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Hastoy B, Clark A, Rorsman P, Lang J. Fusion pore in exocytosis: More than an exit gate? A β-cell perspective. Cell Calcium 2017; 68:45-61. [PMID: 29129207 DOI: 10.1016/j.ceca.2017.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 10/17/2017] [Accepted: 10/24/2017] [Indexed: 12/14/2022]
Abstract
Secretory vesicle exocytosis is a fundamental biological event and the process by which hormones (like insulin) are released into the blood. Considerable progress has been made in understanding this precisely orchestrated sequence of events from secretory vesicle docked at the cell membrane, hemifusion, to the opening of a membrane fusion pore. The exact biophysical and physiological regulation of these events implies a close interaction between membrane proteins and lipids in a confined space and constrained geometry to ensure appropriate delivery of cargo. We consider some of the still open questions such as the nature of the initiation of the fusion pore, the structure and the role of the Soluble N-ethylmaleimide-sensitive-factor Attachment protein REceptor (SNARE) transmembrane domains and their influence on the dynamics and regulation of exocytosis. We discuss how the membrane composition and protein-lipid interactions influence the likelihood of the nascent fusion pore forming. We relate these factors to the hypothesis that fusion pore expansion could be affected in type-2 diabetes via changes in disease-related gene transcription and alterations in the circulating lipid profile. Detailed characterisation of the dynamics of the fusion pore in vitro will contribute to understanding the larger issue of insulin secretory defects in diabetes.
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Affiliation(s)
- Benoit Hastoy
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK.
| | - Anne Clark
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK; Metabolic Research, Institute of Neuroscience and Physiology, University of Goteborg, Medicinaregatan 11, S-41309 Göteborg, Sweden
| | - Jochen Lang
- Laboratoire de Chimie et Biologie des Membranes et Nano-objets (CBMN), CNRS UMR 5248, Université de Bordeaux, Allée de Geoffrey St Hilaire, 33600 Pessac, France.
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Zhu D, Xie L, Kang Y, Dolai S, Bondo Hansen J, Qin T, Xie H, Liang T, Rubin DC, Osborne L, Gaisano HY. Syntaxin 2 Acts as Inhibitory SNARE for Insulin Granule Exocytosis. Diabetes 2017; 66:948-959. [PMID: 28115395 PMCID: PMC5860373 DOI: 10.2337/db16-0636] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 12/24/2016] [Indexed: 01/03/2023]
Abstract
Of the four syntaxins specialized for exocytosis, syntaxin (Syn)-2 is the least understood. In this study, we used Syn-2/epimorphin knockout mice to examine the role of Syn-2 in insulin secretory granule (SG) exocytosis. Unexpectedly, Syn-2 knockout mice exhibited paradoxical superior glucose homeostasis resulting from an enhanced insulin secretion. This was confirmed in vitro by pancreatic islet perifusion showing an amplified biphasic glucose-stimulated insulin secretion arising from an increase in size of the readily releasable pool of insulin SGs and enhanced SG pool refilling. The increase in insulin exocytosis was attributed mainly to an enhanced recruitment of the larger pool of newcomer SGs that undergoes no residence time on plasma membrane before fusion and, to a lesser extent, also the predocked SGs. Consistently, Syn-2 depletion resulted in a stimulation-induced increase in abundance of exocytotic complexes we previously demonstrated as mediating the fusion of newcomer SGs (Syn-3/VAMP8/SNAP25/Munc18b) and predocked SGs (Syn-1A/VAMP2/SNAP25/Muncn18a). This work is the first to show in mammals that Syn-2 could function as an inhibitory SNARE protein that, when relieved, could promote exocytosis in pancreatic islet β-cells. Thus, Syn-2 may serve as a potential target to treat diabetes.
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Affiliation(s)
- Dan Zhu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Li Xie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Subhankar Dolai
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | | | - Tairan Qin
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Huanli Xie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Deborah C Rubin
- Department of Medicine, Washington University School of Medicine in St. Louis, St. Louis, MO
- Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, MO
| | - Lucy Osborne
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Herbert Y Gaisano
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
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Tulachan SS, Doi R, Hirai Y, Kawaguchi Y, Koizumi M, Hembree M, Tei E, Crowley A, Yew H, McFall C, Prasadan K, Preuett B, Imamura M, Gittes GK. Mesenchymal epimorphin is important for pancreatic duct morphogenesis. Dev Growth Differ 2009; 48:65-72. [PMID: 16512851 DOI: 10.1111/j.1440-169x.2006.00846.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Epithelial-mesenchymal interactions are crucial for the proper development of many organs, including the pancreas. Within the pancreas, the ducts are thought to harbor stem/progenitor cells, and possibly to give rise to pancreatic ductal carcinoma. Little is known about the mechanism of formation of pancreatic ducts in the embryo. Pancreatic mesenchyme contains numerous soluble factors which help to sustain the growth and differentiation of exocrine and endocrine structures. Here, we report that one such morphoregulatory mesenchymal protein, epimorphin, plays an important role during pancreatic ductal proliferation and differentiation. We found that epimorphin is expressed in pancreatic mesenchyme during early stages of development, and at mesenchymal-epithelial interfaces surrounding the ducts at later stages. Strong upregulation of epimorphin expression was seen during in vitro pancreatic duct differentiation. Similarly, in vitro pancreatic duct formation was inhibited by a neutralizing antibody against epimorphin, whereas addition of recombinant epimorphin partially rescued duct formation. Together, our study demonstrates the role of epimorphin in pancreatic ductal morphogenesis.
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Affiliation(s)
- Sidhartha S Tulachan
- Department of Surgery, Children's Hospital of Pittsburgh, University of Pittsburgh, Pennsylvania, USA
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Radisky DC, Hirai Y, Bissell MJ. Delivering the message: epimorphin and mammary epithelial morphogenesis. Trends Cell Biol 2003; 13:426-34. [PMID: 12888295 PMCID: PMC2933193 DOI: 10.1016/s0962-8924(03)00146-6] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The mammary gland consists of a highly branched tubular epithelium surrounded by a complex mesenchymal stroma. Epimorphin is an extracellular protein that is expressed by mammary mesenchymal cells that directs epithelial morphogenesis. Depending upon the context of presentation--polar versus apolar--epimorphin can selectively direct two key processes of tubulogenesis: branching morphogenesis (processes involved in tubule initiation and extension) and luminal morphogenesis (required for enlargement of tubule caliber). Here, we outline the fundamentals of mammary gland development and describe the function of epimorphin in these processes. We conclude with a review of recent studies that suggest similar morphogenic roles for epimorphin in other glandular organs.
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Affiliation(s)
- Derek C. Radisky
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Yohei Hirai
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries, Yokohama 244, Japan
| | - Mina J. Bissell
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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Shirasaka T, Iizuka M, Yukawa M, Hirai Y, Horie Y, Itou H, Kon-No S, Fukushima T, Watanabe S. Altered expression of epimorphin in ulcerative colitis. J Gastroenterol Hepatol 2003; 18:570-7. [PMID: 12702050 DOI: 10.1046/j.1440-1746.2003.02972.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
BACKGROUND AND AIM Epimorphin is suggested to play a key role in the morphogenesis of epithelial cells. We focused on epimorphin and attempted to clarify the relationship between expression of this molecule and inflammatory bowel disease (IBD). METHODS Colonic specimens were taken from 23 patients with ulcerative colitis (UC), 15 with Crohn's disease (CD), six with non-IBD colitis, and 10 normal controls. Distribution and expression of epimorphin protein were examined by immunohistochemistry and western blot analysis, and expression of epimorphin messenger (m)RNA by reverse transcription-polymerase chain reaction. Distribution of basic fibroblast growth factor (bFGF) was also examined by immunohistochemistry. RESULTS In the normal colonic mucosa, epimorphin was observed around the epithelial cells, in some fibroblasts, vascular endothelial cells, and macrophages. In UC patients, epimorphin around epithelial cells disappeared or decreased, and the number of epimorphin-containing cells (mean + standard error/mm2) was significantly increased in active UC patients (1550.8 +/- 144.2) compared with patients in remission (692.8 +/- 45.8), CD patients (790.0 +/- 31.2), non-IBD colitis patients (710.8 +/- 29.2), and controls (664.8 +/- 39.6) (P < 0.01). The number of bFGF-containing cells was significantly increased in active UC and CD patients compared with UC patients in remission, CD and non-IBD colitis patients, and controls (P < 0.05 or P < 0.01). Total expression of epimorphin protein and mRNA was increased in the active stage of UC. Expression of the 34 kDa epimorphin isoform decreased or disappeared in 20 out of 23 cases of UC. CONCLUSION Our results suggest that altered expression of epimorphin contributes to impaired healing and chronic inflammation in the colonic mucosa of UC patients.
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Affiliation(s)
- Tomoyuki Shirasaka
- First Department of Internal Medicine, Akita University School of Medicine, Akita, Biomedical Research and Development Department, Sumitomo Electric Industries, and Department of Surgery, Yokohama Municipal Hospital, Yokohama, Japan
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Bratanova-Tochkova TK, Cheng H, Daniel S, Gunawardana S, Liu YJ, Mulvaney-Musa J, Schermerhorn T, Straub SG, Yajima H, Sharp GWG. Triggering and augmentation mechanisms, granule pools, and biphasic insulin secretion. Diabetes 2002; 51 Suppl 1:S83-90. [PMID: 11815463 DOI: 10.2337/diabetes.51.2007.s83] [Citation(s) in RCA: 186] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The insulin secretory response by pancreatic beta-cells to an acute "square wave" stimulation by glucose is characterized by a first phase that occurs promptly after exposure to glucose, followed by a decrease to a nadir, and a prolonged second phase. The first phase of release is due to the ATP-sensitive K(+) (K(ATP)) channel-dependent (triggering) pathway that increases [Ca(2+)](i) and has been thought to discharge the granules from a "readily releasable pool." It follows that the second phase entails the preparation of granules for release, perhaps including translocation and priming for fusion competency before exocytosis. The pathways responsible for the second phase include the K(ATP) channel-dependent pathway because of the need for elevated [Ca(2+)](i) and additional signals from K(ATP) channel-independent pathways. The mechanisms underlying these additional signals are unknown. Current hypotheses include increased cytosolic long-chain acyl-CoA, the pyruvate-malate shuttle, glutamate export from mitochondria, and an increased ATP/ADP ratio. In mouse islets, the beta-cell contains some 13,000 granules, of which approximately 100 are in a "readily releasable" pool. Rates of granule release are slow, e.g., one every 3 s, even at the peak of the first phase of glucose-stimulated release. As both phases of glucose-stimulated insulin secretion can be enhanced by agents such as glucagon-like peptide 1, which increases cyclic AMP levels and protein kinase A activity, or acetylcholine, which increases diacylglycerol levels and protein kinase C activity, a single "readily releasable pool" hypothesis is an inadequate explanation for insulin secretion. Multiple pools available for rapid release or rapid conversion of granules to a rapidly releasable state are required.
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Hirai Y, Radisky D, Boudreau R, Simian M, Stevens ME, Oka Y, Takebe K, Niwa S, Bissell MJ. Epimorphin mediates mammary luminal morphogenesis through control of C/EBPbeta. J Cell Biol 2001; 153:785-94. [PMID: 11352939 PMCID: PMC2192384 DOI: 10.1083/jcb.153.4.785] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have shown previously that epimorphin (EPM), a protein expressed on the surface of myoepithelial and fibroblast cells of the mammary gland, acts as a multifunctional morphogen of mammary epithelial cells. Here, we present the molecular mechanism by which EPM mediates luminal morphogenesis. Treatment of cells with EPM to induce lumen formation greatly increases the overall expression of transcription factor CCAAT/enhancer binding protein (C/EBP)β and alters the relative expression of its two principal isoforms, LIP and LAP. These alterations were shown to be essential for the morphogenetic activities, since constitutive expression of LIP was sufficient to produce lumen formation, whereas constitutive expression of LAP blocked EPM-mediated luminal morphogenesis. Furthermore, in a transgenic mouse model in which EPM expression was expressed in an apolar fashion on the surface of mammary epithelial cells, we found increased expression of C/EBPβ, increased relative expression of LIP to LAP, and enlarged ductal lumina. Together, our studies demonstrate a role for EPM in luminal morphogenesis through control of C/EBPβ expression.
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Affiliation(s)
- Yohei Hirai
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries Ltd., Yokohama 244, Japan
| | - Derek Radisky
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
| | - Rosanne Boudreau
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
| | - Marina Simian
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
| | - Mary E. Stevens
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
| | - Yumiko Oka
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries Ltd., Yokohama 244, Japan
| | - Kyoko Takebe
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries Ltd., Yokohama 244, Japan
| | - Shinichiro Niwa
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries Ltd., Yokohama 244, Japan
| | - Mina J. Bissell
- Life Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720
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Abstract
Regulated beta -granule exocytosis is critical for the ability of the beta -cell to finely control body glucose homeostasis. This is now understood to be a multistage process whereby beta -granules are transported from biosynthetic/storage sites in the cell cytoplasm and targeted to specific regions of the plasma membrane. Exocytosis is achieved when these granules are triggered to fuse with the membrane by an elevated cytosolic Ca(2+). Dramatic advances have been made recently in our understanding of the protein-protein interactions and regulatory signals that govern intracellular transport and fusion. Although best understood for exocytosis from neurons and neuroendocrine cells, similar processes are thought to be conserved in the beta -cell.
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Affiliation(s)
- R A Easom
- Department of Molecular Biology & Immunology, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX 76107-2699, USA.
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