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Koh DHZ, Naito T, Na M, Yeap YJ, Rozario P, Zhong FL, Lim KL, Saheki Y. Visualization of accessible cholesterol using a GRAM domain-based biosensor. Nat Commun 2023; 14:6773. [PMID: 37880244 PMCID: PMC10600248 DOI: 10.1038/s41467-023-42498-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Accepted: 10/12/2023] [Indexed: 10/27/2023] Open
Abstract
Cholesterol is important for membrane integrity and cell signaling, and dysregulation of the distribution of cellular cholesterol is associated with numerous diseases, including neurodegenerative disorders. While regulated transport of a specific pool of cholesterol, known as "accessible cholesterol", contributes to the maintenance of cellular cholesterol distribution and homeostasis, tools to monitor accessible cholesterol in live cells remain limited. Here, we engineer a highly sensitive accessible cholesterol biosensor by taking advantage of the cholesterol-sensing element (the GRAM domain) of an evolutionarily conserved lipid transfer protein, GRAMD1b. Using this cholesterol biosensor, which we call GRAM-W, we successfully visualize in real time the distribution of accessible cholesterol in many different cell types, including human keratinocytes and iPSC-derived neurons, and show differential dependencies on cholesterol biosynthesis and uptake for maintaining levels of accessible cholesterol. Furthermore, we combine GRAM-W with a dimerization-dependent fluorescent protein (ddFP) and establish a strategy for the ultrasensitive detection of accessible plasma membrane cholesterol. These tools will allow us to obtain important insights into the molecular mechanisms by which the distribution of cellular cholesterol is regulated.
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Affiliation(s)
- Dylan Hong Zheng Koh
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Tomoki Naito
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Minyoung Na
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Yee Jie Yeap
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Pritisha Rozario
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Franklin L Zhong
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
- Skin Research Institute of Singapore (SRIS), Singapore, 308232, Singapore
| | - Kah-Leong Lim
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
- National Neuroscience Institute, Singapore, 308433, Singapore
| | - Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore.
- Institute of Resource Development and Analysis, Kumamoto University, Kumamoto, 860-0811, Japan.
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2
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Naito T, Yang H, Koh DHZ, Mahajan D, Lu L, Saheki Y. Regulation of cellular cholesterol distribution via non-vesicular lipid transport at ER-Golgi contact sites. Nat Commun 2023; 14:5867. [PMID: 37735529 PMCID: PMC10514280 DOI: 10.1038/s41467-023-41213-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 08/28/2023] [Indexed: 09/23/2023] Open
Abstract
Abnormal distribution of cellular cholesterol is associated with numerous diseases, including cardiovascular and neurodegenerative diseases. Regulated transport of cholesterol is critical for maintaining its proper distribution in the cell, yet the underlying mechanisms remain unclear. Here, we show that lipid transfer proteins, namely ORP9, OSBP, and GRAMD1s/Asters (GRAMD1a/GRAMD1b/GRAMD1c), control non-vesicular cholesterol transport at points of contact between the ER and the trans-Golgi network (TGN), thereby maintaining cellular cholesterol distribution. ORP9 localizes to the TGN via interaction between its tandem α-helices and ORP10/ORP11. ORP9 extracts PI4P from the TGN to prevent its overaccumulation and suppresses OSBP-mediated PI4P-driven cholesterol transport to the Golgi. By contrast, GRAMD1s transport excess cholesterol from the Golgi to the ER, thereby preventing its build-up. Cells lacking ORP9 exhibit accumulation of cholesterol at the Golgi, which is further enhanced by additional depletion of GRAMD1s with major accumulation in the plasma membrane. This is accompanied by chronic activation of the SREBP-2 signalling pathway. Our findings reveal the importance of regulated lipid transport at ER-Golgi contacts for maintaining cellular cholesterol distribution and homeostasis.
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Affiliation(s)
- Tomoki Naito
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Haoning Yang
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Dylan Hong Zheng Koh
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Divyanshu Mahajan
- School of Biological Sciences, Nanyang Technological University, Singapore, 637551, Singapore
| | - Lei Lu
- School of Biological Sciences, Nanyang Technological University, Singapore, 637551, Singapore
| | - Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore.
- Institute of Resource Development and Analysis, Kumamoto University, Kumamoto, 860-0811, Japan.
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3
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Ruiz M, Devkota R, Kaper D, Ruhanen H, Busayavalasa K, Radović U, Henricsson M, Käkelä R, Borén J, Pilon M. AdipoR2 recruits protein interactors to promote fatty acid elongation and membrane fluidity. J Biol Chem 2023:104799. [PMID: 37164154 DOI: 10.1016/j.jbc.2023.104799] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 04/28/2023] [Accepted: 04/29/2023] [Indexed: 05/12/2023] Open
Abstract
The human AdipoR2 and its C. elegans homolog PAQR-2 are multi-pass plasma membrane proteins that protect cells against membrane rigidification. However, how AdipoR2 promotes membrane fluidity mechanistically is not clear. Using 13C-labelled fatty acids, we show that AdipoR2 can promote the elongation and incorporation of membrane-fluidizing polyunsaturated fatty acids into phospholipids. To elucidate the molecular basis of these activities, we performed immunoprecipitations of tagged AdipoR2 and PAQR-2 expressed in HEK293 cells or whole C. elegans, respectively, and identified co-immunoprecipitated proteins using mass spectroscopy. We found that several of the evolutionarily conserved AdipoR2/PAQR-2 interactors are important for fatty acid elongation and incorporation into phospholipids. We experimentally verified some of these interactions, namely with the dehydratase HACD3 that is essential for the third of four steps in long-chain fatty acid elongation, and ACSL4 that is important for activation of unsaturated fatty acids and their channeling into phospholipids. We conclude that AdipoR2 and PAQR-2 can recruit protein interactors to promote the production and incorporation of unsaturated fatty acids into phospholipids.
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Affiliation(s)
- Mario Ruiz
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Ranjan Devkota
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Delaney Kaper
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Hanna Ruhanen
- Helsinki University Lipidomics Unit, Helsinki Institute of Life Science, Biocenter Finland, Helsinki, Finland; Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
| | - Kiran Busayavalasa
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Uroš Radović
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Marcus Henricsson
- Department of Molecular and Clinical Medicine/Wallenberg Laboratory, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden
| | - Reijo Käkelä
- Helsinki University Lipidomics Unit, Helsinki Institute of Life Science, Biocenter Finland, Helsinki, Finland; Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
| | - Jan Borén
- Department of Molecular and Clinical Medicine/Wallenberg Laboratory, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden
| | - Marc Pilon
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden.
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4
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Lu W, Helou YA, Shrinivas K, Liou J, Au-Yeung BB, Weiss A. The phosphatidylinositol-transfer protein Nir3 promotes PI(4,5)P 2 replenishment in response to TCR signaling during T cell development and survival. Nat Immunol 2023; 24:136-147. [PMID: 36581712 PMCID: PMC9810531 DOI: 10.1038/s41590-022-01372-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 10/26/2022] [Indexed: 12/31/2022]
Abstract
Hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C-γ (PLCγ1) represents a critical step in T cell antigen receptor (TCR) signaling and subsequent thymocyte and T cell responses. PIP2 replenishment following its depletion in the plasma membrane (PM) is dependent on delivery of its precursor phosphatidylinositol (PI) from the endoplasmic reticulum (ER) to the PM. We show that a PI transfer protein (PITP), Nir3 (Pitpnm2), promotes PIP2 replenishment following TCR stimulation and is important for T cell development. In Nir3-/- T lineage cells, the PIP2 replenishment following TCR stimulation is slower. Nir3 deficiency attenuates calcium mobilization in double-positive (DP) thymocytes in response to weak TCR stimulation. This impaired TCR signaling leads to attenuated thymocyte development at TCRβ selection and positive selection as well as diminished mature T cell fitness in Nir3-/- mice. This study highlights the importance of PIP2 replenishment mediated by PITPs at ER-PM junctions during TCR signaling.
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Affiliation(s)
- Wen Lu
- Rosalind Russell and Ephraim P. Engleman Rheumatology Research Center, Departments of Medicine and of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA, USA
| | - Ynes A Helou
- Rosalind Russell and Ephraim P. Engleman Rheumatology Research Center, Departments of Medicine and of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA, USA.,Clade Therapeutics, Cambridge, MA, USA
| | - Krishna Shrinivas
- NSF-Simons Center for Mathematical & Statistical Analysis of Biology, Harvard University, Cambridge, MA, USA
| | - Jen Liou
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Byron B Au-Yeung
- Division of Immunology, Lowance Center for Human Immunology, Department of Medicine, Emory University, Atlanta, GA, USA
| | - Arthur Weiss
- Rosalind Russell and Ephraim P. Engleman Rheumatology Research Center, Departments of Medicine and of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA, USA.
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5
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Campos-peña V, Pichardo-rojas P, Sánchez-barbosa T, Ortíz-islas E, Rodríguez-pérez CE, Montes P, Ramos-palacios G, Silva-adaya D, Valencia-quintana R, Cerna-cortes JF, Toral-rios D. Amyloid β, Lipid Metabolism, Basal Cholinergic System, and Therapeutics in Alzheimer’s Disease. Int J Mol Sci 2022; 23:12092. [PMID: 36292947 PMCID: PMC9603563 DOI: 10.3390/ijms232012092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 10/04/2022] [Accepted: 10/06/2022] [Indexed: 12/05/2022] Open
Abstract
The presence of insoluble aggregates of amyloid β (Aβ) in the form of neuritic plaques (NPs) is one of the main features that define Alzheimer’s disease. Studies have suggested that the accumulation of these peptides in the brain significantly contributes to extensive neuronal loss. Furthermore, the content and distribution of cholesterol in the membrane have been shown to have an important effect on the production and subsequent accumulation of Aβ peptides in the plasma membrane, contributing to dysfunction and neuronal death. The monomeric forms of these membrane-bound peptides undergo several conformational changes, ranging from oligomeric forms to beta-sheet structures, each presenting different levels of toxicity. Aβ peptides can be internalized by particular receptors and trigger changes from Tau phosphorylation to alterations in cognitive function, through dysfunction of the cholinergic system. The goal of this review is to summarize the current knowledge on the role of lipids in Alzheimer’s disease and their relationship with the basal cholinergic system, as well as potential disease-modifying therapies.
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6
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Perez-Salas U, Porcar L, Garg S, Ayee MAA, Levitan I. Effective Parameters Controlling Sterol Transfer: A Time-Resolved Small-Angle Neutron Scattering Study. J Membr Biol 2022; 255:423-435. [PMID: 35467109 DOI: 10.1007/s00232-022-00231-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2021] [Accepted: 03/19/2022] [Indexed: 11/29/2022]
Abstract
Though cholesterol is the most prevalent and essential sterol in mammalian cellular membranes, its precursors, post-synthesis cholesterol products, as well as its oxidized derivatives play many other important physiological roles. Using a non-invasive in situ technique, time-resolved small angle neutron scattering, we report on the rate of membrane desorption and corresponding activation energy for this process for a series of sterol precursors and post-synthesis cholesterol products that vary from cholesterol by the number and position of double bonds in B ring of cholesterol's steroid core. In addition, we report on sterols that have oxidation modifications in ring A and ring B of the steroid core. We find that sterols that differ in position or the number of double bonds in ring B have similar time and energy characteristics, while oxysterols have faster transfer rates and lower activation energies than cholesterol in a manner generally consistent with known sterol characteristics, like Log P, the n-octanol/water partitioning coefficient. We find, however, that membrane/water partitioning which is dependent on lipid-sterol interactions is a better predictor, shown by the correlation of the sterols' tilt modulus with both the desorption rates and activation energy.
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Affiliation(s)
- Ursula Perez-Salas
- Physics Department, University of Illinois at Chicago, Chicago, IL, 60607, USA.
| | - Lionel Porcar
- Institut Laue Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France
| | - Sumit Garg
- Physics Department, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Manuela A A Ayee
- Department of Engineering, Dordt University, Sioux Center, IA, USA
| | - Irena Levitan
- Division of Pulmonary, Critical Care, Sleep and Allergy, Department of Medicine, University of Illinois at Chicago, Chicago, IL, 60607, USA
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7
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Abstract
We have long known that lipids traffic between cellular membranes via vesicles but have only recently appreciated the role of nonvesicular lipid transport. Nonvesicular transport can be high volume, supporting biogenesis of rapidly expanding membranes, or more targeted and precise, allowing cells to rapidly alter levels of specific lipids in membranes. Most such transport probably occurs at membrane contact sites, where organelles are closely apposed, and requires lipid transport proteins (LTPs), which solubilize lipids to shield them from the aqueous phase during their transport between membranes. Some LTPs are cup like and shuttle lipid monomers between membranes. Others form conduits allowing lipid flow between membranes. This review describes what we know about nonvesicular lipid transfer mechanisms while also identifying many remaining unknowns: How do LTPs facilitate lipid movement from and into membranes, do LTPs require accessory proteins for efficient transfer in vivo, and how is directionality of transport determined?
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Affiliation(s)
- Karin M Reinisch
- Department of Cell Biology, Yale School of Medicine, New Haven, CT
| | - William A Prinz
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
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8
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Karamysheva ZN, Moitra S, Perez A, Mukherjee S, Tikhonova EB, Karamyshev AL, Zhang K. Unexpected Role of Sterol Synthesis in RNA Stability and Translation in Leishmania. Biomedicines 2021; 9:696. [PMID: 34205466 DOI: 10.3390/biomedicines9060696] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/09/2021] [Accepted: 06/15/2021] [Indexed: 01/16/2023] Open
Abstract
Leishmania parasites are trypanosomatid protozoans that cause leishmaniasis affecting millions of people worldwide. Sterols are important components of the plasma and organellar membranes. They also serve as precursors for the synthesis of signaling molecules. Unlike animals, Leishmania does not synthesize cholesterol but makes ergostane-based sterols instead. C-14-demethylase is a key enzyme involved in the biosynthesis of sterols and an important drug target. In Leishmania parasites, the inactivation of C-14-demethylase leads to multiple defects, including increased plasma membrane fluidity, mitochondrion dysfunction, hypersensitivity to stress and reduced virulence. In this study, we revealed a novel role for sterol synthesis in the maintenance of RNA stability and translation. Sterol alteration in C-14-demethylase knockout mutant leads to increased RNA degradation, reduced translation and impaired heat shock response. Thus, sterol biosynthesis in Leishmania plays an unexpected role in global gene regulation.
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9
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Naito T, Saheki Y. GRAMD1-mediated accessible cholesterol sensing and transport. Biochim Biophys Acta Mol Cell Biol Lipids 2021; 1866:158957. [PMID: 33932585 DOI: 10.1016/j.bbalip.2021.158957] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 04/09/2021] [Accepted: 04/19/2021] [Indexed: 01/19/2023]
Abstract
Cholesterol, an essential lipid for cell signaling and structural integrity of cellular membranes, is highly enriched in the plasma membrane (PM). However, the regulatory mechanisms that control its biosynthesis and uptake both reside in the endoplasmic reticulum (ER). Thus, the ER needs to constantly monitor the levels of PM cholesterol. This is in part mediated by regulated transport of a biochemically defined pool of cholesterol, termed "accessible" cholesterol, from the PM to the ER via evolutionarily conserved ER-anchored lipid transfer proteins, the GRAMD1s/Asters (GRAMD1a/1b/1c) (Lam/Ltc proteins in yeast). GRAMD1s possess cytosolically exposed GRAM domain and StART-like domain followed by a transmembrane ER anchor. They form homo- and hetero-meric complexes and move to the contacts formed between the ER and the PM by sensing a transient expansion of the accessible pool of cholesterol in the PM via the GRAM domain and facilitate its extraction and transport to the ER via the StART-like domain. The GRAMD1b GRAM domain possesses distinct, but synergistic sites, for recognizing accessible cholesterol and anionic lipids, including phosphatidylserine, within the PM. This property of the GRAM domain contributes to regulated tethering of the PM to ER membrane where GRAMD1s are anchored and fine-tunes StART-like domain-dependent accessible cholesterol transport. Thus, cells use GRAMD1s to sense the levels of cholesterol in the PM and regulate transport of accessible PM cholesterol to the ER in order to maintain cholesterol homeostasis.
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10
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Kobierski J, Wnętrzak A, Chachaj-Brekiesz A, Filiczkowska A, Petelska AD, Dynarowicz-Latka P. How the replacement of cholesterol by 25-hydroxycholesterol affects the interactions with sphingolipids: The Langmuir Monolayer Study complemented with theoretical calculations. J R Soc Interface 2021; 18:20210050. [PMID: 33726539 DOI: 10.1098/rsif.2021.0050] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
In this paper, a representative of chain-oxidized sterols, 25-hydroxycholesterol (25-OH), has been studied in Langmuir monolayers mixed with the sphingolipids sphingomyelin (SM) and ganglioside (GM1) to build lipid rafts. A classical Langmuir monolayer approach based on thermodynamic analysis of interactions was complemented with microscopic visualization of films (Brewster angle microscopy), surface-sensitive spectroscopy (polarization modulation-infrared reflection-absorption spectroscopy) and theoretical calculations (density functional theory modelling and molecular dynamics simulations). Strong interactions between 25-OH and both investigated sphingolipids enabled the formation of surface complexes. As known from previous studies, 25-OH in pure monolayers can be anchored to the water surface with a hydroxyl group at either C(3) or C(25). In this study, we investigated how the presence of additional strong interactions with sphingolipids modifies the surface arrangement of 25-OH. Results have shown that, in the 25-OH/GM1 system, there are no preferences regarding the orientation of the 25-OH molecule in surface complexes and two types of complexes are formed. On the other hand, SM enforces one specific orientation of 25-OH: being anchored with the C(3)-OH group to the water. The strength of interactions between the studied sphingolipids and 25-OH versus cholesterol is similar, which indicates that cholesterol may well be replaced by oxysterol in the lipid raft system. In this way, the composition of lipid rafts can be modified, changing their rheological properties and, as a consequence, influencing their proper functioning.
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Affiliation(s)
- Jan Kobierski
- Department of Pharmaceutical Biophysics, Faculty of Pharmacy, Jagiellonian University Medical College, Medyczna 9, 30-688 Kraków, Poland
| | - Anita Wnętrzak
- Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland
| | - Anna Chachaj-Brekiesz
- Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland
| | - Anna Filiczkowska
- Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
| | - Aneta D Petelska
- Faculty of Chemistry, University of Bialystok, Ciołkowskiego 1 K, 15-425 Bialystok, Poland
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11
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Ercan B, Naito T, Koh DHZ, Dharmawan D, Saheki Y. Molecular basis of accessible plasma membrane cholesterol recognition by the GRAM domain of GRAMD1b. EMBO J 2021; 40:e106524. [PMID: 33604931 PMCID: PMC7957428 DOI: 10.15252/embj.2020106524] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 12/16/2020] [Accepted: 01/08/2021] [Indexed: 12/25/2022] Open
Abstract
Cholesterol is essential for cell physiology. Transport of the "accessible" pool of cholesterol from the plasma membrane (PM) to the endoplasmic reticulum (ER) by ER-localized GRAMD1 proteins (GRAMD1a/1b/1c) contributes to cholesterol homeostasis. However, how cells detect accessible cholesterol within the PM remains unclear. We show that the GRAM domain of GRAMD1b, a coincidence detector for anionic lipids, including phosphatidylserine (PS), and cholesterol, possesses distinct but synergistic sites for sensing accessible cholesterol and anionic lipids. We find that a mutation within the GRAM domain of GRAMD1b that is associated with intellectual disability in humans specifically impairs cholesterol sensing. In addition, we identified another point mutation within this domain that enhances cholesterol sensitivity without altering its PS sensitivity. Cell-free reconstitution and cell-based assays revealed that the ability of the GRAM domain to sense accessible cholesterol regulates membrane tethering and determines the rate of cholesterol transport by GRAMD1b. Thus, cells detect the codistribution of accessible cholesterol and anionic lipids in the PM and fine-tune the non-vesicular transport of PM cholesterol to the ER via GRAMD1s.
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Affiliation(s)
- Bilge Ercan
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Tomoki Naito
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | | | - Dennis Dharmawan
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.,Institute of Resource Development and Analysis, Kumamoto University, Kumamoto, Japan
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12
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Abstract
Sterol contributes to the structural integrity of cellular membranes and plays an important role in the regulation of cell signaling in eukaryotes. It is either produced in the endoplasmic reticulum or taken up from the extracellular environment. In most eukaryotic cells, however, the majority of sterol is enriched in the plasma membrane. Thus, the transport of sterol between the plasma membrane and other organelles, including the endoplasmic reticulum, is crucial for maintaining sterol homeostasis. While vesicular transport that relies on membrane budding and fusion reactions plays an important role in bulk sterol transport, this mode of transport is slow and non-selective. Growing evidence suggests a critical role of nonvesicular transport mediated by evolutionarily conserved families of lipid transfer proteins in more rapid and selective delivery of sterol. Some lipid transfer proteins act primarily at the sites of contacts formed between the endoplasmic reticulum and other organelles or the plasma membrane without membrane fusion. In this review, we describe the similarities and differences of sterol biosynthesis and uptake in mammals and yeast and discuss the role of their lipid transfer proteins in maintaining plasma membrane sterol homeostasis.
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Affiliation(s)
- Dylan Hong Zheng Koh
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore 308232, Singapore
| | - Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore 308232, Singapore
- Institute of Resource Development and
Analysis, Kumamoto University, Kumamoto 860-0811, Japan
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13
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Howard R, Scheiner A, Cunningham J, Gatenby R. Cytoplasmic convection currents and intracellular temperature gradients. PLoS Comput Biol 2019; 15:e1007372. [PMID: 31682599 DOI: 10.1371/journal.pcbi.1007372] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Accepted: 09/03/2019] [Indexed: 11/19/2022] Open
Abstract
Intracellular thermometry has recently demonstrated temperatures in the nucleus, mitochondria, and centrosome to be significantly higher than those of the cytoplasm and cell membrane. This local thermogenesis and the resulting temperature gradient could facilitate the development of persistent, self-organizing convection currents in the cytoplasm of large eukaryotes. Using 3-dimensional computational simulations of intracellular fluid motion, we quantify the convective velocities that could result from the temperature differences observed experimentally. Based on these velocities, we identify the conditions necessary for this temperature-driven bulk flow to dominate over random thermal diffusive motion at the scale of a single eukaryotic cell. With temperature gradients of the order 1°C and diffusion coefficients comparable to those described in the literature, Péclet numbers ≥ 1 are feasible and permit comparable or greater effects of convection than diffusion in determining intracellular mass flux. In addition to the temperature gradient, the resulting flow patterns would also depend on the spatial localization of the heat source, the shape of the cell membrane, and the complex intracellular structure including the cytoskeleton. While this intracellular convection would be highly context-dependent, in certain settings, convective motion could provide a previously unrecognized mechanism for directed, bulk transport within eukaryotic cells.
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14
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Fiore M, Maniti O, Girard-Egrot A, Monnard PA, Strazewski P. Glass Microsphere-Supported Giant Vesicles for the Observation of Self-Reproduction of Lipid Boundaries. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201710708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Michele Fiore
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires; Université de Lyon; Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918 69622 Villeurbanne Cedex France
| | - Ofelia Maniti
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires; Université de Lyon; Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918 69622 Villeurbanne Cedex France
| | - Agnes Girard-Egrot
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires; Université de Lyon; Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918 69622 Villeurbanne Cedex France
| | - Pierre-Alain Monnard
- Institute of Physics, Chemistry and Pharmacy; University of Southern Denmark; Campusvej 55 5230 Odense M Denmark
| | - Peter Strazewski
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires; Université de Lyon; Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918 69622 Villeurbanne Cedex France
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15
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Fiore M, Maniti O, Girard-Egrot A, Monnard PA, Strazewski P. Glass Microsphere-Supported Giant Vesicles for the Observation of Self-Reproduction of Lipid Boundaries. Angew Chem Int Ed Engl 2017; 57:282-286. [PMID: 29105911 DOI: 10.1002/anie.201710708] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Indexed: 01/03/2023]
Abstract
Growth and division experiments on phospholipid boundaries were carried out using glass microsphere-supported phospholipid (DOPC) giant vesicles (GVs) fed with a fatty acid solution (oleic acid) at two distinct feeding rates. Both fast and slow feeding methods produced daughter GVs. Under slow feeding conditions the membrane growth process (evagination, buds, filaments) was observed in detail by fluorescence microscopy. The density difference between supported mother vesicles and newly formed daughter vesicles allowed their easy separation. Mass spectrometric analysis of the resulting mother and daughter GVs showed that the composition of both vesicle types was a mixture of original supported phospholipids and added fatty acids reflecting the total composition of amphiphiles after the feeding process. Thus, self-reproduction of phospholipid vesicles can take place under preservation of the lipid composition but different aggregate size.
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Affiliation(s)
- Michele Fiore
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Université de Lyon, Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918, 69622, Villeurbanne Cedex, France
| | - Ofelia Maniti
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Université de Lyon, Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918, 69622, Villeurbanne Cedex, France
| | - Agnes Girard-Egrot
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Université de Lyon, Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918, 69622, Villeurbanne Cedex, France
| | - Pierre-Alain Monnard
- Institute of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark
| | - Peter Strazewski
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Université de Lyon, Claude Bernard Lyon 1, 43 bvd du 11 Novembre 1918, 69622, Villeurbanne Cedex, France
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16
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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: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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17
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Abstract
The endoplasmic reticulum (ER) has a broad localization throughout the cell and forms direct physical contacts with all other classes of membranous organelles, including the plasma membrane (PM). A number of protein tethers that mediate these contacts have been identified, and study of these protein tethers has revealed a multiplicity of roles in cell physiology, including regulation of intracellular Ca2+ dynamics and signaling as well as control of lipid traffic and homeostasis. In this review, we discuss the cross talk between the ER and the PM mediated by direct contacts. We review factors that tether the two membranes, their properties, and their dynamics in response to the functional state of the cell. We focus in particular on the role of ER-PM contacts in nonvesicular lipid transport between the two bilayers mediated by lipid transfer proteins.
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Affiliation(s)
- Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, 308232, Singapore;
| | - Pietro De Camilli
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Kavli Institute for Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, Connecticut 06510;
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18
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Iaea DB, Mao S, Lund FW, Maxfield FR. Role of STARD4 in sterol transport between the endocytic recycling compartment and the plasma membrane. Mol Biol Cell 2017; 28:1111-1122. [PMID: 28209730 PMCID: PMC5391187 DOI: 10.1091/mbc.e16-07-0499] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 02/03/2017] [Accepted: 02/08/2017] [Indexed: 11/23/2022] Open
Abstract
The kinetics of sterol transport between the plasma membrane and the endocytic recycling compartment is measured using fluorescence microscopy. STARD4, a small, soluble sterol transport protein, is responsible for 25% of the total transport and 33% of nonvesicular transport. Elevated cholesterol dramatically increases sterol transport rate constants. Cholesterol is an essential constituent of membranes in mammalian cells. The plasma membrane and the endocytic recycling compartment (ERC) are both highly enriched in cholesterol. The abundance and distribution of cholesterol among organelles are tightly controlled by a combination of mechanisms involving vesicular and nonvesicular sterol transport processes. Using the fluorescent cholesterol analogue dehydroergosterol, we examined sterol transport between the plasma membrane and the ERC using fluorescence recovery after photobleaching and a novel sterol efflux assay. We found that sterol transport between these organelles in a U2OS cell line has a t1/2 =12–15 min. Approximately 70% of sterol transport is ATP independent and therefore is nonvesicular. Increasing cellular cholesterol levels dramatically increases bidirectional transport rate constants, but decreases in cholesterol levels have only a modest effect. A soluble sterol transport protein, STARD4, accounts for ∼25% of total sterol transport and ∼33% of nonvesicular sterol transport between the plasma membrane and ERC. This study shows that nonvesicular sterol transport mechanisms and STARD4 in particular account for a large fraction of sterol transport between the plasma membrane and the ERC.
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Affiliation(s)
- David B Iaea
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065.,Weill Cornell Medical College, Rockefeller University, and Memorial Sloan-Kettering Cancer Center Tri-Institutional Chemical Biology Program, New York, NY 10065
| | - Shu Mao
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Frederik W Lund
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Frederick R Maxfield
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065 .,Weill Cornell Medical College, Rockefeller University, and Memorial Sloan-Kettering Cancer Center Tri-Institutional Chemical Biology Program, New York, NY 10065
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19
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Xu J, Jiang D, Qin Y, Xia J, Jiang D, Chen HY. C3N4 Nanosheet Modified Microwell Array with Enhanced Electrochemiluminescence for Total Analysis of Cholesterol at Single Cells. Anal Chem 2017; 89:2216-2220. [PMID: 28192948 DOI: 10.1021/acs.analchem.6b04635] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Jingjing Xu
- State
Key Laboratory of Analytical Chemistry for Life Science, School of
Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
| | - Depeng Jiang
- Department
of Respiratory Medicine, The Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China
| | - Yanling Qin
- Department
of Respiratory Medicine, The Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China
| | - Juan Xia
- Department
of Respiratory Medicine, The Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China
| | - Dechen Jiang
- State
Key Laboratory of Analytical Chemistry for Life Science, School of
Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
| | - Hong-Yuan Chen
- State
Key Laboratory of Analytical Chemistry for Life Science, School of
Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
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20
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Busija AR, Patel HH, Insel PA. Caveolins and cavins in the trafficking, maturation, and degradation of caveolae: implications for cell physiology. Am J Physiol Cell Physiol 2017; 312:C459-C477. [PMID: 28122734 DOI: 10.1152/ajpcell.00355.2016] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 01/23/2017] [Accepted: 01/24/2017] [Indexed: 01/09/2023]
Abstract
Caveolins (Cavs) are ~20 kDa scaffolding proteins that assemble as oligomeric complexes in lipid raft domains to form caveolae, flask-shaped plasma membrane (PM) invaginations. Caveolae ("little caves") require lipid-lipid, protein-lipid, and protein-protein interactions that can modulate the localization, conformational stability, ligand affinity, effector specificity, and other functions of proteins that are partners of Cavs. Cavs are assembled into small oligomers in the endoplasmic reticulum (ER), transported to the Golgi for assembly with cholesterol and other oligomers, and then exported to the PM as an intact coat complex. At the PM, cavins, ~50 kDa adapter proteins, oligomerize into an outer coat complex that remodels the membrane into caveolae. The structure of caveolae protects their contents (i.e., lipids and proteins) from degradation. Cellular changes, including signal transduction effects, can destabilize caveolae and produce cavin dissociation, restructuring of Cav oligomers, ubiquitination, internalization, and degradation. In this review, we provide a perspective of the life cycle (biogenesis, degradation), composition, and physiologic roles of Cavs and caveolae and identify unanswered questions regarding the roles of Cavs and cavins in caveolae and in regulating cell physiology.1.
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Affiliation(s)
- Anna R Busija
- Department of Anesthesiology, University of California, San Diego, La Jolla, California.,Department of Pharmacology, University of California, San Diego, La Jolla, California
| | - Hemal H Patel
- Department of Anesthesiology, University of California, San Diego, La Jolla, California
| | - Paul A Insel
- Department of Medicine, University of California, San Diego, La Jolla, California; and .,Department of Pharmacology, University of California, San Diego, La Jolla, California
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21
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Gumí-Audenis B, Costa L, Carlá F, Comin F, Sanz F, Giannotti MI. Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids. Membranes (Basel) 2016; 6:E58. [PMID: 27999368 PMCID: PMC5192414 DOI: 10.3390/membranes6040058] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 12/12/2016] [Accepted: 12/14/2016] [Indexed: 11/17/2022]
Abstract
Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information.
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Affiliation(s)
- Berta Gumí-Audenis
- Nanoprobes and Nanoswitches group, Institute for Bioengineering of Catalunya (IBEC), Barcelona 08028, Spain.
- Physical Chemistry Department, Universitat de Barcelona, Barcelona 08028, Spain.
- European Synchrotron Radiation Facility (ESRF), Grenoble 38043, France.
- Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid 28028, Spain.
| | - Luca Costa
- Structure and Dynamics of Nucleoproteic and Membrane Assemblies, Centre de Biochimie Structurale (CBS), Montpellier 34090, France.
| | - Francesco Carlá
- European Synchrotron Radiation Facility (ESRF), Grenoble 38043, France.
| | - Fabio Comin
- European Synchrotron Radiation Facility (ESRF), Grenoble 38043, France.
| | - Fausto Sanz
- Nanoprobes and Nanoswitches group, Institute for Bioengineering of Catalunya (IBEC), Barcelona 08028, Spain.
- Physical Chemistry Department, Universitat de Barcelona, Barcelona 08028, Spain.
- Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid 28028, Spain.
| | - Marina I Giannotti
- Nanoprobes and Nanoswitches group, Institute for Bioengineering of Catalunya (IBEC), Barcelona 08028, Spain.
- Physical Chemistry Department, Universitat de Barcelona, Barcelona 08028, Spain.
- Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid 28028, Spain.
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22
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Elustondo P, Martin LA, Karten B. Mitochondrial cholesterol import. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:90-101. [PMID: 27565112 DOI: 10.1016/j.bbalip.2016.08.012] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 08/15/2016] [Accepted: 08/19/2016] [Indexed: 02/06/2023]
Abstract
All animal subcellular membranes require cholesterol, which influences membrane fluidity and permeability, fission and fusion processes, and membrane protein function. The distribution of cholesterol among subcellular membranes is highly heterogeneous and the cholesterol content of each membrane must be carefully regulated. Compared to other subcellular membranes, mitochondrial membranes are cholesterol-poor, particularly the inner mitochondrial membrane (IMM). As a result, steroidogenesis can be controlled through the delivery of cholesterol to the IMM, where it is converted to pregnenolone. The low basal levels of cholesterol also make mitochondria sensitive to changes in cholesterol content, which can have a relatively large impact on the biophysical and functional characteristics of mitochondrial membranes. Increased mitochondrial cholesterol levels have been observed in diverse pathological conditions including cancer, steatohepatitis, Alzheimer disease and Niemann-Pick Type C1-deficiency, and are associated with increased oxidative stress, impaired oxidative phosphorylation, and changes in the susceptibility to apoptosis, among other alterations in mitochondrial function. Mitochondria are not included in the vesicular trafficking network; therefore, cholesterol transport to mitochondria is mostly achieved through the activity of lipid transfer proteins at membrane contact sites or by cytosolic, diffusible lipid transfer proteins. Here we will give an overview of the main mechanisms involved in mitochondrial cholesterol import, focusing on the steroidogenic acute regulatory protein StAR/STARD1 and other members of the StAR-related lipid transfer (START) domain protein family, and we will discuss how changes in mitochondrial cholesterol levels can arise and affect mitochondrial function. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.
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Affiliation(s)
- Pia Elustondo
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Laura A Martin
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Barbara Karten
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada.
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23
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Abstract
Cholesterol plays an important role in determining the biophysical properties of membranes in mammalian cells, and the concentration of cholesterol in membranes is tightly regulated. Cholesterol moves among membrane organelles by a combination of vesicular and nonvesicular transport pathways, but the details of these transport pathways are not well understood. In this review, we discuss the mechanisms for nonvesicular sterol transport with an emphasis on the role of STARD4, a small, soluble, cytoplasmic sterol transport protein. STARD4 can rapidly equilibrate sterol between membranes, especially membranes with anionic lipid headgroups. We also discuss the sterol transport in late endosomes and lysosomes, which is mediated by a soluble protein, NPC2, and a membrane protein, NPC1. Homozygous mutations in these proteins lead to a lysosomal lipid storage disorder, Niemann-Pick disease type C. Many of the disease-causing mutations in NPC1 are associated with degradation of the mutant NPC1 proteins in the endoplasmic reticulum. Several histone deacetylase inhibitors have been found to rescue the premature degradation of the mutant NPC1 proteins, and one of these is now in a small clinical trial.
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Affiliation(s)
- Frederick R Maxfield
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - David B Iaea
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - Nina H Pipalia
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
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24
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Wüstner D, Lund FW, Röhrl C, Stangl H. Potential of BODIPY-cholesterol for analysis of cholesterol transport and diffusion in living cells. Chem Phys Lipids 2016; 194:12-28. [DOI: 10.1016/j.chemphyslip.2015.08.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Revised: 08/07/2015] [Accepted: 08/12/2015] [Indexed: 01/04/2023]
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25
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Lee BJ, Kim JY. Identification of the Best Anthropometric Predictors of Serum High- and Low-Density Lipoproteins Using Machine Learning. IEEE J Biomed Health Inform 2015; 19:1747-56. [DOI: 10.1109/jbhi.2014.2350014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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26
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Gulati S, Balderes D, Kim C, Guo ZA, Wilcox L, Area-Gomez E, Snider J, Wolinski H, Stagljar I, Granato JT, Ruggles KV, DeGiorgis JA, Kohlwein SD, Schon EA, Sturley SL. ATP-binding cassette transporters and sterol O-acyltransferases interact at membrane microdomains to modulate sterol uptake and esterification. FASEB J 2015. [PMID: 26220175 DOI: 10.1096/fj.14-264796] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A key component of eukaryotic lipid homeostasis is the esterification of sterols with fatty acids by sterol O-acyltransferases (SOATs). The esterification reactions are allosterically activated by their sterol substrates, the majority of which accumulate at the plasma membrane. We demonstrate that in yeast, sterol transport from the plasma membrane to the site of esterification is associated with the physical interaction of the major SOAT, acyl-coenzyme A:cholesterol acyltransferase (ACAT)-related enzyme (Are)2p, with 2 plasma membrane ATP-binding cassette (ABC) transporters: Aus1p and Pdr11p. Are2p, Aus1p, and Pdr11p, unlike the minor acyltransferase, Are1p, colocalize to sterol and sphingolipid-enriched, detergent-resistant microdomains (DRMs). Deletion of either ABC transporter results in Are2p relocalization to detergent-soluble membrane domains and a significant decrease (53-36%) in esterification of exogenous sterol. Similarly, in murine tissues, the SOAT1/Acat1 enzyme and activity localize to DRMs. This subcellular localization is diminished upon deletion of murine ABC transporters, such as Abcg1, which itself is DRM associated. We propose that the close proximity of sterol esterification and transport proteins to each other combined with their residence in lipid-enriched membrane microdomains facilitates rapid, high-capacity sterol transport and esterification, obviating any requirement for soluble intermediary proteins.
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Affiliation(s)
- Sonia Gulati
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Dina Balderes
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Christine Kim
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Zhongmin A Guo
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Lisa Wilcox
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Estela Area-Gomez
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Jamie Snider
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Heimo Wolinski
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Igor Stagljar
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Juliana T Granato
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Kelly V Ruggles
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Joseph A DeGiorgis
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Sepp D Kohlwein
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Eric A Schon
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Stephen L Sturley
- *Institute of Human Nutrition, Department of Neurology, **Department of Genetics and Development, and Department of Pediatrics, Columbia University Medical Center, New York, New York, USA; Department of Biological Sciences and Department of Chemistry, Columbia University, New York, New York, USA; Donnelly Center for Cellular and Biomolecular Research, Toronto, Ontario, Canada; Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Graz, Austria; Department of Biology, Providence College, Providence, Rhode Island, USA; and Marine Biological Laboratory, Woods Hole, Massachusetts, USA
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Moser von Filseck J, Mesmin B, Bigay J, Antonny B, Drin G. Building lipid 'PIPelines' throughout the cell by ORP/Osh proteins. Biochem Soc Trans 2014; 42:1465-70. [PMID: 25233433 DOI: 10.1042/BST20140143] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In eukaryotic cells, a sterol gradient exists between the early and late regions of the secretory pathway. This gradient seems to rely on non-vesicular transport mechanisms mediated by specialized carriers. The oxysterol-binding protein-related protein (ORP)/oxysterol-binding homology (Osh) family has been assumed initially to exclusively include proteins acting as sterol sensors/transporters and many efforts have been made to determine their mode of action. Our recent studies have demonstrated that some ORP/Osh proteins are not mere sterol transporters, but sterol/phosphatidylinositol 4-phosphate [PI(4)P] exchangers. They exploit the PI(4)P gradient at the endoplasmic reticulum (ER)/Golgi interface, or at membrane-contact sites between these compartments, to actively create a sterol gradient. Other recent reports have suggested that all ORP/Osh proteins bind PI(4)P and recognize a second lipid that is not necessary sterol. We have thus proposed that ORP/Osh proteins use PI(4)P gradients between organelles to convey various lipid species.
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Abstract
The transport of lipids from their synthesis site at the endoplasmic reticulum (ER) to different target membranes could be mediated by both vesicular and nonvesicular transport mechanisms. Nonvesicular lipid transport appears to be the major transport route of certain lipid species, and could be mediated by either spontaneous lipid transport or by lipid-transfer proteins (LTPs). Although nonvesicular lipid transport has been extensively studied for more than four decades, its underlying mechanism, advantage and regulation, have not been fully explored. In particular, the function of LTPs and their involvement in intracellular lipid movement remain largely controversial. In this article, we describe the pathways by which lipids are synthesized at the ER and delivered to different cellular membranes, and discuss the role of LTPs in lipid transport both in vitro and in intact cells.
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Affiliation(s)
- Sima Lev
- Molecular Cell Biology Department, Weizmann Institute of Science, Rehovot 76100, Israel.
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Hymel D, Peterson BR. Synthetic cell surface receptors for delivery of therapeutics and probes. Adv Drug Deliv Rev 2012; 64:797-810. [PMID: 22401875 PMCID: PMC3359398 DOI: 10.1016/j.addr.2012.02.007] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 02/18/2012] [Accepted: 02/20/2012] [Indexed: 11/17/2022]
Abstract
Receptor-mediated endocytosis is a highly efficient mechanism for cellular uptake of membrane-impermeant ligands. Cells use this process to acquire nutrients, initiate signal transduction, promote development, regulate neurotransmission, and maintain homeostasis. Natural receptors that participate in receptor-mediated endocytosis are structurally diverse, ranging from large transmembrane proteins to small glycolipids embedded in the outer leaflet of cellular plasma membranes. Despite their vast structural differences, these receptors share common features of binding to extracellular ligands, clustering in dynamic membrane regions that pinch off to yield intracellular vesicles, and accumulation of receptor-ligand complexes in membrane-sealed endosomes. Receptors typically dissociate from ligands in endosomes and cycle back to the cell surface, whereas internalized ligands are usually delivered into lysosomes, where they are degraded, but some can escape and penetrate into the cytosol. Here, we review efforts to develop synthetic cell surface receptors, defined as nonnatural compounds, exemplified by mimics of cholesterol, that insert into plasma membranes, bind extracellular ligands including therapeutics, probes, and endogenous proteins, and engage endocytic membrane trafficking pathways. By mimicking natural mechanisms of receptor-mediated endocytosis, synthetic cell surface receptors have the potential to function as prosthetic molecules capable of seamlessly augmenting the endocytic uptake machinery of living mammalian cells.
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Affiliation(s)
- David Hymel
- Department of Medicinal Chemistry, The University of Kansas, Lawrence, KS 66045, United States
| | - Blake R. Peterson
- Department of Medicinal Chemistry, The University of Kansas, Lawrence, KS 66045, United States
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Alvarez-Vasquez F, Riezman H, Hannun YA, Voit EO. Mathematical modeling and validation of the ergosterol pathway in Saccharomyces cerevisiae. PLoS One 2011; 6:e28344. [PMID: 22194828 PMCID: PMC3237449 DOI: 10.1371/journal.pone.0028344] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2011] [Accepted: 11/06/2011] [Indexed: 11/22/2022] Open
Abstract
The de novo biosynthetic machinery for both sphingolipid and ergosterol production in yeast is localized in the endoplasmic reticulum (ER) and Golgi. The interconnections between the two pathways are still poorly understood, but they may be connected in specialized membrane domains, and specific knockouts strongly suggest that both routes have different layers of mutual control and are co-affected by drugs. With the goal of shedding light on the functional integration of the yeast sphingolipid-ergosterol (SL-E) pathway, we constructed a dynamic model of the ergosterol pathway using the guidelines of Biochemical Systems Theory (BST) (Savageau., J. theor. Biol., 25, 365–9, 1969). The resulting model was merged with a previous mathematical model of sphingolipid metabolism in yeast (Alvarez-Vasquez et al., J. theor. Biol., 226, 265–91, 2004; Alvarez-Vasquez et al., Nature433, 425–30, 2005). The S-system format within BST was used for analyses of consistency, stability, and sensitivity of the SL-E model, while the GMA format was used for dynamic simulations and predictions. Model validation was accomplished by comparing predictions from the model with published results on sterol and sterol-ester dynamics in yeast. The validated model was used to predict the metabolomic dynamics of the SL-E pathway after drug treatment. Specifically, we simulated the action of drugs affecting sphingolipids in the endoplasmic reticulum and studied changes in ergosterol associated with microdomains of the plasma membrane (PM).
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Affiliation(s)
- Fernando Alvarez-Vasquez
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, United States of America.
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31
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Lee CYD, Tse W, Smith JD, Landreth GE. Apolipoprotein E promotes β-amyloid trafficking and degradation by modulating microglial cholesterol levels. J Biol Chem 2011; 287:2032-44. [PMID: 22130662 DOI: 10.1074/jbc.m111.295451] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Allelic variation in the apolipoprotein E (APOE) gene is the major risk factor of sporadic Alzheimer disease. ApoE is the primary cholesterol carrier in the brain. Previously, we demonstrated that intracellular degradation of β-amyloid (Aβ) peptides by microglia is dramatically enhanced in the presence of apoE. However, the molecular mechanisms subserving this effect remain unknown. This study reports a mechanistic link between apoE-regulated cholesterol homeostasis and Aβ degradation. We demonstrate that promoting intracellular Aβ degradation by microglia is a common feature of HDL apolipoproteins, including apoE and apoA-I. This effect was not dependent on the direct interaction of apoE and Aβ. Regulation of Aβ degradation was achieved by solely manipulating cellular cholesterol levels. The expression and the activity of Aβ degrading enzymes, however, were not regulated by cholesterol. We observed that reducing cellular cholesterol levels by apoE resulted in faster delivery of Aβ to lysosomes and enhanced degradation. Moreover, apoE facilitated the recycling of Rab7, a small GTPase responsible for recruiting the motor complex to late endosomes/lysosomes. These data indicate that faster endocytic trafficking of Aβ-containing vesicles in the presence of apoE resulted from efficient recycling of Rab7 from lysosomes to early endosomes. Thus, apoE-induced intracellular Aβ degradation is mediated by the cholesterol efflux function of apoE, which lowers cellular cholesterol levels and subsequently facilitates the intracellular trafficking of Aβ to lysosomes for degradation. These findings demonstrate a direct role of cholesterol in the intracellular Aβ degradation.
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Affiliation(s)
- C Y Daniel Lee
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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32
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Goedeke L, Fernández-Hernando C. Regulation of cholesterol homeostasis. Cell Mol Life Sci 2012; 69:915-30. [PMID: 22009455 DOI: 10.1007/s00018-011-0857-5] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Revised: 09/29/2011] [Accepted: 09/29/2011] [Indexed: 01/24/2023]
Abstract
Cholesterol homeostasis is among the most intensely regulated processes in biology. Since its isolation from gallstones at the time of the French Revolution, cholesterol has been extensively studied. Insufficient or excessive cellular cholesterol results in pathological processes including atherosclerosis and metabolic syndrome. Mammalian cells obtain cholesterol from the circulation in the form of plasma lipoproteins or intracellularly, through the synthesis of cholesterol from acetyl coenzyme A (acetyl-CoA). This process is tightly regulated at multiple levels. In this review, we provide an overview of the multiple mechanisms by which cellular cholesterol metabolism is regulated. We also discuss the recent advances in the post-transcriptional regulation of cholesterol homeostasis, including the role of small non-coding RNAs (microRNAs). These novel findings may open new avenues for the treatment of dyslipidemias and cardiovascular diseases.
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Abstract
The expression of a small sterol transport protein, STARD4, is regulated by cholesterol levels. We show that the abundance of STARD4 regulates the sensitivity of the SREBP-2 system to changes in cholesterol, providing an additional layer of regulation in the cholesterol homeostatic mechanism. Nonvesicular transport of cholesterol plays an essential role in the distribution and regulation of cholesterol within cells, but it has been difficult to identify the key intracellular cholesterol transporters. The steroidogenic acute regulatory-related lipid-transfer (START) family of proteins is involved in several pathways of nonvesicular trafficking of sterols. Among them, STARD4 has been shown to increase intracellular cholesteryl ester formation and is controlled at the transcriptional level by sterol levels in cells. We found that STARD4 is very efficient in transporting sterol between membranes in vitro. Cholesterol levels are increased in STARD4-silenced cells, while sterol transport to the endocytic recycling compartment (ERC) and to the endoplasmic reticulum (ER) are enhanced upon STARD4 overexpression. STARD4 silencing attenuates cholesterol-mediated regulation of SREBP-2 activation, while its overexpression amplifies sterol sensing by SCAP/SREBP-2. To analyze STARD4's mode of action, we compared sterol transport mediated by STARD4 with that of a simple sterol carrier, methyl-β-cyclodextrin (MCD), when STARD4 and MCD were overexpressed or injected into cells. Interestingly, STARD4 and cytosolic MCD act similarly by increasing the rate of transfer of sterol to the ERC and to the ER. Our results suggest that cholesterol transport mediated by STARD4 is an important component of the cholesterol homeostasis regulatory machinery.
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Affiliation(s)
- Bruno Mesmin
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
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Machta BB, Papanikolaou S, Sethna JP, Veatch SL. Minimal model of plasma membrane heterogeneity requires coupling cortical actin to criticality. Biophys J 2011; 100:1668-77. [PMID: 21463580 DOI: 10.1016/j.bpj.2011.02.029] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Revised: 01/12/2011] [Accepted: 02/11/2011] [Indexed: 12/13/2022] Open
Abstract
We present a minimal model of plasma membrane heterogeneity that combines criticality with connectivity to cortical cytoskeleton. The development of this model was motivated by recent observations of micron-sized critical fluctuations in plasma membrane vesicles that are detached from their cortical cytoskeleton. We incorporate criticality using a conserved order parameter Ising model coupled to a simple actin cytoskeleton interacting through point-like pinning sites. Using this minimal model, we recapitulate several experimental observations of plasma membrane raft heterogeneity. Small (r ∼ 20 nm) and dynamic fluctuations at physiological temperatures arise from criticality. Including connectivity to the cortical cytoskeleton disrupts large fluctuations, prevents macroscopic phase separation at low temperatures (T ≤ 22°C), and provides a template for long-lived fluctuations at physiological temperature (T = 37°C). Cytoskeleton-stabilized fluctuations produce significant barriers to the diffusion of some membrane components in a manner that is weakly dependent on the number of pinning sites and strongly dependent on criticality. More generally, we demonstrate that critical fluctuations provide a physical mechanism for organizing and spatially segregating membrane components by providing channels for interaction over large distances.
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Abstract
Eukaryotic cells possess a remarkable diversity of lipids, which distribute among cellular membranes by well-characterized vesicle trafficking pathways. However, transport of lipids by alternate, or "nonvesicular," routes is also critical for lipid synthesis, metabolism, and proper membrane partitioning. In the past few years, considerable progress has been made in characterizing the mechanisms of nonvesicular lipid transport and how it may go awry in particular diseases, but many fundamental questions remain for this rising field.
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Affiliation(s)
- William A Prinz
- Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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36
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Skov M, Tønnesen CK, Hansen GH, Danielsen EM. Dietary cholesterol induces trafficking of intestinal Niemann-Pick Type C1 Like 1 from the brush border to endosomes. Am J Physiol Gastrointest Liver Physiol 2011; 300:G33-40. [PMID: 21051527 DOI: 10.1152/ajpgi.00344.2010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The transmembrane protein Niemann-Pick C1 Like 1 (NPC1L1) belongs to the Niemann-Pick C1 (NPC1) family of cholesterol transporters and is mainly expressed in the liver and the small intestine. NPC1L1 is believed to be the main transporter responsible for the absorption of dietary cholesterol. Like NPC1, NPC1L1 contains a sterol sensing domain, suggesting that it might be sensitive to dietary cholesterol. To test this hypothesis, mucosal explants were cultured in the presence or absence of cholesterol. In the absence of cholesterol NPC1L1 was localized mainly in the brush border of the enterocyte, colocalizing with the brush border enzyme aminopeptidase N (APN), and only a minor part was present in intracellular compartments. In contrast, following culture in the presence of cholesterol a major part of NPC1L1 was found in intracellular compartments positive for the early endosomal marker early endosome antigen 1, whereas only a minor fraction was left in the brush border. Neither APN, lactase, nor sucrase-isomaltase was endocytosed in parallel, demonstrating that this is a selective cholesterol-induced endocytosis of NPC1L1. Conceivably either the induced internalization could be due to NPC1L1 acting as an endocytic cholesterol receptor or it could be a mechanism to reduce the cholesterol uptake. The fluorescent cholesterol analog NBD-cholesterol readily labeled the cytoplasm also under conditions nonpermissible for endocytosis, arguing against a receptor-mediated uptake. We therefore propose that cholesterol is absorbed by NPC1L1 acting as a membrane transporter and that NPC1L1 is internalized to an endosomal compartment to reduce the absorption of cholesterol.
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Affiliation(s)
- Marianne Skov
- Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark.
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37
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González-damián J, Ortega-blake I. Effect of Membrane Structure on the Action of Polyenes II: Nystatin Activity along the Phase Diagram of Ergosterol- and Cholesterol-Containing POPC Membranes. J Membr Biol 2010; 237:41-9. [DOI: 10.1007/s00232-010-9301-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Accepted: 08/27/2010] [Indexed: 01/14/2023]
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Abstract
The movement of lipids within and between intracellular membranes is mediated by different lipid transport mechanisms and is crucial for maintaining the identities of different cellular organelles. Non-vesicular lipid transport has a crucial role in intracellular lipid trafficking and distribution, but its underlying mechanisms remain unclear. Lipid-transfer proteins (LTPs), which regulate diverse lipid-mediated cellular processes and accelerate vectorial transport of lipid monomers between membranes in vitro, could potentially mediate non-vesicular intracellular lipid trafficking. Understanding the mechanisms by which lipids are transported and distributed between cellular membranes, and elucidating the role of LTPs in intracellular lipid transport and homeostasis, are currently subjects of intensive study.
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Marín MP, Esteban-Pretel G, Ponsoda X, Romero AM, Ballestín R, López C, Megías L, Timoneda J, Molowny A, Canales JJ, Renau-Piqueras J. Endocytosis in Cultured Neurons Is Altered by Chronic Alcohol Exposure. Toxicol Sci 2010; 115:202-13. [DOI: 10.1093/toxsci/kfq040] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Abstract
Despite the determination of thousands of high-resolution structures of soluble proteins, many features of integral membrane proteins render them difficult targets for the structural biologist. Among these, the most important challenge is in expressing sufficient quantities of active protein to support downstream purification and structure determination efforts. Over 190 unique membrane protein structures have now been solved, and noticeable trends in successful expression strategies are beginning to emerge. A number of groups have also explored high-throughput (HTP) methods for membrane protein expression, with varying degrees of success. Here we review the current state of expressing membrane proteins for functional and structural studies. We first survey successful methods that have already yielded levels of membrane protein expression sufficient for structure determination. HTP methods are also examined since these aim to explore large numbers of targets and can predict reasonable starting points for many membrane proteins. Since HTP techniques may fail, particularly for certain classes of eukaryotic targets, detailed strategies for the expression of two prominent classes of eukaryotic protein families, G-protein-coupled receptors and ion channels, are also summarized.
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Affiliation(s)
- Christopher M M Koth
- Department of Structural Biology, Genentech, South San Francisco, California 94080, USA
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41
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Woo HK, Go EP, Hoang L, Trauger SA, Bowen B, Siuzdak G, Northen TR. Phosphonium labeling for increasing metabolomic coverage of neutral lipids using electrospray ionization mass spectrometry. Rapid Commun Mass Spectrom 2009; 23:1849-1855. [PMID: 19449318 PMCID: PMC3052201 DOI: 10.1002/rcm.4076] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Mass spectrometry has become an indispensable tool for the global study of metabolites (metabolomics), primarily using electrospray ionization mass spectrometry (ESI-MS). However, many important classes of molecules such as neutral lipids do not ionize well by ESI and go undetected. Chemical derivatization of metabolites can enhance ionization for increased sensitivity and metabolomic coverage. Here we describe the use of tris(2,4,6,-trimethoxyphenyl)phosphonium acetic acid (TMPP-AA) to improve liquid chromatography (LC)/ESI-MS detection of hydroxylated metabolites (i.e. lipids) from serum extracts. Cholesterol which is not normally detected from serum using ESI is observed with attomole sensitivity. This approach was applied to identify four endogenous lipids (hexadecanoyl-sn-glycerol, dihydrotachysterol, octadecanol, and alpha-tocopherol) from human serum. Overall, this approach extends the types of metabolites which can be detected using standard ESI-MS instrumentation and demonstrates the potential for targeted metabolomics analysis.
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Affiliation(s)
- Hin-Koon Woo
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Eden P. Go
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Linh Hoang
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Sunia A. Trauger
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Benjamin Bowen
- Harrington Department of Bioengineering, Arizona State University, PO Box 879709, Tempe, AZ 85287, USA
| | - Gary Siuzdak
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Trent R. Northen
- Department of Molecular Biology, Scripps Center for Mass Spectrometry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
- Department of GTL Bioenergy and Structural Biology, Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
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42
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Mesmin B, Maxfield FR. Intracellular sterol dynamics. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:636-45. [PMID: 19286471 DOI: 10.1016/j.bbalip.2009.03.002] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 02/27/2009] [Accepted: 03/03/2009] [Indexed: 01/17/2023]
Abstract
We review the cellular mechanisms implicated in cholesterol trafficking and distribution. Recent studies have provided new information about the distribution of sterols within cells, including analysis of its transbilayer distribution. The cholesterol interaction with other lipids and its engagement in various trafficking processes will determine its proper level in a specific membrane; making the cholesterol distribution uneven among the various intracellular organelles. The cholesterol content is important since cholesterol plays an essential role in membranes by controlling their physicochemical properties as well as key cellular events such as signal transduction and protein trafficking. Cholesterol movement between cellular organelles is highly dynamic, and can be achieved by vesicular and non-vesicular processes. Various studies have analyzed the proteins that play a significant role in these processes, giving us new information about the relative importance of these two trafficking pathways in cholesterol transport. Although still poorly characterized in many trafficking routes, several potential sterol transport proteins have been described in detail; as a result, molecular mechanisms for sterol transport among membranes start to be appreciated.
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Boadu E, Bilbey NJ, Francis GA. Cellular cholesterol substrate pools for adenosine-triphosphate cassette transporter A1-dependent high-density lipoprotein formation. Curr Opin Lipidol 2008; 19:270-6. [PMID: 18460918 DOI: 10.1097/mol.0b013e3282feea99] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW The removal of cellular cholesterol and phospholipids to apolipoprotein A-I (apoA-I), facilitated by the membrane transporter ATP-binding cassette transporter A1 (ABCA1), is the rate-limiting step in the formation of high density lipoprotein particles. This review summarizes recent literature concerning the relative contributions of different cellular pools of cholesterol used by ABCA1 in the initial lipidation of apoA-I for high density lipoprotein particle formation. RECENT FINDINGS Cell culture studies have shown that apart from lipidating apoA-I directly, ABCA1 can also mediate cholesterol delivery indirectly to apoA-I in the plasma membrane. Moreover, it is now clear that the late endosome/lysosome pool of cholesterol is a critical part of the total cholesterol substrate pool for ABCA1. Internalization of ABCA1 appears to be a requirement for maximum ABCA1-mediated cholesterol mobilization for high density lipoprotein formation. SUMMARY Current evidence suggests that ABCA1-mediated cholesterol efflux to apoA-I involves mobilization of cholesterol from plasma membrane, endoplasmic reticulum, trans-Golgi network, late endocytic and lysosomal compartments, and cholesteryl ester droplets. Apart from lipidating apoA-I directly, ABCA1 has also been found to efflux cholesterol indirectly to apoA-I in plasma membranes.
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Affiliation(s)
- Emmanuel Boadu
- The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research and Division of Endocrinology and Metabolism, Department of Medicine, University of British Columbia, Vancouver, BC, Canada
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Mahammad S, Parmryd I. Cholesterol homeostasis in T cells. Methyl-beta-cyclodextrin treatment results in equal loss of cholesterol from Triton X-100 soluble and insoluble fractions. Biochim Biophys Acta 2008; 1778:1251-8. [PMID: 18373974 DOI: 10.1016/j.bbamem.2008.02.010] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 02/05/2008] [Accepted: 02/25/2008] [Indexed: 01/17/2023]
Abstract
Methyl-beta-cyclodextrin (MBCD) is frequently used to acutely deplete cells of cholesterol. A widespread assumption is that MBCD preferentially targets cholesterol in lipid rafts and that sensitivity to MBCD is proof of lipid raft involvement in a cellular process. To analyse any MBCD preference systematically, progressive cholesterol depletion of Jurkat T cells was performed using MBCD and [3H]-cholesterol. It was found that at 37 degrees C, MBCD extracts similar proportions of cholesterol from the Triton X-100 resistant (lipid raft enriched) as it does from other cellular fractions and that the cells rapidly reestablish the relative differences in cholesterol concentration between different compartments. Moreover, cells restore the cholesterol level in the plasma membrane by mobilising cholesterol from intracellular cholesterol stores. Interestingly, mere incubation at 0 degrees C caused a loss of plasma membrane cholesterol with a concomitant increase in cholesteryl esters and adiposomes. Moreover, only 35% of total cholesterol could be extracted by MBCD at 0 degrees C and was accompanied by a complete loss of plasma membrane and endocytotic recycling centre filipin staining. This study clearly shows that MBCD does not specifically extract cholesterol from any cellular fraction, that cholesterol redistributes upon temperature changes and that intracellular cholesterol stores can be used to replenish plasma membrane cholesterol.
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Affiliation(s)
- Saleemulla Mahammad
- Department of Cell Biology, The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden
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45
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Affiliation(s)
- Irwin M Arias
- National Institutes of Health, National Institute of Child Health and Human Development, Bethesda, MD, USA.
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Kainu V, Hermansson M, Somerharju P. Electrospray Ionization Mass Spectrometry and Exogenous Heavy Isotope-labeled Lipid Species Provide Detailed Information on Aminophospholipid Acyl Chain Remodeling. J Biol Chem 2008; 283:3676-3687. [DOI: 10.1074/jbc.m709176200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
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Abstract
Plant lipid-transfer proteins (LTPs) are abundant, small, lipid binding proteins that are capable of exchanging lipids between membranes in vitro. Despite their name, a role in intracellular lipid transport is considered unlikely, based on their extracellular localization. A number of other biological roles, including antimicrobial defense, signaling, and cell wall loosening, have been proposed, but conclusive evidence is generally lacking, and these functions are not well correlated with in vitro activity or structure. A survey of sequenced plant genomes suggests that the two biochemically characterized families of LTPs are phylogenetically restricted to seed plants and are present as substantial gene families. This review aims to summarize the current understanding of LTP biochemistry, as well as the evidence supporting the proposed in vivo roles of these proteins within the emerging post-genomic framework.
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Affiliation(s)
- Trevor H Yeats
- Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA
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Boonyarattanakalin S, Martin SE, Sun Q, Peterson BR. A synthetic mimic of human Fc receptors: defined chemical modification of cell surfaces enables efficient endocytic uptake of human immunoglobulin-G. J Am Chem Soc 2007; 128:11463-70. [PMID: 16939269 PMCID: PMC2528877 DOI: 10.1021/ja062377w] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Binding of ligands to macromolecular receptors on the surface of mammalian cells often results in ligand uptake through receptor-mediated endocytosis. Certain human leukocytes and epithelial cells express Fc receptors (FcRs) that bind and internalize antibodies through this mechanism. To mimic this process, we synthesized an artificial FcR comprising the membrane anchor N-alkyl-3beta-amino-5alpha-cholestane linked to a disulfide-constrained cyclic peptide, termed FcIII, known to exhibit high affinity and specificity for the Fc region of human IgG. Treatment of human Jurkat lymphocytes that lack natural FcRs with the synthetic FcR (1 microM, 1 h) installed an average of approximately 6.2 x 10(5) synthetic receptor molecules per cell surface. These treated cells gained the capacity to internalize human IgG at levels greater than human THP-1 cells that express the natural receptors FcgammaRI and FcgammaRII. By linking binding motifs for circulating ligands to membrane anchors that cycle between the cell surface and intracellular endosomes, minimalistic cell surface receptors can be used to destroy targeted ligands by endocytosis. These small mimics of macromolecular receptors may be useful for controlling the extracellular abundance of ligands involved in disease.
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Abstract
We studied the trafficking of sterols, lipids and proteins in Niemann-Pick type C (NPC) cells. The NPC is an inherited disorder involving the accumulation of sterol and lipids in modified late-endosome/lysosome-like storage organelles. Most sterol accumulation studies in NPC cells have been carried out using low-density lipoprotein (LDL) as the sterol source, and it has been shown that sterol efflux from late endosomes is impaired in NPC cells. In this study, we used a fluorescent sterol analog, dehydroergosterol, which can be quickly and efficiently delivered to the plasma membrane. Thus, we were able to study the trafficking kinetics of the non-LDL-derived sterol pool, and we found that dehydroergosterol accumulates in the storage organelles over the course of several hours in NPC cells. We also found that dialkylindocarbocyanine lipid-mimetic analogs that recycle efficiently from early endosomes in wild-type cells are targeted to late endosomal organelles in NPC cells, and transferrin receptors recycle slowly and inefficiently in NPC cells. These data are consistent with multiple trafficking defects in both early and late endosomes in NPC cells.
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Affiliation(s)
- Nina H Pipalia
- Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 10021, USA
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Abstract
We recently showed that transport of ergosterol from the ER (endoplasmic reticulum) to the sterol-enriched PM (plasma membrane) in yeast occurs by a non-vesicular (Sec18p-independent) mechanism that results in the equilibration of sterol pools in the two organelles [Baumann, Sullivan, Ohvo-Rekilä, Simonot, Pottekat, Klaassen, Beh and Menon (2005) Biochemistry 44, 5816–5826]. To explore how this occurs, we tested the role of proteins that might act as sterol transporters. We chose to study oxysterol-binding protein homologues (Osh proteins), a family of seven proteins in yeast, all of which contain a putative sterol-binding pocket. Recent structural analyses of one of the Osh proteins [Im, Raychaudhuri, Prinz and Hurley (2005) Nature (London) 437, 154–158] suggested a possible transport cycle in which Osh proteins could act to equilibrate ER and PM pools of sterol. Our results indicate that the transport of newly synthesized ergosterol from the ER to the PM in an OSH deletion mutant lacking all seven Osh proteins is slowed only 5-fold relative to the isogenic wild-type strain. Our results suggest that the Osh proteins are not sterol transporters themselves, but affect sterol transport in vivo indirectly by affecting the ability of the PM to sequester sterols.
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Affiliation(s)
- D P Sullivan
- Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 10021, USA
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