Figure 2.

Apical and basolateral endocytosis in RhoAWT, RhoAV14, or RhoAN19 cells. [¹²⁵I]IgA was bound to the apical (A, C, and E) or basolateral (B, D, and F) surface of the cells for 60 min at 4°C. The RhoAWT (A and B), RhoAV14 (C and D), or RhoAN19 (E and F) cells, cultured in the presence of 20 ng/ml DC (+DC) or 0–5 pg/ml DC (−DC or 5pg/ml DC), were washed and then incubated at 37°C for the times indicated. Medium was collected, and the cells were then rapidly cooled on ice. [¹²⁵I]IgA was stripped from the cell surface by a sequential treatment of trypsin and acid at 4°C, and the filters were then cut out of their holders. Total [¹²⁵I]IgA initially bound to the cells included ligand released into the medium, ligand stripped from the cell surface with trypsin and acid, and cell-associated ligand not sensitive to stripping (endocytosed). Shown is the percentage of total ligand endocytosed (mean ± SEM; n ≥ 4). Statistical significance was assessed with the use of a t test. Values for which p < 0.05 are marked with asterisks. Endocytosis values from filters that were never warmed to 37°C were subtracted from the endocytosis values of cells that were allowed to internalize ligand at 37°C.