Identification of 5α, 6α-epoxycholesterol as a novel modulator of liver X receptor activity

• Published in: Molecular pharmacology Vol. 78; no. 6; pp. 1046 - 1058
• Main Authors: Berrodin, Thomas J, Shen, Qi, Quinet, Elaine M, Yudt, Matthew R, Freedman, Leonard P, Nagpal, Sunil
• Format: Journal Article
• Language: English
• Published: United States 01.12.2010
• Subjects: Animals; Cell Line, Tumor; Cells, Cultured; Cholesterol - analogs & derivatives; Cholesterol - chemistry; Cholesterol - metabolism; Cholesterol - physiology; Humans; Liver X Receptors; Mice; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Orphan Nuclear Receptors - agonists; Orphan Nuclear Receptors - deficiency; Orphan Nuclear Receptors - metabolism; Protein Binding - physiology; Protein Transport - physiology
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.110.065193

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.