β-catenin-mediated signaling: A molecular target for early chemopreventive intervention

Dysregulation of Wnt signaling appears to be a critical event in the formation of intestinal tumors and some other cancers. Accumulating data from preclinical studies strongly suggest that targeted disruption of β-catenin-mediated TCF signaling is a promising strategy for early chemopreventive intervention, particularly with respect to intestinal tumorigenesis. While the search for potent inhibitors is just getting underway, the ability of several synthetic and naturally occurring agents to decrease the transcriptional activity of a luciferase reporter plasmid under the control of TCF-4 regulatory elements (pTOPFLASH) has been demonstrated already. Additional enthusiasm for this approach is provided by data from several groups, which indicate that sulindac, sulindac sulfone and indomethacin can modulate the subcellular localization of β-catenin in vivo, resulting in either decreased nuclear compartmentalization or enhanced localization of β-catenin to the plasma membrane. Although the mechanism by which agents disrupt β-catenin-mediated TCF signaling remains to be elucidated, possibilities include: (1) physical inhibition of the β-catenin/TCF complex formation, (2) upregulation of the ubiquitin-mediated proteosomal degradation of β-catenin, (3) accelerated nuclear export of β-catenin and (4) enhanced sequestration of β-catenin by E-cadherin. The common role of β-catenin in both Wnt signaling and cell adhesion provides a unique opportunity to develop chemopreventive therapies that both prevent the development of cancer and delay tumor progression.