College of Pharmacy, Dongguk University, Seoul 100-715, Republic of Korea.
Eur J Cancer. 2013 May;49(7):1692-705. doi: 10.1016/j.ejca.2012.11.036. Epub 2013 Jan 2.
Epithelial-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 (A549(TG2)) and Tgase-2 silenced A549 cells (A549(shTG2)). JNK activation was significantly increased in A549(TG2) cells and decreased in A549(shTG2) cells. In contrast, PP2A expression was decreased in A549(TG2) and A549 cells and increased in A549(shTG2) cells. The involvement of Tgase-2 in N-cadherin expression was also confirmed in an in vivo lung cancer orthotopic model by injection of A549(WT) and A549(shTG2) cells into SCID mice. Tgase-2 expressing A549(WT) 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 A549(shTG2) 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.
上皮-间充质转化（EMT）是肿瘤细胞启动转移的关键事件，导致 E-钙黏蛋白向 N-钙黏蛋白的转换。在 TGF-β1 诱导的 A549 肺癌细胞或其他肺癌细胞 EMT 中，转谷氨酰胺酶-2（Tgase-2）的表达增加。Tgase-2 在 TGF-β1 诱导的 EMT 中 N-钙黏蛋白转换中的作用和潜在机制尚不清楚。本研究采用化学抑制剂、基因沉默和过表达的方法，在 A549 细胞中研究了 Tgase-2 的作用及其机制。胱胺或 Tgase-2 基因沉默抑制 TGF-β1 诱导的 EMT。抑制 Tgase-2 或 c-Jun-N 末端激酶（JNK）抑制剂 SP600125 可显著减少 N-钙黏蛋白的表达，而过表达 Tgase-2 则增加 N-钙黏蛋白的表达。使用过表达 Tgase-2 的 A549 细胞（A549（TG2））和沉默 Tgase-2 的 A549 细胞（A549（shTG2）），研究了 Tgase-2 与 TGF-β1 诱导的 A549 细胞 EMT 之间的关系。A549（TG2）细胞中 JNK 活性显著增加，A549（shTG2）细胞中 JNK 活性降低。相反，A549（TG2）和 A549 细胞中 PP2A 的表达减少，而 A549（shTG2）细胞中 PP2A 的表达增加。在将 A549（WT）和 A549（shTG2）细胞注入 SCID 小鼠的体内肺癌原位模型中，也证实了 Tgase-2 参与 N-钙黏蛋白表达。与 A549（shTG2）细胞注射组相比，表达 Tgase-2 的 A549（WT）细胞注射组小鼠肺组织中 N-钙黏蛋白表达增加，JNK 激活增加，而 PP2A 表达减少。这些结果表明，Tgase-2 通过下调 PP2A 诱导 JNK 激活，从而诱导 TGF-β1 诱导的 EMT 中 N-钙黏蛋白的表达，并且 Tgase-2/PP2A/JNK 可能是影响 A549 肺癌细胞 EMT 中 N-钙黏蛋白转换的新轴。
