Decreased expression of glutaredoxin 1 is required for transforming growth factor-β1-mediated epithelial-mesenchymal transition of EpRas mammary epithelial cells

Transforming growth factor-β (TGF-β) is a cytokine important in inducing epithelial-mesenchymal transition (EMT), a crucial morphological event in a wide range of physiological and pathological cellular processes. In this study, we demonstrate that TGF-β1 induces the EMT phenotype through decreasing the expression of the glutaredoxin 1 (Grx1) gene, an anti-oxidant enzyme, in H-Ras transformed EpH4 mammary epithelial cells (EpRas), but not in the parental EpH4 cells. TGF-β1-induced reduction of Grx1 expression caused an increase of intracellular reactive oxygen species (ROS) in EpRas cells, and pre-treatment of the ROS scavenger N-acetylcysteine (NAC) inhibited TGF-β1-induced EMT. Grx1-overexpressing EpRas cells showed a reduction in intracellular ROS generation and suppressed the expression of mesenchymal markers upon treatment of TGF-β1. In addition, MEK/MAP kinase and phosphatidylinositol-3 kinase (PI3K) signaling were found to mediate the decrease in Grx1 expression upon TGF-β1 treatment, depending on the presence of Ras protein. Thus our findings strongly suggest that TGF-β1 promotes EMT by increasing intracellular ROS levels via down-regulation of the Grx1 gene in EpRas cells.