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Powers HR, Jenjak SE, Volkman BF, Sahoo D. Development and validation of a purification system for functional full-length human SR-B1 and CD36. J Biol Chem 2023; 299:105187. [PMID: 37625590 PMCID: PMC10509710 DOI: 10.1016/j.jbc.2023.105187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 07/31/2023] [Accepted: 08/18/2023] [Indexed: 08/27/2023] Open
Abstract
Scavenger receptor class B type 1 (SR-B1) and CD36 are both members of the class B scavenger receptor family that play important roles in lipoprotein metabolism and atherosclerotic disease. SR-B1 is the primary receptor for high-density lipoproteins, while CD36 is the receptor responsible for the internalization of oxidized low-density lipoproteins. Despite their importance, class B scavenger receptor structure has only been studied by functional domain or peptide fragments-there are currently no reports of utilizing purified full-length protein. Here we report the successful expression and purification of full-length human SR-B1 and CD36 using an Spodoptera frugiperda insect cell system. We demonstrate that both SR-B1 and CD36 retained their normal functions in Spodoptera frugiperda cells, including lipoprotein binding, lipid transport, and the formation of higher order oligomers in the plasma membrane. Purification schemes for both scavenger receptors were optimized and their purity was confirmed by SDS-PAGE. Both purified scavenger receptors were assessed for stability by thermal shift assay and shown to maintain stable melting temperatures up to 6 weeks post-purification. Microscale thermophoresis was used to demonstrate that purified SR-B1 and CD36 were able to bind their native lipoprotein ligands. Further, there was no difference in affinity of SR-B1 for high-density lipoprotein or CD36 for oxidized low-density lipoprotein, when comparing glycosylated and deglycosylated receptors. These studies mark a significant step forward in creating physiologically relevant tools to study scavenger receptor function and lay the groundwork for future functional studies and determination of receptor structure.
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Affiliation(s)
- Hayley R Powers
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Shawn E Jenjak
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Brian F Volkman
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Daisy Sahoo
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, USA; Division of Endocrinology & Molecular Medicine, Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin, USA; Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
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2
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Nishigami M, Uno Y, Tsumoto K. Microscopic Observation of Membrane Fusion between Giant Liposomes and Baculovirus Budded Viruses Activated by the Release of a Caged Proton. MEMBRANES 2023; 13:membranes13050507. [PMID: 37233568 DOI: 10.3390/membranes13050507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 05/02/2023] [Accepted: 05/05/2023] [Indexed: 05/27/2023]
Abstract
Baculovirus (Autographa californica multiple nucleopolyhedrovirus, AcMNPV) is an envelope virus possessing a fusogenic protein, GP64, which can be activated under weak acidic conditions close to those in endosomes. When the budded viruses (BVs) are bathed at pH 4.0 to 5.5, they can bind to liposome membranes with acidic phospholipids, and this results in membrane fusion. In the present study, using the caged-proton reagent 1-(2-nitrophenyl)ethyl sulfate, sodium salt (NPE-caged-proton), which can be uncaged by irradiation with ultraviolet light, we triggered the activation of GP64 by lowering the pH and observed membrane fusion on giant liposomes (giant unilamellar vesicles, GUVs) by visualizing the lateral diffusion of fluorescence emitted from a lipophilic fluorochrome (octadecyl rhodamine B chloride, R18) that stained viral envelopes of BVs. In this fusion, entrapped calcein did not leak from the target GUVs. The behavior of BVs prior to the triggering of membrane fusion by the uncaging reaction was closely monitored. BVs appeared to accumulate around a GUV with DOPS, implying that BVs preferred phosphatidylserine. The monitoring of viral fusion triggered by the uncaging reaction could be a valuable tool for revealing the delicate behavior of viruses affected by various chemical and biochemical environments.
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Affiliation(s)
- Misako Nishigami
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu 514-8507, Mie, Japan
| | - Yuki Uno
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu 514-8507, Mie, Japan
| | - Kanta Tsumoto
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu 514-8507, Mie, Japan
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3
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Powers HR, Sahoo D. SR-B1's Next Top Model: Structural Perspectives on the Functions of the HDL Receptor. Curr Atheroscler Rep 2022; 24:277-288. [PMID: 35107765 PMCID: PMC8809234 DOI: 10.1007/s11883-022-01001-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/23/2021] [Indexed: 02/04/2023]
Abstract
PURPOSE OF REVIEW The binding of high-density lipoprotein (HDL) to its primary receptor, scavenger receptor class B type 1 (SR-B1), is critical for lowering plasma cholesterol levels and reducing cardiovascular disease risk. This review provides novel insights into how the structural elements of SR-B1 drive efficient function with an emphasis on bidirectional cholesterol transport. RECENT FINDINGS We have generated a new homology model of full-length human SR-B1 based on the recent resolution of the partial structures of other class B scavenger receptors. Interrogating this model against previously published observations allows us to generate structurally informed hypotheses about SR-B1's ability to mediate HDL-cholesterol (HDL-C) transport. Furthermore, we provide a structural perspective as to why human variants of SR-B1 may result in impaired HDL-C clearance. A comprehensive understanding of SR-B1's structure-function relationships is critical to the development of therapeutic agents targeting SR-B1 and modulating cardiovascular disease risk.
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Affiliation(s)
- Hayley R. Powers
- grid.30760.320000 0001 2111 8460Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI USA
| | - Daisy Sahoo
- grid.30760.320000 0001 2111 8460Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI USA ,grid.30760.320000 0001 2111 8460Department of Medicine, Division of Endocrinology & Molecular Medicine, Medical College of Wisconsin, Milwaukee, WI USA ,grid.30760.320000 0001 2111 8460Cardiovascular Center, H4930 Health Research Center, Medical College of Wisconsin, 8701 W. Watertown Plank Road, Milwaukee, WI 53226 USA
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4
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Boguś MI, Wrońska AK, Kaczmarek A, Boguś-Sobocińska M. In vitro screening of 65 mycotoxins for insecticidal potential. PLoS One 2021; 16:e0248772. [PMID: 33735295 PMCID: PMC7971479 DOI: 10.1371/journal.pone.0248772] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 03/05/2021] [Indexed: 12/22/2022] Open
Abstract
The economic losses and threats to human and animal health caused by insects and the pathogens transmitted by them require effective and environmentally-friendly methods of controlling them. One such group of natural biocontrol agents which may be used as biopesticides is that of the entomopathogenic fungi and their toxic secondary metabolites (mycotoxins). The present in vitro work examined the insecticidal potential of 65 commercially-available mycotoxins against the insect Sf-9 cell line. Mammalian Caco-2 and THP-1 cell lines served as reference controls to select insecticidal mycotoxins harmless to mammalian cells. All tested mycotoxins significantly reduced the in vitro proliferation of the Sf-9 cells and evoked morphological changes. Ten of the mycotoxins found to strongly inhibit Sf-9 proliferation also had moderate or no effect on Caco-2 cells. The THP-1 cells were highly resistant to the tested mycotoxins: doses 103 times higher were needed to affect viability and morphology (1 μg/ml for THP-1 versus 1 ng/ml for Sf-9 and Caco-2). Nine mycotoxins significantly decreased Sf-9 cell proliferation with minor effects on mammalian cells: cyclosporins B and D, cytochalasin E, gliotoxin, HC toxin, paxilline, penitrem A, stachybotrylactam and verruculogen. These may be good candidates for future biopesticide formulations.
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Affiliation(s)
- Mieczysława Irena Boguś
- Witold Stefański Institute of Parasitology, Polish Academy of Sciences, Warszawa, Poland
- Biomibo ul, Warszawa, Poland
- * E-mail:
| | - Anna Katarzyna Wrońska
- Witold Stefański Institute of Parasitology, Polish Academy of Sciences, Warszawa, Poland
| | - Agata Kaczmarek
- Witold Stefański Institute of Parasitology, Polish Academy of Sciences, Warszawa, Poland
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Moreno MJ, Teles Martins PA, Bernardino EF, Abel B, Ambudkar SV. Characterization of the Lipidome and Biophysical Properties of Membranes from High Five Insect Cells Expressing Mouse P-Glycoprotein. Biomolecules 2021; 11:biom11030426. [PMID: 33799403 PMCID: PMC8001469 DOI: 10.3390/biom11030426] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 03/11/2021] [Accepted: 03/12/2021] [Indexed: 12/31/2022] Open
Abstract
The lipid composition of biomembranes influences the properties of the lipid bilayer and that of the proteins. In this study, the lipidome and the lipid/protein ratio of membranes from High Five™ insect cells overexpressing mouse P-glycoprotein was characterized. This provides a better understanding of the lipid environment in which P-glycoprotein is embedded, and thus of its functional and structural properties. The relative abundance of the distinct phospholipid classes and their acyl chain composition was characterized. A mass ratio of 0.57 ± 0.11 phospholipids to protein was obtained. Phosphatidylethanolamines are the most abundant phospholipids, followed by phosphatidylcholines. Membranes are also enriched in negatively charged lipids (phosphatidylserines, phosphatidylinositols and phosphatidylglycerols), and contain small amounts of sphingomyelins, ceramides and monoglycosilatedceramides. The most abundant acyl chains are monounsaturated, with significant amounts of saturated chains. The characterization of the phospholipids by HPLC-MS allowed identification of the combination of acyl chains, with palmitoyl-oleoyl being the most representative for all major phospholipid classes except for phosphatidylserines, which are mostly saturated. A mixture of POPE:POPC:POPS in the ratio 45:35:20 is proposed for the preparation of simple representative model membranes. The adequacy of the model membranes was further evaluated by characterizing their surface potential and fluidity.
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Affiliation(s)
- Maria João Moreno
- Coimbra Chemistry Center, Chemistry Department, FCTUC, University of Coimbra, 3004-535 Coimbra, Portugal; (P.A.T.M.); (E.F.B.)
- CNC—Center for Neuroscience and Cell Biology, University of Coimbra, 3004-535 Coimbra, Portugal
- Correspondence:
| | | | - Eva F. Bernardino
- Coimbra Chemistry Center, Chemistry Department, FCTUC, University of Coimbra, 3004-535 Coimbra, Portugal; (P.A.T.M.); (E.F.B.)
| | - Biebele Abel
- Laboratory of Cell Biology, CCR, National Cancer Institute, NIH, Bethesda, MD 20892, USA; (B.A.); (S.V.A.)
| | - Suresh V. Ambudkar
- Laboratory of Cell Biology, CCR, National Cancer Institute, NIH, Bethesda, MD 20892, USA; (B.A.); (S.V.A.)
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6
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Cholesterol as a modulator of cannabinoid receptor CB 2 signaling. Sci Rep 2021; 11:3706. [PMID: 33580091 PMCID: PMC7881127 DOI: 10.1038/s41598-021-83245-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 01/20/2021] [Indexed: 11/21/2022] Open
Abstract
Signaling through integral membrane G protein-coupled receptors (GPCRs) is influenced by lipid composition of cell membranes. By using novel high affinity ligands of human cannabinoid receptor CB2, we demonstrate that cholesterol increases basal activation levels of the receptor and alters the pharmacological categorization of these ligands. Our results revealed that (2-(6-chloro-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)imino)benzo[d]thiazol-3(2H)-yl)ethyl acetate ligand (MRI-2646) acts as a partial agonist of CB2 in membranes devoid of cholesterol and as a neutral antagonist or a partial inverse agonist in cholesterol-containing membranes. The differential effects of a specific ligand on activation of CB2 in different types of membranes may have implications for screening of drug candidates in a search of modulators of GPCR activity. MD simulation suggests that cholesterol exerts an allosteric effect on the intracellular regions of the receptor that interact with the G-protein complex thereby altering the recruitment of G protein.
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7
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Binding specificity of ostreolysin A6 towards Sf9 insect cell lipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183307. [PMID: 32298680 DOI: 10.1016/j.bbamem.2020.183307] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 02/24/2020] [Accepted: 04/07/2020] [Indexed: 01/05/2023]
Abstract
Oyster mushrooms (Pleurotus spp.) have recently been shown to produce insecticidal bi-component protein complexes based on the aegerolysin proteins. A role for these proteins is thus indicated for defence and protection of the mushroom, and we propose their use as new environmentally friendly bioinsecticides. These aegerolysin-based protein complexes permeabilise artificial lipid vesicles through aegerolysin binding to an insect-specific sphingolipid, ceramide phosphoethanolamine (CPE), and they are cytotoxic for the Spodoptera frugiferda (Sf9) insect cell line. Tandem mass spectrometry analysis of the Sf9 lipidome uncovered lipids not previously reported in the literature, including in particular C14 sphingosine-based CPE molecular species, which comprised ~4 mol% of the whole lipidome. Further analysis of the lipid binding specificity of an aegerolysin from P. ostreatus, ostreolysin A6 (OlyA6), to lipid vesicles composed of commercial lipids, to lipid vesicles composed of the total lipid extract from Sf9 cells, and to HPLC-separated Sf9 cell lipid fractions containing ceramides, confirmed CPE as the main OlyA6 receptor, but also highlighted the importance of membrane cholesterol for formation of strong and stable interactions of OlyA6 with artificial and natural lipid membranes. Binding assays performed with glycan arrays and surface plasmon resonance, which included invertebrate-specific glycans, excluded these saccharides as potential additional OlyA6 receptors.
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8
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Muresan XM, Narzt MS, Woodby B, Ferrara F, Gruber F, Valacchi G. Involvement of cutaneous SR-B1 in skin lipid homeostasis. Arch Biochem Biophys 2019; 666:1-7. [DOI: 10.1016/j.abb.2019.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 03/06/2019] [Accepted: 03/09/2019] [Indexed: 12/16/2022]
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9
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Morel E, Ghezzal S, Lucchi G, Truntzer C, Pais de Barros JP, Simon-Plas F, Demignot S, Mineo C, Shaul PW, Leturque A, Rousset M, Carrière V. Cholesterol trafficking and raft-like membrane domain composition mediate scavenger receptor class B type 1-dependent lipid sensing in intestinal epithelial cells. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1863:199-211. [PMID: 29196159 DOI: 10.1016/j.bbalip.2017.11.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 11/13/2017] [Accepted: 11/27/2017] [Indexed: 02/02/2023]
Abstract
Scavenger receptor Class B type 1 (SR-B1) is a lipid transporter and sensor. In intestinal epithelial cells, SR-B1-dependent lipid sensing is associated with SR-B1 recruitment in raft-like/ detergent-resistant membrane domains and interaction of its C-terminal transmembrane domain with plasma membrane cholesterol. To clarify the initiating events occurring during lipid sensing by SR-B1, we analyzed cholesterol trafficking and raft-like domain composition in intestinal epithelial cells expressing wild-type SR-B1 or the mutated form SR-B1-Q445A, defective in membrane cholesterol binding and signal initiation. These features of SR-B1 were found to influence both apical cholesterol efflux and intracellular cholesterol trafficking from plasma membrane to lipid droplets, and the lipid composition of raft-like domains. Lipidomic analysis revealed likely participation of d18:0/16:0 sphingomyelin and 16:0/0:0 lysophosphatidylethanolamine in lipid sensing by SR-B1. Proteomic analysis identified proteins, whose abundance changed in raft-like domains during lipid sensing, and these included molecules linked to lipid raft dynamics and signal transduction. These findings provide new insights into the role of SR-B1 in cellular cholesterol homeostasis and suggest molecular links between SR-B1-dependent lipid sensing and cell cholesterol and lipid droplet dynamics.
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Affiliation(s)
- Etienne Morel
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France
| | - Sara Ghezzal
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France
| | - Géraldine Lucchi
- Clinical Innovation Proteomic Platform CLIPP, Université Bourgogne Franche-Comté, F-21000 Dijon, France
| | - Caroline Truntzer
- Clinical Innovation Proteomic Platform CLIPP, Université Bourgogne Franche-Comté, F-21000 Dijon, France
| | - Jean-Paul Pais de Barros
- Plateforme de Lipidomique, INSERM UMR1231, Université de Bourgogne Franche Comté, F-21000 Dijon, France
| | - Françoise Simon-Plas
- Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, F-21000 Dijon, France
| | - Sylvie Demignot
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France; EPHE, PSL Research University, F-75006 Paris, France
| | - Chieko Mineo
- Center for Pulmonary and Vascular Biology, Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Philip W Shaul
- Center for Pulmonary and Vascular Biology, Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Armelle Leturque
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France
| | - Monique Rousset
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France
| | - Véronique Carrière
- Centre de Recherche des Cordeliers, INSERM, UMPC Université Paris 6, Université Paris Descartes Paris 5, CNRS, F-75006 Paris, France.
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10
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Chadwick AC, Holme RL, Chen Y, Thomas MJ, Sorci-Thomas MG, Silverstein RL, Pritchard KA, Sahoo D. Acrolein impairs the cholesterol transport functions of high density lipoproteins. PLoS One 2015; 10:e0123138. [PMID: 25849485 PMCID: PMC4388475 DOI: 10.1371/journal.pone.0123138] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 02/17/2015] [Indexed: 12/22/2022] Open
Abstract
High density lipoproteins (HDL) are considered athero-protective, primarily due to their role in reverse cholesterol transport, where they transport cholesterol from peripheral tissues to the liver for excretion. The current study was designed to determine the impact of HDL modification by acrolein, a highly reactive aldehyde found in high abundance in cigarette smoke, on the cholesterol transport functions of HDL. HDL was chemically-modified with acrolein and immunoblot and mass spectrometry analyses confirmed apolipoprotein crosslinking, as well as acrolein adducts on apolipoproteins A-I and A-II. The ability of acrolein-modified HDL (acro-HDL) to serve as an acceptor of free cholesterol (FC) from COS-7 cells transiently expressing SR-BI was significantly decreased. Further, in contrast to native HDL, acro-HDL promotes higher neutral lipid accumulation in murine macrophages as judged by Oil Red O staining. The ability of acro-HDL to mediate efficient selective uptake of HDL-cholesteryl esters (CE) into SR-BI-expressing cells was reduced compared to native HDL. Together, the findings from our studies suggest that acrolein modification of HDL produces a dysfunctional particle that may ultimately promote atherogenesis by impairing functions that are critical in the reverse cholesterol transport pathway.
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Affiliation(s)
- Alexandra C. Chadwick
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Rebecca L. Holme
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Yiliang Chen
- Blood Research Institute, Blood Center of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Michael J. Thomas
- Department of Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America
| | - Mary G. Sorci-Thomas
- Department of Pathology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America
| | - Roy L. Silverstein
- Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Blood Research Institute, Blood Center of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Kirkwood A. Pritchard
- Department of Surgery, Children’s Research Institute, Milwaukee, Wisconsin, United States of America
| | - Daisy Sahoo
- Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- * E-mail:
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11
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Etebari K, Hussain M, Asgari S. Suppression of scavenger receptors transcription by parasitoid factors. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2012; 38:517-524. [PMID: 23000265 DOI: 10.1016/j.dci.2012.08.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Revised: 08/28/2012] [Accepted: 08/28/2012] [Indexed: 06/01/2023]
Abstract
Scavenger receptors (SR) are a group of membrane proteins that play central roles in various functions, such as immune responses in insects. Members of different SR classes were identified from Plutella xylostella larval transcriptome. SR B1 and B3 were found to be differentially expressed in larvae and pupae. Expression of P. xylostella SR genes was significantly altered during immune challenge induced in P. xylostella cells (Px) and parasitized larvae. Maternal factors injected into the larvae by the endoparasitoid wasp Diadegma semiclausum at oviposition include venom and ichnovirus (DsIV) genes to suppress the host immune system. Transient expression of two DsIV genes, Vankyrin1 and Repeat element 4 (Rep4), in Px cells led to significant down-regulation of both SR B1 and B3 transcript levels, while DsIV Rep4 expression did not change the relative transcription levels of SR B3. In conclusion, it appears that the two members of the SR family play important roles in innate immune responses in P. xylostella and that each member of this group may play different roles in the host-parasitoid interaction.
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Affiliation(s)
- Kayvan Etebari
- School of Biological Sciences, The University of Queensland, St. Lucia, Australia
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12
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Cigarette smoke affects keratinocytes SRB1 expression and localization via H2O2 production and HNE protein adducts formation. PLoS One 2012; 7:e33592. [PMID: 22442701 PMCID: PMC3307738 DOI: 10.1371/journal.pone.0033592] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/11/2012] [Indexed: 11/19/2022] Open
Abstract
Scavenger Receptor B1 (SR-B1), also known as HDL receptor, is involved in cellular cholesterol uptake. Stratum corneum (SC), the outermost layer of the skin, is composed of more than 25% cholesterol. Several reports support the view that alteration of SC lipid composition may be the cause of impaired barrier function which gives rise to several skin diseases. For this reason the regulation of the genes involved in cholesterol uptake is of extreme significance for skin health. Being the first shield against external insults, the skin is exposed to several noxious substances and among these is cigarette smoke (CS), which has been recently associated with various skin pathologies. In this study we first have shown the presence of SR-B1 in murine and human skin tissue and then by using immunoblotting, immunoprecipitation, RT-PCR, and confocal microscopy we have demonstrated the translocation and the subsequent lost of SR-B1 in human keratinocytes (cell culture model) after CS exposure is driven by hydrogen peroxide (H2O2) that derives not only from the CS gas phase but mainly from the activation of cellular NADPH oxidase (NOX). This effect was reversed when the cells were pretreated with NOX inhibitors or catalase. Furthermore, CS caused the formation of SR-B1-aldheydes adducts (acrolein and 4-hydroxy-2-nonenal) and the increase of its ubiquitination, which could be one of the causes of SR-B1 loss. In conclusion, exposure to CS, through the production of H2O2, induced post-translational modifications of SR-B1 with the consequence lost of the receptor and this may contribute to the skin physiology alteration as a consequence of the variation of cholesterol uptake.
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13
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McIntosh AL, Atshaves BP, Storey SM, Landrock KK, Landrock D, Martin GG, Kier AB, Schroeder F. Loss of liver FA binding protein significantly alters hepatocyte plasma membrane microdomains. J Lipid Res 2012; 53:467-480. [PMID: 22223861 PMCID: PMC3276470 DOI: 10.1194/jlr.m019919] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Revised: 12/21/2011] [Indexed: 12/13/2022] Open
Abstract
Although lipid-rich microdomains of hepatocyte plasma membranes serve as the major scaffolding regions for cholesterol transport proteins important in cholesterol disposition, little is known regarding intracellular factors regulating cholesterol distribution therein. On the basis of its ability to bind cholesterol and alter hepatic cholesterol accumulation, the cytosolic liver type FA binding protein (L-FABP) was hypothesized to be a candidate protein regulating these microdomains. Compared with wild-type hepatocyte plasma membranes, L-FABP gene ablation significantly increased the proportion of cholesterol-rich microdomains. Lack of L-FABP selectively increased cholesterol, phospholipid (especially phosphatidylcholine), and branched-chain FA accumulation in the cholesterol-rich microdomains. These cholesterol-rich microdomains are important, owing to enrichment therein of significant amounts of key transport proteins involved in uptake of cholesterol [SR-B1, ABCA-1, P-glycoprotein (P-gp), sterol carrier binding protein (SCP-2)], FA transport protein (FATP), and glucose transporters 1 and 2 (GLUT1, GLUT2) insulin receptor. L-FABP gene ablation enhanced the concentration of SCP-2, SR-B1, FATP4, and GLUT1 in the cholesterol-poor microdomains, with functional implications in HDL-mediated uptake and efflux of cholesterol. Thus L-FABP gene ablation significantly impacted the proportion of cholesterol-rich versus -poor microdomains in the hepatocyte plasma membrane and altered the distribution of lipids and proteins involved in cholesterol uptake therein.
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Affiliation(s)
- Avery L McIntosh
- Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Barbara P Atshaves
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI 48824
| | - Stephen M Storey
- Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Kerstin K Landrock
- Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Danilo Landrock
- Department of Pathobiology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Gregory G Martin
- Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Ann B Kier
- Department of Pathobiology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
| | - Friedhelm Schroeder
- Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and.
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14
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Valacchi G, Sticozzi C, Lim Y, Pecorelli A. Scavenger receptor class B type I: a multifunctional receptor. Ann N Y Acad Sci 2011; 1229:E1-7. [DOI: 10.1111/j.1749-6632.2011.06205.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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15
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Scavenger receptor class B type I and the hypervariable region-1 of hepatitis C virus in cell entry and neutralisation. Expert Rev Mol Med 2011; 13:e13. [PMID: 21489334 DOI: 10.1017/s1462399411001785] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hepatitis C virus (HCV) infection is a leading cause of chronic liver disease worldwide and represents a major public health problem. Viral attachment and entry - the first encounter of the virus with the host cell - are major targets of neutralising immune responses. Thus, a detailed understanding of the HCV entry process offers interesting opportunities for the development of novel therapeutic strategies. Different cellular or soluble host factors mediate HCV entry, and considerable progress has been made in recent years to decipher how they induce HCV attachment, internalisation and membrane fusion. Among these factors, the scavenger receptor class B type I (SR-BI/SCARB1) is essential for HCV replication in vitro, through its interaction with the HCV E1E2 surface glycoproteins and, more particularly, the HVR1 segment located in the E2 protein. SR-BI is an interesting receptor because HCV, whose replication cycle intersects with lipoprotein metabolism, seems to exploit some aspects of its physiological functions, such as cholesterol transfer from high-density lipoprotein (HDL), during cell entry. SR-BI is also involved in neutralisation attenuation and therefore could be an important target for therapeutic intervention. Recent results suggest that it should be possible to identify inhibitors of the interaction of HCV with SR-BI that do not impair its important physiological properties, as discussed in this review.
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16
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Nieland TJ, Xu S, Penman M, Krieger M. Negatively cooperative binding of high-density lipoprotein to the HDL receptor SR-BI. Biochemistry 2011; 50:1818-30. [PMID: 21254782 PMCID: PMC3065119 DOI: 10.1021/bi101657j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Scavenger receptor class B, type I (SR-BI), is a high-density lipoprotein (HDL) receptor, which also binds low-density lipoprotein (LDL), and mediates the cellular selective uptake of cholesteryl esters from lipoproteins. SR-BI also is a coreceptor for hepatitis C virus and a signaling receptor that regulates cell metabolism. Many investigators have reported that lipoproteins bind to SR-BI via a single class of independent (not interacting), high-affinity binding sites (one site model). We have reinvestigated the ligand concentration dependence of (125)I-HDL binding to SR-BI and SR-BI-mediated specific uptake of [(3)H]CE from [(3)H]CE-HDL using an expanded range of ligand concentrations (<1 μg of protein/mL, lower than previously reported). Scatchard and nonlinear least-squares model fitting analyses of the binding and uptake data were both inconsistent with a single class of independent binding sites binding univalent lipoprotein ligands. The data are best fit by models in which SR-BI has either two independent classes of binding sites or one class of sites exhibiting negative cooperativity due to either classic allostery or ensemble effects ("lattice model"). Similar results were observed for LDL. Application of the "infinite dilution" dissociation rate method established that the binding of (125)I-HDL to SR-BI at 4 °C exhibits negative cooperativity. The unexpected complexity of the interactions of lipoproteins with SR-BI should be taken into account when interpreting the results of experiments that explore the mechanism(s) by which SR-BI mediates ligand binding, lipid transport, and cell signaling.
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Affiliation(s)
- Thomas J.F. Nieland
- Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, MA 02139
- Broad Institute of Harvard and MIT, 7 Cambridge Center, Cambridge, MA 02142
| | - Shangzhe Xu
- Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, MA 02139
| | - Marsha Penman
- Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, MA 02139
| | - Monty Krieger
- Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, MA 02139
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17
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Nieland TJF, Xu S, Penman M, Krieger M. Negatively cooperative binding of high-density lipoprotein to the HDL receptor SR-BI. Biochemistry 2011. [PMID: 21254782 DOI: 10.1021/bi1011657j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Scavenger receptor class B, type I (SR-BI), is a high-density lipoprotein (HDL) receptor, which also binds low-density lipoprotein (LDL), and mediates the cellular selective uptake of cholesteryl esters from lipoproteins. SR-BI also is a coreceptor for hepatitis C virus and a signaling receptor that regulates cell metabolism. Many investigators have reported that lipoproteins bind to SR-BI via a single class of independent (not interacting), high-affinity binding sites (one site model). We have reinvestigated the ligand concentration dependence of (125)I-HDL binding to SR-BI and SR-BI-mediated specific uptake of [(3)H]CE from [(3)H]CE-HDL using an expanded range of ligand concentrations (<1 μg of protein/mL, lower than previously reported). Scatchard and nonlinear least-squares model fitting analyses of the binding and uptake data were both inconsistent with a single class of independent binding sites binding univalent lipoprotein ligands. The data are best fit by models in which SR-BI has either two independent classes of binding sites or one class of sites exhibiting negative cooperativity due to either classic allostery or ensemble effects ("lattice model"). Similar results were observed for LDL. Application of the "infinite dilution" dissociation rate method established that the binding of (125)I-HDL to SR-BI at 4 °C exhibits negative cooperativity. The unexpected complexity of the interactions of lipoproteins with SR-BI should be taken into account when interpreting the results of experiments that explore the mechanism(s) by which SR-BI mediates ligand binding, lipid transport, and cell signaling.
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Affiliation(s)
- Thomas J F Nieland
- Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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18
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Mawatari H, Yoneda M, Fujita K, Nozaki Y, Shinohara Y, Sasaki H, Iida H, Takahashi H, Inamori M, Abe Y, Kobayashi N, Kubota K, Kirikoshi H, Nakajima A, Saito S. Association between phospholipids and free cholesterol in high-density lipoprotein and the response to hepatitis C treatment in Japanese with genotype 1b. J Viral Hepat 2010; 17:859-65. [PMID: 20070501 DOI: 10.1111/j.1365-2893.2009.01253.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Pegylated interferon and ribavirin combination therapy is the standard treatment for patients with chronic hepatitis C (CHC), but treatment failure can be difficult to predict. We and others have reported a relation between lipid values and sustained viral responses in patients with CHC. However, the relationship between lipid values and treatment failure has not been previously reported. The present study investigated the association between the profiles of phospholipids and free cholesterol (FC), the main constitutive ingredients of the surface of lipoprotein, classified according to particle size and hepatitis C treatment, and determined the usefulness of these parameters for predicting the outcome of treatment. Fifty-five patients with CHC (33 men and 22 women) were included in the study. The serum total cholesterol, triglyceride, phospholipids, and FC levels in the lipoprotein subclasses were determined using high-performance liquid chromatography with gel permeation columns, enabling the lipoproteins to be classified into 13 subclasses according to particle size. According to a univariate analysis, the treatment failure group had a significantly higher serum phospholipid level overall in the high-density lipoprotein (HDL) and medium HDL fractions as well as a higher serum FC level in the HDL fraction and all HDL subclass fractions compared with the corresponding values in the non-nonvirological response group. Higher serum phospholipid and FC concentrations in the HDL subclasses were predictive of a failure to respond in patients with genotype 1b.
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Affiliation(s)
- H Mawatari
- Gastroenterology Division, Yokohama City University School of Medicine, Fukuura, Kanazawa-ku, Yokohama City, Japan
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19
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Kamiya K, Kobayashi J, Yoshimura T, Tsumoto K. Confocal microscopic observation of fusion between baculovirus budded virus envelopes and single giant unilamellar vesicles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1625-31. [DOI: 10.1016/j.bbamem.2010.05.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 05/06/2010] [Accepted: 05/10/2010] [Indexed: 01/02/2023]
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20
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Truong TQ, Aubin D, Falstrault L, Brodeur MR, Brissette L. SR-BI, CD36, and caveolin-1 contribute positively to cholesterol efflux in hepatic cells. Cell Biochem Funct 2010; 28:480-9. [DOI: 10.1002/cbf.1680] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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21
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Storey SM, Atshaves BP, McIntosh AL, Landrock KK, Martin GG, Huang H, Ross Payne H, Johnson JD, Macfarlane RD, Kier AB, Schroeder F. Effect of sterol carrier protein-2 gene ablation on HDL-mediated cholesterol efflux from cultured primary mouse hepatocytes. Am J Physiol Gastrointest Liver Physiol 2010; 299:G244-54. [PMID: 20395534 PMCID: PMC2904118 DOI: 10.1152/ajpgi.00446.2009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2009] [Accepted: 04/13/2010] [Indexed: 01/31/2023]
Abstract
Although HDL-mediated cholesterol transport to the liver is well studied, cholesterol efflux from hepatocytes back to HDL is less well understood. Real-time imaging of efflux of 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-amino)-23,24-bisnor-5-cholen-3beta-ol (NBD-cholesterol), which is poorly esterified, and [(3)H]cholesterol, which is extensively esterified, from cultured primary hepatocytes of wild-type and sterol carrier protein-2 (SCP-2) gene-ablated mice showed that 1) NBD-cholesterol efflux was affected by the type of lipoprotein acceptor, i.e., HDL3 over HDL2; 2) NBD-cholesterol efflux was rapid (detected in 1-2 min) and resolved into fast [half time (t((1/2))) = 2.4 min, 6% of total] and slow (t((1/2)) = 26.5 min, 94% of total) pools, consistent with protein- and vesicle-mediated cholesterol transfer, respectively; 3) SCP-2 gene ablation increased efflux of NBD-cholesterol, as well as [(3)H]cholesterol, albeit less so due to competition by esterification of [(3)H]cholesterol, but not NBD-cholesterol; and 4) SCP-2 gene ablation increased initial rate (2.3-fold) and size (9.7-fold) of rapid effluxing sterol, suggesting an increased contribution of molecular cholesterol transfer. In addition, colocalization, double-immunolabeling fluorescence resonance energy transfer, and electron microscopy, as well as cross-linking coimmunoprecipitation, indicated that SCP-2 directly interacted with the HDL receptor, scavenger receptor class B type 1 (SRB1), in hepatocytes. Other membrane proteins in cholesterol efflux [SRB1 and ATP-binding cassettes (ABC) A-1, ABCG-1, ABCG-5, and ABCG-8] and several soluble/vesicle-associated proteins facilitating intracellular cholesterol trafficking (StARDs, NPCs, ORPs) were not upregulated. However, loss of SCP-2 elicited twofold upregulation of liver fatty acid-binding protein (L-FABP), a protein with lower affinity for cholesterol but higher cytosolic concentration than SCP-2. Ablation of SCP-2 and L-FABP decreased HDL-mediated NBD-cholesterol efflux. These results indicate that SCP-2 expression plays a significant role in HDL-mediated cholesterol efflux by regulating the size of rapid vs. slow cholesterol efflux pools and/or eliciting concomitant upregulation of L-FABP in cultured primary hepatocytes.
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Affiliation(s)
- Stephen M Storey
- Departmens of Physiology and Pharmacology, Texas Veterinary Medical Center, Texas A & M University, College Station, TX 77843-4466, USA
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22
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Cellular cholesterol delivery, intracellular processing and utilization for biosynthesis of steroid hormones. Nutr Metab (Lond) 2010; 7:47. [PMID: 20515451 PMCID: PMC2890697 DOI: 10.1186/1743-7075-7-47] [Citation(s) in RCA: 286] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Accepted: 06/01/2010] [Indexed: 11/28/2022] Open
Abstract
Steroid hormones regulate diverse physiological functions such as reproduction, blood salt balance, maintenance of secondary sexual characteristics, response to stress, neuronal function and various metabolic processes. They are synthesized from cholesterol mainly in the adrenal gland and gonads in response to tissue-specific tropic hormones. These steroidogenic tissues are unique in that they require cholesterol not only for membrane biogenesis, maintenance of membrane fluidity and cell signaling, but also as the starting material for the biosynthesis of steroid hormones. It is not surprising, then, that cells of steroidogenic tissues have evolved with multiple pathways to assure the constant supply of cholesterol needed to maintain optimum steroid synthesis. The cholesterol utilized for steroidogenesis is derived from a combination of sources: 1) de novo synthesis in the endoplasmic reticulum (ER); 2) the mobilization of cholesteryl esters (CEs) stored in lipid droplets through cholesteryl ester hydrolase; 3) plasma lipoprotein-derived CEs obtained by either LDL receptor-mediated endocytic and/or SR-BI-mediated selective uptake; and 4) in some cultured cell systems from plasma membrane-associated free cholesterol. Here, we focus on recent insights into the molecules and cellular processes that mediate the uptake of plasma lipoprotein-derived cholesterol, events connected with the intracellular cholesterol processing and the role of crucial proteins that mediate cholesterol transport to mitochondria for its utilization for steroid hormone production. In particular, we discuss the structure and function of SR-BI, the importance of the selective cholesterol transport pathway in providing cholesterol substrate for steroid biosynthesis and the role of two key proteins, StAR and PBR/TSO in facilitating cholesterol delivery to inner mitochondrial membrane sites, where P450scc (CYP11A) is localized and where the conversion of cholesterol to pregnenolone (the common steroid precursor) takes place.
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23
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Huang H, McIntosh AL, Atshaves BP, Ohno-Iwashita Y, Kier AB, Schroeder F. Use of dansyl-cholestanol as a probe of cholesterol behavior in membranes of living cells. J Lipid Res 2010; 51:1157-72. [PMID: 20008119 PMCID: PMC2853442 DOI: 10.1194/jlr.m003244] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 12/11/2009] [Indexed: 12/21/2022] Open
Abstract
While plasma membrane cholesterol-rich microdomains play a role in cholesterol trafficking, little is known about the appearance and dynamics of cholesterol through these domains in living cells. The fluorescent cholesterol analog 6-dansyl-cholestanol (DChol), its biochemical fractionation, and confocal imaging of L-cell fibroblasts contributed the following new insights: i) fluorescence properties of DChol were sensitive to microenvironment polarity and mobility; (ii) DChol taken up by L-cell fibroblasts was distributed similarly as cholesterol and preferentially into cholesterol-rich vs. -poor microdomains resolved by affinity chromatography of purified plasma membranes; iii) DChol reported similar polarity (dielectric constant near 18) but higher mobility near phospholipid polar head group region for cholesterol in purified cholesterol-rich versus -poor microdomains; and iv) real-time confocal imaging, quantitative colocalization analysis, and fluorescence resonance energy transfer with cholesterol-rich and -poor microdomain markers confirmed that DChol preferentially localized in plasma membrane cholesterol-rich microdomains of living cells. Thus, DChol sensed a unique, relatively more mobile microenvironment for cholesterol in plasma membrane cholesterol-rich microdomains, consistent with the known, more rapid exchange dynamics of cholesterol from cholesterol-rich than -poor microdomains.
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Affiliation(s)
- Huan Huang
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843
| | - Avery L. McIntosh
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843
| | - Barbara P. Atshaves
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824
| | - Yoshiko Ohno-Iwashita
- Biomembrane Research Group, Tokyo Metropolitan Institute of Gerontology, Tokyo 173-0015, Japan
| | - Ann B. Kier
- Department of Pathobiology, Texas A&M University, TVMC, College Station, TX 77843
| | - Friedhelm Schroeder
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843
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24
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Schroeder F, Huang H, McIntosh AL, Atshaves BP, Martin GG, Kier AB. Caveolin, sterol carrier protein-2, membrane cholesterol-rich microdomains and intracellular cholesterol trafficking. Subcell Biochem 2010; 51:279-318. [PMID: 20213548 DOI: 10.1007/978-90-481-8622-8_10] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
While the existence of membrane lateral microdomains has been known for over 30 years, interest in these structures accelerated in the past decade due to the discovery that cholesterol-rich microdomains serve important biological functions. It is increasingly appreciated that cholesterol-rich microdomains in the plasma membranes of eukaryotic cells represent an organizing nexus for multiple cellular proteins involved in transmembrane nutrient uptake (cholesterol, fatty acid, glucose, etc.), cell-signaling, immune recognition, pathogen entry, and many other roles. Despite these advances, however, relatively little is known regarding the organization of cholesterol itself in these plasma membrane microdomains. Although a variety of non-sterol markers indicate the presence of microdomains in the plasma membranes of living cells, none of these studies have demonstrated that cholesterol is enriched in these microdomains in living cells. Further, the role of cholesterol-rich membrane microdomains as targets for intracellular cholesterol trafficking proteins such as sterol carrier protein-2 (SCP-2) that facilitate cholesterol uptake and transcellular transport for targeting storage (cholesterol esters) or efflux is only beginning to be understood. Herein, we summarize the background as well as recent progress in this field that has advanced our understanding of these issues.
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Affiliation(s)
- Friedhelm Schroeder
- Department of Physiology and Pharmacology, Texas A&M University, TVMC College Station, TX, 77843-4466, USA.
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25
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Neumann S, Coudreuse DYM, van der Westhuyzen DR, Eckhardt ERM, Korswagen HC, Schmitz G, Sprong H. Mammalian Wnt3a is released on lipoprotein particles. Traffic 2009; 10:334-43. [PMID: 19207483 DOI: 10.1111/j.1600-0854.2008.00872.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Little is known about the release and intercellular transport of Wnt proteins from mammalian cells. Lipoproteins may act as carriers for the intercellular movement and gradient formation of the lipid-linked morphogens Wingless and Hedgehog in Drosophila. To investigate whether such a mechanism can occur in mammals, we have studied Wnt release in cultured mammalian cells. Wnt3a associated with lipoproteins in the culture medium and not with extracellular vesicles or exosomes. Although Wnt3a was associated with both high-density lipoproteins (HDL) and low-density lipoproteins, only HDL allowed Wnt3a release from mouse fibroblasts. Remarkably, Wnt3a lacking its palmitate moiety was released in a lipoprotein-independent manner, demonstrating the dual role of palmitoylation in membrane and lipoprotein binding. We additionally found that Wnt3a can be released from enterocyte cell lines on endogenously expressed lipoproteins. We further discuss the physiological implications of our findings.
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Affiliation(s)
- Sylvia Neumann
- Department of Membrane Enzymology, Bijvoet Center/Institute of Biomembranes, Utrecht University, Padualaan 8, Utrecht, The Netherlands.
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26
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Connelly MA. SR-BI-mediated HDL cholesteryl ester delivery in the adrenal gland. Mol Cell Endocrinol 2009; 300:83-8. [PMID: 18840501 DOI: 10.1016/j.mce.2008.09.011] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 09/04/2008] [Indexed: 10/21/2022]
Abstract
In adrenocortical cells, scavenger receptor class B, type I (SR-BI) is localized in specialized plasma membrane compartments, called microvillar channels, that retain high density lipoprotein particles (HDL) and are sites for the selective uptake of cholesteryl esters (CE). Formation of microvillar channels is regulated by adrenocorticotropic hormone (ACTH) and requires SR-BI expression. Subsequent to SR-BI-mediated delivery to the plasma membrane, HDL-CE is metabolized to free cholesterol by hormone sensitive lipase and transported to the mitochondria for steroid synthesis via START domain proteins. The relevance of SR-BI to adrenal steroidogenesis is evident by the impairment of glucocorticoid-mediated stress response in the absence of SR-BI-mediated HDL-CE uptake in mice. On the molecular level, SR-BI mediates HDL-CE selective uptake by forming a hydrophobic channel. In addition, SR-BI facilitates bi-directional flux of cholesterol by modifying the phospholipid content of the plasma membrane. SR-BI most likely accomplishes these functions by forming homo-oligomers in the plasma membrane. Examination of SR-BI oligomerization using fluorescence resonance energy transfer spectroscopy revealed that SR-BI multimerizes via its C-terminal region. Overall, SR-BI is the cell surface receptor responsible for selective uptake of lipoprotein cholesterol and its ultimate delivery to sites of hormone synthesis in steroidogenic tissues.
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Affiliation(s)
- Margery A Connelly
- Metabolic Diseases, Johnson & Johnson Pharmaceutical Research and Development, LLC, Welsh & McKean Roads, Spring House, PA 19477-0776, United States.
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27
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Dreux M, Dao Thi VL, Fresquet J, Guérin M, Julia Z, Verney G, Durantel D, Zoulim F, Lavillette D, Cosset FL, Bartosch B. Receptor complementation and mutagenesis reveal SR-BI as an essential HCV entry factor and functionally imply its intra- and extra-cellular domains. PLoS Pathog 2009; 5:e1000310. [PMID: 19229312 PMCID: PMC2636890 DOI: 10.1371/journal.ppat.1000310] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Accepted: 01/23/2009] [Indexed: 12/11/2022] Open
Abstract
HCV entry into cells is a multi-step and slow process. It is believed that the
initial capture of HCV particles by glycosaminoglycans and/or lipoprotein
receptors is followed by coordinated interactions with the scavenger receptor
class B type I (SR-BI), a major receptor of high-density lipoprotein (HDL), the
CD81 tetraspanin, and the tight junction protein Claudin-1, ultimately leading
to uptake and cellular penetration of HCV via low-pH endosomes.
Several reports have indicated that HDL promotes HCV entry through interaction
with SR-BI. This pathway remains largely elusive, although it was shown that HDL
neither associates with HCV particles nor modulates HCV binding to SR-BI. In
contrast to CD81 and Claudin-1, the importance of SR-BI has only been addressed
indirectly because of lack of cells in which functional complementation assays
with mutant receptors could be performed. Here we identified for the first time
two cell types that supported HCVpp and HCVcc entry upon ectopic SR-BI
expression. Remarkably, the undetectable expression of SR-BI in rat hepatoma
cells allowed unambiguous investigation of human SR-BI functions during HCV
entry. By expressing different SR-BI mutants in either cell line, our results
revealed features of SR-BI intracellular domains that influence HCV infectivity
without affecting receptor binding and stimulation of HCV entry induced by
HDL/SR-BI interaction. Conversely, we identified positions of SR-BI ectodomain
that, by altering HCV binding, inhibit entry. Finally, we characterized
alternative ectodomain determinants that, by reducing SR-BI cholesterol uptake
and efflux functions, abolish HDL-mediated infection-enhancement. Altogether, we
demonstrate that SR-BI is an essential HCV entry factor. Moreover, our results
highlight specific SR-BI determinants required during HCV entry and
physiological lipid transfer functions hijacked by HCV to favor infection. More than 180 million people are chronically infected by hepatitis C virus (HCV),
a leading cause of liver failure and cancer, stimulating the need to fully
define the biology of HCV infection for developing novel and effective
therapeutics. During the first steps of infection, the virus is taken up and
penetrates hepatocytes. HCV entry is thought to be a coordinated multi-step
process mediated by specific factors, including CD81, Claudin-1, and the
scavenger receptor BI (SR-BI). Whereas the involvement of CD81 and Claudin-1 was
demonstrated by rendering susceptible cells that are otherwise refractory, SR-BI
complementation assays were lacking, raising questions as to its functions
during HCV entry. Here, we identify one hepatoma rat cell line, in which SR-BI
complementation assay and targeted mutagenesis could be performed. We therefore
demonstrate that SR-BI is an essential HCV entry factor. Our results shed light
on SR-BI intracellular domain functions in HCV entry, and, further, emphasize
the remarkable capacity of HCV to hijack the lipid transfer function of SR-BI,
hence favoring infection.
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Affiliation(s)
- Marlène Dreux
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
| | - Viet Loan Dao Thi
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
| | - Judith Fresquet
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
| | | | | | - Géraldine Verney
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
| | - David Durantel
- Université de Lyon, UCB-Lyon1, IFR62; INSERM, U871; Hospices
civils de Lyon (HCL), Lyon, France
| | - Fabien Zoulim
- Université de Lyon, UCB-Lyon1, IFR62; INSERM, U871; Hospices
civils de Lyon (HCL), Lyon, France
| | - Dimitri Lavillette
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
| | - François-Loïc Cosset
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
- * E-mail:
| | - Birke Bartosch
- Université de Lyon, UCB-Lyon1, IFR128; INSERM, U758; Ecole
Normale Supérieure de Lyon, Lyon, France
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28
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McIntosh AL, Atshaves BP, Huang H, Gallegos AM, Kier AB, Schroeder F. Fluorescence techniques using dehydroergosterol to study cholesterol trafficking. Lipids 2008; 43:1185-208. [PMID: 18536950 PMCID: PMC2606672 DOI: 10.1007/s11745-008-3194-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2008] [Accepted: 05/09/2008] [Indexed: 12/22/2022]
Abstract
Cholesterol itself has very few structural/chemical features suitable for real-time imaging in living cells. Thus, the advent of dehydroergosterol [ergosta-5,7,9(11),22-tetraen-3beta-ol, DHE] the fluorescent sterol most structurally and functionally similar to cholesterol to date, has proven to be a major asset for real-time probing/elucidating the sterol environment and intracellular sterol trafficking in living organisms. DHE is a naturally occurring, fluorescent sterol analog that faithfully mimics many of the properties of cholesterol. Because these properties are very sensitive to sterol structure and degradation, such studies require the use of extremely pure (>98%) quantities of fluorescent sterol. DHE is readily bound by cholesterol-binding proteins, is incorporated into lipoproteins (from the diet of animals or by exchange in vitro), and for real-time imaging studies is easily incorporated into cultured cells where it co-distributes with endogenous sterol. Incorporation from an ethanolic stock solution to cell culture media is effective, but this process forms an aqueous dispersion of DHE crystals which can result in endocytic cellular uptake and distribution into lysosomes which is problematic in imaging DHE at the plasma membrane of living cells. In contrast, monomeric DHE can be incorporated from unilamellar vesicles by exchange/fusion with the plasma membrane or from DHE-methyl-beta-cyclodextrin (DHE-MbetaCD) complexes by exchange with the plasma membrane. Both of the latter techniques can deliver large quantities of monomeric DHE with significant distribution into the plasma membrane. The properties and behavior of DHE in protein-binding, lipoproteins, model membranes, biological membranes, lipid rafts/caveolae, and real-time imaging in living cells indicate that this naturally occurring fluorescent sterol is a useful mimic for probing the properties of cholesterol in these systems.
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Affiliation(s)
- Avery L. McIntosh
- Department of Physiology and Pharmacology Texas A&M University, TVMC College Station, TX 77843-4466
| | - Barbara P. Atshaves
- Department of Physiology and Pharmacology Texas A&M University, TVMC College Station, TX 77843-4466
| | - Huan Huang
- Department of Physiology and Pharmacology Texas A&M University, TVMC College Station, TX 77843-4466
| | - Adalberto M. Gallegos
- Department of Pathobiology Texas A&M University, TVMC College Station, TX 77843-4467
| | - Ann B. Kier
- Department of Pathobiology Texas A&M University, TVMC College Station, TX 77843-4467
| | - Friedhelm Schroeder
- Department of Physiology and Pharmacology Texas A&M University, TVMC College Station, TX 77843-4466
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Dreux M, Cosset FL. The scavenger receptor BI and its ligand, HDL: partners in crime against HCV neutralizing antibodies. J Viral Hepat 2007; 14 Suppl 1:68-76. [PMID: 17958646 DOI: 10.1111/j.1365-2893.2007.00919.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Better knowledge of the viral and host factors that determine HCV clearance vs. persistence at the acute stage of infection is needed in order to improve antiviral therapy and develop efficient vaccines. Spontaneous HCV clearance is associated with a strong, early and broad cellular immune response. Yet, several observations suggest that antibody-mediated neutralisation occurs during HCV infection in vivo and that polyclonal antibodies to HCV can be protective. The recent development of HCV infection assays has confirmed that sera from HCV-infected patients neutralise infection in vitro. Recent studies have demonstrated that Nt-antibodies, of narrow specificity, are induced during the early phase of infection and could play a role in controlling viral infection or clearance. Yet, high-titre, broadly cross-reacting Nt-antibodies are readily detected in chronically infected patients, suggesting that their effectiveness is limited in patients who do not resolve the disease. The factors that mitigate the impact of the Nt-antibody response need to be clarified. Here we review some essential features of the Nt-antibody responses to HCV. We then discuss an original mechanism that HCV may use in vivo to attenuate Nt-antibodies, which involves the hyper-variable region-1 of the HCV-E2 glycoprotein, high-density lipoprotein (HDL) and the physiologic activity of the scavenger receptor BI, a receptor shared by both HCV and HDL.
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Affiliation(s)
- M Dreux
- Université de Lyon, (UCB-Lyon1), IFR128, Lyon; INSERM, U758, Lyon, France
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30
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Dreux M, Boson B, Ricard-Blum S, Molle J, Lavillette D, Bartosch B, Pécheur EI, Cosset FL. The exchangeable apolipoprotein ApoC-I promotes membrane fusion of hepatitis C virus. J Biol Chem 2007; 282:32357-69. [PMID: 17761674 DOI: 10.1074/jbc.m705358200] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cell entry of hepatitis C virus (HCV) is strikingly linked to lipoproteins and their receptors. Particularly, high density lipoprotein (HDL) enhances infectivity of HCV by involving the lipid-transfer function of the scavenger receptor BI, a receptor for both HDL and HCV. Here, we demonstrate that apoC-I, an exchangeable apolipoprotein that predominantly resides in HDL, specifically enhances HCVcc and HCVpp infectivity and increases the fusion rates between viral and target membranes via a direct interaction with the HCV surface. We identify the hypervariable region 1, located at the N terminus of the HCV E2 glycoprotein, as an essential viral component that modulates apoC-I-mediated enhancement of HCV fusion properties. The affinity of apoC-I for the HCV membrane may predispose it for fusion with a target membrane via alterations of its outer phospholipid layer. Conversely, we found that excess apoC-I provided as lipoprotein-free protein induces the disruption of the HCV membrane and subsequent loss of infectivity. Furthermore, our data indicate that HDL neither interacts nor spontaneously exchanges apoC-I with HCV virions. Because apoC-I is not present in serum as a lipoprotein-free form, our results suggest that HDL-embedded apoC-I could be released from the lipoprotein particle through a fine-tuned mechanism regulated via a triple interplay between hypervariable region 1, HDL, and scavenger receptor BI, resulting in optimal apoC-I recruitment on the viral membrane. These results provide the first description of a host serum factor helping the fusion process of an enveloped virus.
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Affiliation(s)
- Marlène Dreux
- Université de Lyon, (UCB-Lyon1), IFR128, INSERM, U758, and Ecole Normale Supérieure de Lyon, Lyon, F-69007, France
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31
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Atshaves BP, McIntosh AL, Payne HR, Gallegos AM, Landrock K, Maeda N, Kier AB, Schroeder F. SCP-2/SCP-x gene ablation alters lipid raft domains in primary cultured mouse hepatocytes. J Lipid Res 2007; 48:2193-211. [PMID: 17609524 DOI: 10.1194/jlr.m700102-jlr200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although reverse cholesterol transport from peripheral cell types is mediated through plasma membrane microdomains termed lipid rafts, almost nothing is known regarding the existence, protein/lipid composition, or structure of these putative domains in liver hepatocytes, cells responsible for the net removal of cholesterol from the body. Lipid rafts purified from hepatocyte plasma membranes by a nondetergent affinity chromatography method were: i) present at 33 +/- 3% of total plasma membrane protein; ii) enriched in key proteins of the reverse cholesterol pathway [scavenger receptor class B type I (SR-B1), ABCA1, P-glycoprotein (P-gp), sterol carrier protein-2 (SCP-2)]; iii) devoid of caveolin-1; iv) enriched in cholesterol, sphingomyelin, GM1, and phospholipids low in polyunsaturated fatty acid and double bond index; and v) exhibited an intermediate liquid-ordered lipid phase with significant transbilayer fluidity gradient. Ablation of the gene encoding SCP-2 significantly altered lipid rafts to: i) increase the proportion of lipid rafts present, thereby increasing raft total content of ABCA1, P-gp, and SR-B1; ii) increase total phospholipids while decreasing GM1 in lipid rafts; iii) decrease the fluidity of lipid rafts, consistent with the increased intermediate liquid-ordered phase; and iv) abolish the lipid raft transbilayer fluidity gradient. Thus, despite the absence of caveolin-1 in liver hepatocytes, lipid rafts represented nearly one-third of the mouse hepatocyte plasma membrane proteins and displayed unique protein, lipid, and biophysical properties that were differentially regulated by SCP-2 expression.
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Affiliation(s)
- Barbara P Atshaves
- Department of Physiology and Pharmacology, Texas A&M University, Texas Veterinary Medical Center, College Station, TX 77843-4466, USA
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32
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Orlowski S, Coméra C, Tercé F, Collet X. Lipid rafts: dream or reality for cholesterol transporters? EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:869-85. [PMID: 17576551 DOI: 10.1007/s00249-007-0193-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 05/11/2007] [Accepted: 05/15/2007] [Indexed: 01/12/2023]
Abstract
As a key constituent of the cell membranes, cholesterol is an endogenous component of mammalian cells of primary importance, and is thus subjected to highly regulated homeostasis at the cellular level as well as at the level of the whole body. This regulation requires adapted mechanisms favoring the handling of cholesterol in aqueous compartments, as well as its transfer into or out of membranes, involving membrane proteins. A membrane exhibits functional properties largely depending on its lipid composition and on its structural organization, which very often involves cholesterol-rich microdomains. Then there is the appealing possibility that cholesterol may regulate its own transmembrane transport at a purely functional level, independently of any transcriptional regulation based on cholesterol-sensitive nuclear factors controling the expression level of lipid transport proteins. Indeed, the main cholesterol "transporters" presently believed to mediate for instance the intestinal absorption of cholesterol, that are SR-BI, NPC1L1, ABCA1, ABCG1, ABCG5/G8 and even P-glycoprotein, all present privileged functional relationships with membrane cholesterol-containing microdomains. In particular, they all more or less clearly induce membrane disorganization, supposed to facilitate cholesterol exchanges with the close aqueous medium. The actual lipid substrates handled by these transporters are not yet unambiguously determined, but they likely concern the components of membrane microdomains. Conversely, raft alterations may provide specific modulations of the transporter activities, as well as they can induce indirect effects via local perturbations of the membrane. Finally, these cholesterol transporters undergo regulated intracellular trafficking, with presumably some relationships to rafts which remain to be clarified.
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Affiliation(s)
- Stéphane Orlowski
- SB2SM/IBTS and URA 2096 CNRS, CEA, Centre de Saclay, 91191, Gif-sur-Yvette cedex, France.
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Parathath S, Darlington YF, de la Llera Moya M, Drazul-Schrader D, Williams DL, Phillips MC, Rothblat GH, Connelly MA. Effects of amino acid substitutions at glycine 420 on SR-BI cholesterol transport function. J Lipid Res 2007; 48:1386-95. [PMID: 17372332 DOI: 10.1194/jlr.m700086-jlr200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Scavenger receptor class B type I (SR-BI) facilitates the uptake of HDL cholesteryl esters (CEs) in a two-step process involving binding of HDL to its extracellular domain and transfer of HDL core CEs to a metabolically active membrane pool, where they are subsequently hydrolyzed by a neutral CE hydrolase. Recently, we characterized a mutant, G420H, which replaced glycine 420 in the extracellular domain of SR-BI with a histidine residue and had a profound effect on SR-BI function. The G420H mutant receptor exhibited a reduced ability to mediate selective HDL CE uptake and was unable to deliver HDL CE for hydrolysis, despite the fact that it retained the ability to bind HDL. This did not hold true if glycine 420 was replaced with an alanine residue; G420A maintained wild-type HDL binding and cholesterol transport activity. To further understand the role that glycine 420 plays in SR-BI function and why there was a disparity between replacing glycine 420 with a histidine versus an alanine, we generated a battery of point mutants by substituting glycine 420 with amino acids possessing side chains that were charged, hydrophobic, polar, or bulky and tested the resulting mutants for their ability to support HDL binding, HDL cholesterol transport, and delivery for hydrolysis. The results indicated that substitution with a negatively charged residue or a proline impaired cell surface expression of SR-BI or its interaction with HDL, respectively. Furthermore, substitution of glycine 420 with a positively charged residue reduced HDL CE uptake as well as its subsequent hydrolysis.
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Affiliation(s)
- Saj Parathath
- Department of Pharmacological Sciences, University Medical Center, Stony Brook University, Stony Brook, NY 11794-8651, USA
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Marsche G, Frank S, Raynes J, Kozarsky K, Sattler W, Malle E. The lipidation status of acute-phase protein serum amyloid A determines cholesterol mobilization via scavenger receptor class B, type I. Biochem J 2007; 402:117-24. [PMID: 17034364 PMCID: PMC1783981 DOI: 10.1042/bj20061406] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
During the acute-phase reaction, SAA (serum amyloid A) replaces apoA-I (apolipoprotein A-I) as the major HDL (high-density lipoprotein)-associated apolipoprotein. A remarkable portion of SAA exists in a lipid-free/lipid-poor form and promotes ABCA1 (ATP-binding cassette transporter A1)-dependent cellular cholesterol efflux. In contrast with lipid-free apoA-I and apoE, lipid-free SAA was recently reported to mobilize SR-BI (scavenger receptor class B, type I)-dependent cellular cholesterol efflux [Van der Westhuyzen, Cai, de Beer and de Beer (2005) J. Biol. Chem. 280, 35890-35895]. This unique property could strongly affect cellular cholesterol mobilization during inflammation. However, in the present study, we show that overexpression of SR-BI in HEK-293 cells (human embryonic kidney cells) (devoid of ABCA1) failed to mobilize cholesterol to lipid-free or lipid-poor SAA. Only reconstituted vesicles containing phospholipids and SAA promoted SR-BI-mediated cholesterol efflux. Cholesterol efflux from HEK-293 and HEK-293[SR-BI] cells to lipid-free and lipid-poor SAA was minimal, while efficient efflux was observed from fibroblasts and CHO cells (Chinese-hamster ovary cells) both expressing functional ABCA1. Overexpression of SR-BI in CHO cells strongly attenuated cholesterol efflux to lipid-free SAA even in the presence of an SR-BI-blocking IgG. This implies that SR-BI attenuates ABCA1-mediated cholesterol efflux in a way that is not dependent on SR-BI-mediated re-uptake of cholesterol. The present in vitro experiments demonstrate that the lipidation status of SAA is a critical factor governing cholesterol acceptor properties of this amphipathic apolipoprotein. In addition, we demonstrate that SAA mediates cellular cholesterol efflux via the ABCA1 and/or SR-BI pathway in a similar way to apoA-I.
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Affiliation(s)
- Gunther Marsche
- *Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, A-8010 Graz, Austria
| | - Sǎsa Frank
- *Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, A-8010 Graz, Austria
| | - John G. Raynes
- †Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K
| | - Karen F. Kozarsky
- ‡GlaxoSmithKline, 709 Swedeland Rd, King of Prussia, PA 19406, U.S.A
| | - Wolfgang Sattler
- *Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, A-8010 Graz, Austria
| | - Ernst Malle
- *Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, A-8010 Graz, Austria
- To whom correspondence should be addressed (email )
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Harder CJ, Meng A, Rippstein P, McBride HM, McPherson R. SR-BI undergoes cholesterol-stimulated transcytosis to the bile canaliculus in polarized WIF-B cells. J Biol Chem 2006; 282:1445-55. [PMID: 17105723 DOI: 10.1074/jbc.m604627200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The scavenger receptor BI (SR-BI) is highly expressed in hepatocytes, where it mediates the uptake of lipoprotein cholesterol, promotes the secretion of cholesterol into bile, and protects against atherosclerosis. Despite a strong correlation between the hepatic expression of SR-BI and biliary cholesterol secretion, little is known about SR-BI trafficking in response to changes in sterol availability. Using a well characterized polarized hepatocyte cell model, WIF-B, we determine that in cholesterol-depleted cells, SR-BI is extensively located on the basolateral surface, where it can access circulating lipoproteins. However, in response to cholesterol loading, SR-BI undergoes a slow transcytosis to the apical bile canaliculus independently of lipoprotein binding and new protein synthesis. In cholesterol-replete WIF-B cells, SR-BI that resides on the canalicular membrane is dynamically associated with defined microdomains and does not rapidly recycle to and from the subapical or basolateral regions. Taken together, these data demonstrate that hepatic SR-BI transcytosis is regulated by cholesterol and suggest that SR-BI has a stationary function on the bile canaliculus.
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Affiliation(s)
- Christopher J Harder
- Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, Ottawa, Ontario K1Y 4W7, Canada
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36
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Abstract
Scavenger receptor class B, type I (SR-BI) is the receptor for high density lipoprotein (HDL) that mediates cellular uptake of HDL cholesteryl ester (CE) and is a major route for cholesterol delivery to steroidogenic pathways. SR-BI is localized in specialized microvillar channel plasma membrane compartments that retain HDL and are sites for HDL CE selective uptake. In fact, adrenal gland microvillar channel formation is regulated by adrenocorticotropin hormone and requires SR-BI expression. SR-BI-mediated uptake of HDL CE is a two-step process requiring high affinity HDL binding followed by transfer of CE to the membrane. SR-BI delivers HDL CE to sites in the membrane where it is readily metabolized to free cholesterol by cell type-specific neutral CE hydrolases. The most likely candidate for the hydrolysis of HDL CE delivered via SR-BI in the adrenal gland is hormone sensitive lipase. New data in adrenocortical cells as well as the study of a mutant SR-BI receptor lend insight into the mechanism of cholesterol transfer from plasma HDL to the steroidogenic pathway in endocrine cells.
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Affiliation(s)
- Margery A Connelly
- Department of Pharmacological Sciences, University Medical Center, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA.
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