Notch-mediated growth inhibition/apoptosis occurs in human pre-B ALL cell lines. (A) Growth inhibition in 4 pre-B ALL cell lines is seen after retroviral transduction with intracellular Notch1 (ICN1). This graph shows the percentage of GFP⁺ (ICN1 transduced) cells versus days from transduction (normalized to day 2). All cell lines were also transduced with the control vector MigR1 (representative control shown). The P values were from repeated-measures ANOVA. (B) By using a subclone of the JM-1 pre-B ALL cell line stably transduced with tamoxifen-inducible ER-ICN1 retrovirus, apoptosis is shown by annexin V staining, comparing tamoxifen exposure to ethanol control. (C) Hes1 expression was measured by RT-PCR in the tamoxifen-induced cells from panel B. GAPDH was used as a cDNA control. A representative image from 2 experiments is shown.