Figure 3.

DNA synthesis shows greater serum-induction and less rapamycin sensitivity in Myc null cells. Cells were arrested by confluence followed by serum starvation for 48 hours. Cells were then stimulated to re-enter the cell cycle with 10% fetal bovine serum in the presence of DMSO control, or rapamycin as described.¹¹³ Cells were then pulsed with tritiated thymidine for 2 hours, and harvested for scintillation counting as described.¹¹⁴ (A) Myc null (myc^−/−—HO15) and wild type (myc^+/+—TGR) cells stimulated with serum for 20 hours. (B) Increased sensitivity of Myc null cells to Rapamycin is independent of cell cycle position. Cells were arrested by confluence followed by serum starvation for 48 hours. Cells were stimulated to re-enter the cell cycle with 10% fetal bovine serum in the presence DMSO or rapamycin. The cells were then grown for the indicated times, pulsed with tritiated thymidine for 2 hours, and harvested for scintillation counting. Shown is the fold-reduction in thymidine uptake comparing the rapamycin treated samples to the DMSO treated control samples at each indicated time point for each cell type. (C) Same as in (A), above, except that cyclin D1 null (D) mouse embryonic cells, and their wild type counterparts, were used.