BCR-ABL DELAYS APOPTOSIS UPSTREAM OF PROCASPASE-3 ACTIVATION

The p210(bcr-abl) protein was shown to inhibit apoptosis induced by DN A damaging agents, Apoptotic DNA fragmentation is delayed in the bcr-a bl(+) K562 and KCL-22 compared with the bcr-abl(-) U937 and HL-60 cell lines when treated with etoposide concentrations that induce similar DNA damage in the four cell lines. By the use of a cell-free system, w e show that nuclei from untreated cells that express p210(bcr-abl) rem ain sensitive to apoptotic DNA fragmentation induced by triton-soluble extracts from p210(bcr-abl-) cells treated with etoposide. In the fou r tested cell lines, apoptotic DNA fragmentation is associated with a decreased expression of procaspase-3 (CPP32/Yama/apopain) and its clea vage into a p17 active fragment, whereas the long isoform of procaspas e-2 (ICH-1L) remains unchanged and the poly(adenosine diphosphate-ribo se)polymerase protein is cleaved. These events are delayed in bcr-abl( +) compared with bcr-abl(-) cell lines. The role of p210(bcr-abl) in t his delay is confirmed by comparing the effect of etoposide on the gra nulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent UT7 c ells and the bcr-abl-transfected (GM-CSF)-dependent UT7/9 clone. We co nclude that the cytosolic pathway that leads to apoptotic DNA fragment ation in etoposide-treated leukemic cells is delayed upstream of proca spase-3-mediated events in bcr-abl(+) cell lines. (C) 1998 by The Amer ican Society of Hematology.