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

---

Query: EC:2.7.11.24 (mitogen-activated protein kinase)
95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lipid rafts are microdomains of plasma membranes enriched in cholesterol and sphingolipids in the outer layer. We determined whether kappa opioid receptors (KOR) in human placenta and FLAG (DYKDDDDK)-tagged human KOR (FLAG-hKOR) expressed in Chinese hamster ovary (CHO) cells are localized in lipid rafts and whether changes in cholesterol contents affect hKOR properties and signaling. Lipid rafts were prepared from placenta membranes and CHO cells expressing FLAG-hKOR using the Na2CO3 method and fractionation through a sucrose density gradient. The majority of the KOR in the placenta and FLAG-hKOR in CHO cells, determined by [3H]diprenorphine binding and/or immunoblotting with an anti-FLAG antibody, was present in low-density fractions, coinciding with high levels of caveolin-1 and cholesterol, markers of lipid rafts, which indicated that the KOR is localized in lipid rafts. Pretreatment with 2% methyl beta-cyclodextrin (MCD) reduced cholesterol content by approximately 48% and changed the cells from spindle-shaped to spherical. MCD treatment disrupted lipid rafts, shifted caveolin-1 and FLAG-hKOR to higher density fractions, increased the affinity of (-)-(trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U50,488H) for the hKOR, and greatly increased U50,488H-induced [35S]guanosine 5'-O-(3-thio)triphosphate binding and p42/44 mitogen-activated protein kinase phosphorylation. Cholesterol replenishment reversed all the MCD effects. Caveolin-1 immunoprecipitated with Galphai proteins and MCD treatment reduced caveolin-1 associated with Galphai proteins, which may contribute to the enhanced agonist-induced G protein activation. Caveolin-1 also immunoprecipitated with FLAG-hKOR, but MCD treatment had no effect on the association. Thus, the KOR is located in lipid rafts and its localization in the microdomains greatly affects coupling to G proteins.
...
PMID:Localization of the kappa opioid receptor in lipid rafts. 1650 60

Cholesterol is essential for cell viability, and homeostasis of cellular cholesterol is crucial to various cell functions. Here we examined the effect of cholesterol depletion on apoptosis and the mechanisms underlying this effect in NIH3T3 cells. We show that chronic cholesterol depletion achieved with lipoprotein-deficient serum (LPDS) and 25-hydroxycholesterol (25-HC) treatment resulted in a significant increase in cellular apoptosis and caspase-3 activation. This effect is not due to a deficiency of nonsterol isoprenoids, intermediate metabolites of the cholesterol biosynthetic pathway, but rather to low cholesterol levels, since addition of cholesterol together with LPDS and 25-HC nearly abolished apoptosis, whereas addition of farnesyl pyrophosphate or geranylgeranyl-pyrophosphate did not reverse the cell viability loss induced by LPDS plus 25-HC treatment. These effects were accompanied by an increase in ERK, JNK and p38 MAPK activity. However, only the inhibition of p38 MAPK with the specific inhibitor SB203580 or the overexpression of a kinase defective MKK6 resulted in a significant decrease in apoptosis and caspase-3 cleavage induced by cholesterol depletion. Furthermore, LPDS plus 25-HC increased RhoA activity, and this effect was reversed by addition of exogenous cholesterol. Finally, overexpression of the dominant negative N19RhoA inhibited p38 MAPK phosphorylation and apoptosis induced by low cholesterol levels. Together, our results demonstrate that cholesterol depletion induces apoptosis through a RhoA- and p38 MAPK-dependent mechanism.
...
PMID:RhoA and p38 MAPK mediate apoptosis induced by cellular cholesterol depletion. 1669 60

Cholesterol 7 alpha-hydroxylase (CYP7A1) of the bile acid biosynthesis pathway is suppressed by bile acids and inflammatory cytokines. Bile acids are known to induce inflammatory cytokines to activate the mitogen-activated protein kinase/c-Jun N-terminal kinase (JNK) signaling pathway that inhibits CYP7A1 gene transcription. c-Jun has been postulated to mediate bile acid inhibition of CYP7A1. However, the c-Jun target involved in the regulation of CYP7A1 is unknown. Human primary hepatocytes and HepG2 cells were used as models to study chenodeoxycholic acid (CDCA) and interleukin-1 beta (IL-1 beta) regulation of human CYP7A1 gene expression via real-time polymerase chain reaction, reporter assays, co-immunoprecipitation and chromatin immunocipitation (ChIP) assays. IL-1 beta and CDCA reduced CYP7A1 but induced c-Jun messenger RNA expression in human primary hepatocytes. IL-1beta inhibited human CYP7A1 reporter activity via the HNF4 alpha binding site. A JNK-specific inhibitor blocked the inhibitory effect of IL-1 beta on HNF4 alpha expression and CYP7A1 reporter activity. c-Jun inhibited HNF4 alpha and PPARgamma coactivator-1 alpha (PGC-1 alpha) coactivation of CYP7A1 reporter activity, whereas a dominant negative c-Jun did not. Co-immunoprecipitation and ChIP assays revealed that IL-1 beta and CDCA reduced HNF4 alpha bound to the CYP7A1 chromatin, and that c-Jun interacted with HNF4 alpha and blocked HNF4 alpha recruitment of PGC-1 alpha to the CYP7A1 chromatin. In conclusion, IL-1 beta and CDCA inhibit HNF4 alpha but induce c-Jun, which in turn blocks HNF 4 alpha recruitment of PGC-1 alpha to the CYP7A1 chromatin and results in inhibition of CYP7A1 gene transcription. The JNK/c-Jun signaling pathway inhibits bile acid synthesis and protects hepatocytes against the toxic effect of inflammatory agents.
...
PMID:Bile acids and cytokines inhibit the human cholesterol 7 alpha-hydroxylase gene via the JNK/c-jun pathway in human liver cells. 1672 32

Cholesterol, p38 MAPK and NFkappaB have been shown to participate in inflammation and cellular differentiation. Here, we examined the effect of cholesterol on NFkappaB-dependent transcription and the mechanisms underlying this effect in NIH3T3 cells. We show that chronic cholesterol depletion achieved with lipoprotein-deficient serum (LPDS) and 25-hydroxycholesterol (25-HC) treatment resulted in a significant increase in NFkappaB-dependent transcription, NFkappaB-DNA binding, IkappaBalpha degradation and p65/NFkappaB translocation to the nucleus, and the addition of exogenous cholesterol reversed these effects. Previously, we have shown that low cell cholesterol levels activate p38 MAPK. Here, we found that inhibition of p38 MAPK with the specific inhibitor SB203580 blocked the increase in NFkappaB activity, IkappaBalpha degradation and p65/NFkappaB translocation to the nucleus induced by cholesterol depletion. Moreover, the inhibition of the p38 MAPK downstream effector MSK1 with the specific inhibitor H89, or the overexpression of a kinase defective MSK1 abrogated the NFkappaB-dependent transcription induced by cholesterol depletion. On the other hand, the transactivation potential of p65/NFkappaB depends on phosphorylation of S276 by MSK1. We observed that cholesterol depletion increased the p65/NFkappaB transactivation capacity. This effect was reversed by cell cholesterol repletion or incubation with the SB203580 inhibitor. Moreover, the expression of a p65/NFkappaB S276A mutant was insensitive to cholesterol depletion. Together, our results demonstrate that cholesterol depletion induces NFkappaB transcriptional activity, not only by affecting the IkappaBalpha degradation and the translocation of p65/NFkappaB to the nucleus, but also regulating the p65/NFkappaB transactivating potential through a p38 MAPK/MSK1 mediated pathway.
...
PMID:Low cell cholesterol levels increase NFkappaB activity through a p38 MAPK-dependent mechanism. 1680 24

This study was undertaken to explore the possibility that cholesterol deficiency may perturb the physiological functions of astrocytes, thus rendering cells vulnerable to the cytotoxicity induced by glutamate (Glu). Cholesterol deprivation induces astrocyte stellation, which is accompanied by disruption of cortical actin, and phosphorylation of extracellular signal-regulated kinase (ERK) in an astrocyte-specific manner. Moreover, cholesterol reduction decreases the activity of glutamine synthetase (GS) while enhancing the capacity of Glu transporter. Using [(3)H]d-aspartate as a tracer, we found a marked efflux of [(3)H]d-aspartate from cholesterol-deficient astrocytes after Glu stimulation. Changes in the actin cytoskeleton, cell morphology, ERK phosphorylation and GS level gradually recovered in astrocytes after the withdrawal of cholesterol depletion. Moreover, withdrawal of cholesterol deprivation attenuated cell loss in cholesterol-deficient astrocytes during Glu exposure. Taken together, our data suggest that, upon Glu exposure, there would be an increase in intracellular Glu as a consequence of enhanced Glu uptake and reduced degradation of Glu by GS in cholesterol-deficient astrocytes. This in turn leads to a concentration gradient favoring Glu release, thereby causing the accumulation of cytotoxic levels of Glu extracellularly. It is thus concluded that the detrimental effect of cholesterol deprivation may, in part, arise from the impairment in Glu homeostasis.
...
PMID:Cholesterol deficiency perturbs actin signaling and glutamate homeostasis in hippocampal astrocytes. 1682 67

Our previous work demonstrated that the type I GnRH receptor (GnRHR) resides exclusively and constitutively within membrane rafts in alphaT3-1 gonadotropes and that this association was necessary for the ability of the receptor to couple to the ERK signaling pathway. G(alphaq), c-raf, and calmodulin have also been shown to reside in this compartment, implicating a raft-associated multiprotein signaling complex as a functional link between the GnRHR and ERK signaling. In the studies reported here, we used subcellular fractionation and coimmunoprecipitation to analyze the behavior of ERKs with respect to this putative signaling platform. ERK 2 associated partially and constitutively with low-density membranes both in alphaT3-1 cells and in whole mouse pituitary. Cholesterol depletion of alphaT3-1 cells reversibly blocked the association of both the GnRHR and ERKs with low-density membranes and uncoupled the ability of GnRH to activate ERK. Analysis of the kinetics of recovery of ERK inducibility after cholesterol normalization supported the conclusion that reestablishment of the association of the GnRHR and ERKs with the membrane raft compartment was not sufficient for reconstitution of signaling activity. In alphaT3-1 cells, the GnRHR and ERK2 coimmunoprecipitated from low-density membrane fractions prepared either in the presence or absence of detergent. The GnRHR also partitioned into low-density, detergent-resistant membrane fractions in mouse pituitary and coimmunoprecipitated with ERK2 from these fractions. Collectively, these data support a model in which coupling of the GnRHR to the ERK pathway in gonadotropes involves the assembly of a multiprotein signaling complex in association with specialized microdomains of the plasma membrane.
...
PMID:Signaling complexes associated with the type I gonadotropin-releasing hormone (GnRH) receptor: colocalization of extracellularly regulated kinase 2 and GnRH receptor within membrane rafts. 1706 98

We have previously shown that dietary red palm oil (RPO) supplementation improves functional recovery in hearts subjected to ischaemia-reperfusion. However, little knowledge exists concerning the effects of RPO supplementation of a high-cholesterol diet on ischaemia-reperfusion injury. The signalling mechanisms responsible for RPO's effects in the presence of cholesterol also remain to be elucidated. Therefore, the aim of the present study was to examine the effects of RPO, given with a high-cholesterol diet, on mitogen-activated protein kinase (MAPK) phosphorylation and apoptosis. Long-Evans rats were fed a control diet, a control diet containing 2% cholesterol, or a control diet containing 2% cholesterol and 7 g RPO per kg (CRPO) for 5 weeks. Hearts were excised and mounted on an isolated working heart perfusion apparatus. Cardiac function was measured after which hearts were freeze-clamped and used to assess MAPK phosphorylation and to evaluate apoptosis. Cholesterol supplementation caused a poor aortic output (AO) recovery compared with the control group (35.5 (sem 6.2) v. 55.4 (sem 2.5) %), but when RPO was added, the percentage AO increased significantly. The cholesterol group's poor AO was associated with a significant increase in p38-MAPK phosphorylation, whereas the CRPO-supplemented group showed as significant reduction in p38-MAPK phosphorylation when compared with the cholesterol-supplemented group. This significant reduction in p38-MAPK was also associated with reduced apoptosis as indicated by significant reductions in caspase-3 and poly(ADP-ribose) polymerase cleavage.
...
PMID:Dietary red palm oil reduces ischaemia-reperfusion injury in rats fed a hypercholesterolaemic diet. 1734 77

Cholesterol metabolism is particularly active in malignant, proliferative cells, whereas cholesterol starvation has been shown to inhibit cell proliferation. Inhibition of enzymes involved in cholesterol biosynthesis at steps before the formation of 7-dehydrocholesterol has been shown to selectively affect cell cycle progression from G(2) phase in human promyelocytic HL-60 cells. In the present work, we explored whether cholesterol starvation by culture in cholesterol-free medium and treatment with different distal cholesterol biosynthesis inhibitors induces differentiation of HL-60 cells. Treatment with SKF 104976, an inhibitor of lanosterol 14-alpha demethylase, or with zaragozic acid, which inhibits squalene synthase, caused morphologic changes alongside respiratory burst activity and expression of cluster of differentiation antigen 11c (CD11c) but not cluster of differentiation antigen 14. These effects were comparable to those produced by all-trans retinoic acid, which induces HL-60 cells to differentiate following a granulocyte lineage. In contrast, they differed from those produced by vitamin D(3), which promotes monocyte differentiation. The specificity of the response was confirmed by addition of cholesterol to the culture medium. Treatment with PD 98059, an inhibitor of extracellular signal-regulated kinase, abolished both the activation of NADPH oxidase and the expression of the CD11c marker. In sharp contrast, BM 15766, which inhibits sterol Delta(7)-reductase, failed to induce differentiation or arrest cell proliferation. These results show that changes in the sterol composition may trigger a differentiation response and highlight the potential of cholesterol pathway inhibition as a possible tool for use in cancer therapy.
...
PMID:Cholesterol starvation induces differentiation of human leukemia HL-60 cells. 1740 48

Cholesterol is a major component of skin lipids and acts as a regulator of vesicular trafficking and signal transduction. However, the function of cholesterol on matrix metalloproteinases (MMPs) expression of human skin is not fully understood. Here, we investigated the effects of cholesterol on MMP-9 expression in normal human keratinocytes (NHK) and HaCaT cells. Basal level of MMP-9 expression was decreased by cholesterol in NHK. On the other hand, MMP-9 expression was increased by the cholesterol depletion agent, methyl-beta-cyclodextrin (MbetaCD), while it was inhibited by cholesterol repletion in HaCaT cells. MbetaCD induced ERK and JNK phosphorylation were prevented by cholesterol repletion. The inhibition of ERK and JNK decreased MbetaCD-induced MMP-9 expression. Therefore, our results suggest that cholesterol regulates MMP-9 expression through ERK and JNK-dependent pathways.
...
PMID:Cholesterol inhibits MMP-9 expression in human epidermal keratinocytes and HaCaT cells. 1764 35

Alpha(1)-Adrenoceptors and extracellular signal-regulated kinases 1 and 2 (ERK1/2) regulate salivary secretion. However, whether alpha(1)-adrenoceptors couple to ERK1/2 activation and the specific alpha(1)-adrenoceptor subtypes involved in salivary glands is unknown. Western blotting of ERK1/2 phosphorylation showed phenylephrine activated ERK1/2 by 2-3-fold in submandibular gland slices and 3-4-fold in submandibular acinar (SMG-C10) cells with an EC(50) of 2.7+/-2 microM. ERK1/2 activation was blocked by either prazosin or HEAT, indicating alpha(1)-adrenoceptors stimulate ERK1/2 in native glands and SMG-C10 cells. Inhibition of [(125)I]HEAT binding by 5-methylurapidil (selective for alpha(1A) over alpha(1B/)alpha(1D)), but not BMY 7378 (selective for alpha(1D) over alpha(1A/)alpha(1B)), was biphasic and best-fit by a two-site binding model with K(i)(H) and K(i)(L) values for 5-methylurapidil of 0.64+/-0.3 and 91+/-7 nM, respectively, in SMG-C10 membranes. From these binding data, we obtained subtype-selective concentrations of 5-methylurapidil to determine the alpha(1)-adrenoceptor subtype/s activating ERK1/2 in SMG-C10 cells. 5-methylurapidil (20 nM) did not affect phenylephrine- or A-61603- (alpha(1A)-selective agonist) induced ERK1/2 activation; whereas, 30 microM chloroethylclonidine (alpha(1B)-selective antagonist) inhibited ERK1/2 activation by phenylephrine, indicating alpha(1B)-adrenoceptors, but not alpha(1A)-adrenoceptors, activate ERK1/2 in submandibular cells. We also examined alpha(1)-adrenoceptor location and dependence on cholesterol-rich microdomains for activating ERK1/2. Sucrose density gradient centrifugation showed 71+/-3% of alpha(1)-adrenoceptor binding sites were in plasma membranes. Cholesterol-disrupting agents filipin and methyl-beta-cyclodextrin inhibited phenylephrine-stimulated ERK1/2. These results show only alpha(1B)-adrenoceptors activate ERK1/2 and suggest subtype-specific ERK1/2 signaling by alpha(1B)-adrenoceptors may be determined by localization to cholesterol-rich microdomains in submandibular cells.
...
PMID:Characterization of the alpha1-adrenoceptor subtype activating extracellular signal-regulated kinase in submandibular gland acinar cells. 1793 47


<< Previous 1 2 3 4 5 6 7 8 Next >>

---