Fig. 6. C/EBPβ directs differentiation of a multipotent hematopoietic cell line. (A) β-Estradiol induces nuclear localization of the C/EBPβ-ER fusion protein followed by granulocytic differentiation. (i) Stably transfected K562 cells were subjected to immunofluorescence using an anti-C/EBPβ antibody after treatment for 24 h with vehicle only (left panel) or β-estradiol (right panel). Cell maturation was evaluated by morphology (ii) and by NBT reduction assay (iii) following 48 h of treatment with vehicle only (left panel) or β-estradiol (right panel). (B) Cell surface expression of CD11b was determined by FACS. Cells transfected with empty ER vector or with C/EBPβ-ER were treated with vehicle only or with β-estradiol for 72 h. (C) RNA expression of the G-CSF receptor (upper panel) or C/EBPε (lower panel) was assessed using northern blot analysis. As indicated in the figure, cells infected with empty vector (ER) or C/EBPβ-ER were treated for different times with β-estradiol.