Down-regulation of beta-catenin TCF signaling is linked to colonic epithelial cell differentiation

The beta -catenin TCF pathway is implicated in the regulation of colonic ep ithelial cell proliferation, but its role in the regulation of cell differe ntiation is unknown. The colon carcinoma cell line, Caco-2, spontaneously u ndergoes G(0)/G(1) cell cycle arrest and differentiates along the absorptiv e cell lineage over 21 days in culture. In parallel, we show that beta -cat enin-TCF activity and complex formation are significantly down-regulated. T he down-regulation of beta -catenin-TCF signaling was independent of APC, w hich we characterized as having a nonsense mutation in codon 1367 in Caco-2 cells, but was associated with a decrease in TCF-4 protein levels. Total b eta -catenin levels increased during Caco-2 cell differentiation, although this was attributable to an increase in the membrane, E-cadherin-associated , fraction of beta -catenin. Importantly, down-regulation of beta -catenin- TCF signaling in undifferentiated Caco-2 cells by three different mechanism s, ectopic expression of E-cadherin, wild-type APC, or dominant negative TC F-4, resulted in an increase in the promoter activities of two genes that a re well-established markers of cell differentiation, alkaline phosphatase a nd intestinal fatty acid binding protein, These studies demonstrate, theref ore, that in addition to its established role in the regulation of cell pro liferation, down-regulation of the beta -catenin-TCF pathway is associated with the promotion of a more-differentiated phenotype in colonic epithelial cells.