Lef1 delays apoptosis after inhibition of Notch1 signaling. E2A^−/− lymphoma lines 0531 (A) and 1.F9 (B) were infected with MigR1-Lef1 for 24 hours (□), divided in 2, and treated with DMSO (▩) or GSI (■). The percentage of cells expressing GFP was measured at the indicated time by flow cytometry. One of 2 experiments for 0531 and 1 of 3 experiments for 1.F9 are shown. P < .03, paired Student t test, for the percentage of GFP in DMSO versus GSI-treated Lef1-expressing cultures at 72 (0531) or 96 (1.F9) hours. (C) MigR1 and MigR1-Lef1–infected cultures were divided in 2 and treated with DMSO (light gray histogram) or GSI (black histogram); 48 hours later, expression of GFP (top row) or forward light scatter on GFP⁺ cells (bottom row) was measured by flow cytometry. (D) GFP⁺ cells were sorted from MigR1 or MigR1-Lef1–infected cultures and treated with DMSO or GSI for 18 hours prior to addition of BrdU and cell-cycle analysis. The percentage of cells in G₁ (light gray), S (white), G₂/M (dark gray) and sub-G₁ (black) phases of the cell cycle are represented. One of 2 experiments is shown.