Zinc depletion‐induced apoptosis is mediated through Ca 2+ ‐ dependent depolarization of mitochondria membrane in human breast cancer MDA‐MB‐231 cells

We have previously shown that zinc depletion induces a Ca 2+ ‐ dependent apoptosis in MDA‐MB‐231 cells. This zinc depletioninduced apoptosis is associated with an increased Bax:Bcl‐2 ratio and an elevated caspase‐9 and −3 activities while caspase‐8 activity remains unchanged. We hypothesized that Ca 2+ ‐dependent depolarization of the mitochondrial membrane is involved in zinc depletion‐induced apoptosis. To test this hypothesis, MDA‐MB‐ 231 cells were cultured in DMEM+10% FBS for 3 days followed by treating the cells with N,N,N′,N′‐tetrakis[2‐ pyridylmethyl]ethylenediamine (TPEN; 20μM) alone for 0–24h or in the presence of 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid acetoxymethyl ester (BAPTA; 0–20μM) for 24h. Mitochondrial membrane potential was assessed by a DiOC 6 flow cytometric assay. TPEN caused depolarization of the mitochondrial membrane in a treatment duration‐dependent manner (2–24h; R 2 =0.99). BAPTA reduced TPEN‐induced depolarization of the mitochondrial membrane by 62–79%. Collectively, these results indicated that zinc depletion‐induced apoptosis was mediated through a Ca 2+ ‐dependent depolarization of the mitochondrial membrane in MDA‐MB‐231 cells. Supported by NSERC.