circEIF4G3靶向miR-101调控EZH2的表达促进乳腺癌阿霉素耐药的分子机制研究

Doxorubicin resistance is one of the most difficult problems regarding treatment of breast cancer clinically. Our previous study demonstrated that inhibition of EZH2 down-regulated MDR1 expression and promoted apoptosis of doxorubicin-resistant breast cancer cells. Through a circRNA-seq and preliminary experiment，we found that circEIF4G3 was highly expressed in doxorubicin resistance breast cancer cell lines and tissues. Bioinformatic analysis indicated that circEIF4G3 might interact with miR-101 and EZH2 was the target gene of miR-101. Further experiments revealed that overexpression of circEIF4G3 promoted proliferation of breast cancer cells by downregulating miR-101 and upregulating EZH2 expression. Downregulation of circEIF4G3 can enhance the sensitivity of drug-resistant cells to doxorubicin. Dual luciferase reporter gene assay confirmed that circEIF4G3 can bind to miR-101.Therefore, we propose a scientific hypothesis that circEIF4G3 can act as a sponge of miR-101 to promote doxorubicin resistance in breast cancer via regulating EZH2 and promote MDR1 expression and EMT. In this project, PDX model and other methods will be used to elucidate the molecular mechanism of circEIF4G3 on promoting doxorubicin resistance. Ultimately, this project could provide a new theoretical basis and potential therapeutic target for the study of drug resistance of breast cancer.

阿霉素耐药是临床上治疗乳腺癌所面临的最棘手的问题之一，其耐药机制仍远未阐明。申请者前期证实抑制EZH2可下调MDR1并促进阿霉素耐药乳腺癌细胞凋亡。本项目通过环状RNA测序和预实验发现，circEIF4G3在阿霉素耐药乳腺癌中高表达。生物信息学分析得到与之互作的miR-101及其靶基因EZH2。进一步实验发现过表达circEIF4G3可下调miR-101和上调EZH2，并促进乳腺癌细胞增殖。下调circEIF4G3可增强耐药细胞对阿霉素的敏感性。荧光素酶报告实验证实circEIF4G3与miR-101结合。由此我们提出科学假说：circEIF4G3可通过海绵吸附miR-101解除对EZH2的负调控作用，促进MDR1表达和EMT，促进乳腺癌细胞对阿霉素产生耐药性。本项目拟通过构建PDX模型等方法，阐明circEIF4G3促进阿霉素耐药的分子机制，为乳腺癌耐药的研究提供新的理论依据和治疗靶点。

乳腺癌是女性最常见的恶性肿瘤，转移与耐药是乳腺癌治疗失败的主要原因。深入探讨乳腺癌转移与耐药的分子机制，寻找新型准确生物标志物及开发出新的治疗靶标显得尤为重要。环状RNA是一类新的具有由反式剪接而形成的闭合环状结构的非编码RNAs。大部分circRNAs主要位于细胞质中，因其具有组织特异性、时序特异性、疾病特异性以及高稳定性等生物学特点而备受关注，有望成为一种新型的肿瘤分子标志物。本课题前期通过高通量测序和预实验等方法发现了多个差异表达的circRNAs，包括circEIF4G3和circIQCH等。本课题探讨了circIQCH在乳腺癌中的表达、生物学功能及其调控乳腺癌增殖、转移等的分子机制。结果发现circIQCH（hsa_circ_0104345）在乳腺癌中表达上调，敲低circIQCH表达抑制乳腺癌细胞增殖、迁移、侵袭和转移。机制研究发现，circIQCH充当miR-145的“分子海绵”吸附miR-145促进DNMT3A的表达，抑制抑癌基因PTEN和BRCA1的表达，从而促进乳腺癌的进展。我们的研究表明circIQCH/miR-145/DNMT3A信号轴在乳腺癌生长和转移中发挥着关键的作用。因此，circIQCH有望成为乳腺癌的潜在治疗靶点。