Author response: A novel GTP-binding protein–adaptor protein complex responsible for export of Vangl2 from the trans Golgi network

Planar cell polarity (PCP) requires the asymmetric sorting of distinct signaling receptors to distal and proximal surfaces of polarized epithelial cells. We have examined the transport of one PCP signaling protein, Vangl2, from the trans Golgi network (TGN) in mammalian cells. Using siRNA knockdown experiments, we find that the GTP-binding protein, Arfrp1, and the clathrin adaptor complex 1 (AP-1) are required for Vangl2 transport from the TGN. In contrast, TGN export of Frizzled 6, which localizes to the opposing epithelial surface from Vangl2, does not depend on Arfrp1 or AP-1. Mutagenesis studies identified a YYXXF sorting signal in the C-terminal cytosolic domain of Vangl2 that is required for Vangl2 traffic and interaction with the μ subunit of AP-1. We propose that Arfrp1 exposes a binding site on AP-1 that recognizes the Vangl2 sorting motif for capture into a transport vesicle destined for the proximal surface of a polarized epithelial cell.

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The small GTP-binding protein rab6p is distributed from medial Golgi to the trans-Golgi network as determined by a confocal microscopic approach

Journal of Cell Science ◽

10.1242/jcs.103.3.785 ◽

1992 ◽

Vol 103 (3) ◽

pp. 785-796 ◽

Cited By ~ 12

Author(s):

C. Antony ◽

C. Cibert ◽

G. Geraud ◽

A. Santa Maria ◽

B. Maro ◽

...

Keyword(s):

Golgi Apparatus ◽

G Protein ◽

Cell Lines ◽

Binding Protein ◽

Rab Proteins ◽

Gtp Binding Protein ◽

Trans Golgi Network ◽

Gtp Binding ◽

Golgi Network ◽

Exocytic Pathway

A key role in the regulation of membrane traffic is played by the rab proteins, members of a family of ras-related small GTP-binding proteins. This family comprises at least 25 identified members, the intracellular localization of only a few of which has been investigated. rab6p has been shown to be distributed along the exocytic pathway in association with the medial and trans regions of the Golgi apparatus. A confocal laser scanning microscopic (CLSM) approach coupled with image analysis was used to compare the localization of rab6p with selected reference Golgi markers by double immunofluorescence on culture cell lines. CLSM analysis shows that, under a set of well-defined conditions, one can investigate the possible colocalization of known markers of Golgi compartments and orientate a couple of labeled Golgi antigens with regard to the polarity of the Golgi apparatus. Thus, having validated the CLSM analysis, the localization of rab6p was studied and compared with some of these markers and the VSV-G protein in VSV (vesicular stomatitis virus)-infected cells blocked at 20 degrees C. rab6p is shown to be associated in all the cell lines used with the last cisternae of the Golgi apparatus and particularly with the trans-Golgi network (TGN), the site of protein sorting at the exit of the Golgi apparatus. These results were supported by an electron microscopic study using double-immunolabeled cryosections: rab6p was found in some flat cisternae of the Golgi stack and colocalized with the VSV-G protein in the TGN. Our results show that the small GTP-binding protein rab6p is distributed from medial Golgi to TGN along the exocytic pathway.

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Solubilization and characterization of leukotriene B4 receptor-GTP binding protein complex from porcine spleen

Biochemical and Biophysical Research Communications ◽

10.1016/0006-291x(90)91951-n ◽

1990 ◽

Vol 166 (1) ◽

pp. 342-348 ◽

Cited By ~ 23

Author(s):

Ichiro Miki ◽

Tsuyoshi Watanabe ◽

Motonao Nakamura ◽

Yousuke Seyama ◽

Michio Ui ◽

...

Keyword(s):

Protein Complex ◽

Binding Protein ◽

Leukotriene B4 ◽

Gtp Binding Protein ◽

Gtp Binding ◽

Leukotriene B4 Receptor

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Exomer: a coat complex for transport of select membrane proteins from the trans-Golgi network to the plasma membrane in yeast

The Journal of Cell Biology ◽

10.1083/jcb.200605106 ◽

2006 ◽

Vol 174 (7) ◽

pp. 973-983 ◽

Cited By ~ 86

Author(s):

Chao-Wen Wang ◽

Susan Hamamoto ◽

Lelio Orci ◽

Randy Schekman

Keyword(s):

Plasma Membrane ◽

Membrane Proteins ◽

Cell Surface ◽

Protein Complex ◽

Adaptor Protein ◽

Nucleotide Exchange ◽

Trans Golgi Network ◽

Peripheral Proteins ◽

Golgi Network

Ayeast plasma membrane protein, Chs3p, transits to the mother–bud neck from a reservoir comprising the trans-Golgi network (TGN) and endosomal system. Two TGN/endosomal peripheral proteins, Chs5p and Chs6p, and three Chs6p paralogues form a complex that is required for the TGN to cell surface transport of Chs3p. The role of these peripheral proteins has not been clear, and we now provide evidence that they create a coat complex required for the capture of membrane proteins en route to the cell surface. Sec7p, a Golgi protein required for general membrane traffic and functioning as a nucleotide exchange factor for the guanosine triphosphate (GTP)–binding protein Arf1p, is required to recruit Chs5p to the TGN surface in vivo. Recombinant forms of Chs5p, Chs6p, and the Chs6p paralogues expressed in baculovirus form a complex of approximately 1 MD that binds synthetic liposomes in a reaction requiring acidic phospholipids, Arf1p, and the nonhydrolyzable GTPγS. The complex remains bound to liposomes centrifuged on a sucrose density gradient. Thin section electron microscopy reveals a spiky coat structure on liposomes incubated with the full complex, Arf1p, and GTPγS. We termed the novel coat exomer for its role in exocytosis from the TGN to the cell surface. Unlike other coats (e.g., coat protein complex I, II, and clathrin/adaptor protein complex), the exomer does not form buds or vesicles on liposomes.

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Adaptor protein complex 4 deficiency: a paradigm of childhood-onset hereditary spastic paraplegia caused by defective protein trafficking

Human Molecular Genetics ◽

10.1093/hmg/ddz310 ◽

2020 ◽

Vol 29 (2) ◽

pp. 320-334 ◽

Cited By ~ 7

Author(s):

Robert Behne ◽

Julian Teinert ◽

Miriam Wimmer ◽

Angelica D’Amore ◽

Alexandra K Davies ◽

...

Keyword(s):

Protein Complex ◽

Protein Trafficking ◽

Hereditary Spastic Paraplegia ◽

Adaptor Protein ◽

Spastic Paraplegia ◽

Childhood Onset ◽

Trans Golgi Network ◽

Wide Range ◽

Golgi Network ◽

The Impact

Abstract Deficiency of the adaptor protein complex 4 (AP-4) leads to childhood-onset hereditary spastic paraplegia (AP-4-HSP): SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). This study aims to evaluate the impact of loss-of-function variants in AP-4 subunits on intracellular protein trafficking using patient-derived cells. We investigated 15 patient-derived fibroblast lines and generated six lines of induced pluripotent stem cell (iPSC)-derived neurons covering a wide range of AP-4 variants. All patient-derived fibroblasts showed reduced levels of the AP4E1 subunit, a surrogate for levels of the AP-4 complex. The autophagy protein ATG9A accumulated in the trans-Golgi network and was depleted from peripheral compartments. Western blot analysis demonstrated a 3–5-fold increase in ATG9A expression in patient lines. ATG9A was redistributed upon re-expression of AP4B1 arguing that mistrafficking of ATG9A is AP-4-dependent. Examining the downstream effects of ATG9A mislocalization, we found that autophagic flux was intact in patient-derived fibroblasts both under nutrient-rich conditions and when autophagy is stimulated. Mitochondrial metabolism and intracellular iron content remained unchanged. In iPSC-derived cortical neurons from patients with AP4B1-associated SPG47, AP-4 subunit levels were reduced while ATG9A accumulated in the trans-Golgi network. Levels of the autophagy marker LC3-II were reduced, suggesting a neuron-specific alteration in autophagosome turnover. Neurite outgrowth and branching were reduced in AP-4-HSP neurons pointing to a role of AP-4-mediated protein trafficking in neuronal development. Collectively, our results establish ATG9A mislocalization as a key marker of AP-4 deficiency in patient-derived cells, including the first human neuron model of AP-4-HSP, which will aid diagnostic and therapeutic studies.

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Solubilization of the vasopressin receptor from rat liver plasma membranes. Evidence for a receptor X GTP-binding protein complex.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(19)75969-9 ◽

1986 ◽

Vol 261 (36) ◽

pp. 16871-16877

Author(s):

T J Fitzgerald ◽

R J Uhing ◽

J H Exton

Keyword(s):

Rat Liver ◽

Protein Complex ◽

Plasma Membranes ◽

Binding Protein ◽

Vasopressin Receptor ◽

Gtp Binding Protein ◽

Gtp Binding ◽

Liver Plasma Membranes ◽

Rat Liver Plasma Membranes

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Small GTP-binding Protein RalA Associates with Weibel-Palade Bodies in Endothelial Cells

Thrombosis and Haemostasis ◽

10.1055/s-0037-1614349 ◽

1999 ◽

Vol 82 (09) ◽

pp. 1177-1181 ◽

Cited By ~ 27

Author(s):

Hubert de Leeuw ◽

Pauline Wijers-Koster ◽

Jan van Mourik ◽

Jan Voorberg

Keyword(s):

Endothelial Cells ◽

Binding Proteins ◽

Binding Protein ◽

Control Release ◽

Small Gtpase ◽

Gtp Binding Protein ◽

Two Dimensional Gel Electrophoresis ◽

Gtp Binding Proteins ◽

Dense Granules ◽

Gtp Binding

SummaryIn endothelial cells von Willebrand factor (vWF) and P-selectin are stored in dense granules, so-called Weibel-Palade bodies. Upon stimulation of endothelial cells with a variety of agents including thrombin, these organelles fuse with the plasma membrane and release their content. Small GTP-binding proteins have been shown to control release from intracellular storage pools in a number of cells. In this study we have investigated whether small GTP-binding proteins are associated with Weibel-Palade bodies. We isolated Weibel-Palade bodies by centrifugation on two consecutive density gradients of Percoll. The dense fraction in which these subcellular organelles were highly enriched, was analysed by SDS-PAGE followed by GTP overlay. A distinct band with an apparent molecular weight of 28,000 was observed. Two-dimensional gel electrophoresis followed by GTP overlay revealed the presence of a single small GTP-binding protein with an isoelectric point of 7.1. A monoclonal antibody directed against RalA showed reactivity with the small GTP-binding protein present in subcellular fractions that contain Weibel-Palade bodies. The small GTPase RalA was previously identified on dense granules of platelets and on synaptic vesicles in nerve terminals. Our observations suggest that RalA serves a role in regulated exocytosis of Weibel-Palade bodies in endothelial cells.

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Rap1b Association with the Platelet Cytoskeleton Occurs in the Absence of Glycoproteins IIb/IIIa

Thrombosis and Haemostasis ◽

10.1055/s-0037-1615073 ◽

1998 ◽

Vol 79 (04) ◽

pp. 832-836 ◽

Cited By ~ 3

Author(s):

Thomas Fischer ◽

Christina Duffy ◽

Gilbert White

Keyword(s):

Molecular Weight ◽

Divalent Cation ◽

Binding Proteins ◽

Binding Protein ◽

Platelet Membrane ◽

Low Molecular Weight ◽

Membrane Glycoproteins ◽

Gtp Binding Protein ◽

Gtp Binding Proteins ◽

Gtp Binding

SummaryPlatelet membrane glycoproteins (GP) IIb/IIIa and rap1b, a 21 kDa GTP binding protein, associate with the triton-insoluble, activation-dependent platelet cytoskeleton with similar rates and divalent cation requirement. To examine the possibility that GPIIb/IIIa was required for rap1b association with the cytoskeleton, experiments were performed to determine if the two proteins were linked under various conditions. Chromatography of lysates from resting platelets on Sephacryl S-300 showed that GPIIb/IIIa and rap1b were well separated and distinct proteins. Immunoprecipitation of GPIIb/IIIa from lysates of resting platelets did not produce rap1b or other low molecular weight GTP binding proteins and immunoprecipitation of rap1b from lysates of resting platelets did not produce GPIIb/IIIa. Finally, rap1b was associated with the activation-dependent cytoskeleton of platelets from a patient with Glanzmann’s thrombasthenia who lacks surface expressed glycoproteins IIb and IIIa. Based on these findings, we conclude that no association between GPIIb/IIIa and rap1b is found in resting platelets and that rap1b association with the activation-dependent cytoskeleton is at least partly independent of GPIIb/IIIa.

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