ERα signaling through slug regulates E-cadherin and EMT

The ER alpha signaling pathway is one of the most important and most studied pathways in human breast cancer, yet numerous questions still exist such as how hormonally responsive cancers progress to a more aggressive and hormonally independent phenotype. We have noted that human breast cancers exhibit a strong direct correlation between ER alpha and E-cadherin expression by immunohistochemistry, suggesting that ER alpha signaling might regulate E-cadherin and implying that this regulation might influence epithelial-mesenchymal transition (EMT) and tumor progression. To investigate this hypothesis and the mechanisms behind it, we studied the effects of ER alpha signaling in ER alpha-transfected ER alpha-negative breast carcinoma cell lines, the MDA-MB-468 and the MDA-MB-231 and the effects of ER alpha knockdown in naturally expressing ER alpha-positive lines, MCF-7 and T47D. When ER alpha was overexpressed in the ER alpha-negative lines, 17 beta-estradiol (E2) decreased slug and increased E-cadherin. Clones maximally exhibiting these changes grew more in clumps and became less invasive in Matrigel. When ER alpha was knocked down in the ER alpha-positive lines, slug increased, E-cadherin decreased, cells became spindly and exhibited increased Matrigel invasion. ER alpha signaling decreased slug expression by two different mechanisms: directly, by repression of slug transcription by the formation of a corepressor complex of ligand-activated ER alpha, HDAC inhibitor (HDAC1), and nuclear receptor corepressor (N-CoR) that bound the slug promoter in three half-site estrogen response elements (EREs); indirectly by phosphorylation and inactivation of GSK-3 beta through phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt). The GSK-3 beta inactivation, in turn, repressed slug expression and increased E-cadherin. In human breast cancer cases, there was a strong inverse correlation between slug and ER alpha and E-cadherin immunoreactivity. Our findings indicate that ER alpha signaling through slug regulates E-cadherin and EMT. Oncogene (2010) 29, 1451-1462; doi:10.1038/onc.2009.433; published online 18 January 2010