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Pulli K, Saarimäki-Vire J, Ahonen P, Liu X, Ibrahim H, Chandra V, Santambrogio A, Wang Y, Vaaralahti K, Iivonen AP, Känsäkoski J, Tommiska J, Kemkem Y, Varjosalo M, Vuoristo S, Andoniadou CL, Otonkoski T, Raivio T. A splice site variant in MADD affects hormone expression in pancreatic β cells and pituitary gonadotropes. JCI Insight 2024; 9:e167598. [PMID: 38775154 PMCID: PMC11141940 DOI: 10.1172/jci.insight.167598] [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: 06/27/2023] [Accepted: 04/12/2024] [Indexed: 06/02/2024] Open
Abstract
MAPK activating death domain (MADD) is a multifunctional protein regulating small GTPases RAB3 and RAB27, MAPK signaling, and cell survival. Polymorphisms in the MADD locus are associated with glycemic traits, but patients with biallelic variants in MADD manifest a complex syndrome affecting nervous, endocrine, exocrine, and hematological systems. We identified a homozygous splice site variant in MADD in 2 siblings with developmental delay, diabetes, congenital hypogonadotropic hypogonadism, and growth hormone deficiency. This variant led to skipping of exon 30 and in-frame deletion of 36 amino acids. To elucidate how this mutation causes pleiotropic endocrine phenotypes, we generated relevant cellular models with deletion of MADD exon 30 (dex30). We observed reduced numbers of β cells, decreased insulin content, and increased proinsulin-to-insulin ratio in dex30 human embryonic stem cell-derived pancreatic islets. Concordantly, dex30 led to decreased insulin expression in human β cell line EndoC-βH1. Furthermore, dex30 resulted in decreased luteinizing hormone expression in mouse pituitary gonadotrope cell line LβT2 but did not affect ontogeny of stem cell-derived GnRH neurons. Protein-protein interactions of wild-type and dex30 MADD revealed changes affecting multiple signaling pathways, while the GDP/GTP exchange activity of dex30 MADD remained intact. Our results suggest MADD-specific processes regulate hormone expression in pancreatic β cells and pituitary gonadotropes.
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Affiliation(s)
- Kristiina Pulli
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Jonna Saarimäki-Vire
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Pekka Ahonen
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Xiaonan Liu
- Institute of Biotechnology, Helsinki Institute of Life Science (HiLIFE), University of Helsinki, Helsinki, Finland
| | - Hazem Ibrahim
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Vikash Chandra
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Alice Santambrogio
- Centre for Craniofacial and Regenerative Biology, King’s College London, London, United Kingdom
- Department of Medicine III, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Yafei Wang
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Kirsi Vaaralahti
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Anna-Pauliina Iivonen
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
| | - Johanna Känsäkoski
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
- Department of Physiology, Faculty of Medicine
| | - Johanna Tommiska
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
- Department of Physiology, Faculty of Medicine
| | - Yasmine Kemkem
- Centre for Craniofacial and Regenerative Biology, King’s College London, London, United Kingdom
| | - Markku Varjosalo
- Institute of Biotechnology, Helsinki Institute of Life Science (HiLIFE), University of Helsinki, Helsinki, Finland
| | - Sanna Vuoristo
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
- Department of Obstetrics and Gynecology; and
- HiLIFE, University of Helsinki, Helsinki, Finland
| | - Cynthia L. Andoniadou
- Centre for Craniofacial and Regenerative Biology, King’s College London, London, United Kingdom
- Department of Medicine III, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Timo Otonkoski
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
- New Children’s Hospital, Helsinki University Hospital, Pediatric Research Center, Helsinki, Finland
| | - Taneli Raivio
- Stem Cells and Metabolism Research Program (STEMM), Research Programs Unit, Faculty of Medicine, and
- Department of Physiology, Faculty of Medicine
- New Children’s Hospital, Helsinki University Hospital, Pediatric Research Center, Helsinki, Finland
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2
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Schneeberger PE, Kortüm F, Korenke GC, Alawi M, Santer R, Woidy M, Buhas D, Fox S, Juusola J, Alfadhel M, Webb BD, Coci EG, Abou Jamra R, Siekmeyer M, Biskup S, Heller C, Maier EM, Javaher-Haghighi P, Bedeschi MF, Ajmone PF, Iascone M, Peeters H, Ballon K, Jaeken J, Rodríguez Alonso A, Palomares-Bralo M, Santos-Simarro F, Meuwissen MEC, Beysen D, Kooy RF, Houlden H, Murphy D, Doosti M, Karimiani EG, Mojarrad M, Maroofian R, Noskova L, Kmoch S, Honzik T, Cope H, Sanchez-Valle A, Gelb BD, Kurth I, Hempel M, Kutsche K. Biallelic MADD variants cause a phenotypic spectrum ranging from developmental delay to a multisystem disorder. Brain 2020; 143:2437-2453. [PMID: 32761064 PMCID: PMC7447524 DOI: 10.1093/brain/awaa204] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 05/04/2020] [Accepted: 05/07/2020] [Indexed: 12/22/2022] Open
Abstract
In pleiotropic diseases, multiple organ systems are affected causing a variety of clinical manifestations. Here, we report a pleiotropic disorder with a unique constellation of neurological, endocrine, exocrine, and haematological findings that is caused by biallelic MADD variants. MADD, the mitogen-activated protein kinase (MAPK) activating death domain protein, regulates various cellular functions, such as vesicle trafficking, activity of the Rab3 and Rab27 small GTPases, tumour necrosis factor-α (TNF-α)-induced signalling and prevention of cell death. Through national collaboration and GeneMatcher, we collected 23 patients with 21 different pathogenic MADD variants identified by next-generation sequencing. We clinically evaluated the series of patients and categorized the phenotypes in two groups. Group 1 consists of 14 patients with severe developmental delay, endo- and exocrine dysfunction, impairment of the sensory and autonomic nervous system, and haematological anomalies. The clinical course during the first years of life can be potentially fatal. The nine patients in Group 2 have a predominant neurological phenotype comprising mild-to-severe developmental delay, hypotonia, speech impairment, and seizures. Analysis of mRNA revealed multiple aberrant MADD transcripts in two patient-derived fibroblast cell lines. Relative quantification of MADD mRNA and protein in fibroblasts of five affected individuals showed a drastic reduction or loss of MADD. We conducted functional tests to determine the impact of the variants on different pathways. Treatment of patient-derived fibroblasts with TNF-α resulted in reduced phosphorylation of the extracellular signal-regulated kinases 1 and 2, enhanced activation of the pro-apoptotic enzymes caspase-3 and -7 and increased apoptosis compared to control cells. We analysed internalization of epidermal growth factor in patient cells and identified a defect in endocytosis of epidermal growth factor. We conclude that MADD deficiency underlies multiple cellular defects that can be attributed to alterations of TNF-α-dependent signalling pathways and defects in vesicular trafficking. Our data highlight the multifaceted role of MADD as a signalling molecule in different organs and reveal its physiological role in regulating the function of the sensory and autonomic nervous system and endo- and exocrine glands.
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Affiliation(s)
- Pauline E Schneeberger
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Fanny Kortüm
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Georg Christoph Korenke
- Klinik für Neuropädiatrie und angeborene Stoffwechselerkrankungen, Klinikum Oldenburg, Oldenburg, Germany
| | - Malik Alawi
- Bioinformatics Core Unit, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - René Santer
- Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Mathias Woidy
- Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Daniela Buhas
- Division of Medical Genetics, Department of Specialized Medicine, McGill University Health Centre, Montreal, Canada
- Human Genetics Department, McGill University, Montreal, Canada
| | - Stephanie Fox
- Division of Medical Genetics, Department of Specialized Medicine, McGill University Health Centre, Montreal, Canada
- Human Genetics Department, McGill University, Montreal, Canada
| | | | - Majid Alfadhel
- Division of Genetics, Department of Pediatrics, King Abdullah specialized Children's Hospital, King Abdulaziz Medical City, Ministry of National Guard-Health Affairs (MNGHA), Riyadh, Saudi Arabia
- Medical Genomics Research Department, King Abdullah International Medical Research Center (KAIMRC), Ministry of National Guard-Health Affairs (MNGHA), Riyadh, Saudi Arabia
- King Saud Bin Abdulaziz University for Health Sciences, Ministry of National Guard-Health Affairs (MNGHA), Riyadh, Saudi Arabia
| | - Bryn D Webb
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, USA
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, USA
- Mindich Child Health and Development Institute, Icahn School of Medicine at Mount Sinai, New York, USA
| | - Emanuele G Coci
- Department for Neuropediatrics, University Children's Hospital, Ruhr University Bochum, Bochum, Germany
- Department of Pediatrics, Prignitz Hospital, Brandenburg Medical School, Germany
| | - Rami Abou Jamra
- Institute of Human Genetics, University Medical Center Leipzig, Leipzig, Germany
| | - Manuela Siekmeyer
- Universitätsklinikum Leipzig - AöR, University of Leipzig, Hospital for Children and Adolescents, Leipzig, Germany
| | - Saskia Biskup
- CeGaT GmbH and Praxis für Humangenetik Tübingen, Tübingen, Germany
| | - Corina Heller
- CeGaT GmbH and Praxis für Humangenetik Tübingen, Tübingen, Germany
| | - Esther M Maier
- Dr. von Hauner Children's Hospital, University of Munich, Munich, Germany
| | | | - Maria F Bedeschi
- Medical Genetic Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Paola F Ajmone
- Child and Adolescent Neuropsychiatric Unit, Fondazione IRCCS Cà Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Maria Iascone
- Laboratorio di Genetica Medica, ASST Papa Giovanni XXIII, Bergamo, Italy
| | - Hilde Peeters
- Center for Human Genetics, KU Leuven, Leuven, Belgium
| | - Katleen Ballon
- Centre for Developmental Disabilities, Department of Development and Regeneration, KU Leuven, Leuven, Belgium
| | - Jaak Jaeken
- Center for Metabolic Diseases, KU Leuven, Leuven, Belgium
| | - Aroa Rodríguez Alonso
- Unidad de Patología Compleja, Servicio de Pediatría, Hospital Universitario La Paz, Madrid, Spain
| | - María Palomares-Bralo
- Instituto de Genética Médica y Molecular (INGEMM), Hospital Universitario La Paz, IdiPAZ, CIBERER, ISCIII, Madrid, Spain
| | - Fernando Santos-Simarro
- Instituto de Genética Médica y Molecular (INGEMM), Hospital Universitario La Paz, IdiPAZ, CIBERER, ISCIII, Madrid, Spain
| | | | - Diane Beysen
- Department of Pediatric Neurology, University Hospital Antwerp, Antwerp, Belgium
| | - R Frank Kooy
- Department of Medical Genetics, University of Antwerp, Antwerp, Belgium
| | - Henry Houlden
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - David Murphy
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | | | - Ehsan G Karimiani
- Next Generation Genetic Polyclinic, Mashhad, Iran
- Genetics Research Centre, Molecular and Clinical Sciences Institute, St. George's, University, London, UK
| | - Majid Mojarrad
- Department of Medical Genetics, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
- Medical Genetics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
- Genetic Center of Khorasan Razavi, Mashhad, Iran
| | - Reza Maroofian
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Lenka Noskova
- Research Unit for Rare Diseases, Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Stanislav Kmoch
- Research Unit for Rare Diseases, Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Tomas Honzik
- Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University and General University Hospital, Prague, Czech Republic
| | - Heidi Cope
- Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Amarilis Sanchez-Valle
- Division of Genetics and Metabolism, College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Bruce D Gelb
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, USA
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, USA
- Mindich Child Health and Development Institute, Icahn School of Medicine at Mount Sinai, New York, USA
| | - Ingo Kurth
- Institute of Human Genetics, Medical Faculty, RWTH Aachen University, Aachen, Germany
- Institute of Human Genetics, Jena University Hospital, Jena, Germany
| | - Maja Hempel
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Kerstin Kutsche
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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Structural Insights into the Regulation Mechanism of Small GTPases by GEFs. Molecules 2019; 24:molecules24183308. [PMID: 31514408 PMCID: PMC6767298 DOI: 10.3390/molecules24183308] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 09/09/2019] [Accepted: 09/10/2019] [Indexed: 12/12/2022] Open
Abstract
Small GTPases are key regulators of cellular events, and their dysfunction causes many types of cancer. They serve as molecular switches by cycling between inactive guanosine diphosphate (GDP)-bound and active guanosine triphosphate (GTP)-bound states. GTPases are deactivated by GTPase-activating proteins (GAPs) and are activated by guanine-nucleotide exchange factors (GEFs). The intrinsic GTP hydrolysis activity of small GTPases is generally low and is accelerated by GAPs. GEFs promote GDP dissociation from small GTPases to allow for GTP binding, which results in a conformational change of two highly flexible segments, called switch I and switch II, that enables binding of the gamma phosphate and allows small GTPases to interact with downstream effectors. For several decades, crystal structures of many GEFs and GAPs have been reported and have shown tremendous structural diversity. In this review, we focus on the latest structural studies of GEFs. Detailed pictures of the variety of GEF mechanisms at atomic resolution can provide insights into new approaches for drug discovery.
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4
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Sanzà P, Evans RD, Briggs DA, Cantero M, Montoliu L, Patel S, Sviderskaya EV, Itzen A, Figueiredo AC, Seabra MC, Hume AN. Nucleotide exchange factor Rab3GEP requires DENN and non-DENN elements for activation and targeting of Rab27a. J Cell Sci 2019; 132:jcs.212035. [PMID: 30898842 PMCID: PMC6526710 DOI: 10.1242/jcs.212035] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 03/11/2019] [Indexed: 02/04/2023] Open
Abstract
Rab GTPases are compartment-specific molecular switches that regulate intracellular vesicular transport in eukaryotes. GDP/GTP exchange factors (GEFs) control Rab activation, and current models propose that localised and regulated GEF activity is important in targeting Rabs to specific membranes. Here, we investigated the mechanism of GEF function using the Rab27a GEF, Rab3GEP (also known as MADD), in melanocytes as a model. We show that Rab3GEP-deficient melanocytes (melan-R3GKO) manifest partial disruption of melanosome dispersion, a read-out of Rab27a activation and targeting. Using rescue of melanosome dispersion in melan-R3GKO cells and effector pull-down approaches we show that the DENN domain of Rab3GEP (conserved among RabGEFs) is necessary, but insufficient, for its cellular function and GEF activity. Finally, using a mitochondrial re-targeting strategy, we show that Rab3GEP can target Rab27a to specific membranes in a GEF-dependent manner. We conclude that Rab3GEP facilitates the activation and targeting of Rab27a to specific membranes, but that it differs from other DENN-containing RabGEFs in requiring DENN and non-DENN elements for both of these activities and by lacking compartment-specific localisation.
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Affiliation(s)
- Paolo Sanzà
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Richard D Evans
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Deborah A Briggs
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Marta Cantero
- Centro Nacional de Biotecnologia (CNB-CSIC), Madrid 28049, Spain.,CIBERER-ISCIII, Madrid 28029, Spain
| | - Lluis Montoliu
- Centro Nacional de Biotecnologia (CNB-CSIC), Madrid 28049, Spain.,CIBERER-ISCIII, Madrid 28029, Spain
| | - Shyamal Patel
- Cell Biology and Genetics Research Centre, Molecular and Clinical Sciences Research Institute, St. George's, University of London, London SW17 0RE, UK
| | - Elena V Sviderskaya
- Cell Biology and Genetics Research Centre, Molecular and Clinical Sciences Research Institute, St. George's, University of London, London SW17 0RE, UK
| | - Aymelt Itzen
- Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry, Technische Universität München, Garching 85748, Germany
| | - Ana C Figueiredo
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto 4200-135, Portugal.,i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto 4200-135, Portugal
| | - Miguel C Seabra
- CEDOC Faculdade de Ciencias Medicas, Universidade Nova de Lisboa, Lisbon 1169-056, Portugal
| | - Alistair N Hume
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
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Rab3-GEF Controls Active Zone Development at the Drosophila Neuromuscular Junction. eNeuro 2016; 3:eN-NWR-0031-16. [PMID: 27022630 PMCID: PMC4791486 DOI: 10.1523/eneuro.0031-16.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 02/29/2016] [Indexed: 02/05/2023] Open
Abstract
Synaptic signaling involves the release of neurotransmitter from presynaptic active zones (AZs). Proteins that regulate vesicle exocytosis cluster at AZs, composing the cytomatrix at the active zone (CAZ). At the Drosophila neuromuscular junction (NMJ), the small GTPase Rab3 controls the distribution of CAZ proteins across release sites, thereby regulating the efficacy of individual AZs. Here we identify Rab3-GEF as a second protein that acts in conjunction with Rab3 to control AZ protein composition. At rab3-GEF mutant NMJs, Bruchpilot (Brp) and Ca2+ channels are enriched at a subset of AZs, leaving the remaining sites devoid of key CAZ components in a manner that is indistinguishable from rab3 mutant NMJs. As the Drosophila homologue of mammalian DENN/MADD and Caenorhabditis elegans AEX-3, Rab3-GEF is a guanine nucleotide exchange factor (GEF) for Rab3 that stimulates GDP to GTP exchange. Mechanistic studies reveal that although Rab3 and Rab3-GEF act within the same mechanism to control AZ development, Rab3-GEF is involved in multiple roles. We show that Rab3-GEF is required for transport of Rab3. However, the synaptic phenotype in the rab3-GEF mutant cannot be fully explained by defective transport and loss of GEF activity. A transgenically expressed GTP-locked variant of Rab3 accumulates at the NMJ at wild-type levels and fully rescues the rab3 mutant but is unable to rescue the rab3-GEF mutant. Our results suggest that although Rab3-GEF acts upstream of Rab3 to control Rab3 localization and likely GTP-binding, it also acts downstream to regulate CAZ development, potentially as a Rab3 effector at the synapse.
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Cheng Y, Wang J, Wang Y, Ding M. Synaptotagmin 1 directs repetitive release by coupling vesicle exocytosis to the Rab3 cycle. eLife 2015; 4. [PMID: 25710274 PMCID: PMC4374511 DOI: 10.7554/elife.05118] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 02/23/2015] [Indexed: 01/09/2023] Open
Abstract
In response to Ca2+ influx, a synapse needs to release neurotransmitters quickly while immediately preparing for repeat firing. How this harmonization is achieved is not known. In this study, we found that the Ca2+ sensor synaptotagmin 1 orchestrates the membrane association/disassociation cycle of Rab3, which functions in activity-dependent recruitment of synaptic vesicles. In the absence of Ca2+, synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein. Rab3 GAP resides on synaptic vesicles, and synaptotagmin 1 is essential for the synaptic localization of Rab3 GAP. In the presence of Ca2+, synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3. Without synaptotagmin 1, the tight coupling between vesicle exocytosis and Rab3 membrane disassociation is disrupted. We uncovered the long-sought molecular apparatus linking vesicle exocytosis to Rab3 cycling and we also revealed the important function of synaptotagmin 1 in repetitive synaptic vesicle release. DOI:http://dx.doi.org/10.7554/eLife.05118.001 Neurons communicate with one another at junctions called synapses. The arrival of an electrical signal called an action potential causes calcium ions to enter the first cell, which in turn triggers the release of molecules called neurotransmitters into the gap between the neurons. The binding of these molecules to receptors on the second cell then enables the action potential to be regenerated. For cells to respond rapidly and reliably to incoming electrical signals, they must maintain a supply of vesicles—the packages that contain neurotransmitters—close to the site where they are released from the first cell. The vesicles are held in contact with the cell membrane by a structure called the docking complex. A number of the proteins in this docking complex have been identified, including two that have been referred to as the ‘yin and yang’ of vesicle fusion: synaptotagmin, which promotes fusion, and Rab3, which limits it. However, little is known about how these and other proteins interact to keep vesicles docked at the membrane. Cheng, Wang et al. have now clarified the docking process with the aid of experiments in nematode worms. In resting neurons that are not releasing neurotransmitters, synaptotagmin (‘yin’) binds to an enzyme called GAP and prevents it from converting GTP—an energy-storage molecule—into GDP. Given that Rab3 (‘yang’) requires a molecule of GTP to power its own activity, the actions of synaptotagmin ensure that Rab3 has enough energy to remain bound to other proteins within the docking complex. However, when an action potential arrives, calcium ions enter the neuron, and some of them bind to synaptotagmin. This disrupts its interaction with the GAP enzyme, which thus becomes free to convert the GTP molecule bound to Rab3 into GDP. The loss of its energy source causes Rab3 to separate from its binding partners, and docking complex collapses. As a result, vesicles fuse with the membrane and release neurotransmitter molecules into the synapse. Given that Rab3 and synaptotagmin have changed little over the course of evolution, it is highly likely that the same indirect interaction between these two proteins also regulates the release of transmitter at synapses in the mammalian brain. DOI:http://dx.doi.org/10.7554/eLife.05118.002
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Affiliation(s)
- Yunsheng Cheng
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Jiaming Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Yu Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
| | - Mei Ding
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
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Pelletán LE, Suhaiman L, Vaquer CC, Bustos MA, De Blas GA, Vitale N, Mayorga LS, Belmonte SA. ADP ribosylation factor 6 (ARF6) promotes acrosomal exocytosis by modulating lipid turnover and Rab3A activation. J Biol Chem 2015; 290:9823-41. [PMID: 25713146 DOI: 10.1074/jbc.m114.629006] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Indexed: 11/06/2022] Open
Abstract
Regulated secretion is a central issue for the specific function of many cells; for instance, mammalian sperm acrosomal exocytosis is essential for egg fertilization. ARF6 (ADP-ribosylation factor 6) is a small GTPase implicated in exocytosis, but its downstream effectors remain elusive in this process. We combined biochemical, functional, and microscopy-based methods to show that ARF6 is present in human sperm, localizes to the acrosomal region, and is required for calcium and diacylglycerol-induced exocytosis. Results from pulldown assays show that ARF6 exchanges GDP for GTP in sperm challenged with different exocytic stimuli. Myristoylated and guanosine 5'-3-O-(thio)triphosphate (GTPγS)-loaded ARF6 (active form) added to permeabilized sperm induces acrosome exocytosis even in the absence of extracellular calcium. We explore the ARF6 signaling cascade that promotes secretion. We demonstrate that ARF6 stimulates a sperm phospholipase D activity to produce phosphatidic acid and boosts the synthesis of phosphatidylinositol 4,5-bisphosphate. We present direct evidence showing that active ARF6 increases phospholipase C activity, causing phosphatidylinositol 4,5-bisphosphate hydrolysis and inositol 1,4,5-trisphosphate-dependent intra-acrosomal calcium release. We show that active ARF6 increases the exchange of GDP for GTP on Rab3A, a prerequisite for secretion. We propose that exocytic stimuli activate ARF6, which is required for acrosomal calcium efflux and the assembly of the membrane fusion machinery. This report highlights the physiological importance of ARF6 as a key factor for human sperm exocytosis and fertilization.
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Affiliation(s)
- Leonardo E Pelletán
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Laila Suhaiman
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Cintia C Vaquer
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Matías A Bustos
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Gerardo A De Blas
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Nicolas Vitale
- the Département Neurotransmission et Sécrétion Neuroendocrine, Institut des Neurosciences Cellulaires et Intégratives (UPR 3212), CNRS et Université de Strasbourg, 5 Rue Blaise Pascal, 67084 Strasbourg, France
| | - Luis S Mayorga
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
| | - Silvia A Belmonte
- From the Instituto de Histología y Embriología, CONICET, Facultad de Ciencias Médicas, CC56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina and
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Liew GM, Ye F, Nager AR, Murphy JP, Lee JS, Aguiar M, Breslow DK, Gygi SP, Nachury MV. The intraflagellar transport protein IFT27 promotes BBSome exit from cilia through the GTPase ARL6/BBS3. Dev Cell 2014; 31:265-278. [PMID: 25443296 DOI: 10.1016/j.devcel.2014.09.004] [Citation(s) in RCA: 150] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Revised: 08/26/2014] [Accepted: 09/11/2014] [Indexed: 01/02/2023]
Abstract
The sorting of signaling receptors into and out of cilia relies on the BBSome, a complex of Bardet-Biedl syndrome (BBS) proteins, and on the intraflagellar transport (IFT) machinery. GTP loading onto the Arf-like GTPase ARL6/BBS3 drives assembly of a membrane-apposed BBSome coat that promotes cargo entry into cilia, yet how and where ARL6 is activated remains elusive. Here, we show that the Rab-like GTPase IFT27/RABL4, a known component of IFT complex B, promotes the exit of BBSome and associated cargoes from cilia. Unbiased proteomics and biochemical reconstitution assays show that, upon disengagement from the rest of IFT-B, IFT27 directly interacts with the nucleotide-free form of ARL6. Furthermore, IFT27 prevents aggregation of nucleotide-free ARL6 in solution. Thus, we propose that IFT27 separates from IFT-B inside cilia to promote ARL6 activation, BBSome coat assembly, and subsequent ciliary exit, mirroring the process by which BBSome mediates cargo entry into cilia.
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Affiliation(s)
- Gerald M Liew
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Fan Ye
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Andrew R Nager
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - J Patrick Murphy
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Jaclyn S Lee
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Mike Aguiar
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - David K Breslow
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Steven P Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Maxence V Nachury
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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9
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Blank U, Madera-Salcedo IK, Danelli L, Claver J, Tiwari N, Sánchez-Miranda E, Vázquez-Victorio G, Ramírez-Valadez KA, Macias-Silva M, González-Espinosa C. Vesicular trafficking and signaling for cytokine and chemokine secretion in mast cells. Front Immunol 2014; 5:453. [PMID: 25295038 PMCID: PMC4170139 DOI: 10.3389/fimmu.2014.00453] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/05/2014] [Indexed: 12/31/2022] Open
Abstract
Upon activation mast cells (MCs) secrete numerous inflammatory compounds stored in their cytoplasmic secretory granules by a process called anaphylactic degranulation, which is responsible for type I hypersensitivity responses. Prestored mediators include histamine and MC proteases but also some cytokines and growth factors making them available within minutes for a maximal biological effect. Degranulation is followed by the de novo synthesis of lipid mediators such as prostaglandins and leukotrienes as well as a vast array of cytokines, chemokines, and growth factors, which are responsible for late phase inflammatory responses. While lipid mediators diffuse freely out of the cell through lipid bilayers, both anaphylactic degranulation and secretion of cytokines, chemokines, and growth factors depends on highly regulated vesicular trafficking steps that occur along the secretory pathway starting with the translocation of proteins to the endoplasmic reticulum. Vesicular trafficking in MCs also intersects with endocytic routes, notably to form specialized cytoplasmic granules called secretory lysosomes. Some of the mediators like histamine reach granules via specific vesicular monoamine transporters directly from the cytoplasm. In this review, we try to summarize the available data on granule biogenesis and signaling events that coordinate the complex steps that lead to the release of the inflammatory mediators from the various vesicular carriers in MCs.
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Affiliation(s)
- Ulrich Blank
- INSERM UMRS 1149 , Paris , France ; CNRS ERL8252 , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'excellence INFLAMEX , Paris , France
| | - Iris Karina Madera-Salcedo
- INSERM UMRS 1149 , Paris , France ; CNRS ERL8252 , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'excellence INFLAMEX , Paris , France
| | - Luca Danelli
- INSERM UMRS 1149 , Paris , France ; CNRS ERL8252 , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'excellence INFLAMEX , Paris , France
| | - Julien Claver
- INSERM UMRS 1149 , Paris , France ; CNRS ERL8252 , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'excellence INFLAMEX , Paris , France
| | - Neeraj Tiwari
- INSERM UMRS 1149 , Paris , France ; CNRS ERL8252 , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'excellence INFLAMEX , Paris , France
| | | | - Genaro Vázquez-Victorio
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México , México City , México
| | | | - Marina Macias-Silva
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México , México City , México
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10
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Ruete MC, Lucchesi O, Bustos MA, Tomes CN. Epac, Rap and Rab3 act in concert to mobilize calcium from sperm's acrosome during exocytosis. Cell Commun Signal 2014; 12:43. [PMID: 25159528 PMCID: PMC4156617 DOI: 10.1186/s12964-014-0043-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 06/19/2014] [Indexed: 11/11/2022] Open
Abstract
Background Exocytosis of sperm’s single secretory granule or acrosome (acrosome reaction, AR) is a highly regulated event essential for fertilization. The AR begins with an influx of calcium from the extracellular milieu and continues with the synthesis of cAMP and the activation of its target Epac. The cascade bifurcates into a Rab3-GTP-driven limb that assembles the fusion machinery and a Rap-GTP-driven limb that mobilizes internal calcium. Results To understand the crosstalk between the two signaling cascades, we applied known AR inhibitors in three experimental approaches: reversible, stage-specific blockers in a functional assay, a far-immunofluorescence protocol to detect active Rab3 and Rap, and single cell-confocal microscopy to visualize fluctuations in internal calcium stores. Our model system was human sperm with their plasma membrane permeabilized with streptolysin O and stimulated with external calcium. The inhibition caused by reagents that prevented the activation of Rap was reversed by mobilizing intracellular calcium pharmacologically, whereas that caused by AR inhibitors that impeded Rab3’s binding to GTP was not. Both limbs of the exocytotic cascade joined at or near the stage catalyzed by Rab3 in a unidirectional, hierarchical connection in which the intra-acrosomal calcium mobilization arm was subordinated to the fusion protein arm; somewhere after Rab3, the pathways became independent. Conclusions We delineated the sequence of events that connect an external calcium signal to internal calcium mobilization during exocytosis. We have taken advantage of the versatility of the sperm model to investigate how cAMP, calcium, and the proteinaceous fusion machinery coordinate to accomplish secretion. Because the requirement of calcium from two different sources is not unique to sperm and fusion proteins are highly conserved, our findings might contribute to elucidate mechanisms that operate in regulated exocytosis in other secretory cell types. Electronic supplementary material The online version of this article (doi:10.1186/s12964-014-0043-0) contains supplementary material, which is available to authorized users.
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11
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Cazares VA, Subramani A, Saldate JJ, Hoerauf W, Stuenkel EL. Distinct actions of Rab3 and Rab27 GTPases on late stages of exocytosis of insulin. Traffic 2014; 15:997-1015. [PMID: 24909540 DOI: 10.1111/tra.12182] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Revised: 06/04/2014] [Accepted: 06/04/2014] [Indexed: 12/16/2022]
Abstract
Rab GTPases associated with insulin-containing secretory granules (SGs) are key in targeting, docking and assembly of molecular complexes governing pancreatic β-cell exocytosis. Four Rab3 isoforms along with Rab27A are associated with insulin granules, yet elucidation of the distinct roles of these Rab families on exocytosis remains unclear. To define specific actions of these Rab families we employ Rab3GAP and/or EPI64A GTPase-activating protein overexpression in β-cells from wild-type or Ashen mice to selectively transit the entire Rab3 family or Rab27A to a GDP-bound state. Ashen mice carry a spontaneous mutation that eliminates Rab27A expression. Using membrane capacitance measurements we find that GTP/GDP nucleotide cycling of Rab27A is essential for generation of the functionally defined immediately releasable pool (IRP) and central to regulating the size of the readily releasable pool (RRP). By comparison, nucleotide cycling of Rab3 GTPases, but not of Rab27A, is essential for a kinetically rapid filling of the RRP with SGs. Aside from these distinct functions, Rab3 and Rab27A GTPases demonstrate considerable functional overlap in building the readily releasable granule pool. Hence, while Rab3 and Rab27A cooperate to generate release-ready SGs in β-cells, they also direct unique kinetic and functional properties of the exocytotic pathway.
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Affiliation(s)
- Victor A Cazares
- Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, 48109, USA; Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI, 48109, USA
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12
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Li LC, Wang Y, Carr R, Haddad CS, Li Z, Qian L, Oberholzer J, Maker AV, Wang Q, Prabhakar BS. IG20/MADD plays a critical role in glucose-induced insulin secretion. Diabetes 2014; 63:1612-23. [PMID: 24379354 PMCID: PMC3994957 DOI: 10.2337/db13-0707] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Pancreatic β-cell dysfunction is a common feature of type 2 diabetes. Earlier, we had cloned IG20 cDNA from a human insulinoma and had shown that IG20/MADD can encode six different splice isoforms that are differentially expressed and have unique functions, but its role in β-cell function was unexplored. To investigate the role of IG20/MADD in β-cell function, we generated conditional knockout (KMA1ko) mice. Deletion of IG20/MADD in β-cells resulted in hyperglycemia and glucose intolerance associated with reduced and delayed glucose-induced insulin production. KMA1ko β-cells were able to process insulin normally but had increased insulin accumulation and showed a severe defect in glucose-induced insulin release. These findings indicated that IG20/MADD plays a critical role in glucose-induced insulin release from β-cells and that its functional disruption can cause type 2 diabetes. The clinical relevance of these findings is highlighted by recent reports of very strong association of the rs7944584 single nucleotide polymorphism (SNP) of IG20/MADD with fasting hyperglycemia/diabetes. Thus, IG20/MADD could be a therapeutic target for type 2 diabetes, particularly in those with the rs7944584 SNP.
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Affiliation(s)
- Liang-cheng Li
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
- School of Pharmaceutical Sciences, Xiamen University at Xiang'an, Xiamen, Fujian, China
| | - Yong Wang
- Department of Surgery, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Ryan Carr
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Christine Samir Haddad
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Ze Li
- Department of Surgery, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Lixia Qian
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Jose Oberholzer
- Department of Surgery, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Ajay V. Maker
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
- Department of Surgery, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Qian Wang
- Department of Surgery, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Bellur S. Prabhakar
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, IL
- Corresponding author: Bellur S. Prabhakar,
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13
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Brochetta C, Suzuki R, Vita F, Soranzo MR, Claver J, Madjene LC, Attout T, Vitte J, Varin-Blank N, Zabucchi G, Rivera J, Blank U. Munc18-2 and syntaxin 3 control distinct essential steps in mast cell degranulation. THE JOURNAL OF IMMUNOLOGY 2013; 192:41-51. [PMID: 24323579 DOI: 10.4049/jimmunol.1301277] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Mast cell degranulation requires N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) and mammalian uncoordinated18 (Munc18) fusion accessory proteins for membrane fusion. However, it is still unknown how their interaction supports fusion. In this study, we found that small interfering RNA-mediated silencing of the isoform Munc18-2 in mast cells inhibits cytoplasmic secretory granule (SG) release but not CCL2 chemokine secretion. Silencing of its SNARE-binding partner syntaxin 3 (STX3) also markedly inhibited degranulation, whereas combined knockdown produced an additive inhibitory effect. Strikingly, while Munc18-2 silencing impaired SG translocation, silencing of STX3 inhibited fusion, demonstrating unique roles of each protein. Immunogold studies showed that both Munc18-2 and STX3 are located on the granule surface, but also within the granule matrix and in small nocodazole-sensitive clusters of the cytoskeletal meshwork surrounding SG. After stimulation, clusters containing both effectors were detected at fusion sites. In resting cells, Munc18-2, but not STX3, interacted with tubulin. This interaction was sensitive to nocodazole treatment and decreased after stimulation. Our results indicate that Munc18-2 dynamically couples the membrane fusion machinery to the microtubule cytoskeleton and demonstrate that Munc18-2 and STX3 perform distinct, but complementary, functions to support, respectively, SG translocation and membrane fusion in mast cells.
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Affiliation(s)
- Cristiana Brochetta
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
| | - Ryo Suzuki
- Laboratory of Molecular Immunogenetics, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, 20892
| | - Francesca Vita
- Department of Life Sciences Department of Physiology and Pathology, University of Trieste, Italy
| | - Maria Rosa Soranzo
- Department of Life Sciences Department of Physiology and Pathology, University of Trieste, Italy
| | - Julien Claver
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
| | - Lydia Celia Madjene
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
| | - Tarik Attout
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
| | - Joana Vitte
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
| | - Nadine Varin-Blank
- Inserm U978, 93000 Bobigny, France.,Laboratoire d'excellence "Inflamex," Unité de Formation et de Recherche Santé-Médecine-Biologie Humaine, 93000 Bobigny, France
| | - Giuliano Zabucchi
- Department of Life Sciences Department of Physiology and Pathology, University of Trieste, Italy
| | - Juan Rivera
- Laboratory of Molecular Immunogenetics, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, 20892
| | - Ulrich Blank
- Inserm UMRS-699, 75018 Paris, France.,Université Paris Diderot, Sorbonne Paris Cite, Laboratoire d'excellence INFLAMEX, 75018 Paris, France
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14
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Exome array analysis identifies new loci and low-frequency variants influencing insulin processing and secretion. Nat Genet 2012; 45:197-201. [PMID: 23263489 DOI: 10.1038/ng.2507] [Citation(s) in RCA: 216] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Accepted: 11/26/2012] [Indexed: 12/15/2022]
Abstract
Insulin secretion has a crucial role in glucose homeostasis, and failure to secrete sufficient insulin is a hallmark of type 2 diabetes. Genome-wide association studies (GWAS) have identified loci contributing to insulin processing and secretion; however, a substantial fraction of the genetic contribution remains undefined. To examine low-frequency (minor allele frequency (MAF) 0.5-5%) and rare (MAF < 0.5%) nonsynonymous variants, we analyzed exome array data in 8,229 nondiabetic Finnish males using the Illumina HumanExome Beadchip. We identified low-frequency coding variants associated with fasting proinsulin concentrations at the SGSM2 and MADD GWAS loci and three new genes with low-frequency variants associated with fasting proinsulin or insulinogenic index: TBC1D30, KANK1 and PAM. We also show that the interpretation of single-variant and gene-based tests needs to consider the effects of noncoding SNPs both nearby and megabases away. This study demonstrates that exome array genotyping is a valuable approach to identify low-frequency variants that contribute to complex traits.
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15
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Lorentz A, Baumann A, Vitte J, Blank U. The SNARE Machinery in Mast Cell Secretion. Front Immunol 2012; 3:143. [PMID: 22679448 PMCID: PMC3367400 DOI: 10.3389/fimmu.2012.00143] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 05/17/2012] [Indexed: 11/13/2022] Open
Abstract
Mast cells are known as inflammatory cells which exert their functions in allergic and anaphylactic reactions by secretion of numerous inflammatory mediators. During an allergic response, the high-affinity IgE receptor, FcεRI, becomes cross-linked by receptor-bound IgE and antigen resulting in immediate release of pre-synthesized mediators – stored in granules – as well as in de novo synthesis of various mediators like cytokines and chemokines. Soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptors (SNARE) proteins were found to play a central role in regulating membrane fusion events during exocytosis. In addition, several accessory regulators like Munc13, Munc18, Rab GTPases, secretory carrier membrane proteins, complexins, or synaptotagmins were found to be involved in membrane fusion. In this review we summarize our current knowledge about the SNARE machinery and its mechanism of action in mast cell secretion.
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Affiliation(s)
- Axel Lorentz
- Department of Nutritional Medicine, University of Hohenheim Stuttgart, Germany
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16
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Lopez CI, Pelletán LE, Suhaiman L, De Blas GA, Vitale N, Mayorga LS, Belmonte SA. Diacylglycerol stimulates acrosomal exocytosis by feeding into a PKC- and PLD1-dependent positive loop that continuously supplies phosphatidylinositol 4,5-bisphosphate. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1186-99. [PMID: 22609963 DOI: 10.1016/j.bbalip.2012.05.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Revised: 04/04/2012] [Accepted: 05/07/2012] [Indexed: 01/08/2023]
Abstract
Acrosomal exocytosis involves a massive fusion between the outer acrosomal and the plasma membranes of the spermatozoon triggered by stimuli that open calcium channels at the plasma membrane. Diacylglycerol has been implicated in the activation of these calcium channels. Here we report that this lipid promotes the efflux of intraacrosomal calcium and triggers exocytosis in permeabilized human sperm, implying that diacylglycerol activates events downstream of the opening of plasma membrane channels. Furthermore, we show that calcium and diacylglycerol converge in a signaling pathway leading to the production of phosphatidylinositol 4,5-bisphosphate (PIP(2)). Addition of diacylglycerol promotes the PKC-dependent activation of PLD1. Rescue experiments adding phosphatidic acid or PIP(2) and direct measurement of lipid production suggest that both PKC and PLD1 promote PIP(2) synthesis. Inhibition of different steps of the pathway was reverted by adenophostin, an agonist of IP(3)-sensitive calcium channels, indicating that PIP(2) is necessary to keep these channels opened. However, phosphatidic acid, PIP(2), or adenophostin could not trigger exocytosis by themselves, indicating that diacylglycerol must also activate another factor. We found that diacylglycerol and phorbol ester stimulate the accumulation of the GTP-bound form of Rab3A. Together our results indicate that diacylglycerol promotes acrosomal exocytosis by i) maintaining high levels of IP(3) - an effect that depends on a positive feedback loop leading to the production of PIP(2) - and ii) stimulating the activation of Rab3A, which in turn initiates a cascade of protein interactions leading to the assembly of SNARE complexes and membrane fusion.
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Affiliation(s)
- Cecilia I Lopez
- Instituto de Histología y Embriología, Universidad Nacional de Cuyo, Mendoza, Argentina
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17
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Abstract
The DENN domain is a common, evolutionarily ancient, and conserved protein module, yet it has gone largely unstudied; until recently, little was known regarding its functional roles. New studies reveal that various DENN domains interact directly with members of the Rab family of small GTPases and that DENN domains function enzymatically as Rab-specific guanine nucleotide exchange factors. Thus, DENN domain proteins appear to be generalized regulators of Rab function. Study of these proteins will provide new insights into Rab-mediated membrane trafficking pathways.
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Affiliation(s)
- Andrea L. Marat
- From the Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
| | - Hatem Dokainish
- From the Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
| | - Peter S. McPherson
- From the Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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18
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Yoshimura SI, Gerondopoulos A, Linford A, Rigden DJ, Barr FA. Family-wide characterization of the DENN domain Rab GDP-GTP exchange factors. ACTA ACUST UNITED AC 2010; 191:367-81. [PMID: 20937701 PMCID: PMC2958468 DOI: 10.1083/jcb.201008051] [Citation(s) in RCA: 246] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Target or substrate Rab GTPases are identified for 17 proteins with DENN domains. A key requirement for Rab function in membrane trafficking is site-specific activation by GDP-GTP exchange factors (GEFs), but the majority of the 63 human Rabs have no known GEF. We have performed a systematic characterization of the 17 human DENN domain proteins and demonstrated that they are specific GEFs for 10 Rabs. DENND1A/1B localize to clathrin patches at the plasma membrane and activate Rab35 in an endocytic pathway trafficking Shiga toxin to the trans-Golgi network. DENND2 GEFs target to actin filaments and control Rab9-dependent trafficking of mannose-6-phosphate receptor to lysosomes. DENND4 GEFs target to a tubular membrane compartment adjacent to the Golgi, where they activate Rab10, which suggests a function in basolateral polarized sorting in epithelial cells that compliments the non-DENN GEF Sec2 acting on Rab8 in apical sorting. DENND1C, DENND3, DENND5A/5B, MTMR5/13, and MADD activate Rab13, Rab12, Rab39, Rab28, and Rab27A/27B, respectively. Together, these findings provide a basis for future studies on Rab regulation and function.
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Affiliation(s)
- Shin-ichiro Yoshimura
- Cancer Research Centre and 2 Institute of Integrative Biology, University of Liverpool, Liverpool L3 9TA, England, UK
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19
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Li P, Jayarama S, Ganesh L, Mordi D, Carr R, Kanteti P, Hay N, Prabhakar BS. Akt-phosphorylated mitogen-activated kinase-activating death domain protein (MADD) inhibits TRAIL-induced apoptosis by blocking Fas-associated death domain (FADD) association with death receptor 4. J Biol Chem 2010; 285:22713-22. [PMID: 20484047 DOI: 10.1074/jbc.m110.105692] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MADD plays an essential role in cancer cell survival. Abrogation of endogenous MADD expression results in significant spontaneous apoptosis and enhanced susceptibility to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. However, the regulation of MADD function is largely unknown. Here, we demonstrate that endogenous MADD is phosphorylated at three highly conserved sites by Akt, and only the phosphorylated MADD can directly interact with the TRAIL receptor DR4 thereby preventing Fas-associated death domain recruitment. However, in cells susceptible to TRAIL treatment, TRAIL induces a reduction in MADD phosphorylation levels resulting in MADD dissociation from, and Fas-associated death domain association with DR4, which allows death-inducing signaling complex (DISC) formation leading to apoptosis. Thus, the pro-survival function of MADD is dependent upon its phosphorylation by Akt. Because Akt is active in most cancer cells and phosphorylated MADD confers resistance to TRAIL-induced apoptosis, co-targeting Akt-MADD axis is likely to increase efficacy of TRAIL-based therapies.
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Affiliation(s)
- Peifeng Li
- Department of Microbiology and Immunology, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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20
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Marat AL, McPherson PS. The connecdenn family, Rab35 guanine nucleotide exchange factors interfacing with the clathrin machinery. J Biol Chem 2010; 285:10627-37. [PMID: 20154091 PMCID: PMC2856271 DOI: 10.1074/jbc.m109.050930] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Revised: 12/15/2009] [Indexed: 11/06/2022] Open
Abstract
Rabs constitute the largest family of monomeric GTPases, yet for the majority of Rabs relatively little is known about their activation and recruitment to vesicle-trafficking pathways. We recently identified connecdenn (DENND1A), which contains an N-terminal DENN (differentially expressed in neoplastic versus normal cells) domain, a common and evolutionarily ancient protein module. Through its DENN domain, connecdenn functions enzymatically as a guanine-nucleotide exchange factor (GEF) for Rab35. Here we identify two additional connecdenn family members and demonstrate that all connecdenns function as Rab35 GEFs, albeit with different levels of activity. The DENN domain of connecdenn 1 and 2 binds Rab35, whereas connecdenn 3 does not, indicating that Rab35 binding and activation are separable functions. Through their highly divergent C termini, each of the connecdenns binds to clathrin and to the clathrin adaptor AP-2. Interestingly, all three connecdenns use different mechanisms to bind AP-2. Characterization of connecdenn 2 reveals binding to the beta2-ear of AP-2 on a site that overlaps with that used by the autosomal recessive hypercholesterolemia protein and betaarrestin, although the sequence used by connecdenn 2 is unique. Loss of connecdenn 2 function through small interference RNA knockdown results in an enlargement of early endosomes, similar to what is observed upon loss of Rab35 activity. Our studies reveal connecdenn DENN domains as generalized GEFs for Rab35 and identify a new AP-2-binding motif, demonstrating a complex link between the clathrin machinery and Rab35 activation.
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Affiliation(s)
- Andrea L. Marat
- From the Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
| | - Peter S. McPherson
- From the Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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21
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Allaire PD, Marat AL, Dall'Armi C, Di Paolo G, McPherson PS, Ritter B. The Connecdenn DENN domain: a GEF for Rab35 mediating cargo-specific exit from early endosomes. Mol Cell 2010; 37:370-82. [PMID: 20159556 DOI: 10.1016/j.molcel.2009.12.037] [Citation(s) in RCA: 159] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Revised: 10/08/2009] [Accepted: 12/08/2009] [Indexed: 12/26/2022]
Abstract
The DENN domain is an evolutionarily ancient protein module. Mutations in the DENN domain cause developmental defects in plants and human diseases, yet the function of this common module is unknown. We now demonstrate that the connecdenn/DENND1A DENN domain functions as a guanine nucleotide exchange factor (GEF) for Rab35 to regulate endosomal membrane trafficking. Loss of Rab35 activity causes an enlargement of early endosomes and inhibits MHC class I recycling. Moreover, it prevents early endosomal recruitment of EHD1, a common component of tubules involved in endosomal cargo recycling. Our data reveal an enzymatic activity for a DENN domain and demonstrate that distinct Rab GTPases can recruit a common protein machinery to various sites within the endosomal network to establish cargo-selective recycling pathways.
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Affiliation(s)
- Patrick D Allaire
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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22
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Abstract
Glucose-stimulated insulin secretion from the islet beta-cell involves a sequence of metabolic events and an interplay between a wide range of signaling pathways leading to the generation of second messengers (e.g., cyclic nucleotides, adenine and guanine nucleotides, soluble lipid messengers) and mobilization of calcium ions. Consequent to the generation of necessary signals, the insulin-laden secretory granules are transported from distal sites to the plasma membrane for fusion and release of their cargo into the circulation. The secretory granule transport underlies precise changes in cytoskeletal architecture involving a well-coordinated cross-talk between various signaling proteins, including small molecular mass GTP-binding proteins (G proteins) and their respective effector proteins. The purpose of this article is to provide an overview of current understanding of the identity of small G proteins (e.g., Cdc42, Rac1, and ARF-6) and their corresponding regulatory factors (e.g., GDP/GTP-exchange factors, GDP-dissociation inhibitors) in the pancreatic beta-cell. Plausible mechanisms underlying regulation of these signaling proteins by insulin secretagogues are also discussed. In addition to their positive modulatory roles, certain small G proteins also contribute to the metabolic dysfunction and demise of the islet beta-cell seen in in vitro and in vivo models of impaired insulin secretion and diabetes. Emerging evidence also suggests significant insulin secretory abnormalities in small G protein knockout animals, further emphasizing vital roles for these proteins in normal health and function of the islet beta-cell. Potential significance of these experimental observations from multiple laboratories and possible avenues for future research in this area of islet research are highlighted.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Avenue, Detroit, MI 48202-3489, USA.
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23
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Branham MT, Bustos MA, De Blas GA, Rehmann H, Zarelli VEP, Treviño CL, Darszon A, Mayorga LS, Tomes CN. Epac activates the small G proteins Rap1 and Rab3A to achieve exocytosis. J Biol Chem 2009; 284:24825-39. [PMID: 19546222 DOI: 10.1074/jbc.m109.015362] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Exocytosis of the acrosome (the acrosome reaction) relies on cAMP production, assembly of a proteinaceous fusion machinery, calcium influx from the extracellular medium, and mobilization from inositol 1,4,5-trisphosphate-sensitive intracellular stores. Addition of cAMP to human sperm suspensions bypasses some of these requirements and elicits exocytosis in a protein kinase A- and extracellular calcium-independent manner. The relevant cAMP target is Epac, a guanine nucleotide exchange factor for the small GTPase Rap. We show here that a soluble adenylyl cyclase synthesizes the cAMP required for the acrosome reaction. Epac stimulates the exchange of GDP for GTP on Rap1, upstream of a phospholipase C. The Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP induces a phospholipase C-dependent calcium mobilization in human sperm suspensions. In addition, our studies identify a novel connection between cAMP and Rab3A, a secretory granule-associated protein, revealing that the latter functions downstream of soluble adenylyl cyclase/cAMP/Epac but not of Rap1. Challenging sperm with calcium or 8-pCPT-2'-O-Me-cAMP boosts the exchange of GDP for GTP on Rab3A. Recombinant Epac does not release GDP from Rab3A in vitro, suggesting that the Rab3A-GEF activation by cAMP/Epac in vivo is indirect. We propose that Epac sits at a critical point during the exocytotic cascade after which the pathway splits into two limbs, one that assembles the fusion machinery into place and another that elicits intracellular calcium release.
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Affiliation(s)
- María T Branham
- Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología-Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Médicas, CC 56, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina
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24
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Kurada BRVVSN, Li LC, Mulherkar N, Subramanian M, Prasad KV, Prabhakar BS. MADD, a splice variant of IG20, is indispensable for MAPK activation and protection against apoptosis upon tumor necrosis factor-alpha treatment. J Biol Chem 2009; 284:13533-13541. [PMID: 19289468 PMCID: PMC2679454 DOI: 10.1074/jbc.m808554200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Revised: 02/24/2009] [Indexed: 11/06/2022] Open
Abstract
We investigated the physiological role of endogenous MAPK-activating death domain-containing protein (MADD), a splice variant of the IG20 gene, that can interact with TNFR1 in tumor necrosis factor-alpha (TNFalpha)-induced activation of NF-kappaB, MAPK, ERK1/2, JNK, and p38. Using exon-specific short hairpin RNAs expressing lentiviruses, we knocked down the expression of all IG20 splice variants or MADD, which is overexpressed in cancer cells. Abrogation of MADD expression rendered cells highly susceptible to TNFalpha-induced apoptosis in the absence of cycloheximide. It also resulted in a dramatic loss in TNFalpha-induced activation of MAPK without any apparent effect on NF-kappaB activation. This observation was substantiated by an accompanying loss in the activation of p90RSK, a key downstream target of MAPK, whereas the NF-kappaB-regulated interleukin 6 levels remained unaffected. Endogenous MADD knockdown, however, did not affect epidermal growth factor-induced MAPK activation thereby demonstrating the specific requirement of MADD for TNF receptor-mediated MAPK activation. Re-expression of short hairpin RNA-resistant MADD in the absence of endogenous IG20 expression rescued the cells from TNFalpha-induced apoptosis. The requirement for MADD was highly specific for TNFalpha-induced activation of MAPK but not the related JNK and p38 kinases. Loss of MADD expression resulted in reduced Grb2 and Sos1/2 recruitment to the TNFR1 complex and decreased Ras and MEKK1/2 activation. These results demonstrate the essential role of MADD in protecting cancer cells from TNFalpha-induced apoptosis by specifically activating MAPKs through Grb2 and Sos1/2 recruitment, and its potential as a novel cancer therapeutic target.
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Affiliation(s)
- Bapi Raju V V S N Kurada
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Liang Cheng Li
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Nirupama Mulherkar
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Mahesh Subramanian
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Kanteti V Prasad
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Bellur S Prabhakar
- Department of Microbiology and Immunology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612.
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25
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Li LC, Sheng JR, Mulherkar N, Prabhakar BS, Meriggioli MN. Regulation of apoptosis and caspase-8 expression in neuroblastoma cells by isoforms of the IG20 gene. Cancer Res 2008; 68:7352-61. [PMID: 18794122 DOI: 10.1158/0008-5472.can-07-6311] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The IG20 gene undergoes alternative splicing resulting in the differential expression of six putative splice variants. Four of these (IG20pa, MADD, IG20-SV2, and DENN-SV) are expressed in virtually all human tissues. However, investigations examining alternative splicing of the IG20 gene to date have been largely limited to nonneural malignant and nonmalignant cells. In this study, we investigated the expression of alternative splice isoforms of the IG20 gene in human neuroblastoma cells. We found that six IG20 splice variants (IG20-SVs) were expressed in two human neuroblastoma cell lines (SK-N-SH and SH-SY5Y), highlighted by the expression of two unique splice isoforms (i.e., KIAA0358 and IG20-SV4). Similarly, we found enriched expression of these two IG20-SVs in human neural tissues derived from cerebral cortex, hippocampus, and, to a lesser extent, spinal cord. Using gain-of-function studies and siRNA technology, we determined that these "neural-enriched isoforms" exerted significant and contrasting effects on vulnerability to apoptosis in neuroblastoma cells. Specifically, expression of KIAA0358 exerted a potent antiapoptotic effect in both the SK-N-SH and SH-SY5Y neuroblastoma cell lines, whereas expression of IG20-SV4 had proapoptotic effects directly related to the activation of caspase-8 in these cells, which have minimal or absent constitutive caspase-8 expression. These data indicate that the pattern of expression of these neural-enriched IG20-SVs regulates the expression and activation of caspase-8 in certain neuroblastoma cells, and that manipulation of IG20-SV expression pattern may represent a potent therapeutic strategy in the therapy of neuroblastoma and perhaps other cancers.
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Affiliation(s)
- Liang Cheng Li
- Department of Neurology, University of Illinois at Chicago, Chicago, Illinois 60523, USA
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26
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Figueiredo AC, Wasmeier C, Tarafder AK, Ramalho JS, Baron RA, Seabra MC. Rab3GEP is the non-redundant guanine nucleotide exchange factor for Rab27a in melanocytes. J Biol Chem 2008; 283:23209-16. [PMID: 18559336 PMCID: PMC2516999 DOI: 10.1074/jbc.m804134200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Rab GTPases regulate discrete steps in vesicular transport pathways. Rabs require activation by specific guanine nucleotide exchange factors (GEFs) that stimulate the exchange of GDP for GTP. Rab27a controls motility and regulated exocytosis of secretory granules and related organelles. In melanocytes, Rab27a regulates peripheral transport of mature melanosomes by recruiting melanophilin and myosin Va. Here, we studied the activation of Rab27a in melanocytes. We identify Rab3GEP, previously isolated as a GEF for Rab3a, as the non-redundant Rab27a GEF. Similar to Rab27a-deficient ashen melanocytes, Rab3GEP-depleted cells show both clustering of melanosomes in the perinuclear area and loss of the Rab27a effector Mlph. Consistent with a role as an activator, levels of Rab27a-GTP are decreased in cells lacking Rab3GEP. Recombinant Rab3GEP exhibits guanine nucleotide exchange activity against Rab27a and Rab27b in vitro, in addition to its previously documented activity against Rab3. Our results indicate promiscuity in Rab GEF action and suggest that members of related but functionally distinct Rab subfamilies can be controlled by common activators.
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Affiliation(s)
- Ana C Figueiredo
- Molecular Medicine, National Heart and Lung Institute, Imperial College London, London SW7 2AZ, United Kingdom
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27
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Itzen A, Pylypenko O, Goody RS, Alexandrov K, Rak A. Nucleotide exchange via local protein unfolding--structure of Rab8 in complex with MSS4. EMBO J 2006; 25:1445-55. [PMID: 16541104 PMCID: PMC1440319 DOI: 10.1038/sj.emboj.7601044] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2005] [Accepted: 02/20/2006] [Indexed: 11/08/2022] Open
Abstract
Rab GTPases function as essential regulators of vesicle transport in eukaryotic cells. MSS4 was shown to stimulate nucleotide exchange on Rab proteins associated with the exocytic pathway and to have nucleotide-free-Rab chaperone activity. A detailed kinetic analysis of MSS4 interaction with Rab8 showed that MSS4 is a relatively slow exchange factor that forms a long-lived nucleotide-free complex with RabGTPase. In contrast to other characterized exchange factor-GTPase complexes, MSS4:Rab8 complex binds GTP faster than GDP, but still ca. 3 orders of magnitude more slowly than comparable complexes. The crystal structure of the nucleotide-free MSS4:Rab8 complex revealed that MSS4 binds to the Switch I and interswitch regions of Rab8, forming an intermolecular beta-sheet. Complex formation results in dramatic structural changes of the Rab8 molecule, leading to unfolding of the nucleotide-binding site and surrounding structural elements, facilitating nucleotide release and slowing its rebinding. Coupling of nucleotide exchange activity to a cycle of GTPase unfolding and refolding represents a novel nucleotide exchange mechanism.
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Affiliation(s)
- Aymelt Itzen
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | - Olena Pylypenko
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | - Roger S Goody
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | | | - Alexey Rak
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
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28
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Mahoney TR, Liu Q, Itoh T, Luo S, Hadwiger G, Vincent R, Wang ZW, Fukuda M, Nonet ML. Regulation of synaptic transmission by RAB-3 and RAB-27 in Caenorhabditis elegans. Mol Biol Cell 2006; 17:2617-25. [PMID: 16571673 PMCID: PMC1474797 DOI: 10.1091/mbc.e05-12-1170] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Rab small GTPases are involved in the transport of vesicles between different membranous organelles. RAB-3 is an exocytic Rab that plays a modulatory role in synaptic transmission. Unexpectedly, mutations in the Caenorhabditis elegans RAB-3 exchange factor homologue, aex-3, cause a more severe synaptic transmission defect as well as a defecation defect not seen in rab-3 mutants. We hypothesized that AEX-3 may regulate a second Rab that regulates these processes with RAB-3. We found that AEX-3 regulates another exocytic Rab, RAB-27. Here, we show that C. elegans RAB-27 is localized to synapse-rich regions pan-neuronally and is also expressed in intestinal cells. We identify aex-6 alleles as containing mutations in rab-27. Interestingly, aex-6 mutants exhibit the same defecation defect as aex-3 mutants. aex-6; rab-3 double mutants have behavioral and pharmacological defects similar to aex-3 mutants. In addition, we demonstrate that RBF-1 (rabphilin) is an effector of RAB-27. Therefore, our work demonstrates that AEX-3 regulates both RAB-3 and RAB-27, that both RAB-3 and RAB-27 regulate synaptic transmission, and that RAB-27 potentially acts through its effector RBF-1 to promote soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) function.
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Affiliation(s)
- Timothy R. Mahoney
- *Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Qiang Liu
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030; and
| | - Takashi Itoh
- Fukuda Initiative Research Unit, RIKEN, Wako, Saitama 351-0198, Japan
| | - Shuo Luo
- *Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Gayla Hadwiger
- *Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Rose Vincent
- *Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Zhao-Wen Wang
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030; and
| | - Mitsunori Fukuda
- Fukuda Initiative Research Unit, RIKEN, Wako, Saitama 351-0198, Japan
| | - Michael L. Nonet
- *Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
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29
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Shurin GV, Tourkova IL, Chatta GS, Schmidt G, Wei S, Djeu JY, Shurin MR. Small Rho GTPases Regulate Antigen Presentation in Dendritic Cells. THE JOURNAL OF IMMUNOLOGY 2005; 174:3394-400. [PMID: 15749872 DOI: 10.4049/jimmunol.174.6.3394] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Dendritic cells (DC) are involved in the regulation of innate and adaptive immunity. However, the molecular mechanisms maintaining DC function remain to be elucidated. In this study, we report on the role of small Rho GTPases: Cdc42, Rac1, and RhoA in the regulation of DC adherence, Ag presentation, migration, chemotaxis, and endocytosis. Murine DC were transfected with vaccinia virus-based constructs, encoding dominant-negative or constitutively active (ca) mutant forms of Rho GTPases. We demonstrate that Cdc42 plays a major role in the regulation of DC adhesion, because caCdc42-transfected DC had significant up-regulation of adhesion to extracellular matrix, which was blocked by the Rho GTPase inhibitor toxin B (ToxB). In contrast, caRho-transfected DC only modestly elevated DC adhesion, and caRac had no effect. Additionally, caCdc42 and caRho increased the ability of DC to present OVA peptide to specific T cells. This effect was abrogated by ToxB. Activation of Cdc42 in DC significantly inhibited spontaneous and chemokine-induced DC migration. Furthermore, uptake of dextran 40 by DC was significantly enhanced by Rho GTPase activators cytotoxic necrotizing factor 1 and PMA, and reduced by ToxB. caCdc42 also increased endocytotic activity of DC, whereas dominant-negative Cdc42 blocked it. Thus, Rho GTPases Cdc42, RhoA, and Rac1 regulate DC functions that are critical for DC-mediated immune responses in vivo.
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Affiliation(s)
- Galina V Shurin
- Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA
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30
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Abstract
The Rab GTPase effector Noc2 was brought into the limelight by a recent publication that demonstrated its requirements at different stages of regulated exocytosis. Noc2 knockout resulted in distinct abnormalities in endocrine and exocrine cells, ranging from the accumulation of secretory granules of increased size to impairments in the regulated release of their secretory products. Explanations for these defects are beginning to emerge and they promise to reveal some of the most jealously kept secrets of regulated exocytosis.
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Affiliation(s)
- Séverine Cheviet
- Department of Cell Biology and Morphology, University of Lausanne, Switzerland
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31
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Abstract
DENN/MADD is a component of a signalling protein complex that is localized to the cytosol and exerts multiple functions by using different binding partners. Human DENN/MADD is physically the same death-domain protein as rat Rab3 GDP/GTP exchange protein (Rab3GEP). DENN/MADD regulates the recycling of Rab3 small G proteins under normal conditions and has an essential role in Ca(2+)-dependent neurotransmitter release and exocytosis. It is also involved in blocking the apoptosis of neuronal cells under conditions of cytotoxic stress. Recent research supports an important role for DENN/MADD in neuroprotection: reduced endogenous DENN/MADD expression and enhanced pro-apoptotic signalling has been found in brains affected by Alzheimer's disease.
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Affiliation(s)
- Jun Miyoshi
- Department of Molecular Biology, Osaka Medical Centre for Cancer and Cardiovascular Diseases, Osaka 537-8511, Japan.
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