Brazilin induces FOXO3A-dependent autophagic cell death by disturbing calcium homeostasis in osteosarcoma cells

We exposed MG-63 cells to different concentrations of brazilin (5, 10 and 20 µM) for 24 h. Western blotting, immunocytofluorescence, luciferase reporter assays, and RT-PCR were used to evaluate whether brazilin activates FOXO family-dependent autophagy.

Brazilin increased autophagic flux in the human osteosarcoma cell line MG-63, as evidenced by the upregulation of LC3-II and the downregulation of P62/SQSTM1. Moreover, the pharmacological or genetic blockade of autophagy decreased brazilin-induced cell death, indicating that brazilin triggered autophagic cell death in MG-63 cells. Specifically, brazilin induced FOXO3A(Ser7) phosphorylation, activated FOXO3A nuclear translocation and increased FOXO3A reporter activity, which contributed to the expression of autophagy-related genes and subsequently initiated autophagic cell death in MG-63 cells. Importantly, the increased expression and nuclear translocation of FOXO3A were tightly related to the disturbance of calcium homeostasis, which could be prevented by chelating intracellular calcium.

Taken together, these data demonstrate that brazilin induces osteosarcoma cell death by inducing excessive autophagy, which is mediated through the Ca²⁺-FOXO3A pathway. Our study provides a new anti-tumour mechanism for brazilin treatment in osteosarcoma patients.