H3K4me3阅读子BAP18与ERα形成正反馈调控机制及其乳腺癌生物学功能解析

Estrogen receptor α (ERα) is a member of steroid hormone receptor superfamily. In the presence of ligand, ERα exerts its biological function by regulating transcription of target genes. Co-regulators are recruited for regulating these processes. ERα and its co-regulators play essential roles in breast cancer progression and endocrine therapy resistance. Thus, identification of ERα co-regulators as a potential therapy target for breast cancer is important. However, whether BAP18 possesses a temporal and spatial specificity to regulate transcription? How is BAP18 itself transcription induced and regulated? How does BAP18 influence the progression of breast cancer? These questions are still needed to be clarified. In the previous study, a histone H3K4me3 reader, BAP18 has been identified to be involved in transcription regulation. Further study indicates that depletion of BAP18 influences H3K4me3 and H4Ac modification levels at the estrogen-response elements of ERα target genes, and BAP18 may interact with WDR5, ASH2L, and DYP30 to modulate ERα action. Importantly, our data have demonstrated that ERα-E2 signaling is able to induce BAP18 itself transcription, suggesting that BAP18 could form a positive feedback regulation with ERα in breast cancer. Furthermore, our results have shown that BAP18 depletion inhibits ERα-positive breast cancer cell growth, and influences cell cycle progress. The expression of BAP18 is positive correlated with that of ERα in breast cancer samples. All above results indicate that BAP18 may participate in modulation of histone modification through the recruitment of other important histone modification enzymes to promote ERα-mediated transcriptional activity, and play a crucial role in breast cancer progression. Using ChIP, Co-IP, real time PCR, RNA-seq, and ChIP-seq experiments, the aim of our project is to analyze the new epigenetic mechanism underlying modulation function of BAP18 on ERα-mediated transactivation to bring insight into its temporal and spatial specificity. Moreover, EMSA, luciferase assay, and ChIP assay will be performed to clarify that BAP18 acts as a new target gene induced by ERα. We will further study the role of BAP18 in breast cancer growth, tamoxifen resistance, and tumor invasion and metastasis to analyze whether the funtion of BAP18 in breast cancer is related to ERα. In the future, we will try to supply experimental evidences and new targets for the early detection and therapy of breast cancer.

雌激素受体α（ERα）作为核受体超家族成员通常以配体依赖方式介导基因转录，并招募一系列辅调节因子参与调控其转录活性。ERα及其辅调节因子在乳腺癌进程中扮演着重要角色。申请人早期利用果蝇模型筛选出BAP18作为一种新的H3K4me3 reader调控基因转录。然而BAP18的转录调控功能是否具有时空特异性，它本身的转录是如何被诱导和调控，BAP18如何影响乳腺癌进程等仍有待深入研究。本项目前期研究发现BAP18上调ERα介导基因转录；同时其本身转录受ERα-E2调节，提示BAP18可能与ERα形成正反馈调控回路。此外，敲低BAP18影响了乳腺癌细胞生长及细胞周期进程。本项目试图阐明BAP18调控ERα转录活性的表观遗传学新机制，揭示其调控转录的时空特异性，明确BAP18是ERα新的下游调控基因，解析BAP18在乳腺癌中的作用及其与ERα的依存关联，为乳腺癌早期诊断和治疗提供实验依据和新靶点。

雌激素受体α（ERα）信号通路在ERα阳性乳腺癌发生发展进程中发挥关键作用。ERα与E2 (estrogen)结合后诱导下游靶基因转录，在此过程中，ERα招募一系列辅调节因子参与调控ERα介导的基因转录活性，从而发挥其生物学功能。ERα功能调控在乳腺癌进程及内分泌治疗耐药等方面起重要作用，因此ERα辅调节因子作为乳腺癌治疗中有潜能的药物靶点越来越受到关注。在本项目中，我们筛选出了BAP18作为一种H3K4me3 阅读子参与上调ERα介导的基因转录；敲低BAP18改变ERα靶基因反应元件(ERE) 区组蛋白H3K4me3及H4Ac水平；有趣的是，在实验中，我们发现E2添加可诱导BAP18基因表达，且该作用受E2拮抗剂抑制，提示BAP18可能是ERα/E2信号通路的下游调控基因；生物学功能方面，我们结果证实敲低BAP18抑制了多种ERα阳性乳腺癌细胞的生长/增殖，并影响细胞周期进程。BAP18在乳腺癌组织标本中呈显著高表达，且BAP18在乳腺癌组织标本中的高表达与ERα呈明显的正相关。在本项目资助下，我们深入解析了BAP18参与上调ERα介导基因转录活性的表观遗传学新机制，鉴定了COMPASS-like 蛋白复合物与BAP18互作，并证实BAP18作为组蛋白H3K4me3阅读子在COMPASS-like与ERα相互作用过程中起到重要的桥梁蛋白作用，BAP18通过招募COMPASS-like蛋白复合物促进ERα靶基因启动子区的ERE上的H3K4me3和H4Ac水平，从而促进ERα介导基因转录活性。此外，我们通过细胞和小鼠体内实验进一步证实了BAP18在乳腺癌生长及内分泌治疗耐药等方面显著的促进作用。该项目的研究为乳腺癌特别是内分泌治疗耐受乳腺癌的早期诊断和寻找新的治疗策略提供了理论依据和新思路。. 在本项目资助下，项目负责人带领实验团队也对其他性激素受体辅调节因子的鉴定及其在性激素受体相关肿瘤中的作用做了一系列的研究工作，作为责任作者在国际公认的学术杂志上发表了13篇SCI论文，成功获得2项研究专利；在人才培养方面取得了很好的效果，有多名博士后顺利出站，并有6名博士生和1名硕士研究生顺利毕业。