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The Efficient Cellular Uptake of High Density Lipoprotein Lipids via Scavenger Receptor Class B Type I Requires Not Only Receptor-mediated Surface Binding but Also Receptor-specific Lipid Transfer Mediated by Its Extracellular Domain

1998; Elsevier BV; Volume: 273; Issue: 41 Linguagem: Inglês

10.1074/jbc.273.41.26338

ISSN

1083-351X

Autores

Xiang-ju Gu, Bernardo L. Trigatti, Shangzhe Xu, Susan Acton, Jodie L. Babitt, Monty Krieger,

Tópico(s)

Diabetes, Cardiovascular Risks, and Lipoproteins

Resumo

The class B type I scavenger receptor, (SR-BI), is a member of the CD36 superfamily of proteins and is a physiologically relevant, high affinity cell surface high density lipoprotein (HDL) receptor that mediates selective lipid uptake. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated uptake via coated pits and vesicles (e.g. the low density lipoprotein receptor pathway) in that it involves efficient transfer of the lipids, but not the outer shell proteins, from HDL to cells. The abilities of SR-BI and CD36, both of which are class B scavenger receptors, to bind HDL and mediate cellular uptake of HDL-associated lipid when transiently expressed in COS cells were examined. For these experiments, the binding of HDL to cells was assessed using either 125I- or Alexa (a fluorescent dye)-HDL in which the apolipoproteins on the surface of the HDL particles were covalently modified. Lipid transfer was measured using HDL noncovalently labeled by the fluorescent lipid 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate. Although both mSR-BI and human CD36 (hCD36) could mediate the binding of HDL in a punctate pattern across the surfaces of cells, only mSR-BI efficiently mediated the transfer of lipid to the cells. Analysis of point mutants established that the major sites of fatty acylation of mSR-BI are Cys462 and Cys470 and that fatty acylation is not required for receptor clustering, HDL binding, or efficient lipid transfer. Generation of mSR-BI/hCD36 domain swap chimeras showed that the differences in lipid uptake activities between mSR-BI and hCD36 were not due to differences between their two sets of transmembrane and cytoplasmic domains but rather result from differences in their large extracellular loop domains. These results show that high affinity binding to a cell surface receptor is not sufficient to ensure efficient cellular lipid uptake from HDL. Thus, SR-BI-mediated binding combined with SR-BI-dependent facilitated transfer of lipid from the HDL particle to the cell appears to be the most likely mechanism for the bulk of the selective uptake of cholesteryl esters from HDL to the liver and steroidogenic tissues. The class B type I scavenger receptor, (SR-BI), is a member of the CD36 superfamily of proteins and is a physiologically relevant, high affinity cell surface high density lipoprotein (HDL) receptor that mediates selective lipid uptake. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated uptake via coated pits and vesicles (e.g. the low density lipoprotein receptor pathway) in that it involves efficient transfer of the lipids, but not the outer shell proteins, from HDL to cells. The abilities of SR-BI and CD36, both of which are class B scavenger receptors, to bind HDL and mediate cellular uptake of HDL-associated lipid when transiently expressed in COS cells were examined. For these experiments, the binding of HDL to cells was assessed using either 125I- or Alexa (a fluorescent dye)-HDL in which the apolipoproteins on the surface of the HDL particles were covalently modified. Lipid transfer was measured using HDL noncovalently labeled by the fluorescent lipid 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate. Although both mSR-BI and human CD36 (hCD36) could mediate the binding of HDL in a punctate pattern across the surfaces of cells, only mSR-BI efficiently mediated the transfer of lipid to the cells. Analysis of point mutants established that the major sites of fatty acylation of mSR-BI are Cys462 and Cys470 and that fatty acylation is not required for receptor clustering, HDL binding, or efficient lipid transfer. Generation of mSR-BI/hCD36 domain swap chimeras showed that the differences in lipid uptake activities between mSR-BI and hCD36 were not due to differences between their two sets of transmembrane and cytoplasmic domains but rather result from differences in their large extracellular loop domains. These results show that high affinity binding to a cell surface receptor is not sufficient to ensure efficient cellular lipid uptake from HDL. Thus, SR-BI-mediated binding combined with SR-BI-dependent facilitated transfer of lipid from the HDL particle to the cell appears to be the most likely mechanism for the bulk of the selective uptake of cholesteryl esters from HDL to the liver and steroidogenic tissues. high density lipoprotein scavenger receptor class B type I bovine serum albumin murine SR-BI human CD36 phosphate-buffered saline polymerase chain reaction Chinese hamster ovary 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate. The protective role of HDL1 against cardiovascular disease is commonly attributed to its ability to remove excess cholesterol from cells in the arterial wall and transport it to the liver for disposal, a process called reverse cholesterol transport (1Glomset J.A. J. Lipid Res. 1968; 9: 155-167Abstract Full Text PDF PubMed Google Scholar,2Eisenberg S. J. Lipid Res. 1984; 25: 1017-1058Abstract Full Text PDF PubMed Google Scholar). In addition to delivering cholesterol to the liver, HDL has been shown to be a significant source of cholesterol both for steroidogenesis and for cholesterol storage depots in steroidogenic tissues (adrenal gland, ovary, testis) and cells (3Kovanen P.T. Schneider W.J. Hillman G.M. Goldstein J.L. Brown M.S. J. Biol. Chem. 1979; 254: 5498-5505Abstract Full Text PDF PubMed Google Scholar, 4Gwynne J.T. Strauss III, J.F. Endocr. Rev. 1982; 3: 299-329Crossref PubMed Scopus (440) Google Scholar, 5Azhar S. Stewart D. Reaven E. J. 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Natl., Acad. Sci. U. S. A. 1998; 95: 4077-4080Crossref PubMed Scopus (114) Google Scholar, 27Acton S.L. Scherer P.E. Lodish H.F. Krieger M. J. Biol. Chem. 1994; 269: 21003-21009Abstract Full Text PDF PubMed Google Scholar, 28Rigotti A. Acton S.L. Krieger M. J. Biol. Chem. 1995; 270: 16221-16224Abstract Full Text Full Text PDF PubMed Scopus (487) Google Scholar, 29Murao K. Terpstra V. Green S.R. Kondratenko N. Steinberg D. Quehenberger O. J. Biol. Chem. 1997; 272: 17551-17557Abstract Full Text Full Text PDF PubMed Scopus (286) Google Scholar, 30Calvo D. Gomez-Coronado D. Lasuncion M.A. Vega M.A. Arterioscler. Thromb. Vasc. Biol. 1997; 17: 2341-2349Crossref PubMed Scopus (210) Google Scholar) was recently shown to be the first molecularly well defined cell surface HDL receptor (21Acton S. Rigotti A. Landschulz K.T. Xu S. Hobbs H.H. Krieger M. Science. 1996; 271: 518-520Crossref PubMed Scopus (1974) Google Scholar). Subsequent studies (reviewed in Refs. 9Rigotti A. Trigatti B. Babitt J. Penman M. Xu S. Krieger M. Curr. Opin. Lipidol. 1997; 8: 181-188Crossref PubMed Scopus (176) Google Scholar and 26Krieger M. Proc. Natl., Acad. Sci. U. S. A. 1998; 95: 4077-4080Crossref PubMed Scopus (114) Google Scholar) have demonstrated that SR-BI is a physiologically relevant HDL receptor that mediates selective cholesterol uptake (9Rigotti A. Trigatti B. Babitt J. Penman M. Xu S. Krieger M. Curr. Opin. Lipidol. 1997; 8: 181-188Crossref PubMed Scopus (176) Google Scholar, 21Acton S. Rigotti A. Landschulz K.T. Xu S. Hobbs H.H. Krieger M. Science. 1996; 271: 518-520Crossref PubMed Scopus (1974) Google Scholar, 26Krieger M. Proc. Natl., Acad. Sci. U. S. A. 1998; 95: 4077-4080Crossref PubMed Scopus (114) Google Scholar). In cultured mammalian cells, SR-BI binding to HDL (apparently via its apolipoproteins (Ref. 31Xu S. Laccotripe M. Huang X. Rigotti A. Zannis V.I. Krieger M. J. Lipid. Res. 1997; 38: 1289-1298Abstract Full Text PDF PubMed Google Scholar; also see Ref. 28Rigotti A. Acton S.L. Krieger M. J. Biol. Chem. 1995; 270: 16221-16224Abstract Full Text Full Text PDF PubMed Scopus (487) Google Scholar) results in efficient selective uptake (21Acton S. Rigotti A. Landschulz K.T. Xu S. Hobbs H.H. Krieger M. Science. 1996; 271: 518-520Crossref PubMed Scopus (1974) Google Scholar). Although SR-BI has been shown to cluster in caveolae-like domains (32Babitt J. Trigatti B. Rigotti A. Smart E.J. Anderson R.G.W. Xu S. Krieger M. J. Biol. Chem. 1997; 272: 13242-13249Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar), the detailed mechanism of SR-BI-mediated selective uptake has not been defined. For example, it has been uncertain if SR-BI mediates selective uptake merely by bringing HDL in close proximity to the plasma membrane or if SR-BI or other cellular components directly facilitate the lipid transfer after HDL is bound to the cell. In vivo SR-BI is expressed in adult mice (21Acton S. Rigotti A. Landschulz K.T. Xu S. Hobbs H.H. Krieger M. Science. 1996; 271: 518-520Crossref PubMed Scopus (1974) Google Scholar), rats (33Landschulz K.T. Pathak R.K. Rigotti A. Krieger M. Hobbs H.H. J. Clin. Invest. 1996; 98: 984-995Crossref PubMed Scopus (461) Google Scholar), cows (34Rajapaksha W.R. McBride M. Robertson L. O'Shaughnessy P.J. Mol. Cell. Endocrinol. 1997; 134: 59-67Crossref PubMed Scopus (44) Google Scholar), and humans (29Murao K. Terpstra V. Green S.R. Kondratenko N. Steinberg D. Quehenberger O. J. Biol. Chem. 1997; 272: 17551-17557Abstract Full Text Full Text PDF PubMed Scopus (286) Google Scholar, 35Cao G. Garcia C.K. Wyne K.L. Schultz R.A. Parker K.L. Hobbs H.H. J. Biol. Chem. 1997; 272: 33068-33076Abstract Full Text Full Text PDF PubMed Scopus (227) Google Scholar) at high levels in precisely those tissues (liver, steroidogenic) that are most active in selective uptake of HDL cholesterol (12Glass C. Pittman R.C. Weinstein D.B. Steinberg D. Proc. Natl. Acad. Sci. U. S. A. 1983; 80: 5435-5439Crossref PubMed Scopus (420) Google Scholar, 13Leitersdorf E. Stein O. Eisenberg S. Stein Y. Biochim. Biophys. Acta. 1984; 796: 72-82Crossref PubMed Scopus (65) Google Scholar, 14Glass C. Pittman R.C. Civen M. Steinberg D. J. Biol. Chem. 1985; 260: 744-750Abstract Full Text PDF PubMed Google Scholar). The temporal and spatial expression of SR-BI during murine embryogenesis suggests that SR-BI plays a role in delivering cholesterol to the developing fetus (36Hatzopoulos A.K. Rigotti A. Rosenberg R.D. Krieger M. J. Lipid Res. 1998; 39: 495-508Abstract Full Text Full Text PDF PubMed Google Scholar, 37Wyne K.L. Woollett L.A. J. Lipid Res. 1998; 39: 518-530Abstract Full Text Full Text PDF PubMed Google Scholar). Furthermore, in vivo studies with mice and rats, as well as experiments with murine and human cultured cell lines, have shown that SR-BI expression in steroidogenic tissues is coordinately regulated with steroidogenesis (33Landschulz K.T. Pathak R.K. Rigotti A. Krieger M. Hobbs H.H. J. Clin. Invest. 1996; 98: 984-995Crossref PubMed Scopus (461) Google Scholar, 34Rajapaksha W.R. McBride M. Robertson L. O'Shaughnessy P.J. Mol. Cell. Endocrinol. 1997; 134: 59-67Crossref PubMed Scopus (44) Google Scholar, 38Rigotti A. Edelman E.R. Seifert P. Iqbal S.N. DeMattos R.B. Temel R.E. Krieger M. Williams D.L. J. Biol. Chem. 1996; 271: 33545-33549Abstract Full Text Full Text PDF PubMed Scopus (204) Google Scholar, 39Wang N. Weng W. Breslow J.L. Tall A.R. J. Biol. Chem. 1996; 271: 21001-21004Abstract Full Text Full Text PDF PubMed Scopus (191) Google Scholar, 40Liu J. Voutilainen R. Heikkila P. Kahri A.I. J. Clin. Endocrinol. Metab. 1997; 82: 2522-2527PubMed Google Scholar). Fluiter et al. have also reported additional strong correlative evidence for the importance of SR-BI in selective cholesterol uptake by hepatocytes in vitro and in vivo (41Fluiter K. van Berkel T.J. Biochem. J. 1997; 326: 515-519Crossref PubMed Scopus (43) Google Scholar, 42Flutier K. van der Westhuijzen D.R. van Berkel T.J. J. Biol. Chem. 1998; 273: 8434-8438Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar). Direct evidence for a physiologically relevant role of SR-BI in HDL metabolism and selective uptake has recently appeared (reviewed in Ref.26Krieger M. Proc. Natl., Acad. Sci. U. S. A. 1998; 95: 4077-4080Crossref PubMed Scopus (114) Google Scholar). Temel et al. (10Temel R.E. Trigatti B. DeMattos R.B. Azhar S. Krieger M. Williams D.L. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 13600-13605Crossref PubMed Scopus (207) Google Scholar) used a SR-BI-specific blocking antibody to provide the first evidence that SR-BI is directly involved in mediating selective uptake in a physiologic system (hormone-stimulated cultured adrenocortical cells). Kozarsky et al. (43Kozarsky K.F. Donahee M.H. Rigotti A. Iqbal S.N. Edelman E.R. Krieger M. Nature. 1997; 387: 414-417Crossref PubMed Scopus (625) Google Scholar) used a recombinant adenovirus to dramatically induce hepatic overexpression of SR-BI in mice. The consequent virtual disappearance of plasma HDL and doubling of biliary cholesterol indicated that SR-BI may play roles in hepatic HDL metabolism, in determining plasma HDL concentrations, and possibly in mediating cholesterol efflux from cells (a suggestion recently confirmed byin vitro studies of efflux (44Ji Y. Jian B. Wang N. Sun Y. de la Llera Moya M. Phillips M.C. Rothblat G.H. Swaney J.B. Tall A.R. J. Biol. Chem. 1997; 272: 20982-20985Abstract Full Text Full Text PDF PubMed Scopus (629) Google Scholar, 45Jian B. de la Llera-Moya M. Ji Y. Wang N. Phillips M.C. Swaney J.B. Tall A.R. Rothblat G.H. J. Biol. Chem. 1998; 273: 5599-5606Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar)). The first targeted disruption (null mutation) of the SR-BI gene in mice by Rigottiet al. (46Rigotti A. Trigatti B.L. Penman M. Rayburn H. Herz J. Krieger M. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 12610-12615Crossref PubMed Scopus (746) Google Scholar) and their analysis of the heterozygous and homozygous mutant animals definitively established that SR-BI can play a key role in determining plasma HDL cholesterol levels, almost certainly because reduced expression of SR-BI resulted in decreased selective cholesterol uptake in the liver. These findings were recently confirmed by subsequent analysis of mice that exhibit partially reduced levels of SR-BI expression (47Varban M.L. Rinninger F. Wang N. Fairchild-Huntress V. Dunmore J.H. Fang Q. Gosselin M.L. Dixon K.L. Deeds J.D. Acton S.L. Tall A.R. Huszar D. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 4619-4624Crossref PubMed Scopus (265) Google Scholar) and that resemble the heterozygous null mutants of Rigotti et al. (46Rigotti A. Trigatti B.L. Penman M. Rayburn H. Herz J. Krieger M. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 12610-12615Crossref PubMed Scopus (746) Google Scholar). Based on the in vitro activity and tissue distribution of the human SR-BI (29Murao K. Terpstra V. Green S.R. Kondratenko N. Steinberg D. Quehenberger O. J. Biol. Chem. 1997; 272: 17551-17557Abstract Full Text Full Text PDF PubMed Scopus (286) Google Scholar,35Cao G. Garcia C.K. Wyne K.L. Schultz R.A. Parker K.L. Hobbs H.H. J. Biol. Chem. 1997; 272: 33068-33076Abstract Full Text Full Text PDF PubMed Scopus (227) Google Scholar), it is reasonable to suggest that the function of SR-BI in humans (originally called CLA-1 (48Calvo D. Vega M.A. J. Biol. Chem. 1993; 268: 18929-18935Abstract Full Text PDF PubMed Google Scholar)) may be similar to that in mice. Thus, SR-BI, the first well characterized receptor for selective uptake, may influence the development and progression of atherosclerosis, and it is an attractive candidate for therapeutic intervention in this disease (9Rigotti A. Trigatti B. Babitt J. Penman M. Xu S. Krieger M. Curr. Opin. Lipidol. 1997; 8: 181-188Crossref PubMed Scopus (176) Google Scholar, 21Acton S. Rigotti A. Landschulz K.T. Xu S. Hobbs H.H. Krieger M. Science. 1996; 271: 518-520Crossref PubMed Scopus (1974) Google Scholar, 26Krieger M. Proc. Natl., Acad. Sci. U. S. A. 1998; 95: 4077-4080Crossref PubMed Scopus (114) Google Scholar, 43Kozarsky K.F. Donahee M.H. Rigotti A. Iqbal S.N. Edelman E.R. Krieger M. Nature. 1997; 387: 414-417Crossref PubMed Scopus (625) Google Scholar, 46Rigotti A. Trigatti B.L. Penman M. Rayburn H. Herz J. Krieger M. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 12610-12615Crossref PubMed Scopus (746) Google Scholar). SR-BI is a member of the CD36 superfamily of proteins, which includes CD36 (reviewed in Ref. 49Greenwalt D.E. Lipsky R.H. Ockenhouse C.F. Ikeda H. Tandon N.N. Jamieson G.A. Blood. 1992; 80: 1105-1115Crossref PubMed Google Scholar), LIMPII (a lysosomal protein) (50Vega M.A. Segui-Real B. Garcia J.A. Cales C. Rodriguez F. Vanderkerckhove J. 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On day 1, cells were transfected with the plasmids using the DEAE-dextran method as described previously (27Acton S.L. Scherer P.E. Lodish H.F. Krieger M. J. Biol. Chem. 1994; 269: 21003-21009Abstract Full Text PDF PubMed Google Scholar). Cells were harvested with trypsin and replated in medium B containing 1 mm sodiumn-butyrate (m

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