Heterogeneity between triple negative breast cancer cells due to differential activation of Wnt and PI3K/AKT pathways

• MDA-MB-231 cell culture has fibroblast-like (F) and semi-epithelial (SE) cells.
• F cells have a higher migration and tumorigenesis capacity than SE cells.
• In F cells, β-catenin accumulates and displays increased transcriptional activity.
• In F cells, the activity of Wnt and EGFR/PI3K/mTORC2/AKT pathways is increased.
• Molecular markers of cancer stem cells are more abundant in the F clone.

The lack of a successful treatment for triple-negative breast cancer demands the study of the heterogeneity of cells that constitute these tumors. With this aim, two clones from triple negative breast MDA-MB-231 cancer cells were isolated: One with fibroblast-like appearance (F) and another with semi-epithelial (SE) morphology. Cells of the F clone have a higher migration and tumorigenesis capacity than SE cells, suggesting that these cells are in a more advanced stage of epithelial to mesenchymal transformation. In agreement, F cells have a diminished expression of the tight junction proteins claudins 1 and 4, and an increased content of β-catenin. The latter is due to an augmented activity of the canonical Wnt route and of the EGFR/PI3K/mTORC2/AKT pathway favoring the cytoplasmic accumulation of β-catenin and its transcriptional activity. In addition, F cells display increased phosphorylation of β-catenin at Tyr654 by Src. These changes favor in F cells, the over-expression of Snail that promotes EMT. Finally, we observe that both F and SE cells display markers of cancer stem cells, which are more abundant in the F clone.