Activation of the caspase cascade during Stx1-induced apoptosis in Burkitt's lymphoma cells

Abstract

Shiga toxin 1 (Stx1) produced by Escherichia coli has been reported to induce apoptosis in many different cell types, including Burkitt's lymphoma (BL) cells. Since it has been established that the caspases play essential roles as the effector molecules in the apoptotic process in most cases, we examined the kinetics of caspase activation during the process of Stx1-mediated apoptosis of BL cells. Using Ramos BL cells that are highly sensitive to Stx1-mediated cytotoxicity, we observed that multiple caspases, including caspase-3, -7, and -8 were promptly activated following Stx1 treatment, as indicated by both the procaspase cleavages and enhancement of cleavage of the tetrapeptide substrates of the caspases. In addition, the inhibition assay revealed that caspase-8 is located upstream of both caspase-3 and -7, suggesting that Stx1-mediated apoptosis utilizes a similar caspase cascade to that involved in Fas-mediated apoptosis. Neither anti-Fas mAb nor TNF-alpha, however, affected the Stx1-mediated apoptosis of Ramos cells. Although the precise mechanism of Stx1-mediated activation of caspase-8 is still unclear, we have demonstrated that crosslinkage of CD77, a functional receptor for Stx1, with specific antibody is sufficient to induce activation of caspase-8. Our findings should provide new insight into the understanding of the molecular basis of Stx1-mediated cell injury.

Two Distinct Gb3/CD77 Signaling Pathways Leading to Apoptosis Are Triggered by Anti-Gb3/CD77 mAb and Verotoxin-1

“…These data are the first to show that a cell can be resistant to one CD77 ligand and sensitive to another and that a glycosphingolipid can mediate two different cell death pathways. Our data confirm previous reports that caspases are involved in VT-1-induced apoptosis (18,19,37). We also showed that VT-1 triggered mitochondrial changes that, in part, rely on caspase-8 activation.…”

“…Recent reports have shed light on both toxin-and anti-Gb3/CD77 mAb-induced apoptotic pathways (6,18,19), but various questions remain unresolved: Is ligand binding to Gb3/CD77 sufficient to induce apoptosis? Do ligands trigger a single intracellular mechanism?…”

Shiga toxin binding to globotriaosyl ceramide induces intracellular signals that mediate cytoskeleton remodeling in human renal carcinoma-derived cells

“…However, recent studies have shown that the B-subunit also has biological effects on target cells through a mechanism mediated by intracellular signals upon binding to Gb3 (Katagiri et al, 1999;Kiyokawa et al, 2001;Mangeney et al, 1993;Mori et al, 2000;Taga et al, 1997). Although Stx1-B-induced intracellular signals are known to mediate apoptosis in Burkitt's lymphoma cells, their biological effect on other cell species has not been clarified.…”

Shiga Toxin 1 Induces Apoptosis in the Human Myelogenous Leukemia Cell Line THP-1 by a Caspase-8-Dependent, Tumor Necrosis Factor Receptor-Independent Mechanism

“…Fujii et al (12) reported that Stxinduced HeLa cell apoptosis occurs via a pathway requiring caspase-8, -6, and -3, but not caspase-9. In contrast to studies using holotoxin molecules, binding toxin receptors with purified Stx B-subunits or anti-Gb 3 antibodies has been reported to be sufficient to induce caspase-8 activation and apoptosis in Burkitt's lymphoma cells (20). Finally, it is unknown whether Stxs directly activate apoptosis in all cell types or if additional host factors are required in some instances.…”