G-protein coupled estrogen receptor 1 activation by daidzein and G-1 in triple negative breast cancer

Breast cancer is considered as the main cause of death worldwide. Triple negative breast cancer (TNBC) is an aggressive subtype characterized by the absence of hormonal receptors and HER₂, also known for lacking molecular targets and resistance to chemotherapy. G-protein coupled estrogen receptor 1 (GPER1) has emerged as a promising therapeutic target in breast cancer, particularly in TNBC. GPER1's agonists are various, including natural and synthetic ones, like phytoestrogens whose effect through GPER1 is not yet fully understood. This study investigated the possible effect of daidzein, a soy-bean derived phytoestrogen, on GPER1's expression and downstream ERK and AKT pathway activation in a triple negative breast cancer cell line. MDA-MB-231 breast cancer cells were treated with increasing concentrations of daidzein (D) or 10 μM of G-1 for 12 and 24 h, with or without GPER1's selective antagonist G-36. Western blot was used to assess GPER1 expression and ERK and AKT phosphorylation status. Our results revealed that daidzein upregulated multiple GPER1 forms in a dose-and-time-dependent manner and promoted the phosphorylation of ERK and AKT. These effects were suppressed by G-36, confirming GPER1 specific involvement. Similarly to daidzein, G-1 upregulated the expression of GPER1 forms, but down-regulated ERK and AKT phosphorylation. CONCLUSION: These results demonstrate the functional complexity of GPER1 signalling through different agonists and that daidzein modulates the expression of multiple GPER1 forms in TNBC cells in a GPER1-dependent manner, suggesting a potential therapeutic application for this phytoestrogen in non-classical estrogen signaling.