Induction of RARα2 expression during myelomonocytic maturation of leukemia cells. (A) Baseline expression levels of RARα1 and α2 in untreated myeloid leukemia cell lines and patient samples. Data are presented as mean (numbers above bars) ± SD from triplicates. (B) Levels of RARα1 and α2 expression 48 hours after induction with ATRA and/or G/GM-CSF compared with untreated control. The panels show the mean ± SD of one representative experiment done in triplicate. The results have been repeated in independent experiments: U937, n = 3; NB-4, n = 2; Kasumi, n = 1. Standard curves based on plasmid DNA, or concentrated samples using 2 different housekeeping genes were used to quantify the expression levels of RARα1 and α2. Negative controls without template were included in each experiment.