TFRC and breast carcinoma: To study the effect of USMB on endocytosis, we treated retinal pigment epithelial cells (ARPE-19 cells, RPE henceforth) or MDA-MB-231 breast cancer cells with USMB and measured the impact on the membrane traffic of TfR (to measure clathrin-mediated endocytosis), and horseradish peroxidase or fluorescent dextran uptake (to measure fluid-phase uptake).