Retinoid-mediated down-regulation of Bcl-2 expression and effects of Bcl-2 overexpression on apoptosis induced by combined CI-1040 and retinoids. OCI-AML3 cells were pretreated with CI-1040 (0.5 μM) for 30 minutes and then exposed to ATRA (1 μM) or 9-cis RA (0.1 μM). (A) Bcl-2 cytoplasmic expression was then assessed by cytofluorimetric analysis. Results are expressed as mean fluorescence index (MFI) after 48 hours (□) and 96 hours (⊡) of treatment and represent the average ± SD of 3 independent experiments. (B) Control vector–transfected (Neo, □) and Bcl-2–transfected (Bcl-2, ⊡) OCI-AML3 cells were treated as described for panel A. Apoptosis was then evaluated by flow cytometric analysis of annexin V binding after 48 hours (top panel) and 96 hours (bottom panel) of incubation. Results are expressed as the net apoptosis induction (percentage of apoptosis in treated cells minus percentage of apoptosis in control cells) and represent the average ± SD of 3 independent experiments.