转录因子Mga通过维系肿瘤细胞干性促进基底样乳腺癌转移的机制研究

Breast cancer is the most common cancer type in female. The malignant phenotypes of Basal-like breast cancer (BLBC) is the most malignant subtype with fast progression and high relapse rate, which is thought to be an attribute of stem-like phenotypes of tumor cells. No specific treatment exists for BLBC. One of the ‘core basal phenotype’ is CK5, which marks tumor cells with a similar transcription profile to tumor stem cells. We found transcription factor Mga bond the promoter of CK5 coding gene and activated its expression. Mga, in the PRC1 complex, maintains stemness of embryonic stem cells. Analysis of breast cancer databases found that Mga expression levels were significantly higher in invasive carcinomas than in normal mammary tissues, correlated with high relapse rate. The key scientific question is the mechanisms by which Mga, in complexes of PRC1, activates CK5 expression, maintains tumor cell stemness, and promotes BLBC metastasis. In this project, we propose to overexpress, or knock-out mga combined with rescue experiments in breast cancer cells and mice, to test the functions and of Mga in CK5 expression and BLBC metastasis; we will use Co-IP, immune-fluorescence, ChIP-Seq, and bioinformatics approaches to elucidate downstream signals of Mga and PRC1 complexes in stemness maintenance and metastasis; we will use breast cancer tissue microarray for immuno-histochemistry and clinical data analysis, to uncover the clinical significance of Mga. Successful completion of this project will provide a potential target and experimental basis for BLBC treatment.

乳腺癌是女性最常见癌症。基底样乳腺癌进展快，易复发，其恶性表型与肿瘤细胞干性相关，尚无有效治疗方法。基底样乳腺癌核心表型之一为CK5，所标记的细胞与肿瘤干细胞表型相似。我们发现转录因子Mga结合CK5编码基因启动子并激活其转录。Mga与PRC1形成复合体，维系胚胎干细胞干性。对数据库分析发现Mga在浸润性乳腺癌中的表达显著高于正常组织，表达量与乳腺癌高复发正相关。关键科学问题是Mga通过PRC1维系肿瘤细胞干性，促进基底样乳腺癌转移的机制。本项目拟利用乳腺癌细胞系和转基因小鼠，通过Mga基因过表达、敲除及回补方法，明确Mga在CK5转录及癌转移中的作用；通过免疫沉淀、免疫荧光、ChIP-seq及生物信息学等手段，明确Mga及PRC1的下游因子，探讨其在肿瘤细胞干性和癌转移中的作用；利用乳腺癌组织芯片免疫组化检测和临床资料分析，明确Mga的临床意义，为基底样乳腺癌治疗提供备选标靶和实验依据。

乳腺癌是女性第一大恶性肿瘤，严重威胁女性健康。由于不同种类乳腺细胞产生的乳腺癌临床表型和愈后截然不同，从各个类型细胞特征入手有助于深入了解乳腺癌，并提供新型治疗方案。本项目研究了乳腺基底细胞和末端乳芽帽细胞特征在乳腺癌中的功能。首先，我们鉴定了四个基底细胞相关转录因子，包括stk38，relA，prdm1和mga。其中，stk38，relA，和mga富集在krt5基因启动子，而prdm1富集于krt8基因启动子。在正常乳腺组织中，stk38和relA在基底细胞和腺上皮细胞中均有表达，prdm1和mga表达在腺上皮细胞中。进一步分析发现stk38和relA促进krt5转录，prdm1对krt5转录无影响，而mga抑制krt5表达。这些数据表明stk38和relA促进krt5表达，是基底细胞的命运决定因子。其次，我们深入研究了乳腺末端乳芽帽细胞特性对乳腺癌转移的影响，发现Par3L通过与HMMR结合指导细胞有丝分裂纺锤体垂直于基底，从而促进乳腺癌转移。利用细胞谱系追踪等技术我们发现Par3L标记肿瘤转移起始细胞；Par3L通过与HMMR结合，指导纺锤体垂直于基底，使癌细胞向肿瘤外浸润；在Par3L阴性细胞HMMR通过与CGNL1结合指导纺锤体平行于基底，抑制肿瘤细胞浸润。这一发现为乳腺癌转移提供新的理论基础，为乳腺癌治疗提供新的靶点。