Ostrowski M C, Huang A L, Kessel M, Wolford R G, Hager G L
EMBO J. 1984 Aug;3(8):1891-9. doi: 10.1002/j.1460-2075.1984.tb02064.x.
Addition of the transcriptional enhancers present in the U3 region of the Harvey murine sarcoma virus (HaMuSV) long terminal repeat (LTR) to recombinant chimeras in which the HaMuSV transforming gene (Ha-v-ras) is expressed from the mouse mammary tumor virus (MMTV) promoter increases the ability of the MMTV v-ras chimeras to transform mouse fibroblasts in culture 50- to 100-fold. Significant stimulation of transfection efficiency occurs only when glucocorticoids are present in the culture medium. Glucocorticoids also elevate the steady-state concentration of MMTV-initiated v-ras mRNA in cell lines isolated from these transfections, and MMTV-v-ras fusion transcripts are initiated at the normal MMTV cap site; potential cryptic initiation events associated with the enhancer could not be detected. The ability of the enhancer to increase the transcriptional activity of the MMTV promoter was also studied in acute transfection assays where expression of the chloramphenical acetyl transferase (CAT) gene is driven by the MMTV promoter. In this system the strong positive effect on MMTV transcription is again obtained only when the cells are hormone treated. These experiments indicate that the hormone-regulatory region is capable of modulating the function of an exogenously introduced enhancer element.
将哈维鼠肉瘤病毒（HaMuSV）长末端重复序列（LTR）的U3区域中存在的转录增强子添加到重组嵌合体中，在该重组嵌合体中，HaMuSV转化基因（Ha-v-ras）由小鼠乳腺肿瘤病毒（MMTV）启动子表达，这使得MMTV v-ras嵌合体在培养物中转化小鼠成纤维细胞的能力提高了50至100倍。仅当培养基中存在糖皮质激素时，转染效率才会受到显著刺激。糖皮质激素还会提高从这些转染分离的细胞系中MMTV启动的v-ras mRNA的稳态浓度，并且MMTV-v-ras融合转录本在正常的MMTV帽位点起始；未检测到与增强子相关的潜在隐蔽起始事件。在急性转染试验中也研究了增强子增加MMTV启动子转录活性的能力，在该试验中，氯霉素乙酰转移酶（CAT）基因的表达由MMTV启动子驱动。在该系统中，只有当细胞接受激素处理时，才能再次获得对MMTV转录的强烈正向作用。这些实验表明，激素调节区域能够调节外源引入的增强子元件的功能。
