Reexpression of CDK6 in c-Jun^Δ/Δ cells rescues the proliferative defect. (A) Immunoblot analysis of the enforced expression of CDK6 with a pMSCV-Cdk6-puro retrovirus in c-Jun^Δ/Δ cells. β-ACTIN served as the loading control. (B) [³H]-thymidine incorporation in c-Jun^fl/fl, c-Jun^Δ/Δ-puro, and c-Jun^Δ/Δ-Cdk6-puro cell lines (n = 3; 2-tailed t test, c-Jun^fl/fl vs c-Jun^Δ/Δ-puro, P = .0053; c-Jun^Δ/Δ-puro vs c-Jun^Δ/Δ-Cdk6-puro, P = .0029). (C) Cell-cycle profiles of c-Jun^fl/fl (n = 5) and c-Jun^Δ/Δ-Cdk6-puro (n = 4) cells gated on living cells. One representative set of data is depicted. (D) 1 × 10⁶c-Jun^fl/fl, c-Jun^Δ/Δ-puro, and c-Jun^Δ/Δ-Cdk6-puro p185^BCR-ABL–transformed cells were injected subcutaneously into Nu/Nu mice. Two independent cell lines for each cell type were injected into mice (2-tailed t test, c-Jun^fl/fl [n = 17] vs c-Jun^Δ/Δ-puro [n = 17], P < .0001; c-Jun^Δ/Δ-puro [n = 17] vs c-Jun^Δ/Δ-Cdk6-puro [n = 11], P = .0017).