c-Jun^Δ/Δp185^BCR-ABL–transformed cell lines demonstrate a proliferative defect. (A) [³H]-thymidine incorporation of fetal liver–derived c-Jun^fl/fl (n = 3) and c-Jun^Δ/Δ (n = 4; 2-tailed t test, P = .0142) p185^BCR-ABL-transformed cell lines. (B) 1 × 10⁵p185^BCR-ABL-transformed c-Jun^fl/fl (n = 3) and c-Jun^Δ/Δ cells (n = 3) were plated and total cell numbers were determined after 48, 96, and 144 hours. (C) Cell-cycle profiles of c-Jun^fl/fl (n = 5) and c-Jun^Δ/Δ (n = 4) cells (2-tailed t test, G₁ phase, P = .0333; S phase, P = .0173) gated on living cells. One representative set of data is depicted. (D) Tumor weights of Nu/Nu mice that were subcutaneously injected with 1 × 10⁶c-Jun^fl/fl and c-Jun^Δ/Δ leukemic cells. Three independent cell lines for each cell type were injected into 9 mice (2-tailed t test, P = .0007). (E) Injection of c-Jun^fl/flp53^−/− (n = 11) and c-Jun^fl/flCD19-Cre^+/−p53^−/− (n = 7) newborn mice with a replication-deficient Ab-MuLV–encoding retrovirus resulted in B-lymphoid leukemia/lymphoma (mean survival, 31 vs 44 days in c-Jun^fl/flp53^−/− and c-Jun^fl/flCD19-Cre^+/−p53^−/− mice, P = .0213).