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Zhao K, Matsunaga K, Mizuno K, Wang H, Okunishi K, Izumi T. Functional hierarchy among different Rab27 effectors involved in secretory granule exocytosis. eLife 2023; 12:82821. [PMID: 36803984 PMCID: PMC9988257 DOI: 10.7554/elife.82821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 02/21/2023] [Indexed: 02/23/2023] Open
Abstract
The Rab27 effectors are known to play versatile roles in regulated exocytosis. In pancreatic beta cells, exophilin-8 anchors granules in the peripheral actin cortex, whereas granuphilin and melanophilin mediate granule fusion with and without stable docking to the plasma membrane, respectively. However, it is unknown whether these coexisting effectors function in parallel or in sequence to support the whole insulin secretory process. Here, we investigate their functional relationships by comparing the exocytic phenotypes in mouse beta cells simultaneously lacking two effectors with those lacking just one of them. Analyses of prefusion profiles by total internal reflection fluorescence microscopy suggest that melanophilin exclusively functions downstream of exophilin-8 to mobilize granules for fusion from the actin network to the plasma membrane after stimulation. The two effectors are physically linked via the exocyst complex. Downregulation of the exocyst component affects granule exocytosis only in the presence of exophilin-8. The exocyst and exophilin-8 also promote fusion of granules residing beneath the plasma membrane prior to stimulation, although they differentially act on freely diffusible granules and those stably docked to the plasma membrane by granuphilin, respectively. This is the first study to diagram the multiple intracellular pathways of granule exocytosis and the functional hierarchy among different Rab27 effectors within the same cell.
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Affiliation(s)
- Kunli Zhao
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Kohichi Matsunaga
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Kouichi Mizuno
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Hao Wang
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Katsuhide Okunishi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
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Li PH, He JY, Cai YJ, Wei YS, Zhu XL, Yang JDH, Yang SQ, Zhou S, Qin QW, Sun HY. Molecular cloning, inducible expression and function analysis of Epinephelus coioides Sec6 response to SGIV infection. FISH & SHELLFISH IMMUNOLOGY 2022; 124:462-471. [PMID: 35483595 DOI: 10.1016/j.fsi.2022.04.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 03/19/2022] [Accepted: 04/21/2022] [Indexed: 06/14/2023]
Abstract
Exocyst complex component 3 Sec6 of mammals, one of the components of the exocyst complex, participates in numerous cellular functions, such as promoting cell migration and inhibiting apoptosis. In this study, the Sec6 was obtained from Epinephelus coioides, an economically important cultured fish. The full length of E. coioides Sec6 was 2655 bp including a 245 bp 5' UTR, a 154 bp 3' UTR, and a 2256 bp open reading frame (ORF) encoding 751 amino acids, with a molecular mass of 86.76 kDa and a theoretical pI of 5.57. Sec6 mRNA was detected in all the tissues examined, but the expression level is different in these tissues. Using fluorescence microscopy, Sec6 were distributed in both the nucleus and the cytoplasm. After SGIV infection, the expression of E. coioides Sec6 was significantly up-regulated in both trunk kidney and spleen response to Singapore grouper iridovirus (SGIV), an important pathogens of E. coioides. Sec6 could increase the SGIV-induced cytopathic effects (CPE), the expression of the SGIV genes VP19, LITAF, MCP, ICP18 and MCP, and the viral titers. Besides, E. coioides Sec6 significantly downregulated the promoter of NF-κB and AP-1, and inhibited the SGIV-induced apoptosis. The results demonstrated that E. coioides Sec6 might play important roles in SGIV infection.
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Affiliation(s)
- Pin-Hong Li
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, 510642, PR China
| | - Jia-Yang He
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Yi-Jie Cai
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Yu-Si Wei
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Xiang-Long Zhu
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Jia-Deng-Hui Yang
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Shi-Qi Yang
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China
| | - Sheng Zhou
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, 510642, PR China
| | - Qi-Wei Qin
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China; Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, PR China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266000, PR China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, 510642, PR China.
| | - Hong-Yan Sun
- University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, 510642, PR China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, 510642, PR China.
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Sulaiman N, Yaseen Hachim M, Khalique A, Mohammed AK, Al Heialy S, Taneera J. EXOC6 (Exocyst Complex Component 6) Is Associated with the Risk of Type 2 Diabetes and Pancreatic β-Cell Dysfunction. BIOLOGY 2022; 11:biology11030388. [PMID: 35336762 PMCID: PMC8945791 DOI: 10.3390/biology11030388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 02/25/2022] [Accepted: 02/25/2022] [Indexed: 11/16/2022]
Abstract
EXOC6 and EXOC6B (EXOC6/6B) components of the exocyst complex are involved in the secretory granule docking. Recently, EXOC6/6B were anticipated as a molecular link between dysfunctional pancreatic islets and ciliated lung epithelium, making diabetic patients more prone to severe SARS-CoV-2 complications. However, the exact role of EXOC6/6B in pancreatic β-cell function and risk of T2D is not fully understood. Herein, microarray and RNA-sequencing (RNA-seq) expression data demonstrated the expression of EXOC6/6B in human pancreatic islets. Expression of EXOC6/6B was not affected by diabetes status. Exploration of the using the translational human pancreatic islet genotype tissue-expression resource portal (TIGER) revealed three genetic variants (rs947591, rs2488071 and rs2488073) in the EXOC6 gene that were associated (p < 2.5 × 10−20) with the risk of T2D. Exoc6/6b silencing in rat pancreatic β-cells (INS1-832/13) impaired insulin secretion, insulin content, exocytosis machinery and glucose uptake without cytotoxic effect. A significant decrease in the expression Ins1, Ins1, Pdx1, Glut2 and Vamp2 was observed in Exoc6/6b-silenced cells at the mRNA and protein levels. However, NeuroD1, Gck and InsR were not influenced compared to the negative control. In conclusion, our data propose that EXOC6/6B are crucial regulators for insulin secretion and exocytosis machinery in β-cells. This study identified several genetic variants in EXOC6 associated with the risk of T2D. Therefore, EXOC6/6B could provide a new potential target for therapy development or early biomarkers for T2D.
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Affiliation(s)
- Nabil Sulaiman
- Department of Family Medicine, College of Medicine, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates;
| | - Mahmood Yaseen Hachim
- College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai P.O. Box 505055, United Arab Emirates; (M.Y.H.); (S.A.H.)
| | - Anila Khalique
- Sharjah Institute for Medical Research, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates; (A.K.); (A.K.M.)
| | - Abdul Khader Mohammed
- Sharjah Institute for Medical Research, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates; (A.K.); (A.K.M.)
| | - Saba Al Heialy
- College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai P.O. Box 505055, United Arab Emirates; (M.Y.H.); (S.A.H.)
| | - Jalal Taneera
- Sharjah Institute for Medical Research, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates; (A.K.); (A.K.M.)
- Department of Basic Sciences, College of Medicine, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates
- Correspondence: ; Tel.: +971-6505-7743
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Apken LH, Oeckinghaus A. The RAL signaling network: Cancer and beyond. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2020; 361:21-105. [PMID: 34074494 DOI: 10.1016/bs.ircmb.2020.10.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The RAL proteins RALA and RALB belong to the superfamily of small RAS-like GTPases (guanosine triphosphatases). RAL GTPases function as molecular switches in cells by cycling through GDP- and GTP-bound states, a process which is regulated by several guanine exchange factors (GEFs) and two heterodimeric GTPase activating proteins (GAPs). Since their discovery in the 1980s, RALA and RALB have been established to exert isoform-specific functions in central cellular processes such as exocytosis, endocytosis, actin organization and gene expression. Consequently, it is not surprising that an increasing number of physiological functions are discovered to be controlled by RAL, including neuronal plasticity, immune response, and glucose and lipid homeostasis. The critical importance of RAL GTPases for oncogenic RAS-driven cellular transformation and tumorigenesis still attracts most research interest. Here, RAL proteins are key drivers of cell migration, metastasis, anchorage-independent proliferation, and survival. This chapter provides an overview of normal and pathological functions of RAL GTPases and summarizes the current knowledge on the involvement of RAL in human disease as well as current therapeutic targeting strategies. In particular, molecular mechanisms that specifically control RAL activity and RAL effector usage in different scenarios are outlined, putting a spotlight on the complexity of the RAL GTPase signaling network and the emerging theme of RAS-independent regulation and relevance of RAL.
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Affiliation(s)
- Lisa H Apken
- Institute of Molecular Tumor Biology, Faculty of Medicine, University of Münster, Münster, Germany
| | - Andrea Oeckinghaus
- Institute of Molecular Tumor Biology, Faculty of Medicine, University of Münster, Münster, Germany.
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Glutamatergic Receptor Trafficking and Delivery: Role of the Exocyst Complex. Cells 2020; 9:cells9112402. [PMID: 33153008 PMCID: PMC7693776 DOI: 10.3390/cells9112402] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 10/21/2020] [Accepted: 10/23/2020] [Indexed: 12/29/2022] Open
Abstract
Cells comprise several intracellular membrane compartments that allow them to function properly. One of these functions is cargo movement, typically proteins and membranes within cells. These cargoes ride microtubules through vesicles from Golgi and recycling endosomes to the plasma membrane in order to be delivered and exocytosed. In neurons, synaptic functions employ this cargo trafficking to maintain inter-neuronal communication optimally. One of the complexes that oversee vesicle trafficking and tethering is the exocyst. The exocyst is a protein complex containing eight subunits first identified in yeast and then characterized in multicellular organisms. This complex is related to several cellular processes, including cellular growth, division, migration, and morphogenesis, among others. It has been associated with glutamatergic receptor trafficking and tethering into the synapse, providing the molecular machinery to deliver receptor-containing vesicles into the plasma membrane in a constitutive manner. In this review, we discuss the evidence so far published regarding receptor trafficking and the exocyst complex in both basal and stimulated levels, comparing constitutive trafficking and long-term potentiation-related trafficking.
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Grabek KR, Cooke TF, Epperson LE, Spees KK, Cabral GF, Sutton SC, Merriman DK, Martin SL, Bustamante CD. Genetic variation drives seasonal onset of hibernation in the 13-lined ground squirrel. Commun Biol 2019; 2:478. [PMID: 31886416 PMCID: PMC6925185 DOI: 10.1038/s42003-019-0719-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 11/28/2019] [Indexed: 01/23/2023] Open
Abstract
Hibernation in sciurid rodents is a dynamic phenotype timed by a circannual clock. When housed in an animal facility, 13-lined ground squirrels exhibit variation in seasonal onset of hibernation, which is not explained by environmental or biological factors. We hypothesized that genetic factors instead drive variation in timing. After increasing genome contiguity, here, we employ a genotype-by-sequencing approach to characterize genetic variation in 153 ground squirrels. Combined with datalogger records (n = 72), we estimate high heritability (61-100%) for hibernation onset. Applying a genome-wide scan with 46,996 variants, we identify 2 loci significantly (p < 7.14 × 10-6), and 12 loci suggestively (p < 2.13 × 10-4), associated with onset. At the most significant locus, whole-genome resequencing reveals a putative causal variant in the promoter of FAM204A. Expression quantitative trait loci (eQTL) analyses further reveal gene associations for 8/14 loci. Our results highlight the power of applying genetic mapping to hibernation and present new insight into genetics driving its onset.
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Affiliation(s)
- Katharine R. Grabek
- Department of Genetics and Department of Biomedical Data Science, Stanford University School of Medicine, Stanford, CA USA
- Fauna Bio Incorporated, Berkeley, CA USA
| | - Thomas F. Cooke
- Department of Genetics, Stanford University School of Medicine, Stanford, CA USA
- Whitehead Institute for Biomedical Research, Cambridge, MA USA
| | - L. Elaine Epperson
- Center for Genes, Environment and Health, National Jewish Health, Denver, CO, USA
| | - Kaitlyn K. Spees
- Department of Genetics, Stanford University School of Medicine, Stanford, CA USA
| | - Gleyce F. Cabral
- Department of Genetics, Stanford University School of Medicine, Stanford, CA USA
- Laboratório de Genética Humana e Médica, Universidade Federal do Pará, Rua Augusto Corrêa, 1 - 66.075-110, Belem, PA Brazil
| | - Shirley C. Sutton
- Department of Genetics and Department of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA USA
| | - Dana K. Merriman
- Department of Biology, University of Wisconsin Oshkosh, Oshkosh, WI USA
| | - Sandra L. Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO USA
| | - Carlos D. Bustamante
- Department of Genetics and Department of Biomedical Data Science, Stanford University School of Medicine, Stanford, CA USA
- Chan Zuckerberg Biohub, San Francisco, CA USA
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7
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Sec6 enhances cell migration and suppresses apoptosis by elevating the phosphorylation of p38 MAPK, MK2, and HSP27. Cell Signal 2018; 49:1-16. [DOI: 10.1016/j.cellsig.2018.04.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 04/27/2018] [Accepted: 04/30/2018] [Indexed: 11/20/2022]
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8
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Wang X, Chung KP, Lin W, Jiang L. Protein secretion in plants: conventional and unconventional pathways and new techniques. JOURNAL OF EXPERIMENTAL BOTANY 2017; 69:21-37. [PMID: 28992209 DOI: 10.1093/jxb/erx262] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Protein secretion is an essential process in all eukaryotic cells and its mechanisms have been extensively studied. Proteins with an N-terminal leading sequence or transmembrane domain are delivered through the conventional protein secretion (CPS) pathway from the endoplasmic reticulum (ER) to the Golgi apparatus. This feature is conserved in yeast, animals, and plants. In contrast, the transport of leaderless secretory proteins (LSPs) from the cytosol to the cell exterior is accomplished via the unconventional protein secretion (UPS) pathway. So far, the CPS pathway has been well characterized in plants, with several recent studies providing new information about the regulatory mechanisms involved. On the other hand, studies on UPS pathways in plants remain descriptive, although a connection between UPS and the plant defense response is becoming more and more apparent. In this review, we present an update on CPS and UPS. With the emergence of new techniques, a more comprehensive understanding of protein secretion in plants can be expected in the future.
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Affiliation(s)
- Xiangfeng Wang
- State Key Laboratory of Agrobiotechnology, Centre for Cell and Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, China
| | - Kin Pan Chung
- State Key Laboratory of Agrobiotechnology, Centre for Cell and Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, China
| | - Weili Lin
- State Key Laboratory of Agrobiotechnology, Centre for Cell and Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, China
| | - Liwen Jiang
- State Key Laboratory of Agrobiotechnology, Centre for Cell and Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, China
- CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, China
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Tang JS, Li QR, Li JM, Wu JR, Zeng R. Systematic Synergy of Glucose and GLP-1 to Stimulate Insulin Secretion Revealed by Quantitative Phosphoproteomics. Sci Rep 2017; 7:1018. [PMID: 28432305 PMCID: PMC5430885 DOI: 10.1038/s41598-017-00841-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 03/15/2017] [Indexed: 12/28/2022] Open
Abstract
GLP-1 synergizes with glucose in regulating pancreatic β-cell function, including facilitating β-cell survival and insulin secretion. Though it has been widely accepted that phosphorylation is extremely important in regulating β-cell functions, our knowledge to the global mechanism is still limited. Here we performed a quantitative phosphoproteomics study to systematically present the synergistic regulation of INS-1E cell phosphoproteome mediated by glucose and GLP-1. We generated the largest pancreatic β-cell phosphoproteome by identifying 25,327 accurately localized phosphorylation sites on 5,389 proteins. Our results discovered several novel kinases regulated by glucose, GLP-1 or their synergism, and some of these kinases might act as downstream molecules of GLP-1 mediated PKA signaling cascade. A few phosphosites were regulated by both GLP-1 and glucose alone, and these target proteins were highly related to their biological function on pancreatic β-cells. Finally, we found glucose and GLP-1 executed their synergistic effect at multiple levels, especially at pathway level. Both GLP-1 and glucose participated in regulating every single step of the secretion pathway, and systematically synergized their effects in inducing insulin secretion.
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Affiliation(s)
- Jia-Shu Tang
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China
| | - Qing-Run Li
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China
| | - Jia-Ming Li
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China
| | - Jia-Rui Wu
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China. .,Department of Life Sciences, ShanghaiTech University, 99 Haike Road, Shanghai, 201210, China.
| | - Rong Zeng
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China. .,Department of Life Sciences, ShanghaiTech University, 99 Haike Road, Shanghai, 201210, China.
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10
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Abstract
Exocytosis is a fundamental cellular process whereby secreted molecules are packaged into vesicles that move along cytoskeletal filaments and fuse with the plasma membrane. To function optimally, cells are strongly dependent on precisely controlled delivery of exocytotic cargo. In mammalian cells, microtubules serve as major tracks for vesicle transport by motor proteins, and thus microtubule organization is important for targeted delivery of secretory carriers. Over the years, multiple microtubule-associated and cortical proteins have been discovered that facilitate the interaction between the microtubule plus ends and the cell cortex. In this review, we focus on mammalian protein complexes that have been shown to participate in both cortical microtubule capture and exocytosis, thereby regulating the spatial organization of secretion. These complexes include microtubule plus-end tracking proteins, scaffolding factors, actin-binding proteins, and components of vesicle docking machinery, which together allow efficient coordination of cargo transport and release.
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Affiliation(s)
- Ivar Noordstra
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, Netherlands
| | - Anna Akhmanova
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, Netherlands
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11
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Tanaka T, Goto K, Iino M. Diverse Functions and Signal Transduction of the Exocyst Complex in Tumor Cells. J Cell Physiol 2016; 232:939-957. [DOI: 10.1002/jcp.25619] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 09/23/2016] [Indexed: 12/11/2022]
Affiliation(s)
- Toshiaki Tanaka
- Department of Anatomy and Cell Biology; School of Medicine; Yamagata University; Yamagata Japan
- Department of Dentistry, Oral and Maxillofacial Surgery; Plastic and Reconstructive Surgery; School of Medicine; Yamagata University; Yamagata Japan
| | - Kaoru Goto
- Department of Anatomy and Cell Biology; School of Medicine; Yamagata University; Yamagata Japan
| | - Mitsuyoshi Iino
- Department of Dentistry, Oral and Maxillofacial Surgery; Plastic and Reconstructive Surgery; School of Medicine; Yamagata University; Yamagata Japan
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Liu J, Zhang H, Lian X, Converse R, Zhu L. Identification of Interacting Motifs Between Armadillo Repeat Containing 1 (ARC1) and Exocyst 70 A1 (Exo70A1) Proteins in Brassica oleracea. Protein J 2015; 35:34-43. [DOI: 10.1007/s10930-015-9644-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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13
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β-Cell Insulin Secretion Requires the Ubiquitin Ligase COP1. Cell 2015; 163:1457-67. [PMID: 26627735 DOI: 10.1016/j.cell.2015.10.076] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Revised: 09/22/2015] [Accepted: 10/19/2015] [Indexed: 11/20/2022]
Abstract
A variety of signals finely tune insulin secretion by pancreatic β cells to prevent both hyper-and hypoglycemic states. Here, we show that post-translational regulation of the transcription factors ETV1, ETV4, and ETV5 by the ubiquitin ligase COP1 (also called RFWD2) in β cells is critical for insulin secretion. Mice lacking COP1 in β cells developed diabetes due to insulin granule docking defects that were fully rescued by genetic deletion of Etv1, Etv4, and Etv5. Genes regulated by ETV1, ETV4, or ETV5 in the absence of mouse COP1 were enriched in human diabetes-associated genes, suggesting that they also influence human β-cell pathophysiology. In normal β cells, ETV4 was stabilized upon membrane depolarization and limited insulin secretion under hyperglycemic conditions. Collectively, our data reveal that ETVs negatively regulate insulin secretion for the maintenance of normoglycemia.
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Zou W, Yadav S, DeVault L, Jan YN, Sherwood DR. RAB-10-Dependent Membrane Transport Is Required for Dendrite Arborization. PLoS Genet 2015; 11:e1005484. [PMID: 26394140 PMCID: PMC4578882 DOI: 10.1371/journal.pgen.1005484] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 08/05/2015] [Indexed: 01/07/2023] Open
Abstract
Formation of elaborately branched dendrites is necessary for the proper input and connectivity of many sensory neurons. Previous studies have revealed that dendritic growth relies heavily on ER-to-Golgi transport, Golgi outposts and endocytic recycling. How new membrane and associated cargo is delivered from the secretory and endosomal compartments to sites of active dendritic growth, however, remains unknown. Using a candidate-based genetic screen in C. elegans, we have identified the small GTPase RAB-10 as a key regulator of membrane trafficking during dendrite morphogenesis. Loss of rab-10 severely reduced proximal dendritic arborization in the multi-dendritic PVD neuron. RAB-10 acts cell-autonomously in the PVD neuron and localizes to the Golgi and early endosomes. Loss of function mutations of the exocyst complex components exoc-8 and sec-8, which regulate tethering, docking and fusion of transport vesicles at the plasma membrane, also caused proximal dendritic arborization defects and led to the accumulation of intracellular RAB-10 vesicles. In rab-10 and exoc-8 mutants, the trans-membrane proteins DMA-1 and HPO-30, which promote PVD dendrite stabilization and branching, no longer localized strongly to the proximal dendritic membranes and instead were sequestered within intracellular vesicles. Together these results suggest a crucial role for the Rab10 GTPase and the exocyst complex in controlling membrane transport from the secretory and/or endosomal compartments that is required for dendritic growth. Dendrites are cellular extensions from neurons that gather information from other neurons or cues from the external environment to convey to the nervous system of an organism. Dendrites are often extensively branched, raising the question of how neurons supply plasma membrane and dendrite specific proteins from the source of synthesis inside the cell to developing dendrites. We have examined membrane trafficking in the PVD neuron in the nematode worm C. elegans to investigate how new membrane and dendrite proteins are trafficked. The PVD neuron is easy to visualize and has remarkably long and widely branched dendrites positioned along the skin of the worm, which transmits information about harsh touch and cold temperature to the nervous system. We have discovered that a key organizer of vesicle trafficking, the RAB-10 protein, localizes to membrane vesicles and is required to traffic these vesicles that contain plasma membrane and dendrite proteins to the growing PVD dendrite. Further, our work revealed that a complex of proteins, termed the exocyst, that helps fuse membrane vesicles at the plasma membrane, localizes with RAB-10 and is required for dendrite branching. Together, our work has revealed a novel mechanism for how neurons build dendrites that could be used to help repair damaged neurons in human diseases and during aging.
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Affiliation(s)
- Wei Zou
- Department of Biology, Duke University, Durham, North Carolina, United States of America
| | - Smita Yadav
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, California, United States of America
| | - Laura DeVault
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, California, United States of America
| | - Yuh Nung Jan
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, California, United States of America
| | - David R. Sherwood
- Department of Biology, Duke University, Durham, North Carolina, United States of America
- * E-mail:
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15
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Shirakawa R, Horiuchi H. Ral GTPases: crucial mediators of exocytosis and tumourigenesis. J Biochem 2015; 157:285-99. [DOI: 10.1093/jb/mvv029] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 02/07/2015] [Indexed: 11/12/2022] Open
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16
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Inoue M, Akama T, Jiang Y, Chun TH. The exocyst complex regulates free fatty acid uptake by adipocytes. PLoS One 2015; 10:e0120289. [PMID: 25768116 PMCID: PMC4359155 DOI: 10.1371/journal.pone.0120289] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 02/03/2015] [Indexed: 11/19/2022] Open
Abstract
The exocyst is an octameric molecular complex that drives vesicle trafficking in adipocytes, a rate-limiting step in insulin-dependent glucose uptake. This study assessed the role of the exocyst complex in regulating free fatty acid (FFA) uptake by adipocytes. Upon differentiating into adipocytes, 3T3-L1 cells acquire the ability to incorporate extracellular FFAs in an insulin-dependent manner. A kinetic assay using fluoresceinated FFA (C12 dodecanoic acid) uptake allows the real-time monitoring of FFA internalization by adipocytes. The insulin-dependent uptake of C12 dodecanoic acid by 3T3-L1 adipocytes is mediated by Akt and phosphatidylinositol 3 (PI3)-kinase. Gene silencing of the exocyst components Exo70 and Sec8 significantly reduced insulin-dependent FFA uptake by adipocytes. Consistent with the roles played by Exo70 and Sec8 in FFA uptake, mCherry-tagged Exo70 and HA-tagged Sec8 partially colocalize with lipid droplets within adipocytes, suggesting their active roles in the development of lipid droplets. Tubulin polymerization was also found to regulate FFA uptake in collaboration with the exocyst complex. This study demonstrates a novel role played by the exocyst complex in the regulation of FFA uptake by adipocytes.
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Affiliation(s)
- Mayumi Inoue
- Division of Metabolism, Endocrinology & Diabetes (MEND), Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, United States of America
| | - Takeshi Akama
- Division of Metabolism, Endocrinology & Diabetes (MEND), Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Yibin Jiang
- Division of Metabolism, Endocrinology & Diabetes (MEND), Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Tae-Hwa Chun
- Division of Metabolism, Endocrinology & Diabetes (MEND), Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
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17
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par-1, atypical pkc, and PP2A/B55 sur-6 are implicated in the regulation of exocyst-mediated membrane trafficking in Caenorhabditis elegans. G3-GENES GENOMES GENETICS 2014; 4:173-83. [PMID: 24192838 PMCID: PMC3887533 DOI: 10.1534/g3.113.006718] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The exocyst is a conserved protein complex that is involved in tethering secretory vesicles to the plasma membrane and regulating cell polarity. Despite a large body of work, little is known how exocyst function is controlled. To identify regulators for exocyst function, we performed a targeted RNA interference (RNAi) screen in Caenorhabditis elegans to uncover kinases and phosphatases that genetically interact with the exocyst. We identified seven kinase and seven phosphatase genes that display enhanced phenotypes when combined with hypomorphic alleles of exoc-7 (exo70), exoc-8 (exo84), or an exoc-7;exoc-8 double mutant. We show that in line with its reported role in exocytotic membrane trafficking, a defective exoc-8 caused accumulation of exocytotic soluble NSF attachment protein receptor (SNARE) proteins in both intestinal and neuronal cells in C. elegans. Down-regulation of the phosphatase protein phosphatase 2A (PP2A) phosphatase regulatory subunit sur-6/B55 gene resulted in accumulation of exocytic SNARE proteins SNB-1 and SNAP-29 in wild-type and in exoc-8 mutant animals. In contrast, RNAi of the kinase par-1 caused reduced intracellular green fluorescent protein signal for the same proteins. Double RNAi experiments for par-1, pkc-3, and sur-6/B55 in C. elegans suggest a possible cooperation and involvement in postembryo lethality, developmental timing, as well as SNARE protein trafficking. Functional analysis of the homologous kinases and phosphatases in Drosophila median neurosecretory cells showed that atypical protein kinase C kinase and phosphatase PP2A regulate exocyst-dependent, insulin-like peptide secretion. Collectively, these results characterize kinases and phosphatases implicated in the regulation of exocyst function, and suggest the possibility for interplay between the par-1 and pkc-3 kinases and the PP2A phosphatase regulatory subunit sur-6 in this process.
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18
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Hilderink J, Otto C, Slump C, Lenferink A, Engelse M, van Blitterswijk C, de Koning E, Karperien M, van Apeldoorn A. Label-free detection of insulin and glucagon within human islets of Langerhans using Raman spectroscopy. PLoS One 2013; 8:e78148. [PMID: 24167603 PMCID: PMC3805587 DOI: 10.1371/journal.pone.0078148] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 09/09/2013] [Indexed: 01/25/2023] Open
Abstract
Intrahepatic transplantation of donor islets of Langerhans is a promising therapy for patients with type 1 diabetes. It is of critical importance to accurately monitor islet quality before transplantation, which is currently done by standard histological methods that are performed off-line and require extensive sample preparation. As an alternative, we propose Raman spectroscopy which is a non-destructive and label-free technique that allows continuous real-time monitoring of the tissue to study biological changes as they occur. By performing Raman spectroscopic measurements on purified insulin and glucagon, we showed that the 520 cm(-1) band assigned to disulfide bridges in insulin, and the 1552 cm(-1) band assigned to tryptophan in glucagon are mutually exclusive and could therefore be used as indirect markers for the label-free distinction between both hormones. High-resolution hyperspectral Raman imaging for these bands showed the distribution of disulfide bridges and tryptophan at sub-micrometer scale, which correlated with the location of insulin and glucagon as revealed by conventional immunohistochemistry. As a measure for this correlation, quantitative analysis was performed comparing the Raman images with the fluorescence images, resulting in Dice coefficients (ranging between 0 and 1) of 0.36 for insulin and 0.19 for glucagon. Although the use of separate microscope systems with different spatial resolution and the use of indirect Raman markers cause some image mismatch, our findings indicate that Raman bands for disulfide bridges and tryptophan can be used as distinctive markers for the label-free detection of insulin and glucagon in human islets of Langerhans.
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Affiliation(s)
- Janneke Hilderink
- Department of Developmental BioEngineering, University of Twente, Enschede, The Netherlands
| | - Cees Otto
- Department of Medical Cell Biophysics, University of Twente, Enschede, The Netherlands
| | - Cees Slump
- Department of Systems and Signals, University of Twente, Enschede, The Netherlands
| | - Aufried Lenferink
- Department of Medical Cell Biophysics, University of Twente, Enschede, The Netherlands
| | - Marten Engelse
- Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Eelco de Koning
- Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands
| | - Marcel Karperien
- Department of Developmental BioEngineering, University of Twente, Enschede, The Netherlands
| | - Aart van Apeldoorn
- Department of Developmental BioEngineering, University of Twente, Enschede, The Netherlands
- * E-mail:
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19
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Xie L, Zhu D, Kang Y, Liang T, He Y, Gaisano HY. Exocyst sec5 regulates exocytosis of newcomer insulin granules underlying biphasic insulin secretion. PLoS One 2013; 8:e67561. [PMID: 23844030 PMCID: PMC3699660 DOI: 10.1371/journal.pone.0067561] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Accepted: 05/20/2013] [Indexed: 11/24/2022] Open
Abstract
The exocyst complex subunit Sec5 is a downstream effector of RalA-GTPase which promotes RalA-exocyst interactions and exocyst assembly, serving to tether secretory granules to docking sites on the plasma membrane. We recently reported that RalA regulates biphasic insulin secretion in pancreatic islet β cells in part by tethering insulin secretory granules to Ca2+ channels to assist excitosome assembly. Here, we assessed β cell exocytosis by patch clamp membrane capacitance measurement and total internal reflection fluorescence microscopy to investigate the role of Sec5 in regulating insulin secretion. Sec5 is present in human and rodent islet β cells, localized to insulin granules. Sec5 protein depletion in rat INS-1 cells inhibited depolarization-induced release of primed insulin granules from both readily-releasable pool and mobilization from the reserve pool. This reduction in insulin exocytosis was attributed mainly to reduction in recruitment and exocytosis of newcomer insulin granules that undergo minimal docking time at the plasma membrane, but which encompassed a larger portion of biphasic glucose stimulated insulin secretion. Sec5 protein knockdown had little effect on predocked granules, unless vigorously stimulated by KCl depolarization. Taken together, newcomer insulin granules in β cells are more sensitive than predocked granules to Sec5 regulation.
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Affiliation(s)
- Li Xie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Dan Zhu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yu He
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Herbert Y. Gaisano
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- * E-mail:
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20
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Osman MA, Sarkar FH, Rodriguez-Boulan E. A molecular rheostat at the interface of cancer and diabetes. Biochim Biophys Acta Rev Cancer 2013; 1836:166-76. [PMID: 23639840 DOI: 10.1016/j.bbcan.2013.04.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 04/23/2013] [Indexed: 12/17/2022]
Abstract
Epidemiology studies revealed the connection between several types of cancer and type 2 diabetes (T2D) and suggested that T2D is both a symptom and a risk factor of pancreatic cancer. High level of circulating insulin (hyperinsulinemia) in obesity has been implicated in promoting aggressive types of cancers. Insulin resistance, a symptom of T2D, pressures pancreatic β-cells to increase insulin secretion, leading to hyperinsulinemia, which in turn leads to a gradual loss of functional β-cell mass, thus indicating a fine balance and interplay between β-cell function and mass. While the mechanisms of these connections are unclear, the mTORC1-Akt signaling pathway has been implicated in controlling β-cell function and mass, and in mediating the link of cancer and T2D. However, incomplete understating of how the pathway is regulated and how it integrates body metabolism has hindered its efficacy as a clinical target. The IQ motif containing GTPase activating protein 1 (IQGAP1)-Exocyst axis is a growth factor- and nutrient-sensor that couples cell growth and division. Here we discuss how IQGAP1-Exocyst, through differential interactions with Rho-type of small guanosine triphosphatases (GTPases), acts as a rheostat that modulates the mTORC1-Akt and MAPK signals, and integrates β-cell function and mass with insulin signaling, thus providing a molecular mechanism for cancer initiation in diabetes. Delineating this regulatory pathway may have the potential of contributing to optimizing the efficacy and selectivity of future therapies for cancer and diabetes.
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Affiliation(s)
- Mahasin A Osman
- Warren Alpert Medical School, Division of Biology and Medicine, Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, RI 02912, USA.
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21
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Fendrych M, Synek L, Pecenková T, Drdová EJ, Sekeres J, de Rycke R, Nowack MK, Zársky V. Visualization of the exocyst complex dynamics at the plasma membrane of Arabidopsis thaliana. Mol Biol Cell 2013; 24:510-20. [PMID: 23283982 PMCID: PMC3571873 DOI: 10.1091/mbc.e12-06-0492] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The exocyst complex localizes to distinct foci at the plasma membrane of Arabidopsis thaliana cells. Their localization at the plasma membrane is insensitive to BFA treatment but is decreased in an exocyst-subunit mutant. In turn, exocyst-subunit mutants show decreased exocytosis. The exocyst complex, an effector of Rho and Rab GTPases, is believed to function as an exocytotic vesicle tether at the plasma membrane before soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex formation. Exocyst subunits localize to secretory-active regions of the plasma membrane, exemplified by the outer domain of Arabidopsis root epidermal cells. Using variable-angle epifluorescence microscopy, we visualized the dynamics of exocyst subunits at this domain. The subunits colocalized in defined foci at the plasma membrane, distinct from endocytic sites. Exocyst foci were independent of cytoskeleton, although prolonged actin disruption led to changes in exocyst localization. Exocyst foci partially overlapped with vesicles visualized by VAMP721 v-SNARE, but the majority of the foci represent sites without vesicles, as indicated by electron microscopy and drug treatments, supporting the concept of the exocyst functioning as a dynamic particle. We observed a decrease of SEC6–green fluorescent protein foci in an exo70A1 exocyst mutant. Finally, we documented decreased VAMP721 trafficking to the plasma membrane in exo70A1 and exo84b mutants. Our data support the concept that the exocyst-complex subunits dynamically dock and undock at the plasma membrane to create sites primed for vesicle tethering.
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Affiliation(s)
- Matyás Fendrych
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Prague 6, Czech Republic.
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22
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Brozzi F, Lajus S, Diraison F, Rajatileka S, Hayward K, Regazzi R, Molnár E, Váradi A. MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway. Mol Biol Cell 2012; 23:4444-55. [PMID: 22993210 PMCID: PMC3496617 DOI: 10.1091/mbc.e12-05-0369] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Myosin- and Rab-interacting protein is not a classic receptor for MyoVa on large, dense-core secretory granules (SGs), but it aids in PKA-dependent phosphorylation of MyoVa-associated proteins on SGs in endocrine and neuroendocrine cells. Myosin- and Rab-interacting protein (MyRIP), which belongs to the protein kinase A (PKA)–anchoring family, is implicated in hormone secretion. However, its mechanism of action is not fully elucidated. Here we investigate the role of MyRIP in myosin Va (MyoVa)-dependent secretory granule (SG) transport and secretion in pancreatic beta cells. These cells solely express the brain isoform of MyoVa (BR-MyoVa), which is a key motor protein in SG transport. In vitro pull-down, coimmunoprecipitation, and colocalization studies revealed that MyRIP does not interact with BR-MyoVa in glucose-stimulated pancreatic beta cells, suggesting that, contrary to previous notions, MyRIP does not link this motor protein to SGs. Glucose-stimulated insulin secretion is augmented by incretin hormones, which increase cAMP levels and leads to MyRIP phosphorylation, its interaction with BR-MyoVa, and phosphorylation of the BR-MyoVa receptor rabphilin-3A (Rph-3A). Rph-3A phosphorylation on Ser-234 was inhibited by small interfering RNA knockdown of MyRIP, which also reduced cAMP-mediated hormone secretion. Demonstrating the importance of this phosphorylation, nonphosphorylatable and phosphomimic Rph-3A mutants significantly altered hormone release when PKA was activated. These data suggest that MyRIP only forms a functional protein complex with BR-MyoVa on SGs when cAMP is elevated and under this condition facilitates phosphorylation of SG-associated proteins, which in turn can enhance secretion.
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Affiliation(s)
- Flora Brozzi
- Centre for Research in Biomedicine, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom
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23
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Imai A, Yoshie S, Haga-Tsujimura M, Nashida T, Shimomura H. Exocyst subunits are involved in isoproterenol-induced amylase release from rat parotid acinar cells. Eur J Oral Sci 2012; 120:123-31. [PMID: 22409218 DOI: 10.1111/j.1600-0722.2012.00952.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Exocytosis of secretory granules in parotid acinar cells requires multiple events: tethering, docking, priming, and fusion with a luminal plasma membrane. The exocyst complex, which is composed of eight subunits (Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84) that are conserved in yeast and mammalian cells, is thought to participate in the exocytotic pathway. However, to date, no exocyst subunit has been identified in salivary glands. In the present study, we investigated the expression and function of exocyst subunits in rat parotid acinar cells. The expression of mRNA for all eight exocyst subunits was detected in parotid acinar cells by RT-PCR, and Sec6 and Sec8 proteins were localized on the luminal plasma membrane. Sec6 interacted with Sec8 after 5 min of stimulation with isoproterenol. In addition, antibodies to-Sec6 and Sec8 inhibited isoproterenol-induced amylase release from streptolysin O-permeabilized parotid acinar cells. These results suggest that an exocyst complex of eight subunits is required for amylase release from parotid acinar cells.
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Affiliation(s)
- Akane Imai
- Department of Biochemistry, School of Life Dentistry at Niigata, The Nippon Dental University, Chuo-ku, Niigata, Japan.
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24
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Liu J, Guo W. The exocyst complex in exocytosis and cell migration. PROTOPLASMA 2012; 249:587-97. [PMID: 21997494 DOI: 10.1007/s00709-011-0330-1] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2011] [Accepted: 09/28/2011] [Indexed: 05/08/2023]
Abstract
Exocytosis is a fundamental membrane trafficking event in eukaryotic cells in which membrane proteins or lipids are incorporated into the plasma membrane and vesicle contents are secreted to the exterior of the cell. The exocyst, an evolutionarily conserved octameric protein complex, plays a crucial role in the targeting of secretory vesicles to the plasma membrane during exocytosis. The exocyst has been shown to be involved in diverse cellular processes requiring polarized exocytosis such as yeast budding, epithelial polarity establishment, and neurite outgrowth. Recently, the exocyst has also been implicated in cell migration through mechanisms independent of its role in exocytosis. In this review, we will first summarize our knowledge on the exocyst complex at a molecular and structural level. Then, we will discuss the specific functions of the exocyst in exocytosis in various cell types. Finally, we will review the emerging roles of the exocyst during cell migration and tumor cell invasion.
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Affiliation(s)
- Jianglan Liu
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA
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25
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Myrip couples the capture of secretory granules by the actin-rich cell cortex and their attachment to the plasma membrane. J Neurosci 2012; 32:2564-77. [PMID: 22396429 DOI: 10.1523/jneurosci.2724-11.2012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Exocytosis of secretory granules (SGs) requires their delivery to the actin-rich cell cortex followed by their attachment to the plasma membrane (PM). How these reactions are executed and coordinated is still unclear. Myrip, which is also known as Slac-2c, binds to the SG-associated GTPase Rab27 and is thought to promote the delivery of SGs to the PM by recruiting the molecular motor myosin Va. Myrip also interacts with actin and the exocyst complex, suggesting that it may exert multiple roles in the secretory process. By combining total internal reflection fluorescence microscopy, single-particle tracking, a photoconversion-based assay, and mathematical modeling, we show that, in human enterochromaffin cells, Myrip (1) inhibits a class of SG motion characterized by fast and directed movement, suggesting that it facilitates the dissociation of SGs from microtubules; (2) enhances their motion toward the PM and the probability of SG attachment to the PM; and (3) increases the characteristic time of immobilization at the PM, indicating that it is a component of the molecular machinery that tether SGs to the PM. Remarkably, while the first two effects of Myrip depend on its ability to recruit myosin Va on SGs, the third is myosin Va independent but relies on the C-terminal domain of Myrip. We conclude that Myrip couples the retention of SGs in the cell cortex, their transport to the PM, and their attachment to the PM, and thus promotes secretion. These three steps of the secretory process are thus intimately coordinated.
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Essid M, Gopaldass N, Yoshida K, Merrifield C, Soldati T. Rab8a regulates the exocyst-mediated kiss-and-run discharge of the Dictyostelium contractile vacuole. Mol Biol Cell 2012; 23:1267-82. [PMID: 22323285 PMCID: PMC3315810 DOI: 10.1091/mbc.e11-06-0576] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
A molecular dissection of contractile vacuole (CV) discharge shows that Rab8a is recruited to the CV a few seconds before the exocyst. Together they tether it to the plasma membrane and commit it to fusion. GTP hydrolysis is necessary for vacuole detethering, a process in which LvsA, a protein of the Chédiak–Higashi family, plays a crucial role. Water expulsion by the contractile vacuole (CV) in Dictyostelium is carried out by a giant kiss-and-run focal exocytic event during which the two membranes are only transiently connected but do not completely merge. We present a molecular dissection of the GTPase Rab8a and the exocyst complex in tethering of the contractile vacuole to the plasma membrane, fusion, and final detachment. Right before discharge, the contractile vacuole bladder sequentially recruits Drainin, a Rab11a effector, Rab8a, the exocyst complex, and LvsA, a protein of the Chédiak–Higashi family. Rab8a recruitment precedes the nucleotide-dependent arrival of the exocyst to the bladder by a few seconds. A dominant-negative mutant of Rab8a strongly binds to the exocyst and prevents recruitment to the bladder, suggesting that a Rab8a guanine nucleotide exchange factor activity is associated with the complex. Absence of Drainin leads to overtethering and blocks fusion, whereas expression of constitutively active Rab8a allows fusion but blocks vacuole detachment from the plasma membrane, inducing complete fragmentation of tethered vacuoles. An indistinguishable phenotype is generated in cells lacking LvsA, implicating this protein in postfusion detethering. Of interest, overexpression of a constitutively active Rab8a mutant reverses the lvsA-null CV phenotype.
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Affiliation(s)
- Miriam Essid
- Départment de Biochimie, Faculté des Sciences, Université de Genève, Geneva, Switzerland
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27
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Vázquez-Martínez R, Díaz-Ruiz A, Almabouada F, Rabanal-Ruiz Y, Gracia-Navarro F, Malagón MM. Revisiting the regulated secretory pathway: from frogs to human. Gen Comp Endocrinol 2012; 175:1-9. [PMID: 21907200 DOI: 10.1016/j.ygcen.2011.08.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 08/16/2011] [Accepted: 08/20/2011] [Indexed: 01/01/2023]
Abstract
The regulated secretory pathway is a hallmark of endocrine and neuroendocrine cells. This process comprises different sequential steps, including ER-associated protein synthesis, ER-to-Golgi protein transport, Golgi-associated posttranslational modification, sorting and packing of secretory proteins into carrier granules, cytoskeleton-based granule transport towards the plasma membrane and tethering, docking and fusion of granules with specialized releasing zones in the plasma membrane. Each one of these steps is tightly regulated by a large number of factors that function in a spatially and temporarily coordinated fashion. During the past three decades, much effort has been devoted to characterize the precise role of the yet-known proteins participating in the different steps of this process and to identify new regulatory factors in order to obtain a unifying picture of the secretory pathway. In spite of this and given the enormous complexity of the process, certain steps are not fully understood yet and many players remain to be identified. In this review, we offer a summary of the current knowledge on the main molecular mechanisms that govern and ensure the correct release of secretory proteins. In addition, we have integrated the advance on the field made possible by studies carried out in non-mammalian vertebrates, which, although not very numerous, have substantially contributed to acquire a mechanistic understanding of the regulated secretory pathway.
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Affiliation(s)
- Rafael Vázquez-Martínez
- Department of Cell Biology, Physiology and Immunology, Instituto Maimónides de Investigación Biomédica, University of Córdoba, 14014-Córdoba, Spain.
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28
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Chen LC, Chen CC, Liang Y, Tsang NM, Chang YS, Hsueh C. A novel role for TNFAIP2: its correlation with invasion and metastasis in nasopharyngeal carcinoma. Mod Pathol 2011; 24:175-84. [PMID: 21057457 DOI: 10.1038/modpathol.2010.193] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Tumor necrosis factor alpha (TNFα) is an inflammatory cytokine that is present in the microenvironment of many tumors and is known to promote tumor progression. To examine how TNFα modulates the progression and metastasis of nasopharyngeal carcinoma, we used Affymetrix chips to identify TNFα-inducible genes that are dysregulated in this tumor. Elevated expression of TNFAIP2, which encodes TNFα-inducible protein 2 and not previously known to be associated with cancer, was found and confirmed by quantitative RT-PCR of TNFAIP2 expression in nasopharyngeal carcinoma and adjacent normal tissues. Immunohistochemical analysis showed that the TNFAIP2 protein was highly expressed in tumor cells. Analysis of 95 nasopharyngeal carcinoma biopsy specimens revealed that high TNFAIP2 expression was significantly correlated with high-level intratumoral microvessel density (P=0.005) and low distant metastasis-free survival (P=0.001). A multivariate analysis further confirmed that TNFAIP2 was an independent prognostic factor for nasopharyngeal carcinoma (P=0.002). In vitro, TNFα treatment of nasopharyngeal carcinoma HK1 cells was found to induce TNFAIP2 expression, and siRNA-based knockdown of TNFAIP2 dramatically reduced the migration and invasion of nasopharyngeal carcinoma HK1 cells. These results collectively suggest for the first time that TNFAIP2 is a cell migration-promoting protein and its expression predicts distant metastasis. Our data suggest that TNFAIP2 may serve as an independent prognostic indicator for nasopharyngeal carcinoma.
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Affiliation(s)
- Lih-Chyang Chen
- Chang Gung Molecular Medicine Research Center, Chang Gung University, Taoyuan, Taiwan
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29
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Lopez JP, Turner JR, Philipson LH. Glucose-induced ERM protein activation and translocation regulates insulin secretion. Am J Physiol Endocrinol Metab 2010; 299:E772-85. [PMID: 20739507 PMCID: PMC2980361 DOI: 10.1152/ajpendo.00199.2010] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A key step in regulating insulin secretion is insulin granule trafficking to the plasma membrane. Using live-cell time-lapse confocal microscopy, we observed a dynamic association of insulin granules with filamentous actin and PIP2-enriched structures. We found that the scaffolding protein family ERM, comprising ezrin, radixin, and moesin, are expressed in β-cells and target both F-actin and PIP2. Furthermore, ERM proteins are activated via phosphorylation in a glucose- and calcium-dependent manner. This activation leads to a translocation of the ERM proteins to sites on the cell periphery enriched in insulin granules, the exocyst complex docking protein Exo70, and lipid rafts. ERM scaffolding proteins also participate in insulin granule trafficking and docking to the plasma membrane. Overexpression of a truncated dominant-negative ezrin construct that lacks the ERM F-actin binding domain leads to a reduction in insulin granules near the plasma membrane and impaired secretion. Conversely, overexpression of a constitutively active ezrin results in more granules near the cell periphery and an enhancement of insulin secretion. Diabetic mouse islets contain less active ERM, suggestive of a novel mechanism whereby impairment of insulin granule trafficking to the membrane through a complex containing F-actin, PIP2, Exo70, and ERM proteins contributes to defective insulin secretion.
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Affiliation(s)
- James P Lopez
- Dept. of Medicine, The Univ. of Chicago, IL 60637, USA
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Jurczyk A, Pino SC, O'Sullivan-Murphy B, Addorio M, Lidstone EA, Diiorio P, Lipson KL, Standley C, Fogarty K, Lifshitz L, Urano F, Mordes JP, Greiner DL, Rossini AA, Bortell R. A novel role for the centrosomal protein, pericentrin, in regulation of insulin secretory vesicle docking in mouse pancreatic beta-cells. PLoS One 2010; 5:e11812. [PMID: 20676397 PMCID: PMC2910730 DOI: 10.1371/journal.pone.0011812] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Accepted: 06/24/2010] [Indexed: 01/02/2023] Open
Abstract
The centrosome is important for microtubule organization and cell cycle progression in animal cells. Recently, mutations in the centrosomal protein, pericentrin, have been linked to human microcephalic osteodysplastic primordial dwarfism (MOPD II), a rare genetic disease characterized by severe growth retardation and early onset of type 2 diabetes among other clinical manifestations. While the link between centrosomal and cell cycle defects may account for growth deficiencies, the mechanism linking pericentrin mutations with dysregulated glucose homeostasis and pre-pubertal onset of diabetes is unknown. In this report we observed abundant expression of pericentrin in quiescent pancreatic β-cells of normal animals which led us to hypothesize that pericentrin may have a critical function in β-cells distinct from its known role in regulating cell cycle progression. In addition to the typical centrosome localization, pericentrin was also enriched with secretory vesicles in the cytoplasm. Pericentrin overexpression in β-cells resulted in aggregation of insulin-containing secretory vesicles with cytoplasmic, but not centrosomal, pericentriolar material and an increase in total levels of intracellular insulin. RNAi- mediated silencing of pericentrin in secretory β-cells caused dysregulated secretory vesicle hypersecretion of insulin into the media. Together, these data suggest that pericentrin may regulate the intracellular distribution and secretion of insulin. Mice transplanted with pericentrin-depleted islets exhibited abnormal fasting hypoglycemia and inability to regulate blood glucose normally during a glucose challenge, which is consistent with our in vitro data. This previously unrecognized function for a centrosomal protein to mediate vesicle docking in secretory endocrine cells emphasizes the adaptability of these scaffolding proteins to regulate diverse cellular processes and identifies a novel target for modulating regulated protein secretion in disorders such as diabetes.
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Affiliation(s)
- Agata Jurczyk
- Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
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31
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Ding F, Yang JC, Yuan F, Wang BS. Progress in mechanism of salt excretion in recretohalopytes. ACTA ACUST UNITED AC 2010. [DOI: 10.1007/s11515-010-0032-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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32
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Sato M, Mori Y, Matsui T, Aoki R, Oya M, Yanagihara Y, Fukuda M, Tsuboi T. Role of the polybasic sequence in the Doc2alpha C2B domain in dense-core vesicle exocytosis in PC12 cells. J Neurochem 2010; 114:171-81. [PMID: 20403080 DOI: 10.1111/j.1471-4159.2010.06739.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The double C2 (Doc2) family is characterized by an N-terminal Munc13-1-interacting domain and C-terminal tandem C2 domains, and it comprises three isoforms, Doc2alpha, Doc2beta, and Doc2gamma, in humans and mice. Doc2alpha, the best-characterized, brain-specific isoform, exhibits Ca(2+)-dependent phospholipid-binding activity through its C2A domain, and the Ca(2+)-binding activity is thought to be important for the regulation of Ca(2+)-dependent exocytosis. In contrast to the C2A domain, however, nothing is known about the physiological functions of the C2B domain in regulated exocytosis. In this study, we demonstrated by a mutation analysis that the polybasic sequence in the C2B domain of Doc2alpha (306 KKSKHKTCVKKK 317) is required for binding of syntaxin-1a/synaptosome-associated protein of 25 kDa (SNAP-25) heterodimer. We also investigated the effect of Lys-to-Gln (named KQ) mutations in the polybasic sequence of the C2B domain on vesicle dynamics by total internal reflection fluorescence microscopy in PC12 cells. A Doc2alpha(KQ) mutant, which lacks binding activity toward syntaxin-1a/SNAP-25 heterodimer, significantly decreased the number of plasma membrane-docked vesicles before stimulation and strongly inhibited high-KCl-induced exocytosis from the plasma membrane-docked vesicles. These results indicate that the polybasic sequence in the C2B domain functions as a binding site for syntaxin-1a/SNAP-25 heterodimer and controls the number of 'readily releasable' vesicles in neuroendocrine cells.
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Affiliation(s)
- Mai Sato
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Meguro, Tokyo, Japan
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Abstract
The exocyst is an octameric vesicle tethering complex that functions upstream of SNARE mediated exocytotic vesicle fusion with the plasma membrane. All proteins in the complex have been conserved during evolution, and genes that encode the exocyst subunits are present in the genomes of all plants investigated to date. Although the plant exocyst has not been studied in great detail, it is likely that the basic function of the exocyst in vesicle tethering is conserved. Nevertheless, genomic and genetic studies suggest that the exocyst complex in plants may have more diversified roles than that in budding yeast. In this review, we compare the knowledge about the exocyst in plant cells to the well-studied exocyst in budding yeast, in order to explore similarities and differences in expression and function between these organisms, both of which have walled cells.
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Affiliation(s)
- Ying Zhang
- Laboratory of Plant Cell Biology, Wageningen University, Wageningen, The Netherlands
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Burchfield JG, Lopez JA, Mele K, Vallotton P, Hughes WE. Exocytotic vesicle behaviour assessed by total internal reflection fluorescence microscopy. Traffic 2010; 11:429-39. [PMID: 20070611 DOI: 10.1111/j.1600-0854.2010.01039.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The regulated trafficking or exocytosis of cargo-containing vesicles to the cell surface is fundamental to all cells. By coupling the technology of fluorescently tagged fusion proteins with total internal reflection fluorescence microscopy (TIRFM), it is possible to achieve the high spatio-temporal resolution required to study the dynamics of sub-plasma membrane vesicle trafficking and exocytosis. TIRFM has been used in a number of cell types to visualize and dissect the various steps of exocytosis revealing how molecules identified via genetic and/or biochemical approaches are involved in the regulation of this process. Here, we summarize the contribution of TIRFM to our understanding of the mechanism of exocytosis and discuss the novel methods of analysis that are required to exploit the large volumes of data that can be produced using this technique.
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Affiliation(s)
- James G Burchfield
- The Garvan Institute of Medical Research, 384 Victoria Street, Sydney, New South Wales 2010, Australia
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The GTPase RalA regulates different steps of the secretory process in pancreatic beta-cells. PLoS One 2009; 4:e7770. [PMID: 19890390 PMCID: PMC2766836 DOI: 10.1371/journal.pone.0007770] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Accepted: 10/11/2009] [Indexed: 12/25/2022] Open
Abstract
Background RalA and RalB are multifuntional GTPases involved in a variety of cellular processes including proliferation, oncogenic transformation and membrane trafficking. Here we investigated the mechanisms leading to activation of Ral proteins in pancreatic β-cells and analyzed the impact on different steps of the insulin-secretory process. Methodology/Principal Findings We found that RalA is the predominant isoform expressed in pancreatic islets and insulin-secreting cell lines. Silencing of this GTPase in INS-1E cells by RNA interference led to a decrease in secretagogue-induced insulin release. Real-time measurements by fluorescence resonance energy transfer revealed that RalA activation in response to secretagogues occurs within 3–5 min and reaches a plateau after 10–15 min. The activation of the GTPase is triggered by increases in intracellular Ca2+ and cAMP and is prevented by the L-type voltage-gated Ca2+ channel blocker Nifedipine and by the protein kinase A inhibitor H89. Defective insulin release in cells lacking RalA is associated with a decrease in the secretory granules docked at the plasma membrane detected by Total Internal Reflection Fluorescence microscopy and with a strong impairment in Phospholipase D1 activation in response to secretagogues. RalA was found to be activated by RalGDS and to be severely hampered upon silencing of this GDP/GTP exchange factor. Accordingly, INS-1E cells lacking RalGDS displayed a reduction in hormone secretion induced by secretagogues and in the number of insulin-containing granules docked at the plasma membrane. Conclusions/Significance Taken together, our data indicate that RalA activation elicited by the exchange factor RalGDS in response to a rise in intracellular Ca2+ and cAMP controls hormone release from pancreatic β-cell by coordinating the execution of different events in the secretory pathway.
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Sugawara K, Shibasaki T, Mizoguchi A, Saito T, Seino S. Rab11 and its effector Rip11 participate in regulation of insulin granule exocytosis. Genes Cells 2009; 14:445-56. [PMID: 19335615 DOI: 10.1111/j.1365-2443.2009.01285.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rab GTPases and their effectors play important roles in membrane trafficking between cellular compartments in eukaryotic cells. In the present study, we examined the roles of Rab11B and its effectors in insulin secretion in pancreatic beta-cells. In the mouse insulin-secreting cell line MIN6, Rab11 was co-localized with insulin-containing granules, and over-expression of the GTP- or the GDP-bound form of Rab11B significantly inhibited regulated secretion, indicating involvement of Rab11B in regulated insulin secretion. To determine the downstream signal of Rab11-mediated insulin secretion, we examined the effects of various Rab11-interacting proteins on insulin secretion, and found that Rip11 is involved in cAMP-potentiated insulin secretion but not in glucose-induced insulin secretion. Analyses by immunocytochemistry and subcellular fractionation revealed Rip11 to be co-localized with insulin granules. The inhibitory effect of the Rip11 mutant was not altered in MIN6 cells lacking Epac2, which mediates protein kinase A (PKA)-independent potentiation of insulin secretion, compared with wild-type MIN6 cells. In addition, Rip11 was found to be phosphorylated by PKA in MIN6 cells. The present study shows that both Rab11 and its effector Rip11 participate in insulin granule exocytosis and that Rip11, as a substrate of PKA, regulates the potentiation of exocytosis by cAMP in pancreatic beta-cells.
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Affiliation(s)
- Kenji Sugawara
- Division of Cellular and Molecular Medicine, Department of Physiology and Cell Biology, Kobe University Graduate School of Medcine, Kobe 650-0017, Japan
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Saito T, Shibasaki T, Seino S. Involvement of Exoc3l, a protein structurally related to the exocyst subunit Sec6, in insulin secretion. ACTA ACUST UNITED AC 2008; 29:85-91. [PMID: 18480549 DOI: 10.2220/biomedres.29.85] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The exocyst is an octameric complex involved in docking or tethering of secretory vesicles to fusion sites of the plasma membrane. Sec6 is the core subunit of the exocyst complex. Here we identify an isoform of Sec6, deposited as Exocyst complex component 3-like (Exoc3l) in the database, by in silico screening using rat Sec6 as a probe. The amino acid sequence of Exoc3l has 31% identity and 53% similarity with that of Sec6. RT-PCR analysis reveals that Exoc3l is expressed in insulin-secreting MIN6 cells as well as in various tissues including pancreatic islets and brain. In co-immunoprecipitation experiments, Exoc3l was found to interact with Sec5, Sec8, and Sec10, all of which are binding partners of Sec6 in the exocyst complex. Furthermore, overexpression of a deletion mutant of Exoc3l in MIN6 cells suppressed glucose-stimulated secretion. These results suggest that Exoc3l is involved in regulated exocytosis of insulin granules.
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Affiliation(s)
- Tetsuya Saito
- Division of Cellular and Molecular Medicine, Kobe University Graduate School of Medicine, Kobe, Japan
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Review: Molecular mechanism of docking of dense-core vesicles to the plasma membrane in neuroendocrine cells. Med Mol Morphol 2008; 41:68-75. [DOI: 10.1007/s00795-008-0400-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Accepted: 03/04/2008] [Indexed: 02/06/2023]
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Laramie JM, Wilk JB, Williamson SL, Nagle MW, Latourelle JC, Tobin JE, Province MA, Borecki IB, Myers RH. Polymorphisms near EXOC4 and LRGUK on chromosome 7q32 are associated with Type 2 Diabetes and fasting glucose; the NHLBI Family Heart Study. BMC MEDICAL GENETICS 2008; 9:46. [PMID: 18498660 PMCID: PMC2409301 DOI: 10.1186/1471-2350-9-46] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Accepted: 05/22/2008] [Indexed: 12/04/2022]
Abstract
Background The chromosome 7q32 region is linked to metabolic syndrome and obesity related traits in the Family Heart Study. As part of a fine mapping study of the region, we evaluated the relationship of polymorphisms to fasting glucose levels and Type 2 diabetes. Methods Thirty-nine HapMap defined tag SNPs in a 1.08 Mb region and a novel deletion polymorphism were genotyped in 2,603 participants of the NHLBI Family Heart Study (FHS). Regression modeling, adjusting for BMI, age, sex, smoking and the TCF7L2 polymorphism, was used to evaluate the association of these polymorphisms with T2D and fasting glucoses levels. Results The deletion polymorphism confers a protective effect for T2D, with homozygous deletion carriers having a 53% reduced risk compared to non-deleted carriers. Among non-diabetics, the deletion was significantly associated with lower fasting glucose levels in men (p = 0.038) but not women (p = 0.118). In addition, seven SNPs near the deletion were significantly associated (p < 0.01) to diabetes. Conclusion Chromosome 7q32 contains both SNPs and a deletion that were associated to T2D. Although the deletion region contains several islands of strongly conserved sequence, it is not known to contain a transcribed gene. The closest nearby gene, EXOC4, is involved in insulin-stimulated glucose transport and may be a candidate for this association. Further work is needed to determine if the deletion represents a functional variant or may be in linkage disequilibrium with a functional mutation influencing EXOC4 or another nearby gene.
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Affiliation(s)
- Jason M Laramie
- Department of Neurology, Boston University School of Medicine, Boston, MA, USA.
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40
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Lopez JA, Kwan EP, Xie L, He Y, James DE, Gaisano HY. The RalA GTPase is a central regulator of insulin exocytosis from pancreatic islet beta cells. J Biol Chem 2008; 283:17939-45. [PMID: 18426794 DOI: 10.1074/jbc.m800321200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
RalA is a small GTPase that is thought to facilitate exocytosis through its direct interaction with the mammalian exocyst complex. In this study, we report an essential role for RalA in regulated insulin secretion from pancreatic beta cells. We employed lentiviral-mediated delivery of RalA short hairpin RNAs to deplete endogenous RalA protein in mouse pancreatic islets and INS-1 beta cells. Perifusion of mouse islets depleted of RalA protein exhibited inhibition of both first and second phases of glucose-stimulated insulin secretion. Consistently, INS-1 cells depleted of RalA caused a severe inhibition of depolarization-induced insulin exocytosis determined by membrane capacitance, including a reduction in the size of the ready-releasable pool of insulin granules and a reduction in the subsequent mobilization and exocytosis of the reserve pool of granules. Collectively, these data suggest that RalA is a critical component in biphasic insulin release from pancreatic beta cells.
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Affiliation(s)
- Jamie A Lopez
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, NSW, Australia
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41
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Konopka CA, Bednarek SY. Variable-angle epifluorescence microscopy: a new way to look at protein dynamics in the plant cell cortex. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2008; 53:186-96. [PMID: 17931350 DOI: 10.1111/j.1365-313x.2007.03306.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Live-cell microscopy imaging of fluorescent-tagged fusion proteins is an essential tool for cell biologists. Total internal reflection fluorescence microscopy (TIRFM) has joined confocal microscopy as a complementary system for the imaging of cell surface protein dynamics in mammalian and yeast systems because of its high temporal and spatial resolution. Here we present an alternative to TIRFM, termed variable-angle epifluorescence microscopy (VAEM), for the visualization of protein dynamics at or near the plasma membrane of plant epidermal cells and root hairs in whole, intact seedlings that provides high-signal, low-background and near real-time imaging. VAEM uses highly oblique subcritical incident angles to decrease background fluorophore excitation. We discuss the utilities and advantages of VAEM for imaging of fluorescent fusion-tagged marker proteins in studying cortical cytoskeletal and membrane proteins. We believe that the application of VAEM will be an invaluable imaging tool for plant cell biologists.
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Affiliation(s)
- Catherine A Konopka
- Program in Cell and Molecular Biology and Department of Biochemistry, University of Wisconsin - Madison, 433 Babcock Drive, Madison, WI 53706, USA
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Bao Y, Lopez JA, James DE, Hunziker W. Snapin Interacts with the Exo70 Subunit of the Exocyst and Modulates GLUT4 Trafficking. J Biol Chem 2008; 283:324-331. [DOI: 10.1074/jbc.m706873200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Goehring AS, Pedroja BS, Hinke SA, Langeberg LK, Scott JD. MyRIP anchors protein kinase A to the exocyst complex. J Biol Chem 2007; 282:33155-67. [PMID: 17827149 PMCID: PMC3508720 DOI: 10.1074/jbc.m705167200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The movement of signal transduction enzymes in and out of multi-protein complexes coordinates the spatial and temporal resolution of cellular events. Anchoring and scaffolding proteins are key to this process because they sequester protein kinases and phosphatases with a subset of their preferred substrates. The protein kinase A-anchoring family of proteins (AKAPs), which target the cAMP-dependent protein kinase (PKA) and other enzymes to defined subcellular microenvironments, represent a well studied group of these signal-organizing molecules. In this report we demonstrate that the Rab27a GTPase effector protein MyRIP is a member of the AKAP family. The zebrafish homolog of MyRIP (Ze-AKAP2) was initially detected in a two-hybrid screen for AKAPs. A combination of biochemical, cell-based, and immunofluorescence approaches demonstrate that the mouse MyRIP ortholog targets the type II PKA holoenzyme via an atypical mechanism to a specific perinuclear region of insulin-secreting cells. Similar approaches show that MyRIP interacts with the Sec6 and Sec8 components of the exocyst complex, an evolutionarily conserved protein unit that controls protein trafficking and exocytosis. These data indicate that MyRIP functions as a scaffolding protein that links PKA to components of the exocytosis machinery.
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Affiliation(s)
- April S. Goehring
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Benjamin S. Pedroja
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Simon A. Hinke
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Lorene K. Langeberg
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - John D. Scott
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
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Kawato M, Shirakawa R, Kondo H, Higashi T, Ikeda T, Okawa K, Fukai S, Nureki O, Kita T, Horiuchi H. Regulation of platelet dense granule secretion by the Ral GTPase-exocyst pathway. J Biol Chem 2007; 283:166-174. [PMID: 17938170 DOI: 10.1074/jbc.m705340200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Non-hydrolyzable GTP analogues, such as guanosine 5'-(beta, gamma-imido)triphosphate (GppNHp), induce granule secretion from permeabilized platelets in the absence of increased intracellular Ca(2+). Here, we show that the GppNHp-induced dense granule secretion from permeabilized platelets occurred concomitantly with the activation of small GTPase Ral. This secretion was inhibited by the addition of GTP-Ral-binding domain (RBD) of Sec5, which is a component of the exocyst complex known to function as a tethering factor at the plasma membrane for vesicles. We generated an antibody against Sec5-RBD, which abolished the interaction between GTP-Ral and the exocyst complex in vitro. The addition of this antibody inhibited the GppNHp-induced secretion. These data indicate that Ral mediates the GppNHp-induced dense granule secretion from permeabilized platelets through interaction with its effector, the exocyst complex. Furthermore, GppNHp enhanced the Ca(2+) sensitivity of dense granule secretion from permeabilized platelets, and this enhancement was inhibited by Sec5-RBD. In intact platelets, the association between Ral and the exocyst complex was induced by thrombin stimulation with a time course similar to that of dense granule secretion and Ral activation. Taken together, our results suggest that the Ral-exocyst pathway participates in the regulation of platelet dense granule secretion by enhancing the Ca(2+) sensitivity of the secretion.
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Affiliation(s)
- Mitsunori Kawato
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Ryutaro Shirakawa
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Hirokazu Kondo
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Tomohito Higashi
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Tomoyuki Ikeda
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Katsuya Okawa
- Frontier Technology Center, Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Shuya Fukai
- Department of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan; Life Science Division, Synchrotron Radiation Research Organization, University of Tokyo, Tokyo, 113-0032, Japan
| | - Osamu Nureki
- Department of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan
| | - Toru Kita
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Hisanori Horiuchi
- Department of Cardiovascular Medicine, Kyoto University, Kyoto, 606-8507, Japan.
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Liu J, Zuo X, Yue P, Guo W. Phosphatidylinositol 4,5-bisphosphate mediates the targeting of the exocyst to the plasma membrane for exocytosis in mammalian cells. Mol Biol Cell 2007; 18:4483-92. [PMID: 17761530 PMCID: PMC2043555 DOI: 10.1091/mbc.e07-05-0461] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The exocyst is an evolutionarily conserved octameric protein complex that tethers post-Golgi secretory vesicles at the plasma membrane for exocytosis. To elucidate the mechanism of vesicle tethering, it is important to understand how the exocyst physically associates with the plasma membrane (PM). In this study, we report that the mammalian exocyst subunit Exo70 associates with the PM through its direct interaction with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)). Furthermore, we have identified key conserved residues at the C-terminus of Exo70 that are crucial for the interaction of Exo70 with PI(4,5)P(2). Disrupting Exo70-PI(4,5)P(2) interaction abolished the membrane association of Exo70. We have also found that wild-type Exo70 but not the PI(4,5)P(2)-binding-deficient Exo70 mutant is capable of recruiting other exocyst components to the PM. Using the ts045 vesicular stomatitis virus glycoprotein trafficking assay, we demonstrate that Exo70-PI(4,5)P(2) interaction is critical for the docking and fusion of post-Golgi secretory vesicles, but not for their transport to the PM.
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Affiliation(s)
- Jianglan Liu
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018
| | - Xiaofeng Zuo
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018
| | - Peng Yue
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018
| | - Wei Guo
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018
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Takaya A, Kamio T, Masuda M, Mochizuki N, Sawa H, Sato M, Nagashima K, Mizutani A, Matsuno A, Kiyokawa E, Matsuda M. R-Ras regulates exocytosis by Rgl2/Rlf-mediated activation of RalA on endosomes. Mol Biol Cell 2007; 18:1850-60. [PMID: 17344481 PMCID: PMC1855010 DOI: 10.1091/mbc.e06-08-0765] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
R-Ras is a Ras-family small GTPase that regulates various cellular functions such as apoptosis and cell adhesion. Here, we demonstrate a role of R-Ras in exocytosis. By the use of specific anti-R-Ras antibody, we found that R-Ras was enriched on both early and recycling endosomes in a wide range of cell lines. Using a fluorescence resonance energy transfer-based probe for R-Ras activity, R-Ras activity was found to be higher on endosomes than on the plasma membrane. This high R-Ras activity on the endosomes correlated with the accumulation of an R-Ras effector, the Rgl2/Rlf guanine nucleotide exchange factor for RalA, and also with high RalA activity. The essential role played by R-Ras in inducing high levels of RalA activity on the endosomes was evidenced by the short hairpin RNA (shRNA)-mediated suppression of R-Ras and by the expression of R-Ras GAP. In agreement with the reported role of RalA in exocytosis, the shRNA of either R-Ras or RalA was found to suppress calcium-triggered exocytosis in PC12 pheochromocytoma cells. These data revealed that R-Ras activates RalA on endosomes and that it thereby positively regulates exocytosis.
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Affiliation(s)
- Akiyuki Takaya
- *Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Yamadaoka, Osaka 565-0871, Japan
- Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Takahiro Kamio
- *Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Yamadaoka, Osaka 565-0871, Japan
| | - Michitaka Masuda
- Department of Structural Analysis, National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
| | - Naoki Mochizuki
- Department of Structural Analysis, National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
| | - Hirofumi Sawa
- Laboratory of Molecular and Cellular Pathology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
| | - Mami Sato
- Laboratory of Molecular and Cellular Pathology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
| | - Kazuo Nagashima
- Laboratory of Molecular and Cellular Pathology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
| | - Akiko Mizutani
- Basic Medical Science and Molecular Medicine, Tokai University School of Medicine, Kanagawa 259-1193, Japan; and
| | - Akira Matsuno
- Department of Neurosurgery, Teikyo University Ichihara Hospital, Chiba 299-0111, Japan
| | - Etsuko Kiyokawa
- Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Michiyuki Matsuda
- *Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Yamadaoka, Osaka 565-0871, Japan
- Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
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47
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Wang S, Hsu SC. The molecular mechanisms of the mammalian exocyst complex in exocytosis. Biochem Soc Trans 2007; 34:687-90. [PMID: 17052175 DOI: 10.1042/bst0340687] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Exocytosis is a highly ordered vesicle trafficking pathway that targets proteins to the plasma membrane for membrane addition or secretion. Research over the years has discovered many proteins that participate at various stages in the mammalian exocytotic pathway. At the early stage of exocytosis, co-atomer proteins and their respective adaptors and GTPases have been shown to play a role in the sorting and incorporation of proteins into secretory vesicles. At the final stage of exocytosis, SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) and SNARE-associated proteins are believed to mediate the fusion of secretory vesicles at the plasma membrane. There are multiple events that may occur between the budding of secretory vesicles from the Golgi and the fusion of these vesicles at the plasma membrane. The most obvious and best-known event is the transport of secretory vesicles from Golgi to the vicinity of the plasma membrane via microtubules and their associated motors. At the vicinity of the plasma membrane, however, it is not clear how vesicles finally dock and fuse with the plasma membrane. Identification of proteins involved in these events should provide important insights into the mechanisms of this little known stage of the exocytotic pathway. Currently, a protein complex, known as the sec6/8 or the exocyst complex, has been implicated to play a role at this late stage of exocytosis.
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Affiliation(s)
- S Wang
- Department of Cell Biology and Neuroscience, Rutgers University, Nelson Biological Laboratories, 604 Allison Rd, D419, Piscataway, NJ 08854, USA
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48
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Li G, Han L, Chou TC, Fujita Y, Arunachalam L, Xu A, Wong A, Chiew SK, Wan Q, Wang L, Sugita S. RalA and RalB function as the critical GTP sensors for GTP-dependent exocytosis. J Neurosci 2007; 27:190-202. [PMID: 17202486 PMCID: PMC6672288 DOI: 10.1523/jneurosci.2537-06.2007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although it has been established that the activation of GTPases by non-hydrolyzable GTP stimulates neurotransmitter release from many different secretory cell types, the underlying mechanisms remain unclear. In the present study we aimed to elucidate the functional role(s) for endogenous Ras-like protein A (RalA) and RalB GTPases in GTP-dependent exocytosis. For this purpose stable neuroendocrine pheochromocytoma 12 (PC12) cell lines were generated in which the expressions of both RalA and RalB were strongly downregulated. In these double knock-down cells GTP-dependent exocytosis was reduced severely and was restored after the expression of RalA or RalB was reintroduced by transfection. In contrast, Ca2+-dependent exocytosis and the docking of dense core vesicles analyzed by electron microscopy remained unchanged in the double knock-down cells. Furthermore, the transfected RalA and RalB appeared to be localized primarily on the dense core vesicles in undifferentiated and nerve growth factor-differentiated PC12 cells. Our results indicate that endogenous RalA and RalB function specifically as GTP sensors for the GTP-dependent exocytosis of dense core vesicles, but they are not required for the general secretory pathways, including tethering of vesicles to the plasma membrane and Ca2+-dependent exocytosis.
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Affiliation(s)
- Gang Li
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Liping Han
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Ting-Chieh Chou
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Yoshihito Fujita
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
| | - Lakshmanan Arunachalam
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Ainan Xu
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
| | - Aaron Wong
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
| | - Soon-Kwang Chiew
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
| | - Qi Wan
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Li Wang
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
| | - Shuzo Sugita
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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49
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Abstract
The mechanisms by which insulin-containing dense core secretory vesicles approach and finally fuse with the plasma membrane are of considerable current interest: defects in these processes may be one of the contributing factors to Type 2 diabetes. In this review, we discuss the molecular mechanisms involved in vesicle trafficking within the pancreatic beta-cell and the mechanisms whereby these may be regulated. We then go on to describe recent evidence that suggests that vesicle fusion at the plasma membrane is a partly reversible process ("kiss and run" or "cavity recapture"). We propose that vesicles may participate in a exo-endocytotic cycle in which a proportion of those that have already undergone an interaction with the plasma membrane may exchange exocytotic machinery with maturing vesicles.
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Affiliation(s)
- Guy A Rutter
- Department of Biochemistry, School of Medical Sciences, University Walk University of Bristol, Bristol, United Kingdom.
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50
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Huet S, Karatekin E, Tran VS, Fanget I, Cribier S, Henry JP. Analysis of transient behavior in complex trajectories: application to secretory vesicle dynamics. Biophys J 2006; 91:3542-59. [PMID: 16891360 PMCID: PMC1614485 DOI: 10.1529/biophysj.105.080622] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Analysis of trajectories of dynamical biological objects, such as breeding ants or cell organelles, is essential to reveal the interactions they develop with their environments. Many previous works used a global characterization based on parameters calculated for entire trajectories. In cases where transient behavior was detected, this usually concerned only a particular type, such as confinement or directed motion. However, these approaches are not appropriate in situations in which the tracked objects may display many different types of transient motion. We have developed a method to exhaustively analyze different kinds of transient behavior that the tracked objects may exhibit. The method discriminates stalled periods, constrained and directed motions from random dynamics by evaluating the diffusion coefficient, the mean-square displacement curvature, and the trajectory asymmetry along individual trajectories. To detect transient motions of various durations, these parameters are calculated along trajectories using a rolling analysis window whose width is variable. The method was applied to the study of secretory vesicle dynamics in the subplasmalemmal region of human carcinoid BON cells. Analysis of transitions between transient motion periods, combined with plausible assumptions about the origin of each motion type, leads to a model of dynamical subplasmalemmal organization.
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Affiliation(s)
- Sébastien Huet
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, UPR 1929, Université Paris 7 Denis Diderot, Paris, F-75005, France
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