Actinonin induces apoptosis in U937 leukemia cells.

We have previously shown that actinonin causes inhibition of cellular proliferation in U937 leukemia cells. In this report we demonstrate that the inhibition of cell growth by actinonin occurs through the induction of apoptosis. Signs of apoptosis at high actinonin concentration included DNA fragmentation, exposure of phosphatidylserine and condensation of cell nuclei. Apoptosis caused by actinonin was inhibited by Z-VAD-FMK, a broad specificity inhibitor of caspases, implicating the caspase pathway of apoptosis. Further, apoptosis was associated with a large increase in intracellular caspase-3 and -7 activities.