Abstract
We have previously demonstrated induction of O‐acetylated sialoglycoproteins on lymphoblasts of childhood acute lymphoblastic leukaemia (ALL). These molecules promote survival of lymphoblasts by preventing apoptosis. Although O‐acetylated sialoglycoproteins are over expressed, the status of O‐acetylation of gangliosides and their role in lymphoblasts survival remains to be explored in ALL patients. Here, we have observed enhanced levels of 9‐O‐acetylated GD3 (9‐O‐AcGD3) in the lymphoblasts of patients and leukaemic cell line versus disialoganglioside GD3 in comparison to the normal cells. Localization of GD3 and 9‐O‐AcGD3 on mitochondria of patient's lymphoblasts has been demonstrated by immuno‐electron microscopy. The exogenous administration of GD3‐induced apoptosis in lymphoblasts as evident from the nuclear fragmentation and sub G0/G1 apoptotic peak. In contrast, 9‐O‐AcGD3 failed to induce such apoptosis. We further explored the mitochondria‐dependent pathway triggered during GD3‐induced apoptosis in lymphoblasts. GD3 caused a time‐dependent depolarization of mitochondrial membrane potential, release of cytochrome c and 7.4‐ and 8‐fold increased in caspase 9 and caspase 3 activity respectively. However, under identical conditions, an equimolar concentration of 9‐O‐AcGD3 failed to induce similar effects. Interestingly, 9‐O‐AcGD3 protected the lymphoblasts from GD3‐induced apoptosis when administered in equimolar concentrations simultaneously. In situ de‐O‐acetylation of 9‐O‐AcGD3 with sodium salicylate restores the GD3‐responsiveness to apoptotic signals. Although both GD3 and 9‐O‐acetyl GD3 localize to mitochondria, these two structurally related molecules may play different roles in ALL‐disease biology. Taken together, our results suggest that O‐acetylation of GD3, like that of O‐acetylated sialoglycoproteins, might be a general strategy adopted by leukaemic blasts towards survival in ALL. J. Cell. Biochem. 105: 724–734, 2008. © 2008 Wiley‐Liss, Inc.