EPO promotes STAT5 signaling and increases Bcl-XL expression in ETV6-RUNX1⁺ mouse cells. (A) EMSA assay. Uninduced and ETV6- RUNX1-expressing BaF3 1/27 cells were incubated with 20 U/mL EPO for 2 days. Equal amounts of nuclear extracts were incubated with a γ-³²P labeled β-casein promoter probe to analyze EPOR signaling through STAT5 DNA binding activity. In cells expressing ETV6-RUNX1, EPO triggers activated STAT5 complexes (marked) compared with non–ETV6-RUNX1–expressing cells. S indicates supershift (see also supplemental Figure 4). (B) Quantitative PCR analysis of Bcl-XL expression in uninduced (1/27) and ETV6-RUNX1–expressing BaF3 1/27 cells (1/27M) grown in the presence of 20 U/mL EPO for 4 or 10 days, respectively. (C) Western blot analysis of Bcl-XL expression in uninduced and ETV6-RUNX1–expressing BaF3 1/27 cells grown for 2 days in the presence or absence of IL-3 or EPO. (D) Quantitative PCR analysis of Bcl-XL expression in bone marrow Sca1⁺ cells isolated from wild-type and ETV6-RUNX1⁺ transgenic mice (n = 6).