Cho Yoshitake, Noshiro Mitsuhide, Choi Mihwa, Morita Kentaro, Kawamoto Takeshi, Fujimoto Katsumi, Kato Yukio, Makishima Makoto
Division of Biochemistry, Department of Biomedical Sciences, Nihon University School of Medicine, Itabashi-ku, Tokyo, Japan.
Mol Pharmacol. 2009 Dec;76(6):1360-9. doi: 10.1124/mol.109.057000. Epub 2009 Sep 28.
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 RXRalpha transactivation. DEC1 and DEC2 interacted directly with RXRalpha, and ligand addition enhanced their association. DEC1 and DEC2 modified interaction of RXRalpha 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 RXRalpha 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 Lxralpha, Lxrbeta, and Rxralpha 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.
基本螺旋-环-螺旋蛋白分化胚胎软骨细胞1（DEC1）和DEC2参与昼夜节律控制。由于膳食营养物质的代谢与昼夜调节有关，我们研究了DEC1和DEC2对代谢物感应核受体（包括视黄酸X受体（RXR）和肝X受体（LXR））功能的影响，这些核受体是配体依赖性转录因子。转染实验表明，DEC1和DEC2抑制RXR的配体依赖性反式激活。用小干扰RNA敲低内源性DEC1和DEC2表达可增强配体依赖性RXRα反式激活。DEC1和DEC2直接与RXRα相互作用，添加配体可增强它们的结合。DEC1和DEC2改变了RXRα与辅因子蛋白的相互作用。使用DEC1和DEC2突变体的转染实验表明，DEC2的C末端区域是抑制所必需的，而DEC1和DEC2中的LXXLL基序是RXRα抑制所必需的。DEC1和DEC2抑制LXR靶基因的诱导，与LXR靶基因的启动子结合，并在配体处理后从启动子上解离。敲低内源性DEC1和DEC2可增强肝细胞中LXR靶基因的表达。Dec1、Dec2和Srebp-1c在小鼠肝脏中的表达呈现昼夜节律，而Lxralpha、Lxrbeta和Rxralpha的表达则没有节律性。DEC1和DEC2还抑制其他RXR异二聚体的反式激活，如法尼醇X受体、维生素D受体和视黄酸受体。因此，DEC1和DEC2的抑制功能可能扩展到其他RXR异二聚体核受体。
