Diminution of ₂ promoter/enhancer function by PD98059. The constructs pCAT-Basic and p₂2592-CAT were transfected into uninduced K562 cells (□), K562 cells treated with PDB (40 nmol/L; ▪), and K562 cells treated for 15 minutes with PD98059 (50 μmol/L) before the addition of PDB (40 nmol/L; ⊠). Cotransfection with RSV-luciferase was used to control for transfection efficiency. After 48 hours of incubation, cell extracts were assayed. After normalization for transfection efficiency, CAT activity of the constructs was determined using thin-layer chromatography. The mean and standard deviation of CAT activity in uninduced K562 cells, PDB-induced K562 cells, or K562 cells treated with PD98059 and PDB was determined. CAT activity relative to the pCAT-Basic construct in uninduced K562, which was assigned a value of 1.0, is shown.