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

Phenolic antioxidant butylated hydroxyanisole (BHA) is a commonly used food preservative with broad biological activities, including protection against acute toxicity of chemicals, modulation of macromolecule synthesis and immune response, induction of phase II detoxifying enzymes, and especially its potential tumor-promoting activities. Understanding the molecular basis underlying these diverse biological actions of BHA is thus of great importance. Here we demonstrate that BHA is capable of activating distinct mitogen-activated protein kinases (MAPKs), extracellular signal-regulated protein kinase 2 (ERK2), and c-Jun N-terminal kinase 1 (JNK1). Activation of ERK2 by BHA was rapid and transient, whereas the JNK1 activation was relatively delayed and persistent. A major metabolite of BHA, tert-butylhydroquinone (tBHQ), also activated ERK2 but weakly stimulated JNK1 activity. Furthermore, tBHQ activation of ERK2 was late and prolonged, showing a kinetics different from that induced by BHA. ERK2 activation by both compounds required the involvement of an upstream signaling kinase MAPK/ERK kinase (MEK), as evidenced by the inhibitory effect of a MEK inhibitor, PD98059. Pretreatment with N-acetyl-L-cysteine, glutathione, or vitamin E attenuated ERK2 but not JNK1 activation by BHA and tBHQ. Modulation of intracellular H2O2 levels by direct addition of catalase or pretreatment with a catalase inhibitor, aminotriazole, also affected BHA- and tBHQ-stimulated ERK2 activity but not JNK1, indicating the involvement of oxidative stress in the ERK2 activation by these two compounds. However, we did not observe any generation of H2O2 after exposure of cells to BHA or tBHQ using a H2O2-sensitive fluorescent probe, 2',7'-dichlorofluorescein diacetate. Instead, BHA and tBHQ substantially reduced the amount of intracellular H2O2. Furthermore, BHA and tBHQ activation of ERK2 was strongly inhibited by ascorbic acid and a peroxidase inhibitor, sodium azide, suggesting the potential role of phenoxyl radicals and/or their derivatives. Taken together, our results indicate that (i) BHA and its metabolite tBHQ differentially regulate MAPK pathways, and (ii) oxidative stress due to the generation of reactive intermediates, possibly phenoxyl radicals but not H2O2, is responsible for the ERK2 activation by BHA and tBHQ, whereas the JNK1 activation may require a distinct yet unknown mechanism.
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PMID:Butylated hydroxyanisole and its metabolite tert-butylhydroquinone differentially regulate mitogen-activated protein kinases. The role of oxidative stress in the activation of mitogen-activated protein kinases by phenolic antioxidants. 936 Sep 68

Transforming growth factor (TGF)-beta is a potent growth suppressor of epithelial cells. Resistance to TGF-beta, however, occurs frequently in solid tumors of epithelial origin and contributes to the uncontrolled growth of these tumors. Although mutant receptor proteins contribute to TGF-beta insensitivity, deregulation of TGF-beta signaling cascades represents an equally important mechanism underlying TGF-beta resistance. Identification of abnormal regulation of signaling components in tumor epithelial cells will lead to the development of selective therapeutic approaches to repair the relevant signaling cascade(s) and reverse the growth anomaly. Within the past few years, great strides have been made in defining signaling pathways for TGF-beta. For example, our laboratory has demonstrated a direct correlation between TGF-beta-mediated growth inhibition of epithelial cells and activation of Ras and three members of the mitogen-activated protein kinase (MAPK) superfamily. The TGF-beta signaling events were sustained, dose-dependent, and absent in TGF-beta-resistant cells. Further, up-regulation of both p27Kip1 and p21Cip1, nuclear events important for the growth inhibitory effect of TGF-beta, are completely dependent upon the activation of Ras. However, Ras-independent pathways are also activated simultaneously with the Ras/MAPK pathways to mediate the final TGF-beta growth inhibitory outcome. One such pathway includes the SMAD signaling components that control TGF-beta-mediated gene transcription, currently under active study by a number of laboratories, including our own. Future efforts in this field will focus on defining the significance of these signaling proteins and pathways in mediating specific TGF-beta responses. Moreover, additional novel signaling proteins are sure to be identified.
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PMID:Transforming growth factor-beta signaling in epithelial cells. 936 79

Members of the epidermal growth-factor-receptor tyrosine-kinase (EGFR) family play important roles both in normal growth regulation/cell differentiation and in the genesis and progression of human neoplasia. In the present study, we analysed distinct heregulin (HRG) signals mediated by the HRG receptors HER3 and HER4. In overexpression cell systems, we demonstrate that HRG-induced transformation by "kinase-impaired" HER3 is dependent on coexpression of kinase active HER2. In cells coexpressing HER2 and HER4, however, both kinases significantly contribute to the HRG-induced mitogenic stimulus. In addition, we show that HER3 is no substrate of HRG-activated HER4. Analysis of EGFR crosstalk in a panel of human carcinoma cell lines revealed mainly HRG-induced activation of HER2/HER3, whereas HER4 activation is also detectable to various extents. Evidence for HRG-induced activation of HER3 and/or HER4 indicates relevance of cell-specific expression patterns of these high- and low-affinity HRG receptors in the modulation of a ligand-induced stimulus. Specific signal modulation and definition can be demonstrated further by distinct time courses of mitogen-activated protein (MAP) kinase (MAPK) activation, which are induced by distinct HRG isotypes via differential binding to HER2/HER3 versus HER2/HER4. In concert, these mechanisms of signal modulation may be decisive for the diverse biological activities of HRG in different cell types.
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PMID:Distinct characteristics of heregulin signals mediated by HER3 or HER4. 936 20

The adrenocorticotropic hormone (ACTH) inhibits the growth of Y1 mouse adrenocortical tumor cells as well as normal adrenocortical cells in culture but stimulates adrenocortical cell growth in vivo. In this study, we investigated this paradoxical effect of ACTH on cell proliferation in Y1 adrenal cells and have unmasked a growth-promoting effect of the hormone. Y1 cells were arrested in the G1 phase of the cell cycle by serum starvation and monitored for progression through S phase by measuring [3H]thymidine incorporation into DNA and by measuring the number of nuclei labeled with bromodeoxyuridine. Y1 cells were stimulated to progress through S phase and to divide after a brief pulse of ACTH (up to 2 h). This effect of ACTH appeared to be cAMP independent, since ACTH also induced cell cycle progression in Kin-8, a Y1 mutant with defective cAMP-dependent protein kinase activity. The growth-promoting effect of ACTH in Y1 was preceded by the rapid activation of p44 and p42 mitogen-activated protein kinases and by the accumulation of c-FOS protein. In contrast, continuous treatment with ACTH (14 h) inhibited cell cycle progression in Y1 cells by a cAMP-dependent pathway. The inhibitory effect of ACTH mapped to the midpoint of G1. Together, the results demonstrate a dual effect of ACTH on cell cycle progress, a cAMP-independent growth-promoting effect early in G1 possibly mediated by mitogen-activated protein kinase and c-FOS, and a cAMP-dependent inhibitory effect at mid-G1. It is suggested that the growth-inhibitory effect of ACTH at mid-G1 represents an ACTH-regulated check point that limits cell cycle progression.
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PMID:Unmasking a growth-promoting effect of the adrenocorticotropic hormone in Y1 mouse adrenocortical tumor cells. 936 63

Tumor-necrosis factor(TNF)-alpha inhibited in a dose-dependent fashion the proliferation of epidermal-growth-factor(EGF)-stimulated MCF-7 breast cancer cells with an IC50 of 0.25 nM. A comparable TNF-alpha-mediated inhibition of p42/44 mitogen-activated protein (MAP) kinase activity was observed in 10 nM EGF-stimulated cells. The MAP kinase activity dropped 50% within 3 min of TNF-alpha (1 nM) addition to EGF-stimulated MCF-7 cells. EGF and TNF-alpha, when added independently, led to a transient stimulation of MAP kinase activity with maximal activations within 6-8 min and 1-2 min, respectively. These observations suggest that MAP kinase activity in EGF-stimulated MCF-7 cells is modulated by the growth-inhibitory receptor pathways of TNF-alpha. Phosphorylation measurements on western blots determined the involvement of several individual MAP kinases, namely p42/44 MAP kinases, p38 MAP kinase and c-Jun N2-terminal kinase 1 (JNK1), in EGF and TNF-alpha-induced signalling. Phosphorylation of p42 and p38 MAP kinases only was observed after treatment with either TNF-alpha or EGF. A combination of both ligands inhibited p42 and p38 MAP kinase phosphorylation in MCF-7 cells. In contrast, no JNK1 phosphorylation was detected in these cells. Simultaneous addition of okadaic acid, a potent inhibitor of phosphatases 1 and 2A, blocked the decay of EGF-stimulated MAP kinase activity over 40 min. TNF-alpha added to EGF-stimulated and okadaic-acid-treated cells increased the MAP kinase activity twofold within 1 min. Similarly, okadaic acid treatment partly reverted the TNF-alpha-inhibited growth of MCF-7 cells. These experiments suggest that phosphatases are involved in the rapid shut-down by TNF-alpha of p42 MAP kinase activity.
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PMID:Tumor-necrosis factor-alpha modulates mitogen-activated protein kinase activity of epidermal-growth-factor-stimulated MCF-7 breast cancer cells. 937 Mar 49

Recently, TAP42 was isolated as a high copy suppressor of sit4-, a yeast phosphatase related to protein phosphatase 2A (PP2A). TAP42 is related to the murine alpha4 protein, which was discovered independently by its association with Ig-alpha in the B cell receptor complex. Herein we show that a glutathione S-transferase (GST)-alpha4 fusion protein bound the catalytic subunit (C) of human PP2A from monomeric or multimeric preparations of PP2A in a "pull-down" assay. In an overlay assay, the GST-alpha4 protein bound to the phosphorylated and unphosphorylated forms of C that were separated in two-dimensional gels and immobilized on filters. The results show direct and exclusive binding of alpha4 to C. This is unusual because all known regulatory B subunits, or tumor virus antigens, bind stably only to the AC dimer of PP2A. The alpha4-C form of PP2A had an increased activity ratio compared with the AC form of PP2A when myelin basic protein phosphorylated by mitogen-activated protein kinase and phosphorylase a were used as substrates. Recombinant alpha4 cleaved from GST was phosphorylated by p56(lck) tyrosine kinase and protein kinase C. A FLAG-tagged alpha4 expressed in COS7 cells was recovered as a protein containing phosphoserine and coimmunoprecipitated with the C but not the A subunit of PP2A. Treatment of cells with rapamycin prevented the association of PP2A with FLAG-alpha4. The results reveal a novel heterodimer alpha4-C form of PP2A that may be involved in rapamycin-sensitive signaling pathways in mammalian cells.
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PMID:B cell receptor-associated protein alpha4 displays rapamycin-sensitive binding directly to the catalytic subunit of protein phosphatase 2A. 938 Jun 85

Addition of insulin-like growth factor I (IGF-I) to quiescent breast tumor-derived MCF-7 cells causes stimulation of cyclin D1 synthesis, hyperphosphorylation of the retinoblastoma protein pRb, DNA synthesis, and cell division. All of these effects are independent of the mitogen-activated protein kinase (MAPK) pathway since none of them is blocked by PD098059, the specific inhibitor of the MAPK activating kinase MEK1. This observation is consistent with the finding that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a strong inducer of MAPK activity in MCF-7 cells, effectively inhibits proliferation. The anti-proliferative effect of TPA in these cells may be accounted for, at least in part, by the MAPK-dependent stimulation of the synthesis of p21(WAF1/CIP1), an inhibitor of cyclin/cyclin-dependent kinase complexes. In contrast, all of the observed stimulatory effects of IGF-I on cell cycle progression, cyclin D1 synthesis, and pRb hyperphosphorylation were blocked by the specific phosphatidylinositol 3-kinase inhibitor LY294002, suggesting that phosphatidylinositol 3-kinase activity but not MAPK activity is required for transduction of the mitogenic IGF-I signal in MCF-7 cells.
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PMID:Mitogenic signaling of insulin-like growth factor I in MCF-7 human breast cancer cells requires phosphatidylinositol 3-kinase and is independent of mitogen-activated protein kinase. 938 70

The tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), acutely stimulates the tyrosine phosphorylation of proteins of approximately 190, 120, and 70 kDa in the well differentiated Fao rat hepatoma cell line. This phosphorylation is dependent on protein kinase C (PKC) and is abolished by down-regulation of PKC or pretreatment with a PKC inhibitor. Purification of the 190-kDa tyrosine-phosphorylated protein revealed that it consists of both ErbB2 and ErbB3. Following PMA-induced tyrosine phosphorylation, ErbB2 and ErbB3 were able to associate with the SH2 domains of several signaling proteins including the p85alpha subunit of phosphatidylinositol 3-kinase, Syp, and Grb2. The 120-kDa protein phosphorylated in response to PMA consists of at least two proteins: focal adhesion kinase that exhibits a minor increase in tyrosine phosphorylation following treatment with PMA, and a major 120-kDa tyrosine-phosphorylated species in PMA-stimulated Fao cells which as yet is unidentified. Similarly, the 70-kDa tyrosine-phosphorylated protein also appears to represent more than one protein, including paxillin and a second protein of similar mobility which appears to be the major tyrosine phosphorylation in response to PMA. Both ErbB2 and paxillin also exhibit reduced migration on SDS-polyacrylamide gel electrophoresis following PMA treatment, suggesting that they are also phosphorylated on serine/threonine residues. The mobility shift of both of these proteins is abolished by treatment with inhibitors of PKC or mitogen-activated protein kinase/extracellular signal-related kinase kinase. These results suggest a novel mechanism of cross-talk between the serine/threonine kinase PKC and tyrosine phosphorylation pathways. The activation of ErbB2 and ErbB3 that is initiated by PMA may contribute to the tumor promoting activity of these compounds.
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PMID:Cross-talk between phorbol ester-mediated signaling and tyrosine kinase proto-oncogenes. I. Activation of protein kinase C stimulates tyrosine phosphorylation and activation of ErbB2 and ErbB3. 938 71

Point mutations, deletions, and recombinations of the RET proto-oncogene are associated with several inherited human diseases of neural crest-derived cells: Hirschsprung's disease, familial medullary thyroid carcinoma, and the multiple endocrine neoplasia (MEN) syndromes, types 2A and 2B. RET expression is restricted to normal and malignant cells of neural crest origin, such as human neuroblastoma cells. To better understand the role of the activated RET oncogene in neural crest cells, we transfected two adherent human neuroblastoma tumor cell lines with oncogenic MEN2 mutant RET cDNAs. Transfectant clones from both cell lines overexpressing MEN2B RET demonstrated a marked increase in the cell fraction growing in suspension. Both control and MEN2B cells formed tumors at the site of injection in all cases. However, mice injected with MEN2B cells developed lung metastases at a much higher frequency than control mice. Only RET protein derived from MEN2A transfectant cells had increased autokinase activity, whereas MEN2B transfectant cells demonstrated selective activation of the mitogen-activated protein kinase, Jun kinase-1 (Jnk1). These results indicate a biochemical signaling pathway that may link oncogenic RET with the metastatic process.
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PMID:Expression of multiple endocrine neoplasia 2B RET in neuroblastoma cells alters cell adhesion in vitro, enhances metastatic behavior in vivo, and activates Jun kinase. 939 66

The mitogen-activated protein kinase (MAPK) cascade acts as a focal point for signal transduction following activation of both G-protein-linked and tyrosine kinase growth factor receptors. A common intermediate between both of these diverse receptor subtypes includes the small guanosine triphosphate (GTP)-binding protein, p21ras. Point mutations of p21ras have been identified in various tumor types and lead to constitutive activation of this protein and subsequent activation of downstream pathways including the MAPK cascade. Using an in vivo model of hepatocellular carcinoma (HCC), we investigated the abundance and function of individual components of the MAPK cascade and the presence of specific p21ras mutations in this model. Expression of components of the MAPK cascade were determined in tumor and adjacent, non-neoplastic liver specimens by Western blot analysis and functional activity confirmed by substrate phosphorylation assays. Mutations in p21ras were analyzed using an enzyme-linked immunosorbent assay. In tumor, extracellular regulated kinases (ERKs) ERK1, ERK2, and mitogen-activated ERK-regulated kinase-1 (MEK1) were elevated by three- to fourfold as compared with adjacent nontumorigenic normal liver. In contrast, MEK2 was elevated by only 28%. Substrate phosphorylation and detection of phosphorylated ERK1/2 proteins showed increased functional activity of these proteins of the same magnitude as that observed for protein expression. Mutations in p21ras were not detected in this experimental model of HCC. We conclude that HCC is associated with marked changes in expression and function of components of the MAPK cascade independent of common p21ras mutations.
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PMID:Altered expression of mitogen-activated protein kinases in a rat model of experimental hepatocellular carcinoma. 939 88


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