Ectopic SOX4 expression reduces PU.1 mRNA levels in vitro and in vivo. (A) PU.1 mRNA levels were analyzed by quantitative RT-PCR in HL 60 cells electroporated with pIRES2-GFP (Vector) or pIRES2-GFP-SOX4 (SOX4) constructs, and normalized to β-ACTIN mRNA levels. Four independent electroporation experiments were performed and analyzed (P = .019). (B) Quantitative RT-PCR analysis of Sfpi1 mRNA levels in Sox4-induced leukemic and preleukemic spleen tissues versus normal spleens and Lin⁻ cells (fold change). Leukemic spleens: #1852 to #7588 (Sox4/WT tumors, dark gray) and #7612 to #9459 (Sox4/Sfpi1 tumors, black); normal spleens: wild-type spleens (1 and 2, brown), preleukemic spleens: #9513 and #4920 (Sox4/WT group, gray), and Neo/Sfpi1 spleens (#4648 and #3776, light brown). Sox4/WT tumors versus Sox4/Sfpi1 tumors (P = .045). Normal spleen versus Sox4/WT preleukemic spleen (P = .044). Normal spleen versus Neo/Sfpi1 spleens (P = .003).