Transglutaminase-2 induces N-cadherin expression in TGF-β1-induced epithelial mesenchymal transition via c-Jun-N-terminal kinase activation by protein phosphatase 2A down-regulation

sEpithelial–mesenchymal-transition (EMT) is a key event for tumour cells to initiate metastasis leading to switching of E-cadherin to N-cadherin. Transglutaminase-2 (Tgase-2) expression is increased in TGF-β1-induced EMT in A549 lung cancer cells or other lung cancer cells. The role and underlying mechanism of Tgase-2 in N-cadherin switching of TGF-β1-induced EMT are not known. The involvement and mechanisms of Tgase-2 were investigated in A549 cells using chemical inhibitors, gene silencing and over-expression.TGF-β1-induced EMT was suppressed by cystamine or gene silencing of Tgase-2. Suppression of Tgase-2 or the c-Jun-N-terminal kinase (JNK) inhibitor, SP600125, significantly reduced and over-expression of Tgase-2 increased the expression of N-cadherin. The relationship between Tgase-2 and JNK in the TGF-β1-induced EMT of A549 cells was examined using Tgase-2 over-expressed A549 cells (A549TG2) and Tgase-2 silenced A549 cells (A549shTG2). JNK activation was significantly increased in A549TG2 cells and decreased in A549shTG2 cells. In contrast, PP2A expression was decreased in A549TG2 and A549 cells and increased in A549shTG2 cells. The involvement of Tgase-2 in N-cadherin expression was also confirmed in an in vivo lung cancer orthotopic model by injection of A549WT and A549shTG2 cells into SCID mice. Tgase-2 expressing A549WT cells-injected mice group showed increased expressions of N-cadherin and JNK activation, but decreased expression of PP2A in lung cancer tissue comparing with the A549shTG2 cells-injected group. These results suggested that Tgase-2 induces N-cadherin expression of TGF-β1-induced EMT via JNK activation by PP2A down-regulation, and Tgase-2/PP2A/JNK might be a novel axis that affects N-cadherin switching in the EMT of A549 lung cancer cells.