Nickel-induced epithelial-mesenchymal transition by reactive oxygen species generation and E-cadherin promoter hypermethylation

Epithelial-mesenchymal transition (EMT) is considered a critical event in the pathogenesis of lung fibrosis and tumor metastasis. During EMT, the expression of differentiation markers switches from cell-cell junction proteins such as E-cadherin to mesenchymal markers such as fibronectin. Although nickel-containing compounds have been shown to be associated with lung carcinogenesis, the role of nickel in the EMT process in bronchial epithelial cells is not clear. The aim of this study was to examine whether nickel contributes to EMT in human bronchial epithelial cells. We also attempted to clarify the mechanisms involved in NiCl₂-induced EMT. Our results showed that NiCl₂ induced EMT phenotype marker alterations such as upregulation of fibronectin and down-regulation of E-cadherin. In addition, the potent antioxidant N-acetylcysteine blocked EMT and expression of HIF-1α induced by NiCl₂, whereas the DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine restored the down-regulation of E-cadherin induced by NiCl₂. Promoter hypermethylation of E-cadherin, determined by quantitative real time methyl-specific PCR and bisulfate sequencing, was also induced by NiCl₂. These results shed new light on the contribution of NiCl₂ to carcinogenesis. Specifically, NiCl₂ induces down-regulation of E-cadherin by reactive oxygen species generation and promoter hypermethylation. This study demonstrates for the first time that nickel induces EMT in bronchial epithelial cells.