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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nerve growth factor (NGF)-stimulated neurite outgrowth in the rat PC12 tumor cell line recently has been shown to depend on the activation of the mitogen-activated protein (MAP) kinase kinase 1 (MEK1) (Pang et al.: J Biol Chem 270:13585-13588, 1995). In this study we have analyzed whether or not function of the MAP kinase pathway is necessary for NGF-stimulated neurite outgrowth in two subtypes of primary neurons derived from the embryonic chick peripheral nervous system (PNS). Treatment of p21ras-dependent dorsal root ganglion (DRG) sensory neurons (E9) with the MEK1 inhibitor PD98059 at concentrations up to 100 microM did not prevent NGF-stimulated neurite outgrowth. At this concentration NGF-stimulated tyrosine phosphorylation of MAP kinase p42 as well as MAP kinase activity both were decreased by approximately 80%. Essentially the same results were obtained with p21ras-independent sympathetic neurons (E12). We conclude that, in contrast to the PC12 tumor cell line, NGF-stimulated MAP kinase activity is not necessary for neurite outgrowth of DRG sensory and sympathetic neurons derived from the chick PNS.
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PMID:Nerve growth factor-stimulated mitogen-activated protein kinase activity is not necessary for neurite outgrowth of chick dorsal root ganglion sensory and sympathetic neurons. 897 6

Taxol, a natural product with significant anti-tumor activity, stabilizes microtubules and arrests cells in the G2/M phase of the cell cycle. It has been reported that taxol has additional effects in cells, including an increase in tyrosine phosphorylation of proteins and activation of MAP kinase. We investigated a possible effect of taxol on tyrosine phosphorylation of Shc and on formation of the Shc/Grb-2 complex in the murine macrophage-like cell line RAW 264.7. Shc, an SH2 domain containing adaptor protein, was immunoprecipitated from lysates of taxol-treated cells with anti-phosphotyrosine antibody and its identity determined by Western blotting with anti-Shc antibody. Non-denatured Shc containing protein complexes were immunoprecipitated with anti-Shc antibody, and analysis with an anti-Grb2 antibody revealed the presence of the 24-kDa Grb2 protein. Taxol also activated Raf-1 kinase and ERK1/ERK2 MAP kinases in these cells. These results demonstrate that taxol affects tyrosine phosphorylation of Shc and this may result in the activation of the Raf-1/MAPK cascade.
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PMID:Taxol induces tyrosine phosphorylation of Shc and its association with Grb2 in murine RAW 264.7 cells. 900 67

Pituitary adenylate-cyclase-activating polypeptide (PACAP) has been shown to possess mitogenic activity in various tumor cells. The present study was designed to investigate signal transduction mechanisms and expression of the proto-oncogenes c-fos and c-jun linked to the mitogenic effect of PACAP in the pancreatic carcinoma cell line AR4-2J. PACAP-(1-27)-peptide and PACAP-(1-38)-peptide, but not the structurally related vasoactive intestinal polypeptide (VIP), potently stimulated [3H]thymidine incorporation and cell number at doses of 0.1-10 nM. Both molecular forms of PACAP strongly increased formation of cAMP and inositol trisphosphate, elevated cytosolic Ca2+ levels and induced mitogen-activated protein (MAP) kinase activity. Quantitative reverse-transcription PCR revealed that PACAP-(1-27)-peptide and PACAP-(1-38)-peptide elevated c-fos mRNA levels 50-100-fold, whereas c-jun mRNA levels increased only moderately (2-3-fold). The effect of PACAP on c-fos and c-jun expression in AR4-2J cells was rapid (20 min), transient (1-2 h), dose-dependent IC50, 0.5 nM) and was abolished by the specific PACAP receptor antagonist PACAP-(6-38)-peptide or inhibitors of protein kinase C or tyrosine kinases. Compared with PACAP, epidermal growth factor and gastrin equipotently stimulated c-fos transcription whereas VIP, secretin, forskolin or phorbolester showed only marginal effects. Both PACAP (1-27)-peptide and PACAP-(1-38)-peptide strongly increased the DNA binding activity of the c-fos/ c-jun heterodimer transcription factor AP-1 at 10 nM and also stimulated AP-1 transcriptional activity up to 20-fold in AR4-2J cells. These findings indicate that the mitogenic effect of PACAP mediated via activation of the GTP-binding protein coupled PACAP/VIP-1 (PV1) receptor is linked to the MAP kinase cascade, increased expression of the proto-oncogenes c-fos and c-jun and activation of the heterodimeric transcription factor AP-1.
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PMID:Pituitary adenylate-cyclase-activating polypeptide stimulates proto-oncogene expression and activates the AP-1 (c-Fos/c-Jun) transcription factor in AR4-2J pancreatic carcinoma cells. 902 70

Endothelin 1 (ET-1) is produced in ovarian cancer cell lines and has been shown to act through ET(A) receptors as an autocrine growth factor to promote tumor cell proliferation in vitro. In OVCA 433 cells, the efficacy of ET-1 as a stimulus of [3H]thymidine incorporation was equivalent to that of epidermal growth factor. ET-1 also stimulated the rapid expression of c-fos, an action mediated by ET(A) receptors. The mitogenic action of ET-1 was not mediated by a pertussis toxin-sensitive G protein. An analysis of the effects of inhibition and depletion of protein kinase C (PKC) on mitogenic responses demonstrated that PKC was necessary but not sufficient for maximal stimulation by ET-1. In quiescent OVCA 433 cells, ET-1-induced stimulation of [3H]thymidine incorporation was prevented by two structurally distinct inhibitors of tyrosine kinase, herbimycin A and genistein. These results indicate that both PKC and protein tyrosine kinase participate in ET-1-stimulated mitogenic signaling. ET-1 rapidly stimulated tyrosine phosphorylation of several cellular proteins, among which p125FAK and p42 mitogen-activated protein kinase were identified. The additivity between the potent mitogenic actions of ET-1 and epidermal growth factor is consistent with the independence of their signal transduction pathways in ovarian cancer cells. These findings also indicate that intracellular signaling between the ET(A) receptor and a yet unidentified tyrosine kinase is involved in the mitogenic response to ET-1.
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PMID:Activation of mitogenic signaling by endothelin 1 in ovarian carcinoma cells. 910 18

Mitogen-activated protein (MAP) kinases act as transducers of extracellular signaling via tyrosine kinase-growth factor receptors and G-protein-linked receptors to elements regulating transcription. The activity, abundance, and localization of MAP kinase was investigated in normal and malignant neoplasia of the breast. In carcinoma of the breast, MAP kinase was heavily phosphorylated on tyrosyl residues and its activity elevated 5-10-fold over benign conditions, such as fibroadenoma and fibrocystic disease. By in situ reverse transcription-polymerase chain reaction, hyperexpression of MAP kinase mRNA can be localized to malignant, epithelial cells. Metastatic cells within involved lymph nodes of patients with breast cancer also display hyperexpression of MAP kinase. In spite of persistent activation via phosphorylation, MAP kinase expression is upregulated 5-20-fold and this hyperexpression may be a critical element to initiation as well as the metastatic potential of various forms of human breast cancer.
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PMID:Hyperexpression of mitogen-activated protein kinase in human breast cancer. 911 86

The oncogenic proteins encoded by papovaviruses, the tumor antigens, have been extensively used as model systems to study mitogenic signaling and cell transformation. These proteins stimulate cell growth in cultured cells and induce tumors in virus infected or transgenic animals. One of these proteins, polyomavirus middle-T, acts like a constitutively activated tyrosine growth factor receptor. Middle-T recruits several cellular enzymes into a multifunctional complex located at cellular membranes. This results in the activation of cellular enzymes involved in the regulation of cell signaling, like tyrosine kinases of the Src family, a phosphatidylinositol 3-kinase and a GDP/GTP exchange factor for Ras. These activities are all required for stimulation of cell growth by middle-T and activate members of the MAP kinase family. Here we investigate the role of T antigen-activated pathways in the stimulation of transcription of immediate early genes. These genes are essential for progression of resting cells into S phase. Our data show that Rho family GTPases play an essential role in cell transformation by middle-T. Furthermore, we demonstrate that the c-fos promoter is activated by two Ras-initiated signaling cascades. One is Raf-dependent and requires binding of SHC and PI 3-kinase to the middle-T complex. This pathway signals via ternary complex factor (TCF) to the serum response element (SRE) of the c-fos promoter. Signaling to TCF by Raf also depends on functional Rac, but not CDC42, as demonstrated in luciferase reporter assays with an ETS domain-containing promoter. The second pathway is Raf-independent, does not require SHC but functional PI 3-kinase, and transduces signals via Rac to serum response factor (SRF). Microinjection of dominant negative Rac1 blocks nuclear translocation of ERK1 in middle-T-expressing cells. This lends support to the idea that the two signaling cascades initiated by Ras show crosstalk at the level of MAP kinase-mediated signaling to nuclear transcription factors.
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PMID:A role for the small GTPase Rac in polyomavirus middle-T antigen-mediated activation of the serum response element and in cell transformation. 912 74

Peroxisome proliferators (PPs) are a class of nongenotoxic carcinogens in the rodent liver. The induction of immediate-early gene expression in immortalized mouse liver cells by the PPs Wy-14, 643, monoethylhexyl phthalate, ciprofibrate ethyl ester, and clofibrate suggested that they may be activating growth-regulatory signal transduction pathways. We report that incubation of quiescent ML457 cells with Wy-14,643 resulted in the appearance of two tyrosine-phosphorylated bands of approximately 44 and 42 kDa with maximal phosphorylation at 20 min. These two proteins were identified as extracellular signal-regulated kinases (ERKs) ERK1 and ERK2 (also known as mitogen-activated protein kinases, or MAPKs). Stimulation of quiescent ML457 cells with monoethylhexyl phthalate, ciprofibrate ethyl ester, and clofibrate also resulted in tyrosine phosphorylation of ERK1 and ERK2; however, the steroid PP dehydroepiandrosterone sulfate, which does not induce immediate-early gene expression, did not induce phosphorylation of ERK1 and ERK2. Kinase activity of ERK1 and ERK2 was stimulated by the PPs, consistent with their phosphorylation. The PPs also induced phosphorylation of the upstream regulator MAPK/ERK kinase (MEK). Preincubation of quiescent cells with MEK inhibitor PD98059 blocked activation of ERK1 and ERK2 by the PPs, implicating MEK activation as a requirement for PP-induced ERK activation. In addition, pretreatment with PD98059 greatly reduced the PP-induced expression of immediate-early genes c-fos, egr-1, and to a lesser extent junB. Induction of ERK phosphorylation and junB expression by Wy-14,643 was also seen in rat hepatocytes. These results attribute many of the effects of PPs on immediate-early gene expression to the activation of the MEK/ERK signal transduction pathway and add the PPs to the growing number of tumor promoters that modulate signaling proteins.
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PMID:Peroxisome proliferators activate extracellular signal-regulated kinases in immortalized mouse liver cells. 914 71

Lipopolysaccharide (LPS) stimulates immune responses by interacting with the membrane receptor CD14 to induce the generation of cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1, and IL-6. The mechanism by which the LPS signal is transduced from the extracellular environment to the nuclear compartment is not well defined. Recently, an increasing amount of evidence suggests that protein tyrosine kinases especially the Src-family kinases Hck, Fgr, and Lyn, play important roles in LPS signaling. To directly address the physiological function of Hck, Fgr and Lyn in LPS signaling, a genetic approach has been used to generate null mutations of all three kinases in a single mouse strain. hck-/-fgr-/-lyn-/- mice are moderately healthy and fertile; macrophages cultured from these mice express normal levels of CD14 and no other Src-family kinases were detected. Although the total protein phosphotyrosine level is greatly reduced in macrophages derived from hck-/-fgr-/-lyn-/- mice, functional analyses indicate that both elicited peritoneal (PEMs) and bone marrow-derived macrophages (BMDMs) from triple mutant mice have no major defects in LPS-induced activation. Nitrite production and cytokine secretion (IL-1, IL-6, and TNF-alpha) are normal or even enhanced in hck-/-fgr-/-lyn-/- macrophages after LPS stimulation. The development of tumor cell cytotoxicity is normal in triple mutant BMDMs and only partially impaired in PEMs after LPS stimulation. Furthermore, the activation of the ERK1/2 and JNK kinases, as well as the transcription factor NF-kappaB, are the same in normal and mutant macrophages after LPS stimulation. The current study provides direct evidence that three Src-family kinases Hck, Fgr, and Lyn are not obligatory for LPS-initiated signal transduction.
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PMID:Lipopolysaccharide (LPS)-induced macrophage activation and signal transduction in the absence of Src-family kinases Hck, Fgr, and Lyn. 915 3

We have studied nerve growth factor (NGF)-induced differentiation of PC12 cells to identify PKC isozymes important for neuronal differentiation. Previous work showed that tumor-promoting phorbol esters and ethanol enhance NGF-induced mitogen-activated protein (MAP) kinase activation and neurite outgrowth by a PKC-dependent mechanism. Ethanol also increases expression of PKCdelta and PKCepsilon, suggesting that one these isozymes regulates responses to NGF. To examine this possibility, we established PC12 cell lines that express a fragment encoding the first variable domain of PKCepsilon (amino acids 2-144), which acts as an isozyme-specific inhibitor of PKCepsilon in cardiac myocytes. Phorbol ester-stimulated translocation of PKCepsilon was markedly reduced in these PC12 cell lines. In addition, phorbol ester and ethanol did not enhance NGF-induced MAP kinase activation or neurite outgrowth in these cells. In contrast, phorbol ester and ethanol increased neurite outgrowth and MAP kinase phosphorylation in cells expressing a fragment derived from the first variable domain of PKCdelta. These results demonstrate that PKCepsilon mediates enhancement of NGF-induced signaling and neurite outgrowth by phorbol esters and ethanol in PC12 cells.
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PMID:An inhibitory fragment derived from protein kinase Cepsilon prevents enhancement of nerve growth factor responses by ethanol and phorbol esters. 916 79

The molecular basis of the polymorphic tumor rejection antigens of chemically induced sarcomas of inbred mice remains a mystery, despite the discovery of these antigens over 40 years ago and their critical importance to the foundation of tumor immunology. In an analysis of a panel of BALB/c 3-methylcholanthrene-induced tumors, we identified one tumor, CMS5, that elicited a strong cytotoxic T cell response with exquisite specificity for CMS5. A stable cloned line of T cells with this specificity (C18) was used to screen a CMS5 cDNA expression library. The gene encoding the C18-defined antigen was identified as a mutated form of a mouse mitogen-activated protein kinase, ERK2, and a peptide incorporating the resulting amino acid substitution (lysine to glutamine) was efficiently recognized by C18. Vaccination with this peptide elicited specific resistance to CMS5 challenge. Extensive efforts to isolate antigen-loss variants of CMS5 were unsuccessful, suggesting that the mutated mitogen-activated protein kinase is essential for maintenance of the malignant phenotype.
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PMID:Mutated mitogen-activated protein kinase: a tumor rejection antigen of mouse sarcoma. 917 54


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