Expression of GATA-1, GATA-2, ERK, and PI3 kinase proteins, and p21 mRNA in parental and SAR-transfected K562 cells. (A) Comparison of GATA-1 and GATA-2 protein levels in parental K562 cells (grown in the presence or absence of HU for 3 days), vector-transfected cells, and SAR-expressing cells. Left panel shows Western blot; right panel, fold increase over untransfected K562 cells. (B) p21 mRNA levels in SAR-expressing cells and vector controls detected by hybridization. (C) Total and phosphorylated ERK in SAR transfectants and K562 cells treated with HU for 3 days. (D) PI3 kinase protein in SAR-transfected and vector control K562 cells. Samples containing 50 μg protein were subjected to electrophoresis on Tris-glycine gels and to Western blotting with antibodies directed against either phosphorylated ERK, total ERK, or PI3 kinase. Error bars indicate standard deviation of the mean of 3 independent experiments.