Vibrio parahaemolyticus thermostable direct hemolysin can induce an apoptotic cell death in Rat-1 cells from inside and ouside of the cells

Rat-1 cells exposed to Vibrio parahaemolyticus thermostable direct hemolysi n (TDH) developed morphological changes including shrinkage of the cells an d reduction in the size of nuclei. Cells either microinjected with TDH or t ransfected with the tdh gene also showed morphological changes similar to t hose induced by externally added toxin. Furthermore, TDH-exposed or tdh-tra nsfected cells both showed chromatin condensation and DNA fragmentation whi ch suggest cells undergoing apoptosis. In contrast, expression of a TDH mut ant (R7) did not reveal any cytotoxic effects. We demonstrate that expresse d TDH was distributed in the cytoplasm. The interleukin-l P-converting enzy me-related pretease inhibitor ZVAD-FMK did not inhibit TDH cytotoxicity. Ou r results suggest that TDH can induce its cytotoxicity both from outside an d from inside the cells and killed the cells through apoptosis. (C) 2001 Fe deration of European Microbiological Societies. Published by Elsevier Scien ce B.V,.411 rights reserved.