γ-Tocotrienol reversal of epithelial-to-mesenchymal transition in human breast cancer cells is associated with inhibition of canonical Wnt signalling

Abstract

Objectives: Frizzled-7 (FZD7) receptor-dependent activation of the canonical Wnt/β-catenin pathway plays a crucial role in epithelial-to-mesenchymal transition (EMT) and breast cancer metastasis. FZD7 and its co-receptor, low-density lipoprotein receptor-related protein 6 (LRP6), are highly expressed in MDA-MB-231 and T-47D breast cancer cells, and endogenous ligands for FZD7 include Wnt3a and Wnt5a/b. γ-Tocotrienol, a natural isoform of vitamin E, inhibits human breast cancer cell proliferation and EMT. Here, studies have been conducted to investigate the role of the canonical Wnt pathway in mediating inhibitory effects of γ-tocotrienol on EMT in human breast cancer cells. Materials and methods: MDA-MB-231, T-47D and MCF-10A cells were maintained in serum-free defined media containing selected doses of γ-tocotrienol. Cell viability was determined using the MTT colorimetric assay, Western blot analysis was used to measure protein expression and the wound-healing assay was employed to study cell mobility and migration. Immunohistochemical fluorescence staining visualized expression and localization of EMT cell markers. Results: γ-Tocotrienol was found to induce dose-responsive inhibition of MDA-MB-231 and T-47D cell growth at doses that had no effect on immortalized normal MCF-10A mammary epithelial cells. These growth inhibitory effects were associated with suppression in canonical Wnt signalling, reversal of EMT and significant reduction in breast cancer cell motility. Conclusions: γ-Tocotrienol suppression of metastatic breast cancer cell proliferation and EMT was associated with suppression of the canonical Wnt/β-catenin signalling pathway.