Endocytosis inhibitors or competitors were prepared as 100X DMSO stocks and were added for a final concentration of 1% DMSO in all samples. Cells were treated with 5nM Streptavidin-AF647 and 500nM Angiopep-2 for 6h unless otherwise noted. Cells were trypsinized and resuspended in PBS + 1% BSA containing 1ug/mL propidium iodide for flow cytometry.