Reduced expression of c-myc and E2A in the pre-B cells from mb.1-Rap1A17 Tg mice and restoration of IL-7 response by c-myc. (A) BM B220⁺ cells from Rap1A17^f (□) and mb.1-Rap1A17 ( and ■) Tg littermates were infected with empty retrovirus (pMX or pMC), pMX-CA Stat5a, pMC-bcl-2, or pMC-CA PI3K and cultured in the presence of IL-7. The cells were harvested on days 1 and 5, and the numbers of GFP⁺ B220⁺ cells were assessed by flow cytometric analysis. Fold increases (D5/D1) in the GFP⁺ B220⁺ cell numbers are indicated. Similar results were obtained in 2 independent experiments, and the means are indicated. (B) B220⁺ CD25⁺ cells were isolated from the BM of Rap1A17^f (□) and mb.1-Rap1A17 (■) Tg littermates, RNAs were extracted immediately, and quantitative RT-PCR was performed for the indicated genes. The means and SEs of the relative expression in the cells from mb.1-Rap1A17 to those from Rap1A17^f littermates (3 mice each) are indicated. (C) B220⁺ cells enriched from the BM of Rap1A17^f (□) and mb.1-Rap1A17 (■) Tg littermates were infected with empty MIG or MIG containing c-myc, and cultured in the presence of IL-7. The means and SEs of fold increases in the GFP⁺ B220⁺ cell numbers in 3 independent experiments are indicated. (D) The 2E8 cells were infected with empty MIG (□) or MIG containing Rap1A17 (■), and the sorted GFP⁺ cells were starved for IL-7 for 24 hours followed by the restimulation with IL-7. On day 1, the cells were lysed and immunoblotted with the indicated antibodies (left). Relative signal intensities are shown. The fold increases of the cells to the original input were also determined on days 3 and 7 (right). The means of 2 independent experiments with similar results are shown.