Abstract
The basic helix-loop-helix proteins differentiated embryo chondrocyte 1 (DEC1) and DEC2 are involved in circadian rhythm control. Because the metabolism of dietary nutrients has been linked to circadian regulation, we examined the effect of DEC1 and DEC2 on the function of the metabolite-sensing nuclear receptors, ligand-dependent transcription factors, including retinoid X receptor (RXR) and liver X receptor (LXR). Transfection assays showed that DEC1 and DEC2 repressed ligand-dependent transactivation by RXR. Knockdown of endogenous DEC1 and DEC2 expression with small interfering RNAs augmented ligand-dependent RXRα transactivation. DEC1 and DEC2 interacted directly with RXRα, and ligand addition enhanced their association. DEC1 and DEC2 modified interaction of RXRα with cofactor proteins. Transfection assays using DEC1 and DEC2 mutants revealed that the C-terminal region of DEC2 is required for repression and that an LXXLL motif in DEC1 and DEC2 is necessary for RXRα repression. DEC1 and DEC2 repressed the induction of LXR target genes, associated with the promoter of an LXR target gene, and dissociated from the promoter with ligand treatment. Knockdown of endogenous DEC1 and DEC2 enhanced the LXR target gene expression in hepatocytes. Expression of Dec1, Dec2, and Srebp-1c showed a circadian rhythm in the liver of mice, whereas that of Lxrα, Lxrβ, and Rxrα was not rhythmic. DEC1 and DEC2 also repressed the transactivation of other RXR heterodimers, such as farnesoid X receptor, vitamin D receptor, and retinoic acid receptor. Thus, the repressor function of DEC1 and DEC2 may be extended to other RXR heterodimer nuclear receptors.
Footnotes
This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas [Grant 18077005]; and a grant to promote open research for young academics and specialists from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.057000
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ABBREVIATIONS:
- DEC
- differentiated embryo chondrocyte
- RAR
- retinoic acid receptor
- RXR
- retinoid X receptor
- LXR
- liver X receptor
- 9CRA
- 9-cis retinoic acid
- FXR
- farnesoid X receptor
- VDR
- vitamin D receptor
- SMRT
- silencing mediator of retinoic acid and thyroid hormone receptor
- GFP
- green fluorescent protein
- SRC-1
- steroid receptor coactivator 1
- DRIP205
- vitamin D receptor-interacting protein 205
- NCoR
- nuclear receptor corepressor
- SREBP-1c
- sterol regulatory element-binding protein 1c
- HEK
- human embryonic kidney
- siRNA
- small interfering RNA
- GST
- glutathione transferase
- ChIP
- chromatin immunoprecipitation
- ZT
- zeitgeber time
- AF2
- activation function 2
- HDAC
- histone deacetylase
- ABCA1
- ATP-binding cassette transporter A1
- HIF-1α
- hypoxia-inducing factor 1α
- PCR
- polymerase chain reaction
- BMAL1
- brain and muscle Arnt-like protein-1
- CHAPS
- 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate
- T0901317
- N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl]phenyl]-benzenesulfonamide
- tk
- thymidine kinase.
- Received April 10, 2009.
- Accepted September 24, 2009.
- © 2009 The American Society for Pharmacology and Experimental Therapeutics
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