Ferritin heavy chain-mediated iron homeostasis and subsequent increased reactive oxygen species production are essential for epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) plays a critical role in tumor progression. To obtain a broad view of the molecules involved in EMT, we carried out a comparative proteomic analysis of transforming growth factor-β1 (TGF-β1)-induced EMT in AML-12 murine hepatocytes. A total of 36 proteins with significant alterations in abundance were identified. Among these proteins, ferritin heavy chain (FHC), a cellular iron storage protein, was characterized as a novel modulator in TGF-β1-induced EMT. In response to TGF-β1, there was a dramatic decrease in the FHC levels, which caused iron release from FHC and, therefore, increased the intracellular labile iron pool (LIP). Abolishing the increase in LIP blocked TGF-β1-induced EMT. In addition, increased LIP levels promoted the production of reactive oxygen species (ROS), which in turn activated p38 mitogen-activated protein kinase. The elimination of ROS inhibited EMT, whereas H₂O₂ treatment rescued TGF-β1-induced EMT in cells in which the LIP increase was abrogated. Overexpression of exogenous FHC attenuated the increases in LIP and ROS production, leading to a suppression of EMT. We also showed that TGF-β1-mediated down-regulation of FHC occurs via 3′ untranslated region-dependent repression of the translation of FHC mRNA. Moreover, we found that FHC down-regulation is an event that occurs between the early and highly invasive advanced stages in esophageal adenocarcinoma and that depletion of LIP or ROS suppresses the migration of tumor cells. Our data show that cellular iron homeostasis regulated by FHC plays a critical role in TGF-β1-induced EMT.