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Infection and Immunity, March 2002, p. 1279-1286, Vol. 70, No. 3
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.3.1279-1286.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Cloned Shiga Toxin 2 B Subunit Induces Apoptosis in Ramos Burkitt's Lymphoma B Cells

Paola Marcato, George Mulvey, and Glen D. Armstrong*

Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada

Received 17 September 2001/ Returned for modification 29 November 2001/ Accepted 6 December 2001

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.

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, 1-21 Medical Sciences Bldg., University of Alberta, Edmonton, Alberta T6G 2H7, Canada. Phone: (780) 492-2303. Fax: (780) 492-7521. E-mail: glen.armstrong{at}ualberta.ca.

Infection and Immunity, March 2002, p. 1279-1286, Vol. 70, No. 3
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.3.1279-1286.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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