Identification and characterization of novel complexes controling chromatin structure

基因表达是通过染色质重塑和组蛋白修饰来控制的。这种染色质结构重排是由多个亚基组成的核复合体进行的。在本研究中，鉴定和表征核复合物以支持激素诱导的核受体转录控制，对与性类固醇激素受体相关的复合物进行生化纯化。通过这样的生化筛选，我们可以鉴定出几种含有组蛋白修饰酶的复合物。其中一个复合体是含有组蛋白乙酰转移酶的新型复合体，该复合体含有共激活雌激素受体的组蛋白乙酰化酶，而另一个复合体是含有共抑制雌激素和雄激素受体的组蛋白去乙酰化酶。此外，我们可以鉴定出一种新的泛素E3连接酶来降解性类固醇受体蛋白。之前，我们已经证明，通过配体结合激活的二恶英受体（AhR）在转录控制中通过受体-受体蛋白的直接相互作用协同激活非配体性类固醇受体（Ohtake et al., Nature, 423, 545- 550,2003）。然而，AhR对配体类固醇受体的转抑制作用仍在研究中。通过生化纯化含有AhR和性类固醇受体的复合物，我们已经证明配体AhR是配体依赖的E3泛素连接酶，可以降解类固醇受体，从而抵消性类固醇激素的生物作用（Ohtake et al., Nature, 446,562 -566, 2007）。

Gene expression is controlled through chromatin remodeling and histon modifications. Such chromatin structure rearrangement is conducted by a number of nuclear complexes composed of multiple subunits. In the present study, to identify and characterize the nuclear complexes to support hormone-induced transcriptional controls by nuclear receptors, a biochemical purification of complexes associating with sex steroid hormone receptors. By such biochemical screening, we could identify several complexes containing histone modifying enzymes. One of the complex was a novel complex containing histone acetyltransferase to coactivate estrogen receptor, while another complex was a histone deacetylase to corepress estrogen and androgen receptors. Moreover, we could identify a novel ubiquitin E3 ligase to degrate sex steroid receptor proteins. Previously, we had shown that activated dioxin receptor(AhR) by ligand binding coactivates unliganded sex steroid receptors in transcriptional controls through direct receptor-receptor protein interaction (Ohtake et al., Nature, 423, 545-550, 2003). However, transrepression of liganded steroid receptors by AhR was still under investigation. By biochemical purification of a complex containing AhR and sex steroid receptors, we have demonstrated that liganded AhR is ligand- dependent E3 ubiquitin ligase to degrate steroid receptors, thereby counteracting biological actions of sex steroid hormones (Ohtake et al., Nature, 446, 562-566, 2007).