Inhibition of Notch1 signaling inhibits survival of E2A^–/– lymphomas. (A) E2A^–/– lymphoma lines 0531, 1.F9, and 0714 and the Notch1-deficient p53^–/– lymphoma 16610D9 were treated with GSI or vehicle (DMSO), and the number of viable cells was determined every 24 hours. Relative viability is the number of viable cells (GSI)/number of viable cells (DMSO) × 100. (B) Relative viability of Notch1-expressing p53^–/– lymphoma lines treated with GSI or DMSO. (C) Lymphomas were treated with GSI or vehicle (DMSO) starting 24 hours after infection with MigR1 (▦) or MigR1-ICN (▪) virus. Number of viable cells was determined 48 hours later. Infection efficiency was greater than 90% for all populations. (D) 16610D9 (♦), 0531 (•), 1.F9 (▴), and K052FA2C1 (▪) lines were infected with MigR1 (open symbols) or MigR1-DNMAML (filled symbols), and the percentage of cells expressing GFP was determined every 24 hours by FACS. Relative GFP is the percentage GFP⁺ divided by the percentage GFP⁺ at 24 hours after infection. Infection efficiency for each line was 60% to 80%. (E) MigR1-infected cells (▦) and MigR1-DN MAML–infected cells (▪) were incubated with DHE for 30 minutes starting 48 hours after infection. The percentage of GFP⁺ cells demonstrating increased fluorescence staining with DHE is shown.