Copper modulates cell fate through the PLK1–FOXO3a–β-catenin signaling pathway by differentially regulating cuproptosis and EMT

Copper is essential for cellular homeostasis and can induce cuproptosis, a novel form of cell death. However, its effect on cancer progression, specifically through the regulation of epithelial-mesenchymal transition (EMT)-a primary driver of metastasis and treatment resistance in human cancers-remains unclear. This study assessed the dual role of copper in colorectal cancer cells, focusing on the polo-like kinase 1-forkhead box O3a-beta catenin (PLK1-FOXO3a-β-catenin) signaling pathway. Treatment with CuCl₂ (hereby referred to as Cu) alone facilitated EMT in SW480 and LoVo cells by upregulating PLK1 and downregulating FOXO3a that enhanced β-catenin activity without inducing cell death. In contrast, co-treatment with Cu and copper ionophore elesclomol (Cu-ES) triggered cuproptosis, a unique copper-dependent form of cell death, accompanied by mitochondrial dysfunction, dihydrolipoamide S-acetyltransferase aggregation, and ATP depletion. Specifically, Cu-ES treatment suppressed EMT by reducing PLK1 and activating FOXO3a that suppressed β-catenin-mediated transcription. Additionally, while Cu treatment alone had minimal effect on FOXO3a nuclear localization, Cu-ES treatment significantly enhanced FOXO3a nuclear translocation and its interaction with β-catenin, resulting in EMT gene repression. The PLK1 inhibitor BI-2536 recapitulated the effects of Cu-ES and exhibited synergistic activity when combined with Cu-ES, enhancing both cell death and EMT suppression. These findings highlight a novel regulatory mechanism of EMT through copper signaling and support copper-based combination therapies as a promising approach to simultaneously inhibit tumor growth and metastasis in colorectal cancer.