Caspase-3 activation and apoptosis induction coupled with the retrograde transport of shiga toxin: inhibition by brefeldin A.

Caspase proteolytic activities, such as caspase-3, -2 and -6, of THP-1 human monocytic cells were markedly increased in a time- and dose-dependent manner by treatment with purified Shiga toxin 1 (Stx1) or Stx2. Caspase-3 activation was strictly correlated with internucleosomal DNA fragmentation and chromatin condensation of the cells. In addition, the specific caspase-3 inhibitor, Ac-DEVD-CHO, decreased the percentage of apoptotic cells. The purified B-subunit of Stx1 did not induce apoptosis in THP-1 cells. Caspase-3 activation, DNA fragmentation and chromatin condensation caused by Stx were completely blocked by pretreatment of cells with brefeldin A, an inhibitor of Golgi functions. The findings suggest that Stx1 as well as Stx2 activate caspase-3, which plays a critical role in apoptosis, and that the apoptotic signals rise after Stx is transported to the Golgi apparatus.