Figure 6.

EIPA prevents maturation of tubulovesicular structures into multivesicular bodies and caveolin-1 entry to these structures. (A) EM images of internalized and clustered α2β1 integrin after 2 h with EIPA or U73122 or without drugs (CONTROL). Bars, 200 nm. The proportional distribution of α2β1 integrin in tubulovesicular versus multivesicular structures after EIPA treatment was counted from 150 to 200 structures. (B) Cells were labeled for caveolin-1 (green) and internalized α2β1 integrin (red) after 2 h. Drugs were added 30 min before the experiment. Colocalization between internalized integrin and endogenous caveolin-1 was calculated from 30 cells for each case from three independent experiments. Bars, 10 μm. (C) Immuno-EM labeling of caveolin-1 (5-nm protein A gold) and α2β1 integrin (10-nm protein A gold) after 2-h internalization in control cells or after EIPA treatment. Caveolin-1 was immunolabeled after fixation and permeabilization of the cells, whereas α2β1 integrin was immunolabeled on the plasma membrane before internalization. Arrows indicate some of the caveolin-1 labels in the sections. Bars, 200 nm.