51
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Baba T, Balla T. Emerging roles of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate as regulators of multiple steps in autophagy. J Biochem 2021; 168:329-336. [PMID: 32745205 DOI: 10.1093/jb/mvaa089] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 07/17/2020] [Indexed: 12/13/2022] Open
Abstract
Inositol phospholipids are low-abundance regulatory lipids that orchestrate diverse cellular functions in eukaryotic organisms. Recent studies have uncovered involvement of the lipids in multiple steps in autophagy. The late endosome-lysosome compartment plays critical roles in cellular nutrient sensing and in the control of both the initiation of autophagy and the late stage of eventual degradation of cytosolic materials destined for elimination. It is particularly notable that inositol lipids are involved in almost all steps of the autophagic process. In this review, we summarize how inositol lipids regulate and contribute to autophagy through the endomembrane compartments, primarily focusing on PI4P and PI(4,5)P2.
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Affiliation(s)
- Takashi Baba
- Department of Biological Informatics and Experimental Therapeutics, Graduate School of Medicine, Akita University, 1-1-1 Hondo, Akita, 010-8543, Japan.,Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, 35A Convent Drive, Bethesda, MD 20892-3752, USA
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, 35A Convent Drive, Bethesda, MD 20892-3752, USA
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52
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Hewlett B, Singh NP, Vannier C, Galli T. ER-PM Contact Sites - SNARING Actors in Emerging Functions. Front Cell Dev Biol 2021; 9:635518. [PMID: 33681218 PMCID: PMC7928305 DOI: 10.3389/fcell.2021.635518] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 01/21/2021] [Indexed: 11/13/2022] Open
Abstract
The compartmentalisation achieved by confining cytoplasm into membrane-enclosed organelles in eukaryotic cells is essential for maintaining vital functions including ATP production, synthetic and degradative pathways. While intracellular organelles are highly specialised in these functions, the restricting membranes also impede exchange of molecules responsible for the synchronised and responsive cellular activities. The initial identification of contact sites between the ER and plasma membrane (PM) provided a potential candidate structure for communication between organelles without mixing by fusion. Over the past decades, research has revealed a far broader picture of the events. Membrane contact sites (MCSs) have been recognized as increasingly important actors in cell differentiation, plasticity and maintenance, and, upon dysfunction, responsible for pathological conditions such as cancer and neurodegenerative diseases. Present in multiple organelles and cell types, MCSs promote transport of lipids and Ca2+ homoeostasis, with a range of associated protein families. Interestingly, each MCS displays a unique molecular signature, adapted to organelle functions. This review will explore the literature describing the molecular components and interactions taking place at ER-PM contact sites, their functions, and implications in eukaryotic cells, particularly neurons, with emphasis on lipid transfer proteins and emerging function of SNAREs.
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Affiliation(s)
- Bailey Hewlett
- INSERM U1266, Institut de Psychiatrie et Neurosciences de Paris, Université de Paris, Paris, France
| | - Neha Pratap Singh
- INSERM U1266, Institut de Psychiatrie et Neurosciences de Paris, Université de Paris, Paris, France
| | - Christian Vannier
- INSERM U1266, Institut de Psychiatrie et Neurosciences de Paris, Université de Paris, Paris, France
| | - Thierry Galli
- INSERM U1266, Institut de Psychiatrie et Neurosciences de Paris, Université de Paris, Paris, France.,GHU PARIS Psychiatrie and Neurosciences, Paris, France
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53
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Li C, Qian T, He R, Wan C, Liu Y, Yu H. Endoplasmic Reticulum-Plasma Membrane Contact Sites: Regulators, Mechanisms, and Physiological Functions. Front Cell Dev Biol 2021; 9:627700. [PMID: 33614657 PMCID: PMC7889955 DOI: 10.3389/fcell.2021.627700] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 01/13/2021] [Indexed: 12/13/2022] Open
Abstract
The endoplasmic reticulum (ER) forms direct membrane contact sites with the plasma membrane (PM) in eukaryotic cells. These ER-PM contact sites play essential roles in lipid homeostasis, ion dynamics, and cell signaling, which are carried out by protein-protein or protein-lipid interactions. Distinct tethering factors dynamically control the architecture of ER-PM junctions in response to intracellular signals or external stimuli. The physiological roles of ER-PM contact sites are dependent on a variety of regulators that individually or cooperatively perform functions in diverse cellular processes. This review focuses on proteins functioning at ER-PM contact sites and highlights the recent progress in their mechanisms and physiological roles.
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Affiliation(s)
- Chenlu Li
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Tiantian Qian
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Ruyue He
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Chun Wan
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, United States
| | - Yinghui Liu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Haijia Yu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
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54
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Tábara LC, Morris JL, Prudent J. The Complex Dance of Organelles during Mitochondrial Division. Trends Cell Biol 2021; 31:241-253. [PMID: 33446409 DOI: 10.1016/j.tcb.2020.12.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 11/28/2020] [Accepted: 12/07/2020] [Indexed: 12/17/2022]
Abstract
Mitochondria are dynamic organelles that undergo cycles of fission and fusion events depending on cellular requirements. During mitochondrial division, the GTPase dynamin-related protein-1 is recruited to endoplasmic reticulum (ER)-induced mitochondrial constriction sites where it drives fission. However, the events required to complete scission of mitochondrial membranes are not well understood. Here, we emphasize the recently described roles for Golgi-derived phosphatidylinositol 4-phosphate (PI4P)-containing vesicles in the last steps of mitochondrial division. We then propose how trans-Golgi network vesicles at mitochondria-ER contact sites and PI4P generation could mechanistically execute mitochondrial division, by recruiting PI4P effectors and/or the actin nucleation machinery. Finally, we speculate on mechanisms to explain why such a complex dance of different organelles is required to facilitate the remodelling of mitochondrial membranes.
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Affiliation(s)
- Luis-Carlos Tábara
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, The Keith Peters Building, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0XY, UK
| | - Jordan L Morris
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, The Keith Peters Building, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0XY, UK
| | - Julien Prudent
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, The Keith Peters Building, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0XY, UK.
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55
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Klemm RW. Getting in Touch Is an Important Step: Control of Metabolism at Organelle Contact Sites. CONTACT (THOUSAND OAKS (VENTURA COUNTY, CALIF.)) 2021; 4:2515256421993708. [PMID: 37366381 PMCID: PMC10243586 DOI: 10.1177/2515256421993708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Revised: 01/19/2021] [Accepted: 01/19/2021] [Indexed: 06/28/2023]
Abstract
Metabolic pathways are often spread over several organelles and need to be functionally integrated by controlled organelle communication. Physical organelle contact-sites have emerged as critical hubs in the regulation of cellular metabolism, but the molecular understanding of mechanisms that mediate formation or regulation of organelle interfaces was until recently relatively limited. Mitochondria are central organelles in anabolic and catabolic pathways and therefore interact with a number of other cellular compartments including the endoplasmic reticulum (ER) and lipid droplets (LDs). An interesting set of recent work has shed new light on the molecular basis forming these contact sites. This brief overview describes the discovery of unanticipated functions of contact sites between the ER, mitochondria and LDs in de novo synthesis of storage lipids of brown and white adipocytes. Interestingly, the factors involved in mediating the interaction between these organelles are subject to unexpected modes of regulation through newly uncovered Phospho-FFAT motifs. These results suggest dynamic regulation of contact sites between organelles and indicate that spatial organization of organelles within the cell contributes to the control of metabolism.
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Affiliation(s)
- Robin W. Klemm
- Department of Physiology,
Anatomy and Genetics, University of Oxford, UK
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56
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Cabral-Dias R, Awadeh Y, Botelho RJ, Antonescu CN. Detection of Plasma Membrane Phosphoinositide Dynamics Using Genetically Encoded Fluorescent Protein Probes. Methods Mol Biol 2021; 2251:73-89. [PMID: 33481232 DOI: 10.1007/978-1-0716-1142-5_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The dynamic phosphorylation of phosphatidylinositol produces seven distinct but interconvertible phosphatidylinositol phosphates (PIPs). Each PIP exhibits specific enrichment in a subset of membrane compartments as a result of dynamic phosphorylation and dephosphorylation by lipid kinases and phosphatases, and/or by vesicle-mediated transport. Several PIPs are found within the plasma membrane, such as phosphatidylinositol-4-phosphate [PI(4)P], phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], phosphatidylinositol-3,4-bisphosphate [PI(3,4)P2], and phosphatidylinositol-3,4,5-trisphosphate (PIP3), and these control many aspects of cell physiology, including receptor signaling and membrane traffic. As a result, measurement of the cell surface abundance of these PIPs is a valuable resource to allow understanding of the regulation and function of these cell surface lipids. Here, we describe methods based on quantification of the localization of genetically encoded fluorescent PIP probes to the cell surface by either spinning disc confocal microscopy or total internal reflection fluorescence microscopy that allow detection of changes in cell surface levels of PI(4,5)P2, PI(3,4)P2, and PIP3. These methods can also be applied to the measurement of other PIPs or lipid species at the cell surface, and thus represent a useful resource for the study of the cell biology of PIPs.
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Affiliation(s)
- Rebecca Cabral-Dias
- Department of Chemistry and Biology and the Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada
| | - Yasmin Awadeh
- Department of Chemistry and Biology and the Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada
| | - Roberto J Botelho
- Department of Chemistry and Biology and the Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada
| | - Costin N Antonescu
- Department of Chemistry and Biology and the Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada.
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57
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Du X, Yang H. Triacylglycerol Measurement in HeLa Cells. Bio Protoc 2020; 10:e3852. [PMID: 33659499 DOI: 10.21769/bioprotoc.3852] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Revised: 10/26/2020] [Accepted: 10/27/2020] [Indexed: 11/02/2022] Open
Abstract
Lipid droplets store triacylglycerols (triglycerides) and sterol esters to regulate lipid and energy homeostasis. Triacylglycerol measurement is often performed during the investigation of lipid droplet formation and growth. This protocol describes a reliable method using a fluorometric lipid quantification kit to measure triacylglycerols extracted from HeLa cells, which were treated with oleic acid to trigger the formation of lipid droplets. The lipid quantification kit employs a lipid-binding molecule that emits bright fluorescence only when bound to extracted triacylglycerols, whose content can be quantified by a simple fluorescence readout.
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Affiliation(s)
- Ximing Du
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, 2052, Australia
| | - Hongyuan Yang
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, 2052, Australia
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58
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Kimura AK, Kimura T. Phosphatidylserine biosynthesis pathways in lipid homeostasis: Toward resolution of the pending central issue for decades. FASEB J 2020; 35:e21177. [PMID: 33205488 DOI: 10.1096/fj.202001802r] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 10/17/2020] [Accepted: 10/26/2020] [Indexed: 12/28/2022]
Abstract
Enzymatic control of lipid homeostasis in the cell is a vital element in the complex organization of life. Phosphatidylserine (PS) is an essential anionic phospholipid of cell membranes, and conducts numerous roles for their structural and functional integrity. In mammalian cells, two distinct enzymes phosphatidylserine synthases-1 (PSS1) and -2 (PSS2) in the mitochondria-associated membrane (MAM) in the ER perform de novo synthesis of PS. It is based on base-exchange reactions of the preexisting dominant phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE). While PSS2 specifically catalyzes the reaction "PE → PS," whether or not PSS1 is responsible for the same reaction along with the reaction "PC → PS" remains unsettled despite its fundamental impact on the major stoichiometry. We propose here that a key but the only report that appeared to have put scientists on hold for decades in answering to this issue may be viewed consistently with other available research reports; PSS1 utilizes the two dominant phospholipid classes at a similar intrinsic rate. In this review, we discuss the issue in view of the current information for the enzyme machineries, membrane structure and dynamics, intracellular network of lipid transport, and PS synthesis in health and disease. Resolution of the pending issue is thus critical in advancing our understanding of roles of the essential anionic lipid in biology, health, and disease.
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Affiliation(s)
- Atsuko K Kimura
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - Tomohiro Kimura
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
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59
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Salo VT, Hölttä-Vuori M, Ikonen E. Seipin-Mediated Contacts as Gatekeepers of Lipid Flux at the Endoplasmic Reticulum–Lipid Droplet Nexus. ACTA ACUST UNITED AC 2020. [DOI: 10.1177/2515256420945820] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Lipid droplets (LDs) are dynamic cellular hubs of lipid metabolism. While LDs contact a plethora of organelles, they have the most intimate relationship with the endoplasmic reticulum (ER). Indeed, LDs are initially assembled at specialized ER subdomains, and recent work has unraveled an increasing array of proteins regulating ER-LD contacts. Among these, seipin, a highly conserved lipodystrophy protein critical for LD growth and adipogenesis, deserves special attention. Here, we review recent insights into the role of seipin in LD biogenesis and as a regulator of ER-LD contacts. These studies have also highlighted the evolving concept of ER and LDs as a functional continuum for lipid partitioning and pinpointed a role for seipin at the ER-LD nexus in controlling lipid flux between these compartments.
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Affiliation(s)
- Veijo T. Salo
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Elina Ikonen
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
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60
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Tillman MC, Imai N, Li Y, Khadka M, Okafor CD, Juneja P, Adhiyaman A, Hagen SJ, Cohen DE, Ortlund EA. Allosteric regulation of thioesterase superfamily member 1 by lipid sensor domain binding fatty acids and lysophosphatidylcholine. Proc Natl Acad Sci U S A 2020; 117:22080-22089. [PMID: 32820071 PMCID: PMC7486800 DOI: 10.1073/pnas.2003877117] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Nonshivering thermogenesis occurs in brown adipose tissue to generate heat in response to cold ambient temperatures. Thioesterase superfamily member 1 (Them1) is transcriptionally up-regulated in brown adipose tissue upon exposure to the cold and suppresses thermogenesis in order to conserve energy reserves. It hydrolyzes long-chain fatty acyl-CoAs that are derived from lipid droplets, preventing their use as fuel for thermogenesis. In addition to its enzymatic domains, Them1 contains a C-terminal StAR-related lipid transfer (START) domain with unknown ligand or function. By complementary biophysical approaches, we show that the START domain binds to long-chain fatty acids, products of Them1's enzymatic reaction, as well as lysophosphatidylcholine (LPC), lipids shown to activate thermogenesis in brown adipocytes. Certain fatty acids stabilize the START domain and allosterically enhance Them1 catalysis of acyl-CoA, whereas 18:1 LPC destabilizes and inhibits activity, which we verify in cell culture. Additionally, we demonstrate that the START domain functions to localize Them1 near lipid droplets. These findings define the role of the START domain as a lipid sensor that allosterically regulates Them1 activity and spatially localizes it in proximity to the lipid droplet.
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Affiliation(s)
- Matthew C Tillman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Norihiro Imai
- Joan and Sanford I. Weill Department of Medicine, Weill Cornell Medical College, New York, NY 10065
| | - Yue Li
- Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215
| | - Manoj Khadka
- Emory Integrated Lipidomics Core, Emory University, Atlanta, GA 30322
| | - C Denise Okafor
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Puneet Juneja
- Robert P. Apkarian Integrated Electron Microscopy Core, Emory University, Atlanta, GA 30322
| | - Akshitha Adhiyaman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Susan J Hagen
- Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215
| | - David E Cohen
- Joan and Sanford I. Weill Department of Medicine, Weill Cornell Medical College, New York, NY 10065
| | - Eric A Ortlund
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322;
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61
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Delfosse V, Bourguet W, Drin G. Structural and Functional Specialization of OSBP-Related Proteins. ACTA ACUST UNITED AC 2020. [DOI: 10.1177/2515256420946627] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Lipids are precisely distributed in the eukaryotic cell where they help to define organelle identity and function, in addition to their structural role. Once synthesized, many lipids must be delivered to other compartments by non-vesicular routes, a process that is undertaken by proteins called Lipid Transfer Proteins (LTPs). OSBP and the closely-related ORP and Osh proteins constitute a major, evolutionarily conserved family of LTPs in eukaryotes. Most of these target one or more subcellular regions, and membrane contact sites in particular, where two organelle membranes are in close proximity. It was initially thought that such proteins were strictly dedicated to sterol sensing or transport. However, over the last decade, numerous studies have revealed that these proteins have many more functions, and we have expanded our understanding of their mechanisms. In particular, many of them are lipid exchangers that exploit PI(4)P or possibly other phosphoinositide gradients to directionally transfer sterol or PS between two compartments. Importantly, these transfer activities are tightly coupled to processes such as lipid metabolism, cellular signalling and vesicular trafficking. This review describes the molecular architecture of OSBP/ORP/Osh proteins, showing how their specific structural features and internal configurations impart unique cellular functions.
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Affiliation(s)
- Vanessa Delfosse
- Centre de Biochimie Structurale, Inserm, CNRS, Univ Montpellier, Montpellier, France
| | - William Bourguet
- Centre de Biochimie Structurale, Inserm, CNRS, Univ Montpellier, Montpellier, France
| | - Guillaume Drin
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d’Azur, Valbonne, France
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62
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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: 32] [Impact Index Per Article: 8.0] [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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63
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Bohnert M. Tether Me, Tether Me Not—Dynamic Organelle Contact Sites in Metabolic Rewiring. Dev Cell 2020; 54:212-225. [DOI: 10.1016/j.devcel.2020.06.026] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 06/17/2020] [Accepted: 06/20/2020] [Indexed: 02/04/2023]
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64
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Wang T, Wei Q, Liang L, Tang X, Yao J, Lu Y, Qu Y, Chen Z, Xing G, Cao X. OSBPL2 Is Required for the Binding of COPB1 to ATGL and the Regulation of Lipid Droplet Lipolysis. iScience 2020; 23:101252. [PMID: 32650117 PMCID: PMC7348002 DOI: 10.1016/j.isci.2020.101252] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 05/03/2020] [Accepted: 06/04/2020] [Indexed: 12/22/2022] Open
Abstract
The accumulation of giant lipid droplets (LDs) increases the risk of metabolic disorders including obesity and insulin resistance. The lipolysis process involves the activation and transfer of lipase, but the molecular mechanism is not completely understood. The translocation of ATGL, a critical lipolysis lipase, from the ER to the LD surface is mediated by an energy catabolism complex. Oxysterol-binding protein-like 2 (OSBPL2/ORP2) is one of the lipid transfer proteins that regulates intracellular cholesterol homeostasis. A recent study has proven that Osbpl2−/− pigs exhibit hypercholesterolemia and obesity phenotypes with an increase in adipocytes. In this study, we identified that OSBPL2 links the endoplasmic reticulum (ER) with LDs, binds to COPB1, and mediates ATGL transport. We provide important insights into the function of OSBPL2, indicating that it is required for the regulation of lipid droplet lipolysis. LD lipolysis is impaired in OSBPL2/osbpl2b-mutant HepG2 cells and zebrafish OSBPL2 interacts with COPB1, a subunit of the COPI complex located on LDs Altered COPI complexes on LDs may perturb the trafficking of lipolysis lipase ATGL
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Affiliation(s)
- Tianming Wang
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China
| | - Qinjun Wei
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China; Jiangsu Key Laboratory of Xenotransplantation, Nanjing Medical University, Nanjing 211166, China; The Laboratory Center for Basic Medical Sciences, Nanjing Medical University, Nanjing 211166, China
| | - Lihong Liang
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China
| | - Xujun Tang
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China
| | - Jun Yao
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China; Jiangsu Key Laboratory of Xenotransplantation, Nanjing Medical University, Nanjing 211166, China
| | - Yajie Lu
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China; Jiangsu Key Laboratory of Xenotransplantation, Nanjing Medical University, Nanjing 211166, China
| | - Yuan Qu
- Jiangsu Cancer Hospital, Nanjing 210009, China
| | - Zhibin Chen
- Department of Otolaryngology, the First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China
| | - Guangqian Xing
- Department of Otolaryngology, the First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China
| | - Xin Cao
- Department of Medical Genetics, School of Basic Medical Science, Nanjing Medical University, Nanjing 211166, China; Jiangsu Key Laboratory of Xenotransplantation, Nanjing Medical University, Nanjing 211166, China; The Laboratory Center for Basic Medical Sciences, Nanjing Medical University, Nanjing 211166, China.
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65
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ORP5 and ORP8: Sterol Sensors and Phospholipid Transfer Proteins at Membrane Contact Sites? Biomolecules 2020; 10:biom10060928. [PMID: 32570981 PMCID: PMC7356933 DOI: 10.3390/biom10060928] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 06/13/2020] [Accepted: 06/16/2020] [Indexed: 02/07/2023] Open
Abstract
Oxysterol binding related proteins 5 and 8 (ORP5 and ORP8) are two close homologs of the larger oxysterol binding protein (OSBP) family of sterol sensors and lipid transfer proteins (LTP). Early studies indicated these transmembrane proteins, anchored to the endoplasmic reticulum (ER), bound and sensed cholesterol and oxysterols. They were identified as important for diverse cellular functions including sterol homeostasis, vesicular trafficking, proliferation and migration. In addition, they were implicated in lipid-related diseases such as atherosclerosis and diabetes, but also cancer, although their mechanisms of action remained poorly understood. Then, alongside the increasing recognition that membrane contact sites (MCS) serve as hubs for non-vesicular lipid transfer, added to their structural similarity to other LTPs, came discoveries showing that ORP5 and 8 were in fact phospholipid transfer proteins that rather sense and exchange phosphatidylserine (PS) for phosphoinositides, including phosphatidylinositol-4-phosphate (PI(4)P) and potentially phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2). Evidence now points to their action at MCS between the ER and various organelles including the plasma membrane, lysosomes, mitochondria, and lipid droplets. Dissecting exactly how this unexpected phospholipid transfer function connects with sterol regulation in health or disease remains a challenge for future studies.
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Abstract
How the distinct lipid composition of organelles is determined and maintained is still poorly understood. In this issue, Du et al. (2019. J. Cell Biol.https://doi.org/10.1083/jcb.201905162) show that the lipid transfer protein ORP5 functions at ER-LD contact sites, regulating lipid droplet levels of phosphatidylserine and phosphatidylinositol-4-phosphate.
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Affiliation(s)
- Mike F. Renne
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Brooke M. Emerling
- Sanford Burnham Prebys Medical Discovery Institute, Cancer Metabolism and Signaling Networks Program, La Jolla, CA
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Hanada K. Organelle contacts: Sub-organelle zones to facilitate rapid and accurate inter-organelle trafficking of lipids. Traffic 2019; 21:189-196. [PMID: 31705775 DOI: 10.1111/tra.12716] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 11/01/2019] [Accepted: 11/05/2019] [Indexed: 12/27/2022]
Abstract
When one person wants to communicate securely with another, he/she should contact the other person directly. This rule applies not only to human society, but also to the intracellular micro-society. In the past two decades, it has become increasingly clear that the sub-organelle regions called membrane contact sites (MCSs) are pivotal for inter-organelle transport of lipids in cells, as highlighted in the thematic review series "Interorganelle trafficking of lipids" held in Traffic in 2014-2015. In this commentary, we will describe how the currently prevailing model for lipid trafficking at MCSs was generated, and comment on three important issues that have not been explored: (a1) the principles guiding the generation of an asymmetrical inter-organelle flow of lipids in cells, (b2) the advantages in lipid trafficking at organelle contacts, and (c3) the dynamic network of inter-organelle lipid trafficking.
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Affiliation(s)
- Kentaro Hanada
- Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Tokyo, Japan
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