title: Transbilayer phospholipid movements in ABCA1-deficient cells.
abstract: Tangier disease is an inherited disorder that results in a deficiency in circulating levels of HDL. Although the disease is known to be caused by mutations in the ABCA1 gene, the mechanism by which lesions in the ABCA1 ATPase effect this outcome is not known. The inability of ABCA1 knockout mice (ABCA1-/-) to load cholesterol and phospholipids onto apoA1 led to a proposal that ABCA1 mediates the transbilayer externalization of phospholipids, an activity integral not only to the formation of HDL particles but also to another, distinct process: the recognition and clearance of apoptotic cells by macrophages. Expression of phosphatidylserine (PS) on the surface of both macrophages and their apoptotic targets is required for efficient engulfment of the apoptotic cells, and it has been proposed that ABCA1 is required for transbilayer externalization of PS to the surface of both cell types. To determine whether ABCA1 is responsible for any of the catalytic activities known to control transbilayer phospholipid movements, these activities were measured in cells from ABCA1-/- mice and from Tangier individuals as well as ABCA1-expressing HeLa cells. Phospholipid movements in either normal or apoptotic lymphocytes or in macrophages were not inhibited when cells from knockout and wildtype mice or immortalized cells from Tangier individuals vs normal individuals were compared. Exposure of PS on the surface of normal thymocytes, apoptotic thymocytes and elicited peritoneal macrophages from wildtype and knockout mice or B lymphocytes from normal and Tangier individuals, as measured by annexin V binding, was also unchanged. No evidence was found of ABCA1-stimulated active PS export, and spontaneous PS movement to the outer leaflet in the presence or absence of apoA1 was unaffected by the presence or absence of ABCA1. Normal or Tangier B lymphocytes and macrophages were also identical in their ability to serve as targets or phagocytes, respectively, in apoptotic cell clearance assays. No evidence was found to support the suggestion that ABCA1 is involved in transport to the macrophage cell surface of annexins I and II, known to enhance phagocytosis of apoptotic cells. These results show that mutations in ABCA1 do not measurably reduce the rate of transbilayer movements of phospholipids in either the engulfing macrophage or the apoptotic target, thus discounting catalysis of transbilayer movements of phospholipids as the mechanism by which ABCA1 facilitates loading of phospholipids and cholesterol onto apoA1.
authors: Department of Biology, Amherst College, Amherst, Massachusetts, United States of America. plwilliamson@amherst.edu
authors: Patrick
authors: P
authors: Williamson
authors: Margaret S
authors: MS
authors: Halleck
authors: Jonathan
authors: J
authors: Malowitz
authors: Susan
authors: S
authors: Ng
authors: Xiaoxuan
authors: X
authors: Fan
authors: Stephen
authors: S
authors: Krahling
authors: Alan T
authors: AT
authors: Remaley
authors: Robert A
authors: RA
authors: Schlegel
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010718:Phosphatidylserines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D013631:Tangier Disease / Q000235:genetics / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008051:Lipid Bilayers; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D002118:Calcium
references: Lancet. 1999 Oct 16;354(9187):1341-6
references: 10533863
references: Blood. 2005 Jul 15;106(2):542-9
references: 15790791
references: Nat Genet. 2000 Feb;24(2):192-6
references: 10655069
references: Proc Natl Acad Sci U S A. 2000 Apr 11;97(8):4245-50
references: 10760292
references: Nature. 2000 Jun 8;405(6787):647-55
references: 10864315
references: Nat Cell Biol. 2000 Jul;2(7):399-406
references: 10878804
references: Cell Death Differ. 2000 Jul;7(7):645-53
references: 10889509
references: J Biol Chem. 2000 Sep 15;275(37):28634-40
references: 10893411
references: J Biol Chem. 2000 Oct 20;275(42):33053-8
references: 10918065
references: J Biol Chem. 2000 Nov 3;275(44):34508-11
references: 10918070
references: Biochemistry. 2000 Nov 21;39(46):14113-20
references: 11087359
references: Nat Cell Biol. 1999 Nov;1(7):454-6
references: 10559991
references: Biochem Biophys Res Commun. 2001 Jan 26;280(3):818-23
references: 11162594
references: J Biol Chem. 2001 Mar 30;276(13):9955-60
references: 11150301
references: J Biol Chem. 2001 Jun 29;276(26):23742-7
references: 11309399
references: Biochemistry. 2001 Jul 10;40(27):8065-72
references: 11434775
references: Cell Death Differ. 2001 Jun;8(6):551-63
references: 11536005
references: J Cell Sci. 2001 Oct;114(Pt 20):3631-42
references: 11707515
references: Clin Chem. 2001 Dec;47(12):2089-97
references: 11719471
references: J Biol Chem. 2002 May 17;277(20):17797-803
references: 11893753
references: Biochim Biophys Acta. 2002 Dec 30;1585(2-3):53-63
references: 12531537
references: J Biol Chem. 2005 Jul 15;280(28):26321-9
references: 15905177
references: Biochemistry. 2006 Mar 28;45(12):3981-7
references: 16548525
references: Endocrinology. 2003 Mar;144(3):1062-73
references: 12586783
references: J Lipid Res. 2003 Apr;44(4):828-36
references: 12562845
references: J Leukoc Biol. 2003 Nov;74(5):846-56
references: 12960250
references: Mol Cell. 2004 May 7;14(3):277-87
references: 15125832
references: Mol Biol Cell. 2004 Jun;15(6):2863-72
references: 15064349
references: Biochim Biophys Acta. 2004 Mar 22;1636(2-3):119-28
references: 15164759
references: Curr Opin Struct Biol. 2004 Aug;14(4):426-31
references: 15313236
references: Eur J Immunol. 1981 Oct;11(10):805-15
references: 7308288
references: Genetics. 1991 Sep;129(1):79-94
references: 1936965
references: J Immunol. 1992 Apr 1;148(7):2207-16
references: 1545126
references: Biochemistry. 1992 Jul 14;31(27):6355-60
references: 1627574
references: J Immunol. 1992 Dec 15;149(12):4029-35
references: 1281199
references: Biochemistry. 1993 Mar 9;32(9):2337-44
references: 8443175
references: Biochemistry. 1995 Aug 22;34(33):10448-55
references: 7654698
references: J Exp Med. 1995 Nov 1;182(5):1597-601
references: 7595231
references: EMBO J. 1996 Jan 15;15(2):226-35
references: 8617198
references: Biochim Biophys Acta. 2002 Dec 30;1585(2-3):64-71
references: 12531538
references: Science. 1996 Jun 7;272(5267):1495-7
references: 8633245
references: Mol Biol Cell. 1997 May;8(5):767-78
references: 9168465
references: Nature. 1998 Apr 2;392(6675):505-9
references: 9548256
references: Cell. 1998 Jun 12;93(6):951-60
references: 9635425
references: Cell Death Differ. 1999 Feb;6(2):183-9
references: 10200565
references: Cell Death Differ. 1999 Mar;6(3):262-70
references: 10200577
references: Cell Death Differ. 1999 Jun;6(6):583-92
references: 10381656
references: Nat Genet. 1999 Aug;22(4):336-45
references: 10431236
references: Nat Genet. 1999 Aug;22(4):347-51
references: 10431237
references: Nat Genet. 1999 Aug;22(4):352-5
references: 10431238
references: J Lipid Res. 1999 Oct;40(10):1769-81
references: 10508196
references: Cell Mol Life Sci. 2005 May;62(9):971-88
references: 15761668
references: Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12685-90
references: 10535983