Ribosome-inactivating protein and apoptosis: abrin causes cell death via mitochondrial pathway in Jurkat cells.

Abrin belongs to the type II family of ribosome-inactivating proteins comprising a galactose-binding B chain coupled with a toxic A chain through a single disulphide linkage. Apart from its RNA-N-glycosidase activity, another role that has been recently ascribed to abrin was the induction of apoptosis. Studies were undertaken to determine the kinetics of these two activities. In the present study, we report that the signal for apoptosis is triggered at a time point later than the inhibition of protein synthesis. This apoptotic pathway induced by abrin is caspase 3-dependent but caspase 8-independent and involves mitochondrial membrane potential damage and reactive oxygen species production. Overexpression of B-cell lymphocytic-leukaemia proto-oncogene 2 was found to block this apoptotic pathway.