Cytoskeletal disruption is the key factor that triggers apoptosis in okadaic acid-treated neuroblastoma cells.

Okadaic acid (OA) is a tumour promoter that induces apoptosis in several cell models. Following previous findings, the objective of this work was to elucidate the pathways involved in OA-triggered apoptosis in BE(2)-M17 cells by using a combination of pharmacological agents and apoptosis-related assays. OA-induced apoptosis involves disruption of F-actin cytoskeleton, activation of caspase-3, collapse of mitochondrial membrane potential, DNA fragmentation and decreased levels of monomeric Bcl-2 and Bax proteins. All the agents tested were unable to obliterate changes in F-actin levels, caspase-3 activation or DNA fragmentation, but all of them prevented OA-induced decrease of mitochondrial potential and changes in Bax/Bcl-2 levels. Taken together, these results demonstrate that collapse of mitochondrial membrane potential is accessory in the execution of apoptosis, which is directly dependent on cytoskeletal changes. Mitochondrial changes are mediated by complex associations among the Bcl-2 proteins. Cytochrome c release from mitochondria is a late event, occurring 24 h after OA exposure. Moreover, okadaic acid triggers activation of upstream caspases resembling the extrinsic pathway of apoptosis.