SCF-induced phosphorylation of PP2A correlates with increased fetal hemoglobin during erythroid differentiation. CD34⁺ cells were cultured in EPO-containing medium for 6 days before the addition of SCF. (A) Cells were incubated with SCF (50 ng/mL) for the indicated times, and whole cell lysates (30 μg) were analyzed by immunoblot for phosphorylation of PP2A. (B) Cells were incubated with SCF (50 ng/mL) from day 6 to day 14, and total cell lysates (30 μg) harvested on the indicated culture days were analyzed by immunoblot for phosphorylation of PP2A, COUP-TFII, or fetal hemoglobin expression. The lowest panel shows the same blot stripped and reprobed with total β-actin antibody to confirm that similar amounts of protein extracts were analyzed in each lane. Representative immunoblots from 3 independent experiments are shown.