FIG. 8.

The role of Erk and PI3K activation in cell proliferation induced by two pulses of EGFR signaling in BT20 and MDCK cells. (A) Effect of wortmannin and U1026 on cell proliferation induced by two pulses of EGFR signaling from both standard and endosomal treatments. Cells were treated discontinuously at 0 h and again at 8 h with surface EGF (EGF) or endosome EGF (endo) pulses. The cell proliferation assay is described in Materials and Methods. W, treatment with wortmannin (100 nM); U, treatment with U1026 (10 μM). (B and C) Immunoblot analysis of the inhibition of Erk (B) and Akt (C) phosphorylation by U1026 (B) and wortmannin (C) on both MDCK and BT20 cells following an initial pulse of endosome EGFR stimulation (treatment). Wash and recovery of Erk and Akt activation were assayed in the last column of each blot. Here, cells were washed after the first pulse at 0 h, and lysates were assayed for recovery following the second endosome EGF pulse treatment at 8 h. Cell treatment and immunoblot analysis are described in Materials and Methods.