Inhibition of Wnt-2 and galectin-3 synergistically destabilizes P-catenin and induces apoptosis in human colorectal cancer cells

Constitutive activation of the Writ pathway as a result of APC, AX1N1 or CTNNB1 mutations has been found in most colorectal cancers. For a long time, this aberrant Wnt activation has been thought to be independent of upstream signals. However, recent studies indicate that upstream signals retain their ability to regulate the Writ pathway even in the presence of downstream mutations. Wnt-2 is well known for its overexpression in colorectal cancer. Galectin-3 (Gal-3), a multifunctional carbohydrate binding protein implicated in a variety of biological functions, has recently been reported to interact with beta-catenin. In this study, we investigated roles of Wnt-2 and Gal-3 in the regulation of canonical Wnt/ beta-catenin signaling. We found that siRNA silencing of either Wnt2 or Gal-3 expression inhibited TCF-reporter activity, decreased cytosolic P-catenin level and induced apoptosis in human colorectal cancer, cells containing downstream mutations. More interestingly, we showed that inhibition of both Wnt-2 and Gal-3 had synergistic effects on suppressing canonical Wnt signaling and inducing apoptosis, suggesting that aberrant canonical Wnt/p-catenin signaling in colorectal cancer can be regulated at multiple levels. The combined inhibition of Wnt-2 and Gal-3 may be of superior therapeutic advantage to inhibition by either one of them, giving rise to a potential development of novel drugs for the targeted treatment of colorectal cancer.(c) 2007 Wiley-Liss, Inc.