Stimulation of steroid receptor coactivator-3 (SRC-3) gene overexpression by a positive regulatory loop of E2F1 and SRC-3
Stimulation of steroid receptor coactivator-3 (SRC-3) gene overexpression by a positive regulatory loop of E2F1 and SRC-3
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DOI：
10.1210/me.2005-0522
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发表时间：
2006-12-01
影响因子：
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通讯作者：
Xu, Jianming
中科院分区：
文献类型：
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作者：
Mussi, Paola;Yu, Chundong;Xu, Jianming
类固醇受体辅激活因子3（SRC-3，在乳腺癌1中扩增，或ACTR）是核受体和某些其他转录因子如E2F1的转录辅激活因子。SRC-3在乳腺癌中过表达，并且其过表达足以在体内引起乳腺癌。然而，控制内源性SRC-3过表达的机制尚不清楚。在本研究中，我们确定了SRC-3基因的第一个外显子，并分析了SRC-3基因的5 '调控序列。我们在SRC-3的5 '调控序列中发现了三个进化保守区（ECR），并且ECR 2对SRC-3启动子活性做出了主要贡献。ECR 2区（bp-250/+350）含有多个特异性蛋白1（Sp1）结合位点和两个E2F1结合位点。我们发现，E2F1可以显着激活ECR 2启动子活性的剂量依赖性方式。此外，E2F1的过表达显著增加了内源性SRC-3基因的启动子活性，并增强了SRC-3在体内的表达。相反，E2F1的敲低降低了SRC-3的表达。我们证明SRC-3启动子上的E2F1活性机制不依赖于E2F结合位点，而是依赖于位于bp +150/+160的Sp1元件。Sp1、E2F1和SRC-3被特异性地募集到该Sp1位点，并且E2F1和Sp1之间的相互作用对于调节SRC-3表达是必不可少的。此外，SRC-3共激活E2F1活性，从而在体内额外刺激SRC-3表达的进一步增加。这些结果表明，在具有过度活跃的E2F1的细胞中，例如在乳腺癌细胞中遇到的情况，存在由E2F1和SRC-3组成的正反馈调节环以维持高水平的SRC-3和E2F1活性，这可能部分地解释SRC-3过表达的致癌作用。
Steroid receptor coactivator 3 (SRC-3, amplified in breast cancer 1, or ACTR) is a transcriptional coactivator for nuclear receptors and certain other transcription factors such as E2F1. SRC-3 is overexpressed in breast cancers, and its overexpression is sufficient to cause mammary carcinomas in vivo. However, the mechanisms controlling endogenous SRC-3 overexpression are unknown. In this study, we identified the first exon and analyzed the 5' regulatory sequence of the SRC-3 gene. We found three evolutionarily conserved regions (ECRs) in the 5' SRC-3 regulatory sequence, and ECR2 makes a major contribution to the SRC-3 promoter activity. The ECR2 region (bp -250/+350) contains several specificity protein 1 (Sp1) binding sites and two E2F1 binding sites. We show that E2F1 can significantly activate the ECR2 promoter activity in a dose-dependent manner. Furthermore, overexpression of E2F1 significantly increases the promoter activity of the endogenous SRC-3 gene and boosts SRC-3 expression in vivo. Conversely, knockdown of E2F1 reduces SRC-3 expression. We demonstrate that the mechanism of E2F1 activity on SRC-3 promoter is independent of the E2F binding sites but relies on the Sp1 element located at bp +150/+160. Sp1, E2F1, and SRC-3 are specifically recruited to this Sp1 site and the interaction between E2F1 and Sp1 is essential to modulate SRC-3 expression. Moreover, SRC-3 coactivates E2F1 activity and thereby additively stimulates a further increase in SRC-3 expression in vivo. These results suggest that in cells with hyperactive E2F1, such as the case encountered in breast cancer cells, there is a positive feedback regulatory loop consisting of E2F1 and SRC-3 to maintain high levels of SRC-3 and E2F1 activity, which may partially interpret the oncogenic role of SRC-3 overexpression.