51
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Affiliation(s)
- Peter J Quinn
- Division of Life Sciences, King's College London, 150 Stamford Street, London SE1 9NN, UK
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52
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Khursigara C, Abul-Milh M, Lau B, Girón JA, Lingwood CA, Barnett Foster DE. Enteropathogenic Escherichia coli virulence factor bundle-forming pilus has a binding specificity for phosphatidylethanolamine. Infect Immun 2001; 69:6573-9. [PMID: 11598024 PMCID: PMC100029 DOI: 10.1128/iai.69.11.6573-6579.2001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The bundle-forming pilus (BFP) of enteropathogenic Escherichia coli (EPEC), an established virulence factor encoded on the EPEC adherence factor (EAF) plasmid, has been implicated in the formation of bacterial autoaggregates and in the localized adherence of EPEC to cultured epithelial cells. While understanding of the pathogenic mechanism of this organism is rapidly improving, a receptor ligand for BFP has not yet been identified. We now report, using both solid-phase and liposome binding assays, that BFP expression correlates with phosphatidylethanolamine (PE) binding. In a thin-layer chromatogram overlay assay, specific recognition of PE was documented for BFP-expressing strains, including E2348/69, a wild-type EPEC clinical isolate, as well as a laboratory strain, HB101, transformed with a bfp-carrying plasmid. Strains which did not express BFP did not bind PE, including a bfpA disruptional mutant of E2348/69, EAF plasmid-cured E2348/69, and HB101. E2348/69 also aggregated PE-containing liposomes but not phosphatidylcholine- or phosphatidylserine-containing liposomes, while BFP-negative strains did not produce aggregates with any tested liposomes. Purified BFP preparations bound commercial PE standards as well as a PE-containing band within lipid extracts from human epithelial cells and from E2348/69. Our results therefore indicate a specific interaction between BFP and PE and suggest that PE may serve as a BFP receptor for bacterial autoaggregation and may promote localized adherence to host cells, both of which contribute to bacterial pathogenesis.
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Affiliation(s)
- C Khursigara
- Department of Chemistry, Biology and Chemical Engineering, Ryerson University, Toronto, Ontario, Canada
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53
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Abraham EH, Sterling KM, Kim RJ, Salikhova AY, Huffman HB, Crockett MA, Johnston N, Parker HW, Boyle WE, Hartov A, Demidenko E, Efird J, Kahn J, Grubman SA, Jefferson DM, Robson SC, Thakar JH, Lorico A, Rappa G, Sartorelli AC, Okunieff P. Erythrocyte membrane ATP binding cassette (ABC) proteins: MRP1 and CFTR as well as CD39 (ecto-apyrase) involved in RBC ATP transport and elevated blood plasma ATP of cystic fibrosis. Blood Cells Mol Dis 2001; 27:165-80. [PMID: 11358378 DOI: 10.1006/bcmd.2000.0357] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In addition to the better-known roles of the erythrocyte in the transport of oxygen and carbon dioxide, the concept that the red blood cell is involved in the transport and release of ATP has been evolving (J. Luthje, Blut 59, 367, 1989; G. R. Bergfeld and T. Forrester, Cardiovasc. Res. 26, 40, 1992; M. L. Ellsworth et al., Am. J. Physiol. 269, H2155, 1995; R. S. Sprague et al., Am. J. Physiol. 275, H1726, 1998). Membrane proteins involved in the release of ATP from erythrocytes now appear to include members of the ATP binding cassette (ABC) family (C. F. Higgins, Annu. Rev. Cell Biol. 8, 67, 1992; C. F. Higgins, Cell 82, 693, 1995). In addition to defining physiologically the presence of ABC proteins in RBCs, accumulating gel electrophoretic evidence suggests that the cystic fibrosis transmembrane conductance regulator (CFTR) and the multidrug resistance-associated protein (MRP1), respectively, constitute significant proteins in the red blood cell membrane. As such, this finding makes the mature erythrocyte compartment a major mammalian repository of these important ABC proteins. Because of its relative structural simplicity and ready accessibility, the erythrocyte offers an ideal system to explore details of the physiological functions of ABC proteins. Moreover, the presence of different ABC proteins in a single membrane implies that interaction among these proteins and with other membrane proteins may be the norm and not the exception in terms of modulation of their functions.
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Affiliation(s)
- E H Abraham
- Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
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54
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Bobrowska-Hägerstrand M, Wróbel A, Rychlik B, Bartosz G, Söderström T, Shirataki Y, Motohashi N, Molnár J, Michalak K, Hägerstrand H. Monitoring of MRP-like activity in human erythrocytes: inhibitory effect of isoflavones. Blood Cells Mol Dis 2001; 27:894-900. [PMID: 11783953 DOI: 10.1006/bcmd.2001.0459] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A method to fluorometrically monitor efflux of 2',7'-bis-(carboxypropyl)-5(6)-carboxyfluorescein (BCPCF) from human erythrocytes was developed. Genistein, daidzein, sophoraisoflavone A, and licoisoflavone A induced 50% inhibition (IC(50)) of BCPCF efflux at 15-70 microM. The IC(50) value of the most efficient isoflavone, licoisoflavone A (15-25 microM), was comparable to that of indomethacin (approximately 10 microM) and markedly lower than for probenecid (100-200 microM), both known MRP1 inhibitors. Our results indicate that the human erythrocyte is a useful cell model in screening potential MRP inhibitors, that BCPCF is a good substrate for MRP, and that some isoflavones at low concentrations inhibit MRP-mediated efflux.
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55
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Pomorski T, Hrafnsdóttir S, Devaux PF, van Meer G. Lipid distribution and transport across cellular membranes. Semin Cell Dev Biol 2001; 12:139-48. [PMID: 11292380 DOI: 10.1006/scdb.2000.0231] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In eukaryotic cells, the membranes of different intracellular organelles have different lipid composition, and various biomembranes show an asymmetric distribution of lipid types across the membrane bilayer. Membrane lipid organization reflects a dynamic equilibrium of lipids moving across the bilayer in both directions. In this review, we summarize data supporting the role of specific membrane proteins in catalyzing transbilayer lipid movement, thereby controlling and regulating the distribution of lipids over the leaflets of biomembranes.
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Affiliation(s)
- T Pomorski
- Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands
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56
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Pantaler E, Kamp D, Haest CW. Acceleration of phospholipid flip-flop in the erythrocyte membrane by detergents differing in polar head group and alkyl chain length. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1509:397-408. [PMID: 11118549 DOI: 10.1016/s0005-2736(00)00322-9] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The detergents, alkyltrimethylammonium bromide, N-alkyl-N, N-dimethyl-3-ammonio-1-propanesulfonate (zwittergent), alkane sulfonate, alkylsulfate, alkyl-beta-D-glucopyranoside, alkyl-beta-D-maltoside, dodecanoyl-N-methylglucamide, polyethylene glycol monoalkyl ether and Triton X-100, all produce a concentration-dependent acceleration of the slow passive transbilayer movement of NBD-labeled phosphatidylcholine in the human erythrocyte membrane. Above a threshold concentration, which was well below the CMC and characteristic for each detergent, the flip rate increases exponentially upon an increase of the detergent concentration in the medium. The detergent-induced flip correlates with reported membrane-expanding effects of the detergents at antihemolytic concentrations. From the dependence of the detergent concentration required for a defined flip acceleration on the estimated membrane volume, membrane/water partition coefficients for the detergents could be determined and effective detergent concentrations in the membrane calculated. The effective membrane concentrations are similar for most types of detergents but are 10-fold lower for octaethylene glycol monoalkyl ether and Triton X-100. The effectiveness of a given type of detergent is rather independent of its alkyl chain length. Since detergents do not reduce the high temperature dependence of the flip process the detergent-induced flip is proposed to be due to an enhanced probability of formation of transient hydrophobic structural defects in the membrane barrier which may result from perturbation of the interfacial region of the bilayer by inserted detergent molecules.
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Affiliation(s)
- E Pantaler
- Institute for Problems of Cryobiology and Cryomedicine of the Ukrainian National Academy of Sciences, Kharkov
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57
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Mao Q, Deeley RG, Cole SP. Functional reconstitution of substrate transport by purified multidrug resistance protein MRP1 (ABCC1) in phospholipid vesicles. J Biol Chem 2000; 275:34166-72. [PMID: 10942765 DOI: 10.1074/jbc.m004584200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 190-kDa multidrug resistance protein MRP1 (ABCC1) is a polytopic transmembrane protein belonging to the ATP-binding cassette transporter superfamily. In addition to conferring resistance to various antineoplastic agents, MRP1 is a transporter of conjugated organic anions, including the cysteinyl leukotriene C(4) (LTC(4)). We previously characterized the ATPase activity of reconstituted immunoaffinity-purified native MRP1 and showed it could be stimulated by its organic anion substrates (Mao, Q., Leslie, E. M., Deeley, R. G., and Cole, S. P. C. (1999) Biochim. Biophys. Acta 1461, 69-82). Here we show that purified reconstituted MRP1 is also capable of active transport of its substrates. Thus LTC(4) uptake by MRP1 proteoliposomes was osmotically sensitive and could be inhibited by two MRP1-specific monoclonal antibodies. LTC(4) uptake was also markedly reduced by the competitive inhibitor, S-decyl-glutathione, as well as by the MRP1 substrates 17 beta-estradiol 17-beta-(d-glucuronide), oxidized glutathione, and vincristine in the presence of reduced glutathione. The K(m) for ATP and LTC(4) were 357 +/- 184 microm and 366 +/- 38 nm, respectively, and 2.14 +/- 0.75 microm for 17 beta-estradiol 17-beta-(d-glucuronide). Transport of vincristine required the presence of both ATP and GSH. Conversely, GSH transport was stimulated by vincristine and verapamil. Our data represent the first reconstitution of transport competent purified native MRP1 and confirm that MRP1 is an efflux pump, which can transport conjugated organic anions and co-transport vincristine together with GSH.
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Affiliation(s)
- Q Mao
- Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada
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58
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Lo YL. Phospholipids as multidrug resistance modulators of the transport of epirubicin in human intestinal epithelial Caco-2 cell layers and everted gut sacs of rats. Biochem Pharmacol 2000; 60:1381-90. [PMID: 11008132 DOI: 10.1016/s0006-2952(00)00451-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Phospholipids have been increasingly used as carriers for the delivery of a variety of drugs. Studies using cancer chemotherapeutic agents such as epirubicin encapsulated in liposomes, which are made of phospholipids and other ingredients, have generally shown reduced toxicity and enhanced therapeutic efficacy. The recent investigation of the role of P-glycoprotein (P-gp) in phospholipid translocation has opened a new area of research on the possible use of phospholipids as multidrug resistance (MDR) modulators. This study investigated the effects of liposomal encapsulation, empty liposome pretreatment, or free lipid pretreatment on the uptake and transport of epirubicin in the human colon adenocarcinoma cell line Caco-2 and in everted gut sacs of rat jejunum and ileum. Epirubicin uptake experiments, using a flow cytometer, showed that both liposomal encapsulation and empty liposome pretreatment increased the intracellular accumulation of epirubicin in Caco-2 cells significantly. These two treatments substantially increased apical-to-basolateral absorption of epirubicin across Caco-2 monolayers and markedly improved mucosal-to-serosal absorption of epirubicin in rat jejunum and ileum. Enhancement also was observed with both liposome encapsulation and empty liposome pretreatment in the reduction of basolateral-to-apical efflux of epirubicin across Caco-2 monolayers. However, because diffusion of free dipalmitoyl phosphatidylcholine (DPPC) or dipalmitoyl phosphatidylethanolamine (DPPE) lipids across the cell membrane is very slow, these free lipids showed marginal effects on absorption and/or secretion of epirubicin in both Caco-2 cells and rat gut sacs. The study suggests that inhibition of P-gp or other transporter proteins located in the intestines may be partially involved in the reduction of epirubicin efflux. In conclusion, the therapeutic efficacy of epirubicin may be improved by using phospholipids as excipients and MDR modulators in the formulations. Liposomal formulations may have important applications to circumvent drug resistance in cancer chemotherapy.
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Affiliation(s)
- Y L Lo
- Department of Pharmacy, Chia Nan University of Pharmacy and Science, Tainan Hsien, Taiwan 717, Republic of China.
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59
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Borst P, Zelcer N, van Helvoort A. ABC transporters in lipid transport. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1486:128-44. [PMID: 10856718 DOI: 10.1016/s1388-1981(00)00053-6] [Citation(s) in RCA: 220] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Since it was found that the P-glycoproteins encoded by the MDR3 (MDR2) gene in humans and the Mdr2 gene in mice are primarily phosphatidylcholine translocators, there has been increasing interest in the possibility that other ATP binding cassette (ABC) transporters are involved in lipid transport. The evidence reviewed here shows that the MDR1 P-glycoprotein and the multidrug resistance (-associated) transporter 1 (MRP1) are able to transport lipid analogues, but probably not major natural membrane lipids. Both transporters can transport a wide range of hydrophobic drugs and may see lipid analogues as just another drug. The MDR3 gene probably arose in evolution from a drug-transporting P-glycoprotein gene. Recent work has shown that the phosphatidylcholine translocator has retained significant drug transport activity and that this transport is inhibited by inhibitors of drug-transporting P-glycoproteins. Whether the phosphatidylcholine translocator also functions as a transporter of some drugs in vivo remains to be seen. Three other ABC transporters were recently shown to be involved in lipid transport: ABCR, also called Rim protein, was shown to be defective in Stargardt's macular dystrophy; this protein probably transports a complex of retinaldehyde and phosphatidylethanolamine in the retina of the eye. ABC1 was shown to be essential for the exit of cholesterol from cells and is probably a cholesterol transporter. A third example, the ABC transporter involved in the import of long-chain fatty acids into peroxisomes, is discussed in the chapter by Hettema and Tabak in this volume.
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Affiliation(s)
- P Borst
- Division of Molecular Biology and Centre for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam.
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60
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Daleke DL, Lyles JV. Identification and purification of aminophospholipid flippases. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1486:108-27. [PMID: 10856717 DOI: 10.1016/s1388-1981(00)00052-4] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transbilayer phospholipid asymmetry is a common structural feature of most biological membranes. This organization of lipids is generated and maintained by a number of phospholipid transporters that vary in lipid specificity, energy requirements and direction of transport. These transporters can be divided into three classes: (1) bidirectional, non-energy dependent 'scramblases', and energy-dependent transporters that move lipids (2) toward ('flippases') or (3) away from ('floppases') the cytofacial surface of the membrane. One of the more elusive members of this family is the plasma membrane aminophospholipid flippase, which selectively transports phosphatidylserine from the external to the cytofacial monolayer of the plasma membrane. This review summarizes the characteristics of aminophospholipid flippase activity in intact cells and describes current strategies to identify and isolate this protein. The biochemical characteristics of candidate flippases are critically compared and their potential role in flippase activity is evaluated.
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Affiliation(s)
- D L Daleke
- Department of Biochemistry and Molecular Biology and Medical Sciences Program, Indiana University, Bloomington 47405, USA.
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61
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Rauch C, Farge E. Endocytosis switch controlled by transmembrane osmotic pressure and phospholipid number asymmetry. Biophys J 2000; 78:3036-47. [PMID: 10827982 PMCID: PMC1300887 DOI: 10.1016/s0006-3495(00)76842-1] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The dynamics of endocytosis in living K562 cells was investigated after the osmotic pressure of the external medium was decreased and the transmembrane phospholipid number asymmetry was increased. When the external pressure was decreased by a factor of 0.54, a sudden inhibition of endocytosis was observed. Under these conditions, the endocytosis suddenly recovered after the phospholipid number asymmetry was increased. The phospholipid asymmetry was generated by the addition of exogenous phosphatidylserine, which is translocated by the endogenous flippase activity to the inner layer of the membrane. The recovery of endocytosis is thus consistent with the view that the phospholipid number asymmetry can act as a budding force for endocytosis. Moreover, we quantitatively predict both the inhibition and recovery of endocytosis as first-order phase transitions, using a general model that assumes the existence of a transmembrane surface tension asymmetry as the budding driving force. In this model, the tension asymmetry is considered to be elastically generated by the activity of phospholipid pumping. We finally propose that cells may trigger genetic transcription responses after the internalization of cytokine-receptor complexes, which could be controlled by variations in the cytosolic or external pressure.
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Affiliation(s)
- C Rauch
- Groupe "Mécanique et Génétique du Développement Embryonnaire," UMR 168 Physico-Chimie Curie, Institut Curie, 75248 Paris Cedex 05, France
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62
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Hipfner DR, Deeley RG, Cole SP. Structural, mechanistic and clinical aspects of MRP1. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1461:359-76. [PMID: 10581367 DOI: 10.1016/s0005-2736(99)00168-6] [Citation(s) in RCA: 278] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The cDNA encoding ATP-binding cassette (ABC) multidrug resistance protein MRP1 was originally cloned from a drug-selected lung cancer cell line resistant to multiple natural product chemotherapeutic agents. MRP1 is the founder of a branch of the ABC superfamily whose members (from species as diverse as plants and yeast to mammals) share several distinguishing structural features that may contribute to functional and mechanistic similarities among this subgroup of transport proteins. In addition to its role in resistance to natural product drugs, MRP1 (and related proteins) functions as a primary active transporter of structurally diverse organic anions, many of which are formed by the biotransformation of various endo- and xenobiotics by Phase II conjugating enzymes, such as the glutathione S-transferases. MRP1 is involved in a number of glutathione-related cellular processes. Glutathione also appears to play a key role in MRP1-mediated drug resistance. This article reviews the discovery of MRP1 and its relationships with other ABC superfamily members, and summarizes current knowledge of the structure, transport functions and relevance of this protein to in vitro and clinical multidrug resistance.
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Affiliation(s)
- D R Hipfner
- Cancer Research Laboratories, Queen's University, Kingston, Ont., Canada
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63
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The role of different P-glycoproteins in hepatobiliary secretion of fluorescently labeled short-chain phospholipids. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)32418-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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64
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Bevers EM, Comfurius P, Dekkers DW, Zwaal RF. Lipid translocation across the plasma membrane of mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1439:317-30. [PMID: 10446420 DOI: 10.1016/s1388-1981(99)00110-9] [Citation(s) in RCA: 286] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The plasma membrane, which forms the physical barrier between the intra- and extracellular milieu, plays a pivotal role in the communication of cells with their environment. Exchanging metabolites, transferring signals and providing a platform for the assembly of multi-protein complexes are a few of the major functions of the plasma membrane, each of which requires participation of specific membrane proteins and/or lipids. It is therefore not surprising that the two leaflets of the membrane bilayer each have their specific lipid composition. Although membrane lipid asymmetry has been known for many years, the mechanisms for maintaining or regulating the transbilayer lipid distribution are still not completely understood. Three major players have been presented over the past years: (1) an inward-directed pump specific for phosphatidylserine and phosphatidylethanolamine, known as aminophospholipid translocase; (2) an outward-directed pump referred to as 'floppase' with little selectivity for the polar headgroup of the phospholipid, but whose actual participation in transport of endogenous lipids has not been well established; and (3) a lipid scramblase, which facilitates bi-directional migration across the bilayer of all phospholipid classes, independent of the polar headgroup. Whereas a concerted action of aminophospholipid translocase and floppase could, in principle, account for the maintenance of lipid asymmetry in quiescent cells, activation of the scramblase and concomitant inhibition of the aminophospholipid translocase causes a collapse of lipid asymmetry, manifested by exposure of phosphatidylserine on the cell surface. In this article, each of these transporters will be discussed, and their physiological importance will be illustrated by the Scott syndrome, a bleeding disorder caused by impaired lipid scrambling. Finally, phosphatidylserine exposure during apoptosis will be briefly discussed in relation to inhibition of translocase and simultaneous activation of scramblase.
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Affiliation(s)
- E M Bevers
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.
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65
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Marx U, Polakowski T, Pomorski T, Lang C, Nelson H, Nelson N, Herrmann A. Rapid transbilayer movement of fluorescent phospholipid analogues in the plasma membrane of endocytosis-deficient yeast cells does not require the Drs2 protein. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 263:254-63. [PMID: 10429211 DOI: 10.1046/j.1432-1327.1999.00497.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Evidence is presented that endocytosis-deficient Saccharomyces cerevisiae end4 yeast cells rapidly internalize the fluorescent phospholipid analogues 1-palmitoyl-2-{6-[7-nitro-2,1, 3-benzoxadiazol-4-yl(NBD)amino] caproyl}phosphatidylcholine (P-C6-NBD-PtdCho) and P-C6-NBD-phosphatidylserine (P-C6-NBD-PtdSer). Both analogues redistributed between the exoplasmic and cytoplasmic leaflet with a half-time of < 15 min at 0 degrees C. The plateau of internalized analogues was about 70%. Transbilayer movement is probably protein-mediated, as the flip-flop of both analogues was very slow in liposomes composed of plasma-membrane lipids. Rapid analogue internalization was not abolished on depletion of intracellular ATP by about 90%. For P-C6-NBD-PtdCho only was a moderate decrease in the plateau of internalized analogues of about 20% observed, while that of P-C6-NBD-PtdSer was not affected. The Drs2 protein plays only a minor role, if any, in the rapid transbilayer movement of analogues in S. cerevisiae end4 cells. In S. cerevisiae end4 Deltadrs2 cells harbouring both an end4 allele and a drs2 null allele, about 60% and 50% of P-C6-NBD-PtdCho and P-C6-NBD-PtdSer, respectively, became internalized within 15 min at 0 degrees C. The preferential orientation of P-C6-NBD-PtdSer to the cytoplasmic leaflet is in qualitative agreement with the sequestering of endogenous phosphatidylserine to the cytoplasmic leaflet, as assessed by binding of annexin V. Virtually no binding of annexin V to spheroplasts of the parent wild-type strain or the mutant strains was observed. Likewise, no difference in the exposure of endogenous aminophospholipids to the exoplasmic leaflet between these strains was found by labelling with trinitrobenzenesulfonic acid. Thus, lipid asymmetry, at least of aminophospholipids, was preserved in S. cerevisiae end4 cells independently of the presence of the Drs2 protein.
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Affiliation(s)
- U Marx
- Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie/Biophysik, Germany
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66
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Raggers RJ, van Helvoort A, Evers R, van Meer G. The human multidrug resistance protein MRP1 translocates sphingolipid analogs across the plasma membrane. J Cell Sci 1999; 112 ( Pt 3):415-22. [PMID: 9885294 DOI: 10.1242/jcs.112.3.415] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recently, we have provided evidence that the ABC-transporter MDR1 P-glycoprotein translocates analogs of various lipid classes across the apical plasma membrane of polarized LLC-PK1 cells transfected with MDR1 cDNA. Here, we show that expression of the basolateral ABC-transporter MRP1 (the multidrug resistance protein) induced lipid transport to the exoplasmic leaflet of the basolateral plasma membrane of LLC-PK1 cells at 15 degreesC. C6-NBD-glucosylceramide synthesized on the cytosolic side of the Golgi complex, but not C6-NBD-sphingomyelin synthesized in the Golgi lumen, became accessible to depletion by BSA in the basal culture medium. This suggests the absence of vesicular traffic and direct translocation of C6-NBD-glucosylceramide by MRP1 across the basolateral membrane. In line with this, transport of the lipid to the exoplasmic leaflet depended on the intracellular glutathione concentration and was inhibited by the MRP1-inhibitors sulfinpyrazone and indomethacin, but not by the MDR1 P-glycoprotein inhibitor PSC 833. In contrast to the broad substrate specificity of the MDR1 P-glycoprotein, MRP1 selectively transported C6-NBD-glucosylceramide and C6-NBD-sphingomyelin, the latter only when it was released from the Golgi lumen by brefeldin A. This shows the specific nature of the lipid translocation. We conclude that the transport activity of MDR1 P-glycoprotein and MRP1 must be taken into account in studies on the transport of lipids to the cell surface.
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Affiliation(s)
- R J Raggers
- Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, PO Box 22700, The Netherlands
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67
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Frickenhaus S, Herrmann A, Heinrich R. Compensating lipid fluxes generated by the aminophospholipid translocase. Mol Membr Biol 1998; 15:213-20. [PMID: 10087508 DOI: 10.3109/09687689709044323] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
By a combined kinetic and thermodynamic model on the transbilayer dynamics and asymmetric distribution of lipids in the red blood cell, compensating lipid fluxes to the exoplasmic leaflet have been analysed, counterbalancing the active transport of aminophospholipids to the cytoplasmic monolayer by the aminophospholipid translocase. The compensating fluxes are assumed to be of passive nature generated by forces of lateral mechanical stress and of lipid concentration differences between the two monolayers. These forces are shown to be caused and maintained by the operation of the aminophospholipid translocase. Simulations reveal that a reduction of the compensating fluxes upon ATP-depletion can be attributed to the inhibition of the aminophospholipid translocase. Thus, a Mg(2+)- and ATP-dependence of the outward movement of phospholipid analogues in the plasma membrane of red blood cells can be expected independent of the existence and operation of an ATP-dependent 'floppase' activity.
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Affiliation(s)
- S Frickenhaus
- Humboldt-University Berlin, Institute of Biology, Germany.
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