Escherichia coli Shiga toxins induce apoptosis in epithelial cells that isregulated by the Bcl-2 family

Human intestinal cells lack globotriaosylceramide (Gb(3)), the receptor for Shiga toxin-l (Stx1) and Shiga toxin-a (Stx2). Therefore, the role of thes e toxins in mediating intestinal disease during infection with Shiga toxin- producing Escherichia coli is unclear. The aims of this study were to deter mine whether Stx1 and Stx2 induce apoptosis in epithelial cells expressing (HEp-2, Caco-2) or lacking (T84) Gb(3) and to characterize the role of the Bcl-2 family. Stx1 (12.5 ng/ml) induced apoptosis in both HEp-2 (21.9 +/- 7 .9% vs. 0.8 +/- 0.3%, P = 0.01) and Caco-2 (10.1 +/- 1.2% vs. 3.1 +/- 0.4%, P = 0.006) cells but not in Gb(3)-deficient T84 cells. Toxin-mediated apop tosis of HEp-2 cells was associated with enhanced expression of the proapop totic protein Bar. Inhibition of caspase activation prevented toxin-stimula ted apoptosis. In addition, overexpression of Bcl-2 by transient transfecti on blocked Stx1-stimulated cell death. These findings indicate that Shiga t oxins produced by E. coli signal Gb(3)-expressing epithelial cells to under go apoptosis in association with enhanced Bar expression, thereby resulting in activation of the caspase cascade.