Intracellular Signaling Events in CD77-Mediated Apoptosis of Burkitt's Lymphoma Cells

Abstract

In the hematopoietic system CD77, a glycolipid surface antigen, is restricted to group I Burkitt's lymphoma (BL) cell lines and a subset of germinal center B lymphocytes. Recently, we have reported that recombinant B subunits of Verotoxin, which specifically binds to CD77, induce programmed cell death of CD77+ BL cells. Here, we show that an anti-CD77 monoclonal antibody (38.13) immobilized on tissue culture dishes also induces apoptosis, and we have explored the signal transducing events leading to this cell death. We show that ligation of CD77 antigen causes an increase of the intracellular Ca2+ concentration owing to an influx of extracellular Ca2+ through calcium channels. Chelation of extracellular Ca2+ with EGTA partially prevents anti-CD77–induced apoptosis, indicating that this process is probably Ca2+ dependent. We show that the cross-linking of CD77 provokes an increase of intracellular cAMP levels followed by cAMP-dependent protein kinase activation. We report that BL cells produce ceramide when they are exposed to 38.13 but, unexpectedly, without a concomitant decrease in sphingomyelin or CD77 content. Finally, we provide evidence that C2-ceramide, calcium ionophore, and forskolin (which increases intracellular levels of cAMP) independently induce apoptosis of CD77+ BL cells and, moreover, that C2-ceramide and forskolin strongly synergize to cause cell death. The possible role of CD77-mediated apoptosis in the B cell selection that occurs in germinal centers is discussed.

NALP‐3 inflammasome silencing attenuates ceramide‐induced transepithelial permeability

“…Ceramide quantification used a diacylglycerol (DAG) kinase assay as mentioned earlier (Taga et al, 1997). Cells were extracted using methanol:chloroform:1 N HCl (100:100:1, v/v/v).…”

The extrafollicular-to-follicular transition of human B lymphocytes: induction of functional globotriaosylceramide (CD77) on high threshold occupancy of CD40

“…At high concentration, the B subunit of Verotoxin-1 is sufficient for driving programmed cell death in BL lines [19]. Crosslinking CD77 with immobilized 38.13 mAb has revealed that the resulting apoptosis is both Ca 2+ dependent and accompanied by the production of ceramide [20]. These observations have prompted the suggestion that CD77 may be contributing to the regulation of apoptosis in GC B cell populations [21].…”

Shiga toxin A subunit mutant ofEscherichia coliO157:H7 releases outer membrane vesicles containing the B-pentameric complex

“…Slight reduction of absorbance in the case of DM/STx(À), compared with PBS control, may indicate that the amounts of cellular proteins could be affected by STxB or other toxic factor(s) remaining in the OMVs. As previous reports have shown that STxB alone can be apoptotic in the cell line expressing higher levels of Gb3 (Taga et al, 1997;Marcato et al, 2002), it seems that the STxB pentamers of the DM/STx(À) OMVs (b) (a) Fig. 3.…”