Estrogen receptor beta inhibits cholesterol biosynthesis through overexpression of mir-181a-5p in Triple Negative Breast Cancer. Estrogen receptor beta inhibits cholesterol biosynthesis through overexpression of mir-181a-5p in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is a highly heterogeneous disease representing the most aggressive breast cancer (BC) subtype. Lack of Estrogen Receptor alpha (ERα), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2/neu) expression makes TNBC immune to common therapies, significantly limiting the treatment options and suggesting the need to identify novel therapeutic targets. It was previously reported that Estrogen Receptor beta (ERβ) is expressed in a fraction of TNBC patients, where its presence correlates with improved patient outcome. Recently, we demonstrated an oncosuppressive ERβ effect in TNBC cell models expressing exogenous ERβ. On the other hand, it was shown that ERβ is involved in miRNA-mediated gene regulation in hormone-responsive BC cells, suggesting similar effect also in TNBC. To verify this hypothesis, we performed small non-coding RNA (sncRNA) sequencing on three engineered cell lines belonging to different TNBC molecular subtypes. ERβ-specific changes of sncRNA profile revealed that the major part of deregulated molecules are subtype specific, with only few commonly regulated ones. In order to validate the obtained results, we performed sncRNA profiling of 12 ERβ positive and 32 ERβ negative TNBC tissues, whose receptor status was assessed by immunohistochemistry in our previous research. Also here, ERβ-specific group of deregulated sncRNAs was identified. Interestingly, comparison of obtained in vitro and in vivo results revealed 2 differentially expressed miRNAs, displaying the same behavior in all three analyzed cell lines and tissues. In concordance with our previous results, IPA signaling pathway analysis performed on genes targeted by deregulated miRNAs highlighted downregulation of cholesterol biosynthesis pathway and upregulation of several signaling processes. Taken together, these findings suggest that ERβ is able to exert its oncosuppressive role in TNBC through miRNA-mediated regulation of gene expression.

三阴性乳腺癌（Triple negative breast cancer, TNBC）是一种高度异质性疾病，是恶性程度最高的乳腺癌（breast cancer, BC）亚型。由于缺乏雌激素受体α（Estrogen Receptor alpha, ERα）、孕激素受体（progesterone receptor, PR）及表皮生长因子受体2（epidermal growth factor receptor 2, HER2/neu）的表达，TNBC对常规治疗产生耐药性，极大限制了临床治疗选择，同时也提示亟需发掘全新的治疗靶点。既往研究表明，部分三阴性乳腺癌患者体内可检测到雌激素受体β（Estrogen Receptor beta, ERβ）的表达，且该受体的表达与患者预后改善呈正相关。近期，本团队在外源表达ERβ的TNBC细胞模型中证实了ERβ的抑癌效应。另一方面，已有研究显示，在激素响应性乳腺癌细胞中，ERβ参与了微小RNA（microRNA, miRNA）介导的基因调控过程，这提示在TNBC中可能也存在类似的调控效应。为验证这一假说，本团队针对三种隶属于不同TNBC分子亚型的工程化细胞系，开展了小分子非编码RNA（small non-coding RNA, sncRNA）测序实验。ERβ特异性的sncRNA表达谱变化分析显示，绝大多数失调的sncRNA分子具有亚型特异性，仅少数存在共同调控特征。为验证上述实验结果，本团队对12例ERβ阳性、32例ERβ阴性的TNBC组织开展了sncRNA谱分析；这些组织的受体状态已在本团队既往研究中通过免疫组织化学方法完成评估。在此队列中，本团队同样鉴定出了ERβ特异性的失调sncRNA群体。值得注意的是，对比体外与体内实验结果，本团队发现2个差异表达的miRNAs，它们在全部三种分析的细胞系及组织中均表现出一致的表达变化趋势。与本团队既往研究结果一致，针对失调miRNA靶基因开展的IPA信号通路分析显示，胆固醇生物合成通路显著下调，而多条信号通路则显著上调。综上，上述研究结果表明，ERβ可通过miRNA介导的基因表达调控，在TNBC中发挥其抑癌功能。