Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin.
Carbone Comprehensive Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin.
Endocrinology. 2019 Oct 1;160(10):2427-2440. doi: 10.1210/en.2019-00299.
Estrogen receptor α (ER) is the target of endocrine therapies in ER-positive breast cancer (BC), but their therapeutic effectiveness diminishes with disease progression. Most metastatic BCs retain an ER-positive status, but ER expression levels are reduced. We asked how the bone tumor microenvironment (TME) regulates ER expression. We observed ESR1 mRNA and ER protein downregulation in BC cells treated with conditioned media (CM) from patient-derived, cancer-activated bone marrow stromal cells (BMSCs) and the BMSC cell line HS5. Decreases in ESR1 mRNA were attributed to decreases in nascent transcripts as well as decreased RNA polymerase II occupancy and H3K27Ac levels on the ESR1 promoter and/or distal enhancer (ENH1). Repression extended to neighboring genes of ESR1, including ARMT1 and SYNE1. Although ERK/MAPK signaling pathway can repress ER expression by other TME cell types, MAPK inhibition did not reverse decreases in ER expression by BMSC-CM. ESR1 mRNA and ER protein half-lives in MCF7 cells were unchanged by BMSC-CM treatment. Whereas ER phosphorylation was induced, ER activity was repressed by BMSC-CM as neither ER occupancy at known binding sites nor estrogen response element-luciferase activity was detected. BMSC-CM also repressed expression of ER target genes. In cells expressing the Y537S and D538G ESR1 mutations, BMSC-CM reduced ESR1, but expression of target genes PGR and TFF1 remained significantly elevated compared with that of control wild-type cells. These studies demonstrate that BMSCs can transcriptionally corepress ESR1 with neighboring genes and inhibit receptor activity, but the functional consequences of the BMSC TME can be limited by metastasis-associated ESR1 mutations.
雌激素受体 α(ER)是 ER 阳性乳腺癌(BC)内分泌治疗的靶点,但随着疾病的进展,其治疗效果会减弱。大多数转移性 BC 仍然保持 ER 阳性状态,但 ER 表达水平降低。我们想知道骨肿瘤微环境(TME)如何调节 ER 表达。我们观察到 BC 细胞在用患者来源的、癌症激活的骨髓基质细胞(BMSC)和 BMSC 细胞系 HS5 的条件培养基(CM)处理后,ESR1 mRNA 和 ER 蛋白下调。ESR1 mRNA 的减少归因于新生转录本的减少以及 RNA 聚合酶 II 在 ESR1 启动子和/或远端增强子(ENH1)上的占据和 H3K27Ac 水平的减少。这种抑制扩展到 ESR1 附近的基因,包括 ARMT1 和 SYNE1。虽然 ERK/MAPK 信号通路可以通过其他 TME 细胞类型抑制 ER 表达,但 MAPK 抑制并不能逆转 BMSC-CM 对 ER 表达的抑制作用。BMSC-CM 处理对 MCF7 细胞中 ER 表达的半衰期没有影响。虽然 ER 磷酸化被诱导,但 ER 活性被 BMSC-CM 抑制,因为在已知的结合位点或雌激素反应元件-荧光素酶活性均未检测到 ER 占据。BMSC-CM 还抑制 ER 靶基因的表达。在表达 Y537S 和 D538G ESR1 突变的细胞中,BMSC-CM 降低了 ESR1,但与对照野生型细胞相比,靶基因 PGR 和 TFF1 的表达仍然显著升高。这些研究表明,BMSCs 可以与邻近基因共同转录抑制 ESR1,并抑制受体活性,但 BMSC TME 的功能后果可能受到转移相关 ESR1 突变的限制。