ERβ1 represses basal-like breast cancer epithelial to mesenchymal transition by destabilizing EGFR

Introduction: Epithelial to mesenchymal transition (EMT) is associated with the basal-like breast cancer phenotypes. Sixty percent of basal-like cancers have been shown to express wild-type estrogen receptor beta (ER beta 1). However, it is still unclear whether the ER beta expression is related to EMT, invasion and metastasis in breast cancer. In the present study, we examined whether ER beta 1 through regulating EMT can influence invasion and metastasis in basal-like cancers.

Methods: Basal-like breast cancer cells (MDA-MB-231 and Hs578T), in which ER beta 1 was either overexpressed or down-regulated were analyzed for their ability to migrate and invade (wound-healing assay, matrigel-coated Transwell assay) as well as for the expression of EMT markers and components of the EGFR pathway (immunoblotting, RT-PCR). Co-immunoprecipitation and ubiquitylation assays were employed to examine whether ER beta 1 alters epidermal growth factor receptor (EGFR) protein degradation and the interaction between EGFR and the ubiquitin ligase c-Cbl. The metastatic potential of the ER beta 1-expressing MDA-MB-231 cells was evaluated in vivo in a zebrafish xenotransplantation model and the correlation between ER beta 1 and E-cadherin expression was examined in 208 clinical breast cancer specimens by immunohistochemistry.

Results: Here we show that ER beta 1 inhibits EMT and invasion in basal-like breast cancer cells when they grow either in vitro or in vivo in zebrafish. The inhibition of EMT correlates with an ER beta 1-mediated up-regulation of miR-200a/b/429 and the subsequent repression of ZEB1 and SIP1, which results in increased expression of E-cadherin. The positive correlation of ER beta 1 and E-cadherin expression was additionally observed in breast tumor samples. Downregulation of the basal marker EGFR through stabilization of the ubiquitin ligase c-Cbl complexes and subsequent ubiquitylation and degradation of the activated receptor is involved in the ER beta 1-mediated repression of EMT and induction of EGFR signaling abolished the ability of ER beta 1 to sustain the epithelial phenotype.

Conclusions: Taken together, the results of our study strengthen the association of ER beta 1 with the regulation of EMT and propose the receptor as a potential crucial marker in predicting metastasis in breast cancer.