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 EC50 of approximately 2 μM in peptide recruitment. Furthermore, 5,6-EC bound to LXRα in a radiolabeled ligand displacement assay (EC50 = 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.
Footnotes
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.065193.
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ABBREVIATIONS:
- LXR
- liver X receptor
- ABCA1
- ATP-binding cassette family transporter A1
- ACACA
- acetyl-coenzyme A carboxylase α
- Apo
- apolipoprotein
- EC
- epoxycholesterol
- FASN
- fatty acid synthase
- Ivl
- involucrin
- KO
- knockout
- LBD
- ligand binding domain
- LDLR
- low density lipoprotein receptor
- MFI
- mean fluorescence intensity
- NRIP
- nuclear receptor interacting protein
- OHC
- hydroxycholesterol
- PLTP
- phospholipid transfer protein
- SCD
- steroyl CoA desaturase
- SMRT
- silencing mediator of retinoic acid and thyroid hormone receptor
- SRC
- steroid receptor coactivator
- SREBF
- sterol response element binding factor
- VDR
- vitamin D receptor
- wt
- wild type
- PCR
- polymerase chain reaction
- FBS
- fetal bovine serum
- TLDA
- TaqMan Low-Density Array
- NF-κB
- nuclear factor κB
- ATCC
- American Type Culture Collection
- PMSF
- phenylmethylsulfonyl fluoride
- CHAPS
- 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate
- GST
- glutathione transferase
- T0901317
- N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl]phenyl]-benzenesulfonamide
- MTG
- monothioglycerol.
- Received March 30, 2010.
- Accepted September 13, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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