COUPLING OF THE MURINE PROTEIN-TYROSINE-PHOSPHATASE PEST TO THE EPIDERMAL GROWTH-FACTOR (EGF) RECEPTOR THROUGH A SRC-HOMOLOGY-3 (SH3) DOMAIN-MEDIATED ASSOCIATION WITH GRB2

The involvement of murine protein tyrosine phosphatase-PEST (MPTP-PEST ) in signal transduction pathways is suggested by its ability to depho sphorylate phosphotyrosine residues, its interaction with the adaptor protein SHC and by the presence of five proline-rich stretches in its non-catalytic carboxyl terminus, Proline-rich sequences have been iden tified as binding sites for Src homology 3 (SH3) domains found in prot eins associated with signal transduction events. The ability of these sequences to act as SH3 domain recognition motifs was investigated usi ng bacterially expressed SH3 domains derived from several different si gnalling proteins. In vitro binding assays indicate that four of these proline-rich sequences constitute specific binding sites for both SH3 domains of the adaptor molecule Grb2, Wild type Grb2, but not Grb2 pr oteins corresponding to loss-of-function mutants in the Caenorhabditis elegans sem-5 protein, associate with MPTP-PEST in vivo. Experiments in EGF receptor expressing cells show that the interaction between MPT P-PEST and Grb2 results in the binding of this complex to activated EG F receptors. In addition, identification of putative substrate(s) of M PTP-PEST have revealed a candidate protein of similar to 120 kDa which is tyrosine phosphorylated upon EGF stimulation. Together, these resu lts describe a novel SH3 domain-dependent recruitment of a protein tyr osine phosphatase to an activated receptor tyrosine kinase and establi sh a potential role for MPTP-PEST in signalling pathways at the molecu lar level.