The partial agonist activity of antagonist-occupied steroid receptors is controlled by a novel hinge domain-binding coactivator L7/SPA and the corepressors N-CoR or SMRT.
The partial agonist activity of antagonist-occupied steroid receptors is controlled by a novel hinge domain-binding coactivator L7/SPA and the corepressors N-CoR or SMRT.
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DOI：
10.1210/mend.11.6.0004
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发表时间：
1997-06
影响因子：
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通讯作者：
T. Jackson;J. Richer;D. L. Bain;G. Takimoto;L. Tung;K. Horwitz
中科院分区：
文献类型：
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作者：
T. Jackson;J. Richer;D. L. Bain;G. Takimoto;L. Tung;K. Horwitz
类固醇受体拮抗剂，如抗雌激素他莫昔芬或抗前列腺素RU 486，可能在组织和肿瘤中具有不适当的激动剂样作用。为了解释这一悖论，我们假设，辅激活剂是无意中带来的DNA结合，拮抗剂占据受体的启动子。以人孕激素受体（PR）铰链激素结合域（H-HBD）作为诱饵对HeLa cDNA文库进行双杂交筛选，其中酵母细胞用RU 486处理。我们已经分离出两个有趣的类固醇受体相互作用的蛋白质，调节转录在相反的方向。第一个是L7/SPA，这是一种先前描述的27-kDa蛋白质，含有碱性区亮氨酸拉链结构域，不具有已知的核功能。当与他莫昔芬占据的雌激素受体（hER）或RU 486占据的hPR或糖皮质激素受体（hGR）共表达时，L7/SPA使拮抗剂的部分激动剂活性增加3至10倍，但对激动剂介导的转录没有影响。L7/SPA与hPR的相互作用映射到铰链区，并且实际上，hPR铰链区抑制拮抗剂介导的转录的L7/SPA依赖性诱导。有趣的是，缺乏部分激动剂作用的纯拮抗剂，如抗雌激素ICI 164，384或抗雌激素ZK 98299，不能被L7/SPA上调。我们还分离、克隆和测序了270 kDa小鼠（m）甲状腺/维甲酸受体辅阻遏物的人类同源物（hN-CoR）。hN-CoR与hPR-HBD的结合图谱。mN-CoR和相关的人辅阻遏物SMRT抑制RU 486或他莫昔芬介导的部分激动剂活性超过90%。这种抑制被hPR H-HBD的过表达完全压制。此外，这两种辅阻遏物逆转了L7/SPA产生的拮抗剂依赖性转录上调。我们的数据表明，拮抗剂占据的类固醇受体的转录方向可以控制由启动子结合受体的转录复合物的共激活子的比例corepressors招募。在正常组织和混合拮抗剂的激动剂活性占主导地位的耐药乳腺癌中，类固醇受体可能优先与辅激活剂结合。这表明了一种策略，通过该策略可以消除这种部分激动剂活性，并且通过该策略可以筛选这种活性的候选受体配体。
Steroid receptor antagonists, such as the antiestrogen tamoxifen or the antiprogestin RU486, can have inappropriate agonist-like effects in tissues and tumors. To explain this paradox we postulated that coactivators are inadvertently brought to the promoters of DNA-bound, antagonist-occupied receptors. The human (h) progesterone receptor (PR) hinge-hormone binding domain (H-HBD) was used as bait in a two-hybrid screen of a HeLa cDNA library, in which the yeast cells were treated with RU486. We have isolated and characterized two interesting steroid receptor-interacting proteins that regulate transcription in opposite directions. The first is L7/SPA, a previously described 27-kDa protein containing a basic region leucine zipper domain, having no known nuclear function. When coexpressed with tamoxifen-occupied estrogen receptors (hER) or RU486-occupied hPR or glucocorticoid receptors (hGR), L7/SPA increases the partial agonist activity of the antagonists by 3- to 10-fold, but it has no effect on agonist-mediated transcription. The interaction of L7/SPA with hPR maps to the hinge region, and indeed, the hPR hinge region squelches L7/SPA-dependent induction of antagonist-mediated transcription. Interestingly, pure antagonists that lack partial agonist effects, such as the antiestrogen ICI164,384 or the antiprogestin ZK98299, cannot be up-regulated by L7/SPA. We also isolated, cloned, and sequenced the human homolog (hN-CoR) of the 270-kDa mouse (m) thyroid/retinoic acid receptor corepressor. Binding of hN-CoR maps to the hPR-HBD. mN-CoR, and a related human corepressor, SMRT, suppress RU486 or tamoxifen-mediated partial agonist activity by more than 90%. This suppression is completely squelched by overexpression of the hPR H-HBD. Additionally, both corepressors reverse the antagonist-dependent transcriptional up-regulation produced by L7/SPA. Our data suggest that the direction of transcription by antagonist-occupied steroid receptors can be controlled by the ratio of coactivators to corepressors recruited to the transcription complex by promoter-bound receptors. In normal tissues and in hormone-resistant breast cancers in which the agonist activity of mixed antagonists predominates, steroid receptors may be preferentially bound by coactivators. This suggests a strategy by which such partial agonist activity can be eliminated and by which candidate receptor ligands can be screened for this activity.