MYB调节乳腺癌细胞生长的新机制

Estrogen receptor α (ERα) overexpression plays an important role in breast tumorigenesis. The transcription factor MYB, whose expression is elevated by estrogen, promotes the growth of ERα-positive, but not ERα-negative, breast cancer cells. The mechanism underlying this process is unknown. We showed for the first time that MYB could enhance the activity of ERα promoter and ERα expression, as well as its transcriptional activity and target gene expression. These results indicate that MYB may regulate the proliferation of ERα positive breast cancer cells through a positive feedback loop. On the basis of the above mentioned observations, we will further investigate MYB regulation of ERα expression using the methods including luciferase reporter system, RNA interfere, qRT-PCR and Western blot. With the methods of chromatin immunoprecipitation (ChIP), EMSA, immunoprecipitation and GST Pull-down, we will make an intensive study of the mechanism underlying MYB regulation of ERα expression. We will examine if the effect of MYB on proliferation and tumor formation of breast cancer cells as well as transformation of human mammary epithelial cells (HMECs) through ERα. Besides, we will study the relationship between MYB expression and outcome of endocrine therapy in breast cancer patients. The research may contribute to the identification of new target for breast cancer diagnosis and treatment.

雌激素受体α（ERα）表达水平的升高在乳腺癌的发生中发挥极其重要的作用。转录因子MYB作为雌激素上调的基因，能够促进ERα阳性乳腺癌细胞的生长，而对ERα阴性细胞的生长没有明显影响，但其机制还不清楚。本研究首次发现MYB能够升高ERα启动子的活性以及ERα的表达水平、转录活性和下游基因的表达。以上结果提示MYB可能以正反馈的机制调节ERα阳性乳腺癌细胞的生长。本申请拟在上述工作基础上，利用报告基因、RNA干扰、qRT-PCR、Western blot等实验进一步研究MYB对ERα表达的调节；利用染色质免疫沉淀、凝胶迁移阻滞、免疫共沉淀等方法研究MYB调节ERα的分子机制；确定MYB是否通过ERα影响乳腺癌细胞生长、成瘤能力和正常乳腺上皮细胞的转化以及MYB与乳腺癌内分泌治疗预后的关系，为发现新的乳腺癌诊断和治疗靶标打下基础。

雌激素信号通路在乳腺癌的发生发展中发挥重要作用，60%的乳腺癌患者雌激素受体ER alpha 表达水平升高。转录因子Myb作为雌激素上调的基因，能够促进ER alpha 阳性乳腺癌细胞的生长，而对ER alpha 阴性细胞的生长没有明显影响，但其机制还不清楚。本研究首次发现Myb 能够升高ER alpha 启动子的活性，作用区域为ER alpha 启动子的-743—-754bp区域，乳腺癌细胞中过量表达Myb升高ER alpha 的表达水平、转录活性和下游基因Cat-D和pS2的表达。染色质免疫共沉淀实验显示Myb能够直接结合到ER alpha 的启动子上。我们还发现miR548能够抑制Myb的表达，其机制是靶向Myb的3’UTR区。过量表达miR548抑制ER alpha 的表达水平和雌激素信号通路的活性。进一步研究发现miR548/Myb调节乳腺癌细胞的增殖和成瘤能力，而且miR548对细胞增殖的调控依赖于Myb。最后，利用乳腺癌标本，我们检测了miR548和Myb在癌和癌旁组织中的表达水平，肿瘤组织中miR548的表达显著低于癌旁相对正常组织，miR548的表达与Myb的表达呈负相关。上述研究阐明了Myb在ER alpha阳性乳腺癌细胞中特异的促癌机制，提示Myb 可能以正反馈的机制调节ER alpha 阳性乳腺癌细胞的生长，miR548/Myb可能成为乳腺癌诊断和治疗的靶点。