Gads is a novel SH2 and SH3 domain-containing adaptor protein that binds to tyrosine-phosphorylated Shc

Shc proteins are important substrates of receptor and cytoplasmic tyrosine kinases that couple activated receptors to downstream signaling enzymes. Ph osphorylation of Shc tyrosine residues 239 and 317 leads to recruitment of the Grb2-Sos complex, thus linking Shc phosphorylation to Ras activation. W e have used phosphorylated peptides corresponding to the regions spanning t yrosine 239/240 and 317 of Shc in an expression library screen to identify additional downstream targets of Shc. Here we report the identification of Gads, a novel adaptor protein most similar to Grb2 and Grap that contains a mino and carboxy terminal SH3 domains flanking a central SH2 domain and a 1 20 amino acid unique region. Gads is most highly expressed in the thymus an d spleen of adult animals and in human leukemic cell lines, The binding spe cificity of the Gads SH2 domain is similar to Grb2 and mediates the interac tion of Gads with Shc, Bcr-Abl and c-kit, Gads does not interact with Sos, Cbl or Sam68, although the isolated carboxy terminal Gads SH3 domain is abl e to bind these molecules in vitro. Our results suggest that the unique str ucture of Gads regulates its interaction with downstream SH3 domain-binding proteins and that Gads may function to couple tyrosine-phosphorylated prot eins such as Shc, Bcr-Abl and activated receptor tyrosine kinases to downst ream effectors distinct from Sos and Ras.