Mutant p53 protein, Bcl-2/Bax ratios and apoptosis in paediatric acute lymphoblastic leukaemia.
OBJECTIVE
The Bcl-2 family of proteins regulates a late step in the apoptosis pathway. Bcl-2 protein is believed to be involved in imparting resistance to programmed cell death or apoptosis induced by chemotherapeutic agents and radiation. The anti-apoptotic function of the Bcl-2 protein appears to be modulated by its ability to heterodimerize with other members of the gene family, predominantly Bax, a protein favouring induction of apoptosis. Susceptibility to undergoing apoptosis may, therefore, be dependent on the ratio between Bcl-2 and Bax. Both Bax and Bcl-2 are regulated by the tumour-suppressor protein p53. The present study therefore aims to study the significance of the Bcl-2:Bax ratio, p53 expression and apoptosis in paediatric acute lymphoblastic leukaemia (ALL).


METHODS
Expression of Bax, Bcl-2 and p53 was determined by immunocytochemistry, and apoptosis was evaluated by an enzymatic end-labelling technique using biotin-dUTP and further confirmed by annexin binding. The presence of mutant p53 was determined using a mutant-p53-specific enzyme-linked immunosorbent assay (ELISA).


RESULTS
A total of 32 cases and 20 controls were evaluated. Bcl-2 was found to be expressed in 22/32 of the ALL cases. Pretreatment (spontaneous) apoptosis was observed in 23/32 cases. The mean pretreatment apoptotic index was 11.34 +/- 2.04% with a median value of 7.5%.


CONCLUSIONS
There was a positive correlation between apoptosis and Bax expression (r = 0.5044; P = 0.0038). There was good correlation between the immunoreactivity of p53 and detection of mutant p53 by ELISA (r = 0.4605; P = 0.0079). The apoptosis index showed a negative borderline correlation to the expression of Bcl-2 protein (r = -0.3181; P = 0.076). There was an inverse correlation between extent of apoptosis and the presence of mutant p53 protein (r = -0.4732; P = 0.006). p53 protein expression also showed a correlation with both Bcl-2 (r = 0.4647; P = 0.007) and Bax (r = 0.4128; P = 0.018). The Bcl-2/Bax ratio, however, showed no significant correlation with apoptosis (r = -0.3131; P = 0.08) or with p53 expression. No significant association was evident between clinical and laboratory parameters with the Bcl-2/Bax protein expression except lymphadenopathy (r = 0.5774; P = 0.03). However, Bax expression showed a borderline correlation with the immediate tumour response to chemotherapy (r = -0.338; P = 0.0628). These patients are being followed-up to look for any association between clinical outcome, Bcl-2/Bax ratio and apoptosis.
Srinivas
G
G
Division of Laboratory Medicine, Regional Cancer Centre, Kerala, India.
Kusumakumary
P
P
Nair
M K
MK
Panicker
K R
KR
Pillai
M R
MR
D017209:Apoptosis; D002648:Child; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D009154:Mutation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism* / Q000473:pathology*; D011237:Predictive Value of Tests; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein