The human ABCG1 gene: identification of LXR response elements that modulate expression in macrophages and liver.
The ABC transporter ABCG1 (ATP binding cassette transporter G1), expressed in macrophages, liver, and other tissues, has been implicated in the efflux of cholesterol to high density lipoprotein. The ABCG1 gene is transcriptionally activated by cholesterol loading and activators of liver X receptors (LXRs) and retinoid X receptors (RXRs) through genomic sequences that have not been fully characterized. Here we show that ABCG1 mRNA is induced by LXR agonists in RAW264.7 macrophage cells, HepG2 hepatoma cells, and primary mouse hepatocytes. We identify two evolutionarily highly conserved LXR response elements (LXREs), LXRE-A and LXRE-B, located in the first and second introns of the human ABCG1 gene. Each element conferred robust LXR-agonist responsiveness to ABCG1 promoter-directed luciferase gene constructs in RAW264.7 and HepG2 cells. Overexpression of LXR/RXR activated the ABCG1 promoter in the presence of LXRE-A or LXRE-B sequences. In gel-shift assays, LXR/RXR heterodimers bound to wild-type but not to mutated LXRE-A and LXRE-B sequences. In chromatin immunoprecipitation assays, LXR and RXR were detected at LXRE-A and -B regions of DNA of human THP-1 macrophages. These studies clarify the mechanism of transcriptional upregulation of the ABCG1 gene by oxysterols in macrophages and liver, two key tissues where ABCG1 expression may affect cholesterol balance and atherogenesis.
Sabol
Steven L
SL
Molecular Disease Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. slsabol@mail.nih.gov
Brewer
H Bryan
HB
Santamarina-Fojo
Silvia
S
D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000077556:Alitretinoin; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000819:agonists / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D008264:Macrophages / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000235:genetics*; D020218:Response Elements / Q000235:genetics*; D047488:Retinoid X Receptors / Q000819:agonists; D016415:Sequence Alignment; D013449:Sulfonamides / Q000494:pharmacology; D024363:Transcription Initiation Site; D014212:Tretinoin / Q000494:pharmacology; D015854:Up-Regulation; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D000077556:Alitretinoin; D004268:DNA-Binding Proteins; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D047488:Retinoid X Receptors; D013449:Sulfonamides; D014212:Tretinoin; C419353:ABCG1 protein, human; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides