Grandien K, Berkenstam A, Gustafsson J A
Department of Medical Nutrition, Karolinska Institute, NOVUM, Huddinge, Sweden.
Int J Biochem Cell Biol. 1997 Dec;29(12):1343-69. doi: 10.1016/s1357-2725(97)89967-0.
The estrogen receptor (ER) is a ligand-activated transcription factor and a member of a large family of nuclear hormone receptors. As a mediator of estrogen hormone action, the ER is involved in many important physiological processes. ER gene expression has been demonstrated to be restricted to certain tissues and under complex hormonal control. However, the molecular mechanisms involved have remained largely unknown. Due to this lack of knowledge an investigation was undertaken to characterize the promoter organization of ER gene and investigate its expression. Approximately 3 kb of the 5' flanking region of the human ER (hER) gene was isolated and sequenced. By performing RT-PCR and RACE experiments it was shown that the hER gene is transcribed from three different promoters. Transcription of the hER gene from these promoters yields three different mRNA isoforms with unique 5' untranslated regions (5'UTRs), but identical coding regions. The expression pattern of the hER mRNA isoforms was investigated by RT-PCR. Both the A- and B-mRNA isoforms were found to be expressed in breast and uterus, whereas expression of the C-transcript was predominantly detected in liver. In bone cells only expression of the B-mRNA could be detected. The steady-state levels of the A- and B-transcripts in normal breast and uterus were quantified and compared with the hER mRNA levels in established cancer cell lines derived from the same tissues. This demonstrated approximately equal levels of the two transcripts in normal tissues whereas the A-mRNA was the most abundant isoform in the cancer cell lines investigated. Approximately 4.5 kb of the 5' flanking region of the rat ER (rER) gene were sequenced. Sequence analysis and PCR experiments suggested that the promoter organization of the rat and human ER genes is only partially conserved which might indicate species-specific differences in the regulation of ER expression. In conclusion, this work suggests tissue-specific alternative promoter usage as a mechanism in the regulation of human and rat ER gene expression.
雌激素受体（ER）是一种配体激活的转录因子，属于核激素受体大家族的一员。作为雌激素作用的介质，ER参与许多重要的生理过程。已证明ER基因表达局限于某些组织，并受复杂的激素控制。然而，其中涉及的分子机制在很大程度上仍不清楚。由于缺乏这方面的知识，因此开展了一项研究来表征ER基因的启动子结构并研究其表达。分离并测序了人ER（hER）基因5'侧翼区域约3 kb的片段。通过进行RT-PCR和RACE实验表明，hER基因从三个不同的启动子转录。这些启动子转录的hER基因产生三种不同的mRNA异构体，具有独特的5'非翻译区（5'UTR），但编码区相同。通过RT-PCR研究了hER mRNA异构体的表达模式。发现A-和B-mRNA异构体均在乳腺和子宫中表达，而C-转录本的表达主要在肝脏中检测到。在骨细胞中仅能检测到B-mRNA的表达。对正常乳腺和子宫中A-和B-转录本的稳态水平进行了定量，并与源自相同组织的已建立癌细胞系中的hER mRNA水平进行了比较。这表明在正常组织中这两种转录本的水平大致相等，而在所研究的癌细胞系中A-mRNA是最丰富的异构体。对大鼠ER（rER）基因5'侧翼区域约4.5 kb的片段进行了测序。序列分析和PCR实验表明，大鼠和人ER基因的启动子结构仅部分保守，这可能表明ER表达调控存在物种特异性差异。总之，这项工作表明组织特异性的可变启动子使用是调节人和大鼠ER基因表达的一种机制。
