A list of 20 subfamilies of human RTKs along with their family members and respective extracellular and intracellular domains
Family name | Members | Ligands | Extracellular domain | Intracellular domain | γ-secretase cleavage | Nuclear localization status | Mechanism of nuclear localization |
---|---|---|---|---|---|---|---|
EGFR | ErbB1, ErbB2, ErbB3, ErbB4* | EGF, transforming GF A (TGFA), heparin-binding EGF-like GF (HBEGF), betacellulin (BTC), Amphiregulin (AREG), epiregulin (EREG), epigen (EPGN) | 2-Cysteine rich domains | JM domain, tyrosine kinase domain, a C-terminal regulatory region | Yes | Yes | Clathrin mediated endocytosis [35], retro-translocation by ER-associated trafficking machinery [36], nuclear localization signals (NLS) sequence [34] |
InsR | InsR*, IGF1R*, IRR | INS-like GF-1 (IGF-1), IGF-2, INS | 2-Chains α and β, 2-leucine rich domain separated by a cysteine rich domain, 3-fibronectin type III (FNIII) domains | Tyrosine kinase domain | Yes | Yes | The possible mechanism includes SUMOylation/via microtubules with the help of some proteins [p150Glued, AREG, importin-β, ran-binding protein 2 (RanBP2)] or clathrin mediated endocytosis [37], NLS |
PDGFR | PDGFRα, PDGFRβ, Kit, fibromyalgia syndrome-like tyrosine kinase 3 ligand (FLT3L), colony stimulating factor 1 (CSF1)* | Platelet-derived GF (PDGF), PDGF-A, PDGF-AA, PDGF-AB, PDGF-AB/BB, PDGF-B, PDGF-BB, PDGF-C, PDGF-CC, PDGF-D, PDGF-DD | 5-Ig-like domains | JM domain, tyrosine kinase containing a long kinase insert domain region, a C-terminal extension | Yes | Yes | Mediated by clathrin coated pits, β-importin, via TATA element modulatory factor 1 (TMF1) positive Golgi vesicles [38] |
VEGFR | VEGFR1*, VEGFR2*, VEGFR3* | Vascular endothelial GF (VEGF)-A, VEGF-B, neuropilin-1, placental GF (PlGF), VEGF-C, VEGF-D | 7-Ig-like domains | JM domain, tyrosine kinase domain | Yes | Yes | Mediated by VEGF stimulation and complex formation with tissue transglutaminase II for endothelial cells [39], endocytosis [40] |
FGFR | FGFR1, FGFR2, FGFR3*, FGFR4* | Fibroblast GF (FGF) 1–22 | 3-Ig-like domains | JM region, tyrosine kinase domain | Yes | Yes | Importin-β-mediated interferons (INFS) mechanism [34] clathrin mediated endocytosis [41] |
CCK | CCK4/PTK7* | Coreceptor for Wnt signaling | 7-Ig domains | Catalytic domain lacking tyrosine kinase activity | Yes | Yes | - |
NGFR | TRKA*, TRKB*, TRKC | NGF, BDNF, Neurotrophin 3 (NT3), NT4 | 3-Leucine repeats flanked by cysteine clusters and 2-Ig-like domains | Tyrosine kinase domain | Yes | Yes | Mediated by Carrier vesicles [42], NLS, and phosphorylation dependent process [43], mediated by importins [44] |
Hepatocyte GF receptor (HGFR) | MET*, Recepteur d’ origine nantais (RON) | Hepatocyte GF (HGF) | Sema domain, a PSI domain, and 4-Ig-like plexins transcription factors (IPT) domains | JM domain, tyrosine kinase domain, carboxy-terminal tail region | Yes | Yes | Mediated by Gab1 and importin-β, NLS [43], integral trafficking from ER to the nuclear envelop transport (INTERNET) [34] |
Erythropoietin-producing human hepatocellular receptor (EPHR) | EPHA1, EPHA2*, EPHA3, EPHA4*, EPHA5*, EPHA6, EPHA7*, EPHA8, EPHA10, EPHB1, EPHB2*, EPHB3*, EPHB4*, EPHB6* | Ephrin A (1–5), ephrin B (1–3) | Cysteine-rich domain and 2 FNIII repeats | Tyrosine kinase domain | Yes | Yes | pH-Dependent nuclear localization signal [34] |
Axl | Axl*, Mer*, TYRO3* | Growth arrest specific gene 6 (Gas 6) | 2-Ig-like domains and 2-FNIII domains | Tyrosine kinase domain | Yes | Yes | NLS [45] |
Tie | Tie*, TEK | Angiopoietin (ANG) GFs (ANG1, ANG2, ANG4) | 2-Ig-like, 1-EGF, 3-FNIII domains | Tyrosine kinase domain | Yes | Yes | Caveolin mediated nuclear translocation [46] |
RYK | RYK* | Wnt1, Wnt3a | Leucine-rich domain with a WIF-type Wnt binding region | Tyrosine kinase domain lacking kinase activity | Yes | Yes | Chaperone mediated, suppressor of Mek null 1/2 (smek1/2) functions as a chaperone and regulates nuclear translocation [47] |
DDR | DDR1, DDR2 | Collagen (I, IV, V, VI, VIII), collagen (I, III, X) | Discoidin domain, discoidin-like domain, extracellular juxtamembrane region | JM domain, tyrosine kinase domain | - | Yes | Stimulation with collagen leads to interaction with Sec61 translocon subunit beta (SEC61B) and results in nuclear translocation [48] |
ROS | ROS | - | 6-FNIII like domains | Tyrosine kinase domain | - | - | - |
Leukocyte tyrosine kinase (LTK) | LTK, ALK | ALK and LTK ligand 1 (ALKAL1), ALKAL2 | 2-Meprin A-5 protein and receptor protein phosphatase mu (2-MAM) domains 1-Ldla motif, cysteine rich and glycine rich domains | JM domain, tyrosine kinase domain | - | - | - |
ROR | ROR1, ROR2 | Wnt5a | Ig-domain, cysteine-rich domains, and kringle-like domains | Tyrosine kinase domain, proline-rich, serine-threonine rich domains | - | Yes | Cleavage releasing mechanism in addition to Ran-GTPase pathway [45] |
MUSK | MUSK* | Agrin | 3-Ig-like and 1-cysteine rich frizzled-like domain | A JM domain, a kinase domain, and a short cytoplasmic tail | Yes | - | - |
LMR | Apoptosis associated tyrosine kinase (AATYK), AATYK, AATYK3 | A short extracellular domain containing leucine residues | Tyrosine kinase domain | - | - | - | |
Ret | Ret | Glial cell line-derived neurotrophic factor (GDNF), neuturin, artemin, persephin, growth differentiation factor-15 (GDF-15) | 4-Cadherin like domain, a cysteine rich domain | JM domain, kinase domain, a C-terminal tail | - | Yes | - |
STYK1 | STYK1 | - | It has a truncated extracellular domain, a single transmembrane domain | A relatively short intracellular domain possessing tyrosine kinase activity | - | - | - |
The RTKs marked in asterisks (*) are reported to be cleaved by the γ-secretase enzyme [49, 50], and those in bold text are known to have nuclear localization. Noticeably, some of the RTKs undergo both γ-secretase cleavage and nuclear localization. -: no information is available as of now