Calcium-mediated activation of PI3K and p53 leads to apoptosis in thyroid carcinoma cells

The molecular mechanism responsible for cadmium-induced cell death in thyroid cancer cells (FRO) is unknown. We demonstrated that apoptosis of FRO cells induced by cadmium was concentration and time dependent. Cadmium caused the rapid elevation of intracellular calcium and induced phosphorylation of Akt, p53, JNK, ERK and p38. Inhibition of PI3K/Akt attenuated the cadmium-induced apoptosis, but the inhibition of JNK inhibitor, ERK or p38 aggravated it, indicating that activation of PI3K/Akt was a pro-apoptosis signal in response to cadmium treatment, whereas the activation of stress-activated protein kinase JNK, ERK and p38 functioned as survival signals to counteract the cadmium-induced apoptosis. Buffering of the calcium response attenuated mitochondrial impairment, recovered the cadmium-activated Akt, p53, JNK, ERK and p38, and subsequently blocked the apoptosis. These results suggested that apoptosis induced by cadmium in FRO cells was initiated by the rapid elevation of intracellular calcium, followed by calcium-mediated activation of PI3K/Akt and mitochondrial impairment.