Léveillard T, Wasylyk B
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS, INSERM, ULP, 1 Rue Laurent Fries, BP 163, 67404 Illkirch cedex, France.
J Biol Chem. 1997 Dec 5;272(49):30651-61. doi: 10.1074/jbc.272.49.30651.
MDM2 proto-oncogene expression is aberrant in many human tumors. Its normal role is to modulate the functions of p53. The N terminus of MDM2 interacts with p53, whereas the properties of the rest of the molecule are poorly understood. We show that MDM2 binds to the general transcription factor TFIID in vivo. The C-terminal Ring finger interacts with TAFII250/CCG1, and the central acidic domain interacts with TBP. Expression of MDM2 activates the cyclin A gene promoter but not c-fos, showing that the effects of MDM2 are specific. Deletion of the C-terminal region of MDM2 abolishes activation, showing that the C-terminal domain of MDM2 is functionally important. We found that increasing MDM2 expression to higher levels inhibits the cyclin A promoter. Inhibition appears to result from titration of general transcription factors because MDM2 overexpression inhibits c-fos as well as other promoters in vivo and basal transcription in vitro. The mechanisms of repression of the cyclin A and fos promoters appear to be different. Cyclin A repression is lost by deleting the C terminus, whereas that of c-fos is lost by removal of the acidic domain. These results reinforce the conclusion that the C terminus of MDM2 mediates effects on the cyclin A promoter. MDM2 transformed cells contain elevated levels of cyclin A mRNA, showing that activation occurs under physiological conditions. There is a positive correlation between MDM2 binding to TAFII250 and MDM2 activation of the cyclin A promoter. The C-terminal region of MDM2, which contains the Ring finger, interacts with TAFII250 and is required for regulation of the cyclin A promoter by MDM2. Our results link the activity of MDM2, a transforming protein implicated in many human tumors, with cyclin A, a regulator of the cell cycle.
MDM2原癌基因在许多人类肿瘤中表达异常。其正常作用是调节p53的功能。MDM2的N末端与p53相互作用，而该分子其余部分的特性了解甚少。我们发现MDM2在体内与通用转录因子TFIID结合。C末端的环指结构域与TAFII250/CCG1相互作用，而中央酸性结构域与TBP相互作用。MDM2的表达激活细胞周期蛋白A基因启动子，但不激活c-fos，表明MDM2的作用具有特异性。删除MDM2的C末端区域会消除激活作用，表明MDM2的C末端结构域在功能上很重要。我们发现将MDM2表达增加到更高水平会抑制细胞周期蛋白A启动子。抑制似乎是由于通用转录因子的滴定导致的，因为MDM2过表达在体内抑制c-fos以及其他启动子，并在体外抑制基础转录。细胞周期蛋白A和fos启动子的抑制机制似乎不同。通过删除C末端可消除细胞周期蛋白A的抑制作用，而通过去除酸性结构域可消除c-fos的抑制作用。这些结果强化了MDM2的C末端介导对细胞周期蛋白A启动子作用的结论。MDM2转化的细胞中细胞周期蛋白A mRNA水平升高，表明在生理条件下会发生激活。MDM2与TAFII250的结合与MDM2对细胞周期蛋白A启动子的激活之间存在正相关。MDM2的包含环指结构域的C末端区域与TAFII250相互作用，是MDM2调节细胞周期蛋白A启动子所必需的。我们的结果将MDM2（一种与许多人类肿瘤相关的转化蛋白）的活性与细胞周期蛋白A（一种细胞周期调节剂）联系起来。
