Western blot analysis of caspases -3,-8,-9 and cytochrome c in U937 cells treated with PTX, MG132 or PTX + MG132. U937 cells were cultured and treated with 8 mM PTX, 1 μM MG132, or PTX + MG132. After 24 hours, the cells were harvested and lysed. Equivalent amounts of individual lysates were placed on 10% SDS gradient polyacrylamide gels for electrophoresis and then were electrotransferred to Immobilon-P PVDF membranes. A representative study is shown and two additional experiments yielded similar results.