1
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Iswanto ABB, Vu MH, Shon JC, Kumar R, Wu S, Kang H, Kim DR, Son GH, Kim WY, Kwak YS, Liu KH, Kim SH, Kim JY. α1-COP modulates plasmodesmata function through sphingolipid enzyme regulation. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2024; 66:1639-1657. [PMID: 38888228 DOI: 10.1111/jipb.13711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 04/30/2024] [Indexed: 06/20/2024]
Abstract
Callose, a β-1,3-glucan plant cell wall polymer, regulates symplasmic channel size at plasmodesmata (PD) and plays a crucial role in a variety of plant processes. However, elucidating the molecular mechanism of PD callose homeostasis is limited. We screened and identified an Arabidopsis mutant plant with excessive callose deposition at PD and found that the mutated gene was α1-COP, a member of the coat protein I (COPI) coatomer complex. We report that loss of function of α1-COP elevates the callose accumulation at PD by affecting subcellular protein localization of callose degradation enzyme PdBG2. This process is linked to the functions of ERH1, an inositol phosphoryl ceramide synthase, and glucosylceramide synthase through physical interactions with the α1-COP protein. Additionally, the loss of function of α1-COP alters the subcellular localization of ERH1 and GCS proteins, resulting in a reduction of GlcCers and GlcHCers molecules, which are key sphingolipid (SL) species for lipid raft formation. Our findings suggest that α1-COP protein, together with SL modifiers controlling lipid raft compositions, regulates the subcellular localization of GPI-anchored PDBG2 proteins, and hence the callose turnover at PD and symplasmic movement of biomolecules. Our findings provide the first key clue to link the COPI-mediated intracellular trafficking pathway to the callose-mediated intercellular signaling pathway through PD.
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Affiliation(s)
- Arya Bagus Boedi Iswanto
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Minh Huy Vu
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Jong Cheol Shon
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Kyungpook National University, Daegu, 702-701, Korea
| | - Ritesh Kumar
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Shuwei Wu
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Hobin Kang
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Da-Ran Kim
- Departement of Plant Medicine, Gyeongsang National University, Jinju, 52828, Korea
| | - Geon Hui Son
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Woe Yoen Kim
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
| | - Youn-Sig Kwak
- Departement of Plant Medicine, Gyeongsang National University, Jinju, 52828, Korea
| | - Kwang Hyeon Liu
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Kyungpook National University, Daegu, 702-701, Korea
| | - Sang Hee Kim
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
- Division of Life Science, Gyeongsang National University, Jinju, 52828, Korea
| | - Jae-Yean Kim
- Division of Applied Life Science (BK21 FOUR Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju, 52828, Korea
- Division of Life Science, Gyeongsang National University, Jinju, 52828, Korea
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2
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Barker CJ, Illies C, Gaboardi GC, Berggren PO. Inositol pyrophosphates: structure, enzymology and function. Cell Mol Life Sci 2009; 66:3851-71. [PMID: 19714294 PMCID: PMC11115731 DOI: 10.1007/s00018-009-0115-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 07/13/2009] [Accepted: 07/20/2009] [Indexed: 02/04/2023]
Abstract
The stereochemistry of the inositol backbone provides a platform on which to generate a vast array of distinct molecular motifs that are used to convey information both in signal transduction and many other critical areas of cell biology. Diphosphoinositol phosphates, or inositol pyrophosphates, are the most recently characterized members of the inositide family. They represent a new frontier with both novel targets within the cell and novel modes of action. This includes the proposed pyrophosphorylation of a unique subset of proteins. We review recent insights into the structures of these molecules and the properties of the enzymes which regulate their concentration. These enzymes also act independently of their catalytic activity via protein-protein interactions. This unique combination of enzymes and products has an important role in diverse cellular processes including vesicle trafficking, endo- and exocytosis, apoptosis, telomere length regulation, chromatin hyperrecombination, the response to osmotic stress, and elements of nucleolar function.
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Affiliation(s)
- Christopher John Barker
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, 171 76 Stockholm, Sweden
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3
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Abstract
Phosphoinositides (PIs) undergo phosphorylation/dephosphorylation cycles through organelle-specific PI kinases and PI phosphatases that lead to distinct subcellular distributions of the individual PI species. Specific PIs control the correct timing and location of many trafficking events. Their ultimate mode of action is not always well defined, but it includes localized recruitment of transport machinery, allosteric regulation of PI-binding proteins and changes in the physical properties of the membrane.
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Affiliation(s)
- Maria Antonietta De Matteis
- Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, via Nazionale, 66030 Santa Maria Imbaro, Chieti, Italy.
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4
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Abstract
Lipid signaling by phosphoinositides (PIP(n)s) involves an array of proteins with lipid recognition, kinase, phosphatase, and phospholipase functions. Understanding PIP(n) pathway signaling requires identification and characterization of PIP(n)-interacting proteins. Moreover, spatiotemporal localization and physiological function of PIP(n)-protein complexes must be elucidated in cellular and organismal contexts. For protein discovery to functional elucidation, reporter-linked phosphoinositides or tethered PIP(n)s have been essential. The phosphoinositide 3-kinase (PI 3-K) signaling pathway has recently emerged as an important source of potential "druggable" therapeutic targets in human pathophysiology in both academic and pharmaceutical environments. This review summarizes the chemistry of PIP(n) affinity probes and their use in identifying macromolecular targets. The process of target validation will be described, i.e., the use of tethered PIP(n)s in determining PIP(n) selectivity in vitro and in establishing the function of PIP(n)-protein complexes in living cells.
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Affiliation(s)
- Glenn D Prestwich
- Department of Medicinal Chemistry, The University of Utah, 419 Wakara Way, Suite 205, Salt Lake City, UT 84108, USA.
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5
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Rohde HM, Cheong FY, Konrad G, Paiha K, Mayinger P, Boehmelt G. The human phosphatidylinositol phosphatase SAC1 interacts with the coatomer I complex. J Biol Chem 2003; 278:52689-99. [PMID: 14527956 DOI: 10.1074/jbc.m307983200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The Saccharomyces cerevisiae SAC1 gene encodes an integral membrane protein of the endoplasmic reticulum (ER) and the Golgi apparatus. Yeast SAC1 mutants display a wide array of phenotypes including inositol auxotrophy, cold sensitivity, secretory defects, disturbed ATP transport into the ER, or suppression of actin gene mutations. At present, it is not clear how these phenotypes relate to the finding that SAC1 displays polyphosphoinositide phosphatase activity. Moreover, it is still an open question whether SAC1 functions similarly in mammalian cells, since some phenotypes are yeast-specific. Potential protein interaction partners and, connected to that, possible regulatory circuits have not been described. Therefore, we have cloned human SAC1 (hSAC1), show that it behaves similar to ySac1p in terms of substrate specificity, demonstrate that the endogenous protein localizes to the ER and Golgi, and identify for the first time members of the coatomer I (COPI) complex as interaction partners of hSAC1. Mutation of a putative COPI interaction motif (KXKXX) at its C terminus abolishes interaction with COPI and causes accumulation of hSAC1 in the Golgi. In addition, we generated a catalytically inactive mutant, demonstrate that its lipid binding capacity is unaltered, and show that it accumulates in the Golgi, incapable of interacting with the COPI complex despite the presence of the KXKXX motif. These results open the possibility that the enzymatic function of hSAC1 provides a switch for accessibility of the COPI interaction motif.
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Affiliation(s)
- Holger M Rohde
- Boehringer Ingelheim Austria GmbH, Dr. Boehringer-Gasse 5-11, 1121 Vienna, Austria
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6
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Kular GS, Chaudhary A, Prestwich G, Swigart P, Wetzker R, Cockcroft S. Co-operation of phosphatidylinositol transfer protein with phosphoinositide 3-kinase gamma in vitro. ADVANCES IN ENZYME REGULATION 2002; 42:53-61. [PMID: 12123706 DOI: 10.1016/s0065-2571(01)00023-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Gursant S Kular
- Research Unit Molecular Cell Biology, University of Jena, Germany
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7
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Abstract
Phosphoinositides act as precursors of second messengers and membrane ligands for protein modules. Specific lipid kinases and phosphatases are located and differentially regulated in cell organelles, generating a non-uniform distribution of phosphoinositides. Although it is not clear whether and how the phosphoinositide pools are integrated, it is certain that they locally control fundamental processes, including membrane trafficking. This applies to the Golgi complex, where a direct, central role of the phosphatidylinositol 4,5-bisphosphate precursor phosphatidylinositol 4-phosphate has recently been reported.
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Affiliation(s)
- Maria De Matteis
- Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, 66030, Santa Maria Imbaro, Chieti, Italy.
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8
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Chen R, Kang VH, Chen J, Shope JC, Torabinejad J, DeWald DB, Prestwich GD. A monoclonal antibody to visualize PtdIns(3,4,5)P(3) in cells. J Histochem Cytochem 2002; 50:697-708. [PMID: 11967281 DOI: 10.1177/002215540205000511] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3)] is a second messenger produced in response to agonist stimulation. Traditionally, visualization of phosphoinositide polyphosphates (PtdInsP(n)) in living cells is accomplished using chimeric green fluorescent protein (GFP)-pleckstrin homology (PH) domain proteins, while PtdInsP(n) quantitation is accomplished by extraction and separation of radiolabeled cellular PtdInsP(n)s. Here we describe preparation of a covalent protein-PtdIns(3,4,5)P(3) immunogen, characterization of binding selectivity of an anti-PtdIns(3,4,5)P(3) IgM, and immunodetection of PtdIns(3,4,5)P(3) in stimulated mammalian cells. This antibody has greater than three orders of magnitude selectivity for binding PtdIns(3,4,5)P(3) relative to its precursor, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)), and is therefore optimal for studies of cell function. The immunodetection in platelet-derived growth factor (PDGF)-stimulated NIH 3T3 cells was benchmarked against HPLC analysis of [3H]-myo-inositol-labeled cellular PtdInsP(n)s. In addition, the changes in subcellular amounts and localizations of both PtdIns(3,4,5)P(3) and PtdIns(4,5)P(2) in stimulated NIH 3T3 fibroblasts and human neutrophils were observed by immunofluorescence. In insulin- or PDGF-stimulated fibroblasts, PtdIns(3,4,5)P(3) levels increased in the cytoplasm, peaking at 10 min. In contrast, increases in the PtdIns(4,5)P(2) levels were detected in nuclei, corresponding to the production of new substrate following depletion by phosphoinositide (PI) 3-kinase.
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Affiliation(s)
- Riyan Chen
- Center for Cell Signaling, Salt Lake City, Utah 84108, USA
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9
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Whitley P, Gibbard AM, Koumanov F, Oldfield S, Kilgour EE, Prestwich GD, Holman GD. Identification of centaurin-alpha2: a phosphatidylinositide-binding protein present in fat, heart and skeletal muscle. Eur J Cell Biol 2002; 81:222-30. [PMID: 12018390 DOI: 10.1078/0171-9335-00242] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We describe here the cloning, expression and characterisation of centaurin-alpha2 from a rat adipocyte cDNA library. The centaurin-alpha2 cDNA contains an open reading frame, which codes for a protein of 376 amino acids with predicted mass of 43.5 kDa. Centaurin-alpha2 shares 51-59% identity with centaurin-alpha1 proteins and has the same domain organisation, consisting of a predicted N-terminal ArfGAP domain followed by two successive pleckstrin homology domains. Despite the sequence similarity, there are a number of notable differences between the previously characterised centaurin-alpha1 proteins and the newly described centaurin-alpha2: (i) in vitro lipid binding experiments with centaurin-alpha2 do not reveal the same selectivity for phosphatidylinositol 3,4,5-trisphosphate over phosphatidylinositol 4,5-bisphosphate that has been shown for centaurin-alpha; (ii) unlike centaurin-alpha1 which is expressed mainly in the brain, centaurin-alpha2 has a broad tissue distribution, being particularly abundant in fat, heart and skeletal muscle; (iii) in contrast to centaurin-alpha1 which is found in both membrane and cytosolic fractions, endogenous centaurin-alpha2 is exclusively present in the dense membrane fractions of cell extracts, suggesting a constitutive membrane association. Insulin stimulation, which stimulates phosphatidylinositol 3,4,5-trisphosphate production, does not alter the subcellular distribution of centaurin-alpha2 between adipocyte membrane fractions. This observation is consistent with the lack of specificity of centaurin-alpha2 for phosphatidylinositol 3,4,5-trisphosphate over phosphatidylinositol 4,5-bisphosphate.
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Affiliation(s)
- Paul Whitley
- Department of Biology and Biochemistry, University of Bath, United Kingdom
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10
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Li X, Rivas MP, Fang M, Marchena J, Mehrotra B, Chaudhary A, Feng L, Prestwich GD, Bankaitis VA. Analysis of oxysterol binding protein homologue Kes1p function in regulation of Sec14p-dependent protein transport from the yeast Golgi complex. J Cell Biol 2002; 157:63-77. [PMID: 11916983 PMCID: PMC2173257 DOI: 10.1083/jcb.200201037] [Citation(s) in RCA: 200] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Oxysterol binding proteins (OSBPs) comprise a large conserved family of proteins in eukaryotes. Their ubiquity notwithstanding, the functional activities of these proteins remain unknown. Kes1p, one of seven members of the yeast OSBP family, negatively regulates Golgi complex secretory functions that are dependent on the action of the major yeast phosphatidylinositol/phosphatidylcholine Sec14p. We now demonstrate that Kes1p is a peripheral membrane protein of the yeast Golgi complex, that localization to the Golgi complex is required for Kes1p function in vivo, and that targeting of Kes1p to the Golgi complex requires binding to a phosphoinositide pool generated via the action of the Pik1p, but not the Stt4p, PtdIns 4-kinase. Localization of Kes1p to yeast Golgi region also requires function of a conserved motif found in all members of the OSBP family. Finally, we present evidence to suggest that Kes1p may regulate adenosine diphosphate-ribosylation factor (ARF) function in yeast, and that it may be through altered regulation of ARF that Kes1p interfaces with Sec14p in controlling Golgi region secretory function.
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Affiliation(s)
- Xinmin Li
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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11
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Boehm M, Aguilar RC, Bonifacino JS. Functional and physical interactions of the adaptor protein complex AP-4 with ADP-ribosylation factors (ARFs). EMBO J 2001; 20:6265-76. [PMID: 11707398 PMCID: PMC125733 DOI: 10.1093/emboj/20.22.6265] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AP-4 is a member of the family of heterotetrameric adaptor protein (AP) complexes that mediate the sorting of integral membrane proteins in post-Golgi compartments. This complex consists of four subunits (epsilon, beta4, mu4 and sigma4) and localizes to the cytoplasmic face of the trans-Golgi network (TGN). Here, we show that the recruitment of endogenous AP-4 to the TGN in vivo is regulated by the small GTP-binding protein ARF1. In addition, we demonstrate a direct interaction of the epsilon and mu4 subunits of AP-4 with ARF1. epsilon binds only to ARF1-GTP and requires residues in the switch I and switch II regions of ARF1. In contrast, mu4 binds equally well to the GTP- and GDP-bound forms of ARF1 and is less dependent on switch I and switch II residues. These observations establish AP-4 as an ARF1 effector and suggest a novel mode of interaction between ARF1 and an AP complex involving both constitutive and regulated interactions.
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Affiliation(s)
| | | | - Juan S. Bonifacino
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
Corresponding author e-mail:
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12
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De La Vega LA, Stockert RJ. Regulation of the insulin and asialoglycoprotein receptors via cGMP-dependent protein kinase. Am J Physiol Cell Physiol 2000; 279:C2037-42. [PMID: 11078721 DOI: 10.1152/ajpcell.2000.279.6.c2037] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Biotin regulation of asialoglycoprotein receptor expression and insulin receptor activity has been established in two human hepatoblastoma cell lines, Hep G2 and HuH-7. Second messenger cGMP mimics the effect of biotin on asialoglycoprotein receptor expression at the translational level. Metabolic labeling and subsequent immunoprecipitation indicate that the loss of insulin receptor activity during biotin deprivation was due to suppression of receptor synthesis. Evidence for posttranscriptional regulation of insulin receptor synthesis was provided by rapid biotin induction of receptor synthesis without an increase in gene transcript number. Addition of a cGMP-dependent protein kinase (cGK) inhibitor prevented biotin induction of the insulin and asialoglycoprotein receptors, suggesting that protein phosphorylation propagates the cGMP signal transduction cascade. Coatomer protein COPI was recently identified as the trans-acting factor that regulates in vitro translation of the asialoglycoprotein receptor. Biotin repletion of the culture medium resulted in the hyperphosphorylation of alpha-COP, which was prevented by simultaneous addition of the cGK inhibitor. These findings suggest that the end point of this cGMP signal cascade is modulated by cGK and that a phosphorylation reaction governs the expression of both receptor proteins.
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Affiliation(s)
- L A De La Vega
- Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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13
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Kong AM, Speed CJ, O'Malley CJ, Layton MJ, Meehan T, Loveland KL, Cheema S, Ooms LM, Mitchell CA. Cloning and characterization of a 72-kDa inositol-polyphosphate 5-phosphatase localized to the Golgi network. J Biol Chem 2000; 275:24052-64. [PMID: 10806194 DOI: 10.1074/jbc.m000874200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inositol-polyphosphate 5-phosphatase enzyme family removes the 5-position phosphate from both inositol phosphate and phosphoinositide signaling molecules. We have cloned and characterized a novel 5-phosphatase, which demonstrates a restricted substrate specificity and tissue expression. The 3.9-kb cDNA predicts for a 72-kDa protein with an N-terminal proline rich domain, a central 5-phosphatase domain, and a C-terminal CAAX motif. The 3. 9-kilobase mRNA showed a restricted expression but was abundant in testis and brain. Antibodies against the sequence detected a 72-kDa protein in the testis in the detergent-insoluble fraction. Indirect immunofluorescence of the Tera-1 cell line using anti-peptide antibodies to the 72-kDa 5-phosphatase demonstrated that the enzyme is predominantly located to the Golgi. Expression of green fluorescent protein-tagged 72-kDa 5-phosphatase in COS-7 cells revealed that the enzyme localized predominantly to the Golgi, mediated by the N-terminal proline-rich domain, but not the C-terminal CAAX motif. In vitro, the protein inserted into microsomal membranes on the cytoplasmic face of the membrane. Immunoprecipitated recombinant 72-kDa 5-phosphatase hydrolyzed phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3, 5-bisphosphate, forming phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3-phosphate, respectively. We propose that the novel 5-phosphatase hydrolyzes phosphatidylinositol 3,4, 5-trisphosphate and phosphatidylinositol 3,5-bisphosphate on the cytoplasmic Golgi membrane and thereby may regulate Golgi-vesicular trafficking.
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Affiliation(s)
- A M Kong
- Department of Biochemistry and Molecular Biology and Department of Anatomy and Cell Biology, Monash University, Clayton, Victoria 3168, Australia
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14
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Abstract
Photoactivatable ligands are important tools used in drug discovery and drug development. These ligands enable researchers to identify the targets of drugs, to determine the affinity and selectivity of the drug-target interaction, and to identify the binding site on the target. Examples are presented from three fundamentally different approaches: (1) photoaffinity labeling of target macromolecules; (2) photoactivation and release of 'caged ligands'; and (3) photoimmobilization of ligands onto surfaces.
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Affiliation(s)
- G Dormán
- ComGenex, Budapest, 1027 Bem rkp. 33-34, Hungary.
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15
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Gaidarov I, Keen JH. Phosphoinositide-AP-2 interactions required for targeting to plasma membrane clathrin-coated pits. J Cell Biol 1999; 146:755-64. [PMID: 10459011 PMCID: PMC2156139 DOI: 10.1083/jcb.146.4.755] [Citation(s) in RCA: 222] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The clathrin-associated AP-2 adaptor protein is a major polyphosphoinositide-binding protein in mammalian cells. A high affinity binding site has previously been localized to the NH(2)-terminal region of the AP-2 alpha subunit (Gaidarov et al. 1996. J. Biol. Chem. 271:20922-20929). Here we used deletion and site- directed mutagenesis to determine that alpha residues 21-80 comprise a discrete folding and inositide-binding domain. Further, positively charged residues located within this region are involved in binding, with a lysine triad at positions 55-57 particularly critical. Mutant peptides and protein in which these residues were changed to glutamine retained wild-type structural and functional characteristics by several criteria including circular dichroism spectra, resistance to limited proteolysis, and clathrin binding activity. When expressed in intact cells, mutated alpha subunit showed defective localization to clathrin-coated pits; at high expression levels, the appearance of endogenous AP-2 in coated pits was also blocked consistent with a dominant-negative phenotype. These results, together with recent work indicating that phosphoinositides are also critical to ligand-dependent recruitment of arrestin-receptor complexes to coated pits (Gaidarov et al. 1999. EMBO (Eur. Mol. Biol. Organ.) J. 18:871-881), suggest that phosphoinositides play a critical and general role in adaptor incorporation into plasma membrane clathrin-coated pits.
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Affiliation(s)
- Ibragim Gaidarov
- Kimmel Cancer Institute and the Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
| | - James H. Keen
- Kimmel Cancer Institute and the Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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16
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Abstract
Enzymes that modify phospholipids play necessary, but poorly understood, roles in constitutive membrane traffic. Local production of specific phosphoinositides is required for endocytosis and regulated exocytosis, and enzymes that produce and consume phosphoinositides are components of post-Golgi membrane vesicles. Both biochemical and genetic data indicate that regulation of the membrane content of phosphatidic acid, diacylglycerol and phosphoinositides is necessary for protein traffic from the Golgi complex. Evidence for a regulatory role for lipids earlier in the constitutive secretory pathway is more limited and controversial. Although the mechanisms that regulate traffic between the endoplasmic reticulum and Golgi might be qualitatively different from those that control later membrane transport pathways, recent studies suggest that production of specific lipids is important for transport both into and out of the Golgi. As discussed in this article, one potential mechanism for the involvement of lipids is to control the GTPase cycle of a small GTP-binding protein, ARF (ADP-ribosylation factor).
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Affiliation(s)
- M G Roth
- Dept of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235-9038, USA.
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17
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Blader IJ, Cope MJ, Jackson TR, Profit AA, Greenwood AF, Drubin DG, Prestwich GD, Theibert AB. GCS1, an Arf guanosine triphosphatase-activating protein in Saccharomyces cerevisiae, is required for normal actin cytoskeletal organization in vivo and stimulates actin polymerization in vitro. Mol Biol Cell 1999; 10:581-96. [PMID: 10069805 PMCID: PMC25189 DOI: 10.1091/mbc.10.3.581] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Recent cloning of a rat brain phosphatidylinositol 3,4, 5-trisphosphate binding protein, centaurin alpha, identified a novel gene family based on homology to an amino-terminal zinc-binding domain. In Saccharomyces cerevisiae, the protein with the highest homology to centaurin alpha is Gcs1p, the product of the GCS1 gene. GCS1 was originally identified as a gene conditionally required for the reentry of cells into the cell cycle after stationary phase growth. Gcs1p was previously characterized as a guanosine triphosphatase-activating protein for the small guanosine triphosphatase Arf1, and gcs1 mutants displayed vesicle-trafficking defects. Here, we have shown that similar to centaurin alpha, recombinant Gcs1p bound phosphoinositide-based affinity resins with high affinity and specificity. A novel GCS1 disruption strain (gcs1Delta) exhibited morphological defects, as well as mislocalization of cortical actin patches. gcs1Delta was hypersensitive to the actin monomer-sequestering drug, latrunculin-B. Synthetic lethality was observed between null alleles of GCS1 and SLA2, the gene encoding a protein involved in stabilization of the actin cytoskeleton. In addition, synthetic growth defects were observed between null alleles of GCS1 and SAC6, the gene encoding the yeast fimbrin homologue. Recombinant Gcs1p bound to actin filaments, stimulated actin polymerization, and inhibited actin depolymerization in vitro. These data provide in vivo and in vitro evidence that Gcs1p interacts directly with the actin cytoskeleton in S. cerevisiae.
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Affiliation(s)
- I J Blader
- Departments of Neurobiology and Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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18
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Gaidarov I, Krupnick JG, Falck JR, Benovic JL, Keen JH. Arrestin function in G protein-coupled receptor endocytosis requires phosphoinositide binding. EMBO J 1999; 18:871-81. [PMID: 10022830 PMCID: PMC1171180 DOI: 10.1093/emboj/18.4.871] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Internalization of agonist-activated G protein-coupled receptors is mediated by non-visual arrestins, which also bind to clathrin and are therefore thought to act as adaptors in the endocytosis process. Phosphoinositides have been implicated in the regulation of intracellular receptor trafficking, and are known to bind to other coat components including AP-2, AP180 and COPI coatomer. Given these observations, we explored the possibility that phosphoinositides play a role in arrestin's function as an adaptor. High-affinity binding sites for phosphoinositides in beta-arrestin (arrestin2) and arrestin3 (beta-arrestin2) were identified, and dissimilar effects of phosphoinositide and inositol phosphate on arrestin interactions with clathrin and receptor were characterized. Alteration of three basic residues in arrestin3 abolished phosphoinositide binding with complete retention of clathrin and receptor binding. Unlike native protein, upon agonist activation, this mutant arrestin3 expressed in COS1 cells neither supported beta2-adrenergic receptor internalization nor did it concentrate in coated pits, although it was recruited to the plasma membrane. These findings indicate that phosphoinositide binding plays a critical regulatory role in delivery of the receptor-arrestin complex to coated pits, perhaps by providing, with activated receptor, a multi-point attachment of arrestin to the plasma membrane.
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Affiliation(s)
- I Gaidarov
- Kimmel Cancer Institute and the Departments of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA 19107, USA
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Hsu VW, Peters PJ. Current views in intracellular transport: insights from studies in immunology. Adv Immunol 1998; 70:369-415. [PMID: 9755342 DOI: 10.1016/s0065-2776(08)60391-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- V W Hsu
- Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Profit AA, Chen J, Gu QM, Chaudhary A, Prasad K, Lafer EM, Prestwich GD. Probing the phosphoinositide binding site of the clathrin assembly protein AP-2 with photoaffinity labels. Arch Biochem Biophys 1998; 357:85-94. [PMID: 9721186 DOI: 10.1006/abbi.1998.0796] [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: 11/22/2022]
Abstract
The relative binding specificities of the subunitsof bovine assembly protein AP-2 for the phosphatidylinositol polyphosphates (PtdInsPn) and inositol polyphosphates (InsPn) were determined by photoaffinitylabeling. Three types of benzophenone-containing photoprobes were employed: (i) the water-solubleP-1- or P-2-tethered p-benzoyldihydrocinnamoyl-InsPn (BZDC-InsPn) analogs, (ii) P-1-linked phosphotriester PtdInsPn analogs that sampled the interface between the water and lipid phases, and (iii) sn-1-O-acyl-linked PtdInsPn analogs that interacted with proteins penetrating the bilayer. The InsPn and PtdInsPn probes bind with highest selectivity and affinity to the two alpha subunit isoforms, with certain probes and conditions resulting in strong labeling of the 50-kDa mu subunit. Three main conclusions were reached: (i) head group recognition predominated over acyl chain recognition, (ii) the PtdInsPn binding site of alpha-AP-2 prefers more highly phosphorylated species, and (iii) the protein-acyl chain interactions showed high capacity but low selectivity.
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Affiliation(s)
- A A Profit
- Department of Chemistry, University at Stony Brook, Stony Brook, New York 11794-3400, USA
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Kearns MA, Monks DE, Fang M, Rivas MP, Courtney PD, Chen J, Prestwich GD, Theibert AB, Dewey RE, Bankaitis VA. Novel developmentally regulated phosphoinositide binding proteins from soybean whose expression bypasses the requirement for an essential phosphatidylinositol transfer protein in yeast. EMBO J 1998; 17:4004-17. [PMID: 9670016 PMCID: PMC1170734 DOI: 10.1093/emboj/17.14.4004] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Phosphatidylinositol transfer proteins (PITPs) have been shown to play important roles in regulating a number of signal transduction pathways that couple to vesicle trafficking reactions, phosphoinositide-driven receptor-mediated signaling cascades, and development. While yeast and metazoan PITPs have been analyzed in some detail, plant PITPs remain entirely uncharacterized. We report the identification and characterization of two soybean proteins, Ssh1p and Ssh2p, whose structural genes were recovered on the basis of their abilities to rescue the viability of PITP-deficient Saccharomyces cerevisiae strains. We demonstrate that, while both Ssh1p and Ssh2p share approximately 25% primary sequence identity with yeast PITP, these proteins exhibit biochemical properties that diverge from those of the known PITPs. Ssh1p and Ssh2p represent high-affinity phosphoinositide binding proteins that are distinguished from each other both on the basis of their phospholipid binding specificities and by their substantially non-overlapping patterns of expression in the soybean plant. Finally, we show that Ssh1p is phosphorylated in response to various environmental stress conditions, including hyperosmotic stress. We suggest that Ssh1p may function as one component of a stress response pathway that serves to protect the adult plant from osmotic insult.
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Affiliation(s)
- M A Kearns
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294-0005, USA
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Chaudhary A, Chen J, Gu QM, Witke W, Kwiatkowski DJ, Prestwich GD. Probing the phosphoinositide 4,5-bisphosphate binding site of human profilin I. CHEMISTRY & BIOLOGY 1998; 5:273-81. [PMID: 9578635 DOI: 10.1016/s1074-5521(98)90620-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND Profilin is a widely and highly expressed 14 kDa protein that binds actin monomers, poly(L-proline) and polyphosphoinositol lipids. It participates in regulating actin-filament dynamics that are essential for many types of cell motility. We sought to investigate the site of interaction of profilin with phosphoinositides. RESULTS Human profilin I was covalently modified using three tritium-labeled 4-benzoyldihydrocinnamoyl (BZDC)-containing photoaffinity analogs of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The P-1-tethered D-myoinositol 1,4,5-trisphosphate (Ins(1,4,5)P3) modified profilin I efficiently and specifically; the covalent labeling could be displaced by co-incubation with an excess of PtdIns(4,5)P2 but not with Ins(1,4,5)P3. The acyl-modified PtdIns(4,5)P2 analog showed little protein labeling even at very low concentrations, whereas the head-group-modified PtdIns(4,5)P2 phosphotriester-labeled monomeric and oligomeric profilin. Mass spectroscopic analyses of CNBr digests of [3H]BZDC-Ins(1,4,5)P3-modified recombinant profilin suggested that modification was in the amino-terminal helical CNBr fragment. Edman degradation confirmed Ala1 of profilin I (residue 4 of the recombinant protein) was modified. Molecular models show a minimum energy conformation in which the hydrophobic region of the ligand contacts the amino-terminal helix whereas the 4,5-bisphosphate interacts with Arg135 and Arg136 of the carboxy-terminal helix. CONCLUSIONS The PtdIns(4,5)P2-binding site of profilin I includes a bisphosphate interaction with a base-rich motif in the carboxy-terminal helix and contact between the lipid moiety of PtdIns(4,5)P2 and a hydrophobic region of the aminoterminal helix of profilin. This is the first direct evidence for a site of interaction of the lipid moiety of a phosphoinositide bisphosphate analog with profilin.
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Affiliation(s)
- A Chaudhary
- Department of Chemistry, University at Stony Brook, New York 11794-3400, USA
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