The SH2 and SH3 domains of mammalian Grb2 couple the EGF receptor to the Ras activator mSos1

Abstract

Many tyrosine kinases, including the receptors for hormones such as epidermal growth factor (EGF), nerve growth factor and insulin, transmit intracellular signals through Ras proteins. Ligand binding to such receptors stimulates Ras guanine-nucleotide-exchange activity and increases the level of GTP-bound Ras, suggesting that these tyrosine kinases may activate a guanine-nucleotide releasing protein (GNRP). In Caenorhabditis elegans and Drosophila, genetic studies have shown that Ras activation by tyrosine kinases requires the protein Sem-5/drk, which contains a single Src-homology (SH) 2 domain and two flanking SH3 domains. Sem-5 is homologous to the mammalian protein Grb2, which binds the autophosphorylated EGF receptor and other phosphotyrosine-containing proteins such as Shc through its SH2 domain. Here we show that in rodent fibroblasts, the SH3 domains of Grb2 are bound to the proline-rich carboxy-terminal tail of mSos1, a protein homologous to Drosophila Sos. Sos is required for Ras signalling and contains a central domain related to known Ras-GNRPs. EGF stimulation induces binding of the Grb2-mSos1 complex to the autophosphorylated EGF receptor, and mSos1 phosphorylation. Grb2 therefore appears to link tyrosine kinases to a Ras-GNRP in mammalian cells.

Disabled-2 (Dab2) is an SH3 domain-binding partner of Grb2

“…The full-length GST-Grb2, but not GST itself, bound Dab2 from a BAC1.2F5 cell lysate . While the SH2 domain failed to bind Sos, both the C-and N-terminal SH3 domains of Grb2 bound mSos1, with the N-terminal SH3 domain being more e ective than the C-terminal domain, similar to results published previously (Egan et al, 1993;Rozakis-Adcock et al, 1993;Li et al, 1993;Buday and Downward, 1993). The constructs of the Grb2 fusion protein and results of this experiment are illustrated in Figure 6b.…”

New insights into protein‐tyrosine kinase receptor signaling complexes

“…regions of sequence in their carboxy-termini to the SH3 domains of Grb-2 (Buday & Downward, 1993;Egan et al, 1993;Gale et al, 1993;Li et al, 1993;Olivier et al, 1993;Rozakis-Adcock et al, 1993;Simon et al, 1993). This is the first clear description of a physiological ligand for an SH3 domain.…”

“…It would appear that Grb-2 and Sos proteins are associated constitutively, but only function to activate Ras upon receptor stimulation. This leads to recruitment of the Grb-2/Sos complex to the membrane and results in the phosphorylation of the Sos protein (Rozakis-Adcock et al, 1993). Presumably Sos is then able to convert the inactive GDPbound form of Ras to an active GTP-bound form by nucleotide exchange.…”

Allelic deletion at 11q23.3-q25 is an early event in cervical neoplasia

“…It is generally accepted that the function of adaptor protein Grb2 links protein tyrosine kinases to the Ras/MAPK signaling pathway. This is achieved through recruitment of the guanine nucleotide exchange factor Sos (Simon et al, 1993;Egan et al, 1993;Rozakis-Adcock et al, 1993;Li et al, 1993;Gale et al, 1993). The understanding of Grb2 function was supported by biochemical studies as well as by genetic analysis in Caenorbabditis elegans and Drosophila.…”