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

Fluid shear stress activates a member of the mitogen-activated protein (MAP) kinase family, extracellular signal-regulated kinase (ERK), by mechanisms dependent on cholesterol in the plasma membrane in bovine aortic endothelial cells (BAEC). Caveolae are microdomains of the plasma membrane that are enriched with cholesterol, caveolin, and signaling molecules. We hypothesized that caveolin-1 regulates shear activation of ERK. Because caveolin-1 is not exposed to the outside, cells were minimally permeabilized by Triton X-100 (0.01%) to deliver a neutralizing, polyclonal caveolin-1 antibody (pCav-1) inside the cells. pCav-1 then bound to caveolin-1 and inhibited shear activation of ERK but not c-Jun NH(2)-terminal kinase. Epitope mapping studies showed that pCav-1 binds to caveolin-1 at two regions (residues 1-21 and 61-101). When the recombinant proteins containing the epitopes fused to glutathione-S-transferase (GST-Cav(1-21) or GST-Cav(61-101)) were preincubated with pCav-1, only GST-Cav(61-101) reversed the inhibitory effect of the antibody on shear activation of ERK. Other antibodies, including m2234, which binds to caveolin-1 residues 1-21, had no effect on shear activation of ERK. Caveolin-1 residues 61-101 contain the scaffolding and oligomerization domains, suggesting that binding of pCav-1 to these regions likely disrupts the clustering of caveolin-1 or its interaction with signaling molecules involved in the shear-sensitive ERK pathway. We suggest that caveolae-like domains play a critical role in the mechanosensing and/or mechanosignal transduction of the ERK pathway.
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PMID:Caveolin-1 regulates shear stress-dependent activation of extracellular signal-regulated kinase. 1074 26

Nerve growth factor (NGF) induces survival and differentiation of the neural crest-derived PC12 cell line. Caveolae are cholesterol-enriched, caveolin-containing plasma membrane microdomains involved in vesicular transport and signal transduction. Here we demonstrate the presence of caveolae in PC12 cells and their involvement in NGF signaling. Our results showed the expression of caveolin-1 by Western blot and confocal immuno-microscopy. The presence of plasma membrane caveolae was directly shown by rapid-freeze deep-etching electron microscopy. Moreover, combined deep-etching and immunogold techniques revealed the presence of the NGF receptor TrkA in the caveolae of PC12 cells. These data together with the cofractionation of Shc, Ras, caveolin, and TrkA in the caveolae fraction supported a role for these plasma membrane microdomains in NGF signaling. To approach this hypothesis, caveolae were disrupted by treatment of PC12 cells with cholesterol binding drugs. Either filipin or cyclodextrin treatment increased basal levels of MAPK phosphorylation. In contrast, pretreatment of PC12 cells with these drugs inhibited the NGF- but not the epidermal growth factor-induced MAPK phosphorylation without affecting the TrkA autophosphorylation. Taken together, our results demonstrate the presence of caveolae in PC12 cells, which contain the high affinity NGF receptor TrkA, and the specific involvement of these cholesterol-enriched plasma membrane microdomains in the propagation of the NGF-induced signal.
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PMID:PC12 cells have caveolae that contain TrkA. Caveolae-disrupting drugs inhibit nerve growth factor-induced, but not epidermal growth factor-induced, MAPK phosphorylation. 1098 88

Squamous cell carcinomas of the lung and cervix arise by neoplastic transformation of their respective tissue epithelia. In the case of cervical carcinomas, an increasing body of evidence implicates the human papillomavirus, HPV (types 16 and 18), as playing a pivotal role in this malignant transformation process. The HPV early genes E6 and E7 are known to inactivate the tumor suppressors p53 and Rb, respectively; this leads to disruption of cell cycle regulation, predisposing cells to a cancerous phenotype. However, the role of caveolin-1 (a putative tumor suppressor) in this process remains unknown. Here, we show that caveolin-1 protein expression is consistently reduced in a panel of lung and cervical cancer derived cell lines and that this reduction is not due to hyperactivation of p42/44 MAP kinase (a known negative regulator of caveolin-1 transcription). Instead, we provide evidence that this down-regulation event is due to expression of the HPV E6 viral oncoprotein, as stable expression of E6 in NIH 3T3 cells is sufficient to dramatically reduce caveolin-1 protein levels. Furthermore, we demonstrate that p53-a tumor suppressor inactivated by E6-is a positive regulator of caveolin-1 gene transcription and protein expression. SiHa cells are derived from a human cervical squamous carcinoma, harbor a fully integrated copy of the HPV 16 genome (including E6), and show dramatically reduced levels of caveolin-1 expression. We show here that adenoviral-mediated gene transfer of the caveolin-1 cDNA to SiHa cells restores caveolin-1 protein expression and abrogates their anchorage-independent growth in soft agar. Taken together, our results suggest that the HPV oncoprotein E6 down-regulates caveolin-1 via inactivation of p53 and that replacement of caveolin-1 expression can partially revert HPV-mediated cell transformation.
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PMID:Caveolin-1 expression is down-regulated in cells transformed by the human papilloma virus in a p53-dependent manner. Replacement of caveolin-1 expression suppresses HPV-mediated cell transformation. 1107 33

Environmental stressors have been recently shown to activate intracellular mitogen-activated protein (MAP) kinases, such as p38 MAP kinase, leading to changes in cellular functioning. However, little is known about the downstream elements in these signaling cascades. In this study, we show that caveolin-1 is phosphorylated on tyrosine 14 in NIH 3T3 cells after stimulation with a variety of cellular stressors (i.e. high osmolarity, H2O2, and UV light). To detect this phosphorylation event, we employed a phosphospecific monoclonal antibody probe that recognizes only tyrosine 14-phosphorylated caveolin-1. Since p38 MAP kinase and c-Src have been previously implicated in the stress response, we next assessed their role in the tyrosine phosphorylation of caveolin-1. Interestingly, we show that the p38 inhibitor (SB203580) and a dominant-negative mutant of c-Src (SRC-RF) both block the stress-induced tyrosine phosphorylation of caveolin-1 (Tyr(P)(14)). In contrast, inhibition of the p42/44 MAP kinase cascade did not affect the tyrosine phosphorylation of caveolin-1. These results indicate that extracellular stressors can induce caveolin-1 tyrosine phosphorylation through the activation of well established upstream elements, such as p38 MAP kinase and c-Src kinase. However, heat shock did not promote the tyrosine phosphorylation of caveolin-1 and did not activate p38 MAP kinase. Finally, we show that after hyperosmotic shock, tyrosine-phosphorylated caveolin-1 is localized near focal adhesions, the major sites of tyrosine kinase signaling. In accordance with this localization, disruption of the actin cytoskeleton dramatically potentiates the tyrosine phosphorylation of caveolin-1. Taken together, our results clearly define a novel signaling pathway, involving p38 MAP kinase activation and caveolin-1 (Tyr(P)(14)). Thus, tyrosine phosphorylation of caveolin-1 may represent an important downstream element in the signal transduction cascades activated by cellular stress.
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PMID:Cellular stress induces the tyrosine phosphorylation of caveolin-1 (Tyr(14)) via activation of p38 mitogen-activated protein kinase and c-Src kinase. Evidence for caveolae, the actin cytoskeleton, and focal adhesions as mechanical sensors of osmotic stress. 1109 59

Caveolae are plasma membrane microdomains that have been implicated in the regulation of several intracellular signaling pathways. Previous studies suggest that caveolin-1, the main structural protein of caveolae, could function as a tumor suppressor. Caveolin-1 is highly expressed in terminally differentiated mesenchymal cells including adipocytes, endothelial cells, and smooth muscle cells. To study whether caveolin-1 is a possible tumor suppressor in human mesenchymal tumors, we have analyzed the expression using immunohistochemistry in normal mesenchymal tissues, 22 benign and 79 malignant mesenchymal tumors. Caveolin-1 was found to be expressed in fibromatoses, leiomyomas, hemangiomas, and lipomas at high levels comparable to normal mesenchymal tissues. The expression of caveolin-1 was slightly reduced in four of six well-differentiated liposarcomas and strongly reduced or lost in three of three fibrosarcomas, 17 of 20 leiomyosarcomas, 16 of 16 myxoid/round cell/pleomorphic liposarcomas, five of eight angiosarcomas, 15 of 18 malignant fibrous histiocytomas, and eight of eight synovial sarcomas. The immunohistochemical findings were confirmed by Western blot analysis in a number of tumors. High levels of both the 24-kd [alpha]- and the 21-kd [beta]-isoform of caveolin-1 were detected in the nontumorigenic human fibroblast cell line IMR-90. In contrast, in HT-1080 human fibrosarcoma cells, caveolin-1 is strongly down-regulated. We show that the [alpha]-isoform of caveolin-1 is potently up-regulated in HT-1080 cells by inhibition of the mitogen-activated protein kinase-signaling pathway with the specific inhibitor PD 98059, whereas the specific inhibitor of DNA methylation 5-aza-2'-deoxycytidine only marginally up-regulates caveolin-1. In addition, re-expression of caveolin-1 in HT-1080 fibrosarcoma cells potently inhibited colony formation. From these we conclude that caveolin-1 is likely to act as a tumor suppressor gene in human sarcomas.
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PMID:Down-regulation of caveolin-1, a candidate tumor suppressor gene, in sarcomas. 1123 32

Growth factor-induced signaling by receptor tyrosine kinases (RTKs) plays a central role in embryonic development and in pathogenesis and, hence, is tightly controlled by several regulatory proteins. Recently, Sprouty, an inhibitor of Drosophila development-associated RTK signaling, has been discovered. Subsequently, four mammalian Sprouty homologues (Spry-1-4) have been identified. Here, we report the functional characterization of two of them, Spry-1 and -2, in endothelial cells. Overexpressed Spry-1 and -2 inhibit fibroblast growth factor- and vascular endothelial growth factor-induced proliferation and differentiation by repressing pathways leading to p42/44 mitogen-activating protein (MAP) kinase activation. In contrast, although epidermal growth factor-induced proliferation of endothelial cells was also inhibited by Spry-1 and -2, activation of p42/44 MAP kinase was not affected. Biochemical and immunofluorescence analysis of endogenous and overexpressed Spry-1 and -2 reveal that both Spry-1 and -2 are anchored to membranes by palmitoylation and associate with caveolin-1 in perinuclear and vesicular structures. They are phosphorylated on serine residues and, upon growth factor stimulation, a subset is recruited to the leading edge of the plasma membrane. The data indicate that mammalian Spry-1 and -2 are membrane-anchored proteins that negatively regulate angiogenesis-associated RTK signaling, possibly in a RTK-specific fashion.
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PMID:Mammalian sprouty-1 and -2 are membrane-anchored phosphoprotein inhibitors of growth factor signaling in endothelial cells. 1123 63

We looked for mutations in the caveolin-1 gene, encoding a critical molecule for membrane signaling to cell growth, in 92 primary human breast cancers, and we report here the identification of a mutation in caveolin-1 at codon 132 (P132L) in 16% of cases. The mutation-positive cases were mostly invasive scirrhous carcinomas. In cell lines expressing the same mutant of caveolin-1, we observed that the mutant Caveolin-1 expression seemed to induce cellular transformation and activation of mitogen-activated protein kinase-signaling pathway and to promote invasion-ability as well as altered actin networks in the cells. These results provide, for the first time, genetic evidence that a functioning Caveolin-1 mutation may have a role in the malignant progression of human breast cancer.
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PMID:Invasion activating caveolin-1 mutation in human scirrhous breast cancers. 1128 96

Expression of caveolin-1 in the human mammary adenocarcinoma cell line MCF-7 causes ligand-independent concentration of oestrogen receptor alpha (ERalpha) in the nucleus, and potentiates ligand-independent and ligand-dependent transcription from an oestrogen response element-driven reporter gene. Furthermore, caveolin-1 co-immunoprecipitates with ERalpha [Schlegel, Wang, Katzenellenbogen, Pestell and Lisanti (1999) J. Biol. Chem. 274, 33551-33556]. In the present study we show that caveolin-1 binds directly to ERalpha. This interaction is mediated by residues 82-101 of caveolin-1 (i.e. the caveolin scaffolding domain) and residues 1-282 of ERalpha. The caveolin-binding domain of ERalpha includes the ligand-independent transactivation domain, activation function (AF)-1, but lacks the hormone-binding domain and the ligand-gated transactivation domain, AF-2. In co-transfection studies, caveolin-1 potentiates the transcriptional activation of ERalpha(1-282), a truncation mutant that has intact AF-1 and DNA-binding domains. Since AF-1 activity is regulated largely by phosphorylation we determined that co-expression with caveolin-1 increased the basal phosphorylation of ERalpha(1-282), but blocked the epidermal growth factor-dependent increase in phosphorylation. Indeed, caveolin-1 interacted with and potentiated the transactivation of an ERalpha mutant that cannot be phosphorylated by extracellular signal-regulated kinase (ERK)1/2 [ERalpha(Ser(118)-->Ala)]. Thus caveolin-1 is a novel ERalpha regulator that drives ERK1/2-independent phosphorylation and activation of AF-1.
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PMID:Ligand-independent activation of oestrogen receptor alpha by caveolin-1. 1156 84

Recent evidence supports the existence of a plasma membrane ER. In many cells, E2 activates signal transduction and cell proliferation, but the steroid inhibits signaling and growth in other cells. These effects may be related to interactions of ER with signal-modulating proteins in the membrane. It is also unclear how ER moves to the membrane. Here, we demonstrate ER in purified vesicles from endothelial cell plasma membranes and colocalization of ERalpha with the caveolae structural coat protein, caveolin-1. In human vascular smooth muscle or MCF-7 (human breast cancer) cell membranes, coimmunoprecipitation shows that ER associates with caveolin-1 and -2. Importantly, E2 rapidly and differentially stimulates ER-caveolin association in vascular smooth muscle cells but inhibits association in MCF-7 cells. E2 also stimulates caveolin-1 and -2 protein synthesis and activates a caveolin-1 promoter/luciferase reporter in smooth muscle cells. However, the steroid inhibits caveolin synthesis in MCF-7 cells. To determine a function for caveolin-ER interaction, we expressed caveolin-1 in MCF-7 cells. This stimulated ER translocation to the plasma membrane and also inhibited E2-induced ERK (MAPK) activation. Both functions required the caveolin-1 scaffolding domain. Depending upon the target cell, membrane ERs differentially associate with caveolin, and E2 differentially modulates the synthesis of this signaling-inhibitory scaffold protein. This may explain the discordant signaling and actions of E2 in various cell types. In addition, caveolin-1 is capable of facilitating ER translocation to the membrane.
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PMID:ERs associate with and regulate the production of caveolin: implications for signaling and cellular actions. 1177 42

Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) receptors have been reported to signal via caveolin-containing membranes called caveolae. In contrast, others report that EGF and PDGF receptors are exclusively associated with caveolin-devoid membranes called rafts. Our subcellular fractionation and coimmunoprecipitation studies demonstrate that, in the absence of ligand, EGF and PDGF receptors are associated with rafts. However, in the presence of ligand, EGF and PDGF receptors transiently associate with caveolae. Surprisingly, pretreatment of cells with EGF prevents PDGF-dependent phosphorylation of PDGF receptors and extracellular signal-regulated kinase (ERK) 1/2 kinase activation. Furthermore, cells pretreated with PDGF prevent EGF-dependent phosphorylation of EGF receptors and ERK1/2 kinase activation. Radioligand binding studies demonstrate that incubation of cells with EGF or PDGF causes both EGF and PDGF receptors to be reversibly sequestered from the extracellular space. Experiments with methyl-beta-cyclodextrin, filipin, and antisense caveolin-1 demonstrate that sequestration of the receptors is dependent on cholesterol and caveolin-1. We conclude that ligand-induced stimulation of EGF or PDGF receptors can cause the heterologous desensitization of the other receptor by sequestration in cholesterol-rich, caveolin-containing membranes or caveolae.
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PMID:Heterologous desensitization of EGF receptors and PDGF receptors by sequestration in caveolae. 2773 24


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