A, HUVEC were untreated (shaded) or treated with TNF (10 ng/ml; dashed line), cycloheximide (2.5 μg/ml; solid line), or a combination of TNF plus cycloheximide (dotted line). Each treatment was performed in the absence of presence of zVADfmk (25 μM). Cells were harvested, incubated in PBS containing PI, and analyzed by FACS. The population percentage that was membrane-permeable and took up PI was determined from region M1 and illustrated in B. Ctl, control. C, HUVEC were treated as described in A, then the percentage of the population with hypodiploid DNA was determined by FACS. D, WT and IKKα−/− MEFs were either untreated (shaded) or treated with LTα1β2 (solid line) either alone or in combination with zVADfmk (25 μM) as shown. Cells were harvested, incubated in PBS containing PI, and analyzed by FACS. The membrane-permeable population percentage that took up PI was determined from region M1 and is shown in the histogram in panel E.