Abstract IA-20: EMT in tumor invasion and metastasis

Abstract Most colorectal adenocarcinomas (CRC) have mutations in the APC gene leading to overexpression of the Wnt-pathway effector β-catenin. By acting as a transcriptional activator, nuclear β-catenin is involved in two fundamental processes in embryonic development: epithelial to mesenchymal transition (EMT) and generation of stem cells. We have previously shown, that in particular tumor cells at the invasive front of CRCs accumulate nuclear β-catenin, undergo an EMT and aberrantly express EMT-associated transcriptional repressors, like ZEB1. The amount of such cells strongly correlates with clinical outcome and metastasis formation. We further showed that ZEB1 represses target genes involved in basement membrane formation and epithelial cell polarity. Moreover we report that ZEB1 directly suppresses transcription of members of the miRNA-200 family, which strongly activate epithelial differentiation in pancreatic, colorectal and breast cancer cells. Notably, the EMT-activators TGFβ2 and ZEB1 itself are predominant targets downregulated by these miRNAs. These results indicate that ZEB1 triggers a microRNA-mediated positive feedbackloop, which stabilizes EMT and promotes invasion of cancer cells. In contrast tumor cells in central tumor areas are differentiated and often show membranous, E-cadherin-bound β-catenin. Strikingly, metastases show again a differentiated phenotype and lack nuclear beta-catenin, indicating a mesenchymo-epithelial re-transition (MET) and a regulatory role of the tumor environment during malignant tumor progression. Based on the developmental functions of beta-catenin and our data we propose, that the EMT-associated tumor cells at the invasive front act as “migrating cancer stem cells” which can re-differentiate and, depending on the range of dissemination, give raise to the primary carcinoma and metastases. We suggest that both primary tumors and metastases are derived from a pool of EMT-associated “migrating cancer stem cells” at the tumor host interface. They are defined by strong nuclear beta-catenin accumulation and EMT-phenotype, which gives these epithelial tumor cells a feature driving malignant tumor progression including metastasis: the unusual combination of a migratory and stem cell phenotype. Citation Information: Cancer Res 2009;69(23 Suppl):IA-20.