Figure 2.

ErbB2 is not endocytosed in nonstimulated cells. (A and B) Immunogold detection of ErbB2 in ultracryosections of SKBR3 cells (postembedding labeling) with the polyclonal antibody 2242 against the intracellular portion of the receptor and the mAb Sc-08 against the extracellular portion of the receptor. In both cases, ErbB2 is detected on protrusions but not in clathrin-coated pits (CP) or endosomes (EN). (C) Confocal images of cells stained with 2242 or Sc-08 in combination with the monoclonal anti-TfR antibody B3/25 or the polyclonal anti-TfR antibody 309i. Note that ErbB2 is only present on the cell surface and not seen in TfR-containing endosomes. Bars, 200 nm (A and B) and 5 μm (C).