Repression of Erg by TFAP4 in MYC⁺ developing B cells is required for tumor suppression. Expression of Erg in pretransformed B220⁺ IgM⁻ pro/pre-B cells from Eμ-Myc Tfap4^+/+ mice and Eμ-Myc Tfap4^+/− mice (A) and pro/pre-B tumor cells from Eμ-Myc Tfap4^+/+, Eμ-Myc Tfap4^+/−, and Eμ-Myc Tfap4^−/− mice (B), as determined by RNA sequencing. (C) Colocalization of TFAP4 binding and accessible chromatin in the Erg locus (red vertical lines indicate exons; black horizontal lines represent introns) in developing B cells, pre-B cells (B220⁺ IgM⁻), pro/pre-B cells (CD19⁺); Fr.BC (CD19⁺ IgM⁻ CD43⁺ CD24⁺), and Fr.D (CD19⁺ IgM⁻ CD43⁻ B220⁺). Y-axes show tag counts in 10⁷ mapped reads. The Gene Expression Omnibus accession number for each dataset is indicated. (D) Expression of Tfap4, Myc, and Erg mRNA in developing B cells from the Immunological Genome Project database. (E) Sorting strategy for MYC⁺ and MYC⁻ pro-B cells in Myc^+/MYC-GFP protein reporter mice (far left, near left, and near right panels).²¹ Expression of Erg mRNA in MYC⁺ vs MYC⁻ pro-B cells (far right panel). mRNA expression measured by quantitative reverse transcription polymerase chain reaction was normalized to Hprt1. (F) Expression of Erg in MYC⁺ pro-B cells from Tfap4^+/+, Tfap4^+/−, and Tfap4^−/− mice harboring the MYC-GFP reporter. (G) Expression of Erg in CD19⁺ IgM^– pro/pre-B cells from Eμ-Myc^–Tfap4^+/+ (non-Tg), Eμ-Myc Tfap4^+/+, Tfap4^+/− and Tfap4^−/− mice prior to tumor development. (H) Survival of Tfap4-haploinsufficient Eμ-Myc mice with restricted Erg expression (Cd79a^icre/+ [n = 20], median survival, 131 days; Erg^F/+ Cd79a^icre/+ [n = 8], median survival, 93.5 days; Tfap4^F/+ Erg^F/+ Cd79a^icre/+ [n = 17], median survival, 94 days; Tfap4^F/+ Cd79a^icre/+ [n = 9], median survival, 62 days). (I) Frequencies of immature (Rag1 and/or VpreB1–expressing and surface Ig⁻) and mature (Rag1 and VpreB1–nonexpressing and surface Ig⁻ or Ig⁺) B-cell tumors in Eμ-Myc mice with the indicated genotypes (Eμ-Myc Tfap4^F/+Cd79a^icre/+, n = 3; Eμ-Myc Tfap4^F/+Erg^F/+Cd79a^icre, n = 6). *P < .05, **P < .01, ***P < .001, ****P < .0001, unpaired t test (A,E), one-way ANOVA with Tukey’s post hoc test (B,F-G), log-rank test, adjusted for multiple comparisons (H). ATAC-seq, assay for transposase-accessible chromatin with sequencing; ChIP-seq, chromatin immunoprecipitation sequencing; Fr., fraction; Imm, immature; Lg, large; ns, no statistical significance; RNA-seq, RNA sequencing; RPKM, reads per kilobase of transcript, per million mapped reads; Sm, small; TSS, transcription start site; α-, anti-.