Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:O95477 (membrane-bound)
 29,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated the signaling pathways mediating 1-pS Ca2+ channel activation by PDGF in cultured rat mesangial cells. In cell-attached patches, intrapipette PDGF-BB (PDGF B chain homodimer isoform) (50 ng/ml) dramatically stimulates channel activity (P < 0.003, n = 6). Tyrosine kinase inhibition (100 microM genistein or 10 microM tryphostin 9) abolished PDGF-induced channel activation (P < 0.02, n = 6). In excised patches, the effect of tyrosine kinase inhibition could be reversed by 200 microM GTPgammaS (P < 0.02, n = 4). In contrast, 200 microM GDPbetaS inhibited PDGF-induced channel activity (P < 0.04, n = 6). Pertussis toxin (250 ng/ml) had no effect on PDGF-induced channel activity (P = 0.45, n = 6). When excised patches were exposed to anti-Ras antibody (5 microg/ml), PDGF-induced channel activity was abolished (P < 0.002, n = 11). Western immunoblots revealed that PDGF-BB binding stimulates the formation of a membrane-bound complex consisting of growth factor receptor-binding protein 2, son of sevenless, and the PDGF-beta receptor. Complex formation was abolished by genistein. In mesangial cells, the intrinsic tyrosine kinase activity of the PDGF-beta receptor stimulates the formation of a membrane-bound growth factor receptor-binding protein 2/son of sevenless/PDGF-beta receptor complex and activation of the pertussis toxin-insensitive GTP-binding protein, p21-Ras, which leads to the opening of 1-pS Ca2+ channels.
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PMID:Ca2+ channel activation by platelet-derived growth factor-induced tyrosine phosphorylation and Ras guanine triphosphate-binding proteins in rat glomerular mesangial cells. 863 14

The HER-2/neu gene product, p185(neu), is a membrane-bound receptor with tyrosine kinase activity. High levels of p185(neu) is correlated with intrinsic chemoresistance of non-small cell lung cancer (NSCLC) cell lines. We investigated the effects of tyrphostin AG825, a selective tyrosine kinase inhibitor preferentially inhibiting HER-2/neu kinase, on the chemosensitivities and on the drug-induced cell cycle changes of NSCLC cell lines that expressed different levels of p185(neu). Compared to the low-p185(neu) expressing cell lines, we found that the high-p185(neu) expressing cell lines were more resistant to doxorubicin, etoposide, and cis-diamminedichloroplatinum(II) but more sensitive to AG825. AG825 was able to significantly enhance the chemosensitivities of the high-p185(neu) expressing cell lines, whereas it had little effect on the chemosensitivities of the low-p185(neu) expressing cells, with a few exceptions in which minor antagonistic effects were observed. Although high concentrations of AG825 could reduce the drug-induced G(2) arrest that was accompanied by the activation of phosphorylated p34(cdc2), we failed to find any remarkably differential effects of AG825 on drug-induced G(2), arrest and the accompanying phosphorylation status of p34(cdc2) of the high- and and the low-p185(neu) expressing cell lines. In summary, tyrphostin AG825 can enhance chemosensitivity in high- but not in low-p185(neu) expressing NSCLC cell lines. This differential effect cannot be explained by the alterations of drug-induced cell cycle changes by AG825. Our results provide a rationale to develop p185(neu)- specific tyrphostin and to test them in combination with anticancer agents in vivo and in clinical trials.
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PMID:Enhancement of chemosensitivity by tyrphostin AG825 in high-p185(neu) expressing non-small cell lung cancer cells. 864 Jul 63

To understand the signalling mechanisms involved in the dual stimulatory effects of endothelin-1 (ET-1) on DNA synthesis and melanization in cultured human melanocytes, we analysed the biological profile of ET-1 receptor and determined the effects of ET-1 on the protein kinase C, cyclic AMP system and mitogen-activated protein kinase (MAP kinase) in comparison with their relevant stimulants. The photoaffinity labelling of ET-1 receptors with Denny-Jaff reagents revealed an ET-1 receptor with a molecular mass of 51 kDa in human melanocytes. The ET(A) receptor subtype-sensitive antagonist BQ123(50 nM) or pertussis toxin (100 ng/ml) significantly suppressed the ET-1-induced intracellular calcium mobilization, indicating the presence of pertussis toxin-sensitive G-protein-coupled ET(A) receptors. An assay of protein kinase C activity revealed that 10nM ET-1 translocated cytosolic protein kinase C to membrane-bound protein kinase C within 5 min of the start of incubation. In contrast, receptor-mediated melanocyte activation by ET-1 was accompanied by an elevated level of cyclic AMP (4-fold over control) after 10-60 min of incubation, whereas 60 min of incubation of human melanocytes with c-Kit or c-Met ligands such as stem cell factor (10 nM) or basic fibroblast growth factor (10 nM) did not elevate the cyclic AMP level. We have also demonstrated that a specific tyrosine kinase inhibitor, tyrphostin B-42 (10 microM), inhibited the ET-1-induced growth stimulation, suggesting the involvement of the tyrosine kinase pathway in growth stimulation. Consistently, an assay of MAP kinase revealed that ET-1 caused a 10-fold activation of MAP kinase after 5 min of incubation with human melanocytes in a similar way to tyrosine kinase ligands such as stem cell factor and hepatocyte growth factor. Further, the DNA synthesis stimulated by the c-Kit ligand stem cell factor at a concentration of 1 nM was synergistically enhanced by 5 nM ET-1. These results suggest that ET-induced dual cellular events in human melanocytes are closely associated with cross-talk between the protein kinase C and A and tyrosine kinase pathways.
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PMID:Signalling mechanisms of endothelin-induced mitogenesis and melanogenesis in human melanocytes. 866 Feb 99

The glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein Thy-1 is one of the most abundant molecules expressed on the surface of rat mast cells and rat basophilic leukemia (RBL) cells. The finding that Thy-1 from detergent-solubilized RBL-2H3 cells forms complexes with src-related protein-tyrosine kinase p56/p53lyn suggested that this kinase may play a key role in Thy-1-mediated mast-cell activation. The molecular mechanism of this activation is, however, unknown. Here we show that in RBL-2H3-derived cells extracted by the standard procedure with several non-ionic detergents, the majority of Thy-1 and p56/p53lyn were not released into postnuclear supernatant but remained associated with the detergent-resistant cytoskeletal/nuclear fraction. Pretreatment of the cells with the cholesterol-complexing agents, saponin or digitonin, resulted in complete solubilization of Thy-1 and p56/p53lyn in non-ionic detergents and dissociation of the complexes; this implies that cholesterol plays a crucial role in stabilization of the complexes. This conclusion was supported by double immunofluorescence colocalization experiments which also allowed us to estimate the size of the insoluble complexes to be about 0.1 micron. Sequential treatment with saponin and Nonidet P-40 was used to fractionate tyrosine-phosphorylated proteins during Thy-1-mediated activation of RBL-2H3 cells. Among the soluble cytoplasmic proteins the most dramatic change in tyrosine phosphorylation was found in pp72, whereas pp40 and pp33 were found mainly in the membrane fraction. Our data suggest that surface aggregation of GPI-anchored Thy-1 molecules leads to aggregation of p56/p53lyn kinase located in the same membrane microdomain, followed by transphosphorylation of both soluble and membrane-bound substrates.
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PMID:Thy-1-mediated activation of rat mast cells: the role of Thy-1 membrane microdomains. 866 26

Extracellular proteins play an essential role in the formation, differentiation, and maintenance of multicellular organisms. Despite that, the systematic identification of genes encoding these proteins has not been possible. We describe here a highly efficient method to isolate genes encoding secreted and membrane-bound proteins by using a single-step selection in yeast. Application of this method, termed signal peptide selection, to various tissues yielded 559 clones that appear to encode known or novel extracellular proteins. These include members of the transforming growth factor and epidermal growth factor protein families, endocrine hormones, tyrosine kinase receptors, serine/threonine kinase receptors, seven transmembrane receptors, cell adhesion molecules, extracellular matrix proteins, plasma proteins, and ion channels. The eventual identification of most, or all, extracellular signaling molecules will advance our understanding of fundamental biological processes and our ability to intervene in disease states.
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PMID:Selection for genes encoding secreted proteins and receptors. 869 53

The beta-amyloid protein (A beta) peptide plays an important role in Alzheimer's disease, but the potential actions of physiologic levels of A beta (225-625 pM) have not been explored. We recently showed that picomolar doses of A beta can stimulate tyrosine phosphorylation of neuronal cells and now show that leads to the activation of the lipid kinase phosphatidylinositol 3-kinase (PI3 kinase). Three independent lines of evidence support the hypothesis that A beta is activating PI3 kinase through a tyrosine kinase-mediated mechanism. Immunoblotting studies show that A beta induces tyrosine phosphorylation of p85 as well as association of the p85 subunit of PI3 kinase with tyrosine-phosphorylated proteins. Studies of membrane proteins show that A beta induces a translocation of p85 to membrane-bound glycoproteins, which are likely to be receptors. Finally, direct studies of PI3 kinase activity in both anti-phosphotyrosine immunocomplexes and wheat germ agglutinin precipitates show that A beta increases formation of the product of PI3 kinase. Wortmannin, a selective inhibitor of PI3 kinase, blocks this A beta-stimulated PI3 kinase activity. Thus, physiologic levels of A beta stimulate tyrosine phosphorylation and PI3 kinase activity.
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PMID:Physiologic levels of beta-amyloid activate phosphatidylinositol 3-kinase with the involvement of tyrosine phosphorylation. 875 3

Cross-linking of surface immunoglobulin M (sIgM) on normal mature B cells induces different signaling consequences, including DNA synthesis (positive signaling) and cell cycle arrest and/or death by apoptosis (negative signaling). Presumably, the difference depends on the intensity of sIgM cross-linking: relatively weak cross-linking induces DNA synthesis, moderate cross-linking induces DNA synthesis with cell cycle arrest at the G2/M interphase, and intense cross-linking induces apoptosis. In vivo experiments with transgenic mice have shown that relatively weak cross-linking of sIgM by soluble antigens induces anergy in autoreactive B cells, whereas intense sIgM cross-linking by membrane-bound forms of antigens induces deletion of them. However, it is still unknown whether the different intensities of sIgM cross-linking generate qualitatively different signals responsible for DNA synthesis or cell death or whether they generate qualitatively the same but quantitatively different signals, and the quantitative difference is responsible for the induction of positive or negative signaling. The sIgM-mediated negative signaling presumably plays an important role in the induction and maintenance of B cell tolerance, and sIgD and sIgG also possess the machinery necessary for negative signaling. Negative signaling through sIgM is dependent on tyrosine kinase(s) and Ca2+ influx and is sensitive to cyclosporin A in certain types of B cells but not in all B cells. It has been suggested that there are different intracellular signaling pathways that transduce negative signaling via sIgM, and that activation-induced B cell death by sIgM cross-linking does not necessarily show DNA fragmentation and the morphology of apoptosis. On the other hand, sIgM-mediated B cell death may be inhibited in the presence of appropriate co-stimulators such as IL-4, alpha-, and beta-interferons and CD40-mediated signaling. The CD40-mediated signaling effectively inhibits sIgM-mediated B cell apoptosis in many but not all experimental systems. Although homotypic cell adhesion through the LFA-1/ICAM-1 dependent pathway was shown to be involved in certain types of CD40-mediated inhibition of sIgM-mediated negative signaling, it is still not known how the cytokines and CD40-mediated signaling inhibit sIgM-mediated B cell death. The molecular mechanisms responsible for sIgM-mediated negative signaling and for the inhibitory signaling against sIgM-mediated negative signaling need further elucidation.
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PMID:IgM-mediated B cell apoptosis. 883 51

Erythropoietin (EPO) induces endothelin expression in endothelial cells (EC) and has angiogenic effects. We investigated the intracellular signal transduction of EPO in EC and tested the hypothesis that the proliferative effects of EPO may be mediated by cytosolic calcium, changes in intracellular pH, or tyrosine phosphorylation. Cytosolic calcium and pH were measured with fura-2 and BCECF. Protein phosphorylation was assessed with 32P-labeled EC and two-dimensional (2D) gel chromatography. Tyrosine phosphorylation was measured using specific antityrosine antibodies and confocal microscopy. Proliferation was measured by thymidine incorporation and cell count. No effects of EPO on cytosolic calcium and pH were observed. In contrast, erythropoietin increased phosphorylation of 94, 70, 42, 40, 29 and 25 kDa proteins at five minutes and 60 minutes. Most of the early proteins were tyrosine phosphorylated. Confocal microscopy showed cytosolic as well as membrane-bound tyrosine phosphorylation in resting cells and an EPO-induced translocation of immunoreactivity to the nucleus. Immunostaining for the transcription factor STAT-5 showed that EPO induced a nuclear translocation of STAT-5. EPO 0.5, 2, and 4 U/ml increased proliferation, an effect that was prevented by incubation with the tyrosine kinase inhibitor genistein. We conclude that EPO induces proliferation in EC initially via tyrosine phosphorylation of six distinct proteins, and that the phosphorylation and nuclear translocation of the transcription factor STAT-5 is important for the effects of EPO on EC.
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PMID:Signal transduction of erythropoietin in endothelial cells. 884 Feb 76

The growth hormone (GH) receptor belongs to the superfamily of transmembrane proteins that includes the prolactin (PRL) receptor and a number of cytokine receptors. Two forms exist for the GH receptor: the membrane-bound form is a protein of 620 amino acid residues with a unique transmembrane domain; the GH-binding protein (GHBP), which is a soluble short form, is identical to the extracellular domain of the membrane receptor. In man and many other species, GHBP is believed to result from proteolytic cleavage of the membrane receptor; in human tissues, only one mRNA form of 4.5 kb encoding the full-length receptor has been detected. In rodents, GHBP is encoded by a specific mRNA of 1.2kb. Binding of GH to its receptor results in dimerization of the receptor, phosphorylation of the tyrosine kinase JAK2 and of the receptor, followed by a cascade of protein phosphorylations. Transcription factors belonging to the signal transducers and activators of transcription (STAT) family are involved in the effects of GH on the transcription of genes such as c-fos, serine protease inhibitor Spi 2.1 and beta-casein. GH is able to activate several STAT proteins including STAT1, 3 and 5. The JAK-STAT pathway is a main pathway for GH effects on gene transcription. Other signalling molecules are involved in GH action through different pathways: GH is able to activate mitogen activated protein (MAP) kinases; the hormone can utilize insulin receptor substrate-1 (IRS-1) and induces the association of phosphatidylinositol 3-kinase with IRS-1. Two main functional regions have been defined in the cytoplasmic domain of the GH receptor by testing the activity of mutant forms of the receptor in several systems: Box 1, a proline-rich sequence in the membrane proximal part, is necessary for all GH effects and is probably the region of association with JAK2; the C-terminal region is required for the induction of specific genes. Other molecules involved in the mechanisms of action of GH remain to be identified. As the same signalling pathways are used by many ligands, explanations for the specificity of the cellular effects have to be determined.
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PMID:Growth hormone receptor signalling. 885 42

The hippocampus and septum play central roles in one of the most important spheres of brain function: learning and memory. Although their topographic connections have been known for two decades and topography may be critical for cognitive functions, the basis for hippocamposeptal topographic projection is unknown. We now report for the first time that Elf-1, a membrane-bound eph family ligand, is a candidate molecular tag for the genesis of the hippocamposeptal topographic projection. Elf-1 is expressed in an increasing gradient from dorsal to ventral septum. Furthermore, Elf-1 selectively allows growth of neurites from topographically appropriate lateral hippocampal neurons, while inhibiting neurite outgrowth by medial hippocampal neurons. Complementary to the expression of Elf-1, an eph family receptor, Bsk, is expressed in the hippocampus in a lateral to medial gradient, consistent with a function as a receptor for Elf-1. Further, Elf-1 specifically bound Bsk, eliciting tyrosine kinase activity. We conclude that the Elf-1/Bsk ligand-receptor pair exhibits traits of a chemoaffinity system for the organization of hippocamposeptal topographic projections.
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PMID:Regulation of topographic projection in the brain: Elf-1 in the hippocamposeptal system. 885 26


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