In Vitro Cell-Free Assay: Test compounds in aqueous solution were added at a volume of 10 microliters, to a reaction mixture comprising 10 microliters Assay Dilution Buffer (ADB; 20 mM MOPS, pH 7.2, 25 mM beta-glycerolphosphate, 5 mM EGTA, 1 mM sodium orthovanadate and 1 mM dithiothreitol), 10 microliters of substrate peptide (RRRDDDSDDD, dissolved in ADB at a concentration of 1 mM), 10 microliters of recombinant human CK2 (25 ng dissolved in ADB; Upstate). Reactions were initiated by the addition of 10 microliters of ATP Solution (90% 75 mM MgCl2, 75 micromolar ATP dissolved in ADB; 10% [gamma-33P]ATP (stock 1 mCi/100 ul; 3000 Ci/mmol (Perkin Elmer) and maintained for 10 minutes at 30 degrees C. The reactions were quenched with 100 microliters of 0.75% phosphoric acid, then transferred to and filtered through a phosphocellulose filter plate (Millipore). After washing each well 5 times with 0.75% phosphoric acid, the plate was dried under vacuum for 5 min.
Modulation of Endogenous Assay: The human leukemia Jurkat T-cell line was maintained in RPMI 1640 (Cambrex) supplemented with 10% fetal calf serum and 50 ng/ml Geutamycin. Before treatment cells were washed, resuspended at a density of about 106 cells/milliliter in medium containing 1% fetal calf serum and incubated in the presence of indicated mounts of drug for two hours. Cells were recovered by centrifugation, lysed using a hypotonic buffer (20 mM Tris/HCl pH 7.4; 2 mM EDTA; 5 mM EGTA; 10 mM mercaptoethanol; 10 mM NaF; 1 uM Okadaic acid; 10% v/v glycerol; 0.05% NP-40; 1% Protease Inhibitor Cocktail) and protein from the cleared lysate was diluted to 1 microgram per microliter in Assay Dilution Buffer (ADB; 20 mM MOPS, pH 7.2, 25 mM β-glycerolphosphate, 5 mM EGTA, 1 mM sodium orthovanadate and 1 mM dithiothreitol). To 20 microliters of diluted protein was added 10 microliters of substrate peptide (RRRDDDSDDD, dissolved in ADB at a concentration of 1 mM) and 10 microliters of PKA Inhibitor cocktail (Upstate).