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/me.11.6.693
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发表时间：
1997-06-01
影响因子：
--
通讯作者：
Horwitz, KB
中科院分区：
文献类型：
--
作者：
Jackson, TA;Richer, JK;Horwitz, KB
类固醇受体拮抗剂，例如抗雌激素他莫昔芬或抗孕激素 RU486，可能在组织和肿瘤中产生不适当的激动剂样作用。为了解释这个悖论，我们假设共激活因子无意中被带到了 DNA 结合、拮抗剂占据的受体的启动子处。人 (h) 黄体酮受体 (PR) 铰链激素结合结构域 (H-HBD) 在 HeLa cDNA 文库的双杂交筛选中用作诱饵，其中酵母细胞用 RU486 处理。我们分离并表征了两种有趣的类固醇受体相互作用蛋白，它们以相反的方向调节转录。第一个是 L7/SPA，这是一种先前描述的 27 kDa 蛋白质，含有碱性区域亮氨酸拉链结构域，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 RU486 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，事实上，hPR 铰链区抑制了 L7/SPA 依赖性拮抗剂介导的转录诱导。有趣的是，缺乏部分激动剂作用的纯拮抗剂，例如抗雌激素 ICI164,384 或抗孕激素 ZK98299，不能被 L7/SPA 上调。我们还分离、克隆并测序了 270 kDa 小鼠 (m) 甲状腺/视黄酸受体辅阻遏物的人类同源物 (hN-CoR)。 hN-CoR 与 hPR-HBD 的结合。 mN-CoR 和相关的人类辅阻遏物 SMRT 可抑制 RU486 或他莫昔芬介导的部分激动剂活性超过 90%。 hPR H-HBD 的过度表达完全抑制了这种抑制。此外，两种辅阻遏物都能逆转 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通过启动子结合受体招募到转录复合物的共激活子与辅阻遏物的比例来控制。在正常组织和激素抵抗性乳腺癌中，混合拮抗剂的激动剂活性占主导地位，类固醇受体可能优先与共激活剂结合。这提出了一种策略，通过该策略可以消除这种部分激动剂活性，并可以通过该策略筛选候选受体配体的这种活性。
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.