Akt and ERK activation, and effect of MAPK inhibitors. (A-B) Relative level of total and phosphorylated Akt in extracts (40 μg protein per lane) obtained from untreated U-937 cells (Cont) and cells treated for the indicated time periods with 4 μMAs₂O₃ (A); and from cells treated for the indicated time periods with As₂O₃ and LY294002, alone and in combination (B). (C) Frequency of apoptotic cells (mean ± standard deviation of 4 determinations) in cultures treated for 24 hours with 4 μM As₂O₃, alone or with LY294002, either in the absence (-) or the presence of 10 μM SP600125 (SP) or 10 μM SB203580 (SB). (D) Relative level of total (t-ERK) and phosphorylated (p-ERK) ERKs in extracts (10 μg protein per lane) obtained from untreated cells and cells treated for the indicated time periods with As₂O₃ and LY294002, alone and in combination. All drugs were applied simultaneously. All other conditions were as in Figure 1.