Figure 2.
A specific level of MYC expression correlates with proliferation, death, and cell size. A, MYC-expressing tumor cells grown in tissue culture were treated in culture with different concentrations of doxycycline (0.01–20 ng/mL). MYC expression was analyzed by Western blot. The expression of the MYC target genes odc and cyclin D1 are also shown. B, cells that express decreasing levels of MYC have lowered growth rates. Cells were plated at the density of 0.2 × 106/mL and counted every 6 h. C, cells with decreasing levels of MYC have lowered rates of proliferation and arrest when cells express a threshold level of MYC (◆). Cells were treated with BrdUrd for 1 h in the tissue culture medium and analyzed for BrdUrd incorporation by FACS using an anti-BrdUrd antibody. ●, cells with decreasing levels of MYC increase the level of cell death at the threshold level of MYC expression. Apoptosis was measured by FACS for the incorporation of Annexin V and 7AAD. Cells that incorporated both Annexin V and 7AAD were considered as undergoing apoptosis. D, cells with decreasing levels of MYC cease to divide and decrease in size. Cell numbers were counted in culture and cell size was measured using forward scatter by flow cytometry.