Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have established the human nck sequence as a new oncogene. Nck encodes one SH2 and three SH3 domains, the Src homology motifs found in nonreceptor tyrosine kinases, Ras GTPase-activating protein, phosphatidylinositol 3-kinase, and phospholipase C-gamma. Overexpression of human nck in 3Y1 rat fibroblasts results in transformation as judged by alteration of cell morphology, colony formation in soft agar, and tumor formation in nude BALB/c mice. However, overexpression of nck does not induce detectable elevation of the phosphotyrosine content of specific proteins, as is observed for v-crk, another SH2/SH3-containing oncogene. Despite this fact, we demonstrate that Nck retains the ability to bind tyrosine phosphorylated proteins in vitro, using a fusion protein of Nck with glutathione-S-transferase (GST). Moreover, when incubated with lysates prepared from v-src-transformed 3Y1 cells or the nck-overexpressing cell lines, GST-Nck binds to both p60v-src and serine/threonine kinases, respectively. Although phosphotyrosine levels are not elevated in the nck-expressing fibroblasts, vanadate treatment of these cells results in a phosphotyrosine pattern that is altered from the parental 3Y1 pattern, suggestive of a perturbation of indigenous tyrosine kinase pathways. These results suggest the possibility that human nck induces transformation in 3Y1 fibroblasts by virtue of its altered affinity or specificity for the normal substrates of its rat homolog and that Nck may play a role in linking tyrosine and serine/threonine kinase pathways within the cell.
 ...
PMID:The SH2- and SH3-containing Nck protein transforms mammalian fibroblasts in the absence of elevated phosphotyrosine levels. 128 Mar 26

Src homology 2 (SH2) domain-mediated interactions with phosphotyrosine residues are critical in many intracellular signal transduction pathways. Attempts to understand the determinants of specificity and selectivity of these interactions have prompted many binding studies that have used several techniques. Some discrepancies, in both the absolute and relative values of the dissociation constants for particular interactions, are apparent. To establish the correct dissociation constants and to understand the origin of these differences, we have analyzed three previously determined interactions using the techniques of surface plasmon resonance and isothermal titration calorimetry. We find that the binding of SH2 domains to phosphopeptides is weaker than generally presumed. A phosphopeptide based on the hamster polyoma middle tumor antigen interacts with the SH2 domain from Src with an equilibrium dissociation constant (Kd) of 600 nM; a phosphopeptide based on one binding site from the platelet-derived growth factor receptor binds to the N-terminal SH2 domain of the 1-phosphatidylinositol 3-kinase p85 subunit with a Kd of 300 nM; and a phosphopeptide based on the C terminus of Lck binds to the SH2 domain of Lck with a Kd of 4 microM. In addition, we demonstrate that avidity effects that result from the dimerization of glutathione S-transferase fusion proteins with SH2 domains could be responsible for overestimates of affinities for these interactions previously studied by surface plasmon resonance.
 ...
PMID:Measurement of the binding of tyrosyl phosphopeptides to SH2 domains: a reappraisal. 753 27

The exposure of mammalian cells to ultraviolet radiation (UV) may lead to DNA damage resulting in mutation and thus possibly cancer, while irradiation can further act as a potent tumor promoter. In addition UV induces p21ras-mediated signalling leading to activation of transcription factors such as AP-1 and NF-kappa B, as well as activation of the Src tyrosine kinase. This 'UV-response' has been well studied in mammalian cells and furthermore is conserved in yeast, however the most upstream components of this signal transduction pathway have remained elusive. Here we show that UV rapidly activates both the EGF receptor and insulin receptor, as shown by tyrosine phosphorylation of these receptors. We demonstrate that this activation is due to autophosphorylation as it only occurs in cells containing receptors with a functional kinase domain. We have further analysed the propagation of the UV-induced signal to downstream events such as, IRS-1 and Shc tyrosine phosphorylation, phosphatidylinositol 3-kinase activation, leukotriene synthesis, MAP kinase activation and gene induction all of which are activated by UV irradiation. Importantly, we demonstrate that in cells expressing a 'kinase-dead' receptor mutant the UV-response is inhibited, blocking leukotriene synthesis, MAP kinase activation and transcriptional induction. Furthermore, prior-stimulation of cells with UV appears to reduce further responsiveness to addition of growth factor suggesting a common signaling pathway. These data demonstrate a critical role for receptor-mediated events in regulating the response mammalian cells to UV exposure.
 ...
PMID:UV activation of receptor tyrosine kinase activity. 754 96

Tumor necrosis factor-alpha (TNF) has been suggested to be the mediator of insulin resistance in infection, tumor cachexia, and obesity. We have previously shown that TNF diminishes insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1). The current work examines potential mechanisms that mediate this event. TNF effect on IRS-1 in Fao hepatoma cells was not associated with a significant reduction in insulin receptor tyrosine kinase activity as measured in vitro but impaired the association of IRS-1 with phosphatidylinositol 3-kinase, localizing TNF impact to IRS-1. TNF did not increase protein-tyrosine phosphatase activity and protein-tyrosine phosphatase inhibition by vanadate did not change TNF effect on IRS-1 tyrosine phosphorylation, suggesting that protein-tyrosine phosphatases are not involved in this TNF effect. In contrast, TNF increased IRS-1 phosphorylation on serine residues, leading to a decrease in its electrophoretic mobility. TNF effect on IRS-1 tyrosine phosphorylation was not abolished by inhibiting protein kinase C using staurosporine, while inactivation of Ser/Thr phosphatases by calyculin A and okadaic acid mimicked it. Our data suggest that TNF induces serine phosphorylation of IRS-1 through inhibition of serine phosphatases or activation of serine kinases other than protein kinase C. This increased serine phosphorylation interferes with insulin-induced tyrosine phosphorylation of IRS-1 and impairs insulin action.
 ...
PMID:Tumor necrosis factor alpha-induced phosphorylation of insulin receptor substrate-1 (IRS-1). Possible mechanism for suppression of insulin-stimulated tyrosine phosphorylation of IRS-1. 755 52

The tumor promoter phorbol 12-myristate 13-acetate (PMA) and hormonal activators of protein kinase C (PKC) commonly stimulate phospholipase D (PLD)-mediated formation of phosphatidic acid from phosphatidylcholine (PtdCho) in fibroblasts and other cell types. On the basis that phosphatidic acid is a mitogen, PLD is often considered to have a major role in the regulation of cell growth by PKC activators. However, we found that in NIH 3T3 fibroblasts wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), strongly inhibited DNA synthesis induced by 100 nM PMA, while it actually enhanced PMA-stimulated PtdCho hydrolysis. These results indicate that stimulation of PLD activity is either not required or not sufficient for the mitogenic action of PMA.
 ...
PMID:Wortmannin has opposite effects on phorbol ester-induced DNA synthesis and phosphatidylcholine hydrolysis. 767 24

Because mutations in receptor tyrosine kinases may contribute to cellular transformation, studies were undertaken to examine c-kit in human leukemia. Isoforms of c-kit have been characterized in the human megakaryoblastic leukemia cell line M-07. Deletion of the four amino acids Gly-Asn-Asn-Lys in the extracellular domain represents an alternatively spliced isoform that has been shown by others, in mice, to be associated with constitutive receptor autophosphorylation (Reith et al, EMBO J 10:2451, 1991). Additional isoforms differ in the inclusion or exclusion of a serine residue in the interkinase domain, a region that contains the binding site for phosphatidylinositol 3-kinase. By RNase protection analysis, we have shown coexpression of the Gly-Asn-Asn-Lys+ and Gly-Asn-Asn-Lys- isoforms, with dominance of the Gly-Asn-Asn-Lys- transcript, in normal human bone marrow, normal melanocytes, a range of tumor cell lines, and the blasts of 23 patients with acute myeloid leukemia. Analysis of transcripts for the Ser+ and Ser- isoforms also showed coexpression in all normal and leukemic cells examined. The ratios of isoform expression for both the Gly-Asn-Asn-Lys and Ser variants were relatively constant, providing no evidence in the tumors examined that upregulation of one isoform contributes to the neoplastic process.
 ...
PMID:Expression of isoforms of the human receptor tyrosine kinase c-kit in leukemic cell lines and acute myeloid leukemia. 768 88

Transformation of cells in culture by polyomavirus is mediated by one of its early gene products, middle-sized tumor antigen (MTAg). This protein forms multiple complexes with cellular enzymes such as tyrosine kinases (pp60c-src), a phosphatidylinositol 3-kinase, and phosphatase 2A. Association with MTAg leads to the activation of pp60c-src through interference with phosphorylation at Tyr-527, a site negatively regulating src kinase activity. MTAg abrogates mitosis-specific activation of pp60c-src, resulting in constitutive high kinase activity of the enzyme throughout all phases of the cell cycle. Here we report that MTAg is transiently modified during mitosis, resulting in an increase in its apparent molecular size on SDS/acrylamide gels. Similarly, MTAg isolated from interphase cells and phosphorylated by the cell cycle-regulated serine/threonine kinase p34cdc2 in vitro has increased molecular mass. The large molecular mass form of the protein can be converted to the authentic 56-kDa form upon dephosphorylation by potato acid phosphatase. Two putative phosphorylation sites for a cdc2-like kinase were identified as Thr-160 and -291, respectively. Conversion of Thr-160 to Ala resulted in a transformation-defective mutant protein that was still capable of associating with pp60c-src, phosphatidylinositol 3-kinase, and phosphatase 2A, while the corresponding mutant in position 291 was wild type with respect to all parameters measured so far. These data suggest that phosphorylation by p34cdc2 or a related cell cycle-regulated kinase modulates the interaction of MTAg with cellular targets that are crucial for cell transformation.
 ...
PMID:Mitosis-specific phosphorylation of polyomavirus middle-sized tumor antigen and its role during cell transformation. 769 Jan 42

Polyomavirus-infected cells express three proteins in the early phase of the lytic cycle, the so-called tumor antigens. Two of them, large- and middle-T antigens, are also required for virus-mediated transformation of primary cells, while middle-T alone is sufficient to transform established cells in culture. Cell transformation by middle-T is strictly dependent on the ability of this protein to associate with cellular enzymes like members of the Src family of tyrosine kinases, a phosphatidylinositol 3-kinase, phosphatase 2A and SHC, an adapter protein linking GDP/GTP exchange factors to tyrosine kinase receptors. A carboxy-terminal stretch of 22 hydrophobic amino acids is required for targeting middle-T and associated proteins to cellular membranes. Here we show in an in vitro system that middle-T fusion proteins carrying an amino-terminal hemagglutinin leader sequence are capable to bind to and enter the lumen of dog pancreas microsomes supporting the concept that the carboxy-terminus of middle-T is an authentic membrane-targeting domain. Furthermore, wild-type middle-T, but not a truncated protein lacking the putative membrane anchor, specifically associates with artificial lipid bilayers.
 ...
PMID:Membrane association of polyomavirus middle-T antigen in an in vitro system. 776 90

Following ligand binding, the epidermal growth factor receptor (EGF-R) autophosphorylates itself on tyrosine residues located in its carboxyl terminus; in vitro, three sites are highly phosphorylated, while two other sites are phosphorylated to lesser extents. In the presence of the Src protein-tyrosine kinase, in vitro phosphorylation of the minor autophosphorylation sites was increased, and four additional residues were phosphorylated. Following EGF stimulation, two (Tyr-891 and Tyr-920) were found to be phosphorylated in a colorectal cell line (DLD-1) and in a breast tumor cell line (MCF7). The remaining in vitro sites were not found to be highly phosphorylated in vivo. The sequences surrounding Tyr-891 and Tyr-920 match the reported consensus binding sequences for the SH2 domains of Src and the regulatory domain of phosphatidylinositol 3-kinase (p85 alpha), respectively. In vitro, both of these proteins were found to bind to Src-phosphorylated EGF-R with approximately 100-fold greater affinity than to autophosphorylated EGF-R, demonstrating that Src creates new sites for SH2 binding. Furthermore, Csk-inactivated Src was activated by interaction with Src-phosphorylated EGF-R but not by autophosphorylated EGF-R. Upon EGF treatment of MCF7 or three colorectal carcinoma cell lines (WiDr, DLD-1, and LS174T), the EGF-R coimmunoprecipitated with both p85 alpha and Src. Evidence is also presented that suggests that an EGF-R-related protein, ErbB2, may be involved in similar Src-mediated interactions. These data demonstrate that EGF-R is phosphorylated in vivo at non-autophosphorylation sites and that these novel sites can act as docking sites for Src, P85 alpha, and potentially other SH2-containing proteins. In addition, the data suggest a tyrosine phosphatase-independent mechanism for the elevation of Src activity in cells exposed to growth factors. Overexpression of Src, EGF-R, and/or ErbB2 in breast and colorectal tumor cells suggests the potential that such interactions may contribute to the transformed phenotype of these carcinomas.
 ...
PMID:Src phosphorylation of the epidermal growth factor receptor at novel sites mediates receptor interaction with Src and P85 alpha. 779 56

The transforming protein of mouse polyomavirus, the mouse middle T antigen (MomT), and its counterpart in the hamster polyomavirus, the hamster middle T antigen (HamT), interact with a number of cellular proteins. Among these are members of the Src family of tyrosine kinases, the phosphatidylinositol 3-kinase, the serine/threonine phosphatase PP2A and the adaptor protein Shc (in the case of MomT). However, both the relative affinity of these antigens for the members of the Src family and the tumor profile induced by their respective viruses are quite distinct. Particularly noteworthy are the preferential binding of Fyn by HamT and the induction of lymphoid malignancies by the hamster polyomavirus. Here we report that, when expressed in fibroblasts, HamT also associated with phospholipase C gamma (PLC gamma), which led to an increased intracellular concentration of inositol-1, 4, 5-trisphosphate. We also show that expression of HamT in the mouse T cell line EL4 was sufficient to induce transcription from interleukin-2 (IL-2), NFAT and NF kappa B reporter constructs. The immunosuppressant FK506 as well as dominant negative alleles of Ras and Raf inhibited HamT-induced IL-2 transcription. This, together with the observation of NFAT responses, suggests that the action of HamT depended at least in part on the integrity of signal transduction pathways elicited by activated PLC gamma. Furthermore, dominant negative Fyn but not the equivalent allele of Lck blocked HamT activation of IL-2 transcription, while both Lck and Fyn dominant negative alleles blocked LT cell receptor-mediated IL-2 transcriptional activation. These results support the hypothesis that Fyn is involved in signal transduction events leading to IL-2 transcriptional activation in T cells. Finally, the activation of IL-2 transcription by HamT and not by MomT shown here parallels the ability of the hamster polyomavirus to induce lymphoid malignancies.
 ...
PMID:Induction of interleukin-2 transcription by the hamster polyomavirus middle T antigen: a role for Fyn in T cell signal transduction. 787


1 2 3 4 5 6 7 8 9 10 Next >>