Fig. 4. H2O2 requires a time lag to induce the SAPK-suppressing effect. The U937 cells were pre-exposed to 0.05 mM H2O2 for the indicated periods, followed by a challenge with 1 mM H2O2 either for 15 minutes for the analysis of the MKK4 and MKK7 activities, or for 30 minutes for SAPK (top). The intensity of each band was quantified by using Tina 2.0 software. The challenge-induced fold stimulation of each kinase was determined over its basal level obtained from the cells that did not receive H2O2 in the whole incubation (bottom). The values are the mean of three separate experiments. The standard deviations were routinely less than 15% of the means. Circle, SAPK; square, MKK4; triangle, MKK7.
