151
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Kantheti P, Qiao X, Diaz ME, Peden AA, Meyer GE, Carskadon SL, Kapfhamer D, Sufalko D, Robinson MS, Noebels JL, Burmeister M. Mutation in AP-3 delta in the mocha mouse links endosomal transport to storage deficiency in platelets, melanosomes, and synaptic vesicles. Neuron 1998; 21:111-22. [PMID: 9697856 DOI: 10.1016/s0896-6273(00)80519-x] [Citation(s) in RCA: 307] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The mouse mutant mocha, a model for the Hermansky-Pudlak storage pool deficiency syndrome, is characterized by defective platelets, coat and eye color dilution, lysosomal abnormalities, inner ear degeneration, and neurological deficits. Here, we show that mocha is a null allele of the delta subunit of the adaptor-like protein complex AP-3, which is associated with coated vesicles budding from the trans-Golgi network, and that AP-3 is missing in mocha tissues. In mocha brain, the ZnT-3 transporter is reduced, resulting in a lack of zinc-associated Timm historeactivity in hippocampal mossy fibers. Our results demonstrate that the AP-3 complex is responsible for cargo selection to lysosome-related organelles such as melanosomes and platelet dense granules as well as to neurotransmitter vesicles.
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Affiliation(s)
- P Kantheti
- Mental Health Research Institute and Department of Psychiatry, University of Michigan, Ann Arbor 48109, USA
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152
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Aroeti B, Okhrimenko H, Reich V, Orzech E. Polarized trafficking of plasma membrane proteins: emerging roles for coats, SNAREs, GTPases and their link to the cytoskeleton. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1376:57-90. [PMID: 9666078 DOI: 10.1016/s0304-4157(98)00005-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- B Aroeti
- Department of Cell and Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
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153
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Abstract
Synaptic vesicles can be coated in vitro in a reaction that is ARF-, ATP-, and temperature-dependent and requires synaptic vesicle membrane proteins. The coat is largely made up of the heterotetrameric complex, adaptor protein 3, recently implicated in Golgi-to-vacuole traffic in yeast. Depletion of AP3 from brain cytosol inhibits small vesicle formation from PC12 endosomes in vitro. Budding from washed membranes can be reconstituted with purified AP3 and recombinant ARF1. We conclude that AP3 coating is involved in at least one pathway of small vesicle formation from endosomes.
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Affiliation(s)
- V Faúndez
- Department of Biochemistry and Biophysics and Hormone Research Institute, University of California, San Francisco 94143-0534, USA
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154
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Jareb M, Banker G. The polarized sorting of membrane proteins expressed in cultured hippocampal neurons using viral vectors. Neuron 1998; 20:855-67. [PMID: 9620691 DOI: 10.1016/s0896-6273(00)80468-7] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
One model of neuronal polarity (Dotti and Simons, 1990) proposes that neurons and polarized epithelia use similar mechanisms to sort membrane proteins. To explore this hypothesis, we used viral vectors to express proteins in cultured neurons and assessed their distribution using quantitative immunofluorescence microscopy. Basolateral epithelial proteins were polarized to dendrites; more significantly, mutations of sequences required for their basolateral targeting in epithelia also disrupted dendritic targeting. Unexpectedly, apical proteins were not polarized to axons but were expressed at roughly equal amounts in dendrites and axons. These data provide strong evidence that targeting of basolateral and dendritic proteins depends on common mechanisms. In contrast, the sorting of proteins to the axon requires signals that are not present in apical proteins.
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Affiliation(s)
- M Jareb
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville 22908, USA
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155
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Vowels JJ, Payne GS. A dileucine-like sorting signal directs transport into an AP-3-dependent, clathrin-independent pathway to the yeast vacuole. EMBO J 1998; 17:2482-93. [PMID: 9564031 PMCID: PMC1170590 DOI: 10.1093/emboj/17.9.2482] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Transport of yeast alkaline phosphatase (ALP) to the vacuole depends on the clathrin adaptor-like complex AP-3, but does not depend on proteins necessary for transport through pre-vacuolar endosomes. We have identified ALP sequences that direct sorting into the AP-3-dependent pathway using chimeric proteins containing residues from the ALP cytoplasmic domain fused to sequences from a Golgi-localized membrane protein, guanosine diphosphatase (GDPase). The full-length ALP cytoplasmic domain, or ALP amino acids 1-16 separated from the transmembrane domain by a spacer, directed GDPase chimeric proteins from the Golgi complex to the vacuole via the AP-3 pathway. Mutation of residues Leu13 and Val14 within the ALP cytoplasmic domain prevented AP-3-dependent vacuolar transport of both chimeric proteins and full-length ALP. This Leucine-Valine (LV)-based sorting signal targeted chimeric proteins and native ALP to the vacuole in cells lacking clathrin function. These results identify an LV-based sorting signal in the ALP cytoplasmic domain that directs transport into a clathrin-independent, AP-3-dependent pathway to the vacuole. The similarity of the ALP sorting signal to mammalian dileucine sorting motifs, and the evolutionary conservation of AP-3 subunits, suggests that dileucine-like signals constitute a core element for AP-3-dependent transport to lysosomal compartments in all eukaryotic cells.
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Affiliation(s)
- J J Vowels
- Department of Biological Chemistry, UCLA School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
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156
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Nordeng TW, Gorvel JP, Bakke O. Intracellular transport of molecules engaged in the presentation of exogenous antigens. Curr Top Microbiol Immunol 1998; 232:179-215. [PMID: 9557399 DOI: 10.1007/978-3-642-72045-1_9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- T W Nordeng
- Department of Biology, University of Oslo, Norway
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157
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Bremnes T, Lauvrak V, Lindqvist B, Bakke O. A region from the medium chain adaptor subunit (mu) recognizes leucine- and tyrosine-based sorting signals. J Biol Chem 1998; 273:8638-45. [PMID: 9535838 DOI: 10.1074/jbc.273.15.8638] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tyrosine-based sorting signals in the cytosolic tails of membrane proteins have been found to bind directly to the medium chain subunit (mu) of the adaptor complexes AP-1 and AP-2. For the leucine-based signals, an interaction with AP-1 and AP-2 has been reported, but no specific interacting subunit has been demonstrated. After searching for molecules interacting with the leucine-based sorting signals within the cytosolic tail of the major histocompatibility complex class II-associated invariant chain using a phage display approach, we identified phage clones with homology to a conserved region of the AP-1 and AP-2 mu chains. To investigate the relevance of these findings, we have expressed regions of mouse mu1 and mu2 chains on phage gene product III and investigated the binding to tail sequences from various transmembrane proteins with known endosomal targeting signals. Enzyme-linked immunosorbent binding assays showed that these phages specifically recognized peptides containing functional leucine- and tyrosine-based sorting signals, suggesting that these regions of the mu1 and mu2 chains interact with both types of sorting signals.
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Affiliation(s)
- T Bremnes
- Department of Molecular Cell Biology, Division of Biology, University of Oslo, 0316 Oslo, Norway
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158
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Aridor M, Weissman J, Bannykh S, Nuoffer C, Balch WE. Cargo selection by the COPII budding machinery during export from the ER. J Cell Biol 1998; 141:61-70. [PMID: 9531548 PMCID: PMC2132735 DOI: 10.1083/jcb.141.1.61] [Citation(s) in RCA: 240] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/1997] [Revised: 12/21/1997] [Indexed: 02/07/2023] Open
Abstract
Cargo is selectively exported from the ER in COPII vesicles. To analyze the role of COPII in selective transport from the ER, we have purified components of the mammalian COPII complex from rat liver cytosol and then analyzed their role in cargo selection and ER export. The purified mammalian Sec23-24 complex is composed of an 85-kD (Sec23) protein and a 120-kD (Sec24) protein. Although the Sec23-24 complex or the monomeric Sec23 subunit were found to be the minimal cytosolic components recruited to membranes after the activation of Sar1, the addition of the mammalian Sec13-31 complex is required to complete budding. To define possible protein interactions between cargo and coat components, we recruited either glutathione-S-transferase (GST)-tagged Sar1 or GST- Sec23 to ER microsomes. Subsequently, we solubilized and reisolated the tagged subunits using glutathione-Sepharose beads to probe for interactions with cargo. We find that activated Sar1 in combination with either Sec23 or the Sec23-24 complex is necessary and sufficient to recover with high efficiency the type 1 transmembrane cargo protein vesicular stomatitis virus glycoprotein in a detergent-soluble prebudding protein complex that excludes ER resident proteins. Supplementing these minimal cargo recruitment conditions with the mammalian Sec13-31 complex leads to export of the selected cargo into COPII vesicles. The ability of cargo to interact with a partial COPII coat demonstrates that these proteins initiate cargo sorting on the ER membrane before budding and establishes the role of GTPase-dependent coat recruitment in cargo selection.
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Affiliation(s)
- M Aridor
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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159
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Okamoto CT, Karam SM, Jeng YY, Forte JG, Goldenring JR. Identification of clathrin and clathrin adaptors on tubulovesicles of gastric acid secretory (oxyntic) cells. Am J Physiol Cell Physiol 1998; 274:C1017-29. [PMID: 9575799 DOI: 10.1152/ajpcell.1998.274.4.c1017] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
gamma-Adaptin and clathrin heavy chain were identified on tubulovesicles of gastric oxyntic cells with the anti-gamma-adaptin monoclonal antibody (MAb) 100/3 and an anti-clathrin heavy chain MAb (MAb 23), respectively. In Western blots, crude gastric microsomes from rabbit and rat and density gradient-purified, H-K-ATPase-rich microsomes from these same species were immunoreactive for gamma-adaptin and clathrin. In immunofluorescent labeling of isolated rabbit gastric glands, anti-gamma-adaptin and anti-clathrin heavy chain immunoreactivity appeared to be concentrated in oxyntic cells. In primary cultures of rabbit oxyntic cells, the immunocytochemical distribution of gamma-adaptin immunoreactivity was similar to that of the tubulovesicular membrane marker in oxyntic cells, the H-K-ATPase. Further biochemical characterization of the tubulovesicular gamma-adaptin-containing complex suggested that it has a subunit composition that is typical of that for a clathrin adaptor: in addition to the gamma-adaptin subunit, it contains a beta-adaptin subunit and other subunits of apparent molecular masses of 50 kDa and 19 kDa. From solubilized gastric microsomes from rabbit, gamma-adaptin could be copurified with the major cargo protein of tubulovesicles, the H-K-ATPase. Thus this tubulovesicular coat may bind directly to the H-K-ATPase and may thereby mediate the regulated trafficking of the H-K-ATPase at the apical membrane of the oxyntic cell during the gastric acid secretory cycle. Given the similarities of the regulated trafficking of the H-K-ATPase with recycling of cargo through the apical recycling endosome of many epithelial cells, we propose that tubulovesicular clathrin and adaptors may regulate some part of an apical recycling pathway in other epithelial cells.
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Affiliation(s)
- C T Okamoto
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles 90033, USA
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160
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Press B, Feng Y, Hoflack B, Wandinger-Ness A. Mutant Rab7 causes the accumulation of cathepsin D and cation-independent mannose 6-phosphate receptor in an early endocytic compartment. J Cell Biol 1998; 140:1075-89. [PMID: 9490721 PMCID: PMC2132709 DOI: 10.1083/jcb.140.5.1075] [Citation(s) in RCA: 221] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/1997] [Revised: 01/08/1998] [Indexed: 02/06/2023] Open
Abstract
Stable BHK cell lines inducibly expressing wild-type or dominant negative mutant forms of the rab7 GTPase were isolated and used to analyze the role of a rab7-regulated pathway in lysosome biogenesis. Expression of mutant rab7N125I protein induced a dramatic redistribution of cation-independent mannose 6-phosphate receptor (CI-MPR) from its normal perinuclear localization to large peripheral endosomes. Under these circumstances approximately 50% of the total receptor and several lysosomal hydrolases cofractionated with light membranes containing early endosome and Golgi markers. Late endosomes and lysosomes were contained exclusively in well-separated, denser gradient fractions. Newly synthesized CI-MPR and cathepsin D were shown to traverse through an early endocytic compartment, and functional rab7 was crucial for delivery to later compartments. This observation was evidenced by the fact that 2 h after synthesis, both markers were more prevalent in fractions containing light membranes. In addition, both were sensitive to HRP-DAB- mediated cross-linking of early endosomal proteins, and the late endosomal processing of cathepsin D was impaired. Using similar criteria, the lysosomal membrane glycoprotein 120 was not found accumulated in an early endocytic compartment. The data are indicative of a post-Golgi divergence in the routes followed by different lysosome-directed molecules.
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Affiliation(s)
- B Press
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500, USA
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161
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Bryant NJ, Stevens TH. Vacuole biogenesis in Saccharomyces cerevisiae: protein transport pathways to the yeast vacuole. Microbiol Mol Biol Rev 1998; 62:230-47. [PMID: 9529893 PMCID: PMC98912 DOI: 10.1128/mmbr.62.1.230-247.1998] [Citation(s) in RCA: 227] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Delivery of proteins to the vacuole of the yeast Saccharomyces cerevisiae provides an excellent model system in which to study vacuole and lysosome biogenesis and membrane traffic. This organelle receives proteins from a number of different routes, including proteins sorted away from the secretory pathway at the Golgi apparatus and endocytic traffic arising from the plasma membrane. Genetic analysis has revealed at least 60 genes involved in vacuolar protein sorting, numerous components of a novel cytoplasm-to-vacuole transport pathway, and a large number of proteins required for autophagy. Cell biological and biochemical studies have provided important molecular insights into the various protein delivery pathways to the yeast vacuole. This review describes the various pathways to the vacuole and illustrates how they are related to one another in the vacuolar network of S. cerevisiae.
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Affiliation(s)
- N J Bryant
- Institute of Molecular Biology, University of Oregon, Eugene 97403-1229, USA
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162
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Abstract
Major histocompatibility complex (MHC) class II molecules are required for the presentation of antigenic peptides that are derived predominantly from internalized proteins. The assembly of MHC class II/peptide complexes occurs within endosomal compartments of antigen-presenting cells (APCs). Therefore, for assembly to occur, MHC class II molecules, foreign proteins, and accessory molecules must be sorted to appropriate intracellular sites. My laboratory is trying to understand how proteins are sorted to various antigen-processing compartments as well as to conventional endosomal organelles. Using chimeric marker proteins and a variety of biochemical and genetic approaches, we are addressing the specificity of protein sorting and the mechanisms by which sorting signals are deciphered. By using a similar chimeric protein approach to target endogenous proteins to distinct compartments, we hope to address the role of processing events in each compartment in the generation of MHC class II ligands.
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Affiliation(s)
- M S Marks
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104-6082, USA.
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163
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Yoon Y, Pitts KR, Dahan S, McNiven MA. A novel dynamin-like protein associates with cytoplasmic vesicles and tubules of the endoplasmic reticulum in mammalian cells. J Cell Biol 1998; 140:779-93. [PMID: 9472031 PMCID: PMC2141745 DOI: 10.1083/jcb.140.4.779] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Dynamins are 100-kilodalton guanosine triphosphatases that participate in the formation of nascent vesicles during endocytosis. Here, we have tested if novel dynamin-like proteins are expressed in mammalian cells to support vesicle trafficking processes at cytoplasmic sites distinct from the plasma membrane. Immunological and molecular biological methods were used to isolate a cDNA clone encoding an 80-kilodalton novel dynamin-like protein, DLP1, that shares up to 42% homology with other dynamin-related proteins. DLP1 is expressed in all tissues examined and contains two alternatively spliced regions that are differentially expressed in a tissue-specific manner. DLP1 is enriched in subcellular membrane fractions of cytoplasmic vesicles and endoplasmic reticulum. Morphological studies of DLP1 in cultured cells using either a specific antibody or an expressed green fluorescent protein (GFP)- DLP1 fusion protein revealed that DLP1 associates with punctate cytoplasmic vesicles that do not colocalize with conventional dynamin, clathrin, or endocytic ligands. Remarkably, DLP1-positive structures coalign with microtubules and, most strikingly, with endoplasmic reticulum tubules as verified by double labeling with antibodies to calnexin and Rab1 as well as by immunoelectron microscopy. These observations provide the first evidence that a novel dynamin-like protein is expressed in mammalian cells where it associates with a secretory, rather than endocytic membrane compartment.
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Affiliation(s)
- Y Yoon
- Center for Basic Research in Digestive Diseases and Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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164
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Affiliation(s)
- D A Lewin
- Yale University School of Medicine, Department of Cell Biology, New Haven, CT 06520-8002, USA.
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165
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Abstract
Vesicular coat proteins mediate the formation of nascent vesicles and select the cargo to be incorporated therein. As additional coat proteins are discovered that regulate vesicular traffic along very specific intracellular pathways, the possibility looms of regulating the intracellular trafficking and targeting of therapeutic agents by modulation of the action of vesicular coat proteins. Examples are provided of coat proteins thought to regulate the trafficking of pharmaceutically relevant molecules via clathrin-mediated endocytosis, caveolae-mediated endocytosis, and transcytosis.
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Affiliation(s)
- CT Okamoto
- Department of Pharmaceutical Sciences, University of Southern California, Los Angeles CA 90033, USA
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166
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Stepp JD, Huang K, Lemmon SK. The yeast adaptor protein complex, AP-3, is essential for the efficient delivery of alkaline phosphatase by the alternate pathway to the vacuole. J Cell Biol 1997; 139:1761-74. [PMID: 9412470 PMCID: PMC2132655 DOI: 10.1083/jcb.139.7.1761] [Citation(s) in RCA: 187] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/1997] [Revised: 10/25/1997] [Indexed: 02/05/2023] Open
Abstract
A novel clathrin adaptor-like complex, adaptor protein (AP)-3, has recently been described in yeast and in animals. To gain insight into the role of yeast AP-3, a genetic strategy was devised to isolate gene products that are required in the absence of the AP-3 mu chain encoded by APM3. One gene identified by this synthetic lethal screen was VPS45. The Vps pathway defines the route that several proteins, including carboxypeptidase Y, take from the late Golgi to the vacuole. However, vacuolar alkaline phosphatase (ALP) is transported via an alternate, intracellular route. This suggested that the apm3-Delta vps45 synthetic phenotype could be caused by a block in both the alternate and the Vps pathways. Here we demonstrate that loss of function of the AP-3 complex results in slowed processing and missorting of ALP. ALP is no longer localized to the vacuole membrane by immunofluorescence, but is found in small punctate structures throughout the cell. This pattern is distinct from the Golgi marker Kex2p, which is unaffected in AP-3 mutants. We also show that in the apm3-Delta mutant some ALP is delivered to the vacuole by diversion into the Vps pathway. Class E vps mutants accumulate an exaggerated prevacuolar compartment containing membrane proteins on their way to the vacuole or destined for recycling to the Golgi. Surprisingly, in AP-3 class E vps double mutants these proteins reappear on the vacuole. We suggest that some AP-3-dependent cargo proteins that regulate late steps in Golgi to vacuole transport are diverted into the Vps pathway allowing completion of transfer to the vacuole in the class E vps mutant.
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Affiliation(s)
- J D Stepp
- Department of Molecular Biology and Microbiology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106, USA
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167
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van de Loo JW, Creemers JW, Bright NA, Young BD, Roebroek AJ, Van de Ven WJ. Biosynthesis, distinct post-translational modifications, and functional characterization of lymphoma proprotein convertase. J Biol Chem 1997; 272:27116-23. [PMID: 9341152 DOI: 10.1074/jbc.272.43.27116] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Proprotein convertases are responsible for the endoproteolytic processing of prohormones, neuropeptide precursors, and other proproteins within the constitutive and regulated secretory pathways. Cleavage occurs carboxyl-terminally of basic amino acid motifs, such as RX(K/R)R, RXXR, and (R/K)R. As already available for the other known mammalian members of this enzyme family, we here define structural and functional features of human lymphoma proprotein convertase (LPC). Analysis of expression of recombinant LPC in stably transfected Chinese hamster ovary cells reveals biosynthesis of a 92-kDa nonglycosylated precursor (proLPC) and a 102-kDa endoglycosidase H-sensitive glycosylated form of proLPC. Only the latter is further processed and after propeptide removal converted into a complexly N-glycosylated mature form of LPC of about 92 kDa. Co-expression experiments of truncated LPC with an active site mutant of LPC (LPCS265A) indicate that prodomain removal of LPC occurs via an autoproteolytic, intramolecular mechanism, as was demonstrated before for some of the other members of this enzyme family. Prodomain removal is shown to be required for LPC to exit the endoplasmic reticulum. As far as subcellular localization is concerned, immunocytochemical, ultrastructural, and biochemical analyses show that LPC is concentrated in the trans-Golgi network, associated with membranes, and not secreted. Carboxyl-terminal domains are critically involved in this cellular retention, because removal of both the hydrophobic region and the cytoplasmic tail of LPC results in secretion. Of interest are the observations that LPC is not phosphorylated like furin but is palmitoylated in its cytoplasmic tail. Finally, substrate specificity of LPC is similar to that of furin but not identical. Whereas for furin a basic substrate residue at position P-2 is dispensable, it is essential for LPC. For optimal LPC substrate processing activity, an arginine at position P-6 is preferred over an arginine at P-4.
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Affiliation(s)
- J W van de Loo
- Laboratory for Molecular Oncology, Center for Human Genetics, University of Leuven and Flanders Interuniversity Institute for Biotechnology, Herestraat 49, 3000 Leuven, Belgium
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168
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Aguilar RC, Ohno H, Roche KW, Bonifacino JS. Functional domain mapping of the clathrin-associated adaptor medium chains mu1 and mu2. J Biol Chem 1997; 272:27160-6. [PMID: 9341158 DOI: 10.1074/jbc.272.43.27160] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The clathrin-associated adaptors AP-1 and AP-2 are heterotetrameric complexes involved in the recognition of sorting signals present within the cytosolic domain of integral membrane proteins. The medium chains of these complexes, mu1 and mu2, have been implicated in two types of interaction: assembly with the beta1 and beta2 chains of the corresponding complexes and recognition of tyrosine-based sorting signals. In this study, we report the results of a structure-function analysis of the mu1 and mu2 chains aimed at identifying regions of the molecules that are responsible for each of the two interactions. Analyses using the yeast two-hybrid system and proteolytic digestion experiments suggest that mu1 and mu2 have a bipartite structure, with the amino-terminal one-third (residues 1-145 of mu1 and mu2) being involved in assembly with the beta chains and the carboxyl-terminal two-thirds (residues 147-423 of mu1 and 164-435 of mu2) binding tyrosine-based sorting signals. These observations support a model in which the amino-terminal one-third of mu2 is embedded within the core of the AP-2 complex, while the carboxyl-terminal two-thirds of the protein are exposed to the medium, placing this region in a position to interact with tyrosine-based sorting signals.
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Affiliation(s)
- R C Aguilar
- Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892-5430, USA
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169
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Fletcher CF, Okano HJ, Gilbert DJ, Yang Y, Yang C, Copeland NG, Jenkins NA, Darnell RB. Mouse chromosomal locations of nine genes encoding homologs of human paraneoplastic neurologic disorder antigens. Genomics 1997; 45:313-9. [PMID: 9344654 DOI: 10.1006/geno.1997.4925] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The paraneoplastic neurologic disorders (PND) are a rare group of neurologic syndromes that arise when an immune response to systemic tumors expressing neuronal proteins ("onconeural antigens") develops into an autoimmune neuronal degeneration. The use of patient antisera to clone the genes encoding PND antigens has led to new insight into the mechanism of these autoimmune disorders. The tumor antigens can now be grouped into three classes: (1) neuron-specific RNA-binding proteins, (2) nerve terminal vesicle-associated proteins, and (3) cytoplasmic signaling proteins. To understand better the evolutionary relatedness of these genes and to evaluate them as candidates for inherited neurological disorders, we have determined the mouse chromosomal locations of nine of these genes-Hua, Hub, Huc, Hud, Nova1, Nova2, Natpb, Cdr2, and Cdr3. These data suggest that the Hua-Hud genes arose from gene duplication and dispersion, while the other genes are dispersed in the genome. We also predict the chromosomal locations of these genes in human and discuss the potential of these genes as candidates for uncloned mouse and human mutations.
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Affiliation(s)
- C F Fletcher
- ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA
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170
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Cowles CR, Odorizzi G, Payne GS, Emr SD. The AP-3 adaptor complex is essential for cargo-selective transport to the yeast vacuole. Cell 1997; 91:109-18. [PMID: 9335339 DOI: 10.1016/s0092-8674(01)80013-1] [Citation(s) in RCA: 329] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Three distinct adaptor protein (AP) complexes involved in protein trafficking have been identified. AP-1 and AP-2 mediate protein sorting at the trans-Golgi network and plasma membrane, respectively, whereas the function of AP-3 has not been defined. A screen for factors specifically involved in transport of alkaline phosphatase (ALP) from the Golgi to the vacuole/lysosome has identified Ap16p and Ap15p of the yeast AP-3 complex. Deletion of each of the four AP-3 subunits results in selective mislocalization of ALP and the vacuolar t-SNARE, Vam3p (but not CPS and CPY), while deletion of AP-1 and AP-2 subunits has no effect on vacuolar protein delivery. This study, therefore, provides evidence that the AP-3 complex functions in cargo-selective protein transport from the Golgi to the vacuole/lysosome.
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Affiliation(s)
- C R Cowles
- Division of Cellular and Molecular Medicine and Howard Hughes Medical Institute, University of California, San Diego 92093-0668, USA
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171
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Abstract
The mechanisms that permit neurons to establish axons and dendrites involve an interplay between a cell's genetic program and signals in its environment. Recent experiments have identified some of the important extracellular molecules that regulate dendritic development and have furthered our understanding of the endogenous cell biological mechanisms that underlie protein sorting. Some of the signaling pathways that allow extracellular cues to regulate neuronal morphogenesis are also being elucidated.
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Affiliation(s)
- D Higgins
- State University of New York School of Medicine, Department of Pharmacology 102 Farber Hall, Buffalo, New York, 14214, USA.
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172
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West MA, Bright NA, Robinson MS. The role of ADP-ribosylation factor and phospholipase D in adaptor recruitment. J Cell Biol 1997; 138:1239-54. [PMID: 9298980 PMCID: PMC2132562 DOI: 10.1083/jcb.138.6.1239] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/1997] [Revised: 06/27/1997] [Indexed: 02/05/2023] Open
Abstract
AP-1 and AP-2 adaptors are recruited onto the TGN and plasma membrane, respectively. GTPgammaS stimulates the recruitment of AP-1 onto the TGN but causes AP-2 to bind to an endosomal compartment (Seaman, M.N.J., C.L. Ball, and M.S. Robinson. 1993. J. Cell Biol. 123:1093-1105). We have used subcellular fractionation followed by Western blotting, as well as immunofluorescence and immunogold electron microscopy, to investigate both the recruitment of AP-2 adaptors onto the plasma membrane and their targeting to endosomes, and we have also examined the recruitment of AP-1 under the same conditions. Two lines of evidence indicate that the GTPgammaS-induced targeting of AP-2 to endosomes is mediated by ADP-ribosylation factor-1 (ARF1). First, GTPgammaS loses its effect when added to ARF-depleted cytosol, but this effect is restored by the addition of recombinant myristoylated ARF1. Second, adding constitutively active Q71L ARF1 to the cytosol has the same effect as adding GTPgammaS. The endosomal membranes that recruit AP-2 adaptors have little ARF1 or any of the other ARFs associated with them, suggesting that ARF may be acting catalytically. The ARFs have been shown to activate phospholipase D (PLD), and we find that addition of exogenous PLD has the same effect as GTPgammaS or Q71L ARF1. Neomycin, which inhibits endogenous PLD by binding to its cofactor phosphatidylinositol 4,5-bisphosphate, prevents the recruitment of AP-2 not only onto endosomes but also onto the plasma membrane, suggesting that both events are mediated by PLD. Surprisingly, however, neither PLD nor neomycin has any effect on the recruitment of AP-1 adaptors onto the TGN, even though AP-1 recruitment is ARF mediated. These results indicate that different mechanisms are used for the recruitment of AP-1 and AP-2.
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Affiliation(s)
- M A West
- University of Cambridge, Department of Clinical Biochemistry, Cambridge CB2 2QR, United Kingdom
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173
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Identification of a somatodendritic targeting signal in the cytoplasmic domain of the transferrin receptor. J Neurosci 1997. [PMID: 9236215 DOI: 10.1523/jneurosci.17-16-06038.1997] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Neurons are highly polarized cells that must sort proteins synthesized in the cell body for transport into the axon or the dendrites. Given the amount of time and energy needed to deliver proteins to the distal processes, neurons must have high fidelity mechanisms that ensure proper polarized protein trafficking. Although a variety of proteins are localized either to the somatodendritic domain or to the axon (), the question of whether there are signal-dependent mechanisms that sort proteins to distinct neuronal domains is only beginning to be addressed. To determine sequence requirements for the polarized sorting of transmembrane proteins into dendrites, we expressed mutant transferrin receptors in cultured rat hippocampal neurons, using a defective herpes virus vector. Wild-type human transferrin receptor colocalized with the endogenous protein in dendritic endosomes and was strictly excluded from axons, despite overexpression. Polarized targeting was abolished by deletion of cytoplasmic amino acids 7-10, 11-14, or 19-28, but not 29-42 or 43-58. These deletions also increased the appearance of transferrin receptor on the plasma membrane, implying that endocytosis and dendritic targeting are mediated by overlapping signals and similar molecular mechanisms. In addition, we have characterized a specialized para-Golgi endosome poised to play a critical role in the polarized recycling of transmembrane proteins.
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174
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Urbé S, Tooze SA, Barr FA. Formation of secretory vesicles in the biosynthetic pathway. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1358:6-22. [PMID: 9296516 DOI: 10.1016/s0167-4889(97)00050-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- S Urbé
- Imperial Cancer Research Fund, London, UK
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175
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West AE, Neve RL, Buckley KM. Identification of a somatodendritic targeting signal in the cytoplasmic domain of the transferrin receptor. J Neurosci 1997; 17:6038-47. [PMID: 9236215 PMCID: PMC6568350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/1997] [Revised: 05/19/1997] [Accepted: 05/29/1997] [Indexed: 02/04/2023] Open
Abstract
Neurons are highly polarized cells that must sort proteins synthesized in the cell body for transport into the axon or the dendrites. Given the amount of time and energy needed to deliver proteins to the distal processes, neurons must have high fidelity mechanisms that ensure proper polarized protein trafficking. Although a variety of proteins are localized either to the somatodendritic domain or to the axon (), the question of whether there are signal-dependent mechanisms that sort proteins to distinct neuronal domains is only beginning to be addressed. To determine sequence requirements for the polarized sorting of transmembrane proteins into dendrites, we expressed mutant transferrin receptors in cultured rat hippocampal neurons, using a defective herpes virus vector. Wild-type human transferrin receptor colocalized with the endogenous protein in dendritic endosomes and was strictly excluded from axons, despite overexpression. Polarized targeting was abolished by deletion of cytoplasmic amino acids 7-10, 11-14, or 19-28, but not 29-42 or 43-58. These deletions also increased the appearance of transferrin receptor on the plasma membrane, implying that endocytosis and dendritic targeting are mediated by overlapping signals and similar molecular mechanisms. In addition, we have characterized a specialized para-Golgi endosome poised to play a critical role in the polarized recycling of transmembrane proteins.
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Affiliation(s)
- A E West
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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176
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Faúndez V, Horng JT, Kelly RB. ADP ribosylation factor 1 is required for synaptic vesicle budding in PC12 cells. J Cell Biol 1997; 138:505-15. [PMID: 9245782 PMCID: PMC2141633 DOI: 10.1083/jcb.138.3.505] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/1997] [Revised: 06/11/1997] [Indexed: 02/04/2023] Open
Abstract
Carrier vesicle generation from donor membranes typically progresses through a GTP-dependent recruitment of coats to membranes. Here we explore the role of ADP ribosylation factor (ARF) 1, one of the GTP-binding proteins that recruit coats, in the production of neuroendocrine synaptic vesicles (SVs) from PC12 cell membranes. Brefeldin A (BFA) strongly and reversibly inhibited SV formation in vivo in three different PC12 cell lines expressing vesicle-associated membrane protein-T Antigen derivatives. Other membrane traffic events remained unaffected by the drug, and the BFA effects were not mimicked by drugs known to interfere with formation of other classes of vesicles. The involvement of ARF proteins in the budding of SVs was addressed in a cell-free reconstitution system (Desnos, C., L. Clift-O'Grady, and R.B. Kelly. 1995. J. Cell Biol. 130:1041-1049). A peptide spanning the effector domain of human ARF1 (2-17) and recombinant ARF1 mutated in its GTPase activity, both inhibited the formation of SVs of the correct size. During in vitro incubation in the presence of the mutant ARFs, the labeled precursor membranes acquired different densities, suggesting that the two ARF mutations block at different biosynthetic steps. Cell-free SV formation in the presence of a high molecular weight, ARF-depleted fraction from brain cytosol was significantly enhanced by the addition of recombinant myristoylated native ARF1. Thus, the generation of SVs from PC12 cell membranes requires ARF and uses its GTPase activity, probably to regulate coating phenomena.
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Affiliation(s)
- V Faúndez
- Department of Biochemistry and Biophysics, The Hormone Research Institute, University of California, San Francisco, California 94143-0534, USA
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177
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Malide D, Dwyer NK, Blanchette-Mackie EJ, Cushman SW. Immunocytochemical evidence that GLUT4 resides in a specialized translocation post-endosomal VAMP2-positive compartment in rat adipose cells in the absence of insulin. J Histochem Cytochem 1997; 45:1083-96. [PMID: 9267469 DOI: 10.1177/002215549704500806] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Insulin stimulates glucose transport in rat adipose cells through the translocation of GLUT4 from a poorly defined intracellular compartment to the cell surface. We employed confocal microscopy to determine the in situ localization of GLUT4 relative to vesicle, Golgi, and endosomal proteins in these physiological insulin target cells. Three-dimensional analyses of GLUT4 immunostaining in basal cells revealed an intracellular punctate, patchy distribution both in the perinuclear region and scattered throughout the cytoplasm. VAMP2 closely associates with GLUT4 in many punctate vesicle-like structures. A small fraction of GLUT4 overlaps with TGN38-mannosidase II, gamma-adaptin, and mannose-6-phosphate receptors in the perinuclear region, presumably corresponding to late endosome and trans-Golgi network structures. GLUT4 does not co-localize with transferrin receptors, clathrin, and Igp-120. After insulin treatment, GLUT4 partially redistributes to the cell surface and decreases in the perinuclear area. However, GLUT4 remains co-localized with TGN38-mannosidase II and gamma-adaptin. Therefore, the basal compartment from which GLUT4 is translocated in response to insulin comprises specialized post-endosomal VAMP2-positive vesicles, distinct from the constitutively recycling endosomes. These results are consistent with a kinetic model in which GLUT4 is sequestered through two or more intracellular pools in series.
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Affiliation(s)
- D Malide
- Experimental Diabetes, Metabolism, and Nutrition Section, National Institutes of Health, Bethesda, Maryland 20892-1420, USA
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178
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Ooi CE, Moreira JE, Dell'Angelica EC, Poy G, Wassarman DA, Bonifacino JS. Altered expression of a novel adaptin leads to defective pigment granule biogenesis in the Drosophila eye color mutant garnet. EMBO J 1997; 16:4508-18. [PMID: 9303295 PMCID: PMC1170077 DOI: 10.1093/emboj/16.15.4508] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Drosophila eye pigmentation defects have thus far been attributed to mutations in genes encoding enzymes required for biosynthesis of pigments and to ABC-type membrane transporters for pigments or their precursors. We report here that a defect in a gene encoding a putative coat adaptor protein leads to the eye color defect of garnet mutants. We first identified a human cDNA encoding delta-adaptin, a structural homolog of the alpha- and gamma-adaptin subunits of the clathrin coat adaptors AP-1 and AP-2, respectively. Biochemical analyses demonstrated that delta-adaptin is a component of the adaptor-like complex AP-3 in human cells. We then isolated a full-length cDNA encoding the Drosophila ortholog of delta-adaptin and found that transcripts specified by this cDNA are altered in garnet mutant flies. Examination by light and electron microscopy indicated that these mutant flies have reduced numbers of eye pigment granules, which correlates with decreased levels of both pteridine (red) and ommachrome (brown) pigments. Thus, the eye pigmentation defect in the Drosophila garnet mutant may be attributed to compromised function of a coat protein involved in intracellular transport processes required for biogenesis or function of pigment granules.
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Affiliation(s)
- C E Ooi
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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179
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Müsch A, Cohen D, Rodriguez-Boulan E. Myosin II is involved in the production of constitutive transport vesicles from the TGN. J Cell Biol 1997; 138:291-306. [PMID: 9230072 PMCID: PMC2138203 DOI: 10.1083/jcb.138.2.291] [Citation(s) in RCA: 156] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/1997] [Revised: 05/01/1997] [Indexed: 02/04/2023] Open
Abstract
The participation of nonmuscle myosins in the transport of organelles and vesicular carriers along actin filaments has been documented. In contrast, there is no evidence for the involvement of myosins in the production of vesicles involved in membrane traffic. Here we show that the putative TGN coat protein p200 (Narula, N., I. McMorrow, G. Plopper, J. Doherty, K.S. Matlin, B. Burke, and J.L. Stow. 1992. J. Cell Biol. 114: 1113-1124) is myosin II. The recruitment of myosin II to Golgi membranes is dependent on actin and is regulated by G proteins. Using an assay that studies the release of transport vesicles from the TGN in vitro, we provide functional evidence that p200/myosin is involved in the assembly of basolateral transport vesicles carrying vesicular stomatitis virus G protein (VSVG) from the TGN of polarized MDCK cells. The 50% reduced efficiency in VSVG vesicle release from the TGN in vitro after depletion of p200/myosin II could be reestablished to control levels by the addition of purified nonmuscle myosin II. Several inhibitors of the actin-stimulated ATPase activity of myosin specifically inhibited the release of VSVG-containing vesicles from the TGN.
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Affiliation(s)
- A Müsch
- Dyson Institute of Vision Research, Department of Ophthalmology, Department of Cell Biology and Anatomy, Cornell University Medical College, New York 10021, USA
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180
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Panek HR, Stepp JD, Engle HM, Marks KM, Tan PK, Lemmon SK, Robinson LC. Suppressors of YCK-encoded yeast casein kinase 1 deficiency define the four subunits of a novel clathrin AP-like complex. EMBO J 1997; 16:4194-204. [PMID: 9250663 PMCID: PMC1170045 DOI: 10.1093/emboj/16.14.4194] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In Saccharomyces cerevisiae, the redundant YCK1 and YCK2 genes (Yeast Casein Kinase 1) are required for viability. We describe here the molecular analysis of four mutations that eliminate the requirement for Yck activity. These mutations alter proteins that resemble the four subunits of clathrin adaptors (APs), with highest sequence similarity to those of the recently identified AP-3 complex. The four yeast subunits are associated in a high-molecular-weight complex. These proteins have no essential function and are not redundant for function with other yeast AP-related proteins. Combination of suppressor mutations with a clathrin heavy chain mutation (chc1-ts) confers no synthetic growth defects. However, a yck(ts) mutation shows a strong synthetic growth defect with chc1-ts. Moreover, endocytosis of Ste3p is dramatically decreased in yck(ts) cells and is partially restored by the AP suppressor mutations. These results suggest that vesicle trafficking at the plasma membrane requires the activity of Yck protein kinases, and that the new AP-related complex may participate in this process.
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Affiliation(s)
- H R Panek
- LSU Medical Center, Department of Biochemistry and Molecular Biology, Shreveport, LA 71130, USA
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181
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Ramjaun AR, Micheva KD, Bouchelet I, McPherson PS. Identification and characterization of a nerve terminal-enriched amphiphysin isoform. J Biol Chem 1997; 272:16700-6. [PMID: 9195986 DOI: 10.1074/jbc.272.26.16700] [Citation(s) in RCA: 151] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Amphiphysin is a nerve terminal-enriched protein thought to function in synaptic vesicle endocytosis, in part through Src homology 3 (SH3) domain-mediated interactions with dynamin and synaptojanin. Here, we report the characterization of a novel amphiphysin isoform (termed amphiphysin II) that was identified through a homology search of the data base of expressed sequence tags. Antibodies specific to amphiphysin II recognize a 90-kDa protein on Western blot that is brain-specific and highly enriched in nerve terminals. Like amphiphysin (now referred to as amphiphysin I), amphiphysin II binds to dynamin and synaptojanin through its SH3 domain. Further, both proteins bind directly to clathrin in an SH3 domain-independent manner. Taken together, these data suggest that amphiphysin II may participate with amphiphysin I in the regulation of synaptic vesicle endocytosis.
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Affiliation(s)
- A R Ramjaun
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Québec H3A 2B4, Canada
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182
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Dell'Angelica EC, Ooi CE, Bonifacino JS. Beta3A-adaptin, a subunit of the adaptor-like complex AP-3. J Biol Chem 1997; 272:15078-84. [PMID: 9182526 DOI: 10.1074/jbc.272.24.15078] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Recent studies have described a widely expressed adaptor-like complex, named AP-3, which is likely involved in protein sorting in exocytic/endocytic pathways. The AP-3 complex is composed of four distinct subunits. Here, we report the identification of one of the subunits of this complex, which we call beta3A-adaptin. The predicted amino acid sequence of beta3A-adaptin reveals that the protein is closely related to the neuron-specific protein beta-NAP (61% overall identity) and more distantly related to the beta1- and beta2-adaptin subunits of the clathrin-associated adaptor complexes AP-1 and AP-2, respectively. Sequence comparisons also suggest that beta3A-adaptin has a domain organization similar to beta-NAP and to beta1- and beta2-adaptins. beta3A-adaptin is expressed in all tissues and cells examined. Co-purification and co-precipitation analyses demonstrate that beta3A-adaptin corresponds to the approximately 140-kDa subunit of the ubiquitous AP-3 complex, the other subunits being delta-adaptin, p47A (now called mu3A) and sigma3 (A or B). beta3A-adaptin is phosphorylated on serine residues in vivo while the other subunits of the complex are not detectably phosphorylated. beta3A-adaptin is not present in significant amounts in clathrin-coated vesicles. The characteristics of beta3A-adaptin reported here lend support to the idea that AP-3 is a structural and functional homolog of the clathrin-associated adaptors AP-1 and AP-2.
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Affiliation(s)
- E C Dell'Angelica
- Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
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183
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Simpson F, Peden AA, Christopoulou L, Robinson MS. Characterization of the adaptor-related protein complex, AP-3. J Cell Biol 1997; 137:835-45. [PMID: 9151686 PMCID: PMC2139840 DOI: 10.1083/jcb.137.4.835] [Citation(s) in RCA: 285] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/1996] [Revised: 03/06/1997] [Indexed: 02/04/2023] Open
Abstract
We have recently shown that two proteins related to two of the adaptor subunits of clathrincoated vesicles, p47 (mu3) and beta-NAP (beta3B), are part of an adaptor-like complex not associated with clathrin (Simpson, F., N.A. Bright, M.A. West, L.S. Newman, R.B. Darnell, and M.S. Robinson, 1996. J. Cell Biol. 133:749-760). In the present study we have searched the EST database and have identified, cloned, and sequenced a ubiquitously expressed homologue of beta-NAP, beta3A, as well as homologues of the alpha/gamma and sigma adaptor subunits, delta and sigma3, which are also ubiquitously expressed. Antibodies raised against recombinant delta and sigma3 show that they are the other two subunits of the adaptor-like complex. We are calling this complex AP-3, a name that has also been used for the neuronalspecific phosphoprotein AP180, but we feel that it is a more appropriate designation for an adaptor-related heterotetramer. Immunofluorescence using anti-delta antibodies reveals that the AP-3 complex is associated with the Golgi region of the cell as well as with more peripheral structures. These peripheral structures show only limited colocalization with endosomal markers and may correspond to a postTGN biosynthetic compartment. The delta subunit is closely related to the protein product of the Drosophila garnet gene, which when mutated results in reduced pigmentation of the eyes and other tissues. Because pigment granules are believed to be similar to lysosomes, this suggests either that the AP-3 complex may be directly involved in trafficking to lysosomes or alternatively that it may be involved in another pathway, but that missorting in that pathway may indirectly lead to defects in pigment granules.
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Affiliation(s)
- F Simpson
- University of Cambridge, Department of Clinical Biochemistry, Cambridge CB2 2QR, United Kingdom
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184
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Abstract
Clathrin-coated vesicles are responsible for the sorting transport of membrane proteins within cells. Their co of the self-assembling protein clathrin, and adaptor r. interact with the vesicle cargo and localize clathrin tc Recently, novel clathrin-like and adaptor-like proteins identified. Here, Frances Brodsky discusses various in these findings, including the possibility that the novel expanded functions beyond the conventional roles of the in coated-vesicle formation. In this context, the mech which coats influence vesicle formation is reconsidere.
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185
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Dell'Angelica EC, Ohno H, Ooi CE, Rabinovich E, Roche KW, Bonifacino JS. AP-3: an adaptor-like protein complex with ubiquitous expression. EMBO J 1997; 16:917-28. [PMID: 9118953 PMCID: PMC1169692 DOI: 10.1093/emboj/16.5.917] [Citation(s) in RCA: 313] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We have identified two closely related human proteins (sigma3A and sigma3B) that are homologous to the small chains, sigma1 and sigma2, of clathrin-associated adaptor complexes. Northern and Western blot analyses demonstrate that the products of both the sigma3A and sigma3B genes are expressed in a wide variety of tissues and cell lines. sigma3A and sigma3B are components of a large complex, named AP-3, that also contains proteins of apparent molecular masses of 47, 140 and 160 kDa. In non-neuronal cells, the 47 kDa protein most likely corresponds to the medium chain homolog p47A, and the 140 kDa protein is a homolog of the neuron-specific protein beta-NAP. Like other members of the medium-chain family, the p47A chain is capable of interacting with the tyrosine-based sorting signal YQRL from TGN38. Immunofluorescence microscopy analyses show that the sigma3-containing complex is present both in the area of the TGN and in peripheral structures, some of which contain the transferrin receptor. These results suggest that the sigma3 chains are components of a novel, ubiquitous adaptor-like complex involved in the recognition of tyrosine-based sorting signals.
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Affiliation(s)
- E C Dell'Angelica
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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186
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Abstract
Transport vesicles need coat proteins in order to form. The coat proteins are recruited from the cytosol onto a particular membrane, where they drive vesicle budding and select the vesicle cargo. So far, three types of coated transport vesicles have been purified and characterized, and candidates for components of other types of coats have been identified. This review gives a brief overview of what is known about the various coats and their role in transport vesicle formation.
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187
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Banting G, Ponnambalam S. TGN38 and its orthologues: roles in post-TGN vesicle formation and maintenance of TGN morphology. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1355:209-17. [PMID: 9060992 DOI: 10.1016/s0167-4889(96)00146-2] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- G Banting
- Department of Biochemistry, University of Bristol, UK
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188
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Abstract
Adaptors are multifunctional linker proteins that, as a coated vesicle assembles, tether the clathrin lattice to the underlying membrane bud site. Each adaptor is composed of four distinct protein submits, but how these assemble into the functional complex is not clear. Here, some features of the protein sequences are discussed in an attempt to develop a speculative, low-resolution structural model of possible subunit interactions.
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189
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Abstract
Clathrin-coated vesicles were the first discovered and remain the most extensively characterized transport vesicles. They mediate endocytosis of transmembrane receptors and transport of newly synthesized lysosomal hydrolases from the trans-Golgi network to the lysosome. Cell-free assays for coat assembly, membrane binding, and coated vesicle budding have provided detailed functional and structural information about how the major coat constituents, clathrin and the adaptor protein complexes, interact with each other, with membranes, and with the sorting signals found on cargo molecules. Coat constituents not only serve to shape the budding vesicle, but also play a direct role in the packaging of cargo, suggesting that protein sorting and vesicle budding are functionally integrated. The functional interplay between the coated vesicle machinery and its cargo could ensure sorting fidelity and packaging efficiency and might enable modulation of vesicular trafficking in response to demand.
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Affiliation(s)
- S L Schmid
- Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA
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190
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Abstract
Endocytosis in eukaryotic cells is characterized by the continuous and regulated formation of prolific numbers of membrane vesicles at the plasma membrane. These vesicles come in several different varieties, ranging from the actin-dependent formation of phagosomes involved in particle uptake, to smaller clathrin-coated vesicles responsible for the internalization of extracellular fluid and receptor-bound ligands. In general, each of these vesicle types results in the delivery of their contents to lysosomes for degradation. The membrane components of endocytic vesicles, on the other hand, are subject to a series of highly complex and iterative molecular sorting events resulting in their targeting to specific destinations. In recent years, much has been learned about the function of the endocytic pathway and the mechanisms responsible for the molecular sorting of proteins and lipids. This review attempts to integrate these new concepts with long-established views of endocytosis to present a more coherent picture of how the endocytic pathway is organized and how the intracellular transport of internalized membrane components is controlled. Of particular importance are emerging concepts concerning the protein-based signals responsible for molecular sorting and the cytosolic complexes responsible for the decoding of these signals.
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Affiliation(s)
- I Mellman
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002, USA
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191
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Seaman MN, Sowerby PJ, Robinson MS. Cytosolic and membrane-associated proteins involved in the recruitment of AP-1 adaptors onto the trans-Golgi network. J Biol Chem 1996; 271:25446-51. [PMID: 8810314 DOI: 10.1074/jbc.271.41.25446] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The AP-1 adaptor complex is recruited from the cytosol onto the trans-Golgi network membrane, where it co-assembles with clathrin into a coat that drives vesicle budding. The GTPase ARF1 has been shown to be required for AP-1 recruitment, and here we demonstrate that we can reconstitute full GTPgammaS-dependent recruitment of adaptors onto an enriched trans-Golgi network membrane fraction by adding purified AP-1 and recombinant myristylated ARF1, indicating that these are the only soluble proteins required for binding. To identify some of the membrane proteins involved in recruitment, we have incubated permeabilized metabolically labeled cells with cytosol under conditions that promote adaptor binding, then cross-linked the samples with 3,3'dithiobis(sulfosuccinimidylproprionate), denatured by boiling in SDS, and immunoprecipitated with antibodies against the various subunits. Under these conditions, the adaptor subunits co-precipitate not only with each other and with clathrin, but also with three novel proteins: p75, which is specifically cross-linked to gamma-adaptin; p80, which is specifically cross-linked to beta'-adaptin; and p60, which is specifically cross-linked to AP47. These proteins are all candidates for components of the adaptor docking site on the trans-Golgi network membrane.
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Affiliation(s)
- M N Seaman
- Department of Clinical Biochemistry, University of Cambridge, Cambridge CB2 2QR, United Kingdom
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