title: Autoregulation of the human liver X receptor alpha promoter.
abstract: Previous work has implicated the nuclear receptors liver X receptor alpha (LXR alpha) and LXR beta in the regulation of macrophage gene expression in response to oxidized lipids. Macrophage lipid loading leads to ligand activation of LXRs and to induction of a pathway for cholesterol efflux involving the LXR target genes ABCA1 and apoE. We demonstrate here that autoregulation of the LXR alpha gene is an important component of this lipid-inducible efflux pathway in human macrophages. Oxidized low-density lipoprotein, oxysterols, and synthetic LXR ligands induce expression of LXR alpha mRNA in human monocyte-derived macrophages and human macrophage cell lines but not in murine peritoneal macrophages or cell lines. This is in contrast to peroxisome proliferator-activated receptor gamma (PPAR gamma)-specific ligands, which stimulate LXR alpha expression in both human and murine macrophages. We further demonstrate that LXR and PPAR gamma ligands cooperate to induce LXR alpha expression in human but not murine macrophages. Analysis of the human LXR alpha promoter led to the identification of multiple LXR response elements. Interestingly, the previously identified PPAR response element (PPRE) in the murine LXR alpha gene is not conserved in humans; however, a different PPRE is present in the human LXR 5'-flanking region. These results have implications for cholesterol metabolism in human macrophages and its potential to be regulated by synthetic LXR and/or PPAR gamma ligands. The ability of LXR alpha to regulate its own promoter is likely to be an integral part of the macrophage physiologic response to lipid loading.
authors.affiliation: Howard Hughes Medical Institute, University of California, Los Angeles, 90095-1662, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Laffitte
authors.forename: S B
authors.initials: SB
authors.lastname: Joseph
authors.forename: R
authors.initials: R
authors.lastname: Walczak
authors.forename: L
authors.initials: L
authors.lastname: Pei
authors.forename: D C
authors.initials: DC
authors.lastname: Wilpitz
authors.forename: J L
authors.initials: JL
authors.lastname: Collins
authors.forename: P
authors.initials: P
authors.lastname: Tontonoz
mesh_terms: D016475:3T3 Cells; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D001057:Apolipoproteins E / Q000378:metabolism; D001483:Base Sequence; D002478:Cells, Cultured; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation / Q000187:drug effects; D006706:Homeostasis; D006801:Humans; D008077:Lipoproteins, LDL / Q000494:pharmacology; D000071518:Liver X Receptors; D008264:Macrophages / Q000166:cytology / Q000187:drug effects; D051379:Mice; D008969:Molecular Sequence Data; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D011988:Receptors, Thyroid Hormone / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D001057:Apolipoproteins E; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D008077:Lipoproteins, LDL; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D014157:Transcription Factors; C032629:acetyl-LDL; C099252:oxidized low density lipoprotein