Regulated expression of the Shiga toxin B gene induces apoptosis in mammalian fibroblastic cells.
Shiga toxins (Stxs) produced by enterohaemorrhagic Escherichia coli may induce colonic ulceration, bloody diarrhoea and acute renal failure. The A subunit (StxA) is known to inhibit protein synthesis, whereas the B subunits (StxB) bind to Gb3 on the cell surface. However, the mechanisms by which Stxs kill target cells remain unclear. Stx1A or Stx1B genes were introduced into pcDNA3.1 vectors and transfected into NIH3T3 and HeLa cells. The Stx1B gene-transfected cells became apoptotic with accompanying DNA fragmentation, whereas the Stx1A gene-transfected cells were found to be necrotic and no DNA fragmentation occurred. The HeLa/C4 cells integrated with the Stx1B gene with a tetracycline-inducible promoter eventually produced cytoplasmic Stx1B, leading to DNA fragmentation on the addition of doxycycline. These apoptotic changes were abrogated by pretreatment with Z-VAD-fmk. These results suggest that the transfected Stx1B gene induces apoptosis by activating the caspase cascade after Stx1B expression in the cytoplasm.
Nakagawa
I
I
Department of Oral Microbiology, Osaka University Faculty of Dentistry, Suita-Osaka, 565-0871, Japan. ichiro@dent.osaka-u.ac.jp
Nakata
M
M
Kawabata
S
S
Hamada
S
S
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001427:Bacterial Toxins / Q000235:genetics* / Q000633:toxicity; D001483:Base Sequence; D020169:Caspases / Q000378:metabolism; D053938:DNA Fragmentation; D017931:DNA Primers / Q000235:genetics; D019453:Escherichia coli O157 / Q000235:genetics* / Q000472:pathogenicity; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006367:HeLa Cells; D006801:Humans; D007375:Interleukin-1 / Q000096:biosynthesis; D051379:Mice; D010957:Plasmids / Q000235:genetics; D022603:Shiga Toxins; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D001427:Bacterial Toxins; D017931:DNA Primers; D007375:Interleukin-1; D022603:Shiga Toxins; D014409:Tumor Necrosis Factor-alpha; D020169:Caspases