CONTROLLING EPIDERMAL GROWTH-FACTOR (EGF)-STIMULATED RAS ACTIVATION IN INTACT-CELLS BY A CELL-PERMEABLE PEPTIDE MIMICKING PHOSPHORYLATED EGF RECEPTOR

Epidermal growth factor (EGF)-stimulated Ras activation involves speci fic interactions between the EGF receptor (EGFR), the adaptor proteins Grb2 and She, and the nucleotide exchange factor Sos-1. Study and con trol of these protein-protein interactions in vivo can be greatly prom oted by introducing intracellular reagents that mimic EGFR functions, Here, we showed that a synthetic phosphopeptide encompassing the autop hosphorylation site 1068 of EGFR formed a complex with endogenous Grb2 after this peptide was delivered into intact cells by a cell-permeabl e peptide import technique, Consequently, this intracellular peptide i nhibited EGF-induced EGFR/Grb2 associations but not EGFR/Shc or Shc/GF b2 associations. Peptide-mediated disruption of the EGF/Grb2/Sos-1 cas cade led to reduced Ras activation and mitogen-activated protein kinas e activation. These results indicate that the binding of Grb2 to the p hosphorylated Tyr-1068 of EGFR is crucial to the EGF-induced Ras/mitog en-activated protein kinase signaling pathway. The application of cell -permeable peptides to this study demonstrates a useful biochemical to ol to probe and control various intracellular processes involved in si gnal transduction and gene transcription.