Solomon D L, Philipp A, Land H, Eilers M
Imperial Cancer Research Fund, London, UK.
Oncogene. 1995 Nov 2;11(9):1893-7.
Conflicting results have been published regarding the regulation of cyclin D1 mRNA in rat fibroblasts expressing a hormone-regulated Myc protein, MycER. We confirm that activation of MycER with oestrogen rapidly induces cyclin D1 mRNA, even in the presence of cycloheximide. However, we show that this is an artefact resulting from an oestrogen-activated transcriptional activation domain in the oestrogen receptor part of the MycER chimaera. First, addition of 4-hydroxy-tamoxifen (4OHT), which does not activate this domain, allows association of MycER with Max and induces cell proliferation in serum-starved Rat-1-MycER cells without affecting cyclin D1 mRNA levels or the activity of D1 promoter-luciferase constructs. Second, Rat-1 cells expressing a mutant MycER with a hormone-binding domain that still binds 4OHT but no longer binds oestrogen, are driven into the cell cycle in response to 4OHT but fail to up-regulate cyclin D1 mRNA. Finally, Rat-1 cells in which wild-type human c-Myc expression can be induced, also progress into the cell cycle without increased D1 mRNA expression.
关于在表达激素调节型Myc蛋白MycER的大鼠成纤维细胞中细胞周期蛋白D1 mRNA的调控，已发表了相互矛盾的结果。我们证实，即使存在放线菌酮，用雌激素激活MycER也能迅速诱导细胞周期蛋白D1 mRNA。然而，我们表明这是一个假象，是由MycER嵌合体雌激素受体部分中雌激素激活的转录激活域导致的。首先，添加不激活该结构域的4-羟基他莫昔芬（4OHT），可使MycER与Max结合，并在血清饥饿的Rat-1-MycER细胞中诱导细胞增殖，而不影响细胞周期蛋白D1 mRNA水平或D1启动子-荧光素酶构建体的活性。其次，表达具有仍能结合4OHT但不再结合雌激素的激素结合域的突变型MycER的Rat-1细胞，在响应4OHT时进入细胞周期，但未能上调细胞周期蛋白D1 mRNA。最后，野生型人c-Myc表达可被诱导的Rat-1细胞，也能在不增加D1 mRNA表达的情况下进入细胞周期。
