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Microtubules depolymerization caused by the CK1 inhibitor IC261 may be not mediated by CK1 blockage. PLoS One 2014; 9:e100090. [PMID: 24937750 PMCID: PMC4061085 DOI: 10.1371/journal.pone.0100090] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 05/21/2014] [Indexed: 12/18/2022] Open
Abstract
The ubiquitously expressed serine/threonine specific casein kinase 1 (CK1) family plays important roles in the regulation of various physiological processes. Small-molecule inhibitors, such as the CK1δ/ε selectively inhibitor IC261, have been used to antagonize CK1 phosphorylation events in cells in many studies. Here we present data to show that, similarly to the microtubule destabilizing agent nocodazole, IC261 depolymerizes microtubules in interphase cells. IC261 treatment of interphase cells affects the morphology of the TGN and Golgi apparatus as well as the localization of CK1δ, which co-localizes with COPI positive membranes. IC261-induced depolymerization of microtubules is rapid, reversible and can be antagonized by pre-treatment of cells with taxol. At lower concentrations of IC261, mitotic spindle microtubule dynamics are affected; this leads to cell cycle arrest and, depending on the cellular background, to apoptosis in a dose-dependent manner. In addition, FACS analysis revealed that IC261 could induce apoptosis independent of cell cycle arrest. In summary this study provides additional and valuable information about various IC261-induced effects that could be caused by microtubule depolymerization rather than by inhibition of CK1. Data from studies that have used IC261 as an inhibitor of CK1 should be interpreted in light of these observations.
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2
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Séron K, Couturier C, Belouzard S, Bacart J, Monté D, Corset L, Bocquet O, Dam J, Vauthier V, Lecœur C, Bailleul B, Hoflack B, Froguel P, Jockers R, Rouillé Y. Endospanins regulate a postinternalization step of the leptin receptor endocytic pathway. J Biol Chem 2011; 286:17968-81. [PMID: 21454707 PMCID: PMC3093871 DOI: 10.1074/jbc.m111.224857] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 03/07/2011] [Indexed: 12/22/2022] Open
Abstract
Endospanin-1 is a negative regulator of the cell surface expression of leptin receptor (OB-R), and endospanin-2 is a homologue of unknown function. We investigated the mechanism for endospanin-1 action in regulating OB-R cell surface expression. Here we show that endospanin-1 and -2 are small integral membrane proteins that localize in endosomes and the trans-Golgi network. Antibody uptake experiments showed that both endospanins are transported to the plasma membrane and then internalized into early endosomes but do not recycle back to the trans-Golgi network. Overexpression of endospanin-1 or endospanin-2 led to a decrease of OB-R cell surface expression, whereas shRNA-mediated depletion of each protein increased OB-R cell surface expression. This increased cell surface expression was not observed with OB-Ra mutants defective in endocytosis or with transferrin and EGF receptors. Endospanin-1 or endospanin-2 depletion did not change the internalization rate of OB-Ra but slowed down its lysosomal degradation. Thus, both endospanins are regulators of postinternalization membrane traffic of the endocytic pathway of OB-R.
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Affiliation(s)
- Karin Séron
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8204, 59021 Lille, France
- the Institut National de la Santé et de la Recherche Médicale Unité 1019, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Cyril Couturier
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
- the Institut Cochin, Unité Mixte de Recherche 8104, CNRS, Department of Cell Biology, Université Paris Descartes, 75014 Paris, France
- INSERM Unité 1016, 75014 Paris, France
| | - Sandrine Belouzard
- the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8204, 59021 Lille, France
- the Institut National de la Santé et de la Recherche Médicale Unité 1019, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Johan Bacart
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Didier Monté
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
- CNRS, Unité Mixte de Recherche 8161, 59021 Lille, France
| | - Laetitia Corset
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Olivier Bocquet
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Julie Dam
- the Institut Cochin, Unité Mixte de Recherche 8104, CNRS, Department of Cell Biology, Université Paris Descartes, 75014 Paris, France
- INSERM Unité 1016, 75014 Paris, France
| | - Virginie Vauthier
- the Institut Cochin, Unité Mixte de Recherche 8104, CNRS, Department of Cell Biology, Université Paris Descartes, 75014 Paris, France
- INSERM Unité 1016, 75014 Paris, France
| | - Cécile Lecœur
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
| | - Bernard Bailleul
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
- INSERM Unité 1011, 59021 Lille, France
| | - Bernard Hoflack
- the Biotechnological Center, Dresden University of Technology, 01307 Dresden, Germany, and
| | - Philippe Froguel
- From the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8199, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
- the Department of Genomic Medicine, Hammersmith Hospital, Imperial College London, London SW7 2AZ, United Kingdom
| | - Ralf Jockers
- the Institut Cochin, Unité Mixte de Recherche 8104, CNRS, Department of Cell Biology, Université Paris Descartes, 75014 Paris, France
- INSERM Unité 1016, 75014 Paris, France
| | - Yves Rouillé
- the Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8204, 59021 Lille, France
- the Institut National de la Santé et de la Recherche Médicale Unité 1019, 59021 Lille, France
- the Université Lille Nord de France, Lille 59021, France
- the Institut Pasteur de Lille, 59021 Lille, France
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3
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Li Y, Fischer-Colbrie R, Dahlström A. Neuroendocrine secretory protein 55 (NESP55) in the spinal cord of rat: An immunocytochemical study. J Comp Neurol 2007; 506:733-44. [DOI: 10.1002/cne.21562] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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4
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Costanzo RV, Vilá-Ortíz GJ, Perandones C, Carminatti H, Matilla A, Radrizzani M. Anp32e/Cpd1 regulates protein phosphatase 2A activity at synapses during synaptogenesis. Eur J Neurosci 2006; 23:309-24. [PMID: 16420440 DOI: 10.1111/j.1460-9568.2005.04555.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Anp32e/Cpd1, a member of the acidic nuclear phosphoprotein (Anp)32 family, is characterized by the presence of an amino terminal domain containing four leucine-rich repeats and a carboxyl-terminal low-compositional complexity acidic region. In previous studies performed to understand the biological role of Anp32e/Cpd1, we showed a predominant presence of Anp32e/Cpd1 in the nucleus. However, when Anp32e/Cpd1 is in the cytoplasm, it co-localizes spatially with protein phosphatase 2A (PP2A) near cell membranes, far from the synapses. In the present work, we show that Anp32e/Cpd1 is also present as a membrane-bound 74/76-kDa protein with a widespread distribution in the brain. We reveal that the expression, synthesis and half-life of this high-molecular-weight form of Anp32e/Cpd1 are spatially and temporally correlated with the cerebellar synaptogenesis period. We demonstrate that synaptic Anp32e/Cpd1 co-localizes, interacts and inhibits PP2A activity, and that phosphorylation of Anp32/Cpd1 is required for the Anp32e-PP2A interaction. Also, subcellular localization was shown with electronic microscopy. Finally, we examine Anp32e/Cpd1 and PP2A distribution in two ataxic mutant models, weaver and staggerer, and show that their co-localization in Purkinje cell dendrites depends on parallel fibre/Purkinje cell contacts. Based on these observations, we propose that Anp32e/Cpd1 mediates synaptogenesis process by modulating PP2A activity.
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Affiliation(s)
- Roxana V Costanzo
- Centro Nacional de Genética Médica, A.N.L.I.S, Programa Nacional de Genética Médica, Avenue, Las Heras 2670 (1425), Buenos Aires, Argentina
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5
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Snyder CM, Mardones GA, Ladinsky MS, Howell KE. GMx33 associates with the trans-Golgi matrix in a dynamic manner and sorts within tubules exiting the Golgi. Mol Biol Cell 2005; 17:511-24. [PMID: 16236792 PMCID: PMC1345686 DOI: 10.1091/mbc.e05-07-0682] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The trans-Golgi matrix consists of a group of proteins dynamically associated with the trans-Golgi and thought to be involved in anterograde and retrograde Golgi traffic, as well as interactions with the cytoskeleton and maintenance of the Golgi structure. GMx33 is localized to the cytoplasmic face of the trans-Golgi and is also present in a large cytoplasmic pool. Here we demonstrate that GMx33 is dynamically associated with the trans-Golgi matrix, associating and dissociating with the Golgi in seconds. GMx33 can be locked onto the trans-Golgi matrix by GTPgammaS, indicating that its association is regulated in a GTP-dependent manner like several other Golgi matrix proteins. Using live-cell imaging we show that GMx33 exits the Golgi associated with tubules and within these tubules GMx33 segregates from transmembrane proteins followed by fragmentation of the tubules into smaller tubules and vesicles. Within vesicles produced by an in vitro budding reaction, GMx33 remains segregated in a matrixlike tail region that sometimes contains Golgin-245. This trans-matrix often links a few vesicles together. Together these data suggest that GMx33 is a member of the trans-Golgi matrix and offer clues regarding the role of the trans-Golgi matrix in sorting and exit from the Golgi.
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Affiliation(s)
- Christopher M Snyder
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO 80045, USA
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6
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Bauer RA, Overlease RL, Lieber JL, Angleson JK. Retention and stimulus-dependent recycling of dense core vesicle content in neuroendocrine cells. J Cell Sci 2004; 117:2193-202. [PMID: 15126621 DOI: 10.1242/jcs.01093] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We have used fluorescence imaging of individual exocytic events in combination with immunogold electron microscopy and FM1-43 photoconversion to study the stimulus-dependent recycling of dense core vesicle content in isolated rat pituitary lactotrophs. Secretory stimulation with high external [K+] resulted in 100 exocytic sites per cell that were labeled by extracellular antibodies against the peptide hormone prolactin. Morphological analysis demonstrated that the prolactin was retained and internalized in intact dense cores. Vesicles containing non-secreted, internalized prolactin did not colocalize with DiI-LDL that had been chased into lysosomes but did transiently colocalize with internalized transferrin. The recycling vesicles also trafficked through a syntaxin 6-positive compartment but not the TGN38-positive trans-Golgi. Recycling vesicles, which returned to the cell surface in a slow basal manner, could also be stimulated to undergo exocytosis with a high release probability during subsequent exocytic stimulation with external K+. These studies suggest a functional role for recycling vesicles that retain prolactin.
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Affiliation(s)
- Roslyn A Bauer
- Department of Biological Sciences, University of Denver, Denver, CO 80208, USA
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7
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Bäck N, Litonius E, Mains RE, Eipper BA. Fluoride causes reversible dispersal of Golgi cisternae and matrix in neuroendocrine cells. Eur J Cell Biol 2004; 83:389-402. [PMID: 15506563 DOI: 10.1078/0171-9335-00405] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A role for heterotrimeric G proteins in the regulation of Golgi function and formation of secretory granules is generally accepted. We set out to study the effect of activation of heterotrimeric G proteins by aluminum fluoride on secretory granule formation in AtT-20 corticotropic tumor cells and in melanotrophs from the rat pituitary. In AtT-20 cells, treatment with aluminum fluoride or fluoride alone for 60 min induced complete dispersal of Golgi, ER-Golgi intermediate compartment and Golgi matrix markers, while betaCOP immunoreactiviy retained a juxtanuclear position and TGN38 was unaffected. Electron microscopy showed compression of Golgi cisternae followed by conversion of the Golgi stacks into clusters of tubular and vesicular elements. In the melanotroph of the rat pituitary a similar compression of Golgi cisternae was observed, followed by a progressive loss of cisternae from the stacks. As shown in other cells, brefeldin A induced redistribution of the Golgi matrix protein GM130 to punctate structures in the cytoplasm in AtT-20 cells, while mannosidase II immunoreactivity was completely dispersed. Fluoride induced a complete dispersal of mannosidase II and GM130 immunoreactivity. The effect of fluoride was fully reversible with reestablishment of normal mannosidase II and GM130 immunoreactivity within 2 h. After 1 h of recovery, showing varying stages of reassembly, the patterns of mannosidase II and GM130 immunoreactivity were identical in individual cells, indicating that Golgi matrix and cisternae reassemble with similar kinetics during recovery from fluoride treatment. Instead of a specific aluminum fluoride effect on secretory granule formation in the trans-Golgi network, we thus observe a unique form of Golgi dispersal induced by fluoride alone, possibly via its action as a phosphatase inhibitor.
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Affiliation(s)
- Nils Bäck
- Department of Anatomy, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland.
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8
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Kupzig S, Korolchuk V, Rollason R, Sugden A, Wilde A, Banting G. Bst-2/HM1.24 is a raft-associated apical membrane protein with an unusual topology. Traffic 2003; 4:694-709. [PMID: 12956872 DOI: 10.1034/j.1600-0854.2003.00129.x] [Citation(s) in RCA: 350] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
An expression screen of a rat cDNA library for sequences encoding Golgi-localized integral membrane proteins identified a protein with an apparent novel topology, i.e. with both an N-terminal transmembrane domain and a C-terminal glycosyl-phosphatidylinositol (GPI) anchor. Our data are consistent with this. Thus, the protein would have a topology that, in mammalian cells, is shared only by a minor, but pathologically important, topological isoform of the prion protein (PrP). The human orthologue of this protein has been described previously (BST-2 or HM1.24 antigen) as a cell surface molecule that appears to be involved in early pre-B-cell development and which is present at elevated levels at the surface of myeloma cells. We show that rat BST-2/HM1.24 has both a cell surface and an intracellular (juxtanuclear) location and is efficiently internalized from the cell surface. We also show that the cell surface pool of BST-2/HM1.24 is predominantly present in the apical plasma membrane of polarized cells. The fact that rat BST-2/HM1.24 apparently possesses a GPI anchor led us to speculate that it might exist in cholesterol-rich lipid microdomains (lipid rafts) at the plasma membrane. Data from several experiments are consistent with this localization. We present a model in which BST-2/HM1.24 serves to link adjacent lipid rafts within the plasma membrane.
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Affiliation(s)
- Sabine Kupzig
- Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
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9
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Poupon V, Stewart A, Gray SR, Piper RC, Luzio JP. The role of mVps18p in clustering, fusion, and intracellular localization of late endocytic organelles. Mol Biol Cell 2003; 14:4015-27. [PMID: 14517315 PMCID: PMC206996 DOI: 10.1091/mbc.e03-01-0040] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Delivery of endocytosed macromolecules to mammalian cell lysosomes occurs by direct fusion of late endosomes with lysosomes, resulting in the formation of hybrid organelles from which lysosomes are reformed. The molecular mechanisms of this fusion are analogous to those of homotypic vacuole fusion in Saccharomyces cerevisiae. We report herein the major roles of the mammalian homolog of yeast Vps18p (mVps18p), a member of the homotypic fusion and vacuole protein sorting complex. When overexpressed, mVps18p caused the clustering of late endosomes/lysosomes and the recruitment of other mammalian homologs of the homotypic fusion and vacuole protein sorting complex, plus Rab7-interacting lysosomal protein. The clusters were surrounded by components of the actin cytoskeleton, including actin, ezrin, and specific unconventional myosins. Overexpression of mVps18p also overcame the effect of wortmannin treatment, which inhibits membrane traffic out of late endocytic organelles and causes their swelling. Reduction of mVps18p by RNA interference caused lysosomes to disperse away from their juxtanuclear location. Thus, mVps18p plays a critical role in endosome/lysosome tethering, fusion, intracellular localization and in the reformation of lysosomes from hybrid organelles.
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Affiliation(s)
- Viviane Poupon
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, CB2 2XY Cambridge, United Kingdom
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Ito A, Koma YI, Sohda M, Watabe K, Nagano T, Misumi Y, Nojima H, Kitamura Y. Localization of the PP2A B56gamma regulatory subunit at the Golgi complex: possible role in vesicle transport and migration. THE AMERICAN JOURNAL OF PATHOLOGY 2003; 162:479-89. [PMID: 12547706 PMCID: PMC1851168 DOI: 10.1016/s0002-9440(10)63842-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The BL6 subline was derived from the F10 line, which was derived from the B16 mouse melanoma cell line. BL6 cells are more invasive than F10 cells and differ genetically from F10 cells by an alteration of the gene encoding the B56gamma regulatory subunit of protein phosphatase 2A (PP2A). This alteration results in the transcription of mRNA encoding a truncated variant of the B56gamma1 isoform (Deltagamma1). When F10 cells were stained with a polyclonal antibody that recognizes three B56gamma isoforms, B56gamma1, B56gamma2, and B56gamma3, the immunofluorescent signals co-localized well with the cis-Golgi marker proteins. When BL6 cells were fractionated in a sucrose gradient, B56gamma1 and B56gamma2, but not B56gamma3, were present in the Golgi-enriched fraction. This fraction also contained the catalytic subunit of PP2A. FLAG-tagged Deltagamma1 preferentially localized to the trans-Golgi area rather than the cis-Golgi. This localization was the same as that of FLAG-tagged B56gamma1. NIH3T3 cells stably expressing Deltagamma1 transported a mutant viral protein from the endoplasmic reticulum to the plasma membrane much faster than wild-type cells. Their directional migration, as assessed by the advance of cells into a cell-free area, was also elevated. As Deltagamma1 reduces the activity of the B56gamma-containing PP2A holoenzymes, these results suggest that the normal holoenzymes suppress vesicle transport and that Deltagamma1 might increase the invasive ability of BL6 cells by activating Golgi function.
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Affiliation(s)
- Akihiko Ito
- Department of Pathology, Osaka University Medical School/Graduate School of Frontier Bioscience, Suita, Osaka, Japan.
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11
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Tamaki H, Yamashina S. Structural integrity of the Golgi stack is essential for normal secretory functions of rat parotid acinar cells: effects of brefeldin A and okadaic acid. J Histochem Cytochem 2002; 50:1611-23. [PMID: 12486083 DOI: 10.1177/002215540205001205] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We examined the effects of specific inhibitors, brefeldin A (BFA) and okadaic acid (OA), on the ultrastructural organization of the Golgi apparatus and distributions of amylase, Golgi-associated proteins, and cathepsin D in the rat parotid acinar cells. BFA induced a rapid regression of the Golgi stack into rudimentary Golgi clusters composed of tubulovesicules, in parallel with a redistribution of the Golgi-resident proteins and a coat protein (beta-COP) into the region of the rough endoplasmic reticulum (rER) or cytosol. The rapid disruption of the Golgi stack could also be induced by the effect of OA. However, redistribution of the Golgi proteins in rER or cytosol could not be observed and beta-COP was not dispersed but was retained on the rudimentary Golgi apparatus. These findings suggested that the mechanism of OA in inducing degeneration of the Golgi stack was markedly different from that of BFA. In addition, missorting of amylase, a Golgi protein, and cathepsin D into incorrect transport pathways is apparent in the course of the disruption of the Golgi stack by OA. These Golgi-disrupting effects are reversible and the reconstruction of the stacked structure of the Golgi apparatus started immediately after the removal of inhibitors. In the recovery processes, missorting was also observed until the integrated structure of the Golgi apparatus was completely reconstructed. This suggested that the integrated structure of the Golgi apparatus was quite necessary for the occurrence of normal secretory events, including proper sorting of molecules.
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Affiliation(s)
- Hideaki Tamaki
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan.
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12
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Rapsyn escorts the nicotinic acetylcholine receptor along the exocytic pathway via association with lipid rafts. J Neurosci 2002. [PMID: 12388596 DOI: 10.1523/jneurosci.22-20-08891.2002] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The 43 kDa receptor-associated protein rapsyn is a myristoylated peripheral protein that plays a central role in nicotinic acetylcholine receptor (AChR) clustering at the neuromuscular junction. In a previous study, we demonstrated that rapsyn is specifically cotransported with AChR via post-Golgi vesicles targeted to the innervated surface of the Torpedo electrocyte (Marchand et al., 2000). In the present study, to further elucidate the mechanisms for sorting and assembly of postsynaptic proteins, we analyzed the dynamics of the intracellular trafficking of fluorescently labeled rapsyn in the transient-expressing COS-7 cell system. Our approach was based on fluorescence, time-lapse imaging, and immunoelectron microscopies, as well as biochemical analyses. We report that newly synthesized rapsyn associates with the trans-Golgi network compartment and traffics via vesiculotubular organelles toward the cell surface of COS-7 cells. The targeting of rapsyn organelles appeared to be mediated by a microtubule-dependent transport. Using cotransfection experiments of rapsyn and AChR, we observed that these two molecules codistribute within distal exocytic routes and at the plasma membrane. Triton X-100 extraction on ice and flotation gradient centrifugation demonstrated that rapsyn and AChR are recovered in low-density fractions enriched in two rafts markers: caveolin-1 and flotillin-1. We propose that sorting and targeting of these two companion molecules are mediated by association with cholesterol-sphingolipid-enriched raft microdomains. Collectively, these data highlight rapsyn as an itinerant vesicular protein that may play a dynamic role in the sorting and targeting of its companion receptor to the postsynaptic membrane. These data also raise the interesting hypothesis of the participation of the raft machinery in the targeting of signaling molecules to synaptic sites.
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Lee SS, Banting G. Characterisation of the lumenal domain of TGN38 and effects of elevated expression of TGN38 on glycoprotein secretion. Eur J Cell Biol 2002; 81:609-21. [PMID: 12494998 DOI: 10.1078/0171-9335-00279] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The TGN-localised, type I integral membrane protein TGN38 has previously been suggested to play a role as a cargo transporter within mammalian cells. We have undertaken a series of experiments designed to address this hypothesis, and, in so doing, have partially characterised the glycosylation status of the lumenal domain of TGN38. We find that elevated expression of different regions of the lumenal domain of TGN38 has no reproducible effect on secretion from stably transfected NRK cells expressing the different lumenal domain constructs; neither does it affect the gross morphology of organelles of the secretory and endocytic pathways. However, we observed that, whilst elevated expression of full-length TGN38 in stably transfected NRK cells does not have any significant effect on the morphology of organelles of the secretory and endocytic pathways, it does lead to a change in the pattern of protein secretion from these cells. In particular, elevated expression of full-length TGN38 led to increased secretion of a 48-kDa glycoprotein identified as plasminogen activator inhibitor-1.
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Affiliation(s)
- San San Lee
- Department of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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14
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Marchand S, Devillers-Thiéry A, Pons S, Changeux JP, Cartaud J. Rapsyn escorts the nicotinic acetylcholine receptor along the exocytic pathway via association with lipid rafts. J Neurosci 2002; 22:8891-901. [PMID: 12388596 PMCID: PMC6757681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023] Open
Abstract
The 43 kDa receptor-associated protein rapsyn is a myristoylated peripheral protein that plays a central role in nicotinic acetylcholine receptor (AChR) clustering at the neuromuscular junction. In a previous study, we demonstrated that rapsyn is specifically cotransported with AChR via post-Golgi vesicles targeted to the innervated surface of the Torpedo electrocyte (Marchand et al., 2000). In the present study, to further elucidate the mechanisms for sorting and assembly of postsynaptic proteins, we analyzed the dynamics of the intracellular trafficking of fluorescently labeled rapsyn in the transient-expressing COS-7 cell system. Our approach was based on fluorescence, time-lapse imaging, and immunoelectron microscopies, as well as biochemical analyses. We report that newly synthesized rapsyn associates with the trans-Golgi network compartment and traffics via vesiculotubular organelles toward the cell surface of COS-7 cells. The targeting of rapsyn organelles appeared to be mediated by a microtubule-dependent transport. Using cotransfection experiments of rapsyn and AChR, we observed that these two molecules codistribute within distal exocytic routes and at the plasma membrane. Triton X-100 extraction on ice and flotation gradient centrifugation demonstrated that rapsyn and AChR are recovered in low-density fractions enriched in two rafts markers: caveolin-1 and flotillin-1. We propose that sorting and targeting of these two companion molecules are mediated by association with cholesterol-sphingolipid-enriched raft microdomains. Collectively, these data highlight rapsyn as an itinerant vesicular protein that may play a dynamic role in the sorting and targeting of its companion receptor to the postsynaptic membrane. These data also raise the interesting hypothesis of the participation of the raft machinery in the targeting of signaling molecules to synaptic sites.
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Affiliation(s)
- Sophie Marchand
- Biologie Cellulaire des Membranes, Département de Biologie Cellulaire, Institut Jacques Monod, Centre National de la Recherche Scientifique, Universités Paris 6 et 7, 75251, Paris Cedex 05, France
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15
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Storey H, Stewart A, Vandenabeele P, Luzio JP. The p55 tumour necrosis factor receptor TNFR1 contains a trans-Golgi network localization signal in the C-terminal region of its cytoplasmic tail. Biochem J 2002; 366:15-22. [PMID: 11985495 PMCID: PMC1222747 DOI: 10.1042/bj20020048] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2002] [Revised: 04/29/2002] [Accepted: 05/02/2002] [Indexed: 11/17/2022]
Abstract
It has been reported in some human cells that, in addition to a plasma membrane localization, members of the tumour necrosis factor receptor superfamily may be localized to the Golgi complex. We have shown by immunofluorescence and immunoelectron microscopy that the p55 tumour necrosis factor receptor, TNFR1, is principally localized to the trans-Golgi network in the human breast carcinoma cell line, MCF7. Chimaeras consisting of the extracellular and transmembrane domains of CD8 together with the cytoplasmic tail of TNFR1 were targeted to the trans-Golgi network in stably transfected rat fibroblastic cells. Deletions in the cytoplasmic tails of these chimaeras demonstrated the requirement for the C-terminal sequence of 23 amino acids for this targeting. The 23 amino acid sequence is mostly outside the death domain and contains both an acid patch and a dileucine motif. Interaction of this sequence with membrane traffic adaptor proteins may play an important role in controlling the responses of cells to tumour necrosis factor, since binding of signalling adaptor proteins has only been demonstrated for plasma membrane, and not Golgi-localized, TNFR1.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antigens, CD/chemistry
- Antigens, CD/physiology
- Blotting, Western
- CD8 Antigens/biosynthesis
- Cell Line
- Cycloheximide/pharmacology
- Cytoplasm/metabolism
- Electrophoresis, Polyacrylamide Gel
- Fibroblasts/metabolism
- Fluorescent Antibody Technique, Indirect
- Glycoproteins
- Golgi Apparatus/metabolism
- Humans
- Membrane Glycoproteins/metabolism
- Membrane Proteins
- Microscopy, Fluorescence
- Models, Genetic
- Molecular Sequence Data
- Protein Structure, Tertiary
- Protein Synthesis Inhibitors/pharmacology
- Rats
- Receptors, Tumor Necrosis Factor/chemistry
- Receptors, Tumor Necrosis Factor/physiology
- Receptors, Tumor Necrosis Factor, Type I
- Sequence Homology, Amino Acid
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- Helen Storey
- Department of Clinical Biochemistry and Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K
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16
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Kawamoto K, Yoshida Y, Tamaki H, Torii S, Shinotsuka C, Yamashina S, Nakayama K. GBF1, a guanine nucleotide exchange factor for ADP-ribosylation factors, is localized to the cis-Golgi and involved in membrane association of the COPI coat. Traffic 2002; 3:483-95. [PMID: 12047556 DOI: 10.1034/j.1600-0854.2002.30705.x] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Formation of coated carrier vesicles, such as COPI-coated vesicles from the cis-Golgi, is triggered by membrane binding of the GTP-bound form of ADP-ribosylation factors. This process is blocked by brefeldin A, which is an inhibitor of guanine nucleotide exchange factors for ADP-ribosylation factor. GBF1 is one of the guanine nucleotide-exchange factors for ADP-ribosylation factor and is localized in the Golgi region. In the present study, we have determined the detailed subcellular localization of GBF1. Immunofluorescence microscopy of cells treated with nocodazole or incubated at 15 degrees C has suggested that GBF1 behaves similarly to proteins recycling between the cis-Golgi and the endoplasmic reticulum. Immunoelectron microscopy has revealed that GBF1 localizes primarily to vesicular and tubular structures apposed to the cis-face of Golgi stacks and minor fractions to the Golgi stacks. GBF1 overexpressed in cells causes recruitment of class I and class II ADP-ribosylation factors onto Golgi membranes. Furthermore, overexpressed GBF1 antagonizes various effects of brefeldin A, such as inhibition of membrane recruitment of ADP-ribosylation factors and the COPI coat, and redistribution of Golgi-resident and itinerant proteins. These observations indicate that GBF1 is involved in the formation of COPI-coated vesicles from the cis-Golgi or the pre-Golgi intermediate compartment through activating ADP-ribosylation factors.
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Affiliation(s)
- Kazumasa Kawamoto
- Institute of Biological Sciences and Gene Research Center, University of Tsukuba, Tsukuba Science City, Ibaraki 305-8572, Japan
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17
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Klomp AEM, Tops BBJ, Van Denberg IET, Berger R, Klomp LWJ. Biochemical characterization and subcellular localization of human copper transporter 1 (hCTR1). Biochem J 2002; 364:497-505. [PMID: 12023893 PMCID: PMC1222595 DOI: 10.1042/bj20011803] [Citation(s) in RCA: 153] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The human copper transporter 1 gene (hCTR1) was previously identified by functional complementation in ctr1-deficient yeast. Overexpression of hCTR1 in wild-type yeast leads to increased sensitivity to copper toxicity, and mice with a homozygous disruption at the Ctr1 locus die early during embryogenesis. It is proposed that hCTR1 is responsible for high-affinity copper uptake into human cells, but the underlying molecular mechanisms are unknown. To begin to investigate the biochemical characteristics of hCTR1, a polyclonal antiserum was raised against recombinant hCTR1-fusion peptides. Biosynthetic studies using this antiserum revealed that hCTR1 was synthesized as a precursor protein of 28 kDa containing N-linked oligosaccharides, and is then converted to a mature protein of approx. 35 kDa, which is ubiquitously expressed. Immunofluorescence studies showed that subcellular hCTR1 localization differed markedly between cell types. In some cell lines, hCTR1 was located predominantly in an intracellular vesicular perinuclear compartment, and in others hCTR1 was located predominantly at the plasma membrane. In contrast with the copper export P-type ATPases mutated in Wilson disease and Menkes disease, the localization of hCTR1 was not influenced by copper concentrations. Inhibition of endocytosis by methyl-beta-cyclodextrin caused a partial redistribution of hCTR1 to the cell surface of HeLa cells. Taken together, the results in this study suggest a cell-specific control of copper uptake, which involves subcellular localization of the hCTR1 protein.
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Affiliation(s)
- Adriana E M Klomp
- Department of Metabolic Diseases, University Medical Center Utrecht, Lundlaan 6, 3584 EA Utrecht, The Netherlands
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18
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Rous BA, Reaves BJ, Ihrke G, Briggs JAG, Gray SR, Stephens DJ, Banting G, Luzio JP. Role of adaptor complex AP-3 in targeting wild-type and mutated CD63 to lysosomes. Mol Biol Cell 2002; 13:1071-82. [PMID: 11907283 PMCID: PMC99620 DOI: 10.1091/mbc.01-08-0409] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2001] [Revised: 12/05/2001] [Accepted: 12/05/2001] [Indexed: 01/01/2023] Open
Abstract
CD63 is a lysosomal membrane protein that belongs to the tetraspanin family. Its carboxyterminal cytoplasmic tail sequence contains the lysosomal targeting motif GYEVM. Strong, tyrosine-dependent interaction of the wild-type carboxyterminal tail of CD63 with the AP-3 adaptor subunit mu 3 was observed using a yeast two-hybrid system. The strength of interaction of mutated tail sequences with mu 3 correlated with the degree of lysosomal localization of similarly mutated human CD63 molecules in stably transfected normal rat kidney cells. Mutated CD63 containing the cytosolic tail sequence GYEVI, which interacted strongly with mu 3 but not at all with mu 2 in the yeast two-hybrid system, localized to lysosomes in transfected normal rat kidney and NIH-3T3 cells. In contrast, it localized to the cell surface in transfected cells of pearl and mocha mice, which have genetic defects in genes encoding subunits of AP-3, but to lysosomes in functionally rescued mocha cells expressing the delta subunit of AP-3. Thus, AP-3 is absolutely required for the delivery of this mutated CD63 to lysosomes. Using this AP-3-dependent mutant of CD63, we have shown that AP-3 functions in membrane traffic from the trans-Golgi network to lysosomes via an intracellular route that appears to bypass early endosomes.
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Affiliation(s)
- Brian A Rous
- University of Cambridge, Department of Clinical Biochemistry, Cambridge Institute for Medical Research, Cambridge, CB2 2XY, United Kingdom
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19
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Kusano I, Kageyama A, Tamura T, Oda T, Muramatsu T. Enhancement of diphtheria toxin-induced apoptosis in Vero cells by combination treatment with brefeldin A and okadaic acid. Cell Struct Funct 2001; 26:279-88. [PMID: 11831360 DOI: 10.1247/csf.26.279] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In the present study, we compared the abilities of ricin and diphtheria toxin to induce apoptosis in Vero cells. The cytolysis and DNA fragmentation by ricin paralleled its protein synthesis inhibitory activity. However, unlike ricin, diphtheria toxin could induce neither cytolysis nor DNA fragmentation in Vero cells up to very high concentration, in spite of the fact that Vero cells were even more sensitive to protein synthesis inhibition by diphtheria toxin than ricin. Interestingly, coexistence of brefeldin A (BFA) and okadaic acid (OA) significantly enhanced diphtheria toxin-mediated cytolysis and DNA fragmentation without affecting the activity of protein synthesis inhibition. Ammonium chloride almost completely abolished the ability of diphtheria toxin to induce apoptosis in the presence of BFA and OA as well as the protein synthesis inhibitory activity. The mutant CRM 197, which does not catalyze the ADP ribosylation of elongation factor-2 (EF-2), failed to induce apoptosis in Vero cells even in the presence of BFA and OA. Thus, translocation of diphtheria toxin into the cytosol and subsequent enzymatic inactivation of EF-2 may be necessary steps to induce apoptosis. Taken together our results suggest that protein synthesis inhibition by toxins is not sufficient to induce apoptosis, and underlying mechanisms of apoptosis induction may be distinct between ricin and diphtheria toxin. Since a morphological change in the Golgi complex was observed in Vero cells treated with BFA and OA, modulation of the Golgi complex by these reagents may be partly responsible for enhanced apoptosis induction by diphtheria toxin.
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Affiliation(s)
- I Kusano
- Division of Biochemistry, Faculty of Fisheries, Nagasaki University, Japan
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20
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Yan R, Han P, Miao H, Greengard P, Xu H. The transmembrane domain of the Alzheimer's beta-secretase (BACE1) determines its late Golgi localization and access to beta -amyloid precursor protein (APP) substrate. J Biol Chem 2001; 276:36788-96. [PMID: 11466313 DOI: 10.1074/jbc.m104350200] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Release of Abeta peptides from beta-amyloid precursor protein (APP) requires sequential cleavage by two endopeptidases, beta- and gamma-secretases. beta-Secretase was recently identified as a novel membrane-bound aspartyl protease, named BACE1, Asp2, or memapsin 2. Employing confocal microscopy and subcellular fractionation, we have found that BACE1 is largely situated in the distal Golgi membrane with a minor presence in the endoplasmic reticulum, endosomes, and plasma membrane in human neuroblastoma SHEP cells and in mouse Neuro-2a cell lines expressing either endogenous mouse BACE1 or additional exogenous human BACE1. The major cellular beta-secretase activity is located in the late Golgi apparatus, consistent with its cellular localization. Furthermore, we demonstrate that the single transmembrane domain of BACE1 alone determines the retention of BACE1 to the Golgi compartments, through examination of recombinant proteins of various BACE1 fragments fused to a reporter green fluorescence protein. In addition, we show that the transmembrane domain of BACE1 is required for the access of BACE1 enzymatic activity to the cellular APP substrate and hence for the optimal generation of the C-terminal fragment of APP (CTF99). The results suggest a molecular and cell biological mechanism for the regulation of beta-secretase activity in vivo.
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Affiliation(s)
- R Yan
- Department of Cell & Molecular Biology, Pharmacia Corporation, Kalamazoo, Michigan 49007, USA.
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21
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Murayama K, Fujimura T, Morita M, Shindo N. One-step subcellular fractionation of rat liver tissue using a Nycodenz density gradient prepared by freezing-thawing and two-dimensional sodium dodecyl sulfate electrophoresis profiles of the main fraction of organelles. Electrophoresis 2001; 22:2872-80. [PMID: 11565782 DOI: 10.1002/1522-2683(200108)22:14<2872::aid-elps2872>3.0.co;2-d] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In the present study, we describe a new procedure using freezing-thawing to density gradient solution of Nycodenz for one-step separation of organelles from the rat liver and subsequent proteome analysis of subcellular fractions. To prepare two-dimensional electrophoresis (2-D PAGE) profiles of tissue organelles, we performed one-step subcellular fractionation of rat liver homogenate using a density gradient of Nycodenz solution, which resulted in the separation of the cytosolic fraction from the postnuclear supernatant. The density gradient of Nycodenz was prepared from a 20% solution in a centrifuge tube by freezing-thawing overnight at -20 degrees C and at room temperature for a few hours without the initial centrifugation procedure. The shape of the gradient density curve was dependent on Nycodenz concentration and tube size. After fractionation, the protein profiles were examined using one-dimensional sodium dodecyl sulfate (SDS)-PAGE. The organelles were confirmed using Western blotting. Our results indicate that our procedure provides a simple method for the separation of organelle fractions from the rat liver tissue.
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Affiliation(s)
- K Murayama
- Division of Biochemical Analysis, Juntendo University School of Medicine, Tokyo, Japan.
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22
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Sato K, Muroi M, Nakamura M, Fujimura M, Takatsuki A. Co-existing proteins interfere with the action of nordihydroguaiaretic acid on retrograde Golgi-to-ER protein trafficking in NRK cells and alpha-glucosidase reaction in vitro. Biosci Biotechnol Biochem 2001; 65:996-8. [PMID: 11388491 DOI: 10.1271/bbb.65.996] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Induction of retrograde trafficking of mannosidase II and TGN38 in NRK cells and inhibition of alpha-glucosidase in vitro by nordihydroguaiaretic acid (NDGA) were strongly interfered with by serum, serum albumin, or other unrelated proteins added to the medium or incubation mixture. These observations indicate that NDGA interacts with diverse kinds of proteins, and therefore, pharmacological effects of NDGA at cellular levels should be carefully interpreted.
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Affiliation(s)
- K Sato
- Animal and Cellular Systems Laboratory, RIKEN (The Institute of Physical and Chemical Research) Hirosawa, Wako-shi, Saitama, Japan
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23
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Varlamov O, Kalinina E, Che FY, Fricker LD. Protein phosphatase 2A binds to the cytoplasmic tail of carboxypeptidase D and regulates post-trans-Golgi network trafficking. J Cell Sci 2001; 114:311-22. [PMID: 11148133 DOI: 10.1242/jcs.114.2.311] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Carboxypeptidase D (CPD) is a transmembrane protein that processes proteins in the trans-Golgi network (TGN). A 20-residue region within the cytoplasmic tail of CPD binds protein phosphatase 2A (PP2A). PP2A also binds to the cytoplasmic tails of other secretory pathway proteins: peptidylglycine-(amino)-amidating mono-oxygenase, the cation-independent mannose-6-phosphate receptor and TGN38. The CPD tail is phosphorylated on Thr residues in the AtT-20 cell line. The CPD tail can also be phosphorylated by purified protein kinase A, protein kinase C and casein kinase II. Both the in vitro and the in vivo phosphorylated CPD tail can be dephosphorylated by purified PP2A. The binding of CPD tail peptide to PP2A does not influence phosphatase activity. The rate of transport of CPD from the TGN to the cell surface of AtT-20 cells is decreased 45% by okadaic acid, a PP2A inhibitor. Microinjection of the CPD tail into AtT-20 cells inhibits the transition of CPD from endosomal compartments to the TGN. However, okadaic acid does not affect the rate of budding of CPD from the TGN into nascent vesicles or the rate of uptake from the cell surface into endosomal compartments. These results are consistent with the model that PP2A is involved in the trafficking of proteins between a TGN recycling loop and a cell-surface recycling loop, but is not involved in the individual recycling loops.
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Affiliation(s)
- O Varlamov
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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24
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Okazaki Y, Ohno H, Takase K, Ochiai T, Saito T. Cell surface expression of calnexin, a molecular chaperone in the endoplasmic reticulum. J Biol Chem 2000; 275:35751-8. [PMID: 10956670 DOI: 10.1074/jbc.m007476200] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The folding and assembly of nascent proteins in the endoplasmic reticulum are assisted by the molecular chaperone calnexin, which is itself retained within the endoplasmic reticulum. It was up to now assumed that calnexin was selectively expressed on the surface of immature thymocytes because of a particular characteristic of the protein sorting machinery in these cells. We now report that a small fraction of calnexin is normally expressed on the surface of various cells such as mastocytoma cells, murine splenocytes, fibroblast cells, and human HeLa cells. Surface biotinylation followed by chase culture of living cells revealed that calnexin is continuously delivered to the cell surface and then internalized for lysosomal degradation. These results suggest that there is continuous exocytosis and endocytosis of calnexin, and the amount of calnexin on the plasma membrane results from the balance of the rates of these two events. To study the structural requirement of calnexin for surface expression, we created deletion mutants of calnexin and found that the luminal domain, particularly the glycoprotein binding domain, is necessary. These findings suggest that the surface expression of calnexin depends on the association with glycoproteins and that calnexin may play a certain role as a chaperone on the plasma membrane as well.
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Affiliation(s)
- Y Okazaki
- Department of Molecular Genetics, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
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25
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Bannykh SI, Bannykh GI, Fish KN, Moyer BD, Riordan JR, Balch WE. Traffic pattern of cystic fibrosis transmembrane regulator through the early exocytic pathway. Traffic 2000; 1:852-70. [PMID: 11208075 DOI: 10.1034/j.1600-0854.2000.011105.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The pathway of transport of the cystic fibrosis transmembrane regulator (CFTR) through the early exocytic pathway has not been examined. In contrast to most membrane proteins that are concentrated during export from the ER and therefore readily detectable at elevated levels in pre-Golgi intermediates and Golgi compartments, wild-type CFTR could not be detected in these compartments using deconvolution immunofluorescence microscopy. To determine the basis for this unusual feature, we analyzed CFTR localization using quantitative immunoelectron microscopy (IEM). We found that wild-type CFTR is present in pre-Golgi compartments and peripheral tubular elements associated with the cis and trans faces of the Golgi stack, albeit at a concentration 2-fold lower than that found in the endoplasmic reticulum (ER). delta F508 CFTR, a mutant form that is not efficiently delivered to the cell surface and the most common mutation in cystic fibrosis, could also be detected at a reduced concentration in pre-Golgi intermediates and peripheral cis Golgi elements, but not in post-Golgi compartments. Our results suggest that the low level of wild-type CFTR in the Golgi region reflects a limiting step in selective recruitment by the ER export machinery, an event that is largely deficient in delta F508. We raise the possibility that novel modes of selective anterograde and retrograde traffic between the ER and the Golgi may serve to regulate CFTR function in the early secretory compartments.
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Affiliation(s)
- S I Bannykh
- Scripps Research Institute, Departments of Cell and Molecular Biology, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA
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26
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Abstract
TGN38 luminal domain (TGN38LD) was expressed in Cos-7 cells to identify potential binding partners. The luminal domain was secreted but, surprisingly, a significant portion bound to the plasma membrane. Cells overexpressing TGN38LD or the full-length molecule detached from the substratum and left footprints positive for TGN38. Unexpectedly, in these cells, TGN38 colocalizes with integrin alpha 5 beta 1 at the Golgi, the cell surface or in the footprints and an increased amount of both integrin subunits on the plasma membrane was observed. Under physiological conditions when TGN38 is not overexpressed, it interacts with integrin beta 1. This was demonstrated by reciprocal co-immunoprecipitation of integrin beta 1 and TGN38. Functional analysis reveals that modification of the trafficking of TGN38 results in a parallel change in the distribution of integrin alpha 5 beta 1, leading to the conclusion that TGN38 is involved in the trafficking of integrin beta 1.
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Affiliation(s)
- J Wang
- Department of Cellular & Structural Biology, Box B-111, University of Colorado School of Medicine, 4200 E 9th Ave., Denver, CO 80262, USA
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27
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Pons M, Ihrke G, Koch S, Biermer M, Pol A, Grewal T, Jäckle S, Enrich C. Late endocytic compartments are major sites of annexin VI localization in NRK fibroblasts and polarized WIF-B hepatoma cells. Exp Cell Res 2000; 257:33-47. [PMID: 10854052 DOI: 10.1006/excr.2000.4861] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Annexin VI is an abundant calcium- and phospholipid-binding protein whose intracellular distribution and function are still controversial. Using a highly specific antibody, we have studied the distribution of annexin VI in NRK fibroblasts and the polarized hepatic cell line WIF-B by confocal microscopy. In NRK cells, annexin VI was almost exclusively found associated with endocytic compartments, which were defined by their ability to receive fluid-phase marker internalized from the cell surface. However, extensive colocalization of annexin VI and the endocytic marker was only observed after about 45 min, indicating that annexin VI was primarily in late endocytic compartments or (pre)lysosomes. Consistent with this, annexin VI was predominantly seen on structures that contained the lysosomal protein lgp120, although not on dense core lysosomes by electron microscopy. Two major populations of annexin VI-containing structures were present in polarized WIF-B hepatocytes. One correlated to lgp120-positive (pre)lysosomes and was still observed after treatment with brefeldin A (BFA), while the other appeared to be partially associated with Golgi membranes and was BFA-sensitive. The striking association with prelysosomal compartments in NRK and WIF-B cells suggests that annexin VI could play a role in fusion events in the late endocytic pathway, possibly by acting as a tether between membranes.
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Affiliation(s)
- M Pons
- Departament de Biologia Cel.lular, IDIBAPS, Universitat de Barcelona, Spain
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28
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Culvenor JG, Evin G, Cooney MA, Wardan H, Sharples RA, Maher F, Reed G, Diehlmann A, Weidemann A, Beyreuther K, Masters CL. Presenilin 2 expression in neuronal cells: induction during differentiation of embryonic carcinoma cells. Exp Cell Res 2000; 255:192-206. [PMID: 10694435 DOI: 10.1006/excr.1999.4791] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Mutations in the presenilin 1 and 2 (PS1 and PS2) genes cause most cases of early onset Alzheimer's disease. The genes encode two homologous multipass membrane proteins. Since the endogenous expression of PS2 has been poorly analyzed to date, we studied PS2 expression and localization in cultured human neuroblastoma cells and mouse neuronal cells. PS2 was mainly detected as a full-length protein of about 52 kDa in these cells and in brain, in contrast to PS1 that is mainly detected as endoproteolytic N-terminal and C-terminal fragments. Using immunofluorescence we found that like PS1, PS2 colocalized with markers of the endoplasmic reticulum-Golgi intermediate compartment, ERGIC-53 and beta-COP. Double labeling for PS1 and PS2 indicated that both proteins are colocalized in neuroblastoma SH-SY5Y cells. To study PS2 expression during differentiation, mouse embryonic carcinoma P19 cells were treated with retinoic acid. We found minimal PS2 expression in undifferentiated cells, an increase from day 2, and a maximum at day 8 after treatment. PS1 expression remained constant during this period. The differential expression of PS1 and PS2 within the P19 cells following retinoic acid treatment indicates different utilization or temporal requirements for these proteins during neuronal differentiation.
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Affiliation(s)
- J G Culvenor
- Department of Pathology, University of Melbourne, Parkville, Victoria, 3052, Australia.
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29
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Ihrke G, Gray SR, Luzio JP. Endolyn is a mucin-like type I membrane protein targeted to lysosomes by its cytoplasmic tail. Biochem J 2000; 345 Pt 2:287-96. [PMID: 10620506 PMCID: PMC1220758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Endolyn (endolyn-78) is a membrane protein found in lysosomal and endosomal compartments of mammalian cells. Unlike 'classical' lysosomal membrane proteins, such as lysosome-associated membrane protein (lamp)-1, it is also present in a subapical compartment in polarized WIF-B hepatocytes. The structural features that determine sorting of endolyn are unknown. We have identified a rat endolyn cDNA by expression screening. The cDNA encodes a ubiquitously expressed type I membrane protein with a short cytoplasmic tail of 13 amino acids and many putative sites for N- and O-linked glycosylation in the predicted luminal domain. Endolyn is closely related to two human mucin-like proteins, multi-glycosylated core protein (MGC)-24 and CD164 (MGC-24v), expressed in gastric carcinoma cells and bone marrow stromal and haematopoietic precursor cells respectively. The predicted transmembrane and cytoplasmic tail domains of endolyn, as well as parts of its luminal domain, also show some similarities with lamp-1 and lamp-2. Like these and other known lysosomal membrane proteins, endolyn contains a YXXO motif at the C-terminus of its cytoplasmic tail (where O is a bulky hydrophobic amino acid), but with no preceding glycine. Nonetheless, the last ten amino acids of this tail, when transplanted on to human CD8, caused efficient targeting of the chimaeric protein to endosomes and lysosomes in transfected normal rat kidney cells.
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Affiliation(s)
- G Ihrke
- Department of Clinical Biochemistry, Wellcome Trust Centre for the Study of Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 2XY, U.K.
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30
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Watson RT, Pessin JE. Functional cooperation of two independent targeting domains in syntaxin 6 is required for its efficient localization in the trans-golgi network of 3T3L1 adipocytes. J Biol Chem 2000; 275:1261-8. [PMID: 10625671 DOI: 10.1074/jbc.275.2.1261] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
To identify the targeting domains of syntaxin 6 responsible for its localization to the trans-Golgi network (TGN), we examined the subcellular distribution of enhanced green fluorescent protein (EGFP) epitope-tagged syntaxin 6/syntaxin 4 chimerae and syntaxin 6 truncation/deletion mutants in 3T3L1 adipocytes. Expression of EGFP-syntaxin 6 resulted in a perinuclear distribution identical to endogenous syntaxin 6 as determined both by confocal fluorescence microscopy and subcellular fractionation. Furthermore, both the endogenous and the expressed EGFP-syntaxin 6 fusion protein were localized to a brefeldin A-insensitive but okadaic acid-sensitive compartment characteristic of the TGN. In contrast, EGFP-syntaxin 6 constructs lacking the H2 domain were excluded from the TGN and were instead primarily localized to the plasma membrane. Although syntaxin 4 was localized to the plasma membrane, syntaxin 6/syntaxin 4 chimerae and syntaxin 6 truncations containing the H2 domain of syntaxin 6 were predominantly directed to the TGN. Importantly, the syntaxin 6 H2 domain fused to the transmembrane domain of syntaxin 4 was also localized to the TGN, demonstrating that the H2 domain was sufficient to confer TGN localization. In addition to the H2 domain, a tyrosine-based plasma membrane internalization signal (YGRL) was identified between the H1 and H2 domains of syntaxin 6. Deletion of this sequence resulted in the accumulation of the EGFP-syntaxin 6 reporter construct at the plasma membrane. Together, these data demonstrate that syntaxin 6 utilizes two distinct domains to drive its specific subcellular localization to the TGN.
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Affiliation(s)
- R T Watson
- Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242, USA
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31
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Abstract
Skeletal muscle has a nonconventional Golgi complex (GC), the organization of which has been a subject of controversy in the past. We have now examined the distribution of the GC by immunofluorescence and immunogold electron microscopy in whole fibers from different rat muscles, both innervated and experimentally denervated. The total number of GC elements, small polarized stacks of cisternae, is quite similar in all fibers, but their intracellular distribution is fiber type-dependent. Thus, in slow-twitch, type I fibers, approximately 75% of all GC elements are located within 1 micrometer from the plasma membrane, and each nucleus is surrounded by a belt of GC elements. In contrast, in the fast-twitch type IIB fibers, most GC elements are in the fiber core, and most nuclei only have GC elements at their poles. Intermediate, type IIA fibers also have an intermediate distribution of GC elements. Interestingly, the distribution of microtubules, with which GC elements colocalize, is fiber type-dependent as well. At the neuromuscular junction, the distribution of GC elements and microtubules is independent of fiber type, and junctional nuclei are surrounded by GC elements in all fibers. After denervation of the hindlimb muscles, GC elements as well as microtubules converge toward a common pattern, that of the slow-twitch fibers, in all fibers. Our data suggest that innervation regulates the distribution of microtubules, which in turn organize the Golgi complex according to muscle fiber type.
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32
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Ralston E, Lu Z, Ploug T. The organization of the Golgi complex and microtubules in skeletal muscle is fiber type-dependent. J Neurosci 1999; 19:10694-705. [PMID: 10594053 PMCID: PMC6784920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
Skeletal muscle has a nonconventional Golgi complex (GC), the organization of which has been a subject of controversy in the past. We have now examined the distribution of the GC by immunofluorescence and immunogold electron microscopy in whole fibers from different rat muscles, both innervated and experimentally denervated. The total number of GC elements, small polarized stacks of cisternae, is quite similar in all fibers, but their intracellular distribution is fiber type-dependent. Thus, in slow-twitch, type I fibers, approximately 75% of all GC elements are located within 1 micrometer from the plasma membrane, and each nucleus is surrounded by a belt of GC elements. In contrast, in the fast-twitch type IIB fibers, most GC elements are in the fiber core, and most nuclei only have GC elements at their poles. Intermediate, type IIA fibers also have an intermediate distribution of GC elements. Interestingly, the distribution of microtubules, with which GC elements colocalize, is fiber type-dependent as well. At the neuromuscular junction, the distribution of GC elements and microtubules is independent of fiber type, and junctional nuclei are surrounded by GC elements in all fibers. After denervation of the hindlimb muscles, GC elements as well as microtubules converge toward a common pattern, that of the slow-twitch fibers, in all fibers. Our data suggest that innervation regulates the distribution of microtubules, which in turn organize the Golgi complex according to muscle fiber type.
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Affiliation(s)
- E Ralston
- Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4062, USA.
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33
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Stephens DJ, Banting G. Direct interaction of the trans-Golgi network membrane protein, TGN38, with the F-actin binding protein, neurabin. J Biol Chem 1999; 274:30080-6. [PMID: 10514494 DOI: 10.1074/jbc.274.42.30080] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TGN38 is a type I integral membrane protein that constitutively cycles between the trans-Golgi network (TGN) and plasma membrane. The cytosolic domain of TGN38 interacts with AP2 clathrin adaptor complexes via the tyrosine-containing motif (-SDYQRL-) to direct internalization from the plasma membrane. This motif has previously been shown to direct both internalization and subsequent TGN targeting of TGN38. We have used the cytosolic domain of TGN38 in a two-hybrid screen, and we have identified the brain-specific F-actin binding protein neurabin-I as a TGN38-binding protein. We demonstrate a direct interaction between TGN38 and the ubiquitous homologue of neurabin-I, neurabin-II (also called spinophilin). We have used a combination of yeast two-hybrid and in vitro protein interaction assays to show that this interaction is dependent on the serine (but not tyrosine) residue of the known TGN38 trafficking motif. We show that TGN38 interacts with the coiled coil region of neurabin in vitro and binds preferentially with the dimeric form of neurabin. TGN38 and neurabin also interact in vivo as demonstrated by coimmunoprecipitation from stably transfected PC12 cells. These data suggest that neurabin provides a direct physical link between TGN38-containing membranes and the actin cytoskeleton.
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Affiliation(s)
- D J Stephens
- Department of Biochemistry, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom
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34
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Simonova M, Weissleder R, Sergeyev N, Vilissova N, Bogdanov A. Targeting of green fluorescent protein expression to the cell surface. Biochem Biophys Res Commun 1999; 262:638-42. [PMID: 10471377 DOI: 10.1006/bbrc.1999.1251] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have previously reported on GPI-anchored fusion proteins that bind radioactive isotopes. We targeted their expression to the cell surface to obtain a marker protein detectable by nuclear and optical imaging (1, 2). Here we suggest a novel approach for targeting a model protein (GFP) to the exoplasmic surface of the plasma membrane. An expression vector (pcPEP-GFP) was constructed containing GFP cDNA fused with the fragment encoding the N-terminal cytoplasmic domain and signal peptide/membrane anchoring domain of the rabbit neutral endopeptidase (PEP-GFP). Flow cytometry showed green fluorescence in 45% of cells transfected with GFP and in 34% of cells transfected with PEP-GFP (24 h after transfection). Fluorescence microscopy of fixed cells stained with rhodaminated anti-GFP antibodies showed positive reaction only in the case of PEP-GFP-transfected cells indicating cell-surface expression. The PEP-GFP fusion protein was identified as a component of the light microsomal and Golgi fractions by immunoblotting.
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Affiliation(s)
- M Simonova
- Center for Molecular Imaging Research, Massachusetts General Hospital, Building 149, 13th Street, Charlestown, Massachusetts, 02129, USA
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35
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Ghosh SK, Field J, Frisardi M, Rosenthal B, Mai Z, Rogers R, Samuelson J. Chitinase secretion by encysting Entamoeba invadens and transfected Entamoeba histolytica trophozoites: localization of secretory vesicles, endoplasmic reticulum, and Golgi apparatus. Infect Immun 1999; 67:3073-81. [PMID: 10338523 PMCID: PMC96624 DOI: 10.1128/iai.67.6.3073-3081.1999] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Entamoeba histolytica, the protozoan parasite that phagocytoses bacteria and host cells, has a vesicle/vacuole-filled cytosol like that of macrophages. In contrast, the infectious cyst form has four nuclei and a chitin wall. Here, anti-chitinase antibodies identified hundreds of small secretory vesicles in encysting E. invadens parasites and in E. histolytica trophozoites overexpressing chitinase under an actin gene promoter. Abundant small secretory vesicles were also identified with antibodies to the surface antigen Ariel and with a fluorescent substrate of cysteine proteinases. Removal of an N-terminal signal sequence directed chitinase to the cytosol. Addition of a C-terminal KDEL peptide, identified on amebic BiP, retained chitinase in a putative endoplasmic reticulum, which was composed of a few vesicles of mixed sizes. A putative Golgi apparatus, which was Brefeldin A sensitive and composed of a few large, perinuclear vesicles, was identified with antibodies to ADP-ribosylating factor and to epsilon-COP. We conclude that the amebic secretory pathway is similar to those of other eukaryotic cells, even if its appearance is somewhat different.
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Affiliation(s)
- S K Ghosh
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115, USA
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36
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Abstract
The Golgi complex of mammalian cells is composed of cisternal stacks that function in processing and sorting of membrane and luminal proteins during transport from the site of synthesis in the endoplasmic reticulum to lysosomes, secretory vacuoles, and the cell surface. Even though exceptions are found, the Golgi stacks are usually arranged as an interconnected network in the region around the centrosome, the major organizing center for cytoplasmic microtubules. A close relation thus exists between Golgi elements and microtubules (especially the stable subpopulation enriched in detyrosinated and acetylated tubulin). After drug-induced disruption of microtubules, the Golgi stacks are disconnected from each other, partly broken up, dispersed in the cytoplasm, and redistributed to endoplasmic reticulum exit sites. Despite this, intracellular protein traffic is only moderately disturbed. Following removal of the drugs, scattered Golgi elements move along reassembling microtubules back to the centrosomal region and reunite into a continuous system. The microtubule-dependent motor proteins cytoplasmic dynein and kinesin bind to Golgi membranes and have been implicated in vesicular transport to and from the Golgi complex. Microinjection of dynein heavy chain antibodies causes dispersal of the Golgi complex, and the Golgi complex of cells lacking cytoplasmic dynein is likewise spread throughout the cytoplasm. In a similar manner, kinesin antibodies have been found to inhibit Golgi-to-endoplasmic reticulum transport in brefeldin A-treated cells and scattering of Golgi elements along remaining microtubules in cells exposed to a low concentration of nocodazole. The molecular mechanisms in the interaction between microtubules and membranes are, however, incompletely understood. During mitosis, the Golgi complex is extensively reorganized in order to ensure an equal partitioning of this single-copy organelle between the daughter cells. Mitosis-promoting factor, a complex of cdc2 kinase and cyclin B, is a key regulator of this and other events in the induction of cell division. Cytoplasmic microtubules depolymerize in prophase and as a result thereof, the Golgi stacks become smaller, disengage from each other, and take up a perinuclear distribution. The mitotic spindle is thereafter put together, aligns the chromosomes in the metaphase plate, and eventually pulls the sister chromatids apart in anaphase. In parallel, the Golgi stacks are broken down into clusters of vesicles and tubules and movement of protein along the exocytic and endocytic pathways is inhibited. Using a cell-free system, it has been established that the fragmentation of the Golgi stacks is due to a continued budding of transport vesicles and a concomitant inhibition of the fusion of the vesicles with their target membranes. In telophase and after cytokinesis, a Golgi complex made up of interconnected cisternal stacks is recreated in each daughter cell and intracellular protein traffic is resumed. This restoration of a normal interphase morphology and function is dependent on reassembly of a radiating array of cytoplasmic microtubules along which vesicles can be carried and on reactivation of the machinery for membrane fusion.
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Affiliation(s)
- J Thyberg
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, S-171 77, Sweden.
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37
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Evidence for the participation of the neuron-specific CDK5 activator P35 during laminin-enhanced axonal growth. J Neurosci 1998. [PMID: 9822744 DOI: 10.1523/jneurosci.18-23-09858.1998] [Citation(s) in RCA: 133] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cultures of cerebellar macroneurons were used to study the pattern of expression, subcellular localization, and function of the neuronal cdk5 activator p35 during laminin-enhanced axonal growth. The results obtained indicate that laminin, an extracellular matrix molecule capable of selectively stimulating axonal extension and promoting MAP1B phosphorylation at a proline-directed protein kinase epitope, selectively stimulates p35 expression, increases its association with the subcortical cytoskeleton, and accelerates its redistribution to the axonal growth cones. Besides, suppression of p35, but not of a highly related isoform designated as p39, by antisense oligonucleotide treatment selectively reduces cdk5 activity, laminin-enhanced axonal elongation, and MAP1b phosphorylation. Taken collectively, the present results suggest that cdk5/p35 may serve as an important regulatory linker between environmental signals (e.g., laminin) and constituents of the intracellular machinery (e.g., MAP1B) involved in axonal elongation.
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38
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Paglini G, Pigino G, Kunda P, Morfini G, Maccioni R, Quiroga S, Ferreira A, Cáceres A. Evidence for the participation of the neuron-specific CDK5 activator P35 during laminin-enhanced axonal growth. J Neurosci 1998; 18:9858-69. [PMID: 9822744 PMCID: PMC6793278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/1998] [Revised: 09/09/1998] [Accepted: 09/11/1998] [Indexed: 02/09/2023] Open
Abstract
Cultures of cerebellar macroneurons were used to study the pattern of expression, subcellular localization, and function of the neuronal cdk5 activator p35 during laminin-enhanced axonal growth. The results obtained indicate that laminin, an extracellular matrix molecule capable of selectively stimulating axonal extension and promoting MAP1B phosphorylation at a proline-directed protein kinase epitope, selectively stimulates p35 expression, increases its association with the subcortical cytoskeleton, and accelerates its redistribution to the axonal growth cones. Besides, suppression of p35, but not of a highly related isoform designated as p39, by antisense oligonucleotide treatment selectively reduces cdk5 activity, laminin-enhanced axonal elongation, and MAP1b phosphorylation. Taken collectively, the present results suggest that cdk5/p35 may serve as an important regulatory linker between environmental signals (e.g., laminin) and constituents of the intracellular machinery (e.g., MAP1B) involved in axonal elongation.
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Affiliation(s)
- G Paglini
- Instituto Mercedes y Martín Ferreyra, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 5000 Cordoba, Argentina
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39
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Takahashi S, Odani N, Tomokiyo K, Furuta K, Suzuki M, Ichikawa A, Negishi M. Localization of a cyclopentenone prostaglandin to the endoplasmic reticulum and induction of BiP mRNA. Biochem J 1998; 335 ( Pt 1):35-42. [PMID: 9742210 PMCID: PMC1219749 DOI: 10.1042/bj3350035] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cyclopentenone prostaglandins (PGs) are transported into cells and stimulate the expression of various stress genes, such as that coding for BiP (an ER luminal protein). To reveal the site of action of the PGs for the induction of stress-gene expression, we introduced a fluorescent probe, pyrene, into two types of PG analogue, GIF0010 (a cyclopentenone type) and GIF0037 (a cyclopentanone type) and examined their intracellular localization in normal rat kidney cells and their ability to induce the BiP gene expression. GIF0010 accumulated around the nuclei and coincided with BiP, a resident protein in the endoplasmic reticulum (ER) and markedly induced BiP gene expression. By contrast, GIF0037 and pyrene neither accumulated in the cell nor induced BiP gene expression. Thus the ER localization of GIF0010 and the induction of gene expression by GIF0010 are ascribed to the cyclopentenone structure. Treatment with cycloheximide inhibited both the accumulation of GIF0010 and the induction of the BiP mRNA, suggesting that the ER localization of the PG and subsequent gene expression require the nascent protein synthesis. These results demonstrate that the cyclopentenone PG is specifically accumulated in the ER, transducing a signal for BiP gene expression in the nuclei.
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Affiliation(s)
- S Takahashi
- Department of Physiological Chemistry, Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
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40
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Hannah MJ, Weiss U, Huttner WB. Differential extraction of proteins from paraformaldehyde-fixed cells: lessons from synaptophysin and other membrane proteins. Methods 1998; 16:170-81. [PMID: 9790863 DOI: 10.1006/meth.1998.0664] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
While investigating the localization of synaptophysin in PC12 cells using immunofluorescence microscopy, we noticed a striking difference in its apparent subcellular distribution depending on whether digitonin or Triton X-100 was used as permeabilization agent of paraformaldehyde (PFA)-fixed cells. We found that this difference was due to epitope inaccessibility in the digitonin-treated cells combined with an almost quantitative extraction of the antigen on Triton X-100 permeabilization. Both phenomena were differential with respect to the various synaptophysin-containing compartments. The extraction of antigen from PFA-fixed cells was also seen with other membrane proteins but not with cytosolic proteins and proteins in the lumen of the secretory pathway. Significantly, some of the membrane proteins were extracted from the PFA-fixed cells in higher-molecular-weight forms which we believe represent their in vivo oligomeric states. The implications of our observations are discussed with respect to the method of immunofluorescence microscopy and also to the possible use of paraformaldehyde as an in vivo crosslinker for the study of membrane protein quaternary structure.
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Affiliation(s)
- M J Hannah
- Department of Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, Heidelberg, D-69120, Germany
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41
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Ploug T, van Deurs B, Ai H, Cushman SW, Ralston E. Analysis of GLUT4 distribution in whole skeletal muscle fibers: identification of distinct storage compartments that are recruited by insulin and muscle contractions. J Cell Biol 1998; 142:1429-46. [PMID: 9744875 PMCID: PMC2141761 DOI: 10.1083/jcb.142.6.1429] [Citation(s) in RCA: 222] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The effects of insulin stimulation and muscle contractions on the subcellular distribution of GLUT4 in skeletal muscle have been studied on a preparation of single whole fibers from the rat soleus. The fibers were labeled for GLUT4 by a preembedding technique and observed as whole mounts by immunofluorescence microscopy, or after sectioning, by immunogold electron microscopy. The advantage of this preparation for cells of the size of muscle fibers is that it provides global views of the staining from one end of a fiber to the other and from one side to the other through the core of the fiber. In addition, the labeling efficiency is much higher than can be obtained with ultracryosections. In nonstimulated fibers, GLUT4 is excluded from the plasma membrane and T tubules. It is distributed throughout the muscle fibers with approximately 23% associated with large structures including multivesicular endosomes located in the TGN region, and 77% with small tubulovesicular structures. The two stimuli cause translocation of GLUT4 to both plasma membrane and T tubules. Quantitation of the immunogold electron microscopy shows that the effects of insulin and contraction are additive and that each stimulus recruits GLUT4 from both large and small depots. Immunofluorescence double labeling for GLUT4 and transferrin receptor (TfR) shows that the small depots can be further subdivided into TfR-positive and TfR-negative elements. Interestingly, we observe that colocalization of TfR and GLUT4 is increased by insulin and decreased by contractions. These results, supported by subcellular fractionation experiments, suggest that TfR-positive depots are only recruited by contractions. We do not find evidence for stimulation-induced unmasking of resident surface membrane GLUT4 transporters or for dilation of the T tubule system (Wang, W., P.A. Hansen, B.A. Marshall, J.O. Holloszy, and M. Mueckler. 1996. J. Cell Biol. 135:415-430).
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MESH Headings
- Animals
- Epitopes, B-Lymphocyte/metabolism
- Fluorescent Antibody Technique, Indirect
- Glucose Transporter Type 4
- Golgi Apparatus/metabolism
- Insulin/metabolism
- Insulin/pharmacology
- Male
- Monosaccharide Transport Proteins/metabolism
- Muscle Contraction/physiology
- Muscle Fibers, Skeletal/drug effects
- Muscle Fibers, Skeletal/metabolism
- Muscle Fibers, Skeletal/physiology
- Muscle Fibers, Skeletal/ultrastructure
- Muscle Proteins
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/metabolism
- Muscle, Skeletal/physiology
- Muscle, Skeletal/ultrastructure
- Rabbits
- Rats
- Rats, Wistar
- Receptors, Transferrin/metabolism
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Affiliation(s)
- T Ploug
- Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.
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42
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Molloy SS, Thomas L, Kamibayashi C, Mumby MC, Thomas G. Regulation of endosome sorting by a specific PP2A isoform. J Cell Biol 1998; 142:1399-411. [PMID: 9744873 PMCID: PMC1424221 DOI: 10.1083/jcb.142.6.1399] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The regulated sorting of proteins within the trans-Golgi network (TGN)/endosomal system is a key determinant of their biological activity in vivo. For example, the endoprotease furin activates of a wide range of proproteins in multiple compartments within the TGN/endosomal system. Phosphorylation of its cytosolic domain by casein kinase II (CKII) promotes the localization of furin to the TGN and early endosomes whereas dephosphorylation is required for efficient transport between these compartments (Jones, B.G., L. Thomas, S.S. Molloy, C.D. Thulin, M.D. Fry, K.A. Walsh, and G. Thomas. 1995. EMBO [Eur. Mol. Biol. Organ.] J. 14:5869-5883). Here we show that phosphorylated furin molecules internalized from the cell surface are retained in a local cycling loop between early endosomes and the plasma membrane. This cycling loop requires the phosphorylation state-dependent furin-sorting protein PACS-1, and mirrors the trafficking pathway described recently for the TGN localization of furin (Wan, L., S.S. Molloy, L. Thomas, G. Liu, Y. Xiang, S.L. Ryback, and G. Thomas. 1998. Cell. 94:205-216). We also demonstrate a novel role for protein phosphatase 2A (PP2A) in regulating protein localization in the TGN/endosomal system. Using baculovirus recombinants expressing individual PP2A subunits, we show that the dephosphorylation of furin in vitro requires heterotrimeric phosphatase containing B family regulatory subunits. The importance of this PP2A isoform in directing the routing of furin from early endosomes to the TGN was established using SV-40 small t antigen as a diagnostic tool in vivo. The role of both CKII and PP2A in controlling multiple sorting steps in the TGN/endosomal system indicates that the distribution of itinerant membrane proteins may be acutely regulated via signal transduction pathways.
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Affiliation(s)
- S S Molloy
- Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA
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43
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Takatsu H, Sakurai M, Shin HW, Murakami K, Nakayama K. Identification and characterization of novel clathrin adaptor-related proteins. J Biol Chem 1998; 273:24693-700. [PMID: 9733768 DOI: 10.1074/jbc.273.38.24693] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have identified a human approximately 87-kDa protein, designated as gamma2-adaptin, that is similar to gamma-adaptin (called gamma1-adaptin in this paper), a large chain of the AP-1 clathrin-associated adaptor complex, not only in the primary structure (60% amino acid identity) but also in the domain organization. Northern blot analysis has shown that its mRNA is expressed in a variety of tissues. Analysis using a yeast two-hybrid system has revealed that, similarly to gamma1-adaptin, gamma2-adaptin is capable of interacting not only with the sigma1 chain (called as sigma1A in this paper), the small chain of the AP-1 complex, but also with a novel sigma1-like protein, designated as sigma1B, which shows an 87% amino acid identity to sigma1A; and that, unlike gamma1-adaptin, it is unable to interact with beta1-adaptin, another large chain of the AP-1 complex. Immunofluorescence microscopy analysis has revealed that gamma2-adaptin is localized to paranuclear vesicular structures that are not superimposed on structures containing gamma1-adaptin. Furthermore, unlike gamma1-adaptin, gamma2-adaptin is recruited onto membranes in the presence of a fungal antibiotic, brefeldin A. These data suggest that gamma2-adaptin constitute a novel adaptor-related complex that participates in a transport step different from that of AP-1.
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Affiliation(s)
- H Takatsu
- Institute of Biological Sciences, University of Tsukuba, Tsukuba Science City, Ibaraki 305-8572, Japan
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44
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Roquemore EP, Banting G. Efficient trafficking of TGN38 from the endosome to the trans-Golgi network requires a free hydroxyl group at position 331 in the cytosolic domain. Mol Biol Cell 1998; 9:2125-44. [PMID: 9693371 PMCID: PMC25467 DOI: 10.1091/mbc.9.8.2125] [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: 11/11/2022] Open
Abstract
TGN38 is one of the few known resident integral membrane proteins of the trans-Golgi network (TGN). Since it cycles constitutively between the TGN and the plasma membrane, TGN38 is ideally suited as a model protein for the identification of post-Golgi trafficking motifs. Several studies, employing chimeric constructs to detect such motifs within the cytosolic domain of TGN38, have identified the sequence 333YQRL336 as an autonomous signal capable of localizing reporter proteins to the TGN. In addition, one group has found that an upstream serine residue, S331, may also play a role in TGN38 localization. However, the nature and degree of participation of S331 in the localization of TGN38 remain uncertain, and the effect has been studied in chimeric constructs only. Here we investigate the role of S331 in the context of full-length TGN38. Mutations that abolish the hydroxyl moiety at position 331 (A, D, and E) lead to missorting of endocytosed TGN38 to the lysosome. Conversely, mutation of S331 to T has little effect on the endocytic trafficking of TGN38. Together, these findings indicate that the S331 hydroxyl group has a direct or indirect effect on the ability of the cytosolic tail of TGN38 to interact with trafficking and/or sorting machinery at the level of the early endosome. In addition, mutation of S331 to either A or D results in increased levels of TGN38 at the cell surface. The results confirm that S331 plays a critical role in the intracellular trafficking of TGN38 and further reveal that TGN38 undergoes a signal-mediated trafficking step at the level of the endosome.
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Affiliation(s)
- E P Roquemore
- Department of Biochemistry, University of Bristol School of Medicine, University Walk, Bristol BS8 1TD, England
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45
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Tai AW, Chuang JZ, Sung CH. Localization of Tctex-1, a cytoplasmic dynein light chain, to the Golgi apparatus and evidence for dynein complex heterogeneity. J Biol Chem 1998; 273:19639-49. [PMID: 9677391 DOI: 10.1074/jbc.273.31.19639] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To date, much attention has been focused on the heavy and intermediate chains of the multisubunit cytoplasmic dynein complex; however, little is known about the localization or function of dynein light chains. In this study, we find that Tctex-1, a light chain of cytoplasmic dynein, localizes predominantly to the Golgi apparatus in interphase fibroblasts. Immunofluorescent staining reveals striking juxtanuclear staining characteristic of the Golgi apparatus as well as nuclear envelope and punctate cytoplasmic staining that often decorates microtubules. Tctex-1 colocalization with Golgi compartment markers, its distribution upon treatment with various pharmacological agents, and the cofractionation of Tctex-1-associated membranes with Golgi membranes are all consistent with a Golgi localization. The distribution of Tctex-1 in interphase cells only partially overlaps with the dynein intermediate chain and p150(Glued) upon immunofluorescence, but most of Tctex-1 is redistributed onto mitotic spindles along with other dynein/dynactin subunits. Using sequential immunoprecipitations, we demonstrate that there is a subset of Tctex-1 not associated with the intermediate chain at steady state; the converse also appears to be true. Distinct populations of dynein complexes are likely to exist, and such diversity may occur in part at the level of their light chain compositions.
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Affiliation(s)
- A W Tai
- Department of Cell Biology and Anatomy, Margaret M. Dyson Vision Research Institute, Cornell University Medical College, New York, New York 10021, USA
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Reaves BJ, Roquemore EP, Luzio JP, Banting G. TGN38 cycles via the basolateral membrane of polarized Caco-2 cells. Mol Membr Biol 1998; 15:133-9. [PMID: 9859110 DOI: 10.3109/09687689809074524] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
TGN38 is a heavily glycosylated, type I integral membrane protein which is predominantly localized to the trans Golgi network (TGN), but which constitutively traffics between the TGN and the cell surface. The trafficking of TGN38 has been extensively studied in non-polarized cells, and a short, tyrosine-based, peptide motif within the cytosolic domain of the protein has been shown to be necessary and sufficient for its rapid internalization from the cell surface and efficient delivery to the TGN. Such tyrosine-based motifs have also been shown to act as basolateral targeting signals, whilst N-linked glycans (as occur on the extracytosolic domain of TGN38) can act as apical targeting signals. TGN38 has previously been shown to be sorted to the basolateral surface of polarized canine MDCK cells; a polarized cell line in which biosynthetic sorting decisions concerning the eventual destination of apical or basolateral targeted plasma membrane proteins are made at the TGN. We now show that TGN38 is targeted exclusively to the basolateral domain of polarized human Caco-2 cells, a cell line in which newly synthesized membrane proteins destined for either the apical or basolateral plasma membrane may be sorted for delivery to their final destination either at the TGN or at the cell surface. These data also demonstrate that the heavily glycosylated, extracytosolic domain of TGN38 does not contain a dominant apical targeting signal.
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Affiliation(s)
- B J Reaves
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, UK
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Reaves BJ, Banting G, Luzio JP. Lumenal and transmembrane domains play a role in sorting type I membrane proteins on endocytic pathways. Mol Biol Cell 1998; 9:1107-22. [PMID: 9571243 PMCID: PMC25333 DOI: 10.1091/mbc.9.5.1107] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/1998] [Accepted: 02/27/1998] [Indexed: 02/07/2023] Open
Abstract
Previous studies have shown that when the cytosolic domains of the type I membrane proteins TGN38 and lysosomal glycoprotein 120 (lgp120) are added to a variety of reporter molecules, the resultant chimeric molecules are localized to the trans-Golgi network (TGN) and to lysosomes, respectively. In the present study we expressed chimeric constructs of rat TGN38 and rat lgp120 in HeLa cells. We found that targeting information in the cytosolic domain of TGN38 could be overridden by the presence of the lumenal and transmembrane domains of lgp120. In contrast, the presence of the transmembrane and cytosolic domains of TGN38 was sufficient to deliver the lumenal domain of lgp120 to the trans-Golgi network. On the basis of steady-state localization of the various chimeras and antibody uptake experiments, we propose that there is a hierarchy of targeting information in each molecule contributing to sorting within the endocytic pathway. The lumenal and cytosolic domains of lgp120 contribute to sorting and delivery to lysosomes, whereas the transmembrane and cytosolic domains of TGN38 contribute to sorting and delivery to the trans-Golgi network.
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Affiliation(s)
- B J Reaves
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 2QR, United Kingdom
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Pryde JG, Farmaki T, Lucocq JM. Okadaic acid induces selective arrest of protein transport in the rough endoplasmic reticulum and prevents export into COPII-coated structures. Mol Cell Biol 1998; 18:1125-35. [PMID: 9448010 PMCID: PMC108825 DOI: 10.1128/mcb.18.2.1125] [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] Open
Abstract
Quantitative immunoelectron microscopy and subcellular fractionation established the site of endoplasmic reticulum (ER)-Golgi transport arrest induced by the phosphatase inhibitor okadaic acid (OA). OA induced the disappearance of transitional element tubules and accumulation of the anterograde-transported Chandipura (CHP) virus G protein only in the rough ER (RER) and not at more distal sites. The block was specific to the early part of the anterograde pathway, because CHP virus G protein that accumulated in the intermediate compartment (IC) at 15 degrees C could gain access to Golgi stack enzymes. OA also induced RER accumulation of the IC protein p53/p58 via an IC-RER recycling pathway which was resistant to OA and inhibited by the G protein activator aluminium fluoride. The role of COPII coats in OA transport block was investigated by using immunofluorescence and cell fractionation. In untreated cells the COPII coat protein sec 13p colocalized with p53/p58 in Golgi-IC structures of the juxtanuclear region and peripheral cytoplasm. During OA treatment, p53/p58 accumulated in the RER but was excluded from sec 13p-containing membrane structures. Taken together our data indicate that OA induces an early defect in RER export which acts to prevent entry into COPII-coated structures of the IC region.
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Affiliation(s)
- J G Pryde
- Department of Medicine (RIE), The University of Edinburgh Medical School, Scotland, United Kingdom
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Barnes K, Brown C, Turner AJ. Endothelin-converting enzyme: ultrastructural localization and its recycling from the cell surface. Hypertension 1998; 31:3-9. [PMID: 9449382 DOI: 10.1161/01.hyp.31.1.3] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The potent vasoconstrictor endothelin-1 (ET-1) is secreted constitutively by endothelial cells and has been implicated in the pathophysiology of several cardiovascular diseases. It is generated from its inactive intermediate, big ET-1, through the action of endothelin-converting enzyme (ECE). Using several complementary techniques, we have demonstrated that ECE is present at the cell surface and on intracellular vesicles and that it recycles from the cell surface in endothelial cells. This is the first ultrastructural localization of ECE in lung and the first time big ET-1 and ECE have been colocalized by immunogold in a vesicular population, 50 to 100 nm in diameter. In addition, by double immunogold staining of ultrathin cryosections, we have localized ECE together with angiotensin-converting enzyme on the luminal membrane of endothelial cells. With cell surface biotinylation of a transformed rat endothelial cell line and of human umbilical vein endothelial cells, we have confirmed the presence of ECE on the plasma membrane. After treatment of endothelial cells with chloroquine, ECE and trans-Golgi network 38 protein were shown by immunofluorescence staining to localize to the same intracellular compartment.
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Affiliation(s)
- K Barnes
- Department of Biochemistry and Molecular Biology, University of Leeds, UK.
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Jones SM, Howell KE. Phosphatidylinositol 3-kinase is required for the formation of constitutive transport vesicles from the TGN. J Cell Biol 1997; 139:339-49. [PMID: 9334339 PMCID: PMC2139785 DOI: 10.1083/jcb.139.2.339] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
An 85-kD cytosolic complex (p62(cplx)), consisting of a 62-kD phosphoprotein (p62) and a 25-kD GTPase, has been shown to be essential for the cell-free reconstitution of polymeric IgA receptor (pIgA-R)-containing exocytic transport vesicle formation from the TGN (Jones, S.M., J.R. Crosby, J. Salamero, and K.E. Howell. 1993. J. Cell Biol. 122:775-788). Here the p62(cplx) is identified as a regulatory subunit of a novel phosphatidylinositol 3-kinase (PI3-kinase). This p62(cplx)-associated PI3-kinase activity is stimulated by activation of the p62(cplx)-associated GTPase, and is specific for phosphatidylinositol (PI) as substrate, and is sensitive to wortmannin at micromolar concentrations. The direct role of this p62(cplx)-associated PI3-kinase activity in TGN-derived vesicle formation is indicated by the finding that both lipid kinase activity and the formation of pIgA-R-containing exocytic vesicles from the TGN are inhibited by wortmannin with similar dose-response curves and 50% inhibitory concentrations (3.5 microM). These findings indicate that phosphatidylinositol-3-phosphate (PI[3]P) is required for the formation of TGN-derived exocytic transport vesicles, and that the p62(cplx)-associated PI3-kinase and an activated GTPase are the essential molecules that drive production of this PI(3)P.
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Affiliation(s)
- S M Jones
- Department of Cellular and Structural Biology, University of Colorado School of Medicine, Denver, Colorado 80262, USA
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