Effect of MUC1/β-catenin interaction on the tumorigenic capacity of pancreatic CD133+ cells

Despite the fact that the biological function of cluster of differentiation (CD) 133 remains unclear, this glycoprotein is currently used in the identification and isolation of tumor-initiating cells from certain malignant tumors, including pancreatic cancer. In the present study, the involvement of mucin 1 (MUC1) in the signaling pathways of a highly tumorigenic CD133(+) cellular subpopulation sorted from the pancreatic cancer cell line HPAF-II was evaluated. The expression of MUC1-cytoplasmic domain (MUC1-CD) and oncogenic signaling transducers (epidermal growth factor receptor, protein kinase C delta, glycogen synthase kinase 3 beta and growth factor receptor-bound protein 2), as well as the association between MUC1 and beta-catenin, were characterized in HPAF-II CD133(+) and CD133(low) cell subpopulations and in tumor xenografts generated from these cells. Compared with HPAF CD133(low) cells, HPAF-II CD133(+) cancer cells exhibited increased tumorigenic potential in immunocompromised mice, which was associated with overexpression of MUC1 and with the accordingly altered expression profile of MUC1-associated signaling partners. Additionally, MUC1-CD/beta-catenin interactions were increased both in the HPAF-II CD133(+) cell subpopulation and derived tumor xenografts compared with HPAF CD133(low) cells. These results suggest that, in comparison with HPAF CD133(low) cells, CD133(+) cells exhibit higher expression of MUC1, which contributes to their tumorigenic phenotype through increased interaction between MUC1-CD and beta-catenin, which in turn modulates oncogenic signaling cascades.