycling. Trends Cell Biol 2004; 4:120-6. [PMID: 14731734 DOI: 10.1016/0962-8924(94)90066-3] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Insulin stimulates glucose transport in muscle and fat cells by causing the redistribution of a facilitative glucose transporter, GLUT-4, from an intracellular compartment to the cell surface. But what is this intracellular GLUT-4 compartment? It may be a specialized compartment, perhaps analogous to synaptic vesicles, or may simply be part of the endosomal system. Other constituents of this compartment might be regulators of GLUT-4 movement to the cell surface, and their identification should make it possible to find the link between the insulin signal transduction pathway and GLUT-4 translocation.
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Affiliation(s)
- D E James
- Centre for Molecular Biology and Biotechnology, University of Queensland, St Lucia, Brisbane 4072, Australia
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8
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Shinoda Y, Matsuzaki T, Yokoo-Sugawara M, Suzuki T, Aoki T, Hagiwara H, Kuwano H, Takata K. Introduction and Expression of Glucose Transporters in Pancreatic Acinar Cells by In Vivo Electroporation. Acta Histochem Cytochem 2003. [DOI: 10.1267/ahc.36.77] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Affiliation(s)
- Yasuo Shinoda
- Department of Anatomy and Cell Biology, Gunma University School of Medicine
- First Department of Surgery, Gunma University School of Medicine
| | | | | | - Takeshi Suzuki
- Department of Anatomy and Cell Biology, Gunma University School of Medicine
| | - Takeo Aoki
- Department of Anatomy and Cell Biology, Gunma University School of Medicine
| | - Haruo Hagiwara
- Department of Anatomy and Cell Biology, Gunma University School of Medicine
| | - Hiroyuki Kuwano
- First Department of Surgery, Gunma University School of Medicine
| | - Kuniaki Takata
- Department of Anatomy and Cell Biology, Gunma University School of Medicine
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Hübner K, Windoffer R, Hutter H, Leube RE. Tetraspan vesicle membrane proteins: synthesis, subcellular localization, and functional properties. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 214:103-59. [PMID: 11893164 DOI: 10.1016/s0074-7696(02)14004-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Tetraspan vesicle membrane proteins (TVPs) are characterized by four transmembrane regions and cytoplasmically located end domains. They are ubiquitous and abundant components of vesicles in most, if not all, cells of multicellular organisms. TVP-containing vesicles shuttle between various membranous compartments and are localized in biosynthetic and endocytotic pathways. Based on gene organization and amino acid sequence similarities TVPs can be grouped into three distinct families that are referred to as physins, gyrins, and secretory carrier-associated membrane proteins (SCAMPs). In mammals synaptophysin, synaptoporin, pantophysin, and mitsugumin29 constitute the physins, synaptogyrin 1-4 the gyrins, and SCAMP1-5 the SCAMPs. Members of each family are cell-type-specifically synthesized resulting in unique patterns of TVP coexpression and subcellular colocalization. TVP orthologs have been identified in most multicellular organisms, including diverse animal and plant species, but have not been detected in unicellular organisms. They are subject to protein modification, most notably to phosphorylation, and are part of multimeric complexes. Experimental evidence is reviewed showing that TVPs contribute to vesicle trafficking and membrane morphogenesis.
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Affiliation(s)
- Kirsten Hübner
- Department of Anatomy, Johannes Gutenberg University, Mainz, Germany
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10
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Watson RT, Pessin JE. Subcellular compartmentalization and trafficking of the insulin-responsive glucose transporter, GLUT4. Exp Cell Res 2001; 271:75-83. [PMID: 11697884 DOI: 10.1006/excr.2001.5375] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin increases glucose transport into cells of target tissues, primarily striated muscle and adipose. This is accomplished via the insulin-dependent translocation of the facilitative glucose transporter 4 (GLUT4) from intracellular storage sites to the plasma membrane. Insulin binds to the cell-surface insulin receptor and activates its intrinsic tyrosine kinase activity. The subsequent activation of phosphatidylinositol 3-kinase (PI 3-K) is well known to be necessary for the recruitment of GLUT4 to the cell surface. Both protein kinase B (PKB) and the atypical protein kinase C(lambda/zeta) (PKClambda/zeta) appear to function downstream of PI 3-K, but how these effectors influence GLUT4 translocation remains unknown. In addition, emerging evidence suggests that a second signaling cascade that functions independently of the PI 3-K pathway is also required for the insulin-dependent translocation of GLUT4. This second pathway involves the Rho-family GTP binding protein TC10, which functions within the specialized environment of lipid raft microdomains at the plasma membrane. Future work is necessary to identify the downstream effectors that link TC10, PKB, and PKClambda/zeta to GLUT4 translocation. Progress in this area will come from a better understanding of the compartmentalization of GLUT4 within the cell and of the mechanisms responsible for targeting the transporter to specialized insulin-responsive storage compartments. Furthermore, an understanding of how GLUT4 is retained within and released from these compartments will facilitate the identification of downstream signaling molecules that function proximal to the GLUT4 storage sites.
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Affiliation(s)
- R T Watson
- Department of Physiology and Biophysics, University of Iowa, Iowa, Iowa City 52242, USA
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11
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Thoidis G, Kandror KV. A Glut4-vesicle marker protein, insulin-responsive aminopeptidase, is localized in a novel vesicular compartment in PC12 cells. Traffic 2001; 2:577-87. [PMID: 11489215 DOI: 10.1034/j.1600-0854.2001.20807.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Glut4-containing vesicles represent a regulated recycling compartment in insulin-sensitive fat and skeletal muscle cells, the nature and origin of which are not fully understood. In addition to Glut4 itself, these vesicles compartmentalize a number of proteins, at least one of which, insulin-responsive aminopeptidase, or IRAP, is completely colocalized with Glut4 in insulin-sensitive tissues. However, unlike Glut4, IRAP is expressed in a variety of other tissues and cell lines. Here, we explored the intracellular localization of IRAP in the rat pheochromocytoma cell line PC12. We found that this protein is present in a distinct population of slowly recycling light vesicles. By gradient centrifugations, immunoadsorption and double immunofluorescent staining, these vesicles are different from transferrin-containing endosomes, small synaptic vesicles and secretory granules and may thus represent a novel compartment in PC12 cells. Glut4-GFP chimera transiently expressed in PC12 cells is targeted to IRAP-containing vesicles indicating that cotargeting of Glut4 and IRAP is not specific for adipocytes and myocytes, but is faithful in a foreign cell type. We suggest that PC12 cells may possess a novel type of a vesicular carrier that may represent the homolog of Glut4-vesicles.
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Affiliation(s)
- G Thoidis
- Boston University School of Medicine, Boston, MA 02118, USA
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12
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Bogan JS, McKee AE, Lodish HF. Insulin-responsive compartments containing GLUT4 in 3T3-L1 and CHO cells: regulation by amino acid concentrations. Mol Cell Biol 2001; 21:4785-806. [PMID: 11416153 PMCID: PMC87167 DOI: 10.1128/mcb.21.14.4785-4806.2001] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2000] [Accepted: 04/17/2001] [Indexed: 01/14/2023] Open
Abstract
In fat and muscle, insulin stimulates glucose uptake by rapidly mobilizing the GLUT4 glucose transporter from a specialized intracellular compartment to the plasma membrane. We describe a method to quantify the relative proportion of GLUT4 at the plasma membrane, using flow cytometry to measure a ratio of fluorescence intensities corresponding to the cell surface and total amounts of a tagged GLUT4 reporter in individual living cells. Using this assay, we demonstrate that both 3T3-L1 and CHO cells contain intracellular compartments from which GLUT4 is rapidly mobilized by insulin and that the initial magnitude and kinetics of redistribution to the plasma membrane are similar in these two cell types when they are cultured identically. Targeting of GLUT4 to a highly insulin-responsive compartment in CHO cells is modulated by culture conditions. In particular, we find that amino acids regulate distribution of GLUT4 to this kinetically defined compartment through a rapamycin-sensitive pathway. Amino acids also modulate the magnitude of insulin-stimulated translocation in 3T3-L1 adipocytes. Our results indicate a novel link between glucose and amino acid metabolism.
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Affiliation(s)
- J S Bogan
- Diabetes Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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13
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Palacios S, Lalioti V, Martinez-Arca S, Chattopadhyay S, Sandoval IV. Recycling of the insulin-sensitive glucose transporter GLUT4. Access of surface internalized GLUT4 molecules to the perinuclear storage compartment is mediated by the Phe5-Gln6-Gln7-Ile8 motif. J Biol Chem 2001; 276:3371-83. [PMID: 11031262 DOI: 10.1074/jbc.m006739200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The insulin-sensitive glucose transporter GLUT4 is translocated to the plasma membrane in response to insulin and recycled back to the intracellular store(s) after removal of the hormone. We have used clonal 3T3-L1 fibroblasts and adipocyte-like cells stably expressing wild-type GLUT4 to characterize (a) the intracellular compartment where the bulk of GLUT4 is intracellularly stored and (b) the mechanisms involved in the recycling of endocytosed GLUT4 to the store compartment. Surface internalized GLUT4 is targeted to a large, flat, fenestrated saccular structure resistant to brefeldin A that localized to the vicinity of the Golgi complex is sealed to endocytosed transferrin (GLUT4 storage compartment). Recycling of endocytosed GLUT4 was studied by comparing the cellular distributions of antibody/biotin tagged GLUT4 and GLUT4(Ser(5)), a mutant with the Phe(5)-Gln(6)-Gln(7)-Ile(8) inactivated by the substitution of Ser for Phe(5). Ablation of the Phe(5)-Gln(6)-Gln(7)-Ile(8) inhibits the recycling of endocytosed GLUT4 to the GLUT4 store compartment and results in its transport to late endosomes/lysosomes where it is rapidly degraded.
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Affiliation(s)
- S Palacios
- Centro de Biologia Molecular Severo Ochoa. CSIC. Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid 28049, Spain
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14
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Simpson F, Whitehead JP, James DE. GLUT4--at the cross roads between membrane trafficking and signal transduction. Traffic 2001; 2:2-11. [PMID: 11208163 DOI: 10.1034/j.1600-0854.2001.020102.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
GLUT4 is a mammalian facilitative glucose transporter that is highly expressed in adipose tissue and striated muscle. In response to insulin, GLUT4 moves from intracellular storage areas to the plasma membrane, thus increasing cellular glucose uptake. While the verification of this 'translocation hypothesis' (Cushman SW, Wardzala LJ. J Biol Chem 1980;255: 4758-4762 and Suzuki K, Kono T. Proc Natl Acad Sci 1980;77: 2542-2545) has increased our understanding of insulin-regulated glucose transport, a number of fundamental questions remain unanswered. Where is GLUT4 stored within the basal cell? How does GLUT4 move to the cell surface and what mechanism does insulin employ to accelerate this process? Ultimately we require a convergence of trafficking studies with research in signal transduction. However, despite more than 30 years of intensive research we have still not reached this point. The problem is complex, involving at least two separate signal transduction pathways which feed into what appears to be a very dynamic sorting process. Below we discuss some of these complexities and highlight new data that are bringing us closer to the resolution of these questions.
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Affiliation(s)
- F Simpson
- Institute for Molecular Biosciences and the Department of Physiology and Pharmacology, University of Queensland, Brisbane, Australia
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15
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Malide D, Ramm G, Cushman SW, Slot JW. Immunoelectron microscopic evidence that GLUT4 translocation explains the stimulation of glucose transport in isolated rat white adipose cells. J Cell Sci 2000; 113 Pt 23:4203-10. [PMID: 11069765 DOI: 10.1242/jcs.113.23.4203] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We used an improved cryosectioning technique in combination with quantitative immunoelectron microscopy to study GLUT4 compartments in isolated rat white adipose cells. We provide clear evidence that in unstimulated cells most of the GLUT4 localizes intracellularly to tubulovesicular structures clustered near small stacks of Golgi and endosomes, or scattered throughout the cytoplasm. This localization is entirely consistent with that originally described in brown adipose tissue, strongly suggesting that the GLUT4 compartments in white and brown adipose cells are morphologically similar. Furthermore, insulin induces parallel increases (with similar magnitudes) in glucose transport activity, approximately 16-fold, and cell-surface GLUT4, approximately 12-fold. Concomitantly, insulin decreases GLUT4 equally from all intracellular locations, in agreement with the concept that the entire cellular GLUT4 pool contributes to insulin-stimulated exocytosis. In the insulin-stimulated state, GLUT4 molecules are not randomly distributed on the plasma membrane, but neither are they enriched in caveolae. Importantly, the total number of GLUT4 C-terminal epitopes detected by the immuno-gold method is not significantly different between basal and insulin-stimulated cells, thus arguing directly against a reported insulin-induced unmasking effect. These results provide strong morphological evidence (1) that GLUT4 compartments are similar in all insulin-sensitive cells and (2) for the concept that GLUT4 translocation almost fully accounts for the increase in glucose transport in response to insulin.
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Affiliation(s)
- D Malide
- Experimental Diabetes, Metabolism and Nutrition Section, Diabetes Branch, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
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16
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Martin S, Ramm G, Lyttle CT, Meerloo T, Stoorvogel W, James DE. Biogenesis of insulin-responsive GLUT4 vesicles is independent of brefeldin A-sensitive trafficking. Traffic 2000; 1:652-60. [PMID: 11208153 DOI: 10.1034/j.1600-0854.2000.010809.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Insulin stimulates translocation of GLUT4 from an intracellular compartment to the plasma membrane in adipocytes. As a significant amount of GLUT4 is localised to the TGN, independently of the biosynthetic pathway, one possibility is that trafficking via the TGN is important in either intracellular sequestration or insulin-dependent movement to the cell surface. In this study we have used immuno-electron microscopy to show that GLUT4 is localised to AP-1 vesicles in the TGN region in 3T3-L1 adipocytes. To dissect the role of this trafficking pathway we used brefeldin A (BFA) to disrupt AP-1 association with membranes. Despite a reorganisation of GLUT4 compartments following BFA treatment, the intracellular sequestration of GLUT4, and its insulin-dependent movement to the cell surface, was unaffected. BFA increased the half time of reversal of insulin-stimulated glucose transport from 17 to 30 min but did not prevent complete reversal. Furthermore, following reversal restimulation of glucose transport activity by insulin was not compromised. We conclude that under basal conditions GLUT4 cycles between the TGN and endosomes via the AP-1 pathway. However, neither this pathway, nor any other BFA-sensitive pathway, appears to play a major role in insulin-dependent recruitment of GLUT4 to the cell surface.
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Affiliation(s)
- S Martin
- Centre for Molecular and Cellular Biology and Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia.
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17
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Krasnov PA, Enikolopov G. Targeting of synaptotagmin to neurite terminals in neuronally differentiated PC12 cells. J Cell Sci 2000; 113 ( Pt 8):1389-404. [PMID: 10725222 DOI: 10.1242/jcs.113.8.1389] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We have investigated structural elements that determine the accumulation of synaptotagmin, a major synaptic vesicle protein, in neurite terminals of neuronally differentiated neuroendocrine pheochromocytoma PC12 cells. We performed extensive deletion and point mutagenesis of rat synaptotagmin II, expressed mutant proteins in PC12 cells differentiated by nerve growth factor (NGF) and monitored their intracellular distribution by immunofluorescence. We found a structural element located at the carboxy-terminal domain of the synaptotagmin molecule, which is necessary for its accumulation at the terminal. Using alanine-scanning mutagenesis, we have identified two amino acids in this element, tryptophan W405 and leucine L408, that are critical for correct targeting of synaptotagmin II to neurite terminals. Changing either one of them to alanine prevents the accumulation of the protein at the terminals. These amino acids are evolutionarily conserved throughout the entire synaptotagmin family and also among synaptotagmin-related proteins, suggesting that different synaptotagmins may have similar mechanisms of targeting to neuronal cell terminals.
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Affiliation(s)
- P A Krasnov
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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Provoda CJ, Waring MT, Buckley KM. Evidence for a primary endocytic vesicle involved in synaptic vesicle biogenesis. J Biol Chem 2000; 275:7004-12. [PMID: 10702264 DOI: 10.1074/jbc.275.10.7004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The regulated release of neurotransmitters at synapses is mediated by the fusion of neurotransmitter-filled synaptic vesicles with the plasma membrane. Continuous synaptic activity relies on the constant recycling of synaptic vesicle proteins into newly formed synaptic vesicles. At least two different mechanisms are presumed to mediate synaptic vesicle biogenesis at the synapse as follows: direct retrieval of synaptic vesicle proteins and lipids from the plasma membrane, and indirect passage of synaptic vesicle proteins through an endosomal intermediate. We have identified a vesicle population with the characteristics of a primary endocytic vesicle responsible for the recycling of synaptic vesicle proteins through the indirect pathway. We find that synaptic vesicle proteins colocalize in this vesicle with a variety of proteins known to recycle from the plasma membrane through the endocytic pathway, including three different glucose transporters, GLUT1, GLUT3, and GLUT4, and the transferrin receptor. These vesicles differ from "classical" synaptic vesicles in their size and their generic protein content, indicating that they do not discriminate between synaptic vesicle-specific proteins and other recycling proteins. We propose that these vesicles deliver synaptic vesicle proteins that have escaped internalization by the direct pathway to endosomes, where they are sorted from other recycling proteins and packaged into synaptic vesicles.
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Affiliation(s)
- C J Provoda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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19
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Hashiramoto M, James DE. Characterization of insulin-responsive GLUT4 storage vesicles isolated from 3T3-L1 adipocytes. Mol Cell Biol 2000; 20:416-27. [PMID: 10594043 PMCID: PMC85096 DOI: 10.1128/mcb.20.1.416-427.2000] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Insulin regulates glucose transport in muscle and adipose tissue by triggering the translocation of a facilitative glucose transporter, GLUT4, from an intracellular compartment to the cell surface. It has previously been suggested that GLUT4 is segregated between endosomes, the trans-Golgi network (TGN), and a postendosomal storage compartment. The aim of the present study was to isolate the GLUT4 storage compartment in order to determine the relationship of this compartment to other organelles, its components, and its presence in different cell types. A crude intracellular membrane fraction was prepared from 3T3-L1 adipocytes and subjected to iodixanol equilibrium sedimentation analysis. Two distinct GLUT4-containing vesicle peaks were resolved by this procedure. The lighter of the two peaks (peak 2) was comprised of two overlapping peaks: peak 2b contained recycling endosomal markers such as the transferrin receptor (TfR), cellubrevin, and Rab4, and peak 2a was enriched in TGN markers (syntaxin 6, the cation-dependent mannose 6-phosphate receptor, sortilin, and sialyltransferase). Peak 1 contained a significant proportion of GLUT4 with a smaller but significant amount of cellubrevin and relatively little TfR. In agreement with these data, internalized transferrin (Tf) accumulated in peak 2 but not peak 1. There was a quantitatively greater loss of GLUT4 from peak 1 than from peak 2 in response to insulin stimulation. These data, combined with the observation that GLUT4 became more sensitive to ablation with Tf-horseradish peroxidase following insulin treatment, suggest that the vesicles enriched in peak 1 are highly insulin responsive. Iodixanol gradient analysis of membranes isolated from other cell types indicated that a substantial proportion of GLUT4 was targeted to peak 1 in skeletal muscle, whereas in CHO cells most of the GLUT4 was targeted to peak 2. These results indicate that in insulin-sensitive cells GLUT4 is targeted to a subpopulation of vesicles that appear, based on their protein composition, to be a derivative of the endosome. We suggest that the biogenesis of this compartment may mediate withdrawal of GLUT4 from the recycling system and provide the basis for the marked insulin responsiveness of GLUT4 that is unique to muscle and adipocytes.
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Affiliation(s)
- M Hashiramoto
- Centre for Molecular and Cellular Biology, University of Queensland, Brisbane, Queensland 4072, Australia
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20
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Bogan JS, Lodish HF. Two compartments for insulin-stimulated exocytosis in 3T3-L1 adipocytes defined by endogenous ACRP30 and GLUT4. J Cell Biol 1999; 146:609-20. [PMID: 10444069 PMCID: PMC2150549 DOI: 10.1083/jcb.146.3.609] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Insulin stimulates adipose cells both to secrete proteins and to translocate the GLUT4 glucose transporter from an intracellular compartment to the plasma membrane. We demonstrate that whereas insulin stimulation of 3T3-L1 adipocytes has no effect on secretion of the alpha3 chain of type VI collagen, secretion of the protein hormone adipocyte complement related protein of 30 kD (ACRP30) is markedly enhanced. Like GLUT4, regulated exocytosis of ACRP30 appears to require phosphatidylinositol-3-kinase activity, since insulin-stimulated ACRP30 secretion is blocked by pharmacologic inhibitors of this enzyme. Thus, 3T3-L1 adipocytes possess a regulated secretory compartment containing ACRP30. Whether GLUT4 recycles to such a compartment has been controversial. We present deconvolution immunofluorescence microscopy data demonstrating that the subcellular distributions of ACRP30 and GLUT4 are distinct and nonoverlapping; in contrast, those of GLUT4 and the transferrin receptor overlap. Together with supporting evidence that GLUT4 does not recycle to a secretory compartment via the trans-Golgi network, we conclude that there are at least two compartments that undergo insulin-stimulated exocytosis in 3T3-L1 adipocytes: one for ACRP30 secretion and one for GLUT4 translocation.
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Affiliation(s)
- Jonathan S. Bogan
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479
- Diabetes Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114
| | - Harvey F. Lodish
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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21
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Martin S, Slot JW, James DE. GLUT4 trafficking in insulin-sensitive cells. A morphological review. Cell Biochem Biophys 1999; 30:89-113. [PMID: 10099824 DOI: 10.1007/bf02737886] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
In recent years, there have been major advances in the understanding of both the cell biology of vesicle trafficking between intracellular compartments and the molecular targeting signals intrinsic to the trafficking proteins themselves. One system to which these advances have been profitably applied is the regulation of the trafficking of a glucose transporter, GLUT4, from intracellular compartment(s) to the cell surface in response to insulin. The unique nature of the trafficking of GLUT4 and its expression in highly differentiated cells makes this a question of considerable interest to cell biologists. Unraveling the tangled web of molecular events coordinating GLUT4 trafficking will eventually lead to a greater understanding of mammalian glucose metabolism, as well as fundamental cell biological principles related to organelle biogenesis and protein trafficking.
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Affiliation(s)
- S Martin
- Centre for Molecular and Cellular Biology, University of Queensland, Brisbane, Australia
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22
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Pessin JE, Thurmond DC, Elmendorf JS, Coker KJ, Okada S. Molecular basis of insulin-stimulated GLUT4 vesicle trafficking. Location! Location! Location! J Biol Chem 1999; 274:2593-6. [PMID: 9915783 DOI: 10.1074/jbc.274.5.2593] [Citation(s) in RCA: 329] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- J E Pessin
- Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242, USA.
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23
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Arvan P, Castle D. Sorting and storage during secretory granule biogenesis: looking backward and looking forward. Biochem J 1998; 332 ( Pt 3):593-610. [PMID: 9620860 PMCID: PMC1219518 DOI: 10.1042/bj3320593] [Citation(s) in RCA: 409] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Secretory granules are specialized intracellular organelles that serve as a storage pool for selected secretory products. The exocytosis of secretory granules is markedly amplified under physiologically stimulated conditions. While granules have been recognized as post-Golgi carriers for almost 40 years, the molecular mechanisms involved in their formation from the trans-Golgi network are only beginning to be defined. This review summarizes and evaluates current information about how secretory proteins are thought to be sorted for the regulated secretory pathway and how these activities are positioned with respect to other post-Golgi sorting events that must occur in parallel. In the first half of the review, the emerging role of immature secretory granules in protein sorting is highlighted. The second half of the review summarizes what is known about the composition of granule membranes. The numerous similarities and relatively limited differences identified between granule membranes and other vesicular carriers that convey products to and from the plasmalemma, serve as a basis for examining how granule membrane composition might be established and how its unique functions interface with general post-Golgi membrane traffic. Studies of granule formation in vitro offer additional new insights, but also important challenges for future efforts to understand how regulated secretory pathways are constructed and maintained.
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Affiliation(s)
- P Arvan
- Division of Endocrinology and Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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24
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Wei ML, Bonzelius F, Scully RM, Kelly RB, Herman GA. GLUT4 and transferrin receptor are differentially sorted along the endocytic pathway in CHO cells. J Cell Biol 1998; 140:565-75. [PMID: 9456317 PMCID: PMC2140164 DOI: 10.1083/jcb.140.3.565] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/1997] [Revised: 12/09/1997] [Indexed: 02/06/2023] Open
Abstract
The trafficking of GLUT4, a facilitative glucose transporter, is examined in transfected CHO cells. In previous work, we expressed GLUT4 in neuroendocrine cells and fibroblasts and found that it was targeted to a population of small vesicles slightly larger than synaptic vesicles (Herman, G.A, F. Bonzelius, A.M. Cieutat, and R.B. Kelly. 1994. Proc. Natl. Acad. Sci. USA. 91: 12750-12754.). In this study, we demonstrate that at 37 degrees C, GLUT4-containing small vesicles (GSVs) are detected after cell surface radiolabeling of GLUT4 whereas uptake of radioiodinated human transferrin does not show appreciable accumulation within these small vesicles. Immunofluorescence microscopy experiments show that at 37 degrees C, cell surface-labeled GLUT4 as well as transferrin is internalized into peripheral and perinuclear structures. At 15 degrees C, endocytosis of GLUT4 continues to occur at a slowed rate, but whereas fluorescently labeled GLUT4 is seen to accumulate within large peripheral endosomes, no perinuclear structures are labeled, and no radiolabeled GSVs are detectable. Shifting cells to 37 degrees C after accumulating labeled GLUT4 at 15 degrees C results in the reappearance of GLUT4 in perinuclear structures and GSV reformation. Cytosol acidification or treatment with hypertonic media containing sucrose prevents the exit of GLUT4 from peripheral endosomes as well as GSV formation, suggesting that coat proteins may be involved in the endocytic trafficking of GLUT4. In contrast, at 15 degrees C, transferrin continues to traffic to perinuclear structures and overall labels structures similar in distribution to those observed at 37 degrees C. Furthermore, treatment with hypertonic media has no apparent effect on transferrin trafficking from peripheral endosomes. Double-labeling experiments after the internalization of both transferrin and surface-labeled GLUT4 show that GLUT4 accumulates within peripheral compartments that exclude the transferrin receptor (TfR) at both 15 degrees and 37 degrees C. Thus, GLUT4 is sorted differently from the transferrin receptor as evidenced by the targeting of each protein to distinct early endosomal compartments and by the formation of GSVs. These results suggest that the sorting of GLUT4 from TfR may occur primarily at the level of the plasma membrane into distinct endosomes and that the organization of the endocytic system in CHO cells more closely resembles that of neuroendocrine cells than previously appreciated.
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Affiliation(s)
- M L Wei
- Department of Dermatology, The Hormone Research Institute, University of California, San Francisco, California 94143, USA
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25
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Anderson TJ, Martin S, Berka JL, James DE, Slot JW, Stow JL. Distinct localization of renin and GLUT-4 in juxtaglomerular cells of mouse kidney. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:F26-33. [PMID: 9458820 DOI: 10.1152/ajprenal.1998.274.1.f26] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The insulin-responsive glucose transporter, GLUT-4, is found primarily in adipocytes and skeletal muscle cells, where it is sequestered in a specialized recycling compartment, from which it can be recruited to the cell surface following insulin stimulation. Lower levels of GLUT-4 are also expressed in other tissues, including the kidney, where it is present particularly in cells of the afferent arteriole and juxtaglomerular apparatus (JGA). The exact nature of GLUT-4-containing compartments and their relationship to other regulated trafficking pathways in different cells are not yet well defined. The trafficking of GLUT-4 has been studied in different cells with regulated secretory pathways, and a recent study shows that, in cardiomyocytes, GLUT-4 is sorted and packaged into multiple regulated pathways (J. W. Slot, G. Garruti, S. Martin, V. Oorschot, G. Pshuma, E. W. Kraegen, R. Laybutt, G. Thibault, and D. E. James. J. Cell Biol. 137: 1243-1254, 1997). In the kidney, cells of the JGA synthesize and secrete their major product, renin, via a well-established, regulated, secretory pathway. These cells also express GLUT-4 and thus offer the potential to directly compare the localization and trafficking of GLUT-4 and renin in a unique cell type. The present study was undertaken to investigate the intracellular distribution of GLUT-4 in mouse kidney cortex and to determine whether GLUT-4 and renin are trafficked in the same or in separate regulated pathways. Ultrathin cryosections of mouse kidney were labeled by the immunogold technique and viewed by electron microscopy, demonstrating the distribution of GLUT-4 in cells of the JGA, afferent arteriole, and distal tubule. In granular cells of the JGA, renin was localized in secretory granules of the regulated secretory pathway, whereas GLUT-4 labeling in the same cells was found in a distinct tubulovesicular compartment located adjacent to the trans-Golgi network. We show that granular cells have separate, morphologically distinct compartments for the sequestration of renin and GLUT-4, providing evidence that there may be distinct pathways for the sorting and trafficking of these two proteins.
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Affiliation(s)
- T J Anderson
- Centre for Molecular and Cellular Biology, University of Queensland, Brisbane, Australia
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26
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Malide D, Dwyer NK, Blanchette-Mackie EJ, Cushman SW. Immunocytochemical evidence that GLUT4 resides in a specialized translocation post-endosomal VAMP2-positive compartment in rat adipose cells in the absence of insulin. J Histochem Cytochem 1997; 45:1083-96. [PMID: 9267469 DOI: 10.1177/002215549704500806] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Insulin stimulates glucose transport in rat adipose cells through the translocation of GLUT4 from a poorly defined intracellular compartment to the cell surface. We employed confocal microscopy to determine the in situ localization of GLUT4 relative to vesicle, Golgi, and endosomal proteins in these physiological insulin target cells. Three-dimensional analyses of GLUT4 immunostaining in basal cells revealed an intracellular punctate, patchy distribution both in the perinuclear region and scattered throughout the cytoplasm. VAMP2 closely associates with GLUT4 in many punctate vesicle-like structures. A small fraction of GLUT4 overlaps with TGN38-mannosidase II, gamma-adaptin, and mannose-6-phosphate receptors in the perinuclear region, presumably corresponding to late endosome and trans-Golgi network structures. GLUT4 does not co-localize with transferrin receptors, clathrin, and Igp-120. After insulin treatment, GLUT4 partially redistributes to the cell surface and decreases in the perinuclear area. However, GLUT4 remains co-localized with TGN38-mannosidase II and gamma-adaptin. Therefore, the basal compartment from which GLUT4 is translocated in response to insulin comprises specialized post-endosomal VAMP2-positive vesicles, distinct from the constitutively recycling endosomes. These results are consistent with a kinetic model in which GLUT4 is sequestered through two or more intracellular pools in series.
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Affiliation(s)
- D Malide
- Experimental Diabetes, Metabolism, and Nutrition Section, National Institutes of Health, Bethesda, Maryland 20892-1420, USA
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27
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Abstract
Protein folding that is coupled to disulphide bond formation has many experimental advantages. In particular, the kinetic roles and importance of all the disulphide intermediates can be determined, usually unambiguously. This contrasts with other types of protein folding, where the roles of any intermediates detected are usually not established. Nevertheless, there is considerable confusion in the literature about even the best-characterized disulphide folding pathways. This article attempts to set the record straight.
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28
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Slot JW, Garruti G, Martin S, Oorschot V, Posthuma G, Kraegen EW, Laybutt R, Thibault G, James DE. Glucose transporter (GLUT-4) is targeted to secretory granules in rat atrial cardiomyocytes. J Cell Biol 1997; 137:1243-54. [PMID: 9182659 PMCID: PMC2132533 DOI: 10.1083/jcb.137.6.1243] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/1996] [Revised: 03/27/1997] [Indexed: 02/04/2023] Open
Abstract
The insulin-responsive glucose transporter GLUT-4 is found in muscle and fat cells in the trans-Golgi reticulum (TGR) and in an intracellular tubulovesicular compartment, from where it undergoes insulin-dependent movement to the cell surface. To examine the relationship between these GLUT-4-containing compartments and the regulated secretory pathway we have localized GLUT-4 in atrial cardiomyocytes. This cell type secretes an antihypertensive hormone, referred to as the atrial natriuretic factor (ANF), in response to elevated blood pressure. We show that GLUT-4 is targeted in the atrial cell to the TGR and a tubulo-vesicular compartment, which is morphologically and functionally indistinguishable from the intracellular GLUT-4 compartment found in other types of myocytes and in fat cells, and in addition to the ANF secretory granules. Forming ANF granules are present throughout all Golgi cisternae but only become GLUT4 positive in the TGR. The inability of cyclohexamide treatment to effect the TGR localization of GLUT-4 indicates that GLUT-4 enters the ANF secretory granules at the TGR via the recycling pathway and not via the biosynthetic pathway. These data suggest that a large proportion of GLUT-4 must recycle via the TGR in insulin-sensitive cells. It will be important to determine if this is the pathway by which the insulin-regulatable tubulo-vesicular compartment is formed.
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Affiliation(s)
- J W Slot
- Department of Cell Biology, Medical School, Utrecht University, 3584 CX Utrecht, The Netherlands
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29
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Schweitzer ES, Jeng CJ, Tao-Cheng JH. Selective localization and regulated release of calcitonin gene-related peptide from dense-core vesicles in engineered PC12 cells. J Neurosci Res 1996; 46:519-30. [PMID: 8951664 DOI: 10.1002/(sici)1097-4547(19961201)46:5<519::aid-jnr1>3.0.co;2-m] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Introduction of the gene for calcitonin into the neuroendocrine PC12 cell line resulted in the expression of the neuronal-specific splice product, calcitonin gene-related peptide (CGRP). Expression of this neuropeptide did not require treatment of the PC12 cells with NGF. By all available criteria, including biochemical, immunological, and morphological analysis, we have determined that the CGRP in stably transfected PC12 cells is sorted selectively into the large, dense-core catecholamine-containing secretory vesicles. Conversely, the CGRP is excluded from the small, synaptophysin-rich vesicles present in the same cells. Stimulation conditions that trigger the release of catecholamines cause a parallel burst in the release of CGRP. In all these respects, the engineered PC12 cells process the foreign CGRP in a manner similar to that seen in spinal motor neurons in vivo. These results indicate that this small (37 amino acids) peptide contains sorting information sufficient for targeting to large, dense-core vesicles in heterologous cells, placing very narrow constraints on the possible location of sorting signals. In addition, this CGRP-expressing cell line opens the possibility of studying the physiological role of CGRP in the establishment and maintenance of neuromuscular contacts.
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Affiliation(s)
- E S Schweitzer
- Department of Neurobiology, University of California, Los Angeles Medical School, USA
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30
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Passafaro M, Rosa P, Sala C, Clementi F, Sher E. N-type Ca2+ channels are present in secretory granules and are transiently translocated to the plasma membrane during regulated exocytosis. J Biol Chem 1996; 271:30096-104. [PMID: 8939958 DOI: 10.1074/jbc.271.47.30096] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
An intracellular pool of N-type voltage-operated calcium channels has recently been described in different neuronal cell lines. We have now further characterized the intracellular pool of N-type calcium channels in both IMR32 human neuroblastoma and PC12 rat pheochromocytoma cells. Intracellular N-type calcium channels were found to be accumulated in subcellular fractions where the chromogranin B-containing secretory granules were also enriched. 125I-omega-Conotoxin GVIA binding assays on fixed and permeabilized cells revealed that intracellular N-type calcium channels translocate to the plasma membrane in cells exposed to secretagogues (KCl, ionomycin, and phorbol esters). The kinetics, Ca2+ and protein kinase C dependence, and brefeldin A insensitivity of N-type calcium channels translocation were similar to the regulated release of chromogranin B, while no correlation was found with the constitutive secretion of a heparan sulfate proteoglycan. A PC12 subclone deficient in the regulated but not in the constitutive pathway of secretion had a small intracellular pool of N-type calcium channels, and no secretagogue-induced translocation occurred in these cells. Calcium channel translocation was accompanied by a stronger response of Fura-2-loaded cells to depolarizing stimuli, suggesting that the newly inserted channels are functional.
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Affiliation(s)
- M Passafaro
- CNR Institute of Biotechnologies Applied to Pharmacology, 88021 Roccelletta di Borgia (CZ), Italy.
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31
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Cloherty EK, Diamond DL, Heard KS, Carruthers A. Regulation of GLUT1-mediated sugar transport by an antiport/uniport switch mechanism. Biochemistry 1996; 35:13231-9. [PMID: 8855962 DOI: 10.1021/bi961208t] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Avian erythrocyte sugar transport is stimulated during anoxia and during exposure to inhibitors of oxidative phosphorylation. This stimulation results from catalytic desuppression of the cell surface glucose transporter GLUT1 [Diamond, D., & Carruthers, A. (1993) J. Biol. Chem. 268, 6437-6444]. The present study was undertaken to investigate the mechanisms of GLUT1 suppression/desuppression. Sugar uniport (sugar uptake or exit in the absence of sugar at the opposite side of the membrane) is absent in normoxic avian erythrocytes, but sugar antiport (sugar uptake coupled to sugar exit) is present. Exposure to cyanide and/or to FCCP (mitochondrial inhibitors) stimulates erythrocyte sugar uniport but not sugar antiport. K(m)(app) for 3-O-methylglucose uniport and antiport are unaffected by metabolic poisoning. Ki(app) for inhibitions of 3-O-methylglucose uniport by cytochalasin B and forskolin (sugar export site ligands) are unaffected by progressive stimulation of sugar uniport. Cyanide and FCCP stimulation of 3-O-methylglucose uniport are associated with increased AMP-activated protein kinase activity. Purified human GLUT1 is not phosphorylated by exposure to cytosol extracted from poisoned avian erythrocytes. FCCP does not stimulate GLUT1-mediated 3-O-methylglucose uptake in K562 cells but does increase K562 AMP-activated protein kinase activity. FCCP stimulation of 3-O-methylglucose uniport in resealed erythrocyte ghosts requires cytosolic ATP and/or glutathione. The nonmetabolizable ATP analog AMP-PNP cannot be substituted for ATP in this action. These results are contrasted with allosteric regulation of human erythrocyte sugar transport and suggest that avian erythrocyte sugar transport suppression results from inhibition of carrier uniport function. Uniport suppression is not mediated by interaction with cytosolic molecular species that bind to the sugar export site. The antiport to uniport switch mechanism requires ATP hydrolysis, is associated with elevated AMP-activated kinase function, and, if triggered by this kinase, is mediated by factors absent in K562 cells and downstream from the kinase.
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Affiliation(s)
- E K Cloherty
- Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01605, USA
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32
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Dobson SP, Livingstone C, Gould GW, Tavaré JM. Dynamics of insulin-stimulated translocation of GLUT4 in single living cells visualised using green fluorescent protein. FEBS Lett 1996; 393:179-84. [PMID: 8814285 DOI: 10.1016/0014-5793(96)00879-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Insulin increases glucose uptake by promoting the translocation of the GLUT4 isoform of glucose transporters to the plasma membrane. We have studied this process in living single cells by fusing green fluorescent protein (GFP) to the N-terminus (GFP-GLUT4) or C-terminus (GLUT4-GFP), of GLUT4. Both chimeras were expressed in a perinuclear compartment of CHO cells, and in a vesicular distribution through the cytosol. Insulin promoted an increase in plasma membrane fluorescence as a result of net translocation of the chimeras to the cell surface. GLUT4-GFP, but not GFP-GLUT4, was re-internalised upon the removal of insulin suggesting that a critical internalisation signal sequence exists in the N-terminus of GLUT4. The use of GFP thus allows an analysis of GLUT4 trafficking in single living cells.
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Affiliation(s)
- S P Dobson
- Department of Biochemistry, School of Medical Sciences, University of Bristol, UK
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33
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Thorens B, Roth J. Intracellular targeting of GLUT4 in transfected insulinoma cells: evidence for association with constitutively recycling vesicles distinct from synaptophysin and insulin vesicles. J Cell Sci 1996; 109 ( Pt 6):1311-23. [PMID: 8799820 DOI: 10.1242/jcs.109.6.1311] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In adipocytes and muscle cells, the GLUT4 glucose transporter isoform is present in intracellular vesicles which continuously recycle between an intracytoplasmic location and the plasma membrane. It is not clear whether the GLUT4-vesicles represent a specific kind of vesicle or resemble typical secretory granules or synaptic-like microvesicles. To approach this question, we expressed GLUT4 in the beta cell line RINm5F and determined its intracellular localization by subcellular fractionation and by immunofluorescence and immunoelectron microscopy. GLUT4 was not found in insulin granules but was associated with a subpopulation of smooth-surface vesicles present in the trans-Golgi region and in vesicular structures adjacent to the plasma membrane. In the trans-Golgi region, GLUT4 did not colocalize with synaptophysin or TGN38. Incubation of the cells with horseradish peroxidase (HRP) led to colocalization of HRP and GLUT4 in some endosomal structures adjacent to the plasma membrane and in occasional trans-Golgi region vesicles. When cells were incubated in the presence of Bafilomycin A, analysis by confocal microscopy revealed GLUT4 in numerous large spots present throughout the cytoplasm, many of which costained for TGN38 and synaptophysin. By immunoelectron microscopy, numerous endosomes were observed which stained strongly for GLUT4. Together our data demonstrate that ectopic expression of GLUT4 in insulinoma cells reveals the presence of a subset of vesicular structures distinct from synaptic-like vesicles and insulin secretory granules. Furthermore, they indicate that GLUT4 constitutively recycles between the plasma membrane and its intracellular location by an endocytic route also taken by TGN38 and synaptophysin.
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Affiliation(s)
- B Thorens
- Institute of Pharmacology and Toxicology, University of Lausanne, Switzerland
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34
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Livingstone C, Thomson FJ, Arbuckle MI, Campbell IW, Jess TJ, Kane S, Moyes C, Porter LM, Rice JE, Seatter MJ, Gould GW. Hormonal regulation of the insulin-responsive glucose transporter, GLUT4: some recent advances. Proc Nutr Soc 1996; 55:179-90. [PMID: 8832790 DOI: 10.1079/pns19960019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- C Livingstone
- Division of Biochemistry and Molecular Biology, University of Glasgow
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35
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Liu Y, Peter D, Merickel A, Krantz D, Finn JP, Edwards RH. A molecular analysis of vesicular amine transport. Behav Brain Res 1995; 73:51-8. [PMID: 8788477 DOI: 10.1016/0166-4328(96)00069-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To package classical neurotransmitters into vesicles so that their release can be regulated by activity, neuronal cells express a set of specific vesicular transport proteins. We have used selection in MPP+ to clone the cDNAs encoding two vesicular monoamine transporters, the first members of this novel gene family that now also includes the vesicular transporter for acetylcholine. The sequences show similarity to several bacterial antibiotic resistance proteins, further supporting a role in detoxification and possibly Parkinson's disease. The two vesicular amine transporters show differences in their affinity for substrates, their turnover number and their pharmacology. In particular, the proteins differ in their interactions with the potent inhibitor tetrabenazine and with amphetamines, accounting for several classic pharmacological observations. Since the subcellular localization of the transport proteins determines the site of monoamine storage and the site of monoamine storage appears to differ from other classical transmitters, we have also raised polyclonal antibodies to the transporters and used these to demonstrate localization in dense core vesicles rather than synaptic vesicles. In addition to the implications for monoamine release, these observations also indicate a vesicular amine transporter as the first integral membrane protein restricted to the regulated secretory pathway.
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Affiliation(s)
- Y Liu
- Department of Neurology, UCLA School of Medicine 90024-1769, USA
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36
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Widnell CC. Control of glucose transport by GLUT1: regulated secretion in an unexpected environment. Biosci Rep 1995; 15:427-43. [PMID: 9156574 DOI: 10.1007/bf01204347] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Studies designed to elucidate the mechanism of regulation of the GLUT1 isoform of the glucose transporter in response to a variety of cellular stresses are reviewed. Using ts mutants of vesicular stomatitis virus, it was shown that the viral L gene was responsible for the stimulation of glucose transport in infected cells. Immunofluorescence of GLUT1 demonstrated that the increase in glucose transport was the consequence of a translocation of the transporter from a reservoir in cytoplasmic vesicles to the plasma membrane. When cells were cycled between deficient and standard medium, the change in glucose transport rates was paralleled by a cycling of the transporter between the plasma membrane and the cytoplasmic vesicles. The redistribution of GLUT1 was not a consequence of a general redistribution of recycling plasma membrane proteins. Instead, the findings focus attention on the regulated exocytosis of specific membrane constituents in cells that, until recently, were not thought to exhibit this capacity.
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Affiliation(s)
- C C Widnell
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, PA 15261, USA
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Hudson AW, Birnbaum MJ. Identification of a nonneuronal isoform of synaptotagmin. Proc Natl Acad Sci U S A 1995; 92:5895-9. [PMID: 7597049 PMCID: PMC41608 DOI: 10.1073/pnas.92.13.5895] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Synaptotagmins, which have been found exclusively in neuroendocrine or exocrine tissues, have been implicated in the regulation of secretory vesicle fusion with the plasma membrane. The present paper describes a synaptotagmin isoform (synaptotagmin-5) which exhibits 49% amino acid identity to synaptotagmin-1 and -2. Synaptotagmin-5 mRNA is expressed in rat kidney, adipose tissue, lung, and heart, as well as at higher levels in brain and PC12 cells. Antiserum specific for the synaptotagmin-5 isoform recognizes a protein of about 50 kDa which is about 6-fold more abundant in brain synaptic vesicles than in whole brain membranes.
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Affiliation(s)
- A W Hudson
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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38
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Abstract
Clostridial neurotoxins, tetanus and the botulinum toxins A-G, are high molecular weight proteins consisting of a heavy chain which is responsible for the internalisation and a light chain possessing a zinc-dependent proteolytic activity. They exclusively proteolyse either the vesicle membrane protein, synaptobrevin or two integral plasma membrane proteins, SNAP 25 and syntaxin. Together with cytosolic proteins these proteins form the SNARE complex involved in vesicle exocytosis, and their cleavage blocks the latter process. Clostridial neurotoxins have now become powerful tools to investigate the final events occurring during secretion in neuronal, endocrine, and non-neuronal cells. They are applied to dissect the specific interactions of the SNARE protein complex with cytosolic fusogens and other modulators of exocytosis. Whereas exocytosis is not essential for the survival of cells, the organism as a whole will fall victim to a few nanograms since interneuronal and neuromuscular transmission is vital to muscular control, especially in respiration. Although all clostridial neurotoxins by their light chains attack proteins of the SNARE complex, tetanus toxin and the various botulinum toxins differ dramatically in their clinical symptoms. The biological information for this difference resides on the respective heavy chains which select different transport routes carrying the light chain from the place of entrance to the final compartment of action. So far the different transport vesicles used either by the various botulinum neurotoxins or by tetanus toxin are not yet defined. Nevertheless at least one of the botulinum toxins serves as a beneficial drug in the treatment of severe neuromuscular spasms.
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Affiliation(s)
- G Ahnert-Hilger
- Freie Universität Berlin Universitätsklinikum Benjamin Franklin, Abteilung Gastroenterologie, Germany
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Volchuk A, Sargeant R, Sumitani S, Liu Z, He L, Klip A. Cellubrevin is a resident protein of insulin-sensitive GLUT4 glucose transporter vesicles in 3T3-L1 adipocytes. J Biol Chem 1995; 270:8233-40. [PMID: 7713930 DOI: 10.1074/jbc.270.14.8233] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Insulin stimulates glucose transport in muscle and fat cells by inducing translocation of GLUT4 glucose transporters from a storage site to the cell surface. The mechanism of this translocation and the identity of the storage site are unknown, but it has been hypothesized that transporters recycle between an insulin-sensitive pool, endosomes, and the cell surface. Upon cell homogenization and fractionation, the storage site migrates with light microsomes (LDM) separate from the plasma membrane fraction (PM). Cellubrevin is a recently identified endosomal protein that may be involved in the reexocytosis of recycling endosomes. Here we describe that cellubrevin is expressed in 3T3-L1 adipocytes and is more abundant in the LDM than in the PM. Cellubrevin was markedly induced during differentiation of 3T3-L1 fibroblasts into adipocytes, in parallel with GLUT4, and the development of insulin regulated traffic. In response to insulin, the cellubrevin content decreased in the LDM and increased in the PM, suggesting translocation akin to that of the GLUT4 glucose transporter. Vesicle-associated membrane protein 2 (VAMP-2)/synaptobrevin-II, a protein associated with regulated exocytosis in secretory cells, also redistributed in response to insulin. Both cellubrevin and VAMP-2 were susceptible to cleavage by tetanus toxin. Immunopurified GLUT4-containing vesicles contained cellubrevin and VAMP-2, and immunopurified cellubrevin-containing vesicles contained GLUT4 protein, but undiscernible amounts of VAMP-2. These observations suggest that cellubrevin and VAMP-2 are constituents of the insulin-regulated pathway of membrane traffic. These results are the first demonstration that cellubrevin is present in a regulated intracellular compartment. We hypothesize that cellubrevin and VAMP-2 may be present in different subsets of GLUT4-containing vesicles.
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Affiliation(s)
- A Volchuk
- Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada
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40
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Herman GA, Bonzelius F, Cieutat AM, Kelly RB. A distinct class of intracellular storage vesicles, identified by expression of the glucose transporter GLUT4. Proc Natl Acad Sci U S A 1994; 91:12750-4. [PMID: 7809115 PMCID: PMC45517 DOI: 10.1073/pnas.91.26.12750] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Some cell types have cytoplasmic storage vesicles whose fusion with the cell surface is triggered by an extracellular signal. To explore the relationship between different classes of storage vesicles, we expressed, in the neuro-endocrine cell line PC12, the facilitative glucose transporter GLUT4, which is stored in small cytoplasmic vesicles in fat and muscle cells and mobilized to the cell surface when insulin is present. PC12 cells have two known types of storage vesicles, secretory granules and synaptic vesicles, but GLUT4 is targeted to neither. It is recovered, however, in a class of small vesicles that sediment approximately twice as fast as synaptic vesicles. Immunoelectron microscopy confirmed the presence of such small vesicles in transfected PC12 cells. By velocity sedimentation analysis, GLUT4 vesicles efficiently exclude the synaptic vesicle markers synaptophysin, SV2, and synaptobrevin; the transferrin receptor, a marker of conventional endocytosis; and the polymeric immunoglobulin receptor, a marker of transcytosis. The exclusion of synaptophysin and the transferrin receptor from most of the GLUT4-containing structures was confirmed by confocal immunofluorescence microscopy. Like synaptic vesicles, therefore, GLUT4 vesicles of PC12 cells appear to be a unique type of organelle. A GLUT4-containing organelle of identical sedimentation properties was found in transfected fibroblast cell lines and in rat adipocytes. On stimulation of the adipocytes with insulin, GLUT4 was translocated from the peak of small vesicles to faster sedimenting membranes. We propose that the class of vesicles described here is present in a wide range of cell types and is involved in transient modification of the cell surface.
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Affiliation(s)
- G A Herman
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0534
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41
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Bonzelius F, Herman GA, Cardone MH, Mostov KE, Kelly RB. The polymeric immunoglobulin receptor accumulates in specialized endosomes but not synaptic vesicles within the neurites of transfected neuroendocrine PC12 cells. J Cell Biol 1994; 127:1603-16. [PMID: 7798315 PMCID: PMC2120272 DOI: 10.1083/jcb.127.6.1603] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have expressed in neuroendocrine PC12 cells the polymeric immunoglobulin receptor (pIgR), which is normally targeted from the basolateral to the apical surface of epithelial cells. In the presence of nerve growth factor, PC12 cells extend neurites which contain synaptic vesicle-like structures and regulated secretory granules. By immunofluorescence microscopy, pIgR, like the synaptic vesicle protein synaptophysin, accumulates in both the cell body and the neurites. On the other hand, the transferrin receptor, which normally recycles at the basolateral surface in epithelial cells, and the cation-independent mannose 6-phosphate receptor, a marker of late endosomes, are largely restricted to the cell body. pIgR internalizes ligand into endosomes within the cell body and the neurites, while uptake of ligand by the low density lipoprotein receptor occurs primarily into endosomes within the cell body. We conclude that transport of membrane proteins to PC12 neurites as well as to specialized endosomes within these processes is selective and appears to be governed by similar mechanisms that dictate sorting in epithelial cells. Additionally, two types of endosomes can be identified in polarized PC12 cells by the differential uptake of ligand, a housekeeping type in the cell bodies and a specialized endosome in the neurites. Recent findings suggest that specialized axonal endosomes in neurons are likely to give rise to synaptic vesicles (Mundigl, O., M. Matteoli, L. Daniell, A. Thomas-Reetz, A. Metcalf, R. Jahn, and P. De Camilli. 1993. J. Cell Biol. 122:1207-1221). Although pIgR reaches the specialized endosomes in the neurites of PC12 cells, we find by subcellular fractionation that under a variety of conditions it is efficiently excluded from synaptic vesicle-like structures as well as from secretory granules.
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Affiliation(s)
- F Bonzelius
- Department of Biochemistry and Biophysics and Hormone Research Institute, University of California, San Francisco, California 94143
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42
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Brant AM, Martin S, Gould GW. Expression of the liver-type glucose transporter (GLUT2) in 3T3-L1 adipocytes: analysis of the effects of insulin on subcellular distribution. Biochem J 1994; 304 ( Pt 1):307-11. [PMID: 7998950 PMCID: PMC1137487 DOI: 10.1042/bj3040307] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have expressed the liver-type facilitative glucose transporter, GLUT2, in the insulin-sensitive 3T3-L1 adipocyte clonal cell line in an effort to address the importance of transporter isoform and cellular environment on the ability of insulin to mediate glucose-transporter translocation. Analysis of non-differentiated fibroblastic cell clones transfected with the GLUT2 cDNA identified the presence of this isoform in several independent clones. These clones exhibited increased deoxyglucose and fructose transport rates compared with control cells. Upon differentiation, the fibroblastic clones selected for study achieved > 95% phenotypic conversion into adipocytes. Expression of the GLUT2 protein was maintained throughout the differentiation protocol. Subcellular fractionation revealed that in response to insulin, unlike the native GLUT4, GLUT2 protein did not undergo significant translocation to the plasma membrane; furthermore, the subcellular distribution of the expressed GLUT2 was quite distinct from that of the endogenous GLUT4. 3T3-L1 adipocytes expressing GLUT2 only exhibited a 2-fold increase in insulin-stimulated fructose uptake, further suggesting that GLUT2 does not undergo insulin-stimulated translocation.
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Affiliation(s)
- A M Brant
- Division of Biochemistry, University of Glasgow, Scotland, U.K
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43
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Roush DL, Gottardi CJ, Caplan MJ. Sorting of the gastric H,K-ATPase in endocrine and epithelial cells. Ann N Y Acad Sci 1994; 733:212-22. [PMID: 7978870 DOI: 10.1111/j.1749-6632.1994.tb17271.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- D L Roush
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
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44
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Corvera S, Chawla A, Chakrabarti R, Joly M, Buxton J, Czech MP. A double leucine within the GLUT4 glucose transporter COOH-terminal domain functions as an endocytosis signal. J Cell Biol 1994; 126:979-89. [PMID: 7519625 PMCID: PMC2120130 DOI: 10.1083/jcb.126.4.979] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The unique COOH-terminal 30-amino acid region of the adipocyte/skeletal muscle glucose transporter (GLUT4) appears to be a major structural determinant of this protein's perinuclear localization, from where it is redistributed to the cell surface in response to insulin. To test whether an underlying mechanism of this domain's function involves glucose transporter endocytosis rates, transfected cells were generated expressing exofacial hemagglutinin epitope (HA)-tagged erythrocyte/brain glucose transporter (GLUT1) or a chimera containing the COOH-terminal 30 amino acids of GLUT4 substituted onto this GLUT1 construct. Incubation of COS-7 or CHO cells expressing the HA-tagged chimera with anti-HA antibody at 37 degrees resulted in an increased rate of antibody internalization compared to cells expressing similar levels of HA-tagged GLUT1, which displays a cell surface disposition. Colocalization of the internalized anti-HA antibody in vesicular structures with internalized transferrin and with total transporters was established by digital imaging microscopy, suggesting the total cellular pool of transporters are continuously recycling through the coated pit endocytosis pathway. Mutation of the unique double leucines 489 and 490 in the rat GLUT4 COOH-terminal domain to alanines caused the HA-tagged chimera to revert to the slow endocytosis rate and steady-state cell surface display characteristic of GLUT1. These results support the hypothesis that the double leucine motif in the GLUT4 COOH terminus operates as a rapid endocytosis and retention signal in the GLUT4 transporter, causing its localization to intracellular compartments in the absence of insulin.
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Affiliation(s)
- S Corvera
- Program in Molecular Medicine, University of Massachusetts Medical Center, Worcester 01605
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45
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Colomer V, Rindler MJ, Lowe AW. Apical plasma membrane proteins are not obligatorily stored in secretory granules in exocrine cells. J Cell Sci 1994; 107 ( Pt 8):2271-7. [PMID: 7983185 DOI: 10.1242/jcs.107.8.2271] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Exocrine cells are epithelial cells in which secretory granules undergo fusion with the apical plasma membrane upon secretagogue stimulation. Several apical plasma membrane proteins have been found in secretory granules in cells from pancreas and salivary glands raising the possibility that incorporation into secretory granules followed by exocytosis of the granules accounts for their insertion into the apical plasma membrane. To test this hypothesis, we have expressed the influenza hemagglutinin (HA) in pancreatic AR42J cells, which make zymogen-like granules upon incubation with dexamethasone. The influenza virus HA is known to be specifically targeted to the apical plasma membrane of epithelial cells that lack a regulated pathway and is also known to be excluded from secretory granules in virally-infected pituitary AtT20 cells. Localization of the protein by immunofluorescence microscopy revealed that it accumulated at the plasma membrane of the transfected AR42J cells. HA was not observed in the amylase-rich secretory granules. By immunolabeling of ultrathin cryosections of the transfected cells, HA was also found exclusively on the cell surface, with label over secretory granules not exceeding that seen in control, untransfected cells. In addition, in cell fractionation experiments performed on radiolabeled AR42J cell transformants, HA was not detectable in the secretory granule fractions. These results indicate that HA is not efficiently stored in mature secretory granules and is likely to reach the cell surface via constitutive transport pathways.
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Affiliation(s)
- V Colomer
- Department of Cell Biology, New York University Medical Center, New York
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46
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Verhey K, Birnbaum M. A Leu-Leu sequence is essential for COOH-terminal targeting signal of GLUT4 glucose transporter in fibroblasts. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)41949-1] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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47
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Verhey KJ, Hausdorff SF, Birnbaum MJ. Identification of the carboxy terminus as important for the isoform-specific subcellular targeting of glucose transporter proteins. J Biophys Biochem Cytol 1993; 123:137-47. [PMID: 7691826 PMCID: PMC2119809 DOI: 10.1083/jcb.123.1.137] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Differential trafficking of glucose transporters contributes significantly to the establishment of a cell's capacity for hormone-regulatable hexose uptake. In the true insulin-sensitive peripheral target tissues, muscle and adipose, the transporter isoform GLUT1 residues on the cell surface and interior of the cell whereas the highly homologous isoform GLUT4 displays virtually exclusive intracellular sequestration, allowing the latter to redistribute to the cell surface in response to hormone. These patterns are equally pronounced in cells into which the transporters have been introduced by DNA-mediated gene transfer, suggesting that signals for isoform-specific sorting are recognized in diverse cell types. To determine the primary sequences responsible for the characteristic distributions, chimeric transporters were constructed in which reciprocal domains were exchanged between GLUT1 and GLUT4. In addition, a non-disruptive, species-specific epitope "tag" was introduced into a neutral region of the transporter to allow analysis of reciprocal chimeras using a single antibody. These recombinant transporters were stably expressed in HIH 3T3 and PC12 cells by retrovirus-mediated gene transfer, and were localized by indirect immunofluorescence and laser scanning confocal microscopy, as well as by staining of plasma membrane sheets prepared from these cells. The results indicate that the carboxy-terminal 30 amino acids are primarily responsible for the differential targeting of the glucose transporter isoforms GLUT1 and GLUT4, though there is a lesser additional contribution by the amino-terminal 183 amino acids.
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Affiliation(s)
- K J Verhey
- Department of Cellular and Molecular Physiology, Harvard Medical School, Boston, Massachusetts 02115
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