DRUG-INDUCED APOPTOSIS IN B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA - RELATIONSHIP BETWEEN P53 GENE MUTATION AND BCL-2 BAX PROTEINS IN DRUG-RESISTANCE/

We investigated the relationship among chemosensitivity to drug-induce d apoptosis in vitro, the presence of p53 gene mutations, and the expr ession of bcl-2 and bar proteins in B-cells from B-cell chronic lympho cytic leukemia (B-CLL) patients. Apoptosis was induced with a camptoth ecin analogue, 9-amino-20(s)-camptothecin, or a purine analogue, fluda rabine. Cell death was monitored by propidium iodide staining and FACS analysis. Drug-induced apoptosis in B-CLL cells was p53-independent. Immunoblot analysis of bcl-2 and bar expression revealed a correlation between drug-induced apoptosis and the ratio of endogenous levels of bcl-2 to bar proteins. B-CLL cells with none to low bcl-2/bax ratios w ere drug-sensitive as compared to cells with high ratios that were dru g-resistant Prior to drug treatment, bar protein migrated as a single species of 21 kDa. Following drug-induced apoptosis, anti-bar specific protein complexes of 36-42 kDa were up-regulated. Using two-dimension al gel electrophoresis, bar complexes were disrupted under reducing co nditions to reveal homo- and heterodimers of 18 and 21 kDa suggesting that disulfide interactions were required for complex formation. The d e novo appearance of the 18 kDa anti-bar specific protein together wit h its increased expression in drug-sensitive B-CLL B-cells undergoing cell death suggests a role for this protein in the regulation of apopt osis.