title: Cloned Shiga toxin 2 B subunit induces apoptosis in Ramos Burkitt's lymphoma B cells.
abstract: The Shiga toxins (Stx1 and Stx2), produced by Shigella dysenteriae type 1 and enterohemorrhagic Escherichia coli, consist of one A subunit and five B subunits. The Stx1 and Stx2 B subunits form a pentameric structure that binds to globotriaosylceramide (Gb3-Cer) receptors on eukaryotic cells and promotes endocytosis. The A subunit then inhibits protein biosynthesis, which triggers apoptosis in the affected cell. In addition to its Gb3-Cer binding activity, the data in the following report demonstrate that the Stx2 B pentamer induces apoptosis in Ramos Burkitt's lymphoma B cells independently of A subunit activity. Apoptosis was not observed in A subunit-free preparations of the Stx1 B pentamer which competitively inhibited Stx2 B pentamer-mediated apoptosis. The pancaspase inhibitor, Z-VAD-fmk, prevented apoptosis in Ramos cells exposed to the Stx2 B subunit, Stx1 or Stx2. Brefeldin A, an inhibitor of the Golgi transport system, also prevented Stx2 B subunit-mediated apoptosis. These observations suggest that the Stx2 B subunit must be internalized, via Gb3-Cer receptors, to induce Ramos cell apoptosis. Moreover, unlike the two holotoxins, Stx2 B subunit-mediated apoptosis does not involve inhibition of protein biosynthesis. This study provides further insight into the pathogenic potential of this family of potent bacterial exotoxins.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Paola
authors.initials: P
authors.lastname: Marcato
authors.forename: George
authors.initials: G
authors.lastname: Mulvey
authors.forename: Glen D
authors.initials: GD
authors.lastname: Armstrong
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis; D001402:B-Lymphocytes / Q000187:drug effects*; D020126:Brefeldin A / Q000494:pharmacology; D002051:Burkitt Lymphoma / Q000188:drug therapy*; D003001:Cloning, Molecular; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects; D021122:Protein Subunits; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000302:isolation & purification; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D022622:Shiga Toxin 1 / Q000494:pharmacology; D022641:Shiga Toxin 2 / Q000235:genetics / Q000494:pharmacology*; D014281:Trihexosylceramides / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D015853:Cysteine Proteinase Inhibitors; D021122:Protein Subunits; D019253:Proto-Oncogene Proteins c-bcl-2; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2; D014281:Trihexosylceramides; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C450841:shiga toxin 2 B subunit; D020126:Brefeldin A; C018549:globotriaosylceramide