Functional Interactions Between Estrogen-Related-Receptor Beta (Esrrb) And Transforming Growth Factor-Beta (Tgf-Beta) In The Regulation Of Breast Cancer Stem Cell Dynamics

Breast cancer is a worldwide problem that accounts for almost a quarter of all cancers in women; however, better therapeutic approaches are required since it is estimated that one to three deaths from overtreatment occur for every one death avoided. Our lab is interested in transforming growth factor beta (TGF-β) signaling and its dual role as tumor suppressor/promoter in breast cancer and its therapeutic applications. We previously performed genome-wide ChIP/Chip analysis to identify TGF-β-activated Smad3 target genes in a model of breast cancer progression. We discovered that the estrogen-related-receptor β (ESRRB) transcription factor binding motif was significantly enriched in Smad3 binding regions in breast cancer cell lines. The data suggested that functional interactions between ESRRB and the TGF-β pathway may influence breast cancer progression. ESRRs (α, β, γ) are members of the nuclear orphan receptor family that share significant homology with the estrogen receptors but are not activated by natural estrogens. Additionally, ESRRB maintains pluripotency in embryonic stem cells (ESCs) and is activated by Wnt signaling to promote self-renewal in ESCs. Thus we hypothesized that mechanistically ESRRB/TGF-β may affect breast cancer progression through effects on cancer stem cell (CSC) dynamics and cancer cell differentiation. We showed that ESRRB protein is overexpressed in human breast cancer compared with matched normal breast tissue, and that high expression of ESRRB colocalizes with the stem cell master regulator OCT4 in human breast cancer xenografts. We performed ESRRB knockdown in the MCF10Ca1h, MCF10Ca1a and MDAMB231 breast cancer cell lines and our data demonstrate that ESRRB opposes the inhibitory effects of TGF-β on CSCs as measured by tumorsphere formation assay, while having little or no effect on proliferation of the bulk tumor cell culture in vitro. More importantly, knockdown of ESRRB reduced the in vivo tumorigenicity of all three breast cancer lines and enhanced their histologic differentiation. Extreme limiting dilution assays in vivo showed that knockdown of ESRRB in MDAMB231 cells caused a 78-fold decrease in the relative number of CSCs. In conclusion, our preliminary findings suggest that ESRRB antagonizes the inhibitory effects of TGF-β on CSCs and breast cancer progression, making ESRRB an attractive therapeutic target whose inhibition can restore the tumor suppressive effects of TGF-β and reduce the tumorigenic breast CSC population. Citation Format: Nellie Moshkovich, Misako Sato, Binwu Tang, Yu-an Yang, Kathleen C. Flanders, Mitsutaka Kadota, Howard Yang, Maxwell P. Lee, Lalage M. Wakefield. Functional interactions between estrogen-related-receptor β (ESRRB) and transforming growth factor-beta (TGF-β) in the regulation of breast cancer stem cell dynamics. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2244. doi:10.1158/1538-7445.AM2015-2244