Activation of p53 by doxorubicin and its impact on VCR-induced apoptosis. (A) Nuclear extracts of CEM cells simultaneously stimulated with doxorubicin and VCR as indicated were analyzed by Western blot. Histone H1 served as a loading control. (B) Parental CEM cells stably transfected with shRNA targeting p53 (shp53) or a control mock shRNA sequence were stimulated with doxorubicin and VCR simultaneously. *P < .05 (ANOVA). NS indicates not significant. Western blot was performed of total cellular protein. The concentrations of doxorubicin and VCR, measurement of apoptosis, presentation of data, and statistical analysis were performed as described in Figure 1A. d indicates doxo; V, VCR; h, hour; and co, unstimulated control cells.