Park W, Choi J J, Hwang E S, Lee J H
Center for Clinical Research, Samsung Biomedical Research Institute, and Department of Obstetrics and Gynecology, Samsung Medical Center, 50 Ilwon-dong, Kangnam-ku, Seoul 135-230, Korea.
Clin Cancer Res. 1996 Dec;2(12):2029-35.
By means of reverse transcription-PCR we have identified an alternatively spliced mRNA coding for a variant estrogen receptor (ER) that lacks exon 4 (ERDelta4) and is coexpressed with the wild-type ER mRNA in ovarian carcinomas. Furthermore, Western blot analysis revealed the expression of the ERDelta4 protein in normal as well as neoplastic ovarian tissues along with the wild-type ER, although the relative amounts of the wild-type ER and ERDelta4 proteins varied. The trans-activational properties of this variant were studied in ER-negative COS1 cell lines by cotransfection of the ERDelta4 expression vector and a reporter gene containing the estrogen response element. The ERDelta4 protein was not able to activate transcription of a reporter gene. However, it inhibited estrogen-dependent transcriptional activation in a dominant negative fashion when it was cotransfected with the wild-type ER and reporter plasmid. Because it has been shown that ERDelta4 is not able to bind to its response element, the observed inhibitory effect probably occurs through protein-protein interactions. Although several variants of the ER have been described from cancerous cells, none has been identified in ovarian tissues, and ERDelta4 is the only isoform detected in normal tissues. These results may have implications for understanding the physiological role of ERDelta4 in normal cells, because it may affect the function of the wild-type ER, depending on the level of the variant ER protein relative to that of the wild-type ER.
通过逆转录聚合酶链反应，我们鉴定出一种选择性剪接的信使核糖核酸，其编码一种缺乏外显子4的变异雌激素受体（ERDelta4），并且在卵巢癌中与野生型ER信使核糖核酸共表达。此外，蛋白质免疫印迹分析显示，在正常以及肿瘤性卵巢组织中，ERDelta4蛋白与野生型ER一起表达，尽管野生型ER和ERDelta4蛋白的相对含量有所不同。通过共转染ERDelta4表达载体和含有雌激素反应元件的报告基因，在ER阴性的COS1细胞系中研究了这种变异体的反式激活特性。ERDelta4蛋白无法激活报告基因的转录。然而，当它与野生型ER和报告质粒共转染时，它以显性负性方式抑制雌激素依赖性转录激活。由于已经表明ERDelta4无法与其反应元件结合，观察到的抑制作用可能是通过蛋白质-蛋白质相互作用发生的。尽管已经从癌细胞中描述了几种ER变异体，但在卵巢组织中尚未鉴定出任何一种，并且ERDelta4是在正常组织中检测到的唯一亚型。这些结果可能对理解ERDelta4在正常细胞中的生理作用具有启示意义，因为它可能会影响野生型ER的功能，这取决于变异体ER蛋白相对于野生型ER蛋白的水平。
