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Shirane M. Lipid Transfer-Dependent Endosome Maturation Mediated by Protrudin and PDZD8 in Neurons. Front Cell Dev Biol 2020; 8:615600. [PMID: 33385000 PMCID: PMC7769939 DOI: 10.3389/fcell.2020.615600] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 11/23/2020] [Indexed: 12/16/2022] Open
Abstract
Endosome maturation refers to the conversion of early endosomes (EEs) to late endosomes (LEs) for subsequent fusion with lysosomes. It is an incremental process that involves a combination of endosome fusion and fission and which occurs at contact sites between endosomes and the endoplasmic reticulum (ER), with knowledge of the underlying mechanisms having increased greatly in recent years. Protrudin is an ER-resident protein that was originally shown to regulate neurite formation by promoting endosome trafficking, whereas PDZD8 is a mammalian paralog of a subunit of the yeast ERMES (ER-mitochondrial encounter structure) complex that possesses lipid transfer activity. A complex of protrudin and PDZD8 was recently found to promote endosome maturation by mediating lipid transfer at ER-endosome membrane contact sites. This review focuses on the roles of the protrudin-PDZD8 complex in tethering of endosomes to the ER, in mediating lipid transfer at such contact sites, and in regulating endosome dynamics, especially in neuronal cells. It also addresses the physiological contribution of endosome maturation mediated by this complex to neuronal polarity and integrity.
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Affiliation(s)
- Michiko Shirane
- Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
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52
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Protrudin and PDZD8 contribute to neuronal integrity by promoting lipid extraction required for endosome maturation. Nat Commun 2020; 11:4576. [PMID: 32917905 PMCID: PMC7486383 DOI: 10.1038/s41467-020-18413-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 08/21/2020] [Indexed: 01/08/2023] Open
Abstract
Endosome maturation depends on membrane contact sites (MCSs) formed between endoplasmic reticulum (ER) and endolysosomes (LyLEs). The mechanism underlying lipid supply for this process and its pathophysiological relevance remains unclear, however. Here, we identify PDZD8-the mammalian ortholog of a yeast ERMES subunit-as a protein that interacts with protrudin, which is located at ER-LyLE MCSs. Protrudin and PDZD8 promote the formation of ER-LyLE MCSs, and PDZD8 shows the ability to extract various lipids from the ER. Overexpression of both protrudin and PDZD8 in HeLa cells, as well as their depletion in mouse primary neurons, impairs endosomal homeostasis by inducing the formation of abnormal large vacuoles reminiscent of those apparent in spastin- or REEP1-deficient neurons. The protrudin-PDZD8 system is also essential for the establishment of neuronal polarity. Our results suggest that protrudin and PDZD8 cooperatively promote endosome maturation by mediating ER-LyLE tethering and lipid extraction at MCSs, thereby maintaining neuronal polarity and integrity.
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53
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The short isoform of extended synaptotagmin-2 controls Ca 2+ dynamics in T cells via interaction with STIM1. Sci Rep 2020; 10:14433. [PMID: 32879390 PMCID: PMC7468131 DOI: 10.1038/s41598-020-71489-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Accepted: 08/14/2020] [Indexed: 11/16/2022] Open
Abstract
Ca2+ release-activated Ca2+ (CRAC) channels elevate cytoplasmic Ca2+ concentration, which is essential for T cell activation, differentiation and effector functions. T cell receptor stimulation induces depletion of the endoplasmic reticulum (ER) Ca2+ stores, which is sensed by stromal interaction molecule 1 (STIM1). STIM1 translocates to the ER-plasma membrane (PM) junctions to interact with ORAI1, the pore subunit of the CRAC channels. Here, we show that two members of the extended synaptotagmin (E-Syt) family, E-Syt1, and the short isoform of E-Syt2 (E-Syt2S), contribute to activation of CRAC channels in T cells. Knockdown or deletion of both ESYT1 and ESYT2 reduced store-operated Ca2+ entry (SOCE) and ORAI1-STIM1 clustering in Jurkat T cells. Further, depletion of E-Syts in primary T cells decreased Ca2+ entry and cytokine production. While the ER-PM junctions were reduced in both HeLa and Jurkat T cells deleted for ESYT1 and ESYT2, SOCE was impaired only in Jurkat T cells, suggesting that the membrane-tethering function of E-Syts is distinct from their role in SOCE. Mechanistically, E-Syt2S, the predominant isoform of E-Syt2 in T cells, recruited STIM1 to the junctions via a direct interaction. This study demonstrates a membrane-tethering-independent role of E-Syts in activation of CRAC channels in T cells.
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Balla T, Gulyas G, Kim YJ, Pemberton J. PHOSPHOINOSITIDES AND CALCIUM SIGNALING. A MARRIAGE ARRANGED IN ER-PM CONTACT SITES. CURRENT OPINION IN PHYSIOLOGY 2020; 17:149-157. [PMID: 32944676 DOI: 10.1016/j.cophys.2020.08.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Calcium (Ca2+) ions are critically important in orchestrating countless regulatory processes in eukaryotic cells. Consequently, cells tightly control cytoplasmic Ca2+ concentrations using a complex array of Ca2+-selective ion channels, transporters, and signaling effectors. Ca2+ transport through various cellular membranes is highly dependent on the intrinsic properties of specific membrane compartments and conversely, local Ca2+ changes have profound effects on the membrane lipid composition of such membrane sub-domains. In particular, inositol phospholipids are a minor class of phospholipids that play pivotal roles in the control of Ca2+-dependent signaling pathways. In this review, we will highlight some of the recent advances in this field as well as their impact in defining future research directions.
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Affiliation(s)
- Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Gergo Gulyas
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Yeun Ju Kim
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Joshua Pemberton
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
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55
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Prasad R, Zhou HX. Membrane Association and Functional Mechanism of Synaptotagmin-1 in Triggering Vesicle Fusion. Biophys J 2020; 119:1255-1265. [PMID: 32882186 DOI: 10.1016/j.bpj.2020.08.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 07/23/2020] [Accepted: 08/10/2020] [Indexed: 12/23/2022] Open
Abstract
Upon Ca2+ influx, synaptic vesicles fuse with the presynaptic plasma membrane (PM) to release neurotransmitters. Membrane fusion is triggered by synaptotagmin-1, a transmembrane protein in the vesicle membrane (VM), but the mechanism is under debate. Synaptotagmin-1 contains a single transmembrane helix (TM) and two tandem C2 domains (C2A and C2B). This study aimed to use molecular dynamics simulations to elucidate how Ca2+-bound synaptotagmin-1, by simultaneously associating with VM and PM, brings them together for fusion. Although C2A stably associates with VM via two Ca2+-binding loops, C2B has a propensity to partially dissociate. Importantly, an acidic motif in the TM-C2A linker competes with VM for interacting with C2B, thereby flipping its orientation to face PM. Subsequently, C2B readily associates with PM via a polybasic cluster and a Ca2+-binding loop. The resulting mechanistic model for the triggering of membrane fusion by synaptotagmin-1 reconciles many experimental observations.
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Affiliation(s)
- Ramesh Prasad
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois
| | - Huan-Xiang Zhou
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois; Department of Physics, University of Illinois at Chicago, Chicago, Illinois.
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56
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Nath VR, Mishra S, Basak B, Trivedi D, Raghu P. Extended synaptotagmin regulates membrane contact site structure and lipid transfer function in vivo. EMBO Rep 2020; 21:e50264. [PMID: 32716137 DOI: 10.15252/embr.202050264] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 06/12/2020] [Accepted: 06/22/2020] [Indexed: 12/20/2022] Open
Abstract
Inter-organelle communication between closely apposed membranes is proposed at membrane contact sites (MCS). However, the regulation of MCS structure and their functional relevance in vivo remain debated. The extended synaptotagmins (Esyt) are evolutionarily conserved proteins proposed to function at MCS. However, loss of all three Esyts in yeast or mammals shows minimal phenotypes questioning the functional importance of Esyt. We report that in Drosophila photoreceptors, MCS number is regulated by PLCβ activity. Photoreceptors of a null allele of Drosophila extended synaptotagmin (dEsyt) show loss of ER-PM MCS. Loss of dEsyt results in mislocalization of RDGB, an MCS localized lipid transfer protein, required for photoreceptor structure and function, ultimately leading to retinal degeneration. dEsyt depletion enhanced the retinal degeneration, reduced light responses and slower rates of plasma membrane PIP2 resynthesis seen in rdgB mutants. Thus, dEsyt function and PLCβ signaling regulate ER-PM MCS structure and lipid transfer in Drosophila photoreceptors.
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Affiliation(s)
- Vaisaly R Nath
- National Centre for Biological Sciences-TIFR, Bangalore, India.,School of Biotechnology, Amrita Vishwa Vidyapeetham, Amritapuri, Kollam, Kerala, India
| | - Shirish Mishra
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Bishal Basak
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Deepti Trivedi
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, Bangalore, India
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57
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Zaman MF, Nenadic A, Radojičić A, Rosado A, Beh CT. Sticking With It: ER-PM Membrane Contact Sites as a Coordinating Nexus for Regulating Lipids and Proteins at the Cell Cortex. Front Cell Dev Biol 2020; 8:675. [PMID: 32793605 PMCID: PMC7387695 DOI: 10.3389/fcell.2020.00675] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 07/03/2020] [Indexed: 12/31/2022] Open
Abstract
Membrane contact sites between the cortical endoplasmic reticulum (ER) and the plasma membrane (PM) provide a direct conduit for small molecule transfer and signaling between the two largest membranes of the cell. Contact is established through ER integral membrane proteins that physically tether the two membranes together, though the general mechanism is remarkably non-specific given the diversity of different tethering proteins. Primary tethers including VAMP-associated proteins (VAPs), Anoctamin/TMEM16/Ist2p homologs, and extended synaptotagmins (E-Syts), are largely conserved in most eukaryotes and are both necessary and sufficient for establishing ER-PM association. In addition, other species-specific ER-PM tether proteins impart unique functional attributes to both membranes at the cell cortex. This review distils recent functional and structural findings about conserved and species-specific tethers that form ER-PM contact sites, with an emphasis on their roles in the coordinate regulation of lipid metabolism, cellular structure, and responses to membrane stress.
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Affiliation(s)
- Mohammad F Zaman
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada
| | - Aleksa Nenadic
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada
| | - Ana Radojičić
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada.,Department of Botany, University of British Columbia, Vancouver, BC, Canada
| | - Abel Rosado
- Department of Botany, University of British Columbia, Vancouver, BC, Canada
| | - Christopher T Beh
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada.,The Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC, Canada
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58
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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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59
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Pankratenko AV, Atabekova AK, Morozov SY, Solovyev AG. Membrane Contacts in Plasmodesmata: Structural Components and Their Functions. BIOCHEMISTRY (MOSCOW) 2020; 85:531-544. [DOI: 10.1134/s0006297920050028] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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60
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Balla T, Kim YJ, Alvarez-Prats A, Pemberton J. Lipid Dynamics at Contact Sites Between the Endoplasmic Reticulum and Other Organelles. Annu Rev Cell Dev Biol 2020; 35:85-109. [PMID: 31590585 DOI: 10.1146/annurev-cellbio-100818-125251] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Phospholipids are synthesized primarily within the endoplasmic reticulum and are subsequently distributed to various subcellular membranes to maintain the unique lipid composition of specific organelles. As a result, in most cases, the steady-state localization of membrane phospholipids does not match their site of synthesis. This raises the question of how diverse lipid species reach their final membrane destinations and what molecular processes provide the energy to maintain the lipid gradients that exist between various membrane compartments. Recent studies have highlighted the role of inositol phospholipids in the nonvesicular transport of lipids at membrane contact sites. This review attempts to summarize our current understanding of these complex lipid dynamics and highlights their implications for defining future research directions.
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Affiliation(s)
- Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA;
| | - Yeun Ju Kim
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA;
| | - Alejandro Alvarez-Prats
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA;
| | - Joshua Pemberton
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA;
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61
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Petit JD, Li ZP, Nicolas WJ, Grison MS, Bayer EM. Dare to change, the dynamics behind plasmodesmata-mediated cell-to-cell communication. CURRENT OPINION IN PLANT BIOLOGY 2020; 53:80-89. [PMID: 31805513 DOI: 10.1016/j.pbi.2019.10.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 10/18/2019] [Accepted: 10/21/2019] [Indexed: 06/10/2023]
Abstract
Plasmodesmata pores control the entry and exit of molecules at cell-to-cell boundaries. Hundreds of pores perforate the plant cell wall, connecting cells together and establishing direct cytosolic and membrane continuity. This ability to connect cells in such a way is a hallmark of plant physiology and is thought to have allowed sessile multicellularity in Plantae kingdom. Indeed, plasmodesmata-mediated cell-to-cell signalling is fundamental to many plant-related processes. In fact, there are so many facets of plant biology under the control of plasmodesmata that it is hard to conceive how such tiny structures can do so much. While they provide 'open doors' between cells, they also need to guarantee cellular identities and territories by selectively transporting molecules. Although plasmodesmata operating mode remains difficult to grasp, little by little plant scientists are divulging their secrets. In this review, we highlight novel functions of cell-to-cell signalling and share recent insights into how plasmodesmata structural and molecular signatures confer functional specificity and plasticity to these unique cellular machines.
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Affiliation(s)
- Jules D Petit
- Laboratoire de Biogenèse Membranaire, UMR5200 CNRS, Université de Bordeaux, Villenave d'Ornon, France; Laboratoire de Biophysique Moléculaire aux Interfaces, TERRA Research Centre, GX ABT, Université de Liège, Gembloux, Belgium
| | - Ziqiang Patrick Li
- Laboratoire de Biogenèse Membranaire, UMR5200 CNRS, Université de Bordeaux, Villenave d'Ornon, France
| | - William J Nicolas
- Laboratoire de Biogenèse Membranaire, UMR5200 CNRS, Université de Bordeaux, Villenave d'Ornon, France
| | - Magali S Grison
- Laboratoire de Biogenèse Membranaire, UMR5200 CNRS, Université de Bordeaux, Villenave d'Ornon, France
| | - Emmanuelle M Bayer
- Laboratoire de Biogenèse Membranaire, UMR5200 CNRS, Université de Bordeaux, Villenave d'Ornon, France.
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62
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Öztürk Z, O’Kane CJ, Pérez-Moreno JJ. Axonal Endoplasmic Reticulum Dynamics and Its Roles in Neurodegeneration. Front Neurosci 2020; 14:48. [PMID: 32116502 PMCID: PMC7025499 DOI: 10.3389/fnins.2020.00048] [Citation(s) in RCA: 69] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 01/13/2020] [Indexed: 12/13/2022] Open
Abstract
The physical continuity of axons over long cellular distances poses challenges for their maintenance. One organelle that faces this challenge is endoplasmic reticulum (ER); unlike other intracellular organelles, this forms a physically continuous network throughout the cell, with a single membrane and a single lumen. In axons, ER is mainly smooth, forming a tubular network with occasional sheets or cisternae and low amounts of rough ER. It has many potential roles: lipid biosynthesis, glucose homeostasis, a Ca2+ store, protein export, and contacting and regulating other organelles. This tubular network structure is determined by ER-shaping proteins, mutations in some of which are causative for neurodegenerative disorders such as hereditary spastic paraplegia (HSP). While axonal ER shares many features with the tubular ER network in other contexts, these features must be adapted to the long and narrow dimensions of axons. ER appears to be physically continuous throughout axons, over distances that are enormous on a subcellular scale. It is therefore a potential channel for long-distance or regional communication within neurons, independent of action potentials or physical transport of cargos, but involving its physiological roles such as Ca2+ or organelle homeostasis. Despite its apparent stability, axonal ER is highly dynamic, showing features like anterograde and retrograde transport, potentially reflecting continuous fusion and breakage of the network. Here we discuss the transport processes that must contribute to this dynamic behavior of ER. We also discuss the model that these processes underpin a homeostatic process that ensures both enough ER to maintain continuity of the network and repair breaks in it, but not too much ER that might disrupt local cellular physiology. Finally, we discuss how failure of ER organization in axons could lead to axon degenerative diseases, and how a requirement for ER continuity could make distal axons most susceptible to degeneration in conditions that disrupt ER continuity.
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Affiliation(s)
| | - Cahir J. O’Kane
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
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63
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SMP domain proteins in membrane lipid dynamics. Biochim Biophys Acta Mol Cell Biol Lipids 2020; 1865:158447. [DOI: 10.1016/j.bbalip.2019.04.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 12/20/2018] [Accepted: 01/06/2019] [Indexed: 11/24/2022]
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64
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Prinz WA, Toulmay A, Balla T. The functional universe of membrane contact sites. Nat Rev Mol Cell Biol 2020; 21:7-24. [PMID: 31732717 PMCID: PMC10619483 DOI: 10.1038/s41580-019-0180-9] [Citation(s) in RCA: 345] [Impact Index Per Article: 86.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2019] [Indexed: 12/13/2022]
Abstract
Organelles compartmentalize eukaryotic cells, enhancing their ability to respond to environmental and developmental changes. One way in which organelles communicate and integrate their activities is by forming close contacts, often called 'membrane contact sites' (MCSs). Interest in MCSs has grown dramatically in the past decade as it is has become clear that they are ubiquitous and have a much broader range of critical roles in cells than was initially thought. Indeed, functions for MCSs in intracellular signalling (particularly calcium signalling, reactive oxygen species signalling and lipid signalling), autophagy, lipid metabolism, membrane dynamics, cellular stress responses and organelle trafficking and biogenesis have now been reported.
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Affiliation(s)
- William A Prinz
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
| | - Alexandre Toulmay
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Tamas Balla
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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65
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Pemberton JG, Kim YJ, Balla T. Integrated regulation of the phosphatidylinositol cycle and phosphoinositide-driven lipid transport at ER-PM contact sites. Traffic 2019; 21:200-219. [PMID: 31650663 DOI: 10.1111/tra.12709] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 10/02/2019] [Accepted: 10/16/2019] [Indexed: 12/20/2022]
Abstract
Among the structural phospholipids that form the bulk of eukaryotic cell membranes, phosphatidylinositol (PtdIns) is unique in that it also serves as the common precursor for low-abundance regulatory lipids, collectively referred to as polyphosphoinositides (PPIn). The metabolic turnover of PPIn species has received immense attention because of the essential functions of these lipids as universal regulators of membrane biology and their dysregulation in numerous human pathologies. The diverse functions of PPIn lipids occur, in part, by orchestrating the spatial organization and conformational dynamics of peripheral or integral membrane proteins within defined subcellular compartments. The emerging role of stable contact sites between adjacent membranes as specialized platforms for the coordinate control of ion exchange, cytoskeletal dynamics, and lipid transport has also revealed important new roles for PPIn species. In this review, we highlight the importance of membrane contact sites formed between the endoplasmic reticulum (ER) and plasma membrane (PM) for the integrated regulation of PPIn metabolism within the PM. Special emphasis will be placed on non-vesicular lipid transport during control of the PtdIns biosynthetic cycle as well as toward balancing the turnover of the signaling PPIn species that define PM identity.
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Affiliation(s)
- Joshua G Pemberton
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health, Bethesda, Maryland
| | - Yeun Ju Kim
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health, Bethesda, Maryland
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health, Bethesda, Maryland
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Abstract
Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of lipid traffic is mediated by a large group of lipid transfer proteins (LTPs), which move small numbers of lipids at a time using hydrophobic cavities that stabilize lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with lipid transport and distribution, opening up the possibility of developing therapies that specifically target lipid transfer.
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67
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Collado J, Kalemanov M, Campelo F, Bourgoint C, Thomas F, Loewith R, Martínez-Sánchez A, Baumeister W, Stefan CJ, Fernández-Busnadiego R. Tricalbin-Mediated Contact Sites Control ER Curvature to Maintain Plasma Membrane Integrity. Dev Cell 2019; 51:476-487.e7. [PMID: 31743662 PMCID: PMC6863395 DOI: 10.1016/j.devcel.2019.10.018] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Revised: 09/23/2019] [Accepted: 10/16/2019] [Indexed: 12/23/2022]
Abstract
Membrane contact sites (MCS) between the endoplasmic reticulum (ER) and the plasma membrane (PM) play fundamental roles in all eukaryotic cells. ER-PM MCS are particularly abundant in Saccharomyces cerevisiae, where approximately half of the PM surface is covered by cortical ER (cER). Several proteins, including Ist2, Scs2/22, and Tcb1/2/3 are implicated in cER formation, but the specific roles of these molecules are poorly understood. Here, we use cryo-electron tomography to show that ER-PM tethers are key determinants of cER morphology. Notably, Tcb proteins (tricalbins) form peaks of extreme curvature on the cER membrane facing the PM. Combined modeling and functional assays suggest that Tcb-mediated cER peaks facilitate the transport of lipids between the cER and the PM, which is necessary to maintain PM integrity under heat stress. ER peaks were also present at other MCS, implying that membrane curvature enforcement may be a widespread mechanism to regulate MCS function.
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Affiliation(s)
- Javier Collado
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany; Institute of Neuropathology, University Medical Center Göttingen, Göttingen 37099, Germany; Graduate School of Quantitative Biosciences Munich, Munich 81337, Germany
| | - Maria Kalemanov
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany; Graduate School of Quantitative Biosciences Munich, Munich 81337, Germany
| | - Felix Campelo
- ICFO, Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels 08860, Spain
| | - Clélia Bourgoint
- Department of Molecular Biology, University of Geneva, Geneva 1211, Switzerland
| | - Ffion Thomas
- MRC Laboratory for Molecular Cell Biology, University College London, London, WC1E 6BT, UK
| | - Robbie Loewith
- Department of Molecular Biology, University of Geneva, Geneva 1211, Switzerland; Swiss National Centre for Competence in Research, Program Chemical Biology, Geneva 1211, Switzerland
| | - Antonio Martínez-Sánchez
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany
| | - Christopher J Stefan
- MRC Laboratory for Molecular Cell Biology, University College London, London, WC1E 6BT, UK
| | - Rubén Fernández-Busnadiego
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany; Institute of Neuropathology, University Medical Center Göttingen, Göttingen 37099, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany.
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Hoffmann PC, Bharat TAM, Wozny MR, Boulanger J, Miller EA, Kukulski W. Tricalbins Contribute to Cellular Lipid Flux and Form Curved ER-PM Contacts that Are Bridged by Rod-Shaped Structures. Dev Cell 2019; 51:488-502.e8. [PMID: 31743663 PMCID: PMC6863393 DOI: 10.1016/j.devcel.2019.09.019] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Revised: 08/06/2019] [Accepted: 09/25/2019] [Indexed: 11/25/2022]
Abstract
Lipid flow between cellular organelles occurs via membrane contact sites. Extended-synaptotagmins, known as tricalbins in yeast, mediate lipid transfer between the endoplasmic reticulum (ER) and plasma membrane (PM). How these proteins regulate membrane architecture to transport lipids across the aqueous space between bilayers remains unknown. Using correlative microscopy, electron cryo-tomography, and high-throughput genetics, we address the interplay of architecture and function in budding yeast. We find that ER-PM contacts differ in protein composition and membrane morphology, not in intermembrane distance. In situ electron cryo-tomography reveals the molecular organization of tricalbin-mediated contacts, suggesting a structural framework for putative lipid transfer. Genetic analysis uncovers functional overlap with cellular lipid routes, such as maintenance of PM asymmetry. Further redundancies are suggested for individual tricalbin protein domains. We propose a modularity of molecular and structural functions of tricalbins and of their roles within the cellular network of lipid distribution pathways.
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Affiliation(s)
- Patrick C Hoffmann
- Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Tanmay A M Bharat
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK; Central Oxford Structural Microscopy and Imaging Centre, South Parks Road, Oxford OX1 3RE, UK
| | - Michael R Wozny
- Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Jerome Boulanger
- Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Elizabeth A Miller
- Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Wanda Kukulski
- Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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69
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Fowler PC, Garcia-Pardo ME, Simpson JC, O'Sullivan NC. NeurodegenERation: The Central Role for ER Contacts in Neuronal Function and Axonopathy, Lessons From Hereditary Spastic Paraplegias and Related Diseases. Front Neurosci 2019; 13:1051. [PMID: 31680803 PMCID: PMC6801308 DOI: 10.3389/fnins.2019.01051] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 09/19/2019] [Indexed: 12/17/2022] Open
Abstract
The hereditary spastic paraplegias (HSPs) are a group of inherited neurodegenerative conditions whose characteristic feature is degeneration of the longest axons within the corticospinal tract which leads to progressive spasticity and weakness of the lower limbs. Though highly genetically heterogeneous, the majority of HSP cases are caused by mutations in genes encoding proteins that are responsible for generating and organizing the tubular endoplasmic reticulum (ER). Despite this, the role of the ER within neurons, particularly the long axons affected in HSP, is not well understood. Throughout axons, ER tubules make extensive contacts with other organelles, the cytoskeleton and the plasma membrane. At these ER contacts, protein complexes work in concert to perform specialized functions including organelle shaping, calcium homeostasis and lipid biogenesis, all of which are vital for neuronal survival and may be disrupted by HSP-causing mutations. In this article we summarize the proteins which mediate ER contacts, review the functions these contacts are known to carry out within neurons, and discuss the potential contribution of disruption of ER contacts to axonopathy in HSP.
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Affiliation(s)
- Philippa C Fowler
- UCD School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Dublin, Ireland
| | - M Elena Garcia-Pardo
- UCD School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Dublin, Ireland
| | - Jeremy C Simpson
- UCD School of Biology and Environmental Science, UCD Conway Institute, University College Dublin, Dublin, Ireland
| | - Niamh C O'Sullivan
- UCD School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Dublin, Ireland
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70
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Brault ML, Petit JD, Immel F, Nicolas WJ, Glavier M, Brocard L, Gaston A, Fouché M, Hawkins TJ, Crowet J, Grison MS, Germain V, Rocher M, Kraner M, Alva V, Claverol S, Paterlini A, Helariutta Y, Deleu M, Lins L, Tilsner J, Bayer EM. Multiple C2 domains and transmembrane region proteins (MCTPs) tether membranes at plasmodesmata. EMBO Rep 2019; 20:e47182. [PMID: 31286648 PMCID: PMC6680132 DOI: 10.15252/embr.201847182] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Revised: 05/28/2019] [Accepted: 06/06/2019] [Indexed: 12/20/2022] Open
Abstract
In eukaryotes, membrane contact sites (MCS) allow direct communication between organelles. Plants have evolved a unique type of MCS, inside intercellular pores, the plasmodesmata, where endoplasmic reticulum (ER)-plasma membrane (PM) contacts coincide with regulation of cell-to-cell signalling. The molecular mechanism and function of membrane tethering within plasmodesmata remain unknown. Here, we show that the multiple C2 domains and transmembrane region protein (MCTP) family, key regulators of cell-to-cell signalling in plants, act as ER-PM tethers specifically at plasmodesmata. We report that MCTPs are plasmodesmata proteins that insert into the ER via their transmembrane region while their C2 domains dock to the PM through interaction with anionic phospholipids. A Atmctp3/Atmctp4 loss of function mutant induces plant developmental defects, impaired plasmodesmata function and composition, while MCTP4 expression in a yeast Δtether mutant partially restores ER-PM tethering. Our data suggest that MCTPs are unique membrane tethers controlling both ER-PM contacts and cell-to-cell signalling.
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Affiliation(s)
- Marie L Brault
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - Jules D Petit
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
- Laboratoire de Biophysique Moléculaire aux InterfacesTERRA Research Centre, GX ABTUniversité de LiègeGemblouxBelgium
| | - Françoise Immel
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - William J Nicolas
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
- Present address:
Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaCAUSA
| | - Marie Glavier
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - Lysiane Brocard
- Bordeaux Imaging CentrePlant Imaging PlatformUMS 3420, INRA‐CNRS‐INSERM‐University of BordeauxVillenave‐d'OrnonFrance
| | - Amèlia Gaston
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
- Present address:
UMR 1332 BFPINRAUniversity of BordeauxBordeauxFrance
| | - Mathieu Fouché
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
- Present address:
UMR 1332 BFPINRAUniversity of BordeauxBordeauxFrance
| | | | - Jean‐Marc Crowet
- Laboratoire de Biophysique Moléculaire aux InterfacesTERRA Research Centre, GX ABTUniversité de LiègeGemblouxBelgium
- Present address:
Matrice Extracellulaire et Dynamique Cellulaire MEDyCUMR7369, CNRSUniversité de Reims‐Champagne‐ArdenneReimsFrance
| | - Magali S Grison
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - Véronique Germain
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - Marion Rocher
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
| | - Max Kraner
- Division of BiochemistryDepartment of BiologyFriedrich‐Alexander University Erlangen‐NurembergErlangenGermany
| | - Vikram Alva
- Department of Protein EvolutionMax Planck Institute for Developmental BiologyTübingenGermany
| | - Stéphane Claverol
- Proteome PlatformFunctional Genomic Center of BordeauxUniversity of BordeauxBordeaux CedexFrance
| | | | - Ykä Helariutta
- The Sainsbury LaboratoryUniversity of CambridgeCambridgeUK
| | - Magali Deleu
- Laboratoire de Biophysique Moléculaire aux InterfacesTERRA Research Centre, GX ABTUniversité de LiègeGemblouxBelgium
| | - Laurence Lins
- Laboratoire de Biophysique Moléculaire aux InterfacesTERRA Research Centre, GX ABTUniversité de LiègeGemblouxBelgium
| | - Jens Tilsner
- Biomedical Sciences Research ComplexUniversity of St AndrewsFifeUK
- Cell and Molecular SciencesThe James Hutton InstituteDundeeUK
| | - Emmanuelle M Bayer
- Laboratoire de Biogenèse MembranaireUMR5200, CNRSUniversité de BordeauxVillenave d'OrnonFrance
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71
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A programmable DNA-origami platform for studying lipid transfer between bilayers. Nat Chem Biol 2019; 15:830-837. [PMID: 31320758 PMCID: PMC6650167 DOI: 10.1038/s41589-019-0325-3] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 06/14/2019] [Indexed: 02/07/2023]
Abstract
Non-vesicular lipid transport between bilayers at membrane contact sites plays important physiological roles. Mechanistic insight into the action of lipid transport proteins localized at these sites (bridge/tunnel versus shuttle models) requires a determination of the distance between bilayers at which this transport can occur. Here, we developed DNA-origami nanostructures to organize size-defined liposomes at precise distances and used them to study lipid transfer by the SMP domain of E-Syt1. Pairs of DNA-ring-templated donor and acceptor liposomes were docked through DNA pillars, which determined their distance. The SMP domain was anchored to donor liposomes via an unstructured linker and lipid transfer was assessed via a FRET-based assay. We show that lipid transfer can occur over distances that exceed the length of SMP dimer, compatible with a shuttle model. The DNA nanostructures developed here can be adapted to study other processes occurring where two membranes are closely apposed to each other.
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72
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Bian X, De Camilli P. In Vitro Assays to Measure the Membrane Tethering and Lipid Transport Activities of the Extended Synaptotagmins. Methods Mol Biol 2019; 1949:201-212. [PMID: 30790258 DOI: 10.1007/978-1-4939-9136-5_15] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
The three extended synaptotagmins (E-Syts) are endoplasmic reticulum (ER)-localized membrane proteins that mediate tethering of the ER to the plasma membrane (PM) via C2 domain-dependent interactions regulated by Ca2+ and/or PI(4,5)P2. The E-Syts also contains a Synaptotagmin-like Mitochondrial lipid-binding Protein (SMP) domain, a lipid-harboring module through which they mediate lipid transport between the two adjacent membranes. Here, we describe in vitro liposome-based methods to study the membrane tethering and lipid transport functions of E-Syt1. Its membrane tethering activity is monitored through a turbidity-based assay, and its lipid transport property is analyzed via fluorescence resonance energy transfer (FRET)-based assay. These in vitro methods have enabled us to gain insight into the mechanism of action and regulation of E-Syt1, such as the role of Ca2+ in releasing E-Syt1 from an autoinhibitory conformation. The same methods could be adapted to the study of other lipid transport proteins that function at membrane contact sites.
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Affiliation(s)
- Xin Bian
- Department of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration, and Repair, and Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, USA
| | - Pietro De Camilli
- Department of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration, and Repair, and Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, USA.
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73
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Bozelli JC, Epand RM. Role of membrane shape in regulating the phosphatidylinositol cycle at contact sites. Chem Phys Lipids 2019; 221:24-29. [DOI: 10.1016/j.chemphyslip.2019.03.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 02/25/2019] [Accepted: 03/01/2019] [Indexed: 01/09/2023]
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74
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Liu Y, Zhang C, Li L, Ou B, Yuan L, Zhang T, Fan J, Peng Z. Genome-Wide Association Study of Tacrolimus Pharmacokinetics Identifies Novel Single Nucleotide Polymorphisms in the Convalescence and Stabilization Periods of Post-transplant Liver Function. Front Genet 2019; 10:528. [PMID: 31214251 PMCID: PMC6554639 DOI: 10.3389/fgene.2019.00528] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 05/14/2019] [Indexed: 12/15/2022] Open
Abstract
After liver transplantation, the liver function of a patient is gradually restored over a period of time that can be divided into a convalescence period (CP) and a stabilizing period (SP). The plasma concentration of tacrolimus, an immunosuppressant commonly used to prevent organ rejection, varies as a result of variations in its metabolism. The effects of genetic and clinical factors on the plasma concentration of tacrolimus appear to differ in the CP and SP. To establish a model explaining the variation in tacrolimus trough concentration between individuals in the CP and SP, we conducted a retrospective, single-center, discovery study of 115 pairs of patients (115 donors and 115 matched recipients) who had undergone liver transplantation. Donors and recipients were genotyped by a genome-wide association study (GWAS) using an exome chip. Novel exons were identified that influenced tacrolimus trough concentrations and were verified with bootstrap analysis. In donors, two single-nucleotide polymorphisms showed an effect on the CP (rs1927321, rs1057192) and four showed an effect on the SP (rs776746, rs2667662, rs7980521, rs4903096); in recipients, two single-nucleotide polymorphisms showed an effect in the SP (rs7828796, rs776746). Genetic factors played a crucial role in tacrolimus metabolism, accounting for 44.8% in the SP, which was higher than previously reported. In addition, we found that CYP3A5, which is known to affect the metabolism of tacrolimus, only influenced tacrolimus pharmacokinetics in the SP.
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Affiliation(s)
- Yuan Liu
- Department of Hepatobiliary Pancreatic Surgery, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Chengdong Zhang
- State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai, China
| | - Lei Li
- Department of Hepatobiliary Pancreatic Surgery, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Baochi Ou
- Department of Hepatobiliary Pancreatic Surgery, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Liyun Yuan
- Key Lab of Computational Biology, CAS-MPG Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Tao Zhang
- Department of Organ Transplant, The Second Affiliated Hospital to Guangzhou Medical University, Guangzhou, China
| | - Junwei Fan
- Department of Hepatobiliary Pancreatic Surgery, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Zhihai Peng
- Department of Hepatobiliary Pancreatic Surgery, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
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75
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Valverde DP, Yu S, Boggavarapu V, Kumar N, Lees JA, Walz T, Reinisch KM, Melia TJ. ATG2 transports lipids to promote autophagosome biogenesis. J Cell Biol 2019; 218:1787-1798. [PMID: 30952800 PMCID: PMC6548141 DOI: 10.1083/jcb.201811139] [Citation(s) in RCA: 327] [Impact Index Per Article: 65.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Revised: 03/05/2019] [Accepted: 03/28/2019] [Indexed: 02/07/2023] Open
Abstract
Valverde et al. show that the autophagy protein ATG2 functions in autophagosome biogenesis by transferring lipids at ER–autophagosome contact sites. During macroautophagic stress, autophagosomes can be produced continuously and in high numbers. Many different organelles have been reported as potential donor membranes for this sustained autophagosome growth, but specific machinery to support the delivery of lipid to the growing autophagosome membrane has remained unknown. Here we show that the autophagy protein, ATG2, without a clear function since its discovery over 20 yr ago, is in fact a lipid-transfer protein likely operating at the ER–autophagosome interface. ATG2A can bind tens of glycerophospholipids at once and transfers lipids robustly in vitro. An N-terminal fragment of ATG2A that supports lipid transfer in vitro is both necessary and fully sufficient to rescue blocked autophagosome biogenesis in ATG2A/ATG2B KO cells, implying that regulation of lipid homeostasis is the major autophagy-dependent activity of this protein and, by extension, that protein-mediated lipid transfer across contact sites is a principal contributor to autophagosome formation.
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Affiliation(s)
- Diana P Valverde
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Shenliang Yu
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Venkata Boggavarapu
- Laboratory of Molecular Electron Microscopy, The Rockefeller University, New York, NY
| | - Nikit Kumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Joshua A Lees
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Thomas Walz
- Laboratory of Molecular Electron Microscopy, The Rockefeller University, New York, NY
| | - Karin M Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Thomas J Melia
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
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76
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Lipid transporter TMEM24/C2CD2L is a Ca 2+-regulated component of ER-plasma membrane contacts in mammalian neurons. Proc Natl Acad Sci U S A 2019; 116:5775-5784. [PMID: 30819882 DOI: 10.1073/pnas.1820156116] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Close appositions between the endoplasmic reticulum (ER) and the plasma membrane (PM) are a general feature of all cells and are abundant in neurons. A function of these appositions is lipid transport between the two adjacent bilayers via tethering proteins that also contain lipid transport modules. However, little is known about the properties and dynamics of these proteins in neurons. Here we focused on TMEM24/C2CD2L, an ER-localized SMP domain containing phospholipid transporter expressed at high levels in the brain, previously shown to be a component of ER-PM contacts in pancreatic β-cells. TMEM24 is enriched in neurons versus glial cells and its levels increase in parallel with neuronal differentiation. It populates ER-PM contacts in resting neurons, but elevations of cytosolic Ca2+ mediated by experimental manipulations or spontaneous activity induce its transient redistribution throughout the entire ER. Dissociation of TMEM24 from the plasma membrane is mediated by phosphorylation of an array of sites in the C-terminal region of the protein. These sites are only partially conserved in C2CD2, the paralogue of TMEM24 primarily expressed in nonneuronal tissues, which correspondingly display a much lower sensitivity to Ca2+ elevations. ER-PM contacts in neurons are also sites where Kv2 (the major delayed rectifier K+ channels in brain) and other PM and ER ion channels are concentrated, raising the possibility of a regulatory feedback mechanism between neuronal excitability and lipid exchange between the ER and the PM.
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77
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Tamura Y, Kawano S, Endo T. Organelle contact zones as sites for lipid transfer. J Biochem 2019; 165:115-123. [PMID: 30371789 DOI: 10.1093/jb/mvy088] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Accepted: 10/26/2018] [Indexed: 01/06/2023] Open
Abstract
Since the 1950s, electron microscopic observations have suggested the existence of special regions where the distinct organelle membranes are closely apposed to each other, yet their molecular basis and functions have not been examined for a long time. Recent studies using yeast as a model organism identified multiple organelle-membrane tethering sites/factors, such as ERMES (ER-mitochondria encounter structure), NVJ (Nuclear-vacuole junction), vCLAMP (Vacuole and mitochondria patch) and MICOS (Mitochondrial contact site). Among them, ERMES is the best-characterized contact-site protein complex, which was found to function as not only an organelle-tethering factor but also a phospholipid transfer protein complex. In this review, we will discuss recent advances in the characterization of ERMES and other organelle contact zones, vCLAMP, NVJ and MICOS in yeast.
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Affiliation(s)
- Yasushi Tamura
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata, Japan
| | - Shin Kawano
- Faculty of Life Sciences, Kyoto Sangyo University, Kamigamo-motoyama, Kita-ku, Kyoto, Japan.,Research Center for Protein Dynamics, Kyoto Sangyo University, Kamigamo-motoyama, Kita-ku, Kyoto, Japan
| | - Toshiya Endo
- Faculty of Life Sciences, Kyoto Sangyo University, Kamigamo-motoyama, Kita-ku, Kyoto, Japan.,Research Center for Protein Dynamics, Kyoto Sangyo University, Kamigamo-motoyama, Kita-ku, Kyoto, Japan
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78
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Regulation of targeting determinants in interorganelle communication. Curr Opin Cell Biol 2019; 57:106-114. [PMID: 30807956 DOI: 10.1016/j.ceb.2018.12.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Revised: 12/27/2018] [Accepted: 12/28/2018] [Indexed: 01/02/2023]
Abstract
The field of interorganelle communication is now established as a major aspect of intracellular organisation, with a profusion of material and signals exchanged between organelles. One way to address interorganelle communication is to study the interactions of the proteins involved, particularly targeting interactions, which are a key way to regulate activity. While most peripheral membrane proteins have single determinants for membrane targeting, proteins involved in interorganelle communication have more than one such determinant, sometimes as many as four, as in Vps13. Here we review the targeting determinants, showing how they can be relatively hard to find, how they are regulated, and how proteins integrate information from multiple targeting determinants.
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79
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In Vitro Strategy to Measure Sterol/Phosphatidylinositol-4-Phosphate Exchange Between Membranes. Methods Mol Biol 2019. [PMID: 30790262 DOI: 10.1007/978-1-4939-9136-5_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Recent findings unveiled that Oxysterol-binding protein-related proteins (ORP)/Oxysterol-binding homology (Osh) proteins, which constitute a major family of lipid transfer proteins (LTPs), conserved among eukaryotes, are not all mere sterol transporters or sensors. Indeed, some of them are able to exchange sterol for phosphatidylinositol-4-phosphate (PI4P) or phosphatidylserine (PS) for PI4P between membranes and thereby to use PI4P metabolism to generate sterol or PS gradients in the cell, respectively. Here, we describe a full strategy to measure in vitro a sterol/PI4P exchange process between artificial membranes using Förster resonance energy transfer (FRET)-based assays and a standard spectrofluorometer. Such an approach can serve to better characterize the activity of known sterol/PI4P exchangers, but also to reveal whether ill-defined ORP/Osh proteins or LTPs belonging to other families have such an exchange activity. Besides, this protocol is amenable to test whether molecules can act as Orphilins, which have been found to inhibit the sterol/PI4P exchange activity of certain ORPs. Last, our strategy to measure in real-time PI4P transport using a known lipid-binding domain can serve as a basis for the design of novel in vitro protocols aiming to detect other lipid species.
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80
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Petit JD, Immel F, Lins L, Bayer EM. Lipids or Proteins: Who Is Leading the Dance at Membrane Contact Sites? FRONTIERS IN PLANT SCIENCE 2019; 10:198. [PMID: 30846999 PMCID: PMC6393330 DOI: 10.3389/fpls.2019.00198] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Accepted: 02/05/2019] [Indexed: 05/19/2023]
Abstract
Understanding the mode of action of membrane contact sites (MCSs) across eukaryotic organisms at the near-atomic level to infer function at the cellular and tissue levels is a challenge scientists are currently facing. These peculiar systems dedicated to inter-organellar communication are perfect examples of cellular processes where the interplay between lipids and proteins is critical. In this mini review, we underline the link between membrane lipid environment, the recruitment of proteins at specialized membrane domains and the function of MCSs. More precisely, we want to give insights on the crucial role of lipids in defining the specificity of plant endoplasmic reticulum (ER)-plasma membrane (PM) MCSs and we further propose approaches to study them at multiple scales. Our goal is not so much to go into detailed description of MCSs, as there are numerous focused reviews on the subject, but rather try to pinpoint the critical elements defining those structures and give an original point of view by considering the subject from a near-atomic angle with a focus on lipids. We review current knowledge as to how lipids can define MCS territories, play a role in the recruitment and function of the MCS-associated proteins and in turn, how the lipid environment can be modified by proteins.
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Affiliation(s)
- Jules D. Petit
- UMR5200 CNRS, Laboratory of Membrane Biogenesis, University of Bordeaux, Villenave d’Ornon, France
- Laboratoire de Biophysique Moléculaire aux Interfaces, TERRA Research Centre, GX ABT, Université de Liège, Liège, Belgium
| | - Françoise Immel
- UMR5200 CNRS, Laboratory of Membrane Biogenesis, University of Bordeaux, Villenave d’Ornon, France
| | - Laurence Lins
- Laboratoire de Biophysique Moléculaire aux Interfaces, TERRA Research Centre, GX ABT, Université de Liège, Liège, Belgium
| | - Emmanuelle M. Bayer
- UMR5200 CNRS, Laboratory of Membrane Biogenesis, University of Bordeaux, Villenave d’Ornon, France
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81
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Chen YJ, Quintanilla CG, Liou J. Recent insights into mammalian ER-PM junctions. Curr Opin Cell Biol 2019; 57:99-105. [PMID: 30739879 DOI: 10.1016/j.ceb.2018.12.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Accepted: 12/21/2018] [Indexed: 11/28/2022]
Abstract
ER-PM junctions are subcellular sites where the endoplasmic reticulum (ER) and the plasma membrane (PM) are kept in close appositions, providing a platform for inter-organelle contact. These membrane contact sites are important for many physiological functions in mammalian cells, including excitation-contraction coupling, store-operated Ca2+ entry, and non-vesicular transfer of lipids between the ER and the PM. Here we review recent insights into the 3D structure and spatial organization of ER-PM junctions in mammalian cells as well as molecular mechanisms underlying the formation and functions of mammalian ER-PM junctions.
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Affiliation(s)
- Yu-Ju Chen
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | | | - Jen Liou
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX 75390, USA.
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82
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Xie B, Nguyen PM, Idevall-Hagren O. Feedback regulation of insulin secretion by extended synaptotagmin-1. FASEB J 2018; 33:4716-4728. [PMID: 30589572 DOI: 10.1096/fj.201801878r] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Endoplasmic reticulum (ER)-plasma membrane (PM) contacts are dynamic structures with important roles in the regulation of calcium (Ca2+) and lipid homeostasis. The extended synaptotagmins (E-Syts) are ER-localized lipid transport proteins that interact with PM phosphatidylinositol 4,5-bisphosphate in a Ca2+-dependent manner. E-Syts bidirectionally transfer glycerolipids, including diacylglycerol (DAG), between the 2 juxtaposed membranes, but the biologic significance of this transport is still unclear. Using insulin-secreting cells and live-cell imaging, we now show that Ca2+-triggered exocytosis of insulin granules is followed, in sequence, by PM DAG formation and E-Syt1 recruitment. E-Syt1 counteracted the depolarization-induced DAG formation through a mechanism that required both voltage-dependent Ca2+ influx and Ca2+ release from the ER. E-Syt1 knockdown resulted in prolonged accumulation of DAG in the PM, resulting in increased glucose-stimulated insulin secretion. We conclude that Ca2+-triggered exocytosis is temporally coupled to Ca2+-triggered E-Syt1 PM recruitment and removal of DAG to negatively regulate the same process.-Xie, B., Nguyen, P. M., Idevall-Hagren, O. Feedback regulation of insulin secretion by extended synaptotagmin-1.
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Affiliation(s)
- Beichen Xie
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Phuoc My Nguyen
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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83
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Kumar N, Leonzino M, Hancock-Cerutti W, Horenkamp FA, Li P, Lees JA, Wheeler H, Reinisch KM, De Camilli P. VPS13A and VPS13C are lipid transport proteins differentially localized at ER contact sites. J Cell Biol 2018; 217:3625-3639. [PMID: 30093493 PMCID: PMC6168267 DOI: 10.1083/jcb.201807019] [Citation(s) in RCA: 367] [Impact Index Per Article: 61.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 07/13/2018] [Accepted: 07/17/2018] [Indexed: 01/07/2023] Open
Abstract
Structural and biochemical studies show that VPS13 family proteins are lipid transporters. VPS13A and VPS13C tether the ER to mitochondria and to endosomes/lysosomes, respectively, suggesting lipid dyshomeostasis as the cause of chorea acanthocytosis and Parkinson’s disease resulting from their mutations. Mutations in the human VPS13 genes are responsible for neurodevelopmental and neurodegenerative disorders including chorea acanthocytosis (VPS13A) and Parkinson’s disease (VPS13C). The mechanisms of these diseases are unknown. Genetic studies in yeast hinted that Vps13 may have a role in lipid exchange between organelles. In this study, we show that the N-terminal portion of VPS13 is tubular, with a hydrophobic cavity that can solubilize and transport glycerolipids between membranes. We also show that human VPS13A and VPS13C bind to the ER, tethering it to mitochondria (VPS13A), to late endosome/lysosomes (VPS13C), and to lipid droplets (both VPS13A and VPS13C). These findings identify VPS13 as a lipid transporter between the ER and other organelles, implicating defects in membrane lipid homeostasis in neurological disorders resulting from their mutations. Sequence and secondary structure similarity between the N-terminal portions of Vps13 and other proteins such as the autophagy protein ATG2 suggest lipid transport roles for these proteins as well.
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Affiliation(s)
- Nikit Kumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Marianna Leonzino
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT
| | - William Hancock-Cerutti
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT
| | - Florian A Horenkamp
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - PeiQi Li
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Joshua A Lees
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Heather Wheeler
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT
| | - Karin M Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Pietro De Camilli
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT .,Department of Neuroscience, Yale University School of Medicine, New Haven, CT.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT
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84
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Brunger AT, Leitz J, Zhou Q, Choi UB, Lai Y. Ca 2+-Triggered Synaptic Vesicle Fusion Initiated by Release of Inhibition. Trends Cell Biol 2018; 28:631-645. [PMID: 29706534 PMCID: PMC6056330 DOI: 10.1016/j.tcb.2018.03.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/17/2018] [Accepted: 03/26/2018] [Indexed: 12/20/2022]
Abstract
Recent structural and functional studies of the synaptic vesicle fusion machinery suggest an inhibited tripartite complex consisting of neuronal soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), synaptotagmin, and complexin prior to Ca2+-triggered synaptic vesicle fusion. We speculate that Ca2+-triggered fusion commences with the release of inhibition by Ca2+ binding to synaptotagmin C2 domains. Subsequently, fusion is assisted by SNARE complex zippering and by active membrane remodeling properties of synaptotagmin. This additional, inhibitory role of synaptotagmin may be a general principle since other recent studies suggest that Ca2+ binding to extended synaptotagmin C2 domains enables lipid transport by releasing an inhibited state of the system, and that Munc13 may nominally be in an inhibited state, which is released upon Ca2+ binding to one of its C2 domains.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
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85
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Bean BDM, Dziurdzik SK, Kolehmainen KL, Fowler CMS, Kwong WK, Grad LI, Davey M, Schluter C, Conibear E. Competitive organelle-specific adaptors recruit Vps13 to membrane contact sites. J Cell Biol 2018; 217:3593-3607. [PMID: 30018089 PMCID: PMC6168272 DOI: 10.1083/jcb.201804111] [Citation(s) in RCA: 103] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 06/13/2018] [Accepted: 07/02/2018] [Indexed: 01/24/2023] Open
Abstract
Targeting of Vps13 to membranes is highly dynamic. Bean et al. identify Ypt35 and Mcp1 as adaptors for Vps13 at endosomes and mitochondria, respectively, and show all known Vps13 adaptors use a related motif to compete for Vps13 membrane recruitment. The regulated expansion of membrane contact sites, which mediate the nonvesicular exchange of lipids between organelles, requires the recruitment of additional contact site proteins. Yeast Vps13 dynamically localizes to membrane contacts that connect the ER, mitochondria, endosomes, and vacuoles and is recruited to the prospore membrane in meiosis, but its targeting mechanism is unclear. In this study, we identify the sorting nexin Ypt35 as a novel adaptor that recruits Vps13 to endosomal and vacuolar membranes. We characterize an interaction motif in the Ypt35 N terminus and identify related motifs in the prospore membrane adaptor Spo71 and the mitochondrial membrane protein Mcp1. We find that Mcp1 is a mitochondrial adaptor for Vps13, and the Vps13–Mcp1 interaction, but not Ypt35, is required when ER-mitochondria contacts are lost. All three adaptors compete for binding to a conserved six-repeat region of Vps13 implicated in human disease. Our results support a competition-based model for regulating Vps13 localization at cellular membranes.
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Affiliation(s)
- Björn D M Bean
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Samantha K Dziurdzik
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Kathleen L Kolehmainen
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada.,Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
| | - Claire M S Fowler
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada
| | - Waldan K Kwong
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada
| | - Leslie I Grad
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Michael Davey
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada
| | - Cayetana Schluter
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada
| | - Elizabeth Conibear
- Centre for Molecular Medicine and Therapeutics, British Columbia Children's Hospital Research Institute, University of British Columbia, Vancouver, Canada .,Department of Medical Genetics, University of British Columbia, Vancouver, Canada
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86
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Spang A. The endoplasmic reticulum-the caring mother of the cell. Curr Opin Cell Biol 2018; 53:92-96. [PMID: 30006039 DOI: 10.1016/j.ceb.2018.06.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Revised: 06/06/2018] [Accepted: 06/11/2018] [Indexed: 11/28/2022]
Abstract
In eukaryotic cells, various cellular functions are compartmentalized and performed by sophisticated and specialized organelles. However, the membrane-bounded organelles need to communicate with each other and with the cytoplasm, and sense the outside through the plasma membrane to coordinate various functions and to maintain cellular homeostasis. To maintain homeostasis, the information on the cellular state must be collected and appropriate responses initiated. The endoplasmic reticulum fulfils these functions. In this review, I will discuss various aspects of how the ER senses and relays information and acts to protect the cell, in what sometimes could be interpreted as an altruistic behavior.
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Affiliation(s)
- Anne Spang
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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87
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Phospholipid transport protein function at organelle contact sites. Curr Opin Cell Biol 2018; 53:52-60. [PMID: 29859321 PMCID: PMC6141807 DOI: 10.1016/j.ceb.2018.04.011] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 04/12/2018] [Accepted: 04/29/2018] [Indexed: 11/21/2022]
Abstract
Phospholipids are synthesized at the endoplasmic reticulum (ER), the largest membrane bound organelle that forms membrane contact sites (MCS) with almost every other organelle. MCS are locations at which the membrane es of two organelles are closely positioned to provide a microenvironment where proteins in one membrane can interact with the opposite membrane. Thus, MCS provide an ideal location at which lipid transfer proteins (LTPs) can achieve the efficient transfer of individual classes of lipids from the ER to other organelles via non-vesicular transport. Here we provide an overview of emerging findings on the localization and biochemical activity of LTPs at MCS between the ER and other cellular membranes. The localization of LTPs at MCS offers an elegant cell biological solution to tune local lipid composition to ongoing cell physiology.
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88
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Ernst R, Ballweg S, Levental I. Cellular mechanisms of physicochemical membrane homeostasis. Curr Opin Cell Biol 2018; 53:44-51. [PMID: 29787971 DOI: 10.1016/j.ceb.2018.04.013] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 04/19/2018] [Accepted: 04/29/2018] [Indexed: 12/11/2022]
Abstract
Biological membranes are vital, active contributors to cell function. In addition to specific interactions of individual lipid molecules and lateral organization produced by membrane domains, the bulk physicochemical properties of biological membranes broadly regulate protein structure and function. Therefore, these properties must be homeostatically maintained within a narrow range that is compatible with cellular physiology. Although such adaptiveness has been known for decades, recent observations have dramatically expanded its scope by showing the breadth of membrane properties that must be maintained, and revealing the remarkable diversity of biological membranes, both within and between cell types. Cells have developed a broad palette of sense-and-respond machineries to mediate physicochemical membrane homeostasis, and the molecular mechanisms of these are being discovered through combinations of cell biology, biophysical approaches, and computational modeling.
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Affiliation(s)
- Robert Ernst
- Department of Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany.
| | - Stephanie Ballweg
- Department of Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, 66421 Homburg, Germany
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School at the University of Texas Health Science Center, Houston, TX, USA.
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89
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van Vliet AR, Sassano ML, Agostinis P. The Unfolded Protein Response and Membrane Contact Sites: Tethering as a Matter of Life and Death? ACTA ACUST UNITED AC 2018. [DOI: 10.1177/2515256418770512] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The endoplasmic reticulum (ER) is the most extensive organelle of the eukaryotic cell and constitutes the major site of protein and lipid synthesis and regulation of intracellular Ca2+ levels. To exert these functions properly, the ER network is shaped in structurally and functionally distinct domains that dynamically remodel in response to intrinsic and extrinsic cues. Moreover, the ER establishes a tight communication with virtually all organelles of the cell through specific subdomains called membrane contact sites. These contact sites allow preferential, nonvesicular channeling of key biological mediators including lipids and Ca2+ between organelles and are harnessed by the ER to interface with and coregulate a variety of organellar functions that are vital to maintain homeostasis. When ER homeostasis is lost, a condition that triggers the activation of an evolutionarily conserved pathway called the unfolded protein response (UPR), the ER undergoes rapid remodeling. These dynamic changes in ER morphology are functionally coupled to the modulation or formation of contact sites with key organelles, such as mitochondria and the plasma membrane, which critically regulate cell fate decisions of the ER-stressed cells. Certain components of the UPR have been shown to facilitate the formation of contact sites through various mechanisms including remodeling of the actin cytoskeleton. In this review, we discuss old and emerging evidence linking the UPR machinery to contact site formation in mammalian cells and discuss their important role in cellular homeostasis.
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Affiliation(s)
- Alexander R. van Vliet
- Cell Death Research & Therapy Laboratory, Department of Cellular and Molecular Medicine, KU Leuven-University of Leuven, Belgium
| | - Maria Livia Sassano
- Cell Death Research & Therapy Laboratory, Department of Cellular and Molecular Medicine, KU Leuven-University of Leuven, Belgium
| | - Patrizia Agostinis
- Cell Death Research & Therapy Laboratory, Department of Cellular and Molecular Medicine, KU Leuven-University of Leuven, Belgium
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90
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Besprozvannaya M, Dickson E, Li H, Ginburg KS, Bers DM, Auwerx J, Nunnari J. GRAM domain proteins specialize functionally distinct ER-PM contact sites in human cells. eLife 2018; 7:31019. [PMID: 29469807 PMCID: PMC5823543 DOI: 10.7554/elife.31019] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 02/13/2018] [Indexed: 01/01/2023] Open
Abstract
Endoplasmic reticulum (ER) membrane contact sites (MCSs) are crucial regulatory hubs in cells, playing roles in signaling, organelle dynamics, and ion and lipid homeostasis. Previous work demonstrated that the highly conserved yeast Ltc/Lam sterol transporters localize and function at ER MCSs. Our analysis of the human family members, GRAMD1a and GRAMD2a, demonstrates that they are ER-PM MCS proteins, which mark separate regions of the plasma membrane (PM) and perform distinct functions in vivo. GRAMD2a, but not GRAMD1a, co-localizes with the E-Syt2/3 tethers at ER-PM contacts in a PIP lipid-dependent manner and pre-marks the subset of PI(4,5)P2-enriched ER-PM MCSs utilized for STIM1 recruitment. Data from an analysis of cells lacking GRAMD2a suggest that it is an organizer of ER-PM MCSs with pleiotropic functions including calcium homeostasis. Thus, our data demonstrate the existence of multiple ER-PM domains in human cells that are functionally specialized by GRAM-domain containing proteins.
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Affiliation(s)
- Marina Besprozvannaya
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States
| | - Eamonn Dickson
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, United States
| | - Hao Li
- Laboratory of Integrative and Systems Physiology, EPFL, Lausanne, Switzerland
| | - Kenneth S Ginburg
- Department of Pharmacology, University of California, Davis, Davis, United States
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, United States
| | - Johan Auwerx
- Laboratory of Integrative and Systems Physiology, EPFL, Lausanne, Switzerland
| | - Jodi Nunnari
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States
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91
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Bian X, Saheki Y, De Camilli P. Ca 2+ releases E-Syt1 autoinhibition to couple ER-plasma membrane tethering with lipid transport. EMBO J 2017; 37:219-234. [PMID: 29222176 DOI: 10.15252/embj.201797359] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 11/08/2017] [Accepted: 11/10/2017] [Indexed: 11/09/2022] Open
Abstract
The extended synaptotagmins (E-Syts) are endoplasmic reticulum (ER) proteins that bind the plasma membrane (PM) via C2 domains and transport lipids between them via SMP domains. E-Syt1 tethers and transports lipids in a Ca2+-dependent manner, but the role of Ca2+ in this regulation is unclear. Of the five C2 domains of E-Syt1, only C2A and C2C contain Ca2+-binding sites. Using liposome-based assays, we show that Ca2+ binding to C2C promotes E-Syt1-mediated membrane tethering by releasing an inhibition that prevents C2E from interacting with PI(4,5)P2-rich membranes, as previously suggested by studies in semi-permeabilized cells. Importantly, Ca2+ binding to C2A enables lipid transport by releasing a charge-based autoinhibitory interaction between this domain and the SMP domain. Supporting these results, E-Syt1 constructs defective in Ca2+ binding in either C2A or C2C failed to rescue two defects in PM lipid homeostasis observed in E-Syts KO cells, delayed diacylglycerol clearance from the PM and impaired Ca2+-triggered phosphatidylserine scrambling. Thus, a main effect of Ca2+ on E-Syt1 is to reverse an autoinhibited state and to couple membrane tethering with lipid transport.
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Affiliation(s)
- Xin Bian
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA.,Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, USA
| | - Yasunori Saheki
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA .,Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, USA.,Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
| | - Pietro De Camilli
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA .,Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, USA.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, USA
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