A novel role of Id-1 in regulation of epithelial-to-mesenchymal transition in bladder cancer

Abstract

Background and objective: Inhibitor of differentiation or DNA binding -1 (Id-1) has been shown to be increased in several types of advanced cancer, and to be associated with aggressive and metastatic abilities of cancer cells. Recently, more and more evidence indicates that epithelial-to-mesenchymal transition (EMT) is an important mechanism taking place during tumor invasion and metastasis, but the molecular pathways underlying EMT have not been clearly established. This study was to investigate the expression of Id-1 in bladder cancer and its association with EMT. Materials and methods: A total of 169 tissues, consisting of 147 primary bladder cancers and 22 adjacent normal tissues were included in this study. Id-1, E-cadherin, and β-catenin were examined immunohistochemically in paraffin sections. The pBabe-Id-1 expression retroviral vector and retroviral vectors containing an Id-1-specific small interfering RNA oligonucleotides (si-Id-1) were transfected into 2 bladder cancer cell lines respectively. Then, we used Western blotting and immunofluorescent staining to detect the cellular expression of epithelial markers and mesenchymal markers. The invasion and migration ability of bladder cancer cells were identified by type I collagen invasion assay and wound closure assay. Results: We demonstrated that increased Id-1 expression was associated with advanced tumor stage and grade. In addition, the increased Id-1 expression in bladder tumors was also correlated with decreased membranous E-cadherin and β-catenin expression. In vitro, studies showed that inactivation of the Id-1 gene conferred morphologic transition of bladder cancer cells from a fibroblastic to epithelial appearance, and overexpression of Id-1 could lead to acquisition of a fibroblastic spindle cell phenotype accompanied by loss of cell-to-cell contacts. By Western blotting and immunofluorescent staining, we showed that the expression level of Id-1 was correlated with the expression of mesenchymal markers but was inversely correlated with the expression of epithelial markers. Moreover, results of collagen invasion and wound closure assays showed ectopic Id-1 expression led to increased ability of invasion and migration. Conclusions: Our results suggest that Id-1 may play roles in tumor progression and EMT activation in bladder cancer. © 2011 Elsevier Inc. All rights reserved.