TDD specifically inhibits CME in a concentration-dependent manner. (A) Regulation of TDD expression was achieved by adjusting the Tet concentration in the Tet-off system. 350,000 ARPE cells in a six-well plate were infected with 12 µl TDD recombinant adenovirus and 12 µl tTA recombinant adenoviruses in the presence of the indicated concentrations of Tet. (B and C) Effects of increasing levels of TDD expression on the levels of surface bound TfnR (B) and the rate and efficiency of TfnR uptake (C) assayed in adenovirus-infected ARPE cells in the presence of the indicated concentrations of Tet. (D) Effects of TDD expression (0 ng/ml Tet) on Biotin-Tfn recycling of a 10- or 30-min pulse in adenovirus-infected ARPE/HPV cells with or without Tet. (E and F) Effect of TDD expression (0 ng/ml Tet) on the fluid phase uptake of HRP (E) or CIE (F) of CD44 or CD59 in ARPE/HPV cells. [Tet] = 20 ng/ml in D–F. Data ± SD are from n = 4 replicates. N.S., not significant.