Figure 12.

Transferrin recycling is retarded by tau overexpression. Cells were seeded on cover slips and preincubated with TMR-labeled transferrin in serum-free medium for 2 h. Excess transferrin was removed and tau-stable and mock-transfected cells were fixed in methanol. Residual transferrin fluorescence was then quantitated and plotted (a). Note that, at early time points (7 min), the transferrin fluorescence in tau-stable cells is decreased by ∼10%, whereas in control cells 50% of transferrin is exocytosed in the same time interval. 300 cells were quantitated per time point and cell line. (b) Time course of the exocytosis of transferrin after equilibration of tau-stable and mock-transfected cells with fluorescently labeled transferrin. A significant decrease of exocytosed transferrin can be seen 5–10 min after start of the experiment in tau-stable compared with control cells. Fluorescent signals were normalized to total cell numbers in each experiment. Data represent averages of four independent experiments.