p21-IRS does not disrupt the mitochondrial inner membrane. U937 cells were incubated with medium, p21-IRS, or staurosporine, and Δψm was determined. (A) TMRM fluorescence of cells treated with medium (gray fill), staurosporine (black line), or p21-IRS (dotted line). (B) JC-1 fluorescence. The percentage of cells in each quadrant is shown. (C) p21-IRS does not affect intracellular ATP. U937 cells were treated with p21-IRS or rotenone for 1 hour or 3 hours and intracellular ATP determined. The results shown were the average of 3 replicas. (D) Overexpression of Bcl-2 could not rescue cells from p21-IRS–induced cell death. Jurkat cells overexpressing Bcl-2 were incubated with p21-IRS, staurosporine, or CH-11 for 3 hours, 4 hours, or overnight, respectively, and the percentage of apoptotic cells determined. Results are the average of 3 experiments. (E) The caspase inhibitor Z-VAD does not affect p21-IRS–induced apoptosis. Cells were preincubated with Z-VAD prior to the indicated treatment.