Receptor Tyrosine Kinase

The receptor tyrosine kinases (RTKs) are a large superfamily of receptors that part equally the receptors for a wide array of growth factors, including epidermal growth factor (EGF), nerve growth cistron (NGF), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), insulin and the insulin-like growth factors (IGF), and the ephrins and angiopoietins.

From: Comprehensive Toxicology , 2010

Receptor Tyrosine Kinases

Kelly Karl , ... Kalina Hristova , in Reference Module in Biomedical Sciences, 2021

i Introduction

Receptor tyrosine kinases (RTKs) are a large family of membrane receptors that play various roles in human health and evolution ( Fantl et al., 1993; Lemmon and Schlessinger, 2010; Paul and Hristova, 2019a; Schlessinger, 2000a,b). These receptors are expressed on the prison cell surface where they sense extracellular signals or "ligands" (Kufareva et al., 2017; Lemmon and Schlessinger, 2010; Murai and Pasquale, 2003). For RTKs, ligands are generally small proteins (between 50 and a few hundred amino acids long), which are secreted past cells. The ligands bind to RTKs, promoting RTK dimerization and in some cases, oligomerization, which brings the two kinase domains in shut proximity. As a effect, the kinases phosphorylate each other to activate each other. The activated kinases bind and phosphorylate cytoplasmic effector proteins, triggering cascades of phosphorylation events that control cell growth, differentiation, migration, metabolism, and survival (Lemmon and Schlessinger, 2010; Schlessinger, 2000a,b). RTKs share a like general architecture as they all consist of an extracellular (EC) region, a unmarried-pass transmembrane (TM) helix, and an intracellular (IC) region (Fig. one) (Lemmon and Schlessinger, 2010; Schlessinger, 2000a,b; Trenker and Jura, 2020). Members of the RTK family are subdivided into 20 subfamilies according to their sequence and structural backdrop along with their ligand bounden partners.

Fig. 1

Fig. i. Architecture of the 20 RTK subfamilies.

RTK extracellular regions are different between subfamilies and consist of a broad diversity of structural domains (come across Fig. 1) (Lemmon and Schlessinger, 2010; Schlessinger, 2000a,b). RTKs inside the aforementioned subfamily tend to have similar extracellular domains and thus bind similar ligands. Therefore, each RTK subfamily has a family of ligand binding partners that are known to bind some or all the members of that subfamily. These ligands bind to the receptors with varying affinities. Interestingly, there are some RTKs that practice not bind any of the currently known ligands. The identities of the ligand and the RTK in the complex determine the nature of the signals that are transmitted into the cell (Karl et al., 2020; Trenker and Jura, 2020).

RTKs are classified by the presence of a catalytic kinase domain located on the IC region that is vital for activating downstream signaling cascades that control cellular processes (Lemmon and Schlessinger, 2010; Nishimura et al., 2014; Schlessinger, 2000a,b). Kinase activity requires ATP binding to a conserved active site of the kinase domain. After, ATP hydrolysis occurs resulting in the transfer of a phosphate grouping from ATP to specific tyrosine residues. The first tyrosine that is phosphorylated is the 1 located on the activation loop proximal to the agile site. So, through a procedure that is still not completely understood, other tyrosine residues located on diverse intracellular domain sites too become phosphorylated. Many of the phosphorylated tyrosines serve as docking sites for site-specific adaptor and effector proteins which initiate specific downstream signaling cascades (Lemmon and Schlessinger, 2010; Del Piccolo and Hristova, 2017; Schlessinger, 2014). Inside the same RTK subfamily, these phosphorylation sites tend to be highly conserved. In addition, RTKs in dissimilar subfamilies have different regulatory domains such every bit the juxtamembrane (JM) segment, post-kinase tail, and/or sterile blastoff motif (SAM) domain which can harbor additional phosphorylation sites (Lemmon and Schlessinger, 2010; Schlessinger, 2000a,b). As a result, the manner in which RTKs achieve complete activation can be different for each RTK subfamily, and for each RTK as well.

RTK action is controlled by the lateral interaction between RTKs on the cell surface, as it controls the proximity of the kinase domains and thus the showtime stride in the RTK activation procedure (Chen et al., 2020; Kavran et al., 2014; Paul and Hristova, 2019b; Sarabipour and Hristova, 2016a,b; Singh et al., 2016). Therefore, RTK dimerization and oligomerization is vital for RTK signaling. It has long been known that ligand binding stabilizes RTK dimers and thus information technology was considered that ligands are required for RTK dimerization and oligomerization. Nevertheless, now information technology is known that RTKs more often than not be in monomer-dimer equilibrium in the absence of ligand binding (Paul and Hristova, 2019b). Therefore, unliganded RTK dimers tin can showroom basal levels of activity and tin can induce downstream signaling. In addition, most RTKs take been found to interact with other RTKs, either in the same family unit or between subfamilies, and with other membrane proteins such as cadherins, integrins, and G-protein Coupled Receptors (GPCRs) (Paul and Hristova, 2019a).

Each RTK and its activating ligands plays a specialized role in cellular signaling and thus all RTKs are critical for human development and health. RTK signaling activates downstream signaling cascades including the Ras/MAPK, PLCγ1/PKC, PI3K/Akt, and STAT pathways, which are involved in a wide multifariousness of cellular processes such equally cell proliferation, differentiation, survival, and migration (Chao et al., 2006; Lemmon and Schlessinger, 2010; Li and Hristova, 2006; Neben et al., 2019; Ornitz, 2000; Pasquale, 2010; Schlessinger and Lemmon, 2003; Schlessinger, 2000a,b, 2014; Smith et al., 2018; Dominicus and Bernards, 2014; Timsah et al., 2014; Trenker and Jura, 2020). These signaling pathways are activated past binding and subsequent phosphorylation of specific cytosolic proteins such as Grb2, PLCγ, NCK, FRS2, Shc, Jak, Gab1, SHP2, STAT, and the p85 subunit of PI3K, to name some notable examples. Abnormal RTK activity and signaling has been implicated in many diseases and disorders including various cancers, neurodegenerative diseases, cardiovascular diseases, and developmental disorders (Boye et al., 2009; Browne et al., 2009; Cunningham et al., 2007; Foldynova-Trantirkova et al., 2012; Nessa et al., 2009; Phay and Shah, 2010; Robertson et al., 2000; Vail et al., 2014; Webster and Donoghue, 1997). RTK signaling abnormalities can arise in several ways: (i) overactivation or inhibited activation every bit a result of mutations or deletions (including alternative splicing), (ii) overexpression due to cistron amplification and (iii) the generation of oncogenic fusion proteins resulting from chromosomal translocation. Just about every RTK has been linked to illness. Thus, in efforts to preclude or care for RTK-associated diseases, RTKs have get increasingly pop and promising drug targets (Saraon et al., 2021). In this review, we discuss RTKs in pharmacological context, highlighting some of the RTK subfamilies and the therapeutics that accept been developed to target these receptors to combat affliction.

RTK inhibitors target either the extracellular domain or the kinase domain, as the transmembrane domain is protected by the cell membrane, and its office in RTK activation is still debated (Bocharov et al., 2017). Hither we will begin by describing common architectural motifs of RTKs, as well as their function. Special emphasis will be placed on the structure of the kinase domain. This detailed understanding of the domains will help with the agreement of how inhibitors work.

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New Insights into the Mechanism of Wnt Signaling Pathway Activation

Akira Kikuchi , ... Shinji Matsumoto , in International Review of Cell and Molecular Biology, 2011

4.1.5 Protein tyrosine kinase vii

Poly peptide tyrosine kinase 7 (PTK7) is a single-pass transmembrane protein containing extracellular immunoglobulin domains and an intracellular tyrosine kinase homology domain, although the kinase domain lacks the DFG triplet motif (Lu et al., 2004b). Deletion or disruption of PTK7 generates comparable furnishings as core PCP genes and Wnt5a-like craniorachischisis (Lu et al., 2004b; Paudyal et al., 2010; Shnitsar et al., 2008). In Xenopus embryos, PTK7 recruits Dvl to the plasma membrane which requires its kinase domain, and PTK7 is necessary for Fz7-dependent phosphorylation of Dvl. A kinase motif deletion mutant of PTK7 inhibits neural crest migration (Shnitsar et al., 2008). Although these results implicate that PTK7 is involved in the Wnt5a/β-catenin-independent pathway, it remains to be proved that Wnt5a binds directly to PTK7.

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Chemic and Synthetic Biology Approaches To Understand Cellular Functions - Role A

M. Escarlet Díaz Galicia , ... Raik Grünberg , in Methods in Enzymology, 2019

Abstract

Protein tyrosine kinases (PTKs) are cardinal signaling molecules and important drug targets. Although the efficient recombinant production of active PTKs is important for both pharmaceutical industry and bookish research, almost PTKs are still obtained from conventional, expensive and time-consuming insect-cell based expression. Host toxicity, kinase inactivity, insolubility and heterogeneity are among the reasons idea to preclude PTK expression in Escherichia coli. Herein nosotros review these presumed roadblocks and their possible solutions for bacterial expression of PTKs, and give an overview on kinase activeness assays. Finally, we report our experiences and observations with the kinases Src, Lyn and FAK as examples to illustrate implementation, effects and pitfalls of E. coli expression and in vitro assaying of PTKs.

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Protein Kinases in Drug Discovery

Adam Bajinting , Ho Leung Ng , in Advances in Protein Chemistry and Structural Biology, 2021

Abstract

Receptor tyrosine kinases (RTKs) are of import drug targets for cancer and immunological disorders. Crystal structures of individual RTK domains have contributed greatly to the structure-based drug pattern of clinically used drugs. Low-resolution structures from electron microscopy are now bachelor for the RTKs, EGFR, PDGFR, and Kit. However, at that place are even so no high-resolution structures of full-length RTKs due to the technical challenges of working with these complex, membrane proteins. Hither, we review what has been learned from structural studies of these 3 RTKs regarding their mechanisms of ligand bounden, activation, oligomerization, and inhibition. Nosotros discuss the implications for drug blueprint. More structural data on full-length RTKs may facilitate the discovery of druggable sites and drugs with improved specificity and effectiveness confronting resistant mutants.

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Biasing Receptor Tyrosine Kinase Signaling Pathways

John Watson , ... Andrew Alt , in Biased Signaling in Physiology, Pharmacology and Therapeutics, 2014

Receptor tyrosine kinases (RTK) are a relatively small-scale family unit of integral membrane receptors. However, RTKs comprise nodes at the center of vastly complex signaling networks involving hundreds of signaling proteins. These signaling networks have essential functions in virtually all aspects of creature cell growth, development, and differentiation. Dysregulation of these networks has been implicated in neoplastic and other diseases. The very complexity of RTK-mediated signaling creates opportunities for the identification of pathway-biased synthetic peptide or pocket-size molecule ligands that tin can selectively modulate a portion of an RTK signaling network. Such pathway-biased molecules may afford exquisite selectivity and utility in the treatment of diseases associated with disorders in RTK signaling.

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International Review of Cell and Molecular Biology

K.A. Han , ... J. Ko , in International Review of Jail cell and Molecular Biological science, 2016

2.1.two TrkC

TrkC belongs to a family of receptor tyrosine kinases whose members bind to neurotrophin-3 (NT-3), which exerts trophic action that potentiates neuronal activity ( Kim et al., 1994). However, unlike TrkB and encephalon-derived neurotrophic factor (BDNF), whose roles in synapse evolution have been well documented, the role of TrkC was largely unknown until it was identified as a synaptogenic factor that binds PTPσ (an interaction that involves the first 3 Ig domains of PTPσ) and induces excitatory presynaptic differentiation (Takahashi et al., 2011). Strikingly, TrkC does not bind to LAR or PTPδ (Takahashi et al., 2011). Interestingly, culling splicing inserts at MeA and MeB sites inside the Ig1-3 region modulate the interaction with PTPσ (Takahashi et al., 2011). More intriguingly, the NT-3 binding site in TrkC is distinct from that of PTPσ, suggesting that NT-three/TrkC/PTPσ may form a ternary complex that links NT-3 bounden with the TrkC/PTPσ synaptic adhesion pathway. It was recently shown that TrkC is required for dendritic growth and branching of cerebellar Purkinje neurons, and that NT-3 derived from presynaptic granule neurons is required for TrkC-dependent dendrite morphogenesis through a competitive process (Joo et al., 2014). Although a role for the TrkC/PTPσ circuitous in this context has non yet been investigated, these results suggest that the relative level of NT-3 may regulate TrkC-dependent excitatory evolution, likely by modulating the strength of the TrkC/PTPσ synaptic adhesion pathway. In support of this idea, NT-3 was recently shown to promote TrkC-mediated presynaptic assembly and role in hippocampal neurons (Ammendrup-Johnsen et al., 2015; Fig. 2A ).

Figure 2. Modulatory mechanisms regulating LAR-RPTP-based synaptic adhesion pathways. (A) The 2nd Ig domain of TrkC is required to bind neurotrophin-3 (NT-iii), whereas the first LRR and first Ig domains are required to bind PTPσ. At low local concentrations of NT-3 (left), monomeric TrkC induces presynaptic differentiation via binding to monomeric PTPσ. In contrast, when the NT-iii concentration is high (right), NT-3-binding to TrkC induces dimerization and enhances its synaptogenic action to trigger presynaptic differentiation in contacting axons of cocultured hippocampal neurons. Thus, NT-3 may deed equally a positive regulator of the TrkC-PTPσ synaptic organizing complexes. (B) In the presence of brain-derived neurotrophic factor (BDNF), TrkB is dimerized and binds to the kickoff leucine-rich repeat (LRR) domain of Slitrk5 in the cis configuration, whereas in the absenteeism of BDNF, monomeric TrkB does non bind to Slitrk5, which instead interacts with PTPσ. Thus, BDNF appears to regulate the specific interaction of TrkB with Slitrk5 at excitatory synapses in a local concentration-dependent mode. (C) HSPG bind the showtime immunoglobulin-like domain of LAR-RPTPs via their GAG chains. HSPGs compete for bounden to LAR-RPTPs with other LAR-RPTP-interacting ligands (eg, TrkC). When the local concentration of heparan sulfate (HS) is higher (left), oligomerization of LAR-RPTPs is induced, leading to detachment from other extracellular synaptic adhesion events. In contrast, when the local concentration of HS is low, LAR-RPTPs preferentially interact with ligands other than glypicans (GPCs) (right).

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Tyrosine Kinases

Andree Blaukat , in xPharm: The Comprehensive Pharmacology Reference, 2007

Introduction

Protein tyrosine kinases (PTKs) are enzymes that catalyze the transfer of the-phosphate grouping of ATP to tyrosine residues of protein substrates. The activity of PTKs is controlled in a complex manner past posttranslational modifications and by inter- and intramolecular circuitous formations Hubbard et al (1998), Hubbard and Till (2000). PTKs have been implicated in the regulation of a variety of biological responses such every bit cell proliferation, migration, differentiation, and survival. They have been demonstrated to play important roles in the development of many disease states, including immunodeficiency, atherosclerosis, psoriasis, osteoporosis, diabetes, and cancer.

PTKs can exist subdivided into 2 large families, receptor tyrosine kinases (RTKs) and nonreceptor tyrosine kinases. The human genome encodes for a full of xc tyrosine kinases, of which 32 are nonreceptor PTKs that can be placed in 10 subfamilies (come across figure in Protein information) Robinson et al (2000).

Nonreceptor PTKs are involved in signal transduction pathways of well-nigh all transmembrane receptors Neet and Hunter (1996).

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Receptor Tyrosine Kinases in Cardiac Musculus

Tiffany 50. Shih , Aarif Y. Khakoo , in Muscle, 2012

Biological Part of RTKs

RTKs have emerged as key regulators in many critical cellular processes, including cellular proliferation, differentiation, survival, metabolism, migration, and cell cycle command. Genetic changes, overexpression, or dysregulation of RTKs are implicated in a wide range of diseases. More than specifically, four master mechanisms are thought to mediate abnormal RTK activation: autocrine activation, chromosomal translocation, RTK overexpression, and gain-of-part mutations (3). RTKs have as well been identified in developmental mutations that cake differentiation of a multifariousness of prison cell types in several models, C. elegans, Drosophila, and the mouse. Mechanisms betwixt these species appear to be highly conserved (3,8–10).

RTK mutations and aberrant activation of downstream furnishings accept been linked to cancer, diabetes, inflammation, severe os disorders, arteriosclerosis, and angiogenesis. Therefore, RTKs are a subject area of avid research equally an important drug target in many human diseases, especially in the field of oncology. Two categories of cancer therapies have been developed. The kickoff is minor-molecule inhibitors like imatinib (Gleevec; xi,12) and sunitinib (Sutent) that specifically target the ATP-binding site of intracellular tyrosine kinase domains. The second group, which includes drugs such as trastuzumab (Herceptin; 13,fourteen) and bevacizumab (Avastin), are monoclonal antibodies that interfere with RTK activation and preferentially target RTK-expressing cells for destruction past the immune arrangement (15,16). Despite such breakthroughs in RTK-related therapies, 1 concern is that cancers tin develop resistance to tyrosine kinase inhibitors. Therefore, development of escape mechanisms is crucial in the endeavor to circumvent or prevent the development of resistance, perhaps with combination agents (iii,15–17).

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Molecular Targeted Therapy

Daphne A. Haas-Kogan Medico , Sean M. McBride MD , in Leibel and Phillips Textbook of Radiations Oncology (Third Edition), 2010

Inhibition of Tyrosine Kinase Receptors

Receptor tyrosine kinases (RTKs) play pleiotropic roles in maintaining homeostasis of individual cells, specific tissues, and unabridged organisms. The function of RTKs must be tightly regulated, since they mediate fundamental cellular functions including proliferation, survival, adhesion, and differentiation. RTK molecules share a ligand-binding extracellular portion, a transmembrane department, and an intracellular portion that contains the tyrosine kinase catalytic domain. 1-3 The family of RTKs includes the epidermal growth factor receptor (EGFR), platelet-derived growth cistron receptor (PDGFR), vascular endothelial growth factor receptor (VEGFR), fibroblast growth factor receptor (FGFR), stem-prison cell factor receptor (SCFR), and nervus growth factor receptor (NGFR). Inactivating mutations in various domains of the protein, including cytoplasmic juxtamembrane and extracellular and kinase domains, confer ligand-contained phosphorylation and kinase activation. 4 Activation of RTKs straight contributes to the initiation, progression, and prognosis of several human malignancies. five , half-dozen

Activating mutations occur in distinct domains of RTKs. These RTK domains are likewise targets of pharmacologic inhibitors directed at either the extracellular or intracellular domain. Agents that inhibit poly peptide tyrosine kinases fall into two principal categories: monoclonal antibodies and small-molecule inhibitors.

Monoclonal antibodies (mAbs) can prevent binding of ligands to their receptors, impede the subsequent phosphorylation loop, and thus block signaling through growth gene receptors. 7 , 8 Technical difficulties such every bit detrimental antibodies patients develop confronting rodent antibodies have been addressed by advances in antibiotic construction. ix

Small-molecule inhibitors compete with adenosine triphosphate (ATP) for binding sites in the receptor, blocking signaling through RTKs. 2 In comparing to mAbs, modest-molecular inhibitors confronting RTKs tend to have less specificity and multiple target receptors. They also accept significantly shorter one-half-lives than mAbs.

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Signaling Transduction and Metabolomics

Pere Puigserver , in Hematology (Seventh Edition), 2018

Receptor Tyrosine Kinases

Receptor tyrosine kinases (RTKs) are enzyme-linked receptors localized at the plasma membrane containing an extracellular ligand-binding domain, a transmembrane domain, and an intracellular protein–tyrosine kinase domain. In general, the ligands for RTKs are proteins such as IGF, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and FGF. Ephrins that bind to Eph receptors also grade a big subset of RTK ligands. Colony-stimulating-factor 1 (CSF-i), which is important for macrophage function, is some other example of an RTK ligand. RTKs tin can function as monomers or multimeric subunits assembled at the plasma membrane that, upon ligand binding, cause oligomerization or conformational changes followed by tyrosine (trans)-phosphorylation in the kinase activation loop. Activation of RTKs results in phosphorylation of boosted sites in the cytoplasmic part of the receptor, leading to docking of protein substrates, which initiates the intracellular signaling cascade. These substrates demark to RTK-phosphorylated tyrosines through Src Homology domain-two (SH2) or phosphotyrosine-bounden (PTB) domains. Examples of these types of proteins are insulin receptor substrates or the p85 regulatory subunit of PI3K. RTKs recruit, get together, and phosphorylate different proteins including adaptors and enzymes.

There are mechanisms to finish ligand-induced RTK activity through cellular processes including receptor-mediated endocytosis and/or through a family unit of regulated protein tyrosine phosphatases (PTPs), some of which are transmembrane and accept extracellular domains, suggesting the possibility of ligand-mediated regulation. Interestingly, there is likewise intracellular regulation of PTPs through negative-feedback loops to attenuate the signal or direct control through reactive oxygen species (ROS) (see later discussion).

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