SCF-dependent inhibition of Epo-induced SKT6 cell hemoglobinization. (A and B) SKT6-EE372 cell hemoglobinization is induced by Epo and EGF, but not by SCF. SKT6-EE372 cells were exposed to Epo (20 U/mL), EGF (25 ng/mL), or SCF (100 ng/mL) and, at 72 hours of culture, hemoglobin-positive cells were stained with DAF and scored (>200 cells per sample). Graphed (A) are mean frequencies of hemoglobin-positive cells ± standard deviation (n = 3). Also analyzed by Western blotting were levels of globin expression in Epo-, EGF-, and SCF-exposed SKT6 EE372 cells (B). (C) Concentration-dependent SCF-inhibition of Epo-induced SKT6 cell hemoglobinization. SKT6 cells were exposed for 8 hours to SCF at the concentrations indicated and subsequently were stimulated with Epo (2 U/mL) for 72 hours. As controls, SKT6 cells also were exposed independently to either SCF (100 ng/mL) or Epo (2 U/mL). Hemoglobin-positive cells were stained with DAF, and positive cells were scored (> 200 cells per sample). Mean frequencies of DAF-positive cells ± standard deviations (n = 3) are illustrated.