Torra I P, Tsibulsky V, Delaunay F, Saladin R, Laudet V, Fruchart J C, Kosykh V, Staels B
U.325 INSERM, Département d'Athérosclérose, Institut Pasteur, Lille, France.
Endocrinology. 2000 Oct;141(10):3799-806. doi: 10.1210/endo.141.10.7708.
Rev-erbalpha [NR1D1], a member of the nuclear receptor superfamily, is an orphan receptor that constitutively represses gene transcription. Rev-erbalpha has been shown to play a role in myocyte differentiation and to be induced during adipogenesis. Furthermore, Rev-erbalpha is a regulator of lipoprotein metabolism. It was recently shown that Rev-erbalpha messenger RNA (mRNA) levels oscillate diurnally in rat liver. Here, we report that the circadian rhythm of Rev-erbalpha in liver is maintained in primary cultures of rat hepatocytes. Because glucocorticoids have been shown to regulate other transcription factors with circadian expression, it was furthermore examined whether hepatic Rev-erbalpha expression is also regulated by glucocorticoids. Treatment of rats with dexamethasone resulted in a decrease of Rev-erbalpha mRNA levels by 70% after 6 h. Furthermore, dexamethasone decreased Rev-erbalpha expression in rat primary hepatocytes in a dose-dependent fashion. This effect was mediated by the glucocorticoid receptor because simultaneous addition of the glucocorticoid antagonist RU486 prevented the decrease in Rev-erbalpha mRNA levels by dexamethasone. Protein synthesis inhibition with cycloheximide markedly induced Rev-erbalpha mRNA levels; however, this induction was reduced by dexamethasone supplementation in both rat and human primary hepatocytes. Treatment with actinomycin D blocked the repression of Rev-erbalpha expression by dexamethasone in rat hepatocytes, suggesting that glucocorticoids regulate Rev-erbalpha expression at the transcriptional level. Transient transfection experiments further indicated that Rev-erbalpha promoter activity is repressed by dexamethasone in the presence of cotransfected glucocorticoid receptor. Taken together, these data demonstrate that Rev-erbalpha expression is under the control of both the circadian clock and glucocorticoids in the liver.
视黄醛α[NR1D1]是核受体超家族的成员，是一种组成型抑制基因转录的孤儿受体。视黄醛α已被证明在心肌细胞分化中起作用，并在脂肪生成过程中被诱导。此外，视黄醛α是脂蛋白代谢的调节因子。最近的研究表明，视黄醛α信使核糖核酸（mRNA）水平在大鼠肝脏中呈昼夜节律振荡。在此，我们报告大鼠肝细胞原代培养中肝脏视黄醛α的昼夜节律得以维持。由于糖皮质激素已被证明可调节其他具有昼夜节律表达的转录因子，因此进一步研究了肝脏视黄醛α的表达是否也受糖皮质激素调节。用 dexamethasone 处理大鼠 6 小时后，视黄醛α mRNA 水平降低了 70%。此外，dexamethasone 以剂量依赖的方式降低大鼠原代肝细胞中视黄醛α的表达。这种作用是由糖皮质激素受体介导的，因为同时添加糖皮质激素拮抗剂 RU486 可防止 dexamethasone 降低视黄醛α mRNA 水平。用放线菌酮抑制蛋白质合成可显著诱导视黄醛α mRNA 水平；然而，在大鼠和人类原代肝细胞中，补充 dexamethasone 可降低这种诱导作用。用放线菌素 D 处理可阻断 dexamethasone 对大鼠肝细胞视黄醛α表达的抑制作用，这表明糖皮质激素在转录水平上调节视黄醛α的表达。瞬时转染实验进一步表明，在共转染糖皮质激素受体的情况下，dexamethasone 可抑制视黄醛α启动子活性。综上所述，这些数据表明肝脏中视黄醛α的表达受昼夜节律时钟和糖皮质激素的共同控制。
