T. Suzuki et al., CD24 induces apoptosis in human B cells via the glycolipid-enriched membrane domains/rafts-mediated signaling system, J IMMUNOL, 166(9), 2001, pp. 5567-5577
The glycosylphosphatidylinositol-anchored CD24 protein is a B cell differen
tiation Ag that is expressed on mature resting B cells but disappears upon
Ag stimulation. We used Burkitt's lymphoma (BL) cells, which are thought to
be related to germinal center B cells, to examine the biological effect of
Ab-mediated CD24 cross-linking on human B cells and observed 1) induction
of apoptosis in BL cells mediated by cross-linking of CD24; and 2) synergis
m between the cross-linking of CD24 and that of the B cell receptor for Ag
in the effect on apoptosis induction. We also observed activation of mitoge
n-activated protein kinases following CD24 cross-linking, suggesting that C
D24 mediates the intracellular signaling that leads to apoptosis in BL cell
s. Although CD24 has no cytoplasmic portion to transduce signals intracellu
larly, analysis of biochemically separated glycolipid-enriched membrane (GE
M) fractions indicated enhanced association of CD24 and Lyn protein tyrosin
e kinase in GEM as well as increased Lyn kinase activity after CD24 cross-l
inking, suggesting that CD24 mediates intracellular signaling via a GEM-dep
endent mechanism. Specific microscopic cocapping of CD24 and Lyn, but not o
f other kinases, following CD24 cross-linking supported this idea. We furth
er observed that apoptosis induction by cross-linking is a common feature s
hared by GEM-associated molecules expressed on BL cells, including GPI-anch
ored proteins and glycosphingolipids. CD24-mediated apoptosis in BL cells m
ay provide a model for the cell death mechanism initiated by GEM-associated
molecules, which is closely related to B cell receptor for Ag-mediated apo
ptosis.