201
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Davis W, Tew KD. ATP-binding cassette transporter-2 (ABCA2) as a therapeutic target. Biochem Pharmacol 2017; 151:188-200. [PMID: 29223352 DOI: 10.1016/j.bcp.2017.11.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 11/27/2017] [Indexed: 12/28/2022]
Abstract
The ATP binding cassette transporter ABCA2 is primarily an endolysosomal membrane protein that demonstrates pleiotropic functionalities, coalescing around the maintenance of homeostasis of sterols, sphingolipids and cholesterol. It is most highly expressed in brain tissue and ABCA2 knockout mice express neurological defects consistent with aberrant myelination. Increased expression of the transporter has been linked with resistance to cancer drugs, particularly those possessing a steroid backbone and gene expression (in concert with other genes involved in cholesterol metabolism) was found to be regulated by sterols. Moreover, in macrophages ABCA2 is influenced by sterols and has a role in regulating cholesterol sequestration, potentially important in cardiovascular disease. Accumulating data indicate the critical importance of ABCA2 in mediating movement of sphingolipids within cellular compartments and these have been implicated in various aspects of cholesterol trafficking. Perhaps because the functions of ABCA2 are linked with membrane building blocks, there are reports linking it with human pathologies, including, cholesterolemias and cardiovascular disease, Alzheimer's and cancer. The present review addresses whether there is now sufficient information to consider ABCA2 as a plausible therapeutic target.
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Affiliation(s)
- Warren Davis
- Dept. of Cell & Molecular Pharmacology & Experimental Therapeutics, Medical University of South Carolina, 173 Ashley Avenue, BSB, MSC 509, Charleston, SC 29425, United States
| | - Kenneth D Tew
- Dept. of Cell & Molecular Pharmacology & Experimental Therapeutics, Medical University of South Carolina, 173 Ashley Avenue, BSB, MSC 509, Charleston, SC 29425, United States.
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202
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Bayer EM, Sparkes I, Vanneste S, Rosado A. From shaping organelles to signalling platforms: the emerging functions of plant ER-PM contact sites. CURRENT OPINION IN PLANT BIOLOGY 2017; 40:89-96. [PMID: 28865976 DOI: 10.1016/j.pbi.2017.08.006] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 07/24/2017] [Accepted: 08/15/2017] [Indexed: 06/07/2023]
Abstract
The plant endoplasmic reticulum (ER) defines the biosynthetic site of lipids and proteins destined for secretion, but also contains important signal transduction and homeostasis components that regulate multiple hormonal and developmental responses. To achieve its various functions, the ER has a unique architecture, both reticulated and highly plastic, that facilitates the spatial-temporal segregation of biochemical reactions and the establishment of inter-organelle communication networks. At the cell cortex, the cortical ER (cER) anchors to and functionally couples with the PM through largely static structures known as ER-PM contact sites (EPCS). These spatially confined microdomains are emerging as critical regulators of the geometry of the cER network, and as highly specialized signalling hubs. In this review, we share recent insights into how EPCS regulate cER remodelling, and discuss the proposed roles for plant EPCS components in the integration of environmental and developmental signals at the cER-PM interface.
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Affiliation(s)
- Emmanuelle M Bayer
- Laboratory of Membrane Biogenesis, UMR 5200 CNRS, University of Bordeaux, 71 avenue Edouard Bourlaux, 33140 Villenave d'Ornon, France
| | - Imogen Sparkes
- Biosciences, CLES, Exeter University, Geoffrey Pope Building, Stocker Rd, Exeter EX4 4QD, UK; School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Steffen Vanneste
- Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Abel Rosado
- Department of Botany, Faculty of Sciences, University of British Columbia, Vancouver V6T 1Z4, Canada.
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203
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Kf de Campos M, Schaaf G. The regulation of cell polarity by lipid transfer proteins of the SEC14 family. CURRENT OPINION IN PLANT BIOLOGY 2017; 40:158-168. [PMID: 29017091 DOI: 10.1016/j.pbi.2017.09.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 09/07/2017] [Accepted: 09/11/2017] [Indexed: 06/07/2023]
Abstract
SEC14 lipid transfer proteins are important regulators of phospholipid metabolism. Structural, genetic and cell biological studies in yeast suggest that they help phosphatidylinositol (PtdIns)/phosphoinositide (PIP) kinases to overcome their intrinsic inefficiency to recognize membrane-embedded substrate, thereby playing a key role in PIP homeostasis. Genomes of higher plants encode a high number and diversity of SEC14 proteins, often in combination with other domains. The Arabidopsis SEC14-Nlj16 protein AtSFH1, an important regulator of root hair development, plays an important role in the establishment of PIP microdomains. Key to this mechanism is a highly specific interaction of the Nlj16 domain with PtdIns(4,5)P2 and an interaction-triggered oligomerization of the protein. Nlj16/PtdIns(4,5)P2 interaction depends on a polybasic motif similar to those identified in other regulatory proteins.
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Affiliation(s)
- Marília Kf de Campos
- Institute of Crop Science and Resource Conservation, Department of Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, 53115 Bonn, Germany.
| | - Gabriel Schaaf
- Institute of Crop Science and Resource Conservation, Department of Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, 53115 Bonn, Germany.
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204
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Hirama T, Lu SM, Kay JG, Maekawa M, Kozlov MM, Grinstein S, Fairn GD. Membrane curvature induced by proximity of anionic phospholipids can initiate endocytosis. Nat Commun 2017; 8:1393. [PMID: 29123120 PMCID: PMC5680216 DOI: 10.1038/s41467-017-01554-9] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2016] [Accepted: 09/27/2017] [Indexed: 11/09/2022] Open
Abstract
The plasma membrane is uniquely enriched in phosphatidylserine (PtdSer). This anionic phospholipid is restricted almost exclusively to the inner leaflet of the plasmalemma. Because of their high density, the headgroups of anionic lipids experience electrostatic repulsion that, being exerted asymmetrically, is predicted to favor membrane curvature. We demonstrate that cholesterol limits this repulsion and tendency to curve. Removal of cholesterol or insertion of excess PtdSer increases the charge density of the inner leaflet, generating foci of enhanced charge and curvature where endophilin and synaptojanin are recruited. From these sites emerge tubules that undergo fragmentation, resulting in marked endocytosis of PtdSer. Shielding or reduction of the surface charge or imposition of outward membrane tension minimized invagination and PtdSer endocytosis. We propose that cholesterol associates with PtdSer to form nanodomains where the headgroups of PtdSer are maintained sufficiently separated to limit spontaneous curvature while sheltering the hydrophobic sterol from the aqueous medium.
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Affiliation(s)
- Takashi Hirama
- Program in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada, M5G 1X8.,Department of Respiratory Medicine, Saitama Medical University, Moroyama, Saitama, 3500495, Japan.,Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, Canada, M5B 1T8
| | - Stella M Lu
- Program in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada, M5G 1X8.,Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, Canada, M5B 1T8.,Department of Biochemistry, University of Toronto, Toronto, ON, Canada, M5S 1A8
| | - Jason G Kay
- Department of Oral Biology, School of Dental Medicine, University at Buffalo, Buffalo, NY, 14214, USA
| | - Masashi Maekawa
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, Canada, M5B 1T8.,Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine; Division of Cell Growth and Tumour Regulation, Proteo-Science Center, Ehime University, Toon, Ehime, 7910295, Japan
| | - Michael M Kozlov
- Department of Physiology and Pharmacology, Room 546, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Sergio Grinstein
- Program in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada, M5G 1X8.,Department of Biochemistry, University of Toronto, Toronto, ON, Canada, M5S 1A8.,Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada, M5S 1A8
| | - Gregory D Fairn
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, Canada, M5B 1T8. .,Department of Biochemistry, University of Toronto, Toronto, ON, Canada, M5S 1A8. .,Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada, M5S 1A8. .,Department of Surgery, University of Toronto, Toronto, ON, Canada, M5T 1P5.
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205
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MCC/Eisosomes Regulate Cell Wall Synthesis and Stress Responses in Fungi. J Fungi (Basel) 2017; 3:jof3040061. [PMID: 29371577 PMCID: PMC5753163 DOI: 10.3390/jof3040061] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 10/26/2017] [Accepted: 10/31/2017] [Indexed: 12/20/2022] Open
Abstract
The fungal plasma membrane is critical for cell wall synthesis and other important processes including nutrient uptake, secretion, endocytosis, morphogenesis, and response to stress. To coordinate these diverse functions, the plasma membrane is organized into specialized compartments that vary in size, stability, and composition. One recently identified domain known as the Membrane Compartment of Can1 (MCC)/eisosome is distinctive in that it corresponds to a furrow-like invagination in the plasma membrane. MCC/eisosomes have been shown to be formed by the Bin/Amphiphysin/Rvs (BAR) domain proteins Lsp1 and Pil1 in a range of fungi. MCC/eisosome domains influence multiple cellular functions; but a very pronounced defect in cell wall synthesis has been observed for mutants with defects in MCC/eisosomes in some yeast species. For example, Candida albicans MCC/eisosome mutants display abnormal spatial regulation of cell wall synthesis, including large invaginations and altered chemical composition of the walls. Recent studies indicate that MCC/eisosomes affect cell wall synthesis in part by regulating the levels of the key regulatory lipid phosphatidylinositol 4,5-bisphosphate (PI4,5P2) in the plasma membrane. One general way MCC/eisosomes function is by acting as protected islands in the plasma membrane, since these domains are very stable. They also act as scaffolds to recruit >20 proteins. Genetic studies aimed at defining the function of the MCC/eisosome proteins have identified important roles in resistance to stress, such as resistance to oxidative stress mediated by the flavodoxin-like proteins Pst1, Pst2, Pst3 and Ycp4. Thus, MCC/eisosomes play multiple roles in plasma membrane organization that protect fungal cells from the environment.
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206
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Stefan CJ, Trimble WS, Grinstein S, Drin G, Reinisch K, De Camilli P, Cohen S, Valm AM, Lippincott-Schwartz J, Levine TP, Iaea DB, Maxfield FR, Futter CE, Eden ER, Judith D, van Vliet AR, Agostinis P, Tooze SA, Sugiura A, McBride HM. Membrane dynamics and organelle biogenesis-lipid pipelines and vesicular carriers. BMC Biol 2017; 15:102. [PMID: 29089042 PMCID: PMC5663033 DOI: 10.1186/s12915-017-0432-0] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Discoveries spanning several decades have pointed to vital membrane lipid trafficking pathways involving both vesicular and non-vesicular carriers. But the relative contributions for distinct membrane delivery pathways in cell growth and organelle biogenesis continue to be a puzzle. This is because lipids flow from many sources and across many paths via transport vesicles, non-vesicular transfer proteins, and dynamic interactions between organelles at membrane contact sites. This forum presents our latest understanding, appreciation, and queries regarding the lipid transport mechanisms necessary to drive membrane expansion during organelle biogenesis and cell growth.
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Affiliation(s)
- Christopher J. Stefan
- MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT UK
| | - William S. Trimble
- Cell Biology Program, The Hospital for Sick Children and Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Sergio Grinstein
- Cell Biology Program, The Hospital for Sick Children and Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Guillaume Drin
- Université Côte d’Azur, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | - Karin Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520 USA
| | - Pietro De Camilli
- Department of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Kavli Institute for Neuroscience and Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT 06510 USA
| | | | | | | | - Tim P. Levine
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL UK
| | - David B. Iaea
- Genentech, 1 DNA Way, South San Francisco, CA 94080 USA
| | - Frederick R. Maxfield
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Ave, New York, NY 10065 USA
| | - Clare E. Futter
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL UK
| | - Emily R. Eden
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL UK
| | - Delphine Judith
- Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, London, UK
| | - Alexander R. van Vliet
- Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, London, UK
- Laboratory of Cell Death Research and Therapy, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Patrizia Agostinis
- Laboratory of Cell Death Research and Therapy, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Sharon A. Tooze
- Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, London, UK
| | - Ayumu Sugiura
- Kobe University Graduate School of Medicine, 1-5-6 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047 Japan
| | - Heidi M. McBride
- Montreal Neurological Institute, McGill University, 3801 University Avenue, Montreal, Quebec H3A 2B4 Canada
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207
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Muallem S, Chung WY, Jha A, Ahuja M. Lipids at membrane contact sites: cell signaling and ion transport. EMBO Rep 2017; 18:1893-1904. [PMID: 29030479 DOI: 10.15252/embr.201744331] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 06/10/2017] [Accepted: 09/21/2017] [Indexed: 12/14/2022] Open
Abstract
Communication between organelles is essential to coordinate cellular functions and the cell's response to physiological and pathological stimuli. Organellar communication occurs at membrane contact sites (MCSs), where the endoplasmic reticulum (ER) membrane is tethered to cellular organelle membranes by specific tether proteins and where lipid transfer proteins and cell signaling proteins are located. MCSs have many cellular functions and are the sites of lipid and ion transfer between organelles and generation of second messengers. This review discusses several aspects of MCSs in the context of lipid transfer, formation of lipid domains, generation of Ca2+ and cAMP second messengers, and regulation of ion transporters by lipids.
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Affiliation(s)
- Shmuel Muallem
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, Bethesda, MD, USA
| | - Woo Young Chung
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, Bethesda, MD, USA
| | - Archana Jha
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, Bethesda, MD, USA
| | - Malini Ahuja
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, Bethesda, MD, USA
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208
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Smindak RJ, Heckle LA, Chittari SS, Hand MA, Hyatt DM, Mantus GE, Sanfelippo WA, Kozminski KG. Lipid-dependent regulation of exocytosis in S. cerevisiae by OSBP homolog (Osh) 4. J Cell Sci 2017; 130:3891-3906. [PMID: 28993464 DOI: 10.1242/jcs.205435] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 10/04/2017] [Indexed: 11/20/2022] Open
Abstract
Polarized exocytosis is an essential process in many organisms and cell types for correct cell division or functional specialization. Previous studies established that homologs of the oxysterol-binding protein (OSBP) in S. cerevisiae, which comprise the Osh protein family, are necessary for efficient polarized exocytosis by supporting a late post-Golgi step. We define this step as the docking of a specific sub-population of exocytic vesicles with the plasma membrane. In the absence of other Osh proteins, yeast Osh4p can support this process in a manner dependent upon two lipid ligands, PI4P and sterol. Osh6p, which binds PI4P and phosphatidylserine, is also sufficient to support polarized exocytosis, again in a lipid-dependent manner. These data suggest that Osh-mediated exocytosis depends upon lipid binding and exchange without a strict requirement for sterol. We propose a two-step mechanism for Osh protein-mediated regulation of polarized exocytosis by using Osh4p as a model. We describe a specific in vivo role for lipid binding by an OSBP-related protein (ORP) in the process of polarized exocytosis, guiding our understanding of where and how OSBP and ORPs may function in more complex organisms.
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Affiliation(s)
- Richard J Smindak
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | - Lindsay A Heckle
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | - Supraja S Chittari
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | - Marissa A Hand
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | - Dylan M Hyatt
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | - Grace E Mantus
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
| | | | - Keith G Kozminski
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA .,Department of Cell Biology, University of Virginia, Charlottesville, VA 22908, USA
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209
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Mesmin B, Bigay J, Polidori J, Jamecna D, Lacas-Gervais S, Antonny B. Sterol transfer, PI4P consumption, and control of membrane lipid order by endogenous OSBP. EMBO J 2017; 36:3156-3174. [PMID: 28978670 DOI: 10.15252/embj.201796687] [Citation(s) in RCA: 174] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 08/28/2017] [Accepted: 09/04/2017] [Indexed: 11/09/2022] Open
Abstract
The network of proteins that orchestrate the distribution of cholesterol among cellular organelles is not fully characterized. We previously proposed that oxysterol-binding protein (OSBP) drives cholesterol/PI4P exchange at contact sites between the endoplasmic reticulum (ER) and the trans-Golgi network (TGN). Using the inhibitor OSW-1, we report here that the sole activity of endogenous OSBP makes a major contribution to cholesterol distribution, lipid order, and PI4P turnover in living cells. Blocking OSBP causes accumulation of sterols at ER/lipid droplets at the expense of TGN, thereby reducing the gradient of lipid order along the secretory pathway. OSBP consumes about half of the total cellular pool of PI4P, a consumption that depends on the amount of cholesterol to be transported. Inhibiting the spatially restricted PI4-kinase PI4KIIIβ triggers large periodic traveling waves of PI4P across the TGN These waves are cadenced by long-range PI4P production by PI4KIIα and PI4P consumption by OSBP Collectively, these data indicate a massive spatiotemporal coupling between cholesterol transport and PI4P turnover via OSBP and PI4-kinases to control the lipid composition of subcellular membranes.
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Affiliation(s)
- Bruno Mesmin
- Université Côte d'Azur, Inserm, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | - Joëlle Bigay
- Université Côte d'Azur, Inserm, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | - Joël Polidori
- Université Côte d'Azur, Inserm, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | - Denisa Jamecna
- Université Côte d'Azur, Inserm, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | | | - Bruno Antonny
- Université Côte d'Azur, Inserm, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
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210
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Choy CH, Han BK, Botelho RJ. Phosphoinositide Diversity, Distribution, and Effector Function: Stepping Out of the Box. Bioessays 2017; 39. [PMID: 28977683 DOI: 10.1002/bies.201700121] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 08/31/2017] [Indexed: 12/26/2022]
Abstract
Phosphoinositides (PtdInsPs) modulate a plethora of functions including signal transduction and membrane trafficking. PtdInsPs are thought to consist of seven interconvertible species that localize to a specific organelle, to which they recruit a set of cognate effector proteins. Here, in reviewing the literature, we argue that this model needs revision. First, PtdInsPs can carry a variety of acyl chains, greatly boosting their molecular diversity. Second, PtdInsPs are more promiscuous in their localization than is usually acknowledged. Third, PtdInsP interconversion is likely achieved through kinase-phosphatase enzyme complexes that coordinate their activities and channel substrates without affecting bulk substrate population. Additionally, we contend that despite hundreds of PtdInsP effectors, our attention is biased toward few proteins. Lastly, we recognize that PtdInsPs can act to nucleate coincidence detection at the effector level, as in PDK1 and Akt. Overall, better integrated models of PtdInsP regulation and function are not only possible but needed.
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Affiliation(s)
- Christopher H Choy
- Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada M5B2K3.,Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada M5B2K3
| | - Bong-Kwan Han
- The Intelligent Synthetic Biology Center, Korea Advanced Institute of Science and Technology, Daejeon 34141, South Korea
| | - Roberto J Botelho
- Graduate Program in Molecular Science, Ryerson University, Toronto, ON, Canada M5B2K3.,Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada M5B2K3
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211
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ORP5 and ORP8 bind phosphatidylinositol-4, 5-biphosphate (PtdIns(4,5)P 2) and regulate its level at the plasma membrane. Nat Commun 2017; 8:757. [PMID: 28970484 PMCID: PMC5624964 DOI: 10.1038/s41467-017-00861-5] [Citation(s) in RCA: 146] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 08/02/2017] [Indexed: 12/20/2022] Open
Abstract
ORP5 and ORP8, members of the oxysterol-binding protein (OSBP)-related proteins (ORP) family, are endoplasmic reticulum membrane proteins implicated in lipid trafficking. ORP5 and ORP8 are reported to localize to endoplasmic reticulum–plasma membrane junctions via binding to phosphatidylinositol-4-phosphate (PtdIns(4)P), and act as a PtdIns(4)P/phosphatidylserine counter exchanger between the endoplasmic reticulum and plasma membrane. Here we provide evidence that the pleckstrin homology domain of ORP5/8 via PtdIns(4,5)P2, and not PtdIns(4)P binding mediates the recruitment of ORP5/8 to endoplasmic reticulum–plasma membrane contact sites. The OSBP-related domain of ORP8 can extract and transport multiple phosphoinositides in vitro, and knocking down both ORP5 and ORP8 in cells increases the plasma membrane level of PtdIns(4,5)P2 with little effect on PtdIns(4)P. Overall, our data show, for the first time, that phosphoinositides other than PtdIns(4)P can also serve as co-exchangers for the transport of cargo lipids by ORPs. ORP5/8 are endoplasmic reticulum (ER) membrane proteins implicated in lipid trafficking that localize to ER-plasma membrane (PM) contacts and maintain membrane homeostasis. Here the authors show that PtdIns(4,5)P2 plays a critical role in the targeting and function of ORP5/8 at the PM.
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212
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Lees JA, Messa M, Sun EW, Wheeler H, Torta F, Wenk MR, De Camilli P, Reinisch KM. Lipid transport by TMEM24 at ER-plasma membrane contacts regulates pulsatile insulin secretion. Science 2017; 355:355/6326/eaah6171. [PMID: 28209843 DOI: 10.1126/science.aah6171] [Citation(s) in RCA: 153] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 01/03/2017] [Indexed: 01/10/2023]
Abstract
Insulin is released by β cells in pulses regulated by calcium and phosphoinositide signaling. Here, we describe how transmembrane protein 24 (TMEM24) helps coordinate these signaling events. We showed that TMEM24 is an endoplasmic reticulum (ER)-anchored membrane protein whose reversible localization to ER-plasma membrane (PM) contacts is governed by phosphorylation and dephosphorylation in response to oscillations in cytosolic calcium. A lipid-binding module in TMEM24 transports the phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] precursor phosphatidylinositol between bilayers, allowing replenishment of PI(4,5)P2 hydrolyzed during signaling. In the absence of TMEM24, calcium oscillations are abolished, leading to a defect in triggered insulin release. Our findings implicate direct lipid transport between the ER and the PM in the control of insulin secretion, a process impaired in patients with type II diabetes.
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Affiliation(s)
- Joshua A Lees
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Mirko Messa
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Elizabeth Wen Sun
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Heather Wheeler
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.,Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Federico Torta
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, 117599 Singapore
| | - Markus R Wenk
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, 117599 Singapore
| | - Pietro De Camilli
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA. .,Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.,Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT 06510, USA.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Karin M Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
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213
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Mitigating Motor Neuronal Loss in C. elegans Model of ALS8. Sci Rep 2017; 7:11582. [PMID: 28912432 PMCID: PMC5599522 DOI: 10.1038/s41598-017-11798-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 08/30/2017] [Indexed: 12/13/2022] Open
Abstract
ALS8 is a late-onset familial autosomal dominant form of Amyotrophic Lateral Sclerosis (ALS) caused by a point mutation (P56S) in the VAPB gene (VAMP associated protein isoform B). Here, we generated two C. elegans models of the disease: a transgenic model where human VAPB wild-type (WT) or P56S mutant was expressed in a subset of motor neurons, and a second model that targeted inducible knockdown of the worm’s orthologue, vpr-1. Overexpression of human VAPB in DA neurons caused a backward locomotion defect, axonal misguidance, and premature neuronal death. Knockdown of vpr-1 recapitulated the reduction in VAPB expression associated with sporadic cases of human ALS. It also caused backward locomotion defects as well as an uncoordinated phenotype, and age-dependent, progressive motor neuronal death. Furthermore, inhibiting phosphatidylinositol-4 (PtdIns 4)-kinase activity with PIK-93 reduced the incidence of DA motor neuron loss and improved backward locomotion. This supports the loss of VAPB function in ALS8 pathogenesis and suggests that reducing intracellular PtdIns4P might be an effective therapeutic strategy in delaying progressive loss of motor neurons.
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214
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Gronnier J, Crowet JM, Habenstein B, Nasir MN, Bayle V, Hosy E, Platre MP, Gouguet P, Raffaele S, Martinez D, Grelard A, Loquet A, Simon-Plas F, Gerbeau-Pissot P, Der C, Bayer EM, Jaillais Y, Deleu M, Germain V, Lins L, Mongrand S. Structural basis for plant plasma membrane protein dynamics and organization into functional nanodomains. eLife 2017; 6:e26404. [PMID: 28758890 PMCID: PMC5536944 DOI: 10.7554/elife.26404] [Citation(s) in RCA: 101] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 07/13/2017] [Indexed: 12/31/2022] Open
Abstract
Plasma Membrane is the primary structure for adjusting to ever changing conditions. PM sub-compartmentalization in domains is thought to orchestrate signaling. Yet, mechanisms governing membrane organization are mostly uncharacterized. The plant-specific REMORINs are proteins regulating hormonal crosstalk and host invasion. REMs are the best-characterized nanodomain markers via an uncharacterized moiety called REMORIN C-terminal Anchor. By coupling biophysical methods, super-resolution microscopy and physiology, we decipher an original mechanism regulating the dynamic and organization of nanodomains. We showed that targeting of REMORIN is independent of the COP-II-dependent secretory pathway and mediated by PI4P and sterol. REM-CA is an unconventional lipid-binding motif that confers nanodomain organization. Analyses of REM-CA mutants by single particle tracking demonstrate that mobility and supramolecular organization are critical for immunity. This study provides a unique mechanistic insight into how the tight control of spatial segregation is critical in the definition of PM domain necessary to support biological function.
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Affiliation(s)
- Julien Gronnier
- Laboratoire de Biogenèse Membranaire (LBM), Unité Mixte de Recherche UMR 5200, CNRS, Université de BordeauxBordeauxFrance
| | - Jean-Marc Crowet
- Laboratoire de Biophysique Moléculaire aux InterfacesGX ABT, Université de LiègeGemblouxBelgium
| | - Birgit Habenstein
- Institute of Chemistry and Biology of Membranes and Nanoobjects (UMR5248 CBMN), CNRS, Université de Bordeaux, Institut Polytechnique BordeauxPessacFrance
| | - Mehmet Nail Nasir
- Laboratoire de Biophysique Moléculaire aux InterfacesGX ABT, Université de LiègeGemblouxBelgium
| | - Vincent Bayle
- Laboratoire Reproduction et Développement des PlantesUniversité de Lyon, ENS de Lyon, Université Claude Bernard Lyon 1LyonFrance
| | - Eric Hosy
- Interdisciplinary Institute for Neuroscience, CNRS, University of BordeauxBordeauxFrance
| | - Matthieu Pierre Platre
- Laboratoire Reproduction et Développement des PlantesUniversité de Lyon, ENS de Lyon, Université Claude Bernard Lyon 1LyonFrance
| | - Paul Gouguet
- Laboratoire de Biogenèse Membranaire (LBM), Unité Mixte de Recherche UMR 5200, CNRS, Université de BordeauxBordeauxFrance
| | | | - Denis Martinez
- Institute of Chemistry and Biology of Membranes and Nanoobjects (UMR5248 CBMN), CNRS, Université de Bordeaux, Institut Polytechnique BordeauxPessacFrance
| | - Axelle Grelard
- Institute of Chemistry and Biology of Membranes and Nanoobjects (UMR5248 CBMN), CNRS, Université de Bordeaux, Institut Polytechnique BordeauxPessacFrance
| | - Antoine Loquet
- Institute of Chemistry and Biology of Membranes and Nanoobjects (UMR5248 CBMN), CNRS, Université de Bordeaux, Institut Polytechnique BordeauxPessacFrance
| | - Françoise Simon-Plas
- Agroécologie, AgroSup Dijon, INRA, Université Bourgogne Franche-Comté, F-21000 Dijon, ERL 6003 CNRSDijonFrance
| | - Patricia Gerbeau-Pissot
- Agroécologie, AgroSup Dijon, INRA, Université Bourgogne Franche-Comté, F-21000 Dijon, ERL 6003 CNRSDijonFrance
| | - Christophe Der
- Agroécologie, AgroSup Dijon, INRA, Université Bourgogne Franche-Comté, F-21000 Dijon, ERL 6003 CNRSDijonFrance
| | - Emmanuelle M Bayer
- Laboratoire de Biogenèse Membranaire (LBM), Unité Mixte de Recherche UMR 5200, CNRS, Université de BordeauxBordeauxFrance
| | - Yvon Jaillais
- Laboratoire Reproduction et Développement des PlantesUniversité de Lyon, ENS de Lyon, Université Claude Bernard Lyon 1LyonFrance
| | - Magali Deleu
- Laboratoire de Biophysique Moléculaire aux InterfacesGX ABT, Université de LiègeGemblouxBelgium
| | - Véronique Germain
- Laboratoire de Biogenèse Membranaire (LBM), Unité Mixte de Recherche UMR 5200, CNRS, Université de BordeauxBordeauxFrance
| | - Laurence Lins
- Laboratoire de Biophysique Moléculaire aux InterfacesGX ABT, Université de LiègeGemblouxBelgium
| | - Sébastien Mongrand
- Laboratoire de Biogenèse Membranaire (LBM), Unité Mixte de Recherche UMR 5200, CNRS, Université de BordeauxBordeauxFrance
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215
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The role of oxysterol-binding protein and its related proteins in cancer. Semin Cell Dev Biol 2017; 81:149-153. [PMID: 28733164 DOI: 10.1016/j.semcdb.2017.07.017] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 06/28/2017] [Accepted: 07/14/2017] [Indexed: 01/17/2023]
Abstract
Oxysterol-binding protein (OSBP) and its related proteins (ORPs) constitute a large, evolutionarily conserved family of lipid-binding proteins that are associated with a wide range of cellular activities. The core function of OSBP/ORPs appears to be moving lipids between cellular membranes in a non-vesicular manner. Recent studies have unveiled a novel, counter-transport mechanism of cellular lipid transfer mediated by OSBP/ORPs at the membrane contact sites that involves phosphatidylinositol 4-phosphate. Importantly, the OSBP/ORPs family has also been implicated in cell signalling pathways and cancer development. Here, we summarize recent progress in understanding the role of OSBP/ORPs in cancer development, and discuss how the lipid transfer function of OSBP/ORPs may underpin their role in tumorigenesis.
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216
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Jackson CL, Walch L, Verbavatz JM. Lipids and Their Trafficking: An Integral Part of Cellular Organization. Dev Cell 2017; 39:139-153. [PMID: 27780039 DOI: 10.1016/j.devcel.2016.09.030] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
An evolutionarily conserved feature of cellular organelles is the distinct phospholipid composition of their bounding membranes, which is essential to their identity and function. Within eukaryotic cells, two major lipid territories can be discerned, one centered on the endoplasmic reticulum and characterized by membranes with lipid packing defects, the other comprising plasma-membrane-derived organelles and characterized by membrane charge. We discuss how this cellular lipid organization is maintained, how lipid flux is regulated, and how perturbations in cellular lipid homeostasis can lead to disease.
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Affiliation(s)
- Catherine L Jackson
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, 75013 Paris, France.
| | - Laurence Walch
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, 75013 Paris, France
| | - Jean-Marc Verbavatz
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, 75013 Paris, France
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217
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Nicolas WJ, Grison MS, Trépout S, Gaston A, Fouché M, Cordelières FP, Oparka K, Tilsner J, Brocard L, Bayer EM. Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves. NATURE PLANTS 2017; 3:17082. [PMID: 28604682 DOI: 10.1038/nplants.2017.82] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 05/08/2017] [Indexed: 05/08/2023]
Abstract
Plasmodesmata are remarkable cellular machines responsible for the controlled exchange of proteins, small RNAs and signalling molecules between cells. They are lined by the plasma membrane (PM), contain a strand of tubular endoplasmic reticulum (ER), and the space between these two membranes is thought to control plasmodesmata permeability. Here, we have reconstructed plasmodesmata three-dimensional (3D) ultrastructure with an unprecedented level of 3D information using electron tomography. We show that within plasmodesmata, ER-PM contact sites undergo substantial remodelling events during cell differentiation. Instead of being open pores, post-cytokinesis plasmodesmata present such intimate ER-PM contact along the entire length of the pores that no intermembrane gap is visible. Later on, during cell expansion, the plasmodesmata pore widens and the two membranes separate, leaving a cytosolic sleeve spanned by tethers whose presence correlates with the appearance of the intermembrane gap. Surprisingly, the post-cytokinesis plasmodesmata allow diffusion of macromolecules despite the apparent lack of an open cytoplasmic sleeve, forcing the reassessment of the mechanisms that control plant cell-cell communication.
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Affiliation(s)
- William J Nicolas
- Laboratory of Membrane Biogenesis, UMR5200 CNRS, University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France
| | - Magali S Grison
- Laboratory of Membrane Biogenesis, UMR5200 CNRS, University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France
| | - Sylvain Trépout
- Institut Curie, Centre de Recherche, Bât. 112, Centre Universitaire, 91405 Orsay Cedex, France
| | - Amélia Gaston
- Laboratory of Membrane Biogenesis, UMR5200 CNRS, University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France
| | - Mathieu Fouché
- Laboratory of Membrane Biogenesis, UMR5200 CNRS, University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France
| | - Fabrice P Cordelières
- Bordeaux Imaging Centre, UMS 3420 CNRS, CNRS-INSERM-University of Bordeaux 146, rue Léo Saignat, 33076 Bordeaux Cedex, France
| | - Karl Oparka
- Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3BF, UK
| | - Jens Tilsner
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, UK
- Cell and Molecular Sciences, James Hutton Institute, Dundee DD2 5DA, UK
| | - Lysiane Brocard
- Bordeaux Imaging Centre, Plant Imaging Plateform, UMS 3420, INRA-CNRS-INSERM-University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave-d'Ornon Cedex, France
| | - Emmanuelle M Bayer
- Laboratory of Membrane Biogenesis, UMR5200 CNRS, University of Bordeaux, 71 Avenue Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France
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218
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Chen YJ, Chang CL, Lee WR, Liou J. RASSF4 controls SOCE and ER-PM junctions through regulation of PI(4,5)P 2. J Cell Biol 2017; 216:2011-2025. [PMID: 28600435 PMCID: PMC5496610 DOI: 10.1083/jcb.201606047] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 10/18/2016] [Accepted: 04/27/2017] [Indexed: 11/22/2022] Open
Abstract
RAS association domain family 4 (RASSF4) is involved in tumorigenesis. Chen et al. show that RASSF4 regulates store-operated Ca2+ entry and ER–PM junctions by affecting PI(4,5)P2 levels. RASSF4 interacts with and regulates the activity of ARF6, an upstream regulator of PIP5K and PI(4,5)P2. RAS association domain family 4 (RASSF4) is involved in tumorigenesis and regulation of the Hippo pathway. In this study, we identify new functional roles of RASSF4. First, we discovered that RASSF4 regulates store-operated Ca2+ entry (SOCE), a fundamental Ca2+ signaling mechanism, by affecting the translocation of the endoplasmic reticulum (ER) Ca2+ sensor stromal interaction molecule 1 (STIM1) to ER–plasma membrane (PM) junctions. It was further revealed that RASSF4 regulates the formation of ER–PM junctions and the ER–PM tethering function of extended synaptotagmins E-Syt2 and E-Syt3. Moreover, steady-state PM phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) levels, important for localization of STIM1 and E-Syts at ER–PM junctions, were reduced in RASSF4-knockdown cells. Furthermore, we demonstrated that RASSF4 interacts with and regulates the activity of adenosine diphosphate ribosylation factor 6 (ARF6), a small G protein and upstream regulator of type I phosphatidylinositol phosphate kinases (PIP5Ks) and PM PI(4,5)P2 levels. Overall, our study suggests that RASSF4 controls SOCE and ER–PM junctions through ARF6-dependent regulation of PM PI(4,5)P2 levels, pivotal for a variety of physiological processes.
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Affiliation(s)
- Yu-Ju Chen
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Chi-Lun Chang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Wan-Ru Lee
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Jen Liou
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
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219
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Abstract
[Image: see text]
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Affiliation(s)
- Peiqi Yin
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100176, China
| | - Zhi Hong
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100176, China
| | - Leiliang Zhang
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100176, China.
| | - Youyang Ke
- Department of Emergency, 171st Hospital of PLA, Jiujiang, 332000, China.
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220
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Advances on the Transfer of Lipids by Lipid Transfer Proteins. Trends Biochem Sci 2017; 42:516-530. [PMID: 28579073 PMCID: PMC5486777 DOI: 10.1016/j.tibs.2017.05.001] [Citation(s) in RCA: 145] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 05/02/2017] [Accepted: 05/03/2017] [Indexed: 12/22/2022]
Abstract
Transfer of lipid across the cytoplasm is an essential process for intracellular lipid traffic. Lipid transfer proteins (LTPs) are defined by highly controlled in vitro experiments. The functional relevance of these is supported by evidence for the same reactions inside cells. Major advances in the LTP field have come from structural bioinformatics identifying new LTPs, and from the development of countercurrent models for LTPs. However, the ultimate aim is to unite in vitro and in vivo data, and this is where much progress remains to be made. Even where in vitro and in vivo experiments align, rates of transfer tend not to match. Here we set out some of the advances that might test how LTPs work. LTPs facilitate the essential movement of lipid across aqueous spaces and are defined by in vitro experiments. Recent developments include a novel concept of countercurrent lipid transfer and identification of additional LTP families by bioinformatics. In vivo and in vitro data have yet to converge to one complete model. Advances in in vitro characterisation of LTPs provide an opportunity to unite biochemical experimentation to cellular function.
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221
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Contacts between the endoplasmic reticulum and other membranes in neurons. Proc Natl Acad Sci U S A 2017; 114:E4859-E4867. [PMID: 28559323 DOI: 10.1073/pnas.1701078114] [Citation(s) in RCA: 339] [Impact Index Per Article: 42.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Close appositions between the membrane of the endoplasmic reticulum (ER) and other intracellular membranes have important functions in cell physiology. These include lipid homeostasis, regulation of Ca2+ dynamics, and control of organelle biogenesis and dynamics. Although these membrane contacts have previously been observed in neurons, their distribution and abundance have not been systematically analyzed. Here, we have used focused ion beam-scanning electron microscopy to generate 3D reconstructions of intracellular organelles and their membrane appositions involving the ER (distance ≤30 nm) in different neuronal compartments. ER-plasma membrane (PM) contacts were particularly abundant in cell bodies, with large, flat ER cisternae apposed to the PM, sometimes with a notably narrow lumen (thin ER). Smaller ER-PM contacts occurred throughout dendrites, axons, and in axon terminals. ER contacts with mitochondria were abundant in all compartments, with the ER often forming a network that embraced mitochondria. Small focal contacts were also observed with tubulovesicular structures, likely to be endosomes, and with sparse multivesicular bodies and lysosomes found in our reconstructions. Our study provides an anatomical reference for interpreting information about interorganelle communication in neurons emerging from functional and biochemical studies.
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222
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Chang CL, Chen YJ, Liou J. ER-plasma membrane junctions: Why and how do we study them? BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:1494-1506. [PMID: 28554772 DOI: 10.1016/j.bbamcr.2017.05.018] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 05/09/2017] [Accepted: 05/17/2017] [Indexed: 12/17/2022]
Abstract
Endoplasmic reticulum (ER)-plasma membrane (PM) junctions are membrane microdomains important for communication between the ER and the PM. ER-PM junctions were first reported in muscle cells in 1957, but mostly ignored in non-excitable cells due to their scarcity and lack of functional significance. In 2005, the discovery of stromal interaction molecule 1 (STIM1) mediating a universal Ca2+ feedback mechanism at ER-PM junctions in mammalian cells led to a resurgence of research interests toward ER-PM junctions. In the past decade, several major advancements have been made in this emerging topic in cell biology, including the generation of tools for labeling ER-PM junctions and the unraveling of mechanisms underlying regulation and functions of ER-PM junctions. This review summarizes early studies, recently developed tools, and current advances in the characterization and understanding of ER-PM junctions. This article is part of a Special Issue entitled: Membrane Contact Sites edited by Christian Ungermann and Benoit Kornmann.
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Affiliation(s)
- Chi-Lun Chang
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - 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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223
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Wilhelm LP, Wendling C, Védie B, Kobayashi T, Chenard MP, Tomasetto C, Drin G, Alpy F. STARD3 mediates endoplasmic reticulum-to-endosome cholesterol transport at membrane contact sites. EMBO J 2017; 36:1412-1433. [PMID: 28377464 PMCID: PMC5430228 DOI: 10.15252/embj.201695917] [Citation(s) in RCA: 185] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 03/03/2017] [Accepted: 03/06/2017] [Indexed: 01/04/2023] Open
Abstract
StAR‐related lipid transfer domain‐3 (STARD3) is a sterol‐binding protein that creates endoplasmic reticulum (ER)–endosome contact sites. How this protein, at the crossroad between sterol uptake and synthesis pathways, impacts the intracellular distribution of this lipid was ill‐defined. Here, by using in situ cholesterol labeling and quantification, we demonstrated that STARD3 induces cholesterol accumulation in endosomes at the expense of the plasma membrane. STARD3‐mediated cholesterol routing depends both on its lipid transfer activity and its ability to create ER–endosome contacts. Corroborating this, in vitro reconstitution assays indicated that STARD3 and its ER‐anchored partner, Vesicle‐associated membrane protein‐associated protein (VAP), assemble into a machine that allows a highly efficient transport of cholesterol within membrane contacts. Thus, STARD3 is a cholesterol transporter scaffolding ER–endosome contacts and modulating cellular cholesterol repartition by delivering cholesterol to endosomes.
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Affiliation(s)
- Léa P Wilhelm
- Functional Genomics and Cancer Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U 964, Illkirch, France.,Centre National de la Recherche Scientifique (CNRS), UMR 7104, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Corinne Wendling
- Functional Genomics and Cancer Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U 964, Illkirch, France.,Centre National de la Recherche Scientifique (CNRS), UMR 7104, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Benoît Védie
- AP-HP (Assistance Publique - Hôpitaux de Paris), Hôpital Européen Georges Pompidou, Service de Biochimie, Paris, France
| | - Toshihide Kobayashi
- Université de Strasbourg, Illkirch, France.,Laboratory of Biophotonics and Pharmacology, Centre National de la Recherche Scientifique (CNRS), UMR 7213, Illkirch, France
| | - Marie-Pierre Chenard
- Functional Genomics and Cancer Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.,Université de Strasbourg, Illkirch, France.,Service d'Anatomie Pathologique Générale, Centre Hospitalier Universitaire de Hautepierre, Strasbourg, France
| | - Catherine Tomasetto
- Functional Genomics and Cancer Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France .,Institut National de la Santé et de la Recherche Médicale (INSERM), U 964, Illkirch, France.,Centre National de la Recherche Scientifique (CNRS), UMR 7104, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Guillaume Drin
- Université Côte d'Azur, CNRS Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
| | - Fabien Alpy
- Functional Genomics and Cancer Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France .,Institut National de la Santé et de la Recherche Médicale (INSERM), U 964, Illkirch, France.,Centre National de la Recherche Scientifique (CNRS), UMR 7104, Illkirch, France.,Université de Strasbourg, Illkirch, France
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224
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Luo J, Jiang L, Yang H, Song BL. Routes and mechanisms of post-endosomal cholesterol trafficking: A story that never ends. Traffic 2017; 18:209-217. [DOI: 10.1111/tra.12471] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Revised: 02/08/2017] [Accepted: 02/08/2017] [Indexed: 12/22/2022]
Affiliation(s)
- Jie Luo
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences; Wuhan University; Wuhan China
| | - Luyi Jiang
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences; Wuhan University; Wuhan China
| | - Hongyuan Yang
- School of Biotechnology and Biomolecular Sciences; The University of New South Wales; Sydney Australia
| | - Bao-Liang Song
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences; Wuhan University; Wuhan China
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225
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Deciphering the molecular architecture of membrane contact sites by cryo-electron tomography. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:1507-1512. [PMID: 28330771 DOI: 10.1016/j.bbamcr.2017.03.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 03/13/2017] [Accepted: 03/17/2017] [Indexed: 01/16/2023]
Abstract
At membrane contact sites (MCS) two cellular membranes form tight appositions that play critical roles in fundamental phenomena such as lipid metabolism or Ca2+ homeostasis. The interest for these structures has surged in recent years, bringing about the characterization of a plethora of MCS-resident molecules. How those molecules are structurally organized at MCS remains enigmatic, limiting our understanding of MCS function. Whereas such molecular detail is obscured by conventional electron microscopy sample preparation, cryo-electron tomography (cryo-ET) allows high resolution imaging of cellular landscapes in close-to-native conditions. Here we briefly review the fundamentals of cryo-ET and how recent developments in this technique are beginning to unveil the molecular architecture of MCS. This article is part of a Special Issue entitled: Membrane Contact Sites edited by Christian Ungermann and Benoit Kornmann.
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226
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Manik MK, Yang H, Tong J, Im YJ. Structure of Yeast OSBP-Related Protein Osh1 Reveals Key Determinants for Lipid Transport and Protein Targeting at the Nucleus-Vacuole Junction. Structure 2017; 25:617-629.e3. [PMID: 28319008 DOI: 10.1016/j.str.2017.02.010] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 01/19/2017] [Accepted: 02/22/2017] [Indexed: 01/25/2023]
Abstract
Yeast Osh1 belongs to the oxysterol-binding protein (OSBP) family of proteins and contains multiple targeting modules optimized for lipid transport at the nucleus-vacuole junction (NVJ). The key determinants for NVJ targeting and the role of Osh1 at NVJs have remained elusive because of unknown lipid specificities. In this study, we determined the structures of the ankyrin repeat domain (ANK), and OSBP-related domain (ORD) of Osh1, in complex with Nvj1 and ergosterol, respectively. The Osh1 ANK forms a unique bi-lobed structure that recognizes a cytosolic helical segment of Nvj1. We discovered that Osh1 ORD binds ergosterol and phosphatidylinositol 4-phosphate PI(4)P in a competitive manner, suggesting counter-transport function of the two lipids. Ergosterol is bound to the hydrophobic pocket in a head-down orientation, and the structure of the PI(4)P-binding site in Osh1 is well conserved. Our results suggest that Osh1 performs non-vesicular transport of ergosterol and PI(4)P at the NVJ.
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Affiliation(s)
| | - Huiseon Yang
- College of Pharmacy, Chonnam National University, Gwangju 61186, Republic of Korea
| | - Junsen Tong
- College of Pharmacy, Chonnam National University, Gwangju 61186, Republic of Korea
| | - Young Jun Im
- College of Pharmacy, Chonnam National University, Gwangju 61186, Republic of Korea.
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227
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De Craene JO, Bertazzi DL, Bär S, Friant S. Phosphoinositides, Major Actors in Membrane Trafficking and Lipid Signaling Pathways. Int J Mol Sci 2017; 18:ijms18030634. [PMID: 28294977 PMCID: PMC5372647 DOI: 10.3390/ijms18030634] [Citation(s) in RCA: 145] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 03/02/2017] [Accepted: 03/06/2017] [Indexed: 11/30/2022] Open
Abstract
Phosphoinositides are lipids involved in the vesicular transport of proteins and lipids between the different compartments of eukaryotic cells. They act by recruiting and/or activating effector proteins and thus are involved in regulating various cellular functions, such as vesicular budding, membrane fusion and cytoskeleton dynamics. Although detected in small concentrations in membranes, their role is essential to cell function, since imbalance in their concentrations is a hallmark of many cancers. Their synthesis involves phosphorylating/dephosphorylating positions D3, D4 and/or D5 of their inositol ring by specific lipid kinases and phosphatases. This process is tightly regulated and specific to the different intracellular membranes. Most enzymes involved in phosphoinositide synthesis are conserved between yeast and human, and their loss of function leads to severe diseases (cancer, myopathy, neuropathy and ciliopathy).
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Affiliation(s)
- Johan-Owen De Craene
- Department of Molecular and Cellular Genetics, Université de Strasbourg, CNRS, GMGM UMR 7156, F-67000 Strasbourg, France.
| | - Dimitri L Bertazzi
- Department of Molecular and Cellular Genetics, Université de Strasbourg, CNRS, GMGM UMR 7156, F-67000 Strasbourg, France.
| | - Séverine Bär
- Department of Molecular and Cellular Genetics, Université de Strasbourg, CNRS, GMGM UMR 7156, F-67000 Strasbourg, France.
| | - Sylvie Friant
- Department of Molecular and Cellular Genetics, Université de Strasbourg, CNRS, GMGM UMR 7156, F-67000 Strasbourg, France.
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228
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Altan-Bonnet N. Lipid Tales of Viral Replication and Transmission. Trends Cell Biol 2017; 27:201-213. [PMID: 27838086 PMCID: PMC5318230 DOI: 10.1016/j.tcb.2016.09.011] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2016] [Revised: 09/26/2016] [Accepted: 09/29/2016] [Indexed: 12/22/2022]
Abstract
Positive-strand RNA viruses are the largest group of RNA viruses on Earth and cellular membranes are critical for all aspects of their life cycle, from entry and replication to exit. In particular, membranes serve as platforms for replication and as carriers to transmit these viruses to other cells, the latter either as an envelope surrounding a single virus or as the vesicle containing a population of viruses. Notably, many animal and human viruses appear to induce and exploit phosphatidylinositol 4-phosphate/cholesterol-enriched membranes for replication, whereas many plant and insect-vectored animal viruses utilize phosphatidylethanolamine/cholesterol-enriched membranes for the same purpose; and phosphatidylserine-enriched membrane carriers are widely used by both single and populations of viruses for transmission. Here I discuss the implications for viral pathogenesis and therapeutic development of this remarkable convergence on specific membrane lipid blueprints for replication and transmission.
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Affiliation(s)
- Nihal Altan-Bonnet
- Laboratory of Host-Pathogen Dynamics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
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229
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Strating JR, van Kuppeveld FJ. Viral rewiring of cellular lipid metabolism to create membranous replication compartments. Curr Opin Cell Biol 2017; 47:24-33. [PMID: 28242560 PMCID: PMC7127510 DOI: 10.1016/j.ceb.2017.02.005] [Citation(s) in RCA: 88] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2016] [Revised: 02/02/2017] [Accepted: 02/09/2017] [Indexed: 02/08/2023]
Abstract
Positive-strand RNA (+RNA) viruses (e.g. poliovirus, hepatitis C virus, dengue virus, SARS-coronavirus) remodel cellular membranes to form so-called viral replication compartments (VRCs), which are the sites where viral RNA genome replication takes place. To induce VRC formation, these viruses extensively rewire lipid metabolism. Disparate viruses have many commonalities as well as disparities in their interactions with the host lipidome and accumulate specific sets of lipids (sterols, glycerophospholipids, sphingolipids) at their VRCs. Recent years have seen an upsurge in studies investigating the role of lipids in +RNA virus replication, in particular of sterols, and uncovered that membrane contact sites and lipid transfer proteins are hijacked by viruses and play pivotal roles in VRC formation.
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Affiliation(s)
- Jeroen Rpm Strating
- Utrecht University, Faculty of Veterinary Medicine, Department of Infectious Diseases & Immunology, Division of Virology, Utrecht, The Netherlands.
| | - Frank Jm van Kuppeveld
- Utrecht University, Faculty of Veterinary Medicine, Department of Infectious Diseases & Immunology, Division of Virology, Utrecht, The Netherlands.
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230
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Abstract
The endoplasmic reticulum (ER) has a broad localization throughout the cell and forms direct physical contacts with all other classes of membranous organelles, including the plasma membrane (PM). A number of protein tethers that mediate these contacts have been identified, and study of these protein tethers has revealed a multiplicity of roles in cell physiology, including regulation of intracellular Ca2+ dynamics and signaling as well as control of lipid traffic and homeostasis. In this review, we discuss the cross talk between the ER and the PM mediated by direct contacts. We review factors that tether the two membranes, their properties, and their dynamics in response to the functional state of the cell. We focus in particular on the role of ER-PM contacts in nonvesicular lipid transport between the two bilayers mediated by lipid transfer proteins.
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Affiliation(s)
- Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, 308232, Singapore;
| | - Pietro De Camilli
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Kavli Institute for Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, Connecticut 06510;
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231
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Abstract
Ca2+ influx across the plasma membrane is a key component of the receptor-evoked Ca2+ signaling that mediate numerous cell functions and reload the ER after partial or full ER Ca2+ store depletion. Ca2+ influx is activated in response to Ca2+ release from the ER, a concept developed by Jim Putney, and the channels mediating the influx are thus called store-operated Ca2+ influx channels, or SOCs. The molecular identity of the SOCs has been determined with the identification of the TRPC channels, STIM1 and the Orai channels. These channels are targeted to, operate and are regulated when at the ER/PM junctions. ER/PM junctions are a form of membrane contact sites (MCSs) that are present in all parts of the cells, where the ER makes contacts with cellular membranes and organelles. MCSs have many cellular functions, and are the sites of lipid and Ca2+ transport and delivery between organelles. This short review discusses aspects of MCSs in the context of Ca2+ transport.
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Affiliation(s)
- Woo Young Chung
- From the Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda MD 20892, United States
| | - Archana Jha
- From the Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda MD 20892, United States
| | - Malini Ahuja
- From the Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda MD 20892, United States
| | - Shmuel Muallem
- From the Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda MD 20892, United States.
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232
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Herrera-Cruz MS, Simmen T. Of yeast, mice and men: MAMs come in two flavors. Biol Direct 2017; 12:3. [PMID: 28122638 PMCID: PMC5267431 DOI: 10.1186/s13062-017-0174-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 01/18/2017] [Indexed: 12/15/2022] Open
Abstract
The past decade has seen dramatic progress in our understanding of membrane contact sites (MCS). Important examples of these are endoplasmic reticulum (ER)-mitochondria contact sites. ER-mitochondria contacts have originally been discovered in mammalian tissue, where they have been designated as mitochondria-associated membranes (MAMs). It is also in this model system, where the first critical MAM proteins have been identified, including MAM tethering regulators such as phospho-furin acidic cluster sorting protein 2 (PACS-2) and mitofusin-2. However, the past decade has seen the discovery of the MAM also in the powerful yeast model system Saccharomyces cerevisiae. This has led to the discovery of novel MAM tethers such as the yeast ER-mitochondria encounter structure (ERMES), absent in the mammalian system, but whose regulators Gem1 and Lam6 are conserved. While MAMs, sometimes referred to as mitochondria-ER contacts (MERCs), regulate lipid metabolism, Ca2+ signaling, bioenergetics, inflammation, autophagy and apoptosis, not all of these functions exist in both systems or operate differently. This biological difference has led to puzzling discrepancies on findings obtained in yeast or mammalian cells at the moment. Our review aims to shed some light onto mechanistic differences between yeast and mammalian MAM and their underlying causes. Reviewers: This article was reviewed by Paola Pizzo (nominated by Luca Pellegrini), Maya Schuldiner and György Szabadkai (nominated by Luca Pellegrini).
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Affiliation(s)
- Maria Sol Herrera-Cruz
- Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, T6G2H7, Canada
| | - Thomas Simmen
- Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, T6G2H7, Canada.
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233
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Pantazopoulou A. The Golgi apparatus: insights from filamentous fungi. Mycologia 2017; 108:603-22. [DOI: 10.3852/15-309] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 01/01/2016] [Indexed: 02/06/2023]
Affiliation(s)
- Areti Pantazopoulou
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, Madrid 28040, Spain
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234
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Stein S, Lemos V, Xu P, Demagny H, Wang X, Ryu D, Jimenez V, Bosch F, Lüscher TF, Oosterveer MH, Schoonjans K. Impaired SUMOylation of nuclear receptor LRH-1 promotes nonalcoholic fatty liver disease. J Clin Invest 2017; 127:583-592. [PMID: 28094767 DOI: 10.1172/jci85499] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 11/22/2016] [Indexed: 12/17/2022] Open
Abstract
Hepatic steatosis is caused by metabolic imbalances that could be explained in part by an increase in de novo lipogenesis that results from increased sterol element binding protein 1 (SREBP-1) activity. The nuclear receptor liver receptor homolog 1 (LRH-1) is an important regulator of intermediary metabolism in the liver, but its role in regulating lipogenesis is not well understood. Here, we have assessed the contribution of LRH-1 SUMOylation to the development of nonalcoholic fatty liver disease (NAFLD). Mice expressing a SUMOylation-defective mutant of LRH-1 (LRH-1 K289R mice) developed NAFLD and early signs of nonalcoholic steatohepatitis (NASH) when challenged with a lipogenic, high-fat, high-sucrose diet. Moreover, we observed that the LRH-1 K289R mutation induced the expression of oxysterol binding protein-like 3 (OSBPL3), enhanced SREBP-1 processing, and promoted de novo lipogenesis. Mechanistically, we demonstrated that ectopic expression of OSBPL3 facilitates SREBP-1 processing in WT mice, while silencing hepatic Osbpl3 reverses the lipogenic phenotype of LRH-1 K289R mice. These findings suggest that compromised SUMOylation of LRH-1 promotes the development of NAFLD under lipogenic conditions through regulation of OSBPL3.
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235
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Dong R, Saheki Y, Swarup S, Lucast L, Harper JW, De Camilli P. Endosome-ER Contacts Control Actin Nucleation and Retromer Function through VAP-Dependent Regulation of PI4P. Cell 2017; 166:408-423. [PMID: 27419871 DOI: 10.1016/j.cell.2016.06.037] [Citation(s) in RCA: 287] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Revised: 04/15/2016] [Accepted: 06/17/2016] [Indexed: 12/18/2022]
Abstract
VAP (VAPA and VAPB) is an evolutionarily conserved endoplasmic reticulum (ER)-anchored protein that helps generate tethers between the ER and other membranes through which lipids are exchanged across adjacent bilayers. Here, we report that by regulating PI4P levels on endosomes, VAP affects WASH-dependent actin nucleation on these organelles and the function of the retromer, a protein coat responsible for endosome-to-Golgi traffic. VAP is recruited to retromer budding sites on endosomes via an interaction with the retromer SNX2 subunit. Cells lacking VAP accumulate high levels of PI4P, actin comets, and trans-Golgi proteins on endosomes. Such defects are mimicked by downregulation of OSBP, a VAP interactor and PI4P transporter that participates in VAP-dependent ER-endosomes tethers. These results reveal a role of PI4P in retromer-/WASH-dependent budding from endosomes. Collectively, our data show how the ER can control budding dynamics and association with the cytoskeleton of another membrane by direct contacts leading to bilayer lipid modifications.
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Affiliation(s)
- Rui Dong
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA; Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Yasunori Saheki
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA; Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Sharan Swarup
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Louise Lucast
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA; Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA
| | - J Wade Harper
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Pietro De Camilli
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA; Kavli Institute for Neurosciences, Yale University School of Medicine, New Haven, CT 06510, USA; Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA.
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236
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Endoplasmic Reticulum - Plasma Membrane Crosstalk Mediated by the Extended Synaptotagmins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 997:83-93. [PMID: 28815523 DOI: 10.1007/978-981-10-4567-7_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The endoplasmic reticulum (ER) possesses multiplicity of functions including protein synthesis, membrane lipid biogenesis, and Ca2+ storage and has broad localization throughout the cell. While the ER and most other membranous organelles are highly interconnected via vesicular traffic that relies on membrane budding and fusion reactions, the ER forms direct contacts with virtually all other membranous organelles, including the plasma membrane (PM), without membrane fusion. Growing evidence suggests that these contacts play major roles in cellular physiology, including the regulation of Ca2+ homeostasis and signaling and control of cellular lipid homeostasis. Extended synaptotagmins (E-Syts) are evolutionarily conserved family of ER-anchored proteins that tether the ER to the PM in PM PI(4,5)P2-dependent and cytosolic Ca2+-regulated manner. In addition, E-Syts possess a cytosolically exposed lipid-harboring module that confers the ability to transfer/exchange glycerolipids between the ER and the PM at E-Syts-mediated ER-PM contacts. In this chapter, the functions of ER-PM contacts and their role in non-vesicular lipid transport with special emphasis on the crosstalk between the two bilayers mediated by E-Syts will be discussed.
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237
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Henne WM. Discovery and Roles of ER-Endolysosomal Contact Sites in Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 997:135-147. [PMID: 28815527 DOI: 10.1007/978-981-10-4567-7_10] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Inter-organelle membrane contact sites (MCSs) serve as unique microenvironments for the sensing and exchange of cellular metabolites and lipids. Though poorly defined, ER-endolysosomal contact sites are quickly becoming recognized as centers for inter-organelle lipid exchange and metabolic decision-making. Here, we review the discovery and current state of knowledge of ER-endolysosomal MCSs with particular focus on the molecular players that establish and/or utilize these contact sites in metabolism. We also discuss associations of ER-endolysosomal MCS-associated proteins in human disease, as well as the therapeutic promise these contact sites hold in modulating cellular physiology.
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Affiliation(s)
- William Mike Henne
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX, 75013, USA.
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238
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Abstract
The endoplasmic reticulum (ER) is a crucial organelle for coordinating cellular Ca2+ signaling and protein synthesis and folding. Moreover, the dynamic and complex membranous structures constituting the ER allow the formation of contact sites with other organelles and structures, including among others the mitochondria and the plasma membrane (PM). The contact sites that the ER form with mitochondria is a hot topic in research, and the nature of the so-called mitochondria-associated membranes (MAMs) is continuously evolving. The MAMs consist of a proteinaceous tether that physically connects the ER with mitochondria. The MAMs harness the main functions of both organelles to form a specialized subcompartment at the interface of the ER and mitochondria. Under homeostatic conditions, MAMs are crucial for the efficient transfer of Ca2+ from the ER to mitochondria, and for proper mitochondria bioenergetics and lipid synthesis. MAMs are also believed to be the master regulators of mitochondrial shape and motility, and to form a crucial site for autophagosome assembly. Not surprisingly, MAMs have been shown to be a hot spot for the transfer of stress signals from the ER to mitochondria, most notably under the conditions of loss of ER proteostasis, by engaging the unfolded protein response (UPR). In this chapter after an introduction on ER biology and ER stress, we will review the emerging and key signaling roles of the MAMs, which have a root in cellular processes and signaling cascades coordinated by the ER.
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239
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Ceramide Transport from the Endoplasmic Reticulum to the Trans Golgi Region at Organelle Membrane Contact Sites. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 997:69-81. [PMID: 28815522 DOI: 10.1007/978-981-10-4567-7_5] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Lipids are the major constituents of all cell membranes and play dynamic roles in organelle structure and function. Although the spontaneous transfer of lipids between different membranes rarely occurs, lipids are appropriately transported between different organelles for their metabolism and to exert their functions in living cells. Proteins that have the biochemical capability to catalyze the intermembrane transfer of lipids are called lipid transfer proteins (LTPs). All organisms possess many types of LTPs. Recent studies revealed that LTPs are key players in the interorganelle transport of lipids at organelle membrane contact sites (MCSs). This chapter depicts how LTPs rationally operate at MCSs by using the ceramide transport protein CERT as a typical model for the LTP-mediated interorganelle transport of lipids.
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240
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ER-endosome contact sites in endosome positioning and protrusion outgrowth. Biochem Soc Trans 2016; 44:441-6. [PMID: 27068952 DOI: 10.1042/bst20150246] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Indexed: 01/09/2023]
Abstract
The endoplasmic reticulum (ER) makes abundant contacts with endosomes, and the numbers of contact sites increase as endosomes mature. It is already clear that such contact sites have diverse compositions and functions, but in this mini-review we will focus on two particular types of ER-endosome contact sites that regulate endosome positioning. Formation of ER-endosome contact sites that contain the cholesterol-binding protein oxysterol-binding protein-related protein 1L (ORP1L) is coordinated with loss of the minus-end-directed microtubule motor Dynein from endosomes. Conversely, formation of ER-endosome contact sites that contain the Kinesin-1-binding protein Protrudin results in transfer of the plus-end-directed microtubule motor Kinesin-1 from ER to endosomes. We discuss the possibility that formation of these two types of contact sites is coordinated as a 'gear-shift' mechanism for endosome motility, and we review evidence that Kinesin-1-mediated motility of late endosomes (LEs) to the cell periphery promotes outgrowth of neurites and other protrusions.
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241
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Supramolecular architecture of endoplasmic reticulum-plasma membrane contact sites. Biochem Soc Trans 2016; 44:534-40. [PMID: 27068966 DOI: 10.1042/bst20150279] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Indexed: 11/17/2022]
Abstract
The endoplasmic reticulum (ER) forms membrane contact sites (MCS) with most other cellular organelles and the plasma membrane (PM). These ER-PM MCS, where the membranes of the ER and PM are closely apposed, were discovered in the early days of electron microscopy (EM), but only recently are we starting to understand their functional and structural diversity. ER-PM MCS are nowadays known to mediate excitation-contraction coupling (ECC) in striated muscle cells and to play crucial roles in Ca(2+)and lipid homoeostasis in all metazoan cells. A common feature across ER-PM MCS specialized in different functions is the preponderance of cooperative phenomena that result in the formation of large supramolecular assemblies. Therefore, characterizing the supramolecular architecture of ER-PM MCS is critical to understand their mechanisms of function. Cryo-electron tomography (cryo-ET) is a powerful EM technique uniquely positioned to address this issue, as it allows 3D imaging of fully hydrated, unstained cellular structures at molecular resolution. In this review I summarize our current structural knowledge on the molecular organization of ER-PM MCS and its functional implications, with special emphasis on the emerging contributions of cryo-ET.
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242
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Abstract
Cellular membranes communicate extensively via contact sites that form between two membranes. Such sites allow exchange of specific ions, lipids or proteins between two compartments without content mixing, thereby preserving organellar architecture during the transfer process. Even though the molecular compositions of membrane contact sites are diverse, it is striking that several of these sites, including contact sites between the endoplasmic reticulum (ER) and endosomes, Golgi and the plasma membrane (PM), and contact sites between lysosomes and peroxisomes, contain phosphorylated derivatives of phosphatidylinositol known as phosphoinositides. In this mini-review we discuss the involvement and functions of phosphoinositides in membrane contact sites.
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243
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Maekawa M, Lee M, Wei K, Ridgway ND, Fairn GD. Staurosporines decrease ORMDL proteins and enhance sphingomyelin synthesis resulting in depletion of plasmalemmal phosphatidylserine. Sci Rep 2016; 6:35762. [PMID: 27805006 PMCID: PMC5090970 DOI: 10.1038/srep35762] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 10/05/2016] [Indexed: 12/03/2022] Open
Abstract
Accumulation of phosphatidylserine in the inner leaflet of the plasma membrane is a hallmark of eukaryotes. Sublethal levels of staurosporine and related compounds deplete phosphatidylserine from the plasma membrane and abrogate K-Ras signaling. Here, we report that low-dose staurosporine and related compounds increase sphingomyelin mass. Mass-spectrometry and metabolic tracer analysis revealed an increase in both the levels and rate of synthesis of sphingomyelin in response to sublethal staurosporine. Mechanistically, it was determined that the abundance of the ORMDL proteins, which negatively regulate serine-palmitoyltransferase, are decreased by low-dose staurosporine. Finally, inhibition of ceramide synthesis, and thus sphingomyelin, prevented the displacement of phosphatidylserine and cholesterol from the inner leaflet of the plasma membrane. The results establish that an optimal level of sphingomyelin is required to maintain the distribution of phosphatidylserine and cholesterol in the plasma membrane and further demonstrate a complex relationship between the trafficking of phosphatidylserine and sphingomyelin.
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Affiliation(s)
- Masashi Maekawa
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, ON, Canada
| | - Minhyoung Lee
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, ON, Canada.,Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Kuiru Wei
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, ON, Canada
| | - Neale D Ridgway
- Departments of Pediatrics, and Biochemistry &Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Gregory D Fairn
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, ON, Canada.,Department of Biochemistry, University of Toronto, Toronto, ON, Canada.,Department of Surgery, University of Toronto, Toronto, ON, Canada
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244
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Running up that hill: How to create cellular lipid gradients by lipid counter-flows. Biochimie 2016; 130:115-121. [DOI: 10.1016/j.biochi.2016.08.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 08/07/2016] [Indexed: 11/21/2022]
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245
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Phosphatidylinositol and phosphatidic acid transport between the ER and plasma membrane during PLC activation requires the Nir2 protein. Biochem Soc Trans 2016; 44:197-201. [PMID: 26862206 DOI: 10.1042/bst20150187] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Phospholipase C (PLC)-mediated hydrolysis of the limited pool of plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] requires replenishment from a larger pool of phosphatidylinositol (PtdIns) via sequential phosphorylation by PtdIns 4-kinases and phosphatidylinositol 4-phosphate (PtdIns4P) 5-kinases. Since PtdIns is synthesized in the endoplasmic reticulum (ER) and PtdIns(4,5)P2 is generated in the PM, it has been postulated that PtdIns transfer proteins (PITPs) provide the means for this lipid transfer function. Recent studies identified the large PITP protein, Nir2 as important for PtdIns transfer from the ER to the PM. It was also found that Nir2 was required for the transfer of phosphatidic acid (PtdOH) from the PM to the ER. In Nir2-depleted cells, activation of PLC leads to PtdOH accumulation in the PM and PtdIns synthesis becomes severely impaired. In quiescent cells, Nir2 is localized to the ER via interaction of its FFAT domain with ER-bound VAMP-associated proteins VAP-A and-B. After PLC activation, Nir2 also binds to the PM via interaction of its C-terminal domains with diacylglycerol (DAG) and PtdOH. Through these interactions, Nir2 functions in ER-PM contact zones. Mutations in VAP-B that have been identified in familial forms of amyotrophic lateral sclerosis (ALS or Lou-Gehrig's disease) cause aggregation of the VAP-B protein, which then impairs its binding to several proteins, including Nir2. These findings have shed new lights on the importance of non-vesicular lipid transfer of PtdIns and PtdOH in ER-PM contact zones with a possible link to a devastating human disease.
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Abstract
Most functions of eukaryotic cells are controlled by cellular membranes, which are not static entities but undergo frequent budding, fission, fusion, and sculpting reactions collectively referred to as membrane dynamics. Consequently, regulation of membrane dynamics is crucial for cellular functions. A key mechanism in such regulation is the reversible recruitment of cytosolic proteins or protein complexes to specific membranes at specific time points. To a large extent this recruitment is orchestrated by phosphorylated derivatives of the membrane lipid phosphatidylinositol, known as phosphoinositides. The seven phosphoinositides found in nature localize to distinct membrane domains and recruit distinct effectors, thereby contributing strongly to the maintenance of membrane identity. Many of the phosphoinositide effectors are proteins that control membrane dynamics, and in this review we discuss the functions of phosphoinositides in membrane dynamics during exocytosis, endocytosis, autophagy, cell division, cell migration, and epithelial cell polarity, with emphasis on protein effectors that are recruited by specific phosphoinositides during these processes.
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Affiliation(s)
- Kay O Schink
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, N-0379 Oslo, Norway; , .,Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, N-0379 Oslo, Norway
| | - Kia-Wee Tan
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, N-0379 Oslo, Norway; , .,Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, N-0379 Oslo, Norway
| | - Harald Stenmark
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, N-0379 Oslo, Norway; , .,Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, N-0379 Oslo, Norway.,Centre of Molecular Inflammation Research, Faculty of Medicine, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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247
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Pomorski TG, Menon AK. Lipid somersaults: Uncovering the mechanisms of protein-mediated lipid flipping. Prog Lipid Res 2016; 64:69-84. [PMID: 27528189 DOI: 10.1016/j.plipres.2016.08.003] [Citation(s) in RCA: 128] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 08/10/2016] [Indexed: 12/22/2022]
Abstract
Membrane lipids diffuse rapidly in the plane of the membrane but their ability to flip spontaneously across a membrane bilayer is hampered by a significant energy barrier. Thus spontaneous flip-flop of polar lipids across membranes is very slow, even though it must occur rapidly to support diverse aspects of cellular life. Here we discuss the mechanisms by which rapid flip-flop occurs, and what role lipid flipping plays in membrane homeostasis and cell growth. We focus on conceptual aspects, highlighting mechanistic insights from biochemical and in silico experiments, and the recent, ground-breaking identification of a number of lipid scramblases.
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Affiliation(s)
- Thomas Günther Pomorski
- Faculty of Chemistry and Biochemistry, Molecular Biochemistry, Ruhr University Bochum, Universitätstrasse 150, D-44780 Bochum, Germany; Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg C, Denmark.
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.
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248
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Abstract
PURPOSE OF REVIEW It is now widely acknowledged that phosphatidylserine is a multifunctional bioactive lipid. In this review, we focus on the function of phosphatidylserine in modulating cholesterol metabolism, influencing inflammatory response and regulating coagulation system, and discuss promising phosphatidylserine-based therapeutic approaches and detection techniques in atherosclerosis. RECENT FINDINGS Phosphatidylserine has been suggested to play important roles in physiological processes, such as apoptosis, inflammation, and coagulation. Recent data demonstrate atheroprotective potential of phosphatidylserine, reflecting its capacity to inhibit inflammation, modulate coagulation, and enhance HDL functionality. Furthermore, modern lipidomic approaches have enabled the investigation of phosphatidylserine properties relevant to the lipid-based drug delivery and development of reconstituted HDL. SUMMARY Studies of phosphatidylserine in relation to atherosclerosis represent an area of opportunity. Additional research elucidating mechanisms underlying experimentally observed atheroprotective effects of phosphatidylserine is required to fully explore therapeutic potential of this naturally occurring phospholipid in cardiovascular disease.
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Affiliation(s)
- Maryam Darabi
- National Institute for Health and Medical Research (INSERM); University of Pierre and Marie Curie; AP-HP, Groupe Hospitalier Pitié-Salpétrière, Paris, France
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Tong J, Manik MK, Yang H, Im YJ. Structural insights into nonvesicular lipid transport by the oxysterol binding protein homologue family. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:928-939. [DOI: 10.1016/j.bbalip.2016.01.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Revised: 12/23/2015] [Accepted: 01/14/2016] [Indexed: 10/22/2022]
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250
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Mesmin B. Mitochondrial lipid transport and biosynthesis: A complex balance. J Cell Biol 2016; 214:9-11. [PMID: 27354376 PMCID: PMC4932376 DOI: 10.1083/jcb.201606069] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 06/14/2016] [Indexed: 01/19/2023] Open
Abstract
Little is known about how mitochondrial lipids reach inner membrane-localized metabolic enzymes for phosphatidylethanolamine synthesis. Aaltonen et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201602007) and Miyata et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201601082) now report roles for two mitochondrial complexes, Ups2-Mdm35 and mitochondrial contact site and cristae organizing system, in the biosynthesis and transport of mitochondrial lipids.
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Affiliation(s)
- Bruno Mesmin
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis, 06560 Valbonne, France Centre National de la Recherche Scientifique, 06560 Valbonne, France
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