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Kuppannan A, Jiang YY, Maier W, Liu C, Lang CF, Cheng CY, Field MC, Zhao M, Zoltner M, Turkewitz AP. A novel membrane complex is required for docking and regulated exocytosis of lysosome-related organelles in Tetrahymena thermophila. PLoS Genet 2022; 18:e1010194. [PMID: 35587496 PMCID: PMC9159632 DOI: 10.1371/journal.pgen.1010194] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Revised: 06/01/2022] [Accepted: 04/06/2022] [Indexed: 12/20/2022] Open
Abstract
In the ciliate Tetrahymena thermophila, lysosome-related organelles called mucocysts accumulate at the cell periphery where they secrete their contents in response to extracellular events, a phenomenon called regulated exocytosis. The molecular bases underlying regulated exocytosis have been extensively described in animals but it is not clear whether similar mechanisms exist in ciliates or their sister lineage, the Apicomplexan parasites, which together belong to the ecologically and medically important superphylum Alveolata. Beginning with a T. thermophila mutant in mucocyst exocytosis, we used a forward genetic approach to uncover MDL1 (Mucocyst Discharge with a LamG domain), a novel gene that is essential for regulated exocytosis of mucocysts. Mdl1p is a 40 kDa membrane glycoprotein that localizes to mucocysts, and specifically to a tip domain that contacts the plasma membrane when the mucocyst is docked. This sub-localization of Mdl1p, which occurs prior to docking, underscores a functional asymmetry in mucocysts that is strikingly similar to that of highly polarized secretory organelles in other Alveolates. A mis-sense mutation in the LamG domain results in mucocysts that dock but only undergo inefficient exocytosis. In contrast, complete knockout of MDL1 largely prevents mucocyst docking itself. Mdl1p is physically associated with 9 other proteins, all of them novel and largely restricted to Alveolates, and sedimentation analysis supports the idea that they form a large complex. Analysis of three other members of this putative complex, called MDD (for Mucocyst Docking and Discharge), shows that they also localize to mucocysts. Negative staining of purified MDD complexes revealed distinct particles with a central channel. Our results uncover a novel macromolecular complex whose subunits are conserved within alveolates but not in other lineages, that is essential for regulated exocytosis in T. thermophila.
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Affiliation(s)
- Aarthi Kuppannan
- Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois, United State of America
| | - Yu-Yang Jiang
- Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois, United State of America
| | - Wolfgang Maier
- Bio3/Bioinformatics and Molecular Genetics, Faculty of Biology and ZBMZ, Faculty of Medicine, Albert-Ludwigs-University of Freiburg, Freiburg, Germany
| | - Chang Liu
- Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, United States of America
| | - Charles F. Lang
- Committee on Genetics, Genomics, and Systems Biology, The University of Chicago, Chicago, Illinois, United States of America
| | - Chao-Yin Cheng
- Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois, United State of America
| | - Mark C. Field
- School of Life Sciences, University of Dundee, Dundee, Scotland, United Kingdom
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Minglei Zhao
- Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, United States of America
| | - Martin Zoltner
- Biotechnology and Biomedicine Centre of the Academy of Sciences and Charles University (BIOCEV), Vestec, Czech Republic
| | - Aaron P. Turkewitz
- Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois, United State of America
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2
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Izumi T. In vivo Roles of Rab27 and Its Effectors in Exocytosis. Cell Struct Funct 2021; 46:79-94. [PMID: 34483204 PMCID: PMC10511049 DOI: 10.1247/csf.21043] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 08/31/2021] [Indexed: 11/11/2022] Open
Abstract
The monomeric GTPase Rab27 regulates exocytosis of a broad range of vesicles in multicellular organisms. Several effectors bind GTP-bound Rab27a and/or Rab27b on secretory vesicles to execute a series of exocytic steps, such as vesicle maturation, movement along microtubules, anchoring within the peripheral F-actin network, and tethering to the plasma membrane, via interactions with specific proteins and membrane lipids in a local milieu. Although Rab27 effectors generally promote exocytosis, they can also temporarily restrict it when they are involved in the rate-limiting step. Genetic alterations in Rab27-related molecules cause discrete diseases manifesting pigment dilution and immunodeficiency, and can also affect common diseases such as diabetes and cancer in complex ways. Although the function and mechanism of action of these effectors have been explored, it is unclear how multiple effectors act in coordination within a cell to regulate the secretory process as a whole. It seems that Rab27 and various effectors constitutively reside on individual vesicles to perform consecutive exocytic steps. The present review describes the unique properties and in vivo roles of the Rab27 system, and the functional relationship among different effectors coexpressed in single cells, with pancreatic beta cells used as an example.Key words: membrane trafficking, regulated exocytosis, insulin granules, pancreatic beta cells.
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Affiliation(s)
- Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
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3
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Zhang Y, Xiang R, Fang S, Huang K, Fan Y, Liu T. Experimental Study on the Effect of Tibetan Medicine Triphala on the Proliferation and Apoptosis of Pancreatic Islet β Cells through Incretin–cAMP Signaling Pathway. Biol Pharm Bull 2020; 43:289-295. [DOI: 10.1248/bpb.b19-00562] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
| | | | | | | | - Yuan Fan
- Yunnan University of Chinese Medicine
- The Second Affiliated Hospital of Yunnan University of Chinese Medicine
| | - Tao Liu
- Yunnan Traditional Chinese Medicine Hospital
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4
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Kimura T, Yamaoka M, Terabayashi T, Kaibuchi K, Ishikawa T, Ishizaki T. GDP-Bound Rab27a Dissociates from the Endocytic Machinery in a Phosphorylation-Dependent Manner after Insulin Secretion. Biol Pharm Bull 2020; 42:1532-1537. [PMID: 31474712 DOI: 10.1248/bpb.b19-00242] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glucose-stimulated insulin secretion is controlled by both exocytosis and endocytosis in pancreatic β-cells. Although endocytosis is a fundamental step to maintain cellular responses to the secretagogue, the molecular mechanism of endocytosis remains poorly defined. We have previously shown that in response to high concentrations of glucose, guanosine 5'-diphosphate (GDP)-bound Rab27a is recruited to the plasma membrane where IQ motif-containing guanosine 5'-triphosphatase (GTPase)-activating protein 1 (IQGAP1) is expressed, and that complex formation promotes endocytosis of secretory membranes after insulin secretion. In the present study, the regulatory mechanisms of dissociation of the complex were investigated. Phosphorylation of IQGAP1 on serine (Ser)-1443, a site recognized by protein kinase Cε (PKCε), inhibited the interaction of GDP-bound Rab27a with IQGAP1 in a Cdc42-independent manner. Glucose stimulation caused a translocation of PKCε from the cytosol to the plasma membrane. In addition, glucose-induced endocytosis was inhibited by the knockdown of IQGAP1 with small interfering RNA (siRNA). However, the expression of the non-phosphorylatable or phosphomimetic form of IQGAP1 could not rescue the inhibition, suggesting that a phosphorylation-dephosphorylation cycle of IQGAP1 is required for endocytosis. These results suggest that IQGAP1 phosphorylated by PKCε promotes the dissociation of the IQGAP1-GDP-bound Rab27a complex in pancreatic β-cells, thereby regulating endocytosis of secretory membranes following insulin secretion.
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Affiliation(s)
- Toshihide Kimura
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka.,Department of Pharmacology, Oita University Faculty of Medicine
| | - Mami Yamaoka
- Department of Pharmacology, Oita University Faculty of Medicine
| | | | - Kozo Kaibuchi
- Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University.,Institute for Comprehensive Medical Science, Fujita Health University
| | - Tomohisa Ishikawa
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka
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5
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Zhu C, Song W, Tao Z, Liu H, Xu W, Zhang S, Li H. Deep RNA sequencing of pectoralis muscle transcriptomes during late-term embryonic to neonatal development in indigenous Chinese duck breeds. PLoS One 2017; 12:e0180403. [PMID: 28771592 PMCID: PMC5542427 DOI: 10.1371/journal.pone.0180403] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 06/15/2017] [Indexed: 12/14/2022] Open
Abstract
Pectoral muscle (PM) comprises an important component of overall meat mass in ducks. However, PM has shown arrested or even reduced growth during late embryonic development, and the molecular mechanisms underlying PM growth during the late embryonic to neonatal period in ducks have not been addressed. In this study, we characterized potential candidate genes and signaling pathways related to PM development using RNA sequencing of PM samples selected at embryonic days (E) 21 and 27 and 5 days post-hatch (dph) in two duck breeds (Gaoyou and Jinding ducks). A total of 393 differentially expressed genes (DEGs) were identified, which showed higher or lower expression levels at E27 compared with E21 and 5 dph, reflecting the pattern of PM growth rates. Among these, 43 DEGs were common to all three time points in both duck breeds. These DEGs may thus be involved in regulating this developmental process. Specifically, KEGG pathway analysis of the 393 DEGs showed that genes involved with different metabolism pathways were highly expressed, while genes involved with cell cycle pathways showed lower expression levels at E27. These DEGs may thus be involved in the mechanisms responsible for the phenomenon of static or decreased breast muscle growth in duck breeds during the late embryonic period. These results increase the available genetic information for ducks and provide valuable resources for analyzing the mechanisms underlying the process of PM development.
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Affiliation(s)
- Chunhong Zhu
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Weitao Song
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Zhiyun Tao
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Hongxiang Liu
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Wenjuan Xu
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Shuangjie Zhang
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
| | - Huifang Li
- Jiangsu Institute of Poultry Science, Yangzhou, Jiangsu Province, People’s Republic of China
- * E-mail: ,
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6
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Trexler AJ, Taraska JW. Regulation of insulin exocytosis by calcium-dependent protein kinase C in beta cells. Cell Calcium 2017; 67:1-10. [PMID: 29029784 DOI: 10.1016/j.ceca.2017.07.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 07/25/2017] [Accepted: 07/27/2017] [Indexed: 12/27/2022]
Abstract
The control of insulin release from pancreatic beta cells helps ensure proper blood glucose level, which is critical for human health. Protein kinase C has been shown to be one key control mechanism for this process. After glucose stimulation, calcium influx into beta cells triggers exocytosis of insulin-containing dense-core granules and activates protein kinase C via calcium-dependent phospholipase C-mediated generation of diacylglycerol. Activated protein kinase C potentiates insulin release by enhancing the calcium sensitivity of exocytosis, likely by affecting two main pathways that could be linked: (1) the reorganization of the cortical actin network, and (2) the direct phosphorylation of critical exocytotic proteins such as munc18, SNAP25, and synaptotagmin. Here, we review what is currently known about the molecular mechanisms of protein kinase C action on each of these pathways and how these effects relate to the control of insulin release by exocytosis. We identify remaining challenges in the field and suggest how these challenges might be addressed to advance our understanding of the regulation of insulin release in health and disease.
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Affiliation(s)
- Adam J Trexler
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, United States
| | - Justin W Taraska
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, United States.
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7
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Fan F, Matsunaga K, Wang H, Ishizaki R, Kobayashi E, Kiyonari H, Mukumoto Y, Okunishi K, Izumi T. Exophilin-8 assembles secretory granules for exocytosis in the actin cortex via interaction with RIM-BP2 and myosin-VIIa. eLife 2017; 6. [PMID: 28673385 PMCID: PMC5496739 DOI: 10.7554/elife.26174] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 06/04/2017] [Indexed: 12/15/2022] Open
Abstract
Exophilin-8 has been reported to play a role in anchoring secretory granules within the actin cortex, due to its direct binding activities to Rab27 on the granule membrane and to F-actin and its motor protein, myosin-Va. Here, we show that exophilin-8 accumulates granules in the cortical F-actin network not by direct interaction with myosin-Va, but by indirect interaction with a specific form of myosin-VIIa through its previously unknown binding partner, RIM-BP2. RIM-BP2 also associates with exocytic machinery, Cav1.3, RIM, and Munc13-1. Disruption of the exophilin-8-RIM-BP2-myosin-VIIa complex by ablation or knockdown of each component markedly decreases both the peripheral accumulation and exocytosis of granules. Furthermore, exophilin-8-null mouse pancreatic islets lose polarized granule localization at the β-cell periphery and exhibit impaired insulin secretion. This newly identified complex acts as a physical and functional scaffold and provides a mechanism supporting a releasable pool of granules within the F-actin network beneath the plasma membrane.
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Affiliation(s)
- Fushun Fan
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Kohichi Matsunaga
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Hao Wang
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Ray Ishizaki
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Eri Kobayashi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Hiroshi Kiyonari
- Animal Resource Development Unit, RIKEN Center for Life Science Technologies, Kobe, Japan.,Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe, Japan
| | - Yoshiko Mukumoto
- Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe, Japan
| | - Katsuhide Okunishi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.,Research Program for Signal Transduction, Division of Endocrinology, Metabolism and Signal Research, Gunma University Initiative for Advanced Research, Maebashi, Japan
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8
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Yamaoka M, Ishizaki T, Kimura T. GTP- and GDP-Dependent Rab27a Effectors in Pancreatic Beta-Cells. Biol Pharm Bull 2016; 38:663-8. [PMID: 25947911 DOI: 10.1248/bpb.b14-00886] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Small guanosine triphosphatases (GTPases) participate in a wide variety of cellular functions including proliferation, differentiation, adhesion, and intracellular transport. Conventionally, only the guanosine 5'-triphosphate (GTP)-bound small GTPase interacts with effector proteins, and the resulting downstream signals control specific cellular functions. Therefore, the GTP-bound form is regarded as active, and the focus has been on searching for proteins that bind the GTP form to look for their effectors. The Rab family small GTPase Rab27a is highly expressed in some secretory cells and is involved in the control of membrane traffic. The present study reviews recent progress in our understanding of the roles of Rab27a and its effectors in pancreatic beta-cells. In the basal state, GTP-bound Rab27a controls insulin secretion at pre-exocytic stages via its GTP-dependent effectors. We previously identified novel guanosine 5'-diphosphate (GDP)-bound Rab27-interacting proteins. Interestingly, GDP-bound Rab27a controls endocytosis of the secretory membrane via its interaction with these proteins. We also demonstrated that the insulin secretagogue glucose converts Rab27a from its GTP- to GDP-bound forms. Thus, GTP- and GDP-bound Rab27a regulate pre-exocytic and endocytic stages in membrane traffic, respectively. Since the physiological importance of GDP-bound GTPases has been largely overlooked, we consider that the investigation of GDP-dependent effectors for other GTPases is necessary for further understanding of cellular function.
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Affiliation(s)
- Mami Yamaoka
- Department of Pharmacology, Oita University Faculty of Medicine
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9
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Type II PKAs are anchored to mature insulin secretory granules in INS-1 β-cells and required for cAMP-dependent potentiation of exocytosis. Biochimie 2016; 125:32-41. [PMID: 26898328 DOI: 10.1016/j.biochi.2016.02.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 02/13/2016] [Indexed: 11/23/2022]
Abstract
Specificity of the cAMP-dependent protein kinase (PKA) pathway relies on an extremely sophisticated compartmentalization mechanism of the kinase within a given cell, based on high-affinity binding of PKA tetramer pools to different A-Kinase Anchoring Proteins (AKAPs). We and others have previously shown that AKAPs-dependent PKA subcellular targeting is a requisite for optimal cAMP-dependent potentiation of insulin exocytosis. We thus hypothesized that a PKA pool may directly anchor to the secretory compartment to potentiate insulin exocytosis. Here, using immunofluorescence analyses combined to subcellular fractionations and purification of insulin secretory granules (ISGs), we identified discrete subpools of type II PKAs, RIIα and RIIβ PKAs, along with the catalytic subunit, physically associated with ISGs within pancreatic insulin-secreting β-cells. Ultrastructural analysis of native rodent β-cells confirmed in vivo the occurrence of PKA on dense-core ISGs. Isoform-selective disruption of binding of PKAs to AKAPs reinforced the requirement of type II PKA isoforms for cAMP potentiation of insulin exocytosis. This granular localization of PKA was of critical importance since siRNA-mediated depletion of either RIIα or RIIβ PKAs resulted in a significant reduction of cAMP-dependent potentiation of insulin release. The present work provides evidence for a previously unrecognized pool of type II PKAs physically anchored to the β-cell ISGs compartment and supports a non-redundant function for type II PKAs during cAMP potentiation of exocytosis.
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10
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Conte IL, Hellen N, Bierings R, Mashanov GI, Manneville JB, Kiskin NI, Hannah MJ, Molloy JE, Carter T. Interaction between MyRIP and the actin cytoskeleton regulates Weibel-Palade body trafficking and exocytosis. J Cell Sci 2016; 129:592-603. [PMID: 26675235 PMCID: PMC4760305 DOI: 10.1242/jcs.178285] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 12/03/2015] [Indexed: 12/11/2022] Open
Abstract
Weibel-Palade body (WPB)-actin interactions are essential for the trafficking and secretion of von Willebrand factor; however, the molecular basis for this interaction remains poorly defined. Myosin Va (MyoVa or MYO5A) is recruited to WPBs by a Rab27A-MyRIP complex and is thought to be the prime mediator of actin binding, but direct MyRIP-actin interactions can also occur. To evaluate the specific contribution of MyRIP-actin and MyRIP-MyoVa binding in WPB trafficking and Ca(2+)-driven exocytosis, we used EGFP-MyRIP point mutants with disrupted MyoVa and/or actin binding and high-speed live-cell fluorescence microscopy. We now show that the ability of MyRIP to restrict WPB movement depends upon its actin-binding rather than its MyoVa-binding properties. We also show that, although the role of MyRIP in Ca(2+)-driven exocytosis requires both MyoVa- and actin-binding potential, it is the latter that plays a dominant role. In view of these results and together with the analysis of actin disruption or stabilisation experiments, we propose that the role of MyRIP in regulating WPB trafficking and exocytosis is mediated largely through its interaction with actin rather than with MyoVa.
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Affiliation(s)
- Ianina L Conte
- Cardiovascular and Cell Science Research Institute, St George's University, London SW17 0RE, UK
| | - Nicola Hellen
- The Francis Crick Institute, Mill Hill Laboratory, London NW7 1AA, UK
| | - Ruben Bierings
- The Francis Crick Institute, Mill Hill Laboratory, London NW7 1AA, UK
| | | | | | - Nikolai I Kiskin
- The Francis Crick Institute, Mill Hill Laboratory, London NW7 1AA, UK
| | - Matthew J Hannah
- The Francis Crick Institute, Mill Hill Laboratory, London NW7 1AA, UK
| | - Justin E Molloy
- The Francis Crick Institute, Mill Hill Laboratory, London NW7 1AA, UK
| | - Tom Carter
- Cardiovascular and Cell Science Research Institute, St George's University, London SW17 0RE, UK
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11
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Yamaoka M, Ando T, Terabayashi T, Okamoto M, Takei M, Nishioka T, Kaibuchi K, Matsunaga K, Ishizaki R, Izumi T, Niki I, Ishizaki T, Kimura T. PI3K regulates endocytosis after insulin secretion by mediating signaling crosstalk between Arf6 and Rab27a. J Cell Sci 2015; 129:637-49. [PMID: 26683831 DOI: 10.1242/jcs.180141] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Accepted: 12/03/2015] [Indexed: 01/12/2023] Open
Abstract
In secretory cells, endocytosis is coupled to exocytosis to enable proper secretion. Although endocytosis is crucial to maintain cellular homeostasis before and after secretion, knowledge about secretagogue-induced endocytosis in secretory cells is still limited. Here, we searched for proteins that interacted with the Rab27a GTPase-activating protein (GAP) EPI64 (also known as TBC1D10A) and identified the Arf6 guanine-nucleotide-exchange factor (GEF) ARNO (also known as CYTH2) in pancreatic β-cells. We found that the insulin secretagogue glucose promotes phosphatidylinositol (3,4,5)-trisphosphate (PIP3) generation through phosphoinositide 3-kinase (PI3K), thereby recruiting ARNO to the intracellular side of the plasma membrane. Peripheral ARNO promotes clathrin assembly through its GEF activity for Arf6 and regulates the early stage of endocytosis. We also found that peripheral ARNO recruits EPI64 to the same area and that the interaction requires glucose-induced endocytosis in pancreatic β-cells. Given that GTP- and GDP-bound Rab27a regulate exocytosis and the late stage of endocytosis, our results indicate that the glucose-induced activation of PI3K plays a pivotal role in exocytosis-endocytosis coupling, and that ARNO and EPI64 regulate endocytosis at distinct stages.
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Affiliation(s)
- Mami Yamaoka
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Tomomi Ando
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Takeshi Terabayashi
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Mitsuhiro Okamoto
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Masahiro Takei
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Tomoki Nishioka
- Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University, 65 Tsurumai, Showa, Nagoya, Aichi 466-8550, Japan
| | - Kozo Kaibuchi
- Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University, 65 Tsurumai, Showa, Nagoya, Aichi 466-8550, Japan JST, CREST, 4-1-8 Honcho, Kawaguchi 332-0012, Japan
| | - Kohichi Matsunaga
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
| | - Ray Ishizaki
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
| | - Ichiro Niki
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Toshimasa Ishizaki
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
| | - Toshihide Kimura
- Department of Pharmacology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Yufu, Oita 879-5593, Japan
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12
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Stanic J, Carta M, Eberini I, Pelucchi S, Marcello E, Genazzani AA, Racca C, Mulle C, Di Luca M, Gardoni F. Rabphilin 3A retains NMDA receptors at synaptic sites through interaction with GluN2A/PSD-95 complex. Nat Commun 2015; 6:10181. [PMID: 26679993 PMCID: PMC4703873 DOI: 10.1038/ncomms10181] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Accepted: 11/12/2015] [Indexed: 11/19/2022] Open
Abstract
NMDA receptor (NMDAR) composition and synaptic retention represent pivotal features in the physiology and pathology of excitatory synapses. Here, we identify Rabphilin 3A (Rph3A) as a new GluN2A subunit-binding partner. Rph3A is known as a synaptic vesicle-associated protein involved in the regulation of exo- and endocytosis processes at presynaptic sites. We find that Rph3A is enriched at dendritic spines. Protein-protein interaction assays reveals that Rph3A N-terminal domain interacts with GluN2A(1349-1389) as well as with PSD-95(PDZ3) domains, creating a ternary complex. Rph3A silencing in neurons reduces the surface localization of synaptic GluN2A and NMDAR currents. Moreover, perturbing GluN2A/Rph3A interaction with interfering peptides in organotypic slices or in vivo induces a decrease of the amplitude of NMDAR-mediated currents and GluN2A density at dendritic spines. In conclusion, Rph3A interacts with GluN2A and PSD-95 forming a complex that regulates NMDARs stabilization at postsynaptic membranes.
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Affiliation(s)
- Jennifer Stanic
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
| | - Mario Carta
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, CNRS UMR 5297, Bordeaux 33000, France
| | - Ivano Eberini
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
| | - Silvia Pelucchi
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
| | - Elena Marcello
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
| | - Armando A. Genazzani
- Dipartimento di Scienze del Farmaco, Università degli Studi del Piemonte Orientale ‘Amedeo Avogadro', Novara 28100, Italy
| | - Claudia Racca
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Christophe Mulle
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, CNRS UMR 5297, Bordeaux 33000, France
| | - Monica Di Luca
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
| | - Fabrizio Gardoni
- DiSFeB, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Via Balzaretti 9, Milano 20133, Italy
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Synaptotagmin-7 phosphorylation mediates GLP-1-dependent potentiation of insulin secretion from β-cells. Proc Natl Acad Sci U S A 2015. [PMID: 26216970 DOI: 10.1073/pnas.1513004112] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Glucose stimulates insulin secretion from β-cells by increasing intracellular Ca(2+). Ca(2+) then binds to synaptotagmin-7 as a major Ca(2+) sensor for exocytosis, triggering secretory granule fusion and insulin secretion. In type-2 diabetes, insulin secretion is impaired; this impairment is ameliorated by glucagon-like peptide-1 (GLP-1) or by GLP-1 receptor agonists, which improve glucose homeostasis. However, the mechanism by which GLP-1 receptor agonists boost insulin secretion remains unclear. Here, we report that GLP-1 stimulates protein kinase A (PKA)-dependent phosphorylation of synaptotagmin-7 at serine-103, which enhances glucose- and Ca(2+)-stimulated insulin secretion and accounts for the improvement of glucose homeostasis by GLP-1. A phospho-mimetic synaptotagmin-7 mutant enhances Ca(2+)-triggered exocytosis, whereas a phospho-inactive synaptotagmin-7 mutant disrupts GLP-1 potentiation of insulin secretion. Our findings thus suggest that synaptotagmin-7 is directly activated by GLP-1 signaling and may serve as a drug target for boosting insulin secretion. Moreover, our data reveal, to our knowledge, the first physiological modulation of Ca(2+)-triggered exocytosis by direct phosphorylation of a synaptotagmin.
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The circular RNA Cdr1as, via miR-7 and its targets, regulates insulin transcription and secretion in islet cells. Sci Rep 2015. [PMID: 26211738 PMCID: PMC4515639 DOI: 10.1038/srep12453] [Citation(s) in RCA: 382] [Impact Index Per Article: 42.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Among the identified thousands of circular RNAs (circRNA) in humans and animals, Cdr1as (also known as CiRS-7) was recently demonstrated to act as a powerful miR-7 sponge/inhibitor in developing midbrain of zebrafish, suggesting a novel mechanism for regulating microRNA functions. MiR-7 is abundantly expressed in islet cells, but overexpressing miR-7 in transgenic mouse β cells causes diabetes. Therefore, we infer that Cdr1as expression may inhibit miR-7 function in islet cells, which in turn improves insulin secretion. Here, we show the first characterization of Cdr1as expression in islet cells, which was upregulated by long-term forskolin and PMA stimulation, but not high glucose, indicating the involvement of cAMP and PKC pathways. Remarkably, both insulin content and secretion were significantly increased by overexpression of Cdr1as in islet cells. We further identified a new target Myrip in the Cdr1as/miR-7 pathway that regulates insulin granule secretion, and also another target Pax6 that enhances insulin transcription. Taken together, our findings revealed the effects of the strongly interacting pair of Cdr1as/miR-7 on insulin secretion, which may become a new target for improving β cell function in diabetes.
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15
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Yamaoka M, Ishizaki T, Kimura T. Interplay between Rab27a effectors in pancreatic β-cells. World J Diabetes 2015; 6:508-516. [PMID: 25897360 PMCID: PMC4398906 DOI: 10.4239/wjd.v6.i3.508] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Revised: 12/24/2014] [Accepted: 02/09/2015] [Indexed: 02/05/2023] Open
Abstract
The small GTPase Rab27a is a member of the Rab family that is involved in membrane trafficking in various kinds of cells. Rab27a has GTP- and GDP-bound forms, and their interconversion regulates intracellular signaling pathways. Typically, only a GTP-bound GTPase binds its specific effectors with the resulting downstream signals controlling specific cellular functions. We previously identified novel Rab27a-interacting proteins. Surprisingly, some of these proteins interacted with GDP-bound Rab27a. The present study reviews recent progress in our understanding of the roles of Rab27a and its effectors in the secretory process. In pancreatic β-cells, GTP-bound Rab27a regulates insulin secretion at the pre-exocytotic stages via its GTP-specific effectors such as Exophilin8/Slac2-c/MyRIP and Slp4/Granuphilin. Glucose stimulation causes insulin exocytosis. Glucose stimulation also converts Rab27a from its GTP- to its GDP-bound form. GDP-bound Rab27a interacts with GDP-specific effectors and controls endocytosis of the secretory membrane. Thus, Rab27a cycling between GTP- and GDP-bound forms synchronizes with the recycling of secretory membrane to re-use the membrane and keep the β-cell volume constant.
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Glutamate acts as a key signal linking glucose metabolism to incretin/cAMP action to amplify insulin secretion. Cell Rep 2014; 9:661-73. [PMID: 25373904 PMCID: PMC4536302 DOI: 10.1016/j.celrep.2014.09.030] [Citation(s) in RCA: 118] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Revised: 08/19/2014] [Accepted: 09/15/2014] [Indexed: 11/29/2022] Open
Abstract
Incretins, hormones released by the gut after meal ingestion, are essential for maintaining systemic glucose homeostasis by stimulating insulin secretion. The effect of incretins on insulin secretion occurs only at elevated glucose concentrations and is mediated by cAMP signaling, but the mechanism linking glucose metabolism and cAMP action in insulin secretion is unknown. We show here, using a metabolomics-based approach, that cytosolic glutamate derived from the malate-aspartate shuttle upon glucose stimulation underlies the stimulatory effect of incretins and that glutamate uptake into insulin granules mediated by cAMP/PKA signaling amplifies insulin release. Glutamate production is diminished in an incretin-unresponsive, insulin-secreting β cell line and pancreatic islets of animal models of human diabetes and obesity. Conversely, a membrane-permeable glutamate precursor restores amplification of insulin secretion in these models. Thus, cytosolic glutamate represents the elusive link between glucose metabolism and cAMP action in incretin-induced insulin secretion. Glutamate is derived from the malate-aspartate shuttle upon glucose stimulation Shuttle-derived glutamate is crucial for incretin-induced insulin secretion Cytosolic glutamate is transported into insulin granules via cAMP/PKA signaling Glutamate production by glucose is defective in incretin-unresponsive β cells
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Shibasaki T, Takahashi T, Takahashi H, Seino S. Cooperation between cAMP signalling and sulfonylurea in insulin secretion. Diabetes Obes Metab 2014; 16 Suppl 1:118-25. [PMID: 25200305 DOI: 10.1111/dom.12343] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 04/23/2014] [Indexed: 12/23/2022]
Abstract
Although glucose is physiologically the most important regulator of insulin secretion, glucose-induced insulin secretion is modulated by hormonal and neural inputs to pancreatic β-cells. Most of the hormones and neurotransmitters evoke intracellular signals such as cAMP, Ca²⁺ , and phospholipid-derived molecules by activating G protein-coupled receptors (GPCRs). In particular, cAMP is a key second messenger that amplifies insulin secretion in a glucose concentration-dependent manner. The action of cAMP on insulin secretion is mediated by both protein kinase A (PKA)-dependent and Epac2A-dependent mechanisms. Many of the proteins expressed in β-cells are phosphorylated by PKA in vitro, but only a few proteins in which PKA phosphorylation directly affects insulin secretion have been identified. On the other hand, Epac2A activates the Ras-like small G protein Rap in a cAMP-dependent manner. Epac2A is also directly activated by various sulfonylureas, except for gliclazide. 8-pCPT-2'-O-Me-cAMP, an Epac-selective cAMP analogue, and glibenclamide, a sulfonylurea, synergistically activate Epac2A and Rap1, whereas adrenaline, which suppresses cAMP production in pancreatic β-cells, blocks activation of Epac2A and Rap1 by glibenclamide. Thus, cAMP signalling and sulfonylurea cooperatively activate Epac2A and Rap1. This interaction could account, at least in part, for the synergistic effects of incretin-related drugs and sulfonylureas in insulin secretion. Accordingly, clarification of the mechanism of Epac2A activation may provide therapeutic strategies to improve insulin secretion in diabetes.
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Affiliation(s)
- T Shibasaki
- Divisions of Cellular and Molecular Medicine, Kobe University Graduate School of Medicine, Kobe, Japan
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Fukuda M. Rab27 effectors, pleiotropic regulators in secretory pathways. Traffic 2013; 14:949-63. [PMID: 23678941 DOI: 10.1111/tra.12083] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Revised: 05/13/2013] [Accepted: 05/16/2013] [Indexed: 12/18/2022]
Abstract
Rab27, a member of the small GTPase Rab family, is widely conserved in metazoan, and two Rab27 isoforms, Rab27A and Rab27B, are present in vertebrates. Rab27A was the first Rab protein whose dysfunction was found to cause a human hereditary disease, type 2 Griscelli syndrome, which is characterized by silvery hair and immunodeficiency. The discovery in the 21st century of three distinct types of mammalian Rab27A effectors [synaptotagmin-like protein (Slp), Slp homologue lacking C2 domains (Slac2), and Munc13-4] that specifically bind active Rab27A has greatly accelerated our understanding not only of the molecular mechanisms of Rab27A-mediated membrane traffic (e.g. melanosome transport and regulated secretion) but of the symptoms of Griscelli syndrome patients at the molecular level. Because Rab27B is widely expressed in various tissues together with Rab27A and has been found to have the ability to bind all of the Rab27A effectors that have been tested, Rab27A and Rab27B were initially thought to function redundantly by sharing common Rab27 effectors. However, recent evidence has indicated that by interacting with different Rab27 effectors Rab27A and Rab27B play different roles in special types of secretion (e.g. exosome secretion and mast cell secretion) even within the same cell type. In this review article, I describe the current state of our understanding of the functions of Rab27 effectors in secretory pathways.
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Affiliation(s)
- Mitsunori Fukuda
- Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
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