DNA damage–induced growth arrest of IL-3–treated cells is correlated with a lack of IL-3 induced Akt activity.

(A, B) 32D-Akt (○) or 32D-Akt(KM) (●) cells were cultured over a range of IL-3 concentrations. Percentage of S-phase cells in γ-IR–treated cultures versus nonirradiated cultures was determined, and the fold reduction in S phase was calculated (S−γ/S+γ) (A). Alternatively, the percentage of G2/M cells in the γ-IR–treated versus the nonirradiated cultures was determined, and the fold increase in G2/M was calculated (G2+γ /G2−γ) (B). (C) 32D-Akt or 32D-Akt(KM) cells were left unstimulated (−) or were stimulated with the indicated concentration of IL-3 for 8 minutes. Akt catalytic activity was assayed from cell lysates in an in vitro kinase assay (see “Materials and methods”). Alternatively, whole cell lysates were Western blotted with anti–phospho-Stat-5 (α P-STAT5) or anti–phospho-Erk (α P-Erk) antibodies. As a control for loading, lysates were probed with anti-Erk2 (α Erk) antiserum.