The Laboratory of Signaling and Gene Expression, Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Southwestern Medical Center, Dallas, Texas.
The Division of Basic Research, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas.
Mol Cancer Res. 2019 Dec;17(12):2356-2368. doi: 10.1158/1541-7786.MCR-19-0393. Epub 2019 Sep 24.
The bromodomain family member proteins (BRD; BET proteins) are key coregulators for estrogen receptor alpha (ERα)-mediated transcriptional enhancers. The use of BRD-selective inhibitors has gained much attention as a potential treatment for various solid tumors, including ER-positive breast cancers. However, the roles of individual BET family members have largely remained unexplored. Here, we describe the role of BRDs in estrogen (E2)-dependent gene expression in ERα-positive breast cancer cells. We observed that chemical inhibition of BET family proteins with JQ1 impairs E2-regulated gene expression and growth in breast cancer cells. In addition, RNAi-mediated depletion of each BET family member (BRDs 2, 3, and 4) revealed partially redundant roles at ERα enhancers and for target gene transcription. Furthermore, we found a unique role of BRD3 as a molecular sensor of total BET family protein levels and activity through compensatory control of its own protein levels. Finally, we observed that BRD3 is recruited to a subset of ERα-binding sites (ERBS) that are enriched for active enhancer features, located in clusters of ERBSs likely functioning as "super enhancers," and associated with highly E2-responsive genes. Collectively, our results illustrate a critical and specific role for BET family members in ERα-dependent gene transcription. IMPLICATIONS: BRD3 is recruited to and controls the activity of a subset ERα transcriptional enhancers, providing a therapeutic opportunity to target BRD3 with BET inhibitors in ERα-positive breast cancers.
溴结构域家族成员蛋白（BRD；BET 蛋白）是雌激素受体 alpha（ERα）介导的转录增强子的关键核心调节剂。BRD 选择性抑制剂的应用作为治疗各种实体瘤（包括 ER 阳性乳腺癌）的潜在方法引起了广泛关注。然而，单个 BET 家族成员的作用在很大程度上仍未得到探索。在这里，我们描述了 BRD 在 ERα 阳性乳腺癌细胞中雌激素（E2）依赖性基因表达中的作用。我们观察到，用 JQ1 化学抑制 BET 家族蛋白会损害乳腺癌细胞中 E2 调节的基因表达和生长。此外，RNAi 介导的每个 BET 家族成员（BRD2、3 和 4）的耗竭揭示了在 ERα 增强子和靶基因转录中部分冗余的作用。此外，我们发现 BRD3 作为 BET 家族蛋白总水平和活性的分子传感器具有独特的作用，通过自身蛋白水平的代偿性控制。最后，我们观察到 BRD3 被招募到一组富含活性增强子特征的 ERα 结合位点（ERBS），这些特征位于 ERBS 簇中，可能作为“超级增强子”发挥作用，并与高度 E2 反应性基因相关。总之，我们的结果说明了 BET 家族成员在 ERα 依赖性基因转录中的关键和特异性作用。意义：BRD3 被招募到并控制一组 ERα 转录增强子的活性，为使用 BET 抑制剂在 ERα 阳性乳腺癌中靶向 BRD3 提供了治疗机会。
