Abstract 3906: Twist regulates estrogen receptor expression in breast cancer

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Background: Estrogen receptor alpha (ER) plays a crucial role in breast cancer development and progression due to its role as an effector/mediator of the mitogenic hormone estrogen. However, the role of transcriptional regulation of ER in tumor progression is not completely characterized. While defining the role of the basic helix loop helix transcription factor Twist (TWIST1) in breast cancer development, we identified ER as a downstream target of Twist in breast cells. Methods: A knock-up and knock-down approach in Twist negative and positive cell lines was used in order to characterize the regulation of ER by Twist. We analyzed ER expression by immunoblotting, ER transcriptional activity by promoter assays, DNA binding by chromatin immunoprecipitation, and estrogen independent growth in the presence of stripped serum or the estrogen antagonist tamoxifen (TAM). Additionally, ER promoter methylation was measured by methylation specific quantitative PCR (MS-qPCR). Using orthotopic xenografts in SCID mice, tumor growth was determined in presence of TAM and assayed for vascular permeability and volume by functional magnetic resonance imaging. Finally, the relationship between Twist and ER expression in breast tumors was evaluated by quantitative reverse-transcription PCR (qRTPCR). Results: Twist transcriptionally down-regulated ER expression by direct promoter modulation. Twist over-expression caused estrogen independence and TAM resistance, and induced hypermethylation of the ER promoter. In vivo, Twist expression resulted in estrogen independent growth and resistance to TAM. Twist over-expressing tumor xenografts exhibited high vascular volume and permeability. Moreover, Twist and ER expression were inversely correlated in primary breast cancer patient samples. Conclusion: The regulation of ER by Twist might be an underlying mechanism for ER negativity seen in breast tumors and could have important clinical implications for ER negative breast cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3906.