Expression, regulation, and activity of ABCA1 in human cell lines.
Mutations in the ATP-binding cassette transporter A1 (ABCA1) gene cause familial high-density lipoprotein deficiency and Tangier disease. ABCA1 plays a crucial role in active apolipoprotein A-I (apoA-I) lipidation, a key step in reverse cholesterol transport. We compared ABCA1 transcriptional regulation and cholesterol efflux in human skin fibroblasts, monocyte-derived macrophages and hepatocytes (HepG2). 8-Br-cAMP did not increase ABCA1 transcription in these tissues compared to mouse macrophages. We found that ABCA1 is differentially regulated among tissues. While transcription in HepG2 appears to be constitutive, sterols stimulate ABCA1 transcription in fibroblasts and monocyte-derived macrophages. ApoA-I promoted cholesterol efflux in fibroblasts, macrophages, and HepG2. Cholesterol homeostasis in fibroblasts is tightly regulated, and ABCA1 mRNA closely follows the cellular mass of free cholesterol (dose- and time-dependent manner). To further determine the mechanism used by fibroblasts to maintain sterol balance, we used a competitive inhibition approach with geranylgeranyl pyrophosphate (GGPP) to block the LXR induction pathway. GGPP blocked basal, 22-(R)-hydroxycholesterol- and cholesterol-induced ABCA1 expression. Taken together, these results demonstrate that: (1) ABCA1 expression varies among tissues, and (2) cholesterol conversion to hydroxycholesterol is an important mechanism for the maintenance of cholesterol homeostasis in fibroblasts.
Denis
Maxime
M
Cardiovascular Genetics Laboratory, McGill University Health Center, Royal Victoria Hospital, 687 Pine Avenue West, Montréal, Quebec, Canada H3A 1A1.
Bissonnette
Rachel
R
Haidar
Bassam
B
Krimbou
Larbi
L
Bouvier
Michel
M
Genest
Jacques
J
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D015152:Blotting, Northern; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D015151:Immunoblotting; D008264:Macrophages / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D011106:Polyisoprenyl Phosphates; D012333:RNA, Messenger; D015124:8-Bromo Cyclic Adenosine Monophosphate; D002784:Cholesterol; C002963:geranylgeranyl pyrophosphate