miR-106b-93-25基因簇促进衰老相关分泌表型诱导乳腺癌化疗耐药的作用及机制研究

Chemotherapy is a routine therapeutic approach for the treatment of cancer. Cancer cells can enter the state of therapy-induced senescence (TIS) when treated with chemotherapeutic drugs. Accumulated studies have shown that although senescent cells do not proliferate, they remain metabolically active and assume a novel phenotype, the so-called senescence-associated secretory phenotype (SASP), which may paradoxically contribute to the emergence of chemoresistance, cancer metastasis and cancer stem-like cells. Work performed before we have demonstrated that the overexpression of miR-106-93-25 cluster renders chemoresistance to breast cancer cells. With the overexpression of miR-106b-93-25 cluster,the proportion of BCSC obviously increased in the drug resistant clones after doxorubicin treatment, which induced SASP secreted by the senescent cells. However, the role and regulation of this cluster in breast cancer stem cell (BCSC) drug resistance remains largely unknown. We intend to determine whether miR-106-93-25 cluster can impinge on the microenvironment through SASP, which components of SASP are mainly regulated by miR-106b-93-25 cluster in breast cancer cells and may contribute to chemoresistance and BCSC changes subsequently at cellular level, animal model level and clinical case analysis. In this study, we will investigate whether miR-106b-93-25 cluster could be utilized as a biomarker to predict the risk of drug resistance and poor prognosis in breast cancer patients, which may offer us novel target to reverse breast cancer chemoresistance more effectively.

化疗可导致肿瘤细胞产生衰老相关分泌表型（SASP）。SASP能够通过促进肿瘤细胞耐药并使之增强干细胞特性。前期研究发现，miR-106b-93-25基因簇能够使乳腺癌细胞对化疗药物产生耐受性，其表现为miR-106b-93-25基因簇高表达的乳腺癌细胞能够克服化疗药物诱导的衰老，同时化疗诱导细胞产生SASP后促使存活的耐药克隆中乳腺癌干细胞（BCSC）比例显著增高。但是该基因簇诱导乳腺癌化疗耐药及增强BCSC的机制尚不清楚。以此为基础，本课题拟通过动物、细胞、分子水平试验以及临床病例分析，期望阐明miR-106-93-25 基因簇对SASP、乳腺癌化疗耐药、BCSC的调控作用及相关机制，同时探究该基因簇拟作为乳腺癌复发及化疗耐药“风险标识物”的可能性与价值。此外，本研究不仅能够使我们对肿瘤耐药与肿瘤干细胞进一步深入了解，而且将为逆转肿瘤耐药性及更有效地治疗乳腺癌提供新思路与新靶点。

微小RNA（miRNAs）作为一类进化保守的非编码RNAs，通过与靶基因mRNA的序列互补配对抑制其翻译或启动降解来发挥作用。越来越多的研究结果证实，miRNAs通过发挥促癌或抑癌作用参与调控多种肿瘤的发生与发展。目前共发现多种与乳腺癌相关的miRNA，广泛参与调控乳腺癌的化疗敏感性、侵袭转移、乳腺癌干细胞特性等。本项目主要针对miR-106b-93-25基因簇、miR-218、miR-205在乳腺癌化疗多药耐药性的发生过程中发挥的功能以及参与调控的相关分子机制进行了深入研究。miR-106b-93-25基因簇在乳腺癌细胞中通过靶向下游EP300调控细胞凋亡相关基因的表达，通过抑制细胞凋亡、调控细胞周期，以独立于ABC转运蛋白家族的分子机制诱导乳腺癌细胞紫杉醇耐药的发生；抑制核转录因子EP300表达同样能够诱导乳腺癌细胞紫杉醇耐药的发生。另外通过临床标本检测验证miR-93表达量与乳腺癌患者化疗敏感性负相关，有望成为预测乳腺癌患者化疗敏感性的分子标志物。miR-218在乳腺癌化疗耐药细胞中显著低表达，过表达miR-218后能够部分恢复乳腺癌耐药细胞的化疗敏感性。相关分子机制的研究发现miR-218通过靶向抑制survivin基因表达促进肿瘤细胞凋亡的发生、上调caspase活性从而增加细胞的化疗敏感性。动物实验进一步证明miR-218过表达能够在裸鼠体内显著抑制乳腺癌细胞的增殖速度且对化疗药物敏感性增加。miR-205表达量与接受新辅助化疗的乳腺癌患者的化疗敏感性正相关，且其表达量在化疗耐药乳腺癌细胞中显著降低；过表达miR-205能够增加乳腺癌化疗耐药细胞的化疗敏感性。相关分子机制的研究发现miR-205通过靶向抑制VEGFA与FGF2抑制PI3K/Akt信号通路的活性，调控细胞凋亡相关基因的表达，从而部分逆转乳腺癌细胞的化疗耐药性。动物实验进一步证明过表达 miR-205的乳腺癌细胞在裸鼠体内成瘤性降低、增殖速度减慢，且对化疗药物敏感性增加。以上研究结果不仅是对乳腺癌耐药性形成相关理论的重要补充，与临床数据的结合提示miR-93与miR-205有望成为提示乳腺癌早期耐药与预测预后的分子标志物，具有良好的临床应用前景和潜在的经济效益。