趋化因子受体7（CXCR7）调控雌激素受体α（ERα）的分子机制及其与乳腺癌他莫西芬治疗耐受关系

Tamoxifen is usually used as a primary drug in ERα positive breast cancer. However, there still exist at least 33% of ERα positive patients suffering from tamoxifen therapy resistance. Previous researches indicated that elevated expression of CXCR7 is significantly associated with tamoxifen resistance by in vitro studies and data-mining of clinical transcriptional database. Moreover, CXCR7 is able to inhibit the ubiquitination of ERα, subsequently promote the protein level and transcriptional activity of ERα. It has been widely documented that enhanced protein expression and transcriptional activity of ERα are involved in tamoxifen resistance. Accordingly, I hypothesize that CXCR7-induced tamoxifen resistance attributes to enhanced protein expression and transcriptional activity of ERα. Therefore, the research focus of this project are listed below: Firstly, to further investigate the molecular mechanism of CXCR7-induced resistance to tamoxifen treatment, and attempt to verify the role of the protein level and transcriptional activity of ERα in tamoxifen resistance; Secondly, aim to uncover the pathways through which CXCR7 inhibit the ubiquitination of ERα; Thirdly, dedicate to establish the correlation of CXCR7 with tamoxifen therapy resistance in clinical specimens and animal models, with efforts to assess the potential value of CXCR7 served as therapeutic target for improving the efficiency of tamoxifen therapy. In summary, this project will help to understand the mechanisms of regulatory pathways of ERα, and contribute to solve the difficulty in tamoxifen therapy, which have great biological and clinical significances.

他莫昔芬是ERα阳性乳腺癌患者的重要治疗药物，但约有33%的患者存在耐药。前期体外实验和乳腺癌转录组数据库挖掘发现，CXCR7表达升高与ERα阳性乳腺癌他莫昔芬治疗耐药有关。机制研究发现，CXCR7可以抑制ERα泛素化修饰，促进其蛋白表达、转录活性升高。有报道指出，ERα表达、转录活性升高与他莫昔芬治疗耐受增高相关。申请者认为CXCR7促进他莫昔芬耐药可能与ERα表达和转录活性上升有关。因此，本课题进一步研究目标为：1，CXCR7引起他莫昔芬耐药的分子机制，确认是否与ERα表达和转录活性升高有关；2，CXCR7抑制ERα泛素化修饰的分子机制；3，结合临床组织样本和动物实验确立CXCR7与ERα阳性乳腺癌他莫昔芬治疗耐受关系，评估CXCR7作为潜在治疗靶点对于提高他莫昔芬治疗效果的临床价值。本课题对于明确ERα受调控机制以及解决他莫昔芬治疗耐受这一临床难点具有重要的生物学和临床意义。

乳腺癌是威胁女性生命健康的主要恶性肿瘤之一，近年来我国女性乳腺癌的发病率呈显著上升趋势。约65%-70%的乳腺癌为雌激素受体α（Estrogen Receptor, ERα）阳性。他莫昔芬(Tamoxifen, TAM)是ERα阳性乳腺癌患者的重要治疗药物，5年TAM治疗可以降低其约50%的疾病复发风险，已成为乳腺癌内分泌治疗重要的药物。但约有30%的患者存在耐药。趋化因子受体7（CXCR7）是近年来发现的一个趋化因子受体，该受体在乳腺癌样本中呈高表达，并且与乳腺癌的增值和转移相关。我们在临床数据库中发现，CXCR7高表达患者对TAM治疗敏感性显著低于CXCR7低表达患者；CXCR7在ERα阳性乳腺癌中表达显著高于其他类型乳腺癌（三阴性和和Her2型）。结合免疫组化组织芯片分析发现，CXCR7与ERα的表达在转录水平无显著相关性，但在蛋白水平表达呈正相关。体外实验发现，CXCR7表达升高会显著抑制ERα阳性乳腺癌细胞对TAM的敏感性。机制研究发现，CXCR7的表达升高可以促进ERK1/2信号通路的激活，抑制ERα泛素化修饰，维持其蛋白稳定并提高其转录活性；用siRNA抑制ERα表达后可以恢复TAM的敏感性，表明CXCR7促进ERα蛋白稳定与TAM耐受有关。进一步研究发现，CXCR7表达升高可以抑制BRCA1（泛素连接酶）但促进OTUB1（去泛素化酶）的表达。抑制ERK1/2信号通路后，可以逆转BRCA1和OTUB1表达，并且抑制ERα蛋白稳定性。由此证明，CXCR7表达升高可以通过激活ERK1/2信号通路来调节BRCA1和OTUB1的表达，并调控ERα蛋白质的稳定性和TAM敏感性。CXCR7可以作为潜在治疗靶点从而提高乳腺癌内分泌治疗效果。