Various stimuli including anticancer drugs are capable of initiating the apoptotic death program in human
tumor cells via activation of
caspases. Mitochondria play an essential role for cell apoptotic commitment. Previous studies have shown a potential role of
calpain activation in apoptosis, however, the involved molecular mechanisms remain to be defined. In the current study, we have examined the expression and activation of mitochondrial
calpain in Jurkat T
leukemia cells, MCF-7
breast carcinoma and LNCaP
prostate cancer cells during apoptosis induced by an anticancer
drug (VP-16, tamoxifen) or the specific p38
kinase inhibitor
PD-169316. Our results suggest that increased expression and
autolysis of the mitochondrial
calpain small subunit are tightly associated with
calpain activation in an early stage of apoptosis. In contrast, there were no correlations observed between the early
calpain activation and changes in levels of mitochondrial
calpain large subunit and the endogenous
calpain inhibitor calpastatin. Furthermore, pretreatment with the specific pharmacological
calpain inhibitor calpeptin blocked the
drug-induced
calpain small subunit
autolysis and
calpain activation in mitochondria and inhibited apoptosis-associated
caspase-3 activation, demonstrating that mitochondrial
calpain activation through small subunit cleavage is an essential step for inducing
tumor cell apoptosis by various anticancer drugs.