Human ABCA7 supports apolipoprotein-mediated release of cellular cholesterol and phospholipid to generate high density lipoprotein.
Apolipoprotein-mediated release of cellular cholesterol and phospholipids was induced in HEK293 cells by expressing human ATP-binding cassette transporter A7 (ABCA7) and ABC transporter A1 (ABCA1) proteins, whether transient or stable, to generate cholesterol-rich high density lipoprotein (HDL). Green fluorescent protein (GFP) attached at their C termini did not influence the lipid release reactions. Transfected ABCA7-GFP induced apolipoprotein-mediated assembly of cholesterol-containing HDL also in L929 cells, which otherwise generate only cholesterol-deficient HDL with their endogenous ABCA1. Time-dependent release of cholesterol and phospholipid by apolipoprotein A (apoA)-I was parallel both with ABCA1 and with ABCA7 when highly expressed in HEK293 cells, but dose-dependent profiles of lipid release on apoA-I and apoA-II were somewhat different between ABCA1 and ABCA7. Analyses of the stable clones with ABCA1-GFP (293/2c) and ABCA7-GFP (293/6c) by using the same vector indicated some differences in regulation of their activities by protein kinase modulators. Dibutyryl cyclic AMP increased ABCA1-GFP and the release of cholesterol and phospholipid in 293/2c but increased neither ABCA7-GFP nor the lipid release in 293/6c. Expression of ABCA1-GFP- and apoA-I-mediated lipid release were enhanced in parallel by phorbol 12-myristate 13-acetate (PMA) in 293/2c cells. In contrast, the same treatment of 293/6c increased ABCA7-GFP, but apoA-I-mediated lipid release was significantly suppressed. Despite these different responses to PMA, all of the effects of PMA were reversed by a specific protein kinase C inhibitor Gö6976, suggesting that the changes were in fact due to protein kinase C activation. A thiol protease inhibitor, N-acetyl-Leu-Leu-norleucinal, increased the protein levels of ABCA1-GFP in 293/2c and ABCA7-GFP in 293/6c, indicating their common degradation pathway. The data indicated that human ABCA7 would compensate the function of ABCA1 for release of cell cholesterol in a certain condition(s), but post-transcriptional regulation of their activity is different.
Biochemistry, Molecular Biology and Metabolism 1, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan.
Sumiko
S
Abe-Dohmae
Yuika
Y
Ikeda
Michinori
M
Matsuo
Michi
M
Hayashi
Kei-ichiro
K
Okuhira
Kazumitsu
K
Ueda
Shinji
S
Yokoyama
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000378:metabolism; D001053:Apolipoproteins / Q000502:physiology*; D003994:Bucladesine / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D003001:Cloning, Molecular; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology; D008075:Lipoproteins, HDL / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
C577836:ABCA1 protein, human; C411895:ABCA7 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D001053:Apolipoproteins; D002227:Carbazoles; D015853:Cysteine Proteinase Inhibitors; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D007211:Indoles; D007976:Leupeptins; D008075:Lipoproteins, HDL; D010743:Phospholipids; D011994:Recombinant Proteins; C063261:acetylleucyl-leucyl-norleucinal; C081021:Go 6976; D003994:Bucladesine; D002784:Cholesterol; D013755:Tetradecanoylphorbol Acetate