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STAGSTED JAN. Journey beyond immunology. Regulation of receptor internalization by major histocompatibility complex class I (MHC-I) and effect of peptides derived from MHC-I. APMIS 2011. [DOI: 10.1111/j.1600-0463.1998.tb05657.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Randazzo PA, Hirsch DS. Arf GAPs: multifunctional proteins that regulate membrane traffic and actin remodelling. Cell Signal 2004; 16:401-13. [PMID: 14709330 DOI: 10.1016/j.cellsig.2003.09.012] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The ADP-ribosylation factor (Arf) Arf GTPase-activating proteins (GAPs) are a family of proteins that induce hydrolysis of GTP bound to Arf. A conserved domain containing a zinc finger motif mediates catalysis. The substrate, Arf.GTP, affects membrane trafficking and actin remodelling. Consistent with activity as an Arf regulator, the Arf GAPs affect both of these pathways. However, the Arf GAPs are likely to have Arf-independent activities that contribute to their cellular functions. Structures of the Arf GAPs are diverse containing catalytic, protein-protein interaction and lipid interaction domains in addition to the Arf GAP domain. Some Arf GAPs have been identified and characterized on the basis of activities other than Arf GAP. Here, we describe the Arf GAP family, enzymology of some members of the Arf GAP family and known functions of the proteins. The results discussed illustrate roles for both Arf-dependent and -independent activities in the regulation of cellular architecture.
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Affiliation(s)
- Paul A Randazzo
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, Building. 37 Room 4118, Bethesda, MD 20892, USA.
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Berón W, Mayorga LS, Colombo MI, Stahl PD. Recruitment of coat-protein-complex proteins on to phagosomal membranes is regulated by a brefeldin A-sensitive ADP-ribosylation factor. Biochem J 2001; 355:409-15. [PMID: 11284728 PMCID: PMC1221752 DOI: 10.1042/0264-6021:3550409] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Particle internalization in macrophages is followed by a complex maturation process. We have previously observed that proteins bound to phagocytosed particles are sorted from phagosomes into a heterogeneous population of vesicles that fuse with endosomes. However, the mechanism and the protein machinery involved in the formation of these phagosome-derived vesicles are largely unknown. It has been shown that vesicles coated with coat protein complex type I (COPI) have a role in both secretion and endocytosis. To address the possibility that COPI proteins might participate in the formation of phagosome-derived vesicles we studied the recruitment of beta-COP to highly purified phagosomes. The binding of beta-COP to phagosomal membranes was regulated by nucleotides and inhibited by brefeldin A (BFA). An ADP-ribosylation factor 1 (ARF1) mutant defective in GTP hydrolysis supported the binding of beta-COP to phagosomes independently of added nucleotide. AlF(4) and Gbetagamma subunits, agents known to modulate heterotrimeric G-protein activity, were tested in the beta-COP binding assay. AlF(4) increased beta-COP association, whereas binding was inhibited by the addition of Gbetagamma subunits. Our results suggest that COP proteins are recruited to phagosomal membranes by a mechanism that involves heterotrimeric GTP-binding proteins and a BFA-sensitive ARF. In addition, our findings indicate that COPI proteins are involved in the recycling of components from phagosomes to the cell surface.
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Affiliation(s)
- W Berón
- Instituto de Histología y Embriología-CONICET, Universidad Nacional de Cuyo, Casilla de Correo 56, (5500) Mendoza, Argentina.
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Monni M, Roberti R, Corazzi L. Acidic pH generated by H+-ATPase pumps triggers the activity of a fusogenic protein associated with rat liver endoplasmic reticulum. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:2020-7. [PMID: 11277924 DOI: 10.1046/j.1432-1327.2001.02079.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Fusogenic protein (FP) is a glycoprotein ( approximately 50 kDa), previously purified by us from rat liver endoplasmic reticulum, which explicates fusogenic activity at acidic pH in vitro. To suggest a possible role of FP in membrane fusion, the topology of the protein in the membrane and the conditions in which FP is operating in microsomes have been investigated. Anti-FP polyclonal antibodies inhibited pure FP activity, but not the protein activity in microsomes, suggesting interaction of antibodies with a part of FP concealed in intact membranes. FP activity in microsomes was lost after treatment with Pronase. Western blot analysis of Pronase-treated microsomes showed that the proteolysis removed a fragment ( approximately 5 kDa). This fragment is exposed on the outer surface of microsomes and involved in fusogenic activity, whereas the largest part of FP is embedded in microsomal vesicles. Therefore, FP can be affected by modifications on the cytosolic and luminal sides of microsomal membranes. Indeed, when microsomal lumen was acidified by H+-ATPase activity, binding and fusion of fluorescent labelled liposomes to microsomes occurred. Direct involvement of FP in the fusogenic event was observed by reconstituting pure FP in liposomes with a preformed H+ gradient. FP triggered a fusion process in response to the acidic interior of liposomes, despite an exterior 7.4 pH unable to promote fusogenic protein activity. As intracellular membrane fusion occurs at neutral pH involving the cytosolic sides of membranes, FP may participate in this event by exploiting the acidic pH formed in the lumen of endoplasmic reticulum through H+-translocating ATPase activity.
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Affiliation(s)
- M Monni
- Laboratory of Biochemistry, Department of Internal Medicine, University of Perugia, Italy
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Boshans RL, Szanto S, van Aelst L, D'Souza-Schorey C. ADP-ribosylation factor 6 regulates actin cytoskeleton remodeling in coordination with Rac1 and RhoA. Mol Cell Biol 2000; 20:3685-94. [PMID: 10779358 PMCID: PMC85663 DOI: 10.1128/mcb.20.10.3685-3694.2000] [Citation(s) in RCA: 151] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/1999] [Accepted: 02/22/2000] [Indexed: 11/20/2022] Open
Abstract
In this study, we have documented an essential role for ADP-ribosylation factor 6 (ARF6) in cell surface remodeling in response to physiological stimulus and in the down regulation of stress fiber formation. We demonstrate that the G-protein-coupled receptor agonist bombesin triggers the redistribution of ARF6- and Rac1-containing endosomal vesicles to the cell surface. This membrane redistribution was accompanied by cortical actin rearrangements and was inhibited by dominant negative ARF6, implying that bombesin is a physiological trigger of ARF6 activation. Furthermore, these studies provide a new model for bombesin-induced Rac1 activation that involves ARF6-regulated endosomal recycling. The bombesin-elicited translocation of vesicular ARF6 was mimicked by activated Galphaq and was partially inhibited by expression of RGS2, which down regulates Gq function. This suggests that Gq functions as an upstream regulator of ARF6 activation. The ARF6-induced peripheral cytoskeletal rearrangements were accompanied by a depletion of stress fibers. Moreover, cells expressing activated ARF6 resisted the formation of stress fibers induced by lysophosphatidic acid. We show that the ARF6-dependent inhibition of stress fiber formation was due to an inhibition of RhoA activation and was overcome by expression of a constitutively active RhoA mutant. The latter observations demonstrate that activation of ARF6 down regulates Rho signaling. Our findings underscore the potential roles of ARF6, Rac1, and RhoA in the coordinated regulation of cytoskeletal remodeling.
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Affiliation(s)
- R L Boshans
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana 46556-0369, USA
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Liscovitch M, Czarny M, Fiucci G, Lavie Y, Tang X. Localization and possible functions of phospholipase D isozymes. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1439:245-63. [PMID: 10425399 DOI: 10.1016/s1388-1981(99)00098-0] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The activation of PLD is believed to play an important role in the regulation of cell function and cell fate by extracellular signal molecules. Multiple PLD activities have been characterized in mammalian cells and, more recently, several PLD genes have been cloned. Current evidence indicates that diverse PLD activities are localized in most, if not all, cellular organelles, where they are likely to subserve different functions in signal transduction, membrane vesicle trafficking and cytoskeletal dynamics.
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Affiliation(s)
- M Liscovitch
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel
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Abstract
Insulin modulates many intracellular processes including cellular metabolism, cell proliferation and cell differentiation. Some of these processes involve significant changes in the traffic of intracellular vesicles or in the structural organization of the cell. These phenomena have been linked to the activity of regulatory GTP-binding proteins. Most, if not all functions, of the insulin receptor are associated with its tyrosine kinase activity. Thus, over the past few years, a significant effort has been dedicated to elucidate the cross-talk between the tyrosine kinase activity of the receptor and the regulation of G protein-mediated pathways. Recent progress indicates that G proteins may mediate the control of several of insulin's intracellular functions. These include the regulation of the MAP kinase pathway, the activation of phospholipase D and the regulation of glucose uptake. This article discusses some recent advances in this area.
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Affiliation(s)
- M A Rizzo
- Department of Pharmacology, University of Pittsburgh School of Medicine, PA 15261, USA
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Radhakrishna H, Al-Awar O, Khachikian Z, Donaldson JG. ARF6 requirement for Rac ruffling suggests a role for membrane trafficking in cortical actin rearrangements. J Cell Sci 1999; 112 ( Pt 6):855-66. [PMID: 10036235 DOI: 10.1242/jcs.112.6.855] [Citation(s) in RCA: 255] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ARF6 GTPase regulates a novel endosomal-plasma membrane recycling pathway and influences cortical actin remodeling. Here we examined the relationship between ARF6 and Rac1, a Rho family GTPase, implicated in cortical actin rearrangements. Endogenous Rac1 colocalized with ARF6 at the plasma membrane and on the ARF6 recycling endosome in untransfected HeLa and primary human fibroblast cells. In transfected HeLa cells Rac1 and ARF6 also colocalized. Cells expressing wild-type ARF6 or Rac1 formed actin-containing surface protrusions and membrane ruffles, respectively, upon treatment with the G protein activator aluminum fluoride. Aluminum fluoride-treatment of cells transfected with equivalent amounts of plasmid resulted in enhanced membrane ruffling, with protrusions appearing as Rac expression was lowered. Co-expression of the dominant negative, GTP binding-defective ARF6 T27N mutant inhibited the aluminum fluoride-induced ruffling observed in cells expressing Rac1, and the constitutive ruffling observed in cells expressing the activated Rac1 Q61L mutant. In contrast, co-expression of the GTP-binding-defective, T17N mutant of either Rac1 or Cdc42 with ARF6 did not inhibit the aluminum fluoride-induced surface protrusions, nor did inactivation of Rho with C3-transferase. These observations suggest that ARF6, a non-Rho family GTPase, can, by itself, alter cortical actin and can influence the ability of Rac1 to form lamellipodia, in part, by regulating its trafficking to the plasma membrane.
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Affiliation(s)
- H Radhakrishna
- Laboratory of Cell Biology, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA
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Oda H, Naganuma T, Murayama T, Nomura Y. Inhibition of noradrenaline release from PC12 cells by the long-term treatment with cholera toxin. Neurochem Int 1999; 34:157-65. [PMID: 10213075 DOI: 10.1016/s0197-0186(98)00084-9] [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: 11/24/2022]
Abstract
Guanine nucleotide-binding (G) proteins are required for intracellular vesicular transport and endocytosis. In this study, we investigated the effects of short-term (2 h) and long-term (24 h) treatment with cholera toxin (CTX), which ADP-ribosylates proteins having arginine residues such as the alpha subunit of Gs (G(s alpha)), on exocytosis from the neurosecretory rat pheochromocytoma PC 12 cell line. Short-term treatment with CTX stimulated the accumulation of cyclic AMP, and synergistically enhanced both extracellular Ca2+-dependent [3H]noradrenaline (NA) releases (induced by high K+ and ATP) and Ca2+-independent release (induced by mastoparan, a peptide in wasp venom). Long-term treatment with CTX for 24h inhibited Ca2+-dependent and -independent stimulated [3H]NA release. The inhibitory effect of long-term CTX treatment was not derived from a cyclic AMP-dependent system, because (1) H-89, an inhibitor of protein kinase A, had no effect on the inhibition induced by CTX, (2) the long-term treatment with forskolin did not show an inhibitory effect. [32P]ADP-ribosylation of G(s alpha) and its immunoreactivity with anti-G(s alpha) antiserum in the crude membrane fraction was inhibited in the long-term CTX-treated cells, but not in the long-term forskolin-treated cells. [32P]ADP-ribosylation of G(s alpha) in the membrane fraction of short-term CTX-treated cells was approximately 90% of the level in the control cells. These findings suggest that CTX stimulates [3H]NA release via a cyclic AMP-dependent system in the short-term, and that long-term CTX treatment inhibited its release, maybe via ADP-ribosylation of CTX-sensitive proteins such as G(s alpha).
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Affiliation(s)
- H Oda
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
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Murayama T, Naganuma T, Oda H, Nomura Y. Exocytotic stimulation promotes association of the ADP-ribosylation factor with PC12 cell membranes. Arch Biochem Biophys 1998; 354:144-50. [PMID: 9633609 DOI: 10.1006/abbi.1998.0656] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ADP-ribosylation factors (ARFs) are a family of small molecular, monomeric GTP-binding (G) proteins, initially identified by their ability to enhance cholera toxin (CTX) ADP-ribosyltransferase activity. ARFs have been implicated in protein transport and vesicle and endosome fusion. Although several reports show that synthetic peptides of the N-terminus of ARF inhibited Ca(2+)-dependent exocytosis in permeabilized adrenal chromaffin cells, the role of ARFs in exocytosis has not been established. In this study, we investigated the translocation of ARFs to the membrane fraction from the cytosol fraction in PC12 cells after exocytotic stimulation by measuring the immunoreactivity of ARFs (with anti-ARF anti-serum and with anti-ARF3 antibodies) and enzymatic ARF activity, which enhances the CTX effect. Both the immunoreactivity and the enzymatic activity of ARF in the membrane fraction increased about twofold, significantly, after exocytotic stimulation with ATP and KCl. The translocation of ARF and noradrenaline release was observed in the presence of extracellular CaCl2, but not in the absence of CaCl2. The ARF translocated to the membrane fraction after stimulation in intact cells seemed to be an inactive, perhaps is the GDP form, because ARF did not activate CTX in the absence of guanosine 5'-O-(thiotriphosphate) (GTP gamma S). As previously reported, ARF in the active, GTP gamma S-bound state bound to the membrane fractions. Thus ARF may have been active during translocation and inactivated later. The immunoreactivity of Gs alpha, one of the trimeric G proteins, was not changed before or after stimulation. These findings suggest that ARFs translocate to membranes from the cytosolic fraction after exocytotic stimulation in PC12 cells, and raise the possibility that ARFs regulate exocytosis.
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Affiliation(s)
- T Murayama
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
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Astesano A, Ferrand N, Bendayan M, Rosselin G. Subcellular localization of G-protein alpha subunits in adult rat islets. Ann N Y Acad Sci 1996; 805:549-54. [PMID: 8993437 DOI: 10.1111/j.1749-6632.1996.tb17517.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- A Astesano
- Unité de Recherches sur les Peptides Neurodigestifs et le Diabète, Institut National de la Santé et de la Recherche Médicale, Centre de Recherches Paris Saint-Antoine, France. .-jussieu.fr
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Abstract
Recent studies have shown that mastoparan, an amphiphilic peptide derived from wasp venom, modifies the secretion of neurotransmitters and hormones from a variety of cell types. Mastoparan interacts with heterotrimeric guanine nucleotide-binding proteins (G proteins) such as Gi and G(o), which are ADP-ribosylated by pertussis toxin (PTX) and thereby uncoupled from receptors. Previously, some of the effects of mastoparan including secretion were reported to be modified selectively by PTX but not by cholera toxin (CTX). In the present study, we examined the influence of bacterial toxins on the effects of mastoparan in PC12 cells. Mastoparan stimulated [3H]noradrenaline (NA) release from prelabeled PC12 cells in the absence of CaCl2, although high K+ or ATP-stimulated the release in a Ca(2+)-dependent manner. Pretreatment with CTX, not PTX, for 24 h inhibited mastoparan-stimulated [3H]NA release. Mastoparan inhibited forskolin-stimulated cyclic AMP accumulation in a dose-dependent manner, although mastoparan had no effect by itself. Pretreatment with PTX completely abolished the inhibitory effect of carbachol via Gi on cyclic AMP accumulation and partially reduced the effect of mastoparan. However, the inhibitory effect of 20 microM mastoparan was not modified by pretreatment with PTX. Thus, we investigated the effect of mastoparan on CTX-catalyzed [32P]ADP-ribosylation of proteins in PC12 cells. A subunit of CTX (CTX-A) catalyzed [32P]ADP-ribosylation of many proteins in the cytosolic fraction of PC12 cells. One of these was a 20 kDa protein, named ADP-ribosylating factor (ARF). The addition of mastoparan to assay mixtures inhibited ADP-ribosylation of many proteins including ARF and CTX-A in the presence of the cytosolic fraction. In the absence of the cytosolic fraction, however, mastoparan slightly enhanced ADP-ribosylation of bovine serum albumin and auto-ADP-ribosylation by CTX-A. Mastoparan did not inhibit ADP-ribosylation of the alpha subunit of Gs in the membrane fraction. These findings suggest that 1) mastoparan interacts with PTX-insensitive and CTX-sensitive factor(s) to stimulate NA release, and 2) mastoparan interacts with ARF inhibiting its activity to enhance the ADP-ribosylation reaction by CTX. ARF may be an exocytosis-linked G protein.
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Affiliation(s)
- T Murayama
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
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Emans N, Verkman AS. Real-time fluorescence measurement of cell-free endosome fusion: regulation by second messengers. Biophys J 1996; 71:487-94. [PMID: 8804631 PMCID: PMC1233499 DOI: 10.1016/s0006-3495(96)79250-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A quantitative real-time assay of cell-free endosomal vesicle fusion was developed and applied to study fusion mechanisms in endosomes from baby hamster kidney (BHK-21) cells. The assay is based on an irreversible approximately 10-fold increase in BODIPY-avidin fluorescence on binding of biotinylated conjugates. BODIPY-avidin and biotin-dextran were internalized for 10 min at 37 degrees C into separate populations of BHK-21 cells, and endosome fractions were prepared. Postnuclear supernatant fractions underwent ATP- and temperature-dependent fusion, as measured in a sensitive custom-built microfluorimeter by the continuous increase in BODIPY-avidin fluorescence. Fusion processes of efficiency > 2.5% could be detected with 200-ms time resolution in sample volumes of 50 microL containing endosomes derived from approximately 4 x 10(4) cells. The fusion time course consisted of a distinct lag phase (up to 10 min) in which little fusion occurred, followed by an approximately exponential rise (t 1/2 10-30 min; fusion efficiency approximately 15%). The lag phase was reduced by preincubation of separate endosome fractions with ATP at 37 degrees C and by coincubation of endosomes at 22 degrees C before the assay, suggesting a rate-limiting step involving binding of a soluble protein to the endosome membrane. Endosome fusion was strongly inhibited by GTP gamma S, N-ethylmaleimide, and AIF4-. Endosome fusion was not affected by phorbol myristate acetate but was significantly inhibited by cAMP and bovine brain calmodulin. The results establish a sensitive real-time fluorescence assay to quantify the kinetics and extent of endosome fusion in a cell-free system and demonstrate regulation of early endosome fusion by cytosolic second messengers.
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Affiliation(s)
- N Emans
- Department of Medicine, University of California, San Francisco 94143-0521 USA.
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Colombo MI, Inglese J, D'Souza-Schorey C, Beron W, Stahl PD. Heterotrimeric G proteins interact with the small GTPase ARF. Possibilities for the regulation of vesicular traffic. J Biol Chem 1995; 270:24564-71. [PMID: 7592675 DOI: 10.1074/jbc.270.41.24564] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Trimeric G proteins have emerged as important regulators of membrane trafficking. To explore a role for G beta gamma in endosome fusion, we have taken advantage of beta-adrenergic receptor kinase (beta ARK), an enzyme translocated to membranes by interaction with G beta gamma. The COOH terminus of beta ARK (beta ARKct) has a G beta gamma-binding domain which blocks some G beta gamma-mediated processes. We found that beta ARKct and peptide G, a peptide derived from beta ARKct, inhibit in vitro endosome fusion. Interestingly, peptide G and ARF share sequence similarity. Peptide G and beta ARKct reversed ARF-mediated inhibition of endosome fusion and blocked ARF binding to membranes. Using an ARF fusion protein, we show that both G beta gamma and G alpha s interact with the small GTPase ARF, an interaction that is regulated by nucleotide binding. We conclude that G proteins may participate in the regulation of vesicular trafficking by directly interacting with ARF, a cytosolic factor required for transport.
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Affiliation(s)
- M I Colombo
- Department of Cell Biology and Physiology, Washington University, School of Medicine, St. Louis, Missouri 63110, USA
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Abstract
Since reticulocytes have a high demand for iron, which is required for heme biosynthesis, these cells are highly specialized in the endocytosis of the iron carrier transferrin (Tf). From the resulting endocytic vesicles (EVs), iron is released and the vesicles rapidly return to the cell membrane where they fuse, causing the release of the apotransferrin. Due to a lack of other intracellular compartments, the endocytic vesicles can be readily isolated. In this study, we have investigated the fusogenic properties of EVs, using liposomes as target membranes. Membrane fusion was monitored by a lipid mixing assay based on the relief of fluorescence self-quenching, using octadecylrhodamine B-chloride (R18). Application of this procedure was verified and solidified by analysis of the fusion event by an independent lipid mixing assay, after in situ labeling of EVs, and by determination of the mixing of aqueous contents. We demonstrate that the endocytic vesicles are particularly prone to fuse with target membranes that contain dioleoylphosphatidylethanolamine (DOPE). Relative to DOPE, bilayers composed of phosphatidylserine or phosphatidylcholine show a reduced fusion activity with EV. The specific and strong inhibition of fusion by cyclosporin A and a peptide known to interfere with the propensity of DOPE to adopt the hexagonal HII phase suggests that the mechanism of fusion involves the ability of this lipid to readily adopt non-bilayer phases. ATP, GTP, and/or cytosol are not necessary to obtain fusion. However, trypsin treatment of the endocytic vesicles inhibits fusion, indicating the involvement of (a) protein(s) in the fusion event.
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Affiliation(s)
- M Vidal
- URA 1856 CNRS, Université Montpellier II, France
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Spiro DJ, Taylor TC, Melançon P, Wessling-Resnick M. Cytosolic ADP-ribosylation factors are not required for endosome-endosome fusion but are necessary for GTP gamma S inhibition of fusion. J Biol Chem 1995; 270:13693-7. [PMID: 7775422 DOI: 10.1074/jbc.270.23.13693] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
A specific role for ADP-ribosylation factors (ARFs) in in vitro endosome-endosome fusion has been proposed (Lenhard, J. M., Kahn, R. A., and Stahl, P. D. (1992) J. Biol. Chem. 267, 13047-13052). However, in vivo studies have failed to support a function for ARFs in the endocytic pathway, since an antagonist of ARF activities, brefeldin A, does not interfere with receptor internalization (Schonhorn, J. E., and Wessling-Resnick, M. (1994) Mol. Cell. Biochem. 135, 159-164). This controversy surrounding the exact function of ARF in endocytic vesicle traffic prompted us to critically re-examine the involvement of ARFs in cell-free endosome fusion. Cytosol depleted of ARF activity was capable of supporting in vitro endocytic vesicle fusion but failed to support inhibition of this reaction in the presence of guanosine 5'-3-O-(thio)triphosphate (GTP gamma S). Addition of purified ARF1 restored the ability of the ARF-depleted cytosol to inhibit endosome fusion when incubated with GTP gamma S. Both endocytic vesicle fusion and the GTP gamma S-mediated inhibition of vesicle fusion were unaffected by brefeldin A. Moreover, the ATP requirement and kinetics of cell-free fusion are not altered by brefeldin A or depletion of cytosolic ARFs. These results suggest that cytosolic ARFs are not necessary for endosomal vesicle fusion in vitro but are responsible for inhibition of fusion in the presence of GTP gamma S and cytosolic factors in a brefeldin A-resistant manner.
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Affiliation(s)
- D J Spiro
- Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA
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