Figure 3
Cyclic AMP-elevating agents protect NB4 cells against death induced by a number of cell stressors under conditions relevant for the leukemic bone marrow. (a) NB4 cells were treated for various periods of time and various concentrations of DNR in the absence or presence of PGE2/IBMX (2 μM/0.15 mM) in standard (19% O2, 5% CO2; solid bars) or hypoxic (2% O2, 5% CO2; hatched bars) atmosphere. The % dead cells was scored by microscopy (chromatin condensation and surface morphology), and is given as mean±S.E.M., n=3. Significance by Student t-test: **P<0.01, *P<0.05. (b) NB4 and NB4-LR2 cells were primed with ATRA (1 μM, 24 h). They were next incubated for 5 h with DNR (D; 5 μM) or 6 h with IDA (I; 0.5 μM) or vehicle in the absence or presence of PGE2/IBMX (2 μM/0.1 mM). The % dead cells are shown as upwards solid bars. The % of maturated cells was determined by the nitroblue tetrazolium (NBT) reduction assay, and is given as open, downward bars. The ATRA-resistant NB4-LR2 cells were, as expected, NBT negative. The data are given as mean±S.E.M., n=3. Significance by Student t-test: **P<0.01, *P<0.05. (c) NB4 cells were treated with the HSP90 antagonist geldanamycin (5 μM), the mitochondrial toxin rotenone (5 μM), the proteasome inhibitor bortezomib (0.2 μM) or the glucose antagonist 2-deoxyglucose (10 mM) for the periods of time indicated in the absence or presence of dmPGE2 (2 μM)/IBMX (0.15 mM) or dmPGE2 (2 μM)/aminophylline (0.15 mM). The scoring of dead cells was as a and b
