School of Clinical and Experimental Medicine, Centre for Liver Research, Institute of Biomedical Research, and Cancer Research UK Clinical Trials Unit, School of Cancer Sciences, University of Birmingham, United Kingdom.
Cancer Res. 2010 May 1;70(9):3739-49. doi: 10.1158/0008-5472.CAN-09-3531. Epub 2010 Apr 20.
Pituitary tumor transforming gene (PTTG) binding factor (PBF; PTTG1IP) is a relatively uncharacterized oncoprotein whose function remains obscure. Because of the presence of putative estrogen response elements (ERE) in its promoter, we assessed PBF regulation by estrogen. PBF mRNA and protein expression were induced by both diethylstilbestrol and 17beta-estradiol in estrogen receptor alpha (ERalpha)-positive MCF-7 cells. Detailed analysis of the PBF promoter showed that the region -399 to -291 relative to the translational start site contains variable repeats of an 18-bp sequence housing a putative ERE half-site (gcccctcGGTCAcgcctc). Sequencing the PBF promoter from 122 normal subjects revealed that subjects may be homozygous or heterozygous for between 1 and 6 repeats of the ERE. Chromatin immunoprecipitation and oligonucleotide pull-down assays revealed ERalpha binding to the PBF promoter. PBF expression was low or absent in normal breast tissue but was highly expressed in breast cancers. Subjects with greater numbers of ERE repeats showed higher PBF mRNA expression, and PBF protein expression positively correlated with ERalpha status. Cell invasion assays revealed that PBF induces invasion through Matrigel, an action that could be abrogated both by siRNA treatment and specific mutation. Furthermore, PBF is a secreted protein, and loss of secretion prevents PBF inducing cell invasion. Given that PBF is a potent transforming gene, we propose that estrogen treatment in postmenopausal women may upregulate PBF expression, leading to PBF secretion and increased cell invasion. Furthermore, the number of ERE half-sites in the PBF promoter may significantly alter the response to estrogen treatment in individual subjects.
垂体肿瘤转化基因（PTTG）结合因子（PBF；PTTG1IP）是一种相对未被描述的癌蛋白，其功能仍不清楚。由于其启动子中存在推定的雌激素反应元件（ERE），我们评估了雌激素对 PBF 的调节。二乙基己烯雌酚和 17β-雌二醇均可诱导雌激素受体α（ERα）阳性 MCF-7 细胞中 PBF mRNA 和蛋白的表达。对 PBF 启动子的详细分析表明，相对于翻译起始位点的-399 至-291 区域包含一个 18 个碱基序列的可变重复，该序列包含一个推定的 ERE 半位点（gcccctcGGTCAcgcctc）。对 122 名正常受试者的 PBF 启动子进行测序显示，受试者可能为 ERE 重复 1 至 6 次的纯合子或杂合子。染色质免疫沉淀和寡核苷酸下拉测定显示 ERα与 PBF 启动子结合。PBF 在正常乳腺组织中表达水平较低或缺失，但在乳腺癌中高度表达。具有更多 ERE 重复的受试者具有更高的 PBF mRNA 表达，并且 PBF 蛋白表达与 ERα状态呈正相关。细胞侵袭测定显示，PBF 通过 Matrigel 诱导侵袭，该作用可通过 siRNA 处理和特异性突变来阻断。此外，PBF 是一种分泌蛋白，丧失分泌功能可防止 PBF 诱导细胞侵袭。鉴于 PBF 是一种有效的转化基因，我们推测绝经后妇女的雌激素治疗可能会上调 PBF 的表达，导致 PBF 的分泌增加和细胞侵袭增加。此外，PBF 启动子中 ERE 半位点的数量可能会显著改变个体对雌激素治疗的反应。
