Estrogen Receptor Beta Impacts Hormone-Induced Alternative mRNA Splicing in Breast Cancer Cells

Estrogens play an important role in breast cancer (BC) development and progression, where the two isoforms of the estrogen receptor (ERα and ERβ) are generally co-expressed and mediate the effects of these hormones in cancer cells. ERβ has been suggested to exert an antagonist role toward the oncogenic activities of ERα, and for this reason it is considered an oncosuppressor. As clinical evidence regarding a prognostic role for this receptor subtype in hormone-responsive BC is still limited and conflicting, more knowledge is required on the biological functions of ERβ in cancer cells. We described previously the ERβ and ERα interactomes of BC cells, identifying specific and distinct patterns of protein interactions for the two receptors. In particular, we identified factors involved in mRNA splicing and maturation as important components of both ERα and ERβ pathways. Guided by these findings, we investigated here in depth the differences in the early transcriptional events and RNA splicing patterns induced in ERα vs ERα+ERβ cells, by expressing ERβ in ERα+ human BC MCF-7 cells. High-throughput mRNA sequencing was then performed in both cell lines after stimulation with 17b-estradiol, and the results obtained were compared. We investigated here in depth the differences in the early transcriptional events and RNA splicing patterns induced in ERα vs ERα+ERβ cells, by expressing ERβ in ERα+ human BC MCF-7 cells. High-throughput mRNA sequencing was then performed in both cell lines after stimulation with 17b-estradiol, and the results obtained were compared.

雌激素（Estrogens）在乳腺癌（breast cancer, BC）的发生与发展进程中发挥关键作用，该过程中雌激素受体（estrogen receptor, ER）的两种亚型（ERα与ERβ）通常共表达，并介导此类激素在癌细胞内的生物学效应。已有研究提示ERβ可对ERα的致癌活性产生拮抗作用，因此ERβ被视为一种抑癌因子（oncosuppressor）。不过目前关于该受体亚型在激素敏感性乳腺癌中预后作用的临床证据仍较为有限且存在分歧，亟需进一步明确ERβ在癌细胞内的生物学功能。我们此前曾报道乳腺癌细胞中ERα与ERβ的互作组（interactomes），鉴定出两种受体各自特有的、互不重叠的蛋白质互作模式；其中，参与mRNA剪接与成熟的相关因子是ERα与ERβ信号通路的重要组成部分。基于上述研究发现，本研究通过在表达ERα的人乳腺癌MCF-7细胞中过表达ERβ，深入探究了仅表达ERα的细胞与共表达ERα+ERβ的细胞之间早期转录事件及RNA剪接模式的差异。随后，我们用17β-雌二醇（17b-estradiol）刺激两种细胞系后开展高通量mRNA测序（high-throughput mRNA sequencing），并对所得实验结果进行了对比分析。