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

Abstract

Globotriasosylceramide (Gb3), a neutral glycosphingolipid, is the B-cell differentiation antigen CD77 and acts as the receptor for most Shiga toxins, including verotoxin-1 (VT-1). We have shown that both anti-Gb3/CD77 mAb and VT-1 induce apoptosis in Burkitt's lymphoma cells. We compared the apoptotic pathways induced by these two molecules by selecting cell lines sensitive to only one of these inducers or to both. In all these cell lines (including the apoptosis-resistant line), VT-1 was transported to the endoplasmic reticulum and inhibited protein synthesis similarly, suggesting that VT-1-induced apoptosis is dissociated from these processes. VT-1 triggered a caspase- and mitochondria-dependent pathway (rapid activation of caspases 8 and 3 associated with a loss of mitochondrial membrane potential (Δψm) and the release of cytochrome c from mitochondria). In contrast, the anti-Gb3/CD77 mAb-induced pathway was caspase-independent and only involved partial depolarization of mitochondria. Antioxidant compounds had only marginal effects on VT-1-induced apoptosis but strongly protected cells from anti-Gb3/CD77 mAb-induced apoptosis. VT-1- and anti-Gb3/CD77 mAb-treated cells displayed very different features on electron microscopy. These results clearly indicate that the binding of different ligands to Gb3/CD77 triggers completely different apoptotic pathways. Globotriasosylceramide (Gb3), a neutral glycosphingolipid, is the B-cell differentiation antigen CD77 and acts as the receptor for most Shiga toxins, including verotoxin-1 (VT-1). We have shown that both anti-Gb3/CD77 mAb and VT-1 induce apoptosis in Burkitt's lymphoma cells. We compared the apoptotic pathways induced by these two molecules by selecting cell lines sensitive to only one of these inducers or to both. In all these cell lines (including the apoptosis-resistant line), VT-1 was transported to the endoplasmic reticulum and inhibited protein synthesis similarly, suggesting that VT-1-induced apoptosis is dissociated from these processes. VT-1 triggered a caspase- and mitochondria-dependent pathway (rapid activation of caspases 8 and 3 associated with a loss of mitochondrial membrane potential (Δψm) and the release of cytochrome c from mitochondria). In contrast, the anti-Gb3/CD77 mAb-induced pathway was caspase-independent and only involved partial depolarization of mitochondria. Antioxidant compounds had only marginal effects on VT-1-induced apoptosis but strongly protected cells from anti-Gb3/CD77 mAb-induced apoptosis. VT-1- and anti-Gb3/CD77 mAb-treated cells displayed very different features on electron microscopy. These results clearly indicate that the binding of different ligands to Gb3/CD77 triggers completely different apoptotic pathways. Globotriaosylceramide (Gb3: Galα1→4Galβ1→4Glcβ1→Cer), a neutral glycosphingolipid (GSL), 1The abbreviations used are: GSL, glycosphingolipid; BL, Burkitt's lymphoma; ER, endoplasmic reticulum; Gb3, globotriaosylceramide; GSH-EE, reduced glutathione ethyl ester; NAC, N-acetyl-l-cysteine; Δψm, mitochondrial membrane potential; PPMP, 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol; Stx, Shiga toxin family; VT-1, verotoxin-1; α4Gal-T1, UDP-galactose: LacCer, α1,4-galactosyltransferase; GD3, ganglioside GD3; LacCer, lactosyl ceramide. has been identified as three different entities according to the cell type on which it is found. On erythrocytes, it constitutes the rare Pk blood group antigen (1Marcus D.M. Kundu S.K. Suzuki A. Sem. Hematol. 1981; 18: 63-71PubMed Google Scholar). On lymphocytes, it constitutes the CD77 differentiation antigen and its expression is limited to a subset of germinal center B cells (2Mangeney M. Richard Y. Coulaud D. Tursz T. Wiels J. Eur. J. Immunol. 1991; 21: 1131-1140Crossref PubMed Scopus (160) Google Scholar, 3Hardie D.L. Johnson G.D. Khan M. MacLennan I.C. Eur. J. Immunol. 1993; 23: 997-1004Crossref PubMed Scopus (133) Google Scholar). On endothelial cells, it serves as the natural receptor for bacterial toxins of the Shiga family (Stx) (4Paton J.C. Paton A.W. Clin. Microbiol. Rev. 1998; 11: 450-479Crossref PubMed Google Scholar). The function of Gb3/CD77 has been extensively investigated. We previously reported that the ligation of Gb3/CD77 by specific monoclonal antibodies (mAb) induces apoptosis in Burkitt's lymphoma (BL) cells, the tumoral counterparts of Gb3/CD77(+) germinal center B lymphocytes. We have also demonstrated that this apoptosis involves a rapid, sustained increase in intracellular Ca2+ concentration, a rapid, transient increase in cAMP levels, protein kinase A activation, and, finally, ceramide accumulation (5Mangeney M. Lingwood C.A. Taga S. Caillou B. Tursz T. Wiels J. Cancer Res. 1993; 53: 5314-5319PubMed Google Scholar, 6Taga S. Carlier K. Mishal Z. Capoulade C. Mangeney M. Lécluse Y. Coulaud D. Tétaud C. Pritchard L.L. Tursz T. Wiels J. Blood. 1997; 90: 2757-2767Crossref PubMed Google Scholar). Because Gb3/CD77 is the Shiga toxin receptor, numerous studies have analyzed the role of these toxins and their receptor in pathogenesis (reviewed in Ref. 7Lingwood C.A. Trends Microbiol. 1996; 4: 147-153Abstract Full Text PDF PubMed Scopus (235) Google Scholar). In humans, infection by Stx-producing organisms (some strains of Escherichia coli and Shigella dysenteriae type 1) causes gastrointestinal diseases and the more serious hemolytic uremic syndrome, both of which are responsible for large numbers of deaths (reviewed in Refs. 4Paton J.C. Paton A.W. Clin. Microbiol. Rev. 1998; 11: 450-479Crossref PubMed Google Scholar and 8O'Brien A.D. Tesh V.L. Donohue-Rolfe A. Jackson M.P. Olsnes S. Sandvig K. Lindberg A.A. Keusch G.T. Curr. Top. Microbiol. Immunol. 1992; 180: 65-94Crossref PubMed Scopus (328) Google Scholar). Stx (also called verotoxins (VT) because the E. coli toxins were originally described to be cytotoxic to Vero cells (8O'Brien A.D. Tesh V.L. Donohue-Rolfe A. Jackson M.P. Olsnes S. Sandvig K. Lindberg A.A. Keusch G.T. Curr. Top. Microbiol. Immunol. 1992; 180: 65-94Crossref PubMed Scopus (328) Google Scholar)) are bipartite molecules comprised of an A catalytic subunit and five B subunits that specifically bind Gb3/CD77. The A subunit has RNA N-glycosidase activity; it removes an adenine base from 28 S RNA, thereby inhibiting protein synthesis and killing target cells (9Endo Y. Tsurugi K. Yutsudo T. Takeda Y. Ogasawara T. Igarashi K. Eur J. Biochem. 1988; 171: 45-50Crossref PubMed Scopus (617) Google Scholar). Several recent studies have demonstrated that these toxins also induce apoptosis in various cell types. These studies have led to an ongoing controversy about the relationship between apoptosis and cell death due to protein synthesis inhibition (10Williams J.M. Lea N. Lord J.M. Roberts L.M. Milford D.V. Taylor C.M. Toxicol. Lett. 1997; 91: 121-127Crossref PubMed Scopus (73) Google Scholar, 11Taguchi T. Uchida H. Kiyokawa N. Mori T. Sato N. Horie H. Takeda T. Fujimoto J. Kidney Int. 1998; 53: 1681-1688Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar, 12Arab S. Murakami M. Dirks P. Boyd B. Hubbard S.L. Lingwood C.A. Rutka J.T. J. Neurooncol. 1998; 40: 137-150Crossref PubMed Scopus (58) Google Scholar, 13Marcato P. Mulvey G. Armstrong G.D. Infect. Immun. 2002; 70: 1279-1286Crossref PubMed Scopus (24) Google Scholar). Studies of Stx and Gb3/CD77 have also helped to elucidate intracellular transport events (14Johannes L. Goud B. Traffic. 2000; 1: 119-123Crossref PubMed Scopus (42) Google Scholar, 15Sandvig K. Toxicon. 2001; 39: 1629-1635Crossref PubMed Scopus (170) Google Scholar). It has been shown that the targeting of the toxin to a specific intracellular transport pathway can be determined by the Gb3/CD77 isoform expressed on the cell surface and by the presence or absence of Gb3/CD77 in the lipid raft microdomains of the membrane (16Arab S. Lingwood C.A. J. Cell. Physiol. 1998; 177: 646-660Crossref PubMed Scopus (101) Google Scholar, 17Falguières T. Mallard F. Baron C. Hanau D. Lingwood C.A. Goud B. Salamero J. Johannes L. Mol. Biol. Cell. 2001; 12: 2453-2468Crossref PubMed Scopus (232) Google Scholar). In this study, we investigated the nature of the apoptotic signals mediated by Gb3/CD77. Recent reports have shed light on both toxin- and anti-Gb3/CD77 mAb-induced apoptotic pathways (6Taga S. Carlier K. Mishal Z. Capoulade C. Mangeney M. Lécluse Y. Coulaud D. Tétaud C. Pritchard L.L. Tursz T. Wiels J. Blood. 1997; 90: 2757-2767Crossref PubMed Google Scholar, 18Ching J.C. Jones N.L. Ceponis P.J. Karmali M.A. Sherman P.M. Infect. Immun. 2002; 70: 4669-4677Crossref PubMed Scopus (75) Google Scholar, 19Kiyokawa N. Mori T. Taguchi T. Saito M. Mimori K. Suzuki T. Sekino T. Sato N. Nakajima H. Katagiri Y.U. Takeda T. Fujimoto J. J. Cell. Biochem. 2001; 81: 128-142Crossref PubMed Scopus (32) Google Scholar), but various questions remain unresolved: Is ligand binding to Gb3/CD77 sufficient to induce apoptosis? Do ligands trigger a single intracellular mechanism? What is the relationship between protein synthesis inhibition and apoptosis for toxins? We investigated these issues by comparing the apoptotic mechanisms induced by anti-Gb3/CD77 mAb and verotoxin-1 (VT-1) in various BL cells. Cellular toxicity was strictly dependent on the expression of Gb3/CD77 on the cell surface in both cases, but some cell lines strongly expressing Gb3/CD77 were killed by both inducers, whereas others were only killed by one. Our results indicate that these two ligands trigger different signaling pathways: VT-1-induced apoptosis involves caspase activation and mitochondrial depolarization, whereas oxidative stress seems to mediate anti-Gb3/CD77 mAb-induced cell death. Finally, the ability of VT-1 to induce apoptosis was not correlated with the transport of this molecule to the endoplasmic reticulum (ER) or with the inhibition of protein synthesis. Cell Lines—All cell lines used in this study were originally established from endemic or sporadic cases of Burkitt's lymphoma. The Ramos BL cell line was obtained from ATCC (Rockville, MD), whereas the and cells lines were by G. and the cells by G. These cell lines were in and and with Ramos cells were obtained of in a A. J. M. H. A. J. Biochem. 1992; PubMed Scopus Google Scholar). was obtained from monoclonal was by S. H. S. K. S. Biochem. Res. PubMed Scopus Google Scholar). were with the according to the verotoxin-1 (VT-1) was by C. Lingwood The was from Jackson the c mAb was from the mAb and the mAb were from The used to mAb in apoptosis was obtained from The used for was from The used for was from and ethyl a of reduced glutathione were from The was obtained from A in was The of caspase 8 was from of the Gb3/CD77 Carlier K. Wiels J. M. B. C. H. J. Biol. 2000; Full Text Full Text PDF PubMed Scopus Google was an the was used to cells, which not Gb3/CD77. cells were with of the or by with a of and cells were in with and for were for in this and Gb3/CD77 antigen expression was in a in Gb3/CD77 expression on cells with the cells were with the anti-Gb3/CD77 mAb and the subset of cells with expression was on a The cells were and cells with were of and Cell cells with the anti-Gb3/CD77 mAb and or with VT-1 in of cells were in and for were and in with and analyzed in a of investigated the ability of VT-1 to protein synthesis by cells for in in the presence or absence of VT-1 or as a for protein were on and was in a and and were as previously described L. D. C. Goud B. J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). cells were with for and three with were to for and were in In some cells were with with were on analyzed by and with a of cells with VT-1 or anti-Gb3/CD77 mAb for various of We to a of and the cells for a in the were and in and analyzed in a of and cytochrome c release from the to the by cells as previously described J.C. M. J. Cell Biol. 2001; PubMed Scopus Google Scholar). We cells in of cell and in for were by for and the were were for in and for The mitochondrial were and cell were in was the was for and the were by on to by cytochrome c from mitochondrial and were by on a were by in in and for with the mAb and with were by were by to the and were in in for were for in and in in the were in a of and in with an were with and on a Gb3/CD77(+) BL to by mAb and investigated the of apoptosis by a of Burkitt's lymphoma cell lines with VT-1 or an anti-Gb3/CD77 mAb with a We cell lines that were Gb3/CD77(+) or and we also cells from cells that were originally and Gb3/CD77(+) cells from cells that were originally Ramos cells were established by with PPMP, a and are to as Ramos Gb3/CD77(+) cells were obtained by with the Gb3/CD77 Carlier K. Wiels J. M. B. C. H. J. Biol. 2000; Full Text Full Text PDF PubMed Scopus Google and are to as Cell surface expression of Gb3/CD77 was by an anti-Gb3/CD77 mAb and cells strongly expressed Gb3/CD77 and The cells with the not Gb3/CD77 and with expression of this antigen We the of these cell lines to VT-1 and to an anti-Gb3/CD77 mAb VT-1 and anti-Gb3/CD77 mAb had different apoptosis were in and cells with anti-Gb3/CD77 mAb and whereas cells only to this In contrast, VT-1 strongly induced apoptosis in and cells and whereas it had on cells We investigated the of to VT-1-induced apoptosis was by these cells with and apoptosis was not and Ramos cells were not killed by anti-Gb3/CD77 mAb or VT-1 of apoptosis in various BL cells by ligation of in a of the Gb3/CD77(+) BL cell lines and were sensitive to both anti-Gb3/CD77 mAb and one cell line was sensitive to anti-Gb3/CD77 mAb and one was sensitive to the of apoptosis by anti-Gb3/CD77 mAb and VT-1 is strictly dependent on Gb3/CD77 but this expression is not sufficient to to these apoptosis of the Is in Gb3/CD77(+) BL cells not apoptosis by VT-1, we investigated the pathway by which is by BL cell The transport of to the has been shown to be for toxicity K. B. J. 2000; PubMed Google Scholar). We the of the ER, a previously described subunit L. D. C. Goud B. J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). an the of the it to its in the by by the had been for we the cells and as a and analyzed the by and In to a with a was in and was in in which had not been of the cells with an of this this to was with a of the was in the cells, in in and in Because cells are to VT-1-induced these that the transport of the toxin to the is to trigger apoptosis. VT-1 in Gb3/CD77(+) BL of VT-1 is to be mediated by the inhibition of protein synthesis (9Endo Y. Tsurugi K. Yutsudo T. Takeda Y. Ogasawara T. Igarashi K. Eur J. Biochem. 1988; 171: 45-50Crossref PubMed Scopus (617) Google Scholar). We protein synthesis in the various cell lines and for with VT-1, by a cells were also with a protein synthesis synthesis was inhibited in Ramos and cells with VT-1 and of the of cells, and inhibited in cells of the of was in the cell line of completely inhibited protein synthesis in all BL cell The results obtained with cells indicate that the apoptotic and protein effects of VT-1 can be of protein synthesis with of in a VT-1 whereas mAb investigated the of caspases in the apoptotic pathways induced by VT-1 and anti-Gb3/CD77 is an caspase involved in a of apoptotic pathways. We investigated its activation in BL cells. and cells were with VT-1 or anti-Gb3/CD77 mAb for various of and and activation was by with a mAb that strongly the and the and only the of the in of Ramos cells with VT-1 for whereas of the in cells, VT-1 not induce whereas in cells, the of and was in the three cell lines with anti-Gb3/CD77 mAb or in cells with VT-1 or anti-Gb3/CD77 mAb not and we investigated the of a by In Ramos cells, the was on with VT-1 and in 8 of protein was In cells, a of the was only of with In cells, the was of and in in Ramos cells, the was in these cells. of these three cell lines with anti-Gb3/CD77 mAb not induce of the of cells with VT-1 or anti-Gb3/CD77 mAb not in not caspases are involved in the apoptotic pathway induced by VT-1, whereas the of anti-Gb3/CD77 mAb-induced apoptosis seems to be VT-1 and mAb a of in are a in apoptotic pathways (reviewed in Ref. G. J.C. 2000; PubMed Scopus Google Scholar). We mitochondrial membrane potential (Δψm) and of the cells with VT-1 or anti-Gb3/CD77 We by the In Ramos cells, VT-1 induced a loss of of which mitochondrial membrane depolarization was in all cells In cells, the loss of was and only of cells were 8 of loss and of cells were of loss was in and cells. We investigated activation or from mitochondrial by the effects of a on of the cells with this inhibited the loss of induced by VT-1 of Ramos cells were of cells that had not been and of cells were of mitochondrial depolarization to on We also the BL cell lines for the of with anti-Gb3/CD77 mAb induced a sustained loss of in cells of the cells were of but had on in Ramos cells these cells are as sensitive as to anti-Gb3/CD77 or on in and cells VT-1 and mAb c from in is by the release of cytochrome c from the to the it with and which in We investigated cytochrome c release with VT-1 and anti-Gb3/CD77 mAb by BL cell lines for various of and and as previously described J.C. M. J. Cell Biol. 2001; PubMed Scopus Google Scholar). of the and mitochondrial was an c mAb c in the mitochondrial of Ramos cells with VT-1 of were only and were completely and cytochrome c was in the of these cells of and its in cytochrome c were in the mitochondrial or of cells with anti-Gb3/CD77 of In cells with VT-1, in cytochrome c were in the mitochondrial or contrast, cytochrome c clearly in the of these cells with anti-Gb3/CD77 this release to be as in cytochrome c was in the mitochondrial The cytochrome c in the mitochondrial of cells with VT-1 clearly and was by an increase in cytochrome c in the of these cells with anti-Gb3/CD77 mAb not the cytochrome c VT-1 induces the release of cytochrome c and loss of Our results also that in but not in Ramos cells, anti-Gb3/CD77 mAb induces a depolarization of with a release of cytochrome c caspase with VT-1 and mAb used electron to Ramos cells, which are sensitive to both VT-1- and anti-Gb3/CD77 mAb-induced apoptosis. The features of cells with VT-1 B and and anti-Gb3/CD77 mAb and were very with VT-1 were cells A and also of or and large with anti-Gb3/CD77 mAb were also cells, had their more and the were and more These features are of described by for caspase-independent apoptosis Ref. M. M. Rev. Mol. Cell. Biol. 2001; PubMed Scopus Google Scholar). The and BL from mAb-induced but from VT-1-induced intracellular of seems to be involved in cell death induced by various Several studies have demonstrated that including apoptosis (reviewed in Refs. A. Biol. 1997; PubMed Scopus Google Scholar and J. A. S. Biol. 2000; PubMed Scopus Google and that various apoptosis C. B. D. C. G. F. B. A. Int. Immunol. 1997; PubMed Scopus Google Scholar). We investigated the effects of two and of reduced on the of apoptotic cells induced by anti-Gb3/CD77 mAb and Because and were to Ramos cells, we used cells, which are also sensitive to both anti-Gb3/CD77 mAb and VT-1 of the cells for with or completely protected cells and cells, from the apoptosis induced by anti-Gb3/CD77 but had or only a on VT-1-induced apoptosis of and cells with with for cells. are of the apoptotic pathway induced by anti-Gb3/CD77 whereas or role in the pathway induced by of the of most to T. T. C. K. S. A. PubMed Scopus Google Scholar), that are for (reviewed in Refs. S. Igarashi Y. J. Biochem. PubMed Scopus Google Scholar and A. 1993; PubMed Scopus Google Scholar). studies (including some the of T. J. Biochem. 2000; PubMed Scopus Google Scholar)) have also shown that the of signals by is the cell by on the and of these molecules with molecules and on their intracellular a neutral GSL, has been extensively and shown to apoptotic signals the binding of various the Stx the binding subunit of Stx and anti-Gb3/CD77 mAb (6Taga S. Carlier K. Mishal Z. Capoulade C. Mangeney M. Lécluse Y. Coulaud D. Tétaud C. Pritchard L.L. Tursz T. Wiels J. Blood. 1997; 90: 2757-2767Crossref PubMed Google Scholar, 13Marcato P. Mulvey G. Armstrong G.D. Infect. Immun. 2002; 70: 1279-1286Crossref PubMed Scopus (24) Google Scholar, 15Sandvig K. Toxicon. 2001; 39: 1629-1635Crossref PubMed Scopus (170) Google Scholar, M. P. M. A. L. S. J. 2002; PubMed Scopus Google Scholar, M. S. S. Mol. Microbiol. PubMed Scopus Google Scholar). We investigated the mechanisms of apoptosis by comparing the signaling pathways induced by one of the Stx family (VT-1) and by an anti-Gb3/CD77 mAb in various BL cell We that both pathways were strictly but that the presence of the receptor is not sufficient to trigger apoptosis. Our results also that the VT-1- and pathways are completely are in and These are the to that a cell can be to one CD77 ligand and sensitive to and that a glycosphingolipid can mediate two different cell death pathways. Our reports that caspases are involved in VT-1-induced apoptosis J.C. Jones N.L. Ceponis P.J. Karmali M.A. Sherman P.M. Infect. Immun. 2002; 70: 4669-4677Crossref PubMed Scopus (75) Google Scholar, 19Kiyokawa N. Mori T. Taguchi T. Saito M. Mimori K. Suzuki T. Sekino T. Sato N. Nakajima H. Katagiri Y.U. Takeda T. Fujimoto J. J. Cell. Biochem. 2001; 81: 128-142Crossref PubMed Scopus (32) Google Scholar, S. H. M. F. N. T. Immunol. Microbiol. 2000; PubMed Google Scholar). We also that VT-1 triggered mitochondrial in on The of this activation is of the BL cell of synthesis inhibition by that the transport of the to was in not that the transport of the to was in not in a of the apoptotic pathways induced by and anti-Gb3/CD77 mAb in BL of or on the cell c or on the cell or on the cell or on the cell in a We in apoptosis-resistant cells, VT-1 transport to the as as in sensitive BL cells. of the toxin to the is not a in apoptosis or VT-1 the The of these two is the most as of the cells with A that of the apoptosis P. Mulvey G. Armstrong G.D. Infect. Immun. 2002; 70: 1279-1286Crossref PubMed Scopus (24) Google Scholar, S. H. M. F. N. T. Immunol. Microbiol. 2000; PubMed Google Scholar). Our in cells, apoptosis is inhibited of the toxin to the The inhibition of protein synthesis by VT-1 in cells, in the absence of the relationship between these two processes. it that protein synthesis inhibition triggers strongly that these two are the activation of caspases and in sensitive cells are also with studies have this and have apoptosis induced by the B subunit has some to that protein synthesis inhibition and apoptosis are (5Mangeney M. Lingwood C.A. Taga S. Caillou B. Tursz T. Wiels J. Cancer Res. 1993; 53: 5314-5319PubMed Google Scholar, 12Arab S. Murakami M. Dirks P. Boyd B. Hubbard S.L. Lingwood C.A. Rutka J.T. J. Neurooncol. 1998; 40: 137-150Crossref PubMed Scopus (58) Google Scholar, 13Marcato P. Mulvey G. Armstrong G.D. Infect. Immun. 2002; 70: 1279-1286Crossref PubMed Scopus (24) Google Scholar), whereas study, in which the VT-1 B not induce apoptosis (10Williams J.M. Lea N. Lord J.M. Roberts L.M. Milford D.V. Taylor C.M. Toxicol. Lett. 1997; 91: 121-127Crossref PubMed Scopus (73) Google Scholar), led to the studies with VT-1 and also to T. Uchida H. Kiyokawa N. Mori T. Sato N. Horie H. Takeda T. Fujimoto J. Kidney Int. 1998; 53: 1681-1688Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar, K. B. Cell Res. 1992; PubMed Scopus Google Scholar, J. 2001; 12: PubMed Google Scholar). We are comparing the of various protein synthesis and VT-1 to induce apoptosis in a of Gb3/CD77(+) BL cells. The of BL cells with compounds strongly protected apoptosis. stress has been shown to mediate apoptosis in (reviewed in Ref. J. A. S. Biol. 2000; PubMed Scopus Google Scholar). In these induced apoptosis S. Lett. 1997; PubMed Scopus Google Scholar), were apoptosis A. A. Lett. 1997; PubMed Scopus Google Scholar), or apoptosis J. A. S. Biol. 2000; PubMed Scopus Google Scholar, N. T. Biol. 2001; PubMed Scopus Google Scholar). We that two and strongly protected the cells apoptosis induced by anti-Gb3/CD77 We also that with specific of Ramos and cells to of anti-Gb3/CD77 mAb and not thereby that is an of apoptosis and the role of in this and ceramide were shown to be ceramide was shown to be a of the neutral and by were shown to be of cell death B. N. T. P. L.M. J. Biol. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, A. C. J. G. J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). It was also shown that the of ceramide to induces cytochrome c release and the loss of P. M. S. C. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). Because ceramide in BL cells to an anti-Gb3/CD77 mAb (6Taga S. Carlier K. Mishal Z. Capoulade C. Mangeney M. Lécluse Y. Coulaud D. Tétaud C. Pritchard L.L. Tursz T. Wiels J. Blood. 1997; 90: 2757-2767Crossref PubMed Google Scholar), we are to the role of oxidative stress in anti-Gb3/CD77 mAb-induced apoptosis and to the of ceramide to this signaling as some and also induce a in Δψm, and the release of cytochrome c from C. A. J.C. J. 2000; PubMed Scopus Google Scholar), we are the of Gb3/CD77 on mitochondria. In we that two different apoptotic pathways are triggered of the nature of the ligand binding to the Gb3/CD77 glycosphingolipid a caspase- and mitochondria-dependent pathway or a We for and for of the and