Fig. 3.

Comparison of continuous versus transient ATRA treatment of HL-60 cells, which (A) were untreated (None), continuously treated with ATRA (2 μM) for 9 days, or transiently treated with ATRA for 1 day, followed by culturing in ATRA-free medium for an additional 8 days. All cells were double-stained for CD66 and PI and analyzed by FACS at Day 9. (B) Cell-cycle analysis (permeabilized, PI) was performed at Day 11 on transiently (shaded) versus continuously ATRA-treated (open) HL-60 cells. (C) NB4 cells were untreated (None), continuously treated with ATRA (2 μM) for 5 days, or transiently treated with ATRA for 1 day, followed by culturing in ATRA-free medium for an additional 4 days. All cells were double-stained for CD66 and PI and analyzed by FACS at Day 5. All experiments were repeated at least twice to ensure the validity of results.