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Parchure A, Tian M, Stalder D, Boyer CK, Bearrows SC, Rohli KE, Zhang J, Rivera-Molina F, Ramazanov BR, Mahata SK, Wang Y, Stephens SB, Gershlick DC, von Blume J. Liquid-liquid phase separation facilitates the biogenesis of secretory storage granules. J Cell Biol 2022; 221:e202206132. [PMID: 36173346 PMCID: PMC9526250 DOI: 10.1083/jcb.202206132] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 08/30/2022] [Accepted: 09/01/2022] [Indexed: 02/03/2023] Open
Abstract
Insulin is synthesized by pancreatic β-cells and stored into secretory granules (SGs). SGs fuse with the plasma membrane in response to a stimulus and deliver insulin to the bloodstream. The mechanism of how proinsulin and its processing enzymes are sorted and targeted from the trans-Golgi network (TGN) to SGs remains mysterious. No cargo receptor for proinsulin has been identified. Here, we show that chromogranin (CG) proteins undergo liquid-liquid phase separation (LLPS) at a mildly acidic pH in the lumen of the TGN, and recruit clients like proinsulin to the condensates. Client selectivity is sequence-independent but based on the concentration of the client molecules in the TGN. We propose that the TGN provides the milieu for converting CGs into a "cargo sponge" leading to partitioning of client molecules, thus facilitating receptor-independent client sorting. These findings provide a new receptor-independent sorting model in β-cells and many other cell types and therefore represent an innovation in the field of membrane trafficking.
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Affiliation(s)
- Anup Parchure
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Meng Tian
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Danièle Stalder
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK
| | - Cierra K. Boyer
- Departments of Pharmacology and Neuroscience, Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA
- Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA
| | - Shelby C. Bearrows
- Departments of Pharmacology and Neuroscience, Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA
- Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA
| | - Kristen E. Rohli
- Departments of Pharmacology and Neuroscience, Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA
- Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA
| | - Jianchao Zhang
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI
- Department of Neurology, University of Michigan School of Medicine, Ann Arbor, MI
| | - Felix Rivera-Molina
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Bulat R. Ramazanov
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Sushil K. Mahata
- Department of Medicine, University of California San Diego, La Jolla, CA
- VA San Diego Healthcare System, San Diego, CA
| | - Yanzhuang Wang
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI
- Department of Neurology, University of Michigan School of Medicine, Ann Arbor, MI
| | - Samuel B. Stephens
- Departments of Pharmacology and Neuroscience, Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA
| | - David C. Gershlick
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK
| | - Julia von Blume
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
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2
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Liu Y, Zhang Y, Sun Y, Ding F. A buried glutamate in the cross-β core renders β-endorphin fibrils reversible. NANOSCALE 2021; 13:19593-19603. [PMID: 34812835 PMCID: PMC8674924 DOI: 10.1039/d1nr05679d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Functional amyloids are abundant in living organisms from prokaryotes to eukaryotes playing diverse biological roles. In contrast to the irreversible aggregation of most known pathological amyloids, we postulate that naturally-occurring functional amyloids are reversible under evolutionary pressure to be able to modulate the fibrillization process, reuse the composite peptides, or perform their biological functions. β-Endorphin, an endogenous opioid peptide hormone, forms such kinds of reversible amyloid fibrils in secretory granules for efficient storage and returns to the functional state of monomers upon release into the blood. The environmental change between low pH in secretory granules and neutral pH in extracellular spaces is believed to drive the reversible fibrillization of β-endorphin. Here, we investigate the critical role of a buried glutamate, Glu8, in the pH-responsive disassembly of β-endorphin fibrils using all-atom molecular dynamics simulations along with structure-based pKa prediction. The fibril was stable at pH 5.5 or lower with all the buried Glu8 residues protonated and neutrally charged. After switching to neutral pH, the Glu8 residues of peptides at the outer layers of the ordered fibrils became deprotonated due to partial solvent exposure, causing sheet-to-coil conformational changes and subsequent exposure of adjacent Glu8 residues in the inner chains. Via iterative deprotonation of Glu8 and induced structural disruption, all Glu8 residues would be progressively deprotonated. Electrostatic repulsion between deprotonated Glu8 residues along with their high solvation tendency disrupted the hydrogen bonding between the β1 strands and increased the solvent exposure of those otherwise buried residues in the cross-β core. Overall, our computational study reveals that the strategic positioning of ionizable residues into the cross-β core is a potential approach for designing reversible amyloid fibrils as pH-responsive smart bio-nanomaterials.
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Affiliation(s)
- Yuying Liu
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Yu Zhang
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Yunxiang Sun
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
- Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, USA.
| | - Feng Ding
- Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, USA.
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3
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Ford C, Parchure A, von Blume J, Burd CG. Cargo sorting at the trans-Golgi network at a glance. J Cell Sci 2021; 134:jcs259110. [PMID: 34870705 PMCID: PMC8714066 DOI: 10.1242/jcs.259110] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The Golgi functions principally in the biogenesis and trafficking of glycoproteins and lipids. It is compartmentalized into multiple flattened adherent membrane sacs termed cisternae, which each contain a distinct repertoire of resident proteins, principally enzymes that modify newly synthesized proteins and lipids sequentially as they traffic through the stack of Golgi cisternae. Upon reaching the final compartments of the Golgi, the trans cisterna and trans-Golgi network (TGN), processed glycoproteins and lipids are packaged into coated and non-coated transport carriers derived from the trans Golgi and TGN. The cargoes of clathrin-coated vesicles are chiefly residents of endo-lysosomal organelles, while uncoated carriers ferry cargo to the cell surface. There are outstanding questions regarding the mechanisms of protein and lipid sorting within the Golgi for export to different organelles. Nonetheless, conceptual advances have begun to define the key molecular features of cargo clients and the mechanisms underlying their sorting into distinct export pathways, which we have collated in this Cell Science at a Glance article and the accompanying poster.
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Affiliation(s)
| | | | - Julia von Blume
- Department of Cell Biology, Yale School of Medicine, Yale University, New Haven, CT 06520, USA
| | - Christopher G. Burd
- Department of Cell Biology, Yale School of Medicine, Yale University, New Haven, CT 06520, USA
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4
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Ma CIJ, Burgess J, Brill JA. Maturing secretory granules: Where secretory and endocytic pathways converge. Adv Biol Regul 2021; 80:100807. [PMID: 33866198 DOI: 10.1016/j.jbior.2021.100807] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 03/10/2021] [Accepted: 03/18/2021] [Indexed: 10/21/2022]
Abstract
Secretory granules (SGs) are specialized organelles responsible for the storage and regulated release of various biologically active molecules from the endocrine and exocrine systems. Thus, proper SG biogenesis is critical to normal animal physiology. Biogenesis of SGs starts at the trans-Golgi network (TGN), where immature SGs (iSGs) bud off and undergo maturation before fusing with the plasma membrane (PM). How iSGs mature is unclear, but emerging studies have suggested an important role for the endocytic pathway. The requirement for endocytic machinery in SG maturation blurs the line between SGs and another class of secretory organelles called lysosome-related organelles (LROs). Therefore, it is important to re-evaluate the differences and similarities between SGs and LROs.
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Affiliation(s)
- Cheng-I Jonathan Ma
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Institute of Medical Science, University of Toronto, Medical Sciences Building, Room 2374, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Jason Burgess
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Department of Molecular Genetics, University of Toronto, Medical Sciences Building, Room 4396, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Julie A Brill
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Institute of Medical Science, University of Toronto, Medical Sciences Building, Room 2374, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada; Department of Molecular Genetics, University of Toronto, Medical Sciences Building, Room 4396, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada.
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5
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Cid-Samper F, Gelabert-Baldrich M, Lang B, Lorenzo-Gotor N, Ponti RD, Severijnen LAWFM, Bolognesi B, Gelpi E, Hukema RK, Botta-Orfila T, Tartaglia GG. An Integrative Study of Protein-RNA Condensates Identifies Scaffolding RNAs and Reveals Players in Fragile X-Associated Tremor/Ataxia Syndrome. Cell Rep 2019; 25:3422-3434.e7. [PMID: 30566867 PMCID: PMC6315285 DOI: 10.1016/j.celrep.2018.11.076] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 09/26/2018] [Accepted: 11/19/2018] [Indexed: 12/21/2022] Open
Abstract
Recent evidence indicates that specific RNAs promote the formation of ribonucleoprotein condensates by acting as scaffolds for RNA-binding proteins (RBPs). We systematically investigated RNA-RBP interaction networks to understand ribonucleoprotein assembly. We found that highly contacted RNAs are structured, have long UTRs, and contain nucleotide repeat expansions. Among the RNAs with such properties, we identified the FMR1 3' UTR that harbors CGG expansions implicated in fragile X-associated tremor/ataxia syndrome (FXTAS). We studied FMR1 binding partners in silico and in vitro and prioritized the splicing regulator TRA2A for further characterization. In a FXTAS cellular model, we validated the TRA2A-FMR1 interaction and investigated implications of its sequestration at both transcriptomic and post-transcriptomic levels. We found that TRA2A co-aggregates with FMR1 in a FXTAS mouse model and in post-mortem human samples. Our integrative study identifies key components of ribonucleoprotein aggregates, providing links to neurodegenerative disease and allowing the discovery of therapeutic targets.
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Affiliation(s)
- Fernando Cid-Samper
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Mariona Gelabert-Baldrich
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Benjamin Lang
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Nieves Lorenzo-Gotor
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Riccardo Delli Ponti
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | | | - Benedetta Bolognesi
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Ellen Gelpi
- Neurological Tissue Biobank of the Hospital Clinic and Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Carrer del Rosselló, 149, 08036, Barcelona, Spain; Institute of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria
| | - Renate K Hukema
- Department of Clinical Genetics, Erasmus MC, 3000 CA Rotterdam, the Netherlands
| | - Teresa Botta-Orfila
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain.
| | - Gian Gaetano Tartaglia
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain; Department of Biology 'Charles Darwin', Sapienza University of Rome, P.le A. Moro 5, Rome 00185, Italy; Institució Catalana de Recerca i Estudis Avançats (ICREA), 23 Passeig Lluís Companys, 08010 Barcelona, Spain.
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6
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Thomsen SK, Raimondo A, Hastoy B, Sengupta S, Dai XQ, Bautista A, Censin J, Payne AJ, Umapathysivam MM, Spigelman AF, Barrett A, Groves CJ, Beer NL, Manning Fox JE, McCarthy MI, Clark A, Mahajan A, Rorsman P, MacDonald PE, Gloyn AL. Type 2 diabetes risk alleles in PAM impact insulin release from human pancreatic β-cells. Nat Genet 2018; 50:1122-1131. [PMID: 30054598 PMCID: PMC6237273 DOI: 10.1038/s41588-018-0173-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Accepted: 06/06/2018] [Indexed: 12/30/2022]
Abstract
The molecular mechanisms underpinning susceptibility loci for type 2 diabetes (T2D) remain poorly understood. Coding variants in peptidylglycine α-amidating monooxygenase (PAM) are associated with both T2D risk and insulinogenic index. Here, we demonstrate that the T2D risk alleles impact negatively on overall PAM activity via defects in expression and catalytic function. PAM deficiency results in reduced insulin content and altered dynamics of insulin secretion in a human β-cell model and primary islets from cadaveric donors. Thus, our results demonstrate a role for PAM in β-cell function, and establish molecular mechanisms for T2D risk alleles at this locus.
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Affiliation(s)
- Soren K Thomsen
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
- Vertex Pharmaceuticals Europe Ltd, Milton Park, Abingdon, UK
| | - Anne Raimondo
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
- National Health and Medical Research Council, Canberra, Australia
| | - Benoit Hastoy
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Shahana Sengupta
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
- MRC Harwell Institute, Harwell Campus, Oxfordshire, UK
| | - Xiao-Qing Dai
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Austin Bautista
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Jenny Censin
- Big Data Institute at the Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, UK
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Anthony J Payne
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Mahesh M Umapathysivam
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Aliya F Spigelman
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Amy Barrett
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Christopher J Groves
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Nicola L Beer
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Jocelyn E Manning Fox
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Mark I McCarthy
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Anne Clark
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
| | - Anubha Mahajan
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Patrick E MacDonald
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Anna L Gloyn
- Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, UK.
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK.
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7
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Maeda Y, Kudo S, Tsushima K, Sato E, Kubota C, Kayamori A, Bochimoto H, Koga D, Torii S, Gomi H, Watanabe T, Hosaka M. Impaired Processing of Prohormones in Secretogranin III-Null Mice Causes Maladaptation to an Inadequate Diet and Stress. Endocrinology 2018; 159:1213-1227. [PMID: 29281094 DOI: 10.1210/en.2017-00636] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Accepted: 12/15/2017] [Indexed: 11/19/2022]
Abstract
Secretogranin III (SgIII), a member of the granin family, binds both to another granin, chromogranin A (CgA), and to a cholesterol-rich membrane that is destined for secretory granules (SGs). The knockdown of SgIII in adrenocorticotropic hormone (ACTH)-producing AtT-20 cells largely impairs the regulated secretion of CgA and ACTH. To clarify the physiological roles of SgIII in vivo, we analyzed hormone secretion and SG biogenesis in newly established SgIII-knockout (KO) mice. Although the SgIII-KO mice were viable and fertile and exhibited no overt abnormalities under ordinary rearing conditions, a high-fat/high-sucrose diet caused pronounced obesity in the mice. Furthermore, in the SgIII-KO mice compared with wild-type (WT) mice, the stimulated secretion of active insulin decreased substantially, whereas the storage of proinsulin increased in the islets. The plasma ACTH was also less elevated in the SgIII-KO mice than in the WT mice after chronic restraint stress, whereas the storage level of the precursor proopiomelanocortin in the pituitary gland was somewhat increased. These findings suggest that the lack of SgIII causes maladaptation of endocrine cells to an inadequate diet and stress by impairing the proteolytic conversion of prohormones in SGs, whereas SG biogenesis and the basal secretion of peptide hormones under ordinary conditions are ensured by the compensatory upregulation of other residual granins or factors.
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Affiliation(s)
- Yoshinori Maeda
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
| | - Saki Kudo
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
| | - Ken Tsushima
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
| | - Eri Sato
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
| | - Chisato Kubota
- Biosignal Research Center, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
- Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan
| | - Aika Kayamori
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
| | - Hiroki Bochimoto
- Health Care Administration Center, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
| | - Daisuke Koga
- Department of Microscopic Anatomy and Cell Biology, Asahikawa Medical University, Asahikawa, Japan
| | - Seiji Torii
- Biosignal Research Center, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Hiroshi Gomi
- Department of Veterinary Anatomy, College of Bioresource Sciences, Nihon University, Fujisawa, Japan
| | - Tsuyoshi Watanabe
- Department of Microscopic Anatomy and Cell Biology, Asahikawa Medical University, Asahikawa, Japan
| | - Masahiro Hosaka
- Department of Biotechnology, Laboratory of Molecular Life Sciences, Akita Prefectural University, Akita, Japan
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8
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Chen Y, Gershlick DC, Park SY, Bonifacino JS. Segregation in the Golgi complex precedes export of endolysosomal proteins in distinct transport carriers. J Cell Biol 2017; 216:4141-4151. [PMID: 28978644 PMCID: PMC5716290 DOI: 10.1083/jcb.201707172] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 08/18/2017] [Accepted: 08/24/2017] [Indexed: 01/26/2023] Open
Abstract
Biosynthetic sorting of newly synthesized transmembrane cargos to endosomes and lysosomes is thought to occur at the TGN through recognition of sorting signals in the cytosolic tails of the cargos by adaptor proteins, leading to cargo packaging into coated vesicles destined for the endolysosomal system. Here we present evidence for a different mechanism in which two sets of endolysosomal proteins undergo early segregation to distinct domains of the Golgi complex by virtue of the proteins' luminal and transmembrane domains. Proteins in one Golgi domain exit into predominantly vesicular carriers by interaction of sorting signals with adaptor proteins, but proteins in the other domain exit into predominantly tubular carriers shared with plasma membrane proteins, independently of signal-adaptor interactions. These findings demonstrate that sorting of endolysosomal proteins begins at an earlier stage and involves mechanisms that partly differ from those described by classical models.
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Affiliation(s)
- Yu Chen
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - David C Gershlick
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Sang Yoon Park
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Juan S Bonifacino
- Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
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9
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Bonnemaison ML, Duffy ME, Mains RE, Vogt S, Eipper BA, Ralle M. Copper, zinc and calcium: imaging and quantification in anterior pituitary secretory granules. Metallomics 2016; 8:1012-22. [PMID: 27426256 DOI: 10.1039/c6mt00079g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The anterior pituitary is specialized for the synthesis, storage and release of peptide hormones. The activation of inactive peptide hormone precursors requires a specific set of proteases and other post-translational processing enzymes. High levels of peptidylglycine α-amidating monooxygenase (PAM), an essential peptide processing enzyme, occur in the anterior pituitary. PAM, which converts glycine-extended peptides into amidated products, requires copper and zinc to support its two catalytic activities and calcium for structure. We used X-ray fluorescence microscopy on rat pituitary sections and inductively coupled plasma mass spectrometry on subcellular fractions prepared from rat anterior pituitary to localize and quantify copper, zinc and calcium. X-ray fluorescence microscopy indicated that the calcium concentration in pituitary tissue was about 2.5 mM, 10-times more than zinc and 50-times more than copper. Although no higher than cytosolic levels, secretory granule levels of copper exceeded PAM levels by a factor of 10. Atp7a, which transports copper into the lumen of the secretory pathway, was enriched in endosomes and Golgi, not in secretory granules. If Atp7a transfers copper directly to PAM, this pH-dependent process is likely to occur in Golgi and endosomes.
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Affiliation(s)
- Mathilde L Bonnemaison
- Department of Molecular Biology and Biophysics, UConn Health, 263 Farmington Avenue, Farmington, CT 06030, USA.
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10
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Cawley NX, Li Z, Loh YP. 60 YEARS OF POMC: Biosynthesis, trafficking, and secretion of pro-opiomelanocortin-derived peptides. J Mol Endocrinol 2016; 56:T77-97. [PMID: 26880796 PMCID: PMC4899099 DOI: 10.1530/jme-15-0323] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 02/15/2016] [Indexed: 12/15/2022]
Abstract
Pro-opiomelanocortin (POMC) is a prohormone that encodes multiple smaller peptide hormones within its structure. These peptide hormones can be generated by cleavage of POMC at basic residue cleavage sites by prohormone-converting enzymes in the regulated secretory pathway (RSP) of POMC-synthesizing endocrine cells and neurons. The peptides are stored inside the cells in dense-core secretory granules until released in a stimulus-dependent manner. The complexity of the regulation of the biosynthesis, trafficking, and secretion of POMC and its peptides reflects an impressive level of control over many factors involved in the ultimate role of POMC-expressing cells, that is, to produce a range of different biologically active peptide hormones ready for action when signaled by the body. From the discovery of POMC as the precursor to adrenocorticotropic hormone (ACTH) and β-lipotropin in the late 1970s to our current knowledge, the understanding of POMC physiology remains a monumental body of work that has provided insight into many aspects of molecular endocrinology. In this article, we describe the intracellular trafficking of POMC in endocrine cells, its sorting into dense-core secretory granules and transport of these granules to the RSP. Additionally, we review the enzymes involved in the maturation of POMC to its various peptides and the mechanisms involved in the differential processing of POMC in different cell types. Finally, we highlight studies pertaining to the regulation of ACTH secretion in the anterior and intermediate pituitary and POMC neurons of the hypothalamus.
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Affiliation(s)
- Niamh X Cawley
- Section on Cellular NeurobiologyEunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Zhaojin Li
- Section on Cellular NeurobiologyEunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Y Peng Loh
- Section on Cellular NeurobiologyEunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
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11
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Nespovitaya N, Gath J, Barylyuk K, Seuring C, Meier BH, Riek R. Dynamic Assembly and Disassembly of Functional β-Endorphin Amyloid Fibrils. J Am Chem Soc 2016; 138:846-56. [DOI: 10.1021/jacs.5b08694] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Nadezhda Nespovitaya
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Julia Gath
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Konstantin Barylyuk
- Laboratory
of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
| | - Carolin Seuring
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Beat H. Meier
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Roland Riek
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
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12
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Chen Y, Xia Z, Wang L, Yu Y, Liu P, Song E, Xu T. An efficient two-step subcellular fractionation method for the enrichment of insulin granules from INS-1 cells. BIOPHYSICS REPORTS 2015; 1:34-40. [PMID: 26942217 PMCID: PMC4762126 DOI: 10.1007/s41048-015-0008-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 07/03/2015] [Indexed: 10/25/2022] Open
Abstract
Insulin is one of the key regulators for blood glucose homeostasis. More than 99% of insulin is secreted from the pancreatic β-cells. Within each β-cell, insulin is packaged and processed in insulin secretary granules (ISGs) before its exocytosis. Insulin secretion is a complicated but well-organized dynamic process that includes the budding of immature ISGs (iISGs) from the trans-Golgi network, iISG maturation, and mature ISG (mISG) fusion with plasma membrane. However, the molecular mechanisms involved in this process are largely unknown. It is therefore crucial to separate and enrich iISGs and mISGs before determining their distinct characteristics and protein contents. Here, we developed an efficient two-step subcellular fractionation method for the enrichment of iISGs and mISGs from INS-1 cells: OptiPrep gradient purification followed by Percoll solution purification. We demonstrated that by using this method, iISGs and mISGs can be successfully distinguished and enriched. This method can be easily adapted to investigate SGs in other cells or tissues, thereby providing a useful tool for elucidating the mechanisms of granule maturation and secretion.
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Affiliation(s)
- Yan Chen
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China.,University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Zhiping Xia
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China.,University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Lifen Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China.,University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Yong Yu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China.,University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Pingsheng Liu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China
| | - Eli Song
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China
| | - Tao Xu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China
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13
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Aroso M, Agricola B, Hacker C, Schrader M. Proteoglycans support proper granule formation in pancreatic acinar cells. Histochem Cell Biol 2015; 144:331-46. [PMID: 26105026 DOI: 10.1007/s00418-015-1339-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/07/2015] [Indexed: 12/31/2022]
Abstract
Zymogen granules (ZG) are specialized organelles in the exocrine pancreas which allow digestive enzyme storage and regulated secretion. The molecular mechanisms of their biogenesis and the sorting of zymogens are still incompletely understood. Here, we investigated the role of proteoglycans in granule formation and secretion of zymogens in pancreatic AR42J cells, an acinar model system. Cupromeronic Blue cytochemistry and biochemical studies revealed an association of proteoglycans primarily with the granule membrane. Removal of proteoglycans by carbonate treatment led to a loss of membrane curvature indicating a supportive role in the maintenance of membrane shape and stability. Chemical inhibition of proteoglycan synthesis impaired the formation of normal electron-dense granules in AR42J cells and resulted in the formation of unusually small granule structures. These structures still contained the zymogen carboxypeptidase, a cargo molecule of secretory granules, but migrated to lighter fractions after density gradient centrifugation. Furthermore, the basal secretion of amylase was increased in AR42J cells after inhibitor treatment. In addition, irregular-shaped granules appeared in pancreatic lobules. We conclude that the assembly of a proteoglycan scaffold at the ZG membrane is supporting efficient packaging of zymogens and the proper formation of stimulus-competent storage granules in acinar cells of the pancreas.
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Affiliation(s)
- Miguel Aroso
- Centre for Cell Biology and Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal
| | - Brigitte Agricola
- Department of Cell Biology and Cell Pathology, University of Marburg, 35037, Marburg, Germany
| | - Christian Hacker
- College of Life and Environmental Sciences, Biosciences, University of Exeter, Geoffrey Pope Building, Stocker Road, Exeter, EX4 4QD, UK
| | - Michael Schrader
- Centre for Cell Biology and Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal. .,College of Life and Environmental Sciences, Biosciences, University of Exeter, Geoffrey Pope Building, Stocker Road, Exeter, EX4 4QD, UK.
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14
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Bonnemaison M, Bäck N, Lin Y, Bonifacino JS, Mains R, Eipper B. AP-1A controls secretory granule biogenesis and trafficking of membrane secretory granule proteins. Traffic 2014; 15:1099-121. [PMID: 25040637 DOI: 10.1111/tra.12194] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 02/06/2023]
Abstract
The adaptor protein 1A complex (AP-1A) transports cargo between the trans-Golgi network (TGN) and endosomes. In professional secretory cells, AP-1A also retrieves material from immature secretory granules (SGs). The role of AP-1A in SG biogenesis was explored using AtT-20 corticotrope tumor cells expressing reduced levels of the AP-1A μ1A subunit. A twofold reduction in μ1A resulted in a decrease in TGN cisternae and immature SGs and the appearance of regulated secretory pathway components in non-condensing SGs. Although basal secretion of endogenous SG proteins was unaffected, secretagogue-stimulated release was halved. The reduced μ1A levels interfered with the normal trafficking of carboxypeptidase D (CPD) and peptidylglycine α-amidating monooxygenase-1 (PAM-1), integral membrane enzymes that enter immature SGs. The non-condensing SGs contained POMC products and PAM-1, but not CPD. Based on metabolic labeling and secretion experiments, the cleavage of newly synthesized PAM-1 into PHM was unaltered, but PHM basal secretion was increased in sh-μ1A PAM-1 cells. Despite lacking a canonical AP-1A binding motif, yeast two-hybrid studies demonstrated an interaction between the PAM-1 cytosolic domain and AP-1A. Coimmunoprecipitation experiments with PAM-1 mutants revealed an influence of the luminal domains of PAM-1 on this interaction. Thus, AP-1A is crucial for normal SG biogenesis, function and composition.
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Affiliation(s)
- Mathilde Bonnemaison
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, 06030, USA
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15
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Tewari R, Jarvela T, Linstedt AD. Manganese induces oligomerization to promote down-regulation of the intracellular trafficking receptor used by Shiga toxin. Mol Biol Cell 2014; 25:3049-58. [PMID: 25079690 PMCID: PMC4230593 DOI: 10.1091/mbc.e14-05-1003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Manganese down-regulates the Shiga toxin receptor GPP130, which protects against lethal toxin doses. This study reveals a major aspect of the mechanism. Manganese binds GPP130, inducing GPP130 oligomerization, which is required and sufficient to redirect GPP130 out of the Golgi toward lysosomes. Manganese (Mn) protects cells against lethal doses of purified Shiga toxin by causing the degradation of the cycling transmembrane protein GPP130, which the toxin uses as a trafficking receptor. Mn-induced GPP130 down-regulation, in addition to being a potential therapeutic approach against Shiga toxicosis, is a model for the study of metal-regulated protein sorting. Significantly, however, the mechanism by which Mn regulates GPP130 trafficking is unknown. Here we show that a transferable trafficking determinant within GPP130 bound Mn and that Mn binding induced GPP130 oligomerization in the Golgi. Alanine substitutions blocking Mn binding abrogated both oligomerization of GPP130 and GPP130 sorting from the Golgi to lysosomes. Further, oligomerization was sufficient because forced aggregation, using a drug-controlled polymerization domain, redirected GPP130 to lysosomes in the absence of Mn. These experiments reveal metal-induced oligomerization as a Golgi sorting mechanism for a medically relevant receptor for Shiga toxin.
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Affiliation(s)
- Ritika Tewari
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Timothy Jarvela
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Adam D Linstedt
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
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16
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Vishwanatha K, Bäck N, Mains RE, Eipper BA. A histidine-rich linker region in peptidylglycine α-amidating monooxygenase has the properties of a pH sensor. J Biol Chem 2014; 289:12404-20. [PMID: 24627494 DOI: 10.1074/jbc.m113.545947] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Decreasing luminal pH is thought to play a role in the entry of newly synthesized and endocytosed membrane proteins into secretory granules. The two catalytic domains of peptidylglycine α-amidating monooxygenase (PAM), a type I integral membrane protein, catalyze the sequential reactions that convert peptidyl-Gly substrates into amidated products. We explored the hypothesis that a conserved His-rich cluster (His-Gly-His-His) in the linker region connecting its two catalytic domains senses pH and affects PAM trafficking by mutating these His residues to Ala (Ala-Gly-Ala-Ala; H3A). Purified recombinant wild-type and H3A linker peptides were examined using circular dichroism and tryptophan fluorescence; mutation of the His cluster largely eliminated its pH sensitivity. An enzymatically active PAM protein with the same mutations (PAM-1/H3A) was expressed in HEK293 cells and AtT-20 corticotrope tumor cells. Metabolic labeling followed by immunoprecipitation revealed more rapid loss of newly synthesized PAM-1/H3A than PAM-1; although release of newly synthesized monofunctional PHM/H3A was increased, release of soluble bifunctional PAM/H3A, a product of the endocytic pathway, was decreased. Surface biotinylation revealed rapid loss of PAM-1/H3A, with no detectable return of the mutant protein to secretory granules. Consistent with its altered endocytic trafficking, little PAM-1/H3A was subjected to regulated intramembrane proteolysis followed by release of a small nuclear-targeted cytosolic fragment. AtT-20 cells expressing PAM-1/H3A adopted the morphology of wild-type AtT-20 cells; secretory products no longer accumulated in the trans-Golgi network and secretory granule exocytosis was more responsive to secretagogue.
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17
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Gómez-Lázaro M, Rinn C, Aroso M, Amado F, Schrader M. Proteomic analysis of zymogen granules. Expert Rev Proteomics 2014; 7:735-47. [DOI: 10.1586/epr.10.31] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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18
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Bonnemaison ML, Eipper BA, Mains RE. Role of adaptor proteins in secretory granule biogenesis and maturation. Front Endocrinol (Lausanne) 2013; 4:101. [PMID: 23966980 PMCID: PMC3743005 DOI: 10.3389/fendo.2013.00101] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 07/31/2013] [Indexed: 12/29/2022] Open
Abstract
In the regulated secretory pathway, secretory granules (SGs) store peptide hormones that are released on demand. SGs are formed at the trans-Golgi network and must undergo a maturation process to become responsive to secretagogues. The production of mature SGs requires concentrating newly synthesized soluble content proteins in granules whose membranes contain the appropriate integral membrane proteins. The mechanisms underlying the sorting of soluble and integral membrane proteins destined for SGs from other proteins are not yet well understood. For soluble proteins, luminal pH and divalent metals can affect aggregation and interaction with surrounding membranes. The trafficking of granule membrane proteins can be controlled by both luminal and cytosolic factors. Cytosolic adaptor proteins (APs), which recognize the cytosolic domains of proteins that span the SG membrane, have been shown to play essential roles in the assembly of functional SGs. Adaptor protein 1A (AP-1A) is known to interact with specific motifs in its cargo proteins and with the clathrin heavy chain, contributing to the formation of a clathrin coat. AP-1A is present in patches on immature SG membranes, where it removes cargo and facilitates SG maturation. AP-1A recruitment to membranes can be modulated by Phosphofurin Acidic Cluster Sorting protein 1 (PACS-1), a cytosolic protein which interacts with both AP-1A and cargo that has been phosphorylated by casein kinase II. A cargo/PACS-1/AP-1A complex is necessary to drive the appropriate transport of several cargo proteins within the regulated secretory pathway. The Golgi-localized, γ-ear containing, ADP-ribosylation factor binding (GGA) family of APs serve a similar role. We review the functions of AP-1A, PACS-1, and GGAs in facilitating the retrieval of proteins from immature SGs and review examples of cargo proteins whose trafficking within the regulated secretory pathway is governed by APs.
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Affiliation(s)
- Mathilde L. Bonnemaison
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT, USA
| | - Betty A. Eipper
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT, USA
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT, USA
| | - Richard E. Mains
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT, USA
- *Correspondence: Richard E. Mains, Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3401, USA e-mail:
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19
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Sun M, Watanabe T, Bochimoto H, Sakai Y, Torii S, Takeuchi T, Hosaka M. Multiple sorting systems for secretory granules ensure the regulated secretion of peptide hormones. Traffic 2012; 14:205-18. [PMID: 23171199 DOI: 10.1111/tra.12029] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 11/19/2012] [Accepted: 11/21/2012] [Indexed: 01/13/2023]
Abstract
Prior to secretion, regulated peptide hormones are selectively sorted to secretory granules (SGs) at the trans-Golgi network (TGN) in endocrine cells. Secretogranin III (SgIII) appears to facilitate SG sorting process by tethering of protein aggregates containing chromogranin A (CgA) and peptide hormones to the cholesterol-rich SG membrane (SGM). Here, we evaluated the role of SgIII in SG sorting in AtT-20 cells transfected with small interfering RNA targeting SgIII. In the SgIII-knockdown cells, the intracellular retention of CgA was greatly impaired, and only a trace amount of CgA was localized within the vacuoles formed in the TGN, confirming the significance of SgIII in both the tethering of CgA-containing aggregates and the establishment of the proper SG morphology. Although the intracellular retention of proopiomelanocortin (POMC) was considerably impaired in SgIII-knockdown cells, residual adrenocorticotropic hormone (ACTH)/POMC was still localized to some few remaining SGs together with another granin protein, secretogranin II (SgII), and was secreted in a regulated manner. Biochemical analyses indicated that SgII bound directly to the SGM in a cholesterol-dependent manner and was able to retain the aggregated form of POMC, revealing a latent redundancy in the SG sorting and retention mechanisms, that ensures the regulated secretion of bioactive peptides.
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Affiliation(s)
- Meng Sun
- Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, 371-8512, Japan
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20
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Modulating zymogen granule formation in pancreatic AR42J cells. Exp Cell Res 2012; 318:1855-66. [PMID: 22683857 DOI: 10.1016/j.yexcr.2012.05.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Revised: 05/11/2012] [Accepted: 05/24/2012] [Indexed: 01/07/2023]
Abstract
Zymogen granules (ZG) are specialized organelles in the exocrine pancreas which allow digestive enzyme storage and regulated secretion. To investigate ZG biogenesis, cargo sorting and packaging, suitable cellular model systems are required. Here, we demonstrate that granule formation in pancreatic AR42J cells, an acinar model system, can be modulated by altering the growth conditions in cell culture. We find that cultivation of AR42J cells in Panserin™ 401, a serum-free medium, enhances the induction of granule formation in the presence or absence of dexamethasone when compared to standard conditions including serum. Biochemical and morphological studies revealed an increase in ZG markers on the mRNA and protein level, as well as in granule size compared to standard conditions. Our data indicate that this effect is related to pronounced differentiation of AR42J cells. To address if enhanced expression of ZG proteins promotes granule formation, we expressed several zymogens and ZG membrane proteins in unstimulated AR42J cells and in constitutively secreting COS-7 cells. Neither single expression nor co-expression was sufficient to initiate granule formation in AR42J cells or the formation of granule-like structures in COS-7 cells as described for neuroendocrine cargo proteins. The importance of our findings for granule formation in exocrine cells is discussed.
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21
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Schvartz D, Brunner Y, Couté Y, Foti M, Wollheim CB, Sanchez JC. Improved characterization of the insulin secretory granule proteomes. J Proteomics 2012; 75:4620-31. [PMID: 22569486 DOI: 10.1016/j.jprot.2012.04.023] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2011] [Revised: 02/22/2012] [Accepted: 04/20/2012] [Indexed: 11/15/2022]
Abstract
Insulin secretory granules (ISGs) are pivotal organelles of pancreatic ß-cells and represent a key participant to glucose homeostasis. Indeed, insulin is packed and processed within these vesicles before its release by exocytosis. It is therefore crucial to acquire qualitative and quantitative data on the ISG proteome, in order to increase our knowledge on ISG biogenesis, maturation and exocytosis. Despites efforts made in the past years, the coverage of the ISG proteome is still incomplete and comprises many potential protein contaminants most likely coming from suboptimal sample preparations. We developed here a 3-step gradient purification procedure combined to Stable Isotope Labeling with Amino acids in Cell culture (SILAC) to further characterize the ISG protein content. Our results allowed to build three complementary proteomes containing 1/ proteins which are enriched in mature ISGs, 2/ proteins sharing multiple localizations including ISGs, and finally 3/ proteins sorted out from immature ISGs and/or co-purifying contaminants. As a proof of concept, the ProSAAS, a neuronal protein found in ISGs was further characterized and its granular localization proved. ProSAAS might represent a novel potential target allowing to better understand the defaults in insulin processing and secretion observed during type 2 diabetes progression. This article is part of a special issue entitled: Translational Proteomics.
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Affiliation(s)
- Domitille Schvartz
- Biomedical Proteomics Research Group, Department of Human Protein Sciences, University Medical Center, Geneva, Switzerland
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22
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Borta H, Aroso M, Rinn C, Gomez-Lazaro M, Vitorino R, Zeuschner D, Grabenbauer M, Amado F, Schrader M. Analysis of low abundance membrane-associated proteins from rat pancreatic zymogen granules. J Proteome Res 2010; 9:4927-39. [PMID: 20707389 DOI: 10.1021/pr100052q] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Zymogen granules (ZG) are specialized storage organelles in the exocrine pancreas that allow the sorting, packaging, and regulated apical secretion of digestive enzymes. As there is a critical need for further understanding of the key processes in regulated secretion to develop new therapeutic options in medicine, we applied a suborganellar proteomics approach to identify peripheral membrane-associated ZG proteins. We focused on the analysis of a "basic" group (pH range 6.2-11) with about 46 spots among which 44 were identified by tandem mass spectrometry. These spots corresponded to 16 unique proteins, including rat mast cell chymase (RMCP-1) and peptidyl-prolyl cis-trans isomerase B (PpiB; cyclophilin B), an ER-resident protein. To confirm that these proteins were specific to zymogen granules and not contaminants of the preparation, we conducted a series of validation experiments. Immunoblotting of ZG subfractions revealed that chymase and PpiB behaved like bona fide peripheral membrane proteins. Their expression in rat pancreas was regulated by feeding behavior. Ultrastructural and immunofluorescence studies confirmed their ZG localization. Furthermore, a chymase-YFP fusion protein was properly targeted to ZG in pancreatic AR42J cells. Interestingly, for both proteins, proteoglycan-binding properties have been reported. The importance of our findings for sorting and packaging during ZG formation is discussed.
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Affiliation(s)
- Heike Borta
- Department of Cell Biology and Cell Pathology, Philipps University of Marburg, Robert Koch Strasse 6, Marburg, Germany
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23
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Hosaka M, Watanabe T. Secretogranin III: a bridge between core hormone aggregates and the secretory granule membrane. Endocr J 2010; 57:275-86. [PMID: 20203425 DOI: 10.1507/endocrj.k10e-038] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Secretory granules in endocrine cells selectively store bioactive peptide hormones and amines, which are secreted in a regulated manner upon appropriate stimulation. In addition to bioactive substances, various proteins and lipids characteristic of secretory granules are likely recruited to a restricted space at the trans-Golgi Network (TGN), and the space then matures to the secretory granule. Although experimental findings so far have strongly suggested that aggregation- and receptor-mediated processes are essential for the formation of secretory granules, the putative link between these two processes remains to be clarified. Recently, secretogranin III (SgIII) has been identified as a specific binding protein for chromogranin A (CgA), a representative constituent of the core aggregate within secretory granules, and it was later revealed that SgIII can also bind to the cholesterol-rich membrane domain at the TGN. Based on its multifaceted binding properties, SgIII may act as a central player in the formation of cholesterol-rich membrane platforms. Upon these platforms, essential processes for secretory granule biogenesis coordinately occur; that is, selective recruitment of prohormones, processing and modifying of prohormones, and condensation of mature hormones as an aggregate. This review summarizes the findings and theoretical concepts on the issue to date and then focuses on the putative role of SgIII in secretory granule biogenesis in endocrine cells.
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Affiliation(s)
- Masahiro Hosaka
- Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
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24
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Cruz-Soto ME, Cosío G, Jeziorski MC, Vargas-Barroso V, Aguilar MB, Cárabez A, Berger P, Saftig P, Arnold E, Thebault S, Martínez de la Escalera G, Clapp C. Cathepsin D is the primary protease for the generation of adenohypophyseal vasoinhibins: cleavage occurs within the prolactin secretory granules. Endocrinology 2009; 150:5446-54. [PMID: 19819948 DOI: 10.1210/en.2009-0390] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Vasoinhibins are a family of N-terminal prolactin (PRL) fragments that inhibit blood vessel growth, dilation, permeability, and survival. The aspartyl endoprotease cathepsin D is active at acidic pH and can cleave rat PRL to generate vasoinhibins. We investigated whether and where vasoinhibins could be generated by cathepsin D in the adenohypophysis of rats and mice and whether their production could be gender dependent. Vasoinhibins were detected in primary cultures of rat adenohypophyseal cells by Western blot with antibodies directed against the N terminus of PRL but not the C terminus. Ovariectomized, estrogen-treated females show greater levels of adenohypophyseal vasoinhibins than males. Peptide sequencing analysis revealed that the cleaved form of PRL in rat adenohypophyseal extracts contains the PRL N terminus and a second N terminus starting at Ser(149), the reported cleavage site of cathepsin D in rat PRL. In addition, cathepsin D inhibition by pepstatin A reduced vasoinhibin levels in rat adenohypophyseal cell cultures. Confocal and electron microscopy showed the colocalization of cathepsin D and PRL within rat adenohypophyseal cells and secretory granules, and a subcellular fraction of rat adenohypophysis enriched in secretory granules contained cathepsin D activity able to generate vasoinhibins from PRL. Of note, vasoinhibins were absent in the adenohypophysis of mice lacking the cathepsin D gene but not in wild-type mice. These findings show that cathepsin D is the main protease responsible for the generation of adenohypophyseal vasoinhibins and that its action can take place within the secretory granules of lactotrophs.
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Affiliation(s)
- Martha E Cruz-Soto
- Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus UNAM-Juriquilla, 76230 Querétaro, México
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25
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Zhang X, Bao L, Ma GQ. Sorting of neuropeptides and neuropeptide receptors into secretory pathways. Prog Neurobiol 2009; 90:276-83. [PMID: 19853638 DOI: 10.1016/j.pneurobio.2009.10.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2009] [Revised: 08/11/2009] [Accepted: 10/09/2009] [Indexed: 01/07/2023]
Abstract
There are two major secretory pathways in neurons, the regulated pathway and the constitutive pathway. Neuropeptides and other regulated secretory proteins are known to be sorted into large dense-core vesicles of the regulated pathway in the trans-Golgi network and are secreted upon stimulus-induced increases in intracellular Ca(2+). The newly synthesized cell surface receptors are usually sorted into microvesicles of the constitutive pathway and inserted into the plasma membrane by spontaneous exocytosis. Small-diameter sensory neurons in dorsal root ganglia and pheochromocytoma cells express neuropeptides (e.g., substance P) and several neuropeptide receptors including opioid receptors. The mu-opioid receptors are delivered to the cell surface through the constitutive pathway, whereas another type of opioid receptor, the delta-opioid receptor, is often found in the membrane of large dense-core vesicles and can be inserted into the plasma membrane when exocytosis occurs. Recent studies show that sequences with opposite electrical polarity within the prohormones of substance P are essential for their sorting into large dense-core vesicles. Moreover, the delta-opioid receptor is sorted into large dense-core vesicles by its interaction with protachykinin, a prohormone of substance P. These findings provide insight into the molecular mechanisms that determine the sorting and trafficking of neuropeptides and neuropeptide receptors in neurons.
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Affiliation(s)
- Xu Zhang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, PR China.
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26
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Sobota JA, Bäck N, Eipper BA, Mains RE. Inhibitors of the V0 subunit of the vacuolar H+-ATPase prevent segregation of lysosomal- and secretory-pathway proteins. J Cell Sci 2009; 122:3542-53. [PMID: 19737820 DOI: 10.1242/jcs.034298] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The vacuolar H(+)-ATPase (V-ATPase) establishes pH gradients along secretory and endocytic pathways. Progressive acidification is essential for proteolytic processing of prohormones and aggregation of soluble content proteins. The V-ATPase V(0) subunit is thought to have a separate role in budding and fusion events. Prolonged treatment of professional secretory cells with selective V-ATPase inhibitors (bafilomycin A1, concanamycin A) was used to investigate its role in secretory-granule biogenesis. As expected, these inhibitors eliminated regulated secretion and blocked prohormone processing. Drug treatment caused the formation of large, mixed organelles, with components of immature granules and lysosomes and some markers of autophagy. Markers of the trans-Golgi network and earlier secretory pathway were unaffected. Ammonium chloride and methylamine treatment blocked acidification to a similar extent as the V-ATPase inhibitors without producing mixed organelles. Newly synthesized granule content proteins appeared in mixed organelles, whereas mature secretory granules were spared. Following concanamycin treatment, selected membrane proteins enter tubulovesicular structures budding into the interior of mixed organelles. shRNA-mediated knockdown of the proteolipid subunit of V(0) also caused vesiculation of immature granules. Thus, V-ATPase has a role in protein sorting in immature granules that is distinct from its role in acidification.
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Affiliation(s)
- Jacqueline A Sobota
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030, USA
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Brunner Y, Schvartz D, Couté Y, Sanchez JC. Proteomics of regulated secretory organelles. MASS SPECTROMETRY REVIEWS 2009; 28:844-867. [PMID: 19301366 DOI: 10.1002/mas.20211] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Regulated secretory organelles are important subcellular structures of living cells that allow the release in the extracellular space of crucial compounds, such as hormones and neurotransmitters. Therefore, the regulation of biogenesis, trafficking, and exocytosis of regulated secretory organelles has been intensively studied during the last 30 years. However, due to the large number of different regulated secretory organelles, only a few of them have been specifically characterized. New insights into regulated secretory organelles open crucial perspectives for a better comprehension of the mechanisms that govern cell secretion. The combination of subcellular fractionation, protein separation, and mass spectrometry is also possible to study regulated secretory organelles at the proteome level. In this review, we present different strategies used to isolate regulated secretory organelles, separate their protein content, and identify the proteins by mass spectrometry. The biological significance of regulated secretory organelles-proteomic analysis is discussed as well.
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Affiliation(s)
- Yannick Brunner
- Biomedical Proteomics Research Group, University Medical Center, Geneva, Switzerland
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28
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Abstract
Exocrine, endocrine, and neuroendocrine cells store hormones and neuropeptides in secretory granules (SGs), which undergo regulated exocytosis in response to an appropriate stimulus. These cargo proteins are sorted at the trans-Golgi network into forming immature secretory granules (ISGs). ISGs undergo maturation while they are transported to and within the F-actin-rich cortex. This process includes homotypic fusion of ISGs, acidification of their lumen, processing, and aggregation of cargo proteins as well as removal of excess membrane and missorted cargo. The resulting mature secretory granules (MSGs) are stored in the F-actin-rich cell cortex, perhaps as segregated pools exhibiting specific responses to stimuli for regulated exocytosis. During the last decade our understanding of the maturation of ISGs advanced substantially. The use of biochemical approaches led to the identification of membrane molecules mechanistically involved in this process. Furthermore, live cell imaging in combination with fluorescently tagged marker proteins of SGs provided insights into the dynamics of maturing ISGs, and the functional implications of cytoskeletal elements and motor proteins.
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Biogenesis of Dense-Core Secretory Granules. TRAFFICKING INSIDE CELLS 2009. [PMCID: PMC7122546 DOI: 10.1007/978-0-387-93877-6_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dense core granules (DCGs) are vesicular organelles derived from outbound traffic through the eukaryotic secretory pathway. As DCGs are formed, the secretory pathway can also give rise to other types of vesicles, such as those bound for endosomes, lysosomes, and the cell surface. DCGs differ from these other vesicular carriers in both content and function, storing highly concentrated cores’ of condensed cargo in vesicles that are stably maintained within the cell until a specific extracellular stimulus causes their fusion with the plasma membrane. These unique features are imparted by the activities of membrane and lumenal proteins that are specifically delivered to the vesicles during synthesis. This chapter will describe the DCG biogenesis pathway, beginning with the sorting of DCG proteins from proteins that are destined for other types of vesicle carriers. In the trans-Golgi network (TGN), sorting occurs as DCG proteins aggregate, causing physical separation from non-DCG proteins. Recent work addresses the nature of interactions that produce these aggregates, as well as potentially important interactions with membranes and membrane proteins. DCG proteins are released from the TGN in vesicles called immature secretory granules (ISGs). The mechanism of ISG formation is largely unclear but is not believed to rely on the assembly of vesicle coats like those observed in other secretory pathways. The required cytosolic factors are now beginning to be identified using in vitro systems with purified cellular components. ISG transformation into a mature fusion-competent, stimulus-dependent DCG occurs as endoproteolytic processing of many DCG proteins causes continued condensation of the lumenal contents. At the same time, proteins that fail to be incorporated into the condensing core are removed by a coat-mediated budding mechanism, which also serves to remove excess membrane and membrane proteins from the maturing vesicle. This chapter will summarize the work leading to our current view of granule synthesis, and will discuss questions that need to be addressed in order to gain a more complete understanding of the pathway.
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Ma GQ, Wang B, Wang HB, Wang Q, Bao L. Short elements with charged amino acids form clusters to sort protachykinin into large dense-core vesicles. Traffic 2008; 9:2165-79. [PMID: 18939957 DOI: 10.1111/j.1600-0854.2008.00836.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The sorting of neuropeptide tachykinins into large dense-core vesicles (LDCVs) is a key step in their regulated secretion from neurons. However, the sorting mechanism for protachykinin has not yet to be clearly resolved. In this study, we report that the clustered short elements with charged amino acids regulate the efficiency of protachykinin sorting into LDCVs. A truncation experiment showed that the propeptide and the mature peptide-containing sequence of protachykinin were sorted into LDCVs. These two regions exhibit a polarized distribution of charged amino acids. The LDCV localization of the propeptide was gradually decreased with an increasing number of neutral amino acids. Furthermore, the short element with four to five amino acids containing two charged residues was found to be a basic unit for LDCV sorting that enables regulated secretion. In the native propeptide sequence, these charged short elements were clustered to enhance the intermolecular aggregation by electrostatic interaction and produce a gradual and additive effect on LDCV sorting. The optimal conditions for intermolecular aggregation of protachykinin were at millimolar Ca(2+) concentrations and pH 5.5-6.0. These results demonstrate that the charged short elements are clustered such that they serve as aggregative signals and regulate the efficiency of protachykinin sorting into LDCVs. These findings reveal a novel mechanism for the sorting of neuropeptides into a regulated secretory pathway.
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Affiliation(s)
- Guo-Qiang Ma
- Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, China
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31
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Lui-Roberts WWY, Ferraro F, Nightingale TD, Cutler DF. Aftiphilin and gamma-synergin are required for secretagogue sensitivity of Weibel-Palade bodies in endothelial cells. Mol Biol Cell 2008; 19:5072-81. [PMID: 18815278 DOI: 10.1091/mbc.e08-03-0301] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Formation of secretory organelles requires the coupling of cargo selection to targeting into the correct exocytic pathway. Although the assembly of regulated secretory granules is driven in part by selective aggregation and retention of content, we recently reported that adaptor protein-1 (AP-1) recruitment of clathrin is essential to the initial formation of Weibel-Palade bodies (WPBs) at the trans-Golgi network. A selective co-aggregation process might include recruitment of components required for targeting to the regulated secretory pathway. However, we find that acquisition of the regulated secretory phenotype by WPBs in endothelial cells is coupled to but can be separated from formation of the distinctive granule core by ablation of the AP-1 effectors aftiphilin and gamma-synergin. Their depletion by small interfering RNA leads to WPBs that fail to respond to secretagogue and release their content in an unregulated manner. We find that these non-responsive WPBs have density, markers of maturation, and highly multimerized von Willebrand factor similar to those of wild-type granules. Thus, by also recruiting aftiphilin/gamma-synergin in addition to clathrin, AP-1 coordinates formation of WPBs with their acquisition of a regulated secretory phenotype.
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Affiliation(s)
- Winnie W Y Lui-Roberts
- MRC Laboratory of Molecular Cell Biology, Cell Biology Unit and Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
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32
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Faust F, Gomez-Lazaro M, Borta H, Agricola B, Schrader M. Rab8 is Involved in Zymogen Granule Formation in Pancreatic Acinar AR42J Cells. Traffic 2008; 9:964-79. [DOI: 10.1111/j.1600-0854.2008.00739.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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33
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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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34
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Rindler MJ, Xu CF, Gumper I, Cen C, Sonderegger P, Neubert TA. Calsyntenins are secretory granule proteins in anterior pituitary gland and pancreatic islet alpha cells. J Histochem Cytochem 2007; 56:381-8. [PMID: 18158283 DOI: 10.1369/jhc.7a7351.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Calsyntenins are members of the cadherin superfamily of cell adhesion molecules. They are present in postsynaptic membranes of excitatory neurons and in vesicles in transit to neuronal growth cones. In the current study, calsyntenin-1 (CST-1) and calsyntenin-3 (CST-3) were identified by mass spectrometric analysis (LC-MS/MS) of integral membrane proteins from highly enriched secretory granule preparations from bovine anterior pituitary gland. Immunofluorescence microscopy on thin frozen sections of rat pituitary revealed that CST-1 was present only in gonadotropes where it colocalized with follicle-stimulating hormone in secretory granules. In contrast, CST-3 was present not only in gonadotrope secretory granules but also in those of somatotropes and thyrotropes. Neither protein was detected in mammatropes. In addition, CST-1 was also localized to the glucagon-containing secretory granules of alpha cells in the pancreatic islets of Langerhans. Results indicate that calsyntenins function outside the nervous system and potentially are modulators of endocrine function.
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Affiliation(s)
- Michael J Rindler
- Department of Cell Biology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
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35
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Periz J, Gill AC, Hunt L, Brown P, Tomley FM. The Microneme Proteins EtMIC4 and EtMIC5 of Eimeria tenella Form a Novel, Ultra-high Molecular Mass Protein Complex That Binds Target Host Cells. J Biol Chem 2007; 282:16891-8. [PMID: 17426025 DOI: 10.1074/jbc.m702407200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eimeria tenella, in common with other parasitic protozoa of the phylum Apicomplexa, invades host cells using an actinomyosin-powered "glideosome" complex and requires the secretion of adhesive proteins from the microneme organelles onto the parasite surface. Microneme proteins of E. tenella include EtMIC4, a transmembrane protein that has multiple thrombospondin type I domains and calcium-binding epidermal growth factor-like domains in its extracellular domain, and EtMIC5, a soluble protein composed of 11 tandemly repeated domains that belong to the plasminogen-apple-nematode superfamily. We show here that EtMIC4 and EtMIC5 interact to form an oligomeric, ultrahigh molecular mass protein complex. The complex was purified from lysed parasites by non-denaturing techniques, and the stoichiometry was shown to be [EtMIC4](2):[EtMIC5](1), with an octamer of EtMIC4 bound non-covalently to a tetramer of EtMIC5. The complex is formed within the parasite secretory pathway and is maintained after secretion onto the surface of the parasite. The purified complex binds to a number of epithelial cell lines in culture. Identification and characterization of this complex contributes to an overall understanding of the role of multimolecular protein complexes in specific interactions between pathogens and their hosts during infection.
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Affiliation(s)
- Javier Periz
- Institute for Animal Health, Compton, Newbury, Berkshire, RG20 7NN United Kingdom
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36
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Serrano AG, Cabré EJ, Pérez-Gil J. Identification of a segment in the precursor of pulmonary surfactant protein SP-B, potentially involved in pH-dependent membrane assembly of the protein. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1059-69. [PMID: 17306759 DOI: 10.1016/j.bbamem.2007.01.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2006] [Revised: 01/08/2007] [Accepted: 01/09/2007] [Indexed: 10/23/2022]
Abstract
In the present work, the hydrophobic properties of proSP-B, the precursor of pulmonary surfactant protein SP-B, have been analyzed under different pH conditions, and the sequence segment at position 111-135 of the N-terminal domain of the precursor has been detected as potentially possessing pH-dependent hydrophobic properties. We have studied the structure and lipid-protein interactions of the synthetic peptides BpH, with sequence corresponding to the segment 111-135 of proSP-B, and BpH-W, bearing the conservative substitution F127W to use the tryptophan as an intrinsic fluorescent probe. Peptide BpH-W interacts with both zwitterionic and anionic phospholipid vesicles at neutral pH, as monitored by the blue-shifted maximum emission of its tryptophan reporter. Insertion of tryptophan into the membranes is further improved at pH 5.0, especially in negatively-charged membranes. Peptides BpH and BpH-W also showed pH-dependent properties to insert into phospholipid monolayers. We have also found that the single sequence variation F120K decreases substantially the interaction of this segment with phospholipid surfaces as well as its pH-dependent insertion into deeper regions of the membranes. We hypothesize that this region could be involved in pH-triggered conformational changes occurring in proSP-B along the exocytic pathway of surfactant in type II cells, leading to the exposure of the appropriate segments for processing and assembly of SP-B within surfactant lipids.
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Affiliation(s)
- Alicia G Serrano
- Dept. Bioquímica y Biología Molecular I, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
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37
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Sobota JA, Ferraro F, Bäck N, Eipper BA, Mains RE. Not all secretory granules are created equal: Partitioning of soluble content proteins. Mol Biol Cell 2006; 17:5038-52. [PMID: 17005911 PMCID: PMC1761688 DOI: 10.1091/mbc.e06-07-0626] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Secretory granules carrying fluorescent cargo proteins are widely used to study granule biogenesis, maturation, and regulated exocytosis. We fused the soluble secretory protein peptidylglycine alpha-hydroxylating monooxygenase (PHM) to green fluorescent protein (GFP) to study granule formation. When expressed in AtT-20 or GH3 cells, the PHM-GFP fusion protein partitioned from endogenous hormone (adrenocorticotropic hormone, growth hormone) into separate secretory granule pools. Both exogenous and endogenous granule proteins were stored and released in response to secretagogue. Importantly, we found that segregation of content proteins is not an artifact of overexpression nor peculiar to GFP-tagged proteins. Neither luminal acidification nor cholesterol-rich membrane microdomains play essential roles in soluble content protein segregation. Our data suggest that intrinsic biophysical properties of cargo proteins govern their differential sorting, with segregation occurring during the process of granule maturation. Proteins that can self-aggregate are likely to partition into separate granules, which can accommodate only a few thousand copies of any content protein; proteins that lack tertiary structure are more likely to distribute homogeneously into secretory granules. Therefore, a simple "self-aggregation default" theory may explain the little acknowledged, but commonly observed, tendency for both naturally occurring and exogenous content proteins to segregate from each other into distinct secretory granules.
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Affiliation(s)
- Jacqueline A. Sobota
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Francesco Ferraro
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Nils Bäck
- Department of Anatomy, Institute of Biomedicine, University of Helsinki, FIN-00014, Helsinki, Finland
| | - Betty A. Eipper
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Richard E. Mains
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
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38
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Lara-Lemus R, Liu M, Turner MD, Scherer P, Stenbeck G, lyengar P, Arvan P. Lumenal protein sorting to the constitutive secretory pathway of a regulated secretory cell. J Cell Sci 2006; 119:1833-42. [PMID: 16608874 PMCID: PMC2547412 DOI: 10.1242/jcs.02905] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Newly synthesized secretory granule content proteins are delivered via the Golgi complex for storage within mature granules, whereas constitutive secretory proteins are not stored. Most soluble proteins traveling anterograde through the trans-Golgi network are not excluded from entering immature secretory granules, whether or not they have granule-targeting signals. However, the ;sorting-for-entry' hypothesis suggests that soluble lumenal proteins lacking signals enter transport intermediates for the constitutive secretory pathway. We aimed to investigate how these constitutive secretory proteins are sorted. In a pancreatic beta-cell line, we stably expressed two lumenal proteins whose normal sorting information has been deleted: alkaline phosphatase, truncated to eliminate its glycosylphosphatidylinositol membrane anchor (SEAP); and Cab45361, a Golgi lumenal resident, truncated to eliminate its intracellular retention (Cab308Myc). Both truncated proteins are efficiently secreted, but whereas SEAP enters secretory granules, Cab308Myc behaves as a true constitutive marker excluded from granules. Interestingly, upon permeabilization of organelle membranes with saponin, SEAP is extracted as a soluble protein whereas Cab308Myc remains associated with the membrane. These are among the first data to support a model in which association with the lumenal aspect of Golgi and/or post-Golgi membranes can serve as a means for selective sorting of constitutive secretory proteins.
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Affiliation(s)
- Roberto Lara-Lemus
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Ml 48109, USA
| | - Ming Liu
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Ml 48109, USA
| | - Mark D. Turner
- Centre for Diabetes and Metabolic Medicine, Institute of Cell and Molecular Science, Queen Mary’s School of Medicine and Dentistry, University of London, Whitechapel, London, E1 1BB, UK
| | - Philipp Scherer
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Gudrun Stenbeck
- Bone and Mineral Centre, University College London, London, WC1E 6JJ, UK
| | - Puneeth lyengar
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Peter Arvan
- Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical Center, Ann Arbor, Ml 48109, USA
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Harrison-Lavoie KJ, Michaux G, Hewlett L, Kaur J, Hannah MJ, Lui-Roberts WWY, Norman KE, Cutler DF. P-Selectin and CD63 Use Different Mechanisms for Delivery to Weibel-Palade Bodies. Traffic 2006; 7:647-62. [PMID: 16683915 DOI: 10.1111/j.1600-0854.2006.00415.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The biogenesis of endothelial-specific Weibel-Palade bodies (WPB) is poorly understood, despite their key role in both haemostasis and inflammation. Biogenesis of specialized organelles of haemopoietic cells is often adaptor protein complex 3-dependent (AP-3-dependent), and AP-3 has previously been shown to play a role in the trafficking of both WPB membrane proteins, P-selectin and CD63. However, WPB are thought to form at the trans Golgi network (TGN), which is inconsistent with a role for AP-3, which operates in post-Golgi trafficking. We have therefore investigated in detail the mechanisms of delivery of these two membrane proteins to WPB. We find that P-selectin is recruited to forming WPB in the trans-Golgi by AP-3-independent mechanisms that use sorting information within both the cytoplasmic tail and the lumenal domain of the receptor. In contrast, CD63 is recruited to already-budded WPB by an AP-3-dependent route. These different mechanisms of recruitment lead to the presence of distinct immature and mature populations of WPB in human umbilical vein endothelial cells (HUVEC).
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MESH Headings
- Adaptor Protein Complex 3
- Amino Acid Sequence
- Animals
- Antigens, CD/metabolism
- Base Sequence
- Cells, Cultured
- DNA-Binding Proteins/metabolism
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/ultrastructure
- Humans
- Leukocyte Rolling/physiology
- Mice
- Mice, Inbred C57BL
- Mice, Mutant Strains
- Microscopy, Electron
- Models, Biological
- P-Selectin/chemistry
- P-Selectin/genetics
- P-Selectin/metabolism
- Platelet Membrane Glycoproteins/metabolism
- Protein Sorting Signals/genetics
- Protein Structure, Tertiary
- Protein Transport
- RNA, Small Interfering/genetics
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Tetraspanin 30
- Transcription Factors/metabolism
- Weibel-Palade Bodies/metabolism
- Weibel-Palade Bodies/ultrastructure
- trans-Golgi Network/metabolism
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Affiliation(s)
- Kimberly J Harrison-Lavoie
- MRC Laboratory of Molecular Cell Biology, Cell Biology Unit, University College London, Gower Street, London WC1E 6BT, UK
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40
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Kim T, Zhang CF, Sun Z, Wu H, Loh YP. Chromogranin A deficiency in transgenic mice leads to aberrant chromaffin granule biogenesis. J Neurosci 2006; 25:6958-61. [PMID: 16049171 PMCID: PMC6724839 DOI: 10.1523/jneurosci.1058-05.2005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The biogenesis of dense-core secretory granules (DCGs), organelles responsible for the storage and secretion of neurotransmitters and neuropeptides in chromaffin cells, is poorly understood. Chromogranin A (CgA), which binds catecholamines for storage in the lumen of chromaffin granules, has been shown to be involved in DCG biogenesis in neuroendocrine PC12 cells. Here, we report that downregulation of CgA expression in vivo by expressing antisense RNA against CgA in transgenic mice led to a significant reduction in DCG formation in adrenal chromaffin cells. The number of DCGs formed in CgA antisense transgenic mice was directly correlated with the amount of CgA present in adrenal medulla. In addition, DCGs showed an increase in size, with enlargement in the volume around the dense core, a phenomenon that occurs to maintain constant "free" catecholamine concentration in the lumen of these granules. The extent of DCG swelling was inversely correlated with the number of DCGs formed, as well as the amount of CgA present in the adrenal glands of CgA antisense transgenic mice. These data indicate an essential role of CgA in regulating chromaffin DCG biogenesis and catecholamine storage in vivo.
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Affiliation(s)
- Taeyoon Kim
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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41
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Abstract
Advances in our understanding of the complexity of GnRH actions at the pituitary and the various mechanisms involved in mediating differential LH and FSH biosynthesis and secretion at the gonadotrope, are continually emerging. In this review, we summarise recent studies pertaining to GnRH and GnRH receptor phylogeny, the divergent signalling and trafficking pathways initiated and utilised by GnRH and its receptor, and the pathways that mediate gonadotropin secretion from the gonadotrope.
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Affiliation(s)
- Adam J Pawson
- Human Reproductive Sciences Unit, Medical Research Council, The University of Edinburgh Chancellor's Building, 49 Little France Crescent, Edinburgh EH16 4SB, UK
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42
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Bowman GR, Elde NC, Morgan G, Winey M, Turkewitz AP. Core formation and the acquisition of fusion competence are linked during secretory granule maturation in Tetrahymena. Traffic 2005; 6:303-23. [PMID: 15752136 PMCID: PMC4708285 DOI: 10.1111/j.1600-0854.2005.00273.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The formation of dense core secretory granules is a multistage process beginning in the trans Golgi network and continuing during a period of granule maturation. Direct interactions between proteins in the membrane and those in the forming dense core may be important for sorting during this process, as well as for organizing membrane proteins in mature granules. We have isolated two mutants in dense core granule formation in the ciliate Tetrahymena thermophila, an organism in which this pathway is genetically accessible. The mutants lie in two distinct genes but have similar phenotypes, marked by accumulation of a set of granule cargo markers in intracellular vesicles resembling immature secretory granules. Sorting to these vesicles appears specific, since they do not contain detectable levels of an extraneous secretory marker. The mutants were initially identified on the basis of aberrant proprotein processing, but also showed defects in the docking of the immature granules. These defects, in core assembly and docking, were similarly conditional with respect to growth conditions, and therefore are likely to be tightly linked. In starved cells, the processing defect was less severe, and the immature granules could dock but still did not undergo stimulated exocytosis. We identified a lumenal protein that localizes to the docking-competent end of wildtype granules, but which is delocalized in the mutants. Our results suggest that dense cores have functionally distinct domains that may be important for organizing membrane proteins involved in docking and fusion.
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Affiliation(s)
- Grant R Bowman
- Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
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43
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Wang J, Cawley NX, Voutetakis A, Rodriguez YM, Goldsmith CM, Nieman LK, Hoque ATMS, Frank SJ, Snell CR, Loh YP, Baum BJ. Partial redirection of transgenic human growth hormone secretion from rat salivary glands. Hum Gene Ther 2005; 16:571-83. [PMID: 15916482 DOI: 10.1089/hum.2005.16.571] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Regulated secretory pathway proteins, when delivered as transgenes to salivary glands, are secreted predominantly into saliva. This is not useful for those proteins whose therapeutic function is required systemically, for example, human growth hormone (hGH). One strategy to improve the efficiency of hGH secretion into the bloodstream involves manipulation of existing sorting signals. The C terminus of hGH is highly conserved and contains a domain similar to the regulated pathway sorting domain of pro-opiomelanocortin (POMC). We hypothesized that, similar to POMC, mutation of this domain would divert hGH secretion from the regulated to the constitutive pathway, which in salivary glands leads to the bloodstream. Several mutations were made in the C terminus of the hGH cDNA and tested in vitro. One biologically active mutant containing E174A and E186A substitutions, and with an included C-terminal extension, was studied in greater detail. Compared with wild-type hGH, we found that this mutant hGH accumulated in the Golgi/trans-Golgi network and showed increased basal secretion in AtT20 cells, a model endocrine cell line. Importantly, in vivo, the mutant hGH displayed a relative increase in the proportion of constitutive pathway secretion seen from rat salivary glands, with a significantly lower saliva-versus-serum secretion ratio (p=0.03). Although this mutant is unlikely to be therapeutically beneficial, these results suggest that the final destination of a transgenic secretory protein may be controlled by reengineering its sorting determinants.
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Affiliation(s)
- Jianghua Wang
- Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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De Lisle RC, Norkina O, Roach E, Ziemer D. Expression of pro-Muclin in pancreatic AR42J cells induces functional regulated secretory granules. Am J Physiol Cell Physiol 2005; 289:C1169-78. [PMID: 15987769 DOI: 10.1152/ajpcell.00099.2005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is not clear how protein cargo is sorted to and retained in forming regulated secretory granules (RSG). Here, the sulfated mucin-type glycoprotein pro-Muclin was tested for its ability to induce RSG in the poorly differentiated rat pancreatic cell line AR42J. AR42J cells express RSG content proteins, but they fail to make granules. Adenovirus-pro-Muclin-infected AR42J cells store amylase, accumulate RSG, and respond to hormonal stimulation by secreting the stored protein. Expression of pro-Muclin combined with the inducing effect of dexamethasone resulted in a significant enhancement of the efficiency of regulated secretion. The effect of pro-Muclin was a strong decrease in constitutive secretion compared with dexamethasone-induction alone. A pro-Muclin construct missing the cytosolic tail domain was less effective at improving the efficiency of regulated secretion compared with the full-length construct. Increased expression of cargo (using adenovirus amylase) also modestly enhanced regulated secretion, indicating that part of pro-Muclin's effect may be due to increased expression of cargo protein. Overall, the data show that pro-Muclin acts as a sorting receptor that can induce RSG, and that its cytosolic tail is important in this process.
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Affiliation(s)
- Robert C De Lisle
- Anatomy and Cell Biology, MS 3038, University of Kansas School of Medicine, 3901 Rainbow Blvd., Kansas City, KS 66160, USA.
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Labrador V, Brun C, König S, Roatti A, Baertschi AJ. Peptidyl-Glycine α-Amidating Monooxygenase Targeting and Shaping of Atrial Secretory Vesicles. Circ Res 2004; 95:e98-109. [PMID: 15539631 DOI: 10.1161/01.res.0000150592.88464.ad] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
ANP (atrial natriuretic peptide) is widely recognized as an important vasorelaxant, diuretic, and cardioprotective hormone. Little is known, however, about how ANP-secretory vesicles form within the atrial myocytes. Secretory vesicles were visualized by fluorescence microscope imaging in live rat atrial myocytes expressing proANP–enhanced green fluorescent protein (EGFP), or N-terminal–mutated fusion proteins thought to suppress the calcium-dependent aggregation of proANP. Results showed the following: (1) aggregates of proANP and coexpressed proANP-EGFP recruited peptidylglycine α-amidating monooxygenase (PAM)-1, an abundant atrial integral vesicle membrane protein; (2) coexpressed N-terminal–mutated (Glu23,24→Gln23,24) and N-terminal–deleted proANP-EGFP inhibited recruitment of PAM-1 by up to 60%; (3) 4-phenyl-3-butenoic acid (PBA) (10 μmol/L), a pharmacological inhibitor of the lumenal peptidylglycine α-hydroxylating monooxygenase domain of PAM proteins, inhibited recruitment of endogenous PAM-1 and of coexpressed pro-EGFP–PAM-1; (4) PBA had no effect on exocytosis of the potassium inward rectifier KIR2.1; (5) PBA induced a deformation of the secretory vesicles but did not inhibit docking. These findings suggest that recruitment of PAM-1 to secretory vesicles depends on intact N-terminal proANP and on the lumenal domain of PAM-1. Conversely, PAM-1 participates in shaping the proANP-secretory vesicles. The full text of this article is available online at http://circres.ahajournals.org.
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Affiliation(s)
- Vénus Labrador
- Department of Neuroscience, Centre Médical Universitaire, University of Geneva, Switzerland
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Abstract
Weibel-Palade bodies (WPB) are the regulated secretory organelles of endothelial cells. These cigar-shaped membrane-bound structures function in both hemostasis and inflammation but their biogenesis is poorly understood. Here, we review what is currently known about their formation. The content of WPBs is dominated by the hemostatic factor von Willebrand factor (VWF), whose complex biogenesis ends in the formation of high molecular weight multimers. VWF is also organized into proteinaceous tubules which underlie the striated interior of WPBs as seen in the EM. VWF expression is necessary for formation of WPBs, and its heterologous expression can even lead to the specific recruitment of WPB membrane proteins, including the leukocyte receptor P-selectin, the tetraspanin CD63, and Rab27a. Unusually, the VWF propeptide is implicated in the biogenesis of WPBs, being essential for formation of the storage compartment. The elongation of the cigars and the formation of the tubules are determined by non-covalent interactions between pro- and mature VWF proteins. Surprisingly, high molecular weight multimers seem neither necessary nor sufficient to trigger formation of a storage compartment, and do not seem to have any role in WPB biogenesis. Von Willebrand's disease, usually caused by mutations within VWF, has provided many of the insights into the way in which VWF drives the formation of these organelles.
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Affiliation(s)
- Grégoire Michaux
- Department of Biochemistry, University College London, London WC1E 6BT, UK
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Chang M, Hua C, Isaac E, Litjens T, Hodge G, Karageorgos L, Meikle P. Transthyretin interacts with the lysosome-associated membrane protein (LAMP-1) in circulation. Biochem J 2004; 382:481-9. [PMID: 15200388 PMCID: PMC1133804 DOI: 10.1042/bj20031752] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Revised: 03/08/2004] [Accepted: 06/16/2004] [Indexed: 11/17/2022]
Abstract
LAMP-1 (lysosome-associated membrane protein), a major glycoprotein present in the lysosomal membrane, constitutes up to 50% of total membrane proteins. LAMP-1, expressed at the plasma membrane, is reported to be the major molecule expressing the sialyl-Lewis X antigen. Two forms of LAMP-1 exist; the full-length LAMP-1 [LAMP-1 (+Tail)] has a highly glycosylated lumenal domain, a membrane-spanning domain and a short cytoplasmic tail, and the truncated LAMP-1 [LAMP-1 (-Tail)] contains only the lumenal domain. Soluble LAMP-1 (+/-Tail) has been reported in circulation. LAMP-1 at the cell surface has been shown to interact with E-selectin and galectin and is proposed to function in cell-cell interactions. However, the functional role(s) of soluble LAMP-1 in circulation is unclear. To investigate the functional role of soluble LAMP-1 in circulation, recombinant LAMP-1 (-Tail) and LAMP-1 (+Tail) were produced in HT1080 cells. Two immune-quantification assays were developed to distinguish between the LAMP-1 forms. The interaction and aggregation properties of the different LAMP-1 forms were investigated using the immune-quantification assays. Only LAMP-1 (+Tail) was found to aggregate and interact with plasma proteins. Plasma proteins that interact with LAMP-1 were isolated by affinity chromatography with either the recombinant LAMP-1 (-Tail) or a synthesized peptide consisting of the 14 amino acids of the LAMP-1 cytoplasmic tail. Transthyretin was found to interact with the cytoplasmic tail of LAMP-1. Transthyretin exists as a homotetramer in plasma, as such may play a role in the aggregation of LAMP-1 in circulation.
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Key Words
- affinity chromatography
- lysosome-associated membrane protein (lamp-1)
- plasma protein
- transthyretin
- dex, dexamethasone
- dtt, 1,4-dithiothreitol
- fcs, foetal calf serum
- lamp-1, lysosome-associated membrane protein
- maldi–tof, matrix-assisted laser-desorption ionization–time-of-flight
- mem, modified eagle's medium
- sf, skin fibroblast
- sv40, simian virus 40
- 2d, two-dimensional
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Affiliation(s)
- Melissa H. Y. Chang
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
- ‡Department of Paediatrics, The University of Adelaide, South Australia 5000, Australia
| | - Chi T. Hua
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
| | - Elizabeth L. Isaac
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
| | - Tom Litjens
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
| | - Greg Hodge
- †Department of Haematology, Women's and Children's Hospital, Adelaide, South Australia 5006, Australia
| | - Litsa E. Karageorgos
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
- ‡Department of Paediatrics, The University of Adelaide, South Australia 5000, Australia
| | - Peter J. Meikle
- *Lysosomal Diseases Research Unit, Department of Genetic Medicine, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia
- ‡Department of Paediatrics, The University of Adelaide, South Australia 5000, Australia
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Boulatnikov I, De Lisle RC. Binding of the Golgi sorting receptor muclin to pancreatic zymogens through sulfated O-linked oligosaccharides. J Biol Chem 2004; 279:40918-26. [PMID: 15292166 DOI: 10.1074/jbc.m406213200] [Citation(s) in RCA: 12] [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
Sorting and packaging of regulated secretory proteins involves protein aggregation in the trans-Golgi network and secretory granules. In this work, we characterized the pH-dependent interactions of pancreatic acinar cell-regulated secretory proteins (zymogens) with Muclin, a putative Golgi cargo receptor. In solution, purified Muclin co-aggregated with isolated zymogens at mildly acidic pH. In an overlay assay, [35S]sulfate biosynthetically labeled Muclin bound directly at mildly acidic pH to the zymogen granule content proteins amylase, prolipase, pro-carboxypeptidase A1, pro-elastase II, chymotrypsinogen B, and Reg1. Denaturation of Muclin with reducing agents to break the numerous intrachain disulfide bonds in Muclin's scavenger receptor cysteine-rich and CUB domains did not interfere with binding. Non-sulfated [35S]Met/Cys-labeled Muclin showed decreased binding in the overlay assay. Extensive Pronase E digestion of unlabeled Muclin was used to produce glycopeptides, which competed for binding of [35S]sulfate-labeled Muclin to zymogens. The results demonstrate that the sulfated, O-glycosylated groups are responsible for the pH-dependent interactions of Muclin with the zymogens. The behavior of Muclin fulfils the requirement of a Golgi cargo receptor to bind to regulated secretory proteins under the mildly acidic pH conditions that exist in the trans-Golgi network.
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Affiliation(s)
- Igor Boulatnikov
- Department of Anatomy , University of Kansas School of Medicine, Kansas City, Kansas 66160, USA
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Bauer RA, Overlease RL, Lieber JL, Angleson JK. Retention and stimulus-dependent recycling of dense core vesicle content in neuroendocrine cells. J Cell Sci 2004; 117:2193-202. [PMID: 15126621 DOI: 10.1242/jcs.01093] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We have used fluorescence imaging of individual exocytic events in combination with immunogold electron microscopy and FM1-43 photoconversion to study the stimulus-dependent recycling of dense core vesicle content in isolated rat pituitary lactotrophs. Secretory stimulation with high external [K+] resulted in 100 exocytic sites per cell that were labeled by extracellular antibodies against the peptide hormone prolactin. Morphological analysis demonstrated that the prolactin was retained and internalized in intact dense cores. Vesicles containing non-secreted, internalized prolactin did not colocalize with DiI-LDL that had been chased into lysosomes but did transiently colocalize with internalized transferrin. The recycling vesicles also trafficked through a syntaxin 6-positive compartment but not the TGN38-positive trans-Golgi. Recycling vesicles, which returned to the cell surface in a slow basal manner, could also be stimulated to undergo exocytosis with a high release probability during subsequent exocytic stimulation with external K+. These studies suggest a functional role for recycling vesicles that retain prolactin.
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Affiliation(s)
- Roslyn A Bauer
- Department of Biological Sciences, University of Denver, Denver, CO 80208, USA
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Dannies P. Manipulating the reversible aggregation of protein hormones in secretory granules: potential impact on biopharmaceutical development. BioDrugs 2004; 17:315-24. [PMID: 14498762 DOI: 10.2165/00063030-200317050-00002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Neuroendocrine cells and other secretory cell types are able to store secretory proteins in a concentrated form for extended periods until the release of large quantities of protein is triggered. The proteins are stored in dense core secretory granules. The dense cores of these granules are made up of large, insoluble aggregates that form by self-association. These aggregates solubilise rapidly into monomeric proteins in their native conformations when released from the cells by exocytosis of secretory granules. Formation of aggregates is an early event in secretory granule formation in at least some cell types. The function of secretory granules containing protein aggregates varies, depending upon the contents. This may occur because recognition of an aspect, such as a surface motif, of the aggregate facilitates correct assembly of the membrane proteins necessary for transport and exocytosis of the granules. Understanding the principles necessary for aggregation of protein hormones may help in the formulation of proteins for clinical use. Formation of aggregates of human prolactin has been investigated both in cells and in solution. In cells, the aggregation of human prolactin requires a mildly acidic pH, and is slowed in the presence of a membrane-permeable chelator of zinc. In solution, the aggregation of human prolactin at mildly acidic pH and physiological concentrations of Zn(2+) resembles that which occurs in cells if the reaction is performed with macromolecular crowding, which will mimic the conditions in cells. The factors causing protein aggregation and the extent to which aggregation plays a role in secretory granule formation are likely to vary with the protein and cell type. Further understanding of the principles involved in forming these aggregates that readily disassociate may enhance the ability to formulate protein preparations. Knowledge of the exact residues involved in the protein : protein interfaces in the aggregates of secretory granule proteins may lead to the ability to use small molecules to interfere with self-association and to regulate the storage of secretory granule proteins.
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Affiliation(s)
- Priscilla Dannies
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.
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