title: Escherichia coli STb toxin induces apoptosis in intestinal epithelial cell lines.
abstract: A previous study conducted in our laboratory demonstrated that cells having internalized Escherichia coli STb toxin display apoptotic-like morphology. We therefore investigated if STb could induce programmed cell death in both a human and an animal intestinal epithelial cell lines. HRT-18 (Human Colon Tumor) and IEC-18 (Rat Ileum Epithelial Cells) cell lines were used. As STb is frequently tested in a rat model, the IEC-18 cell line was most relevant to our work. The cell lines were treated with various amounts of purified STb (nanomole range) for a period of 24 h after which cells were harvested and examined for apoptotic characteristics. Caspase-9, the initiator of mitochondrion-mediated apoptosis, and caspase-3, an effector of caspase-9, were both activated following STb intoxication of HRT-18 and IEC-18 cells whereas caspase-8, the initiator caspase of the extrinsic pathway, was not activated. For both cell lines, agarose gel electrophoresis of the cell DNA content reveals laddering of DNA, resulting from DNA fragmentation, a characteristic of apoptosis. Hoechst 33342-stained DNA of STb-treated cell lines, observed using fluorescence microscopy, revealed condensation and fragmentation of the nuclei. Apoptotic indexes calculated from fragmented nuclei of Hoechst 33342-stained DNA for HRT-18 and IEC-18 cells showed an STb dose-dependent response. Overall, these data indicate that STb toxin induces a mitochondrion-mediated caspase-dependent apoptotic pathway.
authors: Groupe de Recherche sur les Maladies Infectieuses du Porc, Université de Montréal, St-Hyacinthe, Québec, Canada.
authors: H Claudia
authors: HC
authors: Syed
authors: J Daniel
authors: JD
authors: Dubreuil
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism / Q000633:toxicity*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D053938:DNA Fragmentation; D054307:Enterotoxigenic Escherichia coli / Q000235:genetics / Q000378:metabolism*; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism / Q000633:toxicity*; D004847:Epithelial Cells / Q000166:cytology* / Q000201:enzymology; D004927:Escherichia coli Infections / Q000201:enzymology / Q000235:genetics / Q000503:physiopathology*; D029968:Escherichia coli Proteins; D006801:Humans; D007422:Intestines / Q000166:cytology* / Q000201:enzymology; D051381:Rats
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C034151:heat stable toxin (E coli); D053148:Caspase 3; D053453:Caspase 9