The importance of calcium influx, calpain and calmodulin for the activation of CaCo-2 cell death pathways by Clostridium perfringens enterotoxin

CaCo-2 cells exhibit apoptosis when treated with low doses of Clostridium perfringens enterotoxin (CPE), but develop oncosis when treated with high CPE doses. This study reports that the presence of extracellular Ca2+ in treatment buffers is important for normal activation of both those cell death pathways in CPE-treated CaCo-2 cells. Normal development of CPE-induced cell death pathway effects, such as morphologic damage, DNA fragmentation, caspase activation, mitochondrial membrane depolarization and cytochrome c release, was strongly inhibited when CaCo-2 cells were CPE-treated in Ca2+-free buffers. When treatment buffers contained Ca2+, CPE caused a rapid increase in CaCo-2 cell Ca2+ levels, apparently because of increased Ca2+ influx through a CPE pore. High CPE doses caused massive changes in cellular Ca2+ levels that appear responsible for activating oncosis, whereas low CPE doses caused less perturbations in cellular Ca2+ levels that appear responsible for activating apoptosis. Both CPE-induced apoptosis and oncosis were found to be calmodulin- and calpain-dependent processes. As Ca2+ levels present in the intestinal lumen resemble those of Ca2+-containing treatment buffers used in this study, perturbations in cellular Ca2+ levels and calpain/calmodulin-dependent processes are also probably important for inducing enterocyte cell death during CPE-mediated gastrointestinal disease.