KLF4 overexpression inhibits propagation of B-lymphoid cell lines and blocks transformation of pre-B cells by BCR-ABL. (A) BCR-ABL–transformed pre-B cells, v-Abl–transformed pre-B cells, BaF/3^p210 cells, A20, M12, or 70Z/3 cells were transfected or transduced with retroviral vectors including empty vector (MIT or MIC), KLF4(ΔTA) (mutant lacking transactivation domain), KLF4(ΔDBD) (lacking DNA binding domain), or KLF2, a closely related transcription factor. The percentage of marker-positive cells was determined 24, 48, and 84 hours after infection. Data were normalized to the percent positive at 24 hours, which was set at 100% for each virus. All graphs depict the mean plus or minus the standard deviation (SD) of 3 to 5 experiments. (B) A colony formation assay using MMTV-tTA/TRE-KLF4 double transgenic or control bone marrow, transformed with BCR-ABL and incubated with or without DOX. Colonies were scored after 7 days (**P < .01). Data are representative of 5 experiments. (C) Bone marrow from indicated mice was grown in the presence of IL-7 for 5 days treated with or without DOX (“D”), and 1 × 10⁶ cells were immunblotted for myc-tagged KLF4 and β-actin as a loading control. 293T cells transfected with myc-tagged KLF4 were used as a positive control. (D) Bone marrow from indicated mice maintained with or without DOX was stained to determine percentages of progenitor IgM⁻ B cells (pre-B cells: IgM⁻, B220⁺, CD43^low; pro-B cells: IgM⁻, B220⁺, CD43^int) and then analyzed by FACS. Cntrl indicates nontransgenic littermates. Results are representative of 5 sets of mice.