KLF4 is expressed at low levels in B cells transformed by p190 BCR/ABL compared with untransformed B cells. (A) cDNA was prepared from purified resting splenic B cells, splenic B cells activated by anti-IgM, B220⁺IgM⁻ precursor cells from the bone marrow of wild-type mice, and BCR-ABL–transformed pre-B cells. Real-time quantitative PCR was performed, expression was normalized to β-actin, the value for BCR-ABL–transformed cells was set to 1, and fold-increase was calculated. Data are representative of at least 4 experiments. *P < .02 relative to the BCR-ABL–transformed cells. Error bars indicate standard deviation (SD). (B) Immunoblots were prepared with lysates from indicated cell preparations. The left blot was probed with rabbit anti-KLF4,²⁴  and the right blots with rabbit anti-KLF4 from Santa Cruz Biotechnology. β-Actin was used as a loading control. v-Abl and BCR-ABL indicate transformed pre-B-cell lines; Imat, 4 hours treatment with imatinib (10 μM), the ABL kinase inhibitor; KLF4⁺, v-Abl cells infected with MIC-KLF4 and sorted for hCD4 24 hours later. The blot on the far right shows cells treated with subtoxic concentrations of imatinib for 24 hours, with sorted KLF4⁺ infected cells used as a positive control. (C) RNA-expression data from the Oncomine microarray database was compiled for different B-cell malignancies and the normal tissue control for that study, either germinal center B cells or tonsil tissue. Numbers on the y-axis represent the number of standard deviations from the median expression value from thousands of genes tested in each microarray experiment and the P values indicate the significance between the normal and cancer tissue for the respective study (*P < .05, **P < .001). (D) Oncomine data derived from a study⁴¹  comparing peripheral blood CD19⁺ B cells, either resting or activated for 6 hours, total germinal center (GC) cells, a large panel of diffuse large B-cell lymphomas, and chronic lymphocytic leukemias. CD19+GC refers to the average of all nontransformed B-cell samples in the study.