Functions of BRD8 in HR+/HER2+ breast cancer

项目摘要 HER 2阳性乳腺癌（BC）患者的结局已显著改善， 使用HER 2导向药物;然而，表达HR和HER 2的激素受体（HR）+/HER 2 + BC 与HR-/HER 2 + BC相比，HER 2对抗HER 2治疗的反应性较低。联合内分泌 治疗加抗HER 2靶向治疗已在临床上进行了研究，但只有一小部分 患者从治疗中获益，表明HR+/HER 2+肿瘤具有不同的生物学特性， 例如ER和HER 2信号串扰。双重HER 2阻断诱导管腔A样 在患者肿瘤和体外模型中的表型。然而，潜在的分子机制 抗HER 2药物对ER信号传导的激活仍不清楚。使用单细胞RNA测序 （scRNA-seq），我们鉴定了含溴结构域蛋白8（BRD 8）作为桥接HER 2的必需枢纽。 和ER信号通路。我们发现，BRD 8是p400组蛋白乙酰化酶复合物的一个组分， 多种抗HER 2药物（包括来那替尼、拉帕替尼和 曲妥珠单抗和BRD 8在响应HER 2阻断ER活化的最高层次。 此外，BRD 8调节除了ER之外的其他生长促进途径。BRD 8基因敲除 显著损害氟维司群耐药细胞系和异种移植物的生长，并且BRD 8敲低 增强HR+/HER 2+细胞对HER 2靶向剂的敏感性。这些初步数据导致 假设BRD 8是连接ER和HER 2途径的重要枢纽，BRD 8介导ER 在HER 2+细胞中响应于HER 2阻断的活化。因此，BRD 8与HER 2联合消融 阻断对于治疗HR+/HER 2 + BC应该是有效的。我们提出了三个目标来检验我们的假设：（1） 在单细胞水平阐明抗HER 2剂在HER 2+细胞中激活BRD 8的机制; (2)确定BRD 8在ER信号传导激活和HER 2后ER非依赖性功能中的作用 阻断;（3）测试BRD 8的消融是否使HR+/HER 2 + BC对抗HER 2阻断敏感。的 研究将在单细胞水平揭示抗HER 2药物诱导BRD 8的细胞间变异性， BRD 8在介导ER/HER 2信号传导串扰和ER非依赖性生长中的新功能 促进功能。这些机制的见解将为开发BRD 8组合消融奠定基础 和HER 2阻断疗法作为HR+/HER 2 + BC的新治疗方案。

PROJECT SUMMARY The outcome for patients with HER2-positive breast cancer (BC) has been significantly improved with the use of HER2-directed agents; however, hormone receptor (HR)+/HER2+ BCs that express both HR and HER2 are less responsive to anti-HER2 therapies as compared with HR-/HER2+ BC. Combined endocrine therapy plus anti-HER2-targeted therapy have been clinically investigated, but only a small subset of patients benefit from the treatment, indicating that HR+/HER2+ tumors have different biological characteristics, such as ER and HER2 signaling crosstalk. Dual HER2-blockade induces a Luminal A-like phenotype both in patients’ tumors and in in vitro models. However, the molecular mechanism underlying activation of ER signaling by anti-HER2 agents remains unclear. Using single cell RNA-sequencing (scRNA-seq), we identified Bromodomain Containing Protein 8 (BRD8) as an essential hub bridging HER2 and ER signaling pathways. We found that, BRD8, a component of p400 histone acetylase complex, was rapidly induced by treatment with a variety of anti-HER2 agents including neratinib, lapatinib and trastuzumab and that BRD8 is at the high hierarchy of ER activation in responsive to HER2 blockade. Furthermore, BRD8 regulates other growth promoting pathways in addition to ER. BRD8 knockout significantly impairs growth of a fulvestrant-resistant cell line and xenografts, and BRD8 knockdown enhances the sensitivity of HR+/HER2+ cells to HER2-targeting agents. These preliminary data lead to the hypothesis that BRD8 is an essential hub linking ER and HER2 pathways and BRD8 mediates ER activation in response to HER2 blockade in HER2+ cells. Therefore, combinatory BRD8 ablation with HER2 blockade should be effective for treating HR+/HER2+ BC. We propose three aims to test our hypothesis: (1) to elucidate the mechanism of BRD8 activation by anti-HER2 agents in HER2+ cells at the single cell level; (2) to define the roles of BRD8 in ER signaling activation and ER-independent functions upon HER2 blockade; (3) to test whether ablation of BRD8 sensitizes HR+/HER2+ BC to anti-HER2 blockade. The studies will reveal, at single-cell level, the cell-cell variability of BRD8 induction by anti-HER2 agents, and the novel functions of BRD8 in mediating ER/HER2 signaling crosstalk and ER-independent growth promoting functions. The mechanistic insights will lay foundation for developing combinatory BRD8 ablation and HER2 blockade therapy as a new treatment regimen for HR+/HER2+ BC.