Leptin-induced epithelial-mesenchymal transition in breast cancer cells requires β-catenin activation via Akt/GSK3- and MTA1/Wnt1 protein-dependent pathways

Perturbations in the adipocytokine profile, especially higher levels of leptin, are a major cause of breast tumor progression and metastasis; the underlying mechanisms, however, are not well understood. In particular, it remains elusive whether leptin is involved in epithelial-mesenchymal transition (EMT). Here, we provide molecular evidence that leptin induces breast cancer cells to undergo a transition from epithelial to spindle-like mesenchymal morphology. Investigating the downstream mediator( s) that may direct leptin-induced EMT, we found functional interactions between leptin, metastasis-associated protein 1 (MTA1), and Wnt1 signaling components. Leptin increases accumulation and nuclear translocation of β-catenin leading to increased promoter recruitment. Silencing of β-catenin or treatment with the small molecule inhibitor, ICG-001, inhibits leptin-induced EMT, invasion, and tumor sphere formation. Mechanistically, leptin stimulates phosphorylation of glycogen synthase kinase 3β (GSK3β) via Akt activation resulting in a substantial decrease in the formation of the GSK3β-LKB1-Axin complex that leads to increased accumulation of β-catenin. Leptin treatment also increases Wnt1 expression that contributes to GSK3β phosphorylation. Inhibition of Wnt1 abrogates leptin stimulated GSK3β phosphorylation. We also discovered that leptin increases the expression of an important modifier of Wnt1 signaling, MTA1, which is integral to leptin-mediated regulation of the Wnt/β-catenin pathway as silencing of MTA1 inhibits leptin-induced Wnt1 expression, GSK3β phosphorylation, and β-catenin activation. Furthermore, analysis of leptin treated breast tumors shows increased expression of Wnt1, pGSK3β, and vimentin along with higher nuclear accumulation of β-catenin and reduced E-cadherin expression providing in vivo evidence for a previously unrecognized cross-talk between leptin and MTA1/Wnt signaling in epithelial-mesenchymal transition of breast cancer cells.