Toyama Tatsuya, Iwase Hirotaka, Yamashita Hiroko, Hara Yasuo, Sugiura Hiroshi, Zhang Zhenhuan, Fukai Ichiro, Miura Yutaka, Riabowol Karl, Fujii Yoshitaka
Department of Surgery II, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan.
J Steroid Biochem Mol Biol. 2003 Oct;87(1):57-63. doi: 10.1016/s0960-0760(03)00388-1.
The ING1 gene was originally cloned as a candidate tumor suppressor of human breast cancer, and recent studies suggest that ING1 proteins are involved in chromatin remodeling functions via physical association with both histone acetyltransferases (HATs) and histone deacetylases (HDACs). In this study, we investigated whether p33(ING1b), one of the major ING1 isoforms, modulated the transcriptional activity of estrogen receptor (ER) alpha. In Cos-7 cells transfected with increasing concentrations of a mammalian expression vector encoding for p33(ING1b), estrogen-induced ERalpha transcriptional activity was found to increase in a dose-dependent manner. As p33(ING1b) expression levels increased, transcription of an ER-responsive reporter gene by either estrogen-inducible full-length ERalpha or activation function (AF) 1 deletion mutant was enhanced, while the AF2 deletion mutant was unaffected by the presence of p33(ING1b). These results showed that p33(ING1b) enhanced estrogen-induced ERalpha activity through the AF2 domain. Our data also demonstrated that the antiestrogens inhibited the transcriptional activity of ERalpha as stimulated by p33(ING1b). Furthermore, a weak physical association was observed between in vitro translated p33(ING1b) and ERalpha. Our data presented here demonstrate that p33(ING1b) acts like a coactivator for ERalpha and stimulates estrogen-induced ERalpha transcriptional activity consistent with a function for p33(ING1b) in chromatin remodeling.
ING1基因最初作为人类乳腺癌的候选肿瘤抑制基因被克隆出来，最近的研究表明，ING1蛋白通过与组蛋白乙酰转移酶（HATs）和组蛋白去乙酰化酶（HDACs）的物理结合参与染色质重塑功能。在本研究中，我们调查了主要的ING1异构体之一p33(ING1b)是否调节雌激素受体（ER）α的转录活性。在转染了浓度递增的编码p33(ING1b)的哺乳动物表达载体的Cos-7细胞中，发现雌激素诱导的ERα转录活性以剂量依赖的方式增加。随着p33(ING1b)表达水平的升高，雌激素诱导的全长ERα或激活功能（AF）1缺失突变体对ER反应性报告基因的转录增强，而AF2缺失突变体不受p33(ING1b)存在的影响。这些结果表明，p33(ING1b)通过AF2结构域增强雌激素诱导的ERα活性。我们的数据还表明，抗雌激素抑制了p33(ING1b)刺激的ERα转录活性。此外，在体外翻译的p33(ING1b)和ERα之间观察到微弱的物理结合。我们在此展示的数据表明，p33(ING1b)作为ERα的共激活因子发挥作用，并刺激雌激素诱导的ERα转录活性，这与p33(ING1b)在染色质重塑中的功能一致。
