Hollywood D P, Hurst H C
Gene Transcription Laboratory, ICRF Oncology Group, Hammersmith Hospital, London, UK.
EMBO J. 1993 Jun;12(6):2369-75. doi: 10.1002/j.1460-2075.1993.tb05891.x.
The c-erbB-2 receptor tyrosine kinase proto-oncogene product is overexpressed in 20-30% of breast carcinomas and this has been shown to correlate with poor prognosis. Previous analysis of tumour-derived lines has demonstrated that although the c-erbB-2 gene is often amplified, overexpression can occur from a single-copy gene. Moreover, whether or not the gene is amplified, overexpressing cells produce 6- to 8-fold more mRNA per gene copy than low-expressing cells. In this paper, we examine the possible mechanisms causing this deregulation of c-erbB-2 mRNA accumulation. Nuclear run-on studies indicated that the extra mRNA accumulation was due to increased transcription of the gene in overexpressing cells. Promoter analyses using c-erbB-2 5' flanking sequences linked to CAT showed that the promoter is more active in overexpressing cells. Coupling promoter deletion functional studies with footprinting experiments, using nuclear extracts derived from both low and overexpressing cells, allowed the identification of a DNA-binding protein, OB2-1, which is considerably more abundant in a range of overexpressing lines. We discuss the possible role of OB2-1 in c-erbB-2 overexpression in breast tumour lines.
c-erbB-2受体酪氨酸激酶原癌基因产物在20% - 30%的乳腺癌中过度表达，并且这已被证明与预后不良相关。先前对肿瘤衍生细胞系的分析表明，虽然c-erbB-2基因经常扩增，但单拷贝基因也可发生过度表达。此外，无论该基因是否扩增，过度表达的细胞每个基因拷贝产生的mRNA比低表达细胞多6至8倍。在本文中，我们研究了导致c-erbB-2 mRNA积累失调的可能机制。细胞核连续标记研究表明，额外的mRNA积累是由于过度表达细胞中该基因转录增加所致。使用与CAT相连的c-erbB-2 5'侧翼序列进行启动子分析表明，该启动子在过度表达细胞中更具活性。将启动子缺失功能研究与足迹实验相结合，使用来自低表达和过度表达细胞的核提取物，鉴定出一种DNA结合蛋白OB2-1，它在一系列过度表达细胞系中含量明显更高。我们讨论了OB2-1在乳腺肿瘤细胞系中c-erbB-2过度表达中的可能作用。
