Inhibition of cathepsin B activity reduces degradation of DQ-collagen IV by SUM149 3D cultures. SUM149 cells were grown as 3D reconstituted basement membrane overlay cultures containing DQ-collagen IV in the presence of either DMSO (vehicle control) or 10 μM CA074. Confocal Z stack images were captured and used to generate 3D reconstructions (see legend for Figure 2 for detail) [see Additional files 3 and 4]. (a) Representative 3D reconstructions of DQ-collagen IV degradation products (green), SUM149 nuclei (stained with Hoechst 33342, blue) and corresponding DIC images (insets). (b) Corresponding intensity map (red being most intense and blue least intense) of DQ-collagen IV degradation products. Magnification, 40×. (c) Quantification of proteolysis in the entire volume of 3D structures measured as the average integrated intensity of fluorescence per cell and expressed as percent control. Results from three independent experiments are presented as mean ± standard deviation; *, P < 0.02.