Induction of active invagination of plasma membranes by Helicobacter pylori cytotoxin, VacA, in cultured gastric cells: An immunoelectron microscopic study

VacA cytotoxin secreted by Helicobacter pylori causes cytoplasmic vacuolation in gastric epithelial cells. To elucidate whether VacA directly affects the cell surface, changes in the membrane structure after VacA treatment were examined in a human gastric epithelial cell culture (AZ-521) at an ultrastructural level. When the time-course changes in the localization of VacA were analyzed by immunoelectron microscopy in AZ-521 cells that had been exposed to VacA, VacA was detected predominantly on the plasma membrane at an early stage of the exposure, and later in endocytotic vesicles and/or tubulo-vesicles. Five to 24 hr after exposure, the VacA was distributed in a limestone cavern like-structure, which was formed by elongated surfaces of plasma membranes, as shown by scanning electron microscopy. Therefore, the binding of VacA to the plasma membrane and the subsequent internalization into the enlarged cavern like-plasma membranes may be involved in the induction of vacuolation of gastric epithelial cells by VacA.