Showing papers on "Receptor tyrosine kinase published in 1999"

Mechanism of Action and In Vivo Role of Platelet-Derived Growth Factor

Abstract: Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Beta-arrestin-dependent formation of beta2 adrenergic receptor-Src protein kinase complexes.

Abstract: The Ras-dependent activation of mitogen-activated protein (MAP) kinase pathways by many receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) requires the activation of Src family tyrosine kinases. Stimulation of beta2 adrenergic receptors resulted in the assembly of a protein complex containing activated c-Src and the receptor. Src recruitment was mediated by beta-arrestin, which functions as an adapter protein, binding both c-Src and the agonist-occupied receptor. beta-Arrestin 1 mutants, impaired either in c-Src binding or in the ability to target receptors to clathrin-coated pits, acted as dominant negative inhibitors of beta2 adrenergic receptor-mediated activation of the MAP kinases Erk1 and Erk2. These data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.

SU5416 Is a Potent and Selective Inhibitor of the Vascular Endothelial Growth Factor Receptor (Flk-1/KDR) That Inhibits Tyrosine Kinase Catalysis, Tumor Vascularization, and Growth of Multiple Tumor Types

Abstract: SU5416, a novel synthetic compound, is a potent and selective inhibitor of the Flk-1/KDR receptor tyrosine kinase that is presently under evaluation in Phase I clinical studies for the treatment of human cancers. SU5416 was shown to inhibit vascular endothelial growth factor-dependent mitogenesis of human endothelial cells without inhibiting the growth of a variety of tumor cells in vitro. In contrast, systemic administration of SU5416 at nontoxic doses in mice resulted in inhibition of subcutaneous tumor growth of cells derived from various tissue origins. The antitumor effect of SU5416 was accompanied by the appearance of pale white tumors that were resected from drug-treated animals, supporting the antiangiogenic property of this agent. These findings support that pharmacological inhibition of the enzymatic activity of the vascular endothelial growth factor receptor represents a novel strategy for limiting the growth of a wide variety of tumor types.

A mechanism for hormone-independent prostate cancer through modulation of androgen receptor signaling by the HER-2/neu tyrosine kinase.

Abstract: Prostate cancer progresses from a hormone-sensitive, androgen-dependent stage to a hormone-refractory, androgen-independent tumor. The androgen receptor pathway functions in these androgen-independent tumors despite anti-androgen therapy. In our LAPC-4 prostate cancer model, androgen-independent sublines expressed higher levels of the HER-2/neu receptor tyrosine kinase than their androgen-dependent counterparts. Forced overexpression of HER-2/neu in androgen-dependent prostate cancer cells allowed ligand-independent growth. HER-2/neu activated the androgen receptor pathway in the absence of ligand and synergized with low levels of androgen to 'superactivate' the pathway. By modulating the response to low doses of androgen, a tyrosine kinase receptor can restore androgen receptor function to prostate cancer cells, a finding directly related to the clinical progression of prostate cancer.

The JAK‐binding protein JAB inhibits Janus tyrosine kinase activity through binding in the activation loop

Abstract: The Janus family of protein tyrosine kinases (JAKs) regulate cellular processes involved in cell growth, differentiation and transformation through their association with cytokine receptors. However, compared with other kinases, little is known about cellular regulators of the JAKs. We have recently identified a JAK-binding protein (JAB) that inhibits JAK signaling in cells. In the studies presented here we demonstrate that JAB specifically binds to the tyrosine residue (Y1007) in the activation loop of JAK2, whose phosphorylation is required for activation of kinase activity. Binding to the phosphorylated activation loop requires the JAB SH2 domain and an additional N-terminal 12 amino acids (extended SH2 subdomain) containing two residues (Ile68 and Leu75) that are conserved in JAB-related proteins. An additional N-terminal 12-amino-acid region (kinase inhibitory region) of JAB also contributes to high-affinity binding to the JAK2 tyrosine kinase domain and is required for inhibition of JAK2 signaling and kinase activity. Our studies define a novel type of regulation of tyrosine kinases and might provide a basis for the design of specific tyrosine kinase inhibitors.

A novel vascular endothelial growth factor encoded by Orf virus, VEGF‐E, mediates angiogenesis via signalling through VEGFR‐2 (KDR) but not VEGFR‐1 (Flt‐1) receptor tyrosine kinases

Abstract: The different members of the vascular endothelial growth factor (VEGF) family act as key regulators of endothelial cell function controlling vasculogenesis, angiogenesis, vascular permeability and endothelial cell survival. In this study, we have functionally characterized a novel member of the VEGF family, designated VEGF-E. VEGF-E sequences are encoded by the parapoxvirus Orf virus (OV). They carry the characteristic cysteine knot motif present in all mammalian VEGFs, while forming a microheterogenic group distinct from previously described members of this family. VEGF-E was expressed as the native protein in mammalian cells or as a recombinant protein in Escherichia coli and was shown to act as a heat-stable, secreted dimer. VEGF-E and VEGF-A were found to possess similar bioactivities, i.e. both factors stimulate the release of tissue factor (TF), the proliferation, chemotaxis and sprouting of cultured vascular endothelial cells in vitro and angiogenesis in vivo. Like VEGF-A, VEGF-E was found to bind with high affinity to VEGF receptor-2 (KDR) resulting in receptor autophosphorylation and a biphasic rise in free intracellular Ca2+ concentration, whilst in contrast to VEGF-A, VEGF-E did not bind to VEGF receptor-1 (Flt-1). VEGF-E is thus a potent angiogenic factor selectively binding to VEGF receptor-2. These data strongly indicate that activation of VEGF receptor-2 alone can efficiently stimulate angiogenesis.

Activating and dominant inactivating c-KIT catalytic domain mutations in distinct clinical forms of human mastocytosis

Abstract: Human mastocytosis is characterized by increased mast cells. It usually occurs as a sporadic disease that is often transient and limited in children and persistent or progressive in adults. The c-KIT protooncogene encodes KIT, a tyrosine kinase that is the receptor for mast cell growth factor. Because mutated KIT can transform cells, we examined c-KIT in skin lesions of 22 patients with sporadic mastocytosis and 3 patients with familial mastocytosis. All patients with adult sporadic mastocytosis had somatic c-KIT mutations in codon 816 causing substitution of valine for aspartate and spontaneous activation of mast cell growth factor receptor (P = 0.0001). A subset of four pediatric onset cases with clinically unusual disease also had codon 816 activating mutations substituting valine, tyrosine, or phenylalanine for aspartate. Typical pediatric patients lacked 816 mutations, but limited sequencing showed three of six had a novel dominant inactivating mutation substituting lysine for glutamic acid in position 839, the site of a potential salt bridge that is highly conserved in receptor tyrosine kinases. No c-KIT mutations were found in the entire coding region of three patients with familial mastocytosis. We conclude that c-KIT somatic mutations substituting valine in position 816 of KIT are characteristic of sporadic adult mastocytosis and may cause this disease. Similar mutations causing activation of the mast cell growth factor receptor are found in children apparently at risk for extensive or persistent disease. In contrast, typical pediatric mastocytosis patients lack these mutations and may express inactivating c-KIT mutations. Familial mastocytosis, however, may occur in the absence of c-KIT coding mutations.

Fibroblast growth factors as multifunctional signaling factors.

Abstract: The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors Their expression is controlled at the levels of transcription, mRNA stability, and translation The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR) FGFRs are required for most biological activities of FGFs HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-β bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton

Angiopoietins 3 and 4: Diverging gene counterparts in mice and humans (angiogenesisytie receptor tyrosine kinaseyvascular endothelial growth factor)

Abstract: The angiopoietins have recently joined the members of the vascular endothelial growth factor family as the only known growth factors largely specific for vascular endothelium. The angiopoietins include a naturally occurring agonist, angiopoietin-1, as well as a naturally occurring antagonist, angiopoietin-2, both of which act by means of the Tie2 receptor. We now report our attempts to use homology- based cloning approaches to identify new members of the angiopoietin family. These efforts have led to the identifica- tion of two new angiopoietins, angiopoietin-3 in mouse and angiopoietin-4 in human; we have also identified several more distantly related sequences that do not seem to be true angiopoietins, in that they do not bind to the Tie receptors. Although angiopoietin-3 and angiopoietin-4 are strikingly more structurally diverged from each other than are the mouse and human versions of angiopoietin-1 and angiopoi- etin-2, they appear to represent the mouse and human coun- terparts of the same gene locus, as revealed in our chromo- somal localization studies of all of the angiopoietins in mouse and human. The structural divergence of angiopoietin-3 and angiopoietin-4 appears to underlie diverging functions of these counterparts. Angiopoietin-3 and angiopoietin-4 have very different distributions in their respective species, and angiopoietin-3 appears to act as an antagonist, whereas angiopoietin-4 appears to function as an agonist. Two families of growth factors have been identified that are largely specific for the vascular endothelium, by virtue of having receptors that are mostly restricted to endothelial cells in their expression. These include vascular endothelial growth factor (VEGF) and its relatives, as well as the more recently discovered angiopoietins (1, 2). These two families seem to work in complementary and coordinated fashion during vas- cular development, with VEGF acting during the early stages of vessel development (3-5), and angiopoietin-1 (6) acting later to promote angiogenic remodeling as well as vessel maturation and stabilization (7, 8). Simply overexpressing angiopoietin-1 by using transgenic approaches leads to hyper- vascularization in vivo (9), suggesting that angiopoietin-1 is present in limiting quantities during angiogenesis in vivo. Angiopoietin-1 has a naturally occurring antagonist, termed angiopoietin-2, which blocks the ability of angiopoietin-1 to activate its receptor, Tie2 (10). Transgenic overexpression of angiopoietin-2 disrupts normal vascular development and results in early embryonic lethality (10). Angiopoietin-2 is the first example of a natural antagonist for a receptor tyrosine kinase in vertebrates, suggesting that activation of the Tie2 receptor must be particularly well titrated in vivo. Evidence suggests that such careful regulation might be involved at sites of vascular change in an otherwise stable adult vasculature. Thus, whereas angiopoietin-1 appears to be widely expressed in the adult in a manner suggesting that it is acting to stabilize vessels, angiopoietin-2 is expressed only at sites of vascular remodeling in the adult (10). It has been suggested that this expression of the antagonist blocks an otherwise constitutive stabilizing signal provided by angiopoietin-1, leading to local-

Discovery of a small molecule insulin mimetic with antidiabetic activity in mice.

Abstract: Insulin elicits a spectrum of biological responses by binding to its cell surface receptor. In a screen for small molecules that activate the human insulin receptor tyrosine kinase, a nonpeptidyl fungal metabolite (L-783,281) was identified that acted as an insulin mimetic in several biochemical and cellular assays. The compound was selective for insulin receptor versus insulin-like growth factor I (IGFI) receptor and other receptor tyrosine kinases. Oral administration of L-783,281 to two mouse models of diabetes resulted in significant lowering in blood glucose levels. These results demonstrate the feasibility of discovering novel insulin receptor activators that may lead to new therapies for diabetes.

Signal transduction by fibroblast growth factor receptors.

Abstract: The fibroblast growth factor family, with its prototype members acidic FGF (FGF-1) and basic FGF (FGF-2), binds to four related receptor tyrosine kinases, expressed on most types of cells in tissue culture. In many respects, the FGF receptors appear similar to other growth factor receptors. Thus, dimerization of receptor monomers upon ligand binding is likely to be a requisite for activation of the kinase domains, leading to receptor trans phosphorylation. FGF receptor-1 (FGFR-1), which shows the broadest expression pattern of the four FGF receptors contains at least seven tyrosine phosphorylation sites. A number of signal transduction molecules are affected by binding with different affinities to these phosphorylation sites. The potential roles of these signal transduction molecules in FGF-induced biological responses and in pathological processes are discussed.

Activating c-kit gene mutations in human germ cell tumors.

Abstract: The c-kit gene encodes a tyrosine kinase receptor (KIT) that is required in normal spermatogenesis and is expressed in seminomas and dysgerminomas, a subset of human germ cell tumors (GCTs). To determine whether activating mutations of the c-kit gene occur in GCTs, primary tissue samples of 33 testicular and ovarian tumors were examined for mutations in the juxtamembrane and phosphotransferase domains by polymerase chain reaction amplification and DNA sequencing. A novel missense mutation (D816H) was found in the phosphotransferase domain in tumors of seminoma/dysgerminoma differentiation. The c-kit alleles in nonneoplastic tissues from these patients were wild type, suggesting that the mutant alleles were acquired and selected for during malignant transformation. In cell transfection experiments, the D816H mutant protein was a constitutively activated kinase and was constitutively phosphorylated on tyrosine residues. This is the first description of an activating c-kit mutation in GCTs and is evidence that the KIT signal transduction pathway is important in the pathogenesis of neoplasms with seminoma differentiation.

c-Abl is activated by growth factors and Src family kinases and has a role in the cellular response to PDGF

Abstract: The c-Abl tyrosine kinase localizes to the cytoplasm and plasma membrane in addition to the nucleus. However, there is little information regarding a role for c-Abl in the cytoplasm/plasma membrane compartments. Here we report that a membrane pool of c-Abl is activated by the growth factors PDGF and EGF in fibroblasts. The pattern and kinetics of activation are similar to growth factor activation of Src family kinases. To determine whether a link existed between activation of c-Abl and members of the Src family, we examined c-Abl kinase activity in cells that expressed oncogenic Src proteins. We found that c-Abl kinase activity was increased by 10- to 20-fold in these cells, and that Src and Fyn kinases directly phosphorylated c-Abl in vitro. Furthermore, overexpression of wild-type Src potentiated c-Abl activation by growth factors, and a kinase-inactive form of Src reduced this activation, showing that Abl activation by growth factors occurs at least in part via activation of Src kinases. Significantly, we show that c-Abl has a functional role in the morphological response to PDGF. Whereas PDGF treatment of serum-starved wild-type mouse embryo fibroblasts resulted in distinct linear or circular/dorsal membrane ruffling, c-Abl-null cells demonstrated dramatically reduced ruffling in response to PDGF, which was rescued by physiological re-expression of c-Abl. These data identify c-Abl as a downstream target of activated receptor tyrosine kinases and Src family kinases, and show for the first time that c-Abl functions in the cellular response to growth factors.

Actin-based motility of vaccinia virus mimics receptor tyrosine kinase signalling.

Abstract: Studies of the actin-based motility of the intracellular pathogens Listeria monocytogenes and Shigella flexneri have provided important insight into the events occurring at the leading edges of motile cells. Like the bacteria Listeria and Shigella, vaccinia virus, a relative of the causative agent of smallpox, uses actin-based motility to spread between cells. In contrast to Listeria or Shigella, the actin-based motility of vaccinia is dependent on an unknown phosphotyrosine protein, but the underlying mechanism remains obscure. Here we show that phosphorylation of tyrosine 112 in the viral protein A36R by Src-family kinases is essential for the actin-based motility of vaccinia. Tyrosine phosphorylation of A36R results in a direct interaction with the adaptor protein Nck and the recruitment of the Ena/VASP family member N-WASP to the site of actin assembly. We also show that Nck and N-WASP are essential for the actin-based motility of vaccinia virus. We suggest that vaccinia virus spreads by mimicking the signalling pathways that are normally involved in actin polymerization at the plasma membrane.

The interleukin-10 signal transduction pathway and regulation of gene expression in mononuclear phagocytes.

Abstract: Interleukin-10 (IL-10) activates a diverse array of functional responses in mononuclear phagocytes. Functional IL-10 receptor (IL-10R) complexes are tetramers consisting of two IL-10R1 polypeptide chains and two IL-10R2 chains. Binding of IL-10 to the extracellular domain of IL-10R1 activates phosphorylation of the receptor-associated Janus tyrosine kinases, JAK1 and Tyk2. These kinases then phosphorylate specific tyrosine residues (Y446 and Y496) on the intracellular domain of the IL-10R1 chain. Once phosphorylated, these tyrosine residues (and their flanking peptide sequences) serve as temporary docking sites for the latent transcription factor, STAT3 (signal transducer and activator of transcription-3). STAT3 binds to these sites via its SH2 (Src homology 2) domain, and is, in turn, tyrosine-phosphorylated by the receptor-associated JAKs. It then homodimerizes and translocates to the nucleus where it binds with high affinity to STAT-binding elements (SBE) in the promoters of various IL-10-responsive genes. One of these genes, SOCS-3 (Suppressor of Cytokine Signaling-3) is a member of a newly identified family of genes that inhibit JAK/STAT-dependent signaling. Moreover, the ability of IL-10 to induce de novo synthesis of SOCS-3 in monocytes correlates with its ability to inhibit expression of many genes in these cells, including endotoxin-inducible cytokines such as tumor necrosis factor-alpha (TNF-alpha) and IL-1. Thus, the ability of IL-10 to inhibit gene expression in monocytes is associated with its ability to rapidly induce synthesis of SOCS-3.

Cytokine-inducible SH2 protein-3 (CIS3/SOCS3) inhibits Janus tyrosine kinase by binding through the N-terminal kinase inhibitory region as well as SH2 domain.

Abstract: Background The Janus family of protein tyrosine kinases (JAKs) regulate cellular processes involved in cell growth, differentiation and transformation through their association with cytokine receptors. We have recently identified the JAK-binding protein, JAB that inhibits various cytokine-dependent JAK signalling pathways. JAB inhibits JAK2 tyrosine kinase activity by binding to the kinase domain (JH1 domain) through the N-terminal kinase inhibitory region (KIR) and the SH2 domain. The SH2 domain of JAB has been shown to bind to the phosphorylated Y1007 in the activation loop of JH1. We also identified another JAK-binding protein, CIS3 (cytokine-inducible SH2-protein 3, or SOCS3) that inhibits signalling of various cytokines. However, the mechanism of JAK signal inhibition by CIS3 has not been clarified. Results We showed that endogenous CIS3 bound to JAK2 in intact cells. The CIS3-SH2 domain bound to the phosphorylated Y1007 of JH1, and inhibited tyrosine kinase activity through the N-terminal KIR. Therefore, CIS3 and JAB inhibit JAK2 tyrosine kinase activity by an essentially similar mechanism. However, we found that the affinity of the SH2 domain of CIS3 to Y1007 was weaker than that of JAB. In contrast, the KIR of CIS3 showed stronger potential for both binding to JH1 and inhibition of JAK kinase activity than that of JAB. Consistent with this notion, chimeras containing CIS3-KIR and JAB-SH2 domain inhibited JAK2 kinase activity more efficiently than the wild-type CIS3 or JAB. Conclusion CIS3 inhibits JAK2 kinase activity by binding to the activation loop through the SH2 domain, and KIR is necessary for kinase inhibition. Although the inhibitory mechanism by CIS3 is similar to that by JAB, the contributions of the SH2 domain and KIR for binding are different between JAB and CIS3. Our study defined the inhibitory mechanism of CIS3 and provides a useful information for creating a novel tyrosine kinase inhibitor.

Controlled Dimerization of ErbB Receptors Provides Evidence for Differential Signaling by Homo- and Heterodimers

Abstract: The four members of the ErbB family of receptor tyrosine kinases are involved in a complex array of combinatorial interactions involving homo- and heterodimers. Since most cell types express more than one member of the ErbB family, it is difficult to distinguish the biological activities of different homo- and heterodimers. Here we describe a method for inducing homo- or heterodimerization of ErbB receptors by using synthetic ligands without interference from the endogenous receptors. ErbB receptor chimeras containing synthetic ligand binding domains (FK506-binding protein [FKBP] or FKBP-rapamycin-binding domain [FRB]) were homodimerized with the bivalent FKBP ligand AP1510 and heterodimerized with the bifunctional FKBP-FRB ligand rapamycin. AP1510 treatment induced tyrosine phosphorylation of ErbB1 and ErbB2 homodimers and recruitment of Src homology 2 domain-containing proteins (Shc and Grb2). In addition, ErbB1 and ErbB2 homodimers activated downstream signaling pathways leading to Erk2 and Akt phosphorylation. However, only ErbB1 homodimers were internalized upon AP1510 stimulation, and only ErbB1 homodimers were able to associate with and induce phosphorylation of c-Cbl. Cells expressing AP1510-induced ErbB1 homodimers were able to associate with and induce phosphorylation of c-Cbl. Cells expressing AP1510-induced ErbB1 homodimers were able to form foci; however, cells expressing ErbB2 homodimers displayed a five- to sevenfold higher focus-forming ability. Using rapamycin-inducible heterodimerization we show that c-Cbl is unable to associate with ErbB1 in a ErbB1-ErbB2 heterodimer most likely because ErbB2 is unable to phosphorylate the c-Cbl binding site on ErbB1. Thus, we demonstrate that ErbB1 and ErbB2 homodimers differ in their abilities to transform fibroblasts and provide evidence for differential signaling by ErbB homodimers and heterodimers. These observations also validate the use of synthetic ligands to study the signaling and biological specificity of selected ErbB dimers in any cell type.

G-protein-coupled receptors act via protein kinase C and Src to regulate NMDA receptors.

Abstract: The N-methyl-D-aspartate (NMDA) receptor contributes to synaptic plasticity in the central nervous system and is both serine-threonine and tyrosine phosphorylated. In CA1 pyramidal neurons of the hippocampus, activators of protein kinase C (PKC) as well as the G-protein-coupled receptor ligands muscarine and lysophosphatidic acid enhanced NMDA-evoked currents. Unexpectedly, this effect was blocked by inhibitors of tyrosine kinases, including a Src required sequence and an antibody selective for Src itself. In neurons from mice lacking c-Src, PKC-dependent upregulation was absent. Thus, G-protein-coupled receptors can regulate NMDA receptor function indirectly through a PKC-dependent activation of the non-receptor tyrosine kinase (Src) signaling cascade.