Abstract P1-01-17: Characterization of novel ESR1 (c.749T>C; p.Met250Thr) mutation in enhancing cellular invasiveness of breast cancer

Emerging evidence has revealed that the mutations in estrogen receptor alpha (ERα) gene (ESR1) is frequently observed in ER+ metastatic breast cancer, and is associated with the aggressively invasive and metastatic phenotype in advanced breast cancer due to the resistance of endocrine therapy. In our previous study, we have identified three novel mutations of ESR1, including ESR1 G74R, D230H and M250T, in the untreated patients with early breast cancer. However, the functional roles for these novel mutations in the cellular biology of breast cancer remain to be elucidated. In this study, we described the molecular mechanism underlying potential roles for the novel mutation ESR1 p.Met250Thr (c.749T>C) in regulating the cellular invasiveness of breast cancer. Firstly, we found, as compared with wild-type (WT) HA-ESR1, forced expression of HA-ESR1 M250T enhanced the invasive capacity of breast cancer MCF-7 cells by using Transwell assay. Moreover, we found that the levels of miR-190 were significantly up-regulated in the MCF-7 (HA-ESR1 M250T) cells, and further verified that miR-190 played an important role in ESR1 M250T-mediated induction of cellular invasiveness by using specific shRNA to knock down miR-190 levels in MCF-7 (HA-ESR1 M250T) cells. Further bioinformatics analysis showed that there were several half Estrogen Response Elements (EREs) in the promoter region of Talin-2, as the host gene of miR-190. Talin-2-driven luciferase reporter assay indicated ESR1 M250T resulted in a higher increase in the luciferase activity than ESR1 WT. Chromatin-immunoprecipitation (ChIP) assay identified a higher binding ability with Talin-2 promoter for ESR1 M250T than ESR1 WT. Collectively, our mechanistic study revealed that the ESR1 M250T mutation, located in the DNA-binding domain, increased the invasive capacity of breast cancer cells via the transcriptional induction of Talin-2 and miR-190. The potential role for ESR1 M250T in affecting the efficacy of endocrine therapy has been under the investigation in our laboratory, and the result from which will help us better elucidate the clinical relevance for novel ESR1 mutations in affecting the sensitivity of endocrine therapy. This study was supported in part by National Natural Science Foundation of China (8160111571) and Guangdong Natural Science Foundation (2016A030313768). Citation Format: Liao N, Zhang G-C, Wang Y, Cao L, Li K, Ren C-Y, Wen L-Z, Shi Y, Zhu W, Chen X. Characterization of novel ESR1 (c.749T>C; p.Met250Thr) mutation in enhancing cellular invasiveness of breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-17.