Gervois P, Chopin-Delannoy S, Fadel A, Dubois G, Kosykh V, Fruchart J C, Najïb J, Laudet V, Staels B
U.325 INSERM, Département d'Athérosclérose, Institut Pasteur de Lille and The Faculté de Pharmacie, Université de Lille II, France.
Mol Endocrinol. 1999 Mar;13(3):400-9. doi: 10.1210/mend.13.3.0248.
Fibrates are widely used hypolipidemic drugs that act by modulating the expression of genes involved in lipid and lipoprotein metabolism. Whereas the activation of gene transcription by fibrates occurs via the nuclear receptor peroxisome proliferator-activated receptor-alpha (PPARalpha) interacting with response elements consisting of a direct repeat of the AGGTCA motif spaced by one nucleotide (DR1), the mechanisms of negative gene regulation by fibrates and PPARalpha are largely unknown. In the present study, we demonstrate that fibrates induce the expression of the nuclear receptor Rev-erbalpha, a negative regulator of gene transcription. Fibrates increase Rev-erbalpha mRNA levels both in primary human hepatocytes and in HepG2 hepatoblastoma cells. In HepG2 cells, fibrates furthermore induce Rev-erbalpha protein synthesis rates. Transfection studies with reporter constructs driven by the human Rev-erbalpha promoter revealed that fibrates induce Rev-erbalpha expression at the transcriptional level via PPARalpha. Site-directed mutagenesis experiments identified a PPAR response element that coincides with the previously identified Rev-erbalpha negative autoregulatory Rev-DR2 element. Electromobility shift assay experiments indicated that PPARalpha binds as heterodimer with 9-cis-retinoic acid receptor to a subset of DR2 elements 5' flanked by an A/T-rich sequence such as in the Rev-DR2. PPARalpha and Rev-erbalpha bind with similar affinities to the Rev-DR2 site. In conclusion, these data demonstrate human Rev-erbalpha as a PPARalpha target gene and identify a subset of DR2 sites as novel PPARalpha response elements. Finally, the PPARalpha and Rev-erbalpha signaling pathways cross-talk through competition for binding to those response elements.
贝特类药物是广泛使用的降血脂药物,其作用机制是调节参与脂质和脂蛋白代谢的基因表达。虽然贝特类药物通过核受体过氧化物酶体增殖物激活受体α(PPARα)与由一个核苷酸间隔的AGGTCA基序直接重复序列(DR1)组成的反应元件相互作用来激活基因转录,但贝特类药物和PPARα对基因负调控的机制在很大程度上尚不清楚。在本研究中,我们证明贝特类药物可诱导核受体Rev-erbα的表达,Rev-erbα是一种基因转录的负调节因子。贝特类药物可增加原代人肝细胞和HepG2肝癌细胞中Rev-erbα的mRNA水平。在HepG2细胞中,贝特类药物还可诱导Rev-erbα蛋白的合成速率。用人Rev-erbα启动子驱动的报告基因构建体进行的转染研究表明,贝特类药物通过PPARα在转录水平上诱导Rev-erbα的表达。定点诱变实验确定了一个PPAR反应元件,该元件与先前确定的Rev-erbα负自调节Rev-DR2元件一致。电泳迁移率变动分析实验表明,PPARα与9-顺式视黄酸受体以异二聚体形式结合到5'端侧翼为富含A/T序列(如Rev-DR2中)的DR2元件亚组上。PPARα和Rev-erbα以相似的亲和力结合到Rev-DR2位点。总之,这些数据证明人Rev-erbα是PPARα的靶基因,并确定了DR2位点亚组为新的PPARα反应元件。最后,PPARα和Rev-erbα信号通路通过竞争结合这些反应元件而相互作用。