Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.12.2 (MEK)
18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

HER2/neu (erbB-2) overexpression has been causally associated with tamoxifen resistance in human breast cancer cells. Forced expression of HER2 in MCF-7 breast cancer cells resulted in mitogen-activated protein kinase (MAPK) hyperactivity and tamoxifen resistance. Inhibition of HER2 and MAPKs with AG1478 and U0126, respectively, as well as dominant-negative MEK-1/2 constructs restored the inhibitory effect of tamoxifen on estrogen receptor (ER)-mediated transcription and cell proliferation. Both AG1478 and U0126 also restored the tamoxifen-mediated association of ER with nuclear receptor corepressor (N-CoR) in the antiestrogen-resistant MCF-7 cells. Treatment with a combination of tamoxifen and a HER2 kinase inhibitor reduced tumor MAPK activity and markedly prevented growth of HER2-overexpressing MCF-7 xenografts in athymic mice. Thus, blockade of HER2 and MAPK signaling may enhance tamoxifen action and abrogate antiestrogen resistance in human breast cancer.
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PMID:Inhibition of HER2/neu (erbB-2) and mitogen-activated protein kinases enhances tamoxifen action against HER2-overexpressing, tamoxifen-resistant breast cancer cells. 1105 87

Three-dimensional tumor growth is dependent on the perpetual recruitment of host blood vessels to the tumor site. This recruitment process (mainly via angiogenesis) is thought to be triggered, at least in part, by the very same set of genetic alterations (activated oncogenes, inactivated/lost tumor suppressor genes) as those responsible for other aspects of malignant transformation (e.g., aberrant mitogenesis, resistance to apoptosis). Potent oncogenes are able to deregulate expression of both angiogenesis stimulators and inhibitors in cancer cells. For example, mutant ras expression is associated with increased production of vascular endothelial growth factor (VEGF) and downregulation of thrombospondin-1 (TSP-1). Upregulation of VEGF and angiogenesis can also be induced by constitutive activation of other oncogenic proteins (e.g., EGFR, Raf, MEK, PI3K) acting at various levels on the Ras signaling pathway. The mode and the magnitude of such proangiogenic influences can be significantly modified by cell type (fibroblastic or epithelial origin), epigenetic factors (hypoxia, changes in cell density), and/or presence of additional genetic lesions (e.g., preceding loss of p16 or p53 tumor suppressor genes). Activated oncogenes (e.g., ras, src, HER-2) induce co-expression of angiogenic properties concomitantly with several highly selectable traits (increased mitogenesis, resistance to apoptosis), a circumstance that may accelerate selection of the angiogenic phenotype at the cell population level. On the other hand oncogene-induced reduction in growth requirements may also endow tumor cells with a diminished (albeit not abrogated) dependence on (close) proximity to blood vessels, i.e., with reduced vascular dependence. Thus, oncogenes can impact several interconnected aspects of cellular growth, survival, and angiogenesis. Experimental evidence suggests that, in principle, many of these properties (including angiogenesis) can be simultaneously suppressed (and tumor stasis or regression induced) by effective use of the specific oncogene antagonists and signal transduction inhibitors.
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PMID:Oncogenes and angiogenesis: signaling three-dimensional tumor growth. 1114 71

HER2, a member of the human epidermal growth factor (EGF) receptor family, not only plays important roles in the progression of breast cancer tumorigenesis and metastasis, but may protect cancer cells from conventional cytotoxic therapies as well. In the current study, we evaluated the effect of targeting HER2 on radiosensitization of human breast cancer cells. Using six breast cancer cell lines with various levels of HER2 (BT474, SKBR3, MDA453, MCF7, ZR75B, and MDA468), we found that trastuzumab (Herceptin), a humanized monoclonal antibody that may inhibit breast cancer cell proliferation but does not induce apoptosis when used alone, enhanced radiation-induced apoptosis of the cells in a HER2 level-dependent manner. We furthered this study in MCF7 cells transfected for high levels of HER2 (MCF7HER2). Compared with parental or control vector-transfected MCF7 cells, MCF7HER2 cells showed increased phosphorylation of at least two important HER2 downstream molecules, protein kinase B/Akt and mitogen-activated protein kinase (MAPK), and increased resistance to radiotherapy, as shown by reduced induction of apoptosis and increased cell clonogenic survival after radiation. Exposure of the cells to trastuzumab down-regulated the levels of HER2 and reduced phosphorylation levels of Akt and MAPK in MCF7HER2 cells, and sensitized these cells to radiotherapy. When specific inhibitors of the phosphatidylinositol 3-kinase (PI3-K) and MAPK kinase (MEK) pathways were used, we found that exposure of MCF7HER2 cells to the PI3-K inhibitor LY294002 inhibited Akt phosphorylation and radiosensitized the cells, whereas the radiosensitization effect by the MEK inhibitor PD98059 was relatively weaker, albeit the phosphorylation of MAPK was reduced by PD98059 treatment. Our results indicate that the PI3-K pathway might be the major pathway for trastuzumab-mediated radiosensitization of breast cancer cells.
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PMID:Sensitization of breast cancer cells to radiation by trastuzumab. 1461 84

The cellular and molecular effects of the proteasome inhibitor bortezomib on breast cancer cells are as yet poorly characterized. Here, in a panel of six breast cancer cell lines, bortezomib reduced viability in a concentration-dependent, time-dependent, and cell line-dependent manner. Proteasome activity was relatively high in two of the three more resistant cell lines. No relationship was observed between bortezomib effects on cell viability and expression/phosphorylation of HER-2, epidermal growth factor receptor (EGFR), AKT, or extracellular signal-regulated kinase 1/2 (ERK1/2). Molecular effects of bortezomib were further studied in SK-BR-3 and BT-474 cells because they share expression of EGFR and overexpression of HER-2 while, in contrast, SK-BR-3 cells were 200-fold more sensitive to this agent. Proteasome activity was inhibited to a similar extent in the two cell lines, and known proteasome substrates accumulated similarly. In SK-BR-3 cells, a marked inhibition of EGFR, HER-2, and AKT phosphorylation was observed at a clinically relevant concentration of bortezomib. In contrast, phosphorylation of Raf/mitogen-activated protein kinase kinase 1/2 (MEK 1/2)/ERK1/2 increased by bortezomib. In BT-474 cells, the effects were much less pronounced. Treatment of SK-BR-3 cells with bortezomib combined with pharmacologic inhibitors of EGFR, phosphatidylinositol 3'-kinase, or MEK resulted in modest or no enhancement of the effects on cell viability. Collectively, these results show that bortezomib has differential cellular and molecular effects in human breast cancer cells. The bortezomib-observed effects on signaling transduction molecules might be relevant to help to design mechanistic-based combination treatments.
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PMID:Differential cellular and molecular effects of bortezomib, a proteasome inhibitor, in human breast cancer cells. 1654 81

We determined the impact of HER2 signaling on two proangiogenic factors, vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8), and on an antiangiogenic factor, thrombospondin-1 (TSP-1). Re-expression of HER2 in MCF-7 and T-47D breast cancer cells that endogenously express low levels of HER2 resulted in elevated expression of VEGF and IL-8 and decreased expression of TSP-1. Inhibition of HER2 with a humanized anti-HER2 antibody (trastuzumab, or Herceptin) or a retrovirus-mediated small interfering RNA against HER2 (siHER2) decreased VEGF and IL-8 expression, but increased TSP-1 expression in BT474 breast cancer cells that express high levels of HER2. These in vitro results were further evaluated by treatment of BT474 xenografts in immunosuppressed mice with trastuzumab. Trastuzumab inhibited growth of BT474 xenografts and decreased microvascular density associated with downregulation of VEGF and IL-8 and with upregulation of TSP-1 expression. Inhibiting the PI3K-AKT pathway decreased VEGF and IL-8 expression. AKT1 overexpession increased VEGF and IL-8 expression, but did not increase TSP-1 expression. A p38 kinase inhibitor, SB203580, instead blocked TSP-1 expression and a p38 activator, MKK6, increased TSP-1 expression. Trastuzumab stimulated sustained p38 activation and SB203580 attenuated the TSP-1 upregulation induced by trastuzumab. HER2 signaling therefore influences the equilibrium between pro- and antiangiogenic factors via distinct signaling pathways. Trastuzumab inhibits angiogenesis and tumor growth, at least in part, through activation of the HER2-p38-TSP-1 pathway and inhibition of the HER2-PI3K-AKT-VEGF/IL-8 pathway.
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PMID:HER2 signaling modulates the equilibrium between pro- and antiangiogenic factors via distinct pathways: implications for HER2-targeted antibody therapy. 1671 32

Identification of the key roles of protein kinases in signaling pathways leading to development of cancer has caused pharmacological interest to concentrate extensively on targeted therapies as a more specific and effective way for blockade of cancer progression. This review will mainly focus on inhibitors targeting these key components of cellular signaling by employing a technology-based point of view with respect to ATP- and non-ATP-competitive small molecule inhibitors and monoclonal antibodies of selected protein kinases, particularly, mammalian target of rapamycin (mTOR), BCR-ABL, MEK, p38 MAPK, EGFR PDGFR, VEGFR, HER2 and Raf. Inhibitors of the heat shock protein Hsp90 are also included in a separate section, as this protein plays an essential role for the maturation/proper activation of cancer-related protein kinases. In the following review, the molecular details of the mode of action of these inhibitors as well as the emergence of drug resistance encountered in several cases are discussed in light of the structural, molecular and clinical studies conducted so far.
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PMID:Protein kinases as drug targets in cancer. 1710 May 68

The role of Epstein-Barr virus (EBV) in the pathogenesis of breast cancer has been of long-standing interest to the field. Breast epithelial cells can be infected by EBV through direct contact with EBV-bearing lymphoblastoid cells, and EBV infection has recently been shown to confer breast cancer cells an increased resistance to chemotherapeutic drugs. In this study, we established EBV-infected breast cancer MCF7 and BT474 cells and demonstrated that EBV infection promotes tumorigenic activity of breast cancer cells. Firstly, we showed that the EBV-infected MCF7-A and BT474-A cells exhibited increased anchorage-independent growth in soft agar. The increased colony formation capacity in soft agar was associated with increased expression and activation of HER2/HER3 signaling cascades, as evidenced by the findings that the treatment of HER2 antibody trastuzumab (Herceptin), phosphatidylinositol 3-kinase inhibitor, or MEK inhibitor completely abolished the tumorigenic capacity. In the EBV-infected breast cancer cells, the expression of EBV latency genes including EBNA1, EBER1, and BARF0 was detected. We next showed that BARF0 alone was sufficient to efficiently up-regulate HER2/HER3 expression and promoted tumorigenic activity in MCF7 and BT474 cells by the use of both overexpression and small interfering RNA knock-down. Collectively, we demonstrated that EBV-encoded BARF0 promotes the tumorigenic activity of breast cancer cells through activation of HER2/HER3 signaling cascades.
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PMID:Dysregulation of HER2/HER3 signaling axis in Epstein-Barr virus-infected breast carcinoma cells. 1737 31

A major challenge to broadening oncology applications for inhibitors of the ubiquitin-proteasome system (UPS) is the identification of UPS-dependent cancer pathways predictive of tumors responsive to peptidomimetic inhibitors of its 20S core protease activity. To inform clinical studies evaluating UPS inhibitors as breast cancer therapeutics, seven phenotypically diverse human breast cancer cell line models were characterized for their cellular and molecular responses to the clinically approved 20S inhibitor bortezomib (PS341; Velcade), focusing on those overexpressing estrogen receptor (ER) or ERBB2/HER2, because these oncogenic receptor pathways are constitutively activated in approximately 80% of all breast cancers. All models demonstrated dose-dependent bortezomib reduction in intracellular 20S activity correlating with cell growth inhibition, and bortezomib IC(50) values (concentrations producing 50% growth inhibition) varied directly with pretreatment 20S activities (r = 0.74; *, p < 0.05), suggesting that basal 20S activity may serve as a clinical predictor of tumor responsiveness to UPS inhibition. Reduction in 20S activity (> 60%) was associated with early (24 h) intracellular relocalization of ER (nucleus to cytoplasm) and ERBB2 (plasma membrane to perinuclear lysosomes), buildup of ubiquitinated and Hsp70-associated receptor, degradation and loss of ER and ERBB2 function, and induction of cellular apoptosis. These models were also used to screen a pharmacologic panel of pathway-targeted anticancer agents [4-hydroxy-3-methoxy-5-(benzothiazolylthiomethyl)benzylidenecyanoacetamide (AG825), 6-(4-bromo-2-chloro-phenylamino)-7-fluoro-3-methyl-3H-benzoimidazole-5-carboxylic acid (2-hydroxy-ethoxy)-amide (AZD6244/ARRY142886), 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride (LY294002), 17-N-allylamino-17-demethoxy geldanamycin (17AAG), and (2E)-N-hydroxy-3-[4-[[(2-hydroxyethyl)[2-(1H-indol-3-yl)ethyl]amino]methyl]phenyl]-2-propenamide (LAQ824)] for those capable of sensitizing to bortezomib. In keeping with the observation that 20S reduction has little effect on mitogen-activated protein kinase kinase 1/2 (MEK1/2) signaling in either ER-positive or ERBB2-positive models, only the MEK-1/2 inhibitor AZD6244 consistently improved the antitumor activity of bortezomib.
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PMID:Proteasome-regulated ERBB2 and estrogen receptor pathways in breast cancer. 1739 24

Tumor-associated fatty acid synthase (FAS) is implicated in tumorigenesis and connected to HER2 (human epidermal growth factor receptor 2) by systemic analyses. Suppression of FAS in cancer cells may lead to growth inhibition and cell apoptosis. Our previous study demonstrated that (-)-epigallocatechin 3-gallate (EGCG), the green tea catechin, could down-regulate FAS expression by suppressing EGFR (epidermal growth factor receptor) signaling and downstream phosphatidylinositol 3-kinase (PI3K)/Akt activation in the MCF-7 breast cancer cell line. Herein, we examined the effects of EGCG on FAS expression modulated by another member of the erbB family, that is, HER2 or HER3. We identified that heregulin-beta1 (HRG-beta1), a HER3 ligand, stimulated dose-dependent FAS expression in breast cancer cell lines MCF-7 and AU565, but not MDA-MB-453. The time-dependent increase in FAS expression after HRG-beta1 stimulation was also observed in MCF-7 cells, and this up-regulation was de novo RNA synthesis dependent. Treatment of MCF-7 cells with EGCG markedly inhibited HRG-beta1-dependent induction of mRNA and protein of FAS. EGCG also decreased the phosphorylation of Akt and extracellular signal-regulated kinase 1/2 that were demonstrated as selected downstream HRG-beta1-responsive kinases required for FAS expression using dominant-negative Akt, PI3K inhibitors (LY294002 and wortmannin), or MEK inhibitor (PD98059). FAS induction by HRG-beta1 was also blocked by AG825, a selective HER2 inhibitor, and by genistein, a selective tyrosine kinase inhibitor, indicating the formation of a heterodimer between HER2 and HER3, and their tyrosine kinase activities are essential for HRG-beta1-mediated elevation of FAS. Additionally, growth inhibition of HRG-beta1-treated cells was parallel to suppression of FAS by EGCG. Taken together, these findings extend our previous study to indicate that EGCG may be useful in the chemoprevention of breast carcinoma in which FAS overexpression results from HER2 or/and HER3 signaling.
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PMID:Tea polyphenol (-)-epigallocatechin 3-gallate suppresses heregulin-beta1-induced fatty acid synthase expression in human breast cancer cells by inhibiting phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase cascade signaling. 1753 58

The growth factor heregulin-beta1 (HRG-beta1), which is expressed in breast cancer, activates the HER-2 signaling pathway through induction of heterodimeric complexes of HER-2 with HER-3 or HER-4. It has been shown in many studies that HRG-beta1 induces the tumorigenicity and metastasis of breast cancer cells. Matrix metalloproteinase (MMP) 9 is a key enzyme in the degradation of extracellular matrices, and its expression may be dysregulated in breast cancer invasion and metastasis. Resveratrol, a major component in grape, exhibited potential anticarcinogenic activities in both in vitro and in vivo studies. However, the inhibitory effect of resveratrol on HER-2-mediated expression of MMP-9 has not been demonstrated yet. In the present study, we investigated the anti-invasive mechanism of resveratrol in human breast cancer cells. Human breast cancer MCF-7 cells were exposed to resveratrol (2, 5 and 10 microM). The expression activity of MMP-9 was measured by zymogram analysis. Phosphorylated levels of HER-2 and mitogen-activated protein kinase (MAPK)/ERK were measured by Western blot analysis. Total actin was used as internal control for protein expression. HRG-beta1 induced the phosphorylation of HER-2/neu receptor and MMP-9 expression in human breast cancer MCF-7 cells. Resveratrol significantly inhibited HRG-beta1-mediated MMP-9 expression in human breast cancer cells. MEK inhibitor induced a marked reduction in MMP-9 expression, and it suggested that ERK1/2 cascade could play an important role in HRG-beta1-mediated MMP-9 expression. Furthermore, resveratrol significantly suppressed HRG-beta1-mediated phosphorylation of ERK1/2 and invasion of breast cancer cells. However, resveratrol had negligible effects on either HRG-beta1-mediated phosphorylation of HER-2 receptor or expression of the tissue inhibitor of MMP, tissue inhibitor metalloproteinase protein 1. Taken together, our results suggest that resveratrol inhibited MMP-9 expression in human breast cancer cells. The inhibitory effects of resveratrol on MMP-9 expression and invasion of breast cancer cells are, in part, associated with the down-regulation of the MAPK/ERK signaling pathway.
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PMID:Resveratrol inhibits heregulin-beta1-mediated matrix metalloproteinase-9 expression and cell invasion in human breast cancer cells. 1765 59


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