Galectin-3 binds to MUC1-N-terminal domain and triggers recruitment of β-catenin in MUC1-expressing mouse 3T3 cells

Background: Galectin-3 is expressed in a variety of tumors and its expression level is related with tumor progression. Aberrant expression of MUC1 in various tumors is also associated with a poor prognosis. It has been reported that MUC1 is a natural ligand of galectin-3. Methods: A stable MUC1 transfectant was produced by introducing MUC1 cDNA into mouse 313 fibroblasts (MUC1/3T3 cells). MUC1 was prepared from MUC1/3T3 cells; MUC1-N-terminal domain (MUCI-ND) and -C-terminal domain (MUC1-CD) were separated by CsCI ultracentrifugation, and then the galectin-3-binding domain was determined by co-immuniprecipitation assay. After ligation of galectin-3 to 3T3/MUC1 cells, MUC1-CD was immunoprecipitated from the cell lysate. The immunoprecipitate was subjected to SDS-PAGE and Western blotting, followed by detection of co-immunoprecipitated beta-catenin. Results: Galectin-3 binds to the N-terminal domain of MUC1 but not to the C-terminal one. Galectin-3 present on the cell surface increased with the expression of MUC1 and is colocalized with MUCl. It should be noted that beta-catenin was detected in the immunoprecipitate with anti-MUC1-CD Ab from a lysate of galectin-3-treated 3T3/MUC1 cells. Conclusions: Galectin-3 binds to MUC1-ND and triggers MUCl-mediated signaling in 3T3/MUC1 cells, leading to recruitment beta-catenin to MUC1-CD. General significance: This signaling may be another MUCl-mediated pathway and function in parallel with a growth factor-dependent MUCl-mediated pathway. (C) 2014 Elsevier B.V. All rights reserved.