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Schäfer JH, Körner C, Esch BM, Limar S, Parey K, Walter S, Januliene D, Moeller A, Fröhlich F. Structure of the ceramide-bound SPOTS complex. Nat Commun 2023; 14:6196. [PMID: 37794019 PMCID: PMC10550967 DOI: 10.1038/s41467-023-41747-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 09/05/2023] [Indexed: 10/06/2023] Open
Abstract
Sphingolipids are structural membrane components that also function in cellular stress responses. The serine palmitoyltransferase (SPT) catalyzes the rate-limiting step in sphingolipid biogenesis. Its activity is tightly regulated through multiple binding partners, including Tsc3, Orm proteins, ceramides, and the phosphatidylinositol-4-phosphate (PI4P) phosphatase Sac1. The structural organization and regulatory mechanisms of this complex are not yet understood. Here, we report the high-resolution cryo-EM structures of the yeast SPT in complex with Tsc3 and Orm1 (SPOT) as dimers and monomers and a monomeric complex further carrying Sac1 (SPOTS). In all complexes, the tight interaction of the downstream metabolite ceramide and Orm1 reveals the ceramide-dependent inhibition. Additionally, observation of ceramide and ergosterol binding suggests a co-regulation of sphingolipid biogenesis and sterol metabolism within the SPOTS complex.
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Affiliation(s)
- Jan-Hannes Schäfer
- Osnabrück University Department of Biology/Chemistry Structural Biology section, 49076, Osnabrück, Germany
| | - Carolin Körner
- Osnabrück University Department of Biology/Chemistry Bioanalytical Chemistry section, 49076, Osnabrück, Germany
| | - Bianca M Esch
- Osnabrück University Department of Biology/Chemistry Bioanalytical Chemistry section, 49076, Osnabrück, Germany
| | - Sergej Limar
- Osnabrück University Department of Biology/Chemistry Bioanalytical Chemistry section, 49076, Osnabrück, Germany
| | - Kristian Parey
- Osnabrück University Department of Biology/Chemistry Structural Biology section, 49076, Osnabrück, Germany
- Osnabrück University Center of Cellular Nanoanalytic Osnabrück (CellNanOs), 49076, Osnabrück, Germany
| | - Stefan Walter
- Osnabrück University Center of Cellular Nanoanalytic Osnabrück (CellNanOs), 49076, Osnabrück, Germany
| | - Dovile Januliene
- Osnabrück University Department of Biology/Chemistry Structural Biology section, 49076, Osnabrück, Germany.
- Osnabrück University Center of Cellular Nanoanalytic Osnabrück (CellNanOs), 49076, Osnabrück, Germany.
| | - Arne Moeller
- Osnabrück University Department of Biology/Chemistry Structural Biology section, 49076, Osnabrück, Germany.
- Osnabrück University Center of Cellular Nanoanalytic Osnabrück (CellNanOs), 49076, Osnabrück, Germany.
| | - Florian Fröhlich
- Osnabrück University Department of Biology/Chemistry Bioanalytical Chemistry section, 49076, Osnabrück, Germany.
- Osnabrück University Center of Cellular Nanoanalytic Osnabrück (CellNanOs), 49076, Osnabrück, Germany.
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2
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Arabiotorre A, Bankaitis VA, Grabon A. Regulation of phosphoinositide metabolism in Apicomplexan parasites. Front Cell Dev Biol 2023; 11:1163574. [PMID: 37791074 PMCID: PMC10543664 DOI: 10.3389/fcell.2023.1163574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Accepted: 07/11/2023] [Indexed: 10/05/2023] Open
Abstract
Phosphoinositides are a biologically essential class of phospholipids that contribute to organelle membrane identity, modulate membrane trafficking pathways, and are central components of major signal transduction pathways that operate on the cytosolic face of intracellular membranes in eukaryotes. Apicomplexans (such as Toxoplasma gondii and Plasmodium spp.) are obligate intracellular parasites that are important causative agents of disease in animals and humans. Recent advances in molecular and cell biology of Apicomplexan parasites reveal important roles for phosphoinositide signaling in key aspects of parasitosis. These include invasion of host cells, intracellular survival and replication, egress from host cells, and extracellular motility. As Apicomplexans have adapted to the organization of essential signaling pathways to accommodate their complex parasitic lifestyle, these organisms offer experimentally tractable systems for studying the evolution, conservation, and repurposing of phosphoinositide signaling. In this review, we describe the regulatory mechanisms that control the spatial and temporal regulation of phosphoinositides in the Apicomplexan parasites Plasmodium and T. gondii. We further discuss the similarities and differences presented by Apicomplexan phosphoinositide signaling relative to how these pathways are regulated in other eukaryotic organisms.
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Affiliation(s)
- Angela Arabiotorre
- Department of Cell Biology and Genetics, College of Medicine Texas A&M Health Sciences Center College Station, Bryan, TX, United States
| | - Vytas A. Bankaitis
- Department of Cell Biology and Genetics, College of Medicine Texas A&M Health Sciences Center College Station, Bryan, TX, United States
- Department of Biochemistry and Biophysics Texas A&M University College Station, College Station, TX, United States
- Department of Chemistry Texas A&M University College Station, College Station, TX, United States
| | - Aby Grabon
- Department of Cell Biology and Genetics, College of Medicine Texas A&M Health Sciences Center College Station, Bryan, TX, United States
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3
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Vormittag S, Ende RJ, Derré I, Hilbi H. Pathogen vacuole membrane contact sites - close encounters of the fifth kind. MICROLIFE 2023; 4:uqad018. [PMID: 37223745 PMCID: PMC10117887 DOI: 10.1093/femsml/uqad018] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 03/30/2023] [Accepted: 04/06/2023] [Indexed: 05/25/2023]
Abstract
Vesicular trafficking and membrane fusion are well-characterized, versatile, and sophisticated means of 'long range' intracellular protein and lipid delivery. Membrane contact sites (MCS) have been studied in far less detail, but are crucial for 'short range' (10-30 nm) communication between organelles, as well as between pathogen vacuoles and organelles. MCS are specialized in the non-vesicular trafficking of small molecules such as calcium and lipids. Pivotal MCS components important for lipid transfer are the VAP receptor/tether protein, oxysterol binding proteins (OSBPs), the ceramide transport protein CERT, the phosphoinositide phosphatase Sac1, and the lipid phosphatidylinositol 4-phosphate (PtdIns(4)P). In this review, we discuss how these MCS components are subverted by bacterial pathogens and their secreted effector proteins to promote intracellular survival and replication.
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Affiliation(s)
| | | | - Isabelle Derré
- Corresponding author. Department of Microbiology, Immunology and Cancer Biology, University of Virginia, 1340 Jefferson Park Ave, Charlottesville, VA 22908, United States. Tel: +1-434-924-2330; E-mail:
| | - Hubert Hilbi
- Corresponding author. Institute of Medical Microbiology, University of Zürich, Gloriastrasse 30, 8006 Zürich, Switzerland. Tel: +41-44-634-2650; E-mail:
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4
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Mao Y, Tan S. Functions and Mechanisms of SAC Phosphoinositide Phosphatases in Plants. FRONTIERS IN PLANT SCIENCE 2021; 12:803635. [PMID: 34975993 PMCID: PMC8717918 DOI: 10.3389/fpls.2021.803635] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Accepted: 11/30/2021] [Indexed: 06/14/2023]
Abstract
Phosphatidylinositol (PtdIns) is one type of phospholipid comprising an inositol head group and two fatty acid chains covalently linked to the diacylglycerol group. In addition to their roles as compositions of cell membranes, phosphorylated PtdIns derivatives, termed phosphoinositides, execute a wide range of regulatory functions. PtdIns can be phosphorylated by various lipid kinases at 3-, 4- and/or 5- hydroxyls of the inositol ring, and the phosphorylated forms, including PtdIns3P, PtdIns4P, PtdIns5P, PtdIns(3,5)P2, PtdIns(4,5)P2, can be reversibly dephosphorylated by distinct lipid phosphatases. Amongst many other types, the SUPPRESSOR OF ACTIN (SAC) family of phosphoinositide phosphatases recently emerged as important regulators in multiple growth and developmental processes in plants. Here, we review recent advances on the biological functions, cellular activities, and molecular mechanisms of SAC domain-containing phosphoinositide phosphatases in plants. With a focus on those studies in the model plant Arabidopsis thaliana together with progresses in other plants, we highlight the important roles of subcellular localizations and substrate preferences of various SAC isoforms in their functions.
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Affiliation(s)
- Yanbo Mao
- MOE Key Laboratory for Cellular Dynamics, School of Life Sciences, Division of Molecular and Cell Biophysics, Division of Life Sciences and Medicine, Hefei National Science Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
| | - Shutang Tan
- MOE Key Laboratory for Cellular Dynamics, School of Life Sciences, Division of Molecular and Cell Biophysics, Division of Life Sciences and Medicine, Hefei National Science Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
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5
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Emerging Prospects for Combating Fungal Infections by Targeting Phosphatidylinositol Transfer Proteins. Int J Mol Sci 2021; 22:ijms22136754. [PMID: 34201733 PMCID: PMC8269425 DOI: 10.3390/ijms22136754] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/11/2021] [Accepted: 06/11/2021] [Indexed: 12/27/2022] Open
Abstract
The emergence of fungal “superbugs” resistant to the limited cohort of anti-fungal agents available to clinicians is eroding our ability to effectively treat infections by these virulent pathogens. As the threat of fungal infection is escalating worldwide, this dwindling response capacity is fueling concerns of impending global health emergencies. These developments underscore the urgent need for new classes of anti-fungal drugs and, therefore, the identification of new targets. Phosphoinositide signaling does not immediately appear to offer attractive targets due to its evolutionary conservation across the Eukaryota. However, recent evidence argues otherwise. Herein, we discuss the evidence identifying Sec14-like phosphatidylinositol transfer proteins (PITPs) as unexplored portals through which phosphoinositide signaling in virulent fungi can be chemically disrupted with exquisite selectivity. Recent identification of lead compounds that target fungal Sec14 proteins, derived from several distinct chemical scaffolds, reveals exciting inroads into the rational design of next generation Sec14 inhibitors. Development of appropriately refined next generation Sec14-directed inhibitors promises to expand the chemical weaponry available for deployment in the shifting field of engagement between fungal pathogens and their human hosts.
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Zhang H, Zhou J, Xiao P, Lin Y, Gong X, Liu S, Xu Q, Wang M, Ren H, Lu M, Wang Y, Zhu J, Xie Z, Li H, Lu K. PtdIns4P restriction by hydrolase SAC1 decides specific fusion of autophagosomes with lysosomes. Autophagy 2020; 17:1907-1917. [PMID: 32693712 DOI: 10.1080/15548627.2020.1796321] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Biogenesis of autophagosomes is the early step of macroautophagy/autophagy and requires membrane acquisition mainly from ER-Golgi-sourced precursor vesicles. Matured autophagosomes fuse with lysosomes for final degradation. However, how this selective fusion is determined remains elusive. Here, we identified Sac1 by a high throughput screen in Saccharomyces cerevisiae to show it was critical for autophagosome-lysosome fusion through its PtdIns4P phosphatase activity. Sac1 deficiency caused a dramatic increase of PtdIns4P at early Golgi apparatus and abnormal incorporation of PtdIns4P into Atg9 vesicles and autophagosomes, which caused failure to recruit SNARE proteins for autophagosome fusion with vacuoles. Sac1 function in autophagy was highly conserved from yeast to mammalian cells. Our work thus suggested that correct upstream lipid incorporation was important for downstream fusion step of autophagy and that Sac1 played a critical and ancient role in this surveillance of lipid integration.Abbreviations: Ape1: aminopeptidase Ι; ATG: autophagy related; EBSS: Earle's balanced salt solution; ER: endoplasmic reticulum; ERGIC: Golgi apparatus and ER-Golgi intermediate compartment; HOPS: homotypic fusion and protein sorting complex; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns4K: phosphoinositide-4-kinase; PtdIns4P: phosphatidylinositol-4-phosphate; SD-N: nitrogen starvation medium; SNARE: soluble N-ethylamide-sensitive factor attachment protein receptor.
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Affiliation(s)
- Hongjun Zhang
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Jiao Zhou
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Peng Xiao
- Department of Neurology, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Yong Lin
- Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Chongqing Medical University, Chongqing, China
| | - Xin Gong
- Department of Respiratory, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Shiyan Liu
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Qingjia Xu
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Minjin Wang
- Department of Clinical Laboratory, West China Hospital, Sichuan University, Chengdu, China
| | - Haiyan Ren
- Department of Respiratory, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Mengji Lu
- Institute of Virology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Yuan Wang
- Department of Neurology, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
| | - Jing Zhu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Zhiping Xie
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Huihui Li
- West China Second University Hospital, Sichuan University, Chengdu, China
| | - Kefeng Lu
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China
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7
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Lipp NF, Ikhlef S, Milanini J, Drin G. Lipid Exchangers: Cellular Functions and Mechanistic Links With Phosphoinositide Metabolism. Front Cell Dev Biol 2020; 8:663. [PMID: 32793602 PMCID: PMC7385082 DOI: 10.3389/fcell.2020.00663] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 07/01/2020] [Indexed: 12/28/2022] Open
Abstract
Lipids are amphiphilic molecules that self-assemble to form biological membranes. Thousands of lipid species coexist in the cell and, once combined, define organelle identity. Due to recent progress in lipidomic analysis, we now know how lipid composition is finely tuned in different subcellular regions. Along with lipid synthesis, remodeling and flip-flop, lipid transfer is one of the active processes that regulates this intracellular lipid distribution. It is mediated by Lipid Transfer Proteins (LTPs) that precisely move certain lipid species across the cytosol and between the organelles. A particular subset of LTPs from three families (Sec14, PITP, OSBP/ORP/Osh) act as lipid exchangers. A striking feature of these exchangers is that they use phosphatidylinositol or phosphoinositides (PIPs) as a lipid ligand and thereby have specific links with PIP metabolism and are thus able to both control the lipid composition of cellular membranes and their signaling capacity. As a result, they play pivotal roles in cellular processes such as vesicular trafficking and signal transduction at the plasma membrane. Recent data have shown that some PIPs are used as energy by lipid exchangers to generate lipid gradients between organelles. Here we describe the importance of lipid counter-exchange in the cell, its structural basis, and presumed links with pathologies.
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Affiliation(s)
- Nicolas-Frédéric Lipp
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Université Côte d'Azur, Valbonne, France
| | - Souade Ikhlef
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Université Côte d'Azur, Valbonne, France
| | - Julie Milanini
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Université Côte d'Azur, Valbonne, France
| | - Guillaume Drin
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Université Côte d'Azur, Valbonne, France
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8
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Wang Y, Mousley CJ, Lete MG, Bankaitis VA. An equal opportunity collaboration between lipid metabolism and proteins in the control of membrane trafficking in the trans-Golgi and endosomal systems. Curr Opin Cell Biol 2019; 59:58-72. [PMID: 31039522 DOI: 10.1016/j.ceb.2019.03.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 03/25/2019] [Accepted: 03/27/2019] [Indexed: 12/18/2022]
Abstract
Recent years have witnessed the evolution of the cell biology of lipids into an extremely active area of investigation. Deciphering the involvement of lipid metabolism and lipid signaling in membrane trafficking pathways defines a major nexus of contemporary experimental activity on this front. Significant effort in that direction is invested in understanding the trans-Golgi network/endosomal system where unambiguous connections between membrane trafficking and inositol lipid and phosphatidylcholine metabolism were first discovered. However, powered by new advances in contemporary cell biology, the march of science is rapidly expanding that window of inquiry to include ever more diverse arms of the lipid metabolome, and to include other compartments of the secretory pathway as well.
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Affiliation(s)
- Yaxi Wang
- Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX 77843-2128, USA
| | - Carl J Mousley
- School of Biomedical Sciences, Curtin Health Innovation Research Institute (CHIRI), Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
| | - Marta G Lete
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, USA
| | - Vytas A Bankaitis
- Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX 77843-2128, USA; Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, USA.
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9
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Panagabko C, Baptist M, Atkinson J. In vitro lipid transfer assays of phosphatidylinositol transfer proteins provide insight into the in vivo mechanism of ligand transfer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1861:619-630. [PMID: 30543784 DOI: 10.1016/j.bbamem.2018.12.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 12/06/2018] [Accepted: 12/07/2018] [Indexed: 11/16/2022]
Abstract
Fluorescence resonance energy transfer (FRET) assays and membrane binding determinations were performed using three phosphatidylinositol transfer proteins, including the yeast Sec14 and two mammalian proteins PITPα and PITPβ. These proteins were able to specifically bind the fluorescent phosphatidylcholine analogue NBD-PC ((2-(12-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine)) and to transfer it to small unilamellar vesicles (SUVs). Rate constants for transfer to vesicles comprising 100% PC were slower for all proteins than when increasing percentages of phosphatidylinositol were incorporated into the same SUVs. The rates of ligand transfer by Sec14 were insensitive to the inclusion of equimolar amounts of another anionic phospholipid phosphatidylserine (PS), but the rates of ligand transfer by both mammalian PITPs were strikingly enhanced by the inclusion of phosphatidic acid (PA) in the receptor SUV. Binding of Sec14 to immobilized bilayers was substantial, while that of PITPα and PITPβ was 3-7 times weaker than Sec14 depending on phospholipid composition. When small proportions of the phosphoinositide PI(4)P were included in receptor SUVs (either with PI or not), Sec14 showed substantially increased rates of NBD-PC pick-up, whereas the PITPs were unaffected. The data are supportive of a role for PITPβ as functional PI transfer protein in vivo, but that Sec14 likely has a more elaborate function.
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Affiliation(s)
- Candace Panagabko
- Department of Chemistry and Centre for Biotechnology, Brock University, St. Catharines, Ontario L2A 3S1, Canada
| | - Matilda Baptist
- Department of Chemistry and Centre for Biotechnology, Brock University, St. Catharines, Ontario L2A 3S1, Canada
| | - Jeffrey Atkinson
- Department of Chemistry and Centre for Biotechnology, Brock University, St. Catharines, Ontario L2A 3S1, Canada.
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10
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Del Bel LM, Griffiths N, Wilk R, Wei HC, Blagoveshchenskaya A, Burgess J, Polevoy G, Price JV, Mayinger P, Brill JA. The phosphoinositide phosphatase Sac1 regulates cell shape and microtubule stability in the developing Drosophila eye. Development 2018; 145:dev151571. [PMID: 29752385 PMCID: PMC6031321 DOI: 10.1242/dev.151571] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 04/30/2018] [Indexed: 12/15/2022]
Abstract
Epithelial patterning in the developing Drosophila melanogaster eye requires the Neph1 homolog Roughest (Rst), an immunoglobulin family cell surface adhesion molecule expressed in interommatidial cells (IOCs). Here, using a novel temperature-sensitive (ts) allele, we show that the phosphoinositide phosphatase Sac1 is also required for IOC patterning. Sac1ts mutants have rough eyes and retinal patterning defects that resemble rst mutants. Sac1ts retinas exhibit elevated levels of phosphatidylinositol 4-phosphate (PI4P), consistent with the role of Sac1 as a PI4P phosphatase. Indeed, genetic rescue and interaction experiments reveal that restriction of PI4P levels by Sac1 is crucial for normal eye development. Rst is delivered to the cell surface in Sac1ts mutants. However, Sac1ts mutant IOCs exhibit severe defects in microtubule organization, associated with accumulation of Rst and the exocyst subunit Sec8 in enlarged intracellular vesicles upon cold fixation ex vivo Together, our data reveal a novel requirement for Sac1 in promoting microtubule stability and suggest that Rst trafficking occurs in a microtubule- and exocyst-dependent manner.
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Affiliation(s)
- Lauren M Del Bel
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
- Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Nigel Griffiths
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
- Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Ronit Wilk
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
| | - Ho-Chun Wei
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Sciences Building Room 8166, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, Canada
| | - Anastasia Blagoveshchenskaya
- Division of Nephrology & Hypertension, Oregon Health & Science University, 3181 S.W. Sam Jackson Park Rd., Portland, Oregon 97239-3098, USA
| | - Jason Burgess
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
- Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Gordon Polevoy
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
| | - James V Price
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Sciences Building Room 8166, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, Canada
| | - Peter Mayinger
- Division of Nephrology & Hypertension, Oregon Health & Science University, 3181 S.W. Sam Jackson Park Rd., Portland, Oregon 97239-3098, USA
| | - Julie A Brill
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada
- Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
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11
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Del Bel LM, Brill JA. Sac1, a lipid phosphatase at the interface of vesicular and nonvesicular transport. Traffic 2018; 19:301-318. [PMID: 29411923 DOI: 10.1111/tra.12554] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/02/2018] [Accepted: 02/02/2018] [Indexed: 12/14/2022]
Abstract
The lipid phosphatase Sac1 dephosphorylates phosphatidylinositol 4-phosphate (PI4P), thereby holding levels of this crucial membrane signaling molecule in check. Sac1 regulates multiple cellular processes, including cytoskeletal organization, membrane trafficking and cell signaling. Here, we review the structure and regulation of Sac1, its roles in cell signaling and development and its links to health and disease. Remarkably, many of the diverse roles attributed to Sac1 can be explained by the recent discovery of its requirement at membrane contact sites, where its consumption of PI4P is proposed to drive interorganelle transfer of other cellular lipids, thereby promoting normal lipid homeostasis within cells.
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Affiliation(s)
- Lauren M Del Bel
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Julie A Brill
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
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12
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Chen D, Yang C, Liu S, Hang W, Wang X, Chen J, Shi A. SAC-1 ensures epithelial endocytic recycling by restricting ARF-6 activity. J Cell Biol 2018; 217:2121-2139. [PMID: 29563216 PMCID: PMC5987724 DOI: 10.1083/jcb.201711065] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 02/06/2018] [Accepted: 02/28/2018] [Indexed: 11/22/2022] Open
Abstract
Arf6/ARF-6 is a crucial regulator of the endosomal phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) pool in endocytic recycling. To further characterize ARF-6 regulation, we performed an ARF-6 interactor screen in Caenorhabditis elegans and identified SAC-1, the homologue of the phosphoinositide phosphatase Sac1p in yeast, as a novel ARF-6 partner. In the absence of ARF-6, basolateral endosomes show a loss of SAC-1 staining in epithelial cells. Steady-state cargo distribution assays revealed that loss of SAC-1 specifically affected apical secretory delivery and basolateral recycling. PI(4,5)P2 levels and the endosomal labeling of the ARF-6 effector UNC-16 were significantly elevated in sac-1 mutants, suggesting that SAC-1 functions as a negative regulator of ARF-6. Further analyses revealed an interaction between SAC-1 and the ARF-6-GEF BRIS-1. This interaction outcompeted ARF-6(guanosine diphosphate [GDP]) for binding to BRIS-1 in a concentration-dependent manner. Consequently, loss of SAC-1 promotes the intracellular overlap between ARF-6 and BRIS-1. BRIS-1 knockdown resulted in a significant reduction in PI(4,5)P2 levels in SAC-1-depleted cells. Interestingly, the action of SAC-1 in sequestering BRIS-1 is independent of SAC-1's catalytic activity. Our results suggest that the interaction of SAC-1 with ARF-6 curbs ARF-6 activity by limiting the access of ARF-6(GDP) to its guanine nucleotide exchange factor, BRIS-1.
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Affiliation(s)
- Dan Chen
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Chao Yang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Sha Liu
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Weijian Hang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Xianghong Wang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Juan Chen
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Anbing Shi
- Department of Biochemistry and Molecular Biology, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China .,Institute for Brain Research, Huazhong University of Science and Technology, Wuhan, Hubei, China.,Key Laboratory of Neurological Disease of National Education Ministry, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
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13
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Zewe JP, Wills RC, Sangappa S, Goulden BD, Hammond GR. SAC1 degrades its lipid substrate PtdIns4 P in the endoplasmic reticulum to maintain a steep chemical gradient with donor membranes. eLife 2018; 7:35588. [PMID: 29461204 PMCID: PMC5829913 DOI: 10.7554/elife.35588] [Citation(s) in RCA: 99] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 02/13/2018] [Indexed: 12/22/2022] Open
Abstract
Gradients of PtdIns4P between organelle membranes and the endoplasmic reticulum (ER) are thought to drive counter-transport of other lipids via non-vesicular traffic. This novel pathway requires the SAC1 phosphatase to degrade PtdIns4P in a 'cis' configuration at the ER to maintain the gradient. However, SAC1 has also been proposed to act in 'trans' at membrane contact sites, which could oppose lipid traffic. It is therefore crucial to determine which mode SAC1 uses in living cells. We report that acute inhibition of SAC1 causes accumulation of PtdIns4P in the ER, that SAC1 does not enrich at membrane contact sites, and that SAC1 has little activity in 'trans', unless a linker is added between its ER-anchored and catalytic domains. The data reveal an obligate 'cis' activity of SAC1, supporting its role in non-vesicular lipid traffic and implicating lipid traffic more broadly in inositol lipid homeostasis and function.
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Affiliation(s)
- James P Zewe
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States
| | - Rachel C Wills
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States
| | - Sahana Sangappa
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States
| | - Brady D Goulden
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States
| | - Gerald Rv Hammond
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States
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14
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Thériault C, Richard D. Characterization of a putative Plasmodium falciparum SAC1 phosphoinositide-phosphatase homologue potentially required for survival during the asexual erythrocytic stages. Sci Rep 2017; 7:12710. [PMID: 28983103 PMCID: PMC5629215 DOI: 10.1038/s41598-017-12762-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Accepted: 09/15/2017] [Indexed: 12/13/2022] Open
Abstract
Despite marked reductions in morbidity and mortality in the last ten years, malaria still takes a tremendous toll on human populations throughout tropical and sub-tropical regions of the world. The absence of an effective vaccine and resistance to most antimalarial drugs available demonstrate the urgent need for new intervention strategies. Phosphoinositides are a class of lipids with critical roles in numerous processes and their specific subcellular distribution, generated through the action of kinases and phosphatases, define organelle identity in a wide range of eukaryotic cells. Recent studies have highlighted important functions of phosphoinositide kinases in several parts of the Plasmodium lifecycle such as hemoglobin endocytosis and cytokinesis during the erythrocytic stage however, nothing is known with regards to the parasite's putative phosphoinositide phosphatases. We present the identification and initial characterization of a putative homologue of the SAC1 phosphoinositide phosphatase family. Our results show that the protein is expressed throughout the asexual blood stages and that it localises to the endoplasmic reticulum and potentially to the Golgi apparatus. Furthermore, conditional knockdown and knockout studies suggest that a minimal amount of the protein are likely required for survival during the erythrocytic cycle.
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Affiliation(s)
- Catherine Thériault
- Centre de recherche en infectiologie du CHU de Québec-Université Laval, Quebec City, Quebec, Canada
| | - Dave Richard
- Centre de recherche en infectiologie du CHU de Québec-Université Laval, Quebec City, Quebec, Canada.
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15
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Mitigating Motor Neuronal Loss in C. elegans Model of ALS8. Sci Rep 2017; 7:11582. [PMID: 28912432 PMCID: PMC5599522 DOI: 10.1038/s41598-017-11798-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 08/30/2017] [Indexed: 12/13/2022] Open
Abstract
ALS8 is a late-onset familial autosomal dominant form of Amyotrophic Lateral Sclerosis (ALS) caused by a point mutation (P56S) in the VAPB gene (VAMP associated protein isoform B). Here, we generated two C. elegans models of the disease: a transgenic model where human VAPB wild-type (WT) or P56S mutant was expressed in a subset of motor neurons, and a second model that targeted inducible knockdown of the worm’s orthologue, vpr-1. Overexpression of human VAPB in DA neurons caused a backward locomotion defect, axonal misguidance, and premature neuronal death. Knockdown of vpr-1 recapitulated the reduction in VAPB expression associated with sporadic cases of human ALS. It also caused backward locomotion defects as well as an uncoordinated phenotype, and age-dependent, progressive motor neuronal death. Furthermore, inhibiting phosphatidylinositol-4 (PtdIns 4)-kinase activity with PIK-93 reduced the incidence of DA motor neuron loss and improved backward locomotion. This supports the loss of VAPB function in ALS8 pathogenesis and suggests that reducing intracellular PtdIns4P might be an effective therapeutic strategy in delaying progressive loss of motor neurons.
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16
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Identification of membrane proteome of Paracoccidioides lutzii and its regulation by zinc. Future Sci OA 2017; 3:FSO232. [PMID: 29134119 PMCID: PMC5676091 DOI: 10.4155/fsoa-2017-0044] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 06/21/2017] [Indexed: 01/09/2023] Open
Abstract
Aim: During infection development in the host, Paracoccidioides spp. faces the deprivation of micronutrients, a mechanism called nutritional immunity. This condition induces the remodeling of proteins present in different metabolic pathways. Therefore, we attempted to identify membrane proteins and their regulation by zinc in Paracoccidioides lutzii. Materials & methods: Membranes enriched fraction of yeast cells of P. lutzii were isolated, purified and identified by 2D LC–MS/MS detection and database search. Results & conclusion: Zinc deprivation suppressed the expression of membrane proteins such as glycoproteins, those involved in cell wall synthesis and those related to oxidative phosphorylation. This is the first study describing membrane proteins and the effect of zinc deficiency in their regulation in one member of the genus Paracoccidioides. The methodology of protein identification allows the characterization of biological processes performed by those molecules. Therefore, we performed a membrane proteomic analysis of Paracoccidioides lutzii and further evaluated the responses of the fungus to zinc deprivation. The results obtained in the work allowed the characterization of membrane proteins present in organelles that are related to different cellular functions. Zinc deprivation changes processes related to cellular physiology and metabolism. These results help us to understand the process of pathogen–host interaction, since zinc deprivation is a condition present during infection.
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17
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Abstract
The endoplasmic reticulum (ER) has a broad localization throughout the cell and forms direct physical contacts with all other classes of membranous organelles, including the plasma membrane (PM). A number of protein tethers that mediate these contacts have been identified, and study of these protein tethers has revealed a multiplicity of roles in cell physiology, including regulation of intracellular Ca2+ dynamics and signaling as well as control of lipid traffic and homeostasis. In this review, we discuss the cross talk between the ER and the PM mediated by direct contacts. We review factors that tether the two membranes, their properties, and their dynamics in response to the functional state of the cell. We focus in particular on the role of ER-PM contacts in nonvesicular lipid transport between the two bilayers mediated by lipid transfer proteins.
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Affiliation(s)
- Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, 308232, Singapore;
| | - Pietro De Camilli
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Kavli Institute for Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, Connecticut 06510;
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18
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Lipid transfer proteins and the tuning of compartmental identity in the Golgi apparatus. Chem Phys Lipids 2016; 200:42-61. [DOI: 10.1016/j.chemphyslip.2016.06.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 11/23/2022]
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19
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Comparative proteomic analysis of engineered Saccharomyces cerevisiae with enhanced free fatty acid accumulation. Appl Microbiol Biotechnol 2015; 100:1407-1420. [PMID: 26450510 DOI: 10.1007/s00253-015-7028-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Revised: 09/13/2015] [Accepted: 09/20/2015] [Indexed: 01/27/2023]
Abstract
The engineered Saccharomyces cerevisiae strain △faa1△faa4 [Acot5s] was demonstrated to accumulate more free fatty acids (FFA) previously. Here, comparative proteomic analysis was performed to get a global overview of metabolic regulation in the strain. Over 500 proteins were identified, and 82 of those proteins were found to change significantly in the engineered strains. Proteins involved in glycolysis, acetate metabolism, fatty acid synthesis, TCA cycle, glyoxylate cycle, the pentose phosphate pathway, respiration, transportation, and stress response were found to be upregulated in △faa1△faa4 [Acot5s] as compared to the wild type. On the other hand, proteins involved in glycerol, ethanol, ergosterol, and cell wall synthesis were downregulated. Taken together with our metabolite analysis, our results showed that the disruption of Faa1 and Faa4 and expression of Acot5s in the engineered strain △faa1△faa4 [Acot5s] not only relieved the feedback inhibition of fatty acyl-CoAs on fatty acid synthesis, but also caused a major metabolic rearrangement. The rearrangement redirected carbon flux toward the pathways which generate the essential substrates and cofactors for fatty acid synthesis, such as acetyl-CoA, ATP, and NADPH. Therefore, our results help shed light on the mechanism for the increased production of fatty acids in the engineered strains, which is useful in providing information for future studies in biofuel production.
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20
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Phosphatidylinositol-4-phosphate-dependent membrane traffic is critical for fungal filamentous growth. Proc Natl Acad Sci U S A 2015; 112:8644-9. [PMID: 26124136 DOI: 10.1073/pnas.1504259112] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The phospholipid phosphatidylinositol-4-phosphate [PI(4)P], generated at the Golgi and plasma membrane, has been implicated in many processes, including membrane traffic, yet its role in cell morphology changes, such as the budding to filamentous growth transition, is unknown. We show that Golgi PI(4)P is required for such a transition in the human pathogenic fungus Candida albicans. Quantitative analyses of membrane traffic revealed that PI(4)P is required for late Golgi and secretory vesicle dynamics and targeting and, as a result, is important for the distribution of a multidrug transporter and hence sensitivity to antifungal drugs. We also observed that plasma membrane PI(4)P, which we show is functionally distinct from Golgi PI(4)P, forms a steep gradient concomitant with filamentous growth, despite uniform plasma membrane PI-4-kinase distribution. Mathematical modeling indicates that local PI(4)P generation and hydrolysis by phosphatases are crucial for this gradient. We conclude that PI(4)P-regulated membrane dynamics are critical for morphology changes.
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21
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Hsu F, Hu F, Mao Y. Spatiotemporal control of phosphatidylinositol 4-phosphate by Sac2 regulates endocytic recycling. ACTA ACUST UNITED AC 2015; 209:97-110. [PMID: 25869669 PMCID: PMC4395482 DOI: 10.1083/jcb.201408027] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Sac2 (INPP5F) is a phosphoinositide 4-phosphatase that specifically hydrolyzes PI(4)P and regulates endocytic recycling. It is well established that the spatial- and temporal-restricted generation and turnover of phosphoinositides (PIs) by a cascade of PI-metabolizing enzymes is a key regulatory mechanism in the endocytic pathway. Here, we demonstrate that the Sac1 domain–containing protein Sac2 is a PI 4-phosphatase that specifically hydrolyzes phosphatidylinositol 4-phosphate in vitro. We further show that Sac2 colocalizes with early endosomal markers and is recruited to transferrin (Tfn)-containing vesicles during endocytic recycling. Exogenous expression of the catalytically inactive mutant Sac2C458S resulted in altered cellular distribution of Tfn receptors and delayed Tfn recycling. Furthermore, genomic ablation of Sac2 caused a similar perturbation on Tfn and integrin recycling as well as defects in cell migration. Structural characterization of Sac2 revealed a unique pleckstrin-like homology Sac2 domain conserved in all Sac2 orthologues. Collectively, our findings provide evidence for the tight regulation of PIs by Sac2 in the endocytic recycling pathway.
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Affiliation(s)
- FoSheng Hsu
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853
| | - Fenghua Hu
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853
| | - Yuxin Mao
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853
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22
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The actin-related protein Sac1 is required for morphogenesis and cell wall integrity in Candida albicans. Fungal Genet Biol 2015; 81:261-70. [PMID: 25575432 DOI: 10.1016/j.fgb.2014.12.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 12/22/2014] [Accepted: 12/27/2014] [Indexed: 01/10/2023]
Abstract
Candida albicans is a common pathogenic fungus and has aroused widespread attention recently. Actin cytoskeleton, an important player in polarized growth, protein secretion and organization of cell shape, displays irreplaceable role in hyphal development and cell integrity. In this study, we demonstrated a homologue of Saccharomyces cerevisiae Sac1, in C. albicans. It is a potential PIP phosphatase with Sac domain which is related to actin organization, hyphal development, biofilm formation and cell wall integrity. Deletion of SAC1 did not lead to insitiol-auxotroph phenotype in C. albicans, but this gene rescued the growth defect of S. cerevisiae sac1Δ in the insitiol-free medium. Hyphal induction further revealed the deficiency of sac1Δ/Δ in hyphal development and biofilm formation. Fluorescence observation and real time PCR (RT-PCR) analysis suggested both actin and the hyphal cell wall protein Hwp1 were overexpressed and mislocated in this mutant. Furthermore, cell wall integrity (CWI) was largely affected by deletion of SAC1, due to the hypersensitivity to cell wall stress, changed content and distribution of chitin in the mutant. As a result, the virulence of sac1Δ/Δ was seriously attenuated. Taken together, this study provides evidence that Sac1, as a potential PIP phosphatase, is essential for actin organization, hyphal development, CWI and pathogenicity in C. albicans.
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23
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Hsu F, Mao Y. The structure of phosphoinositide phosphatases: Insights into substrate specificity and catalysis. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1851:698-710. [PMID: 25264170 DOI: 10.1016/j.bbalip.2014.09.015] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Revised: 09/10/2014] [Accepted: 09/17/2014] [Indexed: 12/17/2022]
Abstract
Phosphoinositides (PIs) are a group of key signaling and structural lipid molecules involved in a myriad of cellular processes. PI phosphatases, together with PI kinases, are responsible for the conversion of PIs between distinctive phosphorylation states. PI phosphatases are a large collection of enzymes that are evolved from at least two disparate ancestors. One group is distantly related to endonucleases, which apply divalent metal ions for phosphoryl transfer. The other group is related to protein tyrosine phosphatases, which contain a highly conserved active site motif Cys-X5-Arg (CX5R). In this review, we focus on structural insights to illustrate current understandings of the molecular mechanisms of each PI phosphatase family, with emphasis on their structural basis for substrate specificity determinants and catalytic mechanisms. This article is part of a Special Issue entitled Phosphoinositides.
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Affiliation(s)
- FoSheng Hsu
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Yuxin Mao
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
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24
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Abstract
The specific interaction of phosphoinositides with proteins is critical for a plethora of cellular processes, including cytoskeleton remodelling, mitogenic signalling, ion channel regulation and membrane traffic. The spatiotemporal restriction of different phosphoinositide species helps to define compartments within the cell, and this is particularly important for membrane trafficking within both the secretory and endocytic pathways. Phosphoinositide homoeostasis is tightly regulated by a large number of inositol kinases and phosphatases, which respectively phosphorylate and dephosphorylate distinct phosphoinositide species. Many of these enzymes have been implicated in regulating membrane trafficking and, accordingly, their dysregulation has been linked to a number of human diseases. In the present review, we focus on the inositol phosphatases, concentrating on their roles in membrane trafficking and the human diseases with which they have been associated.
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25
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Tokuda E, Itoh T, Hasegawa J, Ijuin T, Takeuchi Y, Irino Y, Fukumoto M, Takenawa T. Phosphatidylinositol 4-phosphate in the Golgi apparatus regulates cell-cell adhesion and invasive cell migration in human breast cancer. Cancer Res 2014; 74:3054-66. [PMID: 24706697 DOI: 10.1158/0008-5472.can-13-2441] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Downregulation of cell-cell adhesion and upregulation of cell migration play critical roles in the conversion of benign tumors to aggressive invasive cancers. In this study, we show that changes in cell-cell adhesion and cancer cell migration/invasion capacity depend on the level of phosphatidylinositol 4-phosphate [PI(4)P] in the Golgi apparatus in breast cancer cells. Attenuating SAC1, a PI(4)P phosphatase localized in the Golgi apparatus, resulted in decreased cell-cell adhesion and increased cell migration in weakly invasive cells. In contrast, silencing phosphatidylinositol 4-kinase IIIβ, which generates PI(4)P in the Golgi apparatus, increased cell-cell adhesion and decreased invasion in highly invasive cells. Furthermore, a PI(4)P effector, Golgi phosphoprotein 3, was found to be involved in the generation of these phenotypes in a manner that depends on its PI(4)P-binding ability. Our results provide a new model for breast cancer cell progression in which progression is controlled by PI(4)P levels in the Golgi apparatus.
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Affiliation(s)
- Emi Tokuda
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Toshiki Itoh
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Junya Hasegawa
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Takeshi Ijuin
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Yukiko Takeuchi
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Yasuhiro Irino
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Miki Fukumoto
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
| | - Tadaomi Takenawa
- Authors' Affiliations: Integrated Center for Mass Spectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
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26
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Tani M, Kuge O. Involvement of Sac1 phosphoinositide phosphatase in the metabolism of phosphatidylserine in the yeast Saccharomyces cerevisiae. Yeast 2014; 31:145-58. [PMID: 24578286 DOI: 10.1002/yea.3004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Revised: 01/18/2014] [Accepted: 02/20/2014] [Indexed: 12/11/2022] Open
Abstract
Sac1 is a phosphoinositide phosphatase that preferentially dephosphorylates phosphatidylinositol 4-phosphate. Mutation of SAC1 causes not only the accumulation of phosphoinositides but also reduction of the phosphatidylserine (PS) level in the yeast Saccharomyces cerevisiae. In this study, we characterized the mechanism underlying the PS reduction in SAC1-deleted cells. Incorporation of (32) P into PS was significantly delayed in sac1∆ cells. Such a delay was also observed in SAC1- and PS decarboxylase gene-deleted cells, suggesting that the reduction in the PS level is caused by a reduction in the rate of biosynthesis of PS. A reduction in the PS level was also observed with repression of STT4 encoding phosphatidylinositol 4-kinase or deletion of VPS34 encoding phophatidylinositol 3-kinase. However, the combination of mutations of SAC1 and STT4 or VPS34 did not restore the reduced PS level, suggesting that both the synthesis and degradation of phosphoinositides are important for maintenance of the PS level. Finally, we observed an abnormal PS distribution in sac1∆ cells when a specific probe for PS was expressed. Collectively, these results suggested that Sac1 is involved in the maintenance of a normal rate of biosynthesis and distribution of PS.
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Affiliation(s)
- Motohiro Tani
- Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka, Japan
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27
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PtdIns(4)P signalling and recognition systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 991:59-83. [PMID: 23775691 DOI: 10.1007/978-94-007-6331-9_5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The Golgi apparatus is a sorting platform that exchanges extensively with the endoplasmic reticulum (ER), endosomes (Es) and plasma membrane (PM) compartments. The last compartment of the Golgi, the trans-Golgi Network (TGN) is a large complex of highly deformed membranes from which vesicles depart to their targeted organelles but also are harbored from retrograde pathways. The phosphoinositide (PI) composition of the TGN is marked by an important contingent of phosphatidylinositol-4-phosphate (PtdIns(4)P). Although this PI is present throughout the Golgi, its proportion grows along the successive cisternae and peaks at the TGN. The levels of this phospholipid are controlled by a set of kinases and phosphatases that regulate its concentrations in the Golgi and maintain a dynamic gradient that determines the cellular localization of several interacting proteins. Though not exclusive to the Golgi, the synthesis of PtdIns(4)P in other membranes is relatively marginal and has unclear consequences. The significance of PtdIns(4)P within the TGN has been demonstrated for numerous cellular events such as vesicle formation, lipid metabolism, and membrane trafficking.
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28
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Tan J, Brill JA. Cinderella story: PI4P goes from precursor to key signaling molecule. Crit Rev Biochem Mol Biol 2013; 49:33-58. [PMID: 24219382 DOI: 10.3109/10409238.2013.853024] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Phosphatidylinositol lipids are signaling molecules involved in nearly all aspects of cellular regulation. Production of phosphatidylinositol 4-phosphate (PI4P) has long been recognized as one of the first steps in generating poly-phosphatidylinositol phosphates involved in actin organization, cell migration, and signal transduction. In addition, progress over the last decade has brought to light independent roles for PI4P in membrane trafficking and lipid homeostasis. Here, we describe recent advances that reveal the breadth of processes regulated by PI4P, the spectrum of PI4P effectors, and the mechanisms of spatiotemporal control that coordinate crosstalk between PI4P and cellular signaling pathways.
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Affiliation(s)
- Julie Tan
- Department of Molecular Genetics, University of Toronto , Toronto, Ontario , Canada and
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29
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Wang J, Chen J, Enns CA, Mayinger P. The first transmembrane domain of lipid phosphatase SAC1 promotes Golgi localization. PLoS One 2013; 8:e71112. [PMID: 23936490 PMCID: PMC3731292 DOI: 10.1371/journal.pone.0071112] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 06/25/2013] [Indexed: 01/30/2023] Open
Abstract
The lipid phosphatase Sac1 cycles between endoplasmic reticulum and cisternal Golgi compartments. In proliferating mammalian cells, a canonical dilysine motif at the C-terminus of Sac1 is required for coatomer complex-I (COP-I)-binding and continuous retrieval to the ER. Starvation triggers accumulation of Sac1 at the Golgi. The mechanism responsible for Golgi retention of Sac1 is unknown. Here we show that the first of the two transmembrane regions in human SAC1 (TM1) functions in Golgi localization. A minimal construct containing only TM1 and the adjacent flanking sequences is concentrated at the Golgi. Transplanting TM1 into transferrin receptor 2 (TfR2) induces Golgi accumulation of this normally plasma membrane and endosomal protein, indicating that TM1 is sufficient for Golgi localization. In addition, we determined that the N-terminal cytoplasmic domain of SAC1 also promotes Golgi localization, even when TM1 is mutated or absent. We conclude that the distribution of SAC1 within the Golgi is controlled via both passive membrane thickness-dependent partitioning of TM1 and a retention mechanism that requires the N-terminal cytoplasmic region.
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Affiliation(s)
- Jinzhi Wang
- Division of Nephrology & Hypertension, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Juxing Chen
- The Department of Cell & Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Caroline A. Enns
- The Department of Cell & Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Peter Mayinger
- Division of Nephrology & Hypertension, Oregon Health & Science University, Portland, Oregon, United States of America
- * E-mail:
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30
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Abstract
Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
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Affiliation(s)
- Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Abstract
Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.
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Hsu F, Mao Y. The Sac domain-containing phosphoinositide phosphatases: structure, function, and disease. ACTA ACUST UNITED AC 2013; 8:395-407. [PMID: 24860601 DOI: 10.1007/s11515-013-1258-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Phosphoinositides (PIs) have long been known to have an essential role in cell physiology. Their intracellular localization and concentration must be tightly regulated for their proper function. This spatial and temporal regulation is achieved by a large number of PI kinases and phosphatases that are present throughout eukaryotic species. One family of these enzymes contains a conserved PI phosphatase domain termed Sac. Although the Sac domain is homologous among different Sac domain-containing proteins, all appear to exhibit varied substrate specificity and subcellular localization. Dysfunctions in several members of this family are implicated in a range of human diseases such as cardiac hypertrophy, bipolar disorder, Down's syndrome, Charcot-Marie-Tooth disease (CMT) and Amyotrophic Lateral Sclerosis (ALS). In plant, several Sac domain-containing proteins have been implicated in the stress response, chloroplast function and polarized secretion. In this review, we focus on recent findings in the family of Sac domain-containing PI phosphatases in yeast, mammal and plant, including the structural analysis into the mechanism of enzymatic activity, cellular functions, and their roles in disease pathophysiology.
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Affiliation(s)
- FoSheng Hsu
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Yuxin Mao
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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Forrest S, Chai A, Sanhueza M, Marescotti M, Parry K, Georgiev A, Sahota V, Mendez-Castro R, Pennetta G. Increased levels of phosphoinositides cause neurodegeneration in a Drosophila model of amyotrophic lateral sclerosis. Hum Mol Genet 2013; 22:2689-704. [PMID: 23492670 PMCID: PMC3674808 DOI: 10.1093/hmg/ddt118] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The Vesicle-associated membrane protein (VAMP)-Associated Protein B (VAPB) is the causative gene of amyotrophic lateral sclerosis 8 (ALS8) in humans. Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective death of motor neurons leading to spasticity, muscle atrophy and paralysis. VAP proteins have been implicated in various cellular processes, including intercellular signalling, synaptic remodelling, lipid transport and membrane trafficking and yet, the molecular mechanisms underlying ALS8 pathogenesis remain poorly understood. We identified the conserved phosphoinositide phosphatase Sac1 as a Drosophila VAP (DVAP)-binding partner and showed that DVAP is required to maintain normal levels of phosphoinositides. Downregulating either Sac1 or DVAP disrupts axonal transport, synaptic growth, synaptic microtubule integrity and the localization of several postsynaptic components. Expression of the disease-causing allele (DVAP-P58S) in a fly model for ALS8 induces neurodegeneration, elicits synaptic defects similar to those of DVAP or Sac1 downregulation and increases phosphoinositide levels. Consistent with a role for Sac1-mediated increase of phosphoinositide levels in ALS8 pathogenesis, we found that Sac1 downregulation induces neurodegeneration in a dosage-dependent manner. In addition, we report that Sac1 is sequestered into the DVAP-P58S-induced aggregates and that reducing phosphoinositide levels rescues the neurodegeneration and suppresses the synaptic phenotypes associated with DVAP-P58S transgenic expression. These data underscore the importance of DVAP–Sac1 interaction in controlling phosphoinositide metabolism and provide mechanistic evidence for a crucial role of phosphoinositide levels in VAP-induced ALS.
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Affiliation(s)
- Stuart Forrest
- Center for Integrative Physiology and Euan MacDonald Center for Motor Neuron Disease Research, School of Biomedical Sciences, University of Edinburgh, Edinburgh, UK
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Abstract
The striking morphology of the Golgi complex has fascinated cell biologists since its discovery over 100 years ago. Yet, despite intense efforts to understand how membrane flow relates to Golgi form and function, this organelle continues to baffle cell biologists and biochemists alike. Fundamental questions regarding Golgi function, while hotly debated, remain unresolved. Historically, Golgi function has been described from a protein-centric point of view, but we now appreciate that conceptual frameworks for how lipid metabolism is integrated with Golgi biogenesis and function are essential for a mechanistic understanding of this fascinating organelle. It is from a lipid-centric perspective that we discuss the larger question of Golgi dynamics and membrane trafficking. We review the growing body of evidence for how lipid metabolism is integrally written into the engineering of the Golgi system and highlight questions for future study.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA.
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Wood CS, Hung CS, Huoh YS, Mousley CJ, Stefan CJ, Bankaitis V, Ferguson KM, Burd CG. Local control of phosphatidylinositol 4-phosphate signaling in the Golgi apparatus by Vps74 and Sac1 phosphoinositide phosphatase. Mol Biol Cell 2012; 23:2527-36. [PMID: 22553352 PMCID: PMC3386216 DOI: 10.1091/mbc.e12-01-0077] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Signaling by phosphatidylinositol 4-kinases (PI4Ks) in the Golgi apparatus controls lipid homeostasis and protein-sorting pathways. Signaling is shown to be terminated on the medial cisterna by a complex of a PI4K effector, Vps74, and Sac1, the major PtdIns4P phosphatase in the cell. In the Golgi apparatus, lipid homeostasis pathways are coordinated with the biogenesis of cargo transport vesicles by phosphatidylinositol 4-kinases (PI4Ks) that produce phosphatidylinositol 4-phosphate (PtdIns4P), a signaling molecule that is recognized by downstream effector proteins. Quantitative analysis of the intra-Golgi distribution of a PtdIns4P reporter protein confirms that PtdIns4P is enriched on the trans-Golgi cisterna, but surprisingly, Vps74 (the orthologue of human GOLPH3), a PI4K effector required to maintain residence of a subset of Golgi proteins, is distributed with the opposite polarity, being most abundant on cis and medial cisternae. Vps74 binds directly to the catalytic domain of Sac1 (KD = 3.8 μM), the major PtdIns4P phosphatase in the cell, and PtdIns4P is elevated on medial Golgi cisternae in cells lacking Vps74 or Sac1, suggesting that Vps74 is a sensor of PtdIns4P level on medial Golgi cisternae that directs Sac1-mediated dephosphosphorylation of this pool of PtdIns4P. Consistent with the established role of Sac1 in the regulation of sphingolipid biosynthesis, complex sphingolipid homeostasis is perturbed in vps74Δ cells. Mutant cells lacking complex sphingolipid biosynthetic enzymes fail to properly maintain residence of a medial Golgi enzyme, and cells lacking Vps74 depend critically on complex sphingolipid biosynthesis for growth. The results establish additive roles of Vps74-mediated and sphingolipid-dependent sorting of Golgi residents.
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Affiliation(s)
- Christopher S Wood
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6058, USA
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Beh CT, McMaster CR, Kozminski KG, Menon AK. A detour for yeast oxysterol binding proteins. J Biol Chem 2012; 287:11481-8. [PMID: 22334669 DOI: 10.1074/jbc.r111.338400] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Oxysterol binding protein-related proteins, including the yeast proteins encoded by the OSH gene family (OSH1-OSH7), are implicated in the non-vesicular transfer of sterols between intracellular membranes and the plasma membrane. In light of recent studies, we revisited the proposal that Osh proteins are sterol transfer proteins and present new models consistent with known Osh protein functions. These models focus on the role of Osh proteins as sterol-dependent regulators of phosphoinositide and sphingolipid pathways. In contrast to their posited role as non-vesicular sterol transfer proteins, we propose that Osh proteins coordinate lipid signaling and membrane reorganization with the assembly of tethering complexes to promote molecular exchanges at membrane contact sites.
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Affiliation(s)
- Christopher T Beh
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
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37
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Abstract
PtdIns4P is a key regulator of the secretory pathway and plays an essential role in trafficking from the Golgi. Our recent work demonstrated that spatial control of PtdIns4P at the ER (endoplasmic reticulum) and Golgi co-ordinates secretion with cell growth. The central elements of this regulation are specific phosphoinositide 4-kinases and the phosphoinositide phosphatase Sac1. Growth-dependent translocation of Sac1 between the ER and Golgi modulates the levels of PtdIns4P and anterograde traffic at the Golgi. In yeast, this mechanism is largely dependent on the availability of glucose, but our recent results in mammalian cells suggest that Sac1 phosphatases play evolutionarily conserved roles in the growth control of secretion. Sac1 lipid phosphatase plays also an essential role in the spatial control of PtdIns4P at the Golgi complex. A restricted pool of PtdIns4P at the TGN (trans-Golgi network) is required for Golgi integrity and for proper lipid and protein sorting. In mammalian cells, the stress-activated MAPK (mitogen-activated protein kinase) p38 appears to play a critical role in transmitting nutrient signals to the phosphoinositide signalling machinery at the ER and Golgi. These results suggest that temporal and spatial integration of metabolic and lipid signalling networks at the Golgi is required for controlling the secretory pathway.
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38
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Dyson JM, Fedele CG, Davies EM, Becanovic J, Mitchell CA. Phosphoinositide phosphatases: just as important as the kinases. Subcell Biochem 2012; 58:215-279. [PMID: 22403078 DOI: 10.1007/978-94-007-3012-0_7] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Phosphoinositide phosphatases comprise several large enzyme families with over 35 mammalian enzymes identified to date that degrade many phosphoinositide signals. Growth factor or insulin stimulation activates the phosphoinositide 3-kinase that phosphorylates phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)] to form phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P(3)], which is rapidly dephosphorylated either by PTEN (phosphatase and tensin homologue deleted on chromosome 10) to PtdIns(4,5)P(2), or by the 5-phosphatases (inositol polyphosphate 5-phosphatases), generating PtdIns(3,4)P(2). 5-phosphatases also hydrolyze PtdIns(4,5)P(2) forming PtdIns(4)P. Ten mammalian 5-phosphatases have been identified, which regulate hematopoietic cell proliferation, synaptic vesicle recycling, insulin signaling, and embryonic development. Two 5-phosphatase genes, OCRL and INPP5E are mutated in Lowe and Joubert syndrome respectively. SHIP [SH2 (Src homology 2)-domain inositol phosphatase] 2, and SKIP (skeletal muscle- and kidney-enriched inositol phosphatase) negatively regulate insulin signaling and glucose homeostasis. SHIP2 polymorphisms are associated with a predisposition to insulin resistance. SHIP1 controls hematopoietic cell proliferation and is mutated in some leukemias. The inositol polyphosphate 4-phosphatases, INPP4A and INPP4B degrade PtdIns(3,4)P(2) to PtdIns(3)P and regulate neuroexcitatory cell death, or act as a tumor suppressor in breast cancer respectively. The Sac phosphatases degrade multiple phosphoinositides, such as PtdIns(3)P, PtdIns(4)P, PtdIns(5)P and PtdIns(3,5)P(2) to form PtdIns. Mutation in the Sac phosphatase gene, FIG4, leads to a degenerative neuropathy. Therefore the phosphatases, like the lipid kinases, play major roles in regulating cellular functions and their mutation or altered expression leads to many human diseases.
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Affiliation(s)
- Jennifer M Dyson
- Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, 3800, Clayton, Australia
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39
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Abstract
The Golgi complex is a ribbon-like organelle composed of stacks of flat cisternae interconnected by tubular junctions. It occupies a central position in the endomembrane system as proteins and lipids that are synthesized in the endoplasmic reticulum (ER) pass through the Golgi complex to undergo biosynthetic modification (mainly glycosylation) and to be sorted to their final destinations. In addition the Golgi complex possesses a number of activities, apparently not directly connected with its main role in trafficking and sorting, which have been recently reviewed in Wilson et al. 2011. In spite of the constant massive flux of material the Golgi complex maintains its identity and phosphoinositides (PIs), among other factors, play a central role in this process. The active metabolism of PIs at the Golgi is necessary for the proper functioning of the organelle both in terms of membrane trafficking/sorting and its manifold metabolic and signalling activities. Phosphatidylinositol 4-phosphate (PtdIns4P), in particular, is responsible for the recruitment of numerous cytosolic proteins that recognise and bind PtdIns4P via specific lipid-binding domains. In this chapter we will summarize the findings that have contributed to our current understanding of the role of PIs in the biology of the Golgi complex in terms of the regulation of PI metabolism and the functional roles and regulation of PtdIns4P effectors.
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Affiliation(s)
- Giovanni D'Angelo
- Telethon Institute of Genetics and Medicine, Via Pietro Castellino, 111, 80131, Napoli, Italy,
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40
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Devising Powerful Genetics, Biochemical and Structural Tools in the Functional Analysis of Phosphatidylinositol Transfer Proteins (PITPs) Across Diverse Species. Methods Cell Biol 2012; 108:249-302. [DOI: 10.1016/b978-0-12-386487-1.00013-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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41
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Lee S, Kim S, Nahm M, Kim E, Kim TI, Yoon JH, Lee S. The phosphoinositide phosphatase Sac1 is required for midline axon guidance. Mol Cells 2011; 32:477-82. [PMID: 22042447 PMCID: PMC3887689 DOI: 10.1007/s10059-011-0168-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Accepted: 08/29/2011] [Indexed: 12/23/2022] Open
Abstract
Sac1 phosphoinositide (PI) phosphatases are important regulators of PtdIns(4)P turnover at the ER, Golgi, and plasma membrane (PM) and are involved in diverse cellular processes including cytoskeletal organization and vesicular trafficking. Here, we present evidence that Sac1 regulates axon guidance in the embryonic CNS of Drosophila. Sac1 is expressed on three longitudinal axon tracts that are defined by the cell adhesion molecule Fasciclin II (Fas II). Mutations in the sac1 gene cause ectopic midline crossing of Fas II-positive axon tracts. This phenotype is rescued by neuronal expression of wild-type Sac1 but not by a catalytically-inactive mutant. Finally, sac1 displays dosage-sensitive genetic interactions with mutations in the genes that encode the midline repellent Slit and its axonal receptor Robo. Taken together, our results suggest that Sac1-mediated regulation of PIs is critical for Slit/Robo-dependent axon repulsion at the CNS midline.
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Affiliation(s)
- Seongsoo Lee
- Department of Cell and Developmental Biology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea
- These authors contributed equally to this work
| | - Sungdae Kim
- Interdisciplinary Graduate Program in Genetic Engineering, Seoul National University, Seoul 151-742, Korea
- These authors contributed equally to this work
| | - Minyeop Nahm
- Department of Cell and Developmental Biology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea
| | - Euijae Kim
- Department of Cell and Developmental Biology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea
| | - Tai-Il Kim
- Department of Periodontology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea
| | - Jin Ho Yoon
- Basic Science Research Institute, School of Biological Science and Chemistry, Sungshin Women’s University, Seoul 142-732, Korea
| | - Seungbok Lee
- Department of Cell and Developmental Biology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea
- Interdisciplinary Graduate Program in Genetic Engineering, Seoul National University, Seoul 151-742, Korea
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Ghosh R, Bankaitis VA. Phosphatidylinositol transfer proteins: negotiating the regulatory interface between lipid metabolism and lipid signaling in diverse cellular processes. Biofactors 2011; 37:290-308. [PMID: 21915936 DOI: 10.1002/biof.180] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Phosphoinositides represent only a small percentage of the total cellular lipid pool. Yet, these molecules play crucial roles in diverse intracellular processes such as signal transduction at membrane-cytosol interface, regulation of membrane trafficking, cytoskeleton organization, nuclear events, and the permeability and transport functions of the membrane. A central principle in such lipid-mediated signaling is the appropriate coordination of these events. Such an intricate coordination demands fine spatial and temporal control of lipid metabolism and organization, and consistent mechanisms for specifically coupling these parameters to dedicated physiological processes. In that regard, recent studies have identified Sec14-like phosphatidylcholine transfer protein (PITPs) as "coincidence detectors," which spatially and temporally link the diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. The integral role of PITPs in eukaryotic signal transduction design is amply demonstrated by the mammalian diseases associated with the derangements in the function of these proteins, to stress response and developmental regulation in plants, to fungal dimorphism and pathogenicity, to membrane trafficking in yeast, and higher eukaryotes. This review updates the recent advances made in the understanding of how these proteins, specifically PITPs of the Sec14-protein superfamily, operate at the molecular level and further describes how this knowledge has advanced our perception on the diverse biological functions of PITPs.
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Affiliation(s)
- Ratna Ghosh
- Lineberger Comprehensive Cancer Center, Department of Cell and Developmental Biology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27526-7090, USA.
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Jesch SA, Gaspar ML, Stefan CJ, Aregullin MA, Henry SA. Interruption of inositol sphingolipid synthesis triggers Stt4p-dependent protein kinase C signaling. J Biol Chem 2010; 285:41947-60. [PMID: 20972263 PMCID: PMC3009921 DOI: 10.1074/jbc.m110.188607] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 10/22/2010] [Indexed: 11/06/2022] Open
Abstract
The protein kinase C (PKC)-MAPK signaling cascade is activated and is essential for viability when cells are starved for the phospholipid precursor inositol. In this study, we report that inhibiting inositol-containing sphingolipid metabolism, either by inositol starvation or treatment with agents that block sphingolipid synthesis, triggers PKC signaling independent of sphingoid base accumulation. Under these same growth conditions, a fluorescent biosensor that detects the necessary PKC signaling intermediate, phosphatidylinositol (PI)-4-phosphate (PI4P), is enriched on the plasma membrane. The appearance of the PI4P biosensor on the plasma membrane correlates with PKC activation and requires the PI 4-kinase Stt4p. Like other mutations in the PKC-MAPK pathway, mutants defective in Stt4p and the PI4P 5-kinase Mss4p, which generates phosphatidylinositol 4,5-bisphosphate, exhibit inositol auxotrophy, yet fully derepress INO1, encoding inositol-3-phosphate synthase. These observations suggest that inositol-containing sphingolipid metabolism controls PKC signaling by regulating access of the signaling lipids PI4P and phosphatidylinositol 4,5-bisphosphate to effector proteins on the plasma membrane.
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Affiliation(s)
| | | | - Christopher J. Stefan
- From the Department of Molecular Biology and Genetics and
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, New York 14853
| | | | - Susan A. Henry
- From the Department of Molecular Biology and Genetics and
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44
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Genome-wide screen for inositol auxotrophy in Saccharomyces cerevisiae implicates lipid metabolism in stress response signaling. Mol Genet Genomics 2010; 285:125-49. [PMID: 21136082 DOI: 10.1007/s00438-010-0592-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 11/20/2010] [Indexed: 12/13/2022]
Abstract
Inositol auxotrophy (Ino(-) phenotype) in budding yeast has classically been associated with misregulation of INO1 and other genes involved in lipid metabolism. To identify all non-essential yeast genes that are necessary for growth in the absence of inositol, we carried out a genome-wide phenotypic screening for deletion mutants exhibiting Ino(-) phenotypes under one or more growth conditions. We report the identification of 419 genes, including 385 genes not previously reported, which exhibit this phenotype when deleted. The identified genes are involved in a wide range of cellular processes, but are particularly enriched in those affecting transcription, protein modification, membrane trafficking, diverse stress responses, and lipid metabolism. Among the Ino(-) mutants involved in stress response, many exhibited phenotypes that are strengthened at elevated temperature and/or when choline is present in the medium. The role of inositol in regulation of lipid metabolism and stress response signaling is discussed.
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45
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Graham TR, Burd CG. Coordination of Golgi functions by phosphatidylinositol 4-kinases. Trends Cell Biol 2010; 21:113-21. [PMID: 21282087 DOI: 10.1016/j.tcb.2010.10.002] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Revised: 10/04/2010] [Accepted: 10/05/2010] [Indexed: 12/14/2022]
Abstract
Phosphatidylinositol 4-kinases (PI4Ks) regulate vesicle-mediated export from the Golgi apparatus via phosphatidylinositol 4-phosphate (PtdIns4P) binding effector proteins that control vesicle budding reactions and regulate membrane dynamics. Evidence has emerged from the characterization of Golgi PI4K effectors that vesicle budding and lipid dynamics are tightly coupled via a regulatory network that ensures that the appropriate membrane composition is established before a transport vesicle buds from the Golgi. An important hub of this network is protein kinase D, which regulates the activity of PI4K and several PtdIns4P effectors that control sphingolipid and sterol content of Golgi membranes. Other newly identified PtdIns4P effectors include Vps74/GOLPH3, a phospholipid flippase called Drs2 and Sec2, a Rab guanine nucleotide exchange factor (GEF). These effectors orchestrate membrane transformation events facilitating vesicle formation and targeting. In this review, we discuss how PtdIns4P signaling is integrated with membrane biosynthetic and vesicle budding machineries to potentially coordinate these crucial functions of the Golgi apparatus.
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Affiliation(s)
- Todd R Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA.
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46
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Tani M, Kuge O. Requirement of a specific group of sphingolipid-metabolizing enzyme for growth of yeast Saccharomyces cerevisiae under impaired metabolism of glycerophospholipids. Mol Microbiol 2010; 78:395-413. [DOI: 10.1111/j.1365-2958.2010.07340.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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47
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Liu Y, Bankaitis VA. Phosphoinositide phosphatases in cell biology and disease. Prog Lipid Res 2010; 49:201-17. [PMID: 20043944 PMCID: PMC2873057 DOI: 10.1016/j.plipres.2009.12.001] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Revised: 12/03/2009] [Accepted: 12/03/2009] [Indexed: 01/10/2023]
Abstract
Phosphoinositides are essential signaling molecules linked to a diverse array of cellular processes in eukaryotic cells. The metabolic interconversions of these phospholipids are subject to exquisite spatial and temporal regulation executed by arrays of phosphatidylinositol (PtdIns) and phosphoinositide-metabolizing enzymes. These include PtdIns- and phosphoinositide-kinases that drive phosphoinositide synthesis, and phospholipases and phosphatases that regulate phosphoinositide degradation. In the past decade, phosphoinositide phosphatases have emerged as topics of particular interest. This interest is driven by the recent appreciation that these enzymes represent primary mechanisms for phosphoinositide degradation, and because of their ever-increasing connections with human diseases. Herein, we review the biochemical properties of six major phosphoinositide phosphatases, the functional involvements of these enzymes in regulating phosphoinositide metabolism, the pathologies that arise from functional derangements of individual phosphatases, and recent ideas concerning the involvements of phosphoinositide phosphatases in membrane traffic control.
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Affiliation(s)
- Yang Liu
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7090, USA
| | - Vytas A. Bankaitis
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7090, USA
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48
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Cheong FY, Sharma V, Blagoveshchenskaya A, Oorschot VMJ, Brankatschk B, Klumperman J, Freeze HH, Mayinger P. Spatial regulation of Golgi phosphatidylinositol-4-phosphate is required for enzyme localization and glycosylation fidelity. Traffic 2010; 11:1180-90. [PMID: 20573065 DOI: 10.1111/j.1600-0854.2010.01092.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The enrichment of phosphatidylinositol-4-phosphate (PI(4)P) at the trans Golgi network (TGN) is instrumental for proper protein and lipid sorting, yet how the restricted distribution of PI(4)P is achieved remains unknown. Here, we show that lipid phosphatase Suppressor of actin mutations 1 (SAC1) is crucial for the spatial regulation of Golgi PI(4)P. Ultrastructural analysis revealed that SAC1 is predominantly located at cisternal Golgi membranes but is absent from the TGN, thus confining PI(4)P to the TGN. RNAi-mediated knockdown of SAC1 caused changes in Golgi morphology and mislocalization of Golgi enzymes. Enzymes involved in glycan processing such as mannosidase-II (Man-II) and N-acetylglucosamine transferase-I (GnT-I) redistributed to aberrant intracellular structures and to the cell surface in SAC1 knockdown cells. SAC1 depletion also induced a unique pattern of Golgi-specific defects in N-and O-linked glycosylation. These results indicate that SAC1 organizes PI(4)P distribution between the Golgi complex and the TGN, which is instrumental for resident enzyme partitioning and Golgi morphology.
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Affiliation(s)
- Fei Ying Cheong
- Division of Nephrology & Hypertension, Department of Medicine Oregon Health & Science University, Portland, OR 97239, USA
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Crystal structure of the yeast Sac1: implications for its phosphoinositide phosphatase function. EMBO J 2010; 29:1489-98. [PMID: 20389282 DOI: 10.1038/emboj.2010.57] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Accepted: 03/08/2010] [Indexed: 01/06/2023] Open
Abstract
Sac family phosphoinositide (PI) phosphatases are an essential family of CX(5)R(T/S)-based enzymes, involved in numerous aspects of cellular function such as PI homeostasis, cellular signalling, and membrane trafficking. Genetic deletions of several Sac family members result in lethality in animal models and mutations of the Sac3 gene have been found in human hereditary diseases. In this study, we report the crystal structure of a founding member of this family, the Sac phosphatase domain of yeast Sac1. The 2.0 A resolution structure shows that the Sac domain comprises of two closely packed sub-domains, a novel N-terminal sub-domain and the PI phosphatase catalytic sub-domain. The structure further shows a striking conformation of the catalytic P-loop and a large positively charged groove at the catalytic site. These findings suggest an unusual mechanism for its dephosphorylation function. Homology structural modeling of human Fig4/Sac3 allows the mapping of several disease-related mutations and provides a framework for the understanding of the molecular mechanisms of human diseases.
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50
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Wood CS, Schmitz KR, Bessman NJ, Setty TG, Ferguson KM, Burd CG. PtdIns4P recognition by Vps74/GOLPH3 links PtdIns 4-kinase signaling to retrograde Golgi trafficking. J Cell Biol 2009; 187:967-75. [PMID: 20026658 PMCID: PMC2806290 DOI: 10.1083/jcb.200909063] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Targeting and retention of resident integral membrane proteins of the Golgi apparatus underly the function of the Golgi in glycoprotein and glycolipid processing and sorting. In yeast, steady-state Golgi localization of multiple mannosyltransferases requires recognition of their cytosolic domains by the peripheral Golgi membrane protein Vps74, an orthologue of human GOLPH3/GPP34/GMx33/MIDAS (mitochondrial DNA absence sensitive factor). We show that targeting of Vps74 and GOLPH3 to the Golgi apparatus requires ongoing synthesis of phosphatidylinositol (PtdIns) 4-phosphate (PtdIns4P) by the Pik1 PtdIns 4-kinase and that modulation of the levels and cellular location of PtdIns4P leads to mislocalization of these proteins. Vps74 and GOLPH3 bind specifically to PtdIns4P, and a sulfate ion in a crystal structure of GOLPH3 indicates a possible phosphoinositide-binding site that is conserved in Vps74. Alterations in this site abolish phosphoinositide binding in vitro and Vps74 function in vivo. These results implicate Pik1 signaling in retention of Golgi-resident proteins via Vps74 and show that GOLPH3 family proteins are effectors of Golgi PtdIns 4-kinases.
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Affiliation(s)
- Christopher S. Wood
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Karl R. Schmitz
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Nicholas J. Bessman
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Thanuja Gangi Setty
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Kathryn M. Ferguson
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Christopher G. Burd
- Department of Cell and Developmental Biology, Department of Physiology, and Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
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