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 protein is in a mutant conformation detectable by the anti-p53 antibody PAb 240. Exposure of the cell lines to 1.0 µM ATRA for 72 h caused induction of apoptosis detectable by morphology and the annexin V assay. The number of apoptotic cells according to the annexin V assay varied from 16 ± 8% (OUAML-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-regulation 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 antibody which only detects p53 in wt conformation). At the same time bcl-2 was 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 pathway, although it is associated with the down-regulation of bcl-2.