The β-Catenin/TCF-4 Complex Imposes a Crypt Progenitor Phenotype on Colorectal Cancer Cells

The transactivation of TCF target genes induced by Wnt pathway mutations constitutes the primary transforming event in colorectal cancer (CRC). We show that disruption of β-catenin/TCF-4 activity in CRC cells induces a rapid G1 arrest and blocks a genetic program that is physiologically active in the proliferative compartment of colon crypts. Coincidently, an intestinal differentiation program is induced. The TCF-4 target gene c-MYC plays a central role in this switch by direct repression of the p21CIP1/WAF1 promoter. Following disruption of β-catenin/TCF-4 activity, the decreased expression of c-MYC releases p21CIP1/WAF1 transcription, which in turn mediates G1 arrest and differentiation. Thus, the β-catenin/TCF-4 complex constitutes the master switch that controls proliferation versus differentiation in healthy and malignant intestinal epithelial cells.