The final stage in autophagy pathway is the maturation of autolysosomes and degradation by lysosomal hydrolases. To visualize and quantify lysosomal proteolytic activity, we employed a fluorescent probe DQ Red BSA.35 The probe was nearly undetectable in control cells, dequenching of red fluorescence was observed in cells under nutrient starvation, indicating that starvation stimulates lysosomal activity. Compared with the NC-transfected cells, starvation-induced lysosomal proteolytic activity was markedly reduced in miR-20a-transfected MDA-MB-231 and MCF7 cells. Reduction of lysosomal proteolytic activity was more pronounced in MCF7 cells because MCF7 cells had higher amounts of miR-20a after transfection (Figures 3e and f).