Effect of dexamethasone on Bim, Bcl-2, and Bax expression, loss of mitochondrial transmembrane potential, and caspase activation in ALL xenografts. (A) Bim expression in xenografts cells was determined by immunoblotting of cell lysates prepared at a single time point of treatment with dexamethasone (1 μM, 16 hours), as described in the legend to Figure 5. Immunoblots were also probed with antibodies against Bax, Bcl-2, and actin. (B) Quantitative data illustrating the increase in Bim expression in drug-treated cells over nontreated controls. Expression of the 3 major Bim isoforms was normalized as a percentage of actin controls, and Bim expression in nontreated control cells was subtracted from dexamethasone-treated cells. Data presented are the mean ± SEM of 3 independent experiments. ^*Significantly different from ALL-3, -11, and -16 (P < .01); ns, not significantly different from ALL-3, -11, and -16. The difference between ALL-4 and ALL-3, -11, and -16 approached significance (P = .05). Dexamethasone IC₅₀ values of xenografts are indicated. The proportion of ALL-16 (○) and ALL-19 cells () that exhibited loss of mitochondrial transmembrane potential (MTP) (C) or active caspase-3/7 (D) following exposure to dexamethasone (1 μM). Values for nontreated control cells were subtracted from the respective dexamethasone-treated samples, and data presented are the mean ± SEM of 2 independent experiments.