p53 pathway in apoptosis induced by all-trans-retinoic acid in acute myeloblastic leukaemia cells

The role of the p53 pathway in apoptosis induced by all-trans-retinoic acid (ATRA) was studied in 5 human acute myeloid leukaemia (AML) cell lines, OU -AML-3, -4, -5, -7 and -8, previously established and characterized by the authors. Although all the cell lines have a wild-type (wt) p53 gene, the pr otein is in a muta nt conformation detectable by the anti-p53 antibody PAb 240. Exposure of the cell lines to 1.0 mu M ATRA for 72 h caused induction of apoptosis detectable by morphology and the annexin V assay. The number o f apoptotic cells according to the annexin V assay varied from 16 +/- 8% (O U-AML-7) to 61 +/- 4% (OU-AML-3) in ATRA-treated cells, while it was 7 +/- 6% in control cells. Western blotting and flow cytometry showed down-regula tion of the p53 protein by ATRA. The conformation of p53 remained unchanged , being detectable in flow cytometry by PAb 240, but not by PAb 1620 (an an tibody which only detects p53 in wt conformation). At the same time bcl-2 w as down-regulated as shown by Western blotting and flow cytometry, while no induction of bax was observed by ATRA. On the basis of these results, ATRA -induced apoptosis in these AML cell lines is independent of the p53 pathwa y, although it is associated with the down-regulation of bcl-2. Copyright ( C) 2000 S. Karger AG, Basel.