Abstract
Cisplatin, an effective anticancer agent, can induce tumor cell apoptosis via caspase‐dependent and‐independent pathways. However, the precise mechanism that regulates the pathways remains unclear. In this study, we showed that μ‐calpain mediated both caspase‐dependent and‐independent pathways during cisplatin‐induced apoptosis in human lung adenocarcinoma cells. After cisplatin treatment, calpain activation, as measured by a fluorescent substrate, was an early event, taking place well before apoptosis inducing factor (AIF) release and caspase‐9/‐3 activation. Confocal imaging of cells transfected with AIF‐GFP demonstrated that AIF release occurred about 9 hr after cisplatin treatment. The increase of μ‐calpain activity proved to be a crucial event in the apoptotic machinery, as demonstrated by the significant protection of cell death in samples suppressed the endogenous μ‐calpain expression level, as well as cotreated with the calpain inhibitors, calpeptin and PD150606. Inhibition of μ‐calpain not only significantly reduced caspase‐9/‐3 activities but also completely blocked AIF redistribution. Our study also showed that endogenous mitochondrial μ‐calpain could directly induce the truncation and release of AIF, while caspases and cathepsins were not necessary for this process. In conclusion, the study demonstrated that activation of μ‐calpain played an essential role in regulating both caspase‐dependent and AIF‐mediated caspase‐independent apoptotic pathways in cisplatin‐induced apoptosis. © 2009 UICC