A Lipid-Anchored Grb2-Binding Protein That Links FGF-Receptor Activation to the Ras/MAPK Signaling Pathway

Abstract

Activation of the Ras/MAPK signaling cascade is essential for growth factor-induced cell proliferation and differentiation. In this report, we describe the purification, cloning, and characterization of a novel protein, designated FRS2, that is tyrosine phosphorylated and binds to Grb2/Sos in response to FGF or NGF stimulation. We find that FRS2 is myristylated and that this modification is essential for membrane localization, tyrosine phosphorylation, Grb2/Sos recruitment, and MAPK activation. FRS2 functions as a lipid-anchored docking protein that targets signaling molecules to the plasma membrane in response to FGF stimulation to link receptor activation with the MAPK and other signaling pathways essential for cell growth and differentiation. Finally, we demonstrate that FRS2 is closely related and probably indentical to SNT, the long-sought target of FGF and NGF receptors.

Fibroblast growth factor receptor-1 mediates chemotaxis independently of direct SH2-domain protein binding

“…We have previously shown that activation of FGFR-1 leads to tyrosine phosphorylation of an 89-kDa-component, FRS2 (Kouhara et al, 1997). Tyrosine phosphorylated FRS2 binds the adaptor protein Grb2, which exists in a complex with the nucleotide exchange factor Sos and thereby regulates Ras activity (Klint et al, 1995).…”

Acidic substitution of the activation loop tyrosines in TrkA supports nerve growth factor-independent cell survival and neuronal differentiation

“…NGF stimulation of PC12 cells induces the tyrosine phosphorylation of SNT/FRS-2 (80 ± 90 kDa), a di erentiation-speci®c target of NGF and FGF receptors (Rabin et al, 1993;Kouhara et al, 1997;Meakin et al, 1999). We generated a polyclonal antibody to FRS-2 and, as shown in Figure 10a, demonstrate that it immunoprecipitates tyrosine phosphorylated FRS-2 from NGF-stimulated B5 cells (Meakin et al, 1997).…”

“…From these same studies, though, decreasing MAPK activation, via a dominant negative Rap1 mutant, is not su cient to block neurite outgrowth of PC12 cells (York et al, 1998) suggesting that additional pathways are essential. Other potential pathways include the SH2 domain-containing tyrosine phosphatase, SH-PTP-2 (Wright et al, 1997), the p38 MAPK (Morooka and Nishida, 1998) and FRS-2 (Kouhara et al, 1997;Meakin et al, 1999). In this regard, over-expression of catalytically inactive SH-PTP-2 blocks NGF-dependent PC12 cell di erentiation (Wright et al, 1997) indicating an essential role of SH-PTP-2 in this process.…”

“…In this regard, over-expression of catalytically inactive SH-PTP-2 blocks NGF-dependent PC12 cell di erentiation (Wright et al, 1997) indicating an essential role of SH-PTP-2 in this process. SH-PTP-2 transiently associates with TrkA (Goldsmith and Koizumi, 1997) and also associates with activated FRS-2 (Kouhara et al, 1997;Meakin et al, 1999) suggesting a model in which activation of both prolonged MAPK and FRS-2 are the essential pathways to neuronal di erentiation. Consistent with this model, over-expression of FRS-2 can functionally reconstitute mitotic arrest and di erentiation by a non-responsive TrkA receptor mutant (Meakin et al, 1999).…”

“…Consistent with the model of RTK activation, NGF binding to TrkA stimulates receptor dimerization and trans-phosphorylation of the activation loop tyrosines which, in turn, induce allosteric changes to stabilize the kinase (Heldin, 1995). TrkA then activates a variety of intracellular signaling molecules such as the Shc adapter proteins, Grb-2, Sos, phospholipase Cg-1 (PLCg-1), phosphatidylinositol 3-kinase (PI-3 kinase), Akt, Ras, mitogen-activated protein (MAP) kinases [or extracellular signal-regulated kinases (Erks)], c-yes, protein tyrosine phosphatase-1 C, the SH2-domain containing tyrosine phosphatase SH-PTP-2 ( Kaplan and Miller, 1997), the CSK homologous tyrosine kinase, CHK (Yamashita et al, 1999), and the adapter proteins FRS-2 (Kouhara et al, 1997;Meakin et al, 1999), SH2-B and rAPS (Qian et al, 1998).…”