Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.10.1 (ERK)
 95,504 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the relationship between adenosine triphosphate (ATP) concentration and loss of maintenance of kinase-signalling cascades in primary cortical astrocytes during oxygen-glucose deprivation (OGD) as this may constitute an irreversible step that commits astrocytes to cell death. We report that the phosphorylation of Akt, ERK, JNK and p38 kinases, whose activities depend on serine, threonine and tyrosine phosphorylation, were all increased during OGD. All these phosphorylations were reduced to below detection limits when ATP levels were less than 10% of normal levels. Using ERK and Akt as representative examples, we show that this erasure is not irreversible as both ERK and Akt phosphorylations can be partially restored by addition of glucose under anoxic conditions. We further investigated whether OGD caused any change in phosphatase activity. The PP1/PP2A phosphatase inhibitors okadaic acid and caliculyn A, but not cyclosporine A, delayed the removal of ERK and Akt phosphorylation under OGD. By comparing the extent of phosphorylation increase under OGD and normoxic conditions, we calculate that phosphatase activity was increased by approximately 3.6-fold during OGD. These data show that ATP levels control an important checkpoint in kinase function, and that ATP levels may need to be considered when studies of kinase function in relation to OGD are conducted.
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PMID:Erasure of kinase phosphorylation in astrocytes during oxygen-glucose deprivation is controlled by ATP levels and activation of phosphatases. 1291 35

The HePTP (haematopoietic protein tyrosine phosphatase) is a negative regulator of the ERK2 (extracellular signal-regulated protein kinase 2) and p38 MAP kinases (mitogen-activated protein kinases) in T-cells. This inhibitory function requires a physical association of HePTP through an N-terminal KIM (kinase-interaction motif) with ERK and p38. We previously reported that PKA (cAMP-dependent protein kinase) phosphorylates Ser-23 within the KIM of HePTP, resulting in dissociation of HePTP from ERK2. Here we follow the phosphorylation of this site in intact T-cells. We find that HePTP is phosphorylated at Ser-23 in resting T-cells and that this phosphorylation increases upon treatment of the cells with agents that elevate intracellular cAMP, such as prostaglandin E2. HePTP phosphorylation occurred at discrete regions at the cell surface. Phosphorylation was reduced by inhibitors of PKA and increased by inhibitors of protein phosphatases PP1 and PP2A, but not by inhibitors of calcineurin. In vitro, PP1 efficiently dephosphorylated HePTP at Ser-23, while PP2A was much less efficient. Activation of PP1 by treatment of the cells with ceramide suppressed Ser-23 phosphorylation, as did transfection of the catalytic subunit of PP1. Phosphorylation at Ser-23 is also increased in a transient manner upon T-cell antigen receptor ligation. In contrast, treatment of cells with phorbol ester had no effect on HePTP phosphorylation at Ser-23. We conclude from these results that HePTP is under continuous control by PKA and a serine-specific phosphatase, probably PP1, in T-cells and that this basal phosphorylation at Ser-23 can rapidly change in response to external stimuli. This, in turn, will affect the ability of HePTP to inhibit the ERK and p38 MAP kinases.
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PMID:Haematopoietic protein tyrosine phosphatase (HePTP) phosphorylation by cAMP-dependent protein kinase in T-cells: dynamics and subcellular location. 1461 83

Normal spontaneous apoptosis in neutrophils is enhanced by "stress" stimuli such as tumor necrosis factor-alpha, Fas ligand, and oxidants, and this effect is inhibited by anti-apoptotic stimuli including granulocyte-macrophage colony-stimulating factor, lipopolysaccharide, and formylmethionine-leucine-phenylalanine. In this report we demonstrate that anti-apoptotic stimuli protect neutrophils from stress-induced apoptosis via activation of the ERK/MAPK pathway. The protection occurs downstream of mitochondrial alterations assessed as a decrease in membrane potential concomitant with enhanced cytochrome c release. ERK activation was shown to inhibit apoptosis by maintaining levels of XIAP, which is normally decreased in the presence of the pro-apoptotic/stress stimuli. This report also demonstrates that potent intra- and extracellular oxidants inhibit the protective effect of ERK. Oxidant-dependent inhibition of ERK was because of activation of p38 MAPK and activation of the protein phosphatases PP1 and PP2A. Our data suggest that ERK suppresses stress-induced apoptosis downstream of mitochondrial alterations by maintaining XIAP levels and that oxidants block this effect through activation of p38 and protein phosphatases.
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PMID:Oxidants inhibit ERK/MAPK and prevent its ability to delay neutrophil apoptosis downstream of mitochondrial changes and at the level of XIAP. 1529 76

Previous studies in our laboratory have shown a differential activation of the mitogen-activated protein kinases (MAPKs) in primary bone marrow-derived macrophages following infection with pathogenic Mycobacterium avium compared to the activation following infection with nonpathogenic Mycobacterium smegmatis. Additionally, M. smegmatis-infected macrophages produced significantly elevated levels of tumor necrosis factor alpha (TNF-alpha) compared to the levels produced by M. avium-infected macrophages. The TNF-alpha production was dependent on both p38 and extracellular signal-regulated kinase 1/2 (ERK 1/2) activation. However, the macrophage transcription factors downstream of the MAPKs, which were required for TNF-alpha production, remained undefined. In this study we determined that the transcription factor cyclic AMP response element binding protein (CREB) is significantly more activated in M. smegmatis-infected macrophages than in M. avium-infected macrophages. We also found that CREB activation was dependent on p38 and protein kinase A but not on ERK 1/2 or calmodulin kinase II. Moreover, mutating the cAMP-responsive element on the TNF-alpha promoter resulted in significantly diminished promoter activity following M. smegmatis infection but not M. avium infection. The inability of macrophages infected with M. avium to sustain MAPK activation and to produce high levels of TNF-alpha was due, in part, to an increase in serine/threonine phosphatase PP2A activity. Our studies are the first to demonstrate an important role for the transcription factor CREB in TNF-alpha production by mycobacterium-infected macrophages, as well as a role for M. avium's induction of PP2A phosphatase activity as a mechanism to limit macrophage activation.
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PMID:Differential activation of the transcription factor cyclic AMP response element binding protein (CREB) in macrophages following infection with pathogenic and nonpathogenic mycobacteria and role for CREB in tumor necrosis factor alpha production. 1561 91

Identifying the molecular lesions that are 'mission critical' for tumorigenesis and maintenance is one of the burning questions in contemporary cancer biology. In addition, therapeutic strategies that trigger the lytic and selective death of tumor cells are the unfulfilled promise of cancer research. Fortunately, viruses can provide not only the necessary 'intelligence' to identify the critical players in the cancer cell program but also have great potential as lytic agents for tumor therapy. Recent studies with DNA viruses have contributed to our understanding of critical tumor targets (such as EGFR, PP2A, Rb and p53) and have an impact on the development of novel therapies, including oncolytic viral agents, for the treatment of cancer.
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PMID:DNA tumor viruses -- the spies who lyse us. 1566 29

The regulation of protein phosphorylation requires coordinated interaction between protein kinases and protein phosphatases (PPs). Recent evidence has shown that the Galphaq-protein-coupled metabotropic glutamate receptor (mGluR) 5 up-regulates phosphorylation of MAPK/ERK1/2. However, signaling mechanisms linking mGluR5 to ERK are poorly understood. In this study, roles of a major serine/threonine PP, PP2A, in this event were evaluated in cultured neurons. We found that the PP1/2A inhibitors okadaic acid and calyculin A mimicked the effect of the mGluR5 agonists (RS)-3,5-dihydroxyphenylglycine and (RS)-2-chloro-5-hydroxyphenylglycine in facilitating phosphorylation of ERK1/2 and its upstream kinase, MEK1/2, in a PP2A-dependent but not PP1-dependent manner. Co-administration of either inhibitor with an mGluR5 agonist produced additive phosphorylation of ERK1/2. Enzymatic assays showed a basal level of phosphatase activity of PP2A under normal conditions, and activation of mGluR5 selectively inhibited PP2A, but not PP1, activity. In addition, a physical association of the cytoplasmic C terminus of mGluR5 with PP2A was observed, and ligand activation of mGluR5 reduced mGluR5-PP2A binding. Additional mechanistic studies revealed that mGluR5 activation increased tyrosine (Tyr307) phosphorylation of PP2A, which was dependent on activation of a p60c-Src family tyrosine kinase, but not the epidermal growth factor receptor tyrosine kinase and resulted in dissociation of PP2A from mGluR5 and reduced PP2A activity. Together, we have identified a novel, mGluR5-triggered signaling mechanism involving use- and Src-dependent inactivation of PP2A, which contributes to mGluR5 activation of MEK1/2 and ERK1/2.
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PMID:Role of protein phosphatase 2A in mGluR5-regulated MEK/ERK phosphorylation in neurons. 1566 43

The Raf-1 kinase is an important signaling molecule, functioning in the Ras pathway to transmit mitogenic, differentiative, and oncogenic signals to the downstream kinases MEK and ERK. Because of its integral role in cell signaling, Raf-1 activity must be precisely controlled. Previous studies have shown that phosphorylation is required for Raf-1 activation, and here, we identify six phosphorylation sites that contribute to the downregulation of Raf-1 after mitogen stimulation. Five of the identified sites are proline-directed targets of activated ERK, and phosphorylation of all six sites requires MEK signaling, indicating a negative feedback mechanism. Hyperphosphorylation of these six sites inhibits the Ras/Raf-1 interaction and desensitizes Raf-1 to additional stimuli. The hyperphosphorylated/desensitized Raf-1 is subsequently dephosphorylated and returned to a signaling-competent state through interactions with the protein phosphatase PP2A and the prolyl isomerase Pin1. These findings elucidate a critical Raf-1 regulatory mechanism that contributes to the sensitive, temporal modulation of Ras signaling.
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PMID:Regulation of Raf-1 by direct feedback phosphorylation. 1566 84

In this study, we focus on the potential interaction of pp32/I-1(PP2A) (pp32) with the Raf-MEK-ERK signaling pathway. We show that overexpressed pp32 suppresses Raf-1 activation, thereby downregulating the level of ERK activation. This suppression of Raf-1 requires the C-terminal half of pp32. Conversely, knock-down of PP32 by siRNA enhances ERK and MEK activations. Taken together, we propose that tumor-suppression by pp32 is, at least in part, mediated by downregulation of the Raf-MEK-ERK signaling pathway.
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PMID:pp32/ I-1(PP2A) negatively regulates the Raf-1/MEK/ERK pathway. 1603 54

In previous studies we have shown that all-trans retinoic acid (atRA)-treatment of the atRA-sensitive ovarian carcinoma cell line CA-OV3 repressed AP-1 activity by about 50%, while a similar effect was not observed in the atRA-resistant ovarian carcinoma cell line, SK-OV3. These results suggested that the repression of AP-1 activity may be one of the mechanisms by which atRA inhibits the growth of atRA-sensitive CA-OV3 cells. In the present studies, we investigated further the molecular mechanism by which AP-1 activity is repressed by atRA. We show that the repression of AP-1 activity correlates with an increase in JunB protein expression and a decrease in N-terminal phosphorylation of c-Jun. The decrease in N-terminal phosphorylation of c-Jun does not appear to be modulated by JNK or ERK, since their protein expression patterns and kinase activity do not correlate with the repression of AP-1 activity following treatment with atRA. However, the activity of the protein phosphatase PP2A was found to increase 24 h following atRA treatment in CA-OV3 cells. Moreover, the catalytic subunit of PP2A was found to associate with c-Jun in vivo following atRA treatment. Since the inhibition of AP-1 activity following atRA treatment of CA-OV3 cells was abolished in the presence of specific PP2A inhibitors, it is likely that PP2A plays an important role in the atRA-induced repression of AP-1.
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PMID:Retinoic acid induced repression of AP-1 activity is mediated by protein phosphatase 2A in ovarian carcinoma cells. 1605 10

Squamous cell carcinoma of the head and neck (SCCHN), the 6th most common malignancy in the world, is associated with smoking and has a low 5-year survival rate. Various changes have been described at different stages of SCCHN tumour development, including overexpression of p63, a protein important for development of normal epidermal structures. p63 has been suggested to activate beta-catenin, and nuclear accumulation of beta-catenin is an important event in many cancers. Elevated COX-2 activity and overexpression of EGFR protein has been shown in a variety of human cancers, including SCCHN. An important question for the pathogenesis of SCCHN is when the genetic changes take place during the natural course of the disease, and whether they appear in clinically normal oral mucosa to predispose tumour development. We mapped the expression of p63, COX-2, EGFR, beta-catenin, and PP2A in oral mucosa from smokers/non-smokers and from patients with SCCHN. We also considered if changes occurring in tumours are present in the clinically normal tissue adjacent to the tumour. No direct influence of heavy smoking on the levels of the proteins studied could be seen. Tumours and clinically normal non-neoplastic tissue from SCCHN patients showed increased expression of COX-2 and PP2A. Interestingly, non-neoplastic tissue adjacent to SCCHN also showed increased beta-catenin, although this was not seen in tumours. The data support the notion that pre-existing alterations in clinically normal epithelium exist in patients with SCCHN and could be important for the pathogenesis of the disease and for local recurrences.
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PMID:Expression of p63, COX-2, EGFR and beta-catenin in smokers and patients with squamous cell carcinoma of the head and neck reveal variations in non-neoplastic tissue and no obvious changes in smokers. 1627 22


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