Celastrol arrests cell cycle at G0/G1 phase in U937. Following the treatment, cells were incubated with RNase A and PI, cell cycle was assayed by FCM. A: Panel of flow cytometric histograms showing DNA content in samples treated with various doses of celastrol. X-axis represents DNA content and Y-axis shows cell number. B: Percentages of sample cells in each cell cycle phase. The dose-effects of celastrol on the percentages of U937 cells at each phase of cell cycle are shown. Each value is found as the mean of three independent experiments.