(a) Cellular model system used for the genome-wide siRNA screen. 21,121 individual genes were knocked down using siRNAs and the effects on ADAM17-mediated shedding of AP-HB-EGF were measured by quantifying AP cell-surface staining after PMA stimulation. (b+c) siRNA-transfected AP-HB-EGF HT1080 (b) or AP-HB-EGF HeLa (c) cells were PMA-stimulated, and the cell medium analysed for AP activity. The fold change in AP-HB-EGF release was calculated by setting the unstimulated negative control for each experiment to 1, then normalizing the other raw data to this value, and finally calculating the average of all individual experiments. Data in (b) were compiled from 6 individual experiments and in (c) from 3 individual experiments, each performed in triplicate. (d) AP-HB-EGF MCF-7 cells were siRNA-transfected and stimulated with PMA (left-hand panel) or ionomycin (right-hand panel). Conditioned medium was analysed for AP activity as in (b+c). Data were compiled from 4 individual experiments, each performed in triplicate. In all cases, knockdown was confirmed by western blot. On blots, # denotes a non-specific band. Graphs show mean values ± standard error of the mean (SEM). Data were analysed by ANOVA. **p<0.01, ***p<0.001, ****p<0.0001.