FIG. 1.

A short pulse of either standard or endosomal EGFR signaling is insufficient to stimulate cell proliferation. For standard treatment, MDCK and BT20 cells were plated at 10,000 per coverslip and serum starved for 36 h. Cells were then stimulated for various times with either FBS (10%), EGF (100 ng/ml), or endosomal EGF treatment (see Materials and Methods) in the presence of 25 μM BrdU, after which unbound ligand was removed, and cells were incubated in starvation medium. At 18 h, cells were fixed and assayed for BrdU incorporation.