Opposing Functions of BRD4 Isoforms in Breast Cancer

摘要 改变转录的基因表达的遗传突变和非突变表观遗传控制 正常和受干扰细胞中的程序经常导致需要医疗关注的病理表型。 确定这些异常（特别是癌细胞中的异常）背后的基因靶点和途径至关重要 用于开发适当的疾病治疗方案。然而，癌细胞的异质性 这使得很难制定一个适用于每个患者的通用治疗计划。 在过去的10年里，含溴结构域蛋白4（BRD 4）已经成为一种有前途的癌症 由于其与调节转录程序的活性增强子的广泛关联， 与癌症的发生和发展有关，重要的是， 靶向BRD 4及其相关家族成员，还包括人类中的BRD 2、BRD 3和BRDT。这些 布罗莫结构域和额外末端（BET）家族蛋白抑制剂，如JQ 1和I-BET，显示出巨大的前景， 在培养细胞和动物模型中逆转癌症表型。这些化合物衍生物中的几种是 目前正在临床试验中用于治疗各种类型的癌症和炎性疾病，以及它们的治疗靶点 主要归因于BRD 4长同种型（BRD 4-L，aa 1-1362）。最近我们发现，通过同种型- 特异性敲低和内源性蛋白检测沿着转基因表达，即丰度越低 BRD 4短同种型（BRD 4-S，aa 1-722）实际上是致癌的，而BRD 4-L在乳腺癌中是肿瘤抑制的。 癌细胞增殖和迁移以及乳腺肿瘤的形成和转移。我们的中央 假设是BRD 4同种型具有相反的功能，尽管它们确实具有一些共同的性质， 在肿瘤发展中的作用，将通过解决以下三个具体目标进行严格测试： 1.确定BRD 4-L和BRD 4-S在不同乳腺癌细胞和小鼠模型中的生物学作用 2.阐明BRD 4亚型及其共调节因子在乳腺癌亚型中的作用机制 3.鉴定BRD 4亚型独特和共同调控的基因靶点和途径 由于同种型特异性BRD 4抗体和一类新的磷酸-BRD 4靶向化合物， 与BET布罗莫结构域抑制剂不同的分子作用现在已经在我的研究中成功地开发出来。 实验室，我们在解决BRD 4靶向癌症治疗中涉及的紧迫问题方面处于独特的地位。我们 当前的目标是鉴定由每种BRD 4同种型独特和共同调节的细胞通路 利用生物化学和分子工具、合成化学、全基因组表达和结合分析 阐明BRD 4-L和BRD 4-S参与乳腺癌。我们的最终目标是提供经过验证的 分子途径和新的基因靶点在不久的将来有效的乳腺癌治疗。

Abstract Genetic mutation and non-mutational epigenetic control of gene expression that alter transcription programs in normal and perturbed cells often lead to pathological phenotypes requiring medical attention. Identifying the gene targets and pathways underlying these abnormalities, particularly in cancer cells, is crucial for developing appropriate regimens for disease treatment. Nevertheless, the heterogeneity of cancer cells makes it difficult to develop a universal treatment plan that works for every patient. Over the past 10 years, bromodomain-containing protein 4 (BRD4) has emerged as a promising cancer therapeutic target due to its broad association with active enhancers that modulate transcription programs implicated in cancer initiation and progression, and importantly, the availability of small compound inhibitors targeting BRD4 and its related family members that also include BRD2, BRD3, and BRDT in humans. These bromodomain and extra-terminal (BET) family protein inhibitors, such as JQ1 and I-BET, show great promise in reversing cancer phenotypes in cultured cells and animal models. Several of these compound derivatives are now in clinical trials for treating various types of cancer and inflammatory disease, and their therapeutic targets have been attributed mainly to the BRD4 long isoform (BRD4-L, aa 1-1362). Recently we found, by isoform- specific knockdown and endogenous protein detection along with transgene expression, that the less abundant BRD4 short isoform (BRD4-S, aa 1-722) is in fact oncogenic while BRD4-L is tumor-suppressive in breast cancer cell proliferation and migration as well as in mammary tumor formation and metastasis. Our central hypothesis is that BRD4 isoforms have opposing functions, although they do share some common properties, in tumor development, which will be stringently tested by addressing the following three specific aims: 1. To define the biological role of BRD4-L and BRD4-S in different breast cancer cells and mouse models 2. To elucidate the mechanistic action of BRD4 isoforms and their coregulators in breast cancer subtypes 3. To identify gene targets and pathways uniquely and commonly regulated by BRD4 isoforms Since isoform-specific BRD4 antibodies and a new class of phospho-BRD4-targeting compounds with molecular action distinct from the BET bromodomain inhibitors have now been successfully developed in my lab, we are in a unique position to address pressing issues implicated in BRD4-targeted cancer therapy. Our immediate goals are to identify cellular pathways uniquely and commonly regulated by each BRD4 isoform using biochemical and molecular tools, synthetic chemistry, and genome-wide expression and binding profiling to elucidate BRD4-L and BRD4-S involvement in breast cancer. Our eventual goals are to provide validated molecular pathways and new gene targets for effective breast cancer treatment in the near future.