Tropomyosin receptor kinase B

Tropomyosin receptor kinase B (TrkB),[5] also known as tyrosine receptor kinase B,[5] or BDNF/NT-3 growth factors receptor or neurotrophic tyrosine kinase, receptor, type 2 is a protein that in humans is encoded by the NTRK2 gene.[5][6] TrkB is a receptor for brain-derived neurotrophic factor (BDNF).

NTRK2
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesNTRK2, GP145-TrkB, TRKB, trk-B, neurotrophic receptor tyrosine kinase 2, OBHD, EIEE58
External IDsOMIM: 600456 MGI: 97384 HomoloGene: 4504 GeneCards: NTRK2
Gene location (Human)
Chr.Chromosome 9 (human)[1]
Band9q21.33Start84,668,551 bp[1]
End85,027,070 bp[1]
RNA expression pattern




More reference expression data
Orthologs
SpeciesHumanMouse
Entrez

4915

18212

Ensembl

ENSG00000148053

ENSMUSG00000055254

UniProt

Q16620

P15209

RefSeq (mRNA)

NM_001025074
NM_008745
NM_001282961

RefSeq (protein)

NP_001020245
NP_001269890
NP_032771

Location (UCSC)Chr 9: 84.67 – 85.03 MbChr 13: 58.81 – 59.13 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

Function

Tropomyosin receptor kinase B is the high affinity catalytic receptor for several "neurotrophins", which are small protein growth factors that induce the survival and differentiation of distinct cell populations. The neurotrophins that activate TrkB are: BDNF (Brain Derived Neurotrophic Factor), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3).[5] As such, TrkB mediates the multiple effects of these neurotrophic factors, which includes neuronal differentiation and survival. Research has shown that activation of the TrkB receptor can lead to down regulation of the KCC2 chloride transporter in cells of the CNS.[7]

The TrkB receptor is part of the large family of receptor tyrosine kinases. A "tyrosine kinase" is an enzyme which is capable of adding a phosphate group to certain tyrosines on target proteins, or "substrates". A receptor tyrosine kinase is a "tyrosine kinase" which is located at the cellular membrane, and is activated by binding of a ligand to the receptor's extracellular domain. Other examples of tyrosine kinase receptors include the insulin receptor, the IGF1 receptor, the MuSK protein receptor, the Vascular Endothelial Growth Factor (or VEGF) receptor, etc.

TrkB signaling

Currently, there are three TrkB isoforms in the mammalian CNS. The full-length isoform (TK+) is a typical tyrosine kinase receptor, and transduces the BDNF signal via Ras-ERK, PI3K, and PLCγ. In contrast, two truncated isoforms (TK-: T1 and T2) possess the same extracellular domain, transmembrane domain, and first 12 intracellular amino acid sequences as TK+. However, the C-terminal sequences are the isoform-specific (11 and 9 amino acids, respectively). T1 has the original signaling cascade that is involved in the regulation of cell morphology and calcium influx.

Family members

TrkB is part of a sub-family of protein kinases which includes also TrkA and TrkC. There are other neurotrophic factors structurally related to BDNF: NGF (for Nerve Growth Factor), NT-3 (for Neurotrophin-3) and NT-4 (for Neurotrophin-4). While TrkB mediates the effects of BDNF, NT-4 and NT-3, TrkA is bound and thereby activated only by NGF. Further, TrkC binds and is activated by NT-3.

TrkB binds BDNF and NT-4 more strongly than it binds NT-3. TrkC binds NT-3 more strongly than TrkB does.

LNGFR

There is one other BDNF receptor besides TrkB, called the "LNGFR" (for "low-affinity nerve growth factor receptor"). Unlike TrkB, the LNGFR plays a somewhat less clear role in BDNF 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 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 cancer

Although originally identified as an oncogenic fusion in 1982,[8] only recently has there been a renewed interest in the Trk family as it relates to its role in human cancers because of the identification of NTRK1 (TrkA), NTRK2 (TrkB) and NTRK3 (TrkC) gene fusions and other oncogenic alterations in a number of tumor types. A number of Trk inhibitors are (in 2015) in clinical trials and have shown early promise in shrinking human tumors.[9]

As a drug target

Entrectinib (formerly RXDX-101) is an investigational drug developed by Ignyta, Inc., which has potential antitumor activity. It is a selective pan-trk receptor tyrosine kinase inhibitor (TKI) targeting gene fusions in trkA, trkB (this gene), and trkC (respectively, coded by NTRK1, NTRK2, and NTRK3 genes) that is currently in phase 2 clinical testing.[10]

Ligands

Agonists

Antagonists

Others

Interactions

TrkB has been shown to interact with:

See also

References
  1. GRCh38: Ensembl release 89: ENSG00000148053 - Ensembl, May 2017
  2. GRCm38: Ensembl release 89: ENSMUSG00000055254 - Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 8: Atypical neurotransmitters". In Sydor A, Brown RY (eds.). Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. ISBN 9780071481274. Another common feature of neurotrophins is that they produce their physiologic effects by means of the tropomyosin receptor kinase (Trk) receptor family (also known as the tyrosine receptor kinase family). ...Trk receptors All neurotrophins bind to a class of highly homologous receptor tyrosine kinases known as Trk receptors, of which three types are known: TrkA, TrkB, and TrkC. These transmembrane receptors are glycoproteins whose molecular masses range from 140 to 145 kDa. Each type of Trk receptor tends to bind specific neurotrophins: TrkA is the receptor for NGF, TrkB the receptor for BDNF and NT-4, and TrkC the receptor for NT-3.However, some overlap in the specificity of these receptors has been noted.
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Further reading

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