O-acetylation of GD3 prevents its apoptotic effect and promotes survival of lymphoblasts in childhood acute lymphoblastic leukaemia.
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.
Mukherjee
Kankana
K
Infectious Diseases and Immunology Division, Indian Institute of Chemical Biology, Kolkata, India.
Chava
Anil Kumar
AK
Mandal
Chandan
C
Dey
Sailendra Nath
SN
Kniep
Bernhard
B
Chandra
Sarmila
S
Mandal
Chitra
C
D000107:Acetylation; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002453:Cell Cycle; D002470:Cell Survival; D045304:Cytochromes c / Q000378:metabolism; D005732:Gangliosides / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism* / Q000473:pathology; D053078:Membrane Potential, Mitochondrial; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism*
D005732:Gangliosides; C026226:ganglioside, GD3; D045304:Cytochromes c; C049132:9-O-acetyl-GD3 ganglioside; D053148:Caspase 3