|Neurotrophic tyrosine kinase, receptor, type 1|
PDB rendering based on 1he7.
|External IDs||ChEMBL: GeneCards:|
|RNA expression pattern|
High affinity nerve growth factor receptor also known as neurotrophic tyrosine kinase receptor type 1 or TRK1-transforming tyrosine kinase protein or Trk-A is a protein that in humans is encoded by the NTRK1 gene.
This gene encodes a member of the neurotrophic tyrosine kinase receptor (NTKR) family. This kinase is a membrane-bound receptor that, upon neurotrophin binding, phosphorylates itself (autophosphorylation) and members of the MAPK pathway. The presence of this kinase leads to cell differentiation and may play a role in specifying sensory neuron subtypes. Mutations in this gene have been associated with congenital insensitivity to pain with anhidrosis, self-mutilating behavior, mental retardation and cancer. Alternate transcriptional splice variants of this gene have been found, but only three have been characterized to date.
TrkA is the high affinity catalytic receptor for the neurotrophin, Nerve Growth Factor, or "NGF". As such, it mediates the multiple effects of NGF, which include neuronal differentiation and avoidance of programmed cell death.
Family members 
TrkA is part of a sub-family of protein kinases which includes TrkB and TrkC. Also, there are other neurotrophic factors structurally related to NGF: BDNF (for Brain-Derived Neurotrophic Factor), NT-3 (for Neurotrophin-3) and NT-4 (for Neurotrophin-4). While TrkA mediates the effects of NGF, TrkB is bound and activated by BDNF, NT-4, and NT-3. Further, TrkC binds and is activated by NT-3.
The Low Affinity Nerve Growth Factor Receptor 
There is one other NGF receptor besides TrkA, called the "LNGFR" (for "Low Affinity Nerve Growth Factor Receptor"). As opposed to TrkA, the LNGFR plays a somewhat less clear role in NGF biology. Some researchers have shown the LNGFR binds and serves as a "sink" for neurotrophins. Cells which express both the LNGFR and the Trk receptors might therefore have a greater activity – since they have a higher "microconcentration" of the neurotrophin. It has also been shown, however, that in the absence of a co-expressed TrkA, the LNGFR may signal a cell to die via apoptosis – so therefore cells expressing the LNGFR in the absence of Trk receptors may die rather than live in the presence of a neurotrophin.
Role in disease 
TrkA was originally cloned from a colon tumor; the cancer occurred via a translocation, which resulted in the activation of the TrkA kinase domain. However, TrkA itself does not appear to be an oncogene.
Regulation of TrkA 
The levels of distinct proteins can be regulated by the "ubiquitin/proteasome" system. In this system, a small (7–8 kd)protein called "ubiquitin" is affixed to a target protein, and is thereby targeted for destruction by a structure called the "proteasome". TrkA is targeted for proteasome-mediated destruction by an "E3 ubiquitin ligase" called NEDD-4. This mechanism may be a distinct way to control the survival of a neuron. The extent and maybe type of TrkA ubiquitiniation can be regulated by the other, unrelated receptor for NGF, p75NTR.
TrkA has been shown to interact with:
Small molecules such as amitriptyline and gambogic acid derivatives have been claimed to activate TrkA. Amitriptyline activates TrkA and facilitate the heterodimerisation of TrkA and TrkB in the absence of NGF. Binding of Amitriptyline to TrkA occurs to the Leucine Rich Region (LRR) of the extracellular domain of the receptor, which is distinct from the NGF binding site. Amitryptiline possess neurotrophic activity both in-vitro and in-vivo (mouse model). Gambogic Amide, a derivative of Gambogic acid, selectively activates TrkA (but not TrkB and TrkC) both in-vitro and in-vivo by interacting with the cytoplasmic juxtamembrane domain of TrkA.
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- Nakamura, Takeshi; Komiya Misako, Sone Kiyoaki, Hirose Eiji, Gotoh Noriko, Morii Hiroshi, Ohta Yasutaka, Mori Nozomu (December 2002). "Grit, a GTPase-activating protein for the Rho family, regulates neurite extension through association with the TrkA receptor and N-Shc and CrkL/Crk adapter molecules". Mol. Cell. Biol. 22 (24): 8721–34. doi:10.1128/MCB.22.24.8721-8734.2002. PMC 139861. PMID 12446789.
- Wooten, M W; Seibenhener M L, Mamidipudi V, Diaz-Meco M T, Barker P A, Moscat J (March 2001). "The atypical protein kinase C-interacting protein p62 is a scaffold for NF-kappaB activation by nerve growth factor". J. Biol. Chem. 276 (11): 7709–12. doi:10.1074/jbc.C000869200. PMID 11244088.
- Geetha T, Wooten MW (February 2003). "Association of the atypical protein kinase C-interacting protein p62/ZIP with nerve growth factor receptor TrkA regulates receptor trafficking and Erk5 signaling". J. Biol. Chem. 278 (7): 4730–9. doi:10.1074/jbc.M208468200. PMID 12471037.
- Jadhav T, Geetha T, Jiang J, Wooten MW (July 2008). "Identification of a consensus site for TRAF6/p62 polyubiquitination". Biochem. Biophys. Res. Commun. 371 (3): 521–4. doi:10.1016/j.bbrc.2008.04.138. PMC 2474794. PMID 18457658.
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- Borrello, M G; Pelicci G, Arighi E, De Filippis L, Greco A, Bongarzone I, Rizzetti M, Pelicci P G, Pierotti M A (June 1994). "The oncogenic versions of the Ret and Trk tyrosine kinases bind Shc and Grb2 adaptor proteins". Oncogene 9 (6): 1661–8. PMID 8183561.
- Jang SW, Liu X, Chan CB, Weinshenker D, Hall RA, Xiao G, Ye K. (June 2009). "Amitriptyline is a TrkA and TrkB receptor agonist that promotes TrkA/TrkB heterodimerization and has potent neurotrophic activity.". Chem Biol. 16 (6): 644–656. doi:10.1016/j.chembiol.2009.05.010. PMC 2844702. PMID 19549602.
- Jang SW, Okada M, Sayeed I, Xiao G, Stein D, Jin P, Ye K. (October 2007). "Gambogic amide, a selective agonist for TrkA receptor that possesses robust neurotrophic activity, prevents neuronal cell death.". Proc Natl Acad Sci U S A 104 (41): 16329–16334. doi:10.1073/pnas.0706662104. ISBN [[Special:BookSources/0-7066-6210-4|0-7066-6210-4 [[Category:Articles with invalid ISBNs]]]] Check
|isbn=value (help). PMC 2042206. PMID 17911251.
Further reading 
- Indo Y (2002). "Genetics of congenital insensitivity to pain with anhidrosis (CIPA) or hereditary sensory and autonomic neuropathy type IV. Clinical, biological and molecular aspects of mutations in TRKA(NTRK1) gene encoding the receptor tyrosine kinase for nerve growth factor.". Clin. Auton. Res. 12 (Suppl 1): I20–32. doi:10.1007/s102860200016. PMID 12102460.
- Micera A, Lambiase A, Stampachiacchiere B, et al. (2007). "Nerve growth factor and tissue repair remodeling: trkA(NGFR) and p75(NTR), two receptors one fate.". Cytokine Growth Factor Rev. 18 (3–4): 245–56. doi:10.1016/j.cytogfr.2007.04.004. PMID 17531524.