Apoptosis of C1498 cells in response to PS-341 plus TRAIL. C1498 cells were incubated with PS-341 at 0, 5 nM, or 20 nM for 2 hours prior to the addition of TRAIL (500 ng/mL). After a further 16 hours, cell death was estimated by FACS analysis after Annexin V and propidium iodide staining as described in “Materials and methods.” Percentage of cells in each quadrant is shown. Viable cells are in lower left quadrant.