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More KJ, Kaur H, Simpson AGB, Spiegel FW, Dacks JB. Contractile vacuoles: a rapidly expanding (and occasionally diminishing?) understanding. Eur J Protistol 2024; 94:126078. [PMID: 38688044 DOI: 10.1016/j.ejop.2024.126078] [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: 12/19/2023] [Revised: 03/18/2024] [Accepted: 03/20/2024] [Indexed: 05/02/2024]
Abstract
Osmoregulation is the homeostatic mechanism essential for the survival of organisms in hypoosmotic and hyperosmotic conditions. In freshwater or soil dwelling protists this is frequently achieved through the action of an osmoregulatory organelle, the contractile vacuole. This endomembrane organelle responds to the osmotic challenges and compensates by collecting and expelling the excess water to maintain the cellular osmolarity. As compared with other endomembrane organelles, this organelle is underappreciated and under-studied. Here we review the reported presence or absence of contractile vacuoles across eukaryotic diversity, as well as the observed variability in the structure, function, and molecular machinery of this organelle. Our findings highlight the challenges and opportunities for constructing cellular and evolutionary models for this intriguing organelle.
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Affiliation(s)
- Kiran J More
- Division of Infectious Diseases, Department of Medicine, and Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Harpreet Kaur
- Division of Infectious Diseases, Department of Medicine, and Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Alastair G B Simpson
- Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie University, Halifax, NS, Canada; Department of Biology, Dalhousie University, Halifax, NS, Canada
| | - Frederick W Spiegel
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR, 72701, USA
| | - Joel B Dacks
- Division of Infectious Diseases, Department of Medicine, and Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada; Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic; Centre for Life's Origins and Evolution, Department of Genetics, Evolution, & Environment, University College, London, United Kingdom.
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2
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Huber RJ, Kim WD, Wilson-Smillie MLDM. Mechanisms regulating the intracellular trafficking and release of CLN5 and CTSD. Traffic 2024; 25:e12925. [PMID: 38272448 DOI: 10.1111/tra.12925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 11/20/2023] [Accepted: 11/21/2023] [Indexed: 01/27/2024]
Abstract
Ceroid lipofuscinosis neuronal 5 (CLN5) and cathepsin D (CTSD) are soluble lysosomal enzymes that also localize extracellularly. In humans, homozygous mutations in CLN5 and CTSD cause CLN5 disease and CLN10 disease, respectively, which are two subtypes of neuronal ceroid lipofuscinosis (commonly known as Batten disease). The mechanisms regulating the intracellular trafficking of CLN5 and CTSD and their release from cells are not well understood. Here, we used the social amoeba Dictyostelium discoideum as a model system to examine the pathways and cellular components that regulate the intracellular trafficking and release of the D. discoideum homologs of human CLN5 (Cln5) and CTSD (CtsD). We show that both Cln5 and CtsD contain signal peptides for secretion that facilitate their release from cells. Like Cln5, extracellular CtsD is glycosylated. In addition, Cln5 release is regulated by the amount of extracellular CtsD. Autophagy induction promotes the release of Cln5, and to a lesser extent CtsD. Release of Cln5 requires the autophagy proteins Atg1, Atg5, and Atg9, as well as autophagosomal-lysosomal fusion. Atg1 and Atg5 are required for the release of CtsD. Together, these data support a model where Cln5 and CtsD are actively released from cells via their signal peptides for secretion and pathways linked to autophagy. The release of Cln5 and CtsD from cells also requires microfilaments and the D. discoideum homologs of human AP-3 complex mu subunit, the lysosomal-trafficking regulator LYST, mucopilin-1, and the Wiskott-Aldrich syndrome-associated protein WASH, which all regulate lysosomal exocytosis in this model organism. These findings suggest that lysosomal exocytosis also facilitates the release of Cln5 and CtsD from cells. In addition, we report the roles of ABC transporters, microtubules, osmotic stress, and the putative D. discoideum homologs of human sortilin and cation-independent mannose-6-phosphate receptor in regulating the intracellular/extracellular distribution of Cln5 and CtsD. In total, this study identifies the cellular mechanisms regulating the release of Cln5 and CtsD from D. discoideum cells and provides insight into how altered trafficking of CLN5 and CTSD causes disease in humans.
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Affiliation(s)
- Robert J Huber
- Department of Biology, Trent University, Peterborough, Ontario, Canada
- Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, Canada
| | - William D Kim
- Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, Canada
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3
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Jeong J, Hwang YE, Lee M, Keum S, Song S, Kim JW, Choi JH, Rhee S. Downregulation of AP1S1 causes the lysosomal degradation of EGFR in non-small cell lung cancer. J Cell Physiol 2023; 238:2335-2347. [PMID: 37659097 DOI: 10.1002/jcp.31112] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 06/28/2023] [Accepted: 07/13/2023] [Indexed: 09/04/2023]
Abstract
Matrix stiffness has been shown to play a critical role in cancer progression by influencing various cellular processes, including epidermal growth factor (EGF) signaling. However, the underlying molecular mechanisms are not fully understood. Here, we investigated the role of adaptor-related protein complex 1 subunit sigma 1 (AP1S1), a component of adaptor protein complex-1, in the regulation of EGF receptor (EGFR) intracellular trafficking during cancer cell progression. We found that AP1S1 expression was upregulated under stiff matrix conditions, resulting in the regulation of EGFR trafficking in non-small cell lung adenocarcinoma cells. Knockout of AP1S1 caused the lysosomal degradation of EGFR, leading to suppressed EGF-induced anaplastic lymphoma receptor tyrosine kinase phosphorylation. In addition, the downregulation of AP1S1 increased the sensitivity of H1975 cancer cells, which are resistant to tyrosine kinase inhibitors, to erlotinib. Collectively, our results suggest that AP1S1 could regulate EGFR recycling under stiff matrix conditions, and AP1S1 inhibition could be a novel strategy for treating cancer cells resistant to EGFR-targeted anticancer drugs.
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Affiliation(s)
- Jangho Jeong
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Ye Eun Hwang
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Minwoo Lee
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Seula Keum
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Seongeun Song
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Jung-Woong Kim
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Jee-Hye Choi
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
| | - Sangmyung Rhee
- Department of Life Science, Chung-Ang University, Seoul, Republic of Korea
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Fadil SA, Janetopoulos C. The Polarized Redistribution of the Contractile Vacuole to the Rear of the Cell is Critical for Streaming and is Regulated by PI(4,5)P2-Mediated Exocytosis. Front Cell Dev Biol 2022; 9:765316. [PMID: 35928786 PMCID: PMC9344532 DOI: 10.3389/fcell.2021.765316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 10/20/2021] [Indexed: 12/05/2022] Open
Abstract
Dictyostelium discoideum amoebae align in a head to tail manner during the process of streaming during fruiting body formation. The chemoattractant cAMP is the chemoattractant regulating cell migration during this process and is released from the rear of cells. The process by which this cAMP release occurs has eluded investigators for many decades, but new findings suggest that this release can occur through expulsion during contractile vacuole (CV) ejection. The CV is an organelle that performs several functions inside the cell including the regulation of osmolarity, and discharges its content via exocytosis. The CV localizes to the rear of the cell and appears to be part of the polarity network, with the localization under the influence of the plasma membrane (PM) lipids, including the phosphoinositides (PIs), among those is PI(4,5)P2, the most abundant PI on the PM. Research on D. discoideum and neutrophils have shown that PI(4,5)P2 is enriched at the rear of migrating cells. In several systems, it has been shown that the essential regulator of exocytosis is through the exocyst complex, mediated in part by PI(4,5)P2-binding. This review features the role of the CV complex in D. discoideum signaling with a focus on the role of PI(4,5)P2 in regulating CV exocytosis and localization. Many of the regulators of these processes are conserved during evolution, so the mechanisms controlling exocytosis and membrane trafficking in D. discoideum and mammalian cells will be discussed, highlighting their important functions in membrane trafficking and signaling in health and disease.
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Affiliation(s)
- Sana A. Fadil
- Department of Biological Sciences, University of the Sciences in Philadelphia, Philadelphia, PA, United States
- Department of Natural product, Faculty of Pharmacy, King Abdulaziz University, Saudia Arabia
| | - Chris Janetopoulos
- Department of Biological Sciences, University of the Sciences in Philadelphia, Philadelphia, PA, United States
- The Science Research Institute, Albright College, Reading, PA, United States
- The Department of Cell Biology at Johns Hopkins University School of Medicine, Baltimore, MD, United States
- *Correspondence: Chris Janetopoulos,
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Samson GPB, Legler DF. Membrane Compartmentalization and Scaffold Proteins in Leukocyte Migration. Front Cell Dev Biol 2020; 8:285. [PMID: 32411706 PMCID: PMC7198906 DOI: 10.3389/fcell.2020.00285] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 04/02/2020] [Indexed: 01/14/2023] Open
Abstract
Leukocyte migration across vessels into and within peripheral and lymphoid tissues is essential for host defense against invading pathogens. Leukocytes are specialized in sensing a variety of guidance cues and to integrate environmental stimuli to navigate in a timely and spatially controlled manner. These extracellular signals must be transmitted across the leukocyte’s plasma membrane in a way that intracellular signaling cascades enable directional cell movement. Therefore, the composition of the membrane in concert with proteins that influence the compartmentalization of the plasma membrane or contribute to delineate intracellular signaling molecules are key in controlling leukocyte navigation. This becomes evident by the fact that mislocalization of membrane proteins is known to deleteriously affect cellular functions that may cause diseases. In this review we summarize recent advances made in the understanding of how membrane cholesterol levels modulate chemokine receptor signaling and hence leukocyte trafficking. Moreover, we provide an overview on the role of membrane scaffold proteins, particularly tetraspanins, flotillins/reggies, and caveolins in controlling leukocyte migration both in vitro and in vivo.
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Affiliation(s)
- Guerric P B Samson
- Biotechnology Institute Thurgau at the University of Konstanz, Kreuzlingen, Switzerland
| | - Daniel F Legler
- Biotechnology Institute Thurgau at the University of Konstanz, Kreuzlingen, Switzerland.,Faculty of Biology, University of Konstanz, Konstanz, Germany.,Theodor Kocher Institute, University of Bern, Bern, Switzerland
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The Effect of Overexpressed DdRabS on Development, Cell Death, Vesicular Trafficking, and the Secretion of Lysosomal Glycosidase Enzymes. BIOLOGY 2018; 7:biology7020033. [PMID: 29843387 PMCID: PMC6023087 DOI: 10.3390/biology7020033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 05/11/2018] [Accepted: 05/21/2018] [Indexed: 11/21/2022]
Abstract
Rab GTPases are essential regulators of many cellular processes and play an important role in downstream signaling vital to proper cell function. We sought to elucidate the role of novel D. discoideum GTPase RabS. Cell lines over-expressing DdRabS and expressing DdRabS N137I (dominant negative (DN)) proteins were generated, and it was determined that DdRabS localized to endosomes, ER-Golgi membranes, and the contractile vacuole system. It appeared to function in vesicular trafficking, and the secretion of lysosomal enzymes. Interestingly, microscopic analysis of GFP-tagged DdRabS (DN) cells showed differential localization to lysosomes and endosomes compared to GFP-tagged DdRabS overexpressing cells. Both cell lines over-secreted lysosomal glycosidase enzymes, especially β-glucosidase. Furthermore, DdRabS overexpressing cells were defective in aggregation due to decreased cell–cell cohesion and sensitivity to cAMP, leading to abnormal chemotactic migration, the inability to complete development, and increased induced cell death. These data support a role for DdRabS in trafficking along the vesicular and biosynthetic pathways. We hypothesize that overexpression of DdRabS may interfere with GTP activation of related proteins essential for normal development resulting in a cascade of defects throughout these processes.
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Moreira CMDN, Batista CM, Fernandes JC, Kessler RL, Soares MJ, Fragoso SP. Knockout of the gamma subunit of the AP-1 adaptor complex in the human parasite Trypanosoma cruzi impairs infectivity and differentiation and prevents the maturation and targeting of the major protease cruzipain. PLoS One 2017; 12:e0179615. [PMID: 28759609 PMCID: PMC5536268 DOI: 10.1371/journal.pone.0179615] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 05/31/2017] [Indexed: 11/18/2022] Open
Abstract
The AP-1 Adaptor Complex assists clathrin-coated vesicle assembly in the trans-Golgi network (TGN) of eukaryotic cells. However, the role of AP-1 in the protozoan Trypanosoma cruzi-the Chagas disease parasite-has not been addressed. Here, we studied the function and localization of AP-1 in different T. cruzi life cycle forms, by generating a gene knockout of the large AP-1 subunit gamma adaptin (TcAP1-γ), and raising a monoclonal antibody against TcAP1-γ. Co-localization with a Golgi marker and with the clathrin light chain showed that TcAP1-γ is located in the Golgi, and it may interact with clathrin in vivo, at the TGN. Epimastigote (insect form) parasites lacking TcAP1-γ (TcγKO) have reduced proliferation and differentiation into infective metacyclic trypomastigotes (compared with wild-type parasites). TcγKO parasites have also displayed significantly reduced infectivity towards mammalian cells. Importantly, TcAP1-γ knockout impaired maturation and transport to lysosome-related organelles (reservosomes) of a key cargo-the major cysteine protease cruzipain, which is important for parasite nutrition, differentiation and infection. In conclusion, the defective processing and transport of cruzipain upon AP-1 ablation may underlie the phenotype of TcγKO parasites.
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Affiliation(s)
| | | | | | - Rafael Luis Kessler
- Laboratory of Functional Genomics. Instituto Carlos Chagas/Fiocruz, Curitiba - PR, Brazil
| | - Maurilio José Soares
- Laboratory of Cell Biology, Instituto Carlos Chagas/Fiocruz, Curitiba - PR, Brazil
| | - Stenio Perdigão Fragoso
- Laboratory of Molecular Biology of Trypanosomatids, Instituto Carlos Chagas/Fiocruz, Curitiba - PR, Brazil
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Klinger CM, Ramirez-Macias I, Herman EK, Turkewitz AP, Field MC, Dacks JB. Resolving the homology-function relationship through comparative genomics of membrane-trafficking machinery and parasite cell biology. Mol Biochem Parasitol 2016; 209:88-103. [PMID: 27444378 PMCID: PMC5140719 DOI: 10.1016/j.molbiopara.2016.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 07/12/2016] [Accepted: 07/16/2016] [Indexed: 10/21/2022]
Abstract
With advances in DNA sequencing technology, it is increasingly common and tractable to informatically look for genes of interest in the genomic databases of parasitic organisms and infer cellular states. Assignment of a putative gene function based on homology to functionally characterized genes in other organisms, though powerful, relies on the implicit assumption of functional homology, i.e. that orthology indicates conserved function. Eukaryotes reveal a dazzling array of cellular features and structural organization, suggesting a concomitant diversity in their underlying molecular machinery. Significantly, examples of novel functions for pre-existing or new paralogues are not uncommon. Do these examples undermine the basic assumption of functional homology, especially in parasitic protists, which are often highly derived? Here we examine the extent to which functional homology exists between organisms spanning the eukaryotic lineage. By comparing membrane trafficking proteins between parasitic protists and traditional model organisms, where direct functional evidence is available, we find that function is indeed largely conserved between orthologues, albeit with significant adaptation arising from the unique biological features within each lineage.
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Affiliation(s)
- Christen M Klinger
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada
| | | | - Emily K Herman
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada
| | - Aaron P Turkewitz
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL, USA
| | - Mark C Field
- School of Life Sciences, University of Dundee, Dundee, UK
| | - Joel B Dacks
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada.
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9
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Annesley SJ, Chen S, Francione LM, Sanislav O, Chavan AJ, Farah C, De Piazza SW, Storey CL, Ilievska J, Fernando SG, Smith PK, Lay ST, Fisher PR. Dictyostelium, a microbial model for brain disease. Biochim Biophys Acta Gen Subj 2013; 1840:1413-32. [PMID: 24161926 DOI: 10.1016/j.bbagen.2013.10.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 10/05/2013] [Accepted: 10/10/2013] [Indexed: 12/25/2022]
Abstract
BACKGROUND Most neurodegenerative diseases are associated with mitochondrial dysfunction. In humans, mutations in mitochondrial genes result in a range of phenotypic outcomes which do not correlate well with the underlying genetic cause. Other neurodegenerative diseases are caused by mutations that affect the function and trafficking of lysosomes, endosomes and autophagosomes. Many of the complexities of these human diseases can be avoided by studying them in the simple eukaryotic model Dictyostelium discoideum. SCOPE OF REVIEW This review describes research using Dictyostelium to study cytopathological pathways underlying a variety of neurodegenerative diseases including mitochondrial, lysosomal and vesicle trafficking disorders. MAJOR CONCLUSIONS Generalised mitochondrial respiratory deficiencies in Dictyostelium produce a consistent pattern of defective phenotypes that are caused by chronic activation of a cellular energy sensor AMPK (AMP-activated protein kinase) and not ATP deficiency per se. Surprisingly, when individual subunits of Complex I are knocked out, both AMPK-dependent and AMPK-independent, subunit-specific phenotypes are observed. Many nonmitochondrial proteins associated with neurological disorders have homologues in Dictyostelium and are associated with the function and trafficking of lysosomes and endosomes. Conversely, some genes associated with neurodegenerative disorders do not have homologues in Dictyostelium and this provides a unique avenue for studying these mutated proteins in the absence of endogeneous protein. GENERAL SIGNIFICANCE Using the Dictyostelium model we have gained insights into the sublethal cytopathological pathways whose dysregulation contributes to phenotypic outcomes in neurodegenerative disease. This work is beginning to distinguish correlation, cause and effect in the complex network of cross talk between the various organelles involved. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.
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Affiliation(s)
- S J Annesley
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S Chen
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - L M Francione
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - O Sanislav
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - A J Chavan
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - C Farah
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S W De Piazza
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - C L Storey
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - J Ilievska
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S G Fernando
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - P K Smith
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S T Lay
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - P R Fisher
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086.
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Niu YS, Cai ZZ, Lu Y, Wang MX, Liang S, Zhou F, Miao YG. Characterization of adaptor protein complex-1 in the silkworm, Bombyx mori. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2013; 82:84-95. [PMID: 23300124 DOI: 10.1002/arch.21077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
To investigate the function of adaptor protein complex-1 (AP-1) in the silkworm, we characterized AP-1 in the silkworm by RNAi technique and co-localization methods. As a result, AP-1 was found to exist as cytosolic form and membrane-bound form distinguished by phosphate status, showing molecular mass difference. There was relatively more cytosolic form of AP-1 than its membrane-bound counterpart in the silkworm. However, AP-1 distributed predominantly as cytosolic form in BmN cells. Interruption of AP-1 expression via DsRNA was more efficient in BmN cells than in the insect larval, which led to a tendency to dissociation between subcellular organelles like the Golgi apparatus and the mitochondria. Environmental condition changes like relatively higher temperature and treatment with dimethyl sulfoxide can lead to expression variance of AP-1 both in mRNA and protein level. In BmN cells, both the heavy chain γ and light chain σ could clearly co-localize with AP-1 β, mostly forming pits in cytoplasm. Two isoforms of AP-1 σ corresponded to distinct subcellular distribution pattern, possibly due to C-terminal amino acids difference.
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Affiliation(s)
- Yan-shan Niu
- Key Laboratory of Animal Virology of Ministry of Agriculture, College of Animal Sciences, Zhejiang University, Hangzhou, P. R. China
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Contractile Vacuole Complex—Its Expanding Protein Inventory. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 306:371-416. [DOI: 10.1016/b978-0-12-407694-5.00009-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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12
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New insights into roles of acidocalcisomes and contractile vacuole complex in osmoregulation in protists. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 305:69-113. [PMID: 23890380 DOI: 10.1016/b978-0-12-407695-2.00002-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
While free-living protists are usually subjected to hyposmotic environments, parasitic protists are also in contact with hyperosmotic habitats. Recent work in one of these parasites, Trypanosoma cruzi, has revealed that its contractile vacuole complex, which usually collects and expels excess water as a mechanism of regulatory volume decrease after hyposmotic stress, has also a role in cell shrinking when the cells are submitted to hyperosmotic stress. Trypanosomes also have an acidic calcium store rich in polyphosphate (polyP), named the acidocalcisome, which is involved in their response to osmotic stress. Here, we review newly emerging insights on the role of acidocalcisomes and the contractile vacuole complex in the cellular response to hyposmotic and hyperosmotic stresses. We also review the current state of knowledge on the composition of these organelles and their other roles in calcium homeostasis and protein trafficking.
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13
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Kuhnert O, Baumann O, Meyer I, Gräf R. CP55, a novel key component of centrosomal organization in Dictyostelium. Cell Mol Life Sci 2012; 69:3651-64. [PMID: 22744750 PMCID: PMC11114750 DOI: 10.1007/s00018-012-1040-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 05/03/2012] [Accepted: 05/23/2012] [Indexed: 10/28/2022]
Abstract
Dictyostelium centrosomes consist of a layered core structure surrounded by a microtubule-nucleating corona. At the G2/M transition, the corona dissociates and the core structure duplicates, yielding two spindle pole bodies. Finally, in telophase, the spindle poles mature into two new, complete centrosomes. CP55 was identified in a centrosomal proteome analysis. It is a component of the centrosomal core structure, and persists at the centrosome throughout the entire cell cycle. FRAP experiments revealed that during interphase the majority of centrosomal GFP-CP55 is immobile, which indicates a structural task of CP55 at the centrosome. The CP55null mutant is characterized by increased ploidy, a less structured, slightly enlarged corona, and by supernumerary, cytosolic MTOCs, containing only corona proteins and lacking a core structure. Live cell imaging showed that supernumerary MTOCs arise in telophase. Lack of CP55 also caused premature recruitment of the corona organizer CP148 to mitotic spindle poles, already in metaphase instead of telophase. Forces transmitted through astral microtubules may expel prematurely acquired or loosely attached corona fragments into the cytosol, where they act as independent MTOCs. CP55null cells were also impaired in growth, most probably due to difficulties in centrosome splitting during prophase. Furthermore, although they were still capable of phagocytosis, they appeared unable to utilize phagocytosed nutrients. This inability may be attributed to their partially disorganized Golgi apparatus.
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Affiliation(s)
- Oliver Kuhnert
- Department of Cell Biology, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 26, 14476 Potsdam-Golm, Germany
| | - Otto Baumann
- Department of Animal Physiology, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 26, 14476 Potsdam-Golm, Germany
| | - Irene Meyer
- Department of Cell Biology, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 26, 14476 Potsdam-Golm, Germany
| | - Ralph Gräf
- Department of Cell Biology, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 26, 14476 Potsdam-Golm, Germany
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Niu YS, Wang MX, Liang S, Zhou F, Miao YG. Expression and localization of silkworm adaptor protein complex-1 subunits, which were down-regulated post baculovirus infection. Mol Biol Rep 2012; 39:10775-83. [PMID: 23053975 DOI: 10.1007/s11033-012-1971-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Accepted: 10/01/2012] [Indexed: 12/17/2022]
Abstract
Adaptor protein complexes (APs) function as vesicle coat components in different membrane traffic pathways. In this study the subunits of adaptor protein complex-1 (AP-1) of silkworm Bombyx mori were molecularly characterized. All coding genes for the four subunits were cloned and sequenced. Phylogenic tree for each adaptin was constructed and all subunits were found to be conserved in respective group among organisms. The mRNA expression pattern for each adaptin was similar among tissues. Alternative splicing event was observed in genes encoding both the heavy chain gamma and beta adaptin and the light chain subunit, which could generate other possible adaptin forms. GFP-tagged fusion proteins indicated that AP-1 located in the peripheral plasma area. Furthermore, the BmNPV infection in B. mori cells had differentiated effect on the expression level of AP-1 subunits.
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Affiliation(s)
- Yan-Shan Niu
- Key Laboratory of Animal Virology of Ministry of Agriculture, College of Animal Sciences, Zhejiang University, Hangzhou, 310058, People's Republic of China
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15
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Macro L, Jaiswal JK, Simon SM. Dynamics of clathrin-mediated endocytosis and its requirement for organelle biogenesis in Dictyostelium. J Cell Sci 2012; 125:5721-32. [PMID: 22992464 DOI: 10.1242/jcs.108837] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The protein clathrin mediates one of the major pathways of endocytosis from the extracellular milieu and plasma membrane. In single-cell eukaryotes, such as Saccharomyces cerevisiae, the gene encoding clathrin is not an essential gene, raising the question of whether clathrin conveys specific advantages for multicellularity. Furthermore, in contrast to mammalian cells, endocytosis in S. cerevisiae is not dependent on either clathrin or adaptor protein 2 (AP2), an endocytic adaptor molecule. In this study, we investigated the requirement for components of clathrin-mediated endocytosis (CME) in another unicellular organism, the amoeba Dictyostelium. We identified a heterotetrameric AP2 complex in Dictyostelium that is similar to that which is found in higher eukaryotes. By simultaneously imaging fluorescently tagged clathrin and AP2, we found that, similar to higher eukaryotes, these proteins colocalized to membrane puncta that move into the cell together. In addition, the contractile vacuole marker protein, dajumin-green fluorescent protein (GFP), is trafficked via the cell membrane and internalized by CME in a clathrin-dependent, AP2-independent mechanism. This pathway is distinct from other endocytic mechanisms in Dictyostelium. Our finding that CME is required for the internalization of contractile vacuole proteins from the cell membrane explains the contractile vacuole biogenesis defect in Dictyostelium cells lacking clathrin. Our results also suggest that the machinery for CME and its role in organelle maintenance appeared early during eukaryotic evolution. We hypothesize that dependence of endocytosis on specific components of the CME pathway evolved later, as demonstrated by internalization independent of AP2 function.
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Affiliation(s)
- Laura Macro
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, NY 10065, USA
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16
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Farías GG, Cuitino L, Guo X, Ren X, Jarnik M, Mattera R, Bonifacino JS. Signal-mediated, AP-1/clathrin-dependent sorting of transmembrane receptors to the somatodendritic domain of hippocampal neurons. Neuron 2012; 75:810-23. [PMID: 22958822 PMCID: PMC3439821 DOI: 10.1016/j.neuron.2012.07.007] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/03/2012] [Indexed: 11/22/2022]
Abstract
Plasma membranes of the somatodendritic and axonal domains of neurons are known to have different protein compositions, but the molecular mechanisms that determine this polarized protein distribution remain poorly understood. Herein we show that somatodendritic sorting of various transmembrane receptors in rat hippocampal neurons is mediated by recognition of signals within the cytosolic domains of the proteins by the μ1A subunit of the adaptor protein-1 (AP-1) complex. This complex, in conjunction with clathrin, functions in the neuronal soma to exclude somatodendritic proteins from axonal transport carriers. Perturbation of this process affects dendritic spine morphology and decreases the number of synapses. These findings highlight the primary recognition event that underlies somatodendritic sorting and contribute to the evolving view of AP-1 as a global regulator of cell polarity.
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Affiliation(s)
- Ginny G. Farías
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Loreto Cuitino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Xiaoli Guo
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Xuefeng Ren
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Michal Jarnik
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Rafael Mattera
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Juan S. Bonifacino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
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17
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Dallaire-Dufresne S, Paquet VE, Charette SJ. [Dictyostelium discoideum: a model for the study of bacterial virulence]. Can J Microbiol 2012; 57:699-707. [PMID: 21877947 DOI: 10.1139/w11-072] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The amoeba Dictyostelium discoideum, a bacterial predator, has emerged as a valuable tool for studying bacterial virulence. All its features make this unicellular eukaryote a versatile model organism. It can be used to study virulence factors of pathogenic bacteria as well as host elements involved in resistance to pathogens. The virulence of more than 20 bacterial species pathogenic for humans or animals has been studied using D. discoideum so far. These bacteria are either extracellular or intracellular pathogens. This review presents an overview of the question, with special emphasis on the reasons why D. discoideum is a suitable host model to study bacterial virulence, as well as on the type of information on host–pathogen relationship this amoeba can provide.
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Affiliation(s)
- Stéphanie Dallaire-Dufresne
- Institut de biologie intégrative et des systèmes, Pavillon Charles-Eugène-Marchand, Université Laval, 1030 avenue de la Médecine, Québec, QC G1V 0A6, Canada
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18
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Sosa RT, Weber MM, Wen Y, O'Halloran TJ. A single β adaptin contributes to AP1 and AP2 complexes and clathrin function in Dictyostelium. Traffic 2011; 13:305-16. [PMID: 22050483 DOI: 10.1111/j.1600-0854.2011.01310.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2011] [Revised: 10/31/2011] [Accepted: 10/31/2011] [Indexed: 12/15/2022]
Abstract
The assembly of clathrin-coated vesicles is important for numerous cellular processes, including nutrient uptake and membrane organization. Important contributors to clathrin assembly are four tetrameric assembly proteins, also called adaptor proteins (APs), each of which contains a β subunit. We identified a single β subunit, named β1/2, that contributes to both the AP1 and AP2 complexes of Dictyostelium. Disruption of the gene encoding β1/2 resulted in severe defects in growth, cytokinesis and development. Additionally, cells lacking β1/2 displayed profound osmoregulatory defects including the absence of contractile vacuoles and mislocalization of contractile vacuole markers. The phenotypes of β1/2 null cells were most similar to previously described phenotypes of clathrin and AP1 mutants, supporting a particularly important contribution of AP1 to clathrin pathways in Dictyostelium cells. The absence of β1/2 in cells led to significant reductions in the protein amounts of the medium-sized subunits of the AP1 and AP2 complexes, establishing a role for the β subunit in the stability of the medium subunits. Dictyostelium β1/2 could resemble a common ancestor of the more specialized β1 and β2 subunits of the vertebrate AP complexes. Our results support the essential contribution of a single β subunit to the stability and function of AP1 and AP2 in a simple eukaryote.
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Affiliation(s)
- R Thomas Sosa
- Section of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
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19
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Ulrich PN, Jimenez V, Park M, Martins VP, Atwood J, Moles K, Collins D, Rohloff P, Tarleton R, Moreno SNJ, Orlando R, Docampo R. Identification of contractile vacuole proteins in Trypanosoma cruzi. PLoS One 2011; 6:e18013. [PMID: 21437209 PMCID: PMC3060929 DOI: 10.1371/journal.pone.0018013] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2010] [Accepted: 02/22/2011] [Indexed: 11/19/2022] Open
Abstract
Contractile vacuole complexes are critical components of cell volume regulation
and have been shown to have other functional roles in several free-living
protists. However, very little is known about the functions of the contractile
vacuole complex of the parasite Trypanosoma cruzi, the
etiologic agent of Chagas disease, other than a role in osmoregulation.
Identification of the protein composition of these organelles is important for
understanding their physiological roles. We applied a combined proteomic and
bioinfomatic approach to identify proteins localized to the contractile vacuole.
Proteomic analysis of a T. cruzi fraction enriched for
contractile vacuoles and analyzed by one-dimensional gel electrophoresis and
LC-MS/MS resulted in the addition of 109 newly detected proteins to the group of
expressed proteins of epimastigotes. We also identified different peptides that
map to at least 39 members of the dispersed gene family 1 (DGF-1) providing
evidence that many members of this family are simultaneously expressed in
epimastigotes. Of the proteins present in the fraction we selected several
homologues with known localizations in contractile vacuoles of other organisms
and others that we expected to be present in these vacuoles on the basis of
their potential roles. We determined the localization of each by expression as
GFP-fusion proteins or with specific antibodies. Six of these putative proteins
(Rab11, Rab32, AP180, ATPase subunit B, VAMP1, and phosphate transporter)
predominantly localized to the vacuole bladder. TcSNARE2.1, TcSNARE2.2, and
calmodulin localized to the spongiome. Calmodulin was also cytosolic. Our
results demonstrate the utility of combining subcellular fractionation,
proteomic analysis, and bioinformatic approaches for localization of organellar
proteins that are difficult to detect with whole cell methodologies. The CV
localization of the proteins investigated revealed potential novel roles of
these organelles in phosphate metabolism and provided information on the
potential participation of adaptor protein complexes in their biogenesis.
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Affiliation(s)
- Paul N. Ulrich
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Veronica Jimenez
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Miyoung Park
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Vicente P. Martins
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - James Atwood
- Complex Carbohydrate Research Center,
University of Georgia, Athens, Georgia, United States of America
| | - Kristen Moles
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Dalis Collins
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Peter Rohloff
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Rick Tarleton
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Silvia N. J. Moreno
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
| | - Ron Orlando
- Complex Carbohydrate Research Center,
University of Georgia, Athens, Georgia, United States of America
| | - Roberto Docampo
- Center for Tropical and Emerging Global
Diseases and Department of Cellular Biology, University of Georgia, Athens,
Georgia, United States of America
- * E-mail:
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20
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Maniak M. Dictyostelium as a model for human lysosomal and trafficking diseases. Semin Cell Dev Biol 2010; 22:114-9. [PMID: 21056680 DOI: 10.1016/j.semcdb.2010.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 10/27/2010] [Accepted: 11/01/2010] [Indexed: 11/17/2022]
Abstract
Dictyostelium cells are genetically haploid and therefore easily analyzed for mutant phenotypes. In the past, many tools and molecular markers have been developed for a quantitative and qualitative analysis of the endocytic pathway in these amoebae. This review outlines parallels and discrepancies between mutants in Dictyostelium, the corresponding mammalian cells and the symptoms of human patients affected by lysosomal and trafficking defects. Situations where knowledge from Dictyostelium may potentially help understand human disease and vice versa are also addressed.
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Affiliation(s)
- Markus Maniak
- Abteilung Zellbiologie, Universität Kassel, Kassel, Germany.
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21
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Qiao Y, Jiang W, Lee J, Park B, Choi MS, Piao R, Woo MO, Roh JH, Han L, Paek NC, Seo HS, Koh HJ. SPL28 encodes a clathrin-associated adaptor protein complex 1, medium subunit micro 1 (AP1M1) and is responsible for spotted leaf and early senescence in rice (Oryza sativa). THE NEW PHYTOLOGIST 2010; 185:258-74. [PMID: 19825016 DOI: 10.1111/j.1469-8137.2009.03047.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
To expand our understanding of cell death in plant defense responses, we isolated a novel rice (Oryza sativa) spotted leaf mutant (spl28) that displays a lesion mimic phenotype in the absence of pathogen attack through treatment of Hwacheongbyeo (an elite Korean japonica cultivar) with N-methyl-N-nitrosourea (MNU). Early stage development of the spl28 mutant was normal. However, after flowering, spl28 mutants exhibited a significant decrease in chlorophyll content, soluble protein content, and photosystem II efficiency, and high concentrations of reactive oxygen species (ROS), phytoalexin, callose, and autofluorescent phenolic compounds that localized in or around the lesions. The spl28 mutant also exhibited significantly enhanced resistance to rice blast and bacterial blight. Using a map-based cloning approach, we determined that SPL28 encodes a clathrin-associated adaptor protein complex 1, medium subunit micro 1 (AP1M1), which is involved in the post-Golgi trafficking pathway. A green fluorescent protein (GFP) fusion protein of SPL28 (SPL28::GFP) localized to the Golgi apparatus, and expression of SPL28 complemented the membrane trafficking defect of apm1-1 Delta yeast mutants. SPL28 was ubiquitously expressed and contained a highly conserved adaptor complex medium subunit (ACMS) family domain. SPL28 appears to be involved in the regulation of vesicular trafficking, and SPL28 dysfunction causes the formation of hypersensitive response (HR)-like lesions, leading to the initiation of leaf senescence.
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Affiliation(s)
- Yongli Qiao
- Department of Plant Science, Research Institute for Agriculture and Life Sciences, and Plant Genomics and Breeding Institute, Seoul National University, Seoul, 151-921, Republic of Korea
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22
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Betapudi V, Egelhoff TT. Roles of an unconventional protein kinase and myosin II in amoeba osmotic shock responses. Traffic 2009; 10:1773-84. [PMID: 19843280 DOI: 10.1111/j.1600-0854.2009.00992.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The contractile vacuole (CV) is a dynamic organelle that enables Dictyostelium amoeba and other protist to maintain osmotic homeostasis by expelling excess water. In the present study, we have uncovered a mechanism that coordinates the mechanics of the CV with myosin II, regulated by VwkA, an unconventional protein kinase that is conserved in an array of protozoa. Green fluorescent protein (GFP)-VwkA fusion proteins localize persistently to the CV during both filling and expulsion phases of water. In vwkA null cells, the established CV marker dajumin still localizes to the CV, but these structures are large, spherical and severely impaired for discharge. Furthermore, myosin II cortical localization and assembly are abnormal in vwkA null cells. Parallel analysis of wild-type cells treated with myosin II inhibitors or of myosin II null cells also results in enlarged CVs with impaired dynamics. We suggest that the myosin II cortical cytoskeleton, regulated by VwkA, serves a critical conserved role in the periodic contractions of the CV, as part of the osmotic protective mechanism of protozoa.
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Affiliation(s)
- Venkaiah Betapudi
- Department of Cell Biology, The Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
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23
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Wen Y, Stavrou I, Bersuker K, Brady RJ, De Lozanne A, O'Halloran TJ. AP180-mediated trafficking of Vamp7B limits homotypic fusion of Dictyostelium contractile vacuoles. Mol Biol Cell 2009; 20:4278-88. [PMID: 19692567 DOI: 10.1091/mbc.e09-03-0243] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Clathrin-coated vesicles play an established role in endocytosis from the plasma membrane, but they are also found on internal organelles. We examined the composition of clathrin-coated vesicles on an internal organelle responsible for osmoregulation, the Dictyostelium discoideum contractile vacuole. Clathrin puncta on contractile vacuoles contained multiple accessory proteins typical of plasma membrane-coated pits, including AP2, AP180, and epsin, but not Hip1r. To examine how these clathrin accessory proteins influenced the contractile vacuole, we generated cell lines that carried single and double gene knockouts in the same genetic background. Single or double mutants that lacked AP180 or AP2 exhibited abnormally large contractile vacuoles. The enlarged contractile vacuoles in AP180-null mutants formed because of excessive homotypic fusion among contractile vacuoles. The SNARE protein Vamp7B was mislocalized and enriched on the contractile vacuoles of AP180-null mutants. In vitro assays revealed that AP180 interacted with the cytoplasmic domain of Vamp7B. We propose that AP180 directs Vamp7B into clathrin-coated vesicles on contractile vacuoles, creating an efficient mechanism for regulating the internal distribution of fusion-competent SNARE proteins and limiting homotypic fusions among contractile vacuoles. Dictyostelium contractile vacuoles offer a valuable system to study clathrin-coated vesicles on internal organelles within eukaryotic cells.
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Affiliation(s)
- Yujia Wen
- Department of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
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24
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Vats B, Padh H. DNA passage to nuclei: role of endo-lysosomal circuit in eukaryotic Dictyostelium. Can J Microbiol 2009; 55:617-21. [PMID: 19483791 DOI: 10.1139/w09-004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The understanding of DNA passage in eukaryotic cells is still very ambiguous. The route to the nucleus is difficult owing to the barriers, metabolic as well as membranous, posed by the eukaryotic cells. Endocytosis appears to be the most likely process responsible for the transport but is also the major culprit of low transfection efficiencies. Here, we report a study on a eukaryotic amoeba, Dictyostelium discoideum, where by disruption of the endocytic process at the opportune moment, the transformant number increased. We have observed that by disruption of fluid-phase uptake of calcium phosphate DNA nanoparticles, the number of clones increased with the probable increase in number of foreign genes integrating in the host genome. The method described here leads to the possibility of safe and inexpensive methods for transfer of genes required for heterologous recombinant protein production as well as generating therapeutic recombinant cells.
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Affiliation(s)
- Bhavesh Vats
- Department of Cell and Molecular Biology, B.V. Patel Pharmaceutical Education and Research Development Centre, Thaltej-Gandhinagar Highway, Thaltej, Ahmedabad, India
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25
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Dacks JB, Peden AA, Field MC. Evolution of specificity in the eukaryotic endomembrane system. Int J Biochem Cell Biol 2008; 41:330-40. [PMID: 18835459 DOI: 10.1016/j.biocel.2008.08.041] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2008] [Revised: 08/26/2008] [Accepted: 08/31/2008] [Indexed: 11/25/2022]
Abstract
Two hundred years after Darwin's birth, our understanding of genetic mechanisms and cell biology has advanced to a level unimaginable in the 19th century. We now know that eukaryotic cells contain a huge variety of internal compartments, each with their own function, identity and history. For the compartments that together form the membrane-trafficking system, one of the central questions is how that identity is encoded and how it evolved. Here we review the key components involved in membrane-trafficking events, including SNAREs, Rabs, vesicle coats, and tethers and what is known about their evolutionary history. Our current understanding suggests a possible common mechanism by which the membrane-trafficking organelles might have evolved. This model of increased organellar complexity by gene duplication and co-evolution of multiple, interacting, specificity-encoding proteins could well be applicable to other non-endosymbiotic organelles as well. The application of basic evolutionary principles well beyond their original scope has been exceedingly powerful not only in reconstructing the history of cellular compartments, but for medical and applied research as well, and underlines the contributions of Darwin's ideas in modern biology.
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Affiliation(s)
- Joel B Dacks
- The Molteno Building, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
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26
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Bennett N, Letourneur F, Ragno M, Louwagie M. Sorting of the v-SNARE VAMP7 in Dictyostelium discoideum: A role for more than one Adaptor Protein (AP) complex. Exp Cell Res 2008; 314:2822-33. [DOI: 10.1016/j.yexcr.2008.06.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Revised: 06/11/2008] [Accepted: 06/16/2008] [Indexed: 01/31/2023]
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27
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Calvo-Garrido J, Carilla-Latorre S, Lázaro-Diéguez F, Egea G, Escalante R. Vacuole membrane protein 1 is an endoplasmic reticulum protein required for organelle biogenesis, protein secretion, and development. Mol Biol Cell 2008; 19:3442-53. [PMID: 18550798 DOI: 10.1091/mbc.e08-01-0075] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Vacuole membrane protein 1 (Vmp1) is membrane protein of unknown molecular function that has been associated with pancreatitis and cancer. The social amoeba Dictyostelium discoideum has a vmp1-related gene that we identified previously in a functional genomic study. Loss-of-function of this gene leads to a severe phenotype that compromises Dictyostelium growth and development. The expression of mammalian Vmp1 in a vmp1(-) Dictyostelium mutant complemented the phenotype, suggesting a functional conservation of the protein among evolutionarily distant species and highlights Dictyostelium as a valid experimental system to address the function of this gene. Dictyostelium Vmp1 is an endoplasmic reticulum protein necessary for the integrity of this organelle. Cells deficient in Vmp1 display pleiotropic defects in the secretory pathway and organelle biogenesis. The contractile vacuole, which is necessary to survive under hypoosmotic conditions, is not functional in the mutant. The structure of the Golgi apparatus, the function of the endocytic pathway and conventional protein secretion are also affected in these cells. Transmission electron microscopy of vmp1(-) cells showed the accumulation of autophagic features that suggests a role of Vmp1 in macroautophagy. In addition to these defects observed at the vegetative stage, the onset of multicellular development and early developmental gene expression are also compromised.
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Affiliation(s)
- Javier Calvo-Garrido
- Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28029 Madrid, Spain
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28
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Leishmania adaptor protein-1 subunits are required for normal lysosome traffic, flagellum biogenesis, lipid homeostasis, and adaptation to temperatures encountered in the mammalian host. EUKARYOTIC CELL 2008; 7:1256-67. [PMID: 18515754 DOI: 10.1128/ec.00090-08] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The adaptor protein-1 (AP-1) complex is involved in membrane transport between the Golgi apparatus and endosomes. In the protozoan parasite Leishmania mexicana mexicana, the AP-1 mu1 and sigma1 subunits are not required for growth at 27 degrees C but are essential for infectivity in the mammalian host. In this study, we have investigated the function of these AP-1 subunits in order to understand the molecular basis for this loss of virulence. The mu1 and sigma1 subunits were localized to late Golgi and endosome membranes of the major parasite stages. Parasite mutants lacking either AP-1 subunit lacked obvious defects in Golgi structure, endocytosis, or exocytic transport. However, these mutants displayed reduced rates of endosome-to-lysosome transport and accumulated fragmented, sterol-rich lysosomes. Defects in flagellum biogenesis were also evident in nondividing promastigote stages, and this phenotype was exacerbated by inhibitors of sterol and sphingolipid biosynthesis. Furthermore, both AP-1 mutants were hypersensitive to elevated temperature and perturbations in membrane lipid composition. The pleiotropic requirements for AP-1 in membrane trafficking and temperature stress responses explain the loss of virulence of these mutants in the mammalian host.
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29
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Froquet R, Cherix N, Birke R, Benghezal M, Cameroni E, Letourneur F, Mösch HU, De Virgilio C, Cosson P. Control of cellular physiology by TM9 proteins in yeast and Dictyostelium. J Biol Chem 2008; 283:6764-72. [PMID: 18178563 DOI: 10.1074/jbc.m704484200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TM9 proteins constitute a well defined family, characterized by the presence of a large variable extracellular domain and nine putative transmembrane domains. This family is highly conserved throughout evolution and comprises three members in Dictyostelium discoideum and Saccharomyces cerevisiae and four in humans and mice. In Dictyostelium, previous analysis demonstrated that TM9 proteins are implicated in cellular adhesion. In this study, we generated TM9 mutants in S. cerevisiae and analyzed their phenotype with particular attention to cellular adhesion. S. cerevisiae strains lacking any one of the three TM9 proteins were severely suppressed for adhesive growth and filamentous growth under conditions of nitrogen starvation. In these mutants, expression of the FLO11-lacZ reporter gene was strongly reduced, whereas expression of FRE(Ty1)-lacZ was not, suggesting that TM9 proteins are implicated at a late stage of nutrient-controlled signaling pathways. We also reexamined the phenotype of Dictyostelium TM9 mutant cells, focusing on nutrient-controlled cellular functions. Although the initiation of multicellular development and autophagy was unaltered in Dictyostelium TM9 mutants, nutrient-controlled secretion of lysosomal enzymes was dysregulated in these cells. These results suggest that in both yeast and amoebae, TM9 proteins participate in the control of specific cellular functions in response to changing nutrient conditions.
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Affiliation(s)
- Romain Froquet
- Département de Physiologie et Métabolisme Cellulaire, Centre Médical Universitaire, Université de Genève, rue Michel Servet 1, CH-1211 Genève 4, Switzerland
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30
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Allen CL, Liao D, Chung WL, Field MC. Dileucine signal-dependent and AP-1-independent targeting of a lysosomal glycoprotein in Trypanosoma brucei. Mol Biochem Parasitol 2007; 156:175-90. [PMID: 17869353 DOI: 10.1016/j.molbiopara.2007.07.020] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2007] [Revised: 07/26/2007] [Accepted: 07/30/2007] [Indexed: 12/19/2022]
Abstract
Sorting of trans-membrane proteins destined for the lysosome is achieved by selective inclusion into post-Golgi transport vesicles. In higher eukaryotes sorting may be mediated by a peptidic motif, principally acidic clusters and tyrosine- or dileucine-based cytoplasmic signals or by inclusion of mannose-6-phosphate (M6P) into the N-glycans of lysosomal proteins. In African trypanosomes a major lysosomal trans-membrane protein is CB-1/p67. The cytoplasmic domain of p67 lacks tyrosine and lysine, but does contain a canonical dileucine sequence embedded within an acidic region. AP-1, -3 and -4 adaptin complexes, which recognise tyrosine- and dileucine-sorting signals, are encoded by the trypanosome genome, but the genes for M6P-receptors or activities required to produce M6P are absent, suggesting that lysosomal delivery of p67 is most likely adaptin-mediated. By construction of p67 reporter constructs we show that the dileucine signal is necessary and sufficient for efficient lysosomal delivery of a trans-membrane protein in bloodstream stage trypanosomes. However, this targeting does not require AP-1, as knockdown of the trypanosome gamma-adaptin subunit by RNAi has no detectable effect on the location or maturation of p67. These data suggest that p67 is targeted to the lysosome by dileucine-dependent but AP-1-independent mechanisms.
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Affiliation(s)
- Clare L Allen
- The Molteno Building, Department of Pathology, Tennis Court Road, University of Cambridge, Cambridge CB2 1QP, UK
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31
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Repass SL, Brady RJ, O'Halloran TJ. Dictyostelium Hip1r contributes to spore shape and requires epsin for phosphorylation and localization. J Cell Sci 2007; 120:3977-88. [PMID: 17971415 DOI: 10.1242/jcs.011213] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Clathrin-coated pits assemble on the plasma membrane to select and sequester proteins within coated vesicles for delivery to intracellular compartments. Although a host of clathrin-associated proteins have been identified, much less is known regarding the interactions between clathrin-associated proteins or how individual proteins influence the function of other proteins. In this study, we present evidence of a functional relationship between two clathrin-associated proteins in Dictyostelium, Hip1r and epsin. Hip1r-null cells form fruiting bodies that yield defective spores that lack the organized fibrils typical of wild-type spores. This spore coat defect leads to formation of round, rather than ovoid, spores in Hip1r-null cells that exhibit decreased viability. Like Hip1r-null cells, epsin-null cells also construct fruiting bodies with round spores, but these spores are more environmentally robust. Double-null cells that harbor deletions in both epsin and Hip1r form fruiting bodies, with spores identical in shape and viability to Hip1r single-null cells. In the growing amoeba, Hip1r is phosphorylated and localizes to puncta on the plasma membrane that also contain epsin. Both the phosphorylation state and localization of Hip1r into membrane puncta require epsin. Moreover, expression of the N-terminal ENTH domain of epsin is sufficient to restore both the phosphorylation and the restricted localization of Hip1r within plasma membrane puncta. The results from this study reveal a novel interaction between two clathrin-associated proteins during cellular events in both growing and developing Dictyostelium cells.
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Affiliation(s)
- Shannon Lea Repass
- Department of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin TX 78712, USA
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32
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Development of soil amoeba Dictyostelium discoideum as an expression system for recombinant human erythropoietin. World J Microbiol Biotechnol 2007. [DOI: 10.1007/s11274-007-9395-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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33
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Mercanti V, Charette SJ, Bennett N, Ryckewaert JJ, Letourneur F, Cosson P. Selective membrane exclusion in phagocytic and macropinocytic cups. J Cell Sci 2006; 119:4079-87. [PMID: 16968738 DOI: 10.1242/jcs.03190] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Specialized eukaryotic cells can ingest large particles and sequester them within membrane-delimited phagosomes. Many studies have described the delivery of lysosomal proteins to the phagosome, but little is known about membrane sorting during the early stages of phagosome formation. Here we used Dictyostelium discoideum amoebae to analyze the membrane composition of newly formed phagosomes. The membrane delimiting the closing phagocytic cup was essentially derived from the plasma membrane, but a subgroup of proteins was specifically excluded. Interestingly the same phenomenon was observed during the formation of macropinosomes, suggesting that the same sorting mechanisms are at play during phagocytosis and macropinocytosis. Analysis of mutant strains revealed that clathrin-associated adaptor complexes AP-1, -2 and -3 were not necessary for this selective exclusion and, accordingly, ultrastructural analysis revealed no evidence for vesicular transport around phagocytic cups. Our results suggest the existence of a new, as yet uncharacterized, sorting mechanism in phagocytic and macropinocytic cups.
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Affiliation(s)
- Valentina Mercanti
- Université de Genève, Centre Médical Universitaire, Département de Physiologie Cellulaire et Métabolisme, 1 rue Michel Servet, CH-1211 Genève 4, Switzerland
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Charette SJ, Mercanti V, Letourneur F, Bennett N, Cosson P. A role for adaptor protein-3 complex in the organization of the endocytic pathway in Dictyostelium. Traffic 2006; 7:1528-38. [PMID: 17010123 DOI: 10.1111/j.1600-0854.2006.00478.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Dictyostelium discoideum cells continuously internalize extracellular material, which accumulates in well-characterized endocytic vacuoles. In this study, we describe a new endocytic compartment identified by the presence of a specific marker, the p25 protein. This compartment presents features reminiscent of mammalian recycling endosomes: it is localized in the pericentrosomal region but distinct from the Golgi apparatus. It specifically contains surface proteins that are continuously endocytosed but rapidly recycled to the cell surface and thus absent from maturing endocytic compartments. We evaluated the importance of each clathrin-associated adaptor complex in establishing a compartmentalized endocytic system by studying the phenotype of the corresponding mutants. In knockout cells for mu3, a subunit of the AP-3 clathrin-associated complex, membrane proteins normally restricted to p25-positive endosomes were mislocalized to late endocytic compartments. Our results suggest that AP-3 plays an essential role in the compartmentalization of the endocytic pathway in Dictyostelium.
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Affiliation(s)
- Steve J Charette
- Université de Genève, Centre Médical Universitaire, Département de Physiologie Cellulaire et Métabolisme, 1 rue Michel Servet, CH-1211 Genève 4, Switzerland.
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Heuser J. Evidence for recycling of contractile vacuole membrane during osmoregulation in Dictyostelium amoebae--a tribute to Günther Gerisch. Eur J Cell Biol 2006; 85:859-71. [PMID: 16831485 DOI: 10.1016/j.ejcb.2006.05.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Mercanti V, Blanc C, Lefkir Y, Cosson P, Letourneur F. Acidic clusters target transmembrane proteins to the contractile vacuole in Dictyostelium cells. J Cell Sci 2006; 119:837-45. [PMID: 16478785 DOI: 10.1242/jcs.02808] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mechanisms responsible for the targeting of transmembrane integral proteins to the contractile vacuole (CV) network in Dictyostelium discoideum are unknown. Here we show that the transfer of the cytoplasmic domain of a CV-resident protein (Rh50) to a reporter transmembrane protein (CsA) is sufficient to address the chimera (CsA-Rh50) to the CV. We identified two clusters of acidic residues responsible for this targeting, and these motifs interacted with the gamma-adaptin AP-1 subunit in a yeast protein-protein interaction assay. For the first time we report the existence of an indirect transport pathway from the plasma membrane to the CV via endosomes. Upon internalization, the small fraction of CsA-Rh50 present at the cell surface was first concentrated in endosomes distinct from early and late p80-positive endosomes and then slowly transported to the CV. Together our results suggest the existence of an AP-1-dependent selective transport to the contractile vacuole in Dictyostelium.
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Affiliation(s)
- Valentina Mercanti
- Université de Genève, Centre Médical Universitaire, Département de Physiologie Cellulaire et Métabolisme, CH-1211 Genève 4, Switzerland
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Betapudi V, Mason C, Licate L, Egelhoff TT. Identification and characterization of a novel alpha-kinase with a von Willebrand factor A-like motif localized to the contractile vacuole and Golgi complex in Dictyostelium discoideum. Mol Biol Cell 2005; 16:2248-62. [PMID: 15728726 PMCID: PMC1087232 DOI: 10.1091/mbc.e04-07-0639] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We have identified a new protein kinase in Dictyostelium discoideum that carries the same conserved class of "alpha-kinase" catalytic domain as reported previously in myosin heavy chain kinases (MHCKs) in this amoeba but that has a completely novel domain organization. The protein contains an N-terminal von Willebrand factor A (vWFA)-like motif and is therefore named VwkA. Manipulation of VwkA expression level via high copy number plasmids (VwkA++ cells) or gene disruption (vwkA null cells) results in an array of cellular defects, including impaired growth and multinucleation in suspension culture, impaired development, and alterations in myosin II abundance and assembly. Despite sequence similarity to MHCKs, the purified protein failed to phosphorylate myosin II in vitro. Autophosphorylation activity, however, was enhanced by calcium/calmodulin, and the enzyme can be precipitated from cellular lysates with calmodulin-agarose, suggesting that VwkA may directly bind calmodulin. VwkA is cytosolic in distribution but enriched on the membranes of the contractile vacuole and Golgi-like structures in the cell. We propose that VwkA likely acts indirectly to influence myosin II abundance and assembly behavior and possibly has broader roles than previously characterized alpha kinases in this organism, which all seem to be MHCKs.
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Affiliation(s)
- Venkaiah Betapudi
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106-4970, USA
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Gerisch G, Benjak A, Köhler J, Weber I, Schneider N. GFP-golvesin constructs to study Golgi tubulation and post-Golgi vesicle dynamics in phagocytosis. Eur J Cell Biol 2004; 83:297-303. [PMID: 15511087 DOI: 10.1078/0171-9335-00393] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Dictyostelium cells are professional phagocytes that are optimally suited for the imaging of phagosome processing from particle uptake to exocytosis. In order to design fluorescent probes for monitoring membrane trafficking in the endocytic pathway, we have dissected a membrane protein, golvesin, and have linked fragments of its sequence to GFP. Endogenous golvesin is partitioned between the ER, the Golgi apparatus, endosomes, and the contractile vacuole complex. We have localized signals that are required for exit from the Golgi to post-Golgi compartments to the C-terminal region of the golvesin sequence. One GFP-tagged fragment turned out to be a highly specific Golgi marker and was used to demonstrate the interaction of Golgi tubules with phagosomes. Signals essential for the retrieval of golvesin at the end of phagosome processing were localized to the N-terminal region. A truncated golvesin construct escaping retrieval was employed in recording the delivery of a phagosomal protein to the plasma membrane. Applying this construct to a phagosome filled with multiple particles, we observed that the phagosome is segmented during exocytosis, meaning that sequential release of particles alternates with membrane fusion.
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Lefkir Y, Malbouyres M, Gotthardt D, Ozinsky A, Cornillon S, Bruckert F, Aderem AA, Soldati T, Cosson P, Letourneur F. Involvement of the AP-1 adaptor complex in early steps of phagocytosis and macropinocytosis. Mol Biol Cell 2003; 15:861-9. [PMID: 14617812 PMCID: PMC329399 DOI: 10.1091/mbc.e03-06-0365] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The best described function of the adaptor complex-1 (AP-1) is to participate in the budding of clathrin-coated vesicles from the trans-Golgi network and endosomes. Here, we show that AP-1 is also localized to phagocytic cups in murine macrophages as well as in Dictyostelium amoebae. AP-1 is recruited to phagosomal membranes at this early stage of phagosome formation and rapidly dissociates from maturing phagosomes. To establish the role of AP-1 in phagocytosis, we made used of Dictyostelium mutant cells (apm1(-) cells) disrupted for AP-1 medium chain. In this mutant, phagocytosis drops by 60%, indicating that AP-1 is necessary for efficient phagocytosis. Furthermore, phagocytosis in apm1(-) cells is more affected for large rather than small particles, and cells exhibiting incomplete engulfment are then often observed. This suggests that AP-1 could participate in the extension of the phagocytic cup. Interestingly, macropinocytosis, a process dedicated to fluid-phase endocytosis and related to phagocytosis, is also impaired in apm1(-) cells. In summary, our data suggest a new role of AP-1 at an early stage of phagosome and macropinosome formation.
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Affiliation(s)
- Yaya Lefkir
- Institut de Biologie et Chimie des Protéines, UMR5086-CNRS/Université Lyon I, IFR 128 BioSciences Lyon-Gerland, 69367 Lyon, France
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