Sphingomyelin-dependence of cholesterol efflux mediated by ABCG1

Abstract

ABCG1, one of the half-type ATP binding cassette (ABC) proteins, mediates the efflux of cholesterol to HDL and functions in the reverse cholesterol transport from peripheral cells to the liver. We have shown that ABCG1 mediates the efflux of not only cholesterol but also sphingomyelin (SM) and phosphatidylcholine. Because SM preferentially associates with cholesterol, we examined whether it plays an important role in the ABCG1-mediated efflux of cholesterol. The efflux of cholesterol and SM mediated by ABCG1 was reduced in a mutant CHO-K1 cell line, LY-A, in which the cellular SM level is reduced because of a mutation of the ceramide transfer protein CERT. In contrast, CHO-K1 cells overexpressing CERT showed an increased efflux of cholesterol and SM mediated by ABCG1. The sensitivity of cells to methyl-β-cyclodextrin suggested that cholesterol in nonraft domains was increased due to the disruption of raft domains in LY-A cells. These results suggest that the ABCG1-mediated efflux of cholesterol and SM is dependent on the cellular SM level and distribution of cholesterol in the plasma membrane. ABCG1, one of the half-type ATP binding cassette (ABC) proteins, mediates the efflux of cholesterol to HDL and functions in the reverse cholesterol transport from peripheral cells to the liver. We have shown that ABCG1 mediates the efflux of not only cholesterol but also sphingomyelin (SM) and phosphatidylcholine. Because SM preferentially associates with cholesterol, we examined whether it plays an important role in the ABCG1-mediated efflux of cholesterol. The efflux of cholesterol and SM mediated by ABCG1 was reduced in a mutant CHO-K1 cell line, LY-A, in which the cellular SM level is reduced because of a mutation of the ceramide transfer protein CERT. In contrast, CHO-K1 cells overexpressing CERT showed an increased efflux of cholesterol and SM mediated by ABCG1. The sensitivity of cells to methyl-β-cyclodextrin suggested that cholesterol in nonraft domains was increased due to the disruption of raft domains in LY-A cells. These results suggest that the ABCG1-mediated efflux of cholesterol and SM is dependent on the cellular SM level and distribution of cholesterol in the plasma membrane. ATP binding cassette apolipoprotein A-I Chinese hamster ovary liver X receptor methyl-β-cyclodextrin phosphatidylcholine sphingomyelin scavenger receptor class B type I Cholesterol is essential to the body as a component of cellular membranes and a source of steroid hormones, but excess cholesterol is toxic and a risk factor for arteriosclerosis. Therefore, the removal of cholesterol from peripheral cells and from the body is important. Many ATP binding cassette (ABC) proteins have been reported to be involved in cholesterol homeostasis in the body (1.Takahashi K. Kimura Y. Nagata K. Yamamoto A. Matsuo M. Ueda K. ABC proteins: key molecules for lipid homeostasis.Med. Mol. Morphol. 2005; 38: 2-12Crossref PubMed Scopus (72) Google Scholar). The expression of ABCG1 and ABCA1 is induced by an excess of cholesterol via the nuclear receptors liver X receptor (LXR) and retinoid X receptor. ABCA1 is expressed ubiquitously and mediates the efflux of cholesterol and phosphatidylcholine (PC) to apolipoprotein A-I (apoA-I), which forms pre-β-HDL (2.Lee J.Y. Parks J.S. ATP-binding cassette transporter AI and its role in HDL formation.Curr. Opin. Lipidol. 2005; 16: 19-25Crossref PubMed Scopus (161) Google Scholar, 3.Tanaka A.R. Abe-Dohmae S. Ohnishi T. Aoki R. Morinaga G. Okuhira K-i. Ikeda Y. Kano F. Matsuo M. Kioka N. et al.Effects of mutations of ABCA1 in the first extracellular domain on subcellular trafficking and ATP binding/hydrolysis.J. Biol. Chem. 2003; 278: 8815-8819Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar). Mutations of ABCA1 are responsible for a genetic disease, Tangier disease, which is characterized by severe HDL deficiency (4.Brooks-Wilson A. Marcil M. Clee S.M. Zhang L.H. Roomp K. Dam M.van Yu L. Brewer C. Collins J.A. Molhuizen H.O. et al.Mutations in ABC1 in Tangier disease and familial high-density lipoprotein deficiency.Nat. Genet. 1999; 22: 336-345Crossref PubMed Scopus (1481) Google Scholar, 5.Bodzioch M. Orso E. Klucken J. Langmann T. Bottcher A. Diederich W. Drobnik W. Barlage S. Buchler C. Porsch-Ozcurumez M. et al.The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier disease.Nat. Genet. 1999; 22: 347-351Crossref PubMed Scopus (1328) Google Scholar, 6.Rust S. Rosier M. Funke H. Real J. Amoura Z. Piette J.C. Deleuze J.F. Brewer H.B. Duverger N. Denefle P. et al.Tangier disease is caused by mutations in the gene encoding ATP-binding cassette transporter 1.Nat. Genet. 1999; 22: 352-355Crossref PubMed Scopus (1249) Google Scholar). ABCG1 mediates the efflux of cholesterol to pre-β-HDL and HDL but not to lipid-free apoA-I (7.Wang N. Lan D. Chen W. Matsuura F. Tall A.R. ATP-binding cassette transporters G1 and G4 mediate cellular cholesterol efflux to high-density lipoproteins.Proc. Natl. Acad. Sci. USA. 2004; 101: 9774-9779Crossref PubMed Scopus (870) Google Scholar, 8.Vaughan A.M. Oram J.F. ABCA1 and ABCG1 or ABCG4 act sequentially to remove cellular cholesterol and generate cholesterol-rich HDL.J. Lipid Res. 2006; 47: 2433-2443Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar, 9.Gelissen I.C. Harris M. Rye K.A. Quinn C. Brown A.J. Kockx M. Cartland S. Packianathan M. Kritharides L. Jessup W. ABCA1 and ABCG1 synergize to mediate cholesterol export to apoA-I.Arterioscler. Thromb. Vasc. Biol. 2006; 26: 534-540Crossref PubMed Scopus (334) Google Scholar). Genetic diseases caused by mutations of ABCG1 have not been reported, but chow-fed mice lacking ABCG1 showed an accumulation of phospholipids and neutral lipids including cholesterol and triglyceride in liver and lung (10.Kennedy M.A. Barrera G.C. Nakamura K. Baldan A. Tarr P. Fishbein M.C. Frank J. Francone O.L. Edwards P.A. ABCG1 has a critical role in mediating cholesterol efflux to HDL and preventing cellular lipid accumulation.Cell Metab. 2005; 1: 121-131Abstract Full Text Full Text PDF PubMed Scopus (661) Google Scholar, 11.Baldan A. Tarr P. Vales C.S. Frank J. Shimotake T.K. Hawgood S. Edwards P.A. Deletion of the transmembrane transporter ABCG1 results in progressive pulmonary lipidosis.J. Biol. Chem. 2006; 281: 29401-29410Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar). Therefore, ABCG1 and ABCA1 play an important role in the removal of excess cholesterol from peripheral tissues, including macrophages. We previously reported that ABCG1 mediates the efflux of sphingomyelin (SM) and PC as well as cholesterol from cells (12.Kobayashi A. Takanezawa Y. Hirata T. Shimizu Y. Misasa K. Kioka N. Arai H. Ueda K. Matsuo M. Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.J. Lipid Res. 2006; 47: 1791-1802Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). SM and cholesterol form ordered microdomains (raft domains, detergent-resistant membranes) in the plasma membrane. Because it was assumed that SM influences the membrane dynamics, the effect of change in the SM content of the plasma membrane has been examined, and one report found that treating rat fibloblasts with SMase increased apoA-I- or apoE-dependent efflux of cholesterol (13.Ito J-i. Nagayasu Y. Yokoyama S. Cholesterol-sphingomyelin interaction in membrane and apolipoprotein-mediated cellular cholesterol efflux.J. Lipid Res. 2000; 41: 894-904Abstract Full Text Full Text PDF PubMed Google Scholar). But, in another report, treating human skin fibroblasts with SMase did not increase the apoA-I-dependent efflux of cholesterol or PC and reduced the HDL-mediated efflux of cholesterol (14.Mendez A.J. Lin G. Wade D.P. Lawn R.M. Oram J.F. Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway.J. Biol. Chem. 2001; 276: 3158-3166Abstract Full Text Full Text PDF PubMed Scopus (172) Google Scholar). Because treatment with SMase results in an accumulation of ceramide in the cell, effects of ceramide accumulation in cells could be involved. Therefore, the effect of SM in the plasma membrane on lipid efflux from cells has yet to be clarified. The ceramide transfer protein CERT is a cytosolic protein that has a PH (phosphatidylinositol 4-phosphate binding pleckstrin homology) domain, a coiled-coil domain, and a START (steroidogenic acute regulatory protein-related lipid transfer) domain (15.Hanada K. Kumagai K. Yasuda S. Miura Y. Kawano M. Fukasawa M. Nishijima M. Molecular machinery for non-vesicular trafficking of ceramide.Nature. 2003; 426: 803-809Crossref PubMed Scopus (807) Google Scholar, 16.Hanada K. Discovery of the molecular machinery CERT for endoplasmic reticulum-to-Golgi trafficking of ceramide.Mol. Cell. Biochem. 2006; 286: 23-31Crossref PubMed Scopus (64) Google Scholar). CERT transfers ceramide from the endoplasmic reticulum, where it is synthesized, to the Golgi, where it is used to synthesize SM (17.Kumagai K. Yasuda S. Okemoto K. Nishijima M. Kobayashi S. Hanada K. CERT mediates intermembrane transfer of various molecular species of ceramides.J. Biol. Chem. 2005; 280: 6488-6495Abstract Full Text Full Text PDF PubMed Scopus (170) Google Scholar). This transfer of ceramide is impaired in a Chinese hamster ovary (CHO) mutant cell line, LY-A, due to a misssense mutation of CERT (18.Hanada K. Hara T. Fukasawa M. Yamaji A. Umeda M. Nishijima M. Mammalian cell mutants resistant to a sphingomyelin-directed cytolysin. Genetic and biochemical evidence for complex formation of the LCB1 protein with the LCB2 protein for serine palmitoyltransferase.J. Biol. Chem. 1998; 273: 33787-33794Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). This cell line allowed us to investigate the effects of a reduction in SM without the effects of ceramide accumulation. In the present study, we changed the cellular SM level by using CERT missense mutation, knockdown, and overexpression, and examined the effects of the level on the efflux of cholesterol mediated by ABCG1. We demonstrated that the ABCG1-mediated efflux of cholesterol is correlated with the cellular SM level. The rabbit polyclonal anti-ABCG1 antibody and mouse monoclonal anti-FLAG antibody were purchased from Santa Cruz. The mouse monoclonal anti-vinculin antibody and SMase (from Bacillus cereus) were obtained from Sigma. HDL was acquired from Calbiochem. Other chemicals were purchased from Sigma, Amersham Biosciences, Wako Pure Chemical Industries, and Nacalai Tesque. CHO cells were grown in Ham's F-12 medium supplemented with 10% (v/v) FBS in 5% CO2 at 37°C. HeLaS3 cells were grown in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% (v/v) FBS in 5% CO2 at 37°C. When cultured in a sphingolipid-deficient medium, cells were washed with serum-free medium and incubated in Nutridoma-BO medium [Ham's F-12 medium (for CHO cells) or DMEM (for HeLaS3 cells) containing 1% Nutridoma-SP (Roche Molecular and for a K. Nishijima M. M. A. S. T. Y. are essential for the of Chinese hamster ovary cells. of the of a mutant in by Biol. Chem. Full Text PDF PubMed Google Scholar). CHO-K1 or HeLaS3 cells were with ABCG1, in which human ABCG1 (12.Kobayashi A. Takanezawa Y. Hirata T. Shimizu Y. Misasa K. Kioka N. Arai H. Ueda K. Matsuo M. Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.J. Lipid Res. 2006; 47: 1791-1802Abstract Full Text Full Text PDF PubMed Scopus (154) Google was the of or M. Kumagai K. Nishijima M. Hanada K. trafficking of ceramide from the endoplasmic to the a of Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google using to the and reverse were and the of as a for the of CERT. The are to human CERT. HeLaS3 cells were with the using were in at a of for the the cells were washed with medium and incubated with Ham's F-12 or DMEM containing and The of cholesterol in the medium was or as previously S. S. Y. H. Yokoyama S. of apolipoprotein-mediated HDL induced by in a cell 2000; PubMed Scopus Google Scholar). The SM content of the medium was as by and and of plasma sphingomyelin and Lipid Res. 2006; 47: Full Text Full Text PDF PubMed Scopus Google Scholar). SM was by by with and The at of the was with a Because the HDL to the medium cholesterol and the efflux was by the of cholesterol and SM in the HDL from in the were washed with and cellular lipids were with The cholesterol and SM content was as were washed with and in and 1% containing of of and of were on a 10% and with the rabbit polyclonal anti-ABCG1 or mouse monoclonal cultured on were with in containing of and and with in for the binding of the cells were incubated in 10% in were incubated for 1 with rabbit polyclonal anti-ABCG1 antibody in containing 10% and incubated with for 1 were with a using a were in or at a of or for the cells were washed with medium and incubated with Ham's F-12 medium containing B or methyl-β-cyclodextrin for 1 were incubated in Ham's F-12 medium containing for 1 and the was in the cells was in and the at was with a are as was with of was We previously showed that ABCG1 mediated the efflux of SM and PC as well as cholesterol from cells in an or (12.Kobayashi A. Takanezawa Y. Hirata T. Shimizu Y. Misasa K. Kioka N. Arai H. Ueda K. Matsuo M. Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.J. Lipid Res. 2006; 47: 1791-1802Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). the that which preferentially associates with cholesterol, plays an important role in the ABCG1-mediated efflux of cholesterol, we used a CHO-K1 mutant cell line LY-A, which has a missense mutation in and its with human CERT cell When cells were cultured in medium, the cellular content of SM and cholesterol in LY-A cells was to that in cells LY-A cells were cultured in Nutridoma-BO medium, a sphingolipid-deficient medium, the SM content of LY-A cells was of that of cells The cholesterol content of cells was not changed the When ABCG1 was expressed by a expression level of ABCG1 was by in LY-A and whether the cells were cultured in Nutridoma-BO medium or in medium not that ABCG1 was to the plasma membrane and that the was not by the not the reduction of SM content did not the expression level or subcellular distribution of ABCG1 in CHO of ABCG1 in LY-A cells. LY-A cells or in Nutridoma-BO medium for were or with ABCG1. the cell were were by 10% and ABCG1 was with anti-ABCG1 are by the of ABCG1 in and mutant CHO-K1 cells. LY-A cells cells and CHO-K1 cells were with ABCG1 or ABCG1 were by and with anti-ABCG1 antibody and are shown in and are shown in the effect of cellular SM content on the of ABCG1, we the ABCG1-mediated efflux of SM and cholesterol in the of HDL When the medium containing HDL of SM and of was to HDL cellular lipids by and the content of SM and cholesterol in the medium and When the medium containing HDL was to cells ABCG1, the content of SM and cholesterol in the medium increased to and Therefore, expression of ABCG1 increased the efflux of SM and cholesterol from LY-A cells and as well as from cells and with LY-A and or cells and as previously reported (12.Kobayashi A. Takanezawa Y. Hirata T. Shimizu Y. Misasa K. Kioka N. Arai H. Ueda K. Matsuo M. Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.J. Lipid Res. 2006; 47: 1791-1802Abstract Full Text Full Text PDF PubMed Scopus (154) Google the cells were cultured in were cultured in Nutridoma-BO medium the expression of ABCG1 increased the efflux of SM or cholesterol from LY-A cells and with cells and it increased the efflux of SM and cholesterol from cells and with cells and When was used of the results were obtained not expression of ABCG1 in the of changed cellular of or cholesterol, and SM not of SM and cholesterol from LY-A cells in Nutridoma-BO LY-A cells or in Nutridoma-BO medium for were or with ABCG1. of the the efflux of SM and cholesterol from cells in the of HDL was The of to are as the obtained with the LY-A CERT was using by a for CERT with the ABCG1 expression in HeLaS3 and the efflux of cholesterol to HDL was The effect of CERT was examined by a CERT in a of CERT was by in the cells. The efflux of cholesterol mediated by ABCG1 was by of CERT of CERT did not the efflux of cholesterol from HeLaS3 cells. These results suggest that the in SM content ABCG1-mediated efflux of SM and cholesterol. we examined the effect of of CERT on the efflux of SM and cholesterol from CHO-K1 cells of ABCG1 increased the efflux of SM and cholesterol and with CHO-K1 cells and of CERT with ABCG1 increased the efflux of SM and cholesterol and of CERT did not the efflux of SM and cholesterol, it increased SM content by of CERT did not cholesterol content in CHO-K1 cells of CERT the expression level of ABCG1 not the of ABCG1 to the plasma membrane results were also obtained with HeLaS3 cells These results suggest that an increase in SM content the ABCG1-mediated efflux of SM and cholesterol from cells. shown SM content the ABCG1-mediated efflux of cholesterol, cholesterol content was not changed by the mutation or of CERT. was that the change in the SM level the of cholesterol in the plasma membrane. because LY-A and cells showed sensitivity to which cells by binding to cholesterol at the cellular cells were suggested to of cholesterol molecules in the plasma with a M. Nishijima M. H. T. Hanada K. of sphingomyelin level without accumulation of ceramide in Chinese hamster ovary cells detergent-resistant membrane domains and cellular cholesterol efflux to Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). we examined the sensitivity of cells to and found a LY-A and cells in with a (15.Hanada K. Kumagai K. Yasuda S. Miura Y. Kawano M. Fukasawa M. Nishijima M. Molecular machinery for non-vesicular trafficking of ceramide.Nature. 2003; 426: 803-809Crossref PubMed Scopus (807) Google Scholar). LY-A, and cells were resistant to cultured in LY-A cells were to with CHO-K1 and cultured in Nutridoma-BO These results suggest that the distribution of cholesterol in the plasma membrane is and cholesterol is to the cellular SM level is In study, we examined the effect of the cellular SM level on the efflux of cholesterol mediated by ABCG1. we have shown that ABCG1 mediates the efflux of cholesterol and SM (12.Kobayashi A. Takanezawa Y. Hirata T. Shimizu Y. Misasa K. Kioka N. Arai H. Ueda K. Matsuo M. Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.J. Lipid Res. 2006; 47: 1791-1802Abstract Full Text Full Text PDF PubMed Scopus (154) Google it has not yet been whether the SM level cholesterol Because the treatment with SMase which as a of various cellular we used a CHO-K1 mutant cell line, LY-A, in which the content of SM be without accumulation of ceramide M. Nishijima M. H. T. Hanada K. of sphingomyelin level without accumulation of ceramide in Chinese hamster ovary cells detergent-resistant membrane domains and cellular cholesterol efflux to Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). We also used HeLaS3 in which the SM level was and CHO-K1 in which the SM level was of ABCG1 increased the efflux of SM and cholesterol from LY-A or cells cultured in it did not change cellular of SM and cholesterol that 10% of the lipid was which not be because ABCG1 was expressed in study, not the cells expressed ABCG1. When the SM level in LY-A cells was to of that in ABCG1-mediated efflux of SM and cholesterol from LY-A cells was the expression level of ABCG1 was not The results obtained with LY-A cells were with HeLaS3 in which CERT was by the of which an increase in SM the ABCG1-mediated efflux of SM and cholesterol from CHO-K1 and HeLaS3 cells. has also been reported that scavenger receptor class B type I mediates cholesterol efflux to HDL Y. N. Y. M.C. Tall A.R. receptor cellular cholesterol efflux.J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the expression level of was LY-A and and ABCG1 did not These results suggest that lipid efflux is mediated by ABCG1 and that the ABCG1-mediated efflux of SM and cholesterol is dependent on the cellular SM are for the the expression or subcellular distribution of ABCG1 be by the cellular SM and the of ABCG1 on the plasma membrane be increased the SM level is has been reported that ABCG1 to the but to the plasma membrane I.C. Harris M. Rye K.A. Quinn C. Brown A.J. Kockx M. Cartland S. Packianathan M. Kritharides L. Jessup W. ABCA1 and ABCG1 synergize to mediate cholesterol export to apoA-I.Arterioscler. Thromb. Vasc. Biol. 2006; 26: 534-540Crossref PubMed Scopus (334) Google and is present in membranes as well as in the plasma membrane in and that the distribution in the plasma membrane J.A. A.M. M. Zhang M. J. S. et and trafficking of the human ABCA1 Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). the ABCG1 expressed in LY-A, and HeLaS3 cells was to the plasma and the or subcellular was not changed the examined in is that the transport of ABCG1 is by CERT. This CERT with ABCG1, and the interaction is important for the transport of ABCG1. is because the ABCG1-mediated efflux of cholesterol from LY-A cells was as as that from the cells were incubated in the medium containing 10% is that the cellular cholesterol level or of cholesterol in the plasma membrane is by the cellular SM level. the cellular cholesterol content was not changed by the CERT mutation, as reported M. Nishijima M. H. T. Hanada K. of sphingomyelin level without accumulation of ceramide in Chinese hamster ovary cells detergent-resistant membrane domains and cellular cholesterol efflux to Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). was not changed by the or of the LY-A and cells showed a sensitivity to which cells by binding to cholesterol at the cellular These results suggest that the cellular SM level not the of cholesterol molecules in the plasma membrane. is that ABCG1 SM and cholesterol as to is the the cellular SM level the efflux of cholesterol mediated by ABCG1. the of cholesterol and SM by ABCG1 from LY-A CHO-K1 and cells overexpressing CERT were not but from to that ABCG1 did not mediate a of SM and cholesterol. a is that ABCG1 preferentially functions in raft domains in the plasma membrane. Because SM and cholesterol are important of raft domains, the in the SM level the of raft domains in the plasma membrane. was reported that HDL the efflux of cholesterol from raft domains of human fibroblasts and (14.Mendez A.J. Lin G. Wade D.P. Lawn R.M. Oram J.F. Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway.J. Biol. Chem. 2001; 276: 3158-3166Abstract Full Text Full Text PDF PubMed Scopus (172) Google Scholar, W. H. Bottcher A. A. G. H. G. and lipid efflux from distinct PubMed Scopus Google Scholar). cholesterol to by the mutation of that the distribution of cholesterol in the plasma membrane is These suggest that ABCG1 the raft cholesterol and domains, which cholesterol Fukasawa et M. Nishijima M. H. T. Hanada K. of sphingomyelin level without accumulation of ceramide in Chinese hamster ovary cells detergent-resistant membrane domains and cellular cholesterol efflux to Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google reported that was in ceramide in CHO-K1 and LY-A cultured in Nutridoma-BO the that a mutation in CERT of ceramide in domains, which the cholesterol efflux mediated by ABCG1, be of whether ABCG1 and functions in membrane domains or SM and cholesterol as is was reported that apoA-I cholesterol from HDL cholesterol from rafts of human fibroblasts and (14.Mendez A.J. Lin G. Wade D.P. Lawn R.M. Oram J.F. Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway.J. Biol. Chem. 2001; 276: 3158-3166Abstract Full Text Full Text PDF PubMed Scopus (172) Google Scholar, W. H. Bottcher A. A. G. H. G. and lipid efflux from distinct PubMed Scopus Google Scholar). The treatment of cells with SMase increased the apoA-I-dependent efflux of cholesterol (13.Ito J-i. Nagayasu Y. Yokoyama S. Cholesterol-sphingomyelin interaction in membrane and apolipoprotein-mediated cellular cholesterol efflux.J. Lipid Res. 2000; 41: 894-904Abstract Full Text Full Text PDF PubMed Google it reduced the HDL-mediated efflux (14.Mendez A.J. Lin G. Wade D.P. Lawn R.M. Oram J.F. Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway.J. Biol. Chem. 2001; 276: 3158-3166Abstract Full Text Full Text PDF PubMed Scopus (172) Google Scholar). ABCG1 cholesterol to domains by and the domains from by ABCA1 A.M. Oram J.F. ABCG1 cell cholesterol to domains by lipoprotein but not by Biol. Chem. 2005; 280: Full Text Full Text PDF PubMed Scopus Google Scholar). we have found that the efflux of cholesterol from LY-A cells mediated by ABCA1 is increased cells are cultured in Nutridoma-BO medium in to that mediated by ABCG1 K. K. Hanada K. Kioka N. Matsuo M. Ueda K. cholesterol efflux by ABCA1 from Chinese hamster ovary Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). These suggest that the the efflux of cholesterol ABCA1 and ABCG1. In we have demonstrated that the ABCG1-mediated efflux of cholesterol is dependent on the cellular SM level and with the efflux of These results suggest that lipid efflux by ABCG1 could be by the cellular level and distribution of cholesterol in the plasma membrane. This was by for and from the of and and from the and the and with