ZIC2作为乳腺癌候选抑癌基因的作用及机制

Breast cancer has the highest incidence of malignant tumors in women and is a molecularly heterogeneous disease. Transcription factor(s) serving as the upstream of gene expression regulation, play an important role in the tumorigensis of breast cancer. ZIC2, one of the members of ZIC family proteins, shares a C2H2 type zinc finger structure and plays an important role during the development of the nervous system. Recently, ZIC2 have been shown to be up-regulated in a variety of tumors including oral squamous cell carcinoma, ovarian cancer, cervical cancer and meningioma, and be positively related with poor prognosis in these cancer patients. Whether the expression of ZIC2 is disregulated, and whether it is involve in the breast cancer development and metastasis are still remain elusive. Our preliminary results showed that ZIC2 is lowly expressed in breast cancer compared to paracancerous tissues, and the low expression of ZIC2 is correlated with the worse outcome of breast cancer patients. In vitro and in vivo studies found that the overexpression of ZIC2 can inhibit tumor proliferation and tumorigenisis capacity. ZIC2 can negatively regulate Bmi1 at promoter activity, mRNA and protein levels. In this project, in addition to investigate the potential target gene identified by Luciferase assay, we will further investigate the alternative mechanisms of how ZIC2 is involved in breast cancer through ChIP-seq, microarray, immunoprecipitation and mass spectrum analysis method etc., providing new insight into ZIC2 as a potential tumor suppressor in breast cancer, revealing molecular mechanisms and new treatment strategies for breast cancer.

乳腺癌作为女性发病率最高的恶性肿瘤，是一个分子水平异质性很高的疾病。转录因子作为基因表达调控的上游，在乳腺癌的发生发展过程中起重要的作用。锌指蛋白ZIC2是神经系统的发育过程中重要转录因子。ZIC2在口腔鳞癌、卵巢癌、子宫颈癌和脑膜瘤等肿瘤均表达上调，并与预后不良呈正相关。乳腺癌发生发展中是否存在ZIC2表达异常？及其可能的作用和机制如何？我们的前期研究发现ZIC2在乳腺癌中低表达，且ZIC2的低表达与乳腺癌患者的不良预后相关。体外和体内实验均显示过表达ZIC2可以抑制肿瘤细胞增殖能力和成瘤能力。初步机制研究发现ZIC2可以在启动子活性、mRNA以及蛋白水平上显著下调Bmi1表达。本项目继续探讨已鉴定的潜在靶基因，并拟通过ChIP-seq、表达谱芯片、免疫沉淀和质谱分析等方法深入探讨ZIC2抑制乳腺癌发生发展的机制，为诠释乳腺癌发生发展的分子机制和寻找乳腺癌的治疗新手段提供科学依据。

虽然早期发现和系统治疗提高了乳腺癌的诊断率和临床治愈率，但由于缺乏有效的治疗方法，乳腺癌仍是女性最常见的恶性肿瘤。因此，为了开发潜在的靶向治疗，从而使更多的患者受益，了解癌细胞的功能机制是非常重要的。ZIC家族成员在神经发育和肿瘤发生中起重要作用。在本研究中，我们发现ZIC2在乳腺癌组织中的mRNA和蛋白水平均下调。ZIC2的低表达与乳腺癌患者的不良预后相关，并可作为独立的预后标志物。此外，ZIC2的过表达抑制了细胞的增殖和集落形成能力，而ZIC2的过表达促进了细胞的体外增殖和集落形成能力，促进了体内肿瘤的生长。通过CHIP-SEQ和RNA-SEQ分析，筛选并确定STAT3为ZIC2的潜在靶点，双荧光素酶报告基因实验表明ZIC2与STAT3启动子结合并抑制STAT3的启动子活性，截断STAT3启动子结合位点，ZIC2不能调节STAT3启动子的活性。ZIC2基因敲除可诱导STAT3的表达，使磷酸化的STAT3水平升高。这些结果表明，ZIC2通过直接与STAT3启动子结合来调控STAT3的转录。此外，用siRNA或抑制剂干扰STAT3可消除ZIC2减少引起的致癌效应。综上所述，我们的结果表明，zic2在乳腺癌中是一个有用的预后标记物，并通过调节STAT3作为肿瘤抑制因子，这意味着STAT3抑制剂可能为ZIC2表达下调的乳腺癌患者提供了一种新的治疗选择。