LIP positively regulates Myc transcription in HSPCs. (A) Expression of Myc, which encodes c-Myc, in EML cells retrovirally transduced with control or LIP expression vector (n = 5 per group). In each experiment, the Myc level in the control vector-transduced cells was set to 1, and the values from 5 independent experiments were statistically analyzed using the 2-tailed paired Student t test. (B) Myc expression in control vector- and LIP-transduced LT-HSCs (CD150⁺CD48⁻ KSL cells) obtained from recipients 3 weeks after transplantation (n = 3, technical replicates, representative of 2 independent experiments). mRNA levels were normalized against that of Gapdh. (C) Myc expression in WT and Cebpb^−/− LT-HSCs (CD150⁺CD48⁻ KSL cells) 36 hours after transplantation. mRNA levels were normalized against that of Gapdh (n = 4 biological replicates of 500-1000 pooled cells per group in 2 independent experiments). (D) Relative Myc expression in LT-HSCs obtained from WT- or Cebpb^−/−-reconstituted mice at steady state (day 0) and after 5-FU administration (days 3 and 8) (n = 4 biological replicates of 500-1000 pooled cells per group in 2 independent experiments for days 3 and 8; n = 3 for day 0). (E) ChIP-qPCR analysis using EML cells engineered to express C/EBPβ-estrogen receptor fusion. Data show enrichment of C/EBPβ at the E3 enhancer region of Myc at each time point after treatment with 4′-hydroxytamoxifen. (F) ChIP-qPCR analysis using NIH3T3 cells transduced with control vector or expression vector for LIP, LAP, or LAP* fused to the FLAG tag. FLAG-tagged C/EBPβ isoforms were enriched at the E3 enhancer region of Myc. (G) EML cells were retrovirally transduced with control, LIP, LAP, or LAP* vector, and the transduced cells were purified and subjected to qualitative RT-PCR 48 hours after transduction. Data are presented as means ± SD (n = 3). *P < .05; **P < .01 (determined by the 2-tailed Student t test).