After NGF binding, activated Trk receptors provide multiple docking sites for adaptor proteins and enzymes. Two docking proteins, the Ankyrin-Rich Membrane Spanning protein (ARMS/Kidins220) and Fibroblast growth factor receptor substrate 2 (Frs2), target signaling molecules in response to NGF stimulation and link receptor activation with the MAP kinase (also called the Extracellular signal-Regulated Kinase cascade, ERK) cascade, an essential process for growth factor-induced cell proliferation and differentiation.
A feature of NGF signaling is the sustained activation of the MAPK cascade. This is achieved by the small G protein, Rap1 which binds to and activates B-Raf, an activator of the MAPK cascade. Rap1 is a member of the Ras family of G proteins and like all G proteins, Rap1 is in an inactive state when bound to GDP and is active when bound to GTP. A specific GEF (guanine nucleotide exchange factor) called C3G can activate Rap1 by exchanging GDP for GTP.