Tyrosine receptor kinase

These kinases are allosteric enzymes. When the hormone binds to the binding region on the outside of the cell, it induces a conformarional change in the 

These signal transducers have a large extracellular domain with its ligandbinding site, a single transmembrane domain and an intracellular domain with intrinsic tyrosine kinase activity. 

Ligand binding to the receptor s extracellular domain activates signaling by causing the receptors to form dimers and cross-phosphorylate (autophospho- 

The signaling pathway downstream of the activated receptors is composed of a series of kinases, a kinase cascade. 

The phosphotyrosine sites on the receptor act as docking points for adaptors and effectors, which couple the signal to the kinase cascade. 

One of the major adaptors is the GRB2-SOS complex, which upon docking to the phosphorylated receptor, binds the small G protein Ras and activates it by GDP-GTP exchange in a manner analogous to the heterotrimeric G proteins. 

The various ways in which these downstream Lego components interact can be conveniently illustrated through the action of insulin, a hormone secreted in response to elevated 

Activated PKB (Akt) phosphorylates the following proteins with the indicated anabolic consequences Bad phosphorylation yields P-Bad which then dissociates from a Bcl-2-Bcl-X] complex in the mitochondrial outer membrane and is sequestered by 14.3.3 proteins. Mitochondrial pore blockage by the Bad-free Bcl-2-Bcl-xL complex successively prevents cytochrome c release from mitochondria, blocks procaspase activation by cytochrome c and thus inhibits apoptosis and increases cell survival. Phosphorylation of p70S6 kinase by PKB results in activation of this PK, phosphorylation of ribosomal small subunit protein S6 and enhancement of translation (protein synthesis). Phosphorylation of glycogen synthase (GS) kinase 3 (GSK3) by PKB results in an inactive P-GSK3, a consequent increase in the amount of the active non-phosphorylated form of GS and increased glycogen synthesis. 

The cytokine subfamily 1 includes erythropoietin (EPO) (that increases red blood cell production and has accordingly been involved in sports drug abuse), granulocyte colony stimulating factor (G-GSF) (that stimulates leucocyte differentiation), GH (used clinically for growth impairment due to GH deficiency), prolactin (PRL) (that promotes milk production), IL-4 and IL-7. The members of this family act via homodimeric receptors. The leucocyte-derived cytokines of this group variously modulate haematopoiesis and immune responses. 

Cytokine subfamily 2 includes proteins with heterodimeric a—(3 or ct-gpl30 receptors. Thus, granulocyte macrophage colony stimulating factor (GM-GSF), IL-3 and IL-5 act via a—(3 receptors and share (3 receptors. Cardiotrophin-1 (GT-1), ciliary neurotrophic factor (CTNF), IL-6, IL-1, leukaemia inhibitory factor (LIF) and oncostatin M (OSM) act via heterodimeric a-gpl30 receptors with a shared gpl30 receptor subunit. Leucocyte-derived cytokines of this family have immunomodulatory and haematopoietic effects. 

Cytokines of subfamily 3 include the leucocyte-derived interleukins IL-2, IL-4, IL-7, IL-9 and IL-15 that act via heterotrimeric a—3y receptors and variously modulate haematopoiesis and immune responses. 

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There are five known classes of enzyme-linked receptors (1) receptor tyrosine kinases, which phosphorylate specific tyrosine residues on intracellular signaling proteins (2) tyrosine kinase-associated receptors, such as the prolactin and growth hormone receptors we have already discussed, which... 

Figure 13.24 Six subfamilies of receptor tyrosine kinases involved in cell growth and differentiation. Only one or two members of each subfamily are indicated. Note that the tyrosine kinase domain is interrupted by a "kinase insert region" in some of the subfamilies. The functional significance of the cysteine-rich and immunoglobulin-like domains is unknown.

III. Tyr protein kinases A. Cytosolic tyrosine kinases src, fgr, abl, etc.) B. Receptor tyrosine kinases (RTKs) Plasma membrane receptors for hormones such as epidermal growth factor (EGF) or platelet-derived growth factor (PDGE) Raf (a protein kinase)... 

Phospholipid Insulin Receptor Tyrosin Kinases Growth Factors... 

VEGF receptor blockers Small receptor tyrosine kinase antagonists... 

Angiopoietins are growth factor ligands of the receptor tyrosine kinase Tie-2 which are critical regulators of vascular assembly and differentiation. 

EGFR Receptor tyrosine kinase Inhibition of cell proliferation and colony formation decrease of in vivo tumorigenicity... 

RET Receptor tyrosine kinase Inhibition of colony formation... 

Ephrins are a group of membranous ligands, which function through a family of receptor tyrosine kinases (Ephs). Ephrin/Eph-mediated signaling processes are involved in morphogenetic processes taking place e.g. during the development of the nervous system or the vasculature. 

Growth factor family Receptor tyrosine kinase Major physiological functions... 

Marshall CJ (1995) Specificity of receptor tyrosine kinase signaling transient versus sustained extracellular signal-regulated kinase activation. Cell 80 179-185... 

Marmor MD, Yarden Y (2004) Role of protein ubiquity la-tion in regulating endocytosis of receptor tyrosine kinases. Oncogene 23 2057-2070... 

The insulin receptor is a transmembrane receptor tyrosine kinase located in the plasma membrane of insulin-sensitive cells (e.g., adipocytes, myocytes, hepatocytes). It mediates the effect of insulin on specific cellular responses (e.g., glucose transport, glycogen synthesis, lipid synthesis, protein synthesis). 

Insulin Receptor. Figure 1 Structure and function of the insulin receptor. Binding of insulin to the a-subunits (yellow) leads to activation of the intracellular tyrosine kinase ((3-subunit) by autophosphorylation. The insulin receptor substrates (IRS) bind via a phospho-tyrosine binding domain to phosphorylated tyrosine residues in the juxtamembrane domain of the (3-subunit. The receptor tyrosine kinase then phosphorylates specific tyrosine motifs (YMxM) within the IRS. These tyrosine phosphorylated motifs serve as docking sites for some adaptor proteins with SRC homology 2 (SH2) domains like the regulatory subunit of PI 3-kinase. 

Vanadate (sodium orthovanadate or peroxovanadate) exhibits insulin-like effects in vitro (activation of insulin receptor tyrosine kinase, PI 3-kinase, Akt) and in vivo (diabetic rats, humans). These effects can be explained at least in part by the inhibition of phosphotyrosine phosphatases which deactivate the INSR tyrosine kinase. 

Besides the cytokine receptors that lack intrinsic kinase activity but have associated JAK kinases, STAT proteins can be activated by a variety of G-protein coupled receptors and growth factor receptors with intrinsic tyrosine kinase activity (for example EGF, PDGF, CSF-1, and angiotensin receptor). Increasing evidence suggests a critical role for STAT family members in oncogenesis and aberrant cell proliferation. Constitutively activated STATs have been found in many transformed cell lines and a wide variety of human tumor entities. Numerous non-receptor tyrosine kinases and viral oncoproteins, such as v-Src, v-Abl, v-Sis, and v-Eyk, have been identified to induce DNA-binding activity of STAT proteins. 

NGF binds to the transmembrane receptor tyrosine kinase (trk, or pl40trk), now referred to as TrkA. BDNF binds to TrkB, whereas NT-3 can bind to all three Trk (A,B,C) receptors, with a preference to TrkC, and NT-4/ 5 can bind both TrkA and TrkB. Furthermore, all neurotrophins also bind with equal affnity to a 75 kD transmembrane glycoprotein, p75NTR (also referred to... 

Molecnles that Interfere with Receptor Tyrosine Kinase Activity... 

Besides cytoplasmic protein kinases, membrane receptors can exert protein kinase activity. These so-called receptor tyrosine kinases (RTK) contain a ligandbinding extracellular domain, a transmembrane motif, and an intracellular catalytic domain with specificity for tyrosine residues. Upon ligand binding and subsequent receptor oligomerization, the tyrosine residues of the intracellular domain become phosphory-lated by the intrinsic tyrosine kinase activity of the receptor [3, 4]. The phosphotyrosine residues ftmction as docking sites for other proteins that will transmit the signal received by the RTK. 

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