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Analysis of Low Molecular Weight Substances and Related Processes Influencing Cellular Cholesterol Efflux. Pharmaceut Med 2020; 33:465-498. [PMID: 31933239 PMCID: PMC7101889 DOI: 10.1007/s40290-019-00308-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cholesterol efflux is the key process protecting the vascular system from the development of atherosclerotic lesions. Various extracellular and intracellular events affect the ability of the cell to efflux excess cholesterol. To explore the possible pathways and processes that promote or inhibit cholesterol efflux, we applied a combined cheminformatic and bioinformatic approach. We performed a comprehensive analysis of published data on the various substances influencing cholesterol efflux and found 153 low molecular weight substances that are included in the Chemical Entities of Biological Interest (ChEBI) database. Pathway enrichment was performed for substances identified within the Reactome database, and 45 substances were selected in 93 significant pathways. The most common pathways included the energy-dependent processes related to active cholesterol transport from the cell, lipoprotein metabolism and lipid transport, and signaling pathways. The activators and inhibitors of cholesterol efflux were non-uniformly distributed among the different pathways: the substances influencing ‘biological oxidations’ activate cholesterol efflux and the substances influencing ‘Signaling by GPCR and PTK6’ inhibit efflux. This analysis may be used in the search and design of efflux effectors for therapies targeting structural and functional high-density lipoprotein deficiency.
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Hou S, Madoux F, Scampavia L, Janovick JA, Conn PM, Spicer TP. Drug Library Screening for the Identification of Ionophores That Correct the Mistrafficking Disorder Associated with Oxalosis Kidney Disease. SLAS DISCOVERY 2017; 22:887-896. [PMID: 28346094 DOI: 10.1177/2472555217689992] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Primary hyperoxaluria is the underlying cause of oxalosis and is a life-threatening autosomal recessive disease, for which treatment may require dialysis or dual liver-kidney transplantation. The most common primary hyperoxaluria type 1 (PH1) is caused by genetic mutations of a liver-specific enzyme alanine:glyoxylate aminotransferase (AGT), which results in the misrouting of AGT from the peroxisomes to the mitochondria. Pharmacoperones are small molecules with the ability to modify misfolded proteins and route them correctly within the cells, which may present an effective strategy to treat AGT misrouting in PH1 disorders. We miniaturized a cell-based high-content assay into 1536-well plate format and screened ~4200 pharmacologically relevant compounds including Food and Drug Administration, European Union, and Japanese-approved drugs. This assay employs CHO cells stably expressing AGT-170, a mutant that predominantly resides in the mitochondria, where we monitor for its relocation to the peroxisomes through automated image acquisition and analysis. The miniaturized 1536-well assay yielded a Z' averaging 0.70 ± 0.07. Three drugs were identified as potential pharmacoperones from this pilot screen, demonstrating the applicability of this assay for large-scale high-throughput screening.
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Affiliation(s)
- Shurong Hou
- 1 Department of Molecular Therapeutics, Scripps Research Institute Molecular Screening Center, Scripps Research Institute, Jupiter, FL, USA
| | - Franck Madoux
- 1 Department of Molecular Therapeutics, Scripps Research Institute Molecular Screening Center, Scripps Research Institute, Jupiter, FL, USA.,3 Amgen Inc., Thousand Oaks, CA
| | - Louis Scampavia
- 1 Department of Molecular Therapeutics, Scripps Research Institute Molecular Screening Center, Scripps Research Institute, Jupiter, FL, USA
| | - Jo Ann Janovick
- 2 Departments of Internal Medicine and Cell Biology/Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - P Michael Conn
- 2 Departments of Internal Medicine and Cell Biology/Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - Timothy P Spicer
- 1 Department of Molecular Therapeutics, Scripps Research Institute Molecular Screening Center, Scripps Research Institute, Jupiter, FL, USA
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Quach D, Vitali C, La FM, Xiao AX, Millar JS, Tang C, Rader DJ, Phillips MC, Lyssenko NN. Cell lipid metabolism modulators 2-bromopalmitate, D609, monensin, U18666A and probucol shift discoidal HDL formation to the smaller-sized particles: implications for the mechanism of HDL assembly. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:1968-1979. [PMID: 27671775 DOI: 10.1016/j.bbalip.2016.09.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 08/27/2016] [Accepted: 09/23/2016] [Indexed: 12/17/2022]
Abstract
ATP-binding cassette transporter A1 (ABCA1) mediates formation of disc-shaped high-density lipoprotein (HDL) from cell lipid and lipid-free apolipoprotein A-I (apo A-I). Discoidal HDL particles are heterogeneous in physicochemical characteristics for reasons that are understood incompletely. Discoidal lipoprotein particles similar in characteristics and heterogeneity to cell-formed discoidal HDL can be reconstituted from purified lipids and apo A-I by cell-free, physicochemical methods. The heterogeneity of reconstituted HDL (rHDL) is sensitive to the lipid composition of the starting lipid/apo A-I mixture. To determine whether the heterogeneity of cell-formed HDL is similarly sensitive to changes in cell lipids, we investigated four compounds that have well-established effects on cell lipid metabolism and ABCA1-mediated cell cholesterol efflux. 2-Bromopalmitate, D609, monensin and U18666A decreased formation of the larger-sized, but dramatically increased formation of the smaller-sized HDL. 2-Bromopalmitate did not appear to affect ABCA1 activity, subcellular localization or oligomerization, but induced dissolution of the cholesterol-phospholipid complexes in the plasma membrane. Arachidonic and linoleic acids shifted HDL formation to the smaller-sized species. Tangier disease mutations and inhibitors of ABCA1 activity wheat germ agglutinin and AG 490 reduced formation of both larger-sized and smaller-sized HDL. The effect of probucol was similar to the effect of 2-bromopalmitate. Taking rHDL formation as a paradigm, we propose that ABCA1 mutations and activity inhibitors reduce the amount of cell lipid available for HDL formation, and the compounds in the 2-bromopalmitate group and the polyunsaturated fatty acids change cell lipid composition from one that favors formation of the larger-sized HDL particles to one that favors formation of the smaller-sized species.
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Affiliation(s)
- Duyen Quach
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Cecilia Vitali
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Fiona M La
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Angel X Xiao
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - John S Millar
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Chongren Tang
- Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington, Seattle, WA, USA
| | - Daniel J Rader
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA; Department of Genetics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Michael C Phillips
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Nicholas N Lyssenko
- Division of Translational Medicine and Human Genetics, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.
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Ma W, Lin M, Ding H, Lin G, Zhang Z. β-COP as a Component of Transport Vesicles for HDL Apolipoprotein-Mediated Cholesterol Exocytosis. PLoS One 2016; 11:e0151767. [PMID: 26986486 PMCID: PMC4795675 DOI: 10.1371/journal.pone.0151767] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 03/03/2016] [Indexed: 12/27/2022] Open
Abstract
Objective HDL and its apolipoproteins protect against atherosclerotic disease partly by removing excess cholesterol from macrophage foam cells. But the underlying mechanisms of cholesterol clearance are still not well defined. We investigated roles of vesicle trafficking of coatomer β-COP in delivering cholesterol to the cell surface during apoA-1 and apoE-mediated lipid efflux from fibroblasts and THP-1 macrophages. Methods shRNA knockout, confocal and electron microscopy and biochemical analysis were used to investigate the roles of β-COP in apolipoprotein-mediated cholesterol efflux in fibroblasts and THP-1 macrophages. Results We showed that β-COP knockdown by lentiviral shRNA resulted in reduced apoA-1-mediated cholesterol efflux, while increased cholesterol accumulation and formation of larger vesicles were observed in THP-1 macrophages by laser scanning confocal microscopy. Immunogold electron microscopy showed that β-COP appeared on the membrane protrusion complexes and colocalized with apoA-1 or apoE during cholesterol efflux. This was associated with releasing heterogeneous sizes of small particles into the culture media of THP-1 macrophage. Western blotting also showed that apoA-1 promotes β-COP translocation to the cell membrane and secretion into culture media, in which a total of 17 proteins were identified by proteomics. Moreover, β-COP exclusively associated with human plasma HDL fractions. Conclusion ApoA-1 and apoE promoted transport vesicles consisting of β-COP and other candidate proteins to exocytose cholesterol, forming the protrusion complexes on cell surface, which were then released from the cell membrane as small particles to media.
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Affiliation(s)
- Weilie Ma
- Department of Biochemistry and Molecular Biology, Key Laboratory of Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical University, Dongguan, Guangdong, 523808, China
| | - Margarita Lin
- Department of Biochemistry and Molecular Biology, Key Laboratory of Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical University, Dongguan, Guangdong, 523808, China
| | - Hang Ding
- Department of Biochemistry and Molecular Biology, Key Laboratory of Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical University, Dongguan, Guangdong, 523808, China
| | - Guorong Lin
- Department of Biochemistry and Molecular Biology, Key Laboratory of Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical University, Dongguan, Guangdong, 523808, China
- * E-mail: (GL); (ZZ)
| | - Zhizhen Zhang
- Department of Biochemistry and Molecular Biology, Key Laboratory of Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical University, Dongguan, Guangdong, 523808, China
- * E-mail: (GL); (ZZ)
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Wood WG, Li L, Müller WE, Eckert GP. Cholesterol as a causative factor in Alzheimer's disease: a debatable hypothesis. J Neurochem 2014; 129:559-72. [PMID: 24329875 PMCID: PMC3999290 DOI: 10.1111/jnc.12637] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 11/24/2013] [Accepted: 12/09/2013] [Indexed: 12/17/2022]
Abstract
High serum/plasma cholesterol levels have been suggested as a risk factor for Alzheimer's disease (AD). Some reports, mostly retrospective epidemiological studies, have observed a decreased prevalence of AD in patients taking the cholesterol lowering drugs, statins. The strongest evidence causally linking cholesterol to AD is provided by experimental studies showing that adding/reducing cholesterol alters amyloid precursor protein (APP) and amyloid beta-protein (Ab) levels. However, there are problems with the cholesterol-AD hypothesis. Cholesterol levels in serum/plasma and brain of AD patients do not support cholesterol as a causative factor in AD.Prospective studies on statins and AD have largely failed to show efficacy. Even the experimental data are open to interpretation given that it is well-established that modification of cholesterol levels has effects on multiple proteins, not only amyloid precursor protein and Ab. The purpose of this review, therefore, was to examine the above-mentioned issues, discuss the pros and cons of the cholesterol-AD hypothesis, involvement of other lipids in the mevalonate pathway, and consider that AD may impact cholesterol homeostasis.
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Affiliation(s)
- W. Gibson Wood
- Geriatric Research, Education and Clinical Center, VAMC, Department of Pharmacology, University of Minnesota School of Medicine, Minneapolis, MN 55455 USA
| | - Ling Li
- Department of Experimental and Clinical Pharmacology, College of Pharmacy, University of Minnesota, Minneapolis, MN 55455 USA
| | - Walter E. Müller
- Department of Pharmacology, Biocenter Niederursel, Goethe University, Max-von-Laue-St. 9, 60438 Frankfurt, Germany
| | - Gunter P. Eckert
- Department of Pharmacology, Biocenter Niederursel, Goethe University, Max-von-Laue-St. 9, 60438 Frankfurt, Germany
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Xie Q, Li F, Zhao SP. Ac‑hE‑18A‑NH2, a novel dual‑domain apolipoprotein mimetic peptide, inhibits apoptosis in macrophages by promoting cholesterol efflux. Mol Med Rep 2014; 9:1851-6. [PMID: 24639032 DOI: 10.3892/mmr.2014.2056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 02/25/2014] [Indexed: 11/06/2022] Open
Abstract
A novel synthetic dual-domain apolipoprotein (apo)-mimetic peptide, Ac-hE-18A-NH2, has been proposed to possess several apo A-I- and apo E-mimetic properties. This study investigated the protective effect of this peptide on oxidized low-density lipoprotein (ox-LDL)-induced apoptosis in RAW264.7 cells. For this purpose, RAW264.7 cells were exposed to 50 µg/ml ox-LDL for 48 h, and then incubated with the peptide Ac-hE-18A-NH2 at various concentrations. Apoptosis was detected using annexin V-fluorescein isothiocyanate staining and flow cytometric analysis. The study revealed that the peptide Ac-hE-18A-NH2 (1, 10 and 50 µg/ml) inhibited ox-LDL-mediated apoptosis, and this was accompanied by an increased rate of intracellular cholesterol efflux, and decreased total cholesterol levels in the cells in a concentration-dependent manner. The peptide also decreased caspase-3 activity and increased B-cell lymphoma 2 protein (Bcl-2) expression in macrophages in a dose-dependent manner. Moreover, blockage of cholesterol efflux by brefeldin A decreased the protective effect of Ac-hE-18A-NH2 against ox-LDL induced apoptosis, while increasing the cholesterol efflux by β-cyclodextrin administration led to a marked decrease in the rate of apoptosis of the cells. These findings demonstrate that the apo-mimetic peptide Ac-hE-18A-NH2 exerts a protective effect against apoptosis by reducing the accumulation of cholesterol.
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Affiliation(s)
- Qiong Xie
- Department of Cardiology, Hunan Provincial People's Hospital, Changsha, Hunan 410005, P.R. China
| | - Feng Li
- Department of Cardiothoracic Surgery, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, P.R. China
| | - Shui-Ping Zhao
- Department of Cardiology, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, P.R. China
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Merscher-Gomez S, Guzman J, Pedigo CE, Lehto M, Aguillon-Prada R, Mendez A, Lassenius MI, Forsblom C, Yoo T, Villarreal R, Maiguel D, Johnson K, Goldberg R, Nair V, Randolph A, Kretzler M, Nelson RG, Burke GW, Groop PH, Fornoni A. Cyclodextrin protects podocytes in diabetic kidney disease. Diabetes 2013; 62:3817-27. [PMID: 23835338 PMCID: PMC3806621 DOI: 10.2337/db13-0399] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Diabetic kidney disease (DKD) remains the most common cause of end-stage kidney disease despite multifactorial intervention. We demonstrated that increased cholesterol in association with downregulation of ATP-binding cassette transporter ABCA1 occurs in normal human podocytes exposed to the sera of patients with type 1 diabetes and albuminuria (DKD(+)) when compared with diabetic patients with normoalbuminuria (DKD(-)) and similar duration of diabetes and lipid profile. Glomerular downregulation of ABCA1 was confirmed in biopsies from patients with early DKD (n = 70) when compared with normal living donors (n = 32). Induction of cholesterol efflux with cyclodextrin (CD) but not inhibition of cholesterol synthesis with simvastatin prevented podocyte injury observed in vitro after exposure to patient sera. Subcutaneous administration of CD to diabetic BTBR (black and tan, brachiuric) ob/ob mice was safe and reduced albuminuria, mesangial expansion, kidney weight, and cortical cholesterol content. This was followed by an improvement of fasting insulin, blood glucose, body weight, and glucose tolerance in vivo and improved glucose-stimulated insulin release in human islets in vitro. Our data suggest that impaired reverse cholesterol transport characterizes clinical and experimental DKD and negatively influences podocyte function. Treatment with CD is safe and effective in preserving podocyte function in vitro and in vivo and may improve the metabolic control of diabetes.
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Affiliation(s)
- Sandra Merscher-Gomez
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Johanna Guzman
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Christopher E. Pedigo
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Markku Lehto
- Folkhälsan Institute of Genetics, Folkhälsan Research Center, Biomedicum Helsinki, Helsinki, Finland
- Division of Nephrology, Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
| | - Robier Aguillon-Prada
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Armando Mendez
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Mariann I. Lassenius
- Folkhälsan Institute of Genetics, Folkhälsan Research Center, Biomedicum Helsinki, Helsinki, Finland
- Division of Nephrology, Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
| | - Carol Forsblom
- Folkhälsan Institute of Genetics, Folkhälsan Research Center, Biomedicum Helsinki, Helsinki, Finland
- Division of Nephrology, Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
| | - TaeHyun Yoo
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Rodrigo Villarreal
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Dony Maiguel
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Kevin Johnson
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Ronald Goldberg
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Viji Nair
- University of Michigan, Ann Arbor, Michigan
| | | | | | - Robert G. Nelson
- National Institute of Diabetes and Digestive and Kidney Diseases, Phoenix, Arizona
| | - George W. Burke
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
- Department of Surgery, University of Miami, Miami, Florida
| | - Per-Henrik Groop
- Folkhälsan Institute of Genetics, Folkhälsan Research Center, Biomedicum Helsinki, Helsinki, Finland
- Division of Nephrology, Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
| | - Alessia Fornoni
- Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, Florida
- Corresponding author: Alessia Fornoni,
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An automated system for high-throughput single cell-based breeding. Sci Rep 2013; 3:1191. [PMID: 23378922 PMCID: PMC3561619 DOI: 10.1038/srep01191] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 01/17/2013] [Indexed: 12/17/2022] Open
Abstract
When establishing the most appropriate cells from the huge numbers of a cell library for practical use of cells in regenerative medicine and production of various biopharmaceuticals, cell heterogeneity often found in an isogenic cell population limits the refinement of clonal cell culture. Here, we demonstrated high-throughput screening of the most suitable cells in a cell library by an automated undisruptive single-cell analysis and isolation system, followed by expansion of isolated single cells. This system enabled establishment of the most suitable cells, such as embryonic stem cells with the highest expression of the pluripotency marker Rex1 and hybridomas with the highest antibody secretion, which could not be achieved by conventional high-throughput cell screening systems (e.g., a fluorescence-activated cell sorter). This single cell-based breeding system may be a powerful tool to analyze stochastic fluctuations and delineate their molecular mechanisms.
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Lin S, Zhou C, Neufeld E, Wang YH, Xu SW, Lu L, Wang Y, Liu ZP, Li D, Li C, Chen S, Le K, Huang H, Liu P, Moss J, Vaughan M, Shen X. BIG1, a brefeldin A-inhibited guanine nucleotide-exchange protein modulates ATP-binding cassette transporter A-1 trafficking and function. Arterioscler Thromb Vasc Biol 2012; 33:e31-8. [PMID: 23220274 DOI: 10.1161/atvbaha.112.300720] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
OBJECTIVE Cell-surface localization and intracellular trafficking are essential for the function of ATP-binding cassette transporter A-1 (ABCA1). However, regulation of these activities is still largely unknown. Brefeldin A, an uncompetitive inhibitor of brefeldin A-inhibited guanine nucleotide-exchange proteins (BIGs), disturbs the intracellular distribution of ABCA1, and thus inhibits cholesterol efflux. This study aimed to define the possible roles of BIGs in regulating ABCA1 trafficking and cholesterol efflux, and further to explore the potential mechanism. METHODS AND RESULTS By vesicle immunoprecipitation, we found that BIG1 was associated with ABCA1 in vesicles preparation from rat liver. BIG1 depletion reduced surface ABCA1 on HepG2 cells, and inhibited by 60% cholesterol release. In contrast, BIG1 overexpression increased surface ABCA1 and cholesterol secretion. With partial restoration of BIG1 through overexpression in BIG1-depleted cells, surface ABCA1 was also restored. Biotinylation and glutathione cleavage revealed that BIG1 small interfering RNA dramatically decreased the internalization and recycling of ABCA1. This novel function of BIG1 was dependent on the guanine nucleotide-exchange activity and achieved through activation of ADP-ribosylation factor 1. CONCLUSIONS BIG1, through its ability to activate ADP-ribosylation factor 1, regulates cell-surface levels and function of ABCA1, indicating a transcription-independent mechanism for controlling ABCA1 action.
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Affiliation(s)
- Sisi Lin
- Laboratory of Pharmacology and Toxicology, School of Pharmaceutical Sciences, Sun Yat-sen University, No. 132, East Wai-Huan Rd, College Town, Guangzhou 510006, PR China
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Hossain MA, Tsujita M, Akita N, Kobayashi F, Yokoyama S. Cholesterol homeostasis in ABCA1/LCAT double-deficient mouse. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:1197-205. [DOI: 10.1016/j.bbalip.2009.08.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2009] [Revised: 08/07/2009] [Accepted: 08/24/2009] [Indexed: 10/20/2022]
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Prosdocimo DA, Douglas DC, Romani AM, O'Neill WC, Dubyak GR. Autocrine ATP release coupled to extracellular pyrophosphate accumulation in vascular smooth muscle cells. Am J Physiol Cell Physiol 2009; 296:C828-39. [PMID: 19193865 DOI: 10.1152/ajpcell.00619.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Extracellular inorganic pyrophosphate (PP(i)) is a potent suppressor of physiological calcification in bone and pathological calcification in blood vessels. Ectonucleotide pyrophosphatase/phosphodiesterases (eNPPs) generate PP(i) via the hydrolysis of ATP released into extracellular compartments by poorly understood mechanisms. Here we report that cultured vascular smooth muscle cells (VSMC) from rat aorta generate extracellular PP(i) via an autocrine mechanism that involves ATP release tightly coupled to eNPP activity. The nucleotide analog beta,gamma-methylene ATP (MeATP or AMPPCP) was used to selectively suppress ATP metabolism by eNPPs but not the CD39-type ecto-ATPases. In the absence of MeATP, VSMC generated extracellular PP(i) to accumulate >or=600 nM within 2 h while steadily maintaining extracellular ATP at 1 nM. Conversely, the presence of MeATP completely suppressed PP(i) accumulation while increasing ATP accumulation. Probenecid, which inhibits PP(i) efflux dependent on ANK, a putative PP(i) transporter or transport regulator, reduced extracellular PP(i) accumulation by approximately twofold. This indicates that autocrine ATP release coupled to eNPP activity comprises >or=50% of the extracellular PP(i)-generating capacity of VSMC. The accumulation of extracellular PP(i) and ATP was markedly attenuated by reduced temperature but was insensitive to brefeldin A, which suppresses constitutive exocytosis of Golgi-derived secretory vesicles. The magnitude of extracellular PP(i) accumulation in VSMC cultures increased with time postplating, suggesting that ATP release coupled to PP(i) generation is upregulated as cultured VSMC undergo contact-inhibition of proliferation or deposit extracellular matrix.
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Affiliation(s)
- Domenick A Prosdocimo
- Dept. of Physiology, Case Western Reserve Univ. School of Medicine, 2109 Adelbert Rd., Cleveland, OH 44106, USA
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Abstract
The origins of cholesterol utilized by intestinal ABCA1 were investigated in the human intestinal cell line Caco-2. Influx of apical membrane cholesterol increases ABCA1 mRNA and mass, resulting in enhanced efflux of HDL-cholesterol. Luminal (micellar) cholesterol and newly synthesized cholesterol are not transported directly to ABCA1 but reach the ABCA1 pool after incorporation into the apical membrane. Depleting the apical or the basolateral membrane of cholesterol by cyclodextrin attenuates the amount of cholesterol transported by ABCA1 without altering ABCA1 expression. Filipin added to the apical side but not the basal side attenuates ABCA1-mediated cholesterol efflux, suggesting that apical membrane "microdomains," or rafts, supply cholesterol for HDL. Preventing cholesterol esterification increases the amount of cholesterol available for HDL. Ezetimibe, a Niemann-Pick C1-like 1 protein inhibitor, does not alter ABCA1-mediated cholesterol efflux. U18666A and imipramine, agents that mimic cholesterol trafficking defects of Neimann-Pick type C disease, attenuate cholesterol efflux without altering ABCA1 expression; thus, intestinal NPC1 may facilitate cholesterol movement to ABCA1. ABCA1-mediated cholesterol efflux is independent of cholesterol synthesis. The results suggest that following incorporation into plasma membrane and rafts of the apical membrane, dietary/biliary and newly synthesized cholesterol contribute to the ABCA1 pool and HDL-cholesterol. NPC1 may have a role in this process.
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Affiliation(s)
- F Jeffrey Field
- Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA.
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Southall TD, Terhzaz S, Cabrero P, Chintapalli VR, Evans JM, Dow JAT, Davies SA. Novel subcellular locations and functions for secretory pathway Ca2+/Mn2+-ATPases. Physiol Genomics 2006; 26:35-45. [PMID: 16609144 DOI: 10.1152/physiolgenomics.00038.2006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Secretory pathway Ca2+/Mn2+-ATPases (SPCAs) are important for maintenance of cellular Ca2+and Mn2+homeostasis, and, to date, all SPCAs have been found to localize to the Golgi apparatus. The single Drosophila SPCA gene ( SPoCk) was identified by an in silico screen for novel Ca2+-ATPases. It encoded three SPoCk isoforms with novel, distinct subcellular specificities in the endoplasmic reticulum (ER) and peroxisomes in addition to the Golgi. Furthermore, expression of the peroxisome-associated SPoCk isoform was sexually dimorphic. Overexpression of organelle-specific SPoCk isoforms impacted on cytosolic Ca2+handling in both cultured Drosophila cells and a transporting epithelium, the Drosophila Malpighian (renal) tubule. Specifically, the ER isoform impacted on inositol ( 1 , 4 , 5 )-trisphosphate-mediated Ca2+signaling and the Golgi isoform impacted on diuresis, whereas the peroxisome isoform colocalized with Ca2+“spherites” and impacted on calcium storage and transport. Interfering RNA directed against the common exons of the three SPoCk isoforms resulted in aberrant Ca2+signaling and abolished neuropeptide-stimulated diuresis by the tubule. SPoCk thus contributed to both of the contrasting requirements for Ca2+in transporting epithelia: to transport or store Ca2+in bulk without compromising its use as a signal.
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Affiliation(s)
- Tony D Southall
- Division of Molecular Genetics, Anderson College Complex, University of Glasgow, Glasgow, United Kingdom
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Jiang P, Yan PK, Chen JX, Zhu BY, Lei XY, Yin WD, Liao DF. High density lipoprotein 3 inhibits oxidized low density lipoprotein-induced apoptosis via promoting cholesterol efflux in RAW264.7 cells. Acta Pharmacol Sin 2006; 27:151-7. [PMID: 16412263 DOI: 10.1111/j.1745-7254.2006.00261.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
AIM To investigate the protective effect of high density lipoprotein 3 (HDL3) on oxidized low density lipoprotein (ox-LDL)-induced apoptosis in RAW264.7 cells. METHODS RAW264.7 cells were exposed to 50 mg/L ox-LDL for various durations up to 48 h, and apoptosis was detected using Hoechst 33258 staining and flow cytometric analysis. Total cholesterol levels were detected by high performance liquid chromatography, cholesterol efflux was determined by Tritium labeling, and the cellular lipid droplets were assayed by oil red O staining. RESULTS Treatment with 50 mg/L ox-LDL for 12, 24, and 48 h increased the apoptotic rate of RAW264.7 cells in a time-dependent manner. The peak apoptotic rate (47.7%) was observed after 48 h incubation. HDL3 at various concentrations (50 mg/L, 100 mg/L, and 200 mg/L) inhibited the ox-LDL (50 mg/L for 48 h)-mediated apoptosis that was accompanied by an increased rate of intracellular cholesterol efflux, and decreased total cholesterol levels in cells in a concentration-dependent manner. Blockage of cholesterol efflux by brefeldin decreased the protective effect of HDL3 on ox-LDL-induced apoptosis. Increase of the cholesterol efflux effected by another cholesterol acceptor,beta-cyclodextrin, led to a dramatic decrease in the apoptotic rate of cells. CONCLUSION HDL3 antagonizes ox-LDL-induced apoptosis in RAW264.7 cells, through reducing the accumulation of toxic cholesterol.
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Affiliation(s)
- Pei Jiang
- Division of Pharmacoproteomics, Institute of Pharmacy and Pharmacology, Nanhua University, Hengyang 421001, China
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15
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Waddington EI, Boadu E, Francis GA. Cholesterol and phospholipid efflux from cultured cells. Methods 2005; 36:196-206. [PMID: 15905101 DOI: 10.1016/j.ymeth.2004.12.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Revised: 12/21/2004] [Accepted: 12/21/2004] [Indexed: 10/25/2022] Open
Abstract
The removal of phospholipids and cholesterol from tissues is the major mechanism mediating the initial assembly of high density lipoproteins (HDL), as well as being the main reason HDL are thought to protect against atherosclerosis. Investigations of the mechanisms of HDL assembly and testing of novel HDL-raising agents typically involve assays to determine phospholipid and/or cholesterol removal or "efflux" from cultured cells. The purpose of this chapter is to describe experimental protocols that can be used in the determination of cholesterol and phospholipid efflux from cultured cells by HDL apolipoproteins for the formation of new HDL particles, and the testing of novel HDL-raising therapies in vitro. A protocol is also provided for determining the size and nature of HDL particles formed in cell-conditioned medium using two-dimensional gel electrophoresis.
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Affiliation(s)
- Emma I Waddington
- CIHR Group on Molecular and Cell Biology of Lipids, Departments of Medicine and Biochemistry, University of Alberta, Edmonton, Alta., Canada T6G 2S2
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16
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Zheng H, Kiss RS, Franklin V, Wang MD, Haidar B, Marcel YL. ApoA-I Lipidation in Primary Mouse Hepatocytes. J Biol Chem 2005; 280:21612-21. [PMID: 15797865 DOI: 10.1074/jbc.m502200200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The liver is the major site of both apolipoprotein A-I (apoA-I) synthesis and ATP-binding cassette transporter A1 (ABCA1) expression. Here, we compare the lipidation with cholesterol and phospholipid of newly synthesized human apoA-I (hapoA-I) using adenoviral vector-mediated endogenous expression or exogenously added hapoA-I in wild type and ABCA1-null hepatocytes. Hepatocytes were labeled with [3H]cholesterol (delivered with LDL or methyl-beta-cyclodextrin), [3H]mevalonate, or [3H]choline. ABCA1 deficiency decreased apoA-I phospholipidation by 80%, but acquisition of de novo synthesized and exogenous cholesterol only decreased by 40-60%. The transfer of de novo synthesized cholesterol to apoA-I was decreased at all time points, but that of exogenously delivered cholesterol was independent of ABCA1 activity at the early time points. Progesterone does not affect apoA-I synthesis or its lipidation but inhibited the early phase of apoA-I cholesterol lipidation in both wild type and ABCA1-null hepatocytes. Fast protein liquid chromatography analysis of medium lipoproteins confirmed that with ABCA1 deficiency, the proportion of secreted high density lipoprotein-associated apoA-I and cholesterol decreased by about 50%. The very low density lipoprotein (VLDL)/LDL size fraction also contained a significant level of cholesterol in ABCA1 deficiency, consistent with the result of immunoprecipitations showing the presence of lipoproteins with both apoA-I and murine apoB. ApoA-I lipidation with newly synthesized cholesterol in ABCA1-null hepatocytes was significantly decreased by brefeldin A and monensin. In conclusion, we demonstrate that: (i) whereas most hepatic phospholipidation of apoA-I is mediated by ABCA1, acquisition of cholesterol depends on active transfer from intracellular compartments by ABCA1-dependent and -independent pathways, both sensitive to progesterone and (ii) there is separate regulation of phospholipid and cholesterol lipidation of apoA-I in hepatocytes.
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Affiliation(s)
- Hui Zheng
- Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, University of Ottawa, Ottawa, Ontario K1Y 4W7, Canada
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17
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Matarrese P, Tinari A, Mormone E, Bianco GA, Toscano MA, Ascione B, Rabinovich GA, Malorni W. Galectin-1 Sensitizes Resting Human T Lymphocytes to Fas (CD95)-mediated Cell Death via Mitochondrial Hyperpolarization, Budding, and Fission. J Biol Chem 2005; 280:6969-85. [PMID: 15556941 DOI: 10.1074/jbc.m409752200] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Galectins have emerged as a novel family of immunoregulatory proteins implicated in T cell homeostasis. Recent studies showed that galectin-1 (Gal-1) plays a key role in tumor-immune escape by killing antitumor effector T cells. Here we found that Gal-1 sensitizes human resting T cells to Fas (CD95)/caspase-8-mediated cell death. Furthermore, this protein triggers an apoptotic program involving an increase of mitochondrial membrane potential and participation of the ceramide pathway. In addition, Gal-1 induces mitochondrial coalescence, budding, and fission accompanied by an increase and/or redistribution of fission-associated molecules h-Fis and DRP-1. Importantly, these changes are detected in both resting and activated human T cells, suggesting that Gal-1-induced cell death might become an excellent model to analyze the morphogenetic changes of mitochondria during the execution of cell death. This is the first association among Gal-1, Fas/Fas ligand-mediated cell death, and the mitochondrial pathway, providing a rational basis for the immunoregulatory properties of Gal-1 in experimental models of chronic inflammation and cancer.
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Affiliation(s)
- Paola Matarrese
- Department of Drug Research and Evaluation, and Technology and Health, Istituto Superiore di Sanità, Viale Regina Elena, 299, Rome 00161, Italy
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18
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Cadwallader KA, Uddin M, Condliffe AM, Cowburn AS, White JF, Skepper JN, Ktistakis NT, Chilvers ER. Effect of priming on activation and localization of phospholipase D-1 in human neutrophils. ACTA ACUST UNITED AC 2004; 271:2755-64. [PMID: 15206940 DOI: 10.1111/j.1432-1033.2004.04204.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phospholipase D (PLD) plays a major role in the activation of the neutrophil respiratory burst. However, the repertoire of PLD isoforms present in these primary cells, the precise mechanism of activation, and the impact of cell priming on PLD activity and localization remain poorly defined. RT-PCR analysis showed that both PLD1 and PLD2 isoforms are expressed in human neutrophils, with PLD1 expressed at a higher level. Endogenous PLD1 was detected by immunoprecipitation and Western blotting, and was predominantly membrane-associated under control and primed/stimulated conditions. Immunofluorescence showed that PLD had a punctate distribution throughout the cell, which was not altered after stimulation by soluble agonists. In contrast, PLD localized to the phagolysosome membrane after ingestion of nonopsonized zymosan particles. We also demonstrate that tumour necrosis factor alpha greatly potentiates agonist-stimulated PLD activation, myeloperoxidase release, and superoxide anion generation, and that PLD activation occurs via a phosphatidylinositol 3-kinase-sensitive and brefeldin-sensitive ADP-ribosylation factor GTPase-regulated mechanism. Moreover, propranolol, which causes an increase in PLD-derived phosphatidic acid accumulation, caused a selective increase in agonist-stimulated myeloperoxidase release. Our results indicate that priming is a critical regulator of PLD activation, that the PLD-generated lipid products exert divergent effects on neutrophil functional responses, that PLD1 is the major PLD isoform present in human neutrophils, and that PLD1 actively translocates to the phagosomal wall after particle ingestion.
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Affiliation(s)
- Karen A Cadwallader
- Respiratory Medicine Division, Department of Medicine, University of Cambridge School of Clinical Medicine, Addenbrooke's and Papworth Hospitals, Cambridge, UK.
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19
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Walter M, Forsyth NR, Wright WE, Shay JW, Roth MG. The establishment of telomerase-immortalized Tangier disease cell lines indicates the existence of an apolipoprotein A-I-inducible but ABCA1-independent cholesterol efflux pathway. J Biol Chem 2004; 279:20866-73. [PMID: 15001567 DOI: 10.1074/jbc.m401714200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tangier disease (TD) is a human genetic disorder associated with defective apolipoprotein-I-induced lipid efflux and increased atherosclerotic susceptibility. It has been linked to mutations in the ATP-binding cassette protein A1 (ABCA1). Here we describe the establishment of permanent Tangier cell lines using telomerase. Ectopic expression of the catalytic subunit of human telomerase extended the life span of control and TD skin fibroblasts, and (in contrast to immortalization procedures using viral oncogenes) did not impair apolipoprotein A-I-induced lipid efflux. The key characteristics of TD fibroblasts (reduced cholesterol and phospholipid efflux) were observed both in primary and telomerase-immortalized fibroblasts from two unrelated homozygous patients. Surprisingly, the apolipoprotein-inducible cholesterol efflux in TD cells was significantly improved after immortalization (up to 40% of normal values). In contrast to ABCA1-dependent cholesterol efflux, this efflux was not inhibited by brefeldin A, glybenclamide, or intracellular ATP depletion but was inhibited in the presence of cytochalasin D. Apolipoprotein A-I-dependent cholesterol efflux was inversely correlated with the population doubling number in cell culture and was inhibited up to 40% in near-senescent normal diploid fibroblasts. This inhibition was completely reversed by telomerase. Thus ectopic expression of telomerase is a way to circumvent the lack of critical experimental material and represents a major improvement for studying cholesterol efflux pathways in lipid disorders. Our findings indicate the existence of an ABCA1-independent but cytoskeleton-dependent cholesterol removal pathway that may help to prevent early atherosclerosis in Tangier disease but may also be sensitive to aging phenomena ex vivo and possibly in vivo.
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Affiliation(s)
- Michael Walter
- Department of Biochemistry, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-9038, USA
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20
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Nofer JR, Feuerborn R, Levkau B, Sokoll A, Seedorf U, Assmann G. Involvement of Cdc42 signaling in apoA-I-induced cholesterol efflux. J Biol Chem 2003; 278:53055-62. [PMID: 14563854 DOI: 10.1074/jbc.m305673200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cholesterol efflux, an important mechanism by which high density lipoproteins (HDL) protect against atherosclerosis, is initiated by docking of apolipoprotein A-I (apoA-I), a major HDL protein, to specific binding sites followed by activation of ATP-binding cassette transporter A1 (ABCA1) and translocation of cholesterol from intracellular compartments to the exofacial monolayer of the plasma membrane where it is accessible to HDL. In this report, we investigated potential signal transduction pathways that may link apoA-I binding to cholesterol translocation to the plasma membrane and cholesterol efflux. By using pull-down assays we found that apoA-I substantially increased the amount of activated Cdc42, Rac1, and Rho in human fibroblasts. Moreover, apoA-I induced actin polymerization, which is known to be controlled by Rho family G proteins. Inhibition of Cdc42 and Rac1 with Clostridium difficile toxin B inhibited apoA-I-induced cholesterol efflux, whereas inhibition of Rho with Clostridium botulinum C3-exoenzyme exerted opposite effects. Adenoviral expression of a Cdc42(T17N) dominant negative mutant substantially reduced apoA-I-induced cholesterol efflux, whereas dominant negative Rac1(T17N) had no effect. We further found that two downstream effectors of Cdc42/Rac1 signaling, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK), are activated by apoA-I. Pharmacological inhibition of JNK but not p38 MAPK decreased apoA-I-induced cholesterol efflux, whereas anisomycin and hydrogen peroxide, two direct JNK activators, could partially substitute for apoA-I in its ability to induce cholesterol efflux. These results for the first time demonstrate activation of Rho family G proteins and stress kinases by apoA-I and implicate the involvement of Cdc42 and JNK in the apoA-I-induced cholesterol efflux.
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Affiliation(s)
- Jerzy-Roch Nofer
- Institut für Klinische Chemie und Laboratoriumsmedizin, Westfälische Wilhelms-Universität, D-48129 Münster, Germany.
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21
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Dagher G, Donne N, Klein C, Ferre P, Dugail I. HDL-mediated cholesterol uptake and targeting to lipid droplets in adipocytes. J Lipid Res 2003; 44:1811-20. [PMID: 12867544 DOI: 10.1194/jlr.m300267-jlr200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adipocytes express high levels of the HDL scavenger receptor class B type I in a differentiation-dependent manner. We thus have analyzed the routes of HDL cholesterol trafficking at different phases of adipocyte differentiation in the 3T3-L1 cell line. One novel and salient feature of this paper is the observation of a widespread distribution in the cell cytoplasm of Golgi markers, caveolin-2, and a fluorescent cholesterol analog NBD-cholesterol (NBD-chol), observed in the early phases of adipocyte formation, clearly distinct from that observed in mature fat cells (i.e., with fully formed lipid vesicles). Thus, in cells without visible lipid droplets, Golgi markers (Golgi 58K, Golgin 97, trans-Golgi network 38, Rab 6, and BODIPY-ceramide), caveolin-2, and NBD-chol all colocalize in a widespread distribution in the cell. In contrast, when lipid droplets are fully formed at latter stages, these markers clearly are distributed to distinct cell compartments: a compact juxtanuclear structure for the Golgi markers and caveolin-2, while NDB-chol concentrates in lipid droplets. In addition, disorganization of the Golgi using three different agents (Brefeldin, monensin, and N-ethyl-maleimide) drastically reduces NBD-chol uptake at different phases of adipocyte formation, strongly suggesting that the Golgi apparatus plays a critical role in HDL-mediated NBD uptake and routing to lipid droplets.
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Affiliation(s)
- Georges Dagher
- INSERM Unité 465, Centre de Recherche Biomédicales des Cordeliers (Université Paris 6), 15 rue de l'Ecole de Médecine, 75270 Paris Cedex 06, France.
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22
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Igbavboa U, Pidcock JM, Johnson LNA, Malo TM, Studniski AE, Yu S, Sun GY, Wood WG. Cholesterol distribution in the Golgi complex of DITNC1 astrocytes is differentially altered by fresh and aged amyloid beta-peptide-(1-42). J Biol Chem 2003; 278:17150-7. [PMID: 12584199 DOI: 10.1074/jbc.m301150200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Golgi complex plays an important role in cholesterol trafficking in cells, and amyloid beta-peptides (Abetas) alter cholesterol trafficking. The hypothesis was tested that fresh and aged Abeta-(1-42) would differentially modify Golgi cholesterol content in DINTC1 astrocytes and that the effects of Abeta-(1-42) would be associated with the region of the Golgi complex. Two different methods were used to determine the effects of Abeta-(1-42) on Golgi complex cholesterol. Confocal microscopy showed that fresh Abeta-(1-42) significantly increased cholesterol and that aged Abeta-(1-42) significantly reduced cholesterol content in the Golgi complex. Isolation of the Golgi complex into two fractions using density gradient centrifugation showed effects of aged Abeta-(1-42) similar to those observed with confocal microscopy but revealed the novel finding that fresh Abeta-(1-42) had opposite effects on the two Golgi fractions suggesting a specificity of Abeta-(1-42) perturbation of the Golgi complex. Phosphatidylcholine-phospholipase D activity, cell membrane cholesterol, and apolipoprotein E levels were associated with effects of fresh Abeta-(1-42) on cholesterol distribution but not with effects of aged Abeta-(1-42), arguing against a common mechanism. Extracellular Abeta-(1-42) targets the Golgi complex and disrupts cell cholesterol homeostasis, and this action of Abeta-(1-42) could alter cell functions requiring optimal levels of cholesterol.
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Affiliation(s)
- Urule Igbavboa
- Geriatric Research, Education and Clinical Center, Veterans Affairs Medical Center, Columbia, Missouri 65211, USA
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23
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Gibson Wood W, Eckert GP, Igbavboa U, Müller WE. Amyloid beta-protein interactions with membranes and cholesterol: causes or casualties of Alzheimer's disease. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1610:281-90. [PMID: 12648781 DOI: 10.1016/s0005-2736(03)00025-7] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Amyloid beta-protein (Abeta) is thought to be one of the primary factors causing neurodegeneration in Alzheimer's disease (AD). This protein is an amphipathic molecule that perturbs membranes, binds lipids and alters cell function. Several studies have reported that Abeta alters membrane fluidity but the direction of this effect has not been consistently observed and explanations for this lack of consistency are proposed. Cholesterol is a key component of membranes and cholesterol interacts with Abeta in a reciprocal manner. Abeta impacts on cholesterol homeostasis and modification of cholesterol levels alters Abeta expression. In addition, certain cholesterol lowering drugs (statins) appear to reduce the risk of AD in human subjects. However, the role of changes in the total amount of brain cholesterol in AD and the mechanisms of action of statins in lowering the risk of AD are unclear. Here we discuss data on membranes, cholesterol, Abeta and AD, and propose that modification of the transbilayer distribution of cholesterol in contrast to a change in the total amount of cholesterol provides a cooperative environment for Abeta synthesis and accumulation in membranes leading to cell dysfunction including disruption in cholesterol homeostasis.
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Affiliation(s)
- W Gibson Wood
- Geriatric Research, Education and Clinical Center, VA Medical Center, and Department of Pharmacology, University of Minnesota School of Medicine, Minneapolis, MN 55417, USA.
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24
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Marchetti MC, Di Marco B, Cifone G, Migliorati G, Riccardi C. Dexamethasone-induced apoptosis of thymocytes: role of glucocorticoid receptor-associated Src kinase and caspase-8 activation. Blood 2003; 101:585-93. [PMID: 12393559 DOI: 10.1182/blood-2002-06-1779] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glucocorticoid hormones (GCHs) regulate normal and neoplastic lymphocyte development by exerting antiproliferative and/or apoptotic effects. We have previously shown that dexamethasone (DEX)-activated thymocyte apoptosis requires a sequence of events including interaction with the glucocorticoid receptor (GR), phosphatidylinositol-specific phospholipase C (PI-PLC), and acidic sphingomyelinase (aSMase) activation. We analyzed the mechanisms of GCH-activated apoptosis by focusing on GR-associated Src kinase, cytochrome c release, and caspase-8, -9, and -3 activation. We show here that PI-PLC binds to GR-associated Src kinase, as indicated by coimmunoprecipitation experiments. Moreover, DEX treatment induces PI-PLC phosphorylation and activation. DEX-induced PI-PLC phosphorylation, activation, and apoptosis are inhibited by PP1, a Src kinase inhibitor, thus suggesting that Src-mediated PI-PLC activation is involved in DEX-induced apoptosis. Caspase-9, -8, and -3 activation and cytochrome c release can be detected 1 to 2 hours after DEX treatment. Caspase-9 inhibition does not counter cytochrome c release, caspase-8 and caspase-3 activation, and apoptosis. Caspase-8 inhibition counters cytochrome c release, caspase-9 and caspase-3 activation, and apoptosis, thus suggesting that caspase-8 inhibitor can directly inhibit caspase-9 and/or that DEX-induced caspase-8 activation is upstream to mitochondria and can regulate caspase-3 directly or through cytochrome c release and the consequent caspase-9/caspase-3 activation. DEX-induced caspase-8 activation, like ceramide-induced caspase-8 activation, correlates with the formation of Fas-associated death domain protein (FADD)/caspase-8 complex. Caspase-8 activation is countered by the inhibition of macromolecular synthesis and of Src kinase, PI-PLC, and aSMase activation, suggesting it is downstream in the DEX-activated apoptotic pathway of thymocytes.
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Affiliation(s)
- Maria Cristina Marchetti
- Department of Clinical and Experimental Medicine, Pharmacology Section, University of Perugia, University of L'Aquila, Italy
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25
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Garver WS, Krishnan K, Gallagos JR, Michikawa M, Francis GA, Heidenreich RA. Niemann-Pick C1 protein regulates cholesterol transport to the trans-Golgi network and plasma membrane caveolae. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)31487-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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26
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Fobker M, Voss R, Reinecke H, Crone C, Assmann G, Walter M. Accumulation of cardiolipin and lysocardiolipin in fibroblasts from Tangier disease subjects. FEBS Lett 2001; 500:157-62. [PMID: 11445077 DOI: 10.1016/s0014-5793(01)02578-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Tangier disease (TD) is an inherited disorder of lipid metabolism characterized by very low high density lipoprotein (HDL) plasma levels, cellular cholesteryl ester accumulation and reduced cholesterol excretion in response to HDL apolipoproteins. Molecular defects in the ATP binding cassette transporter 1 (ABCA1) have recently been identified as the cause of TD. ABCA1 plays a key role in the translocation of cholesterol across the plasma membrane, and defective ABCA1 causes cholesterol storage in TD cells. Not only cholesterol efflux, but also phospholipid efflux was shown to be impaired in TD cells. By use of thin layer chromatography, high performance liquid chromatography and time-of-flight secondary ion mass spectrometry, we characterized the cellular phospholipid content in fibroblasts from three homozygous TD patients. The cellular content of the major phospholipids was not found to be significantly altered in TD fibroblasts. However, the two phospholipids cardiolipin and lysocardiolipin, which make up minute amounts in normal cells, were at least 3-5-fold enriched in fibroblasts from TD subjects. A structurally closely related phospholipid (lysobisphosphatidic acid) has recently been shown to be enriched in Niemann-Pick type C, another lipid storage disorder. Altogether these data may indicate that the role of these phospholipids is a regulatory one rather than that of a bulk mediator of cholesterol solubilization in sterol trafficking and efflux.
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Affiliation(s)
- M Fobker
- Institut für Klinische Chemie und Laboratoriumsmedizin, Universität Münster, Germany
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27
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Von Eckardstein A, Langer C, Engel T, Schaukal I, Cignarella A, Reinhardt J, Lorkowski S, Li Z, Zhou X, Cullen P, Assmann G. ATP binding cassette transporter ABCA1 modulates the secretion of apolipoprotein E from human monocyte-derived macrophages. FASEB J 2001; 15:1555-61. [PMID: 11427487 DOI: 10.1096/fj.00-0798com] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Apolipoprotein E (apoE) produced by macrophages in the arterial wall protects against atherosclerosis, but the regulation of its secretion by these cells is poorly understood. Here we investigated the contribution of the adenosine triphosphate binding cassette transporters ABCA1 and ABC8 to the secretion of apoE from either primary human monocyte-derived macrophages (HMDM) or human THP1 macrophages. During incubations of up to 6 h, apoE secretion from both THP1 macrophages and HMDM was stimulated by 8-Br-cAMP, which activates ABCA1 expression. The putative ABCA1 inhibitor glyburide and antisense oligonucleotides directed against ABCA1 mRNA significantly reduced apoE secretion from THP1 macrophages and HMDM. Antisense oligonucleotides directed against ABC8 mRNA also inhibited apoE secretion, although this inhibition was less pronounced and consistent than in the case of ABCA1. ApoE secretion from HMDM of ABCA1-deficient patients with Tangier disease was also decreased. ApoE mRNA expression was not affected by inhibition of ABCA1 or ABC8 in normal HMDM or the lack of functional ABCA1 in HMDM from Tangier disease patients. Inhibition of ABCA1 in HMDM prevented the occurrence of anti-apoE-immunoreactive granular structures in the plasma membrane. We conclude that ABCA1 and, to a lesser extent, ABC8 both promote secretion of apoE from human macrophages.
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Affiliation(s)
- A Von Eckardstein
- Institute of Clinical Chemistry and Laboratory Medicine, Central Laboratory, Westphalian Wilhelms University, D-48129 Münster, Germany.
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28
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El Bawab S, Birbes H, Roddy P, Szulc ZM, Bielawska A, Hannun YA. Biochemical characterization of the reverse activity of rat brain ceramidase. A CoA-independent and fumonisin B1-insensitive ceramide synthase. J Biol Chem 2001; 276:16758-66. [PMID: 11278489 DOI: 10.1074/jbc.m009331200] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously purified a membrane-bound ceramidase from rat brain and recently cloned the human homologue. We also observed that the same enzyme is able to catalyze the reverse reaction of ceramide synthesis. To obtain insight into the biochemistry of this enzyme, we characterized in this study this reverse activity. Using sphingosine and palmitic acid as substrates, the enzyme exhibited Michaelis-Menten kinetics; however, the enzyme did not utilize palmitoyl-CoA as substrate. Also, the activity was not inhibited in vitro and in cells by fumonisin B1, an inhibitor of the CoA-dependent ceramide synthase. The enzyme showed a narrow pH optimum in the neutral range, and there was very low activity in the alkaline range. Substrate specificity studies were performed, and the enzyme showed the highest activity with d-erythro-sphingosine (Km of 0.16 mol %, and Vmax of 0.3 micromol/min/mg), but d-erythro-dihydrosphingosine and the three unnatural stereoisomers of sphingosine were poor substrates. The specificity for the fatty acid was also studied, and the highest activity was observed for myristic acid with a Km of 1.7 mol % and a Vmax of 0.63 micromol/min/mg. Kinetic studies were performed to investigate the mechanism of the reaction, and Lineweaver-Burk plots indicated a sequential mechanism. Two competitive inhibitors of the two substrates were identified, l-erythro-sphingosine and myristaldehyde, and inhibition studies indicated that the reaction followed a random sequential mechanism. The effect of lipids were also tested. Most of these lipids showed moderate inhibition, whereas the effects of phosphatidic acid and cardiolipin were more potent with total inhibition at around 2.5-5 mol %. Paradoxically, cardiolipin stimulated ceramidase activity. These results define the biochemical characteristics of this reverse activity. The results are discussed in view of a possible regulation of this enzyme by the intracellular pH or by an interaction with cardiolipin and/or phosphatidic acid.
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Affiliation(s)
- S El Bawab
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, South Carolina 29425, USA
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29
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Neufeld EB, Remaley AT, Demosky SJ, Stonik JA, Cooney AM, Comly M, Dwyer NK, Zhang M, Blanchette-Mackie J, Santamarina-Fojo S, Brewer HB. Cellular localization and trafficking of the human ABCA1 transporter. J Biol Chem 2001; 276:27584-90. [PMID: 11349133 DOI: 10.1074/jbc.m103264200] [Citation(s) in RCA: 267] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
ABCA1, the ATP-binding cassette protein mutated in Tangier disease, mediates the efflux of excess cellular sterol to apoA-I and thereby the formation of high density lipoprotein. The intracellular localization and trafficking of ABCA1 was examined in stably and transiently transfected HeLa cells expressing a functional human ABCA1-green fluorescent protein (GFP) fusion protein. The fluorescent chimeric ABCA1 transporter was found to reside on the cell surface and on intracellular vesicles that include a novel subset of early endosomes, as well as late endosomes and lysosomes. Studies of the localization and trafficking of ABCA1-GFP in the presence of brefeldin A or monensin, agents known to block intracellular vesicular trafficking, as well as apoA-I-mediated cellular lipid efflux, showed that: (i) ABCA1 functions in lipid efflux at the cell surface, and (ii) delivery of ABCA1 to lysosomes for degradation may serve as a mechanism to modulate its surface expression. Time-lapse fluorescence microscopy revealed that ABCA1-GFP-containing early endosomes undergo fusion, fission, and tubulation and transiently interact with one another, late endocytic vesicles, and the cell surface. These studies establish a complex intracellular trafficking pathway for human ABCA1 that may play important roles in modulating ABCA1 transporter activity and cellular cholesterol homeostasis.
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Affiliation(s)
- E B Neufeld
- NHLBI, National Institutes of Health and the NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
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30
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Mendez AJ, Lin G, Wade DP, Lawn RM, Oram JF. Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway. J Biol Chem 2001; 276:3158-66. [PMID: 11073951 DOI: 10.1074/jbc.m007717200] [Citation(s) in RCA: 161] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Efflux of excess cellular cholesterol mediated by lipid-poor apolipoproteins occurs by an active mechanism distinct from passive diffusion and is controlled by the ATP-binding cassette transporter ABCA1. Here we examined whether ABCA1-mediated lipid efflux involves the selective removal of lipids associated with membrane rafts, plasma membrane domains enriched in cholesterol and sphingomyelin. ABCA1 was not associated with cholesterol and sphingolipid-rich membrane raft domains based on detergent solubility and lack of colocalization with marker proteins associated with raft domains. Lipid efflux to apoA-I was accounted for by decreases in cellular lipids not associated with cholesterol/sphingomyelin-rich membranes. Treating cells with filipin, to disrupt raft structure, or with sphingomyelinase, to digest plasma membrane sphingomyelin, did not impair apoA-I-mediated cholesterol or phosphatidylcholine efflux. In contrast, efflux of cholesterol to high density lipoproteins (HDL) or plasma was partially accounted for by depletion of cholesterol from membrane rafts. Additionally, HDL-mediated cholesterol efflux was partially inhibited by filipin and sphingomyelinase treatment. Apo-A-I-mediated cholesterol efflux was absent from fibroblasts with nonfunctional ABCA1 (Tangier disease cells), despite near normal amounts of cholesterol associated with raft domains and normal abilities of plasma and HDL to deplete cholesterol from these domains. Thus, the involvement of membrane rafts in cholesterol efflux applies to lipidated HDL particles but not to lipid-free apoA-I. We conclude that cholesterol and sphingomyelin-rich membrane rafts do not provide lipid for efflux promoted by apolipoproteins through the ABCA1-mediated lipid secretory pathway and that ABCA1 is not associated with these domains.
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Affiliation(s)
- A J Mendez
- University of Miami School of Medicine, Diabetes Research Institute, Miami, Florida 33101, USA.
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31
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Cellular cholesterol efflux is modulated by phospholipid-derived signaling molecules in familial HDL deficiency/Tangier disease fibroblasts. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31686-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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32
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Utech M, Höbbel G, Rust S, Reinecke H, Assmann G, Walter M. Accumulation of RhoA, RhoB, RhoG, and Rac1 in fibroblasts from Tangier disease subjects suggests a regulatory role of Rho family proteins in cholesterol efflux. Biochem Biophys Res Commun 2001; 280:229-36. [PMID: 11162504 DOI: 10.1006/bbrc.2000.4061] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Tangier disease (TD) is an inherited disorder of lipid metabolism characterized by very low high density lipoprotein (HDL) plasma levels, cellular cholesteryl ester accumulation and reduced cholesterol excretion in response to HDL apolipoproteins. Molecular defects in the ATP binding cassette transporter 1 (ABCA1) have recently been identified as the cause of TD. ABCA1 plays a key role in the translocation of cholesterol across the plasma membrane, and defective ABCA1 causes cholesterol storage in TD cells. However, the exact relationship of many of the biochemical and morphological abnormalities in TD to ABCA1 is unknown. Since small GTP-binding proteins are important regulators of many cellular functions, we characterized these proteins in normal and TD fibroblasts using the [alpha-32P]GTP overlay technique and Western blotting of SDS and isoelectric focusing gels. Our results indicate that GTP-binding proteins of the Rho family (RhoA, RhoB, RhoG, Rac-1) are enriched in fibroblasts from TD patients. The accumulation of small G proteins may have potential implications for the TD phenotype and the regulation of cholesterol excretion in TD cells.
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Affiliation(s)
- M Utech
- Institut für Klinische Chemie und Laboratoriumsmedizin, Universität Munster, Albert-Schweitzer-Str. 33, 48149 Münster, Germany
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33
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von Eckardstein A, Nofer JR, Assmann G. High density lipoproteins and arteriosclerosis. Role of cholesterol efflux and reverse cholesterol transport. Arterioscler Thromb Vasc Biol 2001; 21:13-27. [PMID: 11145929 DOI: 10.1161/01.atv.21.1.13] [Citation(s) in RCA: 511] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
High density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease, and HDL exerts various potentially antiatherogenic properties, including the mediation of reverse transport of cholesterol from cells of the arterial wall to the liver and steroidogenic organs. Enhancement of cholesterol efflux and of reverse cholesterol transport (RCT) is considered an important target for antiatherosclerotic drug therapy. Levels and composition of HDL subclasses in plasma are regulated by many factors, including apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors, and cellular transporters. In vitro experiments as well as genetic family and population studies and investigation of transgenic animal models have revealed that HDL cholesterol plasma levels do not necessarily reflect the efficacy and antiatherogenicity of RCT. Instead, the concentration of HDL subclasses, the mobilization of cellular lipids for efflux, and the kinetics of HDL metabolism are important determinants of RCT and the risk of atherosclerosis.
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Affiliation(s)
- A von Eckardstein
- Institut für Klinische Chemie und Laboratoriumsmedizin, Zentrallaboratorium, Westfälische Wilhelms-Universität Münster, Germany.
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34
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Abstract
Ethanol has a pronounced effect on lipid homeostasis. It is our overall hypothesis that certain lipid carrier proteins are targets of acute and chronic ethanol exposure and that perturbation of these proteins induces lipid dysfunction leading to cellular pathophysiology. These proteins include both intracellular proteins and lipoproteins. This paper examines recent data on the interaction of ethanol with these proteins. In addition, new data are presented on the stimulatory effects of ethanol on low-density-lipoprotein (LDL)-mediated cholesterol uptake into fibroblasts and direct perturbation of the LDL apolipoprotein, apolipoprotein B. A cell model is presented that outlines potential mechanisms thought to be involved in ethanol perturbation of cholesterol transport and distribution.
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Affiliation(s)
- W G Wood
- Geriatric Research, Education and Clinical Center, VA Medical Center, Minneapolis, MN 55417, USA.
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35
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Blanchard F, Duplomb L, Wang Y, Robledo O, Kinzie E, Pitard V, Godard A, Jacques Y, Baumann H. Stimulation of leukemia inhibitory factor receptor degradation by extracellular signal-regulated kinase. J Biol Chem 2000; 275:28793-801. [PMID: 10858440 DOI: 10.1074/jbc.m003986200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Leukemia inhibitory factor (LIF) signals via the heterodimeric receptor complex comprising the LIF receptor alpha subunit (LIFRalpha) and the common signal transducing subunit for interleukin-6 cytokine receptors, gp130. This study demonstrates that in different cell types, the level of LIFRalpha decreases during treatment with LIF or the closely related cytokine oncostatin M (OSM). Moreover, insulin and epidermal growth factor induce a similar LIFRalpha down-regulation. The regulated loss of LIFRalpha is specific since neither gp130 nor OSM receptor beta shows a comparable change in turnover. LIFRalpha down-regulation correlates with reduced cell responsiveness to LIF. Using protein kinase inhibitors and point mutations in LIFRalpha, we demonstrate that LIFRalpha down-regulation depends on activation of extracellular signal-regulated kinase 1/2 and phosphorylation of the cytoplasmic domain of LIFRalpha at serine 185. This modification appears to promote the endosomal/lysosomal pathway of the LIFRalpha. These results suggest that extracellular signal-regulated kinase-activating factors like OSM and growth factors have the potential to lower specifically LIF responsiveness in vivo by regulating LIFRalpha half-life.
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Affiliation(s)
- F Blanchard
- Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, New York 14263, INSERM U463, France.
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36
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Bortnick AE, Rothblat GH, Stoudt G, Hoppe KL, Royer LJ, McNeish J, Francone OL. The correlation of ATP-binding cassette 1 mRNA levels with cholesterol efflux from various cell lines. J Biol Chem 2000; 275:28634-40. [PMID: 10893411 DOI: 10.1074/jbc.m003407200] [Citation(s) in RCA: 250] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Studies show that lipid-free apoA-I stimulates release of cholesterol and phospholipid from fibroblasts and macrophages. ATP-binding cassette 1 (ABC1) is implicated in this release and has been identified as the genetic defect in Tangier disease, evidence that ABC1 is critical to the biogenesis of high density lipoprotein. We quantified levels of ABC1 mRNA, protein, and cholesterol efflux from J774 mouse macrophages +/- exposure to a cAMP analog. Up-regulating ABC1 mRNA correlated to increased cholesterol efflux in a dose- and time-dependent manner. mRNA levels rose after 15 min of exposure while protein levels rose after 1 h, with increased efflux 2-4 h post-treatment. In contrast to cells from wild-type mice, peritoneal macrophages from the Abc1 -/- mouse showed a lower level of basal efflux and no increase with cAMP treatment. The stimulation of efflux exhibits specificity for apoA-I, high density lipoprotein, and other apolipoproteins as cholesterol acceptors, but not for small unilamellar vesicles, bile acid micelles, or cyclodextrin. We have studied a number of cell types and found that while other cell lines express ABC1 constitutively, only J774 and elicited mouse macrophages show a substantial increase of mRNA and efflux with cAMP treatment. ApoA-I-stimulated efflux was detected from the majority of cell lines examined, independent of treatment.
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Affiliation(s)
- A E Bortnick
- MCP Hahnemann University, Department of Biochemistry, Philadelphia, Pennsylvania 19129, USA
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37
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Avdulov NA, Chochina SV, Igbavboa U, Wood WG. Cholesterol efflux to high-density lipoproteins and apolipoprotein A-I phosphatidylcholine complexes is inhibited by ethanol: role of apolipoprotein structure and cooperative interaction of phosphatidylcholine and cholesterol. Biochemistry 2000; 39:10599-606. [PMID: 10956052 DOI: 10.1021/bi0008534] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
There is a substantial body of evidence showing that moderate alcohol consumption is associated with a reduced risk of cardiovascular morbidity and mortality. One of the factors thought to contribute to this reduction in risk is an increase in the level of high-density lipoproteins (HDL) correlated with alcohol consumption. However, HDL levels are elevated in heavy drinkers, but their risk of vascular disease is greater compared with that of moderate drinkers. Ethanol at concentrations observed in heavy drinkers and alcoholics may directly act on HDL and apolipoproteins and in turn modify cholesterol efflux. In this paper, we show that ethanol significantly inhibited cholesterol efflux from fibroblasts to HDL and to apolipoprotein A-I (apoA-I) complexed with phosphatidylcholine (PC). Ethanol significantly inhibited binding of PC to apoA-I, inhibited incorporation of cholesterol only when apoA-I contained PC, and did not alter incorporation of cholesterol into HDL. ApoA-I structure was altered by ethanol as monitored by steady-state fluorescence polarization of tryptophan residues. The absence of ethanol effects on incorporation of cholesterol into HDL versus inhibition of cholesterol incorporation into the apoA-I-PC complex suggests that the effects of ethanol on cholesterol efflux mediated by HDL involve interaction with the cell surface and that efflux mediated by the apoA-I-PC complex is a combination of aqueous diffusion and contact with the cell surface. In addition, effects of ethanol on apoA-I suggest that pre-beta-HDL or lipid-free apoA-I may be more perturbed by ethanol than mature HDL, and such effects may be pathophysiological with respect to the process of reverse cholesterol transport in heavy drinkers and alcoholics.
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Affiliation(s)
- N A Avdulov
- Geriatric Research, Education and Clinical Center, VA Medical Center, and Department of Pharmacology, University of Minnesota School of Medicine, Minneapolis, Minnesota 55417, USA
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38
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Cellular cholesterol efflux in heterozygotes for Tangier disease is markedly reduced and correlates with high density lipoprotein cholesterol concentration and particle size. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32019-8] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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39
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Garver WS, Heidenreich RA, Erickson RP, Thomas MA, Wilson JM. Localization of the murine Niemann-Pick C1 protein to two distinct intracellular compartments. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32376-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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40
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Abstract
Free cholesterol is very efficiently removed from cells by 2-hydroxypropyl-beta-cyclodextrins. The efflux of cholesterol occurs from two distinct kinetic pools: the half-times (t(1/2)) for the two pools in CHO-K1 cells are 15 +/- 5 s and 21 +/- 6 min and they represent 25% +/- 5% and 75% +/- 5% of the readily exchangeable cell cholesterol, respectively. In this study we have determined that the fast pool and the majority of the slow kinetic pool for cholesterol efflux are apparently present in the plasma membrane. Numerous agents that inhibit intracellular cholesterol trafficking are unable to affect either the size or the t(1/2) for efflux of either kinetic pool. In contrast, treatment of the cells with N-ethylmaleimide (NEM), exogenous lipases such as sphingomyelinase and phospholipase C, calcium ionophore A23187, or heat resulted in the dramatic increase in the size of the fast kinetic pool of cholesterol. These changes in the kinetics of cholesterol efflux are not specific to the nature of the extracellular acceptor indicating that they are a consequence of changes in the cell plasma membrane. The above treatments disrupt the normal organization of the lipids in the plasma membrane via either hydrolysis or randomization. The phosphatidylcholine and sphingomyelin present in the plasma membrane are critical for maintaining the two kinetic pools of cholesterol; any alteration in the amount or the location of these phospholipids results in an enhancement of efflux by redistributing cholesterol into the fast kinetic pool.
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Affiliation(s)
- M P Haynes
- Department of Biochemistry, MCP-Hahnemann University, Philadelphia, Pennsylvania 19129, USA
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41
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Michikawa M, Fan QW, Isobe I, Yanagisawa K. Apolipoprotein E exhibits isoform-specific promotion of lipid efflux from astrocytes and neurons in culture. J Neurochem 2000; 74:1008-16. [PMID: 10693931 DOI: 10.1046/j.1471-4159.2000.0741008.x] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many studies have shown that apolipoprotein E (apoE) plays important roles in maintaining intracellular lipid homeostasis in nonneuronal cells. However, little is known about the extracellular transport of lipids in the CNS. In this study, we determined whether and to what degree lipid efflux from astrocytes and neurons depended on apoE. Our results showed that exogenously added apoE promoted the efflux of cholesterol and phosphatidylcholine from both astrocytes and neurons in culture, resulting in the generation of high-density lipoprotein-like particles. The order of potency of the apoE isoforms as lipid acceptors was apoE2 > apoE3 = apoE4 in astrocytes and apoE2 > apoE3 > apoE4 in neurons. Treatment with brefeldin A, monensin, and a protein kinase C inhibitor, H7, abolished the ability of apoE to promote cholesterol efflux from cultured astrocytes, without altering apoE-mediated phosphatidylcholine efflux. In contrast, the efflux of both cholesterol and phosphatidylcholine promoted by apoE was abolished following treatment with heparinase or lactoferrin, which block the interaction of apoE with heparan sulfate proteoglycans (HSPGs) or low-density lipoprotein receptor-related protein (LRP), respectively. This study suggests that apoE promotes lipid efflux from astrocytes and neurons in an isoform-specific manner and that cell surface HSPGs and/or HSPG-LRP pathway may mediate this apoE-promoted lipid efflux.
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Affiliation(s)
- M Michikawa
- Department of Dementia Research, National Institute for Longevity Sciences, Obu, Aichi, Japan.
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42
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Pujuguet P, Simian M, Liaw J, Timpl R, Werb Z, Bissell MJ. Nidogen-1 regulates laminin-1-dependent mammary-specific gene expression. J Cell Sci 2000; 113 ( Pt 5):849-58. [PMID: 10671374 PMCID: PMC2933215 DOI: 10.1242/jcs.113.5.849] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nidogen-1 (entactin) acts as a bridge between the extracellular matrix molecules laminin-1 and type IV collagen, and thus participates in the assembly of basement membranes. To investigate the role of nidogen-1 in regulating cell-type-specific gene expression in mammary epithelium, we designed a culture microecosystem in which each component, including epithelial cells, mesenchymal cells, lactogenic hormones and extracellular matrix, could be controlled. We found that primary and established mesenchymal and myoepithelial cells synthesized and secreted nidogen-1, whereas expression was absent in primary and established epithelial cells. In an epithelial cell line containing mesenchymal cells, nidogen-1 was produced by the mesenchymal cells but deposited between the epithelial cells. In this mixed culture, mammary epithelial cells express (beta)-casein in the presence of lactogenic hormones. Addition of either laminin-1 plus nidogen-1, or laminin-1 alone, to mammary epithelial cells induced (beta)-casein production. We asked whether recombinant nidogen-1 alone could signal directly for (beta)-casein. Nidogen-1 did not induce (beta)-casein synthesis in epithelial cells, but it augmented the inductive capacity of laminin-1. These data suggest that nidogen-1 can cooperate with laminin-1 to regulate (beta)-casein expression. Addition of full-length nidogen-1 to the mixed cultures had no effect on (beta)-casein gene expression; however, a nidogen-1 fragment containing the laminin-1 binding domain, but lacking the type IV collagen-binding domain, had a dominant negative effect on (beta)-casein expression. These data point to a physiological role for nidogen-1 in the basement membrane-induced gene expression by epithelial cells.
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Affiliation(s)
- Philippe Pujuguet
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 83/101, Berkeley, CA 94720, USA
| | - Marina Simian
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 83/101, Berkeley, CA 94720, USA
| | - Jane Liaw
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 83/101, Berkeley, CA 94720, USA
| | - Rupert Timpl
- Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany
| | - Zena Werb
- Department of Anatomy, University of California, San Francisco, CA 94143, USA
| | - Mina J. Bissell
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 83/101, Berkeley, CA 94720, USA
- Author for correspondence ()
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43
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Panousis CG, Zuckerman SH. Regulation of cholesterol distribution in macrophage-derived foam cells by interferon-γ. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32076-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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44
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Reduction in apolipoprotein-mediated removal of cellular lipids by immortalization of human fibroblasts and its reversion by cAMP: lack of effect with Tangier disease cells. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)34893-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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45
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Higgins ME, Davies JP, Chen FW, Ioannou YA. Niemann-Pick C1 is a late endosome-resident protein that transiently associates with lysosomes and the trans-Golgi network. Mol Genet Metab 1999; 68:1-13. [PMID: 10479477 DOI: 10.1006/mgme.1999.2882] [Citation(s) in RCA: 203] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Niemann-Pick type C (NPC) disease is a severe cell lipidosis characterized by the accumulation of unesterified cholesterol in the endosomal/lysosomal system. Recently the primary disease-causing gene, NPC1, was identified, but few clues regarding its potential function(s) could be derived from its predicted amino acid sequence. Therefore, efforts were directed at characterizing the subcellular location of the NPC1 protein. Initial studies with a FLAG-tagged NPC1 cDNA demonstrated that NPC1 is a glycoprotein that associates with the membranes of a population of cytoplasmic vesicles. Immunofluorescence microscopy using anti-NPC1 polyclonal antibodies confirmed this analysis. Double-label immunofluorescence microscopy and subcellular fractionation studies indicated that NPC1 associates predominantly with late endosomes (Rab9 GTPase-positive vesicles) and, to a lesser extent, with lysosomes and the trans-Golgi network. When cholesterol egress from lysosomes was blocked by treatment of cells with U18666A, the NPC1 location shifted from late endosomes to the trans-Golgi network and lysosomes. Subcellular fractionation of liver homogenates from U18666A-treated mice confirmed these observations. These data suggest that U18666A may inhibit the retrograde transport of NPC1 from lysosomes to late endosomes for subsequent transfer to the trans-Golgi network.
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Affiliation(s)
- M E Higgins
- Department of Human Genetics, Mount Sinai School of Medicine, New York, New York 10029, USA
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46
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Wolfbauer G, Albers JJ, Oram JF. Phospholipid transfer protein enhances removal of cellular cholesterol and phospholipids by high-density lipoprotein apolipoproteins. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1439:65-76. [PMID: 10395966 DOI: 10.1016/s1388-1981(99)00077-3] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
High-density lipoprotein (HDL) apolipoproteins remove excess cholesterol from cells by an active transport pathway that may protect against atherosclerosis. Here we show that treatment of cholesterol-loaded human skin fibroblasts with phospholipid transfer protein (PLTP) increased HDL binding to cells and enhanced cholesterol and phospholipid efflux by this pathway. PLTP did not stimulate lipid efflux in the presence of albumin, purified apolipoprotein A-I, and phospholipid vesicles, suggesting specificity for HDL particles. PLTP restored the lipid efflux activity of mildly trypsinized HDL, presumably by regenerating active apolipoproteins. PLTP-stimulated lipid efflux was absent in Tangier disease fibroblasts, induced by cholesterol loading, and inhibited by brefeldin A treatment, indicating selectivity for the apolipoprotein-mediated lipid removal pathway. The lipid efflux-stimulating effect of PLTP was not attributable to generation of prebeta HDL particles in solution but instead required cellular interactions. These interactions increased cholesterol efflux to minor HDL particles with electrophoretic mobility between alpha and prebeta. These findings suggest that PLTP promotes cell-surface binding and remodeling of HDL so as to improve its ability to remove cholesterol and phospholipids by the apolipoprotein-mediated pathway, a process that may play an important role in enhancing flux of excess cholesterol from tissues and retarding atherogenesis.
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Affiliation(s)
- G Wolfbauer
- Department of Medicine, Box 356426, University of Washington, Seattle, WA 98195-6426, USA
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47
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Yagodin S, Pivovarova NB, Andrews SB, Sattelle DB. Functional characterization of thapsigargin and agonist-insensitive acidic Ca2+ stores in Drosophila melanogaster S2 cell lines. Cell Calcium 1999; 25:429-38. [PMID: 10579054 DOI: 10.1054/ceca.1999.0043] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The role of acidic intracellular calcium stores in calcium homeostasis was investigated in the Drosophila Schneider cell line 2 (S2) by means of free cytosolic calcium ([Ca2+]i) and intracellular pH (pHi) imaging together with measurements of total calcium concentrations within intracellular compartments. Both a weak base (NH4Cl, 15 mM) and a Na+/H+ ionophore (monensin, 10 microM) evoked cytosolic alkalinization followed by Ca2+ release from acidic intracellular Ca2+ stores. Pretreatment of S2 cells with either thapsigargin (1 microM), an inhibitor of endoplasmic reticulum Ca(2+)-ATPases, or with the Ca2+ ionophore ionomycin (10 microM) was without effect on the amplitude of Ca2+ release evoked by alkalinization. Application of the cholinergic agonist carbamylcholine (100 microM) to transfected S2-DM1 cells expressing a Drosophila muscarinic acetylcholine receptor (DM1) emptied the InsP3-sensitive Ca2+ store but failed to affect the amplitude of alkalinization-evoked Ca2+ release. Glycyl-L-phenylalanine-beta-naphthylamide (200 microM), a weak hydrophobic base known to permeabilize lysosomes by osmotic swelling, triggered Ca2+ release from internal stores, while application of brefeldin A (10 microM), an antibiotic which disperses the Golgi complex, resulted in a smaller increase in [Ca2+]i. These results suggest that the alkali-evoked calcium release is largely attributable to lysosomes, a conclusion that was confirmed by direct measurements of total calcium content of S2 organelles. Lysosomes and endoplasmic reticulum were the only organelles found to have concentrations of total calcium significantly higher than the cytosol. However, NH4Cl (15 mM) reduced the level of total calcium only in lysosomes. Depletion of acidic Ca2+ stores did not elicit depletion-operated Ca2+ entry. They were refilled upon re-exposure of cells to normal saline ([Ca2+]o = 2 mM), but not by thapsigargin-induced [Ca2+]i elevation in Ca(2+)-free saline.
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Affiliation(s)
- S Yagodin
- Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, UK
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48
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Dexamethasone-Induced Thymocyte Apoptosis: Apoptotic Signal Involves the Sequential Activation of Phosphoinositide-Specific Phospholipase C, Acidic Sphingomyelinase, and Caspases. Blood 1999. [DOI: 10.1182/blood.v93.7.2282] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractGlucocorticoid hormones (GCH) have been implicated as regulators of T-lymphocyte growth and differentiation. In particular, it has been reported that GCH can induce thymocyte apoptosis. However, the molecular mechanisms responsible for this GCH-induced death have not been clarified. In this work, the biochemical events associated with apoptosis induced by Dexamethasone (Dex), a synthetic GCH, in normal mouse thymocytes, have been analyzed. Results indicate that Dex-induced thymocyte apoptosis is attributable to an early ceramide generation caused by the activation of an acidic sphingomyelinase (aSMase). Caspase activity plays a crucial role in Dex-induced apoptosis and is downstream the aSMase activation in that inhibition of the early ceramide generation inhibits caspase activation and thymocyte death. Moreover, Dex treatment rapidly induces diacylglycerol (DAG) generation, through a protein kinase C (PKC) and G-protein–dependent phosphatidylinositol-specific phospholipase C (PI-PLC), an event which precedes and is required for aSMase activation. Indeed, PI-PLC inhibition by U73122 totally prevents Dex-induced aSMase activity, ceramide generation, and consequently, caspase activation and apoptosis. All these effects require Dex interaction with GCH receptor (GR), are countered by the GR antagonist RU486, and precede the GCH/GR-activated transcription and protein synthesis. These observations indicate that GCH activates thymocyte death through a complex signaling pathway that requires the sequential activation of different biochemical events.
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Dexamethasone-Induced Thymocyte Apoptosis: Apoptotic Signal Involves the Sequential Activation of Phosphoinositide-Specific Phospholipase C, Acidic Sphingomyelinase, and Caspases. Blood 1999. [DOI: 10.1182/blood.v93.7.2282.407a23_2282_2296] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glucocorticoid hormones (GCH) have been implicated as regulators of T-lymphocyte growth and differentiation. In particular, it has been reported that GCH can induce thymocyte apoptosis. However, the molecular mechanisms responsible for this GCH-induced death have not been clarified. In this work, the biochemical events associated with apoptosis induced by Dexamethasone (Dex), a synthetic GCH, in normal mouse thymocytes, have been analyzed. Results indicate that Dex-induced thymocyte apoptosis is attributable to an early ceramide generation caused by the activation of an acidic sphingomyelinase (aSMase). Caspase activity plays a crucial role in Dex-induced apoptosis and is downstream the aSMase activation in that inhibition of the early ceramide generation inhibits caspase activation and thymocyte death. Moreover, Dex treatment rapidly induces diacylglycerol (DAG) generation, through a protein kinase C (PKC) and G-protein–dependent phosphatidylinositol-specific phospholipase C (PI-PLC), an event which precedes and is required for aSMase activation. Indeed, PI-PLC inhibition by U73122 totally prevents Dex-induced aSMase activity, ceramide generation, and consequently, caspase activation and apoptosis. All these effects require Dex interaction with GCH receptor (GR), are countered by the GR antagonist RU486, and precede the GCH/GR-activated transcription and protein synthesis. These observations indicate that GCH activates thymocyte death through a complex signaling pathway that requires the sequential activation of different biochemical events.
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Drobnik W, Liebisch G, Biederer C, Tr mbach B, Rogler G, Müller P, Schmitz G. Growth and cell cycle abnormalities of fibroblasts from Tangier disease patients. Arterioscler Thromb Vasc Biol 1999; 19:28-38. [PMID: 9888863 DOI: 10.1161/01.atv.19.1.28] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We have investigated the abnormal proliferation and morphology of fibroblasts from patients with Tangier disease (TD), a high density lipoprotein (HDL) deficiency syndrome that is characterized by impairment of HDL3-mediated lipid efflux and Gi-protein-mediated signaling via phosphatidylinositol-specific phospholipase C (PI-PLC) and phospholipase D (PLD). TD fibroblasts displayed a 30% to 50% reduced in vitro growth rate and a 1.6-fold increased cell surface area. The response to different mitogens was diminished, and asynchronously growing TD fibroblasts showed 4.4+/-0.3% S-phase and 19.1+/-0.5% G2/M-phase cells compared with 9.7+/-0.6% and 7.8+/-0.5%, respectively, in controls. Monensin, but not brefeldin A, induced an S- and G2/M-phase distribution in control cells similar to that found in TD fibroblasts. This effect of monensin was accompanied by an increase of ceramide levels in controls, whereas TD fibroblasts already had a 2.5-fold increased basal ceramide concentration. Incubation of control cells with C2 ceramide and threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) mimicked the effect of monensin on the cell cycle. The inhibition of neither Gi protein function by pertussis toxin nor PLD by butanol resulted in a G2/M-phase arrest. Propranolol, known to increase phosphatidic acid levels, was ineffective in reversing the G2/M-phase arrest in TD fibroblasts. In addition, cDNA sequences and mRNA expression of the participants of PI-PLC or PLD signaling, ie, G-protein subunits alphai1, alphai2, and alphai3; phosphatidylinositol transfer proteins-alpha and -beta; and ADP ribosylation factors 1 and 3 were found to be normal. Thus, growth and cell cycle abnormalities in TD fibroblasts are likely to be related to impaired Golgi function and sphingolipid signaling rather than inoperative G-protein signal transduction. Because PDMP was also found to decrease HDL3-mediated lipid efflux in control but not TD fibroblasts, similar pathways seem to be involved in the disturbances of lipid transport and growth retardation.
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Affiliation(s)
- W Drobnik
- Institut für Klinische Chemie und Laboratoriumsmedizin, Universit at Regensburg, Regensburg, Federal Republic of Germany
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