Treacy M N, Ryan F, Martin F
Department of Pharmacology, University College Dublin, Ireland.
J Steroid Biochem Mol Biol. 1991 Jan;38(1):1-15. doi: 10.1016/0960-0760(91)90395-l.
Glucocorticoid regulation of rat growth hormone (rGH) gene expression has been investigated in a series of gene transfer studies into cells in culture. It has been established that sequences (-12 to -523) immediately flanking the start site for rGH gene transcription behave as a functional glucocorticoid inducible enhancer when associated with a heterologous promoter (RSV), displaying independence of orientation and position in mediating the glucocorticoid effect. The induction of chloramphenicol acetyl transferase (CAT) gene expression in these constructs by dexamethasone was established at the enzyme and mRNA levels and was inhibited in the presence of the antiglucocorticoid, RU 38486. The glucocorticoid inducible enhancer activity was not restricted to pituitary cells. The constructs containing the rGH-5'-flanking sequences, associated with the RSV promoter, also mediated glucocorticoid induction of CAT gene expression when transiently transfected into MH1C1 cells, a hepatoma cell line. The effect was similarly demonstrable on co-transfection of these constructs with a glucocorticoid receptor expression vector into receptor deficient COS cells. Two elements within these rGH sequences (-97 to -111 and -250 to -264) display partial homology with a consensus sequence computed for a group of glucocorticoid regulatory elements. Mutation of both of these elements or of the more proximal element alone (-97/-111) led to a complete loss of ability to mediate glucocorticoid induction of gene expression. However, the rGH sequences still mediated glucocorticoid induction of gene expression when the distal GRE-like element was mutated or deleted. Thus, the proximal rGH GRE-like element is absolutely required to mediate this glucocorticoid inducible enhancer activity.
在一系列针对培养细胞的基因转移研究中，对糖皮质激素对大鼠生长激素（rGH）基因表达的调控进行了研究。已经确定，rGH基因转录起始位点紧邻的序列（-12至-523）与异源启动子（RSV）相关联时，表现为功能性糖皮质激素诱导增强子，在介导糖皮质激素效应时显示出方向和位置的独立性。在酶和mRNA水平上证实了地塞米松对这些构建体中氯霉素乙酰转移酶（CAT）基因表达的诱导作用，并且在抗糖皮质激素RU 38486存在时受到抑制。糖皮质激素诱导增强子活性并不局限于垂体细胞。含有与RSV启动子相关联的rGH 5'侧翼序列的构建体，当瞬时转染到肝癌细胞系MH1C1细胞中时，也介导了糖皮质激素对CAT基因表达的诱导作用。在将这些构建体与糖皮质激素受体表达载体共转染到缺乏受体的COS细胞中时，同样可证明这种效应。这些rGH序列中的两个元件（-97至-111和-250至-264）与为一组糖皮质激素调节元件计算出的共有序列显示出部分同源性。这两个元件或仅近端元件（-97 / -111）的突变导致介导糖皮质激素诱导基因表达的能力完全丧失。然而，当远端GRE样元件发生突变或缺失时，rGH序列仍介导糖皮质激素诱导的基因表达。因此，近端rGH GRE样元件对于介导这种糖皮质激素诱导增强子活性是绝对必需的。
