Transbilayer phospholipid movements in ABCA1-deficient cells.
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.
Williamson
Patrick
P
Department of Biology, Amherst College, Amherst, Massachusetts, United States of America. plwilliamson@amherst.edu
Halleck
Margaret S
MS
Malowitz
Jonathan
J
Ng
Susan
S
Fan
Xiaoxuan
X
Krahling
Stephen
S
Remaley
Alan T
AT
Schlegel
Robert A
RA
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
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
Lancet. 1999 Oct 16;354(9187):1341-6
10533863
Blood. 2005 Jul 15;106(2):542-9
15790791
Nat Genet. 2000 Feb;24(2):192-6
10655069
Proc Natl Acad Sci U S A. 2000 Apr 11;97(8):4245-50
10760292
Nature. 2000 Jun 8;405(6787):647-55
10864315
Nat Cell Biol. 2000 Jul;2(7):399-406
10878804
Cell Death Differ. 2000 Jul;7(7):645-53
10889509
J Biol Chem. 2000 Sep 15;275(37):28634-40
10893411
J Biol Chem. 2000 Oct 20;275(42):33053-8
10918065
J Biol Chem. 2000 Nov 3;275(44):34508-11
10918070
Biochemistry. 2000 Nov 21;39(46):14113-20
11087359
Nat Cell Biol. 1999 Nov;1(7):454-6
10559991
Biochem Biophys Res Commun. 2001 Jan 26;280(3):818-23
11162594
J Biol Chem. 2001 Mar 30;276(13):9955-60
11150301
J Biol Chem. 2001 Jun 29;276(26):23742-7
11309399
Biochemistry. 2001 Jul 10;40(27):8065-72
11434775
Cell Death Differ. 2001 Jun;8(6):551-63
11536005
J Cell Sci. 2001 Oct;114(Pt 20):3631-42
11707515
Clin Chem. 2001 Dec;47(12):2089-97
11719471
J Biol Chem. 2002 May 17;277(20):17797-803
11893753
Biochim Biophys Acta. 2002 Dec 30;1585(2-3):53-63
12531537
J Biol Chem. 2005 Jul 15;280(28):26321-9
15905177
Biochemistry. 2006 Mar 28;45(12):3981-7
16548525
Endocrinology. 2003 Mar;144(3):1062-73
12586783
J Lipid Res. 2003 Apr;44(4):828-36
12562845
J Leukoc Biol. 2003 Nov;74(5):846-56
12960250
Mol Cell. 2004 May 7;14(3):277-87
15125832
Mol Biol Cell. 2004 Jun;15(6):2863-72
15064349
Biochim Biophys Acta. 2004 Mar 22;1636(2-3):119-28
15164759
Curr Opin Struct Biol. 2004 Aug;14(4):426-31
15313236
Eur J Immunol. 1981 Oct;11(10):805-15
7308288
Genetics. 1991 Sep;129(1):79-94
1936965
J Immunol. 1992 Apr 1;148(7):2207-16
1545126
Biochemistry. 1992 Jul 14;31(27):6355-60
1627574
J Immunol. 1992 Dec 15;149(12):4029-35
1281199
Biochemistry. 1993 Mar 9;32(9):2337-44
8443175
Biochemistry. 1995 Aug 22;34(33):10448-55
7654698
J Exp Med. 1995 Nov 1;182(5):1597-601
7595231
EMBO J. 1996 Jan 15;15(2):226-35
8617198
Biochim Biophys Acta. 2002 Dec 30;1585(2-3):64-71
12531538
Science. 1996 Jun 7;272(5267):1495-7
8633245
Mol Biol Cell. 1997 May;8(5):767-78
9168465
Nature. 1998 Apr 2;392(6675):505-9
9548256
Cell. 1998 Jun 12;93(6):951-60
9635425
Cell Death Differ. 1999 Feb;6(2):183-9
10200565
Cell Death Differ. 1999 Mar;6(3):262-70
10200577
Cell Death Differ. 1999 Jun;6(6):583-92
10381656
Nat Genet. 1999 Aug;22(4):336-45
10431236
Nat Genet. 1999 Aug;22(4):347-51
10431237
Nat Genet. 1999 Aug;22(4):352-5
10431238
J Lipid Res. 1999 Oct;40(10):1769-81
10508196
Cell Mol Life Sci. 2005 May;62(9):971-88
15761668
Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12685-90
10535983