101
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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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102
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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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103
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Bucher K, Belli S, Wunderli-Allenspach H, Krämer SD. P-glycoprotein in proteoliposomes with low residual detergent: the effects of cholesterol. Pharm Res 2007; 24:1993-2004. [PMID: 17497080 DOI: 10.1007/s11095-007-9326-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Accepted: 04/25/2007] [Indexed: 11/29/2022]
Abstract
PURPOSE There is evidence that cholesterol affects the ATPase and transport functions of P-glycoprotein (P-gp). To study the influence of cholesterol on P-gp in a well defined lipid environment, we reconstituted P-gp in egg phosphatidylcholine (PhC) and PhC/cholesterol proteoliposomes with negligible residual amounts of detergents. MATERIALS AND METHODS P-gp proteoliposomes were prepared by continuous dialysis from micelles consisting of P-gp, lipids, sodium dodecyl sulfate and cholate. Basal and modulator-induced ATPase activities were studied in an established enzyme assay. Modulator affinities to P-gp and to the lipid bilayers were determined by equilibrium dialysis. RESULTS In the absence of cholesterol the basal ATPase activity was six fold lower than in the presence of 20 or 40% cholesterol, and no P-gp binding and ATPase induction was detected for the tested modulators verapamil and progesterone. In proteoliposomes containing 20 and 40% cholesterol, respectively, the modulators showed significant P-gp binding and ATPase activation. The concentration of the modulators for half maximal activation of the ATPase was higher with 40% than with 20% cholesterol. CONCLUSIONS Cholesterol influences P-gp in three ways: (a) it enhances its basal ATPase activity, (b) it renders P-gp sensitive towards the modulators verapamil and progesterone and (c) it affects the modulator concentration at half maximal ATPase activation.
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Affiliation(s)
- Karsten Bucher
- Department of Chemistry and Applied Biosciences, Institute of Pharmaceutical Sciences, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
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104
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Spitzenberger TJ, Heilman D, Diekmann C, Batrakova E, Kabanov A, Gendelman HE, Elmquist WF, Persidsky Y. Novel delivery system enhances efficacy of antiretroviral therapy in animal model for HIV-1 encephalitis. J Cereb Blood Flow Metab 2007; 27:1033-42. [PMID: 17063148 PMCID: PMC3070745 DOI: 10.1038/sj.jcbfm.9600414] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Most potent antiretroviral drugs (e.g., HIV-1 protease inhibitors) poorly penetrate the blood-brain barrier. Brain distribution can be limited by the efflux transporter, P-glycoprotein (P-gp). The ability of a novel drug delivery system (block co-polymer P85) that inhibits P-gp, to increase the efficacy of antiretroviral drugs in brain was examined using a severe combined immunodeficiency (SCID) mouse model of HIV-1 encephalitis (HIVE). Severe combined immunodeficiency mice inoculated with HIV-1 infected human monocyte-derived macrophages (MDM) into the basal ganglia were treated with P85, antiretroviral therapy (ART) (zidovudine, lamivudine and nelfinavir (NEL)), or P85 and ART. Mice were killed on days 7 and 14, and brains were evaluated for levels of viral infection. Antiviral effects of NEL, P85, or their combination were evaluated in vitro using HIV-1 infected MDM and showed antiretroviral effects of P85 alone. In SCID mice injected with virus-infected MDM, the combination of ART-P85 and ART alone showed a significant decrease of HIV-1 p24 expressing MDM (25% and 33% of controls, respectively) at day 7 while P85 alone group was not different from control. At day 14, all treatment groups showed a significant decrease in percentage of HIV-1 infected MDM as compared with control. P85 alone and combined ART-P85 groups showed the most significant reduction in percentage of HIV-1 p24 expressing MDM (8% to 22% of control) that were superior to the ART alone group (38% of control). Our findings indicate major antiretroviral effects of P85 and enhanced in vivo efficacy of antiretroviral drugs when combined with P85 in a SCID mouse model of HIVE.
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Affiliation(s)
| | - David Heilman
- Center for Neurovirology and Neurodegenerative Disorders, Univ. Nebraska Medical Center, Omaha, NE 68198
- Dept. Pharmacology and Experimental Neuroscience, Univ. Nebraska Medical Center, Omaha, NE 68198
| | - Casey Diekmann
- Center for Neurovirology and Neurodegenerative Disorders, Univ. Nebraska Medical Center, Omaha, NE 68198
- Dept. Pharmacology and Experimental Neuroscience, Univ. Nebraska Medical Center, Omaha, NE 68198
| | - Elena Batrakova
- Dept. Pharmaceutical Sciences, Univ. Nebraska Medical Center, Omaha, NE 68198
| | - Alexander Kabanov
- Dept. Pharmaceutical Sciences, Univ. Nebraska Medical Center, Omaha, NE 68198
| | - Howard E. Gendelman
- Center for Neurovirology and Neurodegenerative Disorders, Univ. Nebraska Medical Center, Omaha, NE 68198
- Dept. Pharmacology and Experimental Neuroscience, Univ. Nebraska Medical Center, Omaha, NE 68198
| | - William F. Elmquist
- Dept. of Pharmaceutics, Univ. of Minnesota, Minneapolis, MN 55455
- Correspondence: William F. Elmquist, Department of Pharmaceutics, University of Minnesota, 308 Harvard Street SE, Minneapolis, MN 55455; Tel. (612) 625-0097; Fax (612) 626-2125;
| | - Yuri Persidsky
- Center for Neurovirology and Neurodegenerative Disorders, Univ. Nebraska Medical Center, Omaha, NE 68198
- Dept. Pharmacology and Experimental Neuroscience, Univ. Nebraska Medical Center, Omaha, NE 68198
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105
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Zastre J, Jackson JK, Wong W, Burt HM. Methoxypolyethylene Glycol-block-polycaprolactone Diblock Copolymers Reduce P-glycoprotein Efflux in the Absence of a Membrane Fluidization Effect while Stimulating P-glycoprotein ATPase Activity. J Pharm Sci 2007; 96:864-75. [PMID: 17094135 DOI: 10.1002/jps.20785] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We have previously shown that amphiphilic diblock copolymers composed of methoxypolyethylene glycol-b-polycaprolactone (MePEG-b-PCL) increased the cellular accumulation and reduced the basolateral to apical flux of the P-glycoprotein substrate, rhodamine 123 (R-123) in caco-2 cells. The purpose of this study was to investigate membrane perturbation effects of MePEG-b-PCL diblock copolymers with erythrocyte membranes and caco-2 cells and the effect on P-gp ATPase activity. The diblock copolymer MePEG(17)-b-PCL(5) induced increasing erythrocyte hemolysis at concentrations which correlated with increasing accumulation of R-123 into caco-2 cells. However, no increase in cellular accumulation of R-123 by non-P-gp expressing cells was observed, suggesting that diblock did not enhance the transmembrane passive diffusion of R-123, but that the accumulation enhancement effect of the diblock in caco-2 cells was likely mediated primarily via P-gp inhibition. Fluorescence anisotropy measurements of membrane fluidity and P-gp ATPase activity demonstrated that MePEG(17)-b-PCL(5) decreased caco-2 membrane fluidity while stimulating ATPase activity approximately threefold at concentrations that maximally enhanced R-123 caco-2 accumulation. These results suggest that inhibition of P-gp efflux by MePEG(17)-b-PCL(5) does not appear to be related to increases in membrane fluidity or through inhibition in P-gp ATPase activities, which are two commonly reported cellular effects for P-gp inhibition mediated by surfactants.
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Affiliation(s)
- Jason Zastre
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College St. Toronto, Ontario, Canada M5S 3M2
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106
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Sharom FJ. Shedding light on drug transport: structure and function of the P-glycoprotein multidrug transporter (ABCB1). Biochem Cell Biol 2007; 84:979-92. [PMID: 17215884 DOI: 10.1139/o06-199] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
P-glycoprotein (Pgp; ABCB1), a member of the ATP-binding cassette (ABC) superfamily, exports structurally diverse hydrophobic compounds from the cell, driven by ATP hydrolysis. Pgp expression has been linked to the efflux of chemotherapeutic drugs in human cancers, leading to multidrug resistance (MDR). The protein also plays an important physiological role in limiting drug uptake in the gut and entry into the brain. Substrates partition into the lipid bilayer before interacting with Pgp, which has been proposed to function as a hydrophobic vacuum cleaner. Low- and medium-resolution structural models of Pgp suggest that the 2 nucleotide-binding domains are closely associated to form a nucleotide sandwich dimer. Pgp is an outwardly directed flippase for fluorescent phospholipid and glycosphingolipid derivatives, which suggests that it may also translocate drug molecules from the inner to the outer membrane leaflet. The ATPase catalytic cycle of the protein is thought to proceed via an alternating site mechanism, although the details are not understood. The lipid bilayer plays an important role in Pgp function, and may regulate both the binding and transport of drugs. This review focuses on the structure and function of Pgp, and highlights the importance of fluorescence spectroscopic techniques in exploring the molecular details of this enigmatic transporter.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B
- ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- ATP Binding Cassette Transporter, Subfamily B, Member 1/physiology
- ATP-Binding Cassette Transporters/metabolism
- Adenosine Triphosphate/metabolism
- Animals
- Awards and Prizes
- Biological Transport/drug effects
- Drug Resistance, Multiple
- Humans
- Models, Biological
- Models, Molecular
- Organic Anion Transporters/metabolism
- Spectrometry, Fluorescence
- Structure-Activity Relationship
- Substrate Specificity
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Affiliation(s)
- Frances J Sharom
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
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107
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Burns MP, Igbavboa U, Wang L, Wood WG, Duff K. Cholesterol distribution, not total levels, correlate with altered amyloid precursor protein processing in statin-treated mice. Neuromolecular Med 2007; 8:319-28. [PMID: 16775383 DOI: 10.1385/nmm:8:3:319] [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] [Received: 12/06/2005] [Revised: 01/06/2006] [Accepted: 01/09/2006] [Indexed: 11/11/2022]
Abstract
There are now a number of studies that suggest that cholesterol might regulate the processing of the amyloid precursor protein to form the neurotoxic peptide Abeta. This research has opened the possibility that cholesterol-lowering drugs might be efficacious as anti-Abeta drugs for use in Alzheimer's disease. The use of HMG-CoA reductase inhibitors (commonly called statins) in vitro and in vivo has proven them to be Abeta-lowering agents, however, the mechanism of action of these drugs is not yet known. One possible mechanism is that they reduce Abeta levels indirectly by reducing cholesterol in the central nervous system (CNS). In this study, we administered three different statins (simvastatin, lovastatin, and atorvastatin) to nontransgenic mice. We found that all three compounds had similar effects on Abeta, reducing both Abeta40 and Abeta42. The statins decreased beta-cleaved C-terminal fragment (CTF) although having no effect on alpha-CTF levels. However, the drugs did not have a similar effect on cholesterol in the CNS. Only lovastatin significantly reduced total cholesterol in isolated plasma membranes. As cholesterol is not distributed evenly in the plasma membrane, we examined bilayer distribution of cholesterol and found that all three statins caused CNS cholesterol to translocate from the cytofacial leaflet to the exofacial leaflet. This data suggests that cholesterol distribution and not total cholesterol levels may be important to Abeta production in the CNS.
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Affiliation(s)
- Mark P Burns
- Center for Dementia Research, Nathan S. Kline Institute/New York University, Orangeburg, NY 10962, USA.
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108
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Pál A, Méhn D, Molnár E, Gedey S, Mészáros P, Nagy T, Glavinas H, Janáky T, von Richter O, Báthori G, Szente L, Krajcsi P. Cholesterol potentiates ABCG2 activity in a heterologous expression system: improved in vitro model to study function of human ABCG2. J Pharmacol Exp Ther 2007; 321:1085-94. [PMID: 17347325 DOI: 10.1124/jpet.106.119289] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
ABCG2, a transporter of the ATP-binding cassette family, is known to play a prominent role in the absorption, distribution, metabolism, and excretion of xenobiotics. Drug-transporter interactions are commonly screened by high-throughput systems using transfected insect and/or human cell lines. The determination of ABCG2-ATPase activity is one method to identify ABCG2 substrate and inhibitors. We demonstrate that the ATPase activities of the human ABCG2 transfected Sf9 cell membranes (MXR-Sf9) and ABCG2-overexpressing human cell membranes (MXR-M) differ. Variation due to disparity in the glycosylation level of the protein had no effect on the transporter. The influence of cholesterol on ABCG2-ATPase activity was investigated because the lipid compositions of insect and human cells are largely different from each other. Differences in cholesterol content, shown by cholesterol loading and depletion experiments, conferred the difference in stimulation of basal ABCG2-ATPase of the two cell membranes. Basal ABCG2-ATPase activity could be stimulated by sulfasalazine, prazosin, and topotecan, known substrates of ABCG2 in cholesterol-loaded MXR-Sf9 and MXR-M cell membranes. In contrast, ABCG2-ATPase could not be stimulated in MXR-Sf9 or in cholesterol-depleted MXR-M membranes. Moreover, cholesterol loading significantly improved the drug transport into inside-out membrane vesicles prepared from MXR-Sf9 cells. MXR-M and cholesterol-loaded MXR-Sf9 cell membranes displayed similar ABCG2-ATPase activity and vesicular transport. Our study indicates an essential role of membrane cholesterol for the function of ABCG2.
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Affiliation(s)
- A Pál
- SOLVO Biotechnology, Central Hungarian Innovations Center, Gyár u. 2., H-2040 Budaörs, Hungary
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109
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Meyer dos Santos S, Meyer Dos Santos S, Weber CC, Franke C, Müller WE, Eckert GP. Cholesterol: Coupling between membrane microenvironment and ABC transporter activity. Biochem Biophys Res Commun 2007; 354:216-21. [PMID: 17223079 DOI: 10.1016/j.bbrc.2006.12.202] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Accepted: 12/23/2006] [Indexed: 01/16/2023]
Abstract
Lipid composition of biological membranes is closely related to the function of the ATP-binding cassette (ABC) transporter P-Glycoprotein (Pgp). Herein, we studied how membrane physico-chemical properties affect Pgp-activity. We effectively modulated the cellular cholesterol content using methyl-beta-cyclodextrin (MbetaCD) and MbetaCD-cholesterol-inclusion complex. Pgp was not liberated from the plasma membrane during cholesterol modulation and functional inhibition of Pgp was related to varying cholesterol levels in the plasma membrane. Our data indicate that membrane fluidity does not solely account for cholesterol dependent modifications of Pgp-activity. Therefore, we isolated lipid rafts and examined distinct membrane microdomains. Both depletion and cholesterol enrichment induces a disassembly of lipid rafts. In cholesterol-depleted cell membranes a shift in the Pgp localisation to detergent soluble fractions was observed. Enrichment of membrane cholesterol changed lipid raft distribution but not the localisation of Pgp. From our data we conclude that Pgp-transport capacity depends on accurate lipid raft properties.
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Affiliation(s)
- Sascha Meyer dos Santos
- Department of Pharmacology, ZAFES, Biocenter Niederursel, N260, Max-von-Laue Str. 9, University of Frankfurt, Germany
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110
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Riou M, Grasseau I, Blesbois E, Kerboeuf D. Relationships between sterol/phospholipid composition and xenobiotic transport in nematodes. Parasitol Res 2007; 100:1125-34. [PMID: 17294217 DOI: 10.1007/s00436-006-0455-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Accepted: 12/22/2006] [Indexed: 10/23/2022]
Abstract
Therapeutic failure limits prophylaxis of nematode diseases and has been mainly attributed to mutations in cellular targets of anthelmintics. Besides these specific mechanisms, alterations of drug transport also occur in parasites resistant to anthelmintics and depend on both the presence of membrane pumps such as P-glycoprotein (Pgp) and on the lipid composition of membranes. We recently showed in the nematode Haemonchus contortus, using eggs as a model, that the total cholesterol (TC) concentration alters the transport of lipophilic molecules due to membrane pumps such as P-glycoprotein and the resistance to anthelmintics. The effect of TC may depend on the presence of other lipids interacting with TC. Therefore, we analysed the lipid composition and its relationship with Pgp and resistance to anthelmintics. Better correlations were found between Pgp and free cholesterol (FC) than with TC. We also showed that the relationships between lipid composition and resistance to anthelmintics or Pgp depended on the equilibrium between FC and phospholipids (PLs), mainly PLs known to be present primarily in either the external leaflets of cell membranes or the internal leaflets. The PLs phosphatidylcholine and phosphatidylethanolamine played the most significant role, but phosphatidic acid also influenced drug resistance.
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Affiliation(s)
- Mickaël Riou
- Multiresistances and Antiparasitic Drugs, INRA: UR1282, Animal Infections and Public Heath, IASP, 37380 Nouzilly, France
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111
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Bandyopadhyay A, Blakeslee JJ, Lee OR, Mravec J, Sauer M, Titapiwatanakun B, Makam SN, Bouchard R, Geisler M, Martinoia E, Friml J, Peer WA, Murphy AS. Interactions of PIN and PGP auxin transport mechanisms. Biochem Soc Trans 2007; 35:137-41. [PMID: 17233620 DOI: 10.1042/bst0350137] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Polarized transport of the plant hormone auxin influences multiple growth processes in plants and is regulated by plasma-membrane-localized efflux and uptake carriers. The PGP (P-glycoprotein) ABC transporters (ATP-binding-cassette transporters), PIN (pin-formed) subfamily of major facilitator proteins and members of AUX/LAX families have been shown to independently transport auxin both in planta and in heterologous systems. However, PIN- and PGP-mediated transport in heterologous systems exhibits decreased substrate specificity and inhibitor-sensitivity compared with what is seen in plants and plant cells. To determine whether PIN–PGP interactions enhance transport specificity, we analysed interactions of the representative auxin-transporting PGPs with PIN1 and AUX1 in planta and in heterologous systems. Here, we provide evidence that PINs and PGPs interact and function both independently and co-ordinately to control polar auxin transport and impart transport specificity and directionality. These interactions take place in protein complexes stabilized by PGPs in detergent-resistant microdomains.
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Affiliation(s)
- A Bandyopadhyay
- Department of Horticulture, Purdue University, West Lafayette, IN 47907-2010, USA
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112
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Kimura Y, Kioka N, Kato H, Matsuo M, Ueda K. Modulation of drug-stimulated ATPase activity of human MDR1/P-glycoprotein by cholesterol. Biochem J 2007; 401:597-605. [PMID: 17029589 PMCID: PMC1820799 DOI: 10.1042/bj20060632] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
MDR1 (multidrug resistance 1)/P-glycoprotein is an ATP-driven transporter which excretes a wide variety of structurally unrelated hydrophobic compounds from cells. It is suggested that drugs bind to MDR1 directly from the lipid bilayer and that cholesterol in the bilayer also interacts with MDR1. However, the effects of cholesterol on drug-MDR1 interactions are still unclear. To examine these effects, human MDR1 was expressed in insect cells and purified. The purified MDR1 protein was reconstituted in proteoliposomes containing various concentrations of cholesterol and enzymatic parameters of drug-stimulated ATPase were compared. Cholesterol directly binds to purified MDR1 in a detergent soluble form and the effects of cholesterol on drug-stimulated ATPase activity differ from one drug to another. The effects of cholesterol on K(m) values of drug-stimulated ATPase activity were strongly correlated with the molecular mass of that drug. Cholesterol increases the binding affinity of small drugs (molecular mass <500 Da), but does not affect that of drugs with a molecular mass of between 800 and 900 Da, and suppresses that of valinomycin (molecular mass >1000 Da). V(max) values for rhodamine B and paclitaxel are also increased by cholesterol, suggesting that cholesterol affects turnover as well as drug binding. Paclitaxel-stimulated ATPase activity of MDR1 is enhanced in the presence of stigmasterol, sitosterol and campesterol, as well as cholesterol, but not ergosterol. These results suggest that the drug-binding site of MDR1 may best fit drugs with a molecular mass of between 800 and 900 Da, and that cholesterol may support the recognition of smaller drugs by adjusting the drug-binding site and play an important role in the function of MDR1.
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Affiliation(s)
- Yasuhisa Kimura
- Laboratory of Cellular Biochemistry, Division of Applied Life Sciences, Kyoto University Graduate School of Agriculture, Kyoto 606-8502, Japan
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113
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Lespine A, Martin S, Dupuy J, Roulet A, Pineau T, Orlowski S, Alvinerie M. Interaction of macrocyclic lactones with P-glycoprotein: Structure–affinity relationship. Eur J Pharm Sci 2007; 30:84-94. [PMID: 17134887 DOI: 10.1016/j.ejps.2006.10.004] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 10/09/2006] [Accepted: 10/20/2006] [Indexed: 01/16/2023]
Abstract
P-glycoprotein (P-gp) is involved in the ATP-dependant cellular efflux of a large number of drugs including ivermectin, a macrocyclic lactone (ML) endectocide, widely used in livestock and human antiparasitic therapy. The interactions of P-gp with ivermectin and other MLs were studied. In a first approach, the ability of ivermectin (IVM), eprinomectin (EPR), abamectin (ABA), doramectin (DOR), selamectin (SEL), or moxidectin (MOX) to inhibit the rhodamine123 efflux was measured in recombinant cells overexpressing P-gp. Then, the influence of these compounds on the P-gp ATPase activity was tested on membrane vesicles prepared from fibroblasts overexpressing P-gp. All the MLs tested increased the intracellular rhodamine123. However, the potency of MOX to inhibit P-gp function was 10 times lower than the other MLs. They all inhibited the basal and decreased the verapamil-stimulated P-gp ATPase activity. But SEL and MOX were less potent than the other MLs when competing with verapamil. According to the structural specificity of SEL and MOX, we conclude that the integrity of the sugar moiety is determinant to achieve the optimal interaction of macrocyclic lactones with P-gp. The structure-affinity relationship for interaction with P-gp is important information for improving ML bioavailability and reversal of multidrug resistance (MDR).
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Affiliation(s)
- Anne Lespine
- INRA-UR66, Laboratoire de Pharmacologie-Toxicologie, BP 3, 31931 Toulouse Cedex 9, France.
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114
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Sarkadi B, Homolya L, Szakács G, Váradi A. Human multidrug resistance ABCB and ABCG transporters: participation in a chemoimmunity defense system. Physiol Rev 2006; 86:1179-236. [PMID: 17015488 DOI: 10.1152/physrev.00037.2005] [Citation(s) in RCA: 540] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In this review we give an overview of the physiological functions of a group of ATP binding cassette (ABC) transporter proteins, which were discovered, and still referred to, as multidrug resistance (MDR) transporters. Although they indeed play an important role in cancer drug resistance, their major physiological function is to provide general protection against hydrophobic xenobiotics. With a highly conserved structure, membrane topology, and mechanism of action, these essential transporters are preserved throughout all living systems, from bacteria to human. We describe the general structural and mechanistic features of the human MDR-ABC transporters and introduce some of the basic methods that can be applied for the analysis of their expression, function, regulation, and modulation. We treat in detail the biochemistry, cell biology, and physiology of the ABCB1 (MDR1/P-glycoprotein) and the ABCG2 (MXR/BCRP) proteins and describe emerging information related to additional ABCB- and ABCG-type transporters with a potential role in drug and xenobiotic resistance. Throughout this review we demonstrate and emphasize the general network characteristics of the MDR-ABC transporters, functioning at the cellular and physiological tissue barriers. In addition, we suggest that multidrug transporters are essential parts of an innate defense system, the "chemoimmunity" network, which has a number of features reminiscent of classical immunology.
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Affiliation(s)
- Balázs Sarkadi
- National Medical Center, Institute of Hematology and Immunology, Membrane Research Group, Budapest, Hungary.
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115
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Pashkovskaya AA, Lukashev EP, Antonov PE, Finogenova OA, Ermakov YA, Melik-Nubarov NS, Antonenko YN. Grafting of polylysine with polyethylenoxide prevents demixing of O-pyromellitylgramicidin in lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:1685-95. [PMID: 16901462 DOI: 10.1016/j.bbamem.2006.06.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Revised: 05/19/2006] [Accepted: 06/06/2006] [Indexed: 01/24/2023]
Abstract
Both natural and synthetic polycations can induce demixing of negatively charged components in artificial and possibly in natural membranes. This process can result in formation of clusters (binding of several components to a polycation chain) and/or domains (aggregation of clusters and formation of a separate phase enriched in some particular component). In order to distinguish between these two phenomena, a model lipid membrane system containing ion channels, formed by a negatively charged peptide, O-pyromellitylgramicidin, and polycations of different structures was used. Microelectrophoresis of liposomes, changes in boundary potential of planar bilayers, the shape of compression curves and potentials of lipid and lipid/peptide monolayers were used to monitor the electrostatic factors in polymer adsorption to the membrane and peptide-polymer interactions. The synthesized PEO-grafted polylysine, PLL-PEO20000, did not induce peptide demixing monitored by stabilization of the gramicidin channels, in contrast to parent polylysine (PLL). Both polymers were shown to bind effectively to negatively charged liposomes and lipid monolayers, suggesting that the ineffectiveness of PLL-PEO20000 was not due to reduction of its binding. It was hypothesized that PLL-PEO20000 could not induce domain formation due to steric hindrance of long PEO chains preventing lateral fusion of clusters. Another copolymer, PLL-PEO4000, having four PEO chains of 4000 Da, exhibited intermediate effect between PLL and PLL-PEO20000, which shows the importance of the copolymer architecture for the effect on the lateral distribution of OPg channels. The model system can be relevant to regulation of lateral organization of ion channels and other components in natural membrane systems.
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Affiliation(s)
- A A Pashkovskaya
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russian Federation
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116
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Ghetie MA, Crank M, Kufert S, Pop I, Vitetta E. Rituximab but not Other anti-CD20 Antibodies Reverses Multidrug Resistance in 2 B lymphoma Cell Lines, Blocks the Activity of P-glycoprotein (P-gp), and Induces P-gp to Translocate out of Lipid Rafts. J Immunother 2006; 29:536-44. [PMID: 16971809 DOI: 10.1097/01.cji.0000211307.05869.6c] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The objective of this study was to investigate the ability of the anti-CD20 antibody, Rituximab (RTX), to inhibit the activity of P-glycoprotein (P-gp), and reverse multidrug resistance (MDR) in 2 P-gp/CD20 lymphoma cell lines. We determined whether RTX would chemosensitize the 2 P-gp cell lines in vitro, and inhibit the ability of the cells to efflux Rhodamine 123. One cell line was infected with an MDR1 vector and the other was generated by drug selection. We also determined whether RTX induced P-gp to translocate out of lipid rafts. RTX chemosensitized 2 different MDR cell lines, inhibited the activity of P-gp in both, and induced P-gp to translocate out of lipid rafts in the 1 cell line that was studied in greater detail. In contrast, 3 other anti-CD20 antibodies did not chemosensitize, inhibit the activity of P-gp, or induce it to translocate out of rafts, despite the fact that 1 antibody recognized the same epitope on CD20. Our results suggest that RTX can chemosensitize 2 CD20/P-gp cell lines in vitro by inhibiting the activity of the P-gp pump. The inhibition of P-gp activity correlated with the ability of RTX to induce P-gp to translocate out of lipid rafts. Although the mechanisms by which RTX effects P-gp translocation and activity are not yet known, they are not associated with acid-sphingomyelinase activation in raft microdomains, as described for the antiproliferative activity of RTX.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/antagonists & inhibitors
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- Animals
- Antibodies, Monoclonal/immunology
- Antibodies, Monoclonal/pharmacology
- Antibodies, Monoclonal, Murine-Derived
- Antigens, CD20/immunology
- Antineoplastic Agents/immunology
- Antineoplastic Agents/pharmacology
- Burkitt Lymphoma
- Cell Line, Tumor
- Cell Survival/drug effects
- Drug Resistance, Multiple/drug effects
- Humans
- Immunoglobulin Fc Fragments/immunology
- Membrane Microdomains/metabolism
- Membrane Proteins/metabolism
- Mice
- Mitochondrial Proteins/metabolism
- Protein Transport
- Rhodamine 123
- Rituximab
- Vincristine/pharmacology
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Affiliation(s)
- Maria-Ana Ghetie
- The Cancer Immunobiology Center, University of Texas Southwestern Medical Center at Dallas, 6000 Harry Hines Boulevard, Dallas, TX 75390-8576, USA
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117
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Wirths S, Lanzavecchia A. ABCB1 transporter discriminates human resting naive B cells from cycling transitional and memory B cells. Eur J Immunol 2006; 35:3433-41. [PMID: 16259010 DOI: 10.1002/eji.200535364] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The exact identification of B cell subsets is instrumental to understand their dynamics under physiological and pathological conditions. Human memory B cells are currently identified according to the expression of CD27, which is absent on naive B cells. We report here that the ATP-binding cassette (ABC)B1 transporter is exclusively present on mature CD27- naive B cells, while it is absent in CD27+ memory B cells and in a heterogeneous subset of CD27- cells that comprise both switch memory and transitional B cells. Thus, ABCB1 activity precisely discriminates naive from transitional and all memory B cells. Using this improved method to discriminate human B cell subsets, and Ki67 staining to identify recently divided cells, we show that in both cord blood and adult peripheral blood, mature naive B cells are quiescent while transitional B cells and memory B cells have a high in vivo turnover.
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Affiliation(s)
- Stefan Wirths
- Institute for Research in Biomedicine, Bellinzona, Switzerland.
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118
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Lewinson O, Adler J, Sigal N, Bibi E. Promiscuity in multidrug recognition and transport: the bacterial MFS Mdr transporters. Mol Microbiol 2006; 61:277-84. [PMID: 16856936 DOI: 10.1111/j.1365-2958.2006.05254.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Multidrug (Mdr) transport is an obstacle to the successful treatment of cancer and infectious diseases, and it is mediated by Mdr transporters that recognize and export an unusually broad spectrum of chemically dissimilar toxic compounds. Therefore, in addition to its clinical significance, the Mdr transport phenomenon presents intriguing and challenging mechanistic queries. Recent studies of secondary Mdr transporters of the major facilitator superfamily (MFS) have revealed that they are promiscuous not only regarding their substrate recognition profile, but also with respect to matters of energy utilization, electrical and chemical flexibility in the Mdr recognition pocket, and surprisingly, also in their physiological functions.
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Affiliation(s)
- Oded Lewinson
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, 76100, Israel
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119
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Langford TD, Letendre SL, Larrea GJ, Masliah E. Changing patterns in the neuropathogenesis of HIV during the HAART era. Brain Pathol 2006; 13:195-210. [PMID: 12744473 PMCID: PMC4842209 DOI: 10.1111/j.1750-3639.2003.tb00019.x] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Rapid progress in the development of highly active antiretroviral therapy has changed the observed patterns in HIV encephalitis and AIDS-related CNS opportunistic infections. Early in the AIDS epidemic, autopsy studies pointed to a high prevalence of these conditions. With the advent of nucleoside reverse transcriptase inhibitors, the prevalence at autopsy of opportunistic infections, such as toxoplasmosis and progressive multifocal leukoencephalopathy, declined while that of HIV encephalitis increased. After the introduction of protease inhibitors, a decline in both HIV encephalitis and CNS opportunistic infections was observed. However, with the increasing resistance of HIV strains to antiretrovirals, there has been a resurgence in the frequency of HIV encephalitis and HIV leukoencephalopathy. HIV leukoencephalopathy in AIDS patients failing highly active antiretroviral therapy is characterized by massive infiltration of HIV infected monocytes/macrophages into the brain and extensive white matter destruction. This condition may be attributable to interactions of anti-retrovirals with cerebrovascular endothelium, astroglial cells and white matter of the brain. These interactions may lead to cerebral ischemia, increased blood-brain barrier permeability and demyelination. Potential mechanisms of such interactions include alterations in host cell signaling that may result in trophic factor dysregulation and mitochondrial injury. We conclude that despite the initial success of combined anti-retroviral therapy, more severe forms of HIV encephalitis appear to be emerging as the epidemic matures. Factors that may contribute to this worsening include the prolonged survival of HIV-infected patients, thereby prolonging the brain's exposure to HIV virions and proteins, the use of increasingly toxic combinations of poorly penetrating drugs in highly antiretroviral-experienced AIDS patients, and selection of more virulent HIV strains with higher replication rates and greater virulence in neural tissues.
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Affiliation(s)
- T. D. Langford
- Departments of Pathology, University of California San Diego, La Jolla
| | - S. L. Letendre
- Departments of Medicine, and University of California San Diego, La Jolla
| | - G. J. Larrea
- Departments of Neurosciences, University of California San Diego, La Jolla
| | - E. Masliah
- Departments of Pathology, University of California San Diego, La Jolla
- Departments of Neurosciences, University of California San Diego, La Jolla
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120
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Xu J, Scheres B. Cell polarity: ROPing the ends together. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:613-8. [PMID: 16182602 DOI: 10.1016/j.pbi.2005.09.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 09/12/2005] [Indexed: 05/04/2023]
Abstract
Cell polarity plays an important role in plant development, but the mechanisms that first establish polarity cues remain obscure. By contrast, a flurry of information has recently emerged on the elaboration of cell shape from such unknown initial cell-polarity cues. Recent studies suggest that Rho-related GTPases in plants (ROPs), and their effector targets among the ROP-interactive CRIB motif-containing proteins (RICs), mediate two antagonistic pathways that have opposing action on cell polarization. ROP proteins appear to interact directly with upstream regulators of the ARP2/3 complex, which are conserved modulators of the actin cytoskeleton. ROP function is dependent on the class 1 ADP-ribosylation factors (ARFs), which are core components of the vesicle transport machinery that are also involved in the polar localization of PIN-FORMED (PIN) family auxin efflux facilitators.
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Affiliation(s)
- Jian Xu
- Department of Molecular Genetics, Utrecht University, Padualaan 8, 3584CH Utrecht, The Netherlands
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121
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Barakat S, Gayet L, Dayan G, Labialle S, Lazar A, Oleinikov V, Coleman A, Baggetto L. Multidrug-resistant cancer cells contain two populations of P-glycoprotein with differently stimulated P-gp ATPase activities: evidence from atomic force microscopy and biochemical analysis. Biochem J 2005; 388:563-71. [PMID: 15693753 PMCID: PMC1138964 DOI: 10.1042/bj20041999] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Considerable interest exists about the localization of P-gp (P-glycoprotein) in DRMs (detergent-resistant membranes) of multidrug resistant cancer cells, in particular concerning the potential modulating role of the closely related lipids and proteins on P-gp activity. Our observation of the opposite effect of verapamil on P-gp ATPase activity from DRM and solubilized-membrane fractions of CEM-resistant leukaemia cells, and results from Langmuir experiments on membrane monolayers from resistant CEM cells, strongly suggest that two functional populations of P-gp exist. The first is located in DRM regions: it displays its optimal P-gp ATPase activity, which is almost completely inhibited by orthovanadate and activated by verapamil. The second is located elsewhere in the membrane; it displays a lower P-gp ATPase activity that is less sensitive to orthovanadate and is inhibited by verapamil. A 40% cholesterol depletion of DRM caused the loss of 52% of the P-gp ATPase activity. Cholesterol repletion allowed recovery of the initial P-gp ATPase activity. In contrast, in the solubilized-membrane-containing fractions, cholesterol depletion and repletion had no effect on the P-gp ATPase activity whereas up to 100% saturation with cholesterol induced a 58% increased P-gp ATPase activity, while no significant modification was observed for the DRM-enriched fraction. DRMs were analysed by atomic force microscopy: 40-60% cholesterol depletion was necessary to remove P-gp from DRMs. In conclusion, P-gp in DRMs appears to contain closely surrounding cholesterol that can stimulate P-gp ATPase activity to its optimal value, whereas cholesterol in the second population seems deprived of this function.
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Affiliation(s)
- Stéphane Barakat
- *Thérapie transcriptionnelle des cellules cancéreuses, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
| | - Landry Gayet
- *Thérapie transcriptionnelle des cellules cancéreuses, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
| | - Guila Dayan
- *Thérapie transcriptionnelle des cellules cancéreuses, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
| | - Stéphane Labialle
- †McGill University, Royal Victoria Hospital, F3.32, 687 Pine avenue West, Montreal, QC, Canada H3A 1A1
| | - Adina Lazar
- ‡Assemblages moléculaires d'intérêt biologique, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
| | - Vladimir Oleinikov
- §Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya 16/10, Moscow B-437, GSP 117997, Russia
| | - Anthony W. Coleman
- ‡Assemblages moléculaires d'intérêt biologique, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
| | - Loris G. Baggetto
- *Thérapie transcriptionnelle des cellules cancéreuses, IBCP - UMR 5086 CNRS UCBL, 7 Passage du Vercors, 69367 Lyon cedex 07, France
- To whom correspondence should be addressed (email )
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122
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Le Goff W, Settle M, Greene DJ, Morton RE, Smith JD. Reevaluation of the role of the multidrug-resistant P-glycoprotein in cellular cholesterol homeostasis. J Lipid Res 2005; 47:51-8. [PMID: 16215259 DOI: 10.1194/jlr.m500255-jlr200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The multidrug resistance P-glycoprotein (P-gp) was recently proposed to redistribute cholesterol in the plasma membrane, suggesting that P-gp could modulate cholesterol efflux to cholesterol acceptors. To address this hypothesis and to reevaluate the role of P-gp in cholesterol homeostasis, we first analyzed the role of P-gp expression on cholesterol efflux in P-gp stably transfected drug-selected LLC-MDR1 cells. Cholesterol efflux to methyl-beta-cyclodextrin (CD) was 4-fold higher in LLC-MDR1 cells compared with control LLC-PK1 cells, indicating that the accessible pool of plasma membrane cholesterol was increased by P-gp expression. However, using the P-gp-inducible cells lines HeLa MDR-Tet and 77.1 MDR-Tet, cholesterol efflux to CD, apolipoprotein A-I, or HDL was not associated with P-gp expression. In addition, we did not observe any effect of P-gp expression on cellular free and esterified cholesterol content, cholesteryl ester uptake from LDL and HDL particles, or acyl-CoA:cholesterol acyltransferase activity. Therefore, we conclude that P-gp expression does not play a major role in cholesterol homeostasis in P-gp-inducible cells and that the effects of P-gp on cholesterol homeostasis previously described in drug-selected cells might result from non-P-gp pathways that were also induced by selection for drug resistance.
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Affiliation(s)
- Wilfried Le Goff
- Department of Cell Biology NC10, Cleveland Clinic Foundation, Cleveland, OH, USA
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123
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Radeva G, Perabo J, Sharom FJ. P-Glycoprotein is localized in intermediate-density membrane microdomains distinct from classical lipid rafts and caveolar domains. FEBS J 2005; 272:4924-37. [PMID: 16176266 DOI: 10.1111/j.1742-4658.2005.04905.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
P-glycoprotein (Pgp), a member of the ATP-binding cassette (ABC) superfamily responsible for the ATP-driven extrusion of diverse hydrophobic molecules from cells, is a cause of multidrug resistance in human tumours. Pgp can also operate as a phospholipid and glycosphingolipid flippase, and has been functionally linked to cholesterol, suggesting that it might be associated with sphingolipid-cholesterol microdomains in cell membranes. We have used nonionic detergent extraction and density gradient centrifugation of extracts from the multidrug-resistant Chinese hamster ovary cell line, CH(R)B30, to address this question. Our data indicate that Pgp is localized in intermediate-density membrane microdomains different from classical lipid rafts enriched in Src-family kinases. We demonstrate that Brij-96 can selectively isolate the Pgp domains, separating them from the caveolar and classical lipid rafts. Pgp was found entirely in the Brij-96-insoluble domains, and only partially in the Triton X-100-insoluble membrane microdomains. We studied the sensitivity of these domains to cholesterol removal, as well as their relationship to GM(1) ganglioside- and caveolin-1-enriched caveolar domains. We found that the buoyant density of the Brij-96-based Pgp-containing microdomains was sensitive to cholesterol removal by methyl-beta-cyclodextrin. The Brij-96 domains retained their structural integrity after cholesterol depletion while, in contrast, the Triton X-100-based caveolin-1/GM(1) microdomains did not. Using confocal fluorescence microscopy, we determined that caveolin-1 and GM(1) colocalized, while Pgp and caveolin-1, or Pgp and GM(1), did not. Our results suggest that Pgp does not interact directly with caveolin-1, and is localized in intermediate-density domains, distinct from classical lipid rafts and caveolae, which can be isolated using Brij-96.
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Affiliation(s)
- Galina Radeva
- Department of Molecular and Cellular Biology, University of Guelph, Ontario, Canada
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124
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Vaughan AM, Oram JF. ABCG1 Redistributes Cell Cholesterol to Domains Removable by High Density Lipoprotein but Not by Lipid-depleted Apolipoproteins. J Biol Chem 2005; 280:30150-7. [PMID: 15994327 DOI: 10.1074/jbc.m505368200] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP binding cassette transporter G1 (ABCG1) mediates the transport of cholesterol from cells to high density lipoprotein (HDL) but not to lipid-depleted apolipoprotein A-I. Here we show that human ABCG1 overexpressed in baby hamster kidney cells in the absence of lipoproteins traffics to the plasma membrane and redistributes membrane cholesterol to cell-surface domains accessible to treatment with the enzyme cholesterol oxidase. Cholesterol removed by HDL was largely derived from these domains in ABCG1 transfectants but not in cells lacking ABCG1. Overexpression of ABCG1 also increased cholesterol esterification, which was decreased by the addition of HDL, suggesting that a proportion of the cell-surface cholesterol not removed by HDL is transported to the intracellular esterifying enzyme acyl-CoA:cholesterol acyltransferase. A 638-amino acid ABCG1, which lacked the 40 N-terminal amino acids of the predicted full-length protein, was fully functional and of a similar size to ABCG1 expressed by cholesterol-loaded human monocyte-derived macrophages. Mutating an essential glycine residue in the Walker A motif abolished ABCG1-dependent cholesterol efflux and esterification and prevented localization of ABCG1 to the cell surface, indicating that the ATP binding domain in ABCG1 is essential for both lipid transport activity and protein trafficking. These studies show that ABCG1 redistributes cholesterol to cell-surface domains where it becomes accessible for removal by HDL, consistent with a direct role of ABCG1 in cellular cholesterol transport.
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Affiliation(s)
- Ashley M Vaughan
- Department of Medicine, Division of Metabolism, Endocrinology and Nutrition, University of Washington, Seattle, Washington 98195-6426, USA.
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125
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Mulas MF, Demuro G, Mulas C, Putzolu M, Cavallini G, Donati A, Bergamini E, Dessi S. Dietary restriction counteracts age-related changes in cholesterol metabolism in the rat. Mech Ageing Dev 2005; 126:648-54. [PMID: 15888318 DOI: 10.1016/j.mad.2004.11.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2004] [Revised: 11/11/2004] [Accepted: 11/26/2004] [Indexed: 11/23/2022]
Abstract
The effects of ageing on the metabolism of cholesterol were examined in three different organs (liver, aorta and brain) of 6-, 12- and 24-month-old male Sprague-Dawley rats. Ageing was associated with a significant increase in intracellular cholesterol esters in all three organs. Steady state mRNA levels of multidrug resistance protein (MDR) and acylCoA:cholesterol acyl transferase (ACAT), enzymes involved in cholesterol import and esterification, were also increased. By contrast, expression of mRNA for neutral cholesterol ester hydrolase (nCEH) and caveolin-1, proteins involved in cholesterol ester hydrolysis and export, were significantly reduced. Dietary restriction is the only intervention shown to extend lifespan and retard age-related declines in function in mammals. To further explore the possible correlation between changes in cholesterol esterification and ageing, we analysed cholesterol metabolism in liver, aorta, and brain of aged rats exposed to two dietary restriction regimens: intermittent (alternate-day) fasting (IF) and food intake restriction (60% of ad libitum feeding). Both dietary regimens attenuated the age-related changes in cholesterol esters and in the expression of genes involved in cholesterol metabolism. These results provide evidence that distinctive age-associated changes in intracellular cholesterol metabolism occur in rats. Furthermore, these modifications can be partially reversed by dietary restriction, a condition known to affect the ageing process. Age-related changes in cholesterol metabolism may play a role in triggering and/or aggravating senescence-related disorders characterized by altered cholesterol homeostasis.
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Affiliation(s)
- M F Mulas
- Dipartimento di Scienze Biomediche e Biotecnologie, Università di Cagliari, Italy
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126
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Abstract
P-glycoprotein (P-gp), coded by the ABCB1 gene, has a wide tissue distribution. The drug transporter is known to limit the bioavailability of a plethora of drugs and xenobiotics including the human immunodeficiency virus (HIV) protease inhibitors. There remains a considerable degree of debate in the literature with respect to the role of ABCB1 polymorphisms in HIV-treatment outcome and some studies have also implicated antiretroviral drugs as inducers of P-gp. Recent evidence indicates a role for P-gp in the inhibition of viral infectivity and/or release and cellular relationships with other infection-related proteins (and cholesterol). It is becoming increasingly clear that future studies on P-gp in HIV should consider both pharmacological and virological issues.
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Affiliation(s)
- Andrew Owen
- Department of Pharmacology and Therapeutics, The University of Liverpool, 70 Pembroke Place, Liverpool, L69 3GF, UK.
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127
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Kobayashi A, Kimura Y, Matsuo M, Ueda K. [ABC proteins as molecular targets for drug discovery]. Nihon Yakurigaku Zasshi 2005; 125:185-93. [PMID: 15930794 DOI: 10.1254/fpj.125.185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
MESH Headings
- ATP Binding Cassette Transporter 1
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily B, Member 1/physiology
- ATP Binding Cassette Transporter, Subfamily G, Member 5
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/physiology
- Animals
- Cholesterol/metabolism
- Drug Design
- Drug Resistance, Multiple/genetics
- Drug Resistance, Neoplasm/genetics
- Glucose/metabolism
- Humans
- Intestinal Absorption/genetics
- Intestine, Small/metabolism
- Lipoproteins/genetics
- Lipoproteins/physiology
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Protein Processing, Post-Translational
- Receptors, Drug/genetics
- Receptors, Drug/physiology
- Sulfonylurea Receptors
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128
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Bucher K, Besse CA, Kamau SW, Wunderli-Allenspach H, Krämer SD. Isolated Rafts from Adriamycin-Resistant P388 Cells Contain Functional ATPases and Provide an Easy Test System for P-glycoprotein?Related Activities. Pharm Res 2005; 22:449-57. [PMID: 15835751 DOI: 10.1007/s11095-004-1883-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE P-glycoprotein (P-gp), a membrane ATPase expelling many structurally unrelated compounds out of cells, is one of the major contributors to multidrug resistance. It is enriched in cold TritonX-100 insoluble membrane domains (i.e., rafts). The purpose of this work was to characterize the ATPase activities of raft preparations from P388 cells overexpressing P-gp (P388/ADR) or devoid of P-gp (P388) and to establish a P-gp-enriched screening system for P-gp-interfering compounds. METHODS Rafts were extracted with cold TritonX-100. The ATPase activity was characterized in 96-well plates using a fluorescence assay. RESULTS The ATPase activity per mg protein was about five times higher in P388/ADR rafts than in crude membranes. The anti-P-gp antibody C219 inhibited 20% of the activity in P388/ADR rafts but only about 10% of the activity in P388/ADR crude membranes and had no effect on the activity of P388 rafts. The known P-gp-activating compounds verapamil, progesterone, and valinomycin revealed the typical bell-shaped activity/concentration profiles in P388/ADR rafts, indicative for activation at low compound concentrations and inhibition at concentrations >10 to 100 microM. The inhibitory effect was also observed in P388 rafts. CONCLUSIONS Extracted rafts are rich in functional ATPases. Rafts from P-gp-overexpressing cells display P-gp-typical ATPase activity and provide an easy, P-gp-enriched screening system.
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Affiliation(s)
- Karsten Bucher
- Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH, Federal Institute of Technology, Zürich, Switzerland
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129
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Bacso Z, Nagy H, Goda K, Bene L, Fenyvesi F, Matkó J, Szabó G. Raft and cytoskeleton associations of an ABC transporter: P-glycoprotein. Cytometry A 2005; 61:105-16. [PMID: 15382145 DOI: 10.1002/cyto.a.20081] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND A novel flow cytometric assay has been described in an accompanying report (Gombos et al., METHODS The kinetics of the decrease in immunofluorescence intensity was analyzed after the addition of the raft-preserving Triton X-100 or Nonidet P-40, both of which disrupt the entire membrane. Mild treatments by both detergents leave cells attached to only those proteins that are anchored to the cytoskeleton by rafts or independent of rafts. Agents that affect microfilaments and modulate membrane levels of cholesterol by cyclodextrin were used to distinguish between the raft-mediated and non-raft-related associations of the Pgp. Confocal microscopy and flow cytometric fluorescence energy transfer measurements were used to confirm colocalization of Pgp with raft constituents. RESULTS The assay was proved to be sensitive enough to resolve differences between the resistance of UIC2-labeled cell-surface Pgps to Triton X-100 versus Nonidet P-40. Approximately 34% of the UIC2 Fab-labeled Pgp molecules were associated with the cytoskeleton through detergent-resistant, cholesterol-sensitive microdomains or directly, whereas approximately 15% were found to be directly linked to the cytoskeleton. Accordingly, confocal microscopy showed that Pgps colocalize with raft markers, mainly in microvilli. Fluorescence resonance energy transfer efficiency data indicating molecular proximity between Pgp and the raft markers CD44, CD59, and G(M1)-gangliosides also suggested that a significant fraction of Pgps resides in raft microdomains. Raft association of Pgp appears to be of functional significance because its modulation markedly affected drug pumping. CONCLUSIONS By using the flow cytometric detergent resistance assay in kinetic mode, we were able to assess the extent of raft association and actin cytoskeleton anchorage of Pgp expressed at physiologically relevant levels. We demonstrated that a significant fraction of Pgp is raft associated on LS-174-T human colon carcinoma cells and that this localization may influence its transporter function. The kinetic flow cytometric detergent resistance assay presented in this report is considered to be generally applicable for the analysis of molecular interactions of membrane proteins expressed at low levels.
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Affiliation(s)
- Zsolt Bacso
- Department of Biophysics and Cell Biology, University of Debrecen, Medical Faculty, Research Centre for Molecular Medicine, Debrecen, Hungary
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130
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Riou M, Koch C, Kerboeuf D. Increased resistance to anthelmintics of Haemonchus contortus eggs associated with changes in membrane fluidity of eggshells during embryonation. Parasitol Res 2005; 95:266-72. [PMID: 15678352 DOI: 10.1007/s00436-004-1288-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2004] [Accepted: 12/02/2004] [Indexed: 11/27/2022]
Abstract
The embryonation of nematode eggs has been shown to increase their resistance to anthelmintics when parasites are submitted to egg hatch assays. Nevertheless, no mechanism has been suggested to explain this phenomenon. Earlier observations by other authors showed that the biochemical composition of eggshells is altered during the embryonation of eggs. The functional consequences of these changes have not been identified. We studied the changes in membrane environment (eggshells) of Haemonchus contortus eggs during the embryonation by fluidity measurements and their effects on nonspecific mechanisms of resistance to anthelmintics. We previously demonstrated that these mechanisms imply P-glycoproteins (Pgp) belonging to the multi-drug resistance (MDR) system and that the Pgp activity is very susceptible to their lipidic environment. The results obtained here show that the embryonation induced a significant and gradual increase in eggshell fluidity which was associated with an increased resistance to anthelmintics. Differences were observed between H. contortus isolates with various levels of resistance which might result from their specific biology and/or membrane composition. The membrane environment changes could act both on the solubilization of anthelmintics into the eggs and on the efflux of these lipophilic molecules by Pgp.
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Affiliation(s)
- Mickaël Riou
- MultiResistances et Antiparasitic drugs, INRA-Tours: UR086-BioAgressors, Health and Environment, 37380 , Nouzilly, France
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131
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Chapter 1 Lipid Rafts and Caveolae Organization. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s1569-2558(05)36001-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
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132
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Borner GHH, Sherrier DJ, Weimar T, Michaelson LV, Hawkins ND, Macaskill A, Napier JA, Beale MH, Lilley KS, Dupree P. Analysis of detergent-resistant membranes in Arabidopsis. Evidence for plasma membrane lipid rafts. PLANT PHYSIOLOGY 2005; 137:104-16. [PMID: 15618420 PMCID: PMC548842 DOI: 10.1104/pp.104.053041] [Citation(s) in RCA: 362] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2004] [Revised: 10/17/2004] [Accepted: 10/23/2004] [Indexed: 05/17/2023]
Abstract
The trafficking and function of cell surface proteins in eukaryotic cells may require association with detergent-resistant sphingolipid- and sterol-rich membrane domains. The aim of this work was to obtain evidence for lipid domain phenomena in plant membranes. A protocol to prepare Triton X-100 detergent-resistant membranes (DRMs) was developed using Arabidopsis (Arabidopsis thaliana) callus membranes. A comparative proteomics approach using two-dimensional difference gel electrophoresis and liquid chromatography-tandem mass spectrometry revealed that the DRMs were highly enriched in specific proteins. They included eight glycosylphosphatidylinositol-anchored proteins, several plasma membrane (PM) ATPases, multidrug resistance proteins, and proteins of the stomatin/prohibitin/hypersensitive response family, suggesting that the DRMs originated from PM domains. We also identified a plant homolog of flotillin, a major mammalian DRM protein, suggesting a conserved role for this protein in lipid domain phenomena in eukaryotic cells. Lipid analysis by gas chromatography-mass spectrometry showed that the DRMs had a 4-fold higher sterol-to-protein content than the average for Arabidopsis membranes. The DRMs were also 5-fold increased in sphingolipid-to-protein ratio. Our results indicate that the preparation of DRMs can yield a very specific set of membrane proteins and suggest that the PM contains phytosterol and sphingolipid-rich lipid domains with a specialized protein composition. Our results also suggest a conserved role of lipid modification in targeting proteins to both the intracellular and extracellular leaflet of these domains. The proteins associated with these domains provide important new experimental avenues into understanding plant cell polarity and cell surface processes.
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Affiliation(s)
- Georg H H Borner
- Department of Biochemistry , University of Cambridge, Cambridge CB2 1QW, UK
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133
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Nagata K, Yamamoto A, Ban N, Tanaka AR, Matsuo M, Kioka N, Inagaki N, Ueda K. Human ABCA3, a product of a responsible gene for abca3 for fatal surfactant deficiency in newborns, exhibits unique ATP hydrolysis activity and generates intracellular multilamellar vesicles. Biochem Biophys Res Commun 2004; 324:262-8. [PMID: 15465012 DOI: 10.1016/j.bbrc.2004.09.043] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2004] [Indexed: 10/26/2022]
Abstract
ABCA3 is highly expressed at the membrane of lamellar bodies in alveolar type II cells, in which pulmonary surfactant is stored. ABCA3 gene mutations cause fatal surfactant deficiency in newborns. We established HEK293 cells stably expressing human ABCA3 and analyzed the function. Exogenously expressed ABCA3 is glycosylated and localized at the intracellular vesicle membrane. ABCA3 is efficiently photoaffinity labeled by 8-azido-[alpha(32)P]ATP, but not by 8-azido-[gamma(32)P]ATP, when the membrane fraction is incubated in the presence of orthovanadate. Photoaffinity labeling of ABCA3 shows unique metal ion-dependence and is largely reduced by membrane pretreatment with 5% methyl-beta-cyclodextrin, which depletes cholesterol. Electron micrographs show that HEK293/hABCA3 cells contain multivesicular, lamellar body-like structures, which do not exist in HEK293 host cells. Some fuzzy components such as lipids accumulate in the vesicles. These results suggest that ABCA3 shows ATPase activity, which is induced by lipids, and may be involved in the biogenesis of lamellar body-like structures.
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Affiliation(s)
- Koh Nagata
- Laboratory of Cellular Biochemistry, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
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134
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Reungpatthanaphong P, Marbeuf-Gueye C, Le Moyec L, Salerno M, Garnier-Suillerot A. Decrease of P-Glycoprotein Activity in K562/ADR Cells by M?CD and Filipin and Lack of Effect Induced by Cholesterol Oxidase Indicate That This Transporter Is Not Located in Rafts. J Bioenerg Biomembr 2004; 36:533-43. [PMID: 15692732 DOI: 10.1007/s10863-004-9000-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The effect of low-density membrane domains on function of the plasma membrane transporter P-glycoprotéine (P-gp), involved in multidrug resistance (MDR) phenotype, has been investigated in K562/ADR cells. To this end we reversibly altered the cholesterol content of K562/ADR cells by using methyl-beta-cyclodextrin as a cholesterol chelator and conversely we repleted them through incubation with cholesterol in culture medium. We also used the cholesterol-binding fluorochrome filipin and cholesterol oxidase. Our data show that either cholesterol depletion or complex formation with filipin resulted in a strong decrease of P-gp activity. However, when cells were incubated with cholesterol oxidase that are known to disrupt rafts, no modification of the P-gp activity was observed. In addition, using a free-detergent methodology to separate by ultracentrifugation, "light," "heavy," and "extra heavy" fractions we show that no P-gp is found in the "light" fraction where rafts are usually detected. Altogether, our data strongly suggest that, in this cell line, P-gp is not localized in rafts.
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Affiliation(s)
- Paiboon Reungpatthanaphong
- Laboratoire de Physicochimie Biomoléculaire et Cellulaire (LPBC/CSSB UMR 7033), Université Paris Nord, 74 rue Marcel Cachin, 93017, Bobigny, France
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135
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Pallis M, Russell N. Strategies for overcoming p-glycoprotein-mediated drug resistance in acute myeloblastic leukaemia. Leukemia 2004; 18:1927-30. [PMID: 15483678 DOI: 10.1038/sj.leu.2403511] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- M Pallis
- Division of Haematology, School of Molecular Medical Sciences, University of Nottingham and Nottingham City Hospital, UK
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136
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Le Goff W, Peng DQ, Settle M, Brubaker G, Morton RE, Smith JD. Cyclosporin A traps ABCA1 at the plasma membrane and inhibits ABCA1-mediated lipid efflux to apolipoprotein A-I. Arterioscler Thromb Vasc Biol 2004; 24:2155-61. [PMID: 15358601 DOI: 10.1161/01.atv.0000144811.94581.52] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE ABCA1 mediates cellular cholesterol and phospholipid efflux to apolipoprotein A-I and other apolipoprotein acceptors. In this study, we analyzed the effect of the immunosuppressant cyclosporin A on the ABCA1-mediated lipid effluxes reactions. METHODS AND RESULTS Cyclosporin A acted as a potent inhibitor of ABCA1 activity in several cell lines. Using the RAW264.7 mouse macrophage cell line, in which ABCA1 and its associated cholesterol efflux activity are inducible by cAMP analogues, cyclosporin A inhibition of cholesterol efflux to apolipoprotein A-I was rapidly reversible after its removal from the culture media, implying that ABCA1 levels were not drastically reduced by cyclosporin A. In fact, cyclosporin A treatment decreased ABCA1 turnover and yielded a 2-fold increase in cell-surface ABCA1. Despite the increase in cell-surface ABCA1, cyclosporin A decreased apolipoprotein A-I uptake, resecretion, and degradation in RAW cells. Finally, consistent with the inhibition of ABCA1 in vitro, cyclosporin A treatment induced a 33% reduction of high-density lipoprotein (HDL) levels in mice. CONCLUSIONS ABCA1 inhibition by cyclosporin A supports a role for ABCA1 endocytic trafficking in ABCA1-mediated lipid efflux and could explain in part the low HDL levels observed in some patients with transplants.
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Affiliation(s)
- Wilfried Le Goff
- Department of Cell Biology NC10, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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137
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Troost J, Lindenmaier H, Haefeli WE, Weiss J. Modulation of cellular cholesterol alters P-glycoprotein activity in multidrug-resistant cells. Mol Pharmacol 2004; 66:1332-9. [PMID: 15308763 DOI: 10.1124/mol.104.002329] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The drug transporter P-glycoprotein (ABCB1) plays an important role in drug distribution and elimination, and when overexpressed it may confer multidrug resistance (MDR). P-glycoprotein is localized in the plasma membrane, especially within rafts and caveolae, characterized as detergent-resistant membranes (DRMs). This study investigated the effect of cholesterol depletion and repletion as well as saturation on subcellular localization and function of P-glycoprotein to determine the effect of DRM localization on P-glycoprotein-mediated drug efflux. In L-MDR1 overexpressing human P-glycoprotein, cholesterol depletion removed P-glycoprotein from the raft membranes into non-DRM fractions, whereas repletion fully reconstituted raft localization. P-glycoprotein function was assessed by realtime monitoring with confocal laser scanning microscopy using BODIPY-verapamil as substrate. Cholesterol depletion reduced P-glycoprotein function in L-MDR1 cells resulting in intracellular substrate accumulation (159% +/- 43, p < 0.001; control = 100%). Cholesterol repletion reduced intracellular substrate fluorescence (120% +/- 36, p < 0.001) and restored the transporter activity. Addition of surplus cholesterol (saturation) even enhanced drug efflux in L-MDR1 cells, leading to reduced intracellular accumulation of BODIPY-verapamil (69% +/- 10, p < 0.001). Transport of BODIPY-verapamil in cells not expressing human P-glycoprotein (LLC-PK1) was not susceptible to cholesterol alterations. These results demonstrate that cholesterol alterations influence P-glycoprotein localization and function, which might contribute to the large interindividual variability of P-glycoprotein activity known from in vivo studies.
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Affiliation(s)
- Joachim Troost
- Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Im Neuenheimer Feld 410, D-69120 Heidelberg, Germany
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138
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Cai C, Zhu H, Chen J. Overexpression of caveolin-1 increases plasma membrane fluidity and reduces P-glycoprotein function in Hs578T/Dox. Biochem Biophys Res Commun 2004; 320:868-74. [PMID: 15240128 DOI: 10.1016/j.bbrc.2004.06.030] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2004] [Indexed: 12/20/2022]
Abstract
Cholesterol is a key lipid in mediating the enzyme activity or signaling pathway of many proteins on the plasma membrane in mammalian cells. In this report, we demonstrate for the first time that after overexpressing caveolin-1, the plasma membrane cholesterol level was decreased by about 12% and 30% for doxorubicin-sensitive and doxorubicin-resistant Hs578T breast cancer cells, respectively. However, the total cholesterol level in both cell lines was increased by about 10%. By measuring fluorescence and flow cytometry using the fluorescence dyes 1,6-diphenyl-1,3,5-hexatriene and Merocyanine 540, we found that overexpressing caveolin-1 resulted in a similar increase in membrane fluidity and loosening of lipid packing density as cholesterol depletion by 1 mM methyl-beta-cyclodextrin (MbetaCD) or 2-hydroxypropyl-beta-cyclodextrin (HbetaCD). Moreover, we found that the transport activity of P-gp was significantly inhibited by 1 mM MbetaCD or HbetaCD, which is also similar to the inhibitory effect of caveolin-1 overexpression. Our data demonstrate for the first time that the reduction of the plasma membrane cholesterol level induced by overexpressing caveolin-1 may indirectly inhibit P-gp transport activity by increasing plasma membrane fluidity.
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Affiliation(s)
- Chuanxi Cai
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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139
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Zhang Z, Zhang X, Wu H, Zhao M. Using 99mTc-sestamibi to evaluate the effects of a chemosensitizer on P-glycoprotein in multidrug-resistant carcinoma cells. Methods Enzymol 2004; 386:212-6. [PMID: 15120253 DOI: 10.1016/s0076-6879(04)86009-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- Zhenwei Zhang
- Department of Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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140
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Troost J, Albermann N, Emil Haefeli W, Weiss J. Cholesterol modulates P-glycoprotein activity in human peripheral blood mononuclear cells. Biochem Biophys Res Commun 2004; 316:705-11. [PMID: 15033457 DOI: 10.1016/j.bbrc.2004.02.102] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2004] [Indexed: 11/29/2022]
Abstract
P-glycoprotein (P-gp) is expressed in a wide range of cell types including peripheral blood mononuclear cells (PBMCs) where it may restrict intracellular accumulation of substrates like antineoplastic agents, HIV protease inhibitors, or rhodamine123. P-gp is known to be located in membrane microdomains, whose structure and function are susceptible to cholesterol alterations. This study evaluated the effect of cholesterol alteration in human PBMCs on P-gp activity. Whereas cholesterol depletion had no effect, cholesterol repletion of depleted cells significantly decreased intracellular rhodamine123 concentrations in lymphocytes to 32.2%+/-2.7 (p<0.001) and to 41.9%+/-3.5 (p<0.001) in monocytes. After cholesterol saturation of native cells intracellular rhodamine123 fluorescence decreased to 12.4%+/-1.6 (p<0.001) in lymphocytes and 12.9%+/-3.5 (p<0.001) in monocytes. These data demonstrate that elevated cellular cholesterol levels can markedly increase P-gp activity in human PBMCs.
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Affiliation(s)
- Joachim Troost
- Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Bergheimer Str. 58, D-69115 Heidelberg, Germany
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141
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Ghetie MA, Marches R, Kufert S, Vitetta ES. An anti-CD19 antibody inhibits the interaction between P-glycoprotein (P-gp) and CD19, causes P-gp to translocate out of lipid rafts, and chemosensitizes a multidrug-resistant (MDR) lymphoma cell line. Blood 2004; 104:178-83. [PMID: 15001473 DOI: 10.1182/blood-2003-12-4255] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously demonstrated that an anti-CD19 monoclonal antibody (MAb; HD37) inhibits the function of the P-glycoprotein (P-gp) pump in a multidrug-resistant (MDR) B-lymphoma cell line, Namalwa/MDR1, and that this effect is not due to the recognition of a cross-reactive epitope on P-gp. In this study, we have used the same cell line to define the mechanisms responsible for the effect of HD37 on the P-gp pump. Using fluorescence resonance energy transfer (FRET), we show that CD19 and P-gp are constitutively associated in cells. In the absence of treatment with anti-CD19, 40% of P-gp molecules expressed by Namalwa/MDR1 cells reside in the low-density lipid (ie, cholesterol-rich) microdomains (lipid rafts). Following treatment of the cells with HD37 and disruption of the interactions between P-gp and CD19, P-gp translocated out of lipid rafts and CD19 translocated into lipid rafts. The effect of chemosensitization on Namalwa/MDR1 cells was specific for CD19; an anti-CD22 MAb had no such effect, although the cells express CD22. These results suggest that anti-CD19 might chemosensitize P-gp(+) cells by interfering with interactions between CD19 and P-gp, rapidly resulting in the translocation of P-gp into a compartment on the plasma membrane where it is no longer active.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/antagonists & inhibitors
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- Antibodies, Monoclonal/immunology
- Antibodies, Monoclonal/metabolism
- Antibodies, Monoclonal/pharmacology
- Antigens, CD19/immunology
- Antigens, CD19/metabolism
- Burkitt Lymphoma/drug therapy
- Burkitt Lymphoma/metabolism
- Cell Line, Tumor
- Cell Membrane/metabolism
- Cell Survival/drug effects
- Cell Survival/immunology
- Drug Resistance, Multiple
- Drug Resistance, Neoplasm
- G(M1) Ganglioside/metabolism
- Gene Expression
- Humans
- Membrane Microdomains/metabolism
- Protein Binding
- Protein Transport
- Rhodamine 123/metabolism
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Affiliation(s)
- Maria-Ana Ghetie
- Cancer Immunobiology Center, University of Texas Southwestern Medical Center at Dallas, 75390, USA
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142
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De Rosa MF, Sillence D, Ackerley C, Lingwood C. Role of multiple drug resistance protein 1 in neutral but not acidic glycosphingolipid biosynthesis. J Biol Chem 2003; 279:7867-76. [PMID: 14662772 DOI: 10.1074/jbc.m305645200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Transfection studies have implicated the multiple drug resistance pump, MDR1, as a glucosyl ceramide translocase within the Golgi complex (Lala, P., Ito, S., and Lingwood, C. A. (2000) J. Biol. Chem. 275, 6246-6251). We now show that MDR1 inhibitors, cyclosporin A or ketoconazole, inhibit neutral glycosphingolipid biosynthesis in 11 of 12 cell lines tested. The exception, HeLa cells, do not express MDR1. Microsomal lactosyl ceramide and globotriaosyl ceramide synthesis from endogenous or exogenously added liposomal glucosyl ceramide was inhibited by cyclosporin A, consistent with a direct role for MDR1/glucosyl ceramide translocase activity in their synthesis. In contrast, cellular ganglioside synthesis in the same cells, was unaffected by MDR1 inhibition, suggesting neutral and acid glycosphingolipids are synthesized from distinct precursor glycosphingolipid pools. Metabolic labeling in wild type and knock-out (MDR1a, 1b, MRP1) mouse fibroblasts showed the same loss of neutral glycosphingolipid (glucosyl ceramide, lactosyl ceramide) but not ganglioside (GM3) synthesis, confirming the proposed role for MDR1 translocase activity. Cryo-immunoelectron microscopy showed MDR1 was predominantly intracellular, largely in rab6-containing Golgi vesicles and Golgi cisternae, the site of glycosphingolipid synthesis. These studies identify MDR1 as the major glucosyl ceramide flippase required for neutral glycosphingolipid anabolism and demonstrate a previously unappreciated dichotomy between neutral and acid glycosphingolipid synthesis.
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Affiliation(s)
- María Fabiana De Rosa
- Research Institute and Department of Pediatric Laboratory Medicine, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
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143
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Al-Shawi MK, Polar MK, Omote H, Figler RA. Transition state analysis of the coupling of drug transport to ATP hydrolysis by P-glycoprotein. J Biol Chem 2003; 278:52629-40. [PMID: 14551217 DOI: 10.1074/jbc.m308175200] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATPase activity associated with P-glycoprotein (Pgp) is characterized by three drug-dependent phases: basal (no drug), drug-activated, and drug-inhibited. To understand the communication between drug-binding sites and ATP hydrolytic sites, we performed steady-state thermodynamic analyses of ATP hydrolysis in the presence and absence of transport substrates. We used purified human Pgp (ABCB1, MDR1) expressed in Saccharomyces cerevisiae (Figler, R. A., Omote, H., Nakamoto, R. K., and Al-Shawi, M. K. (2000) Arch. Biochem. Biophys. 376, 34-46) as well as Chinese hamster Pgp (PGP1). Between 23 and 35 degrees C, we obtained linear Arrhenius relationships for the turnover rate of hydrolysis of saturating MgATP in the presence of saturating drug concentrations (kcat), from which we calculated the intrinsic enthalpic, entropic, and free energy terms for the rate-limiting transition states. Linearity of the Arrhenius plots indicated that the same rate-limiting step was being measured over the temperature range employed. Using linear free energy analysis, two distinct transition states were found: one associated with uncoupled basal activity and the other with coupled drug transport activity. We concluded that basal ATPase activity associated with Pgp is not a consequence of transport of an endogenous lipid or other endogenous substrates. Rather, it is an intrinsic mechanistic property of the enzyme. We also found that rapidly transported substrates bound tighter to the transition state and required fewer conformational alterations by the enzyme to achieve the coupling transition state. The overall rate-limiting step of Pgp during transport is a carrier reorientation step. Furthermore, Pgp is optimized to transport drugs out of cells at high rates at the expense of coupling efficiency. The drug inhibition phase was associated with low affinity drug-binding sites. These results are consistent with an expanded version of the alternating catalytic site drug transport model (Senior, A. E., Al-Shawi, M. K., and Urbatsch, I. L. (1995) FEBS Lett. 377, 285-289). A new kinetic model of drug transport is presented.
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Affiliation(s)
- Marwan K Al-Shawi
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, Virginia 22908-0736, USA.
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Seigneuret M, Garnier-Suillerot A. A structural model for the open conformation of the mdr1 P-glycoprotein based on the MsbA crystal structure. J Biol Chem 2003; 278:30115-24. [PMID: 12777401 DOI: 10.1074/jbc.m302443200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The validity of the structure of the Escherichia coli MsbA lipid transporter as a model from the mdr1 P-glycoprotein has been evaluated. Comparative sequence analyses, motif search and secondary structure prediction indicated that each of the two P-glycoprotein halves is structurally similar to the MsbA monomer and also suggested that the open dimer structure is valid for P-glycoprotein. Homology modeling was used to predict the structure of P-glycoprotein using MsbA as a template. The resulting modeled structure allowed a detailed study of the interactions between the intracellular domain and the nucleotide binding domain and suggested that these contacts are involved in mediating the coupling between nucleotide binding domain conformational changes and transmembrane helices reorientation during transport. In P-glycoprotein, the internal chamber open to the inner leaflet and the inner medium is significantly different in size and charge than in MsbA. These differences can be related to those of the transported substrates. Moreover an ensemble of 20 conserved aromatic residues appears to border the periphery of each side of the chamber in P-glycoprotein. These may be important for size selection and proper positioning of drugs for transport. The relevance of the modeled conformation to P-gp function is discussed.
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Affiliation(s)
- Michel Seigneuret
- Laboratoire de Physochimie Biomoléculaire et Cellulaire, UMR-CNRS 7033, Universitĕ Paris 6, France.
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145
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Vaughan AM, Oram JF. ABCA1 redistributes membrane cholesterol independent of apolipoprotein interactions. J Lipid Res 2003; 44:1373-80. [PMID: 12700343 DOI: 10.1194/jlr.m300078-jlr200] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ATP binding cassette transporter A1 (ABCA1) mediates the transport of phospholipids and cholesterol from cells to lipid-poor HDL apolipoproteins. Cholesterol loading of cells induces ABCA1, implicating cholesterol as its major physiologic substrate. It is believed, however, that ABCA1 is primarily a phospholipid transporter and that cholesterol efflux occurs by diffusion to ABCA1-generated phospholipid-rich apolipoproteins. Here we show that overexpression of ABCA1 in baby hamster kidney cells in the absence of apolipoproteins redistributed membrane cholesterol to cell-surface domains accessible to treatment with the enzyme cholesterol oxidase. The cholesterol removed by apolipoprotein A-I (apoA-I), but not by HDL phospholipids, was derived exclusively from these domains. ABCA1 overexpression also increased cholesterol esterification, which was prevented by addition of apoA-I, suggesting that some of the cell-surface cholesterol not removed by apolipoproteins is transported to the intracellular esterifying enzyme acyl-CoA:cholesterol acyltransferase. ABCA1 expression was essential for cholesterol efflux even when apolipoproteins had already acquired phospholipids during prior exposure to ABCA1-expressing cells. These studies show that ABCA1 redistributes cholesterol to cell-surface domains, where it becomes accessible for removal by apolipoproteins, consistent with a direct role of ABCA1 in cholesterol transport.
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Affiliation(s)
- Ashley M Vaughan
- Department of Medicine, University of Washington, Seattle, WA 98195-6426, USA
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146
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Janvilisri T, Venter H, Shahi S, Reuter G, Balakrishnan L, van Veen HW. Sterol transport by the human breast cancer resistance protein (ABCG2) expressed in Lactococcus lactis. J Biol Chem 2003; 278:20645-51. [PMID: 12668685 DOI: 10.1074/jbc.m301358200] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human breast cancer resistance protein (BCRP, also know as ABCG2, MXR, or ABCP) is one of the more recently discovered ATP-binding cassette (ABC) transporters that confer resistance on cancer cells by mediating multidrug efflux. In the present study, we have obtained functional expression of human BCRP in the Gram-positive bacterium Lactococcus lactis. BCRP expression conferred multidrug resistance on the lactococcal cells, which was based on ATP-dependent drug extrusion. BCRP-mediated ATPase and drug transport activities were inhibited by the BCRP-specific modulator fumitremorgin C. To our knowledge these data represent the first example of the functional expression of a mammalian ABC half-transporter in bacteria. Although members of the ABCG subfamily (such as ABCG1 and ABCG5/8) have been implicated in the transport of sterols, such a role has not yet been established for BCRP. Interestingly, the BCRP-associated ATPase activity in L. lactis was significantly stimulated by (i) sterols including cholesterol and estradiol, (ii) natural steroids such as progesterone and testosterone, and (iii) the anti-estrogen anticancer drug tamoxifen. In addition, BCRP mediated the efflux of [3H]estradiol from lactococcal cells. Our findings suggest that BCRP may play a role in the transport of sterols in human, in addition to its ability to transport multiple drugs and toxins.
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Affiliation(s)
- Tavan Janvilisri
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
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147
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148
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Yunomae K, Arima H, Hirayama F, Uekama K. Involvement of cholesterol in the inhibitory effect of dimethyl-beta-cyclodextrin on P-glycoprotein and MRP2 function in Caco-2 cells. FEBS Lett 2003; 536:225-31. [PMID: 12586368 DOI: 10.1016/s0014-5793(03)00059-0] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We compared the inhibitory effect of various cyclodextrins (CyDs) on P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) function and examined the contribution of cholesterol to the inhibitory effect of 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CyD) on the efflux activity of the function in Caco-2 cell monolayers. Of various CyDs, DM-beta-CyD significantly impaired the efflux activity of P-gp and MRP2. DM-beta-CyD released P-gp and MRP2 from the monolayers in the apical side's transport buffer and decreased the extent of cholesterol as well as P-gp and MRP2 in caveolae of Caco-2 cell monolayers, but not caveolin and flotillin-1. On the other hand, DM-beta-CyD did not change MDR1 and MRP2 mRNA levels. Therefore, these results suggest that the inhibitory effect of DM-beta-CyD on P-gp and MRP2 function, at least in part, could be attributed to the release of these transporters from the apical membranes into the medium as secondary effects through cholesterol-depletion in caveolae after treatment of Caco-2 cell monolayers with DM-beta-CyD.
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Affiliation(s)
- Kiyokazu Yunomae
- Faculty of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Kumamoto 862-0973, Japan
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149
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Abstract
Detergent-resistant membrane microdomains enriched in sphingolipids, cholesterol and glycosylphosphatidylinositol-anchored proteins play essential roles in T cell receptor (TCR) signaling. These 'membrane rafts' accumulate several cytoplasmic lipid-modified molecules, including Src-family kinases, coreceptors CD4 and CD8 and transmembrane adapters LAT and PAG/Cbp, essential for either initiation or amplification of the signaling process, while most other abundant transmembrane proteins are excluded from these structures. TCRs in various T cell subpopulations may differ in their use of membrane rafts. Membrane rafts also seem to be involved in many other aspects of T cell biology, such as functioning of cytokine and chemokine receptors, adhesion molecules, antigen presentation, establishing cell polarity or interaction with important pathogens. Although the concept of membrane rafts explains several diverse biological phenomena, many basic issues, such as composition, size and heterogeneity, under native conditions, as well as the dynamics of their interactions with TCRs and other immunoreceptors, remain unclear, partially because of technical problems.
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Affiliation(s)
- Václav Horejsí
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Praha, Czech Republic.
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150
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Stephens RH, Tanianis-Hughes J, Higgs NB, Humphrey M, Warhurst G. Region-dependent modulation of intestinal permeability by drug efflux transporters: in vitro studies in mdr1a(-/-) mouse intestine. J Pharmacol Exp Ther 2002; 303:1095-101. [PMID: 12438532 DOI: 10.1124/jpet.102.041236] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Information on the extent to which xenobiotics interact with P-glycoprotein (PGP) during transit through the intestine is crucial in determining the influence of PGP on oral drug absorption. We have recently described a novel use of isolated ileum from PGP-deficient mdr1a(-/-) mice to resolve PGP- and non-PGP-dependent drug efflux and provide a definitive measure of intrinsic drug permeability without recourse to inhibitors. The present study uses this approach to investigate the impact of PGP on intestinal permeability of paclitaxel and digoxin in different regions of the mouse intestine (jejunum, ileum, and proximal and distal colon). Absorption of paclitaxel and digoxin in tissues from wild-type mice was low and showed little regional variation. In contrast, absorption of both drugs was markedly higher in mdr1a(-/-) intestine, although the increase was highly region-dependent, with the ileum and distal colon showing the greatest effect and much smaller changes in the jejunum and proximal colon. These effects were accompanied by the abolition of paclitaxel and digoxin secretion in mdr1a(-/-) mice, suggesting that regional variations in intestinal permeability are masked by differential PGP expression, confirmed by immunoblotting studies. Propranolol permeability, which is not influenced by PGP, showed similar regional variation in both wild-type and mdr1a(-/-) tissues, suggesting that differences are at the level of transcellular permeability. These data suggest that the ileum and the distal colon are regions of relatively high transcellular permeability for xenobiotics that are compensated by enhanced expression of PGP.
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Affiliation(s)
- R H Stephens
- Gut Barrier Group, University of Manchester and Salford Hospitals Trust, Hope Hospital, Salford, United Kingdom
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