Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P31749 (AKT)
 22,954 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Considerable biochemical and pharmacological evidence suggests that the activation of ribosomal protein S6 kinases (S6Ks) by activated receptor tyrosine kinases involves multiple co-ordinated input signals. However, the identities of many of these inputs remain poorly described, and their precise involvement in S6K activation has been the subject of great investigative effort. In the present study, we have shown that 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), a selective inhibitor of the Src family of non-receptor tyrosine kinases, interferes with the activation of 70 and 85 kDa S6K gene products (p70S6K1 and p85S6K1) by insulin, insulin-like growth factor 1, sodium orthovanadate and activated alleles of phosphoinositide 3-kinase and H-Ras. PP1 also impedes the activation of AKT/protein kinase B and the extracellular signal-regulated protein kinases 1 and 2 by these various stimuli. Insulin-like growth factor 1 was observed to induce a sustained increase in c-Src autophosphorylation as revealed using anti-phospho-Y416 antisera, but this effect was absent from the cells treated with PP1. To conclude, an activated allele of p70S6K1 is compared with the wild-type allele, resistant to inhibition by PP1 when co-expressed with phosphoinositide-dependent kinase 1 (PDK1), suggesting that PP1 affects p70S6K1 via a PDK1-independent pathway. Thus activation of Src may supply a necessary signal for the activation of p70S6K1 and possibly other S6Ks.
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PMID:The Src-family tyrosine kinase inhibitor PP1 interferes with the activation of ribosomal protein S6 kinases. 1201 87

v-Crk, an oncogene product of avian sarcoma virus CT10, efficiently transforms chicken embryo fibroblasts (CEF). We have recently reported that constitutive activation of the phosphoinositide 3-kinase (PI3K)/AKT pathway plays a critical role in the v-Crk-induced transformation of CEF. In the present study we investigated the molecular mechanism by which v-Crk activates the PI3K/AKT pathway. First, we found that v-Crk promotes the association of the p85 regulatory subunit of PI3K with focal adhesion kinase (FAK) by inducing the phosphorylation of the Y397 residue in FAK. This FAK phosphorylation needs activation of the Src family tyrosine kinase(s) for which the v-Crk SH2 domain is responsible. v-Crk was unable to activate the PI3K/AKT pathway in FAK-null cells, indicating the functional importance of FAK. In addition, we found that H-Ras is also required for the activation of the PI3K/AKT pathway. The v-Crk-induced activation of AKT was greatly enhanced by the overexpression of H-Ras or its guanine nucleotide exchange factor mSOS, which binds to the v-Crk SH3 domain, whereas a dominant-negative mutant of H-Ras almost completely suppressed this activation. Furthermore, we showed that v-Crk stimulates the interaction of H-Ras with the Ras binding domain in the PI3K p110 catalytic subunit. Our data indicated that the v-Crk-induced activation of PI3K/AKT pathway was cooperatively achieved by two distinct interactions. One is the interaction of p85 with tyrosine-phosphorylated FAK promoted by the v-Crk SH2 domain, and another is the interaction of p110 with H-Ras dictated by the v-Crk SH3 domain.
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PMID:v-Crk activates the phosphoinositide 3-kinase/AKT pathway by utilizing focal adhesion kinase and H-Ras. 1224 82

Dystroglycan is a component of the dystrophin-glycoprotein complex (DGC) in muscle and a cell surface receptor for laminin. Numerous muscular dystrophies are the result of disruption of proteins comprising the DGC, but the underlying pathogenetic mechanisms are unknown. Because apoptosis is an early feature of muscular dystrophy in vivo, and perturbation of cell-extracellular matrix associations is known to induce apoptosis, we investigated the role of dystroglycan-laminin interactions in the propagation and maintenance of cell survival signals in muscle cells. We found that disrupting the interaction between alpha-dystroglycan and the extracellular matrix protein laminin induces apoptosis in muscle cells. This increase in apoptosis is mediated in part by caspase activation and can be blocked by a caspase-3 inhibitor. We demonstrate a role for the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway in muscle cell-survival signaling using a pharmacological inhibitor of PI3K. Treatment with this inhibitor resulted in decreased phosphorylation of AKT and its downstream effector glycogen synthase kinase (GSK)-3beta and induced apoptosis in muscle cell cultures. Disruption of dystroglycan-laminin interactions resulted in decreased phosphorylation of AKT and GSK-3beta. Furthermore, activation of AKT prior to the disruption of dystroglycan-laminin protected the muscle cells from the induction of apoptosis. These results support a role for the PI3K/AKT pathway in the propagation of cell-survival signals mediated by the DGC and provide new insight into the molecular pathogenesis associated with the development of muscular dystrophies.
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PMID:Inhibition of dystroglycan binding to laminin disrupts the PI3K/AKT pathway and survival signaling in muscle cells. 1240 86

Protein kinase B (PKB) is the expression product of a proto-oncongen (c-akt), which is involved in the signaling pathways initiated by some growth factors and mediated by phosphoinositide 3-kinase (PI3K). PKB is a direct target of PI3K. Similar to many protein kinases, PKB has a specific AH/PH domain which can mediate the interaction between signaling molecules. The lipid second messengers, PI-3, 4-P2 and PI-3,4,5-P3 produced by PI3K, can bind to the AH/PH domain of PKB and of PDK (phosphoinositide dependent protein kinase). This binding translocates PKB and PDK to the plasma membrane, and activates them. PKB is also activated via phosphorylation by PDK and, in turn, will activate the anti-apoptotic machinery, glucose metabolism (glycogen synthesis, glycolysis and glucose uptake) and protein synthesis. All these lead to cell growth and proliferation.
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PMID:[Protein kinase B and its role in the signal transduction pathway mediated by phosphoinositide 3-kinase]. 1254 28

To be able to detect in situ changes in protein conformation without perturbing the physiological environment would be a major step forward in understanding the precise mechanism occurring in protein interaction. We have developed a novel approach to monitoring conformational changes of proteins in intact cells. A double-labelled fluorescent green fluorescent protein-yellow fluorescent protein (GFP-YFP) fusion protein has been constructed, allowing the exploitation of enhanced-acceptor-fluorescence (EAF)-induced fluorescence resonance energy transfer (FRET). Additionally, a novel fusion partner, YFP(dark), has been designed to act as a sterically hindered control for EAF-FRET. Any conformational changes will cause a variation in FRET, which, in turn, is detected by fluorescence lifetime imaging microscopy ("FLIM"). Protein kinase B (PKB)/Akt, a key component of phosphoinositide 3-kinase-mediated signalling, was selected for this purpose. Although conformational changes in PKB/Akt consequent to lipid binding and phosphorylation have been proposed in models, its behaviour in intact cells has not been tractable. We report here that platelet-derived-growth-factor ("PDGF") stimulation of NIH3T3 cells expressing the GFP-Akt-YFP construct resulted in a loss of FRET at the plasma membrane and hence a change in PKB/Akt conformation. We also show that the GFP-Akt-YFP construct conserves fully its functional integrity. This novel approach of monitoring the in situ conformational changes has broad application for other members of the AGC kinase superfamily and other proteins.
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PMID:Monitoring conformational changes of proteins in cells by fluorescence lifetime imaging microscopy. 1293 65

In this review, we briefly cover the critical requirements for interleukin-7 (IL-7) in thymocyte development and peripheral T-cell homeostasis. Part of the IL-7 effect is antiapoptotic or 'trophic' and we have studied the intracellular pathways involved in lymphocyte survival and death regulated by this cytokine. We review the evidence for a role of the JAK signal transducers and activators of transcription protein (STAT) pathway and phosphoinositide 3-kinase (PI3K)-AKT pathways in survival. The death pathway following IL-7 withdrawal is discussed in terms of the balance of BCL-2 vs. BAX and other death proteins and the role of metabolic disturbances involving glucose metabolism and intracellular pH. The IL-7 survival and death pathways in lymphocytes may be representative of many trophic factors in different cell types; yet we conclude that much of the mechanism remains to be discovered.
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PMID:Death and Baxes: mechanisms of lymphotrophic cytokines. 1275 70

Protein kinase B (PKB/Akt) is a key regulator of cell growth, proliferation and metabolism. It possesses an N-terminal pleckstrin homology (PH) domain that interacts with equal affinity with the second messengers PtdIns(3,4,5)P3 and PtdIns(3,4)P2, generated through insulin and growth factor-mediated activation of phosphoinositide 3-kinase (PI3K). The binding of PKB to PtdIns(3,4,5)P3/PtdIns(3,4)P2 recruits PKB from the cytosol to the plasma membrane and is also thought to induce a conformational change that converts PKB into a substrate that can be activated by the phosphoinositide-dependent kinase 1 (PDK1). In this study we describe two high-resolution crystal structures of the PH domain of PKBalpha in a noncomplexed form and compare this to a new atomic resolution (0.98 A, where 1 A=0.1 nm) structure of the PH domain of PKBalpha complexed to Ins(1,3,4,5)P4, the head group of PtdIns(3,4,5)P3. Remarkably, in contrast to all other PH domains crystallized so far, our data suggest that binding of Ins(1,3,4,5)P4 to the PH domain of PKB, induces a large conformational change. This is characterized by marked changes in certain residues making up the phosphoinositide-binding site, formation of a short a-helix in variable loop 2, and a movement of variable loop 3 away from the lipid-binding site. Solution studies with CD also provided evidence of conformational changes taking place upon binding of Ins(1,3,4,5)P4 to the PH domain of PKB. Our data provides the first structural insight into the mechanism by which the interaction of PKB with PtdIns(3,4,5)P3/PtdIns(3,4)P2 induces conformational changes that could enable PKB to be activated by PDK1.
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PMID:Binding of phosphatidylinositol 3,4,5-trisphosphate to the pleckstrin homology domain of protein kinase B induces a conformational change. 1296 41

EKB-569 is an irreversible inhibitor of epidermal growth factor receptor (EGF-R) tyrosine kinase. It inhibits EGF-induced phosphorylation of EGF-R and the growth of tumors that overexpress EGF-R in animal models. In clinical trials, EKB-569 and all other EGF-R inhibitors cause skin rashes. To understand the latter phenomenon, the effect of EKB-569 on EGF-R as well as downstream signaling to phosphoinositide 3-kinase-protein kinase B (AKT), extracellular signal-regulated kinase 1 and 2 (ERK1/2), or signal transducer and activator of transcription 3 (STAT3) pathways were compared in tumor cell lines and normal human keratinocytes (NHEK) grown in tissue culture. Tumor cell lines that have high (A431 epidermoid and MDA-468 breast carcinomas) and low (MCF-7 breast carcinoma) expression of EGF-R were used. NHEK cells express at least 15-fold less EGF-R than A431 cells. EKB-569 was a potent inhibitor of proliferation in NHEK, A431, and MDA-468 cells (IC(50) = 61, 125, and 260 nM, respectively) but not MCF-7 cells (IC(50) = 3600 nM). EKB-569 was also a potent inhibitor of EGF-induced phosphorylated EGF-R (pEGF-R) in A431 and NHEK cells (IC(50) = 20-80 nM). The reduction in pEGF-R paralleled inhibition of phosphotyrosine-705 STAT3, while the inhibition of phosphorylated AKT and phosphorylated ERK1/2 occurred at higher concentrations of EKB-569 (75-500 nM) in both A431 and NHEK cells. The effects were specific because EKB-569 did not inhibit the nuclear factor-kappaB pathway. It is proposed that skin toxicity associated with EKB-569 is due to inhibition of EGF-R signaling. Downstream signal transduction markers, particularly the activation status of STAT3, may be useful surrogate markers to guide clinical development of EGF-R inhibitors.
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PMID:Phosphorylation of extracellular signal-regulated kinase 1 and 2, protein kinase B, and signal transducer and activator of transcription 3 are differently inhibited by an epidermal growth factor receptor inhibitor, EKB-569, in tumor cells and normal human keratinocytes. 1474 72

Resveratrol (RES), a natural phytoalexin, has antiproliferative activity in human-derived cancer cells and in rodent models of tumor development. We have previously shown that RES induced apoptotic death in estrogen-responsive MCF-7 human breast cancer cells. Recent data have indicated that the estrogen receptor-alpha (ERalpha), through interaction with p85, regulates phosphoinositide 3-kinase (PI3K) activity, revealing a physiologic, nonnuclear function of the ERalpha potentially relevant in cell proliferation and apoptosis. In our study, using MCF-7, we have analyzed the ability of RES to modulate the ERalpha-dependent PI3K pathway. Immunoprecipitation and kinase activity assays showed that RES increased the ERalpha-associated PI3K activity with a maximum stimulatory effect at concentrations close to 10 microM; concentrations >50 microM decreased PI3K activity. Stimulation of PI3K activity by RES was ERalpha-dependent since it could be blocked by the antiestrogen ICI 182,780. RES did not affect p85 protein expression but induced the proteasome-dependent degradation of the ERalpha. Nevertheless, the amount of PI3K immunoprecipitated by the ERalpha remained unchanged in presence of RES, indicating that ERalpha availability was not limiting PI3K activity. Phosphoprotein kinase B (pPKB/AKT) followed the pattern of PI3K activity, whereas RES did not affect total PKB/AKT expression. PKB/AKT downstream target glycogen synthase kinase 3 (GSK3) also showed a phosphorylation pattern that followed PI3K activity. We propose a mechanism through which RES could inhibit survival and proliferation of estrogen-responsive cells by interfering with an ERalpha-associated PI3K pathway, following a process that could be independent of the nuclear functions of the ERalpha.
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PMID:Resveratrol modulates the phosphoinositide 3-kinase pathway through an estrogen receptor alpha-dependent mechanism: relevance in cell proliferation. 1475 Jan 65

The mechanisms of neuronal differentiation in PC12 cells are still not completely understood. Here, we report that the tumor suppressor PTEN has a profound effect on differentiation by affecting several pathways involved in nerve growth factor (NGF) signaling. When overexpressed in PC12 cells, PTEN (phosphatase and tensin homologue deleted on chromosome ten) blocked neurite outgrowth induced by NGF. In addition, these cells failed to demonstrate the transient mitogenic response to NGF, as well as subsequent growth arrest. Consistent with these observations was a finding that PTEN significantly inhibits NGF-mediated activation of the members of mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling pathways, crucial for these processes. While exploring possible mechanisms of PTEN effects on NGF signaling, we discovered a significant down-regulation of both high-affinity (TrkA) and low-affinity (p75) NGF receptors in PTEN-overexpressing clones. Subsequent microarray analysis of several independent clonal isolates revealed a myriad of neuronal genes to be affected by PTEN. All of these changes were validated by quantitative PCR. Of particular interest were the genes for the key enzymes of the dopamine synthesis pathway, receptors for different neurotransmitters, and neuron-specific cytoskeleton proteins, among others. Some, but not all effects could be reproduced by pharmacological inhibitors of PI3K and/or MAPK, suggesting that PTEN may influence some genes by mechanisms independent of these signaling pathways. Our findings may shed new light on the role of this tumor suppressor during normal brain development and suggest a previously uncharacterized mechanism of PTEN action in neuron-like cells.
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PMID:Inhibition of neuronal phenotype by PTEN in PC12 cells. 1499 Jul 93


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