Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hepatocyte growth factor (HGF) and its receptor, Met, play a crucial role in regulating adult skeletal myoblast proliferation and differentiation. Met signaling is mediated by phosphorylation of two carboxy-terminal tyrosines, which act as docking sites for a number of intracellular mediators. These include Grb2 and p85, which couple the receptor with the Ras and phosphatidylinositol 3-kinase (PI3K) pathways, respectively. In this study, we define the role of these effectors in response to HGF by utilizing Met mutants, designed to obtain preferential coupling of Met to either Grb2 or PI3K or both. We found that relative to the wild-type receptor, enhanced binding to Grb2 further increases the incorporation of bromodeoxyuridine and the expression of Twist, while decreasing that of p27(Kip1) and myogenin. Conversely, preferential coupling with PI3K induced cell-cycle withdrawal and differentiation. Whereas enhanced Grb2 binding increased the phosphorylation of the mitogen-activated protein kinase/extracellular signal-regulated protein kinases (MAPK/ERK) and abrogated that of p38 MAPK, PI3K had the opposite effect. PD098059 reversed the inhibitory effects of Met on cell proliferation and differentiation, while wortmannin had only a very marginal effect. Taken together, these data suggest that coupling of Met with Grb2 is necessary for HGF-mediated inhibition of muscle differentiation. This inhibition occurs only when PI3K signaling downstream of Met is low. Imposing an efficient coupling of PI3K to Met would lead to upregulation of muscle regulatory factors and subsequent cell differentiation.
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PMID:Preferential binding of Grb2 or phosphatidylinositol 3-kinase to the met receptor has opposite effects on HGF-induced myoblast proliferation. 1190 Apr 89

We have used a combination of vitamin A (all-trans-retinyl palmitate), 5-fluorouracil (5-FU) and radiation to treat human head and neck squamous cell carcinoma (HNSCC). This chemoradiotherapy is called "FAR therapy." In this study we examined the effects of all-trans-retinoic acid (ATRA), the active metabolite of vitamin A, and ATRA plus 5-FU on two HNSCC cell lines (YCU-N861 and YCU-H891) to gain insight into the molecular mechanisms of FAR therapy. ATRA at 1 mM (the order of concentration found in HNSCC tumors treated with FAR therapy) inhibited cell proliferation and caused G1 cell cycle arrest in both cell lines. This was associated with a decrease in cyclin D1, an increase in p27(Kip1) and a reduction in the hyperphosphorylated form of retinoblastoma protein (pRB). With YCU-N861 cells, ATRA also caused a decrease in Bcl-2 and Bcl-X(L) and an increase in Bax. Both ATRA and 5-FU activated c-Jun N-terminal kinase (JNK) 1 and the combination of both agents resulted in additive or synergistic activation of JNK1, and also enhanced the induction of apoptosis. The YCU-H891 cells, in which the epidermal growth factor receptor (EGFR)-signal transducer and activator of transcription 3 (Stat3) pathway is constitutively activated, were more resistant to treatments with ATRA, 5-FU and the combination of both agents than YCU-N861 cells. A dominant negative Stat3 construct strongly enhanced the cellular sensitivity of this cell line to 5-FU but not to ATRA. In addition there is evidence that activation of Stat3 is associated with cellular resistance to radiation in HNSCC. Therefore, the addition to FAR therapy of agents that inhibit activation of the Stat3 pathway may enhance the clinical response of patients with HNSCC to FAR therapy.
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PMID:The roles of JNK1 and Stat3 in the response of head and neck cancer cell lines to combined treatment with all-trans-retinoic acid and 5-fluorouracil. 1192 16

The ubiquitin-proteasome system is an important regulator of cell growth and apoptosis. The potential of specific proteasome inhibitors to act as novel anti-cancer agents is currently under intensive investigation. Several proteasome inhibitors exert anti-tumour activity in vivo and potently induce apoptosis in tumour cells in vitro, including those resistant to conventional chemotherapeutic agents. By inhibiting NF-kappaB transcriptional activity, proteasome inhibitors may also prevent angiogenesis and metastasis in vivo and further increase the sensitivity of cancer cells to apoptosis. Proteasome inhibitors also exhibit some level of selective cytotoxicity to cancer cells by preferentially inducing apoptosis in proliferating or transformed cells or by overcoming deficiencies in growth-inhibitory or pro-apoptotic molecules. High expression of oncogene products like c-Myc also makes cancer cells more susceptible to proteasome inhibitor-induced apoptosis. The induction of apoptosis by proteasome inhibitors varies between cell types but often occurs following an initial accumulation of short-lived proteins such as p53, p27, pro-apoptotic Bcl-2 family members or activation of the stress kinase JNK. These initial events often result in a perturbation of mitochondria with concomitant release of cytochrome c and activation of the Apaf-1 containing apoptosome complex. This results in activation of the apical caspase-9 followed by activation of effector caspases-3 and -7, which are responsible for the biochemical and morphological changes associated with apoptosis.
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PMID:The proteasome: a novel target for cancer chemotherapy. 1196 Mar 20

Cell spreading on extracellular matrix and associated changes in the actin cytoskeleton (CSK) are necessary for progression through G(1) and entry into S phase of the cell cycle. Pharmacological disruption of CSK integrity inhibits early mitogenic signaling to the extracellular signal-regulated kinase (Erk) subfamily of the mitogen-activated protein kinases (MAPKs) and arrests the cell cycle in G(1). Here we show that this block of G(1) progression is not simply a consequence of inhibition of the MAPK/Erk pathway but instead it reveals the existence of a discrete CSK-sensitive checkpoint. Use of PD98059 to inhibit MAPK/Erk and cytochalasin D (Cyto D) to disrupt the actin CSK at progressive time points in G(1) revealed that the requirement for MAPK/Erk activation lasts only to mid-G(1), while the actin CSK must remain intact up to late G(1) restriction point, R, in order for capillary endothelial cells to enter S phase. Additional analysis using Cyto D pulses defined a narrow time window of 3 h just prior to R in which CSK integrity was shown to be critical for the G(1)/S transition. Cyto D treatment led to down-regulation of cyclin D1 protein and accumulation of the cdk inhibitor, p27(Kip1), independent of cell cycle phase, suggesting that these changes resulted directly from CSK disruption rather than from a general cell cycle block. Together, these data indicate the existence of a distinct time window in late G(1) in which signals elicited by the CSK act independently of early MAPK/Erk signals to drive the cell cycle machinery through the G(1)/S boundary and, hence, promote cell growth.
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PMID:A discrete cell cycle checkpoint in late G(1) that is cytoskeleton-dependent and MAP kinase (Erk)-independent. 1196 94

Although there is abundant evidence that 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] inhibits the growth of several cancer cell types, inhibition of angiogenesis may also play a role in mediating the antitumor effects of 1,25-(OH)(2)D(3.) We examined the ability of 1,25-(OH)(2)D(3) to inhibit the growth of tumor-derived endothelial cells (TDECs) and normal endothelial cells and to modulate angiogenic signaling. 1,25-(OH)(2)D(3) inhibited the growth of TDECs from two tumor models at nanomolar concentrations, but was less potent against normal aortic or yolk sac endothelial cells. The vitamin D analogs Ro-25-6760, EB1089, and ILX23-7553 were also potent inhibitors of TDEC proliferation. Furthermore, the combination of 1,25-(OH)(2)D(3) and dexamethasone had greater activity than either agent alone. 1,25-(OH)(2)D(3) increased vitamin D receptor and p27(Kip1) protein levels in TDECs, whereas phospho-ERK1/2 and phospho-Akt levels were reduced. These changes were not observed in normal aortic endothelial cells. In squamous cell carcinoma and radiation-induced fibrosarcoma-1 cells, 1,25-(OH)(2)D(3) treatment caused a reduction in the angiogenic signaling molecule, angiopoietin-2. In conclusion, 1,25-(OH)(2)D(3) and its analogs directly inhibit TDEC proliferation at concentrations comparable to those required to inhibit tumor cells. Further, 1,25-(OH)(2)D(3) modulates cell cycle and survival signaling in TDECs and affects angiogenic signaling in cancer cells. Thus, our work supports the hypothesis that angiogenesis inhibition plays a role in the antitumor effects of 1,25-(OH)(2)D(3).
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PMID:Antiproliferative effects of 1alpha,25-dihydroxyvitamin D(3) and vitamin D analogs on tumor-derived endothelial cells. 1207 82

Addition of the ErbB-ligand, Heregulinbeta1 (HRG), to breast tumour-derived T47D cells promotes D-cyclin expression, p21(cip1) synthesis, cyclin-dependent kinase (CDK) activation through re-distribution of p27(kip1) and DNA synthesis. In contrast EGF has no effect on T47D cell cycle progression. By comparing these two ligands and the use of specific inhibitors for phosphatidylinositol-3 kinase (PI3K), mitogen-activated protein kinase (MAPK) and p38MAPK, we have identified several molecular mechanisms required for ErbB receptor-mediated proliferation. The PI3K, MAPK and p38MAPK pathways each displayed distinct activation profiles in response to either HRG or EGF, with obvious differences in both the intensity and duration of signal output. Through inhibition of each of these pathways it is apparent that each pathway is necessary, yet insufficient alone, to stimulate proliferation. Each pathway regulates distinct subsets of essential cell cycle regulators and integration of these signal networks is required for the timely expression of these components, which culminates in cell cycle progression. Significantly, the mechanisms controlling ligand-stimulated proliferation through ErbB2 are strikingly similar to the mechanisms through which overexpressed, constitutively activated, ErbB2 orchestrates uncontrolled proliferation in cancer cells. This suggests that downstream effectors of ErbB receptors represent good therapeutic targets for breast cancer.
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PMID:Distinct roles for phosphoinositide 3-kinase, mitogen-activated protein kinase and p38 MAPK in mediating cell cycle progression of breast cancer cells. 1208 35

Normal cellular functions of hamartin and tuberin, encoded by the TSC1 and TSC2 tumor suppressor genes, are closely related to their direct interactions. However, the regulation of the hamartin-tuberin complex in the context of the physiologic role as tumor suppressor genes has not been documented. Here we show that insulin or insulin growth factor (IGF) 1 stimulates phosphorylation of tuberin, which is inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 but not by the mitogen-activated protein kinase inhibitor PD98059. Expression of constitutively active PI3K or active Akt, including Akt1 and Akt2, induces tuberin phosphorylation. We further demonstrate that Akt/PKB associates with hamartin-tuberin complexes, promoting phosphorylation of tuberin and increased degradation of hamartin-tuberin complexes. The ability to form complexes, however, is not blocked. Akt also inhibits tuberin-mediated degradation of p27(kip1), thereby promoting CDK2 activity and cellular proliferation. Our results indicate that tuberin is a direct physiological substrate of Akt and that phosphorylation of tuberin by PI3K/Akt is a major mechanism controlling hamartin-tuberin function.
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PMID:Phosphatidylinositol 3-kinase/Akt pathway regulates tuberous sclerosis tumor suppressor complex by phosphorylation of tuberin. 2782 86

1,25-dihydroxyvitamin D3[1,25(OH)2D3] is a well-known potent regulator of cell growth and differentiation and there is recent evidence of an effect on cell death, tumour invasion and angiogenesis, which makes it a candidate agent for cancer regulation. The classical synthetic pathway of 1,25(OH)2D3 involves 25- and 1 alpha-hydroxylation of vitamin D3, in the liver and kidney, respectively, of absorbed or skin-synthesized vitamin D3. There is recent focus on the importance in growth control of local metabolism of 1,25(OH)2D3, which is a function of local tissue synthetic hydroxylases and particularly the principal catabolizing enzyme, 24-hydroxylase. The classical signalling pathway of 1,25(OH)2D3 employs the vitamin D nuclear receptor (VDR), which is a transcription factor for 1,25(OH)2D3 target genes. Effects of this pathway include inhibition of cellular growth and invasion. Cytoplasmic signalling pathways are increasingly being recognized, which similarly may regulate growth and differentiation but also apoptosis. 1,25(OH)2D3 has a major inhibitory effect on the G1/S checkpoint of the cell cycle by upregulating the cyclin dependent kinase inhibitors p27 and p21, and by inhibiting cyclin D1. Indirect mechanisms include upregulation of transforming growth factor-beta and downregulation of the epidermal growth factor receptor. 1,25(OH)2D3 may induce apoptosis either indirectly through effects on the insulin-like growth receptor and tumour necrosis factor-alpha or more directly via the Bcl-2 family system, the ceramide pathway, the death receptors (e.g. Fas) and the stress-activated protein kinase pathways (Jun N terminal kinase and p38). Inhibition of tumour invasion and metastasis potential has been demonstrated and mechanisms include inhibition of serine proteinases, metalloproteinases and angiogenesis. The lines of evidence for an effect of vitamin D3 in systemic cancer are the laboratory demonstration of relevant effects on cellular growth, differentiation, apoptosis, malignant cell invasion and metastasis; epidemiological findings of an association of the occurrence and outcome of cancers with derangements of vitamin D3/1,25(OH)2D3 and the association of functional polymorphisms of the VDR with the occurrence of certain cancers. In addition, vitamin D3 analogues are being developed as cancer chemotherapy agents. There is accumulating evidence that the vitamin D3/1,25(OH)2D3/VDR axis is similarly important in malignant melanoma (MM). MM cells express the VDR, and the antiproliferative and prodifferentiation effects of 1,25(OH)2D3 have been shown in cultured melanocytes, MM cells and MM xenografts. Recently, an inhibitory effect on the spread of MM cells has been demonstrated, low serum levels of 1,25(OH)2D3 have been reported in MM patients and the VDR polymorphisms have been shown to be associated with both the occurrence and outcome of MM. The relationship between solar irradiation and MM is more complex than for the systemic cancers. As in other cancers, there is evidence of a protective effect of vitamin D3 in MM, but ultraviolet radiation, which is a principal source of vitamin D3, is mutagenic. Further work is necessary on the influence of serum vitamin D3 levels on the occurrence and prognosis of MM, the effects of sun protection measures on serum vitamin D3 levels in temperate climates and epidemiological studies on geographical factors and skin type on the prognosis of MM. Meanwhile, it would seem mandatory to ensure an adequate vitamin D3 status if sun exposure were seriously curtailed, certainly in relation to carcinoma of breast, prostate and colon and probably also MM.
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PMID:Vitamin D and systemic cancer: is this relevant to malignant melanoma? 1217 89

To evaluate the role of the MEK/ERK pathway in NSCLC survival, we analyzed NSCLC cell lines that differed in tumor histology and status of p53, Rb, and K-ras. Constitutive ERK1/2 activity was demonstrated in 17 of 19 cell lines by maintenance of ERK1/2 phosphorylation with serum deprivation. Phosphorylation of ERK1/2 correlated with phosphorylation of MEK1/2 and p90RSK, but was inversely correlated with phosphorylation of c-Raf at S259. With serum deprivation, the MEK inhibitors, PD98059 and U0126, inhibited ERK1/2 activity but did not increase apoptosis. PD98059 and U0126 induced cell cycle arrest in G(0)/G(i) in cells with the highest levels of ERK1/2 activity, which correlated with induction of p27 but not p21. To confirm the cytostatic response to MEK inhibitors, we performed transient transfections with dominant negative forms of MEK or ERK. Surprisingly, dominant negative MEK and ERK mutants increased apoptosis without affecting cell cycle or p27 levels. When combined with paclitaxel, MEK inhibitors had no effect on apoptosis. In contrast, dominant negative ERK2 potentiated paclitaxel-induced apoptosis. Our studies show that constitutive ERK1/2 activity in NSCLC cells promotes cellular survival and chemotherapeutic resistance. Moreover, our data are the first to demonstrate divergent cellular responses to inhibition of the MEK/ERK pathway by small molecule inhibitors or dominant negative mutants.
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PMID:Variable apoptotic response of NSCLC cells to inhibition of the MEK/ERK pathway by small molecules or dominant negative mutants. 1218 40

N-cadherin, a member of the Ca(2+)-dependent cell-cell adhesion molecule family, plays an essential role in skeletal muscle cell differentiation. We show that inhibition of N-cadherin-dependent adhesion impairs the upregulation of the two cyclin-dependent kinase inhibitors p21 and p27, the expression of the muscle-specific genes myogenin and troponin T, and C2C12 myoblast fusion. To determine the nature of N-cadherin-mediated signals involved in myogenesis, we investigated whether N-cadherin-dependent adhesion regulates the activity of Rac1, Cdc42Hs, and RhoA. N-cadherin-dependent adhesion decreases Rac1 and Cdc42Hs activity, and as a consequence, c-jun NH2-terminal kinase (JNK) MAPK activity but not that of the p38 MAPK pathway. On the other hand, N-cadherin-mediated adhesion increases RhoA activity and activates three skeletal muscle-specific promoters. Furthermore, RhoA activity is required for beta-catenin accumulation at cell-cell contact sites. We propose that cell-cell contacts formed via N-cadherin trigger signaling events that promote the commitment to myogenesis through the positive regulation of RhoA and negative regulation of Rac1, Cdc42Hs, and JNK activities.
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PMID:N-cadherin-dependent cell-cell contact regulates Rho GTPases and beta-catenin localization in mouse C2C12 myoblasts. 1221 39


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