NGF TrkA is a ligand-mediated receptor. NGF stimulates dimerization and autophosphorylation of NGF TrkA on tyrosine residues and initiation of intracellular signaling cascades that propagate the signal to the nucleus. Transcription factor becomes phosphorylated on their transcriptional regulatory site, and this phosphorylation event promotes NGF activation of transcription of the immediate early gene. The expression of various genes is influenced and a series of biological response is mediated.
NGF TrkA is a member of the neurotrophic tyrosine kinase receptor (NTKR) family. It is a membrane-bound receptor that, upon neurotrophin binding, phosphorylates itself and members of the MAPK pathway. Isoform TrkA-III promotes angiogenesis and has oncogenic activity when overexpressed. Isoform TrkA-I is found in most non-neuronal tissues. Isoform TrkA-II is primarily expressed in neuronal cells. TrkA-III is specifically expressed by pluripotent neural stem and neural crest progenitors. The presence of NGF TRKA leads to cell differentiation and may play a role in specifying sensory neuron subtypes. Mutations in NGF TRKA gene have been associated with congenital insensitivity to pain, anhidrosis, self-mutilating behavior, mental retardation and cancer. It was originally identified as an oncogene as it is commonly mutated in cancers, particularly colon and thyroid carcinomas. NGF TRKA is required for high-affinity binding to nerve growth factor (NGF), neurotrophin-3 and neurotrophin-4/5 but not brain-derived neurotrophic factor (BDNF). Known substrates for the Trk receptors are SHC1, PI 3-kinase, and PLC-gamma-1. NGF TRKA has a crucial role in the development and function of the nociceptive reception system as well as establishment of thermal regulation via sweating. It also activates ERK1 by either SHC1- or PLC-gamma-1-dependent signaling pathway. Defects in NTRK1 are a cause of congenital insensitivity to pain with anhidrosis and thyroid papillary carcinoma.