TGF-β1-induced epithelial-mesenchymal transition in lung cancer cells involves upregulation of miR-9 and downregulation of its target, E-cadherin

TGF-beta 1 plays an important role in the epithelial-mesenchymal transition (EMT) of epithelial cancers, including non-small cell lung cancer (NSCLC). While the full underlying mechanism remains unclear, miR-9 is known to play a critical role in the regulation of NSCLC cell invasion. We tested whether miR-9 targets E-cadherin and thus affects TGF-beta 1-induced EMT in NSCLC cells by assessing the expression levels of miR-9 and E-cadherin for NSCLC patients and then verifying the targeting of E-cadherin by miR-9 using the dual luciferase reporter system. MiR-9 was significantly upregulated in NSCLC tissues compared with its level in adjacent normal tissues. The expression of E-cadherin in NSCLC tissues was significantly decreased. In addition, we found that TGF-beta 1 significantly upregulated the expression of miR-9 and downregulated the expression of E-cadherin. E-cadherin was confirmed as a direct target gene of miR-9. Using an miR-9 inhibitor reversed the TGF-beta 1-mediated inhibition of E-cadherin expression and upregulation of the mesenchymal marker alpha-SMA. TGF-beta 1 significantly induced cell invasion, and this effect was significantly inhibited by miR-9 inhibitors. TGF-beta 1 induced EMT in NSCLC cells by upregulating miR-9 and downregulating miR-9's target, E-cadherin.