Epithelial-Mesenchymal Transition in Human Alveolar Cells Exposed to Indium Chloride.

For workers in the industry, occupational exposure to indium compounds induces pulmonary disorders, such as interstitial pneumonia. Moreover, lung cancer has been reported in both humans and rodents exposed to indium compounds by inhalation. However, the biological mechanism underlying indium-induced disorders is poorly understood. Epithelial-mesenchymal transition (EMT)-the cellular process of losing epithelial and acquiring mesenchymal characteristics-is linked to fibrosis and cancer progression. Therefore, we examined whether indium exposure elicits EMT in vitro. A549 human alveolar epithelial cells treated with indium chloride at doses of 0-500 μg/mL for 24 h were used to analyze EMT marker expression and cytoarchitecture. Significant downregulation of CDH1 mRNA expression as an epithelial marker after treatments at 125, 250, and 500 μg/mL occurred dose-dependently; conversely, the mesenchymal marker SNAI1 was upregulated. Consistent with mRNAs, the expression levels of EMT marker proteins (i.e., E-cadherin, ZO1, SNAIL, and Vimentin) were changed significantly by treatment. While NF-κB signaling was activated in treated cells, indium-dependent changes of CDH1 and SNAI1 mRNA expression were not affected by BAY 11-7082, an NF-κB inhibitor, suggesting that NF-κB activation may be dispensable for indium-induced EMT. Fibroblast-like morphological characteristics, such as actin stress fiber formation and cell elongation, along with deconstruction of cell-cell adhesion complexes, were observed in treated cells. Overall, our study is the first to demonstrate that EMT is caused by indium compounds. This will contribute biologically to understanding the mechanism of EMT induction and clinically to unveiling the pathophysiology of indium lung disease.