Adapter protein that links activated FGR and NGF receptors to downstream signaling pathways. Plays an important role in the activation of MAP kinases and in the phosphorylation of PIK3R1, the regulatory subunit of phosphatidylinositol 3-kinase, in response to ligand-mediated activation of FGFR1. Modulates signaling via SHC1 by competing for a common binding site on NTRK1. Part of a complex containing FRS2, GRB2, GAB1, PIK3R1 and SOS1. Part of a complex containing GRB2 and CBL. Binds ALK, CKS2, FGFR1, RET, MAPK1/ERK2, MAPK3/ERK1 and SRC. The tyrosine-phosphorylated protein binds the SH2 domains of GRB2 and PTPN11. Interacts with NTRK1, NTRK2 and NTRK3 (phosphorylated upon ligand-binding) (By similarity). Identified in a complex containing FGFR4, NCAM1, CDH2, PLCG1, FRS2, SRC, SHC1, GAP43 and CTTN. Ubiquitous. Expression is highest in brain, kidney, lung and testis. Phosphorylated on tyrosine residues upon stimulation by FGF2 or NGFB. Phosphorylated by ULK2 (in vitro). Phosphorylated on tyrosine residues by activated ALK and FGFR1. Phosphorylated on tyrosine residues upon activation of FGFR2 and FGFR3. Phosphorylated on threonine residues by MAP kinases; this inhibits tyrosine phosphorylation, and thereby down-regulates FRS2-mediated activation of MAP kinases. Ubiquitinated when tyrosine phosphorylated and in a complex with GRB2. The unphosphorylated form is not subject to ubiquitination.