Mutant p53 protein, Bcl-2/Bax ratios and apoptosis in paediatric acute lymphoblastic leukaemia

Purpose: The Bcl-2 family of proteins regulates a late step in the apoptosi s pathway. Bcl-2 protein is believed to be involved in imparting resistance to programmed cell death or apoptosis induced by chemotherapeutic agents a nd radiation. The anti-apoptotic function of the Bcl-2 protein appears to b e modulated by its ability to heterodimerize with other members of the gene family, predominantly Bar, a protein favouring induction of apoptosis. Sus ceptibility to undergoing apoptosis may, therefore, be dependent on the rat io between Bcl-2 and Bar. Both Bar and Bcl-2 are regulated by the tumour-su ppressor protein p53. The present study therefore aims to study the signifi cance of the Bcl-2:Bar ratio, p53 expression and apoptosis in paediatric ac ute lymphoblastic leukaemia (ALL). Methods: Expression of Bar, Bcl-2 and p5 3 was determined by immunocytochemistry, and apoptosis was evaluated by an enzymatic end-labelling technique using biotin-dUTP and further confirmed b y annexin binding. The presence of mutant p53 was determined using a mutant -p53-specific enzyme-linked immunosorbent assay (ELISA). Results: A total o f 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 observe d 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 Bar expression (r = 0.5044; P = 0.0038). There was g ood correlation between the immunoreactivity of p53 and detection of mutant p53 by ELISA (r = 0.4605; P = 0.0079). The apoptosis index showed a negati ve borderline correlation to the expression of Bcl-2 protein (r = -0.3181; P = 0.076). There was an inverse correlation between extent of apoptosis an d 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 Bar (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 lab oratory parameters with the Bcl-2/Bax protein expression except lymphadenop athy (r = 0.5774; P = 0.03). However, Bar expression showed a borderline co rrelation with the immediate tumour response to chemotherapy (r = -0.338; P = 0.0628). These patients are being followed-up to look for any associatio n between clinical outcome, Bcl-2/Bax ratio and apoptosis.