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Yamazaki Y, Kono K. Clathrin-mediated trafficking of phospholipid flippases is required for local plasma membrane/cell wall damage repair in budding yeast. Biochem Biophys Res Commun 2022; 606:156-162. [DOI: 10.1016/j.bbrc.2022.03.129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 03/09/2022] [Accepted: 03/23/2022] [Indexed: 11/02/2022]
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Yin MX, Catimel B, Gregory M, Condron M, Kapp E, Holmes AB, Burgess AW. Synthesis of an inositol hexakisphosphate (IP6) affinity probe to study the interactome from a colon cancer cell line. Integr Biol (Camb) 2016; 8:309-18. [PMID: 26840369 DOI: 10.1039/c5ib00264h] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Inositol hexakisphosphate (InsP6 or IP6) is an important signalling molecule in vesicular trafficking, neurotransmission, immune responses, regulation of protein kinases and phosphatases, activation of ion channels, antioxidant functions and anticancer activities. An IP6 probe was synthesised from myo-inositol via a derivatised analogue, which was immobilised through a terminal amino group onto Dynabeads. Systematic analysis of the IP6 interactome has been performed using the IP6 affinity probe using cytosolic extracts from the LIM1215 colonic carcinoma cell line. LC/MS/MS analysis identified 77 proteins or protein complexes that bind to IP6 specifically, including AP-2 complex proteins and β-arrestins as well as a number of novel potential IP6 interacting proteins. Bioinformatic enrichment analysis of the IP6 interactome reinforced the concept that IP6 regulates a number of biological processes including cell cycle and division, signal transduction, intracellular protein transport, vesicle-mediated transport and RNA splicing.
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Affiliation(s)
- Meng-Xin Yin
- School of Chemistry, Bio21 Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3052, Australia
| | - Bruno Catimel
- Ludwig Institute for Cancer Research, Melbourne-Austin Branch, Olivia Newton-John Cancer & Wellness Centre, Studley Road, Heidelberg, Victoria 3084, Australia
| | - Mark Gregory
- School of Chemistry, Bio21 Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3052, Australia
| | - Melanie Condron
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia. and Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Eugene Kapp
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia. and Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Andrew B Holmes
- School of Chemistry, Bio21 Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3052, Australia
| | - Antony W Burgess
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia. and Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia and Department of Surgery, RMH, University of Melbourne, Parkville, Victoria 3052, Australia
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3
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Stahelin RV, Scott JL, Frick CT. Cellular and molecular interactions of phosphoinositides and peripheral proteins. Chem Phys Lipids 2014; 182:3-18. [PMID: 24556335 DOI: 10.1016/j.chemphyslip.2014.02.002] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Revised: 02/05/2014] [Accepted: 02/05/2014] [Indexed: 12/23/2022]
Abstract
Anionic lipids act as signals for the recruitment of proteins containing cationic clusters to biological membranes. A family of anionic lipids known as the phosphoinositides (PIPs) are low in abundance, yet play a critical role in recruitment of peripheral proteins to the membrane interface. PIPs are mono-, bis-, or trisphosphorylated derivatives of phosphatidylinositol (PI) yielding seven species with different structure and anionic charge. The differential spatial distribution and temporal appearance of PIPs is key to their role in communicating information to target proteins. Selective recognition of PIPs came into play with the discovery that the substrate of protein kinase C termed pleckstrin possessed the first PIP binding region termed the pleckstrin homology (PH) domain. Since the discovery of the PH domain, more than ten PIP binding domains have been identified including PH, ENTH, FYVE, PX, and C2 domains. Representative examples of each of these domains have been thoroughly characterized to understand how they coordinate PIP headgroups in membranes, translocate to specific membrane docking sites in the cell, and function to regulate the activity of their full-length proteins. In addition, a number of novel mechanisms of PIP-mediated membrane association have emerged, such as coincidence detection-specificity for two distinct lipid headgroups. Other PIP-binding domains may also harbor selectivity for a membrane physical property such as charge or membrane curvature. This review summarizes the current understanding of the cellular distribution of PIPs and their molecular interaction with peripheral proteins.
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Affiliation(s)
- Robert V Stahelin
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-South Bend, South Bend, IN 46617, United States; Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, United States; Mike and Josie Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, United States.
| | - Jordan L Scott
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, United States; Mike and Josie Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, United States
| | - Cary T Frick
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, United States
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4
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Lu KY, Tao SC, Yang TC, Ho YH, Lee CH, Lin CC, Juan HF, Huang HC, Yang CY, Chen MS, Lin YY, Lu JY, Zhu H, Chen CS. Profiling lipid-protein interactions using nonquenched fluorescent liposomal nanovesicles and proteome microarrays. Mol Cell Proteomics 2012; 11:1177-90. [PMID: 22843995 DOI: 10.1074/mcp.m112.017426] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Fluorescent liposomal nanovesicles (liposomes) are commonly used for lipid research and/or signal enhancement. However, the problem of self-quenching with conventional fluorescent liposomes limits their applications because these liposomes must be lysed to detect the fluorescent signals. Here, we developed a nonquenched fluorescent (NQF)1 liposome by optimizing the proportion of sulforhodamine B (SRB) encapsulant and lissamine rhodamine B-dipalmitoyl phosphatidylethanol (LRB-DPPE) on a liposomal surface for signal amplification. Our study showed that 0.3% of LRB-DPPE with 200 μm of SRB provided the maximal fluorescent signal without the need to lyse the liposomes. We also observed that the NQF liposomes largely eliminated self-quenching effects and produced greatly enhanced signals than SRB-only liposomes by 5.3-fold. To show their application in proteomics research, we constructed NQF liposomes that contained phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) and profiled its protein interactome using a yeast proteome microarray. Our profiling led to the identification of 162 PI(3,5)P2-specific binding proteins (PI(3,5)P2-BPs). We not only recovered many proteins that possessed known PI(3,5)P2-binding domains, but we also found two unknown Pfam domains (Pfam-B_8509 and Pfam-B_10446) that were enriched in our dataset. The validation of many newly discovered PI(3,5)P2-BPs was performed using a bead-based affinity assay. Further bioinformatics analyses revealed that the functional roles of 22 PI(3,5)P2-BPs were similar to those associated with PI(3,5)P2, including vesicle-mediated transport, GTPase, cytoskeleton, and kinase. Among the 162 PI(3,5)P2-BPs, we found a novel motif, HRDIKP[ES]NJLL that showed statistical significance. A docking simulation showed that PI(3,5)P2 interacted primarily with lysine or arginine side chains of the newly identified PI(3,5)P2-binding kinases. Our study showed that this new tool would greatly benefit profiling lipid-protein interactions in high-throughput studies.
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Affiliation(s)
- Kuan-Yi Lu
- Graduate Institute of Systems Biology and Bioinformatics, National Central University, Jhongli 32001, Taiwan
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Rowland MM, Gong D, Bostic HE, Lucas N, Cho W, Best MD. Microarray analysis of Akt PH domain binding employing synthetic biotinylated analogs of all seven phosphoinositide headgroup isomers. Chem Phys Lipids 2011; 165:207-15. [PMID: 22178158 DOI: 10.1016/j.chemphyslip.2011.12.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 11/29/2011] [Accepted: 12/02/2011] [Indexed: 12/19/2022]
Abstract
Signaling lipids control many of the most important biological pathways, typically by recruiting cognate protein binding targets to cell surfaces, thereby regulating both their function and subcellular localization. A critical family of signaling lipids is that of the phosphatidylinositol polyphosphates (PIP(n)s), which is composed of seven isomers that vary based on phosphorylation pattern. A key protein that is activated upon PIP(n) binding is Akt, which then plays important roles in regulating the cell cycle, and is thus aberrant in disease. Characterization of protein-PIP(n) binding interactions is hindered by the complexity of the membrane environment and of the PIP(n) structures. Herein, we describe two rapid assays of use for characterizing protein-PIP(n) binding interactions. First, a microplate-based binding assay was devised to characterize the binding of effectors to immobilized synthetic PIP(n) headgroup-biotin conjugates corresponding to all seven isomers. The assay was implemented for simultaneous analysis of Akt-PH domain, indicating PI(3,4,5)P(3) and PI(3,4)P(2) as the primary ligands. In addition, density-dependant studies indicated that the amount of ligand immobilized on the surface affected the amplitude of protein binding, but not the affinity, for Akt-PH. Since the PIP(n) ligand motifs used in this analysis lack the membrane environment and glycerolipid backbone, yet still exhibit high-affinity protein binding, these results narrow down the structural requirements for Akt recognition. Additionally, binding detection was also achieved through microarray analysis via the robotic pin printing of ligands onto glass slides in a miniaturized format. Here, fluorescence-based detection provided sensitive detection of binding using minimal amounts of materials. Due to their high-throughput and versatile attributes, these assays provide invaluable tools for probing and perturbing protein-membrane binding interactions.
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Affiliation(s)
- Meng M Rowland
- Department of Chemistry, The University of Tennessee, Knoxville, TN 37996, United States
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Abstract
The majority of cells of the immune system are specialized secretory cells, whose function depends on regulated exocytosis. The latter is mediated by vesicular transport involving the sorting of specialized cargo into the secretory granules (SGs), thereby generating the transport vesicles; their transport along the microtubules and eventually their signal-dependent fusion with the plasma membrane. Each of these steps is tightly controlled by mechanisms, which involve the participation of specific sorting signals on the cargo proteins and their recognition by cognate adaptor proteins, posttranslational modifications of the cargo proteins and multiple GTPases and SNARE proteins. In some of the cells (i.e. mast cells, T killer cells) an intimate connection exists between the secretory system and the endocytic one, whereby the SGs are lysosome related organelles (LROs) also referred to as secretory lysosomes. Herein, we discuss these mechanisms in health and disease states.
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Affiliation(s)
- Anat Benado
- Department of Cell and Developmental Biology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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Best MD, Zhang H, Prestwich GD. Inositol polyphosphates, diphosphoinositol polyphosphates and phosphatidylinositol polyphosphate lipids: Structure, synthesis, and development of probes for studying biological activity. Nat Prod Rep 2010; 27:1403-30. [DOI: 10.1039/b923844c] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Catimel B, Schieber C, Condron M, Patsiouras H, Connolly L, Catimel J, Nice EC, Burgess AW, Holmes AB. The PI(3,5)P2 and PI(4,5)P2 Interactomes. J Proteome Res 2008; 7:5295-313. [DOI: 10.1021/pr800540h] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Bruno Catimel
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Christine Schieber
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Melanie Condron
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Heather Patsiouras
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Lisa Connolly
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Jenny Catimel
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Edouard C. Nice
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Antony W. Burgess
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Andrew B. Holmes
- Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville Victoria 3052, Australia, and School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia
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Sudhahar C, Haney R, Xue Y, Stahelin R. Cellular membranes and lipid-binding domains as attractive targets for drug development. Curr Drug Targets 2008; 9:603-13. [PMID: 18691008 PMCID: PMC5975357 DOI: 10.2174/138945008785132420] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Interdisciplinary research focused on biological membranes has revealed them as signaling and trafficking platforms for processes fundamental to life. Biomembranes harbor receptors, ion channels, lipid domains, lipid signals, and scaffolding complexes, which function to maintain cellular growth, metabolism, and homeostasis. Moreover, abnormalities in lipid metabolism attributed to genetic changes among other causes are often associated with diseases such as cancer, arthritis and diabetes. Thus, there is a need to comprehensively understand molecular events occurring within and on membranes as a means of grasping disease etiology and identifying viable targets for drug development. A rapidly expanding field in the last decade has centered on understanding membrane recruitment of peripheral proteins. This class of proteins reversibly interacts with specific lipids in a spatial and temporal fashion in crucial biological processes. Typically, recruitment of peripheral proteins to the different cellular sites is mediated by one or more modular lipid-binding domains through specific lipid recognition. Structural, computational, and experimental studies of these lipid-binding domains have demonstrated how they specifically recognize their cognate lipids and achieve subcellular localization. However, the mechanisms by which these modular domains and their host proteins are recruited to and interact with various cell membranes often vary drastically due to differences in lipid affinity, specificity, penetration as well as protein-protein and intramolecular interactions. As there is still a paucity of predictive data for peripheral protein function, these enzymes are often rigorously studied to characterize their lipid-dependent properties. This review summarizes recent progress in our understanding of how peripheral proteins are recruited to biomembranes and highlights avenues to exploit in drug development targeted at cellular membranes and/or lipid-binding proteins.
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Affiliation(s)
- C.G. Sudhahar
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46656, USA
- Walther Center for Cancer Research, University of Notre Dame, Notre Dame, IN 46656, USA
| | - R.M. Haney
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-South Bend, South Bend, IN 46617
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46656, USA
| | - Y. Xue
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-South Bend, South Bend, IN 46617
| | - R.V. Stahelin
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-South Bend, South Bend, IN 46617
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46656, USA
- Walther Center for Cancer Research, University of Notre Dame, Notre Dame, IN 46656, USA
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10
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Fox MA, Sanes JR. Synaptotagmin I and II are present in distinct subsets of central synapses. J Comp Neurol 2007; 503:280-96. [PMID: 17492637 DOI: 10.1002/cne.21381] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Synaptotagmin 1 and 2 (syt 1, syt 2) are synaptic vesicle-associated membrane proteins that act as calcium sensors for fast neurotransmitter release from presynaptic nerve terminals. Here we show that widely used monoclonal antibodies, mab 48 and znp-1, stain nerve terminals in multiple species and, in mouse, recognize syt 1 and syt 2, respectively. With these antibodies, we examined the synaptic localization of these synaptotagmin isoforms in the mouse central nervous system. Syt 1 and syt 2 are localized predominantly to different subsets of synapses in retina, hippocampus, cerebellum, and median nucleus of the trapezoid body (MNTB). In the MNTB, syt 1 and syt 2 are present in different presynaptic terminals on the same postsynaptic principal neuron. In retina, horizontal and OFF-bipolar cell terminals contain syt 2, whereas most other terminals contain syt 1. Syt 1 localization in the immature retina resembles that seen in adult; however, syt 2 localization appears strikingly different at perinatal ages and continues to change dramatically prior to eye opening. For example, starburst amacrine cells, which lack syt 2 in adult retina, transiently express syt 2 during the first 2 postnatal weeks. In addition to differences in spatial and temporal distribution, species-specific differences in synaptotagmin localization were observed in retina and cerebellum. The cell-, temporal-, and species-specific expression of synaptotagmin isoforms suggests that each may have distinct functions in neurotransmitter release.
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Affiliation(s)
- Michael A Fox
- Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138, USA
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Hammond GRV, Schiavo G. Polyphosphoinositol lipids: Under-PPInning synaptic function in health and disease. Dev Neurobiol 2007; 67:1232-47. [PMID: 17514716 DOI: 10.1002/dneu.20509] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Phosphoinositides (PPIn) form a unique family of lipids derived by phosphorylation of the parent compound, phosphatidylinositol. Despite being minor constituents of synaptic membranes, these lipids have exceptionally high rates of metabolic turnover and are involved with myriad aspects of pre- and post-synaptic function, from the control of the synaptic vesicle cycle to postsynaptic excitability. In this review, we outline the main synaptic processes known to be regulated by these molecules, focusing mainly but not exclusively on the major species phosphatidylinositol 4-phosphate and phosphatidylinositol (4,5)-bisphosphate. Furthermore, we discuss the enzymes responsible for their synthesis and degradation, with a view to exploring how the activity-dependent control of their enzymatic action can lead to the precise regulation of PPIn levels at the nerve terminal. Also, the modulation of synaptic PPIn turnover by drugs used for the treatment of bipolar disorder is discussed. We propose that the modulation of PPIn levels may act as a central mechanism to coordinate the cascade of synaptic events leading to neurotransmission.
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Affiliation(s)
- Gerald R V Hammond
- Molecular NeuroPathobiology, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, London WC2A 3PX, United Kingdom.
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12
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Pang ZP, Sun J, Rizo J, Maximov A, Südhof TC. Genetic analysis of synaptotagmin 2 in spontaneous and Ca2+-triggered neurotransmitter release. EMBO J 2006; 25:2039-50. [PMID: 16642042 PMCID: PMC1462977 DOI: 10.1038/sj.emboj.7601103] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 03/28/2006] [Indexed: 11/09/2022] Open
Abstract
Synaptotagmin 2 resembles synaptotagmin 1, the Ca2+ sensor for fast neurotransmitter release in forebrain synapses, but little is known about synaptotagmin 2 function. Here, we describe a severely ataxic mouse strain that harbors a single, destabilizing amino-acid substitution (I377N) in synaptotagmin 2. In Calyx of Held synapses, this mutation causes a delay and a decrease in Ca2+-induced but not in hypertonic sucrose-induced release, suggesting that synaptotagmin 2 mediates Ca2+ triggering of evoked release in brainstem synapses. Unexpectedly, we additionally observed in synaptotagmin 2 mutant synapses a dramatic increase in spontaneous release. Synaptotagmin 1-deficient excitatory and inhibitory cortical synapses also displayed a large increase in spontaneous release, demonstrating that this effect was shared among synaptotagmins 1 and 2. Our data suggest that synaptotagmin 1 and 2 perform equivalent functions in the Ca2+ triggering of action potential-induced release and in the restriction of spontaneous release, consistent with a general role of synaptotagmins in controlling 'release slots' for synaptic vesicles at the active zone.
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Affiliation(s)
- Zhiping P Pang
- Departments of Molecular Genetics, Pharmacology, and Biochemistry, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX, USA
| | - Jianyuan Sun
- Departments of Molecular Genetics, Pharmacology, and Biochemistry, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX, USA
| | - Josep Rizo
- Departments of Molecular Genetics, Pharmacology, and Biochemistry, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX, USA
| | - Anton Maximov
- Departments of Molecular Genetics, Pharmacology, and Biochemistry, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX, USA
| | - Thomas C Südhof
- Departments of Molecular Genetics, Pharmacology, and Biochemistry, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX, USA
- Department of Molecular Genetics, Center for Basic Neuroscience, Howard Hughes Medical Institute, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9111 USA. Tel.: +1 214 648 1876; Fax: +1 214 648 1879; E-mail:
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Li L, Shin OH, Rhee JS, Araç D, Rah JC, Rizo J, Südhof T, Rosenmund C. Phosphatidylinositol phosphates as co-activators of Ca2+ binding to C2 domains of synaptotagmin 1. J Biol Chem 2006; 281:15845-52. [PMID: 16595652 DOI: 10.1074/jbc.m600888200] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ca2+-dependent phospholipid binding to the C2A and C2B domains of synaptotagmin 1 is thought to trigger fast neurotransmitter release, but only Ca2+ binding to the C2B domain is essential for release. To investigate the underlying mechanism, we have compared the role of basic residues in Ca2+/phospholipid binding and in release. Mutations in a polybasic sequence on the side of the C2B domain beta-sandwich or in a basic residue in a top Ca2+-binding loop of the C2A domain (R233) cause comparable decreases in the apparent Ca2+ affinity of synaptotagmin 1 and the Ca2+ sensitivity of release, whereas mutation of the residue homologous to Arg233 in the C2B domain (Lys366) has no effect. Phosphatidylinositol polyphosphates co-activate Ca2+-dependent and -independent phospholipid binding to synaptotagmin 1, but the effects of these mutations on release only correlate with their effects on the Ca2+-dependent component. These results reveal clear distinctions in the Ca2+-dependent phospholipid binding modes of the synaptotagmin 1 C2 domains that may underlie their functional asymmetry and suggest that phosphatidylinositol polyphosphates may serve as physiological modulators of Ca2+ affinity of synaptotagmin 1 in vivo.
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Affiliation(s)
- LiYi Li
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
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14
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Ferron M, Vacher J. Characterization of the murine Inpp4b gene and identification of a novel isoform. Gene 2006; 376:152-61. [PMID: 16631325 DOI: 10.1016/j.gene.2006.02.022] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2005] [Revised: 02/14/2006] [Accepted: 02/21/2006] [Indexed: 10/24/2022]
Abstract
Inositol polyphosphate phosphatases and phosphoinositides second messengers have been associated with major cellular functions as growth, differentiation, apoptosis, protein trafficking and motility. To characterize the role of inositol phosphatases in cell physiology, we have isolated the mouse Inositol polyphosphate 4-phosphatase type II (Inpp4b) cDNA. The murine Inpp4b locus was mapped on chromosome 8 in a synthenic region of the human 4q27-31 interval between Il-15 and Usp38. The mouse Inpp4b proteins, alpha and beta isoforms, encoded by this locus contained 927 and 941 amino acids respectively with a consensus phosphatase catalytic site and a conserved C2 domain that are highly similar with the human and rat homologues. Interestingly, we characterized a novel shorter isoform of Inpp4balpha resulting from an alternative translation initiation site and exon 5 skipping. Inpp4b C2 domain interacted with preferential affinity to phosphatidic acid and phosphatidylinositol 3,4,5-triphosphate (PI(3,4,5)P(3)) lipids. While analysis of Inpp4b transcript and protein expression demonstrated a broad tissue distribution for the alpha isoform, as for the paralogue Inpp4aalpha and beta isoforms, it also displayed a limited hematopoietic lineage distribution whereas the Inpp4bbeta isoform had a highly restricted pattern. Importantly, the Inpp4bbeta localized to the Golgi apparatus whereas Inpp4balpha was mainly cytosolic, suggesting a different cellular function for this isoform. Together our characterization of the murine Inpp4b gene expression pattern, cellular sublocalization and interacting lipids support highly specific function for individual Inpp4 phosphatase proteins.
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Affiliation(s)
- Mathieu Ferron
- Institut de recherches cliniques de Montreal, 110 av. des Pins O., Montreal, Qc, Canada
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15
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Morrison B, Tang Z, Jacobs B, Bauer J, Lindner D. Apo2L/TRAIL induction and nuclear translocation of inositol hexakisphosphate kinase 2 during IFN-beta-induced apoptosis in ovarian carcinoma. Biochem J 2005; 385:595-603. [PMID: 15634191 PMCID: PMC1134734 DOI: 10.1042/bj20040971] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Previously, we have reported that overexpression of IHPK2 (inositol hexakisphosphate kinase 2) sensitized NIH-OVCAR-3 ovarian carcinoma cell lines to the growth-suppressive and apoptotic effects of IFN-beta (interferon-beta) treatment and gamma-irradiation. In the present study, we demonstrate that Apo2L/TRAIL (Apo2L/tumour-necrosis-factor-related apoptosis-inducing ligand) is a critical mediator of IFN-induced apoptosis in these cells. Compared with IFN-alpha2, IFN-beta is a more potent inducer of Apo2L/TRAIL and IHPK2 activity. Overexpression of IHPK2 converts IFN-alpha2-resistant cells into cells that readily undergo apoptosis in response to IFN-alpha2. In untreated cells transfected with IHPK2-eGFP (where eGFP stands for enhanced green fluorescent protein), the fusion protein is localized to the cytoplasm and perinuclear region. After treatment with IFN-beta, IHPK2-eGFP translocated to the nucleus. In cells transfected with mutant IHPK2-NLS-eGFP (where NLS stands for nuclear localization sequence), containing point mutations in the NLS, the fusion protein remained trapped in the cytoplasm, even after IFN-beta treatment. Cells expressing mutant NLS mutation were more resistant to IFN-beta. The IC50 value of IHPK2-expressing cells was 2-3-fold lower than vector control. The IC50 value of NLS-mutant-expressing cells was 3-fold higher than vector control. Blocking antibodies to Apo2L/TRAIL or transfection with a dominant negative Apo2L/TRAIL receptor (DR5Delta) inhibited the antiproliferative effects of IFN-beta. Thus overexpression of IHPK2 enhanced apoptotic effects of IFN-beta, and expression of the NLS mutant conferred resistance to IFN-beta. Apo2L/TRAIL expression and nuclear localization of IHPK2 are both required for the induction of apoptosis by IFN-beta in ovarian carcinoma.
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Affiliation(s)
- Bei H. Morrison
- Center for Cancer Drug Development and Discovery, Taussig Cancer Center, Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, U.S.A
| | - Zhuo Tang
- Center for Cancer Drug Development and Discovery, Taussig Cancer Center, Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, U.S.A
| | - Barbara S. Jacobs
- Center for Cancer Drug Development and Discovery, Taussig Cancer Center, Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, U.S.A
| | - Joseph A. Bauer
- Center for Cancer Drug Development and Discovery, Taussig Cancer Center, Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, U.S.A
| | - Daniel J. Lindner
- Center for Cancer Drug Development and Discovery, Taussig Cancer Center, Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, U.S.A
- To whom correspondence should be addressed (email )
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16
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Abstract
Research in the past decade has revealed that many cytosolic proteins are recruited to different cellular membranes to form protein-protein and lipid-protein interactions during cell signaling and membrane trafficking. Membrane recruitment of these peripheral proteins is mediated by a growing number of modular membrane-targeting domains, including C1, C2, PH, FYVE, PX, ENTH, ANTH, BAR, FERM, and tubby domains, that recognize specific lipid molecules in the membranes. Structural studies of these membrane-targeting domains demonstrate how they specifically recognize their cognate lipid ligands. However, the mechanisms by which these domains and their host proteins are recruited to and interact with various cell membranes are only beginning to unravel with recent computational studies, in vitro membrane binding studies using model membranes, and cellular translocation studies using fluorescent protein-tagged proteins. This review summarizes the recent progress in our understanding of how the kinetics and energetics of membrane-protein interactions are regulated during the cellular membrane targeting and activation of peripheral proteins.
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Affiliation(s)
- Wonhwa Cho
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607-7061, USA.
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17
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Dunn R, Klos DA, Adler AS, Hicke L. The C2 domain of the Rsp5 ubiquitin ligase binds membrane phosphoinositides and directs ubiquitination of endosomal cargo. ACTA ACUST UNITED AC 2004; 165:135-44. [PMID: 15078904 PMCID: PMC2172079 DOI: 10.1083/jcb.200309026] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ubiquitin ligases of the Nedd4 family regulate membrane protein trafficking by modifying both cargo proteins and the transport machinery with ubiquitin. Here, we investigate the role of the yeast Nedd4 homologue, Rsp5, in protein sorting into vesicles that bud into the multivesicular endosome (MVE) en route to the vacuole. A mutant lacking the Rsp5 C2 domain is unable to ubiquitinate or sort biosynthetic cargo into MVE vesicles, whereas endocytic cargo is ubiquitinated and sorted efficiently. The C2 domain binds specifically to phosphoinositides in vitro and is sufficient for localization to membranes in intact cells. Mutation of a lysine-rich patch on the surface of the C2 domain abolishes membrane interaction and disrupts sorting of biosynthetic cargo. Translational fusion of ubiquitin to a biosynthetic cargo protein alleviates the requirement for the C2 domain in its MVE sorting. These results demonstrate that the C2 domain specifies Rsp5-dependent ubiquitination of endosomal cargo and suggest that Rsp5 function is regulated by membrane phosphoinositides.
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Affiliation(s)
- Rebecca Dunn
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Hogan 2-100, 2205 Tech Dr., Evanston, IL 60208-3500, USA
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18
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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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19
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Uldry M, Steiner P, Zurich MG, Béguin P, Hirling H, Dolci W, Thorens B. Regulated exocytosis of an H+/myo-inositol symporter at synapses and growth cones. EMBO J 2004; 23:531-40. [PMID: 14749729 PMCID: PMC1271806 DOI: 10.1038/sj.emboj.7600072] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Accepted: 12/16/2003] [Indexed: 01/12/2023] Open
Abstract
Phosphoinositides, synthesized from myo-inositol, play a critical role in the development of growth cones and in synaptic activity. As neurons cannot synthesize inositol, they take it up from the extracellular milieu. Here, we demonstrate that, in brain and PC12 cells, the recently identified H(+)/myo-inositol symporter HMIT is present in intracellular vesicles that are distinct from synaptic and dense-core vesicles. We further show that HMIT can be triggered to appear on the cell surface following cell depolarization, activation of protein kinase C or increased intracellular calcium concentrations. HMIT cell surface expression takes place preferentially in regions of nerve growth and at varicosities and leads to increased myo-inositol uptake. The symporter is then endocytosed in a dynamin-dependent manner and becomes available for a subsequent cycle of stimulated exocytosis. HMIT is thus expressed in a vesicular compartment involved in activity-dependent regulation of myo-inositol uptake in neurons. This may be essential for sustained signaling and vesicular traffic activities in growth cones and at synapses.
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Affiliation(s)
- Marc Uldry
- Institute of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Pascal Steiner
- Faculte des Sciences de la Vie, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | | | - Pascal Béguin
- Institute of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Harald Hirling
- Faculte des Sciences de la Vie, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Wanda Dolci
- Institute of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Bernard Thorens
- Institute of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
- Institute of Physiology, University of Lausanne, Lausanne, Switzerland
- Institute of Pharmacology and Toxicology, University of Lausanne, 27 rue du Bugnon, CH-1005 Lausanne, Switzerland. Tel.: +41 21 692 5390; Fax: +41 21 692 5355; E-mail:
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20
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Abstract
In eukaryotes, phosphatidylserine (PtdSer) can serve as a precursor of phosphatidylethanolamine (PtdEtn) and phosphatidylcholine (PtdCho), which are the major cellular phospholipids. PtdSer synthesis originates in the endoplasmic reticulum (ER) and its subdomain named the mitochondria-associated membrane (MAM). PtdSer is transported to the mitochondria in mammalian cells and yeast, and decarboxylated by PtdSer decarboxylase 1 (Psd1p) to form PtdEtn. A second decarboxylase, Psd2p, is also found in yeast in the Golgi-vacuole. PtdEtn produced by Psd1p and Psd2p can be transported to the ER, where it is methylated to form PtdCho. Organelle-specific metabolism of the aminoglycerophospholipids is a powerful tool for experimentally following lipid traffic that is now enabling identification of new proteins involved in the regulation of this process. Genetic and biochemical experiments demonstrate that transport of PtdSer between the MAM and mitochondria is regulated by protein ubiquitination, which affects events at both membranes. Similar analyses of PtdSer transport to the locus of Psd2p now indicate that a membrane-bound phosphatidylinositol transfer protein and the C2 domain of Psd2p are both required on the acceptor membrane for efficient transport of PtdSer. Collectively, these recent findings indicate that novel multiprotein assemblies on both donor and acceptor membranes participate in interorganelle phospholipid transport.
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Affiliation(s)
- Dennis R Voelker
- Program in Cell Biology, Department of Medicine, National Jewish Medical and Research Center, 1400 Jackson St., Denver, CO 80206, USA.
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21
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Kitamura H, Wu WI, Voelker DR. The C2 domain of phosphatidylserine decarboxylase 2 is not required for catalysis but is essential for in vivo function. J Biol Chem 2002; 277:33720-6. [PMID: 12093819 DOI: 10.1074/jbc.m205672200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphatidylserine decarboxylase 2 (Psd2p) is currently being used to study lipid trafficking processes in intact and permeabilized yeast cells. The Psd2p contains a C2 homology domain and a putative Golgi retention/localization (GR) domain. C2 domains play important functions in membrane binding and docking reactions involving phospholipids and proteins. We constructed a C2 domain deletion variant (C2Delta) and a GR deletion variant (GRDelta) of Psd2p and examined their effects on in vivo function and catalysis. Immunoblotting confirmed that the predicted immature and mature forms of Psd2(C2Delta)p, Psd2(GRDelta)p, and wild type Psd2p were produced in vivo and that the proteins localized normally. Enzymology revealed that the Psd2(C2Delta)p and Psd2(GRDelta)p were catalytically active and could readily be expressed at levels 10-fold higher than endogenous Psd2p. Both Psd2p and Psd2(GRDelta)p expression complemented the growth defect of psd1Deltapsd2Delta strains and resulted in normal aminoglycerophospholipid metabolism. In contrast, the Psd2(C2Delta)p failed to complement psd1Deltapsd2Delta strains, and [(3)H]serine labeling revealed a severe defect in the formation of PtdEtn in both intact and permeabilized cells, indicative of disruption of lipid trafficking. These findings identify an essential, non-catalytic function of the C2 domain of Psd2p and raise the possibility that it plays a direct role in membrane docking and/or PtdSer transport to the enzyme.
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Affiliation(s)
- Hidemitsu Kitamura
- Program in Cell Biology, Department of Medicine, National Jewish Medical and Research Center, Denver, CO 80206, USA
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22
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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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23
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Morrison BH, Bauer JA, Hu J, Grane RW, Ozdemir AM, Chawla-Sarkar M, Gong B, Almasan A, Kalvakolanu DV, Lindner DJ. Inositol hexakisphosphate kinase 2 sensitizes ovarian carcinoma cells to multiple cancer therapeutics. Oncogene 2002; 21:1882-9. [PMID: 11896621 PMCID: PMC2043497 DOI: 10.1038/sj.onc.1205265] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2001] [Revised: 12/11/2001] [Accepted: 12/18/2001] [Indexed: 12/29/2022]
Abstract
We recently identified inositol hexakisphosphate kinase 2 (IP6K2) as a positive regulator of apoptosis. Overexpression of IP6K2 enhances apoptosis induced by interferon-beta (IFN-beta) and cytotoxic agents in NIH-OVCAR-3 ovarian carcinoma cells. In this study, we contrast and compare IFN-beta and radiation-induced death, and show that IP6K2 expression sensitizes tumor cells. Unirradiated NIH-OVCAR-3 cells transfected with IP6K2 formed fewer colonies compared to unirradiated vector-expressing cells. IP6K2 overexpression caused increased radiosensitivity, evidenced by decreased colony forming units (CFU). Both IFN-beta and radiation induced caspase 8. IFN-beta, but not gamma-irradiation, induced TRAIL in NIH-OVCAR-3 cells. Gamma irradiation, but not IFN-beta, induced DR4 mRNA. Apoptotic effects of IFN-beta or gamma-irradiation were blocked by expression of a dominant negative mutant death receptor 5 (DR5Delta) or by Bcl-2. Caspase-8 mRNA induction was more pronounced in IP6K2-expressing cells compared to vector-expressing cells. These data suggest that overexpression of IP6K2 enhances sensitivity of some ovarian carcinomas to radiation and IFN-beta. IP6K2 may function to enhance the expression and/or function of caspase 8 and DR4 following cell injury. Both IFN-beta and gamma-irradiation induce apoptosis through the extrinsic, receptor-mediated pathway, IFN-beta through TRAIL, radiation through DR4, and both through caspase 8. The function of both death inducers is positively regulated by IP6K2.
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Affiliation(s)
- Bei H Morrison
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Joseph A Bauer
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Jiadi Hu
- Department of Microbiology and Immunology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland, MD 21201, USA
| | - Ronald W Grane
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Aylin M Ozdemir
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Mamta Chawla-Sarkar
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Bendi Gong
- Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Alex Almasan
- Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
- Department of Radiation Oncology, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
| | - Dhananjaya V Kalvakolanu
- Department of Microbiology and Immunology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland, MD 21201, USA
| | - Daniel J Lindner
- Center for Cancer Drug Discovery and Development, Taussig Cancer Center, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
- Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA
- Correspondence: DJ Lindner, 9500 Euclid Avenue, R40, Cleveland, OH 44195, USA; E-mail:
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24
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Irigoín F, Ferreira F, Fernández C, Sim RB, Díaz A. myo-Inositol hexakisphosphate is a major component of an extracellular structure in the parasitic cestode Echinococcus granulosus. Biochem J 2002; 362:297-304. [PMID: 11853537 PMCID: PMC1222389 DOI: 10.1042/0264-6021:3620297] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
myo-Inositol hexakisphosphate (IP(6)) is an abundant intracellular component of animal cells. In this study we describe the presence of extracellular IP(6) in the hydatid cyst wall (HCW) of the larval stage of the cestode parasite Echinococcus granulosus. The HCW comprises an inner cellular layer and an outer, acellular (laminated) layer up to 2 mm in thickness that protects the parasite from host immune cells. A compound, subsequently identified as IP(6), was detected in and purified from an HCW extract on the basis of its capacity to inhibit complement activation. The identification of the isolated compound was carried out by a combination of NMR, MS and TLC. The majority of IP(6) in the HCW was found in the acellular layer, with only a small fraction of the compound being extracted from cells. In the laminated layer, IP(6) was present in association with calcium, and accounted for up to 15% of the total dry mass of the HCW. IP(6) was not detected in any other structures or stages of the parasite. Our results imply that IP(6) is secreted by the larval stage of the parasite in a polarized fashion towards the interface with the host. This is the first report of the secretion of IP(6), and the possible implications beyond the biology of E. granulosus are discussed.
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Affiliation(s)
- Florencia Irigoín
- Cátedra de Inmunología, Facultad de Química/Ciencias, Universidad de la República, Avenida Alfredo Navarro 3051, piso 2, CP 11600, Montevideo, Uruguay
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25
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Affiliation(s)
- W Cho
- Department of Chemistry (M/C 111), University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.
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26
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Abstract
We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.
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Affiliation(s)
- R L Rich
- Center for Biomolecular Interaction Analysis, University of Utah, Salt Lake City, UT 84132, USA
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27
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Uldry M, Ibberson M, Horisberger JD, Chatton JY, Riederer BM, Thorens B. Identification of a mammalian H(+)-myo-inositol symporter expressed predominantly in the brain. EMBO J 2001; 20:4467-77. [PMID: 11500374 PMCID: PMC125574 DOI: 10.1093/emboj/20.16.4467] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Inositol and its phosphorylated derivatives play a major role in brain function, either as osmolytes, second messengers or regulators of vesicle endo- and exocytosis. Here we describe the identification and functional characterization of a novel H(+)-myo- inositol co-transporter, HMIT, expressed predominantly in the brain. HMIT cDNA encodes a 618 amino acid polypeptide with 12 predicted transmembrane domains. Functional expression of HMIT in Xenopus oocytes showed that transport activity was specific for myo-inositol and related stereoisomers with a Michaelis-Menten constant of approximately 100 microM, and that transport activity was strongly stimulated by decreasing pH. Electrophysiological measurements revealed that transport was electrogenic with a maximal transport activity reached at pH 5.0. In rat brain membrane preparations, HMIT appeared as a 75-90 kDa protein that could be converted to a 67 kDa band upon enzymatic deglycosylation. Immunofluorescence microscopy analysis showed HMIT expression in glial cells and some neurons. These data provide the first characterization of a mammalian H(+)-coupled myo- inositol transporter. Predominant central expression of HMIT suggests that it has a key role in the control of myo-inositol brain metabolism.
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Affiliation(s)
| | | | | | - Jean-Yves Chatton
- Institute of Pharmacology and Toxicology,
Institute of Physiology and Institute of Cell Biology and Morphology, University of Lausanne, Lausanne, Switzerland Corresponding author e-mail:
| | - Beat M. Riederer
- Institute of Pharmacology and Toxicology,
Institute of Physiology and Institute of Cell Biology and Morphology, University of Lausanne, Lausanne, Switzerland Corresponding author e-mail:
| | - Bernard Thorens
- Institute of Pharmacology and Toxicology,
Institute of Physiology and Institute of Cell Biology and Morphology, University of Lausanne, Lausanne, Switzerland Corresponding author e-mail:
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28
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Santagata S, Boggon TJ, Baird CL, Gomez CA, Zhao J, Shan WS, Myszka DG, Shapiro L. G-protein signaling through tubby proteins. Science 2001; 292:2041-50. [PMID: 11375483 DOI: 10.1126/science.1061233] [Citation(s) in RCA: 295] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Dysfunction of the tubby protein results in maturity-onset obesity in mice. Tubby has been implicated as a transcription regulator, but details of the molecular mechanism underlying its function remain unclear. Here we show that tubby functions in signal transduction from heterotrimeric GTP-binding protein (G protein)-coupled receptors. Tubby localizes to the plasma membrane by binding phosphatidylinositol 4,5-bisphosphate through its carboxyl terminal "tubby domain." X-ray crystallography reveals the atomic-level basis of this interaction and implicates tubby domains as phosphorylated-phosphatidyl- inositol binding factors. Receptor-mediated activation of G protein alphaq (Galphaq) releases tubby from the plasma membrane through the action of phospholipase C-beta, triggering translocation of tubby to the cell nucleus. The localization of tubby-like protein 3 (TULP3) is similarly regulated. These data suggest that tubby proteins function as membrane-bound transcription regulators that translocate to the nucleus in response to phosphoinositide hydrolysis, providing a direct link between G-protein signaling and the regulation of gene expression.
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MESH Headings
- Active Transport, Cell Nucleus
- Adaptor Proteins, Signal Transducing
- Amino Acid Sequence
- Animals
- Cell Membrane/metabolism
- Cell Nucleus/metabolism
- Cells, Cultured
- Crystallography, X-Ray
- GTP-Binding Protein alpha Subunits, Gq-G11
- Gene Expression Regulation
- Heterotrimeric GTP-Binding Proteins/metabolism
- Humans
- Intercellular Signaling Peptides and Proteins
- Intracellular Signaling Peptides and Proteins
- Isoenzymes/metabolism
- Membrane Lipids/metabolism
- Mice
- Models, Biological
- Molecular Sequence Data
- Nuclear Localization Signals
- Obesity/genetics
- Obesity/metabolism
- Phosphatidylinositol 4,5-Diphosphate/metabolism
- Phosphatidylinositol Phosphates/metabolism
- Phospholipase C beta
- Phosphorylation
- Protein Structure, Tertiary
- Proteins/chemistry
- Proteins/genetics
- Proteins/metabolism
- Receptor, Serotonin, 5-HT2C
- Receptors, Muscarinic/metabolism
- Receptors, Serotonin/metabolism
- Recombinant Fusion Proteins/metabolism
- Signal Transduction
- Transcription Factors/chemistry
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Type C Phospholipases/metabolism
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Affiliation(s)
- S Santagata
- Ruttenberg Cancer Center, Structural Biology Program, Department of Physiology and Biophysics, Mount Sinai School of Medicine of New York University, 1425 Madison Avenue New York, NY 10029, USA
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29
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Abstract
Following the discovery of inositol-1,4,5-trisphosphate as a second messenger, many other inositol phosphates were discovered in quick succession, with some understanding of their synthesis pathways and a few guesses at their possible functions. But then it all seemed to go comparatively quiet, with an explosion of interest in the inositol lipids. Now the water-soluble phase is once again becoming a focus of interest. Old and new data point to a new vista of inositol phosphates, with functions in many diverse aspects of cell biology, such as ion-channel physiology, membrane dynamics and nuclear signalling.
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Affiliation(s)
- R F Irvine
- Department of Pharmacology, Tennis Court Road, Cambridge CB2 1QJ, UK.
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30
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Abstract
This review assesses the authenticity of inositol hexakisphosphate (InsP(6)) being a wide-ranging regulator of many important cellular functions. Against a background in which the possible importance of localized InsP(6) metabolism is discussed, there is the facile explanation that InsP(6) is merely an "inactive" precursor for the diphosphorylated inositol phosphates. Indeed, many of the proposed cellular functions of InsP(6) cannot sustain a challenge from the implementation of a rigorous set of criteria, which are designed to avoid experimental artefacts.
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Affiliation(s)
- S B Shears
- Inositol Signaling Section, Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, 27709, Research Triangle Park, NC, USA.
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