GSTπ expression and activity. (A) Relative GSTπ levels in extracts (10μg protein per lane) obtained from untreated cells (Cont) and cells treated for the indicated time periods with LY294002 and As₂O₃, alone and in combination. As₂O₃ was used at 4 μM in the case of U-937 and HL-60, and at 2 μM in the case of NB4 cell cultures. (B) GSTπ activity in untreated U-937 cells and cells subjected for 24 hours to the same treatments as in panel A. The results (mean ± standard deviation of 3 determinations) are expressed in relation to untreated cells (main value, 44.5 ± 6.9 nmol/mg protein/min), which received the arbitrary value of one. All other conditions were as in Figure 1.