Culture, transfection and lysis of COS7 cells COS7 cells were cultured in Dulbecco's modified Eagle medium supplemented with 10% fetal calf serum and 2 mM L-Glutamine. Cells were transfected with human caspase-6 cDNA with a C-terminal DDK tag using the Fugene reagent (Roche) according to manufacturer's instructions. Cells were harvested 0-24 h after transfection by trypsinization. Cell pellets were lysed in 50 mM HEPES pH 7.4, 100 mM NaCl, 1% Igepal, 1 mM EDTA and 10% glycerol with 4.2 mM Pefabloc and 'Complete' protease inhibitor cocktail (Roche) on ice, and protein concentrations were determined in the cleared lysates after centrifugation.