FIGURE 7.

MRP1 and GST P1-1 cooperate in preventing the cytotoxic activity of NO. A, panel i, co-expression of both MRP1 and GST P1-1 (but not GST A1-1 or GST M1-1) is required for maximum resistance against NO as GSNO. WT Vector cells, VP Vector/Vector* cells, and WT/VPα, VPμ, or VPπ cells were incubated with GSNO (0.02–10 mm) for 72 h at 37 °C, and proliferation was assessed. The expression of both GST P1-1 and MRP1 in VPπ cells leads to maximum resistance to the cytotoxicity of GSNO. Panel ii, co-expression of MRP1 and GST P1-1 in VPπ cells leads to greatest sensitivity to GSNO when cells were preincubated with BSO (0.1 mm) for 20 h at 37 °C and then incubated with GSNO (0.02–10 mm) for 72 h at 37 °C; proliferation was assessed after these experiments. B, the cytotoxic effect of GSNO and MRP1 inhibitors on cell proliferation in MRP1 hyper-expressing cells in the absence or presence of GST P1-1. The WTπ and VPπ cells and their relevant vector control cells were incubated with either GSNO (0.02–10 mm) or MK571 (20 μm) and GSNO (0.02–10 mm) (panel i) or GSNO (0.02–10 mm) or sulfinpyrazone (2 mm) and GSNO (0.02–10 mm) (panel ii) for 72 h at 37 °C, and proliferation was assessed. C, the effect of GST inhibitors in cells hyper-expressing MRP1 in the absence or presence of GST P1-1. The WTπ and VPπ cells and their relevant vector control cells were incubated with either GSNO (0.02–10 mm) or ethacrynic acid (200 μm) and GSNO (0.02–10 mm) (panel i) or GSNO (0.02–10 mm) or dicumarol (1.25 mm) and GSNO (0.02–10 mm) (panel ii) for 72 h at 37 °C, and proliferation was assessed. Results are mean ± S.D. (3–5 experiments). ***, p < 0.001.