title: Identification of 5α, 6α-epoxycholesterol as a novel modulator of liver X receptor activity.
abstract: The liver X receptors (LXRα and LXRβ) are members of the nuclear receptor superfamily that function as key transcriptional regulators of a number of biological processes, including cholesterol homeostasis, lipid metabolism, and keratinocyte differentiation. Natural ligands that activate LXRs include oxysterol derivatives such as 25-hydroxycholesterol, 27-hydroxycholesterol, 22(R)-hydroxycholesterol, 20(S)-hydroxycholesterol, and 24(S),25-epoxycholesterol. Related oxysterols, such as 5α,6α-epoxycholesterol (5,6-EC) are present in a number of foods and have been shown to induce atherosclerosis in animal models. Intriguingly, these oxysterols have also been detected in atherosclerotic plaques. Using a variety of biochemical and cellular assays, we demonstrate that 5,6-EC is the first dietary modulator and an endogenous LXR ligand with cell and gene context-dependent antagonist, agonist, and inverse agonist activities. In a multiplexed LXR-cofactor peptide interaction assay, 5,6-EC induced the recruitment of a number of cofactor peptides onto both LXRα and LXRβ and showed an EC(50) of approximately 2 μM in peptide recruitment. Furthermore, 5,6-EC bound to LXRα in a radiolabeled ligand displacement assay (EC(50) = 76 nM), thus demonstrating it to be one of the most potent natural LXRα ligands known to date. Analysis of endogenous gene expression in various cell-based systems indicated the potential of 5,6-EC to antagonize LXR-mediated gene expression. Furthermore, it also induced the expression of some LXR-responsive genes in keratinocytes. These results clearly demonstrate that 5,6-EC is an LXR modulator that may play a role in the development of lipid disorders, such as atherosclerosis, by antagonizing the agonistic action of endogenous LXR ligands.
authors.affiliation: Women’s Health & Musculoskeletal Biology, Wyeth Research, Collegeville, PA, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Berrodin
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Quinet
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Yudt
authors.forename: Leonard P
authors.initials: LP
authors.lastname: Freedman
authors.forename: Sunil
authors.initials: S
authors.lastname: Nagpal
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D006801:Humans; D000071518:Liver X Receptors; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D057093:Orphan Nuclear Receptors / Q000819:agonists / Q000172:deficiency / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology
chemical_list: C119784:5,6-epoxycholesterol; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D002784:Cholesterol