Dependence of p53 on the response to adriamycin is observed in both p53 siRNA treated cells and in untreated cells with low levels of p53. A. DLD-1 colon carcinoma cells treated with increasing doses of adriamycin as indicated in the figure. Cells were treated with an siRNA targeting GFP (blue) or an NTC (red). Cells not treated with adriamycin were treated with DMSO. B. p53 levels following siRNA treatment. An siRNA that targets p53 (blue) or a non-targeting control (red), are shown. siRNA treatments as described in A. C. The fraction of cells within each concentration of adriamycin for the NTC treated sample is shown. The fractions of cells with the highest and lowest 20% of the range of p53 levels (burgundy and teal, respectively) in the untreated sample are shown at each concentration of adriamycin. The range of p53 levels in each bin is 0–200 FU for the lowest bin and 800–1000 FU for the highest bin. D. p53 levels following p53 or NTC siRNA treatment for 48 hours, and adriamycin treatment for 6 hours. siRNA treatments as described in A E. Levels of γ-phosphorylated histone H2A-x levels as a function of p53 levels per cell and adriamycin treatment for 6 hours. Adriamycin doses are as shown in other panels, in a color range from yellow (no adriamycin) to orange (1.222 μM adriamycin). Each data point represents 200–400 cells. F. Same as (E), except cells were not treated with an NTC siRNA. Adriamycin concentrations are indicated in the panel.