TGF-β downregulates E-cadherin expression via a novel ZEB1-dependent mechanism

Zinc finger E-box-binding homeobox 1 (ZEB1) is a core transcription factor regulating epithelial-mesenchymal transition (EMT), and its high expression is associated with malignant cancer phenotypes and a poor prognosis. ZEB1 mediates downregulation of E-cadherin (encoded by CDH1), as a hallmark of cells undergoing EMT. We previously identified two distinct modes of E-cadherin downregulation by ZEB1, namely, basal repression and stimulus-dependent repression. The current study aimed to investigate the mechanisms responsible for stimulus-dependent repression induced by transforming growth factor-β (TGF-β), using ZEB1-knockout cells. Knockout of ZEB1 resulted in upregulation of basal E-cadherin expression and attenuation of its downregulation following TGF-β treatment. TGF-β-induced E-cadherin downregulation required Smad3 signaling, but did not accompany upregulation of ZEB1 expression, suggesting functional modulation of ZEB1. C-terminal binding proteins were required for basal repression but not for TGF-β-induced downregulation. Consistently, basal repression of CDH1 by ZEB1, but not TGF-β-induced downregulation, was accompanied by histone deacetylation in the CDH1 regulatory regions; however, both of these processes required histone deacetylase activity. Histone deacetylase may therefore play a role in regulating the expression/function of factor(s) required for TGF-β-induced CDH1 downregulation. These results suggest that TGF-β downregulates E-cadherin expression via a novel ZEB1-dependent mechanism.