Effect of proteinase K treatment in SKOV3 exosomes uptake. (A) Exos-CFSE (20 μg protein; green) or (B) SKOV3 cells were treated with 100 μg/ml proteinase K for 30 min. Uptake was determined after 4 h of incubation by flow cytometry analysis and compared with uptake of Exos-CFSE with no treatment (solid lines). Unlabelled SKOV3 cells (grey) were used as control for cell autofluorescence. Dashed lines represent Exos-CFSE uptake after proteinase K digestion. The results shown are representative of three independent experiments performed in duplicate.