Role of miR-34a in TGF-β1- and Drug-Induced Epithelial-Mesenchymal Transition in Alveolar Type II Epithelial Cells

Epithelial-mesenchymal transition (EMT) of alveolar type II epithelial cells may play an important role in the pulmonary fibrosis induced by drugs such as bleomycin (BLM) and methotrexate (MTX). In this study, we examined the role of microRNAs (miRNAs) in drug-induced EMT using RLE/Abca3, a cell line having alveolar type II cell-like phenotype. Based on the screening using miRNA microarray analysis, it was found that the expression of some miRNAs, such as miR-34a, was increased by transforming growth factor (TGF)-β1 and BLM. An increase in miR-34a expression due to TGF-β1, BLM, and MTX was also observed in real-time PCR analysis. Therefore, miR-34a was focused upon in further studies. The expression of nectin-1 mRNA and protein, a possible target of miR-34a, was decreased by the treatment with TGF-β1, BLM, and MTX. In addition, when RLE/Abca3 cells were transfected with miR-34a mimic, the expression of nectin-1 mRNA and Abca3 mRNA, another target of miR34a, decreased significantly. Furthermore, the mRNA expression of cytokeratin 19, an epithelial marker, decreased, whereas that of α-smooth muscle actin, a mesenchymal marker, increased in the cells transfected with miR-34a mimic. These results suggest that miR-34a is involved in drug-induced EMT in alveolar epithelial cells, and possibly in lung fibrosis.