Argenton F, Ramoz N, Charlet N, Bernardini S, Colombo L, Bortolussi M
Dipartimento di Biologia, Università di Padova, Italy.
Biochem Biophys Res Commun. 1996 Jul 5;224(1):57-66. doi: 10.1006/bbrc.1996.0984.
The transcription factor GHF1/Pit1, required for the expression of the prolactin (PRL) and other pituitary-specific genes, is highly conserved from fish to mammals but the mechanisms by which it activates transcription are poorly understood. The activity of the promoter (-627/+15 region) of the rainbow trout PRL (tPRL) gene fused to the luciferase reporter gene was studied using GHF1-expressing rat pituitary GC cells. Nuclear extracts of GC cells produced five GHF1-specific footprints in the tPRL promoter, with the position of the two most proximal ones being highly conserved in trout and mammalian GHF1-regulated genes. Deletional and mutational analyses of the tPRL promoter showed that the most proximal GHF1 site alone is sufficient to confer sub-maximal GHF1-dependent transcriptional activity and that a glucocorticoid response element-like motif mediates dexamethasone stimulation. It is suggested that GHF1 molecules bound to different sites of the tPRL promoter cannot interact simultaneously with the transcriptional apparatus. Moreover, GHF1 and the ligand-bound glucocorticoid receptor tethered to their cognate elements in the promoter could cooperate to enhance transcription by interacting simultaneously with different members of the basal transcriptional complex.
转录因子GHF1/Pit1是催乳素（PRL）和其他垂体特异性基因表达所必需的，从鱼类到哺乳动物高度保守，但其激活转录的机制尚不清楚。使用表达GHF1的大鼠垂体GC细胞研究了与荧光素酶报告基因融合的虹鳟PRL（tPRL）基因启动子（-627/+15区域）的活性。GC细胞核提取物在tPRL启动子中产生了五个GHF1特异性足迹，其中两个最靠近近端的足迹位置在鳟鱼和哺乳动物GHF1调控基因中高度保守。tPRL启动子的缺失和突变分析表明，仅最靠近近端的GHF1位点就足以赋予亚最大GHF1依赖性转录活性，并且一个糖皮质激素反应元件样基序介导地塞米松刺激。提示结合到tPRL启动子不同位点的GHF1分子不能同时与转录装置相互作用。此外，GHF1和与启动子中其同源元件相连的配体结合糖皮质激素受体可以通过与基础转录复合物的不同成员同时相互作用来协同增强转录。
