Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Receptor tyrosine kinases of the Axl family are activated by Gas6, the product of growth arrest-specific gene 6. Gas6-Axl signaling is implicated in cell survival, adhesion, and migration. The receptor-binding site of Gas6 is located within a C-terminal pair of laminin G-like (LG) domains that do not resemble any other receptor tyrosine kinase ligand. We report the crystal structure at 2.2-A resolution of a Gas6 fragment spanning both LG domains (Gas6-LG). The structure reveals a V-shaped arrangement of LG domains strengthened by an interdomain calcium-binding site. LG2 of Gas6-LG contains two unusual features: an alpha-helix cradled by one edge of the LG beta-sandwich and a conspicuous patch of surface-exposed hydrophobic residues. Mutagenesis of some residues in this patch reduces Gas6-LG binding to the extracellular domain of Axl as well as Axl activation in glioblastoma cells, identifying a component of the receptor-binding site of Gas6.
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PMID:Crystal structure of a C-terminal fragment of growth arrest-specific protein Gas6. Receptor tyrosine kinase activation by laminin G-like domains. 1221 57

Deregulation of protein kinase activity has been shown to play a central role in the pathogenesis of human cancer. The molecular pathogenesis of chronic myelogenous leukemia (CML) in particular, depends on formation of the bcr-abl oncogene, leading to constitutive expression of the tyrosine kinase fusion protein, Bcr-Abl. Based on these observations, imatinib was developed as a specific inhibitor for the Bcr-Abl protein tyrosine kinase. The expanding understanding of the basis of imatinib-mediated tyrosine kinase inhibition has revealed a spectrum of potential new antitumor applications beyond the powerful activity already reported in the treatment of CML. Imatinib has shown activity in vivo against PDGF-driven tumor models including glioblastoma, dermatofibrosarcoma protuberans and chronic myelomonocytic leukemia. Antiangiogenic effects have been demonstrated by inhibition of PDGF-, VEGF (vascular endothelial growth factor)- and bFGF- (basic fibroblast growth factor) induced angiogenesis in vivo, and by inhibition of angiogenesis and tumor growth in an experimental bone metastasis model. Imatinib has been shown to reduce interstitial fluid pressure in an experimental colonic carcinoma model by blocking PDGF-mediated effects on tumor-associated blood vessels and stromal tissue. It is also a potent inhibitor of the Kit receptor tyrosine kinase, and has demonstrated activity clinically against the Kit-driven gastrointestinal stromal tumor (GIST) and experimentally in small-cell lung cancer cell lines. The pharmacology of imatinib and its activity in various tumor models is discussed.
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PMID:Pharmacology of imatinib (STI571). 1252 70

Activating oncogenic mutations of receptor tyrosine kinases (RTKs) have been reported in several types of cancers. In many cases, genomic rearrangements lead to the fusion of unrelated genes to the DNA coding for the kinase domain of RTKs. All RTK-derived fusion proteins reported so far display oligomerization sequences within the 5' fusion partners that are responsible for oncogenic activation. Here, we report a mechanism by which an altered RTK gains oncogenic potential in a glioblastoma cell line. A microdeletion on 6q21 results in the fusion of FIG, a gene coding for a Golgi apparatus-associated protein, to the kinase domain of the protooncogene c-ROS. The fused protein product FIG-ROS is a potent oncogene, and its transforming potential resides in its ability to interact with and become localized to the Golgi apparatus. Thus we have found a RTK fusion protein whose subcellular location leads to constitutive kinase activation and results in oncogenic transformation.
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PMID:Oncogenic targeting of an activated tyrosine kinase to the Golgi apparatus in a glioblastoma. 1253 61

Aberrant receptor tyrosine kinase signaling plays an important role in the molecular pathogenesis of brain tumors. We have been studying a previously identified human glioblastoma-derived PDGFR-alpha mutant that has an in-frame deletion in the extracellular domain, causing loss of exons 8 and 9 (PDGFR-alpha(delta8,9)). In the primary tumor, this deletion mutant receptor was shown to be amplified and overexpressed. The purpose of this study was to determine the expression, activity, localization, and transformation properties of this deletion mutant. In the absence of serum, or PDGF-AA, PDGFR-alpha(delta8,9) was phosphorylated on tyrosine residues, indicating ligand-independent autoactivation. Localization by staining and cell surface biotinylation studies revealed expression of the deletion mutant predominantly in the cytoplasm, with very little present on the cell surface. To determine if PDGFR-alpha(delta8,9) was oncogenic, we transfected wild-type and mutant receptors into Rat1 cells and performed analyses of cell growth, in vitro transformation, and subcutaneous growth in the nude mouse. PDGFR-alpha(delta8,9)-expressing cells displayed enhanced cell growth and survival in low serum, and formed foci in monolayer cultures. PDGFR-alpha(delta8,9)-expressing Rat1 cells were also tumorigenic when injected subcutaneously into nude mice. Expression of PDGFR-alpha(delta8,9) was also associated with increased c-Jun phosphorylation in the absence of PDGF ligand, demonstrating also that the mutant receptor is associated with altered intracellular signaling. These data demonstrate that PDGFR-alpha(delta8,9) is transforming, and it is the first demonstration of a naturally occurring tumor-derived mutant PDGFR-alpha with oncogenic properties.
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PMID:A human brain tumor-derived PDGFR-alpha deletion mutant is transforming. 1256 64

The transmembrane proto-oncogene receptor tyrosine kinase (RTK) ROS is an orphan receptor that is aberrantly expressed in neoplasms of the central nervous system. Here, we report the fusion of its carboxy-terminal kinase domain to the amino-terminal portion of a protein called FIG (Fused in Glioblastoma) in a human glioblastoma multiforme (GBM). By characterizing both FIG and ROS genes in normal and in U118MG GBM cells, we determined that an intra-chromosomal homozygous deletion of 240 kilobases on 6q21 is responsible for the formation of the FIG-ROS locus. The FIG-ROS transcript is encoded by 7 FIG exons and 9 ROS-derived exons. We also demonstrate that the FIG-ROS locus encodes for an in-frame fusion protein with a constitutively active kinase activity, suggesting that FIG-ROS may act as an oncogene. This is the first example of a fusion RTK protein that results from an intra-chromosomal deletion, and it represents the first fusion RTK protein isolated from a human astrocytoma.
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PMID:Fusion of FIG to the receptor tyrosine kinase ROS in a glioblastoma with an interstitial del(6)(q21q21). 1266 Oct 6

Receptor tyrosine kinase activation contributes to cell viability during cytotoxic therapy. The novel broad spectrum receptor tyrosine kinase inhibitor, SU11248, inhibits vascular endothelial growth factor receptor 2, platelet-derived growth factor receptor, c-kit, and fetal liver tyrosine kinase 3. In this study, we maintained SU11248 plasma levels beyond the completion of radiotherapy to determine whether tumor regrowth can be delayed. The antiangiogenic effects of SU11248 were demonstrated using human umbilical vein endothelial cells in vitro. Apoptosis increased and clonogenic survival decreased when SU11248 was used in combination with radiation from 0 to 6 Gy on endothelial cells. In vivo tumor growth delay was increased in C57B6J mice with Lewis lung carcinoma or glioblastoma multiform (GL261) hind limb tumors. Mice were treated with daily i.p. injections (40 mg/kg) of SU11248 during 7 days of radiation treatment (21 Gy). Combined treatment with SU11248 and radiation significantly reduced tumor volume as compared with either treatment alone. Concomitant reduction in vasculature was confirmed using the dorsal vascular window model. The vascular length established using images taken from a consistent quadrant in the window show the combination therapy was more effective in destroying tumor vasculature than either treatment alone. SU11248 maintenance administration beyond the completion of radiotherapy results in prolongation of tumor control. In summary, SU11248 enhances radiation-induced endothelial cytotoxicity, resulting in tumor vascular destruction and tumor control when combined with fractionated radiotherapy in murine tumor models. Moreover, inhibition of angiogenesis well beyond radiation therapy may be a promising treatment paradigm for refractory human neoplasms.
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PMID:SU11248 maintenance therapy prevents tumor regrowth after fractionated irradiation of murine tumor models. 1287 99

Resistance to chemotherapy is a common feature of malignant gliomas. This resistance is mediated by receptor tyrosine kinase (RTK)-regulated signaling. p21-Ras protein is pivotal in the propagation of the signal originated from many RTKs. Our aim was to investigate whether inhibition of Ras pathway affects the response to cisplatin in malignant gliomas. We found an enhanced sensitivity to cisplatin of two glioblastoma cell lines expressing dominant negative Ras. Moreover, DN-Ras expressing cells, implanted in nude mice, resulted in being extremely sensitive to cisplatin. The growth of all the tumors was significantly inhibited by combining DN-Ras adenovirus infection with cisplatin treatment. The majority of glioma cells expressing DN-Ras underwent apoptosis in response to cisplatin. In vivo, DN-Ras alone did not influence the growth of tumors, suggesting that the effects of Ras-inhibition observed in vitro could not be extrapolated in vivo. The survival signal pathway transduced by Ras was essentially mediated by inhibition of caspase-9 cleavage via PI3K/Akt.
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PMID:Ras inhibition amplifies cisplatin sensitivity of human glioblastoma. 1521 56

Downstream signaling that results from the interaction of hepatocyte growth factor/scatter factor (HGF/SF) with the receptor tyrosine kinase Met plays critical roles in tumor development, progression, and metastasis. This ligand-receptor pair is an attractive target for new diagnostic and therapeutic agents, preclinical development of which requires suitable animal models. The growth of heterotopic and orthotopic Met-expressing human tumor xenografts in conventional strains of immunocompromised mice inadequately replicates the paracrine stimulation by human HGF/SF (hHGF/SF) that occurs in humans with cancer. We have therefore generated a mouse strain transgenic for hHGF/SF (designated hHGF-Tg) on a severe combined immunodeficiency (SCID) background. We report here that the presence of ectopically expressed hHGF/SF ligand significantly enhances growth of heterotopic subcutaneous xenografts derived from human Met-expressing cancer cells, including the lines SK-LMS-1 (human leiomyosarcoma), U118 (human glioblastoma), and DU145 (human prostate carcinoma), but not that of M14-Mel xenografts (human melanoma that expresses insignificant levels of Met). Our results indicate that ectopic hHGF/SF can specifically activate Met in human tumor xenografts. This new hHGF-Tg strain of mice should provide a powerful tool for evaluating drugs and diagnostic agents that target the various pathways influenced by Met activity.
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PMID:Enhanced growth of human met-expressing xenografts in a new strain of immunocompromised mice transgenic for human hepatocyte growth factor/scatter factor. 1553 25

Amplification and mutation of the epidermal growth factor receptor (EGFR) is common in astrocytoma. The most frequently occurring mutation (DeltaEGFR, EGFRvIII) deletes exons 2-7 from this receptor tyrosine kinase (RTK), and signals constitutively in the absence of ligand. DeltaEGFR is not found in normal tissue, and therefore represents an attractive therapeutic target. Here, we show that a small interfering RNA (siRNA) directed against the unique exon 1/exon 8 junction sequence of DeltaEGFR efficiently suppressed expression of DeltaEGFR in rodent fibroblasts and in two human glioblastoma cell lines. SiRNA-mediated depletion of DeltaEGFR led to reduction in the levels of phosphorylated Akt in glioma cells, was associated with increased apoptosis, and induced partial arrest at the G2M phase of the cell cycle. Inhibitors of PI3 kinase cooperated with siRNA treatment, leading to further increases in both cell cycle blockade and apoptosis. Importantly, cell cycle blockade could be reversed, and apoptosis rescued using a conditional allele of Akt, implicating Akt as a primary target of combination therapy. This study demonstrates the therapeutic potential of siRNA to impact DeltaEGFR as a glioma-specific target, and offers a mechanistic rationale for combining siRNA and small molecule inhibitor therapies against distinct components in the EGFR signaling pathway.
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PMID:RNA interference against a glioma-derived allele of EGFR induces blockade at G2M. 1558 Feb 96

Experimental in vivo tumor models are essential for comprehending the dynamic process of human cancer progression, identifying therapeutic targets, and evaluating antitumor drugs. However, current rodent models are limited by high costs, long experimental duration, variability, restricted accessibility to the tumor, and major ethical concerns. To avoid these shortcomings, we investigated whether tumor growth on the chick chorio-allantoic membrane after human glioblastoma cell grafting would replicate characteristics of the human disease. Avascular tumors consistently formed within 2 days, then progressed through vascular endothelial growth factor receptor 2-dependent angiogenesis, associated with hemorrhage, necrosis, and peritumoral edema. Blocking of vascular endothelial growth factor receptor 2 and platelet-derived growth factor receptor signaling pathways by using small-molecule receptor tyrosine kinase inhibitors abrogated tumor development. Gene regulation during the angiogenic switch was analyzed by oligonucleotide microarrays. Defined sample selection for gene profiling permitted identification of regulated genes whose functions are associated mainly with tumor vascularization and growth. Furthermore, expression of known tumor progression genes identified in the screen (IL-6 and cysteine-rich angiogenic inducer 61) as well as potential regulators (lumican and F-box-only 6) follow similar patterns in patient glioma. The model reliably simulates key features of human glioma growth in a few days and thus could considerably increase the speed and efficacy of research on human tumor progression and preclinical drug screening.
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PMID:Accessing key steps of human tumor progression in vivo by using an avian embryo model. 1566


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