beta-catenin activation down-regulates cell-cell junction-related genes and induces epithelial-to-mesenchymal transition in colorectal cancers

Abstract

WNT signaling activation in colorectal cancers (CRCs) occurs through APC inactivation or beta-catenin mutations. Both processes promote beta-catenin nuclear accumulation, which up-regulates epithelial-to-mesenchymal transition (EMT). We investigated beta-catenin localization, transcriptome, and phenotypic differences of HCT116 cells containing a wild-type (HCT116-WT) or mutant beta-catenin allele (HCT116-MT), or parental cells with both WT and mutant alleles (HCT116-P). We then analyzed beta-catenin expression and associated phenotypes in CRC tissues. Wild-type beta-catenin showed membranous localization, whereas mutant showed nuclear localization; both nuclear and non-nuclear localization were observed in HCT116-P. Microarray analysis revealed down-regulation of Claudin-7 and E-cadherin in HCT116-MT vs. HCT116-WT. Claudin-7 was also down-regulated in HCT116-P vs. HCT116-WT without E-cadherin dysregulation. We found that ZEB1 is a critical EMT factor for mutant beta-catenin-mediated loss of E-cadherin and Claudin-7 in HCT116-P and HCT116-MT cells. We also demonstrated that E-cadherin binds to both WT and mutant beta-catenin, and loss of E-cadherin releases beta-catenin from the cell membrane and leads to its degradation. Alteration of Claudin-7, as well as both Claudin-7 and E-cadherin respectively caused tight junction (TJ) impairment in HCT116-P, and dual loss of TJs and adherens junctions (AJs) in HCT116-MT. TJ loss increased cell motility, and subsequent AJ loss further up-regulated that. Immunohistochemistry analysis of 101 CRCs revealed high (14.9%), low (52.5%), and undetectable (32.6%) beta-catenin nuclear expression, and high beta-catenin nuclear expression was significantly correlated with overall survival of CRC patients (P = 0.009). Our findings suggest that beta-catenin activation induces EMT progression by modifying cell-cell junctions, and thereby contributes to CRC aggressiveness.