Transferrin receptor expression in murine erythroleukemia (MEL) cells transfected with a plasmid encoding constitutively active STAT5A. MEL cells were transfected with a plasmid encoding constitutively active STAT5A and GFP or GFP alone. (A,C) Histogram from FACS analyses of gated GFP-positive cells. (A) Phospho-STAT5A levels in MEL cells. (C) Transferrin receptor (CD71) expression in MEL cells. Quantification of phospho-STAT5A (B) and Tfr1 levels (D) in GFP- and STAT5A/GFP-transfected cells. Representative data are from 1 of 3 individual experiments. Error bars represent SEM. *P < .05 compared with GFP-transfected cells.