扁平上皮癌細胞における上皮・間葉移行による高悪性化機構の解析

Epithelial-mesenchymal transition (EMT) is thought to be an important mechanism for gastrulation, neural crest cell migration, invasion and metastasis of cancer cells. This process involves the loss of cell-cell adhesion together with the gain of mesenchymal and migratory properties. Although a correlation has been suggested between EMT and acquisition of more invasive and metastatic activities in cancer, the mechanisms of the more malignant changes by EMT have not been clarified enough in squamous cell carcinoma (SCC) cells. In this study, we analyzed the mechanisms of malignancy enhanced by EMT in SCC cells. Highly invasive SCC cells showed fibroblastic morphology and decreased expression of E-cadherin, elevated expressions of vimentin, MMP-2, SIP1 and δEF-1 compared to the SCC cells with epithelial morphology. Over-expression of Snail in A431 and OM-1 cells resulted in the acquisition of EMT, in terms of down-regulation of E-cadherin and up-regulation of vimentin, MMP-2, SIP1 and δEF-1, accompanied with morphorgical changes to fibroblastic shapes. These cells showed highly migratory behavior and a diffuse type invasion in three-dimensional culture. We further studied the relationships among Snail, SIP1 and TGF-β. Tet-off-induction of Snail, SIP1 or a treatment of TGF-β induced EMT in SCC cells. However, we found that Snail induced SIP1, while SIP1 did not induce Snail expression. TGF-β induced SIP1, but not Snail, in SCC cells, whereas the expression of Snail, but not SIP1, was strongly increased by TGF-β in highly invasive SCC cells with mesenchymal characteristics. Analysis of the MMP-2 promoter revealed that an Ets-1 binding site, located between -1,255 and -1,248 relative to the transcriptional start site, was the critical sequence for the promoter activation by Snail, SIP1 and TGF-β. Over-expression of Snail and SIP1 or treatment of TGF-β resulted in the induction of Ets-1 protein expression. Nuclear proteins extracted from the cells with induced expression of Snail and SIP1 showed increased DNA binding activities to the Ets-1 binding site. Furthermore, over-expression of Ets-1 resulted in increased promoter activity and protein expression of MMP-2. These results indicated that the more malignant changes by EMT were induced through down-regulation of cell-cell adhesion and up-regulation of matrix proteinases and cell migration in SCC cells. EMT induces Ets-1 expression, which activates the MMP-2 promoter and induce MMP-2 expression.

公開日:2010年1月24日で登録したコンテンツは、国立情報学研究所において電子化したものです。