Abstract B115: The epithelial to mesenchymal transition is impaired in colon cancer cells with microsatellite instability

Abstract

Abstract Colorectal cancers (CRC) displaying DNA microsatellite instability (MSI) are associated with a favorable natural history, but the molecular basis for this observation has not been defined. We sought to determine whether the epithelial-to-mesenchymal transition (EMT), a highly conserved process involved in embryogenesis as well as in tumor progression, invasion, and metastasis, is impaired in MSI-positive CRCs that characteristically have a mutant transforming growth factor-β receptor type II (TGFBR2) gene. The induction of EMT by TGF-β1 was analyzed by phase contrast microscopy, immunofluorescence, qRT-PCR, immunoblotting, and cellular migration and invasion assays in MSS (SW480 and HT29) and MSI (DLD1 and HCT116) colon cancer cell lines. Expression of epithelial (E-cadherin) and mesenchymal (vimentin and N-cadherin) markers was evaluated by immunohistochemistry and qRT-PCR in 129 human colorectal tumors. TGF-β1 induced changes in cellular morphology from an epithelial to a fibroblasticlike morphology, changes in gene and protein expression with a reduction in E-cadherin and induction of vimentin, and changes in motility and invasion consistent with the occurrence of EMT only in MSS colon cancer cells. These effects did not require Smad4 but depended upon the recruitment of ERK. Cells with MSI and mutant TGFBR2 failed to exhibit any of these changes in response to TGF-β1. However, tumor cells with MSI but wildtype TGFBR2 underwent EMT in response to TGF-β1, indicating that TGFBR2 genotype is a key determinant of the EMT response in tumors with MSI. In human colorectal tumors, expression of the EMT markers N-cadherin and vimentin was significantly associated with adverse clinicopathologic features and the absence of MSI. These findings define a unique genotype-phenotype relationship between TGFBR2 and EMT that may contribute to the improved prognosis consistently observed in colon cancers with MSI. Furthermore, these results suggest a potential rationale for the therapeutic inhibition of TGF-β signaling in MSS colorectal tumors. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B115.