SMAD4 mediates mesenchymal-epithelial reversion in SW480 colon carcinoma cells

Inactivation of the tumour suppressor gene SMAD4 is a genetically late event in gastrointestinal carcinogenesis. SMAD4 is a transmitter of growth-inhibitory effects of transforming growth factor-beta (TGF-beta), an important tumour promoter capable of inducing an epithelial to mesenchymal transition (EMT). The role of SMAD proteins in late, tumour-promoting effects of TGF-beta is not well understood.The change of molecular differentiation markers typical for EMT upon SMAD4 re-expression in SW480 cells was determined using Western blotting, immunohistochemistry and confocal laser microscopy. The influence of SMAD4 on the migration of SW480 cells was assessed in wound healing and pore migration assays.SMAD4 suppresses invasiveness and mediates reversion of SW480 cells from a mesenchymal-like to a polarized epithelial phenotype, with features of enterocyte-like differentiation. Moreover, SMAD4 reconstitution was associated with down-regulation of endogenous TGF-beta cytokines, suggesting that autocrine TGF-beta signaling may be involved in the EMT.These results provide further evidence for a role of SMAD4 as a regulator of invasion, a process of prime importance in carcinogenesis but hitherto poorly understood in molecular terms.