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(Flintoaca) Alexandru PR, Chiritoiu GN, Lixandru D, Zurac S, Ionescu-Targoviste C, Petrescu SM. EDEM1 regulates the insulin mRNA level by inhibiting the endoplasmic reticulum stress-induced IRE1/JNK/c-Jun pathway. iScience 2023; 26:107956. [PMID: 37822496 PMCID: PMC10562789 DOI: 10.1016/j.isci.2023.107956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 07/22/2023] [Accepted: 09/14/2023] [Indexed: 10/13/2023] Open
Abstract
Pancreatic beta cells produce and secrete insulin as a response to rises in blood glucose. Despite the advances in understanding glucose-regulated insulin transcription and translation the mechanisms triggering the synthesis of new insulin molecules are still incompletely described. In this report, we identify EDEM1 as a new modulator of insulin synthesis and secretion. In the presence of EDEM1, INS-1E cells secrete significantly more insulin upon glucose stimulation compared to control cells. We found that overexpression of EDEM1 inhibited the IRE1/JNK/c-Jun pathway, leading to an increase in the insulin mRNA level. Similarly, EDEM1 transduced human islets secreted significantly more insulin upon stimulation. Furthermore, EDEM1 improved insulin secretion restoring normoglycemia and glucose tolerance in diabetic rats. We propose EDEM1 as a regulator of the UPR via IRE1/XBP1s and IRE1/JNK/c-Jun signaling cascades and insulin transcription in pancreatic β-cells, supporting EDEM1 as a potential target for the treatment of diabetes.
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Affiliation(s)
| | - Gabriela N. Chiritoiu
- Department of Molecular Cell Biology, Institute of Biochemistry, Romanian Academy, 060031 Bucharest, Romania
| | - Daniela Lixandru
- Department of Biochemistry, “Carol Davila” University of Medicine and Pharmacy, 050474 Bucharest, Romania
| | - Sabina Zurac
- Department of Physiology, “Carol Davila” University of Medicine and Pharmacy, 050474 Bucharest, Romania
| | | | - Stefana M. Petrescu
- Department of Molecular Cell Biology, Institute of Biochemistry, Romanian Academy, 060031 Bucharest, Romania
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2
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Mazumdar S, Chitkara D, Mittal A. Exploration and insights into the cellular internalization and intracellular fate of amphiphilic polymeric nanocarriers. Acta Pharm Sin B 2021; 11:903-924. [PMID: 33996406 PMCID: PMC8105776 DOI: 10.1016/j.apsb.2021.02.019] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 12/20/2020] [Accepted: 01/18/2021] [Indexed: 01/01/2023] Open
Abstract
The beneficial or deleterious effects of nanomedicines emerge from their complex interactions with intracellular pathways and their subcellular fate. Moreover, the dynamic nature of plasma membrane accounts for the movement of these nanocarriers within the cell towards different organelles thereby not only influencing their pharmacokinetic and pharmacodynamic properties but also bioavailability, therapeutic efficacy and toxicity. Therefore, an in-depth understanding of underlying parameters controlling nanocarrier endocytosis and intracellular fate is essential. In order to direct nanoparticles towards specific sub-cellular organelles the physicochemical attributes of nanocarriers can be manipulated. These include particle size, shape and surface charge/chemistry. Restricting the particle size of nanocarriers below 200 nm contributes to internalization via clathrin and caveolae mediated pathways. Similarly, a moderate negative surface potential confers endolysosomal escape and targeting towards mitochondria, endoplasmic reticulum (ER) and Golgi. This review aims to provide an insight into these physicochemical attributes of nanocarriers fabricated using amphiphilic graft copolymers affecting cellular internalization. Fundamental principles understood from experimental studies have been extrapolated to draw a general conclusion for the designing of optimized nanoparticulate drug delivery systems and enhanced intracellular uptake via specific endocytic pathway.
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Key Words
- AR, aspect ratio
- Amphiphilic
- CCP, clathrin coated pits
- Cav-1, caveolin-1
- Copolymer
- Cy, cyanine
- DOX, doxorubicin
- ER, endoplasmic reticulum
- FITC, fluorescein isothiocyanate
- HER-2, human epidermal growth factor receptor 2
- IL-2, interleukin
- Internalization
- Intracellular fate
- Nanoparticles
- RBITC, rhodamine B isothiocyanate
- RES, reticuloendothelial system
- Rmax, minimum size threshold value
- Rmin, maximum size threshold value
- SEM, scanning electron microscopy
- SR & LR, short rod and long rod
- TEM, transmission electron microscopy
- mPEG, methoxy poly(ethylene glycol)
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Affiliation(s)
- Samrat Mazumdar
- Department of Pharmacy, Birla Institute of Technology and Science (BITS-PILANI), Pilani, Rajasthan 333031, India
| | - Deepak Chitkara
- Department of Pharmacy, Birla Institute of Technology and Science (BITS-PILANI), Pilani, Rajasthan 333031, India
| | - Anupama Mittal
- Department of Pharmacy, Birla Institute of Technology and Science (BITS-PILANI), Pilani, Rajasthan 333031, India
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3
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Li H, Wei S, Cheng K, Gounko NV, Ericksen RE, Xu A, Hong W, Han W. BIG3 inhibits insulin granule biogenesis and insulin secretion. EMBO Rep 2014; 15:714-22. [PMID: 24711543 DOI: 10.1002/embr.201338181] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
While molecular regulation of insulin granule exocytosis is relatively well understood, insulin granule biogenesis and maturation and its influence on glucose homeostasis are relatively unclear. Here, we identify a novel protein highly expressed in insulin-secreting cells and name it BIG3 due to its similarity to BIG/GBF of the Arf-GTP exchange factor (GEF) family. BIG3 is predominantly localized to insulin- and clathrin-positive trans-Golgi network (TGN) compartments. BIG3-deficient insulin-secreting cells display increased insulin content and granule number and elevated insulin secretion upon stimulation. Moreover, BIG3 deficiency results in faster processing of proinsulin to insulin and chromogranin A to β-granin in β-cells. BIG3-knockout mice exhibit postprandial hyperinsulinemia, hyperglycemia, impaired glucose tolerance, and insulin resistance. Collectively, these results demonstrate that BIG3 negatively modulates insulin granule biogenesis and insulin secretion and participates in the regulation of systemic glucose homeostasis.
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Affiliation(s)
- Hongyu Li
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Shunhui Wei
- Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Kenneth Cheng
- State Key Laboratory of Pharmaceutical Biotechnology, University of Hong Kong, Hong Kong, China Department of Medicine, University of Hong Kong, Hong Kong, China
| | - Natalia V Gounko
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore Joint IMB-IMCB Electron Microscopy Suite, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Russell E Ericksen
- Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Aimin Xu
- State Key Laboratory of Pharmaceutical Biotechnology, University of Hong Kong, Hong Kong, China Department of Medicine, University of Hong Kong, Hong Kong, China Pharmacology and Pharmacy, University of Hong Kong, Hong Kong, China
| | - Wanjin Hong
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Weiping Han
- Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
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4
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Chowdhury A, Satagopam VP, Manukyan L, Artemenko KA, Fung YME, Schneider R, Bergquist J, Bergsten P. Signaling in Insulin-Secreting MIN6 Pseudoislets and Monolayer Cells. J Proteome Res 2013; 12:5954-62. [DOI: 10.1021/pr400864w] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Azazul Chowdhury
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
| | - Venkata P. Satagopam
- Department
of Structural and Computational Biology, EMBL, Meyerhofstrasse
1, D-69126 Heidelberg, Germany
- Luxembourg
Centre For Systems Biomedicine (LCSB), University of Luxembourg, Campus Belval, House of Biomedicine, 7 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg
| | - Levon Manukyan
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
| | - Konstantin A. Artemenko
- Analytical
Chemistry, Department of Chemistry−Biomedical Center and SciLifeLab, Uppsala University, Box
599, SE-75124 Uppsala, Sweden
| | - Yi Man Eva Fung
- Department
of Chemistry, State Key Laboratory of Synthetic
Chemistry, and Open Laboratory of Chemical
Biology of the Institute of Molecular Technology for Drug Discovery
and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Reinhard Schneider
- Department
of Structural and Computational Biology, EMBL, Meyerhofstrasse
1, D-69126 Heidelberg, Germany
- Luxembourg
Centre For Systems Biomedicine (LCSB), University of Luxembourg, Campus Belval, House of Biomedicine, 7 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg
| | - Jonas Bergquist
- Analytical
Chemistry, Department of Chemistry−Biomedical Center and SciLifeLab, Uppsala University, Box
599, SE-75124 Uppsala, Sweden
| | - Peter Bergsten
- Department
of Medical Cell Biology, Uppsala University, Box 571, SE-75123 Uppsala, Sweden
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5
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Martínez-Alonso E, Tomás M, Martínez-Menárguez JA. Morpho-functional architecture of the Golgi complex of neuroendocrine cells. Front Endocrinol (Lausanne) 2013; 4:41. [PMID: 23543640 PMCID: PMC3610015 DOI: 10.3389/fendo.2013.00041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Accepted: 03/14/2013] [Indexed: 12/22/2022] Open
Abstract
In neuroendocrine cells, prohormones move from the endoplasmic reticulum to the Golgi complex (GC), where they are sorted and packed into secretory granules. The GC is considered the central station of the secretory pathway of proteins and lipids en route to their final destination. In most mammalian cells, it is formed by several stacks of cisternae connected by tubules, forming a continuous ribbon. This organelle shows an extraordinary structural and functional complexity, which is exacerbated by the fact that its architecture is cell type specific and also tuned by the functional status of the cell. It is, indeed, one the most beautiful cellular organelles and, for that reason, perhaps the most extensively photographed by electron microscopists. In recent decades, an exhaustive dissection of the molecular machinery involved in membrane traffic and other Golgi functions has been carried out. Concomitantly, detailed morphological studies have been performed, including 3D analysis by electron tomography, and the precise location of key proteins has been identified by immunoelectron microscopy. Despite all this effort, some basic aspects of Golgi functioning remain unsolved. For instance, the mode of intra-Golgi transport is not known, and two opposing theories (vesicular transport and cisternal maturation models) have polarized the field for many years. Neither of these theories explains all the experimental data so that new theories and combinations thereof have recently been proposed. Moreover, the specific role of the small vesicles and tubules which surround the stacks needs to be clarified. In this review, we summarize our current knowledge of the Golgi architecture in relation with its function and the mechanisms of intra-Golgi transport. Within the same framework, the characteristics of the GC of neuroendocrine cells are analyzed.
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Affiliation(s)
- Emma Martínez-Alonso
- Department of Cell Biology and Histology, Medical School, University of MurciaMurcia, Spain
| | - Mónica Tomás
- Department of Human Anatomy and Embryology, Medical School, Valencia UniversityValencia, Spain
| | - José A. Martínez-Menárguez
- Department of Cell Biology and Histology, Medical School, University of MurciaMurcia, Spain
- *Correspondence: José A. Martínez-Menárguez, Department of Cell Biology and Histology, Medical School, University of Murcia, 30100 Murcia, Spain. e-mail:
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6
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Abstract
Since its first visualization in 1898, the Golgi has been a topic of intense morphological research. A typical mammalian Golgi consists of a pile of stapled cisternae, the Golgi stack, which is a key station for modification of newly synthesized proteins and lipids. Distinct stacks are interconnected by tubules to form the Golgi ribbon. At the entrance site of the Golgi, the cis-Golgi, vesicular tubular clusters (VTCs) form the intermediate between the endoplasmic reticulum and the Golgi stack. At the exit site of the Golgi, the trans-Golgi, the trans-Golgi network (TGN) is the major site of sorting proteins to distinct cellular locations. Golgi functioning can only be understood in light of its complex architecture, as was revealed by a range of distinct electron microscopy (EM) approaches. In this article, a general concept of mammalian Golgi architecture, including VTCs and the TGN, is described.
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Affiliation(s)
- Judith Klumperman
- Department of Cell Biology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands.
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7
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Burgess J, Jauregui M, Tan J, Rollins J, Lallet S, Leventis PA, Boulianne GL, Chang HC, Le Borgne R, Krämer H, Brill JA. AP-1 and clathrin are essential for secretory granule biogenesis in Drosophila. Mol Biol Cell 2011; 22:2094-105. [PMID: 21490149 PMCID: PMC3113773 DOI: 10.1091/mbc.e11-01-0054] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Regulated secretion of hormones, digestive enzymes, and other biologically active molecules requires the formation of secretory granules. Clathrin and the clathrin adaptor protein complex 1 (AP-1) are necessary for maturation of exocrine, endocrine, and neuroendocrine secretory granules. However, the initial steps of secretory granule biogenesis are only minimally understood. Powerful genetic approaches available in the fruit fly Drosophila melanogaster were used to investigate the molecular pathway for biogenesis of the mucin-containing "glue granules" that form within epithelial cells of the third-instar larval salivary gland. Clathrin and AP-1 colocalize at the trans-Golgi network (TGN) and clathrin recruitment requires AP-1. Furthermore, clathrin and AP-1 colocalize with secretory cargo at the TGN and on immature granules. Finally, loss of clathrin or AP-1 leads to a profound block in secretory granule formation. These findings establish a novel role for AP-1- and clathrin-dependent trafficking in the biogenesis of mucin-containing secretory granules.
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Affiliation(s)
- Jason Burgess
- Department of Molecular Genetics, University of Toronto, Ontario, Canada
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8
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Morvan J, Tooze SA. Discovery and progress in our understanding of the regulated secretory pathway in neuroendocrine cells. Histochem Cell Biol 2008; 129:243-52. [PMID: 18197413 PMCID: PMC2248607 DOI: 10.1007/s00418-008-0377-z] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/04/2008] [Indexed: 01/24/2023]
Abstract
In this review we start with a historical perspective beginning with the early morphological work done almost 50 years ago. The importance of these pioneering studies is underscored by our brief summary of the key questions addressed by subsequent research into the mechanism of secretion. We then highlight important advances in our understanding of the formation and maturation of neuroendocrine secretory granules, first using in vitro reconstitution systems, then most recently biochemical approaches, and finally genetic manipulations in vitro and in vivo.
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Affiliation(s)
- Joëlle Morvan
- London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London, UK
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9
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Origins of the regulated secretory pathway. THE GOLGI APPARATUS 2008. [PMCID: PMC7121582 DOI: 10.1007/978-3-211-76310-0_30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Modes of transport of soluble (or luminal) secretory proteins synthesized in the endoplasmic reticulum (ER) could be divided into two groups. The socalled constitutive secretory pathway (CSP) is common to all eukaryotic cells, constantly delivering constitutive soluble secretory proteins (CSSPs) linked to the rate of protein synthesis but largely independent of external stimuli. In regulated secretion, protein is sorted from the Golgi into storage/secretory granules (SGs) whose contents are released when stimuli trigger their final fusion with the plasma membrane (Hannah et al. 1999).
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10
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Abstract
Biogenesis of the regulated secretory pathway in the pancreatic beta-cell involves packaging of products, notably proinsulin, into immature secretory granules derived from the trans-Golgi network. Proinsulin is converted to insulin and C-peptide as granules mature. Secretory proteins not entering granules are conveyed by transport intermediates directly to the plasma membrane for constitutive secretion. One of the co-authors, Peter Arvan, has proposed that in addition, small vesicles bud from granules to traffic to the endosomal system. From there, some proteins are secreted by a (post-granular) constitutive-like pathway. He argues that retention in granules is facilitated by condensation, rendering soluble products (notably C-peptide and proinsulin) more available for constitutive-like secretion. Thus he argues that prohormone conversion is potentially important in secretory granule biogenesis. The other co-author, Philippe Halban, argues that the post-granular secretory pathway is not of physiological relevance in primary beta-cells, and contests the importance of proinsulin conversion for retention in granules. Both, however, agree that trafficking from granules to endosomes is important, purging granules of unwanted newly synthesized proteins and allowing their traffic to other destinations. In this Traffic Interchange, the two co-authors attempt to reconcile their differences, leading to a common vision of proinsulin trafficking in primary and transformed cells.
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Affiliation(s)
- Peter Arvan
- Division of Metabolism, University of Michigan Medical Center, Ann Arbor, MI 48109, USA
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11
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Képès F, Rambourg A, Satiat-Jeunemaître B. Morphodynamics of the secretory pathway. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 242:55-120. [PMID: 15598467 DOI: 10.1016/s0074-7696(04)42002-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A careful scrutiny of the dynamics of secretory compartments in the entire eukaryotic world reveals many common themes. The most fundamental theme is that the Golgi apparatus and related structures appear as compartments formed by the act of transporting cargo. The second common theme is the pivotal importance for endomembrane dynamics of shifting back and forth the equilibrium between full and perforated cisternae along the pathway. The third theme is the role of a continuous membrane flow in anterograde transfer of molecules from the endoplasmic reticulum through the Golgi apparatus. The last common theme is the self-regulatory balance between anatomical continuities and discontinuities of the endomembrane system. As this balance depends on secretory activity, it provides a source of morphological variability among cell types or, for a given cell type, according to environmental conditions. Beyond this first source of variability, it appears that divergent strategies pave the evolutionary routes in different eukaryotic kingdoms. These divergent strategies primarily affect the levels of stacking, of stabilization, and of clustering of the Golgi apparatus. They presumably underscore a trade-off between versatility and stability to adapt the secretory function to the degree of environmental variability. Nonequilibrium secretory structures would provide yeasts, and plants to a lesser extent, with the required versatility to cope with ever changing environments, by contrast to the stabler milieu intérieur of homeothermic animals.
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Affiliation(s)
- François Képès
- ATelier de Génomique Cognitive, CNRS UMR 8071/Genopole and Epigenomics Project, Genopole, Evry, France
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12
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Mould JA, Paterson RG, Takeda M, Ohigashi Y, Venkataraman P, Lamb RA, Pinto LH. Influenza B virus BM2 protein has ion channel activity that conducts protons across membranes. Dev Cell 2003; 5:175-84. [PMID: 12852861 DOI: 10.1016/s1534-5807(03)00190-4] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Successful uncoating of the influenza B virus in endosomes is predicted to require acidification of the interior of the virus particle. We report that a virion component, the BM2 integral membrane protein, when expressed in Xenopus oocytes or in mammalian cells, causes acidification of the cells and possesses ion channel activity consistent with proton conduction. Furthermore, coexpression of BM2 with hemagglutinin (HA) glycoprotein prevents HA from adopting its low-pH-induced conformation during transport to the cell surface, and overexpression of BM2 causes a delay in intracellular transport in the exocytic pathway and causes morphological changes in the Golgi. These data are consistent with BM2 equilibrating the pH gradient between the Golgi and the cytoplasm. The transmembrane domain of BM2 protein and the influenza A virus A/M2 ion channel protein both contain the motif HXXXW, and, for both proteins, the His and Trp residues are important for channel function.
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Affiliation(s)
- Jorgen A Mould
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208, USA
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13
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Molinete M, Dupuis S, Brodsky FM, Halban PA. Role of clathrin in the regulated secretory pathway of pancreaticβ-cells. J Cell Sci 2001; 114:3059-66. [PMID: 11686308 DOI: 10.1242/jcs.114.16.3059] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The role of clathrin in the sorting of proinsulin to secretory granules,the formation of immature granules and their subsequent maturation is not known. To this end, primary rat pancreatic β-cells were infected with a recombinant adenovirus co-expressing the Hub fragment, a dominant-negative peptide of the clathrin heavy chain and enhanced green fluorescent protein(EGFP as a marker of infected cells). A population of cells expressing the highest levels of EGFP (and thus Hub) was obtained using a fluorescence-activated cell sorter (FACS). Control cells were infected with an adenovirus expressing EGFP alone. By immunofluorescence, control cells showed intense staining for both clathrin light chain and proinsulin in a perinuclear region. In cells expressing high levels of Hub, the clathrin light-chain signal was faint and diffuse in keeping with its displacement from membranes. There was, however, no detectable effect of Hub expression on proinsulin staining or disposition within the cell. Proinsulin sorting and conversion,and the fate (release and/or degradation) of insulin and C-peptide, was studied by pulse-chase and quantitative reverse phase HPLC. In both Hub-expressing and control cells, >99% of all newly synthesized proinsulin was sorted to the regulated pathway and there was no effect of Hub on proinsulin conversion to insulin. In presence of Hub there was, however, a significant increase in the percentage of C-peptide truncated to des-(27-31)-C-peptide at early times of chase as well as more extensive degradation of C-peptide thereafter. It is concluded that clathrin is not implicated in the sorting or processing of proinsulin or in regulated exocytosis of secretory granules. These results confirm a role for clathrin in the removal of proteases from maturing granules, thus explaining the increased truncation and degradation of C-peptide in cells expressing Hub.
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Affiliation(s)
- M Molinete
- Louis-Jeantet Research Laboratories, University Medical Centre, Geneva 4, Switzerland
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14
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Soyez D, Toullec JY, Ollivaux C, Géraud G. L to D amino acid isomerization in a peptide hormone is a late post-translational event occurring in specialized neurosecretory cells. J Biol Chem 2000; 275:37870-5. [PMID: 10993902 DOI: 10.1074/jbc.m007302200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Modification of the chirality of a single amino acid residue within a peptide chain appears to be novel additional mechanism leading to structural and functional diversification of eukaryotic bioactive peptides. This phenomenon has been studied at the cellular level in a neuroendocrine organ which elaborates a mixture of diastereoisomers of a 72-residue neuropeptide, crustacean hyperglycemic hormone. For the first time, amino acid isomerization has been shown to occur in the perikarya of fully specialized neurosecretory cells, as a late step of the maturation of the hyperglycemic hormone precursor and after propeptide cleavage. The specificity and efficiency of this phenomenon indicates the existence of a new enzyme family involved in the biogenesis of peptide hormones.
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Affiliation(s)
- D Soyez
- Laboratoire Signaux Endocrines et Toxines d'Invertébrés, CNRS EP2028-Univ. Paris 6, France.
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15
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Affiliation(s)
- I Mellman
- Department of Cell Biology, Ludwig Institute for Cancer Research, Yale University School of Medicine, New Haven, Connecticut 06520-8002, USA
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16
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Pauloin A, Tooze SA, Michelutti I, Delpal S, Ollivier-Bousquet M. The majority of clathrin coated vesicles from lactating rabbit mammary gland arises from the secretory pathway. J Cell Sci 1999; 112 ( Pt 22):4089-100. [PMID: 10547368 DOI: 10.1242/jcs.112.22.4089] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Clathrin coated vesicles were isolated from lactating rabbit mammary gland by differential centrifugation, centrifugation on (2)H2O-sucrose cushions and Sephacryl S-1000 chromatography. Mammary epithelial cells contain an unexpectedly high quantity of clathrin coated vesicles which appear heterogeneous in size, with a mean diameter of 95.9+/-10.5 nm and a density of 1.23 g × ml(−1). Analysis of clathrin coated vesicle adaptor composition by SDS-PAGE and western blot showed that only approximately 5–10% of total APs consist of AP-2 in isolated mammary gland clathrin coated vesicles whereas it represents approximately 70% of the total APs from bovine brain clathrin coated vesicles. Cargo molecules known to be transcytosed such as IgG, IgA, and the pIgR were detected in the clathrin coated vesicles, indicating that part of this vesicle population is involved in transcytotic pathways. However, as the vast majority of the clathrin coated vesicles contained AP-1, it was likely that these clathrin coated vesicles were involved in the secretory pathway. Relatively high quantities of furin and cation-independent mannose 6-phosphate receptor were detected in mammary clathrin coated vesicles. By immuno electron microscopy, AP-1 and the cation-independent mannose 6-phosphate receptor were localized in Golgi-associated vesicles and on the membrane of secretory vesicles. The presence of AP-1 in the coat patches on the membrane of secretory vesicles containing casein micelles, and the presence of alpha(s1)-casein in mammary gland clathrin coated vesicles, support a role for AP-1 in the maturation of secretory vesicles. Our data pinpoint the importance of clathrin coated vesicles in lactating mammary epithelial cells, and suggest these vesicles are involved in the transcytotic pathway, in sorting at the trans-Golgi network and in the biogenesis of casein-containing secretory vesicles.
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Affiliation(s)
- A Pauloin
- INRA, Laboratoire de Biologie Cellulaire et Moléculaire, France.
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17
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Abstract
Endocytosis is crucial for an array of cellular functions and can occur through several distinct mechanisms with the capacity to internalize anything from small molecules to entire cells. The clathrin-mediated endocytic pathway has recently received considerable attention because of (i) the identification of an array of molecules that orchestrate the assembly of clathrin-coated vesicles and the selection of the vesicle cargo and (ii) the resolution of structures for a number of these proteins. Together, these data provide an initial three-dimensional framework for understanding the clathrin endocytic machinery.
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Affiliation(s)
- M Marsh
- Medical Research Council Laboratory for Molecular Cell Biology and Department of Biochemistry, University College London, Gower Street, London WC1E 6BT, UK.
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18
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Patel YC, Galanopoulou AS, Rabbani SN, Liu JL, Ravazzola M, Amherdt M. Somatostatin-14, somatostatin-28, and prosomatostatin[1-10] are independently and efficiently processed from prosomatostatin in the constitutive secretory pathway in islet somatostatin tumor cells (1027B2). Mol Cell Endocrinol 1997; 131:183-94. [PMID: 9296377 DOI: 10.1016/s0303-7207(97)00107-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We have characterized the biosynthetic origin of somatostatin-14 (SS-14), SS-28, and pro-SS[1-10] from pro-SS (PSS) in 1027B2 rat islet tumor cells. Because these cells lack regulated secretion and show unresponsiveness of the SS gene to cAMP, we have additionally carried out morphological and functional studies to elucidate the molecular defect in cAMP signalling and to localize the sites of PSS maturation along the secretory pathway. Cell extracts and secretion media were analysed by high performance liquid chromatography and specific C- and N-terminal radioimmunoassays. Electron microscopic sampling of 1027B2 cell cultures showed that most cells had very few dense core secretory granules for heterogeneous sizes. The cells expressed the endoproteases furin, PC1, and PC2 and contained large quantities of fully processed SS-14 and SS-28 with very little unprocessed PSS (ratio SS-14:SS-28:PSS = 39:51:10%). They secreted high concentrations of SS-14, SS-28, and PSS[1-10] constitutively along with PC1 and PC2. Pulse-chase studies demonstrated that PSS is rapidly (within 15 min), and efficiently processed to SS-14, SS-28, and PSS[1-10] via separate biosynthetic pathways: PSS --> SS-14 + 8 kDa; PSS --> SS-28 + 7 kDa; PSS --> PSS[1-10]. Monensin reduced intracellular SS-like immunoreactivity without altering processing efficiency. Transfection with the catalytic subunit of protein kinase A (PKA-C) activated SS promoter-CAT activating indicating that the defect in cAMP-dependent signaling in 1027B2 cells lies at the level of PKA-C. PKA-C overexpression failed to alter the ratio of processed SS-14 and SS-28. These results demonstrate that SS-14, SS-28, and PSS[1-10] are independently synthesized from PSS and that efficient precursor processing can occur within the constitutive secretory pathway in the relative absence of dense core secretory vesicles.
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Affiliation(s)
- Y C Patel
- McGill University, Department of Medicine, Royal Victoria Hospital and Montreal Neurological Institute, Quebec, Canada.
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Hou XE, Li JY, Dahlström A. Clathrin light chain and synaptotagmin I in rat sympathetic neurons. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1997; 62:13-26. [PMID: 9021645 DOI: 10.1016/s0165-1838(96)00103-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Clathrin light chain (clathrin LC) and synaptotagmin I in sympathetic neurons in rat superior cervical ganglia (SCG) were studied using immunofluorescence and confocal microscopy. The distributions of clathrin LC and synaptotagmin I were compared with that of tyrosine hydroxylase (TH) and neuropeptide Y (NPY) in double label experiments. The influence of preganglionic regulation on the expression of clathrin LC and synaptotagmin I in post-ganglionic adrenergic neurons was investigated after cutting the cervical sympathetic trunk. In SCGs and irides of control animals, the calthrin LC- and synaptotagmin-I-positive structures were present in a granular pattern in nerve fibers and varicose terminals. In principal neurons, the two proteins were present in a perinuclear network (the Golgi complex). After decentralization, the synaptotagmin-I- and clathrin LC-positive granules normally present in preganglionic nerve terminals outlining the neuronal somata were no longer observed on day 1, but reappeared, and were increased above control in number and intensity, in axon bundles in the ganglia, on day 3 and up to day 28 post-decentralization. In irides, the fluorescence intensity and density of clathrin LC- and synaptotagmin-I-positive nerve terminals in the dilator plate, were semi-quantified using the confocal microscopy software. It was found that both proteins increased shortly after decentralization. Immunoblot data confirmed the immunohistochemical/confocal microscopy observations. Fast axonal transport of clathrin LC- and synaptotagmin I in preganglionic sympathetic neurons was demonstrated in crush-operated cervical sympathetic trunk. Both proteins rapidly accumulated proximally as well as distally to the crush, demonstrating fast anterograde and retrograde axonal transport (recycling). Thus, clathrin LC and synaptotagmin I are normally present in pre- as well as post-ganglionic sympathetic neurons. The colocalization of clathrin LC with synaptotagmin I in the Golgi complex of the adrenergic neurons may imply that clathrin participates in the synthesis/sorting of the fast transported materials in these neurons. Possible explanations for the increase of the two proteins after decentralization are discussed.
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Affiliation(s)
- X E Hou
- Department of Anatomy and Cell Biology, Göteborg University, Sweden.
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20
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Bäck N, Soinila S. Effect of monensin on secretory granules and basal beta-endorphin secretion in the melanotroph of the rat pituitary. THE HISTOCHEMICAL JOURNAL 1996; 28:591-7. [PMID: 8894662 DOI: 10.1007/bf02331379] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effect of monensin on the Golgi complex, formation of secretory granules and basal beta-endorphin secretion in cultured melanotrophs from the rat pituitary was studied. Earlier studies on the effect of monensin on regulated secretion have generally showed only minor effects on secretory granules. The initial (within 5 min) effect of monensin on the melanotroph was the appearance of large vacuoles at the trans-side of the thiamine pyrophosphatase-positive trans-most Golgi cisternae. This was associated with a dose-dependent inhibition of the condensation of electron-dense secretory products. After 1 h of treatment with 1 microM monensin the Golgi stack was completely vacuolized. At the same time mature secretory granules were enlarged to severalfold their original size, and after 4 h of treatment secretory granules were no longer observed. Despite the marked effects on granule formation and mature secretory granules monensin did not affect the basal release of beta-endorphin-immunoreactive material during continued incubation for up to 4 h, indicating that basal peptide secretion can bypass the monensin block.
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Affiliation(s)
- N Bäck
- Department of Anatomy, University of Helsinki, Finland
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21
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Temesvari LA, Rodriguez-Paris JM, Bush JM, Zhang L, Cardelli JA. Involvement of the vacuolar proton-translocating ATPase in multiple steps of the endo-lysosomal system and in the contractile vacuole system of Dictyostelium discoideum. J Cell Sci 1996; 109 ( Pt 6):1479-95. [PMID: 8799835 DOI: 10.1242/jcs.109.6.1479] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have investigated the effects of Concanamycin A (CMA), a specific inhibitor of vacuolar type H(+)-ATPases, on acidification and function of the endo-lysosomal and contractile vacuole (CV) systems of D. discoideum. This drug inhibited acidification and increased the pH of endo-lysosomal vesicles both in vivo and in vitro in a dose dependent manner. Treatment also inhibited endocytosis and exocytosis of fluid phase, and phagocytosis of latex beads. This report also confirms our previous conclusions (Cardelli et al. (1989) J. Biol. Chem. 264, 3454–3463) that maintenance of acidic pH in lumenal compartments is required for efficient processing and targeting of a lysosomal enzyme, alpha-mannosidase. CMA treatment compromised the function of the contractile vacuole complex as amoebae exposed to a hypo-osmotic environment in the presence of CMA, swelled rapidly and ruptured. Fluorescence microscopy revealed that CMA treatment induced gross morphological changes in D. discoideum cells, characterized by the formation of large intracellular vacuoles containing fluid phase. The reticular membranes of the CV system were also no longer as apparent in drug treated cells. Finally, this is the first report describing cells that can adapt in the presence of CMA; in nutrient medium, D. discoideum overcame the effects of CMA after one hour of drug treatment even in the absence of protein synthesis. Upon adaptation to CMA, normal sized endo-lysosomal vesicles reappeared, endo-lysosomal pH decreased, and the rate of endocytosis, exocytosis and phagocytosis returned to normal. This study demonstrates that the V-H(+)-ATPase plays an important role in maintaining the integrity and function of the endo-lysosomal and CV systems and that D. discoideum can compensate for the loss of a functional V-H(+)-ATPase.
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Affiliation(s)
- L A Temesvari
- Department of Microbiology and Immunology, Louisiana State University, Medical Center, Shreveport 71130, USA
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22
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Sakaguchi T, Leser GP, Lamb RA. The ion channel activity of the influenza virus M2 protein affects transport through the Golgi apparatus. J Cell Biol 1996; 133:733-47. [PMID: 8666660 PMCID: PMC2120830 DOI: 10.1083/jcb.133.4.733] [Citation(s) in RCA: 166] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
High level expression of the M2 ion channel protein of influenza virus inhibits the rate of intracellular transport of the influenza virus hemagglutinin (HA) and that of other integral membrane glycoproteins. HA coexpressed with M2 is properly folded, is not associated with GRP78-BiP, and trimerizes with the same kinetics as when HA is expressed alone. Analysis of the rate of transport of HA from the ER to the cis and medial golgi compartments and the TGN indicated that transport through the Golgi apparatus is delayed. Uncleaved HA0 was not expressed at the cell surface, and accumulation HA at the plasma membrane was reduced to 75-80% of control cells. The delay in intracellular transport of HA on coexpression of M2 was not observed in the presence of the M2-specific ion channel blocker, amantadine, indicating that the Golgi transport delay is due to the M2 protein ion channel activity equilibrating pH between the Golgi lumen and the cytoplasm, and not due to saturation of the intracellular transport machinery. The Na+/H+ ionophore, monensin, which also equilibrates pH between the Golgi lumen and the cytoplasm, caused a similar inhibition of intracellular transport as M2 protein expression did for HA and other integral membrane glycoproteins. EM data showed a dilation of Golgi cisternae in cells expressing the M2 ion channel protein. Taken together, the data suggest a similarity of effects of M2 ion channel activity and monensin on intracellular transport through the Golgi apparatus.
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Affiliation(s)
- T Sakaguchi
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500, USA
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Influence of monensin on the composition of the plasmalemma of Achlya bisexualis ♂ separated by free-flow electrophoresis. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s0953-7562(96)80008-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Abstract
Like non-peptidergic transmitters, neuropeptides and their receptors display a wide distribution in specific cell types of the nervous system. The peptides are synthesized, typically as part of a larger precursor molecule, on the rough endoplasmic reticulum in the cell body. In the trans-Golgi network, they are sorted to the regulated secretory pathway, packaged into so-called large dense-core vesicles, and concentrated. Large dense-core vesicles are preferentially located at sites distant from active zones of synapses. Exocytosis may occur not only at synaptic specializations in axonal terminals but frequently also at nonsynaptic release sites throughout the neuron. Large dense-core vesicles are distinguished from small, clear synaptic vesicles, which contain "classical' transmitters, by their morphological appearance and, partially, their biochemical composition, the mode of stimulation required for release, the type of calcium channels involved in the exocytotic process, and the time course of recovery after stimulation. The frequently observed "diffuse' release of neuropeptides and their occurrence also in areas distant to release sites is paralleled by the existence of pronounced peptide-peptide receptor mismatches found at the light microscopic and ultrastructural level. Coexistence of neuropeptides with other peptidergic and non-peptidergic substances within the same neuron or even within the same vesicle has been established for numerous neuronal systems. In addition to exerting excitatory and inhibitory transmitter-like effects and modulating the release of other neuroactive substances in the nervous system, several neuropeptides are involved in the regulation of neuronal development.
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Affiliation(s)
- G K Zupanc
- Max-Planck-Institut für Entwicklungsbiologie, Abteilung Physikalische Biologie, Tübingen, Germany.
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25
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Rabouille C, Hui N, Hunte F, Kieckbusch R, Berger EG, Warren G, Nilsson T. Mapping the distribution of Golgi enzymes involved in the construction of complex oligosaccharides. J Cell Sci 1995; 108 ( Pt 4):1617-27. [PMID: 7615680 DOI: 10.1242/jcs.108.4.1617] [Citation(s) in RCA: 257] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The distribution of beta 1,2 N-acetylglucosaminyltransferase I (NAGT I), alpha 1,3-1,6 mannosidase II (Mann II), beta 1,4 galactosyltransferase (GalT), alpha 2,6 sialyltransferase (SialylT) was determined by immuno-labelling of cryo-sections from HeLa cell lines. Antibody labelling in the HeLa cell line was made possible by stable expression of epitope-tagged forms of these proteins or forms from species to which specific antibodies were available. NAGT I and Mann II had the same distribution occupying the medial and trans cisternae of the stack. GalT and SialylT also had the same distribution but they occupied the trans cisterna and the trans-Golgi network (TGN). These results generalise our earlier observations on the overlapping distribution of Golgi enzymes and show that each of the trans compartments of the Golgi apparatus in HeLa cells contains unique mixtures of those Golgi enzymes involved in the construction of complex, N-linked oligosaccharides.
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Affiliation(s)
- C Rabouille
- Cell Biology Laboratory, Imperial Cancer Research Fund, London, UK
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26
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Matsuo S, Kurisu K, Kiyomiya K, Kurebe M. Relation between the trans-Golgi network and the Golgi stack on development of the Golgi apparatus of the ameloblast in developing rat molar tooth germs. Anat Rec (Hoboken) 1995; 241:25-33. [PMID: 7879921 DOI: 10.1002/ar.1092410105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND The problem of how the functional compartments of the Golgi apparatus organizes during cell differentiation to become a well-formed Golgi apparatus is as yet an unresolved issue. This study was designed to define the involvement of the trans-Golgi network (TGN) and the Golgi stack in organizing the Golgi apparatus. METHODS The distribution of the TGN marker enzyme was examined in the ameloblast of developing rat molar tooth germs using cytochemistry with Co-enzyme A phosphatase (CoA Pase) and cytidine monophosphatase (CMPase). RESULTS Typically formed Golgi apparatus was observed in the secretory ameloblast but not in the presecretory ameloblast. Organization of the Golgi apparatus through the presecretory ameloblast was noted. In the presecretory ameloblast, Golgi stacks of different sizes and clusters of small vesicles were located in the cytoplasm lateral to the nucleus. The saccules with enzymes marked for TGN were also observed in the cytoplasm lateral to the nucleus. These saccules were adjacent to the cluster of small vesicles and/or the Golgi stack. Upon cell differentiation, Golgi stacks were seen in line along the long axis of the cell, and the file of the stacks in the cytoplasm lateral to the nucleus was formed. The positive saccule was seen in a parallel line equal to the length of the Golgi stacks. CONCLUSIONS In organizing the Golgi apparatus, the development process of the TGN and the Golgi stack appear to be different, and new Golgi stacks seem to be formed through the accumulation of small vesicles near the pre-existing TGN.
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Affiliation(s)
- S Matsuo
- Department of Toxicology, School of Veterinary Medicine, University of Osaka Prefecture, Japan
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Locker JK, Klumperman J, Oorschot V, Horzinek MC, Geuze HJ, Rottier PJ. The cytoplasmic tail of mouse hepatitis virus M protein is essential but not sufficient for its retention in the Golgi complex. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)46923-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
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28
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Ponnambalam S, Rabouille C, Luzio JP, Nilsson T, Warren G. The TGN38 glycoprotein contains two non-overlapping signals that mediate localization to the trans-Golgi network. J Biophys Biochem Cytol 1994; 125:253-68. [PMID: 8163544 PMCID: PMC2120028 DOI: 10.1083/jcb.125.2.253] [Citation(s) in RCA: 124] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The membrane-spanning and cytoplasmic domains of CD4 and CD8 were replaced by those of TGN38. After transient expression in HeLa cells, the location of the hybrid proteins was determined using immunofluorescence and quantitative immuno-electron microscopy, FACS analysis and metabolic labeling. The membrane-spanning domain was found to contain a signal that localized hybrid proteins to the TGN. This was in addition to the signal previously identified in the cytoplasmic domain (Bos, K., C. Wraight, and K. Stanley. 1993. EMBO (Eur. Mol. Biol. Organ) J. 12:2219-2228. Humphrey, J. S., P. J. Peters, L. C. Yuan, and J. S. Bonifacino. 1993. J. Cell Biol. 120:1123-1135. Wong, S. H., and W. Hong. 1993. J. Biol. Chem. 268:22853-22862). The different properties of these two signals suggest that each operates by a different mechanism.
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Affiliation(s)
- S Ponnambalam
- Cell Biology Laboratory, Imperial Cancer Research Fund, Lincoln's Inn Fields, London, United Kingdom
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29
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Affiliation(s)
- P A Halban
- Laboratoires de Recherche Louis Jeantet, Centre Médical Universitaire, Geneva, Switzerland
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30
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Rayne RC, O'Shea M. Reconstitution of adipokinetic hormone biosynthesis in vitro indicates steps in prohormone processing. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 219:781-9. [PMID: 8112329 DOI: 10.1111/j.1432-1033.1994.tb18558.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have used a complete, synthetic precursor to adipokinetic hormone I (AKH I) and oligopeptides derived from this precursor as substrates for prohormone-processing enzymes extracted from AKH-synthesizing neurosecretory cells to reconstitute the post-translational steps in AKH biosynthesis in vitro. The results demonstrate the existence of endoproteolytic activity which cleaves the precursor only at the appropriate processing site (at the C-terminal side of Arg13). Further proteolytic processing of C-terminally extended AKH I (AKH-Gly-Lys-Arg) by a carboxypeptidase H-like activity removes the basic residues producing AKH-Gly-Lys, followed by AKH-Gly. Finally, a peptidylglycine-alpha-amidating-monooxygenase activity produces the amidated bioactive product from the glycine-extended peptide in a two-step process, the first of which requires ascorbate and Cu2+. Our results show that all steps in AKH precursor processing can be reconstituted and studied in vitro, providing a system to characterize the processing enzymes and to investigate the development of enzyme inhibitors for use as potential insecticides.
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Affiliation(s)
- R C Rayne
- Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, England
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31
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Voorhout WF, Weaver TE, Haagsman HP, Geuze HJ, Van Golde LM. Biosynthetic routing of pulmonary surfactant proteins in alveolar type II cells. Microsc Res Tech 1993; 26:366-73. [PMID: 8286782 DOI: 10.1002/jemt.1070260504] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Surfactant proteins A, B, and C (SP-A, SP-B, and SP-C) are synthesized in alveolar type II cells. SP-B and SP-C are both synthesized as large precursor molecules that are proteolytically processed to their mature sizes. In a previous immunoelectron microscopic study, we showed that precursor SP-B is processed to its mature size in multivesicular bodies. In the present study, using a specific antibody against precursor SP-C, we demonstrate that precursor SP-C is present in the same intracellular compartments of the biosynthetic pathway, i.e., endoplasmic reticulum, Golgi complex, and multivesicular bodies, as precursor SP-B. Since mature SP-C is known to be present in multilamellar bodies, this suggests a biosynthetic routing and site of processing of this protein similar to those of SP-B. Double-labeling experiments using antibodies against SP-A, precursor SP-B, precursor SP-C, and an antibody against HA I, an adaptor protein involved in the budding of transport vesicles from the Golgi complex, showed that the different surfactant proteins traverse and exit the Golgi complex via the same route. The surfactant proteins do not exit the Golgi complex via HA I-positive coated buds or vesicles. These data are in accordance with the concept that SP-A, SP-B, and SP-C are transported together through the same biosynthetic pathway via multivesicular bodies to multilamellar bodies.
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Affiliation(s)
- W F Voorhout
- Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands
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Bursztajn S, Jong YJ, Berman SA. Differential distribution of vesicular carriers during differentiation and synapse formation. J Cell Biochem 1993; 53:251-64. [PMID: 8263042 DOI: 10.1002/jcb.240530310] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Coated and noncoated vesicles participate in cellular protein transport. Both acetylcholine receptors (AChR) and acetylcholinesterase (AChE) are transported via coated vesicles, some of which accumulate beneath the neuromuscular synapse where AChRs cluster. To investigate the mechanisms by which these proteins are transported during postsynaptic remodeling, we purified coated vesicles from the bovine brain via column chromatography (Sephacryl S-1000) and raised monoclonal antibodies to epitopes of the vesicular membranes enriched in AChE. We assayed for AChE (coated vesicle enriched), hexosaminidase (lysosomal contaminants), NADH cytochrome C reductase (mitochondrial containing), and protein and demonstrated electron microscopically using negative staining that the vesicular fraction contained 95% pure coated vesicles. We then injected coated vesicle fractions and the fractions from which the coat was removed intraperitoneally into mice and obtained three monoclonal antibodies: C-33, C-172, and F-22. On immunoblots of purified vesicles and cultured skeletal muscle, mAb C-33 stained a 180 Kd band and mAb C-172 stained a 100 kd band. MAb F-22 stained 50 kd and 55 kd bands and was not characterized further. Immunofluorescent microscopy with C-33 and C-172 revealed punctate fluorescence whose distribution depends upon the stage of myotube development. Four days after plating, myotubes showed punctate fluorescence throughout the myotube, whereas those stained 8 days after plating showed a punctate perinuclear distribution. Myotubes innervated by ciliary neurons show punctate fluorescence limited to the nuclear periphery and most concentrated around nuclei which line up beneath neuronal processes. This differential vesicular distribution, observed during myotube differentiation and innervation, suggests that these vesicles participate in vesicular membrane traffic.
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Affiliation(s)
- S Bursztajn
- Laboratory for Molecular Neuroscience, Mailman Research Center, McLean Hospital, Belmont, Massachusetts
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Yilla M, Tan A, Ito K, Miwa K, Ploegh H. Involvement of the vacuolar H(+)-ATPases in the secretory pathway of HepG2 cells. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(17)46739-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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Acton SL, Wong DH, Parham P, Brodsky FM, Jackson AP. Alteration of clathrin light chain expression by transfection and gene disruption. Mol Biol Cell 1993; 4:647-60. [PMID: 8374173 PMCID: PMC300971 DOI: 10.1091/mbc.4.6.647] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The light chain subunits of clathrin, LCa and LCb, have been implicated in the regulation of coated vesicle disassembly and other aspects of clathrin cycling within the cell. The potential for functional specialization of each light chain is suggested by tissue-specific variation in the relative amounts of the two light chains and by conservation of differences between LCa and LCb sequences during evolution. To investigate whether there might be exclusive roles for LCa and LCb in clathrin function, the expression of LCa was manipulated in C1R lymphoid cells and PC12 pheochromocytoma cells by transfection with light chain cDNA. These two cell lines differ in their ratios of LCa to LCb, expressing 86 and 25% LCa, respectively. After transfection with exogenous human LCa cDNA, a PC12 cell derivative was produced that completely lost the ability to manufacture LCa. Loss of LCa expression was found to be because of gene disruption and consequent lack of mRNA transcription. In C1R cells, the normally high level of LCa expression was reduced to 25% by overexpression of transfected LCb cDNA under the control of an inducible promoter. The C1R transfectants with reduced levels of LCa and the LCa-negative PC12 transfectant grow normally and show no change in clathrin distribution, clathrin assembly level, or impairment of endocytosis or secretion compared with wild-type cells and cells transfected with vectors lacking light chain cDNA. However, subtle alterations in the hsc70-mediated clathrin uncoating process were observed for vesicles derived from the LCa-negative cells, reflecting the preferential activity of LCa in stimulating the in vitro uncoating reaction.
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Affiliation(s)
- S L Acton
- Department of Pharmacy, School of Pharmacy and Microbiology and Immunology, University of California, San Francisco 94143-0446
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Abstract
Regulated secretory proteins are stored within specialized vesicles known as secretory granules. It is not known how proteins are sorted into these organelles. Regulated proteins may possess targeting signals which interact with specific sorting receptors in the lumen of the trans-Golgi network (TGN) prior to their aggregation to form the characteristic dense-core of the granule. Alternatively, sorting may occur as the result of specific aggregation of regulated proteins in the TGN. Aggregates may be directed to secretory granules by interaction of a targeting signal on the surface with a sorting receptor. Novel targeting signals which confer on regulated proteins a tendency to aggregate under certain conditions, and in so doing cause them to be incorporated into secretory granules, have been implicated. Specific targeting signals may also play a role in directing membrane proteins to secretory granules.
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Affiliation(s)
- M A Chidgey
- Department of Cell and Structural Biology, University of Manchester, UK
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36
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Roth J, Klöppel G, Madsen OD, Storch MJ, Heitz PU. Distribution patterns of proinsulin and insulin in human insulinomas: an immunohistochemical analysis in 76 tumors. ACTA ACUST UNITED AC 1993; 63:51-61. [PMID: 1362022 DOI: 10.1007/bf02899244] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The distribution of proinsulin and insulin immunoreactivity was studied in 76 human insulinomas and in normal pancreas. One trabecular and two solid insulinomas showed the staining pattern of normal beta cells. A "near normal" staining pattern (perinuclear proinsulin and diffuse or polarized insulin staining) existed in 10 of 27 trabecular and 11 of 44 solid insulinomas. An "intermediate" staining pattern (intense perinuclear as well as weaker diffuse proinsulin staining with diffuse or polarized insulin staining) was observed in 10 of 27 trabecular and 20 of 44 solid insulinomas. Different "abnormal" staining patterns were found in 6 of 27 trabecular and 6 of 44 solid insulinomas. Of the 5 glandular insulinomas, 4 exhibited a "near normal" and one an "abnormal" staining pattern. No correlation was found between any particular staining pattern and the multihormonality or malignancy of the insulinomas. The diffuse labeling for proinsulin in about 50% of the insulinomas is suggestive of abnormal prohormone processing.
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Affiliation(s)
- J Roth
- Department of Pathology, University of Zürich, Switzerland
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Brudzynski K, Martinez V. Synaptophysin-containing microvesicles transport heat-shock protein hsp60 in insulin-secreting beta cells. Cytotechnology 1993; 11:23-33. [PMID: 7763633 DOI: 10.1007/bf00749054] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
58-62 kDa heat-shock proteins (hsp60) are molecular chaperonins involved in the process of protein folding, transmembrane translocation and assembly of oligomeric protein complexes. In eukaryotic cells hsp60 proteins have been found in mitochondria and chloroplasts. However, we have recently documented that, in addition to mitochondria, a hsp60-like protein is present in secretory granules of insulin-secreting beta cells. The pathway by which hsp60 is targeted to secretory granules was unknown. Here we report the existence of microvesicles involved in the transport of hsp60 protein. Immunoelectron microscopy of serial thin-sections of beta cells directly visualized stages associated with hsp60 delivery: attachment of microvesicles to a secretory granule, fusion with the secretory granule membrane and release of hsp60 molecules. Further biochemical and immunological analysis of microvesicles revealed the presence in their membrane of synaptophysin, a major component of synaptic-like microvesicles (SLMV) of neuroendocrine cells. Double immunogold labelling with antibodies to synaptophysin and hsp60 demonstrated co-localization of both proteins in the same microvesicles. Moreover, fusion of synaptophysin-positive microvesicles leaves synaptophysin incorporated, at least transiently, to secretory granule membranes. These findings suggest that, in beta cells, synaptic-like vesicles are involved in the transport and delivery of hsp60 and represent a novel pathway for protein transport and secretion.
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Affiliation(s)
- K Brudzynski
- Robarts Research Institute, University of Western Ontario, London, Canada
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38
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Abstract
The biogenesis of secretory granules in endocrine, neuroendocrine, and exocrine cells is thought to involve a selective aggregation of the regulated secretory proteins into a dense-cored structure. The dense-core is then enveloped by membrane in the trans-Golgi network and buds, forming an immature secretory granule. The immature secretory granule then undergoes a maturation process which gives rise to the mature secretory granule. The recent data on the processes of aggregation, budding and maturation are summarized here. In addition, the current knowledge about the mature secretory granule is reviewed with emphasis on the biogenesis of the membrane of this organelle.
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O'Halloran TJ, Anderson RG. Clathrin heavy chain is required for pinocytosis, the presence of large vacuoles, and development in Dictyostelium. J Cell Biol 1992; 118:1371-7. [PMID: 1522112 PMCID: PMC2289608 DOI: 10.1083/jcb.118.6.1371] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
To investigate the intracellular role of the clathrin heavy chain in living cells, we have used "antisense" RNA to engineer mutant Dictyostelium discoideum cells that are severely deficient in clathrin heavy chain expression. Immunoblots stained with an anti-clathrin heavy chain antiserum revealed that mutant cells contained undetectable amounts of clathrin heavy chain protein. Similarly, Northern blots showed an absence of clathrin heavy chain mRNA. Clathrin heavy chain-deficient Dictyostelium cells were viable, but exhibited growth rates twofold slower than parental cells. Whereas many morphological features of the mutant cells were normal, mutant cells lacked coated pits and coated vesicles. Clathrin-deficient cells were also missing large translucent vacuoles that serve as endosomes and contractile vacuoles. In the absence of clathrin heavy chain, mutant cells displayed three distinct functional defects: (a) impairment in endocytosis of fluid phase markers, but competence in another endocytic pathway, the phagocytosis of solid particles; (b) defects in osmoregulation; and (c) inability to complete the starvation-induced development cycle.
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Affiliation(s)
- T J O'Halloran
- Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas 75235
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Smeekens SP, Chan SJ, Steiner DF. The biosynthesis and processing of neuroendocrine peptides: identification of proprotein convertases involved in intravesicular processing. PROGRESS IN BRAIN RESEARCH 1992; 92:235-46. [PMID: 1302878 DOI: 10.1016/s0079-6123(08)61179-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- S P Smeekens
- Department of Biochemistry and Molecular Biology, University of Chicago, IL
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41
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Abstract
The effect of monensin, an electroneutral ionophore that exchanges Na+ for H+, is investigated on glucose and insulin concentration in serum of female rats. After monensin administration hyperglycemia is observed. Hyperglycemia is concentration and time dependent. In fact serum glucose starts increasing with 0.5 mg/kg b.w. of monensin and increases sharply till 2.5-3.0 mg/kg b.w. The timing of the appearance shows an increase already after few minutes and keeps increasing reaching its maximum between 30-120 minutes. Hyperglycemia is reversed by insulin; if not treated spontaneously it returns to normality in 4-5 hours. An inverse correlation is observed between insulinemia and glycemia. A significant fall in serum insulin concentration can be observed, with or without glucose-stimulation of insulin release, already after five minutes of treatment. Insulinemia returns to normal values after about two hours. The action of monensin on glycemia might therefore be a reversible inhibition of insulin secretion by the beta-cells of the pancreas.
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Affiliation(s)
- A Casu
- Institute of General Pathology, University of Genoa, Italy
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42
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Tooze SA, Flatmark T, Tooze J, Huttner WB. Characterization of the immature secretory granule, an intermediate in granule biogenesis. J Cell Biol 1991; 115:1491-503. [PMID: 1757459 PMCID: PMC2289211 DOI: 10.1083/jcb.115.6.1491] [Citation(s) in RCA: 186] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The events in the biogenesis of secretory granules after the budding of a dense-cored vesicle from the trans-Golgi network (TGN) were investigated in the neuroendocrine cell line PC12, using sulfate-labeled secretogranin II as a marker. The TGN-derived dense-cored vesicles, which we refer to as immature secretory granules, were found to be obligatory organellar intermediates in the biogenesis of the mature secretory granules which accumulate in the cell. Immature secretory granules were converted to mature secretory granules with a half-time of approximately 45 min. This conversion entailed an increase in their size, implying that the maturation of secretory granules includes a fusion event involving immature secretory granules. Pulse-chase labelling of PC12 cells followed by stimulation with high K+, which causes the release of secretogranin II, showed that not only mature, but also immature secretory granules were capable of undergoing regulated exocytosis. The kinetics of secretion of secretogranin II, as well as those of a constitutively secreted heparan sulfate proteoglycan, were reduced by treatment of PC12 cells with nocodazole, suggesting that both secretory granules and constitutive secretory vesicles are transported to the plasma membrane along microtubules. Our results imply that certain membrane proteins, e.g., those involved in the fusion of post-TGN vesicles with the plasma membrane, are sorted upon exit from the TGN, whereas other membrane proteins, e.g., those involved in the interaction of post-TGN vesicles with the cytoskeleton, may not be sorted.
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Affiliation(s)
- S A Tooze
- Cell Biology Programme, European Molecular Biology Laboratory, Heidelberg, Germany
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43
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Lindner R, Ungewickell E. Light-chain-independent binding of adaptors, AP180, and auxilin to clathrin. Biochemistry 1991; 30:9097-101. [PMID: 1909890 DOI: 10.1021/bi00101a027] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Binding of coated vesicle assembly proteins to clathrin causes it to assemble into regular coat structures. The assembly protein fraction of bovine brain coated vesicles comprises AP180, auxilin, and HA1 and HA2 adaptors. Clathrin heavy chains, separated from their light chains, polymerize with unimpaired efficiency when assembly proteins are added. The reassembled coats were purified by sucrose gradient centrifugation and examined for composition by SDS-PAGE and immunoblotting. We found that all four major coat proteins are incorporated in the presence and absence of light chains. Moreover, each of the purified coat proteins is able to associate directly with clathrin heavy chains in preassembled cages as efficiently as with intact clathrin. We conclude that light chains are not essential for the interaction of AP180, auxilin, and HA1 and HA2 with clathrin.
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Affiliation(s)
- R Lindner
- Max-Planck-Institut für Biochemie, Federal Republic of Germany
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44
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Protein discharge from immature secretory granules displays both regulated and constitutive characteristics. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98661-8] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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45
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Brodsky FM, Hill BL, Acton SL, Näthke I, Wong DH, Ponnambalam S, Parham P. Clathrin light chains: arrays of protein motifs that regulate coated-vesicle dynamics. Trends Biochem Sci 1991; 16:208-13. [PMID: 1909824 DOI: 10.1016/0968-0004(91)90087-c] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Polymerization of clathrin triskelions into clathrin coats and subsequent disassembly by the heat shock protein hsc70 control receptor-mediated pathways of intracellular transport. The clathrin light chains are major regulatory elements in these processes. These polypeptides consist of linear arrays of functional domains with distinctive sequence motifs. Comparison of unicellular and multicellular eukaryotes reveals differences in the numbers of clathrin light chains and in the functional domains they contain.
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Affiliation(s)
- F M Brodsky
- Department of Pharmacy, School of Pharmacy, University of California, San Francisco 94143-0446
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46
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Uriu T, Omori K, Omori K, Yamamoto A, Inoue M, Inagaki C. Two types of clathrin-coated vesicles isolated from rat brain: analysis of biochemical properties and cellular origin. J Neurochem 1991; 56:1548-56. [PMID: 1849549 DOI: 10.1111/j.1471-4159.1991.tb02050.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Two major fractions rich in clathrin-coated vesicles (CVs) (fraction I, rho = 1.140 g/cm3; fraction II, rho = 1.113 g/cm3) were separated from rat brain using a sucrose gradient and compared for their cellular origins and Cl- translocation systems. Electron micrographs showed that both fractions contained CVs of different size distributions (fraction I, 85 +/- 9.5 nm in diameter; fraction II, 72 +/- 6.8 nm in diameter). Fraction II contained potent ouabain-sensitive ATPase activity, whereas fraction I contained only a little activity. Immunoblot analysis for the Na+,K(+)-ATPase catalytic subunit, alpha and alpha(+), demonstrated that fraction II exhibited predominantly alpha(+), whose proportion to alpha was analogous to that observed in the extracts of primary cultured neuronal cells. Furthermore, on a sucrose density gradient, cultured neuronal cells yielded fraction II but not fraction I, whereas primary cultured glial cells yielded fraction I but not fraction II. Labeling-chase experiments using 125I-transferrin in cultured neuronal cells showed the internalized ligand in fraction II and the surface-bound ligand in the fraction with lower density (rho = 1.090 g/cm3), a result suggesting that the involvement of Na+,K(+)-ATPase in fraction II is attributable to endocytic vesicles. Cl- uptake in fraction II was approximately threefold higher than that in fraction I. N-Ethylmaleimide (100 microM) completely inhibited the Cl- uptake in fraction I but partially (approximately 50%) inhibited that in fraction II. These findings suggest that the two CV fractions isolated from rat brain originate from different cell types--glial and neuronal cells--and differ in size distribution of CVs, content of Na+,K(+)-ATPase, and mechanism for Cl- uptake.
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Affiliation(s)
- T Uriu
- Department of Pharmacology, Kansai Medical University, Osaka, Japan
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47
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Jung LJ, Scheller RH. Peptide processing and targeting in the neuronal secretory pathway. Science 1991; 251:1330-5. [PMID: 2003219 DOI: 10.1126/science.2003219] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The abdominal ganglion of the marine mollusk Aplysia contains a pair of identified neuronal clusters, the bag cells, which control egg laying by means of a number of unique regulatory mechanisms. Each neuron in the bag cell clusters synthesizes several peptides derived from a single prohormone and packages them into separate vesicles. These vesicles are then differentially localized in specific neuronal processes, thus segregating peptides destined for autocrine and hormonal release sites. Therefore in this system, protein trafficking through the secretory pathway organizes multiple peptide neurochemical messengers to efficiently regulate simple behaviors.
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Affiliation(s)
- L J Jung
- Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Beckman Center, Stanford University, CA 94305
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48
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Kameya T, Kadoya K, Iguchi H, Abe Y, Shimaoka K. Discordant secretion of calcitonin and chromogranin in the human medullary thyroid carcinoma cell line. Endocr Pathol 1991; 2:16-23. [PMID: 32138390 DOI: 10.1007/bf02915322] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
A cell fine of human medullary carcinoma of the thyroid, abundantly producing calcitonin (Ct) and related hormones, has proved remarkably useful as an endocrine tumor model for the study of the secretion mechanism. This cell line (TT cell) was used in studies to elucidate the dynamics of the release of Ct and chromogranin (Cg) to culture medium. The studies evaluated the intracellular concentration of Ct and Cg and the concentration changes elicited by the protein kinase C activator, phorbol ester (TPA); the adenylate cyclase-associated protein kinase A activator, forskolin; and the calcium ionophore, A23187. In addition, immunogold labeling of Ct and Cg was carried out to investigate the ultrastructural changes resulting from the stimulations. All these secretagogues effected the release of Ct and Cg into the medium in a dose-dependent manner, and the rate of the increase in the Ct secretion was consistently and markedly higher than that of Cg in more than certain dosages of the secretagogues. Most cells contained secretory granules immunolabeled for both Ct and Cg, and a considerable decrease was noted in the poststimulation count of the granules containing both substances, with the cells retaining more Cg than Ct. The discordance may be explained by different secretory pathways of the two proteins or different rates of synthesis.
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Affiliation(s)
- Toru Kameya
- Departments of Pathology and Internal Medicine, Kitasato University School of Medicine, Sagamihara, Kanagawa
| | - Kuniko Kadoya
- Departments of Pathology and Internal Medicine, Kitasato University School of Medicine, Sagamihara, Kanagawa
| | - Haruo Iguchi
- Department of Biochemistry, National Kyushu Cancer Center, Fukuoka
| | - Yoshifumi Abe
- Departments of Pathology and Internal Medicine, Kitasato University School of Medicine, Sagamihara, Kanagawa
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49
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Abstract
A combination of cell-free biochemical and morphological studies has revealed that a coated bud-coated vesicle transport system shuttles newly synthesized proteins through the successive processing compartments of the Golgi apparatus. These "Golgi coated vesicles" operate in a manner formally analogous to the clathrin coated pit-coated vesicle system responsible for receptor-mediated endocytosis; however Golgi coated vesicles do not contain clathrin.
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Affiliation(s)
- J E Rothman
- Department of Molecular Biology, Princeton University, New Jersey
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50
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Moore PJ, Swords KM, Lynch MA, Staehelin LA. Spatial organization of the assembly pathways of glycoproteins and complex polysaccharides in the Golgi apparatus of plants. J Biophys Biochem Cytol 1991; 112:589-602. [PMID: 1993733 PMCID: PMC2288847 DOI: 10.1083/jcb.112.4.589] [Citation(s) in RCA: 169] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The Golgi apparatus of plant cells is the site of assembly of glycoproteins, proteoglycans, and complex polysaccharides, but little is known about how the different assembly pathways are organized within the Golgi stacks. To study these questions we have employed immunocytochemical techniques and antibodies raised against the hydroxyproline-rich cell wall glycoprotein, extensin, and two types of complex polysaccharides, an acidic pectic polysaccharide known as rhamnogalacturonan I (RG-I), and the neutral hemicellulose, xyloglucan (XG). Our micrographs demonstrate that individual Golgi stacks can process simultaneously glycoproteins and complex polysaccharides. O-linked arabinosylation of the hydroxyproline residues of extensin occurs in cis-cisternae, and glycosylated molecules pass through all cisternae before they are packaged into secretory vesicles in the monensin-sensitive, trans-Golgi network. In contrast, in root tip cortical parenchyma cells, the anti-RG-I and the anti-XG antibodies are shown to bind to complementary subsets of Golgi cisternae, and several lines of indirect evidence suggest that these complex polysaccharides may also exit from different cisternae. Thus, RG-I type polysaccharides appear to be synthesized in cis- and medial cisternae, and have the potential to leave from a monensin-insensitive, medial cisternal compartment. The labeling pattern for XG suggests that it is assembled in trans-Golgi cisternae and departs from the monensin-sensitive trans-Golgi network. This physical separation of the synthesis/secretion pathways of major categories of complex polysaccharides may prevent the synthesis of mixed polysaccharides, and provides a means for producing secretory vesicles that can be targeted to different cell wall domains.
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Affiliation(s)
- P J Moore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347
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