CLONING AND CHARACTERIZATION OF GRB14, A NOVEL MEMBER OF THE GRB7 GENE FAMILY

Screening of a human breast epithelial cell cDNA library with the tyro sine-phosphorylated C terminus of the epidermal growth factor receptor identified a novel member of the GRB7 gene family, designated GRB14. In addition to a pleckstrin homology domain-containing central region homologous to the Caenorhabditis elegans protein F10E9.6/mig 10 and a C-terminal Src homology 2 (SH2) domain, a conserved N-terminal motif, P(S/A)IPNPFPEL, can now be included as a hallmark of this family. GRB1 4 mRNA was expressed at high levels in the liver, kidney, pancreas, te stis, ovary, heart, and skeletal muscle. Anti-Grb14 antibodies recogni zed a protein of approximately 58 kDa in a restricted range of human c ell lines. Among those of breast cancer origin, GRB14 expression stron gly correlated with estrogen receptor positivity, and differential exp ression was also observed among human prostate cancer cell lines. A GS T-Grb14 SH2 domain fusion protein exhibited strong binding to activate d platelet-derived growth factor (PDGF) receptors (PDGFRs) in vitro, b ut association between Grb14 and beta-PDGFRs could not be detected in vivo. In serum-starved cells, Grb14 was phosphorylated on serine resid ues, which increased with PDGF, but not EGF, treatment. Grb14 is there fore a target for a PDGF-regulated serine kinase, an interaction that does not require PDGFR-Grb14 association.