Transforming growth factor-β1 represses E-cadherin production via Slug expression in lens epithelial cells

PURPOSE. TGF beta is a potent candidate for epithelial-mesenchymal transition (EMT) during the development of anterior polar cataracts in the human lens. The Snail superfamily is involved in EMT through the repression of E-cadherin production. This study was conducted to determine whether the Snail gene family is activated in the process of TGF beta 1-induced EMT and how TGF beta 1 regulates the expression of this gene family. METHODS. Total RNA extracted from human cataract samples was subjected to the real-time PCR quantification of Slug mRNA. Induction of Slug expression by TGF beta 1 (10 ng/mL) in lens epithelial cells was determined by RT-PCR, immunostaining, immunoblot analysis, and Slug promoter analysis. A series of Slug promoter deletion constructs was used to identify the putative regulatory element responsive to TGF signaling. Chromatin immunoprecipitation was performed to determine whether Sp1 associates with the endogenous Slug promoter. Inhibition of Slug expression with Slug siRNA was used to investigate the role of Slug in TGF beta-mediated EMT. RESULTS. Slug levels were highly upregulated in lens epithelial cells obtained from patients with anterior polar cataracts. Treatment of TGF beta 1 induced the expression of Slug in both lens and other epithelial cells in vitro. TGF beta 1-induced Slug expression was significantly inhibited by the MEK- and JNK/ SAPK-specific inhibitors, but not by transfection with dominant-negative forms of Smads or small GTPase proteins, indicating that MAPK pathways are involved in the regulation of Slug expression by TGF beta 1. The Slug promoter analysis revealed that the Spl binding site in the Slug promoter is responsible for TGF beta 1-induced Slug expression. In addition, the TGF beta 1-mediated repression of E-cadherin was significantly inhibited by Slug siRNA. CONCLUSIONS. These data suggest that TGF beta 1 induces Slug expression and that the repression of E-cadherin production by TGF beta 1 is mediated by the induction of Slug in lens epithelial cells.