Effects of ATRA on PLSCR1 expression in the maturation-resistant leukemic cell line NB4-LR1. NB4-LR1 cells were treated with 10^-6 M ATRA for the times indicated. Quantification of CD11b⁺ cells (A), semiquantitative RT-PCR for PLSCR1 mRNA (B), and Western blot for PLSCR1 (C) were performed as detailed in “Materials and methods.” For Western blot of PLSCR1, NB4 cells treated without or with 10^-6 M ATRA for 1 to 2 days were used as controls, demonstrating ATRA-induced up-regulation of PLSCR1 in NB4 cells.